Showing papers on "Thermogravimetric analysis published in 1982"

Kinetics and mechanisms of the oxidation of cobalt at 600–800°C

Abstract: Two-phase layered scales comprising CoO and Co3O4 formed on cobalt during oxidation at 600°, 700°, and 800°C and at oxygen partial pressures in the range 0.001–1 atm. The kinetics, which were obtained by thermogravimetric analysis, obeyed a parabolic rate law after an initial, non-parabolic stage of oxidation. The monoxide consisted of relatively large grains (∼10 μ) and the spinel comprised small grains (⪝3 μ) for all conditions of oxidation. Grain boundary diffusion of cations played a significant role in the growth of the spinel layer. Thermogravimetric data and the steady-state ratio of the oxide layer thicknesses were employed to calculate the rates of thickening of the individual oxide layers and the rate of oxidation of CoO to Co3O4.

Development of a Kinetic Model for In-Situ Combustion and Prediction of the Process Variables using TGA/DSC Techniques

Abstract: This paper describes the development of a kinetic model of the in-situ combustion process from data obtained from Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry A crude oil from Iola County, Kansas, was studied. This oil has a gravity of 19.8/sup 0/ API and a viscosity of 222 cp at 38/sup 0/C and 89 cp at 54/sup 0/C. Data from TGA experiments on Iola crude heated in the presence of air were obtained. Analysis of combustion gases from the TGA was done by gas chromatography to determine the nature of the reactions occurring during the TGA runs. Main reactions/transitions identified were distillation, low temperature oxidation, cracking and combustion. A kinetic model of the TGA process was developed from thermograms. The model is based on the weight of crude oil components which undergo main reactions/transitions. The kinetic model was used to predict the percentage of the crude oil deposited as fuel in the combustion process as well as the time for consumption of the fuel within the combustion zone. By estimating the length of the combustion zone from an energy balance across the region where combustion reactions take place in a combustion tube, it was possible to predict the rate atmore » which fuel was consumed during the process. A combustion tube run was made with silica sand containing 8.0% by weight Iola crude oil in order to test the prediction by the kinetic model derived from thermal analysis techniques. Results of the combustion tube run were in good agreement with predicted values of this work and another run from the literature which was performed on the same crude oil.« less

X‐ray Diffraction as a Tool for Studying Stoichiometry and Kinetics of Solid State Thermal Decomposition Reactions. Application to the Thermal Decomposition of Bischofite MgCl2 · 6H2O

Abstract: High temperature in situ X-ray diffractometry of polycrystalline samples is shown to be a very convenient method both for identification of the various stages of a complicated thermal decomposition reaction and for determination of the kinetics of each stage of the reaction. This method when used together with thermogravimetric and chemical analyses has enabled us to determine the stoichiometry and kinetics of the various stages in the thermal decomposition of bischofite (MgCl2 · 6H2O) to periclase (MgO) in atmospheres of dry nitrogen, moist air and dry steam. The overall reaction rate determined in the laboratory for the conversion of MgCl2 · 6H2O to MgO is similar to that found in industry.

Non-stoichiometric disorder in ?-Nb2O5 at elevated temperatures

Abstract: The electrical conductivity of polycrystallineα-Nb2O5 was determined for the oxygen partial pressure range of 100 to 10−20 atm and temperature range 700 to 1150 ° C. The data were found to be proportional to the −1/6th power of the oxygen partial pressure for the oxygen pressure range 10−20 to 10−9 atm, and proportional toPO2−1/4 for oxygen pressures greater than 10−9 atm. The region of linearity where electrical conductivity varies as the −1/4th power of\(P_{O_2 } \) increased as the temperature was decreased. Thermogravimetric measurements were carried out in the temperature range 950 to 1250 ° C. The deviation from stoichiometry inα-Nb2O5 (x in Nb2O5−x) as a function of partial pressure of oxygen showed two distinct regions, namely a region with an approximately −1/6th dependence on\(P_{O_2 } \) and a region where the deviation was nearly independent of oxygen partial pressure. The electrical conductivity and thermogravimetric data are consistent with the presence of small amounts of acceptor impurities inα-Nb2O5.

