Breaking through the union glass ceiling in France: between organizational opportunities and individual resources

Cécile Guillaume Sophie Pochic

Paru dans Ledwith Sue, Hansen Lise (ed), Gendering and diversifying trade union leadership, Routledge, 2012, p. 245-264

Summary

In France, as in many other countries, women have great difficulties in achieving positional power within union structures, even when equality policies have been implemented, as in the case of CFDT (Confédération Française Démocratique du Travail) since 1981. Following recent developments that put emphasis on women's agency in the union context, this paper explores the structural, organizational and individual factors that have allowed few women to become union leaders. More specifically we will examine the interrelationship between internal equality policies for enhancing women's representation and other less explored dimensions such as the impact of organizing strategies and internal political battles over union identity shift, the evolution of union work and the influence of women's own resources.

In France, as in many other countries, women have great difficulties in achieving positional power within union structures. Although they now account for more than 40% of the membership in some major unions, the gap between the proportion of women who are trade union members and of those who are senior paid or elected officers remains wide [START_REF] Contrepois | France : un accès encore inégal et partiel aux différentes sphères de la représentation syndicale[END_REF][START_REF] Silvera | Le défi de l'approche intégrée de l'égalité pour le syndicalisme en Europe[END_REF]. Most of the "women and trade unions" literature has focused on explaining gendered barriers and constraints that prevent women from gaining higher representation in union structures [START_REF] Briskin | Women, unions and leadership[END_REF]Cockburn, 2001;Colgan andLedwith, 1996, 2002;[START_REF] Dorgan | Battling against the odds: the emergence of senior women trade unionists[END_REF][START_REF] Franzway | Women working in a greedy institution: commitment and emotional labour in the Union Movement[END_REF][START_REF] Kirton | Transforming union women: the role of women trade union officials in union renewal[END_REF][START_REF] Munro | Women, work and trade unions[END_REF]. However, for the last thirty years, a mix of radical and liberal measures [START_REF] Jewson | The theory and practice of equal opportunities policies: liberal and radical approaches[END_REF] has been implemented within some French unions, leading to the promotion of a few female leaders, including one female General Secretary, Nicole Notat, who was elected in 1992 by the 2 nd major French general union confederation (600.000 members) -Confédération Démocratique Française du Travail (CFDT). In 2010, three women out of nine were part of the CFDT national executive committee. At first sight, it is possible to explain these exceptional trajectories by the gender equality policy put in place since 1982 i . But reality is more complex. Following recent developments that put emphasis on women's agency in the union context (Colgan and Ledwith, 2002;Kirton, 2006b;[START_REF] Moore | New trade union activism. Class Consciousness or Social Identity?[END_REF], this paper explores the structural, organizational and individual factors that have allowed a growing number of women to become union leaders. More specifically we will examine the interrelationship between internal equality policies for enhancing women's representation and other less explored dimensions such as the influence of organizing strategies and internal political battles over union identity shift, and the influence of women's own resources.

In the English literature the creation of women trade union leaders has been identified as a key issue for unions, both as a way of challenging the oligarchic nature of union leadership, of instigating organizational changes [START_REF] Healy | Women, power and trade union government in the UK[END_REF], and as a lever to bring the necessary amount of equality and democracy for union renewal (Foley, Baker, 2009). The claim is that once in positions of influence and power, women will be able to use their agency to inject their own beliefs, values and concerns [START_REF] Heery | Do female representatives make a difference? Women FTOs and Trade Unions Work[END_REF][START_REF] Kirton | Transforming union women: the role of women trade union officials in union renewal[END_REF], to act as a role model for the female membership [START_REF] Dorgan | Battling against the odds: the emergence of senior women trade unionists[END_REF][START_REF] Sayce | Small is beautiful? The development of women's activism in a small union[END_REF] and to strive to alter the style and content of union activity [START_REF] Heery | A cracking job for a woman -a profile of women trade union officers[END_REF]. It is indeed argued that women lead differently because of the material experiences of their lives and their "politicised views of empowerment and inclusivity" (Briskin, 2006: 370), but also as a result of their participation in women-only courses (Kirton, 2006a). In many countries with different industrial relations systems, they seem to promote (or to identify with) a "transformational" leadership style that focuses on members' empowerment and participation [START_REF] Briskin | Victimisation and agency: the social construction of union women's leadership[END_REF]. Opposed to a traditional masculine "transactional" leadership style (bureaucratic and hierarchical, based on rewards and punishments), this style is acknowledged as critical for union survival by most researchers.

In the UK, Canada, Australia and the USA, where separate organizing and self-organization structures have been put in place, earlier research has demonstrated that leadership change is related to successful "insurgency" linked to the existence of gender caucuses, networks or structures, such as women's committees or women's groups [START_REF] Cornfield | Integrating US labour leadership[END_REF]. However, if radical measures are needed for under-represented groups to be engaged fully in democratic processes [START_REF] Greene | Advancing Gender Equality in UK Trade Unions: the Role of Women-only Trade Union Education[END_REF], reserved seats and separate training courses are sometimes condemned as being tokenistic or patronizing gestures, marginalizing both the issues and the people involved [START_REF] Cockburn | In the way of women: men's resistance to sex equality in organizations[END_REF][START_REF] Briskin | Union women and separate organizing[END_REF]Kirton and Green, 2002). Regarding the role of women-only education, a whole body of work has analysed its positive effect on women's participation in terms of talent spotting, empowerment, confidence building and networking [START_REF] Greene | Advancing Gender Equality in UK Trade Unions: the Role of Women-only Trade Union Education[END_REF]Kirton, 2006a), confirming the central role of enhancement of self esteem and the need for mentoring programs [START_REF] Kaminski | Women's union leadership: closing the gender gap[END_REF]. Above all, these women-only measures are seen as pivotal to the construction of female activist identity (Colgan and Ledwith, 2000;[START_REF] Greene | Advancing Gender Equality in UK Trade Unions: the Role of Women-only Trade Union Education[END_REF]. They help women to realise that they can be identified as a political category that is a significant arena for the development of women's social gender identity and gender consciousness. This importance of feminist "conscientisation" [START_REF] Ledwith | Feminist praxis in a trade union gender project[END_REF] is highlighted by most research in the UK [START_REF] Cockburn | In the way of women: men's resistance to sex equality in organizations[END_REF][START_REF] Colgan | Sisters Organising -Women and their trade unions[END_REF][START_REF] Kirton | Transforming union women: the role of women trade union officials in union renewal[END_REF][START_REF] Healy | Women, power and trade union government in the UK[END_REF]Kirton 2006a). It is argued that feminist values and beliefs strengthen women's desire to transform union structures and strategies, assuming that identification with feminism and identification with trade union values go hand in hand. The other assumption is that feminist women are more likely to seek upward union careers, or that as they climb women begin to espouse a stronger feminist orientation [START_REF] Kirton | The influences on women joining and participating in trade unions[END_REF]. However, other studies reveal that women unionists are not always in favour of self-organising structures. In a country with strong feminist movements such as Sweden, women seem reluctant to organize separately for structural and ideological reasons. To understand why in France, and particularly within CFDT, the making of women union leaders cannot be explained by women-only structures and feminist values, we will need to retrace the long and discontinuous story of the CFDT gender equality policy.

In the Anglo-Saxon literature, other internal factors are identified as levers for women's promotion, such as the size and the culture of the union [START_REF] Colgan | Sisters Organising -Women and their trade unions[END_REF][START_REF] Sayce | Small is beautiful? The development of women's activism in a small union[END_REF], but more generally the organizational structures and informal practices that contribute to improve or by contrast reinforce gendered inequalities. Participation can be triggered in three main ways, by an injustice or by a certain change and above all by sponsorship (Ledwith et al, 2001). In the case of women, the role of "significant others" and "mentors" [START_REF] Watson | Managers of discontent[END_REF] is crucial and sensitive. As most union leaders are male, women's participation will be highly dependent on whether or not existing/male union leaders adopt a more or less participatory or inclusive approach. These informal and organisational processes are considered to be far more influential in increasing women's representation than formal equality rules, as the recruitment processes of unions are based on interpersonal co-opting and off the record appointment, both for paid officers or elected union positions [START_REF] Guillaume | Le syndicalisme à l'épreuve de la féminisation : la permanence paradoxale du 'plafond de verre' à la CFDT[END_REF]. In this organisational context, some women may have more individual resources (including a supportive partner) and social capital to fight for their position, revealing one of the major issues for equality policies and feminist theories: the internal diversity and hierarchy of the women's category.

Research methods: career narratives and biographical matching

This research utilizes qualitative interview data from a study of women trade unionists carried out over the period 2006-2010, involving one major French trade union confederation -CFDT ii . This case study was included in a cross-national research project on "women in trade unions" in France, the UK and Hungary, which was designed to address the constant underrepresentation of women in union government and the effects of internal equality policy measures [START_REF] Guillaume | The organisational nature of union careers: the touchstone of equality policies? Comparing France and the UK[END_REF] iii . We wanted to explore the barriers and processes that facilitate women's participation, but also to examine women leaders' experience. The notion of "union leader" may cover a wide range of roles and status [START_REF] Kaminski | Women's union leadership: closing the gender gap[END_REF][START_REF] Ledwith | The making of women trade union leaders[END_REF] from local union leader to elite national level officer, some being full time paid officers, other (senior) lay activists or elected leaders. The notion may not necessarily include linear careers and vertical progression for everyone (Kirton, 2006), but it implies a certain level of union participation and responsibility, embracing various forms of activism [START_REF] Briskin | Victimisation and agency: the social construction of union women's leadership[END_REF][START_REF] Greene | Possibilities for remote participation in trade unions: mobilising women activists[END_REF]. We acknowledge that only focusing on formal activism renders invisible the participation of women who find it difficult to take on formal positions, but for the purpose of this article we will put the emphasis on the progression of women within union structures.

