Search Results

You are looking at 11 - 20 of 36 items for :

  • "solid decompositions" x
  • Refine by Access: All Content x
Clear All

The kinetics of isothermal decomposition of ammonium metavanadate (AMV) and its mixtures with MgO, CaO, CuO and NiO — in the molar ratio of 2∶1 — were investigated. The computer — oriented kinetic analysis of theα-t data reveals the validity of Ginstling-Brounshtein equation to describe these reactions. The accelerating effect accompanying the MgO addition can be attributed to its affinity to abstract protons. In case of CaO, the formation of the relatively stable Ca(OH)2 during the proceeding of the decomposition process results in a retarding effect. On the other hand, the higher calculatedE a, value for the AMV + CuO mixture was explained in terms of a solid-solid interaction between CuO and the solid decomposition product, leading to the formation of Cu3(VO4)2. According to electronic factors, the effect of NiO addition on the decomposition process was discussed. It was found that the decomposition process is less favourable in presence ofp-type semiconducting additive.

Restricted access

DTA and TG studies in air were carried out for hydrothermally prepared rhombohedral double carbonates of dolomite type, CaMg(CO3)2, CaMn(CO3)2, CdMg(CO3)2, CdMn(CO3)2 and CdZn(CO3)2. The solid decomposition products in air have been compared to those obtained under hydrothermal conditions with CO2 pressure. The dolomite [CaMg(CO3)2] decomposes in two stages both in air as well as under high CO2 pressure. The other carbonates studied, follow a single stage decomposition in air and a two stage decomposition under hydrothermal condition. In air, the manganese containing carbonates CaMn(CO3)2 and CdMn(CO3)2, decompose to form mixed oxides of CaMnO3 and CdMnO3 respectively, while CdMg(CO3)2 and CdZn(CO3)2 decompose to their respective two mono oxides.

Restricted access

Abstract  

The assumption that potassium permanganate may serve as a kinetics standard in solid decomposition kinetics made a priori on the basis of the mechanism of the congruent dissociative vaporization of KMnO4 and its crystal structure was successfully supported experimentally. As expected, the decomposition rate of KMnO4 does not depend on the kind of foreign gas (He, air, CO2 and Ar) and on the measurement technique (isothermal or dynamic). Other requirements for KMnO4 as an ideal kinetics standard are satisfied as well. The use of the third-law method for determining the molar enthalpy of a reaction
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\left( {\Updelta_{\text{r}} H_{\text{T}}^{\text{o}} / \nu } \right)$$ \end{document}
provides an excellent reproducibility of results. The mean value of
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\Updelta_{\text{r}} H_{\text{T}}^{\text{o}} / \nu$$ \end{document}
from 12 experiments in different gases is 138.3 ± 0.6 kJ mol−1, which coincides with the value of 138.1 kJ mol−1 calculated from the isothermal measurements in different gases by the second-law method. As predicted by theory, the random errors of the second-law and Arrhenius plot methods are 10–20 times greater. In addition, the use of these methods in the case of dynamic measurements is related to large systematic errors caused by an inaccurate selection of the geometrical (contraction) model. The third-law method is practically free of these errors.
Restricted access

The wide variations of calculated activation energies for solid decomposition suggests that there is no discrete activated state. Further, the statistical distribution on which the calculations are based is not a realistic concept. The lowest energy possible — and most frequently occurring — is the energy of the bulk crystal. Within the crystalline solid, vibrational interactions transfer energy so rapidly that a substantial difference from the average energy is not achievable within the crystal. The lack of a statistical distribution rules out the use of the Arrhenius equation unless it is independently verified for the particular system.

Restricted access

The thermal decompositions of nickel(II), copper(II), cobalt(II) and manganese(II) perchlorates were studied by thermal analysis and kinetic measurements. Anhydrous perchlorates could not be prepared by heating and outgassing the samples in vacuum; oxides were obtained as the main solid decomposition products. In the case of cobalt and manganese perchlorates, oxidation of the metal ions was observed during the decomposition. In most cases the decompositions of the perchlorates followed the Avrami-Erofeyev kinetics. A correlation was found between the stabilities of the perchlorates and the effective field strengths of the cations.

Restricted access

The thermal decomposition of ammonium copper chromate was studied by TG, DTG and DTA in the temperature range 30‡ to 1100‡. It was found to occur in four stages. The solid decomposition products in these stages were characterized by chemical, X-ray and IR analysis. Based on the results, a probable mechanism for the overall decomposition of ammonium copper chromate in the above temperature range is discussed.

Restricted access

Abstract  

The non-isothermal decomposition of cobalt acetate tetrahydrate was studied up to 500°C by means of TG, DTG, DTA and DSC techniques in different atmospheres of N2, H2 and in air. The complete course of the decomposition is described on the basis of six thermal events. Two intermediate compounds (i.e. acetyl cobalt acetate and cobalt acetate hydroxide) were found to participate in the decomposition reaction. IR spectroscopy, mass spectrometry and X-ray diffraction analysis were used to identify the solid products of calcination at different temperatures and in different atmospheres. CoO was identified as the final solid product in N2, and Co3O4 was produced in air. A hydrogen atmosphere, on the other hand, produces cobalt metal. Scanning electron microscopy was used to investigate the solid decomposition products at different stages of the reaction. Identification of the volatile gaseous products (in nitrogen and in oxygen) was performed using gas chromatography. The main products were: acetone, acetic acid, CO2 and acetaldehyde. The proportions of these products varied with the decomposition temperature and the prevailing atmosphere. Kinetic parameters (e.g.E and lnA) together with thermodynamic functions (e.g. °H, C p and °S) were calculated for the different decomposition steps.

Restricted access

infrared (in situ FTIR) spectra were recorded by a Nicolet MAGNA-IR 750 spectrometer using KBr pellets with the spectral range of 4000–500 cm −1 in air atmosphere. XRD experiments of the solid decomposition products of CuAc 2 ·H 2 O were carried

Restricted access

appropriate for investigation of the “solid scenario” which is of significant practical interest as LPO is stored and transported in solid phase. For this purpose, solid decomposition had to be studied using TAM at low temperatures in isothermal mode—at least

Restricted access

, balance sensitivity: ±1 × 10 −5 g, temperature accuracy: ±0.5 K, sample mass: 5 × 10 −2 g, particle size: 90–106 μm and crucible: platinum. Comparative runs were always made using samples of same age and particle size. The fraction of solid decomposed

Restricted access