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Synthesis of Sr-doped LaCrO3 powders by combustion method
Influence of the fuel agent
Abstract
Lanthanum strontium chromite (LSC) powders were synthesized by the combustion method, using five different fuels (urea, glycine, ethylene glycol, α-alanine, and citric acid). The ignition of the reagent mixture with urea takes a longer time, and more gases are released by combustion. A calcination step is essential for a good crystallization of the perovskite phase. X-ray diffraction patterns showed formation of perovskite phase and a small amount of SrCrO4 for the sample synthesized with urea after calcination. The crystallite sizes are in the range of 23–33 nm. Scanning electron microscopy revealed the porosity of the powders and the presence of agglomerates, formed by fine particles of different shapes. Thermogravimetric analysis showed a large mass loss for the sample synthesized with citric acid, probably caused by the absence of ignition, with primary polymerization of the precursor reagents.
Abstract
The thermal decomposition reactions of crystalline chelates of general formula Ln(thd)3 (Ln=La,Pr, Nd, Sm and Gd; thd=2,2,6,6-tetramethyl-3,5-heptanedione) have been studied by isothermal thermogravimetry. Several models were proposed initially to calculate the kinetic parameters by isothermal method, thus the time reduced method was used to define the best kinetic models. The Avrami–Erofeev (Am=2, 3 and 4) and R1 and R2 models presented good agreement with experimental data, as well as, linear correlation coefficient (r) and standard deviation (s).
Abstract
The kinetics of thermal decomposition of solid In(S2CNR2)3 complexes, (R=CH3, C2H5, n-C3H7,i-C3H7, n-C4H9 and i-C4H9), has been studied using isothermal and non-isothermal thermogravimetry. Superimposed TG/DTG/DSC curves show that thermal decomposition reactions occur in the liquid phase, except for the In(S2CNMe2)3 and In(S2CNPri 2)3 compounds.
Abstract
The pigments used in ceramic applications are of nature predominantly inorganic and they should be thermally stable, insoluble in glazing, resistant to the chemical and physical agents' attacks. This work aimed at the synthesis by the polymeric precursor method of ZrO2-based inorganic pigments, doped with Fe, Ni, Co, Cr and Cu cations. The fired pigments were characterized by thermogravimetry (TG), differential thermal analysis (DTA) and X-ray diffraction (XRD). Among the metals used to zirconium-doping, the best result was achieved with the cations Cu, which presented the monophase pigment, even as 20 mol% of dopant. Up to the temperature of 1000C the pigments presented a good thermal stability.
Abstract
The high-density polyethylene, thermoplastic widely-used in the production of industrial domestic utilities, was collected in two situations: virgin high-density polyethylene (JV 060) and post-consumption high-density polyethylene (with features of low-density polyethylene). After collecting the samples, they were submitted to natural aging with the quantification of the incident solar radiation for 180 days. The samples were characterized by melt flow index, differential scanning calorimetry, tensile strength, rupture load, elongation at break and infrared. The results showed that after 180 days of exposure the virgin high-density polyethylene presented physical properties similar to the post-consumption polyethylene.
Abstract
The thermogravimetric curves of di-n-propylammonium, di-iso-propylammonium, di-n-butylammonium and di-iso-butylammonium chlorides showed similar profiles, characterized by mass loss in only one stage, corresponding to decomposition of compounds. The following thermal stability order was obtained: [Bu2 nNH2]Cl>[Pr2 nNH2]Cl>[Pr2 iNH2]Cl>[Bu2 iNH2]Cl. The values of activation energy for non-isothermal data obtained by Ozawa and Coats-Redfern integral methods were in agreement and stability order obtained by thermogravimetry were reproduced in both methods. The decomposition reactions of [Pr2 nNH2]Cl, [Pr2 iNH2]Cl and [Bu2 iNH2]Cl were better described by A3 model and [Bu2 nNH2]Cl by A2 model.
Abstract
The thermodynamic and kinetic parameters of the thermal decomposition of Zn(S2CNR2)2 complexes (R=CH3, C2H5 and n-C3H7) were determined with the dynamic thermogravimetric method. Superimposed TG/DTG/DSC curves show that thermal decomposition reactions for chelates with R=C2H5 and n-C3H7 occur in the liquid phase, at temperatures far away from their melting points, whereas for the complex with R=CH3 the thermal decomposition begins at a temperature closer to its melting point, suggesting a rather complex decomposition mechanism.
Abstract
Co80Nb14B6, Co80Nb12B8 and Co80Nb10B10 amorphous alloys were obtained through the melt-spinning process. The ribbons structure was investigated by X-ray diffractometry and the crystallization process and the thermal stability were studied by means of differential thermal analysis and thermomechanical technique. It was observed that the crystallization temperature depends on the alloy composition and occurs in a temperature range between 420 and 730C. The coercive field of all alloys was determined by magnetic susceptibility measurements, the values of which range from 2.78 to 5.95 A m-1.
Abstract
The crystallization behavior of Co75-xFexGe15B10 (x=3.0, 4.6 and 6.0) amorphous alloys was monitored by differential thermal analysis and thermo-mechanical analysis. The crystallization process of the melt spun ribbons was interrupted at 450, 525, 650, 800 and 900C and their microstructures were investigated by X-ray diffractometry. It was observed that the crystallization occurs in a sequential mode attributed to the formation of different types of precipitates. It was shown that the crystallization products change as a function of Fe content. After full crystallization, GeFe, Co3B, FeGe2 and Co2Ge compounds were found as well as a Co rich solid solution.
