Stefano Manfredi

Mauro Tosco

THE MORPHOSYNTAX AND PROSODY OF TOPIC AND FOCUS IN JUBA ARABIC

Juba Arabic is a natural language that is given to South Sudan by God to unite its people.'

INTRODUCTION

This article will discuss the information structure of Juba Arabic, an Arabic-based pidgincreole spoken in South Sudan. In particular, it will deal with the expression of topic and focus, showing how morphosyntactic and prosodical marking interact in order to yield a system of remarkable complexity. The notion of 'Topic' is closely linked to that of presupposition [START_REF] Lambrecht | Information structure and sentence form. Topic, focus, and the mental representations of discourse referents[END_REF] or Common Ground (Krifka 2006;[START_REF] Féry | Information Structure. Notional distinctions, ways of expression[END_REF]. Following Lambrecht (1994: 127), we define a topic as the referent that the proposition is about. Topic elements are discourse referents about which a speaker asserts something relevant. Topic is complementary for us to the comment. Usually, a topic conveys given information; it is left-dislocated, prosodically deaccented, pragmatically identifiable, morphosyntactically definite [START_REF] Chafe | Givenness, contrastiveness, definiteness, subjects, topics and point of view[END_REF][START_REF] Lambrecht | Information structure and sentence form. Topic, focus, and the mental representations of discourse referents[END_REF], and within the scope of pragmatic presupposition. The aboutness relation is also due to the contextual topicality of a referent in discourse, which Lambrecht (1994: 55) defines as 'the degree to which a referent can be taken to be a centre of current interest with respect to which a proposition is interpreted as constituting relevant information. ' The topic is only one of the various elements that can constitute the left-dislocated part of an utterance, called 'Preamble' by Morel and Danon-Boileau (1998). 'Argument-topic', or topic proper, can be opposed to the 'frame setting topic' that 'sets a spatial, temporal or individual framework [...] which limits the applicability of the main predication to a certain restricted domain' (Chafe 1976: 50).

'Focus', for its part, has still a rather vague status in linguistic theory. The only common ground among all the very different interpretations of focus seems to be that the focus is complementary to presupposition. According to Lambrecht (1994: 213), the focus of an utterance is equivalent to whatever is not part of the presupposition; as such, it is particularly prominent in the answer to context questions. Within such an analysis, the focus is a necessary ingredient of any clause, while the topic (the presupposition) may be absent. Other scholars state that focus is mainly a contrastive device: the focus selects among presupposed alternatives (cf. Büring 1997: 29), or runs counter expected ones. This approach is based upon the prominence theory of focus realization (PTF), which is the central claim of Alternative Semantics (cf. [START_REF] Rooth | A theory of focus interpretation[END_REF] and according to which focused items are always prosodically stressed. 1 In our view, focus is a formally marked pragmatic function acting on the most salient information (cf. [START_REF] Dik | On the typology of focus phenomena[END_REF]) in a given communicative setting with the aim of satisfying the speaker's communicative needs (cf. [START_REF] Chafe | Givenness, contrastiveness, definiteness, subjects, topics and point of view[END_REF]) and thereby channeling/modifying the addressee's understanding of the subject matter. We therefore distinguish several types of foci according to their different information scopes.

We will show how topic-and focus-marked utterances can be formally opposed to pragmatically unmarked utterances through the use of specific morpho-syntactic and prosodic configurations showing that topic and focus are not per se part and parcel of every utterance. The following sections will expound the different particles and constructions which are responsible for the expression of topic and focus meanings in Juba Arabic.

After an overview of the main typological features of Juba Arabic as well as of the data and the methodology used for this study in section 2., section 3. will discuss the expression of discourse-unmarked sentences, dealing in separate subsections with declarative, negative sentences, and questions. The description of the syntactic and prosodic configurations of such unmarked utterances will be taken as a point of reference for the following description of structures that involve formal marking for topic and/or focus. Section 4. will tackle the expression of topic under the rubrics of definite, indefinite argument and frame setting topic. The subsections in 5. will be devoted to focus, showing how as many as three different elements can be used in focus strategies, and depicting the role of the Arabic-derived vocative particle ya in triggering the development of two different separate markers. The final section 6. will summarize our findings and address comparative issues and the possible role of substrate in the discourse strategies of Juba Arabic.

OVERVIEW

Juba Arabic (árabi júba; ISO pga; hereafter JA) is a pidgincreole, that is to say an intermediary variety between pidgins and creoles which has become the native language for only a part of its speakers (Bakker 2008: 132). Developed in southern Sudan in the late 19 th century as a means of inter-ethnic communication between Arab traders and mainly Nilotic-speaking populations, at the present time JA is the major vehicular language of South Sudan as well as of large diaspora communities in Sudan, Egypt, United States, Canada and Australia. JA is genetically related to the Ki-Nubi creole spoken in Uganda and Kenya (Tosco and Manfredi 2013: 513).

1. TYPOLOGICAL REMARKS

JA is a pitch-accent language (Manfredi and Petrollino 2013: 56). 2 The pitch accent has both lexical and grammatical import and it is marked here with an acute accent. In its grammatical use, pitch accent is found on verbs, where stems are opposed to their verbal noun and passive through pitch accent on the antepenultimate, penultimate, and last syllable (as in 'kill'); in disyllabic stems (such as 'bring'), the two latter functions are conflated and expressed by an accent on the last syllable, thereby contrasting with the accent on the first syllable which is canonical in verbs. 3 Still other (ambitransitive) verbs (such as worí 'to show' in the table above) are accented on their last syllable in the stem and do not have a morphologically separate VN and 2 Nakao (2013), for his part, argues that Juba Arabic posses a split prosodic system in which both pitch accent and tone are lexically and grammatically distinctive. As far as Ki-Nubi is concerned, Gussenhoven (2006: 218) affirms that it possesses an 'obligatory, cumulative, metrically, bound-accent, with only a single tone being inserted in the accent locations.' 3 The morphologization of pitch contrast in Ki-Nubi is discussed in Owens' article in this volume.

Lexical

PASS. Contrary to Ki-Nubi (Miller 1993: 142), pitch is not used contrastively in nouns in order to mark number. Although many exceptions are found, one can say that the positioning of pitch accent in JA is etymologically determined by the vowel length, with Arabic long vowels being reinterpreted as stressed (e.g. *bārid > bárid 'cold'). A word in JA can be phonetically defined as a unit bearing a single pitch accent. It may in its turn be composed of a lexical word plus an affix or a clitic, as in (1).

bi=rówa [biˈrowa]

IRR=go 'go, will go, should go'

There are only two clitics in JA: bi= 'IRR' and gi=/ge= 'PROG' (both subject to vowel loss if the following verb begins with a vowel or a glide). Different from Ki-Nubi of Kenya and Uganda, the two preverbal markers in JA cannot combine (Tosco 1995: 433). Morphologically, JA nouns and adjectives are monomorphemic, with the exception of the optional use of two suffixes marking the plural, respectively: -át '-PL.N' and -ín '-PL.ADJ.'4 A certain number of affixes (both prefixes and suffixes) are found in a youth variety of JA spoken in Juba which will not be further analysed in the present work. The following word classes can be tentatively established in JA:

• Nouns: an open class, it can be defined morphologically as composed of the elements which can be pluralized through the nominal plural affixes -át and -ín for nouns derived from Arabic active participles, and syntactically defined as possible head of NPs. • Verbs: an open class, it can be defined morphologically as composed of the elements to which the TAM clitics join, as well as the elements which mark valence though accent shift; syntactically, they act as predicates in verbal sentences. Data were obtained in a region in which Sudanese Arabic is the main interethnic language. It is doubtful whether in the case of JA and its Arabic superstrate we can speak of a continuum: in the case of our informants, knowledge of Sudanese Arabic correlates with awareness of separateness and ability to keep it apart from JA -better for informants 1 and 2 than for informant 3.