Kinetics of vaporization of lead sulfide

Abstract: The kinetics of vaporization of lead sulfide were investigated in the temperature range 785 to 993 °C using a thermogravimetric balance. The effect of nonreactive ambient atmosphere on the vaporization kinetics was examined in some detail. Under He-rich He-N2 atmosphere the rate of vaporization was found to be about four times as large, as that under N2-atmosphere. A mathematical model was developed taking into consideration the chemical kinetic and mass-transfer factors. It was found that faster vaporization rates obtained with He-rich atmosphere are due to the higher diffusivity of PbS(g) in He(g). The chemical kinetic aspects of vaporization appear to be unaffected by the ambient atmosphere. The activation energy for vaporization has a value of 198.95 kJ·mole-1 in the temperature range investigated. The evaporation coefficient was found to have values ranging from 0.05 to 0.14.

Thermogravimetric analysis of Swedish shale char. Kinetics of the steam-carbon and carbon dioxide-carbon reactions

Abstract: The kinetics of gasification of shale char from the Swedish Ranstad deposit have been investigated at atmospheric conditions in the temperature range 800-1000/degree/C by thermogravimetric analysis. The reaction rate of fixed carbon can be described by modified Langmuir-Hinshelwood expressions. Similar to coal, strong retarding effects of hydrogen and carbon monoxide were found. The catalytic effect of impregnation with potassium and calcium salts was found to be of minor importance in the temperature range 850-940/degree/C. 19 refs.

Phthalocyanine polymers. III. Poly(nickel phthalocyanine)benzimidazole as a novel high‐temperature‐resistant polymer

Abstract: A new type of poly(nickel phthalocyanine)benzimidazole was prepared by the condensation reaction between nickel (11) 4,4′,4″,4″′-phthalocyanine tetracarboxylic acid dihydrate and 3, 3′-diaminobenzidine. The reaction was investigated by both the melt and solution condensation methods. This polymer showed good thermal and thermo-oxidative stability. Also noteworthy is its high thermal stability with a char yield of 88% at 800°C in nitrogen. No catastrophic decomposition was observed up to 1100°C. A qualitative study of decomposition in both air and nitrogen is presented. Elemental analyses agreed well with the proposed structure. Infrared (IR) and thermogravimetric analysis (TGA) studies were performed to characterize this polymer, and isothermal gravimetric analysis was done to determine its long-term thermal stability. The apparent activation energies for the thermal degradation in air and nitrogen are given.

Kinetics of the thermal degradation of polyimides

Abstract: A number of temperature and kinetic parameters of thermal degradation of polyimides over the temperature range from 20 to 1000° have been determined on the basis of thermogravimetric investigations of a polyimide sample obtained from pyromellitic dianhydride and diaminodiphenyl ether. It was shown that such kinetic parameters as the reaction order and the activation energy of thermal degradation are directly dependent on the conditions under which the thermal analysis is carried out. It was found that when the static and dynamic conditions of the environment of a polymer sample are varied, the thermochemical processes occurring in a polyimide over the temperature range investigated are drastically changed.

Adsorption and decomposition of iron pentacarbonyl on Y zeolites

Abstract: The adsorption isotherms of Fe(CO) 5 on NaY and HY zeolites obtained in McBain balances show micropore adsorption, the saturation at p/p 0 = 0.5 being 39 and 42% per dry wt, respectively. IR results indicate a restricted mobility of the encaged complex. Nevertheless it can thermally be desorbed to a great extend in vacuum. For the first time, well distinguishable decomposition phases of zeolite- adsorbed Fe(CO) 5 , are found by thermogravimetric analysis. These phases are associated with species bearing 2(4) and 1/4(1) CO ligands per Fe in the case of NaY(HY). New evidence is found for the intermediate Fe 3 (CO) 12 . The slow decomposition reaction in inert atmosphere is completed already between 70 and 90°C, providing an iron content of 10.5 ± 0.5 wt%.

