Eric Tafani

Géraldine Michel

Vertical Product Line Extension Strategies: an Evaluation of Brand Halo Effect according to Range Level

Keywords: Vertical product line extension, brand image, halo effect, social representations, central nucleus theory

The brand halo effect for vertical product line extensions is analyzed using the central nucleus theory. The empirical study is based on experimentation linked to six brands in the automotive sector. This research shows that central brand associations are transferred to the vertical product line extension regardless of range level -low, middle or high-end range -and that such transference systematically reinforces linkages between such associations and the product line extensions. In contrast, the transfer of peripheral associations appears to be range-dependent, increasing or decreasing linkages between such associations and the product line extension according to the range level considered.

INTRODUCTION

The brand is a distinctive sign meant to ensure differentiation vis-à-vis of competitive products, providing added value to the branded product [START_REF] Farquhar | Managing brand equity[END_REF]. Over the past twenty years, the brand has emerged as a new form of capital upon which companies rely to launch new products or services. The vertical product line extension strategy has become a common practice for companies seeking to provide a range of products under an existing trademark -from entry-level to premium products -for product categories where branding is a differentiating factor [START_REF] Keller | Strategic brand management[END_REF]. The vertical product line extension represents a new product entry for a brand with levels of performance and prices significantly different from existing ranges of products (e.g., Apple MP3 players under the brands Nano and Shuffle, sold for 40% to 50% less than Apple's lead brand, iPod). Our research focuses on the vertical product line extension strategy, a strategy that, despite extensive development, remains little studied.

Research has shown that the evaluation of vertical product line extensions was influenced by (1) new product launches [START_REF] Kim | Consumer evaluation of vertical brand extensions and core brands[END_REF], (2) functional and symbolic brand characteristics [START_REF] Kim | Consumer evaluation of vertical brand extensions and core brands[END_REF][START_REF] Kirmani | The ownership effect in consumer responses to brand line stretches[END_REF][START_REF] Randall | Capital marque et étendue verticale de la ligne de produits[END_REF] and finally, (3) relationships between the product line extension and existing products of the brand [START_REF] Gochen | How the strength of parent brand associations influence the interaction effects of brand breadth and product similarity with brand extension evaluations[END_REF][START_REF] Kim | An experimental investigation of valuation change due to commonality in vertical product line extension[END_REF]. To our knowledge, no research has studied the effect of the brand image in evaluating vertical brand extensions. Several important questions remain: What is the influence of branding on the perception of the product extension? Does image transfer from brand to extension depend on the vertical position within the product range? Finally, how does this image transfer affect perceptions of the vertical product line extension? On these points, several models of brand equity agree on the need to separate the effect of the brand on the evaluation of the branded extension (halo effect), as well as its effect in terms of preference for branded extension [START_REF] Park | A survey-based method for measuring and understanding brand-equity and its extendibility[END_REF]. Even so, the question of range level and brand image dependence remains open to debate.

Our research aims to illuminate these issues on the basis of the theory of social representations [START_REF] Moscovici | La psychanalyse, son image et son public[END_REF]) and more particularly using Central Nucleus Theory [START_REF] Abric | L'organisation interne des représentations sociales: système central et système périphérique[END_REF]. The significance of this theoretical framework is, on the one hand, to postulate that the brand image is based on a social construct which is a reflection of consumer attitudes toward the studied product category [START_REF] Moliner | Images et représentations sociales[END_REF], and on the other hand, to introduce the distinction between central and peripheral brand associations [START_REF] Michel | L'évolution des marques: approche par la théorie du noyau central[END_REF]. Several studies have shown the adaptive function of the peripheral system that makes it possible to incorporate changing brand practices, while demonstrating the stability of brand core system that ensures image continuity [START_REF] Michel | L'évolution des marques: approche par la théorie du noyau central[END_REF][START_REF] Michel | Co-branding: conditions de succès du produit comarqué[END_REF][START_REF] Aimé | L'impact des différentes stratégies de changement de nom de marque sur la représentation de la marque et l'attitude des consommateurs[END_REF][START_REF] Delassus | Stratégie d'abandon de marque: analyse des transferts des valeurs de la marque abandonnée vers la nouvelle marque[END_REF]. Given the specific functions of core and peripheral systems of representation, the aim of the present study is to determine their respective roles for the perception of a vertical product line extension. To meet this objective, this paper is constructed in four steps. We first introduce the theoretical framework and the experiment conducted on six brands in the automotive sector. The results are then presented and discussed in relation to their theoretical, methodological and managerial implications.

THEORETICAL FOUNDATIONS

Vertical product line extensions, range level and halo effects

A vertical product line extension implies coexistence within a product category of multiple branded offers, differentiated according to price and service and perceived as such by individuals [START_REF] Michel | L'extension de gamme verticale: clarification du concept[END_REF]. The market segment is here defined as a group of homogeneous products in terms of product attributes (of similar form and function). In the automotive market, we may thus identify as segments "urban", "sedan" and "road" with links to automobile size and distinct usage. For each of these segments, a consumer may perceive a range of products differentiated according to price and perceived product value. This definition refers to low, middle and high-end ranges found in most markets. 1 A vertical product line extension strategy raises two basic questions: First, are brand associations systematically transferred to the brand extension or does this transfer depend on range levels of the product? Second, does this transfer increase or decrease the strength of linkages between brand association and vertical extensions? For example, does the Peugeot brand image impact the 107, 307 or 607 models equally, given that these models are in different range levels? Are there then, brand associations of Peugeot which are transferred to the various models regardless of the range level? These issues require a distinction between product and brand performance and invoke the concept of brand halo effects.

Considering the brand and the product as separate components of a single offer, [START_REF] Srinivasan | Network models for estimating brand-specific effects in multiattribute marketing models[END_REF] postulated that consumers pay to use a brand independently of the product.

In this way, brand equity is likely to vary from one product and category to another, as suggested by [START_REF] Park | A survey-based method for measuring and understanding brand-equity and its extendibility[END_REF]. Brand equity is thus defined as the "value added" by a trademark (Farquhar, 1989). In order to capture this added value, it becomes necessary to distinguish the "halo effect" of the brand on the collection of product attributes and the brand's "direct effect" on overall product preference [START_REF] Barwise | Brand-equity: snark or boojum?[END_REF][START_REF] Erdem | Brand equity as a signaling phenomenon[END_REF][START_REF] Park | A survey-based method for measuring and understanding brand-equity and its extendibility[END_REF]. In the light of such a distinction, our research focuses on how far consumer brand perceptions influence the perception of vertical extensions via a "halo effect".

Our research proposes to clarify this issue using the Central Nucleus Theory [START_REF] Abric | L'organisation interne des représentations sociales: système central et système périphérique[END_REF] Brand core system and brand image One of the first questions that arises is the extent to which brands embody social representations. According to [START_REF] Moscovici | La psychanalyse, son image et son public[END_REF], three conditions must be present for the emergence of an object as a social representation: dispersion of information suggesting that individuals do not have exhaustive knowledge of the subject matter, inferential pressures which lead individuals to take a position with regard to an object on the basis of partial information, and finally, increased attention arising from the interest implied as a result of discussions and related communications. These three conditions are satisfied by certain brands, especially those of high awareness among the population studied. Indeed, consumers often have only partial knowledge of brands, including those they use regularly [START_REF] Korchia | Connaissance de la marque: concepts et mesures[END_REF], and are thus led to infer the quality of proposed products on the basis of this information and the communications campaigns to which they are exposed. On this basis, the Central Nucleus Theory has already demonstrated its relevance in the study of brand images [START_REF] Michel | L'évolution des marques: approche par la théorie du noyau central[END_REF]. This conceptual framework suggests a brand image as a structure organized around a core and a peripheral system. The distinction between central and peripheral associations is both qualitative and functional [START_REF] Abric | L'organisation interne des représentations sociales: système central et système périphérique[END_REF]. From a qualitative point of view, central associations are defined as invariable because they are necessarily associated with the brand by a large majority of the members of the subject population. The core system includes a brand's defining attributes; in other words, the sufficient and necessary attributes for consumer identification. In contrast, peripheral associations are variable in that they are often, but not always, associated with the brand. Central and peripheral associations perform functions arising from this qualitative distinction. The invariability of central associations makes them resistant to change and independent of context, allowing them to fulfill structural and organizational functions with respect to the brand; they determine brand meaning. The variability of peripheral associations makes them dependent on context, allowing them in this way to provide adaptive and defensive functions (they buffer the core system). These theoretical foundations allow us to better understand brand halo effects.

According [START_REF] Riezebos | Brand-added value: theory and empirical research about the value of brands to consumers[END_REF] a brand halo effect is the difference in perceived values between branded and generic (unbranded) products. From this perspective, the brand is seen as a signal that allows consumers to make inferences about the attributes of a branded product [START_REF] Erdem | Brand equity as a signaling phenomenon[END_REF]. Indeed, from a cognitive point of view, product brand affiliation activates not only a categorization process (the brand will be perceived as a category of which the product is an examplar), but a process of attribution according to which certain category (brand) attributes will be transferred to the product. The principal structural and functional category models agree on the interdependence of these two processes [START_REF] Murphy | The big book of concepts[END_REF]. Indeed, the categorization process itself assumes the attribution of category properties to the product examplar. Such a transfer, however, does not apply equally to all the properties of the category and the transfer depends, among other things, on the context in which the category is activated [START_REF] Barsalou | Perceptual symbol system[END_REF]. Here, the Central Nucleus Theory offers a conceptual framework that can predict what brand associations will be transferred systematically to the extension product as well as the consequences of this transfer for the strength of the link between the extension product and the brand associations.

