Programmed Heating Rate Research Articles

The deviation of the true heating rate with respect to the programmed one

The paper deals with the influence of the deviation of the true heating rate with respect to the programmed one on the values of non-isothermal kinetic parameters for the solid-gas thermal decompositions of CaC2O4.H2O and [Ni(NH3)6]Br2. An original method, based on integration over small ranges of the variables and making use of local heating rates, was applied in order to determine the non-isothermal kinetic parameter values. The results show significant differences between values of non-isothermal kinetic parameters obtained by using true local heating rates and those obtained by using the programmed heating rate.

Materials characterization by combined thermovoltaic detection (TVD) and thermal analysis (DTA) techniques

Abstract The thermovoltaic detection (TVD) technique is based on measurement of the EMF generated by two dissimilar metal electrodes in contact with the specimen This technique has recently been applied when investigating different types of materials involving thermal decomposition reactions which have more normally been studied by conventional thermal analysis techniques, such as DTA, TG, etc. This paper reports the application of the combined TVD and DTA techniques for thermal characterization of materials The Harrop DTA system has been modified such that measurements by the two techniques can be made simultaneously in the same environment. Data have been obtained on different types of materials, eg., NiSO 4·6H 2O and CoSO 4 · 7H 2O, etc., at a programmed heating rate of 10° C min −1. Results obtained by these techniques are discussed and compared with the corresponding values in the literature.

Influence of pyrolytic techniques on mass spectra of biopolymers with chemical ionization at atmospheric pressure

Three pyrolytic techniques were compared and contrasted for production of mass spectral information from the biopolymers deoxyribonucleic acid, glycogen and bovine serum albumin (BSA) in combination with an atmospheric pressure chemical ionization source of a triple quadrupole mass spectrometer. The mass spectral features of certain biopolymers were affected under oxidative conditions according to the type of pyrolysis probe, pulsed or programmed heating rate, near ambient/ambient ion source pressures (0.97–0.98 atm) and the presence/absence of an air flow over the heating zone. These factors significantly influenced the mass spectral appearance of the DNA nitrogenous base and deoxyribose moiety species and the glucose monomer, dehydration and other pyrolysis products. However, similar mass spectra were obtained for BSA with various source condition combinations and heating probes.

Effect of slurry heating rate on short-contact-time coal liquefaction

The effects of changes in heating rate of a coal/solvent slurry on conversions to pyridine-soluble material have been examined. Dramatic increases in conversions were observed when the coal/solvent mixture was maintained at a temperature of 589 K for 10 min before heating to reaction conditions of 700 K for 5 min. In particular, conversion increased from 32.0 to 76.7 wt % and the ratio of oils to preasphaltenes increased by a factor of four. The temperature range for the greatest effect is observed to be 550–595 K while 450 K shows no change in conversion. The mechanism is thought to be chemisorption of the solvent or solvent occlusion which would increase the concentration of hydrogen donor in the coal matrix thus affecting the reaction environment. Additional studies to further define the details of the programmed heating rate as well as explore the mechanism are needed.

Thermogravimetry-combustion characteristics of high-carbon fluidized-bed cyclone ashes

Thermogravimetry combustion characteristics are obtained for three samples of high-carbon cyclone ash, the samples received from an R & D fluidized bed combustion unit utilizing Ohio No. 6 bituminous coal with limestone. Non-isothermal TG combustion in air (at a programmed heating rate of 2 °C min−1) for a cyclone ash (25.0 wt% carbon) indicates two chemically different combustibles, ≈82 wt% of higher reactivity with maximum weight-loss rate at 490 °C and 18 wt% correspondingly of lower reactivity at 645 °C. Isothermal TG combustion of the same ash at 700 °C and at 850 °C also indicates the presence of the two types of combustibles and gives an Ea of about 150 kJ mol−1 for combustion of the lower reactivity type. Additionally, each of two other samples of cyclone ash (20.1 and 6.9 wt% carbon) contains two types of combustibles as evidenced by TG combustions. Non-isothermal TG combustion of feed coal, a single maximum weight loss at 440 °C, shows the coal has greater reactivity than each of the three ashes. A combustion chemistry explanation for two types of combustibles is suggested by the postulated reactivity order for the organic matter or maceral groups of coal, i.e., vitrinite ⪢ exinite ⪢ inertinite.

A parametric investigation of tar release in coal devolatilization

A parametric investigation of the effects of coal characteristics and devolatilization conditionson the tar component of volatile matter has been performed. A heated grid apparatus is employed with programmed heating rates of ∼102–103 C/sec to final temperatures of 500–1500 C. Fourteen different coals were utilized in the investigation, ranging from lignite to anthracite. The maximum tar fraction of the total volatile yield is a function of the chemical characteristics of the parent coal, amounting to ∼20% of the total volatile yield for a lignite to ∼80% for a medium volatile bituminous coal. The sensitivity of tar yields to changes in devolatilization conditions is also observed to be a function of coal characteristics. Tar formation and release is observed to be endothermic and to perturb the temperature of the grid in immediate contact with the sample. The fuel nitrogen in the parent coal is distributed proportionally in the pyrolysis products. Specifically, the mass fraction of fuel nitrogen in the tars is similar to the mass fraction of the parent coal that evolves as tar. Tar yields are reduced with increases in ambient pressure in the 10−3 to 760 torr range, with greatest reductions occurring in the 10−3 to 200 torr range. The higher pressures increase the secondary reactions of the tars resulting in an increase in light hydrocarbons in the gaseous products. Models of coal devolatilization therefore must explicitly include tar evolution and its dependence on coal characteristics, heating rate and pressure. A model should also deal with the endothermicity of the tar release process.