The following study is based on recordings of spontaneous and semi-spontaneous speech and it does not include any elicited material. The informants provided consistent data in the form of conversations among themselves and narratives. The total duration of the material used for this study amounts to approximately 45 minutes (9500 words). The material has further been transcribed and prosodically segmented in PRAAT so as to be then annotated in ELAN-CorpA as part of the spoken material of the CorpAfroAs corpus [START_REF] Manfredi | Juba Arabic corpus[END_REF]. The prosodic analysis presented in the following paragraphs has been also done in PRAAT. Some of the following examples are coupled with a figure displaying their fundamental frequency and a broad phonetic transcription showing phenomena that are relevant to syllable segmentation (assimilation, elision, gemination/degemination, etc.). Furthermore, examples also display the segmentation of the discourse flow into intonation units. The boundaries of intonation units are detected by one or more of the following: (1) final lengthening; (2) initial rush (anacrusis); (3) pitch reset; (4) pause. We distinguish between units with a minor (i.e. non-terminal) break (signaled by a single slash /) and units with a major (i.e. terminal) break (signaled by a double slash //).

'NEUTRAL' UTTERANCES

In this section we briefly survey the syntactic and prosodic configurations of 'neutral' utterances in JA. As a general remark, we can state that the occurrence of a given utterance (i.e. the basic unit of spoken language) is always pragmatically induced; therefore, it is hard, possibly unachievable, to isolate such a thing as an absolute 'neutral' utterance in natural discourse. In our view, a 'neutral' utterance can only be defined in negative terms as a unit of speech that does not contain any formal marking for topicalization and/or focalization; it is therefore unmarked. It follows that scope relations in 'neutral' utterances are different than in topicalized and focused utterances: 'neutral' utterances are prototypically associated with canonical configurations, both syntactically and prosodically.

DECLARATIVE NOMINAL UTTERANCES

In JA, a declarative nominal utterance is made up of an NP (minimally a noun, with its modifiers following) and a predicate, which can consist of a noun, an adjective or a demonstrative or possessive pronoun. Nothing intervenes between the NP and the following predicate, which means that no copula-like element is found (here JA follows its Arabic lexifier). In syntactic terms, this corresponds to a nominal copular-like sentence. In prosodic terms, declarative nominal utterances are composed of a single intonation unit (hereafter IU) displaying a rising-falling intonation contour, superimposed on the single lexical pitch accents. The highest pitch accent, or sentence accent, falls on the nominal predicate and is followed by a gradual fall of the intonation curve. In fig. 1, the sentence accent is attracted onto the lexically accented first syllable of the attribute gálat 'mistake' at 143 Hz which is then followed by declination in the fundamental frequency. The bottom the predicate pitch range is instead represented by the fist unaccented syllable of the nominal head kalám 'discourse' at 83 Hz.

DECLARATIVE VERBAL UTTERANCES

The basic word order of declarative verbal utterances is SV(O). As in many other languages (Caron et al. forth.), 'neutral' verbal utterances make up a single IU whose unmarked status is signalled by a global declination of the intonation curve. In JA, sentence accent typically falls on the accented syllable of the main verb and the bottom of the intonation curve corresponds to the final syllable of the utterance.

NEGATIVE DECLARATIVE UTTERANCES

Both nominal and verbal negative declarative utterances are marked by the negative operator ma. Verbal negative utterances too show a global declining pattern. However, different from verbal positive declarative utterances, sentence accent systematically coincides with the pitch accent of the negative operator ma.

QUESTIONS

Polar interrogative utterances have the same SV(O) order as declarative verbal utterances and they can be optionally introduced by the sentence initial interrogative particle hal 'Q' as in the following example.

5.

hal íta árifu mára de // Q 2SG know woman PROX.SG 'Do you know this woman?' (inf.2)

In the absence of hal, prosody is a key grammatical element for distinguishing yes/no questions from declarative utterances. Contrasting with the declining intonation contour of declarative utterances, polar questions show a global rising of the intonation curve, whose highest pitch falls on the final syllable of the last word in the utterance.

6.

waláhi ya jek íta árifu // by_God VOC man 2SG know 'By God, man, do you know?' (inf.2)

In fig. 4, the sentence accent reaches 162 Hz and corresponds to the last unaccented syllable of the phonetic word [ˈtaːrif] resulting from the agglutination of the 2SG independent pronoun íta with the following verb árifu 'know.' The bottom of the intonation curve, by contrast, corresponds to the first unaccented syllable of the first word waláhi [waˈlaj] 'by God.'

In Wh-questions, question-words typically occur sentence finally. In prosodic terms, Wh interrogative utterances are marked by the same declining intonation pattern of declarative verbal utterances. However, since all the question-words present a lexical high pitch accent on their last syllable (i.e. munú 'who,' yatú 'which,' šenú 'what'), the bottom of the intonation curve corresponds to the penultimate syllable of the question word. Finally, tag questions are marked by the negative interrogative particle músu 'TAG'. músu is syntactically free, since it can occur both before and after the nominal head of the interrogative sentence or self-standing. Prosodically speaking, tag interrogative utterances show a final emphatic rising of the intonation curve Fig. 6 The prosodic contour of a tag question In fig. 6, the last unaccented syllable of the adverb sáwa 'together', being also the last syllable in the utterance, is the bearer of the sentence accent ([saːˈwa]) and reaches 182Hz). The rising nucleus of the utterance is prepared by a falling pitch on the last syllable of the phonetic word [ˈbakul] resulting from the cliticization of the preverbal marker bi= to the verb ákulu 'eat'.

TOPICS

We turn now to the grammar of topics in JA. Generally speaking, JA marks topicalization both syntactically through left dislocation and prosodically. Two types of argument topic can be distinguished: definite and indefinite. Definite topics are marked by the phrase-final proximal demonstrative pronoun de, while indefinite topics are introduced by the invariable existential copula fi (Caron et al. forth.). JA also presents frame setting topics that can be syntactically opposed to argument topics because of the absence of coreferential expressions (i.e. anaphoric pronouns) in their comment.

DEFINITE ARGUMENT TOPICS

It has repeatedly been argued (e.g. [START_REF] Chafe | Givenness, contrastiveness, definiteness, subjects, topics and point of view[END_REF][START_REF] Lambrecht | Information structure and sentence form. Topic, focus, and the mental representations of discourse referents[END_REF][START_REF] Givón | Mind, Code and Context: Essays in pragmatics[END_REF]) that the pragmatic feature of referent identifiability underlies the distinction between indefinite and definite syntactic expressions. According to Chafe (1976: 32), if the speaker assumes that the hearer can identify a given proposition, he/she is more likely to employ definite linguistic expressions. Lambrecht (1994: 78) goes further in the same direction and argues that, when an identifiable proposition becomes a discourse referent and serves as an argument in another proposition, it may be linguistically designed with the same expression as an entity (i.e. with a personal or demonstrative pronoun).

JA fully accords with these assumptions: when an argument topic makes reference to a previously established referent it is morpho-syntactically marked by a default singular proximal demonstrative pronoun and definite article de 'PROX.SG'. 7 In topicalized definite constituents, de is much more common than in non-topicalized ones, and is also used with semantically definite elements (e.g., proper nouns, as in 12.). Coreferentiality in the comment is marked by anaphoric personal and possessive pronouns, or by oblique anaphoric adverbs such as the locative fógo 'in.ANAPH' which results from the grammaticalization of the prepositional phrase *fog úo 'on 3SG'. As indicated by these resumptive elements, the topic can contain material covering different syntactic roles in the comment: subject (i.e. the argument preceding the verb: (9)), direct object (i.e. the argument following prototypical transitive verbs: (10)), oblique (i.e. any argument other than subject and object: (11)).

9.

[ In fig. 7 the first IU contains an oblique definite topic and it culminates with a sharp rise of the intonation curve accompanying de (127 Hz), then is followed by a pause of almost half a second. The comment constitutes a major IU presenting a declining intonation curve. The anaphoric oblique fógo is coreferential with the topicalized definite phrase; coreferentiality is prosodically marked on the first syllable of the anaphoric fógo, which bears the highest pitch in the comment.