Compared to other countries, the French legislative and welfare context is quite favourable to trade unions. If French unions have the lowest membership level (8%) among OECD countries apart from the US, they have a strong institutional influence, as 95% of workers are covered by a collective agreement iv [START_REF] Visser | Union membership statistics in 24 countries[END_REF]. The other main characteristic of French unionism is the tradition of a pluralistic and politicised labour movement. Workers can choose to be affiliated to general or business trade unions with different ideological lines. Until recently, the amount of time off for different union roles was not linked to the number of members or election scores. It was given equally to five different general unions (CGT, CFDT, CFTC, FO, CFE-CGC) which were considered as legally "legitimate" social partners and which could designate employee representatives in any company with more than 10 employees for "délégué du personnel"; more than 50 for "élu du comité d'entreprise". The French model of industrial relations provides many opportunities for unionists to be "full-time officers", being either elected at the company or branch levels or in other bodies that are in charge of social security or pensions. Many trade unionists combine then different union mandates, working full-time for the union at the local/regional/national level, but still being paid by their previous employer.

Following the Chicago School of Sociology model (Becker, Strauss, 1962;[START_REF] Barley | Careers, Identities, and Institutions: The Legacy of the Chicago School of Sociology[END_REF], we have concentrated on the organizational and individual factors that have allowed these women leaders to reach the intermediate and upper levels of the union hierarchy. Drawing on biographical matching and comparative analysis [START_REF] Crompton | Gender, comparative research and biographical matching[END_REF], we have used career narratives to explore the organizational processes and career norms implicitly required for the making of trade union leaders: the different sequences of a " union career", the necessary steps, main tracks, atypical routes and turning points, and the role of significant others. This career approach emphasizes the articulation and interferences between different spheres (Kirton, 2006b), and the role of the identities of trade unions in the promotion of specific trade unionists' profiles, depending on time periods. Finally, this methodological approach embedded in one specific union context analyzes both the influence of equality policies on women's careers and the role of women's agency in negotiating the barriers and constraints. As CFDT is a general confederation we have purposely selected different cases to emphasize a "contrast of contexts" between affiliated unions with different levels of feminisation and varied equality policies. 32 (white) women have been interviewed, 8 coming from maledominated unions, 16 from female-dominated unions, and 8 from the confederation. In the text, we have chosen to draw on three career narratives that exemplify the respective role of structure, context and agency in the building of women trade unionists' careers. See Table 1.

Table 1. Profiles of the sample of trade unionists

Total 32

Responsibility level

National level (political) (*) 5

National level (technical) 9

Intermediary level (branch, union départementale, syndicat) 10

Local level (entreprise or administration) 8

Location

Paris 29

Other regions 3

Age category

Young (less than 35) 6

Middle (35-49) 14

Senior (more than 50) 12

Membership seniority

New members (less than 10 years) 10

Middle-range members (10 to 19 years) 10

Senior members (more than 20 years) 12

Education level

Graduates (degree or bac+2) 24

A level or under (A-level / bac max.) 8

Family configuration

Children 23

No child 9 (*) national level = confédération and fédération

Gender equality strategy in CFDT: a long and discontinuous story v

Within CFDT, the campaign for gender equality has had a long history that is closely interrelated with the successive shifts of union identity that the confederation has known since the 1960s. Coming from a traditional Catholic background vi , CFDT has progressively adopted a politicised analysis of "working conditions of women" based on the idea of their over-exploitation, thanks to the mobilisation of few female equality officers, who were also identified as being part of the "political minority" that led to the creation of CFDT in 1964. In the 1970s, following the events of May 1968, the union policy has developed towards a classbased orientation, articulating sex and class struggles and extending campaigns to include contraception and abortion rights. Significant strikes were led by CFDT union female leaders in the 1970s [START_REF] Maruani | Les syndicats à l'épreuve du féminisme[END_REF], encouraging a wide range of new grievances (maternity, abortion, equality at work and domestic work), and strong links were built with feminist associations. However, during that 20 year period of time where CFDT took a leading role in the adoption of an equality agenda, the union was reluctant to adopt separate structures for women, replacing the women's committee (Commission Confédérale Femmes -CCF) inherited from CFTC by a mixed committee in 1971, avoiding women's groups at company level and opening women-only training to men [START_REF] Brouster | La prise en charge par la CFDT de la question des femmes dans les années 1960 et 1970[END_REF]. That focus on "mixité" shown by its action to be in favour of internal and external equality, has led CFDT to avoid working with women-only feminist movements, and to promote a "mainstreaming approach".

From 1978, CFDT redefined its union goals and doctrine and started to distance itself from political parties, social movements and societal issues. The elimination of class analysis and socialist values and the acceptance of economic liberalism [START_REF] Defaud | De l'autogestion au syndicalisme de proposition[END_REF] led to the promotion of a mass unionism able to address issues for everyone, including women, and to stop the huge membership decline that started at the end of the 1970s. Specific campaigns were launched in different sectors to attract women members and specific training was designed to promote the new political line and to train future female leaders. In 1982, CFDT adopted a mix of liberal (dedicated financial resources, specific training course, one national equality officer and one annual women's meeting each 8 th march) and radical measures (reserved seats for the NEC, National Executive Committee, and minimum representation for congress delegations). These measures were quite controversial at the time because they were seen as a tool to promote a new leader profile, more in line with the reformist approach (Le Brouster, 2010). It is worth noting that the notion of "democratic deficit" has never been used as such in the union equality policy, even though the idea of "mass unionism" is also linked to members' empowerment goals (Guillaume and Pochic, 2009b).

Compared to the UK, where the equality agenda has been constantly pushed by main unions and the TUC, with a progressive enlargement to include other minority groups, the CFDT case displays a more discontinuous story that is clearly linked to the weakening of "second wave" feminism in France in the 1980s, and to the increasing distance between unionists and feminists since then. The internal equality measures were quickly weakened by the development of "State Feminism" after the election of a socialist president, François Mitterrand in 1981 [START_REF] Mazur | Gender bias and the State, symbolic reform at work in Fifth Republic France[END_REF]. Several feminist union leaders, including Jeannette Laot who had been in charge of equality in the CFDT for 20 years , were absorbed by these structures and ceased to stimulate unions [START_REF] Brouster | Une syndicaliste-féministe : le parcours de Jeannette Laot, 1961-1981[END_REF]. The targeting of 'women' and other under-represented groups (young, managers and professionals, SMEs workers) in the recruitment policy became rather instrumental and was not linked to 'equityseeking' ambition. Since 1995, both the internal and external policies have seemed rather weak. The confederation remains quite reluctant towards any association with feminist movements, as a consequence of its "de-politicization". Despite the promulgation of several equal opportunity laws (Roudy in 1983, Génisson in 2001, equal pay law in 2006) and a 'parity law' adopted in the political field in 2000 (Bereni, 2009), unions including CFDT rarely take the lead on equality bargaining. Since 2004 there has been an unusually high turnover of national equality officers at the confederation level, leading to a lack of equality audits and the end of women's training, research sessions and conferences. The women's committee (CCF) still exists but is now open to men and women and has a secondary role in terms of decision-making (albeit having a direct organisational link with the NEC) and does not produce any "gendered factionalism". Within each CFDT union, the situation is rather diverse, some have kept an active internal equality policy (particularly in male-dominated and industrial unions), including quotas and recommendations, while others have none (particularly in feminised sectors as health care, social care and education). Overall, equality measures and the feminisation of the membership have led to a certain level of feminisation at the upper levels of the confederation and the affiliated unions. Because the Confédération feared being unable to fill more reserved seats, complete parity for the Bureau National (equivalent of the NEC) was not decided on at the last 2010 congress, whereas the major general union CGT had adopted it since 1999 vii . See Table 2.

Radical measures :

-quotas since 1982 : minimum of 10 female members out of 28 for the BN; minimum of 29% of women for the CNC; minimum 3 women for the CE Liberal measures : -equality policies for each federation/region; national, regional and federal equality officers; -women's committee since 1964, equality trainings since the 1970s, annual women's conference since 1987 NB : access to statistics remains quite difficult, apart from the confederation level. Most of the figures we have obtained do not give details for each federation/region.

Exceptional trajectories based on individual resources and workplace contexts

The role of employment characteristics in union activism

In this evolving context, we may wonder how women have managed to break through the glass ceiling. Firstly, career narratives reveal the crucial issue of employment characteristics and workplace contexts in developing a union activist. In most cases, the women interviewed have started their union career at the workplace level, initially with an elected employee representation role within their company (délégué du personnel or élu au Comité d'Entreprise) or in their administration (délégué en CAP). While circumstances vary greatly across generations, the forms of their activism depend mainly on the workplace context. In unionised workplaces with a good social climate, particularly in the public sector, some women have become unionised thanks to the influence of their colleagues but have sometimes remained a passive member for many years. Elsewhere, they have quickly become involved in different forms of union actions and have taken on union responsibilities: strikes on pay and conditions in the 1970s, struggles against downsizing/restructuring or fights for enforcing labour law in the 1990s. As other studies have shown, workplace events appear to be the main socialization arena for union activism, whereas the influence of family background, and of political, religious or youth movements has declined since the 1980s [START_REF] Duriez | Réseaux de sociabilité et adhésion syndicale[END_REF]Guillaume and Pochic, 2009a).

