Non-isothermal Thermogravimetry Research Articles

Thermal analysis and kinetics of the oxidation of vanadium and titanium sulfides

Abstract The kinetics of the oxidation of “V5S8” and V3S4 to V2O3, and “TiS2” and “Ti2S3” to TiO2 was studied by using both isothermal and nonisothermal thermogravimetry. The kinetic equations are 1- (1−∞) 1 1.5 = kt for the vanadium Sulfides and [−ln (1−∞)] 1 1.5 = kt for the titanium sulfides

Studies on thermal decomposition and combustion mechanism of bagasse under non-isothermal conditions

The kinetics of thermal decomposition and combustion of bagasse was investigated by thermal analysis and gas-solid chromatography in the temperature range of 20–600°C. Apparent activation energies (Ea) and an order of reactions (according to non-isothermal thermogravimetry results) were determined. The comparative analysis of processes in inert and oxidizing media enabled the influence of oxidizing medium on the release and combustion of volatile substances to be established.

Kinetics of dehydroxylation and evaluation of the crystallinity of kaolinite

This study presents results on the kinetics of kaolinite dehydroxylation. The accuracy of various methods of determining the values for the kinetic parameters and their sensitivity in detecting the mechanism of reaction is investigated. In particular, the differential order of reaction method of Baker, the general method of Achar et al., the integral method of Boy and Bohme, and the method of Coats and Redfern as modified by Fong and Chen are considered. Kaolinites from well-known sources are used to study the influence of crystallinity on the values of kinetic parameters. The statistical significance of the various mathematical methods for the assessment of the data obtained from non-isothermal thermogravimetry is determined by comparison with experimental and theoretical data using a computer programme developed for this purpose. The study demonstrates that the kinetic parameters can be used to quantify the degree of crystallinity of kaolinite and also confirms other findings that the dehydroxylation of kaolinite is a second-order reaction.

Effectiveness of SO 2 sorbents by thermogravimetry-combustion with coal

A new experimental method is described for non-isothermal thermogravimetry (TG) involving combustion of mixtures of sieved coal with sieved calcium-containing sorbents. This rapid TG method utilizes a baseline for TG combustion of coal alone, derives an equation that gives a semi-quantitative measure (±10% repeatability) of the coal's reactive sulphur retained by the sorbent, the extent of retention of S0 2 generated in situ during combustion varying with different sorbents. The method permits direct variation in separate experiments of the calcium-to-sulphur ratio during combustion and relative ranking of different sorbents by retention of reactive sulphur in combustion. Relative rankings are presented for three pre-calcined natural stones (two limestones and one dolomite); these results correlate with relative rankings from another TG method reported in the literature. It is suggested that this new method is useful for pre-screening the effectiveness of S0 2 sorbents considered for use in fluidizedbed combustion of coal.

Thermal analyses of Ohio bituminous coals

A suite of twenty-one bituminous coal samples from Ohio were analyzed by differential scanning calorimetry (DSC) and non-isothermal thermogravimetry (TG) techniques. Three regions of endothermic activity may be distinguished in the DSC scans in an inert atmosphere. The first peak (25–150°C) corresponds to loss of moisture from the coal, a second, very broad endotherm peaking in the range 400–500°C corresponds to devolatilization of the organic matter and a partially resolved endotherm at temperatures above 550°C probably corresponds to cracking and coking processes subsequent to the pyrolysis step. Evidence obtained from experiments with sealed pans suggest an autocatalytic effect exerted by the pyrolysis products. The use of the DSC technique to quantify the volatile matter content of coal seems less reliable than the proximate analyses obtained from non-isothermal TG in inert and O 2 atmospheres. Good agreement with ASTM values is observed by the latter method for a range of volatile matter and ash content.