INDEFINITE ARGUMENT TOPICS

In the case of presumed non-identifiability of the topic, the speaker commonly resorts to indefinite expressions to mark the introduction of the new referents both into the consciousness of the addressee and the universe of discourse. In JA indefinite argument topics are introduced by the invariable existential copula fi, which can be supplemented by other inherently indefinite elements such as wáhid 'one' (13) or táni 'other' ( 14). ( 13) is a complex topicalized utterance composed of two topics where the left-dislocated wáhid is coreferential with the 3SG possessive pronoun to in the comment.

13.

[fi wáhid] / [min awlád nuér zey de] / ísim to modú // EXS one from sons Nuer like PROX.SG name POSS.3SG Modu 'There is a man, from the Nuer tribe, his name is Modú' (inf.1) In Fig. 8 the existential fi introducing indefinite topics is characterized by an extra-high pitch (149 Hz) followed by a down-step of the intonation curve accompanying the topicalized referent. The topic ends with a final rising intonation on its last syllable (145 Hz) and is followed by a pause. Differently from definite topics, the anaphoric referents of indefinite topics are deaccented since the sentence accent falls on the first syllable of the main verb géni 'stay' (cf. neutral declarative utterances, as in (3)). 14.

[fi akú tái táni henák] / ána bi=rówa géni ma úo EXS brother POSS.1SG other there 1SG IRR=go stay with 3SG henák // there 'There is a friend of mine there, I will go to stay with him there.' (inf.1)

The fact that in our corpus indefinite topics are much less common than definite ones suggests that in JA as elsewhere (cf. Lambrecht's 1994: 165, 'accessibility scale of topics') topicalized referents tends to be identifiable from the discourse.

FRAME SETTING TOPICS

As already stated ( § 2.), frame setting topics typically involve adverbial phrases that restrict the spatial and/or temporal context of the following predication. Similarly to argument topics, frame setting topics are left-dislocated. However, the discourse interpretation of such adverbial expressions involves no anaphoric processing because there is no referent that gets activated by the topic. 15.

[ fi júba ] / nína g=ámulu zey de // in Juba 1PL PROG=do like PROX.SG 'In Juba, we do like that' (inf.1) Fig. 9 shows that frame setting topics present the same prosodic contours as definite and indefinite argument topics (rising intonation followed by a pause and declining on the comment).8

FOCI

JA makes use of three different particles for marking focus. These are the focus-sensitive operator zátu and the dedicated focus markers yawú and yáwu.9 Emphasis is rather expressed by ya in one of its different uses. Despite the fact that these particles have different information scopes, all of them involve essential reference to the information structure of the utterances in which they occur. Furthermore, it is important to remark that focus in JA can be expressed only in situ or, in other words, in constructions where the focused constituent, followed or preceded by a focus sensitive operator or a focus marker, remains in its unmarked position. Accordingly, focus cleft constructions are absent, and focus is always expressed within a single IU. In specific configurations, prosody complements morphosyntax in marking three types of focus:

• Contrastive focus • Information focus • Re-assertive focus

THE REFLEXIVE-CONTRASTIVE PARTICLE ZÁTU

According to [START_REF] Selkirk | Contrastive focus, givenness and the unmarked status of Discourse-New[END_REF], contrastive focus primarily evokes a contrast with other non-focused entities that might fill the same position as the focused item. In this regard, there are different views about whether contrastive focus constituents are dissimilar in their prosodic and syntactic configurations from non-contrastive constituents. Certain scholars (Büring 2006: 28) have proposed that contrastive focus is subject to a grammatical principle for the assignment of sentence accent leading to a grammatical distinction between contrastive and non-contrastive constituents. Others (Gussenhoven 2010: 85) have instead claimed that principles of grammar do not assign contrastive focus any distinctive prosodic prominence. Rooth (1992: 83), for his part, affirms that the 'contrast set' evoked by the focus provides the locus for focus sensitive operators such as 'only', 'even ', and 'also.' In JA a contrastively focused argument is morpho-syntactically marked by zátu following the contrasted argument, while a specific prosodic marking is lacking (Caron et al. forth.). zátu is diachronically related to the emphatic 3SG.M reflexive pronoun *zāt=uh 'PRO.EMPH=3SG.M' of Sudanese Arabic. In JA, when zátu follows a noun or a personal pronoun, it can still express an emphatic reflexive meaning as in (16), not yet a contrastive focus: 16. úo zátu b=wónusu ma ána sáwa // 3SG REFL IRR=talk with 1SG together 'He himself would talk with me' (inf.2) Not surprisingly, the emphasizing function of the pronoun zátu furnished a favourable semantic source for the partial grammaticalization of a contrastive focus marker. In (17.a) the question sets the frame for a possible contrast, asking for a confirmation against any possible alternative solution. A special morpho-syntactic and prosodic contour is instead found when a whole sentence is in contrastive focus: in this case, zátu precedes the focused predication and it bears an extra-high pitch accent (in fig. 12 pitch reaches 171 Hz). The following focused utterance instead correlates with a global declining of the intonation curve. In ( 23). the locative adverb wen 'where' is in focus, while the first occurrence of zátu after the subject pronoun is possible to be interpreted as an emphatic element not necessarily contrastive (as in example ( 16)).

íta

zátu ma árifu móya gi=tála min wen zátu // 2SG CONTR NEG know water PROG=get_out from where CONTR 'You don't know where on earth the water come from' (inf.2) It is also interesting to remark that when zátu directly follows háta 'even,' it expresses a broad scalar focus on the following predication, implying that the predication in focus is less likely than other alternative predications (König 1991: 69;Krifka 1998: 92). Thus, unlike zátu, which simply evokes a contrast, the introduction of háta causes the alternative predications to be ordered on a scale of likelihood; the value of the háta zátu construction is associated with the lowest ranked element on this likelihood scale: In a comparative perspective, it is important to note that the Ki-nubi creole of Uganda also presents a (minor) contrastive focus marker bizátu (derived from Sudanese Arabic *bi=zāt=uh 'by=PRO.EMPH=3SG.M). According to Wellens (2005: 174), bizátu adds emphasis on a preceding pronoun or, alternatively, it highlights the meaning of a following sentence. In spite of these syntactic similarities between JA zátu and Ugandan Ki-Nubi bizátu, it seems that the pragmatic functions of the latter are much more restricted than those of JA zátu. This is presumably due to the grammaticalization of ya as a main contrastive device in Ki-Nubi (cf. 5.2.).

TOWARDS A FOCUS MARKER: THE PARTICLE YA AND ITS MULTIPLE USES

The particle ya is extremely multifunctional. Its Arabic etymological and still very common meaning is vocative, as was exemplified in 6. above. Another example is ( 27), which further shows the more common utterance-final position of vocative expressions in JA:

27.

sekeséke bada kúbu ya zol // drizzle start pour VOC man 'The rain started to fall down, bro' (inf.1) In many cases the vocative value is weakened. In (28) ya is used before a personal pronoun and its meaning seems to be that of calling attention to what is about to be said. In this case, the multifunctional ya is linked with a prosodic prominence (cf. 5.3). IRR=find CONTR 3PL PROG=pierce POSS.3PL 'So, you will find out that they also make mistakes (while speaking) their (Arabic)' (inf.1) Fig. 13 shows an emphatic extra-high pitch reaching almost 650 Hz while the rest of the utterance is linked to a declination of the intonation curve that does not exceed 200 Hz. The translation, where ya is loosely rendered with "so," draws the attention to this truly modal value of a vocative expression, which 'is in fact a request to pay attention' (Izre'el forth.; italics in the original). Interestingly, in Sudanese Arabic ya is frequently coupled in its use as a vocative by the vocative morphemes hōy (male speaker) and hēy (female speaker); alone, ya is used, at least in certain Western Sudanese dialects, such as Baggara (Manfredi forth.a), as a preposition 'up to' or as a disjunctive conjunction 'or. ' If we accept that a vocative is not an extraphrasal nominal case, we can better understand its extension in JA as a marker of emphasis for a following element; most commonly the element in emphasis is a predicate, either nominal (29) or verbal ( 30 úmon ya tában jíbu fíkra // 3PL EMPH obviously bring idea (following a list of nations who introduced the football African Cup of Nations) 'They quite obviously came up with the idea' (inf.1)

