Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-01-14T18:45:29Z No. of bitstreams: 1 ElisangelaBarrosDantas_DISSERT.pdf: 2503846 bytes, checksum: 2247d4ef46af947a6abf96eacbada2b4 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-01-15T17:53:14Z (GMT) No. of bitstreams: 1 ElisangelaBarrosDantas_DISSERT.pdf: 2503846 bytes, checksum: 2247d4ef46af947a6abf96eacbada2b4 (MD5) / Made available in DSpace on 2016-01-15T17:53:14Z (GMT). No. of bitstreams: 1 ElisangelaBarrosDantas_DISSERT.pdf: 2503846 bytes, checksum: 2247d4ef46af947a6abf96eacbada2b4 (MD5) Previous issue date: 2012-06-04 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPq / As ligas de n?quel s?o largamente utilizadas na produ??o de diversos materiais, sobretudo, aqueles que necessitam de resist?ncia mec?nica associada ? resist?ncia ? corros?o, como por exemplo, os a?os inoxid?veis. Outro uso do n?quel ? a produ??o de ligas sinterizadas a partir de p? de n?quel met?lico. Uma alternativa promissora ? produ??o de componentes sinterizados de n?quel com importante redu??o de custos do material de partida ? o emprego de misturas de p?s do tipo NiNiO. Este trabalho teve por objetivo o estudo da redu??o in situ de NiO durante a sinteriza??o de misturas Ni/NiO produzidas por metalurgia do p?. As misturas foram processadas pela t?cnica de metalurgia do p? e pr?-sinterizadas em atmosfera redutora de hidrog?nio. As amostras Ni+15%NiO, Ni+25%NiO e Ni+35%NiO foram estudadas e comparadas com amostras sinterizadas apenas a partir de Ni met?lico. Foram realizados ensaios dilatom?tricos para estudo das condi??es de sinteriza??o das misturas. O material consolidado foi analisado quanto ? sua microestrutura e microdureza. As curvas de dilatometria mostraram que a adi??o de ?xido de n?quel em todas as composi??es ativa a sinteriza??o das misturas estudadas. Nos testes de microdureza foram realizadas indenta??es em pontos distintos da superf?cie das amostras. Todas as composi??es apresentaram valores de microdureza pr?ximos ao do material consolidado a partir de n?quel met?lico. Contudo, as amostras contendo Ni+35%NiO, apresentaram grande dispers?o desses valores. A an?lise microestrutural do material mostrou uma maior concentra??o de vazios e presen?a de ?xidos residuais nas misturas da composi??o Ni+35%NiO. As amostras contendo Ni+15%NiO apresentaram caracter?sticas microestruturais e propriedades mec?nicas semelhantes ao n?quel met?lico consolidado sob as mesmas condi??es das composi??es estudadas neste trabalho e, portanto, apresentaram grande potencial para produ??o de ligas sinterizadas de n?quel / The nickel alloys are widely used in the production of various materials, especially those that require mechanical strength characteristics associated with resistance to corrosion, for example, the stainless steel. Another use is the production of nickel alloy sintered from powder of metallic nickel. A promising alternative for the production of sintered components of nickel with an important reduction in costs of starting material is the use of mixtures of powders of Ni-NiO. This work aimed to study in situ reduction of NiO during sintering mixtures of Ni / NiO produced by powder metallurgy. The nickel mixtures have been processed by the technique of powder metallurgy and were pre-sintered in an oven under plasma reducing atmosphere of hydrogen. Mixtures Ni +15%NiO, Ni +25%NiO and Ni +35%NiO were studied and compared with samples consisting only of metallic Ni. Dilatometric tests were performed to study the sintering conditions of the mixtures. The consolidated material was analyzed for their microstructure and microhardness. Dilatometry graphs showed that the addition of nickel oxide in all compositions the active sintering the mixtures studied. In tests of microhardness indentations were made at different points of the sample surface. All compositions showed microhardness values close to the consolidated material from metallic nickel. However, sample containing Ni+35% NiO, showed a large dispersion of the values of microhardness tests performed at different points of the sample surface. Microstructural analysis of the material showed a higher concentration of voids and the presence of oxides in the waste composition of the mixtures Ni 35% NiO. The samples containing Ni+15%NiO showed microstructural characteristics and mechanical properties similar to metallic nickel consolidated under the same conditions of the compositions studied in this work and therefore had great potential for production of sintered nickel alloys

Submitted by Caroline Xavier (caroline.xavier@pucrs.br) on 2017-06-30T13:23:57Z No. of bitstreams: 1 DIS_DEBORA_DREHER_NABINGER_PARCIAL.pdf: 1830529 bytes, checksum: 7313ef6fa47ca8352c8b7c238d077733 (MD5) / Approved for entry into archive by Caroline Xavier (caroline.xavier@pucrs.br) on 2017-06-30T13:24:07Z (GMT) No. of bitstreams: 1 DIS_DEBORA_DREHER_NABINGER_PARCIAL.pdf: 1830529 bytes, checksum: 7313ef6fa47ca8352c8b7c238d077733 (MD5) / Made available in DSpace on 2017-06-30T13:24:16Z (GMT). No. of bitstreams: 1 DIS_DEBORA_DREHER_NABINGER_PARCIAL.pdf: 1830529 bytes, checksum: 7313ef6fa47ca8352c8b7c238d077733 (MD5) Previous issue date: 2017-02-13 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Metals are some of the more toxic substances in the environment. Nickel is one of them and this heavy metal is naturally present in the earth?s crust. However, excessive levels of nickel lead to environmental contamination and can cause serious and irreversible health problems. The aim of this study was to evaluate the toxicological effects of nickel exposure on cognition and behavior, in larvae and adult zebrafish (Danio rerio). Larvae and adult zebrafish were exposed to four different concentrations (0.025, 2, 5, and 15 mg/L NiCl2) or water (control group) in two treatments: acute and subchronic. Larvae were exposed to NiCl2 for 2 hours (acute treatment: 5-day-old larvae treated for 2 