ABSTRACTPhase formation characteristics of Sr0.7Bi2.4Ta2O9 (SBT) powder, synthesized via sol-gel and pyrolysis process, was investigated by using thermal analysis. Each of the two exotherms, appearing in differential thermal analysis (DTA) scan curves, was identified as crystallization of fluorite phase and transformation of fluorite to aurivillius phase, respectively by using x-ray diffraction (XRD). By applying non-isothermal kinetic analyses to the DTA results, activation energy values for the formation of fluorite and aurivillius phases were determined as 192 and 375 kJ/mol, respectively and Avrami exponent values for each reaction were determined as 0.91 and 0.96, respectively. These activation energy and Avrami exponent values were discussed in detail to understand phase formation mechanism in SBT system.
The glasses with composition of Li2O . 2 SiO2 . n ZrO2 . n TiO2 (where n = 0; 0.015;
0.031; 0.050; 0.075; 0.1; 0.15; 0.2) were prepared and the relationship between structural and
selected parameters of thermal stability vs. crystallization has been studied by differential thermal
analysis. Structural analysis was provided by X–ray diffraction. The order of thermal stability vs.
crystallization representing of activation energy of studied glass systems which increase with higher
addition both oxides. The same order was obtained from the values of XRD. On the comparison the
glasses with zero addition titanium dioxide their activation energy was much higher.
AbstractStability of Pd-Co-Ni-Cu-P metallic glass was investigated in terms of free energy using first principle cluster calculations, thermal analysis, and photoemission spectroscopy measurements. We found that the internal energy of the Pd-based metallic glasses is dominated by the electronic structure near the Fermi level. The analyses on the electronic structure and local atomic arrangements indicate that the substitution of cobalt or a hypothetical atom Co0.5Cu0.5 for nickel in the Pd40Ni40P20 metallic glass decreases the free energy of the Pd-Ni-P metallic glass by increasing entropy without altering significantly internal energy. On the basis of the idea mentioned above, we prepared Pd28Co24Ni24P24, Pd25Co25Ni25P25 and Pd40Co40/3Ni40/3Cu40/3P20 metallic glasses. These metallic glasses certainly showed the nearly highest TX, which directly reflect the activation energy against crystallization, among the Pd-based metallic glasses ever reported.
A research program has been completed in order to analyze structural changes during heating of amorphous alloys belonging to Fe-Ni-P system. Special attention has been given to thermodynamics and mechanism of crystallization, to determine some aspects of development for crystalline phases. Experimental material used to determine characteristics of crystallization consisted in long ribbons, 30 thick and 18 mm wide, fabricated by mean of “Planar Flow casting” as amorphous Fe42Ni38P16B4alloy. Differential Thermal Analysis (DTA) and X-rays diffraction have been used to determine crystallization temperature of this alloy. Curves of differential thermal analysis for heating rates ranging between 1°C/minute and 20 °C/minute have been used to determine activation energy of crystallization.
The 2-carboxybenzaldehyde-1H-benzotriazol-1-aceylhydrazone (C16H13N5O3) has been synthesized and used in preparing thirteen novel rare earth complexes. The complexes were characterized by elemental analysis, FT-IR, and UV-Vis, and the formula is RE (C16H11N5O3)·NO3·xH2O·yC2H5OH (RE=La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Yb) and RE(C16H12N5O3)2·NO3·5H2O (RE=Gd, Dy, Y) .The thermal decomposition processes of the thirteen complexes were studied by thermal gravimetric technology and their apparent activation energy values were calculated by Kissingers and Ozawass method.
Abstract
The thermal decomposition of magnesium-aluminum layered double hydroxides (LDHs) was investigated by thermogravimetry analysis and differential scanning calorimetry (DSC) methods in argon environment. The influence of heating rates (including 2.5, 5, 10, 15 and 20K/min) on the thermal behavior of LDHs was revealed. By the methods of Kissinger and Flynn-Wall-Ozawa, the thermal kinetic parameters of activation energy and pre-exponential factor for the exothermic processes under non-isothermal conditions were calculated using the analysis of corresponding DSC curves.
A crystallization process in an amorphous state under isothermal condition is examined for binary alloys ZrNi and ZrNi2 by differential thermal analysis (DTA). Time dependence of DTA curves is measured at several constant temperatures just below crystallization temperature. The fraction of crystallized volume in amorphous state and its time evolution during isothermal annealing are measured. These data are analyzed by the Johnson-Mehl–Avrami formula. The Avrami exponent is 2.4±0.1 for ZrNi and 3~4 depending on the set temperature for ZrNi2. The activation energy for crystallization of amorphous ZrNi and ZrNi2 was estimated by plots of lnt1/2 vs. 1/T.
Styrene-co-glycidyl methacrylate-fumed silica-clay (ST-co-GMA-fsi-clay) nanocomposites have been prepared via free radical polymerization in the presence of benzoyl peroxide. The nanocomposites are characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), adsorption isotherm, tensile test, thermogravimetric analysis (TGA) and moisture absorption. FT-IR shows the Si-O-C peak that represented ST-co-GMA-fsi bonding while Si-O-Si peak shows the bonding of fsi-clay. The surface morphology shows the well dispersion of clay (1.30E) into ST-co-GMA-fsi nanocomposite. 2wt% of ST-co-GMA-fsi-clay (1.30E) nanocomposite has higher specific surface area and average pore volume with less pore size. Incorporation of 2wt% of clay (1.30E) improves the tensile strength and modulus of the nanocomposites as well as higher thermal stability and activation energy. 2wt% of ST-co-GMA-fsi-clay (1.30E) nanocomposite shows the lowest moisture absorption value.
A numerical treatment of radiative nanofluid 3D flow containing gyrotactic microorganism with anisotropic slip, binary chemical reaction and activation energy