ABSTRACT
In the development of new materials for orthopedic implants, special attention has been given to Ti alloys that show biocompatible alloy elements and that are capable of reducing the elastic modulus. Accordingly, Ti-Nb-Si alloys show great potential for application. Thus, this is a study on the microstructures and properties of Ti-35Nb-xSi alloys (x=0, 0.15, 0.35 and 0.55) (wt%) which were thermally treated and cooled under the following conditions: furnace cooling (FC), air cooling (AC), and water quenching (WQ). The results showed that Si addition is effective to reduce the density of omega precipitates making beta more stable, and to produce grain refinement. Silicides, referred as (Ti,Nb)3Si, were formed for alloys containing 0.55% Si, and its formation presumably occurred during the heating at 1000°C. In all cooling conditions, the hardness values increased with the increasing of Si content, as a result from the strong Si solid solution strengthening effect, while the elastic modulus underwent a continuous reduction due to the reduction of omega precipitates in beta matrix. Lower elastic moduli were observed in water-quenched alloys, which concentration of 0.15% Si was more effective in their reduction, with value around 65 GPa. Regarding Ti-35Nb-xSi alloys (x=0, 0.15 and 0.35), the "double yield point" phenomenon, which is typical of alloys with shape memory effect, was observed. The increase in Si concentration also produced an increase from 382 MPa to 540 MPa in the alloys' mechanical strength. Ti-35Nb-0.55Si alloy, however, showed brittle mechanical behavior which was related to the presence of silicides at the grain boundary.
Subject(s)
Alloys/chemistry , Mechanical Phenomena , Niobium/chemistry , Orthopedics , Prostheses and Implants , Silicon/chemistry , Titanium/chemistry , Materials Testing , Structure-Activity Relationship , Water/chemistryABSTRACT
Amostras de solo foram coletadas no Campus Universitário da UNESP de Araraquara, SP e utilizadas no isolamento e caracterização de fungos com capacidade de sintetizar enzimas pectinolíticas. Estas enzimas vêm despertando crescente interesse na indústria de alimentos. Duzentas e quarenta e seis linhagens foram isoladas em meio PDA e selecionadas, baseadas no formato e tamanho da colônia, morfologia (micélio septado, conídios não septados e negros, cabeça de esporulação em forma de cotonete), após crescimento por 48h a 30ºC. A geração de halo de coloração ao redor das colônias foi acompanhada em meio sólido contendo pectina cítrica 2 por cento (p/V) e avaliada na presença do corante vermelho de rutênio 0,5 por cento. A capacidade de síntese de enzimas pectinolíticas foi avaliada em cultura sólida (índice pectinolítico) e através de fermentação submersa. Vinte e cinco fungos, caracterizados em cultura sólida, forma capazes de sintetizar enzimas pectinolíticas extracelulares em fermentação submersa. A maior atividade pectinolítica (15,0 U/mL) ocorreu no crescimento do isolado CFCF-0492, enquanto o isolado CFCF-CC1 foi o que apresentou o maior acúmulo de biomassa final em cultura submersa. A atividade pectinolítica (medida através do índice paectinolítico) foi melhor preservada quando esporos dos fungos foram mantidos em meio ágar-Czapeck.
