Search Results

You are looking at 1 - 10 of 4,463 items for :

  • "decomposition" x
  • Refine by Access: All Content x
Clear All

Abstract  

An investigation was carried out on the kinetics of thermal decomposition of plumbo-jarosite. The kinetic models of dissociation of the compounds in the ore were identified. The results of the kinetic studies and the mechanism of the process are discussed. The thermal decomposition of plumbo-jarosite occurs in three stages: the first up to 763, the second up to 1023 and the third up to 1223 K, the corresponding activation energy values being 62.2, 60.3 and 98.0 kJ mol–1 , respectively.

Restricted access

Abstract  

We study the hyperbolicity of metric spaces in the Gromov sense. We deduce the hyperbolicity of a space from the hyperbolicity of its “building block components”. These results are valuable since they simplify notably the topology of the space and allow to obtain global results from local information. We also study how the punctures and the decomposition of a Riemann surface in Y-pieces and funnels affect the hyperbolicity of the surface.

Restricted access

Kinetic analysis of thermal decomposition of magnesite

Influence of generated defects and their annealing

Journal of Thermal Analysis and Calorimetry
Authors: V. Jesenák, L. Turčániová, and K. Tkáčová

The excess enthalpy of magnesite accumulated by vibration grinding at low specific grinding energy consumption is due predominantly to an increase in specific surface area; at higher energy supply, it is caused by changes in the X-ray amorphous phase content, and when the supplied energy exceeds ca 2000 kJ kg−1 it is a result of the generation of other kinds of defects. The generated defects are relatively stable below 800 K and are the reason for a broad range of distribution of local molar Gibbs energies. Thus, at low temperatures only the ‘active’ portion of samples is able to decompose. Defects relax above ca 800 K, with rates comparable with the rate of decomposition itself. Accordingly, the efficiency of mechanical activation is impressive only below this temperature.

Restricted access

Abstract  

An isothermal method was applied to measure the thermal decomposition of reactive solids in a sensitive heat flux reaction calorimeter, C80. This technique experimentally clarified the decomposition mechanisms of unstable substances based on the shapes of the heat flow curves, from which autocatalysis, first-order reaction or pseudo-autocatalytic reaction could be recognized. Kinetic parameters were derived from the measured data.

Restricted access

Abstract  

Forest fires are a plague for all countries in the world. Many factors can induce them. The organic matter (‘fuel’) in the plant, is often responsible for the start of the fire. The bio-polymers and mainly the cellulose decompose at about 300C with flammable evolved gas. This decomposition is first order, and the activation energy is about 180 kJ mol−1 . On the other hand, the degradation of the lignin seems more complex, but we observed on many samples, a linearly decomposition of the lignin vs. the heating rate (in the interval close to the start of the forest fire, 300 to 3000C h−1 ). The decomposition of the plant during the heat is mainly dependent on the cellulose level. This degradation is also slightly dependent on the lignin level mainly if the lignin present in this plant is less stable.

Restricted access

Abstract  

At TNO Prins Maurits Laboratory the characterisation and application of energetic materials is one of the main research topics. In this respect, the activities are focussed on using thermal analysis techniques such as TG/DTA and DSC. Standard DSC and TG/DTA techniques usually apply a linear temperature increase. During this gradual temperature change, the sample may pass certain phase changes related to different crystal structures, followed by a melting/decomposition of the material. In this way physicochemical properties like phase change temperatures, melting point, enthalpy of melting, decomposition temperature, etc. can be determined. By applying different heating rates, an analysis of the decomposition kinetics can be performed as well, which gives additional information on the decomposition process of the material. In this way the activation energy of the decomposition process and the 'shelf-life' of the material, when stored at a certain temperature, can be assessed. In a co-operation with the Technical University of Aachen, two relatively new and promising energetic materials were investigated: FOX-7 and HNF. FOX-7, or 1,1-diamino-2,2-dinitroethylene, is a less sensitive explosive, which could find application as a substitute of RDX (less sensitive but with preservation of performance). Hydrazinium nitroformate (HNF) is an oxidiser with potential use as a high-performance, chlorine-free ingredient in rocket propellants. The results of the TG/DTA and DSC tests, as well as the results of the analysis of the decomposition kinetics of these two materials, will be reported and discussed in this paper.

Restricted access

Abstract  

The thermal decomposition of poly(α,α,α′,α′-tetrafluoro-p-xylylene) (parylene AF-4) films with thicknesses of ca. 7.5 and 10 μm has been studied by both dynamic (10°C min−1) and isothermal TG in either nitrogen or oxygen atmospheres. In dynamic studies with nitrogen, gross decomposition occurs between 546.7±1.4 and 589.0±2.6°C, with 26.8±4.4% of the initial mass remaining at 700°C. With oxygen as the purge gas, the onset of decomposition shifts slightly to 530.8±4.2°C. The end of the transition at 587.4±2.6°C is within experimental error of the nitrogen value, but no polymer remains above 600°C. Isothermal data were obtained at 10°C intervals from 420 to 490°C in nitrogen, and from 390 to 450°C in oxygen. Plots of log(Δ%wt/Δt)vs. T−1 are linear throughout the specified range for oxygen and from 420 to 470°C for nitrogen. The calculated activation energies of (147±16) kJ mol−1 and (150±12) kJ mol−1 in N2 and O2, respectively, are equal within experimental error.

Restricted access

Abstract  

The objects for the studies of this paper are iron sulfates where the iron has second or third valences and where coordination between iron, sulfur and oxygen is different. DSC technique is used to investigate thermal stability and enthalpy changes when iron compounds are treated in different gas medium. The main objective is to compare thermal stability and enthalpy of iron oxy-sulphate, often detected as an intermediate, with commonly known iron sulphates. DSC curves of samples with equal mass under different gas medium, determining different partial pressure of oxygen in the gas phase, are the base for comparative study of the sample’s thermal properties. Obtained different values of the enthalpy and mass losses and kinetic parameters demonstrate that the stability of oxy-sulphate strongly depended on the value of oxygen partial pressure in the gas phase. The new evidences from the experimental study help to propose the mechanism of the decomposition and to compare some of the iron sulphates properties.

Restricted access

Abstract  

The paper describes the synthesis, characterization and thermal decomposition of nickel(II) bis(tartrato) nickelate(II) heptahydrate [Ni2(C4H4O6)2]·7H2O. The complex was characterized by elemental analysis, magnetic moment measurement, infrared, ESR and electronic spectroscopy. The experimental evidences indicate that complex is likely to have metal bonding. The thermal decomposition of the complex produced NiO in air at about 360°C and in nitrogen at about 380°C as the final product. Some of the intermediates produced during the thermolysis were isolated by temperature arrest technique and identified by analytical and spectroscopic methods. A tentative reaction mechanism is proposed for the thermal decomposition of the complex in air and nitrogen.

Restricted access

The thermal decomposition of the ferric and nickel acetate salts has been followed. It was found that the heating rate affects the decomposition steps. For a heating rate of 1 K min−1 the product is either Fe2O3 or NiO. For a higher heating rate the suboxides are obtained and reoxidized again on further heating. The decomposition of the mixed salt is an overlap of the DTA for the separate salts but the decomposition reactions are shifted to lower temperatures.

Restricted access