Nanocellulose from Curava Fibers and their Nanocomposites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrical Properties of Textured Niobium-Doped Bismuth Titanate Ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Dielectric relaxation and dc conductivity on the PVOH-CF(3)COONH(4) polymer system

In the present paper, the ionic conductivity and the dielectric relaxation properties on the poly(vinyl alcohol)-CF(3)COONH(4) polymer system have been investigated by means of impedance spectroscopy measurements over wide ranges of frequencies and temperatures. The electrolyte samples were prepared by solution casting technique. The temperature dependence of the sample's conductivity was modeled by Arrhenius and Vogel-Tammann-Fulcher (VTF) equations. The highest conductivity of the electrolyte of 3.41x10 (-aEuro parts per thousand 3) (Omega cm) (-aEuro parts per thousand 1) was obtained at 423 K. For these polymer system two relaxation processes are revealed in the frequency range and temperature interval of the measurements. One is the glass transition relaxation (alpha-relaxation) of the amorphous region at about 353 K and the other is the relaxation associated with the crystalline region at about 423 K. Dielectric relaxation has been studied using the complex electric modulus formalism. It has been observed that the conductivity relaxation in this polymer system is highly non-exponential. From the electric modulus formalism, it is concluded that the electrical relaxation mechanism is independent of temperature for the two relaxation processes, but is dependent on composition.

Hydrodynamic aspects of the amorphous alloy ribbon fabrication

Conditions for as-quenched amorphous ribbon fabrication by a single roll-casting method are analyzed from a hydrodynamic standpoint. The analysis is based on the investigation of the processing conditions for Fe 4 0Ni 40P 14B 6 amorphous ribbons. It is shown that the dependence of ribbon thickness on the ejection pressure for different roll angular velocities and different dimensions of crucible and orifice can be obtained from general considerations on the melt flow regime.

Estudo das alterações lineares na região cervical de blocos M.O.D. fundidos em liga de cobre alumínio, segundo as técnicas de expansão higroscópica e térmica.

The authors studied linear alterations processed on copper-aluminum casten MOD blocks, obtained from two expansion techniques (termic and hygroscopic by immersion). UNITERMS: Investment expansion. Thermic expansion. Hygroscopic expansion. Casten Technique.

Rugosidade superficial de ligas com alto conteúdo de cobre, em função do aquecimento acima da temperatura de fusão.

Being the surface roughness a fundamental property in the fit of the castings, it was determined the roughness of 5 high-copper casting alloys, according to the heating over their melting temperature. That way, the specimens made with smooth plastic in the shape of a rectangular plate, 2 mm x 7 mm x 11 mm were invested into a cristobalite investment. After heating and elimination on the plastic, the molds were filled by 3 g of molten alloy, casted in a electrical casting machine at the casting temperature at 25 degrees C and 50 degrees C overheating. The surface roughness was measured in a roughness analyser, Talysurf. As a result, it was verified that there is a variation of surface roughness among the alloys tested, and the heating of the alloys until 50 degrees C over the melting temperature does not interfere in the roughness.

Efeito das técnicas de fusão sobre a fluidez de ligas do sistema cobre-alumínio.

It was evaluated the castability of four copper-aluminium alloy according the melting casting method used. The specimens were made using polyester mesh screen, with 11 x 11 filaments of 0.26 mm thick, fixed along of two adjacent edges in wax bar, with the sprue attached at their junction. The alloys were in an electrical casting machine and a centrifugal casting machine with an air/gas torch. The castability values were obtained by the percentage of completed segments of the resulting cast alloy screen. It was verified that the use of the electrical casting machine produced higher castability values to the copper-aluminium alloys than those produced by a centrifugal casting machine with an air/gas torch.

Determinação de dureza de ligas de cobre, na forma como são recebidas e após a fundição, em função das técnicas de fusão.

It was evaluated the Vickers hardness of five high-copper casting alloys, in their original package form and after casting, according to the casting method used. That way, ten ingots, supplied by the manufacturers of each alloy, were included in self-curing acrylic resin, polished, numerated and submitted to Vickers hardness test at load of 200 g during 30 seconds. Afterwards the numerated ingots were removed from the acrylic resin and five of those were cast in an electrical casting machine and the other five in a centrifugal casting machine with an air/gas torch. The specimens obtained were included in self-curing acrylic resin, polished and submitted to Vickers hardness test. As a result it was verified that there is a variation of hardness among the alloys tested, and the use of the electrical casting machine produced lower hardness values than those produced when used the centrifugal casting machine with an air/gas torch. Also, there is a decrease of hardness of the cast alloys when they are tested in their original form and after casting.

Fadiga de grampos de retenção em prótese parcial removível. Efeito de ligas, espessuras e técnicas de fusão. Parte I.

