Search results for "Differential Thermal Analysis"
showing 10 items of 66 documents
Low-temperature Ti-containing 3:2 and 2:1 mullite nanocrystals from single-phase gels
2007
Abstract TiO 2 -containig single-phase gels with (Al 2 O 3 + TiO 2 )/(SiO 2 ) molar ratios 3/2 and 2/1 were prepared by gelling mixtures of aluminium nitrate, tetraethylorthosilicate and titanium isopropoxide. Gels were fast heated at several temperatures up to 1100 °C. Dried and heated gels were characterized by differential thermal analysis (DTA), magic angle spinning nuclear magnetic resonance (MAS-NMR), X-ray powder diffraction (XRD), and scanning and transmission electron microscopies (SEM and TEM). Coupled DTA and XRD results of gels fast heated at 900 °C showed the crystallisation of two mullites as well as a small amount of alumina-silica spinel. 27 Al NMR spectra showed the format…
Enrichment and activation of smectite-poor clay
2011
A new method of smectite clay enrichment has been developed. The method is based on dispersing clay in a phosphate solution and sequential coagulation. The product of enrichment is characterized with X-ray powder diffraction, wavelength dispersive X-ray fluorescence spectrometry, differential thermal analysis and thermogravimetry. Sorption of methylene blue and hexadecylpyridinium bromide on raw and purified clays was studied.
Effect of some additives on the development of spinel-based glass-ceramic glazes for floor-tiles
2005
Abstract The feasibility of developing spinel-based glass-ceramic glazes from a glass with composition in the system ZnO–MgO–B 2 O 3 –Al 2 O 3 –SiO 2 was examined. To do it additional fluxes and/or nucleants were added to a parent glass before melting. Pressed pellets of powdered glasses were submitted to standard thermal treatments up to 1200 °C. The crystallization path and the microstructural development at several temperatures were followed by several experimental techniques. The results showed that additions of TiO 2 as nucleant or additional B 2 O 3 as flux to the chosen glass favored the crystallization of cordierite or mullite as main crystalline phase. Glasses which also contained …
Modelling phase transition kinetics of chenodeoxycholic acid with the Runge–Kutta method
2009
Abstract The phase transition kinetics of two chenodeoxycholic acid polymorphic modifications— form I (stable at high temperature), form III (stable at low temperature) and the amorphous phase has been examined under various conditions of temperature and relative humidity. Form III conversion to form I was examined at high temperature conditions and was found to be non-spontaneous, requiring seed crystals for initiation. The formation kinetic model of form I was created incorporating the three-dimensional seed crystal growth, the phase transition rate proportion to the surface area of form I crystals, and the influence of the amorphous phase surface area changes with an empirical stage poin…
Structural transformations in amorphous selenium as studied by the differential thermal analysis and exoelectron emission technique
2007
The parameters (temperature, activation energy) of the surface and volume glass transition (retrification process) in amorphous selenium produced by rapid quenching of the liquid phase have been determined using the EEE and DTA techniques. EEE is a surface effect connected with structural transformations in the surface layer whereas the DTA measurements give the information about the transformations occurring in the volume of the sample. It has been found that the surface retrification of selenium occurs with activation energy smaller than the volume retrification, both observed in the first heating run. The value of activation energy for the volume retrification measured in the second DTA …
DSC Studies and Stability of Frozen Foods
1991
This paper discusses the role played by the “WLF decrease in viscosity” above the temperature of the glass transition (Tg) in the temperature dependence of the stability of frozen foods. In the first part, the complex features observed before the melting endotherm on DSC/DTA thermograms of sugar-water solutions are examined; they are suggested to be representative of a glass transition associated with enthalpy relaxation. In the second part, the values of Tg for some complex foods are discussed. It is shown that ice melting adds an important contribution to the WLF effect on the decrease of the viscosity of the freeze-concentrated phase. The temperature dependence of the deterioration proce…
Different kinds of solid solutions in the V2O5-ZrSiO4-NaF system by sol-gel processes and their characterization
1993
Abstract In the V2O5-ZrSiO4-NaF system, three kinds of substances have been identified by sol-gel methods depending on the V2O5 amounts in the composition. Their characterization by X-ray diffraction, measurements of unit cell parameters, UV-visible (UV-V) spectroscopy, differential thermal analysis and lab colour parameter determination allow the consideration of three kinds of solid solution in the zircon lattice: (a) V+5,V+4-ZrSiO4, thermally stable and with a deep green colour; (b) V+4-ZrSiO4, thermally stable and blue coloured, made by the sol-gel method and with V2O5 amounts lower than 0·03 mol per formula weight; and (c) Na+,F−,V+4-ZrSiO4, a solid solution with a deep blue-turquoise …
Study of the thermal decomposition of bromazepan complexes with Co(II), Ni(II), Cu(II) and Zn(II)
1984
Abstract The thermal behaviour of complexes of bromazepan with Co(II), Ni(II), Cu(II) and Zn(II) was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The complexes decompose in two steps: dehydration and decomposition. A correlation between the dehydration temperatures of MB2Xn and the coordinating ability of X is observed.
Synthesis and characterization of α-hopeite, Zn3(PO4)2·4H2O
1999
Orthorhombic α-Zn3(PO4)2·4H2O, α-hopeite, was synthesized from an aqueous solution of zinc acetate and orthophosphoric acid. The synthesis from these starting materials yielded best results with respect to purity and crystallinity. Structural characteristics of the compound were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and thermogravimetric/differential thermal analysis (TG/DTA). Supplemental data came from surface area, particle size distribution, and density measurements. The obtained compound proved to be highly crystalline and stoichiometric. Dehydration of α-hopeite is accompanied by at least two endothermic effect…
Relaxor ferroelectric PbSc1/2Nb1/2O3—PbZn1/3Nb2/3O3— PbMg1/3Nb2/3O3ceramics
2000
Abstract Original ternary solid solutions PbSc1/2Nb1/2O3 — PbZn1/3Nb2/3O3-PbMg1/3Nb2/3O3 (PSN-PZN-PMN) have been synthesized by solid state reaction from oxides. Ceramic samples have been obtained by both conventional and hot pressing techniques. The density of the obtained hot pressed ceramics reaches 98% of the value calculated from X-ray data. Dense, high quality samples of pure PZN and compositions containing over 0.8 molar parts of PZN could not be obtained — porosity was up to 10% and they were mainly comprised of the cubic pyrochlore phase. Density, porosity, water absorbtivity, and dielectric permittivity and dissipation factor of the ceramic samples have been measured. Data of diff…