The transmission of militant "basic skills" [START_REF] Kaminski | Women's union leadership: closing the gender gap[END_REF] continues to rely on the goodwill of local union activists. In highly unionized sectors (banking, industry, public services), particularly in the 1970s, a vibrant local union allowed new entrants to learn on the job through informal discussions, and to gain confidence progressively. Strikes have also frequently been mentioned as moments of intense sociability and where identification of "good activists" by existing union representative and officials occurs. But since the 1990s, in the context of declining unionization, especially in France where union density is considered really low, women who have become activists in the context of a collective action against restructuring, particularly in small firms, have had to organize members and learn necessary skills by themselves. When participation is in short supply, some of them have experienced union careers in which union roles were rapidly accumulated at the workplace level, in union local, regional or national union structures. Many women have also benefited from the expansion of feminized sectors (health care, social care, local government) and from the CFDT union organizing campaigns targeted towards these sectors.

However, these expanding general opportunities for women favour stable employees in large companies or in public service, trade unions being almost absent from small companies (Dufour et al., 2007). Although women can benefit from their over-representation in the public sector, they are also concentrated in contingent employment (fixed-term contracts, temporary contracts), in SMEs and in the expanding non-organised service sector (hotelrestaurants, supermarkets). Working in public services or in large companies with a tradition of social dialogue facilitates the use of time-off for trade union duties and activities, and the negotiation of a secondment with a guaranteed return to work. In small companies, by contrast, although women have many reasons to unionize [START_REF] Yates | Challenging misconceptions about organizing women into unions[END_REF], union activism is professionally risky and the transition to full-time activism is difficult to finance as trade unions have only a few salaried positions to offer. In our sample, only a tiny minority of women activists has been fired or has resigned from their company (3 out of 35). Most of them remained paid by their former employer, indicating that stable employment integration is a key condition of union involvement (Guillaume and Pochic, 2009a), as in the case of Sylvie.

Sylvie considers that she had become involved in trade unionism "by accident" while trying to get funding for some training in 1995. Having travelled extensively as a choreographer, and as a laboratory technician for two NGOs (Médecins du Monde and La Croix Rouge), she learned that the non-governmental hospital in Paris where she worked was to be closed, and that was the reason why her employer refused to give her training paid leave. Given the lack of reaction by the work council dominated by another union (FO, Force Ouvrière), she was mandated by her colleagues to contact other unions, first CGT and then CFDT. As CFDT was more informed of her situation, she convinced her twenty colleagues to unionize to this union. CFDT mandated her as shop steward to negotiate the redundancy plan, and six months later she won an election to become the work council secretary. To protect her from pressures by her employer, she was appointed by the union as national shop steward (délégué syndical central) for the whole organisation, La Croix Rouge, and she negotiated a part-time secondment as union organizer. Two years later the female general secretary of her local branch (health and social care in Paris), at the end of her mandate, asked Sylvie to be her replacement, with a full time-off secondment. But as she hated the routine and was exhausted as she had twins and had divorced when they were two years old, she started training towards a career change (administrator in social economy). Knowing this, the health and social care federation, a highly feminized and expanding one, offered her a position as federal secretary, in charge of the non-profit sector. She agreed, wanting to transfer her negotiating skills towards managing the federation since she had competencies especially in knowing "how to interact with people, how to transform or influence them." But the workload at the federation level was heavy because there were only 8 national officers (4 women), with few assistants, and they had to be polyvalent in many tasks: "I don't pass the broom, but almost." Even if she had worked with a feminist choreographer when she was a young dancer, and represents a highly feminised membership she defines herself as being 'not feminist'. She identifies with feminine qualities: 'quicker, more efficient, more democratic and less careerist' than men. She considers that the only difficulty for woman trade unionists is work-life balance and employers' sexism. At the time of the interview we were anxious about her next professional move, because she was unable to imagine returning to handle pipettes. Two years later, at 46, she was elected general secretary of her federation, probably because of her union commitment and her competencies, but also thanks to the high level of feminisation of upper management of the federation.

The strong influences of union structures on the making of trade union leaders

Many women have also benefited from equality policies, particularly in predominantly male federations. Although the policy of "mixité" launched since 1982 makes local officials sensitive to the need to bring women into government bodies, this policy is used in a different manner across federations. In male-dominated unions where the pool of female activists is minute (utilities, transport, metallurgy), some women have benefited from a reserved seat or a nomination so that quotas are respected. Women have benefited also from the targeted recruitment strategy aimed at young people and managerial and professional staff -an expanding and stable population in large companies-. Several young women under 40 years old consider that they have been visible and selected because of their assets: being young, female and qualified ix . However, this rapid promotion to positions of leadership is often difficult to handle because those selected sometimes lack knowledge of the codes and rituals of the organization, and are not considered legitimate by grassroots activists.

Alongside formal policies, career narratives also reveal the prevalence of informal rules and processes in the making of trade unionists. Internal co-opting is a presiding factor in the organization of careers at all levels of the union hierarchy. Internal elections are often a formality in order to validate an informal selection by the existing leadership. All the women interviewed have mentioned the support of a male mentor, who has helped them to understand internal politics, and who has guided them onto the good tracks. Although such mentor support is a key factor in accessing positions of power in all types of organizations, it has a significant meaning in a union that has experienced episodes of internal crisis as had the CFDT in 1995 and in 2003. In the context of ideological conflicts and crises concerning the conversion of the CFDT to reformism and to a strategy of social partnership [START_REF] Defaud | De l'autogestion au syndicalisme de proposition[END_REF], this mentoring has been linked to political factionalism and alleged support of the confederation's line. During the 1990s, the CFDT support of governmental reforms on pension schemes crystallized those tensions with the left-wing militants that had arisen in the 1970s, and this support led to the departure of significant numbers of members in 1995 and 2003, particularly in traditionally unionized sectors (transport, utilities, education, research). Subsequently, some women discovered that they had been supported because they embodied this new reformist orientation, or at least had not been seen as too politicized (towards the left-wing). Their nomination or election had the backing of the national structures and was a way of eliminating former militants (often senior men), stigmatised as "opponents" or "dissidents". Taking responsibility in a time of crisis has been a cause of tension concerning personal conflicts with rank-and-file or former officials. After their election, these women have also had to struggle against the issue of tokenism, sometimes being sidelined to minor roles, as in the case of Rebecca.

Rebecca was meant to become a senior business executive. Coming from a middle class background, after gaining a Master in Psychology and a Master of Computer Science she joined an American IT company as a project manager with numerous periods of travel in Europe. When redundancy plans occurred between 1993 and 1995, she helped to develop the recently created CFDT union and took on several union duties at the workplace level. She was then rapidly elected by her local branch (mines and metallurgy in Paris) where she became assistant general secretary. She also entered the executive council of her federation, "because they were looking for women" and because she wanted also to feminize union structures. But after a merger in 2001, she could no longer keep her full time-off agreement and was obliged to re-enter her company as training manager, which was objectively a promotion for her. But two years later, when her boss refused to promote her on the grounds that she would in future be more expensive to lay-off, she decided to make herself available again to the union. The metalwork federation asked her to become national secretary in charge of training matters (thus fulfilling their only female reserved seat). She knew the leadership would support her since it was a move to prevent other leftist candidates from her union from standing. She was elected, and accepted a personal loss of 1,000 euros per month by her change of situation. Her husband, an engineer in a big industrial company, more family-oriented than career-oriented according to her, supported her in that choice and shares domestic responsibilities (they have three children). Three years later, she had to accept job termination because her secondment had ended. Service with the metalwork federation led to a full-time paid union officer role, at age 50. The role was as assistant general secretary of the national union of managerial and professional staff ('CFDT Cadres'), that has an executive board composed of 4 women and 4 men. She is convinced by the 'mixité' policy of the confederation and the necessity to have women at all levels of the union hierarchy, with the help of quotas if necessary, but she also supports a more gender-neutral equality campaign on the extension of parental leave for men.

The "qualification lever" in a male world

The change of the CFDT political strategy based on collective bargaining and expertise tends to favour women graduates from white-collar professions. This professionalization of union activity obviously reinforces the "qualification lever" for educated women, who can use it to enter male-dominated union structures. Many technical skills (in law, in finance, in writing and public-speaking skills) are now required either for union roles at the workplace level to develop an argument on an issue or to understand the labour law and its complex jurisprudence, or for union structures, i.e. being a treasurer without diversion of union funds, organizing a recruitment strategy, or managing teams of volunteer activists. Although there is probably a generational effect, as young women are seemingly more educated than their older counterparts, this does not explain the huge gap in skill level between female and male officials. In our sample, almost all the women hold a university degree. Some of them have entered union positions through external recruitment as technical experts (recruitment, legal action, health and safety, communication, training, research). Other surveys have shown how external recruitment enhances the feminization of the full-time officer level, at the same time reinforcing the qualification gap between them and ordinary members (Kelly and [START_REF] Heery | A cracking job for a woman -a profile of women trade union officers[END_REF][START_REF] Heery | Union workers, union work: a profile of paid union officers in the United Kingdom[END_REF]. Indeed, these new "expertise routes" have allowed the recruitment of paid officers without activist experience, arriving directly at federation or confederation level. These women were private managers or professionals, aged between 30 and 40, without previous experience of militancy but none were activists originating from social or feminist movements x . Young qualified women have also benefited from the willingness of the former General Secretary (Nicole Notat, 1992-2002) to quickly rejuvenate and professionalize the confederation. However, these paid officers have often been criticized as lacking activism experience and many have encountered difficulties of integration, particularly with some political leaders derived from blue-collar sectors. Most of them have been disappointed with the narrow or limited career progression, and have then resigned or have been dismissed, as was the case for Flore.