hours) or 11 days (subchronic treatment: 11-day-old larvae treated since fertilization) and adults were exposed for 12 hours (acute treatment) or 96 hours (subchronic treatment). In both treatments, for larvae and adults, exposed animals had a significant concentration-dependent increase in nickel levels compared to control group. For larvae, the survival rate was similar in both treated groups compared to control. However, a significant delay of hatching, a decreased heartbeat rate and morphological alterations (decrease of body length and ocular area at 5 and 8 days post-fertilization, dpf) were observed in subchronically-treated animals. Aversive and exploratory behavior showed no significant differences among doses in acute treatment. In contrast, larvae analyzed at 5 dpf in subchronic treatment displayed differences in exploratory behavior, showing decrease in distance traveled and mean speed, at 0.025 mg/L, whereas there was an increase at same parameters in higher doses (5 and 15 mg/L). Over the 11 days of treatment, the locomotor behavior decreased significantly, at 15 mg/L, at 8 and 11 dpf. Furthermore, subchronic-treated larvae showed impaired aversive long-term memory in the inhibitory avoidance task in high doses analyzed (2, 5 and 15 mg/L). For adults, acute treatment did not alter the locomotor activity. Besides, animals submitted to the concentration of 15.0 mg/L, in subchronic treatment, showed anxiogenic effects. The social behavior was not altered by treatments. However, the exposure to NiCl2 caused a decrease in aggressive behavior (subchronic treatment) and impaired memory (acute and subchronic treatments) in all doses compared to controls. In order to evaluate if nickel exposure produced alterations in the hematological system, we analyzed different blood cells in adult animals. The results showed that treated animals submitted to the concentration of 2.0 mg/L, in acute and subchronic treatment, presented an increase of monocytes. Furthermore, to verify if the behavioral alterations observed in treated animals were related to mechanisms of neuronal death, analyzes of apoptotic death in larvae and specific markers of neuronal death in larvae and adults were performed. The results of apoptotic death demonstrated a significant increase in cell death in acutely treated larvae at a concentration of 15 mg/L. In the subchronic treatment, at 5 dpf, there was an increase in apoptotic death at concentration of 5 mg/L, at 8 dpf, in concentrations of 5 and 15 mg/L and at 11 dpf, in concentrations of 2 and 5 mg/L. In the analysis of specific markers of neuronal death, the results suggest that NiCl2 concentrations tested in larvae and adults did not alter the protein levels of cell death markers. These results suggest that prolonged exposure to nickel in early life stages of zebrafish development leads to morphological and physiological alterations and cognition and locomotor deficits, whereas it may cause anxiogenic effects, impaired memory and decrease aggressive behavior in adult stage. These morphological and behavioral alterations may be associated to neurotoxic effects damage caused by this metal. / Metais s?o algumas das subst?ncias mais t?xicas de grande preocupa??o ambiental. O n?quel ? um destes agentes, sendo que este metal pesado ? naturalmente presente na crosta terrestre. Entretanto, n?veis excessivos de n?quel levam ? contamina??o ambiental e podem causar s?rios e irrevers?veis problemas de sa?de. O presente estudo visa avaliar os efeitos t?xicos da exposi??o aguda e subcr?nica ao n?quel, em peixe-zebra (Danio rerio), no est?gio larval e adulto. Os animais foram expostos a quatro diferentes concentra??es (0,025, 2, 5 e 15 mg/L NiCl2) ou ?gua (grupo controle) e submetidos a dois tratamentos: agudo e subcr?nico. As larvas foram expostas por 2 horas (tratamento agudo: larvas de 5 dias p?s-fertiliza??o - dpf - tratadas por 2 horas) ou 11 dias (tratamento subcr?nico: larvas tratadas do momento da fertiliza??o at? 11 dpf). Os animais adultos foram expostos por 12 horas (tratamento agudo) ou 96 horas (tratamento subcr?nico). Nos dois tratamentos, larvas e adultos expostos apresentaram um aumento dependente da concentra??o nos n?veis de NiCl2, comparados com animais do grupo controle. A taxa de sobreviv?ncia das larvas e embri?es n?o foi alterada pelos tratamentos. Entretanto, atraso na eclos?o dos ovos, diminui??o dos batimentos card?acos e altera??es morfol?gicas (diminui??o do comprimento corporal e ?rea ocular aos 5 e 8 dpf) foram observados em animais tratados subcronicamente. O comportamento aversivo e explorat?rio n?o mostrou diferen?as significativas entre as concentra??es de NiCl2, no tratamento agudo. Diferentemente, larvas subcronicamente tratadas, analisadas aos 5 dpf, apresentaram diferen?as no comportamento explorat?rio, exibindo diminui??o na dist?ncia percorrida e na velocidade m?dia, na concentra??o de 0,025 mg/L, enquanto houve um aumento dos mesmos par?metros em altas concentra??es (5 e 15 mg/L). Ao longo dos 11 dias de tratamento, o comportamento explorat?rio diminuiu significativamente, na concentra??o de 15 mg/L, aos 8 e 11 dpf. Al?m disso, larvas submetidas ao tratamento subcr?nico com altas concentra??es de NiCl2 (2, 5 e 15 mg/L) apresentaram comprometimento no comportamento aversivo. Em animais adultos, o tratamento agudo n?o promoveu altera??es na atividade locomotora. Por outro lado, animais expostos ? concentra??o de 15 mg/L no tratamento subcr?nico demonstraram efeito ansiog?nico. A intera??o social n?o foi alterada pelos tratamentos. Entretanto, a exposi??o ao NiCl2 levou a uma diminui??o do comportamento agressivo (tratamento subcr?nico) e comprometimento de mem?ria (tratamento agudo e subcr?nico), em todas as concentra??es testadas, quando comparados ao grupo controle. No sentido de avaliar se a exposi??o ao n?quel produziu altera??es no sistema hematol?gico, avaliamos diferentes c?lulas leucocit?rias em