Temperature control in the Perkin-Elmer TGS-2/System 4

A detailed investigation has been made of the relative merits of various possible means of temperature control available with the Perkin-Elmer System 4 microprocessor controller for the TGS-2 thermogravimetric system. The dynamic compensating factor or rate parameter of the controller may be put to far more extensive use than indicated in the instrument operating manual. Temperature calibration by use of magnetic standards has enabled the development of mathematical relationships for the prediction of the appropriate value for the rate factor. Over the entire working range of the instrument and over a wide range of temperature programming rates, it is now possible to select the value of this parameter such that the sample and programmed temperatures agree within ± 2°C. Two procedures have been developed for use at low and high programmed heating rates: the fixed and variable rate factor methods. The merits of these procedures are discussed and compared with the internal calibration method.

Sensory Irritation and Incapacitation Evoked by Thermal Decomposition Products of Polymers and Comparisons with Known Sensory Irritants

A decrease in respiratory rate in mice during exposure to irritating airborne chemicals has been utilized as a response parameter to characterize the degree of upper respiratory tract irritation (sensory irritation) to the thermal decomposition products of various polymers. These included polystyrene, polyvinyl chloride, flexible polyurethane foam, polytetrafluorethylene, a fiber glass reinforced polyester resin, and Douglas Fir. Each of the materials was thermally decomposed in a low-mass vertical furnace in an air atmosphere at a programmed heating rate of 20 degrees C/min. Mice, in groups of four, were exposed to graded concentrations of the thermal decomposition products of each of the above materials. Dose-response curves were obtained by utilizing the maximum percent decrease in respiratory rate as the response parameter during each exposure. Comparison of these dose-response curves with other sensory irritants such as chlorine, ammonia, hydrogen chloride, sulfur dioxide, and toluene diisocyanate gave an indication of the sensory irrtation potential of the thermal decomposition products of these various polymers versus that of well-known single airborne chemical irritants. Total stress and incapacitation of the organism during exposure to sensory irritants such as from the thermal decomposition products of synthetic polymers is discussed.

Sensory irritation evoked by the thermal decomposition products of plasticized poly(vinyl chloride)

AbstractA decrease in respiratory rate in mice during exposure to irritating airborne chemicals has been utilized as a response parameter to characterize the degree of upper respiratory tract irritation (sensory irritation) to the thermal decomposition products of plasticized poly(vinyl chloride). The plasticized poly(vinyl chloride) was placed in a low mass vertical furnace and thermally decomposed in an air atmosphere at a programmed heating rate of 20°C min−1. The thermogravimetric study of the plasticized poly(vinyl chloride) demonstrated that two distinct weight loss fractions occurred during the decomposition process. Groups of four male swiss‐webster mice were exposed to the thermal decomposition products of the first weight loss fraction in the range 0.03–0.77 mg l−1 and to the second weight loss fraction in the range 0.03–0.38 mg l−1. Dose‐response curves were plotted by utilizing the maximum percent decrease in respiratory rate during each exposure as the response parameter. Comparison of these curves to a dose‐response curve for hydrogen chloride showed that both the first and second weight loss fraction of plasticized poly(vinyl chloride) were more potent than hydrogen chloride in terms of sensory irritation. From these dose‐response relationships qualitative and quantitative predictions of human responses to the thermal decomposition products of plasticized.

High-Temperature Thermal Gravimetric Apparatus

A thermal gravimetric apparatus is described that permits accurate weight determinations in a wide variety of atmospheres at temperatures from 50 to 1700 °C. The unique features of the apparatus are its versatility, ease of operation, high accuracy, durability, and low cost. The design can be used with either programmed heating rates or for high-temperature isothermal kinetic studies.

Differential scanning calorimetry of the epoxy cure reaction

AbstractFrom a review of the literature it is shown that kinetics from programmed heating rate experiments are often in serious disagreement with published isothermal data. In every case, including the present, the dynamic kinetic parameters measured on epoxies are significantly larger than the isothermal. Use of a dynamic rate equation provides good agreement between the two experiments. It is also shown that the Kissinger method is correct when applied to DSC of epoxies.

Thermal degradation studies of several pyrrone films

AbstractThe thermal degradation of several polyimidazopyrrolone (pyrrone) films was studied in air and in vacuum over the range of 100–1000°C. by thermogravimetric analysis (TGA), with the use of both isothermal heating and programmed heating rates of 2, 3, 5, and 7.5°C./min. At pressures of 10−6 torr or less, maximum weight losses average 30% at 800°C. Rates of volatilization and activation energies were derived to provide comparison between these ladder‐type polymers. Mass spectrometric analysis of the pyrolysis gases evolved under vacuum conditions showed that CO, CO2, and H2O were the primary volatile products and that they were formed throughout the period of weight loss. Approximate correlation between changes in weight and changes in the total pressure for the vacuum tests indicates that mass spectrometric results could provide quantitative as well as qualitative data. The importance of sample history prior to heating and of sample geometry in developing meaningful and reproducible TGA results is aptly demonstrated. The ability of these materials to absorb readily 5–7 wt.‐% of water under ambient conditions and the effect of this property upon weight loss measurements are shown.

Heating of articles in a boiling layer

1. Boiling layers can replace the heating media used in heat treatment departments. 2. In boiling layers, one can regulate the heating rate and thus have a programmed heating rate.