In prosodic terms, the particle ya as an emphasis marker differs sharply from its use as a vocative and as an attention-calling modal. It operates as a trigger word and it bears a considerably low pitch, while the following presented item has an emphatic high pitch, e.g. in fig. 14, where the verb bíu is characterized by a sharp rise of its lexical pitch that reaches 116Hz. 32. úo ya bíu fi yugánda de // 3SG EMPH buy in Uganda PROX.SG (discussing a man dealing with motorbikes) 'He buys them in Uganda' (inf.2) When the presented item corresponds to the last word of the utterance, as in fig. 15, it correlates with a considerable pitch oscillation ending at the bottom of the intonation curve (132 > 73 Hz): In Ki-Nubi ya further develops into a true focus marker. In Kenyan Ki-Nubi, according to Owens (1996: 151), the most common focus construction consists of a left-dislocated constituent followed by the morpheme ya. This morpheme can mark in principle a constituent in any part of the sentence; interestingly, when used alone ya serves as a presentative locative (in variation with yadá cf. paragraph 5.3.). By contrast, Wellens (2005: 171-172) states that, in Ugandan Ki-Nubi, ya is associated with a contrastive focus highlighting both new and asserted information. As reported by Wellens, ya can both precede or follow the sentence constituent it focuses. The situation in JA is radically different: first of all, ya is not contrastive and it always precedes its scope, be it nominal or verbal, while no left-dislocation is involved (ya can well be the first element of the sentence as in (34)).

34.

ya dínka ma b=wónusu árabi ya zol // EMPH Dinka NEG IRR=talk Arabic VOC man 'Dinka people do not speak Arabic, bro' (inf.1)

The fact that no dislocation is involved in the case of arguments preceding ya is easily shown by the absence of co-referential elements after ya and before the predicate (cf. (29-33)). At the same time, the possible co-occurrence of ya with focus-sensitive operators such as zátu, as in ( 35) and ( 36), clearly shows that we are not faced here with a focus marker.

35.

de ya múškila zátu kúlu // PROX.SG EMPH trouble CONTR all 'This is the real problem' (inf.2)

36.

úmon ya zátu wodí le ánna árabi henák // 3PL EMPH CONTR give to 1PL Arabic there 'They brought us the Arabic language, down there (in South Sudan)' (inf.2)

In diachronic terms, the sequence ya úo 'EMPH 3SG' gave rise to two elements of interest for the information structure of JA: yáwu 'INF' (information focus marker) and yawú 'RE-ASS' (reassertive focus marker). This also forms an interesting case of accentual opposition which does not find its origin in the Arabic superstrate. It has been seen that when used as an attention-calling device (cf. fig. 13, (28) above), ya is prosodically more prominent than the following noun or pronoun. It is thus plausible to assume that the origin of yáwu 'INF' can be found in the lexicalization of the sequence *yá uo, in which the second element, already de-accented, further lost its pronominal value. Along these lines, a further development of yáwu 'INF' has led in (at least certain varieties of) Ki-Nubi to the dropping of final /o/, yielding yaw, which is defined by Wellens (2005: 173) as a sentence-final marker of emphasis (see 5.4.). By contrast, the accent on the last syllable of yawú 'IDF' is possibly the result of the lexicalization of a sentence accent on úo '3SG,' which was emphasized by ya 'EMPH,' therefore being the most salient element of the sequence *ya úo (cf. fig. 14, (32) above). In JA, both yáwu and yawú can be considered dedicated focus markers, since no other use has been recorded.

THE INFORMATION FOCUS MARKER YÁWU

The most common use of yáwu is related to the expression of 'information' focus: i.e., a focus which marks the non-presupposed status of the information it carries (Kiss 2008: 92) One can hypothesize that the presence of the immediately preceding definite argument topic bágara de gives prominence to the anaphoric pronoun úo; shifting yáwu to a post-focal position could be a strategy to balance the salience between the constituents of the utterance.

THE RE-ASSERTIVE FOCUS MARKER YAWÚ

JA yawú is somehow similar to the locative presentative of Kenyan Ki-Nubi yadá (Owens 1996: 152) and Ugandan Ki-Nubi yadé (Wellens 2005: 173), derived from *ya de 'EMPH PROX.SG' (unattested in JA). Like Ki-Nubi clause final yadá / yadé, JA yawú selects a previously textuallygiven element as the most salient information. It is different from a counter-assertive focus, 'in which the speaker is in contrast with a previously assertion, because he/she guesses that the embedded proposition should be already part of the mutual knowledge of conversation' (Zimmermann 2007: 150), because the speakers are aware of the mutually shared status of the focused element, and no contrast is implied. Using yawú the speaker re-asserts the pragmatic salience of the element and brings it to the fore. JA jawú is thus a re-assertive focus. In ( 44

SUMMARY AND CONCLUSIONS

The article has shown that in JA topic and focus-marked sentences can be opposed to 'neutral' (informationally-unmarked) sentences, whose behaviour can be summarized as follows. 1. describes the syntactic and prosodic behaviour of neutral utterances. The Subject (SBJ) is always the first element, except for the optional use of hal in Yes-No questions and the presence of músu in Tag questions. In prosodic terms, declarative nominal utterances are characterized by a rising-falling intonation contour (➚ ➘), in which the subject corresponds to the rising part, and the predicate to the falling part of the contour. Declarative verbal utterances, in their turn, display a very common declination of the fundamental frequency (⇓). In declarative negative verbal utterances the negative marker ma is the most prosodically prominent element (⇑). Wh-question display basically the same pattern of declarative verbal utterances, except for the presence of the sentence-final Wh-word. Yes-No and Tag questions share a very high pitch prominence on the final syllable, but, while Yes-No questions are marked by a gradual rising of the intonation curve, Tag questions remain low (→) until the very last element. All these neutral utterances can be opposed, either syntactic and/or prosodic terms, to topic-and focus-marked utterances.

It has further been shown that morphosyntax and prosody are complementary in marking topicalization in JA. Three types of topic constructions have been identified. In Table 2., the topical material is always a NP. As has been seen, topic is prosodically signalled by rising intonation, with the last syllable (σ) receiving the highest pitch in the IU, which in its turn is followed by a pause.

In the case of definite topics, the PROX.SG marker de, being the last element, receives the highest pitch. Indefinite topics, are introduced by an accented existential copula fi. The comment contains an anaphoric element in both definite and indefinite argument topics. The comment is made up of whatever lexical material (X), followed by the anaphora. The comment is signalled by a declining intonation, whose bottom point lies on the final syllable (σ), be it the final syllable of the anaphora or of any other element following it. Frame setting topics are marked negatively by the absence of coreferential, anaphoric elements. None of these strategies is of course typologically exceptional, nor is the absence of a dedicated topic marker.

Focus constructions, instead, do have (almost-) dedicated markers. Contrastive focus is marked by an "almost-dedicated" marker zátu. It acts alone in marking a contrastive focus on a (preceding) argument or predicate, while it is supplemented by prosody when a whole sentence is in focus. Interestingly, the highest pitch falls in this case on zátu itself therefore running contrary to a well-attested tendency to prosodically stress the focalized item(s) (cf. Büring 1997: 29). Other focus constructions involve the use of the derivates of the multifunctional element ya. In this regards, it should be stressed that the syntactic and semantic differences associated with the use of ya in JA and Ki-Nubi bear witness to different degrees of grammaticalization. In JA, when ya precedes a nominal it acts as a vocative or, with a pronominal, as an attention-calling device; when it precedes a predicate it acts as an element emphasizing the importance and new status of the following element. In Ki-Nubi ya becomes a focus marker, possibly contrastive, with the same functions of zátu in JA. The semantic cline leading to the uses of ya in JA and Ki-Nubi is shown in Table 4.: Prosody complements ya in its different uses in JA: when ya functions as a vocative or as an attention-calling device it is associated with an emphatic high pitch. By contrast, when ya marks emphasis, it is the emphasized element which bears prosodic prominence. These two prosodic configurations are at the basis of the grammaticalization of ya-derived focus markers: yáwu for information focus and yawú for re-assertive focus. Fig. 20 depicts the grammaticalization of the dedicated JA focus markers yawú and yáwu, and of Ki-Nubi yaw and yadá/yadé. While in JA the information and re-assertive focus are grammaticalized respectively from the attention-calling and emphatic uses of the marker ya (with the addition of a 3SG pronoun), in Ki-Nubi the grammaticalization of the emphasis markers yaw and yadá / yadé seems to be, according to [START_REF] Wellens | The Nubi Language of Uganda: An Arabic Creole in Africa[END_REF] description, a further development of a contrastive focus value of ya.

