Federal University of São Carlos

About: Federal University of São Carlos is a education organization based out in São Carlos, Brazil. It is known for research contribution in the topics: Population & Microstructure. The organization has 16471 authors who have published 34057 publications receiving 456654 citations. The organization is also known as: UFSCar & Federal University of São Carlos.

Crystallization of glass-forming liquids: Maxima of nucleation, growth, and overall crystallization rates

Abstract: A set of equations for determining the temperatures and magnitudes of the maximum nucleation, growth, and overall crystallization rates of glass-forming liquids is derived and analyzed The analysis is performed based on the classical theories of nucleation and growth, without introducing additional assumptions such as the Stokes–Einstein–Eyring (SEE) equation, models for specific kinetic mechanisms of aggregation, a specification of the type of temperature dependence of the diffusion coefficient, or specific models for the computation of the driving force of crystallization and the work of critical cluster formation Such approximations are employed only for analytical estimates and to illustrate the general results In particular, it is shown that the magnitude of the maximum of the steady-state nucleation rate Jmax decreases upon increasing the ratio Tmax(nucl)/Tm (Tmax(nucl): temperature of maximum of the steady-state nucleation rate, Tm: melting or liquidus temperature) Similarly, the maximum growth rate, umax, decreases with increasing values of the ratio Tmax(growth)/Tm (Tmax(growth): temperature of maximum of the growth rate) Several experimental results on the crystallization kinetics of glass-forming liquids are interpreted theoretically for the first time employing the concepts developed here

Model for sintering polydispersed glass particles

Abstract: We propose a model to describe the sintering kinetics of polydispersed glass particles, having no adjustable parameter. The model is based on three sintering stages: a pure ‘Frenkel’ (F) first step, a mixed ‘Frenkel/Mackenzie‐ Shuttleworth’ stage, and a third, pure ‘Mackenzie‐Shuttleworth’ (MS) step. The model considers sample shrinkage as the sum of the partial shrinkage of several clusters, each consisting of equally sized particles and each showing independent F or MS behavior. The overall set of clusters mimics the specimen’s real particle size distribution. We then introduce the concept of neck forming ability ‐ nr, which allows the formation of necks among particles of diAerent sizes, relaxing the clustering condition. Using experimental physical parameters: particle size distribution, viscosity, surface energy, and the theoretical nr, the model describes well the sintering kinetics of an alumino-borosilicate glass powder having polydispersed, irregular shaped particles in a variety of temperatures. The sintering kinetics of the real powder is slower, but not far from the calculated kinetics of a monodispersed distribution containing only particles of average size. Thus the model provides a tool for estimating the sintering kinetics of real glass powders, for any size distribution and temperature, thus minimizing the number of laboratory experiments. ” 2001 Elsevier Science B.V. All rights reserved.

Study of Synthesis Variables in the Nanocrystal Growth Behavior of Tin Oxide Processed by Controlled Hydrolysis

Abstract: Tin dioxide nanoparticle suspensions were synthesized at room temperature by the hydrolysis reaction of tin chloride (II) dissolved in ethanol. The effect of the initial tin (II) ion concentration, in the ethanolic solution, on the mean particle size of the nanoparticles was studied. The Sn2+ concentration was varied from 0.0025 to 0.1 M, and all other synthesis parameters were kept fixed. Moreover, an investigation of the effect of agglomeration on the nanoparticle characteristics (i.e., size and morphology) was also done by modifying the pH of the SnO2 suspensions. The different samples were characterized by transmission electron microscopy, optical absorption spectroscopy in the ultraviolet range, and photoluminescence measurements. The results show that higher initial ion concentrations and agglomeration lead to larger nanoparticles. The concentration effect is explained by enhanced growth due to a higher supersaturation of the liquid medium. However, it was observed that the agglomeration of the nano...

Mechanical and morphological characterization of starch/zein blends plasticized with glycerol

Abstract: Blends of starch and zein plasticized with glycerol were prepared by melting in a batch mixer at 160°C. Glycerol was used as plasticizer in contents ranging from 20 to 40 wt % with respect to the starch/zein matrix. These blends were characterized by mechanical tests, dynamic me- chanical analysis, and optical microscopy. In tensile tests, the Young's modulus and ultimate tensile strength in- creased with increasing zein content for all compositions, whereas elongation at break decreased sharply with increas- ing zein content up to 20%, and it remained nearly constant at higher contents of zein, which increased the stiffness of the blends. On the other hand, increase in the glycerol content caused a decrease in mechanical resistance of the blends. Storage modulus increased with increasing zein con- tent and the tan curves showed that the blends exhibited two distinct glass transitions, one for each component, indi- cating a two-phase system, confirming the morphological evidence of micrographs that displayed two separate phases. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4133- 4139, 2006