animais adultos. Os resultados encontrados mostraram um aumento significativo de mon?citos em animais expostos de forma aguda e subcr?nica na concentra??o de 2 mg/L comparado aos controles. Al?m disso, para verificar se as altera??es comportamentais observadas em animais tratados estavam relacionadas com mecanismos de morte celular e neuronal, foram realizadas an?lises de morte apopt?tica em larvas e de marcadores espec?ficos de morte neuronal em larvas e adultos. Os resultados de morte apopt?tica, demonstraram um aumento significativo de morte celular em larvas tratadas de forma aguda na concentra??o de 15 mg/L. No tratamento subcr?nico, aos 5 dpf, houve um aumento de morte apopt?tica na concentra??o de 5 mg/L, em 8 dpf nas concentra??es de 5 e 15 mg/L e em 11 dpf nas concentra??es de 2 e 5 mg/L. Na an?lise de marcadores espec?ficos de morte neuronal, os resultados sugerem que as concentra??es de NiCl2 testadas em larvas e adultos n?o alteraram os n?veis de prote?na dos marcadores de morte celular. Estes resultados sugerem que a exposi??o prolongada ao n?quel, em est?gios iniciais do desenvolvimento do peixe-zebra, leva a altera??es morfol?gicas, fisiol?gicas e d?ficits na cogni??o e locomo??o, enquanto que, em animais adultos, foi observado um efeito ansiog?nico, comprometimento de mem?ria e diminui??o do comportamento agressivo. Estas altera??es morfol?gicas e comportamentais podem estar associadas a efeitos neurot?xicos causados por este metal.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-11-22T21:08:35Z No. of bitstreams: 1 SuzanaAraujoBarbosa_TESE.pdf: 16716381 bytes, checksum: 89faa5fab90c18454c05e07a0fe96e3e (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-11-24T21:58:01Z (GMT) No. of bitstreams: 1 SuzanaAraujoBarbosa_TESE.pdf: 16716381 bytes, checksum: 89faa5fab90c18454c05e07a0fe96e3e (MD5) / Made available in DSpace on 2017-11-24T21:58:01Z (GMT). No. of bitstreams: 1 SuzanaAraujoBarbosa_TESE.pdf: 16716381 bytes, checksum: 89faa5fab90c18454c05e07a0fe96e3e (MD5) Previous issue date: 2017-08-28 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Neste trabalho apresenta-se um estudo, de cunho experimental, de nanopart?culas cristalinas n?o agregadas e monodispersas de tr?s sistemas a base de Ni e/ou Cu, produzidas a partir do m?todo sol-gel e com o aux?lio do pol?mero quitosana. O primeiro sistema ? um nanocomp?sito com di?metro m?dio de 9-27 nm. As amostras cont?m principalmente a fase de Ni e as fases ? e ? do hidreto de n?quel (NiH). A fase ?-NiH apresentou uma contribui??o magn?tica significativa para T<50 K, e os hidretos mostraram-se quimicamente est?veis ao longo de v?rios meses. O segundo sistema tem fase ?nica e referente ao semicondutor i?nico Cu(I)Cl com part?culas esf?ricas de di?metro m?dio de 9 nm. O terceiro sistema consiste na solu??o s?lida de ?tomos de Ni e Cu, e suas amostras cont?m v?rias fases de ligas de NixCu(1-x) para 0,50<x<0,92, com di?metros m?dios na faixa de 11-90 nm. Os resultados de microscopia eletr?nica de transmiss?o sugerem que as fases ricas em Cu est?o dispostas nos contornos das part?culas, enquanto os centros das mesmas parecem ser ricos em Ni. Nas medidas magn?ticas para 300<T<800 K percebeu-se mudan?as na magnetiza??o relacionadas com as transi??es magn?ticas das ligas com 75<x<92. Para temperaturas abaixo da transi??o de Curie (Tc) da liga Ni92Cu8 foi verificado um aumento do sinal magn?tico devido ? fase de Hopkinson. J? para T>Tc foi observada a forma??o da fase de Griffiths, a qual ? devida a clusters de Ni que se encontram dispersos num ambiente rico em Cu. Os par?metros cr?ticos obtidos para esta fase est?o de acordo com a literatura. As an?lises das curvas de histerese revelam uma constante de anisotropia magnetocristalina efetiva (Keff) maior que a constante K1 do Ni puro e esse resultado foi atribu?do a contribui??es de anisotropia de superf?cie. A fase de Griffiths e o valor aumentado de Keff devem ter sua origem nas fases ricas em Cu, na periferia das nanopart?culas. Experimentos de aquecimento das amostras em presen?a de campo magn?tico AC mostraram taxas de absor??o espec?ficas com valores crescentes de acordo com o teor de Ni. A m?xima varia??o de temperatura ocorreu em 200 s, indicando que tais ligas podem ser usadas em hipertermia magn?tica para o tratamento de c?nceres.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-01-20T21:00:39Z No. of bitstreams: 1 AlexsandraRodriguesDoNascimento_TESE.pdf: 3128857 bytes, checksum: db683b893d3db23b5af91852c4aed0e3 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-01-21T20:23:04Z (GMT) No. of bitstreams: 1 AlexsandraRodriguesDoNascimento_TESE.pdf: 3128857 bytes, checksum: db683b893d3db23b5af91852c4aed0e3 (MD5) / Made available in DSpace on 2016-01-21T20:23:04Z (GMT). No. of bitstreams: 1 AlexsandraRodriguesDoNascimento_TESE.pdf: 3128857 bytes, checksum: db683b893d3db23b5af91852c4aed0e3 (MD5) Previous issue date: 2014-09-23 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Diversos materiais est?o atualmente em estudo para o processo de captura de CO2, a exemplo dos ?xidos met?licos e ?xidos met?licos mistos, ze?litas, materiais carbon?ceos, estruturas metal-org?nicas (MOF?s), organos?lica e superf?cies de s?lica modificadas. Neste trabalho, analisou-se a capacidade de adsor??o de CO2 em materiais mesoporosos de diferentes estruturas, como o MCM-48 e SBA-15, sem impregna??o e impregnados com n?quel nas propor??es 5 %, 10 % e 20 % (m/m), denominados como 5Ni-MCM-48, 10NiMCM-48, 20Ni-MCM-48 e 5Ni-SBA-15, 10Ni-SBA-15, 20Ni-SBA-15. Os materiais foram caracterizados atrav?s das an?lises de difra??o de raios X (DRX), an?lise t?rmica (TG e DTG), espectroscopia na regi?o do infravermelho com transformada de Fourier (FT-IR), adsor??o e dessor??o de N2 (BET) e microscopia eletr?nica de varredura (MEV) com EDS. O processo de adsor??o foi realizado variando-se a press?o de 100 - 4000 kPa e mantendo-se a temperatura constante e igual a 