Flore, 41 years old, was one of the experts recruited by Nicole Notat to "change the face" of the CFDT confederation. A graduate in international law, she was not a union member until her recruitment at the confederation, but she had been an activist in the Socialist Party since 1987 and a militant in civil movements sustaining the European construction. While she was a manager in an NGO working on European programmes of education, she learned by a friend that the CFDT was looking for a secretary to take charge of European Affairs in 1996. She was selected over another highly qualified candidate because "I was filling quotas: young, woman and graduate." Her integration into a department comprising former steelworkers, the "dinosaurs" as she calls them, was rather difficult but gradually she acquired legitimacy thanks to her technical and bilingual skills but also by her previous commitment to the Socialist Party. Flore was aware of equality issues, as she had been to women's sessions in the Socialist Party Summer Schools, and came to CFDT attracted by the image of its female General Secretary, but she soon discovered that the confederation "was still a men's world, particularly in my department, fulfilled with men, blue-collar, 50-55 years old". This period was very tiring as she went to Brussels almost every week, whilst living in Paris with her husband also involved in a demanding career (high civil servant and local politician in the West of France). She has no child. Paradoxically, it was a strongly career-minded woman, with an activist background, who managed to destabilize Flore, as the former took the lead of her European project, organizing public debates with activists, as a way to raise her profile and become elected as national secretary. As her position lost its core, after a small bout of depression, Flore began to look for another job, but in 2003, the economy was in recession and "I am now labelled as a 'a pain in the ass'." She finally managed to leave CFDT thanks to the intervention of a CFDT regional leader who sponsored her to become a research assistant in a State administrative department.

Few feminist leaders but more feminine leaders?

By contrast with what is learned from Anglo-Saxon literature, most female CFDT leaders do not display a strongly feminist orientation and will not identify themselves as "feminist", with few exceptions. Most of them refuse to consider women as a specific category and promote egalitarian and mainstream measures. They reject acting as role models for other women and using gender factionalism, as they usually under-estimate how exceptional their own career has been. Some women have "neutralized" their gender identity or even take anti-feminist positions, particularly in male-dominated unions: "I do not like old wives' stuff" says another women talking about a recently organised women's meeting. Nicole Notat was emblematic of this "neutralised" position (Notat, 1996). However, many female CFDT leaders claim that they have a feminine career development in their defence of parallel career paths, more horizontal than vertical (Kirton, 2006b). Many women remain at lower levels, refusing national responsibilities and full time-off, in order to stay in touch with grassroots and the realities of work: "not to lose ground with the company" says one, "not to fall into meetingitis" says another. Such refusal is based on implicit or explicit criticism of the union bureaucracy and a desire to preserve their freedom of action and speech. But this discourse can be seen as a self-limitation and a short-term strategy, as it is very hard to combine paid work and union activities. It is perhaps also a rationalisation of a constrained choice as they are unable to relocate to Paris, or to commute from Monday to Friday, whereas all national positions at federation or confederation level are based in Paris.

Many women leaders also encourage an alternative leadership style, promoting a more cooperative, consensual and professional approach, closer to members' concerns, and seeking to stimulate greater participation in sections or in local unions. Female leaders often see themselves as agents of change and innovation, with an orientation focused primarily towards results (election results, number of members, number of signed collective agreements). However it is very difficult to say if this is a "feminine" trait or a "new entrant" strategy [START_REF] Guillaume | Le syndicalisme à l'épreuve de la féminisation : la permanence paradoxale du 'plafond de verre' à la CFDT[END_REF], as many young men develop also this discourse, in a context where competition exists between old and new legitimacies (servicing / organising, expertise / charisma…). In hierarchical, complex structures where leaders need to coordinate the work of autonomous shop stewards, many say they feel isolated while exercising power. When internal political crises arise, they sometimes have been obliged to use a direct, "tough", even authoritarian style of leadership, in contradiction with what they normally wish to convey: "bang your fist on the table", "pass for a demanding bitch" or "a control freak". The nickname for Nicole Notat for example was "Tzarina". The few women who hold national positions admit that they have had some appetite for power. One strategy was, by taking on an innovative and visible issue, they could build a complementary role alongside other male leaders. However, perhaps because they are still rather young, they consider their conversion has come rather quickly, and have enrolled in university programmes while still working for the union, hoping that this will grant recognition of their union experience. Because separate organizing structures do not yet exist within the union, and as they are few in number at that level, women belong to no formal networks that could compensate for a lack of informal networking, in contrast to the situation for men who have built strong and extensive relationships with other leaders while they were local and regional activists.

Discussion

Many studies have argued that equality policies can be ignored by the union oligarchy, even for quotas and in radical measures. On the contrary this study, like the one led by [START_REF] Healy | Women, power and trade union government in the UK[END_REF], argues that to understand the feminization of union leadership we need to take into consideration that unions are contested organizations from both a gender perspective and a political one [START_REF] Hyman | Understanding European Trade Unionism. Between Market[END_REF], generating conflicting views about their priorities and appropriate forms of action. Although factionalism and/or sponsorship are at the heart of the construction of union careers, there is a complex interplay between political factions/groups and the definition of union recruitment practices and equality policies. In the case of CFDT, the making of female leaders is due less to organized gendered factionalism than to the role of union identity shift in the 1980s, with its implications in terms of the detection of new activist profiles having reformist preferences. Although (young) women have been encouraged to participate it is not so much because their "participatory leadership style is wholly congruent with the view that union renewal is contingent upon increased member activism at the level of the workplace" [START_REF] Kirton | Transforming union women: the role of women trade union officials in union renewal[END_REF], but more because they have been seen as less politicized and less articulate and probably easier to control (Mc Bride, 2001). They are also seen as helpful in organizing more diverse groups and then recruited as organizers, like in the UK The switch to an "organizing model" has indeed allowed the development of specialized positions ("développeur") that have been offered to young officers, women and managerial and professional staff, in accordance with the 'like recruiting like' principle (Guillaume and Pochic, 2009b).

In addition to this membership dimension, several 'expertise routes' have been encouraged both by the evolution of union reformist doctrine and by employer-union relations. Because of its present moderate leadership, CFDT has been involved as a negotiating partner with government or advisor on pension issues, unemployment benefits, working time, minimum wages, health and safety, equality and redundancy. This growing union participation in socioeconomic regulation at the national or local level has led to the promotion of officers and activists with new types of qualification. This need for more qualified officers has presented new opportunities to women with professional expertise or high qualification yet no activist background. As in other organizations, we may argue that women have used the "qualification lever" [START_REF] Crompton | Gendered Jobs and Social Change[END_REF] to enter male-dominated sectors. This account can be linked with other research led in the UK, where full-time women officers were found to be "more likely to have come from a background in professional and managerial work and to have higher education qualifications and to be younger" [START_REF] Heery | A cracking job for a woman -a profile of women trade union officers[END_REF].

Finally, our study leads to the issue of the influence that feminist identity has in the building of a union career for women. Most Anglo-Saxon studies strongly emphasize the fact that "most of the self-identified feminists participated formally, suggesting a stronger union orientation" [START_REF] Kirton | The influences on women joining and participating in trade unions[END_REF]. Interestingly, we did not find such strong feminist orientation amongst our interviewees, especially not among the younger ones. Moreover, most of them refuse to consider women as a specific/political category, and they promote egalitarian and mainstreaming measures. The majority also decline to act as role models for other women, with few exceptions. This can be interpreted in different ways. First we can consider that there is a gap between having feminist beliefs and values and espousing the feminist label (Kirton, 2006a), because being labelled as "feminist" within CFDT could jeopardize the building of one's legitimacy in a confederation, still male-dominated, that promotes general interest versus corporatist or community interest. Secondly, we can deduce that the CFDT doctrine of a general and apolitical union attracts (and retains) women who do not hold strong feminist views. Many women leaders, with feminist beliefs, who joined CFDT in the 1970s left in the 1990s and joined other more "radical" unions such as CGT or SUD (which implies that union values and feminist values do not necessary go hand in hand). Thirdly, we can argue that labour education in France has ceased to be politicized and does not offer the function that women-only courses in the UK still provide in raising feminist beliefs. This issue of raising feminist consciousness does reveal the transforming and diverse links and relationships that exist between feminist movements and unions, from alliance to indifference (like in the case of the CFDT in the 2000's), depending on periods xi and countries.

Finally, this focus placed on feminism by other (non French) studies may reveal the implicit assumptions that researchers wish to validate through their empirical work, and sometimes through their direct participation in women's training and mentoring programs, or commitment as union activists themselves. In France, very few researchers would admit undertaking feminist research, at least among the younger generation, to guard against forfeiting their legitimacy in their academic role. This does not prevent us helping unions in their thinking and actions, though from a relatively neutral standpoint xii even if our interest in gender and trade unions originally stemmed from the experience of Cécile being a young female research officer working for the CFDT confederation between 2001 and 2004, in a very (white and senior) male dominated world.

