L'objectif de ces travaux était l'élaboration, par activation mécanique et frittage SPS, de céramiques à base de titanate de baryum (non dopé, dopé au zirconium et/ou au lanthane) présentant des permittivités élevées et de faibles pertes diélectriques. Les poudres de BaTiO3 (BT) ont été obtenues par activation mécanique suivie d'un traitement de calcination. Différents précurseurs de baryum (BaCO3 et Ba(NO3)2) et de titane (TiO2 anatase et amorphe) ont été utilisés. Il convient de noter que le nitrate de baryum a été utilisé pour la première fois pour la synthèse de BT par activation mécanique. L'utilisation du nitrate de baryum et de titane amorphe en mécanosynthèse, a permis d'obtenir des nanopoudres de BT à faible température (600-700oC), inférieure à celle requise avec BaCO3 comme précurseur de départ (= 900oC). Dans tous les cas, les poudres présentent des grains de taille nanométrique et cristallisent dans la structure cubique. L'effet de la stoechiométrie de la poudre sur la structure et la microstructure de BT a été également analysé. Le mécanisme de formation de BT à partir de (BaCO3 et Ba(NO3)2) a aussi été étudié. Les céramiques ont été mises en forme et frittées par Spark Plasma Sintering (SPS). Les paramètres de frittage SPS ont été optimisés afin d'obtenir des céramiques présentant une densité élevée. Les céramiques subissent ensuite un traitement thermique de recuit. Toutes les céramiques présentent des permittivités colossales (>105) stables dans une large gamme de fréquences (40 à 105 Hz) associées à de faibles pertes diélectriques (<0,08). Nous avons montré une dépendance de la permittivité avec la température pour toutes ces céramiques, à l'exception de celles issues du précurseur BaCO3. De plus, la température de Curie (TC) des céramiques frittées par SPS est décalée vers des valeurs plus faibles (~110oC), comparée à celle de BT obtenu par frittage conventionnel (~120oC). Des céramiques de BaTiO3 dopées au zirconium (Zr) (5 et 10 at.%) ont été élaborées par frittage conventionnel et SPS. Les céramiques frittées de façon conventionnelle cristallisent dans la structure cubique et la densification est de 93%. Les mesures diélectriques en fonction de la température ont montré que la Tc diminue et que le pic de permittivité maximale s'élargit avec l'augmentation du taux de Zr. Après frittage SPS, seules les céramiques de BT dopée à 5% en Zr sont correctement densifiées (98%). Celles-ci présentent des permittivités colossales (105) et de faibles pertes (0,08), peu différentes des céramiques non dopées. Le dopage à 5% de zirconium conduit à une diminution plus importante de la valeur de la température de Curie (Tc= 100°C). Des céramiques totalement densifiées (99%), dopées à 5% au lanthane (La) ont été également élaborées par SPS. Ces céramiques présentent une structure cubique et des permittivités élevées (~106) mais associées à des pertes élevées (>0.1). La permittivité relative est stable dans une large gamme de température allant de -53 à 170oC. Finalement, des céramiques codopées en La et Zr ont été préparées par frittage conventionnel. Ces céramiques ont une densification de 96% et une structure pseudo-cubique, avec une taille de grains de 1 µm. Les mesures diélectriques en fonction de la température montrent la diminution de la Tc avec l'augmentation du taux des dopants. Les valeurs de permittivités les plus élevées, associées à de faibles pertes (e ~5,7 103 et tan d ~0,03) ont été obtenues pour le composé : Ba0,98La0,02Ti0,90Zr0,10O3. / The main objective of this work was the elaboration of barium titanate based ceramics (un-doped and doped by zirconium and/or lanthanum) by mechanical activation and spark plasma sintering (SPS). Our goal was to prepare ceramics presenting high permittivity and low dielectric loss. BaTiO3 powders were obtained by mechanical alloying followed by a calcination treatment. Different barium and titanium precursors (BaCO3, Ba(NO3)2, TiO2 anatase and amorphous) have been used. It worth noting that barium nitrate was used for the first time for the BT synthesis by mechanical activation. The use of barium nitrate and amorphous titanium as precursors in the mechanical alloying process allowed obtaining BT nano-powders at low temperature (600-700oC). All the powders present nanometric grains size and crystallize in cubic structure. The effect of powder stoichiometry on the structure and microstructure of BT was analyzed. The BT formation mechanism starting from BaCO3 and Ba(NO3)2 as precursors was studied too. BT ceramics were sintered using Spark Plasma Sintering. SPS sintering parameters were optimized in order to obtain high density ceramics. Post-annealing heat treatment was performed on ceramics. All obtained ceramics present colossal permittivity (105) stable over a wide frequency range (40 to 105 Hz) associated with low dielectric loss (< 0.08). We have shown permittivity dependence with temperature for all ceramics, except those from BaCO3 precursor. Furthermore, Curie temperature (TC) of all SPS sintered ceramics shifted towards lower values (~110oC), compared to those obtained by conventional sintering (~120oC). Zirconium (Zr) doped BT ceramics (5 and 10 at.%) were elaborated by conventional and SPS sintering. Conventionally sintered ceramics crystallize in the cubic structure and the densification is 93%. Dielectric measurement showing the change of the relative permittivity as a function of temperature showed that TC decreases and the maximal permittivity peak broadens as the Zr rate increases. After SPS sintering, only the 5% of Zr doped ceramics were properly densified (98%). These ceramics present colossal permittivity (105) associated with low dielectric loss (0.08), slightly different of undoped ceramics. Doping by 5% of Zr leads to a significant decrease in the Curie temperature value (TC=100oC). Highly densified (99%) ceramics doped by 5% of lanthanum (La) was obtained by SPS. Those ceramics present a cubic structure and a colossal permittivity (~106), associated with high dielectric loss (>0.1). Relative permittivity is stable over a wide range of temperature ranging from -53 to 170oC. Finally, ceramics codped by La and Zr were prepared by conventional sintering. Those ceramics present a 96% densification and pseudo-cubic structure, with grains size about 1 µm. Dielectric measurements showed the decrease of TC with increasing of dopants rate. The highest values of permittivity (e ~5.7 103 and tan d ~0.03) was obtained for: Ba0.98La0.02Ti0.90Zr0.10O3.

