R. Gajerski

Mechanism of Thermal Decomposition of d-metals Nitrates Hydrates

A series of six nitrates(V) hydrates of 4d-metals as well as mercury and cadmium thermal decomposition was examined by DTA, TG and EGA techniques. It was found that thermal decomposition of d-metals nitrate(V) hydrates proceeds in three stages: partial dehydration, oxo-nitrates and hydroxide nitrates formation and metal oxides formation. General chemical equations for all decomposition stages were proposed. It was found that dehydration of hydrated salts is accompanied by partial decomposition of nitrate(V) groups.

Thermal decomposition of chromium(III) nitrate(V) nanohydrate

Thermal decomposition of Cr(NO3)3·9H2O in helium and in synthetic air was studied by means of TG, DTA, EGA and XRD analysis. The dehydration occurs together with decomposition of nitrate(V) groups. Eight distinct stages of reaction were found. Intermediate products of decomposition are hydroxy- and oxynitrates containing chromium in hexa- and trivalent states. The process carried out in helium leads to at about 260°C and in air is formed at about 200°C. The final product of decomposition (>450°C) is Cr2O3, both in helium and in air.

Investigation of thermal decomposition of CrOx (x≥2.4)

The phase transitions and thermal effects occurring during annealing in air of material with general formula CrOx (x≥2.4) have been investigated. The investigations were performed with TG, DTA, DSC, EGA, XRD and other spectral techniques. The formation of an amorphous phase with average composition Cr5O12 in the range 300-400°C has been observed. Further heating leads to partial loss of oxygen, simultaneous decay of Cr2O5 and CrO2 phases and formation of nonstoichiometric Cr2O3+x. The distinct loss of mass is observed in the range 415-428°C, connected with evolving oxygen and small amount of nitric oxides. Thermal effects accompanying the mass changes depend on the mass of the sample. When the mass decreases, the transition from exothermic to endothermic effects is observed. This phenomenon can be explained as the competition between two processes: reconstruction of the crystalline lattice (endothermic effect) and recombination of the evolved atomic oxygen (exothermic effect).

Structural Properties and Thermal Behavior of Li2CO3–BaCO3 System by DTA, TG and XRD Measurements

The binary system Li2CO3–BaCO3 was studied by means of differential thermal analysis (DTA), thermogravimetry (TG) and X-ray phase analysis. The composition of carbonate and CO2 partial pressure influence on the thermal behavior of carbonate were examined. It was shown that lithium carbonate does not form the substitutional solid solution with barium carbonate, however the possible formation of diluted interstitial solid solutions is discussed. Above the melting temperature the mass loss is observed on TG curves. This loss is the result of both decomposition of lithium carbonate and evaporation of lithium in Li2CO3–BaCO3 system. Increase of CO2 concentration in surrounding gas atmosphere leads to slower decomposition of lithium carbonate and to increase the melting point.

Phase Transition and Thermal Decomposition of [Cd(H2O)6](BF4)2

Phase transition and thermal decomposition of [Cd(H2O)6](BF4)2 were studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetry (TG) methods. The solid-solid phase transition at TC1=324 K and the melting point atTmelt.=391 K were registered. The thermal dehydration process starts just above TC1 and continues up to Tmelt.,where [Cd(H2O)4](BF4)2 in the liquid phase is formed. Then, dehydration and decomposition take place simultaneously until CdF2 is obtained. Final products of the thermal decomposition were identified using quadrupole mass spectrometry (QMS) and X-ray diffraction methods.

Another Approach to the Modified Zhuravlev Equation on the Basis of the Oxidation of V2O4 and V6O13

It has been found that the modified Zhuravlev equation, [(1−α)−1/3−1]2=ktn, which describes the kinetics of oxidation of V2O4 and V6O13 in the temperature range 820–900 K and in the oxygen pressure range 1.0–20 kPa, can be derived via the assumption that the changes in the observed activation energy result from the changing contributions of the two diffusion processes controlling the reaction rate. The values of the observed activation energy are in the range 160–175 kJ mol−1 for V2O4 and 188–201 kJ mol−1 for V6O13 in the scope of the experimental oxygen pressures and temperatures and conversion degrees of 0.1–0.9.