Conclusion

In our study we have tried to articulate different levels of understanding that explain the ongoing, albeit still difficult, feminization of union government. Although the influence of equality and organizing policies is obvious at least in the identification of women as members and possible leaders, it does not explain why some women succeed while many others fail to get elected and promoted. Other factors such as employment characteristics, including timeoff agreements and union rights are quite crucial for the building of a union career, for men and women. France is probably a rather specific case because the legal provisions for union activity are quite comprehensive, at least in big companies or in administrations. However, this more favourable context can produce side effects, as most of the senior union leaders have stopped regular work for so long that they are afraid of leaving their union role, and thus appear reluctant to promote a new generation of leaders. This can create strong inequalities between those (mostly male) who are groomed to become future leaders, being slowly trained to hold gradually more prestigious mandates, and others who are sidelined from taking senior roles. When we look at women CFDT leaders' experiences, it is evident that the influence of political orientations, not only in raising equality but also in promoting organizational and strategic changes, is even more crucial in understanding women's promotion than the role of equality policies towards this advancement. This relation between strategic goals and ideological beliefs is probably one of the aspects that should be carefully addressed when trying to understand how social identity (class, gender, race and ethnicity) and "class consciousness" interact in trade unionists' experience [START_REF] Moore | New trade union activism. Class Consciousness or Social Identity?[END_REF].

network (collectif Confédéral Femmes-Mixité), CGT adopted a radical measure, 'quotas' of 50% for its national levels (NEC and Executive Committee) in 1999 and a charter on internal and external equality in 2007 [START_REF] Silvera | Le nouveau défi de l'égalité pour le syndicalisme français : l'exemple de la charte CGT[END_REF]. viii A 'syndicat' in France is a local general union, affiliated to an industrial federation. In the CFDT, the "syndicats" have a strong political role, as their representatives are the ones who have a mandate to vote during the confederation congress, every 4 years. ix The lack of representativeness of the CFDT membership on the race/ethnicity dimension has never been mentioned in our interviews, as France has a tradition of race-neutral citizenship and unions have not developed equity policies on that topic (even if CFDT had in the 1970s unionized and defended migrant workers).

x Only one woman in our sample had begun her working life as admin at the telephone switchboard of a union federation and later became a paid full-time officer in a male-dominated federation (energy) which had had difficulty in fulfilling its quotas (2 women out of 7 at the Executive Council). xi In the 1970s, most of the CFDT equality officers and female union activists were also involved in feminist movements. All the same, although most UK studies on female union leaders reveal their feminist orientation, we can argue that most of them are 50 years old or over, whereas for younger activists this feminist orientation appears less obvious (Kirton, 2006a). xii As Cécile Guillaume who has participated in several union education sessions and was asked to write a note on equality policies in 2008 for the CFDT National Equality Officer.

Table 2 .

 2 Equality policies

		% of women	Main aspects of equality policies
	CFDT	Local and regional levels
	-600,000	-24% of local union secretaries
	members	('syndicat') viii in 2004 (22% in 2001)
	-women comprise	-27% of regional executives in 2004
	45% in 2010 (42%	(24% in 2001)
	in 2002)
	-General	National Level
	Secretary:	-32 % of federation executives in 2004
	François Chérèque	(29% in 2001)
	(male)	-40 % of Conseil National Confédéral
		(CNC) in 2004
		-37% for the Bureau National (BN) in
		2010
		-33% of the Commission Executive
		(CE) in 2010 (same in 2002)


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Trophic ecology of the pikeperch (Sander lucioperca) in its introduced areas: a stable isotope approach in southwestern France

  is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.

	Aurelia and Céréghino, Régis and Santoul, Frédéric. Trophic ecology of the pikeperch (Sander
	lucioperca) in its introduced areas: a stable isotope approach in southwestern France. (2009)
	Comptes Rendus Biologies, vol. 332 (n° 9). pp. 741-746. ISSN 1631-0691

Dorothée Kopp, Julien Cucherousset, Jari Syväranta, Aurelia Martino, Régis Céréghino, Frédéric Santoul To cite this version: Dorothée Kopp, Julien Cucherousset, Jari Syväranta, Aurelia Martino, Régis Céréghino, et al.. Trophic ecology of the pikeperch (Sander lucioperca) in its introduced areas: a stable isotope approach in southwestern France. Comptes Rendus Biologies, 2009, 332, pp.741-746. 10.1016/j.crvi.2009.04.001. hal-00912965 Open Archive TOULOUSE Archive Ouverte (OATAO) OATAO This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 10171 To link to this article : DOI:10.1016/j.crvi.2009.04.001 URL : http://dx.doi.org/10.1016/j.crvi.2009.04.001

To cite this version : Kopp, Dorothée and Cucherousset, Julien and Syväranta, Jari and Martino,


Mona Ibrahim

Cécile Garcia

Kahina Aït Atmane

Ekrame Berrichi

Lise-Marie Lacroix

Antoine Zwick

Bénédicte Warot-Fonrose

Sébastien Lachaize

Philippe Decorse

Jean- Yves Piquemal

Guillaume Viau
email: gviau@insa-toulouse.fr

Carbon Coating, Carburization and High Temperature Stability Improvement of Cobalt Nanorods

The reactivity of highly crystalline hcp cobalt nanorods (NRs) with organic solvents at high temperature was studied. Cobalt NRs with a mean diameter of 15 nm were first synthesized by the polyol process and then heated at 300 °C in octadecene (ODE), oleylamine (OA) or mixtures of these two solvents. The surface and structural modifications of the Co NRs were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning and transmission electron microscopy (SEM and TEM). A disordered carbon shell was formed at the cobalt rod surface, the thickness of which can be tuned from 5 to 25 nm by increasing the amount of oleylamine in the solvent mixture. This carbon shell partially reduced the native cobalt oxide observed at the surface of the NRs and drastically improved their temperature stability as inferred from in-situ XRD study and TEM. The shape anisotropy and the crystallite anisotropy of the hcp phase are both preserved up to 400 °C for the carbon coated cobalt rods whereas the uncoated NRs lose their anisotropy at 225 °C. Treatments at 300 °C in ODE/OA mixtures for different durations allowed the progressive carburization of Co to Co 2 C. The crystallographic orientation of the Co 2 C grains within the cobalt NRs combined with the different carbon shell thickness on the {1010} and (0001) facets of the rods suggested a preferential carburization from the lateral facets of the hcp cobalt rods.

Introduction

The high saturation magnetization of the metal magnetic nanoparticles (NPs) makes them particularly interesting for several applications. However, Fe, Co and FeCo NPs require, for biomedical applications to increase their stability toward oxidation and to make them biocompatible. [START_REF] Lukanov | CCVD Synthesis of Carbon-Encapsulated Cobalt Nanoparticles for Biomedical Applications[END_REF][START_REF] Mehdaoui | Optimal Size of Nanoparticles for Magnetic Hyperthermia : A Combined Theoretical and Experimental Study[END_REF] The growth of a carbon shell can address this issue [START_REF] Seo | FeCo/Graphitic-Shell Nanocrystals as Advanced Magnetic-Resonance-Imaging and Near-Infrared Agents[END_REF] ; it can also strongly improve their thermal stability [START_REF] Ciuculescu | Single-Crystalline Co Nanowires: Synthesis, Thermal Stability, and Carbon Coating[END_REF][START_REF] Rong | High Thermal Stability of Carbon-Coated L1 0 -FePt Nanoparticles Prepared by Salt-Matrix Annealing[END_REF] and open wider possibilities such as covalent grafting of organic groups or biomolecules that add new functions to the magnetic particles. [START_REF] Tan | Cross-Coupling Reactions on the Surface of Carbon-Coated Cobalt: Expanding the Applicability of Core-Shell Nano-Magnets[END_REF][START_REF] Fuhrer | Immobilized β-Cyclodextrin on Surface-Modified Carbon-Coated Cobalt Nanomagnets: Reversible Organic Contaminant Adsorption and Enrichment from Water[END_REF] Different routes for carbon encapsulated cobalt and iron particles have been described like carbon arc process [START_REF] Seo | FeCo/Graphitic-Shell Nanocrystals as Advanced Magnetic-Resonance-Imaging and Near-Infrared Agents[END_REF][START_REF] Mchenry | Superparamagnetism in Carbon-Coated Co Particles Produced by the Kratschmer Carbon Arc Process[END_REF][START_REF] Seshadri | Cobalt and Nickel Nanoparticles Encapsulated in Carbon Obtained by the Arc Evaporation of Graphite with the Metals[END_REF][START_REF] Bonard | Varying the Size and Magnetic Properties of Carbon-Encapsulated Cobalt Particles[END_REF] or chemical vapour deposition. [START_REF] Lukanov | CCVD Synthesis of Carbon-Encapsulated Cobalt Nanoparticles for Biomedical Applications[END_REF][START_REF] El-Gendy | The Synthesis of Carbon Coated Fe, Co and Ni Nanoparticles and an Examination of their Magnetic Properties[END_REF][START_REF] Wang | Characterization and Magnetic Properties of Carbon-Coated Cobalt Nanocapsules Synthesized by the Chemical Vapor-Condensation Process[END_REF][START_REF] Liu | Large-Scale Preparation of Carbon-Encapsulated Cobalt Nanoparticles by the Catalytic Method[END_REF][START_REF] Li | Fabrication of Carbon-Coated Cobalt Nanoparticles by the Catalytic Method[END_REF] In these methods the cobalt precursors were either ultrafine cobalt oxide powder or organometallic precursors, the cobalt particles were formed at high temperature and therefore exhibit a spherical shape and generally the fcc structure. Amorphous cobalt cores surrounded by a carbon shell were produced by laser ablation of a cobalt target immersed in toluene [START_REF] Kwong | Formation of Core/Shell structured Cobalt/Carbon Nanoparticles by Pulsed Laser Ablation in Toluene[END_REF] or by decomposition of metallocene powders under a laser beam. [START_REF] Huh | Laser Synthesis and Magnetism of Amorphous Iron and Cobalt Carbide Nanoparticles with Carbon Onion[END_REF] Sonochemical decomposition of Fe(CO) 5 in high boiling point aromatic solvent [START_REF] Nikitenko | Synthesis of Highly Magnetic, Air-Stable Iron-Iron Carbide Nanocrystalline Particles by Using Power Ultrasound[END_REF] and thermal decomposition of iron stearate [START_REF] Geng | Direct Conversion of Iron Stearate into Magnetic Fe and Fe 3 C Nanocrystals Encapsulated in Polyhedral Graphite Cages[END_REF] at 900 °C are other examples of one-pot reaction that produced air stable carbon encapsulated Fe and Fe 3 C nanocrystals with high yield. Methods were also developed to coat with a carbon shell monodisperse Co NPs first prepared by wet chemistry. The principle in that case was to carry out a pyrolysis of the organic molecules (surfactants or polymers) anchored at the particle surface. Stable encapsulated cobalt particles were obtained with temperature pyrolysis in the range 700-1000 °C. [START_REF] Lu | Highly Stable Carbon-Protected Cobalt Nanoparticles and Graphite Shells[END_REF][START_REF] Zalich | Structural and Magnetic Properties of Oxidatively Stable Cobalt Nanoparticles Encapsulated in Graphite Shells[END_REF] Milder conditions were found using an aqueous solution of glucose that allowed a carbon coating of cobalt nanostructures by a treatment at 160 °C in hydrothermal conditions. [START_REF] Zhu | Solution Route to Single Crystalline Dendritic Cobalt Nanostructures Coated with Carbon Shells[END_REF] The magnetic nanorods (NRs) and nanowires (NWs) exhibit peculiar properties because of their high magnetic anisotropy. Elongated magnetic objects find applications in composite materials [START_REF] Zadoina | In Situ Synthesis of Cobalt Nanoparticles in Functionalized Liquid Crystalline Polymers[END_REF] or as biosensors. [START_REF] Schrittwieser | Modeling and Development of a Biosensor Based on Optical Relaxation Measurements of Hybrid Nanoparticles[END_REF] Coercivity higher than 6 kOe were measured on cobalt nanorods (NRs) and nanowires (NWs) synthesized by the polyol proces [START_REF] Soumare | Kinetically Controlled Synthesis of Cobalt Nanorods with High Magnetic Coercivity[END_REF] or by organometallic chemistry. [START_REF] Soulantica | Magnetism of single-crystalline Co nanorods[END_REF] Composite materials of well aligned cobalt wires are expected to exhibit high (BH) max values. [START_REF] Maurer | Magnetic Nanowires as Permanent Magnet Materials[END_REF] Nevertheless we showed recently that the thermal stability of the cobalt rods prepared by the polyol process in powder form was limited to 225 °C. [START_REF] Ait Atmane | High Temperature Structural and Magnetic Properties of Cobalt Nanorods[END_REF] Above this temperature the sintering of the rod irreversibly altered their magnetic properties. [START_REF] Ait Atmane | High Temperature Structural and Magnetic Properties of Cobalt Nanorods[END_REF] In situ transmission electron microscopy experiments demonstrated that a controlled encapsulation in a C shell of Ge [START_REF] Sutter | Au-Induced Encapsulation of Ge Nanowires in Protective C Shells[END_REF] and Co 4 nanowires at moderate temperatures increased their thermal stability. Following this idea our goal was to develop a simple method to coat cobalt rods prepared by the polyol process with a thin carbon shell in order to improve their thermal stability. All the methods consisting in the decomposition of a carbon precursor requiring high temperature were not suited for the coating of hcp cobalt particles due to the phase transformation of hcp toward fcc occurring at 450 °C.