Fig. 20 The possible grammaticalization of the dedicated focus markers in JA and Ki-Nubi

While the lexical elements responsible for the expression of topic and focus are Arabic-derived, no such influence is ascertainable in the prosodic means. A possible role of the Nilotic substrate is possible, but unlikely, given the general lack of sensible substratal influence in JA and Ki-Nubi (cf.

Owens, this volume, and contrary to early assumptions: cf. [START_REF] Bureng | Juba Arabic from a Bari Perspective[END_REF]. We are more probably faced with internal developments. We likewise leave open the whole, fascinating issue of the possible typological correlates of this interplay of morphosyntactic and prosodic formal means in the expression of the information structure of pidgins and creoles at large.

Fig. 1

 1 Fig.1The prosodic contour of a declarative nominal utterance

Fig. 2

 2 Fig.2The prosodic contour of a declarative verbal utterance

Fig. 3

 3 Fig.3The prosodic contour of a negative verbal utterance

Fig. 4

 4 Fig.4The prosodic contour of a yes/no question

Fig. 5

 5 Fig.5The prosodic contour of a wh question

Fig. 8

 8 Fig.8The prosodic contour of an indefinite argument topic

Fig. 9

 9 Fig.9The prosodic contour of a frame-setting topic

  17

  abigó the hyena or what?' (inf.1)The answer (17.b) thus includes a contrastive focus marked by zátu and it makes use of the same prosodic contour of neutral declarative nominal utterances (cf. fig.1).

Fig. 10

 10 Fig. 10 The prosodic contour of an argument contrastive focus marked by zátu

Fig. 12

 12 Fig.12The prosodic contour of a sentence contrastive focus marked by zátu

Fig. 13

 13 Fig.13An extra-high pitch falling on ya before a personal pronoun

Fig. 14

 14 Fig.14The prosodic contour of emphasis marked by ya

Fig. 15

 15 Fig.15The prosodic contour of an utterance-final emphasis marked by ya

Age Born in Ethnic affiliation In Khartoum since Other spoken languages inf

	inf.2 21 Juba	Lopit	1997	Lopit
				English
				Sudanese Arabic
	inf.3 39 Juba	Pojulu	1999	Bari
				English
				Sudanese Arabic
	• Prepositions: a closed class, possibly being made up of the following only: ma 'with,' le 'to,'
	min 'from,' fi 'in,' be 'by, though.'
	• Adverbials: a closed class, composed by such elements as héni 'here,' kalás 'definitively,' bes
	'only,' as well as by adjectives with an adverbial use;
	• Conjunctions: a closed class, composed by such elements as wa 'and,' kan 'if,' wála 'or,' laánu
	'because, that.'
	2. 2. DATA, INFORMANTS AND METHODOLOGY
	Our data were collected by Stefano Manfredi in Khartoum and Omdurman in November -
	December 2007. 5 The main informants were three adult males, and for all of them JA was the
	primary (i.e. the usual and most frequently used) language.
	.1 29 Juba	Bari	1995	Bari
				Sudanese Arabic
				Swahili

• Adjectives: an open class, it is composed by the elements which can be pluralized through the adjectival plural affix -ín (as well as by invariable adjectives, mostly borrowed from English); syntactically, they can act as modifiers in NPs as well as predicates.

  Alike Ugandan Ki-Nubi(Wellens 2005: 126) and certain Sudanese Arabic dialects(Manfredi forth.b), also JA marks non-restrictive relative clauses (i.e. relative clauses that modify a definite and highly referential nominal head) by means of the same sentence final proximal demonstrative de as in the following example:The left-dislocated argument is typically realized as a minor IU separated from the comment. Fig.7The prosodic contour of a definite argument topic As for Jibet, (this is) the place were the sergeants of the Sudanese army are sent' (inf.1)

		140
		120
	Pitch (Hz)	100
		80
		70
		dZi bé:t de/	426	mahál al bwo dí fó godu bá:t ta	dZe:O	ta su dán zá tu//
		0						3.093
						Time (s)
	12.	[jibét de] /		mahál al	b=wodí	fógo	dubát	ta
		Jibet	PROX.SG place REL IRR=give in.ANAPH sergeant\PL POSS
		ješ	ta		sudán zátu //
		army POSS Sudan CONTR
		'
		kal				tái	de] /	úo	gi=géni	fi bor sudán //
		maternal_uncle POSS.1SG PROX.SG 3SG PROG=stay in Port_Sudan
		'As for my maternal uncle, he lives in Port Sudan' (inf.1)
	10.	yála / [zélet	de] /	úmon gi=rága	úo	be seménti //
		then	asphalt PROX.SG 3PL	PROG=cover 3SG by cement
		'Then, this asphalt, they covered it with cement' (inf.2)
	11.	[redmíya de] /	ma	fógo	dége∼dége	ketír //
		gravel		PROX.SG NEG in.ANAPH knock∼knock	much
		'As for this gravel, there are not a lot of bumps' (inf.1)
	filán	al	g=álabu		kwes	de
	guy	REL	PROG=play	well	PROX.SG
	'The guy who plays well'

7

  zátu can also be used to contrast a preceding verbal predicate, as in 19. The same morpho-syntactic and prosodic rules of fig.10. apply (cf. fig.3. for a neutral declarative verbal utterance). Fig.11The prosodic contour of a predicate contrastive focus marked by zátu

		0										0.7825
						Time (s)
	17.b	de		ásed zátu //
			PROX.SG lion CONTR
			'This is a lion' (not a hyena or anything else) (inf.3)
	In this context, a possible neutral answer (without zátu) remains perfectly grammatical.
	18.		de		ásed //
			PROX.SG lion
			'This is a lion'
		175
		160
		140
	Pitch (Hz)	100 120
		75
		ú mon	gi	sta	fíd	za:	tu	min	wá	ra	to	tómon//
		0										1.437
							Time (s)
	19. úmon g=istafíd				zátu	min wára ta	tómon //
		3PL			PROG=take_advantage CONTR from behind POSS POSS.3PL
		'They are actually taking advantage of them' (inf.1)

  Even if he wants to defecate, he might do it in the bed' (inf.2)The sequence háta zátu is prosodically independent being enclosed by a minor prosodic boundary. The combination of háta and zátu can also convey a narrow scalar focus on a subject argument. In this case, the focused NP separates háta and zátu as in 26.:

	25. háta zátu /	kan úo	ázu	ákara /	bi=kún fi serír //
	even CONTR if	3SG want defecate IRR=be in bed
	'26. háta habóba		zátu /	bi=rówa árifu	hája ísim	to	giráya //
	even grandmother CONTR IRR=go know thing name POSS.3SG study
	'Even an old woman will know what 'education' means' (inf.1)
	24. háta zátu /	fi júwa	mustéšfa de /	kúlu amúl∼amulú
	even CONTR in inside hospital	PROX.SG all	do\PASS∼ do\PASS
	bulát //
	tiled_floor
	'Even the whole inside of the hospital was tiled' (inf.1)

