I. M. G. Santos

Synthesis and characterization of spinel pigment CaFe2O4 obtained by the polymeric precursor method

The CaFe2O4 composition was studied, in order to analyze its physical and chemical behavior, verifying its stability under industrial conditions, when applied as pigments. The characterization was accomplished using thermal analysis, X-ray diffraction (XRD), nitrogen adsorption, scanning electronic microscopy (SEM) and diffuse reflectance. It observed successions exothermics reactions, adequate in events of thermal decomposition of the organic material, reach your stability in 700 jC. The material became completely crystalline at 800 jC. Between 700 and 1100 jC, the color was stabilized, showing an absorption band in the region of 650 to 750 nm, characteristic of the red color. D 2003 Elsevier B.V. All rights reserved.

NUCLEATING EFFECT AND DYNAMIC CRYSTALLIZATION OF A POLY(PROPYLENE)/TALC SYSTEM

AbstractThe addition of nucleating agents to semicrystalline polymersis largely used in the processing industry of plastic materials to improve some properties of polymers as well as for economical and technological reasons. In this work, the influence of talc concentration on the nucleation efficiency of poly(propylene) (PP), as well as on the non-isothermal kinetics of the crystallization of that system were determined by differential scanning calorimetry (DSC). The nucleating efficiency was determined by Fillons method, and the dynamic nucleation by Ozawas method at cooing rates of 2, 5 and 10°C min–1. The results show that both the degree of crystallinity and the crystallization temperature increase with the filler content and decrease at higher cooling rates and that Ozawas (n,) exponent and the nucleation efficiency increase with temperature and filler content. It was also shown that the nucleating efficiency of talc in poly(propylene) is comparable to the best heterogeneous nucleating agents available.

Thermal Study of the Ceramic Pigments CoxZn(7−x)Sb2O12

Using the Pechini method, pigments with spinel structure (Zn7Sb2O12)were synthesized by substitution of the cation Zn2+ by Co2+, in compounds with different concentrations of Sb2O3. The doping resulted in CoxZn(7–x)Sb2O12 phases(x=1–7) that were isomorphs to spinel, denominated as samples A and B. After thermal treatment at 400°C for 1 h, the powders were characterized by thermogravimetry(TG) and differential thermal analysis (DTA). The results indicate a different behavior whena higher amount of Sb2O3 is used, due to the presence of a secondary phase (ilmenite).

ISOTHERMAL KINETIC STUDY OF CORN AND ITS DERIVATIVES

The thermogravimetric procedures applied to quality control of foods attain the global analysis of quality of the product, through the determination of quality parameters and the thermal stability of products. The kinetic parameters such as order of reaction, apparent activation energy, pre-exponential factors and the thermal decomposition rate constant were determined for the samples of corn and its derivatives by applying isothermal thermogravimetry, utilizing the Arrhenius law. This method presented excellent results as verified with the coherence and data adjustment. The rate constant values showed the expected performance from the chemical point of view.

Synthesis and thermal characterization of zirconium titanate pigments

Vezetéknév

Thermal properties of the orthorhombic CaSnO3 perovskite under pressure from ab initio quasi-harmonic calculations

AbstractStructural, elastic and thermodynamic properties of the orthorhombic CaSnO3 perovskite are theoretically investigated at the ab initio level as a function of temperature and pressure. Harmonic and quasi-harmonic lattice dynamical calculations are performed with the Crystal program, by explicitly accounting for thermal expansion effects and by exploring the effect of several DFT functionals. The anisotropic, directional elastic response of the system is characterized up to 20 GPa of pressure. The thermal lattice expansion and elastic bulk modulus are described at simultaneous temperatures up to 2000 K and pressures up to 20 GPa. The Gibbs free energy of formation of CaSnO3 from CaO and SnO2 as a function of temperature is also addressed by means of fully converged phonon dispersion calculations on the three systems.

New methodology for a faster synthesis of SrSnO3 by the modified Pechini method

SrSnO3, a perovskite-type complex oxide, was synthesized by the modified Pechini method using two different precursors, tin chloride and metallic tin. The first one is already traditional in the literature and it claims about 30 days, only for the cleaning of tin citrate aiming at the elimination of the chloride. The second route was developed by our research group and saves time, taking 6 h to complete the synthesis of the resin. The results show that SrSnO3 obtained from the metallic tin show a higher short range order, leading to a band gap value higher than those reported in the literature, besides a meaningful reduction in the formation of SrCO3, as compared to the one obtained from tin chloride.

Influence of variables on the synthesis of CoFe2O4 pigment by the complex polymerization method

Synthetic inorganic pigments are most widely used in ceramic applications due to their excellent chemical and thermal stability and their lower toxicity to both human and environment as well. In the present work, black ceramic pigment CoFe2O4 has been synthesized by the complex polymerization method (CPM) with good chemical homogeneity. In order to study the influence of variables on the process of obtaining pigment through CPM, 2(5-2) fractional factorial design with resolution III was used. The variables studied in the mathematical modeling were: citric acid/metal concentration, pre-calcination time, calcination temperature, calcination time, and calcination rate. Powder pigments were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible (UV-Vis) spectroscopy. Based on the results, the formation of cobalt ferrite phase (CoFe2O4) with spinel structure was verified. The color of pigments obtained showed dark shades, from black to gray. The model adjusted to the conditions proposed in this study due to the determination coefficient of 99.9% and variance (R2) showed that all factors are significant at the confidence level of 95%.

Thermal Degradation Process of Synthetic Lubricating Oils: Part I—Spectroscopic Study

The characterization of thermal degradation process of synthetic lubricating oils in relation to its spectroscopic properties was evaluated in this work. The fundamental key to understanding synthetic lubricating oxidation is having basic knowledge of the chemistry of lubricants and their degradation. Synthetic lubricants were degraded at different temperatures and times, under air atmosphere. After thermal degradation, lubricant oils were characterized by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR) and gas chromatographic/mass spectrometry (GC/MS). IR, NMR, and GC/MS spectra indicated oxidation reaction products.

Effect of the composition on the thermal behaviour of the SrSn1-xTixO3 precursor prepared by the polymeric precursor method

Strontium stannate titanate Sr(Sn, Ti)O3 is a solid solution between strontium stannate (SrSnO3) and strontium titanate (SrTiO3). In the present study, it was synthesized at low temperature by the polymeric precursor method, derived from the Pechini process. The powders were calcined in oxygen atmosphere in order to eliminate organic matter and to decrease the amount of SrCO3 formed during the synthesis. The powders were annealed at different temperatures to crystallize the samples into perovskites-type structures. All the compositions were studied by thermogravimetry (TG) and differential thermal analysis (DTA), infrared spectroscopy (IR) and X-ray diffraction (XRD). The lattice former, Ti4+ and Sn4+, had a meaningful influence in the mass loss, without changing the profile of the TG curves. On the other hand, DTA curves were strongly modified with the Ti4+:Sn4+ proportion in the system indicating that intermediate compounds may be formed during the synthesis being eliminated at different temperature ranges, while SrCO3 elimination occurs at higher temperature as shown by XRD and IR spectra.