298 K. Na press?o de 100 kPa, as maiores concentra??es de adsor??o ocorreram para os materiais 5Ni-MCM-48 (0,795 mmol g-1 ) e SBA-15 (0,914 mmol g -1 ) n?o impregnado, e, na press?o de 4000 kPa, para os materiais MCM-48 (14,89 mmol g-1 ) e SBA-15 (9,97 mmol g-1 ) n?o impregnados. Os resultados mostraram que a capacidade de adsor??o varia positivamente com a ?rea espec?fica, no entanto, apresenta uma depend?ncia direta com o tipo e geometria dos canais da estrutura porosa. Os dados obtidos foram ajustados atrav?s dos modelos de Langmuir e Freundlich e os par?metros termodin?micos avaliados foram energia livre de Gibbs e entropia do sistema de adsor??o / Several materials are currently under study for the CO2 capture process, like the metal oxides and mixed metal oxides, zeolites, carbonaceous materials, metal-organic frameworks (MOF's) organosilica and modified silica surfaces. In this work, evaluated the adsorption capacity of CO2 in mesoporous materials of different structures, such as MCM-48 and SBA- 15 without impregnating and impregnated with nickel in the proportions 5 %, 10 % and 20 % (m/m), known as 5Ni-MCM-48, 10Ni-MCM-48, 20Ni-MCM-48 and 5Ni-SBA-15, 10NiSBA-15, 20Ni-SBA-15. The materials were characterized by means of X-ray diffraction (XRD), thermal analysis (TG and DTG), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption and desorption (BET) and scanning electron microscopy (SEM) with EDS. The adsorption process was performed varying the pressure of 100 - 4000 kPa and keeping the temperature constant and equal to 298 K. At a pressure of 100 kPa, higher concentrations of adsorption occurred for the materials 5Ni-MCM-48 (0.795 mmol g-1 ) and SBA-15 (0.914 mmol g-1 ) is not impregnated, and at a pressure of 4000 kPa for MCM-48 materials (14.89 mmol g-1) and SBA-15 (9.97 mmol g-1) not impregnated. The results showed that the adsorption capacity varies positively with the specific area, however, has a direct dependency on the type and geometry of the porous structure of channels. The data were fitted using the Langmuir and Freundlich models and were evaluated thermodynamic parameters Gibbs free energy and entropy of the adsorption system

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-06-06T20:22:53Z No. of bitstreams: 1 NagilsonMendesDeSousa_DISSERT.pdf: 26377714 bytes, checksum: 39811438b6914861990ecb38bbfc438f (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-06-08T19:15:26Z (GMT) No. of bitstreams: 1 NagilsonMendesDeSousa_DISSERT.pdf: 26377714 bytes, checksum: 39811438b6914861990ecb38bbfc438f (MD5) / Made available in DSpace on 2016-06-08T19:15:26Z (GMT). No. of bitstreams: 1 NagilsonMendesDeSousa_DISSERT.pdf: 26377714 bytes, checksum: 39811438b6914861990ecb38bbfc438f (MD5) Previous issue date: 2015-09-14 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Nanopart?culas (Nps) s?o importantes no estudo de novos fen?menos na f?sica e no desenvolvimento de novas aplica??es tecnol?gicas. Nanopart?culas magn?ticas met?licas tais como N?quel e Cobalto surgem como objetos promissores devido as suas aplicabilidades em v?rias ?reas da ci?ncia e tecnologia. No presente trabalho apresentamos um estudo sobre o m?todo de s?ntese, caracteriza??o estrutural e magn?tica em nanopart?culas de Ni e Co. As amostras foram preparadas pelo m?todo sol-gel modi cado e formadas nos poros do pol?mero quitosana, a redu??o ocorreu em aus?ncia de uxo de Hidrog?nio. A fase cristalina do Ni e Co ? c?bica de face centrada e seus di?- metros variaram de 59-77nm e 19-50nm, respectivamente. As superf?cies das nanopart?culas foram naturalmente passivadas com seus mon?xidos apresentando estabilidade qu?mica por longos intervalos de tempo. A estrutura formada ? do tipo n?cleo/casca, o que favoreceu as intera??es de exchange bias entre o n?cleo ferromagn?tico (FM) e a casca antiferromagn?tica (AFM). As condi??es de s?ntese foram otimizadas para obter principalmente a fase FM. Ambas NPs foram submetidas ? a??o de um campo magn?tico AC e houve aquecimento r?pido at? atingir temperatura de aproximadamente 140?C em intervalos de tempo de at? 5 min. As amostras dispersadas em ?gua, atingiram temperaturas de 40- 59?C de aquecimento em at? 10 minutos, mostrando potencial para aplica??es em hipertermia magn?tica. / Nanoparticles are importante for the study of new phenomena and for the development of new applications. Metallic magnetic nanoparticles like Cobalt and Nickel are important for their applications in nanoscience and nanotechnology. In this work, we report on the synthesis and characterization of Ni and Co nanoparticles. The nanoparticles were prepared by the modi- ed sol-gel method and were formed in the pore-network of the biopolymer quitosan. The reduction occurred in absence of H2 ux. The metallic particles and their monoxides have a face-centered- cubic structure. The metallic particles sizes ranged from 59 to 77 nm and from 19 to 50 nm for Ni and Co, respectively. Their monoxides chemically passivated the metallic cores, and after several weeks we have not observed further increase in oxidation. The synthesis method was tuned to obtain mainly the ferromagnetic phase. The system behaves like a core/shell structure with a ferromagnetic core and an antiferromagnetic shell. Exchange bias e ect was observed at temperatures below the N?el temperature. Both systems were submitted to an alternated magnetic eld and the heat released by the particles increased the temperature to 140?C in an interval of 5 min. Similar studies in samples dispersed in water increased the temperatures to 40-59?C, these results suggest that these materials are candidates for magnetic hyperthermia.