  . JA yáwu (different from Ki-Nubi yadá) always precedes the focused constituent. It can also precede a verbal predicate, as in (37), where it focalizes the auxiliary verb gi=rówa 'going' in the expression of a near future. PROX.PL INF PROG=go bring cup (discussing the fact that Sudan are no longer winning the Africa Cup) 'Now, what you find it is that other teams, the small ones, are going to win the cup' (inf.1) While utterances marked for emphasis by ya present an emphatic high pitch on the focused item (cf. fig. 14, (32)), yáwu usually carries the highest pitch of the utterance, as in fig. 16, where it precedes a 2SG independent pronoun and reaches 209 Hz: Fig. 16 An information focus marked by yáwu bearing prosodic prominence In other cases, neither yáwu nor the following item bears prosodic prominence, as shown in fig. 17, where the definitional focus yáwu zey de 'it is just like this' corresponds to the comment of the frame-setting topic fi béled de 'in this country': Fig. 17 An information focus marked by yáwu without any prosodic prominence Moreover, a pause (induced here by hesitation) can cause yáwu to be prosodically separated from the focused item, as in 40.a, where yáwu is realized with a long final vowel and the following verbal predicate dóru 'walk' occurs after a pause of 592 mms: Fig. 18 An information focus marked by and prosodically separated from yáwu

	42.	170	bágara de /		úo	wáhid kúlu yáwu //
		150	cow		PROX.SG 3SG one	all	INF
				'(As for) cows, they are all the same' (inf.2)
	100 The corresponding comment with yáwu preceding the focus is obviously perfectly correct as a Pitch (Hz) selfstanding utterance:
		60
	43.			á úo	na	ga:l yáwu wáhid kúlu // ja: de / fi bé	led	de /	jaw	ze:	de //
			0 3SG INF	one	Time (s) all	1.332
	39. ána gále ya 'They are all the same' de /	fi béled	de /	yáwu zey de //
		1SG say	PRES PROX.SG in country PROX.SG INF	like PROX.SG
		'I say: "It, in this country, is like that"' (inf.2)
	37.			íta		gi=já		ligó farik-át	tan-ín	al	sukár∼sukár
				2SG PROG=come find team-PL.N other-PL.ADJ REL small.PL∼small.PL 10
				dol /		yáwu gi=rówa	šílu kas //
		170
		160
		140
		120
	Pitch (Hz)	100
		75
				dZe:O	tó mon ke dé já	wu: /	592	do ru fo go//
		250
									ke dé	dó	ru	fó go//
		200	0						Time (s)	1.953
	75 150 40.a ješ army POSS.3PL so_that INF tómon kedé yáwu / Pitch (Hz) '(They built the bridge) ... so that their army...' (inf.2) 100 40.b kedé dóru fógo //
				wa so_that já	wu walk on.ANAPH tá nu zu rúf	ta	dZú	ba	de //
		0	'... so that (they can) walk on it' (inf.1)	1.303
	Time (s) áynu zurúf INF 2SG see yáwu íta 40.c dóru fógo // 38. wa and walk on.ANAPH condition\PL POSS Juba PROX.SG ta júba de // 'and you know the conditions in Juba' (inf.1) '... (they can) walk on it' (inf.2)
	In (41) yáwu restricts the comment to the subject argument de:
	41. yáwu de			binía / tában //
			INF	PROX.SG girl	obviously
			'(discussing youth language and the word bámba 'girl') This means girl, of course'
			(inf.2)
	The next, and final, example is exceptional insofar as yáwu occurs in post-focal and clause-final
	position:

  And here the lion (...) after three days it bit him' (inf.3) Moreover, different from the focus sensitive particles zátu and ya, yawú is not associated with any prosodic prominence, as shown in fig.19: Fig.19The prosodic contour of a re-assertive focus marked by yawú

	120
	100
	Pitch (Hz)
	80
	70
	), informant 2 focalizes the proper name Modu immediately after it was introduced by his interlocutor in (13) above: 44. munú yawú modú // who RE-ASS Modu 'Who is (this) Modu?' (inf.2) In the same manner, in (45) yawú focalizes the previously mentioned element abigó: 45. abigó fi héna / taláta yom / yawú áda úo // lion EXS here three day RE-ASS bite 3SG de: múf ra: ga/ ja wú da hé na da// Time (s) 0 1.565 46. ya de mufrága / yawú de héna de // PRES PROX.SG stirrer RE-ASS PROX.SG here PROX.SG 'ja: 'This is the wooden spoon. Here it is' (inf.3)

Table 1 .

 1 Neutral utterances in JA

	Declarative	syntax	SBJ	PRED.N
	nominal	prosody	➚	➘ //
	Declarative verbal	syntax	SBJ	PRED.V	(OBJ)
	(positive)	prosody	⇑	➘	⇓ //
	Declarative verbal	syntax	SBJ	ma	PRED.V
	(negative)	prosody	➚	⇑	⇓ //
	Yes-No question	syntax	(hal)	SBJ	PRED
		prosody	⇓	➚	⇑ //
	Wh-question	syntax	SBJ	PRED.V	Wh
		prosody	⇑	➘	⇓ //
	Tag question	syntax	músu	SBJ	PRED
		prosody	⇓	→	⇑ //
	Table

Table 2 .

 2 Types of Topic in JA

	TOPIC	COMMENT

Table 3 .

 3 Contrastive focus in JA

	Argument	syntax	X	zátu
		prosody	➘	⇓ (//)
	Predicate	syntax	X	zátu
		prosody	➘	⇓ (//)
	Sentence	syntax	zátu	X
		prosody	⇑	➘ //

Table 4 .

 4 The diachronic development of ya in Juba Arabic and Ki-Nubi

	value	vocative	attention-calling	emphasis marker	contrastive focus
	historical development
	Sudanese Arabic	✔
	Early Pidgin Arabic	✔	✔ (?)
	Juba Arabic	✔	✔	✔
	Ki-Nubi	✔	✔ (?)	✔ (?)	✔

According toRooth (1992: 78) 'focus indicates the presence of alternatives that are relevant for the interpretation of linguistic expressions'.

Although these are the main values of these affixes, a number of exceptions are found.

Fieldwork in South Sudan was at the time of the collection of data technically almost impossible (due to the difficult political situation).

The accented negative operator ma contrasts with comitative ma 'with' which does not systematically bear the sentence accent (as in 1.). We leave aside the question whether negative utterances are inherently in focus, as proposed among others by[START_REF] Zimmermann | Contrastive focus[END_REF].

It should be noted that, contrary to the accented fi 'EXS' of 14., the preposition fi 'in' is not systematically accented.

Acrolectal varieties of JA also integrated the counter-assertive focus marker mà= from Sudanese Arabic(Caron et al. forth.), which will not be further analysed in the present work.

A number of Arabic frozen adjectival and nominal plural forms are used in JA. Some of them are of wide occurrence, while others are a function of the knowledge of and exposure to Sudanese or Standard Classical Arabic on the part of the speaker. Another example is zurúf 'conditions' in 38.

List of abbreviations, glosses and symbols

ADJ


A comparison of microstructure and of thermal transport properties of yttria and ceria stabilized zirconia coatings deposited by suspension plasma spraying

The single cathode plasma torch SG-100 was used to spray suspension prepared with the use of two kinds of commercial powders ZrO2+8 wt. % Y2O3 (8YSZ) and ZrO2 + 24 wt.% CeO2 + 2.5 wt.% Y2O3 (24CeYSZ). The suspensions were formulated using finely milled solid phase, water and ethanol. The operational spray parameters being the same for each powder were modified by changing: (i) spray distance; and (ii) torch scan linear speed. The coatings microstructures were analyzed with the use of optical and scanning electron microscopes as well as by X-ray diffraction. Their porosities were found with help of the image analysis of metallographically prepared cross-sections. Thermal diffusivity was measured with the use of commercial system LFA 447 NanoFlash® working at the temperatures limited to 300°C. The measurements were made with the use of the coatings sprayed on the steel substrate and a 2-layers numerical model was applied to determine thermal diffusity of the coatings. The obtained data were used to calculate thermal conductivity of stabilized zirconia coatings.

Introduction

Suspension Plasma Spraying (SPS) is one of relatively new methods and is currently very frequently tested to apply the oxide coatings. It was initiated a by the end of last century (in 1997) by the group of researchers from Sherbrooke University in Canada [START_REF] Gitzhofer | Suspension plasma spraying[END_REF]. The innovation of the presented method was the use the feedstock being the suspension of fine solids. However, the use of liquid feedstock instead of dry one, resulted in a change of the processes which became more complex than the standard plasma spraying [START_REF] Pawáowski | The Science and Engineering of Thermal Spray Coatings: Second Edition[END_REF].