More specifically, since the central associations are necessarily (and invariably) related to the brand, it can be argued that they are systematically transferred to the branded products.

Moreover, central associations are more context-dependent than peripheral associations [START_REF] Flament | Approche expérimentale de type psychophysique dans l'étude d'une représentation[END_REF], allowing them to play a structural role with respect to perceptions of the social construct. As such, the transfer of central associations to the extension product strengthens linkages to the vertical extension, regardless of the product's position within the product line. In this respect, central associations become permanent features of a brand's halo effect to be positively and systematically transferred to the vertical extension.

-H1a: Central associations are transferred to the product line extension, regardless of the range level.

-H1b: The brand name revelation reinforces the evaluation of product line extension, for the central associations, regardless of the range level.

As peripheral associations are not necessarily related to the brand (conditionality), it is assumed that the transfer of peripheral associations among branded products is not systematic.

Furthermore, peripheral associations are more sensitive to context than the central associations [START_REF] Flament | Approche expérimentale de type psychophysique dans l'étude d'une représentation[END_REF], thus allowing them to serve an adaptive role. In this way, the transfer of peripheral associations to an extension product could either strengthen or weaken linkages within the vertical extension: depending on the product's position within the product line, this link is strengthened when the brand is perceived as meeting consumer expectations, and on the contrary, weakened where the brand is perceived as unlikely to meet such expectations. Peripheral associations thus constitute the contextual elements of a brand's halo effect, for which the transfer to extension products depends on the range level of products considered and may be positive or negative.

-H2a: The transfer of peripheral associations to the extension product is less frequent than the transfer of central brand associations.

-H2b: The effect of the brand name revelation on the evaluation of the product line extension, for the peripheral associations, is moderated by the range level.

STUDY METHODOLOGY

These four hypotheses were tested in the context of a vertical product line extension strategy within the automotive sector, an industry in which levels of product differentiation are clearly established. We present, on the one hand, the research design and sample population, and on the other hand, the measuring instruments used.

Experimental design and sample population

Brand awareness being a necessary condition in considering whether a brand constitutes an object of social representation, we limited our study to the six automotive brands with the highest volume of light vehicle sales in France for the year 2007: 2 Citroën, Ford, Peugeot, Renault, Toyota and Volkswagen. To study brand halo effects with the product lines, five photographs of a concept-car were presented to the participants (See Appendix 1): three exterior photographs (front, back and profile) and two interior photos (one of the dashboard and a wide-angle shot of the passenger compartment). According to a first variable (range level), the concept-car was presented as low, medium or high-end. Participants were asked to rate the concept-car twice: first, without information as to the manufacturer (blind trial), and a second time, after having been informed that the concept-car would be marketed by one of the six brands studied (open trial). To limit the cognitive costs of the task, a delay of three days was introduced between the blind and open trials. The design allowed the study of perceived changes in the halo effect in a controlled manner and according to a before-and-after research design: three range levels (low, middle and high-end) x two tests (blind and open trials)

x six brands (Citroën, Ford, Peugeot, Renault, Toyota, Volkswagen).

The questionnaire was administered face to face with a sample of 576 people with ordinary, non-commercial driver's licenses, strictly balanced in terms of gender (288 men and 288 women), age (288 people aged under 40 and 288 people aged 40 and over) and socio-2 Data provided by the CCFA (Comité des Constructeurs Français d'Automobiles or, Committee of French Automobile Manufacturers). Renault has a 21.48% market share, Peugeot 16.92%, Citroën 13.43%, Volkswagen 6.91%, Toyota 5.01% and Ford 4.99%.

professional categories (288 SPC+ and 288 SPC-). Overall, the research design included 18 combinations of brand and range levels and 32 participants for each condition, balanced in terms of gender, age and socio-professional category.

Range level as a control variable

In the automotive sector, manufacturers distinguish three range levels, differentiated in terms of quality and price: low-end, mid-range and high-end. 3 The present study manipulated the variable "range level" in order to evaluate the transfer of brand associations to the extension product. The model was pre-tested against a control sample of 96 consumers. For the pre-test, six concept-cars were selected: two low-end models (Scion and Daihatsu), two mid-range (Lancia and Lada) and two high-end (Accura and Buick). Participants were shown an average of five concept-car photos (See Appendix 1): three photographs of the automobile exterior (front, back and profile) and two photographs of the interior (dashboard and passenger compartment). For each of the concept-cars, participants were first asked which manufacturer (brand) would have produced the particular model shown, and then whether it was possible that the concept-car had been manufactured by any of the six manufacturers used in the study: Citroën, Ford, Peugeot, Renault, Toyota and Volkswagen. Responses were collected on a four-point scale including two levels of affirmation, "Certainly yes" and "Probably yes", and two levels of denial, "Probably not" and "Certainly not". Finally, respondents were asked to indicate where in the range level the concept-cars would be positioned: low, middle or high-end. To simplify the categorization task, respondents were presented with examples of automobile models in each range level, following which they were asked to classify each concept-car in terms of one of three range levels: low, middle and high-end. The concept-cars chosen for the study (Buick, Lancia and Daihatsu) were chosen to satisfy two main criteria:

1. In as much as participants were not to be informed as to which manufacturers had designed the concept-cars, a condition of plausibility was necessary to ensure that the concept-cars could have been designed by any of the six manufacturers studied (See Table 1).

3 Data supplied by the Committee of French Automobile Manufacturers (CCFA).

2. Photographs must clearly identify differentiated price and quality factors among the concept-cars as belonging to one of the three range levels considered: low, middle or high-end (See Table 1).

[ Insert Table 1 ]

Measuring brand halo effects

Brand image refers to a concept of perception in which brand associations are identified and evaluated on the basis of their strength, valence and uniqueness [START_REF] Keller | Conceptualizing, measuring and managing customer-based brand equity[END_REF].

Associations represent the sum of what is known about a brand by a consumer, and identification leads to the functional, symbolic and experiential attributes associated with a brand. Such ad hoc brand measures focus on specific brand associations and do not allow comparisons of comparable attributes among competing brands. The social representation approach was chosen for this study because it provides a basis for comparing brands and brand extensions. On this theoretical basis, a series of studies (Tafani, Haguel and Household, 2007) showed that the image of a set of car manufacturers depended on the social representations held by individuals of what constituted a "good car". More specifically, these studies identified fourteen attributes strongly associated with a "good car" and showed that these associations are organized into five dimensions that reflect consumer expectations (See Appendix 2). These five dimensions include quality (standard equipment, finish and comfort), hedonism (status, stylishness, horsepower and aesthetics), economy (price and price/value), confidence (reliability, safety and engineering) and novelty (originality and innovation). The present study is placed in the continuation of this work and proposes to measure the brand halo effect on these fourteen attributes. A brand's halo effect was measured as the difference between the participants' judgment of a generic concept-car versus the same concept but as a branded line extension. Thus, participants were asked twice to evaluate the concept-car in the low, middle and highend ranges: once, without information about the design and manufacture (the blind trial) and a second time, after being informed that the concept-car would be marketed by one of the brands (open trial). Both assessments focused on the social representations summarized by the fourteen attributes of a "good car" (See Appendix 3) and collected on 11-point scales, from "0" for the negative qualification to "10" for its opposite. Thus, "equipment" was evaluated as between "0" (very poorly equipped) and "10" (very well equipped), "comfort" was evaluated as between "0" for (very uncomfortable) and "10" for (very comfortable), and so on. It was considered that brands have halo effects to the extent that differences are observed in attribute associations between blind and open trials: the greater the significance of the observed differences, the greater the transference from the brand to brand extension. Finally, the observed differences between blind and open trials allow us to determine whether a brand strengthens (positive difference) or weakens (negative difference) the relationship between the associated attribute and the product extension studied.

Measuring the central nucleus of the brand

Central brand associations are those attributes which a majority of brand users would consider inseparable from the brand experience. The measure used to isolate central association is a test based on the logic of dual-negation. According to this test, central brand associations are those associations which, when removed from the brand profile, result in massive brand rejection [START_REF] Moliner | Validation expérimentale de l'hypothèse du noyau central des représentations sociales[END_REF]. Using this technique, a question such as the following would be asked in order to test the central nature of the association, "reliability": "In your opinion, could a car that is not reliable be of brand X?" This procedure allowed examination of the centrality for fourteen attributes associated with a "good car" in the image of each of the six brands studied. These responses (96 per brand) were collected according to four-point scales which included two levels of acceptance "Very certainly yes" and "Definitely yes" and two levels of refutation "Certainly not" and "Very certainly not". Here, refutations constitute an indication of the centrality of an association when called into question because a product that lacks a particular association is inconsistent with the considered brand. The chi-square test permitted identification of associations seen as inseparable from the brand by a large majority of individuals, and identification of the core system for each brand.

RESULTS

Core and peripheral systems of car brands

In order to identify the central associations of different automotive brands, the observed frequency of brand rejection in response to challenges to each of the fourteen associations (See Table 2) was compared to a standard chi-square test for which threshold inferences were set at two thirds (cf. [START_REF] Tafani | L'étude expérimentale des représentations sociales[END_REF] because such a test is particularly dependent on the panel size.