The kinetics of the thermal decomposition of green river oil shale kerogen by non-isothermal thermogravimetry

The kinetics of the thermal decomposition of Green River oil shale kerogen have been studied by non-isothermal thermogravimetry. Kerogen decomposes to a bitumen intermediate with an activation energy of 62.10 kJ mole −1 and a frequency factor given by ≈10 6 min −1. The pyrolytic bitumen decomposes into oil, gas and carbonaceous residue with an activation energy of 152.16 kJ mole −1 and a frequency of ≈10 14 min −1. The weight loss data were analyzed by the direct Arrhenius, Coats—Redfern and Freeman—Carroll techniques. The kinetic parameters derived from the three methods are discussed in the light of previous work on the thermal decomposition kinetics of oil shale kerogen. Factors influencing kinetic data such as sample holder geometry, heating rate and atmosphere are critically reviewed. The concept of kinetic order is examined in the light of existing theory for solid-state decomposition reactions and it is shown that first-order kinetics are adequate in explaining the overall trends in the thermal behavior of Green River oil shales.

Effects of heating rate (1–300° h −1) on the non-isothermal thermogravimetry of CuSO 4 · 5 H 2O

The course of the reaction CuSO 4 · 5 H 2O − CuSO 4 · H 2O + 4 H 2O was studied by non-isothermal thermogravimetry with various heating rates ranging from 1 to 300° h −. The measurements were made either in static air, in a dry nitrogen stream, or in water vapor at a reduced pressure (9 mm Hg). In static air, the shape of the TG curve changed drastically at a heating rate of 13 to 15° h −, and this change was explained by considering the nature of the plateaus and inflections present. In a dry nitrogen stream, the dehydration is made much easier at slow heating rates and occurs almost in one step at 2° h −; in water vapor at 9 mm Hg, on the other hand, a very distinct two-step curve is obtained at 1° h −. This can reasonably be compared with the phase diagram of copper sulfate.

Interpretation of quasi-isothermal thermogravimetric weight curves

Quasi-isothermal analysis (QIA) is a very useful technique. Compared to conventional non-isothermal thermogravimetry, close-lying reactions can easily be separated by use of this method and kinetic data can be obtained for each intermediate reaction in a single run. This paper discusses the shape of the weight and temperature curves expected in QIA for different controlling mechanisms, and a method is given for calculating the activation energies from these curves. As an example, the QIA curves obtained in thermal decomposition of ammonium-uranyl carbonate (AUC) are analysed and the kinetics of some of the intermediate reactions are determined.

Thermal decomposition studies: Part X. Thermal decomposition kinetics of calcium oxalate monohydrate — correlations with heating rate and samples mass

Quantitative correlations between kinetic parameters (energy of activation E, pre-exponential factor A) and procedural factors (heating rate, sample mass) in non-isothermal thermogravimetry have been made for the first time. The effect of heating rate and sample mass on the first two stages of thermal decomposition of calcium oxalate monohydrate in a nitrogen atmosphere ▪ has been evaluated in detail using non-isothermal thermogravimetry. Kinetic parameters are calculated from the TG curves using three integral methods (two “exact” and one “approximate”). The values obtained by the “approximate” method are higher than the corresponding values from the “exact” integral methods. For the decomposition of calcium oxalate to carbonate, the kinetic parameters are not much affected by heating rates or sample masses in the ranges studied. For the dehydration of CaC 2O 4 · H 2O, the parameters show a systematic decrease with increase in either heating rate or sample mass. The values of E and log A obtained by all three equations are best correlated to heating rate as rectangular hyperbole of the type: ▪ The best fits for correlation to sample mass are parabolae of the type E (or log A) = constant × (mass) 2 − constant × mass ÷ constant SYMBOLS USED A = pre-exponential factor α = fraction decomposed φ = heating rate in deg min −1 E = energy of activation n = order parameter R = gas constant T i = temperature of inception of reaction T f = temperature of completion of reaction T s = DTG peak temperature Δ T = T − T s

Kinetics of thermal decomposition of some metal oxalates

The thermal decomposition kinetics of oxalates of Zn II, Ni II and Th IV have been studied in air by isothermal and non-isothermal thermogravimetry. The isothermal kinetic results suggest that the mechanism of decomposition of the zinc compound involves rapid nucleation followed by two dimensional growth in the acceleratory region, while in the case of thorium oxalate, the initial nucleation occurs by a chain mechanism on the surface of the reactant followed by the growth of the product from the surface towards the interior. The results on nickel oxalate could not be interpreted in an unambiguous manner. The activation energy and the frequency factor obtained from TG curves compare well with those obtained from the isothermal method. The activation energies for the dehydration of these oxalates have also been evaluated from the thermogravimetric curves.