During the spraying process such physical effects as: evaporation of liquid part of suspension's, in-flight agglomeration and sintering of solids, their melting and vaporization or splats formation on the surface of the element may occur [START_REF] Delbos | Phenomena Involved in Suspension Plasma Spraying Part 2: Zirconia Particle Treatment and Coating Formation[END_REF][START_REF] Fauchais | Parameters controlling liquid plasma spraying: solutions, sols or suspensions[END_REF]. Moreover, the optimal process variables including size and properties of solid phase, spray process parameters, type of the plasma torch and injection mode are not easy to find out. Consquently, the optimization of spray parameters is more difficult in the SPS method in in conventional plasma spraying. On the other hand, the suspension plasma spraying enables obtaining the coatings having finely grained microstructure with very interesting properties. In particular, thermal conductivity of yttria or ceria stabilized zirconia coatings seems to be considerably lower than that obtained by the use of conventional feedstock [START_REF]Progress in Thermal Barrier Coatings[END_REF]. For this reason The SPS coatings are considered to be used as thermal barrier coatings (TBCs) in gas turbines.

The presented experiments were undertaken to characterize microstructure and thermal transport properties of coatings obtained with the use of fine, submicrometric zirconia powders and different spray parameters. The research was carried out aiming the comparison the different properties of zirconia coatings stabilized with different oxides. Finally, the studies allowed evaluating the possibilities of producing TBC with the suspension plasma spraying method.

Experimental procedures

Powders and suspensions preparation

Two commercial powders, namely Metco 204NS having composition ZrO2 + 8 wt. % Y2O3 and Metco 205NS having composition ZrO2 + 24 wt.% CeO2 + 2.5 wt. % Y2O3 were used to spray the coatings. The mean diameters of initial, coarse powders were the same and equal to dvs=38ȝm. The morphology of powders is presented in Fig. 1. The initial powders were ball-milled in order to obtain finer particles. The ball-milling was made using moliNEx system (NETZSCH, Germany). The zirconia balls with the diameter of about 2mm were used as grinding medium and a small addition of ethanol as cooling one. Small addition of the dispersant (Beycostat C213, CECA) was used prevent agglomeration of particles during milling process. The granulometry tests were made based on the laser diffraction analysis (Partica LA-950V2, Horiba). The measurements showed that the resulting powder after 2h of milling had a mean size equal to: dvs=4.5 ȝm (8YSZ) and dvs=3.9 ȝm (24CeYSZ) (Fig. 2.) and a monomodal size distribution. The suspension were prepared from the mixtures of 20 wt. % of solid, 40 wt. % of water and 40 wt. % of ethanol. The zeta potential of suspensions was measured using Zetasizer Nano ZS (Malvern, UK). The suspensions were not stable and dispersant agent was added (Beycostat C213, CECA) to avoid agglomeration of particles. The resulting zeta potential was as low as ȗ = -8.6 mV for 8YSZ powder suspension and ȗ = -6,2 mV for 24CeYSZ. The entire procedure of preparation of powders and suspensions is described in [START_REF] Àatka | Investigation of ceramic coatings obtaned by suspension plasma spraying[END_REF].

Design of spray process experiments

The spray process was realized using an SG-100, DC single cathode and single anode torch of Praxair S.T., (Indianapolis, USA). Plasma torch was installed on a 5-axis IRB-6 industrial robot of ABB (Zürich, Switzerland).The experiment was designed by twolevel full factorial design (2 k ) with k=2 in which the variable parameters were: (i) torch scan velocity (300 and 500 mm/s); and (ii) spray distance (40 and 60 mm). Other important parameters of the process were kept constant, namely electric power equal to 40 kW, working gases composition was Ar -45 slpm with H2 -5 slpm and suspension feed rate was about 39 g/min. The coatings surface temperatures measured at spray experiments are presented in Table 1. The stainless steel samples of O.D.=25 mm and thickness of 3 mm were used as substrates. The substrates were sand blasted using 500 μm white alumina sand and cleaned in ethanol before deposition. The temperature of the top surface of the samples was controlled with the use of the pyrometer during spraying. In order to avoid the overheating of the substrates the process was interrupted after every three scans of the torch and the samples were cooled down by compressed air.

Microstructure characterization

The scanning electron microscope (Jeol JSM-7400) was used to characterize powders and another one (Philips 515) was used to characterize the coatings. The phase composition of coatings was determined with X-ray diffractometer (Bruker D8 Advance) with CuKĮ1 radiation and a range of 2ș angles from 15° to 120°. The pahses were identified using Diffrac+ Eva software.

The coatings porosities and thicknesses were characterized with use of optical microscope (Nikon LV100). The cross-sections of samples were metallographically prepared. The thicknesses of coating was found from 5 measurements in 3 different regions of samples. The porosity was found using image analyzer working with ImageJ software [7].

Thermal diffusivity measurements

Thermal diffusivity was measured with the use of commercial system LFA 447 NanoFlash®, Netzsch. The samples were coated on each face with graphite layer before measurement to provide better propagation of heat and to allow reading of small temperature changes by the detector. The signals were measured with InSb infrared detector. The model used initially to determine thermal diffusivity by flash laser set up for homogenous samples is Cowan model [START_REF] Cowan | Pulse Method of Measuring Thermal Diffusivity at High Temperatures[END_REF]. The multilayer materials require more complex methods of calculation. The analysis of thermal diffusivity was made with the use of 2-layers model with finite pulse duration correction. Thermal contact resistance between the layers and heat losses were also taken into account. The measurements enabled to find the thermal diffusivity of coatings.

Other properties of tested samples, such as density ȡ, heat capacity cp, material and thermal diffusivity of the steel substrate were taken from literature (Table 2) [START_REF] Pankratz | Thermodynamic Properties of Elements and Oxides[END_REF][START_REF] Takeda | Gd1-xAxMnO3 (A = Ca and Sr) for the electrode of solid oxide fuel cells[END_REF][START_REF] Àatka | Thermal diffusivity and conductivity of yttria stabilized zirconia coatings obtained by suspension plasma spraying[END_REF][START_REF] Sokoáowski | Characterization of microstructure and thermal properties of YCSZ coatings obtained by suspension plasma spraying[END_REF]. The thickness of coating and substrate were measured experimentally. The following equation was used to calculate thermal conductivity of 8YSZ and 24CeYSZ coatings:

ߣሺܶሻ ൌ ܽሺܶሻ ή ܿ ሺܶሻ ή ఘ యబబ ଵାଷή οಽ ಽ ሺ்ሻ ሺͳሻ
where:

Ȝ -thermal conductivity [W/(m•K)] a -thermal diffusivity [m 2 /s] cp -specific heat [J/(kg•K)] ȡ300 -apparent density in ambient temperature [kg/m 3 ] ο -thermal dilatation [-]
The entire procedure of collecting the material properties has been thoroughly described in previous studies of the authors [START_REF] Àatka | Thermal diffusivity and conductivity of yttria stabilized zirconia coatings obtained by suspension plasma spraying[END_REF][START_REF] Sokoáowski | Characterization of microstructure and thermal properties of YCSZ coatings obtained by suspension plasma spraying[END_REF]. The data used in present study are presented in Table 2 and Table 3. 3 Results

Microstructure description

The micrographs of coatings surfaces and their crosssections of 8YSZ and coatings showed typical two-zones microstructure of the suspension plasma spraying method in which occur well molten lamella and very fine spherical particles (see e.g. Fig. 3a). The 24CeYSZ coatings microstructure shows a bit more of fine particles and less of well-molten big splats than that of 8YSZ ones (compare Figs 3 a and Fig. 3 c). The SEM images of the cross-sections of 8YSZ coatings (Fig. 3b) showed also well molten lamellae and some pores, which have been formed between them, while the cross-sections of 24CeYSZ coatings (Fig. 3d) were characterized by greater number of pores and microcracks. The phase analysis determined by X-ray diffraction revealed that the major phase for both YSZ and YCSZ were tetragonal zirconia with a small addition of monoclinic phase. The results of phase composition are collected also in Table 3.