La ricerca si propone di indagare sulle forme di cambiamento che stanno interessando l’agricoltura contadina contemporanea in Italia. In particolare, il proposito è quello di individuare le forme attraverso cui i contadini stanno cambiando il proprio rapporto con il mercato e con la società, proponendo stili di vita, di produzione e di consumo sostenibili. Le Teorie sulle Pratiche e gli studi sulla cultura materiale saranno utilizzati per comprendere il rapporto tra pratiche e reti sociali. / The research aims to investigate the forms of change that are affecting contemporary farming in Italy. In particular, the purpose is to identify the forms through which farmers are changing their relationship with the market and with society. Practice Theories and studies on material culture will be used to understand the relationships between practices and social networks.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第23396号 / エネ博第423号 / 新制||エネ||80(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 平藤 哲司, 教授 土井 俊哉, 准教授 三宅 正男 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

The main objective of present diploma thesis is to prepare three different classes of steels, differing by their content of chromium: 9Cr, 14Cr, 17Cr steels and their oxide dispersion strengthened variants. Steels were prepared from atomic and pre-alloyed powders by the mechanical alloying and compacted by the spark plasma sintering method. Used strengthening elements were yttrium, which is most commonly used, and aluminium. Preparation of oxide dispersion was done in two ways: direct adding of yttria and alumina and inner oxidation of aluminium and yttrium. In the experimental part has been found, that it is possible to make oxide dispersion by both ways, but aluminium strengthened steel has to be prepared by inner oxidation to ensure fine oxide dispersion.

This thesis deals with topic of high entropy alloys. The teoretical part explains what are high entropy alloys, how are they different from conventional alloys, how is their chemical composition proposed and what potencial these alloys have. The experimental part describes procedures of preparation of three high entropy alloys witch consists of Co, Cr, Fe, Ni and Ti, where the concentration of all elements except Ti remains the same. These alloys were prepared via mechanical alloying and sintered by SPS process. Crucial part of this thesis is characterization of these three alloys with EDS and XRD supported by hardness measuring and tensile tests.

This diploma thesis is focused on preparation of Mg-Al based bulk materials via powder metallurgy. The bulk materials were prepared by cold pressing, cold pressing followed by sintering, cold pressing followed by sintering and artificial aging, SPS (spark plasma sintering), SPS followed by solution annealing, SPS followed by solution annealing and artificial aging. The prepared materials were characterized in terms of microstructure and physical and mechanical properties. The properties of the prepared materials differed depending on the method of preparation and Al content. All materials after heat treatment were consisted of solid solution (Mg), intermetallic phase Mg17Al12 and MgO. The composition of the materials depended on Al content. Sintering by the SPS method resulted in material with better mechanical properties compared to materials whose first step of preparation was cold pressing.