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-07-22T14:59:52Z No. of bitstreams: 1 ArthurGabrielFerreiraDeOliveira_DISSERT.pdf: 4264908 bytes, checksum: 58d065ffda595ff186504941ad3c583b (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-07-26T21:48:57Z (GMT) No. of bitstreams: 1 ArthurGabrielFerreiraDeOliveira_DISSERT.pdf: 4264908 bytes, checksum: 58d065ffda595ff186504941ad3c583b (MD5) / Made available in DSpace on 2016-07-26T21:48:57Z (GMT). No. of bitstreams: 1 ArthurGabrielFerreiraDeOliveira_DISSERT.pdf: 4264908 bytes, checksum: 58d065ffda595ff186504941ad3c583b (MD5) Previous issue date: 2015-06-15 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Os materiais cer?micos a base de alumina t?m sido bastante utilizados em componentes estruturais principalmente pelo fato de possuir propriedades como alta dureza, in?rcia qu?mica e boa resist?ncia ao desgaste, entretanto, sua baixa tenacidade ? um fator que compromete seu uso em diversas outras aplica??es, tendo a adi??o de n?quel como uma poss?vel solu??o para este problema, nesse contexto, esse trabalho tem como objetivo estudar a adi??o de n?quel em alumina utilizando a rota da metalurgia do p?. O percentual de n?quel adicionado variou em 2, 4 e 6% p e para cada composi??o foi realizada moagem de alta energia em moinho planet?rio por 2, 4, 9 e 16h. Posteriormente as amostras foram compactadas a 300 MPa e sinterizadas em forno ? v?cuo a 1400?C por 2h. As amostras foram caracterizadas quanto as propriedades f?sicas e mec?nicas observando-se no geral uma melhora na sinterabilidade com o aumento do tempo de moagem e teor de n?quel, com diminui??o e homogeneiza??o da porosidade e aumento da dureza, al?m de densidades acima de 80% da te?rica, observou-se tamb?m uma disparidade no tempo de moagem de 4 horas, onde se alcan?ou os maiores valores de dureza (2% de n?quel), de 1068,7 +/- 32,6 HV e densidade cerca de 99% da te?rica / Ceramic materials alumina basis have been widely used in structural components, mainly because owning properties such as high hardness, chemical inertness and good wear resistance, however, the low toughness is a factor that compromises its use in many other applications, featuring the addition of nickel as a possible solution to this problem, in this context, this work aims to study the addition of nickel alumina using the route of powder metallurgy processing of the material. The percentage of nickel were added 2, 4 and 6 wt%; and each composition to high energy milling in a planetary mill was performed for 2, 4, 9 and 16h. Subsequently, the samples were compacted at 300 MPa and sintered in a vacuum oven at 1400?C for 2h. The samples were characterized as the physical and mechanical properties, observing, in general, an improvement in sinterability of the material with increasing grinding time and nickel content, and mixing with a decrease of porosity and increase of hardness, density values above 80% of theoretical were obtained. The milling time of 4 hours and addition of 2% nickel, particularly if achieved higher hardness (HV 1068.7 +/- 32.6) and density of about 99% theoretical density.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-07-03T12:22:22Z No. of bitstreams: 1 SloanyGuedesMedeiros_DISSERT.pdf: 4950272 bytes, checksum: da30052a82bfbac8284e64d77d53e6f5 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-07-05T15:57:09Z (GMT) No. of bitstreams: 1 SloanyGuedesMedeiros_DISSERT.pdf: 4950272 bytes, checksum: da30052a82bfbac8284e64d77d53e6f5 (MD5) / Made available in DSpace on 2017-07-05T15:57:09Z (GMT). No. of bitstreams: 1 SloanyGuedesMedeiros_DISSERT.pdf: 4950272 bytes, checksum: da30052a82bfbac8284e64d77d53e6f5 (MD5) Previous issue date: 2016-08-25 / Comp?sitos de matriz met?lica de n?quel refor?ados por dispers?o de part?culas de NbC e WC s?o materiais promissores por apresentarem elevados n?veis de resist?ncia mec?nica e de resist?ncia ao desgaste. O objetivo principal deste trabalho foi avaliar a microdureza, microestrutura e o comportamento dilatom?trico dos comp?sitos Ni-NbC e dos Ni-WC. Os comp?sitos foram obtidos atrav?s da t?cnica de metalurgia do p? utilizando a moagem de alta energia para proporcionar a dispers?o da fase dura de NbC e WC na matriz de n?quel. O moinho utilizado foi do tipo attritor, com velocidade de 850 rpm durante 2 horas, via ?mido. Os p?s dos comp?sitos foram preparados nas composi??es de 5%, 10%, 15% em massa de NbC e mesmas composi??es para o refor?ado com WC, estes foram granulados utilizando a t?cnica de granula??o em tambor. P?s granulados e n?o-granulados foram compactados a frio utilizando press?o de 600 MPa em matriz uniaxial. A densidade dos compactados ? verde e dos sinterizados foi calculada pelo m?todo geom?trico. Testes de microdureza e an?lise microestrutural foram realizados nas amostras sinterizadas. Durante os ensaios em dilat?metro foram utilizadas as seguintes condi??es: (i) 25?C a 1200?C; (ii) 25?C a 1300?C, ambos os par?metros com patamar isot?rmico de 1 h e taxa de aquecimento de 10?C/min; (iii) 25?C a 1200?C com patamar isot?rmico de 2 h e a mesma taxa de aquecimento. Os resultados mostraram que as amostras sinterizadas de n?quel sem adi??o de refor?os apresentaram maior densifica??o e maiores valores de retra??o quando preparadas a partir da granula??o em tambor. As imagens por MEV das misturas mo?das de Ni-NbC comprovaram certa homogeneiza??o dos p?s, assim como a incorpora??o mec?nica do refor?o cer?mico na matriz de n?quel, entretanto os resultados para Ni-WC n?o indicaram homogeneidade e pouca incorpora??o mec?nica. As amostras sinterizadas de Ni-NbC para todas as composi??es apresentaram maiores valores de densidade na condi??o de sinteriza??o (iii), enquanto que as de Ni-WC obtiveram os menores valores de densidade relativa. Com rela??o ?s imagens obtidas por MEV, os comp?sitos sinterizados com 5% de carbetos foram as que apresentam melhor aspecto microestrutural quanto ? porosidade. Os comp?sitos Ni-NbC10% e Ni-WC15% apresentaram-se com microestrutura mais porosa e com o aparecimento de ?clusters?. A inser??o de NbC na matriz de n?quel apresentou maiores resultados de microdureza do que com a inser??o de WC, entretanto os comp?sitos Ni-WC apresentaram maior homogeneidade nos resultados com desvios padr?es similares para todas as composi??es. / Nickel matrix composites reinforced by dispersed NbC or WC particles are promising materials due to high mechanical strength and wear resistance. The objective of this study was to evaluate the dilatometric behavior, microstructure and microhardness of Ni-NbC and Ni- WC composites. The composites were obtained by powder metallurgy using high energy milling to provide the dispersion of the hard NbC or WC particles in the nickel matrix. An attritor with speed 850 rpm was used to wet mill and mix the powder mixtures for 2 hours. The powders were prepared with 5%, 10% or 15% (wt.