[ Insert Table 2 ] Given this procedure, overall results indicate that each brand image is organized around a distinct core system. Thus, it appears that the central associations for the Citroën brand clearly indicate economic concerns (affordability, value for money). Central associations for the Ford brand reconcile these concerns with an element of confidence: solidity. The same applies to Renault for which confidence is defined in terms of safety, while economic concerns are limited to value for money. However, the core systems for the Peugeot and Toyota brands contain only items related to confidence: safety, reliability and, for Toyota, a reputation for solidity. It appears then that the core systems for these two brands do not include elements of economic concern. This finding suggests that Peugeot and Toyota lose in terms of economic attractiveness what they gain in consumer confidence. The same is true of Volkswagen whose core systems revolve around confidence (safety, reliability and solidity) while including elements of hedonism (horsepower and stylishness) and quality (finish).

These results demonstrate that social representations of a "good car" constitute a frame of reference which reflects the distinctive image of car brands in terms of consumer expectations.

Evaluation of vertical product line extensions

The results of the pre-test (blind trial) evaluations of the concept-car in terms of the fourteen attributes associated with the social representation of a "good car" are provided in Appendix 3. These data were subjected to examination by analysis of variance in order to evaluate the effect of product level (low, middle and high-end) on the extension product.

These tests confirmed the significance of product level in terms of seven central associations (See Table 3): status, horsepower, comfort, engineering, standard equipment, security and price. As it happens, the high-end concept-car is judged more favorably than the low-end concept-car in terms of hedonism (horsepower and status), confidence (safety and solidity) and quality (comfort and standard equipment). The low-end concept-car, however, is considered more affordable than the up-market concept-car. Finally, the mid-range conceptcar occupies an intermediate position for each of these seven associations. These results indicate that participants clearly distinguish among the three concept-cars, not only in terms of price, but also in terms of benefits (quality, confidence and hedonism). This makes it possible to confirm that the three concept-cars are clearly perceived as differentiated vertical product line extensions.

[ Insert Table 3 ]

Brand halo effects with regard to the range level

The brand halo effect for a given association was measured as the difference between the assessments produced in pre-and post-test trials (blind and open trials). As a first step, we conducted a multivariate analysis of variance (Manova) according to the proposed analytical design, three (vertical positions) x six (brands) of the differences between these tests for each of the fourteen associations. This analysis reveals a main effect for vertical position (Wilks λ = 2.50; p<.0001) and for the brand, (Wilks λ = 4.24; p<.0001) indicating that overall, the significance of the brand halo effect varies depending on the range levels and the brand considered. Moreover, the interaction of range levels and brand was significant (λ de Wilks = 1.82; p<.01) and indicated that the brand halo effect was moderated by the range level considered, which supported, therefore, hypothesis H2b. To complete this analysis and test our hypotheses concerning central and peripheral associations, using Student's t, we compared pre-and post-test assessments for each association and each vertical category and brand (See Table 4).

[ Insert Table 4 ]

The two central associations of the Citroën brand (affordability and value for money) are transferred to the line extension whatever the product level considered, with the effect of strengthening linkages between these associations and the extension product, regardless of the vertical product position. The same observation applies in the case of Ford, three central associations of Ford (solidity, value for money and affordability), Renault, two associations (value for money and safety), Peugeot, two associations (safety and reliability), Toyota, three associations (safety, reliability and solidity) and Volkswagen, six associations (safety, reliability, solidity, stylishness, horsepower and finish). Thus, for the 18 associations identified as central, there is transfer to the extension product for each of the three range levels -in other words, a total of 54 transfers -thus confirming hypothesis H1a. Furthermore, it appears that the systematic transfer strengthens the link between the central associations and the extension product, confirming hypothesis H1b. These results indicate that the central associations are permanent features of the brand halo effect and systematically improve the evaluation of the vertical extension.

With regard to peripheral associations, only three are transferred to extension product, regardless of vertical branding position. Thus, for the three range levels, the link between "product finish" and the extension product is reinforced for Volkswagen and reduced for the three French brands. For Volkswagen, the link between "standard equipment" and the extension product is reinforced, while the link between the extension product and "affordability" is diminished. This finding shows that certain peripheral associations are transferred to the extension product, regardless of the vertical position, which negates hypothesis H2a. We must, however, note that the majority of association transfers depend on the vertical range considered. Indeed, it appears that these associations are transferred to the extension product in only 59 of the 188 possible cases, or 31% of cases. It follows that peripheral associations are less systematically transferred than central associations (Chisquare = 79.35; p<.0001). Moreover, correlation analysis shows that overall, the transfer of any type of association (central or peripheral) is positively related to their degree of centrality (r bp = .38): the more central the association, the greater the transference to the extension product, suggesting that the transfer of brand associations to the product extension clearly depends upon the status of these associations.

Finally, we should note that when such transfers occur, they may, for comparable peripheral associations, strengthen or reduce linkages between the association and the extension product depending on the vertical range considered. This is, in fact, the case for the Peugeot and Renault brands' peripheral association, horsepower (See Table 5): product linkages are strengthened at the lower end of the vertical range but weakened at the upper range. This result is crucial because it illustrates the function of certain adaptive peripheral associations whose relationship with the line extension is likely to vary depending on the vertical range considered, thus confirming hypothesis H2b.

[ Insert Table 5 ]

DISCUSSION AND CONCLUSION Several lessons can be learned from this research into theoretical, methodological and managerial fields. From a theoretical point of view, the distinction between halo effect and permanent and contextual associations illustrates the debate concerning the independence or dependence of brand-equity vis-à-vis the vertical product range. In this case, the results suggest that the core system of the brand forms the stable part of the halo effect (i.e., basis common to a whole range of values within a product category) to which one should add peripheral associations depending on the vertical range considered. This result confirms that central brand associations represent elements of brand definition independent of the context in which the brand is located. Thus, when a product extension is represented as an expression of the brand, this product is systematically assigned to the central brand associations. Moreover, this research illustrates the adaptive function of peripheral associations whose relationship with the product extension can be strengthened or weakened depending on the vertical position within the range. It appears however, that certain peripheral associations are marginally able to benefit from the systematic transfer to the brand extension, suggesting that not all peripheral associations fulfill the same adaptive role. Here, we should emphasize that peripheral associations for which systematic transfers were observed, presented high level of refutation, it means that these associations are very close to the brand's central system. This is not unlike the results reported by [START_REF] Flament | Approche expérimentale de type psychophysique dans l'étude d'une représentation[END_REF] who proposed to distinguish within the peripheral system, a first and second periphery (the first being closer to the brand core system than the second) and showed that contextual effects are more pronounced in the second periphery. We are thus invited to consider that it is the degree of centrality of an association that determines its contextual independence and therefore the conditions of transfer to the extension product: the more central the association, the more systematic the transfer. These findings call into question the fact that all elements should have the same peripheral functions and should thus lead us to focus more precisely on the specific roles of the first and second peripheries in the functioning of social representations.

From a methodological point of view, the present study shows that the elements associated with a "good car" provide a relevant framework for the study of images of automotive brands. This brand measure, however, promotes the identification of functional associations at the expense of more symbolic associations. It would be appropriate, therefore, to test these hypotheses using an ad hoc measure of brand image to ensure the transfer of more symbolic associations between the brand and its vertical product line extensions. This research, however, proposes a measure of the halo effect that helps to understand the impact of brand on the perceived attributes of the vertical extension. In fact, comparisons of the various assessments of branded and unbranded products can accurately determine whether a brand strengthens or weakens a brand image associated with a vertical product line extension.

Finally, from a managerial point of view, the distinction between central and peripheral associations provides an explanation as to how a vertical product line extension is vested systematically with some brand attributes (central brand associations), while other attributes (peripheral brand associations) depend on the vertical position within the product range.

Taking the example of Peugeot, this research highlights the fact that reliability and security are transferred to vertical extensions of the Peugeot product line, regardless of position within the vertical range. We note, however, that for Peugeot brand affiliations, the relationship between horsepower and product extension is reinforced at the lower end but weakened in the high-end range. This result suggests that while Peugeot seems able to respond satisfactorily to the horsepower that people expect from a low-end car, this is not the case for higher-end vehicles. This conclusion is not unlike the commercial success of Peugeot in the first two range levels (with the launch of the 205, then the 206 and, more recently, the 307 and 407) and the difficulties the brand has encountered in higher-end range (the failure of the 605, and to a lesser extent, that of the 607). At this level, and within the context of a vertical product line extension, these results would allow identification of message elements on which communication campaigns should focus in order to ensure that line extension imagery matches consumer expectations for a given vertical product position. It might thus appear inappropriate to focus communications efforts on central brand associations because they are already invariably linked to the brand. On the other hand, it may be relevant to focus communications efforts on peripheral brand associations, particularly if the objective is to strengthen consumers' linkages between the brand and peripheral associations. As part of a Peugeot vertical product line extension at the high-end range, it would be important to strengthen the link between horsepower and brand to meet consumer expectations at this quality level.

These conclusions are based on a study of the automotive market and fictitious vertical product line extensions combining, in a sense, the vertical range (price) and the size of the car.

To overcome these limitations, future research should verify the validity of these findings in other markets and for vertical product line extensions specific to other brands. Indeed, the brands studied are associated with significant sales volumes and results might have been more marked if the study had focused on brands positioned in niche markets (e.g., Porsche, Mercedes or Jaguar). It would be important to take into account the positioning variable in order to strengthen the internal validity of this research. Finally, although this study has shown that halo effects may lead to improvements in or the diminishment of certain attributes of the vertical product line extension, it does not allow inference of linkages between halo effects and brand equity. As a result, subsequent studies should integrate the behavioral effects of brand equity to specify the relationship between association transfers, the evaluation of brand extensions and purchase intentions.