Lo scopo di questa ricerca è quello di analizzare l'impatto della migrazione sulle relazioni familiari degli immigrati turchi in Italia e il modo in cui i legami con il paese d’origine possono influenzare le loro esperienze migratorie e i loro piani futuri. Questi aspetti sono stati analizzati in uno studio qualitativo ed esplorativo, attraverso 38 interviste a migranti turchi attualmente residenti nel Nord Italia e identificati con la tecnica del campionamento snowball. L'intervista semi-strutturata è stato il principale strumento di ricerca e, di conseguenza, ha rappresentato la principale fonte di dati primari di questa ricerca. Le relazioni familiari e le esperienze migratorie hanno costituito il focus delle interviste; le domande sono state delineate intorno ad alcuni argomenti ritenuti cruciali come la storia della famiglia, la loro scelta migratoria, il confronto tra "qui" e "là", l'esperienza migratoria e i cambiamenti che questa produce a livello di relazioni familiari, le difficoltà e le reti di comunità. Analizzando una comunità poca studiata in Italia come quella turca, in una prospettiva di relazioni familiari, questa ricerca vuole fornire un contributo originale sia allo studio della migrazione turca sia agli studi familiari in generale. / This research seeks to analyse the impact of migration on family relations of Turkish immigrants in Italy, and the way ties with the country of origin can affect their migration experiences and future plans. These aspects have been analysed in a qualitative study, exploratory in nature, through 38 interviews with Turkish migrants identified by snowballing who are currently residing in Northern Italy. The semi–structured interview is the main research instrument and consequently, it provides the main sources of primary data for this research. The main focus of the interviews was on family relations and the migration experiences; interview questions were outlined around a few major topics such as the history of the family, their migration choice, the comparison between ‘here’ and ‘there’, the migration experience, the changes that it produces at the level of family relations, the difficulties and community networks. By considering such an understudied community in Italy as the Turkish –within a perspective of family relations– this research seeks to provide an original contribution both to the study of the Turkish migration and to family studies in general.

Questo lavoro si propone di analizzare il sistema di scambio su scala locale Sardex.net, che è stato fondato in Sardegna nel 2010, è rivolto alle piccole e medie imprese e utilizza una moneta complementare che si affianca alla valuta ufficiale. Si adotterà una prospettiva prevalentemente sociologica, ma che si avvarrà anche dei contributi che altre discipline, quali l’antropologia, la filosofia e l’economia, possono fornire ai fini di una più ampia comprensione del fenomeno oggetto di studio. Saranno individuati, nei resoconti delle esperienze e delle aspettative dei soggetti coinvolti, aspetti legati allo scambio che mostrino come la pratica monetaria possa essere attuata in modalità differenti da quelle a cui ci ha abituato il sistema del mercato globale, e quali effetti queste differenze possano implicare su diversi piani, da quello economico a quello della coesione sociale e della sostenibilità ambientale. Inoltre si farà luce sui diversi generi di capitale che, oltre a quello finanziario, possono entrare in gioco in un sistema che opera all’interno di un territorio specifico come la Sardegna e si fonda su principi orientati al sostegno dell’economia locale. Saranno infine approfondite le relazioni che intercorrono tra questi diversi generi di capitale e le transazioni che tra loro possono occorrere. / This work is focused on the analysis of a local circuit of exchange addressed to PMI named Sardex.net, established in Sardinia in 2010 and based on a complementary currency. The adopted perspective is mainly sociological, with some contributions belonging to the anthropological, philosophical and economical theories in order to enhance a wider comprehension of the phenomenon. The insight on the experiences and expectations of the people involved aims to bring out issues linked to the exchange that show how the monetary practice can be interpreted in a different way in comparison to the global market’s widespread vision and how this differences affect economy, social cohesion and environmental sustainability. Moreover, different species of capital with social relevance that can play a role in a system of exchange operating in a specific territory such as Sardinia and based on the principle of the support of local economy will be highlighted, together with the relationships and possible transactions occurring between those different species of capital.

This diploma thesis deals with the study of microstructure development during the final stage of sintering of two zirconia based ceramic materials (tetragonal ZrO2 doped with 3 mol% of Y2O3 and cubic ZrO2 doped with 8 mol% of Y2O3). Conventional, microwave and SPS sintering methods were used. Achieved relative densities and mean grain sizes were evaluated for sintered materials. It was found that the non-conventional sintering methods are capable of rapid processing of ceramics with improved microstructure compared to conventional sintering.

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