%) of NbC or WC, and subsequently drum granulated. Both granulated and non-granulated powders were uniaxially cold pressed under 600 MPa. The density of green and sintered samples was measured by the geometric method. Microhardness tests and microstructural analyses were performed on the sintered samples. For dilatometric tests, the following conditions were employed: (i) 25?C to 1200?C; (ii) 25?C to 1300?C, both parameters with isothermal step of 1 h and heating rate of 10 ?C/min; (iii) 25 ? C to 1200 ? C with isothermal step of 2 h and the same heating rate. The results showed that the sintered nickel samples without addition of reinforcements depicted major densification and high retraction when drum granulated. The SEM images of milled mixtures of Ni-NbC confirmed a certain degree of homogenization and the mechanical incorporation of the ceramic particles in the matrix On the other hand, the results for Ni-WC did indicate non-homogeneity and little mechanical incorporation. The sintered samples of all compositions of Ni-NbC showed higher values of density under sintering conditions (iii), whereas Ni-WC depicted the lowest relative density values. With respect to the images obtained by SEM, the sintered composite with 5% of carbides presented better microstructural characteristics regarding porosity. The Ni-NbC10% and Ni-WC15% composites presented porous microstructure and clusters. The addition of NbC in nickel matrix showed higher microhardness results than the one with WC, although Ni-WC composites showed higher homogeneity.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-09-19T19:40:40Z No. of bitstreams: 1 GineideConceicaoDosAnjos_TESE.pdf: 9456899 bytes, checksum: a7ef7464e7481322aada640628a0d15b (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-09-19T23:14:46Z (GMT) No. of bitstreams: 1 GineideConceicaoDosAnjos_TESE.pdf: 9456899 bytes, checksum: a7ef7464e7481322aada640628a0d15b (MD5) / Made available in DSpace on 2017-09-19T23:14:46Z (GMT). No. of bitstreams: 1 GineideConceicaoDosAnjos_TESE.pdf: 9456899 bytes, checksum: a7ef7464e7481322aada640628a0d15b (MD5) Previous issue date: 2017-05-26 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Devido ?s exig?ncias ambientais e ao desenvolvimento da ind?stria qu?mica, a demanda de hidrog?nio vem ganhando destaque importante nos setores energ?tico, de insumo e ambiental. As duas principais rotas utilizadas na obten??o do hidrog?nio s?o as rea??es de reforma a vapor e reforma a seco do metano. A maior dificuldade das rea??es de produ??o de H2 ? encontrar catalisadores est?veis por longos per?odos, que sejam resistentes ao ac?mulo de carbono e seletivos a forma??o do g?s hidrog?nio. Al?m de diminuir o custo do catalisador, a utiliza??o de suportes catal?ticos influ?ncia positivamente nas rea??es de reforma, aumentando a resist?ncia qu?mica e t?rmica durante os processos, al?m disso, proporciona boa dispers?o da fase ativa, evitando sua sinteriza??o e, portanto, melhorando a atividade e estabilidade do catalisador. Neste contexto este trabalho tem como objetivo, utilizar a diatomita como suporte catal?tico para dispersar as fases met?licas de Ni e de Co, avaliando os catalisadores obtidos para o processo de reforma a seco do metano, como tamb?m, avaliar os efeitos da adi??o dos promotores de Ce ou La ao catalisador de melhor efici?ncia na rea??o de reforma a seco do metano. Foram preparados catalisadores monomet?licos e bimet?licos de Ni e Co, com diferentes concentra??es de fase ativa por impregna??o via ?mida. O suporte e os catalisadores foram submetidos ?s seguintes caracteriza??es: difra??o de raios X (DRX), adsor??o e dessor??o de N2, an?lise termogravim?trica (ATG), fluoresc?ncia de raios X (FRX), redu??o ? temperatura programada (RTP) e microscopia eletr?nica de varredura (MEV). Os testes catal?ticos foram realizados em um reator diferencial de leito fixo de quartzo a 700?C. Os produtos formados durante a rea??o foram analisados por cromatografia gasosa. Os resultados mostraram que foi poss?vel preparar os catalisadores mono e bimet?licos de Ni e Co. O catalisador com composi??o de 8% de Ni e 2% de Co suportado em diatomita apresentou uma boa intera??o com o suporte, menores perfis de temperatura de redu??o e melhor estabilidade ao longo das 10h de ra??o. O catalisador contendo 10% de Ni apresentou a maior atividade durante este per?odo. O uso dos promotores de Ce ou La n?o alteraram as propriedades catal?ticas e levaram a uma maior forma??o de coque. Em todos os casos estudados a diatomita se mostrou est?vel qu?mica e termicamente durante a prepara??o dos catalisadores e o teste catal?tico, mostrando-se um excelente suporte para a rea??o de reforma a seco do metano. / Due to environmental requirements and to the development of the chemical industry, the demand for hydrogen has been getting an important focus in the energy, input and environmental sectors. Since the two major methods used in obtaining hydrogen are steam and dry methane reforming reactions. The greatest challenge faced by hydrogen production reactions is to find long-term stable catalysts that are also resistant to carbon accumulation and selective to the formation of hydrogen gas. Besides lowering the cost, the utilization of catalytic supports has important role for the