Initial Sample Weight Research Articles

The effect of heating rate on the thermal degradation of polybutadiene

Using derivative thermogravimetric analysis (DTG), polybutadiene is shown to degrade by two distinct weight loss events when heated dynamically. The volatile products of the first stage are almost exclusively depolymerization products (butadiene and vinylcyclohexene). The residue—cyclized and crosslinked polybutadiene—degrades in the second stage. Increasing the heating rate or sample size results in increased depolymerization; and at a 100°C/min heating rate, up to 50% of the initial sample weight is converted to depolymerization products. Differential scanning calorimetry (DSC) indicates that degradation is exothermic in the temperature range of the first weight loss stage. The determined exothermicity (0.95 kJ/g polybutadiene) is independent of heating rate. Infrared observations show cis—trans isomerization in the same temperature range. Kinetic analysis of the DTG data yields an apparent activation energy of 251 kJ/mole for depolymerization, while for the overall reactions is the first stage, DSC data yield 170 kJ/mole. Why the exothermicity of the degradation is independent of the depolymerization/cyclization ratio is not clear.

スパッタ率測定へのマイクロバランスの応用

The torsion vacuum microbalance technique useful for the determination of the sputtering yield of wall materials for fusion reactors was developed. In order to measure the rate of weight change of the samples during sputtering continuously, it is very important to keep the null point drift of the microbalance as small as possible. The deflection angle of the balance beam was detected and amplified by optical lever, and was transformed to electrical output by linear photopotentiometer. The null point drift was mainly caused by temperature change in the laboratory, which induced relative displacement by thermal expansion between the balance system and the optical measuring system. The drift was reduced less than the equivalent weight of 4 × 10 -7 g/hr when the balance system wosset in the thermostat kept at 20 ± 0.5 °C. The sensitivity of the balance was 8.3 × 10 -7 g/mV.The microbalance technique developed was applied to the measurement of sputtering yield of Cu by Ar+. The measurement was carried out with Ar+ ion energy of 0.22 keV, beam current of 0.51.5 μA, and sputtering time of 2 hrs. The initial weight of Cu sample was 0.4g (15 mm × 15 mm sheet) and the sample temperature during sputtering was about 120 °C. The sputtering yields obtained show good agreement with the results reported by Wehner et al. [8] and Weijsenfeld [9].

Kinetics of the Thermal Dehydration of Hydrous Silicates

AbstractGenerally, the rate of dehydroxylation of clay minerals may be controlled by reaction at the interface between the decomposed and undecomposed mineral, diffusion through the decomposed phase and/or nucleation of the decomposed phase. Only in rare instances are mineral decomposition reactions homogenous. Some examples are presented to illustrate these principles.For macrocrystalline muscovite the initial sample weight rather than the external surface area was found to be a parameter of the rate of weight loss. Upon grinding the muscovite to particles smaller than — 65 mesh, an internal surface area factor strongly influenced the rate. This surface area was related to dislocations shown to be present in muscovite.A rate equation is presented that explains the observed weight loss versus logarithm of time dependence based on a model involving a systematic relief of strain during dehydration.The rate equation for pyrophyllite was exactly the same as that formulated for muscovite. As with muscovite there was a change in free energy of activation throughout the dehydration process. In contradiction to muscovite, the contribution to the free energy of activation was at least partly enthalpy while with muscovite it was an entropy of activation contribution.The dehydration of kaolinite was carried out in vacuum. At pressures of one micron the reaction was found to be diffusion controlled with hydroxyl ions as the likely diffusing species.

Direct-reading balances for percentage moisture content

This paper describes two types of balance which indicate per cent moisture content directly, and in which the initial sample weight may vary within wide limits. They have been designed primarily for measuring the moisture in wool at various stages in processing and for this purpose are used in conjunction with a hot-air drying apparatus. The same balances could be used to determine the percentage content of removable components in many other materials. An analysis of the principles of operation of the balances is given and experimental models are described.

Rate of Thermal Dehydration of Muscovite

By the use of an automatic thermogravimetric apparatus, weight loss versus time data were collected for muscovite at five different temperatures in the range 738° to 817°C. Initial sample weight rather than the external surface area was found to be a parameter of the rate of weight loss. A rate equation is presented that explains the observed logarithmic time dependence based on a model involving a systematic relief of strain during dehydration. These findings are supported by infrared spectra of muscovite in various stages of dehydration. It is also proposed that during dehydration aluminum ions in the octahedral layer shift from 6‐ to 4‐coordinated positions.