In this article we examine the possibility to coat cobalt NRs with a carbon shell thanks to the decomposition of high boiling organic solvents at 300 °C and we report on the thermal stability of these carbon coated Co NRs. We show that a carburization of cobalt can occur depending on the experimental conditions and that these nanorods are also model materials to study how C atoms incorporate in the Co hcp structure to form the cobalt carbide Co 2 C.

Experimental Methods

Synthesis and coating of Co nanorods

Sodium hydroxide was purchased from VWR, ruthenium chloride hydrate (RuCl 3 , x H 2 O) and 1,2 butanediol from Fluka, cobalt acetate tetra hydrate and octadecene (ODE) from Alfa Aesar, lauric acid and oleylamine (OA) from Acros.

Cobalt nanorods were synthesized by reduction of cobalt laurate in a basic solution of 1,2 butanediol according to a procedure previously published. [START_REF] Soumare | Kinetically Controlled Synthesis of Cobalt Nanorods with High Magnetic Coercivity[END_REF] Cobalt laurate (0.08 M) was dispersed in a sodium hydroxide solution (0.08M) of 1,2 butanediol containing ruthenium chloride (2.10 -3 M). The suspension was heated up to 175 °C and this temperature was maintained for 30 min after the solution turned to black indicating the cobalt reduction. The cobalt particles were recovered by centrifugation and washed twice with absolute ethanol. The cobalt rods were characterized by X-ray diffraction and electron microscopy.

The cobalt nanorods were dispersed and heated in a high boiling point organic solvent in order to provoke the solvent decomposition at the surface of NRs. Two different solvents were studied: ODE and OA. Suspensions of cobalt rods in ODE, OA, or a mixture of these two solvents were heated at 180 °C for 30 min under a flux of argon to ensure the complete evaporation of ethanol, and then at 300 °C under Ar atmosphere for a time varying between 30 min to 4h. The treated particles were characterized by Raman spectroscopy, X-ray diffraction, electron microscopy and magnetometry.

Characterizations

Raman spectra were obtained at room temperature with a Dilor XY microspectrometer equipped with a 1024  256 pixel thermoelectrically cooled Jobin-Yvon CCD detector using an excitation line at 514.5 nm from a Spectra Physics Model 165 argon ion laser (power: 150 µW). The carbon and hydrogen mass fractions in the samples were determined using a Flash 2000 Organic Elemental Analyzer from Thermo. Transmission electron microscopy (TEM) characterizations were performed using a Jeol 1400 microscope operating at 120 kV. High resolution transmission electron microscopy (HRTEM) images were obtained with a Tecnai F20 (200 kV) instrument equipped with a spherical aberration corrector. Scanning electron microscopy (SEM) was performed using a Zeiss SUPRA 40 FESEM controlled by a computer workstation. The electron source is a thermal field emission gun (Schottky type).

Images are created using the SMARTSEM software. X-Ray Diffraction (XRD) patterns obtained using Co K  radiation (λ = 1.7889 Å) were recorded on a PANalytical X'Pert Pro diffractometer equipped with an X'celerator detector in the range 20-100 ° with a 0.067 ° step size and 150 s per step. In order to follow the structural evolution of the carbon cobalt nanorods with temperature, in-situ thermal treatments were realized in the range 25-500 °C under a nitrogen atmosphere (N 2 Alphagaz 1 : O 2 < 2 ppm or N 2 Alphagaz 2 : O 2 < 0.1 ppm) using a HTK 1200N high-temperature X-ray diffraction chamber from Anton Paar. The samples were heated inside the high temperature X-ray diffraction chamber from room temperature to the final temperature using a 5 K•min 1 rate and maintained for 2 h at the final temperature prior to the acquisition of the X-ray diffraction pattern. X-ray photoelectron spectroscopy (XPS) signals were recorded using a Thermo VG ESCALAB 250 system equipped with a micro-focused, monochromatic Al K X-ray source (1486.6 eV) and a magnetic lens which increases the electron acceptance angle and hence the sensitivity. A 650 µm sized X-ray beam was used at a power of 200 W (15 kV). The samples were fixed on sample holder using conductive double-sided tape and outgassed in the fast entry lock chamber at 1x10 -7 mbar. The spectra were acquired in the constant analyser energy mode, with a pass energy of 100 and 40 eV for the survey and the narrow regions, respectively.

Charge compensation was achieved with an electron flood gun for insulating samples. The energy and emission current of the electrons were 4 eV and 0.15 to 0.20 mA, respectively.

Avantage software, version 4.67, was used for data digital acquisition and processing. The peak binding energy positions were calibrated by setting the C1s component due to hydrocarbon contamination at 285 eV. Magnetic measurements were performed using a Quantum Design MPMS-5S SQUID magnetometer.

Results and Discussion

A. Carbon coated cobalt nanorods

Chemical analysis revealed that the carbon mass fraction in the cobalt rod samples increased from 3.8% to 23.4% after a chemical treatment of 3h in ODE at 300 °C, while the hydrogen mass fraction increased from 0.85% to 1.5%. The Raman spectra of the cobalt rods heated either in ODE or OA at 300 °C exhibit two bands at 1340 and 1600 cm -1 indexed as the D and G bands of a disordered carbon, respectively (Figure 1). The G band corresponds to the sp 2 C while D band is related to the presence of sp 3 C and reveals the presence of structural defaults.

The intensity ratio I D /I G is a good indicator of the disorder in the carbon layer. [START_REF] Zickler | A Reconsideration of The Relationship Between The Crystallite Size L a of Carbons Determined by X-Ray Diffraction and Raman Spectroscopy[END_REF] In this study the I D /I G ratio varies in the range 0.67 -0.8 depending on the nature of the organic solvent in which the cobalt rods have been treated, the carbon obtained with the treatment in ODE being less disordered (Figure 1). Note that the D and G bands of the carbon can only be observed on the Raman spectra for a low laser power. For higher laser power, the D and G bands vanish and four bands at 190, 470, 510 and 690 cm -1 attributed to Co 3 O 4 appear. This is explained by the fact that the carbon coating may be burnt off when irradiated in air with a high laser power. In such case the Raman spectrum of "naked" hence readily oxidized cobalt rods is then retrieved.