In the end, the Central Nucleus Theory helps to understand brand halo effects, and hence the principle for evaluating vertical extensions. It is clear that this is a key issue in brand management, especially to the extent that it helps define with greater relevance opportunities for product development and public communications.

Table 1 .

 1 Rate of recognition, probability of association to the brands and categorization in a range level.

Table 4 .

 4 Mean value of the halo effect (difference between the post-and the pre-test evaluations) depending on the considered association, range level and brand **p<.05, *p <.10, according to the t-test Note : The signs + and -following the associations respectively indicate whether the transfert reinforces or reduces the linkage between the associations and the vertical extensions.

Table 2 . Refutation frequency for the challenged associations.

 2 Frequency significantly greater (p<.05) than a 2/3 norm, according to the Chi 2 test.

		CITROEN	FORD	PEUGEOT	RENAULT	TOYOTA	VOLKSWAGEN
	Safety	.61	.64	.85*	.83*	.88*	.92*
	Reliability	.60	.64	.81*	.59	.80*	.89*
	Solidity	.41	.80*	.58	.62	.87*	.91*
	Value for the money	.82*	.80*	.59	.83*	.65	.49
	Affordability	.81*	.84*	.63	.60	.42	.32
	Horsepower	.36	.52	.60	.62	.67	.83*
	Finishes	.41	.49	.54	.50	.66	.87*
	Stylishness	.48	.48	.64	.57	.58	.82*
	Comfort	.67	.55	.70	.54	.61	.71
	Equipment	.42	.41	.58	.49	.68	.69
	Originality	.64	.48	.56	.60	.53	.52
	Innovation	.61	.47	.54	.55	.51	.60
	Aesthetics	.35	.39	.54	.49	.59	.65
	Status	.48	.42	.51	.46	.57	.70
		FORD	PEUGEOT	RENAULT	TOYOTA
	Safety	.64	.85*	.83*	.88*
	Reliability	.64	.81*	.59	.80*
	Solidity	.80*	.58	.62	.87*
	Value for the money	.80*	.59	.83*	.65
	Affordability	.84*	.63	.60	.42
	Horsepower	.52	.60	.62	.67
	Finishes	.49	.54	.50	.66
	Stylishness	.48	.64	.57	.58
	Comfort	.55	.70	.54	.61
	Equipment	.41	.58	.49	.68
	Originality	.48	.56	.60	.53
	Innovation	.47	.54	.55	.51
	Aesthetics	.39	.54	.49	.59
	Status	.42	.51	.46	.57

*

Table 3 . Analysis of variance performed on the pre-test (blind-test) evaluations of concept-cars.

 3

Table 5 . Central and Peripheral Associations involved in the brand halo effect.

 5

P.Moati and M. Ranvier (2007), "Contrainte budgétaire des ménages, segmentation des marchés et stratégies de la grande distribution", N° C235, Cahier de recherche du CREDOC.


Alexandre Michau
email: alexandre.michau@cea.fr

Francis Maury

Frédéric Schuster

Fernando Lomello

Jean-Christophe Brachet

Elodie Rouesne

Matthieu Le Saux

Raphaël Boichot

Michel Pons

J.-C Brachet

High-temperature oxidation resistance of chromium-based coatings deposited by DLI-MOCVD for enhanced protection of the inner surface of long tubes

Keywords:

Introduction

Fukushima-Daichii nuclear accident triggered a common international research effort to increase existing safety margins for both nominal and accidental conditions. Among these works, several aspects of nuclear power plants are reviewed worldwide, including the first safety barrier against dispersal of radioactive fission species. This function is ensured in pressurized water reactors by components called fuel cladding tubes, made of zirconium alloy, approximately 4 m long with an inner diameter and a thickness of about 8.4 mm and 0.6 mm respectively. These long tubes, which contain the nuclear fuel, were mainly chosen due to their neutron transparency, in addition to their good corrosion resistance in pressurized water at ~573 K from the primary circuit and their good mechanical properties under irradiation. To increase the safety margins, in particular in hypothetical accidental conditions such as LOCA (LOss of Coolant Accident), both mechanical strength and resistance to oxidation at high temperature of the cladding have to be further improved. These new solutions are developed as Enhanced Accident Tolerant Fuels (EATF) [START_REF] Terrani | Accident tolerant fuel cladding development: promise, status, and challenges[END_REF].

Two solutions with different time scales are currently under viscosity of BEBC, its dilution in toluene was required, both to inject and vaporize it efficiently but also to adjust its concentration in the gas phase. BEBC belongs to the metalorganic bis(arene)M family where M is a transition metal of columns V and VI. Other precursors from the bis (arene)Cr group were previously used to deposit Cr-based coatings by DLI-MOCVD [START_REF] Maury | Multilayer chromium based coatings grown by atmospheric pressure direct liquid injection CVD[END_REF]. It appeared that regardless the bis(arene)Cr precursor when it is mixed with toluene, its thermal decomposition always gives chromium carbide coatings with the same atomic composition and microstructural features [START_REF] Michau | Chromium carbide growth at low temperature by a highly efficient DLI-MOCVD process in effluent recycling mode[END_REF][START_REF] Douard | Thermodynamic simulation of atmospheric DLI-CVD processes for the growth of chromium-based hard coatings using bis(benzene) chromium as molecular source[END_REF][START_REF] Maury | Selection of metalorganic precursors for MOCVD of metallurgical coatings: application to Cr-based coatings[END_REF]. Depending on the deposition temperature, the structure of the coating is amorphous (≤773 K) or polycrystalline (> 773 K) [START_REF] Michau | Chromium carbide growth at low temperature by a highly efficient DLI-MOCVD process in effluent recycling mode[END_REF][START_REF] Douard | Thermodynamic simulation of atmospheric DLI-CVD processes for the growth of chromium-based hard coatings using bis(benzene) chromium as molecular source[END_REF][START_REF] Maury | Selection of metalorganic precursors for MOCVD of metallurgical coatings: application to Cr-based coatings[END_REF]. It is also possible to inhibit the incorporation of carbon into the coatings by adding a sulphur-containing (C 6 H 5 SH) or a chlorine-containing (C 6 Cl 6 ) inhibitor into the precursor solution, leading to the deposition of polycrystalline metal Cr coatings [START_REF] Michau | Evidence for a Cr metastable phase as a tracer in DLI-MOCVD chromium hard coatings usable in high temperature environment[END_REF][START_REF] Douard | Thermodynamic simulation of atmospheric DLI-CVD processes for the growth of chromium-based hard coatings using bis(benzene) chromium as molecular source[END_REF][START_REF] Polikarpov | Chromium films obtained by pyrolysis of chromium bisarene complexes in the presence of chlorinated hydrocarbons[END_REF][START_REF] Luzin | Chromium films obtained by pyrolysis of bis(arene)chromium complexes in presence of sulfur-containing additives[END_REF][START_REF] Maury | Low temperature metallorganic chemical vapor deposition routes to chromium metal thin films using bis(benzene) chromium[END_REF]. Finally, low amounts of silicon can be introduced in the amorphous chromium carbide coatings by incorporating diphenylsilane ((C 6 H 5 ) 2 SiH 2 ) to the precursor solution. Amorphous chromium carbide a-Cr x C y coatings were deposited on flat substrates at 723 K and 6.7 * 10 3 Pa and directly inside cladding tube sections at 673 K and 6.7 * 10 2 Pa by injecting a solution of BEBC and toluene at 3.0 * 10 -1 mol•L -1 .

Crystalline metallic Cr coatings were deposited at 673 K and 6.7 * 10 3 Pa by injecting a single solution of BEBC in toluene at 3.5 * 10 -1 mol•L -1 with an addition of thiophenol C 6 H 5 SH at 7.0 * 10 -3 mol•L -1 . To avoid the columnar growth obtained by this process when a monolithic layer is deposited, a multilayer architecture has been developed. To do this, the growth of the layer was interrupted regularly for about 1 min by stopping the injection of the reactive vapor phase without stopping the reactor heating and the carrier gas flow rate, then it was injected again to start a new sequence without venting the reactor to ambient air. This causes a new nucleation and growth. This cycle was repeated 9 times for the samples studied here.

Mixed amorphous carbide Cr x Si z C y coatings were deposited at 773 and 723 K with a pressure of 6.7 * 10 3 Pa by injecting a single-solution of BEBC in toluene at 3.0 * 10 -1 mol•L -1 with an addition of (C 6 H 5 ) 2 SiH 2 at 4.5 * 10 -2 mol•L -1 (15 mol% compared to BEBC).

In all depositions, the carrier gas was nitrogen with a 500 sccm flow rate. The injection rate of the liquid solution was between 0.3 and 1.0 mL•min -1 . The evaporation chamber was heated at 473 K and was fed with N 2 preheated at 453 K as carrier gas.

Zircaloy-4 (namely Zr-4), stainless steel (SS304L) and silicon flat samples, or directly the inner-wall of Zr-4 tubes were used as substrates. The flat substrates were previously degreased for a few minutes in acetone and an ultrasound alcoholic bath, then dried under a N 2 stream at room temperature and placed under vacuum on the sample-holder in the reactor before deposition. The 1 m long Zr-4 tube segments were cleaned with the alcoholic solution, dried with a N 2 stream and placed under vacuum on the experimental set-up. The silicon substrates were Si(100) wafers passivated by a Si x N y layer approximately 200 nm thick acting as a barrier for the coating. The commercial composition of Zr-4 is given in [START_REF] Grosse | Secondary hydriding during LOCAresults from the QUENCH-L0 test[END_REF].