The authors looked for the verification of the fatigue of retentive clasps utilized on the removable partial denture. According to this, it was idealized and built on assay machine, that through movements, simulate the insertion and removal of the clasp for a pattern tooth, manufactured on cobalt-chromium which has all the preparation normally utilized to the correct confection of this type of prosthesis. It was utilized three different commercial alloys based on cobalt-chromium: L1-Biosil; L2-Steldent; L3-Duracron. It was utilized the T clasp of Roach, with was tested upon three different proportions among width and thickness: E1-1.7;E2-2.0 and E3-2.3 and was casted through two casting techniques: F1-oxygen-gas and F2-oxygen-acetylene. The clasps were tested on the machine, which allowed the reading of the number of insertion and removal cycles made until fatigue appeared. The obtained results were submitted to the statistic analysis and the authors concluded that: a) L3 (Duracrom) obtained the best results followed by L1 (Biosil) and finally L3 (Steldent); b) among the analyzed thickness, the best results were obtained by E3, followed by E2 and after this E1; c) form the casting techniques, F2 gave us the best results.

Fadiga de grampos de retenção em prótese parcial removível. Efeito de ligas, espessuras e técnicas de fusão. Parte II.

The authors tested the T clasp of Roach in three differents proportions among width and thickness: E1-1.7; E2-2.0 and E3-2.3, with a constant length of 15 mm. These clasps were casted with three cobalt-chromium alloys (L1-Biosil; L2-Steldent and L3-Duracrom), through two casting techniques (F1-oxygen-gas and F2-oxygen-acetylene). The fatigue of the clasps were verified by using and assay machine, that through movements, simulate the insertion and removal of the clasps for a pattern which were obtained from a premolar, prepared in a surveyor. This machine detect the fatigue of the clasps and count the number of cycles of insertion and removal realized. The obtained results of the interaction between the analysed factors, were submitted to the statistic analysis and the authors concluded that: a) the interaction of factors, Alloy x Thickness, Alloy x Casting Technique and Thickness x Casting Technique did not change the order of effects that the factors showed separately but gave rise to effects of different magnitude for any observed sense; b) the simultaneous interaction of the factors Alloy x Thickness x Casting Technique confirmed the superiority of the L3 alloy, the thickness E3 and the F2 casting technique.

Metallurgical evaluation of a copper-based alloy for dental castings.

The present study was designed to evaluate the metallurgical properties of an experimental, low-cost copper-zinc-aluminum-nickel alloy for dental castings. Some specimens were subjected to heat treatment after induction casting. The extent of corrosion was determined by measuring weight loss of specimens stored in a sodium sulfite solution. In the as-cast specimens, tests demonstrated the presence of three phases: the first consisted of copper-zinc-aluminum, the second was similar but lower in copper and aluminum, and the third consisted of an intermetallic compound of manganese-nickel-phosphorus. After heat treatment, the first phase remained relatively constant, the second was converted to Cu3Al, and the third increased in volume. The weight loss from the as-cast specimens was eight times that of the heat-treated specimens. It was concluded that the heat treatment substantially changed the microstructure and improved the corrosion resistance of the experimental alloy.

Estudio de los procesos de corrosion de una aleacion metalica de cobre usada en odontologia

Corrosion phenomena in a dental copper-based alloy are experimentally studied using electrochemical techniques. Two heating sources, torch and induction, were used in the casting experiments. In the corrosion essays, the optimum casting cycle and the polarization curves were obtained. It was found that the heating sources have little influence on the corrosion processes of the metallic alloys studied.

Influence of viscoelastic characteristics of the colloidal suspensions on the formation of SnO2 supported membranes

SnO2 supported membranes have been prepared by sol-casting on alumina tubular substrate, using aqueous colloidal suspensions prepared by sol-gel route. The viscoelastic behaviour during sol ageing was analyzed by dinamic rheologial measurements. The complex viscosity and the storage and loss moduli have been followed during the sol-gel transition and the results have been correlated with the linear aggregates growth and the scalar percolation models. The scanning electron microscopy has evidenced that the homogeneity and thickness of the membrane depend on the sol ageing time. Crack-free and homogeneous membranes have been obtained for coated layers of 0.5μm thickness. © 1997 Trans Tech Publications.

Influencia de la refusion en las propiedades mecanicas y composicion quimica de aleaciones odontologicas

The objective of the study presented in this article was to analyze the influence of remelting of two odontological alloys: Dentorium and Steeldent, on the mechanical properties and on the chemical composition. For the two alloys, samples, containing 10% and 50% new alloy, were subjected to tensile test, micrography and chemical analysis. The alloys presented similar mechanical properties, except for the elongation, which presented higher values for the Dentorium 50% new alloy. This is due to the smaller carbides formed in this sample. The remelting itself seems not to be responsible for these differences, but they are probably due to the lack of a good control of the casting process. The micrography showed a dendritic column matrix, with carbides in the interdentric region and inside dendritic grain. In the chemical composition was observed few elements percentage change.

Effect of disinfectant agents on dimensional stability of elastomeric impression materials.

STATEMENT OF PROBLEM: Difficulties in sterilizing impressions by traditional methods have led to chemical disinfection as an alternative, and some studies have shown that disinfectants may adversely affect impressions. PURPOSE: This study investigated the effect of disinfection methods on the dimensional stability of 6 elastomeric materials. MATERIAL AND METHODS: Impression materials were submitted to the following treatments: immersion in 5.25% sodium hypochlorite solution for 10 minutes, immersion in 2% glutaraldehyde solution for 30 minutes, and no immersion (control). After treatments, impressions were poured, and respective stone casts were measured with a Nikon Profile projector and compared with the master model. RESULTS: The elastomeric materials had different reproduction capacities, and the disinfecting treatments did not differ from the control.