reforming reactions, increasing the chemical and thermal resistance during the processes, besides, it provides good dispersion of the active phase, avoiding avoiding the sinterization of the active phase, influencing positively the activity and stability of the catalyst. In this context, this work aims to use diatomite as catalytic support to disperse the metallic phases of Ni and Co, evaluating the catalysts obtained for the methane dry reforming process, as well as evaluating the effects of addition of Ce and La as promoters to the most effective catalysts. Monometallic and bimetallic Ni and Co catalysts were prepared with different active phase concentrations using the wet impregnation methodology. The support and the active phases were evaluated according to the following characterization methods: X-ray diffraction (XRD), adsorption and desorption of N2, thermogravimetric analysis (TGA), X-ray fluorescence (XRF), programmed reduction temperature (TPR) and scanning electron microscopy (SEM). The catalytic tests were performed in a quartz fixed bed differential reactor at 700?C. The products formed during a reaction were analyzed by gas chromatography. The results showed that the mono and bimetallic Ni and Co were formed. The catalyst with 8% of Ni and 2% of Co concentrations supported on diatomite showed good interaction with the support, low reduction temperature profile and and good stability over the 10h test. The catalyst containing 10% Ni had the greatest activity during this reaction. The use Ce or O promoters had no influence to the catalytic properties and led to a higher formation of coke. In all cases studied, the diatomite was shown to be chemical and thermally stable during the preparation of the catalysts and the catalytic test, being considered, therefore, an excellent support for the dry reforming reaction of methane.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-12-12T17:53:46Z No. of bitstreams: 1 MariaJoseSantosLima_TESE.pdf: 8256758 bytes, checksum: 2af332071bb76b3070e1cdcc7d8adcb2 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-12-13T17:58:53Z (GMT) No. of bitstreams: 1 MariaJoseSantosLima_TESE.pdf: 8256758 bytes, checksum: 2af332071bb76b3070e1cdcc7d8adcb2 (MD5) / Made available in DSpace on 2017-12-13T17:58:53Z (GMT). No. of bitstreams: 1 MariaJoseSantosLima_TESE.pdf: 8256758 bytes, checksum: 2af332071bb76b3070e1cdcc7d8adcb2 (MD5) Previous issue date: 2017-07-18 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Neste trabalho foram sintetizados p?s-comp?sitos WC-Ni atrav?s de Carborredu??o da mistura de paratungstato de am?nio hidratado (APT) com o nitrato de n?quel nas propor??es (5% p.Ni, 10% p.Ni e 15% p.Ni) a baixa temperatura (800?C a 950?C) e em curto tempo de rea??o (90 min a 150 min) em um ?nico processo de s?ntese. Os p?s foram caracterizados por difra??o de raios X, microscopia eletr?nica de varredura, espectroscopia de energia dispersiva (EDS), e fluoresc?ncia de raios X (FRX), an?lise de tamanho de part?culas e adsor??o de nitrog?nio pela t?cnica do BET, al?m de medidas de magnetiza??o, coercividade e reman?ncia. O estudo do tamanho de cristalito foi obtido a partir dos dados dos difratogramas de raios X dos p?s-comp?sitos, atrav?s da equa??o de Scherrer. Foi realizado um planejamento experimental fatorial 23 com tr?s pontos centrais com a finalidade avaliar a influ?ncia das condi??es de s?ntese nas vari?veis-resposta. Os par?metros de s?ntese avaliados neste trabalho foram: tempo de rea??o (90min, 120min e 150min), temperatura de s?ntese (800?C, 850?C e 900?C) e concentra??o de n?quel em peso (5%p.Ni, 10%p.Ni e 15%p.Ni). Foi poss?vel produzir p?s-comp?sitos de WC-Ni nonom?tricos nas propor??es desejadas com a pureza desejada, com tamanho m?dio de cristalito variando de 24,2 nm at? 38 nm, com ?rea superficial variando de 24,6 m?/g at? 46,7 m?/g. Os p?s apresentaram morfologia com part?culas de tamanhos e formas variadas, bastante aglomeradas, bem como uma boa dispers?o e homogeneiza??o das fases. As caracter?sticas espec?ficas desses materiais nanom?tricos proporcionam a sua utiliza??o tanto para a produ??o de metal duro como em rea??es catal?ticas. Os p?s-comp?sitos obtidos neste trabalho foram aplicados na produ??o de metal duro-WC-Ni atrav?s de sinteriza??o em fase s?lida e l?quida, utilizando as t?cnicas de sinteriza??o convencional e sinteriza??o por ?spark plasma sintering? para fins de compara??o. Nas amostras sinterizadas, foram realizadas medidas de dureza Vickers e densidade por picnometria. Tamb?m foram realizadas an?lises de DRX, MEV e EDS com mapeamento. Os melhores resultados para as os sinterizados de WC-Ni, foram obtidos para as amostras sinterizadas via SPS a 1350?C, apresentando dureza Vickers (2322 HV) e densidade (97,67 %) superiores as das amostras sinterizadas por sinteriza??o convencional a maiores temperaturas. / In this work WC-Ni composite powders were synthesized by carborreduction of the hydrated ammonium paratungstate (APT) mixture with the nickel nitrate in proportions (5% p.Ni, 10% p.Ni and 15% p.Ni) a low temperature (800 ? C to 950 ? C) and small reaction time (90min to 150min) in a single synthesis process. The powders were characterized mainly by X-ray diffraction, scanning electron microscopy (SEM), dispersive energy spectroscopy (EDS), X-ray fluorescence (FRX), particle size analysis and (BET) and measures of magnetization, coercivity and remanence. The study of crystallite size was obtained from the X-ray diffractograms of post-composites, using the Scherrer equation. A factorial experimental design 23 with three central points was carried out to evaluate the influence of the synthesis conditions on the response variables (crystallite size). The synthesis parameters evaluated in this work were: reaction time (90min, 120min and 150min), synthesis temperature (800 ? C, 850 ? C and 900 ? C) and concentration of nickel by weight (5% p.Ni, 10 % P.Ni and 15% p.Ni). It was possible to produce nanometric WC-Ni composite powders in the desired proportions with the desired purity, with a mean crystallite size varying from 24.2 nm to 38 nm, with a surface area ranging from 24.6m?