Table 1 summarizes the main deposition conditions used for DLI- a Specific conditions applied for the deposition inside Zr-4 cladding tubes.

investigation. The first solution is expected to be implemented at short or mid-term, implying that it would require only incremental technological improvements compared to the current solution. The idea is to increase significantly and relatively quickly the existing safety margins.

The second solution is expected to be a greater challenge for safety margins, with a true technology breakthrough. However, concepts for this long-term solution are less mature. We can cite advanced and promising works on SiC-SiC composites [START_REF] Nakazato | SiC/SiC fuel cladding by Nite process for innovative LWR-cladding forming process development[END_REF][START_REF] Deck | Characterization of SiC-SiC composites for accident tolerant fuel cladding[END_REF][START_REF] Kim | Fabrication and measurement of hoop strength of SiC triplex tube for nuclear fuel cladding applications[END_REF][START_REF] Braun | Chemical compatibility between UO 2 fuel and SiC cladding for LWRs. Application to ATF (Accident-Tolerant Fuels)[END_REF][START_REF] Shapovalov | Strength of SiC f -SiC m composite tube under uniaxial and multiaxial loading[END_REF], monolithic SiC tubes [START_REF] Drieux | Experimental study of the chemical vapor deposition from CH 3 SiHCl 2 /H 2 : application to the synthesis of monolithic SiC tubes[END_REF] and free-standing Mo claddings [START_REF] Beaux | Chemical vapor deposition of Mo tubes for fuel cladding applications[END_REF] by CVD (Chemical Vapor Deposition).

All the short or mid-term solutions are generally based on zirconium alloy cladding tubes, enhanced by a special architecture with one or several other materials, usually an outer protective coating. A single layer of metallic chromium is one of the most investigated solutions. They are deposited by thermal spray [START_REF] Park | Behavior of an improved Zr fuel cladding with oxidation resistant coating under loss-of-coolant accident conditions[END_REF][START_REF] Ševeček | Development of Cr cold spray-coated fuel cladding with enhanced accident tolerance[END_REF][START_REF] Maier | Development of cold spray coatings for accident-tolerant fuel cladding in light water reactors[END_REF], laser cladding [START_REF] Kim | Adhesion property and high-temperature oxidation behavior of Cr-coated Zircaloy-4 cladding tube prepared by 3D laser coating[END_REF] or PVD (Physical Vapor Deposition) [START_REF] Idarraga-Trujillo | Assessment at CEA of coated nuclear fuel cladding for LWRs with increasing margins in LOCA and beyond LOCA conditions[END_REF][START_REF] Park | High temperature steam-oxidation behavior of arc ion plated Cr coatings for accident tolerant fuel claddings[END_REF][START_REF] Bischoff | AREVA NP's enhanced accident-tolerant fuel developments: focus on Cr-coated M5 cladding[END_REF][START_REF] Brachet | Behavior of chromium coated M5(TM) claddings under LOCA conditions fuel[END_REF]. Other coating materials and architectures are developed like non-metallic coatings, pure metals, intermetallics, metallic alloys coatings, oxides, carbides including ternary carbides as MAX phases [START_REF] Tang | Assessment of high-temperature steam oxidation behavior of Zircaloy-4 with Ti 2 AlC coating deposited by magnetron sputtering[END_REF][START_REF] Tang | Evaluation of magnetron sputtered protective Zr-C-Al coatings for accident tolerant Zircaloy claddings[END_REF], nitrides, composites and multilayers [START_REF] Tang | Protective coatings on zirconiumbased alloys as accident-tolerant fuel (ATF) claddings[END_REF].

All protective coatings on zirconium alloys are designed for outerwall deposition on cladding tubes but there is currently no solution for the inner-wall protection [START_REF] Terrani | Accident tolerant fuel cladding development: promise, status, and challenges[END_REF]. In fact, upon LOCA transients, the fuel cladding may experience ballooning and burst. Then, the cladding internal surface can be exposed to steam environment at high temperature, leading to fast inner oxidation and secondary hydriding, which induce significant additional embrittlement of the claddings [START_REF] Brachet | Study of secondary hydriding at high temperature in zirconium based nuclear fuel cladding tubes by coupling information from neutron radiography/tomography, electron probe micro analysis, micro elastic recoil detection analysis and laser induced breakdown spectroscopy microprobe[END_REF][START_REF] Billone | Cladding Embrittlement During Fig. 12. TGA of uncoated and 4 μm Cr x Si z C y coated Zircaloy-4 substrates under dry and wet air, during (a) the heating ramp from room temperature to 1473 K and (b) the 1473 K isothermal annealing. Postulated Loss-of-coolant Accidents[END_REF][START_REF] Nagase | Effect of pre-hydriding on thermal shock resistance of Zircaloy-4 cladding under simulated loss-of-coolant accident conditions[END_REF][START_REF] Grosse | Secondary hydriding during LOCAresults from the QUENCH-L0 test[END_REF].

In order to resist to this harsh environment, internal Cr-based coatings deposited by low pressure DLI-MOCVD (Direct Liquid Injection -MetalOrganic Chemical Vapor Deposition) have been investigated. DLI-MOCVD is indeed a suitable deposition process in order to homogeneously coat the inside of long and narrow tubes with a high shape factor (> 500). Moreover, with an adequately chosen chemical system, consisting of a liquid solution of bis(arene)chromium as molecular precursor in a hydrocarbon solvent, deposition can be performed at sufficiently low temperatures, around 673 K [START_REF] Michau | Evidence for a Cr metastable phase as a tracer in DLI-MOCVD chromium hard coatings usable in high temperature environment[END_REF], to avoid any modification of the metallurgical state of the zirconium alloy. DLI-MOCVD is currently studied in order to protect the inner surface of long cladding tube segments (~1 m). The process is being optimized to ensure a thickness uniformity of the coating along the tube through experimental studies coupled with numerical modeling of the reaction mechanism and the whole deposition reactor [START_REF] Michau | Inner-side coatings for advanced fuel claddings processed by DLI-MOCVD[END_REF].

These hard coatings could also be of use in high temperature corrosive environments such as those encountered in aeronautics, automotive [START_REF] Drozdz | Chromium-based oxidation-resistant coatings for the protection of engine valves in automotive vehicles[END_REF] and some other industries [START_REF] Cai | Mechanical properties, sliding wear and solid particle erosion behaviors of plasma enhanced magnetron sputtering CrSiCN coating systems[END_REF] to protect components with 3D complex geometries.

Experimental details

Materials, deposition process and growth conditions

The deposition process took place in a horizontal hot-wall CVD reactor. A liquid solution of precursor and solvent was injected in a commercial flash-vaporization chamber with the help of a Kemstream system (Direct Liquid Injection) [START_REF] Guillon | Vaporization of solid or liquid organic, organometallic or inorganic compounds, Gases and Instrumentation[END_REF]. Along with nitrogen as carrier gas, the reactive vapor was transported to the reactor consisting either of a quartz tube (24 mm internal diameter) where flat substrates were placed on a stainless steel sample-holder for preliminary experiments or directly of a zirconium alloy tube (8.4 mm internal diameter). Both tubes were placed horizontally inside a 3-zone tubular resistive oven. Additional technical details on the DLI-MOCVD process can be found in [START_REF] Maury | Multilayer chromium based coatings grown by atmospheric pressure direct liquid injection CVD[END_REF][START_REF] Douard | Nanocrystalline chromium-based coatings deposited by DLI-MOCVD under atmospheric pressure from Cr(CO) 6[END_REF] and a sketch of a related set-up in [START_REF] Douard | Nanocrystalline chromium-based coatings deposited by DLI-MOCVD under atmospheric pressure from Cr(CO) 6[END_REF] (the only difference in this reference is that the reactor is vertical and not horizontal as in the present work).

Bis(ethylbenzene)chromium (namely BEBC) was used as liquid molecular precursor diluted in toluene. Because of the relatively high MOCVD process.

Characterization methods and oxidation tests

The behavior of the coated Zr-4 samples in different oxidation tests was studied. In a first approach, mass change of coated and uncoated substrates was measured during thermal cycles using thermogravimetric analyses (TGA; Setaram Sensys Evo) under different atmospheres. Samples (uncoated and coated on all faces) underwent a heating ramp from 298 to 1473 K at 40 K•min -1 followed by an isothermal annealing at 1473 K under dry and wet (27.5% of relative humidity measured at 298 K) air.

Three other oxidation tests, more representative of in-reactor accidental conditions, were performed on both flat samples (uncoated and coated on all faces) and cladding tube segments (uncoated and coated on their inner surface):

-Oxidation test #1: 1373 K for 14 min in static air followed by a 298 K water quench (flat samples); -Oxidation test #2: two-sided oxidation at 1473 K for 10 min in pure (flowing) steam followed by a 298 K water quench (clad segment sample, CEA "DEZIROX-1" facility described in [START_REF] Portier | Influence of long service exposures on the thermal-mechanical behaviour of Zy-4 and M5™ alloys in LOCA conditions[END_REF]); -Oxidation test #3: two-sided oxidation 1473 K for 55 min in pure (flowing) steam followed by a 298 K water quench (clad segment sample, CEA "DEZIROX-1" facility);

The mass gain due to the oxidation was measured after the water quenching and drying of the sample. These last two tests performed under pure flowing steam are representative of LOCA scenario (Design-Based-Accident conditions) whereas TGA and oxidation test #1 were carried out under air.

