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- Author or Editor: K. Tõnsuaadu x
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Abstract
Thermal analysis of Israeli phosphorites by TG/DTA methods complemented with titrimetric and thermogaschromatographic determination of the evolved gases was performed in an oxygen and inert gas flow. The amounts and temperature intervals of H2O, CO2 and SO2 evolvement were established.
Abstract
Two types of thermal effects, caused by substitutions (Ca2+↔ Na+, ↔ CO3 2-, SO4 2-, OH-↔ F-) in synthetic precipitated apatites as well as by sorption of Cd2+, Zn2+, and Cr3+ ions from the solutions were studied by TG/DTA, XRD and FTIR analysis. The temperatures of exothermic effect at 330-340°C and of decomposition of carbonate and sulfate apatites at 650-950°C were shown to depend on the substitutions in the apatite structure.
Abstract
The characteristics of bioaragonite of shells of recent T. decussatus during heating were studied by the means of TG-DTA-EGA (FTIR), XRD, XRF and FTIR. The mass loss recorded up to 2.5% appeared with the higher rates at 110–150, 200–250, 295–300, and 390–415°C at heating of 10°C min−1 up to 500°C. IR analysis of the evolved gases revealed the emission of water and CO2. The lattice constants tend to change with anisotropy character (parameters a and c diminish whilst b tends to grows) and with an overall contraction of cell volume (from 227.36 to 226.84 Å3) during heating was established. The peculiarity of bioaragonite was explained by substitution of H2O and sulphate ion into the lattice. In spite of those substitutions, bioaragonite reveals an orthorhombic structure, which is preserved during the changes up to calcite formation above 380°C.
Abstract
The Y-Zr-O precursors derived from an aqueous sol–gel synthesis have been applied for the preparation of yttria-stabilized zirconia (YSZ) powders and thin films on the corundum (Al2O3) substrate, using dip-coating technique. In this aqueous sol–gel synthesis route, citric acid as a complexing agent has been used for the preparation of stable Y-Zr-O nitrate–citrate sols and gels. Thermal decomposition of dried gels was studied by simultaneous TG/DTA/EGA-FTIR measurements in the dynamic 80%Ar + 20%O2 atmosphere. FTIR and X-ray diffraction analyses were used for the determination of phase purity of the end products obtained at 700, 800 and 900 °C. The morphological features of the prepared YSZ coatings and powders were evaluated using scanning electron microscopy.
Abstract
The reaction of SO2 with synthetic apatites was studied by TG, XRD and IR analyses at 400-1000C. Due to an interaction of apatite with SO2, destruction of apatite and formation of CaSO4 and diphosphate up to 750C takes place. The further calcination leads to the formation of β-Ca3(PO4)2 and a part of the SO2 bound is lost again. The amount of SO2 bound with apatite at calcination depends on the substitution ((F- ↔ OH-, PO4 3- ↔ CO3 2-, Ca2+ ↔ Mg2+) in its structure.
Abstract
Thermal decomposition of precursors for In2S3 thin films obtained by drying aqueous solutions of InCl3 and SC(NH2)2 at the In:S molar ratios of 1:3 (1) and 1:6 (2) was monitored by simultaneous TG/DTA/EGA-FTIR measurements in the dynamic 80%Ar + 20%O2 atmosphere. XRD and FTIR were used to identify the dried precursors and products of the thermal decomposition. The precursors 1 and 2 are complex compounds, while in 2 free SC(NH2)2 is also present. The thermal degradation of 1 and 2 in the temperature range of 30–900 °C consists of four mass loss steps, the total mass loss being 89.1 and 78.5%, respectively. According to XRD, In2S3 is formed below 300 °C, crystalline In2.24(NCN)3 is detected only in 1 above 520 °C and In2O3 is the final decomposition product at 900 °C. The gaseous species evolved include CS2, NH3, H2NCN, HNCS, which upon oxidation yield also COS, SO2, HCN and CO2.
Abstract
In this study the formation of chromium substituted YBa2Cu4O8 (Y-124) superconductors has been investigated by TG/DTA measurements. The YBa2(Cu1−xCrx)4O8 ceramics with nominal compositions of x=0.01, 0.03, 0.05, 0.10 and 0.20 have been prepared by an aqueous sol-gel method using aqueous mixtures of the corresponding metal acetates and nitrates. Homogeneous precursor gels were obtained by complexing metal ions with tartaric acid. To assist the interpretation of the results obtained the synthesis products were additionally characterized by X-ray powder diffraction (XRD) and resistivity measurements. It was determined that doping the YBa2Cu4O8 phase with chromium has a strong effect on the phase purity and superconducting properties of the synthesis products.
Summary Thermal decomposition of dried TiO2 gel, obtained by hydrolysing acetylacetonate-modified titanium(IV) isopropoxide, was monitored by simultaneous TG/DTA/EGA-FTIR measurements in dynamic air up to 900°C. XRD and FTIR were employed to identify the solid reaction products. Thermal degradation of the TiO2 gel consists of five distinct mass loss steps, the total mass loss being 43.8&. EGA by FTIR revealed the release of H2O below 120°C; followed by acetone, isopropyl acetate and 1-propanol around 200-300°C, and finally CO and CO2 up to 550°C. Highly exothermic reaction at 410-550°C is caused by the combustion of carbon residues. Crystalline TiO2-anatase is formed around 500°C and TiO2-rutile close to 800°C.
Titanium(IV) acetylacetonate xerogels for processing titania films
A thermoanalytical study
Abstract
Thermal decomposition of dried crystalline powder obtained from titanium(IV) bis(acetylacetonate) diisopropoxide (75% solution in 2-propanol) (1) was monitored by simultaneous TG/DTA, EGA-FTIR and EGA-MS measurements and the results were compared with those of amorphous powder obtained by gelling of acetylacetonate-modified titanium(IV) tetra-isopropoxide at molar ratio of 1:2 in boiling 2-methoxyethanol (2). Thermal degradation of 1 in the temperature range of 25–700°C consists of 5 steps with a total mass loss of 62.5%. EGA by FTIR and MS revealed the release of H2O below 120°C; followed by an intensive evolution of acetylacetone around 245°C. The release of acetone and acetic acid occurs up to 270°C and that of CO and CO2 up to 530°C.
Abstract
Thermal decomposition of precursor xerogels for TiO2, obtained by gelling of acetylacetonate-modified titanium(IV) tetraisopropoxide (prepared at Ti-alkoxide:acetylacetone molar ratios of 1:1 (Ti-1) and 1:2 (Ti-2)) in boiling 2-methoxyethanol, was monitored by simultaneous TG/DTA/EGA-MS and EGA-FTIR measurements. Thermal degradation processes of Ti-1 and Ti-2 in the temperature range of 30–700C consist of six mass loss steps, the total mass loss being 46.3% and 54.4%, respectively. EGA by FTIR and MS revealed release of H2O below 120C; followed by evolution of acetone and acetic acid between approximately 100 and 320C, and that of CO2 up to 560C. Acetylacetone is evolved to a significant extent from sample Ti-2 at 120–200C.