/g to 46.7 m?/g. The powders presented morphology with particles of varied sizes and shapes, quite agglomerated and also presented a good dispersion and homogenization of the phases. The specific characteristics of these nanometric materials provide their use for both the hard metal in catalytic reactions.Therefore, the composite powders obtained in this work were applied in the production of WC-Ni hard metal by solid and liquid phase sintering using conventional sintering and Spark Plasma Sintering techniques for comparison purposes. In the sintered samples the measurements of Vickers hardness and density by pycnometry were performed. We also performed XRD, SEM and EDS analyzes with mapping. The best results for the sintered WC-Ni were obtained for the sintered samples via SPS at 1350?C, showing Vickers hardness (2322 HV) and density (97.67%) higher than the samples sintered by conventional sintering at higher temperatures. / 2018-08-23

Made available in DSpace on 2014-12-17T14:07:20Z (GMT). No. of bitstreams: 1 MariaRPF_TESE.pdf: 4797522 bytes, checksum: 8d9626466b01e2425f6ea6036398adcf (MD5) Previous issue date: 2014-01-24 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Carbide reinforced metallic alloys potentially improve some important mechanical properties required for the overall use of important engineering materials such as steel and nickel. Nevertheless, improved performance is achieved not only by composition enhancement but also by adequate processing techniques, such as novel sintering methods in the case of powder metallurgy. The method minimizes energy losses in addition to providing uniform heating during sintering. Thus, the general objective of this study was to evaluate the density, hardness, flexural strength, dilatometric behavior and to analyze the microstructure of metal matrix composites based nickel with addition of carbides of tantalum and / or niobium when sintered in a conventional furnace and Plasma assisted debinding and sintering (PADS). Initially, were defineds best parameters of granulation, screening and mixing procedure. After, mixtures of carbonyl Ni and 5%, 10% and 15 wt.% NbC and TaC were prepared in a Y-type mixer under wet conditions during 60 minutes. The mixtures were then dried and granulated using 1.5 wt. % paraffin diluted in hexane. Granulates were cold pressed under 600 MPa. Paraffin was then removed from the pressed pellets during a pre-sintering process carried out in a tubular furnace at 500 ?C during 30 min. The heating rate was 3 ?C/min. The pellets were then sintered using either a plasma assisted reactor or a conventional resistive tubular furnace. For both methods, the heating rate was set to 8 ?C/min up to 1150 ?C. The holding time was 60 minutes. The microstructure of the sintered samples was evaluated by SEM. Brinell hardness tests were also carried out. The results revealed that higher density and higher hardness values were observed in the plasma-assisted sintered samples. Hardness increased with the concentration of carbides in the Ni-matrix. The flexural strength also increased by adding the carbides. The decline was larger for the sample with addition of 5% 5% TaC and NbC. In general, compositions containing added carbide 10% showed less porous and more uniform distribution of carbides in the nickel matrix microstructural appearance. Thus, both added carbide and plasma sintering improved density, hardness, flexural strength and microstructural appearance of the composites / Ligas met?licas refor?adas por carbetos melhoram potencialmente algumas propriedades mec?nicas necess?rias para a utiliza??o de importantes materiais de engenharia, tais como o a?o e o n?quel. No entanto, o desempenho ? conseguido n?o apenas pela melhoria de composi??o, mas tamb?m por t?cnicas de processamento adequadas, tais como, novos m?todos de sinteriza??o, no caso da metalurgia do p?. Desta forma, o objetivo do presente trabalho foi avaliar a dureza, resist?ncia ? flex?o, comportamento dilatom?trico e analisar a microestrutura de comp?sitos de matriz met?lica base n?quel com adi??o de carbetos de t?ntalo e/ou ni?bio quando sinterizados em forno tubular convencional e Plasma assisted debinding sintering (PADS). Os carbetos (5%, 10% e 15% em massa) foram misturados ao p? de n?quel carbonila via ?mido com aux?lio do misturador Y adaptado durante 1h. Ap?s secagem, as misturas foram submetidas ao processo denominado de granula??o em tambor. Utilizou-se 1,5% de parafina (% massa) dilu?da em hexano. Os p?s granulados foram compactados a frio utilizando press?o de 600 MPa. Antes da sinteriza??o a uma taxa de 8 ?C/min com patamar 1h na temperatura de 1150?C tanto em forno tubular quanto em reator PADS, as amostras foram pr?-sinterizadas em forno tubular para extra??o da parafina a uma taxa de 3 ?C/min com patamar 30 min em 500 ?C. A dureza avaliada foi a Brinell e a an?lise microestrutural por MEV. Os resultados mostraram que as amostras sinterizadas assistidas por plasma apresentaram dureza superior ?quelas sinterizadas em forno convencional. As imagens por MEV comprovaram esses maiores valores de durezas, uma vez que a matriz apresentou-se mais densificada. Com rela??o ? adi??o dos carbetos, a dureza aumentou com o aumento da concentra??o dos mesmos. A resist?ncia ? flex?o tamb?m aumentou ao adicionar os carbetos. A retra??o foi maior para a amostra com adi??o de 5% de TaC e 5% NbC. De maneira geral, as composi??es com adi??o de 10% de carbetos apresentaram um aspecto microestrutural menos poroso e com uma distribui??o mais uniforme dos mesmos na matriz de n?quel. Assim, tanto a adi??o de carbetos quanto a sinteriza??o com aux?lio do plasma melhoraram a dureza e o aspecto microestrutural dos comp?sitos