Before and generally after oxidation tests, coating microstructures were observed by Scanning Electron Microscopy (SEM; Leo-435VP), Transmission Electron Microscopy (TEM; (JEOL JEM 2100 equipped with a 200 kV FEG), and Electron Back-Scattered Diffraction (EBSD) analyses (NordlysNano EBSD Detector with the AZtecHKL software installed on a SEM-FEG JEOL JSM-7100TTLS LV). Crystallographic structures of as-deposited coatings were investigated by X-ray Diffraction (XRD) using a Bruker D8-2 diffractometer equipped with a graphite monochromator (Bragg-Brentano configuration; Cu Kα radiation). Their evolution with temperature was studied during in situ High-Temperature (HT) XRD under Ar atmosphere. Chemical compositions of the coatings were measured by Electron Probe MicroAnalysis (EPMA; Cameca SXFive, 15 kV and 20 nA) and Glow Discharge Optical Emission Spectroscopy (GDOES). Rutherford Backscattering Spectrometry (RBS) was performed to estimate the density of Cr x C y coatings using a primary He + ion beam of 2.8 MeV energy for the thinnest films or H + ion beam of 1.5 MeV for the thickest coatings. Finally, chemical environments and bonds within deposited coatings were determined by X-ray Photoelectron Spectroscopy (XPS; Thermo Scientific K-Alpha, equipped with a monochromatic Al X-ray source). SEM and XRD analysis were systematically performed both on as-deposited coatings and after oxidation tests of the samples. The nitridepassivated Si substrates were mainly used for SEM and XRD analyses and thickness measurements on cross-sections obtained by cleavage.

Results and discussion

Cr coatings

Microstructural and chemical composition analysis

When metallic Cr coatings are deposited by this low pressure DLI-MOCVD process as monolithic layers they exhibit a columnar microstructure with inter-column spaces (porosities) open almost from the interface with the substrate to the outer surface, i.e. the external environment and are visible on SEM micrographs [START_REF] Michau | Evidence for a Cr metastable phase as a tracer in DLI-MOCVD chromium hard coatings usable in high temperature environment[END_REF]. As a result, this microstructure is not at all favorable for an efficient diffusion barrier against oxidation at high temperature. A way to overcome this problem is to prevent columnar growth, which can be achieved by a multilayer architecture. Indeed, the columns begin to develop perpendicularly to the surface of the substrate only after a minimum thickness of a few hundred nanometers of a compact sublayer. Thus, by interrupting the growth near such critical thickness, a new nucleation step and growth is caused and the development of the columns is prevented.

Polycrystalline metallic Cr coatings were deposited at 673 K with a multilayer architecture (Fig. 1). Thanks to this layered structuration, they exhibit a denser microstructure than columnar morphology observed for monolithic coatings. It was also observed by XRD and EBSD, as reported in [START_REF] Michau | Evidence for a Cr metastable phase as a tracer in DLI-MOCVD chromium hard coatings usable in high temperature environment[END_REF], that they are mainly constituted of the stable bcc-Cr phase with a relatively low amount (< 6%) of the cubic metastable δ-Cr phase. These coatings undergo an irreversible transformation of the metastable Cr phase into the stable Cr phase by annealing in air at 723 K, and then they form chromium oxides above 823 K. The average atomic composition of as-deposited coatings measured by EPMA is Cr 0.92 C 0.04 O 0,03 S 0.01 . Apart from chromium, they contain a residual amount of carbon and a slight contamination by oxygen and sulphur. Carbon comes from the metalorganic precursor BEBC and traces of sulphur come from thiophenol used as a carbon inhibitor. Indeed, carbon incorporation was prevented by a surface site competition between BEBC derivatives and thiophenol molecules. However, there is likely a small amount of thiophenol that decomposes and incorporates traces of sulphur. The low carbon content indicates that the efficiency of the S-containing inhibitor is not perfect and that C also originates from other side reactions. More details on the chemical and structural characteristics of these metal Cr coatings are reported in [START_REF] Michau | Evidence for a Cr metastable phase as a tracer in DLI-MOCVD chromium hard coatings usable in high temperature environment[END_REF].

Oxidation study

Mass gains of uncoated, 4 μm Cr coated and 6 μm Cr coated Zircaloy-4 samples measured by TGA during heating ramp and isothermal annealing under dry and wet air at 1473 K are presented in Fig. 2. During the heating ramp, as shown in Fig. 2(a), the oxidation kinetics of coated samples is slowed down by the presence of the protective Cr layer. At the end of the heating phase, the mass uptake of coated substrates is comprised between 0.60 and 0.85% (1.6 to 2.2 mg•cm -2 ) while it reaches 2.85% (7.5 mg•cm -2 ) for the uncoated Zircaloy-4 samples under both dry and wet air. There is no effect of the coating thickness either. However, at 1473 K (Fig. 2(b)), the oxidation of coated samples immediately catches up that of uncoated Zircaloy-4 to reach approximately 35% (92 mg•cm -2 ) without providing any delay compared to bare Zr-4 substrate. All samples oxidize at the same rate in Fig. 1. Multilayer metal Cr coating deposited by DLI-MOCVD on Si substrate at 673 K from BEBC precursor with addition of thiophenol as inhibitor of carbon incorporation. The architecture of the coating consists in 9 layers in order to reduce the average grain size and to improve its density. dry or wet air. By neglecting the Cr layer compared to the thickness of the Zircaloy substrate, this mass gain threshold of about 35% is in good agreement with the total transformation of Zr into ZrO 2 (calculated 36%) confirming the complete oxidation of the Zr alloy.

After 14 min at 1373 K in static air followed by a 298 K water quench (test #1), a 2.2 mg•cm -2 mass intake was measured for both 2 μm and 4 μm Cr coated samples. It appears on SEM observations and GDOES profiles that the Cr coating is partially oxidized as shown in Fig. 3. Despite the crystallization of the coating due to high temperature leading to the growth of grains and the disappearance of the multilayer architecture, the coating still acts as a sacrificial protection barrier against Zircaloy-4 oxidation. Several layers can be identified from Fig. 3. First of all, a fully oxidized layer is observed at the external surface (~1.5 μm), followed by a partially oxidized chromium layer constituted of Cr, O and C (~3 μm). Then, a diffusion area (~2 μm) not visible on SEM picture appears on GDOES profile between the coating and the non-oxidized substrate. XRD analyses did not reveal the presence of any crystallized phase at the interface produced by the interdiffusion between elements such as ZrC or intermetallic phases like ZrCr 2 .

The multilayer architecture of Cr coatings developed to improve their density and their polycrystalline structure produces an equiaxiallike microstructure with many small grains with an average grain size approximately equal to the period of the multilayer, i.e. the thickness of the individual sublayers. Subsequently, grain boundaries are essential perpendicular to the interfaces created by the multilayer growth mode as demonstrated by EBSD analyses in the Fig. 6 of [START_REF] Michau | Evidence for a Cr metastable phase as a tracer in DLI-MOCVD chromium hard coatings usable in high temperature environment[END_REF]. This microstructure is not sufficiently optimized and finally grants unsatisfying protection to Zircaloy-4 substrate over 1373 K. Despite the absence of open porosity or grain boundaries induced by a columnar growth directly perpendicular to the surface of the substrate, both the multiplication of interfaces parallel to the substrate and the network of grain boundaries connecting the different sublayers are preferential ways for rapid diffusion of oxygen to the Zr-4 substrate. As a result these DLI-MOCVD Cr coatings exhibit poor performances in our oxidation conditions compared to other Cr-based coatings.

Cr x C y coatings

Microstructural and chemical composition analysis

Amorphous chromium carbide coatings as-deposited by DLI-MOCVD at temperatures lower than 773 K are very dense as deduced from the absence of porosities visible by SEM and TEM analyses [START_REF] Michau | Chromium carbide growth at low temperature by a highly efficient DLI-MOCVD process in effluent recycling mode[END_REF]. This is supported by RBS analyses. Indeed from the atomic composition determined by EPMA and the thickness of the coatings measured by SEM, the density of two amorphous a-Cr x C y coatings deposited at 723 K and 773 K was estimated by RBS equal to 5.4 ± 0.7 g•cm -3 and 6.6 ± 0.6 g•cm -3 , which is very close to 6.7 g•cm -3 for bulk Cr 3 C 2 . Interestingly for barrier coatings, they have a glassy-like microstructure without any grains and grain boundary visible by SEM (Fig. 4) and TEM images recently reported in [START_REF] Michau | Chromium carbide growth at low temperature by a highly efficient DLI-MOCVD process in effluent recycling mode[END_REF]. As-deposited coatings show only broad humps on their XRD patterns at room temperature (Fig. 5) with no evidence of diffraction peaks from polycrystalline phases [START_REF] Michau | Chromium carbide growth at low temperature by a highly efficient DLI-MOCVD process in effluent recycling mode[END_REF]. During in situ HT-XRD (Fig. 5) under Ar atmosphere, it was observed that coatings crystallize partially into Cr 7 C 3 at 853 K, then Cr 3 C 2 appears at 873 K followed by Cr 2 O 3 around 883 K due to traces of oxygen. It is interesting to note that the average atomic composition measured by EPMA is Cr 0.64 C 0.33 O 0.03 which corresponds to a stoichiometry between Cr 7 C 3 and Cr 3 C 2 . More details on the microstructure of this a-Cr x C y coating are reported in a recent paper [START_REF] Michau | Chromium carbide growth at low temperature by a highly efficient DLI-MOCVD process in effluent recycling mode[END_REF].