The scanning electron microscope images show that the cobalt rods treated in ODE at 300 °C for 3h preserve their anisotropic shape but undergo a surface modification (Figure 2a). The transmission electron microscopy images show a thin carbon shell around the cobalt rods (Figure 2b) with a thickness of about 4 nm. HRTEM images show that this shell exhibits locally an onion structure with a distance in the range 3.4-3.5 Å (Figure 2c). X-ray photoelectron spectroscopy was performed on cobalt rods treated at 300 °C for 3h in ODE and on the raw cobalt rods as reference. The main peaks observed in the survey scans of the two samples are C 1s, O 1s and Co 2p peaks centered at ca. 285, 530 and 778-800 eV, respectively (Figure 3a). For the treated rods the C 1s peak intensity increases and becomes much higher than the O 1s peak. This can be interpreted by the deposition of a continuous carbon shell around the rods in good agreement with the TEM images. The Co 2p 3/2 and 2p 1/2 high resolution spectra were fitted with three components corresponding to Co(0), Co(II) and the shake-up (satellites) peaks (Figure 3b). Both for the raw Co NRs and for the NRs treated at 300 °C the first peak maximum was found at 778.2 eV which is consistent with the Co 2p 3/2 binding energy of Co in a zerovalent state. [START_REF] Wagner | NIST X-ray Photoelectron Spectroscopy Database[END_REF] The second peak exhibited a maximum at 781.2 eV and 780.6 eV for the raw Co NRs and for the NRs treated at 300 °C, respectively. This peak is attributed to Co in a 2+ valence state in agreement with the Co 2p3/2 binding energy of Co(OH) 2 and CoO that are generally given in the ranges 781-782 eV and 780-780.9 eV, respectively. [START_REF] Wagner | NIST X-ray Photoelectron Spectroscopy Database[END_REF] The Co(0)/[Co(0)+Co(II)] surface ratio was determined from the integrated peak areas. This ratio was 6% in the raw Co NRs. The main contribution of the Co(II) is well explained by the existence of a thin CoO layer at the surface of the rods that screens the cobalt metal. [START_REF] Maurer | Exchange Bias in Co/CoO Core-Shell Nanowires: Role of The Antiferromagnetic Superparamagnetic Fluctuations[END_REF] In the carbon coated Co NRs the Co(0)/[Co(0)+Co(II)] ratio increased to 17 %. This increasing amount of the Co(0) contribution shows that the chemical reaction at the cobalt surface that leads to a carbon coating also partially reduces the cobalt oxide layer. The small energy shift of the Co(II) contribution from 781.2 eV to 780.6 eV observed with the carbon coating can be interpreted by the elimination of the hydroxyl and carboxylate groups at 300°C in favour of CoO.

It is well established that the cobalt NRs crystallize with the hcp structure with the crystallographic c axis parallel to the long axis of the rods. [START_REF] Soumare | Kinetically Controlled Synthesis of Cobalt Nanorods with High Magnetic Coercivity[END_REF] The zone axis of the cobalt wire in figure 2c is [11 2 0] which means that the long axis of the rods is parallel to the [0002] direction. The crystallite anisotropy is also inferred from the XRD pattern. The two mean crystallite sizes L (101 0) and L (0002) , calculated from the broadening of the Co hcp (1010) and (0002) lines, respectively, are found much different from each other due to the anisotropy of the crystallite. The mean crystallite size L (101 0) is almost the rod diameter showing a good crystallinity in the diameter while the mean crystallite size L (0002) is found much lower than the rod length maybe due to stacking faults as it was already observed in several examples of raw cobalt rods prepared by the polyol process. [START_REF] Soumare | Kinetically Controlled Synthesis of Cobalt Nanorods with High Magnetic Coercivity[END_REF] The cobalt rod structure remains unchanged with the treatment in pure ODE for 3h, the XRD pattern is indexed as pure cobalt with the hcp structure (Figure 4a). We must note that the line corresponding to the carbon graphite at 3.5Å is not visible on the XRD pattern of the carbon coated Co NRs. This can be explained by a very disordered carbon shell with small crystallites leading to very broad peaks that are not easily detected on the XRD pattern. The mean crystallite sizes L (101 0) and L (0002) were found 12 nm and 38 nm, respectively. These values are similar to those measured in the raw Co NRs pattern, showing that the treatment of the cobalt rods at 300 °C in ODE for 3h did not modify the crystallite anisotropy.

B. Transformation to cobalt carbide

Treatments of the cobalt rods at high temperature in ODE/OA mixtures may induce a more dramatic modification of the rod morphology and structure. The XRD patterns of the rods treated in the ODE/OA mixture for different durations are given on Figure 4b-c 4c). After a treatment of 4h at 300 °C in the ODE/OA mixture, the Co metal lines totally disappeared and the compound consisted in a pure cobalt carbide powder (Figure 4d). It is well known that fine cobalt powders are sensitive to carburization when they are prepared in an organic solvent at high temperature. 33 , 34 , 35 The carburization of cobalt can give two different carbides, Co 3 C and Co 2 C. [START_REF] Harris | High Coercivity Cobalt Carbide Nanoparticles Processed Via Polyol Reaction: A New Permanent Magnet Material[END_REF] In these experiments Co 3 C was never observed: the carburization of the hcp cobalt NRs leading only to Co 2 C. Figure 5 presents TEM images of cobalt rods treated in ODE/OA mixtures. The partially carburized cobalt rods obtained after 3h at 300 °C are coated by a thicker carbon layer than in ODE, with a thickness in the range 9-23 nm and a mean value of 16 nm (Figure 5a). The rods still exhibit an anisotropic shape but their surfaces are rough. It is noteworthy that the carbon shell is much thinner at the rod tips (Figure 5a). HRTEM studies of the partially carburized rods treated 3h at 300 °C revealed that the same rod can contain Co 2 C grains inserted in the Co hcp phase (Figure 6). The diffraction pattern calculated from the HRTEM image of the Co grain was indexed as the direction of the hcp Co is less than 2° showing a very small mismatch. The same crystallographic relationship was reported by Nagakura on Co/Co x C thin films. [START_REF] Nagakura | Study of Metallic Carbides by Electron Diffraction Part IV[END_REF] When the Co to Co 2 C carburization was complete after an extended treatment, the particles were no longer anisotropic but consisted in isotropic particles with a size in the range 9-25 nm and a mean size of 15 nm (Figure 5b). These particles are organized in chains embedded in a carbonaceous coating. All the chains have more or less the same diameter (40-50 nm) evidencing the initial anisotropic cobalt particles.

C. High temperature properties of carbon coated cobalt nanorods

The high temperature in-situ X-ray diffraction (HT XRD) patterns under a N 2 atmosphere with O 2 concentration < 2 ppm of Co NRs coated with a thin carbon layer showed that the hcp structure is preserved for temperature up to 400 °C (Figure 7a). 7b). Even if the O 2 content in the nitrogen atmosphere is small the non coated rods were irreversibly oxidized above this temperature contrarily to the carbon coated rods.

The mean crystallite sizes L (101 0) and L (0002) of the carbon coated Co NRs were calculated using the Scherrer formula and plotted as a function of the annealing temperature (Figure 7c).

The L (10 1 0) value is almost constant all over the temperature range 25-400 °C. A small increase is observed at 300 °C concomitant with the CoO elimination. This can be interpreted as the increase of the metal diameter due to the reduction of the native oxide layer. The L (0002) at 400 °C is 36 nm, very close to the RT value (Figure 7c) which means that the anisotropy of the hcp crystallite is retained up to 400 °C. At 450 °C both L (101 0) and L (0002) strongly increase showing that the rod morphology is definitively lost due to the phase transition hcp to fcc. The L (0002) variation in the intermediate range of annealing temperature is more difficult to interpret. L (0002) decreases progressively up to 250 °C and then increases suddenly to reaches at 300 °C the room temperature value (Figure 7c). The minimum of L (0002) corresponds to the maximum of oxidation. The formation of a thicker CoO layer seems to decreases the crystallographic coherence length along the c axis but this decreasing is reversible.

The high temperature in situ X-ray diffraction patterns of the partially carburized Co NRs coated with a thick carbon layer and annealed under a N 2 atmosphere (O 2 < 0.1 ppm) at different temperatures showed that the cobalt carbide disappears between 300 and 350 °C (Figure 8). The pure hcp structure is retrieved above 350 °C. No evidence of CoO crystallization was found in the intermediate temperature patterns in good agreement with our previous observation that prolonged treatment reduces the cobalt oxide native layer. As in the case of the non carburized rods a textural anisotropy is preserved at 400 °C, inferred from the larger broadening of the (101 0) line compared to the (0002) one. Nevertheless, the TEM images showed that the mean aspect ratio decreased after the thermal treatment at 400 °C. This can be interpreted by a morphological modification with the decarburization of the Co 2 C grains located within the rod.

On the other hand the high aspect ratio of the carbon coated Co NRs free of carbide was preserved for annealing up to at 400 °C for 2h as inferred from TEM images (Figure 9). The room temperature magnetic properties of the carbon coated Co NRs were measured before and after the thermal treatment at 400 °C (Figure 10). In both cases the magnetization curve exhibits a remanence to saturation magnetization ratio of 0.5, the expected value for a powder in which particles are randomly oriented in the applied magnetic field. The coercivity is almost constant, it increases from 3500 Oe to 3600 Oe after thermal treatment. Such coercivity values are in good agreement with the previous ones measured on cobalt rods prepared by the polyol process. [START_REF] Soumare | Kinetically Controlled Synthesis of Cobalt Nanorods with High Magnetic Coercivity[END_REF][START_REF] Ait Atmane | High Temperature Structural and Magnetic Properties of Cobalt Nanorods[END_REF] Indeed, according to the Stoner-Wolfarth model, an assembly of the same Co NRs perfectly ordered parallel to the applied field should exhibit a coercivity value of 7000 Oe. The high magnetic anisotropy of these rods comes from the addition of shape anisotropy and magnetocrystalline anisotropy. This study shows that the carbon coating and the subsequent annealing at 400 °C do not lower the magnetic anisotropy.

The saturation magnetization of the carbon coated Co NRs is 103 emu per gram of powder. This value increases to 117 emu.g -1 after annealing at 400 °C for 2h. This increase of 14% corresponds to the loss of organic matter and to the partial reduction of the CoO shell during the annealing process. The saturation magnetization is lower than the bulk cobalt value because an important amount of carbon remains after the annealing.

