Resumo em Inglês:

The kinetic model for change of phases developed by M. Avrami at the end of the thirties has been used to describe the temporal behavior of phase changes. Until today this model is studied and adapted to include broader hypotheses. However, the mathematical format presented by M. Avrami is difficult to be understood by beginners. The purpose of this work is to clarify the mathematical treatment of Avrami's work, going straightforward to the arguments that led to his main results.

Resumo em Inglês:

Cylindrical dental implants made of commercially pure titanium were analysed in four different surface finishes: as-machined, Al2O3 blasted with Al2O3 particles, plasma-sprayed with titanium beads and electrolytically coated with hydroxyapatite. Scanning electron microscopy (SEM) with Energy Dispersive X-ray Analysis (EDX) revealed the topography of the surfaces and provided qualitative results of the chemical composition of the different implants. X-ray Photoelectron Spectroscopy (XPS) was used to perform chemical analysis on the surface of the implants while Laser Scanning Confocal Microscopy (LSM) produced topographic maps of the analysed surfaces. Optical Profilometry was used to quantitatively characterise the level of roughness of the surfaces. The implant that was plasma-sprayed and the hydroxyapatite coated implant showed the roughest surface, followed by the implant blasted with alumina and the as-machined implant. Some remnant contamination from the processes of blasting, coating and cleaning was detected by XPS.

Resumo em Inglês:

Lead lanthanum zirconate titanate [PLZT (9/65/35)] thin films were prepared by dip-coating on Si (100) or Si/Ti/Pt (100) substrates using a polymeric precursor solution and annealed at 650 °C for 3 h. Perovskite phase formation of the PLZT thin films and microstructure were analysed using XRD and SEM. Effects of Si (100), Si/Ti/Pt (100) substrates and atmosphere on crystallization of PLZT thin films were studied. Films deposited on platinum coated silicon (100) show a heterogeneous surface with presence of bubbles. Otherwise, the PLZT (9/65/35) thin films deposited on silicon (100) substrate shows a more uniform surface after annealing in oxygen atmosphere.

Resumo em Inglês:

Evaluations of the fracture toughness in metal matrix composites (Duralcan reinforced with 15% of Al(2)0(3) and SiC) are presented in this work. The application of Elastic Plastic Fracture Mechanics is discussed and the obtained values are compared with the ones obtained by means of Linear Elastic Fracture Mechanics. Results show that J IC derived K JC values are higher than the corresponding values obtained by direct application of the linear elastic methodology. The effect of a heat treatment on the material fracture toughness was also evaluated in which the analyzed approaches showed, not only different toughness values, but also opposite tendencies. A second comparison of the J IC and K JC values obtained in this work with toughness values reported in the literature is presented and discussed.

Resumo em Inglês:

Dense and porous polyHEMA hydrogels were synthesized by bulk and solution radical-initiated polymerization techniques. The morphologic analysis (SEM) of obtained hydrogels showed an amorphous dense structure for the samples obtained by bulk polymerization and a porous structure with non connected porous as a result of bulk polymerization in the presence of water soluble crystals (sucrose/NaCl). The use of solution polymerization technique using different amounts of water as diluent resulted in the formation of a sponge-like structure with connected microporous in case of using water amount equal or higher than 57.5%. The saline solution uptake and dynamic mechanical behavior of dense hydrogels were influenced by the amount of crosslinking between the polymer chains.

Resumo em Inglês:

Medium Density Fiberboard (MDF) is a wood-based composite widely employed in several industrial applications, in addition to its use in structures subjected to dynamic loads. Its fatigue-related aspects, however, have been consistently ignored. This work proposes to study fatigue in MDF, including the following factors: the basic concepts of MDF and fatigue and the statistical design of fatigue experiments in MDF, with the purpose of obtaining accurate information for analysis by means of statistical methods. The results of our tests revealed that the statistical model is suitable to fit the number of cycles in intermediary S and f levels and to determine the levels of the factors that maximize the total number of cycles to failure. It was also found that the proposed design is of great practical interest for fatigue strength in the tension in wood and wood derivatives.

Resumo em Inglês:

Gallium solubility in the Bi12TiO20 (BTO) matrix was investigated by solid state reaction synthesis and Bi12Ti(1-x)Ga xO20 (BTGaO) single crystals were grown by Top Seeded Solution Growth (TSSG). We determined that it is possible to obtain a continuous solid solution from (x)Bi12TiO20: (1-x)Bi12[Ga0.7Bi0.3]O20 and that Ga replaces Ti in the BTO matrix giving Bi12Ti(1-x)Ga(x)O20 up to x < 0.2. BTGaO single crystals grown with an excess of Bi2O3 were transparent, a bleaching effect was observed due to the presence of gallium in the crystalline sillenite structure and their lattice parameter was higher than for pure BTO. The results for BTGaO single crystals showed an increase in the optical activity from rho0 = 6.4° ± 0.3°/mm, for BTO, to rho0 = 9.7° ± 0.3°/mm, for BTGaO grown with x = 0.30 in the melt. The BTGaO crystal presented an activation energy value of 0.48 ± 0.02 eV for 100 °C <= T <= 300 °C.

Resumo em Inglês:

The austenitic stainless steel of orthodontic wires may undergo phase transformation induced by plastic deformation and heat treatment for stress relief. In order to study these changes, arches were made with 0.0215 x 0.027" orthodontic wires and ferromagnetic resonance measurements were performed. The results showed that the best heat treatment for recovery of the austenitic phase seems to be at 450 °C for 3 min.