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In this work, we present an investigation of the magnetic and magnetocaloric properties of Mn0.98Cr(0.02-x)FexAs compounds with x = 0.002, 0.005 and 0.010. Our findings show that as Fe content increases the unit cell volume decreases, which indicates that Fe doping emulates the pressure effect on the crystalline structure. The transition temperature TC decreases as x increases and it can be set at approximate value of room temperature by changing the doping level. In addition, the magnetic entropy change ΔSM was determined using a discontinuous measurement protocol, and realistic values from the magnetocaloric effect presented by MnAs-type compounds under pressure (emulated pressure) could be obtained. The values of ΔSMMAX are very large, around −11 Jkg−1K−1 with ΔH = 15 kOe, which is higher than that observed for most compounds with TC around room temperature. However, ΔSM is confined to a narrow temperature range of 11 K. To overcome this drawback, the composition of a theoretical composite formed by our samples was calculated in order to obtain a table-shaped ΔSM curve. The simulated composite showed a high value of full width at half maximum δTFWHM of 33 K, which is much higher than that of single sample. Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro - FAPERJ E-26/110.393/2014, E-16/210.263/2014 Coordenação de aperfeiçoamento de pessoal de nivel superior - CAPES 485200/2013-9 Fundación de Apoyo a la Investigación del Estado de São Paulo - FAPESP 2012/03480-0 Ministerio de Economía y Competitividad MAT2013-45165-P

Orientação: Prof. Dr. Ana Paula Rosifini Alves Dissertação (Mestrado) - Universidade de Taubaté, Programa de Pós-graduação em Engenharia Mecânica, Mestrado em Engenharia Mecânica, Taubaté, 2004. Made available in DSpace on 2019-08-29T18:44:12Z (GMT). No. of bitstreams: 1 FernandoAntonioEliasClaro.pdf: 10716097 bytes, checksum: 2c92a210c7231e29fa8efd8a68d75337 (MD5) Previous issue date: 2004 Resumo: O objetivo do presente trabalho experimental foi determinar a resistência ao desgaste e a flexibilidade de limas endodônticas tipo K de aço inoxidável e de níquel-titânio disponíveis comercialmente, submeter estas últimas a implantação iônica por imersão em plasma e avaliar os efeitos deste tratamento sobre as mesmas propriedades. A resistência ao desgaste das limas foi determinada "in vitro" utilizando um dispositivo motorizado para a aplicação de movimentos horizontais de limagem sobre placas previamente preparadas de resina fenólica de fixação a quente. A flexibilidade dos instrumentos foi avaliada através do ensaio de momento de dobramento a 30° e 45° conforme especificação número 28 da American Dental Association (A.D.A.). A microdureza no núcleo das limas e na seção transversal das placas de desgaste foi ensaiada pelo método Vickers. Ainda como parte do programa de testes das limas, dimensões funcionais foram medidas com projetor de perfil, o estado de superfície analisado por microscopia eletrônica de varredura e a composição química da superfície dos instrumentos tratados determinada por espectroscopia foto-eletrônica de raios-X. Com os resultados obtidos foi possível concluir que a implantação iônica por imersão em plasma aumentou significativamente a resistência ao desgaste das limas de nitinol sem alterar sua flexibilidade. Abstract: The purpose of the present work was to measure the wear resistance and flexibility of commercially available type K stainless steel and nickel-titanium endodontic files, submit the nitinol files to plasma immersion ion implantation and assess the treatment effects on the same properties. The wear resistance was determined "in vitro" by using an electric powered device designed for the application of filing horizontal movements on previously prepared notched plates made of phenolic thermosetting resin. The instruments flexibility was measured throughout the bending moment test at 30° and 45° according to the American Dental Association (A.D.A.) specification n° 28. The micro hardness on the files core and wear plates cross section was measured by the Vickers method. As part of the files testing program, functional dimensions were measured with a profile projector, the surface state was observed throughout scanning electronic microscopy and the surface chemical composition of treated instruments was determined throughout the X-Rays photoelectron spectroscopy. The results found have led to the conclusion that the surface treatment significantly increased the nitinol files wear resistance without changing its flexibility.