Thermal diffusivity

Thermal diffusivity data for 8YSZ and 24CeYSZ coatings are presented in Fig. 4. Thermal diffusivity values for samples of 8YSZ coatings were in the range from 0.20 to 0.35x10 -6 m 2 /s depending on the spray run (Fig. 4a). The coatings obtained in the run no. 2 have the greatest diffusivity and the samples in the run no. 4 -the lowest. In the case of 24CeYSZ coatings, diffusivity values were in the range of 0.23 to 0.49x10 -6 m 2 /s. As it can be seen, the samples sprayed in the run no. 2 have the greatest diffusivity, while the samples sprayed in the run no. 1 have the lowest one (Fig. 4b).

Thermal conductivity

Thermal conductivity values calculated following equation (1) and shown in Fig. 5 were as follows:

x thermal conductivity values was in the range from 0.47 to 1.03 W/(m•K) for 8YSZ (Fig. 5a).

The increase in thermal conductivity with temperature was found also for these coatings. The highest values were noted for the highest temperature of 523 K at which the measurements were performed. x thermal conductivity values were from 0.46 to 1.07 W/(m•K) for 24CeYSZ coatings (Fig. 5b). The shape of the curves was slightly more constant with temperature than that of 8YSZ coatings.

Discussion

The optimization of the milling parameters allowed obtaining powders with very small diameter for both 8YSZ as well as 24CeYSZ. The use of liquid feedstock being a suspension of submicrometric solids and plasma spraying method enabled to obtain the coatings with finely grained microstructure. This type of structure is difficult to achieve with standard atmospheric plasma spraying (APS) working with dry feedstock. The APS coatings have bigger lamellae and do not have very fine grains [START_REF] Xing | Microstructure development of plasma-sprayed yttria-stabilized zirconia and its effect on electrical conductivity[END_REF]. SEM observation enabled to find that 8YSZ coatings showed more of well molten lamellae and smaller amount of fine sintered powder particles than 24CeYSZ coatings. The total porosity and number of microcracks of 8 YSZ coatings is also lower.The porosity of the 8YSZ coatings depends on spray parameters, namely, increases with the spray distance. The 24CeYSZ coatings did not show such correlation. Moreover greater number of cracks in the 24CeYSZ coatings may be a result of slightly higher deposition temperatures, which have been noted during spraying process. The greater heat flux introduced into coating during its build up was probably associated with the generation of higher thermal stresses during the cooling of samples. It was observed that the values of thermal diffusivity and thermal conductivity of the 8YSZ and 24CeYSZ coatings decrease of their porosity. The only one exception is 24CeYSZ coating sprayed in the run no. 4. However, in spite of higher porosity of 24CeYSZ coatings they do not show lower values of thermal transport properties than 8YSZ ones. A lot of studies have been carried out, which aimed to determine the effect of microstructure, especially porosity, on the thermal properties of zirconia coatings used as thermal barriers. Raghavan et al. [START_REF] Raghavan | The effect of grain size, porosity and yttria content on the thermal conductivity of nanocrystalline zirconia[END_REF] proved that the increase of the micro-porosity in the coating's results in a decrease in thermal conductivity values. On the other hand Carpio et al. [START_REF] Carpio | Correlation of thermal conductivity of suspension plasma sprayed yttria stabilized zirconia coatings with some microstructural effects[END_REF] did not find a clear relationship between the porosity and thermal conductivity value. Apparently this issue still requires more research.

Conclusionq

Microstructure and thermal transport properties of two kinds of zirconia coatings 8(YSZ and 24CeYSZ) deposited by suspension plasma spraying method were investigated in this paper. The powders and suspensions were prepared and characterized. The powders had to been milled because of their great initial size. It allowed obtaining finely grained particles of powders with mean size equal to: dvs=4.5ȝm (8YSZ) and dvs=3.9 ȝm (24CeYSZ). The suspensions were formulated with the use of 40 wt. % of water, 40 wt. % of ethanol and of 20 wt. % of zirconia powder. The coatings were sprayed with similar operational parameters, where the variables were torch scan velocity and spraying distance. SEM microscopes and X-ray diffractometers were used to characterize microstructure of coatings. 8YSZ coatings showed porosity in the range of 8-12%, whereas the 24CeYSZ coatings porosity was in the range of 15-22%. The main phase in both cases was tetragonal ZrO2 (at least 89% for YSZ and at least 95% for YCSZ). The measurements of thermal diffusivity were conducted with the use of laser flash method. The values of thermal diffusivity were similar for 8YSZ and 24CeYSZ coatings (approximately in the range of 0.2-0.5x10 -6 m 2 /s) and allowed calculate thermal conductivity. The values of thermal conductivity were relatively low for both 8YSZ (0.47 to 1.03 W/(m•K)) as well as 24CeYSZ (0.46 to 1.07 W/(m•K)). In the next studies, thermal properties measurements at higher temperatures and also thermomechanical properties tests, especially for YCSZ coatings, are planned.

Literature

Fig. 1

 1 Fig. 1 SEM image (secondary electrons) showing the morphology of commercial (a) 204NS and (b) 205NS powders.

Fig. 2

 2 Fig. 2 SEM photo (secondary electrons) of 8YSZ and 24CeYSZ powders after milling process

Fig. 3 .

 3 Fig. 3. SEM images (secondary electrons) showing (a) top surface of 8YSZ coating, (b) cross-section of 8YSZ coating, (c) top surface of 24CeYSZ coating and (d) cross-section of 24CeYSZ coating

Fig. 4 .

 4 Fig. 4. Thermal diffusivity of (a) 8YSZ and (b) 24CeYSZ coatings[START_REF] Àatka | Thermal diffusivity and conductivity of yttria stabilized zirconia coatings obtained by suspension plasma spraying[END_REF][START_REF] Sokoáowski | Characterization of microstructure and thermal properties of YCSZ coatings obtained by suspension plasma spraying[END_REF]

Fig. 5 .

 5 Fig.5. Thermal conductivity of (a) 8YSZ and (b) 24CeYSZ coatings[START_REF] Àatka | Thermal diffusivity and conductivity of yttria stabilized zirconia coatings obtained by suspension plasma spraying[END_REF][START_REF] Sokoáowski | Characterization of microstructure and thermal properties of YCSZ coatings obtained by suspension plasma spraying[END_REF]

Table 1 Spraying parameters and coatings surface temperature Run Scan velocity [mm/s]

 1

				Max.	Max.
			Spray	surface	surface
			dist.	temp.	temp.
			[mm]	24YSZ	24CeYSZ
				[°C]	[°C]
	1	300	40	570 -690	670 -740
	2	500	40	490 -650	510 -640
	3	400	50	460 -530	450 -600
	4	300	60	410 -570	420-560
	5	500	60	380 -460	390-470

Table 2 Thermal dilatation and specific heat values for 8YSZ and 24CeYSZ coatings [9, 10] Temperature T [K] Specific heat cp of YSZ [J/(kg•K)] Specific heat cp of YCSZ [J/(kg•K)] Thermal dilatation

 2

				ο	[-]
	298	438	427	4.2606.10 -5
	323	453	441	2.5646.10 -4
	373	480	465	6.8840.10 -4
	423	501	485	1.1262.10 -3
	473	518	501	1.5702.10 -3
	523	531	514	2.0206.10 -3

Table 3 Results of microstructure characterization [6, 11]

 3

	Run	Thickness of 8YSZ [ȝm]	Thickness of 24CeYSZ [ȝm]	Porosity of 8YSZ [%]	Porosity of 24CeYSZ [%]	Tetragonal ZrO2 in 8YSZ [%]	Tetragonal ZrO2 in 24VeYSZ [%]
	1	100	53	9	21.5	89.2	95.0
	2	106	90	8	18.7	90.4	96.1
	3	54	78	9	20.3	91.6	95.9
	4	51	101	10	15.1	92.6	95.4
	5	60	88	12	20.6	92.9	95.9

DVS 302

DVS 302