D. Discussion

This work shows that the decomposition of organic solvents at 300 °C is a simple route to coat cobalt nanorods with a thin carbon shell. The pyrolysis of polymers to produce a carbon coating is generally performed in a gas phase at much higher temperature. In our case, milder conditions were necessary to keep both the hcp structure and the anisotropic shape of the rods.

The interest to carry out the carbon coating in a liquid phase is that individual nanorods are coated and remain stabilized in solution: no agglomeration was observed after coating. The 5 nm carbon shell obtained by a treatment in ODE at 300 °C improves the thermal stability of the Co NRs. Indeed the carbon coated Co NRs remain unchanged even after annealing in powder form at 400 °C. This behaviour is very different from the one of raw cobalt NRs. A previous study on the high temperature stability of raw cobalt rods showed that in absence of a carbon coating the anisotropy was lost at 225 °C. [START_REF] Ait Atmane | High Temperature Structural and Magnetic Properties of Cobalt Nanorods[END_REF] At this annealing temperature a strong increase of the mean crystallite sizes L (101 0) and L (0002) was observed, the crystallite lose their anisotropy and the TEM revealed a particle sintering. Thus, we can conclude that the thin carbon coating acts as an efficient barrier for the particle sintering at temperature as high as 400 °C and preserves the particle anisotropy. Moreover, in a slightly oxidative atmosphere the carbon layer can act as a sacrificial shell that preserves the cobalt core from oxidation (Figure 7).

It is well established that small organic molecules like carbon monoxide or ethylene can decompose at the surface of Fischer-Tropsch cobalt catalysts at relatively low temperature and form a carbon deposition, being a cause of deactivation. [START_REF] Tan | Carbon Deposition on Co Catalysts during Fischer-Tropsch Synthesis: A Computational and Experimental Study[END_REF] The carbon coating in our case results certainly from a mechanism similar to the carbon deposition on the Fischer-Tropsch cobalt catalysts.

The thickness of the carbon shell can be varied in the range 5-20 nm, but a thick shell comes along with a carburization. Ping Liu et al. described the formation of Co 2 C nanoparticles in tetra ethylene glycol by a carburization of cobalt particles formed at first in the medium. [START_REF] Zhang | Controlled Synthesis and Magnetic Properties of Hard Magnetic Co x C (x=2, 3) Nanocrystals[END_REF] Our study confirms that the decomposition of organic solvents at the surface of cobalt NRs is a source of carbon atoms that first form a carbon shell at the surface and then diffuse into the metal crystal to form carbide. In this study the carburization of the hcp cobalt NRs leads only to Co 2 C. The formation of Co 2 C is generally described as the result of the intercalation of C atoms in the hcp ABAB stacking of the (0001) dense planes. [START_REF] Zhang | Controlled Synthesis and Magnetic Properties of Hard Magnetic Co x C (x=2, 3) Nanocrystals[END_REF][START_REF] Nagakura | Study of Metallic Carbides by Electron Diffraction Part IV[END_REF][START_REF] Ducreux | Microstructure of Supported Cobalt Fischer-Tropsch Catalysts[END_REF] The cobalt NRs expose mainly {1010} crystallographic facets which is favourable to the C intercalation in the metal array (Figure 11). The crystallographic relationships between the hcp Co grain and the Co 2 C grain inserted in the hcp stacking inferred from the HRTEM study (Figure 6) correspond exactly to this mechanism. The difficulty to insert carbon from the (0001) planes and/or a difference in the catalytic activity for the decomposition of the organic molecules of the two different facets can explain why the carbon shell is much thinner at the rod tips than on the sides (Figure 5a). The formation of a thick carbon coating around the cobalt rods seems related to their ability to form a carbide. This observation reminds results reported on the activity of cobalt-based Fischer-Tropsch catalysts. [START_REF] Ducreux | Microstructure of Supported Cobalt Fischer-Tropsch Catalysts[END_REF] Indeed the higher activity for CO conversion in Fischer-Tropsch conditions of hcp cobalt was explained by the easiest facility of hcp Co particles to form carbide, the C atoms being extracted by the hydrogen to form hydrocarbon molecules. [START_REF] Ducreux | Microstructure of Supported Cobalt Fischer-Tropsch Catalysts[END_REF]

Conclusion

A simple and rapid method to encapsulate cobalt nanorods into a thin carbon layer through a thermal treatment in organic solvents at 300 °C has been described. This carbon shell does not modify the magnetic anisotropy of the cobalt rods and strongly improve their thermal stability.

The Co@C core shell NRs that have been produced are stable up to 400 °C and are promising building blocks for the elaboration of anisotropic nanomaterials by consolidation experiments.

Moreover, the growth of a carbon shell by this method opens the way to a covalent functionalization at the cobalt NRs surface with organic molecules and to the grafting of polymers that will favor the NRs dispersion into a polymeric matrix or to add new functionalities.

This study has also confirmed that the (0001) and the {1010} facets of the hcp cobalt exhibit a different reactivity toward the C insertion and points to possible future works on the use of cobalt particles with well defined morphology as model Fischer-Tropsch catalysts.

FIGURE CAPTIONS

  . These patterns exhibit additional lines attributed to the cobalt carbide Co 2 C. 32 The (111) peak of the orthorhombic Co 2 C (d 111 = 2.12 Å ; 2 = 49.9 °) appears first (Figure 4b). For a longer treatment the (020), (002), and (021) peaks at the distances d 020 = 2.22 Å (2 = 47.45 °), d 002 = 2.185 Å (2 = 48.3 °) and d 021 = 1.98 Å (2 = 53.7 °) are clearly seen on the pattern (Figure

[11 2 0

 2 ] zone axis of the hcp structure showing that the c axis is parallel to the rod axis. The diffraction pattern calculated from the HRTEM image of the Co 2 C grain was indexed as the [100] zone axis of the expected orthorhombic structure (Figure 6). The crystallographic orientation relationships between the carbide and the metal are [100]Co 2 C||[11 2 0]Co hcp and (001)Co 2 C||(0001)Co hcp . The angle between the [001] direction of Co 2 C and the [0001]

  At 450 °C the hcp to fcc phase transformation occurs as predicted by the phase diagram of bulk cobalt. The formation of the fcc phase is clearly seen with the (200) peak, d 200 = 1.77 Å (2 = 60.6°). In the temperature range 100-250 °C there is also the growth of the (111) and (200) fcc cobalt oxide CoO lines, d 111 = 2.46 Å (2 = 42.6°) and d 200 = 2.13 Å (2 = 49.65°), that corresponds to the crystallization of the native oxide layer. Above 250 °C the CoO lines vanish because of the reduction of the cobalt oxide layer by the carbonaceous matter at the particle surface. No trace of re-oxidation of the Co NRs was observed in the temperature range studied. The behaviour of the non coated Co NRs at high temperature under the same atmosphere was very different. At 250°C the (220) line of Co 3 O 4 (d = 2.86 Å, 2 = 36.5 °) appeared. At 350 °C the pattern is indexed as a mixture of hcp Co, CoO and Co 3 O 4 (Figure

Figure 1

 1 Figure 1Raman spectra of cobalt nanowires treated in an organic solvent at 300 °C for 3h :

Figure 2

 2 Figure 2 (a) SEM, (b) TEM and (c) HRTEM images of cobalt rods coated with a thin carbon

Figure 3 X

 3 Figure 3 X-ray photon electron spectra of cobalt rods and cobalt rods coated by a thin carbon

Figure 4

 4 Figure 4 XRD pattern of Co rods treated (a) in ODE for 3h and in a mixture of ODE/OA for

Figure 5

 5 Figure 5 TEM images of cobalt rods treated at 300 °C (a) for 3h in OA and (b) for 4h in a

Figure 6

 6 Figure6HRTEM image of a cobalt rod treated in an ODE/OA mixture at 300 °C for 3h.

Figure 7

 7 Figure 7In-situ X-ray diffraction patterns under N 2 (O 2 < 2 ppm) of (a) carbon coated Co

Figure 8

 8 Figure 8 In situ X-ray diffraction patterns of carbon coated and partially carburized Co

Figure 9

 9 Figure 9 TEM image of carbon coated Co nanorods annealed at 400 °C under N 2 (O 2 < 0.1

Figure 10

 10 Figure 10 Room temperature magnetization curve of carbon coated Co nanorods (black) and

Figure 11

 11 Figure 11 Scheme of formation of a Co 2 C grain in a cobalt rod by intercalation of C atoms

Figure 1 Figure 2 Figure 3 X

 123 Figure 1Raman spectra of cobalt nanowires treated in an organic solvent at 300 °C for 3h :

.

Figure 4

 4 Figure 4 XRD pattern of Co rods treated (a) in ODE for 3h and in a mixture of ODE/OA for

Figure 5 .

 5 Figure 5. TEM images of cobalt rods treated at 300 °C (a) for 3h in OA and (b) for 4h in a

Figure 6

 6 Figure 6 HRTEM image of a cobalt rod treated in an ODE/OA mixture at 300 °C for 3h.

Figure 7

 7 Figure 7 In-situ X-ray diffraction patterns under N 2 (O 2 < 2 ppm) of (a) carbon coated Co

Figure 8

 8 Figure 8 In situ X-ray diffraction patterns of carbon coated and partially carburized Co

Figure 9 Figure 10 .

 910 Figure 9 TEM image of carbon coated Co nanorods annealed at 400 °C under N 2 (O 2 < 0.1

Figure 11 .

 11 Figure 11. Scheme of formation of a Co 2 C grain in a cobalt rod by intercalation of C atoms

Acknowledgement

The authors gratefully acknowledge Dr. S. Nowak and S. Lau for XRD and Raman experiments, respectively. The authors thank the Région Midi-Pyrénées and the European

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µ 0 H (T)

Co@C nanorods