Oxidation study

Three different thicknesses of Cr x C y coatings were tested during TGA, 2.5 μm, 4.5 μm and 9 μm, and the results were compared to the uncoated Zr-4 substrate. When exposed to dry or wet air, coated samples show at the end of the heating phase up to 1473 K a mass gain always lower than 0.15% (0.4 mg•cm -2 ), compared to 2.85% (7.5 mg•cm -2 ) for uncoated Zr-4 substrate. There is no strong difference between coated samples regarding the influence of the coating thickness or the atmosphere in the temperature rise phase as shown in Fig. 6(a).

Unlike Cr coated and uncoated Zircaloy-4 substrates, mass uptakes of Cr x C y coated samples during the 1473 K annealing clearly show a delay to their complete oxidation, as illustrated in Fig. 6(b). It appears that this delay increases with increasing the coating thickness and is higher for dry air than for wet air, to reach a remarkable value > 2 h. SEM observations of oxidized samples show that the presence of the coating is beneficial to their mechanical integrity, acting as a barrier enclosing Zircaloy-4. As it was recently observed for bulk Cr 7 C 3 , the oxidized surface of our coatings consists only of Cr 2 O 3 and does not show any sign of peeling [START_REF] Zhang | Comparison of oxidation behaviors of Cr 7 C 3 at 1173 K and 1273 K[END_REF]. On the contrary, uncoated Zircaloy-4 samples are strongly deteriorated by oxidation and loss some parts.

Oxidation kinetics of amorphous Cr x C y coatings is almost 5 times slower than that of Cr coating with mass gains ranging from 0.3 to 0.5 mg•cm -2 (compared to 2.2 mg•cm -2 ) after oxidation test #1 (1373 K for 14 min in static air followed by a 298 K water quench) for 2.5 μm, 4.5 μm and 9 μm Cr x C y coated Zr-4 samples. Despite their relatively low values, mass gains are increasing with the thickness of coatings. As the oxidation test was similar for all samples, the oxygen content available in the oxidative atmosphere did not limit the oxidation kinetics, which was essentially controlled by the total amount of Cr and C, the coating playing a sacrificial role in the oxidation mechanism.

Despite their high-temperature oxidation and the presence of rare local cracks, the coatings are still adherent to the Zircaloy-4 substrate. Cr x C y coatings constitute an efficient protection for Zircaloy-4 thanks to their excellent conformity and their microstructure, which remains very dense (Fig. 7) even after the oxidation test and the water quench. Indeed, their crystallization does not lead to a noticeable grain growth or to the appearance of grain boundaries, which would have been disadvantageous for oxidation resistance since they are preferential paths for diffusion. The underlying Zircaloy-4 is not oxidized except very locally below some cracks in the coating, as the GDOES profile in Fig. 7 does not show any additional oxygen in the Zr matrix.

Based on Fig. 7, the oxidized microstructure of the coating can be represented as a superposition of several layers: a surface layer of chromia Cr 2 O 3 (~1.5 μm) in direct contact with the oxidative atmosphere, the partially oxidized coating containing Cr, C and O (~2.5 μm) and the non-oxidized coating (~2.0 μm). An inter-diffusion sublayer of approximately 10 μm is present between Cr and C from the coating and Zr from the substrate. XRD analyses revealed the presence of Cr 3 C 2 in the coating after its crystallization due to the sustained thermal treatment, and traces of the ZrC phase, as a result of Cr, C and Zr interdiffusion.

Since amorphous chromium carbide coatings gave promising results under air oxidation, two-sided oxidation tests have then been performed in flowing steam for 600 s (test #2) and 3300 s (test #3) at 1473 K on uncoated and Cr x C y inner-coated clad segments. The conditions are more representative of LOCA. These samples were finally quenched in water at room temperature. They consist in 3 cm-long sections cut from a 1 m-long clad segment with amorphous Cr x C y deposited on its inner surface. The coating thickness varied along the 1 mlong segment, which allowed testing for several coating thicknesses.

Table 2 summarizes the oxidation conditions and the associated mass gain (per unit surface area) values measured.

Taking into account the cladding thickness, the holding for 600 s at 1473 K corresponds to an Equivalent Cladding Reacted (ECR, (*)) value close to 17% for one sided-steam oxidation (and ~34% for two-sided oxidation) according to the "Baker-Just" oxidation rate correlation for an uncoated Zircaloy-4 based cladding [START_REF] Baker | Studies of Metal-water Reactions at High Temperatures[END_REF]. An ECR value of 17% corresponds to the "historical" LOCA regulation limit to ensure significant residual post-quenching clad ductility [START_REF] Hache | The history of LOCA embrittlement criteria[END_REF]. The ECR parameter represents the fraction of the metallic clad wall thickness that has been inner-coated sample. Moreover, it can be observed from EPMA results that the average oxygen content of the inner prior-β Zr layer (α Zr phase with a typical Widmanstätten or parallel-lath structure morphology resulting from the transformation of β Zr during cooling) is higher in the uncoated reference Zircaloy-4 than in the inner-coated sample, and close to the oxygen solubility in the β Zr phase at 1473 K [START_REF] Chung | Pseudobinary zircaloy-oxygen phase diagram[END_REF]. Such an oxygen concentration value in the prior-β Zr layer is known to induce a brittle failure mode at room temperature [START_REF] Chung | Development of an Oxygen Embrittlement Criterion for Zircaloy Cladding Applicable to Loss-of-coolant Accident Conditions in Light-water Reactors[END_REF][START_REF] Brachet | Hydrogen content, preoxidation, and cooling scenario effects on postquench microstructure and mechanical properties of Zircaloy-4 and M5® alloys in LOCA conditions[END_REF][START_REF] Stern | Investigations of the microstructure and mechanical properties of prior-β structure as a function of the oxygen content in two zirconium alloys[END_REF]. Since the inner priorβ Zr layer is known to ensure most of the post-quenching residual ductility and toughness of Zr-based cladding oxidized at high temperature [START_REF] Chung | Development of an Oxygen Embrittlement Criterion for Zircaloy Cladding Applicable to Loss-of-coolant Accident Conditions in Light-water Reactors[END_REF][START_REF] Brachet | Hydrogen content, preoxidation, and cooling scenario effects on postquench microstructure and mechanical properties of Zircaloy-4 and M5® alloys in LOCA conditions[END_REF], the results confirm the beneficial influence of the inner Cr x C y coating by protecting the inner clad surface from early oxygen diffusion.

On cross-sections, it seems a partial detachment of the coating happens in certain place but we think this mainly occurs during the preparation of the sample to obtain the transverse cuts as in Fig. 9. We have not identified at this stage any adhesion problem on Zr-4. Also, on cross-section micrographs as in Fig. 9, cracks are sometimes observed crossing completely the coatings up to the interface with the substrate. Probably most of them originate from the preparation of the sample but it is quite likely that some of these cracks appeared on as-deposited coatings and could be induced for instance by thermal stresses. Indeed, one of these cracks that traversed perpendicularly all the coating appears in Fig. 9(b) on the inner-surface of the cladding. It has been infiltrated by oxygen during the oxidation test and consequently it was entirely coated by chromium oxide up to the Zr-4 substrate, which begins to be locally oxidized, as revealed by the dark contrast delineating the diffusion zone of oxygen in Zr-4 from the bottom of the crack.

Fig. 10 gives more insights into the microstructural evolution of the inner-coated clad segment upon high-temperature steam oxidation. From the detailed SEM-EBSD analysis presented in Fig. 10(c), it can be observed that the outer periphery is composed of nearly 100% of chromium oxide Cr 2 O 3 with submicronic grains, while the rest of the coating displays a complex mixture of partially crystallized carbides (Cr 3 C 2 and Cr 7 C 3 ) and submicronic Cr 2 O 3 oxide grains. It can also be assumed that the non-indexed zones (in dark grey in Fig. 10(b) and (c)) correspond to residual amorphous Cr x C y carbides and/or to nanometric grains which could not be identified by SEM-EBSD due to the instrumental spatial resolution. Additionally, due to some carbon diffusion (also detected from XRD and EPMA measurements) into the underlying Zircaloy-4 substrate, a more or less continuous ZrC layer formed at the Zr/Cr x C y interface. Finally, some porosities can be observed at the vicinity of the crystallized carbides which may be due to the local volume changes associated with the crystallization process (i.e. crystalline carbides formation from the initial amorphous state). One can make also the assumption that the coarser porosities lying near the ZrC/Cr x C y interface have been induced by some local "Kirkendall" effects [START_REF] Smigelskas | Zinc diffusion in alpha brass[END_REF], because of the strongly different diffusivities of the chemical species (C, Cr, Zr) involved into the high-temperature inter-diffusion process between the outer CrC scale and the Zircaloy-4 substrate. However, no significant macroscopic delamination of the partially oxidized Cr x C y inner coating occurred. This indicates that this type of coating has some capacity to survive under the high-temperature steam oxidation and subsequent water quenching typical of hypothetical LOCA events.

An additional high-temperature steam oxidation test has been performed for nearly 1 h (3330 s) at 1474 K (test #3). Fig. 11 shows the resultant microstructures for both 3 cm long uncoated (a) and Cr x C y inner-coated (b) clad sections. Consistently with the mass gain values measured (Table 2), it is obvious from these examinations that for this much longer steam oxidation at 1473 K, the inner coating has almost disappeared and thus was no more protective against high temperature steam oxidation. Part of the Cr originating from the coating was consumed by diffusion in the substrate, as revealed by the EPMA profiles of cross-sections of Fig. 11 (not shown for clarity), and another part formed chromium oxide, which was peeled off and is not visible in the area of Fig. 11.