A thermal analysis study of bisphenol-A-polycarbonate–dimethylsiloxane block copolymers

Abstract: The thermogravimetric analysis (TGA) of three block copolymers of poly(dimethylsiloxane)–Bisphenol-A-polycarbonate was measured in nitrogen and air from just above room temperature to 1000 K. Measurements were made on a Perkin-Elmer TGS-2 system equipped with a System 4 microprocessor controller. Weight loss curves were obtained for heating rates ranging from 1.5 (or lower) to 80°C/min. Results were analyzed according to the method of Flynn and Wall. Two degradation reactions were observed in air and in nitrogen, respectively. In air, the activation energy was found to be 28–35 kcal/mol. In the inert atmosphere, activation energies were 44±3 kcal/mol and 11–27 kcal/mol, respectively. No straightforward relationship was found between the thermal stability of the copolymers and their composition. The morphology of char residues formed at 80°C/min heating rate to 1000 K have been examined in relation to the Si content. The degree of char formation at different heating rates has been established in nitrogen and in air, respectively.

Difference method of evaluation of dynamic integral thermogravimetric curves in decomposition of polypropylene

Abstract: A new differential method of evaluating integral thermogravimetric records of the formation of volatile products during the degradation of polypropylene in air is presented. The method, applied to 0–100% conversion of the polymer to volatile products, may distinguish the initial presence of low molecular compounds in the polymer, as well as changes in the mechanism of degradation of the material.

Thermogravimetric study of the defect structure of β-Ta2O5

Abstract: The defect structure of β-Ta 2 O 5 was investigated by measuring the mass change as a function of the oxygen partial pressure P O 2 (10 −18 −10 −8 atm) in the temperature range 1000–1200 °C The deviation from stoichiometry ( x in Ta 2 O 5− x ) as a function of the partial pressure of oxygen showed two distinct regions, namely a P o 2 −1 6 dependence and a region nearly independent of the oxygen partial pressure The observed thermogravimetric data are described by a majority defect model consisting of doubly ionized oxygen vacancies and the accidental acceptor impurities present in the undoped samples

Thermal characteristics of poly(ethylene terephthalate) fiber grafted with poly(vinyl acetate) and poly(vinyl alcohol)

Abstract: Poly(ethylene terephthalate) (PET) fibers were grafted with poly(vinyl acetate) (PVAc) and poly(vinyl alcohol) (PVA). The effects of graft copolymers PVAc and PVA on morphological properties of PET were evaluated by differential thermal analysis, differential scanning calorimetry, and thermogravimetric analysis. Melting temperature, heat of fusion, and mass fractional crystallinity of PET was not affected by graft PVAc and PVA. No individual glass transition and melting points corresponding to the graft PVAc and PVA were observed, indicating thereby that graft copolymer mainly exists in the form of free chains inside the PET matrix. Poly(vinyl alcohol) graft copolymer degraded at much lower temperatures than poly(vinyl alcohol) in powder form. Thermal stability of PET fiber was not affected by graft PVAc, where as PET–g–PVA showed an additional degradation point at 360°C.

Synthesis of brominated acenaphthylenes and their flame‐retardant effects on ethylene–propylene–diene terpolymer

Abstract: Bromoacenaphthylenes and their condensates as flame-retardant reagents were synthesized by bromination of acenaphthylene using ZnCl/sub 2/ - CF/sub 3/COOH or FeCl/sub 3/ as catalysts and subsequent dehydrobromination. The chief components were identified as bromoacenaphthylene monomers when ZnCl/sub 2/ - CF/sub 3/COOH were used, and as their condensates (mostly trimers) in the case of FeCl/sub 3/. Their performance as flame-retardant reagents for ethylene-propylene-diene terpolymer (EPDM) was evaluated by measuring the oxygen index of finished compounds, and flammability by a vertical flammability test based on UL-94-VO. Both the monomers and the condensates demonstrated high flame-retardant effectiveness. The high efficiency was attributed to their excellent dispersity in the base polymer and their characteristic thermal decomposition behavior. In thermal gravimetric analysis (TGA), they decomposed in a very wide range of temperature (ca.200-560/sup 0/C), which covers the decomposition range of EPDM. This was attributed to the existence of bromines of different thermal stabilities in one molecule. This paper is a part of a series of studies to develop new flame retardants which can give high flame retardancy as well as stabilty against ionizing radiation to EPDM.