However, in hypothetical LOCA situations, oxidation of the cladding inner surface may occur after clad burst occurrence as a result of steam ingress through the burst opening into the gap between the nuclear fuel pellet and the inner clad surface. In such situation, one of the main issues is related to very localized secondary hydriding phenomena (a few centimeters apart from the burst opening) due to steam starvation conditions. It has been observed that in these conditions, secondary hydriding is a very fast process inducing local hydrogen concentration peaks up to thousands of weight-ppm after only a few minutes at 1373-1473 K [START_REF] Brachet | Study of secondary hydriding at high temperature in zirconium based nuclear fuel cladding tubes by coupling information from neutron radiography/tomography, electron probe micro analysis, micro elastic recoil detection analysis and laser induced breakdown spectroscopy microprobe[END_REF][START_REF] Billone | Cladding Embrittlement During Fig. 12. TGA of uncoated and 4 μm Cr x Si z C y coated Zircaloy-4 substrates under dry and wet air, during (a) the heating ramp from room temperature to 1473 K and (b) the 1473 K isothermal annealing. Postulated Loss-of-coolant Accidents[END_REF][START_REF] Nagase | Effect of pre-hydriding on thermal shock resistance of Zircaloy-4 cladding under simulated loss-of-coolant accident conditions[END_REF][START_REF] Grosse | Secondary hydriding during LOCAresults from the QUENCH-L0 test[END_REF]. Such a high hydrogen content may induce a strong local embrittlement of the cladding. Then, it is believed that the inner coating studied here has a high potential to delay efficiently the occurrence of this embrittlement. Some high-temperature additional oxidation tests are thus on-going to better address this issue.

Cr x Si z C y coatings

Microstructural and chemical composition analysis

Silicon is a relatively small element that has a great affinity for many elements and tends to form chemical bonds with a strong covalent character. As a result, it can form many compounds, including ternary carbides. When it is integrated into a structure at low temperature, silicon has the particularity of amorphizing it until a critical composition corresponding to a specific compound of the phase diagram can then crystallizes. In other words, doping with Si increases the crystallization temperature of amorphous carbides. Doping Cr x C y with Si was purposely realized in order to increase the crystallization temperature of the amorphous chromium carbide coatings during intentional or unintentional thermal treatments, providing more time before the appearance of grains boundaries that would favor oxygen diffusion.

It is possible to incorporate small quantities of Si into amorphous chromium carbide coatings before forming crystallized silicides or mixed carbides by adding to the injected solution of BEBC an adequate Si-containing precursor, diphenysilane. Decomposition of the two precursors leads to the growth of mixed amorphous chromium carbide Cr x Si z C y at low temperatures (723 and 773 K). Comparatively to a-Cr x C y coatings, Cr x Si z C y coatings exhibit also a dense and glassy-like microstructure with no visible grains. It is worth noticing that BEBC catalyzes the decomposition of diphenylsilane in the CVD reactor. Indeed, injection of only diphenylsilane in solution with toluene did not allow the growth of Si or SiC coatings in our deposition conditions. Cr x Si z C y coatings deposited by DLI-MOCVD using a one-pot solution with both precursors in toluene have an average composition of Cr 0.66 Si 0.02 C 0.29 O 0.03 .

As-deposited Cr x Si z C y coatings are amorphous and, as expected, in situ HT-XRD analyses under Ar atmosphere have shown that they start to crystallize only from 1023 K, i.e. > 150 K above a-Cr x C y (~853 K). The phases Cr 7 C 3 and CrSi 2 are simultaneously appearing at 1023 K. Coatings start oxidizing at 1123 K due to traces of oxygen and then partially crystallize into Cr 3 C 2 at 1273 K.

Oxidation study

When submitted to TGA (Fig. 12) under dry or wet air, like other Crbased coatings, Cr x Si z C y coatings present a smaller mass uptake than uncoated Zircaloy-4 samples, around 0.30% (0.8 mg•cm -2 ) for a 4 μm thick coating, compared to 2.85% (7.5 mg•cm -2 ) without coating. However, like metallic Cr coatings, they do not delay the complete oxidation of Zircaloy-4 substrates. Their behavior can be ranked in terms of protection efficiency between polycrystalline metallic Cr and amorphous Cr x C y . It is believed that the low Si amount incorporated (around 2 at.%) is not sufficient to form a continuous protective film as SiO 2 or mixed oxides, which should improve the barrier against oxidation.

Conclusions and perspectives

All tested Cr-based coatings deposited by DLI-MOCVD based on the thermal decomposition of BEBC precursor increase the oxidation resistance of Zircaloy-4 under dry air, wet air or pure steam. The temperature required to trigger catastrophic oxidation of coated Zircaloy-4 is always pushed back towards higher values. Amorphous chromium carbide coatings are the most efficient because of their ability to delay complete oxidation of the substrate. They behave like an inner sacrificial protection barrier for the Zircaloy-4 substrate against high-temperature oxidation (1473 K), even under pure steam and after water quenching.

Improved microstructure of metallic Cr coating with a multilayer architecture aiming at increasing its density and its polycrystalline structure finally turn out to be disadvantageous. By multiplying interfaces between layers and perpendicular grain boundaries between the sublayers, the oxidation kinetics is accelerated compared to that of the very dense and glassy-like Cr x C y coatings. Si-doping of Cr x C y is also ineffective regarding oxidation despite the higher crystallization temperature of the coatings under inert atmosphere but probably the influence of the coating composition (not explored here) is a way of improvement.

The successful deposition by DLI-MOCVD of amorphous Cr x C y coatings on the inner-wall of 1 m-long cladding segments allowed the realization of various oxidation tests closer to the LOCA conditions. They demonstrate that this coating is a good candidate for an efficient inner protection of Zr-4 fuel cladding. They also prove that the DLI-MOCVD process is the first studied viable solution to protect the inside of nuclear fuel cladding as recently noticed in a review on this field [START_REF] Terrani | Accident tolerant fuel cladding development: promise, status, and challenges[END_REF].

As perspectives to this work, we will maintain our efforts to conduct new oxidation tests and continue the qualification of amorphous chromium carbide coatings on Zr-based claddings for EATFs. Hydrogen is another subject of study, in order to determine the capability of Cr x C y coatings to prevent from hydrogen diffusion, and thus from the cladding embrittlement due to the hydriding of the Zr-based substrates. Moreover, the behavior of coated claddings under irradiation will be investigated. Finally, upscaling of the process assisted by numerical modeling is already in progress, first by demonstrating the possibility to coat a bundle of 1 m-long clad segments, then by accessing to a fulllength fuel cladding with homogeneous coverage.

Fig. 2 .

 2 Fig. 2. TGA of uncoated, 4 μm Cr coated and 6 μm Cr coated Zircaloy-4 substrates under dry and wet air, during (a) the heating ramp from room temperature to 1473 K and (b) the isothermal annealing at 1473 K.

Fig. 3 .

 3 Fig. 3. GDOES composition profile of a 4 μm Cr coated Zircaloy-4 substrate after oxidation test #1 superimposed to the corresponding back-scattered electrons (BSE) SEM cross-section.

Fig. 4 .

 4 Fig. 4. Amorphous Cr x C y coating deposited by DLI-MOCVD on a Si substrate at 723 K from BEBC precursor.

Fig. 5 .Fig. 6 .

 56 Fig. 5. As-deposited XRD (303 K) and HT-XRD (823 to 1073 K) patterns of an amorphous Cr x C y coating elaborated by DLI-MOCVD on a Si substrate at 773 K.

Fig. 7 .

 7 Fig. 7. GDOES composition profile of a 4.5 μm Cr x C y coated Zircaloy-4 substrate after oxidation test #1 superimposed to an associated SEM cross-section.

Fig. 8 .

 8 Fig. 8. Optical polarized micrographs cross-sections after oxidation test #2 of (a) an uncoated reference Zircaloy-4 clad segment and (b) a Cr x C y inner-coated Zircaloy-4 clad segment (Out. and Int. respectively stand for outer and inner side).

Fig. 9 .

 9 Fig. 9. Superposition of SEM micrographs (BSE mode) and EPMA oxygen profiles corresponding to the clad wall thickness after oxidation test #2 of (a) an uncoated reference Zircaloy-4 clad segment and (b) a Cr x C y inner-coated Zircaloy-4 clad segment.

Fig. 10 .

 10 Fig. 10. Inner surface of a Cr x C y coated clad section after oxidation test #2, (a) SEM observation with BSE, (b) SEM-EBSD quality map and (c) SEM-EBSD map in phase contrast imaging mode.

Fig. 11 .

 11 Fig. 11. Optical polarized micrographs cross-sections after oxidation test #3 of (a) an uncoated reference Zircaloy-4 clad segment and (b) a Cr x C y inner-coated Zircaloy-4 clad segment (Out. and Int. respectively stand for outer and inner side).

Table 1

 1 CVD parameters leading to the deposition of Cr x C y , Cr and Cr x Si z C y coatings in this work.

	CVD parameters	Cr x C y	Cr	Cr x Si z C y
	BEBC/toluene concentration	3.0 * 10 -1	3.5 * 10 -1	3.0 * 10 -1
	(mol•L -1 )
	Deposition temperature (K)	673 a ; 723	673	723; 773
	Total pressure (Pa)	6.7 * 10 2a /	6.7 * 10 3	6.7 * 10 3
		6.7 * 10 3
	Additive	N/A	C 6 H 5 SH	(C 6 H 5 ) 2 SiH 2
	Additive/BEBC ratio (mol%)	N/A	2	15