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- Author or Editor: T. Ozawa x
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Abstract
To satisfy the needs for industrial standards for thermal analysis in the Japanese polymer industry, round-robin tests of differential scanning calorimetry (DSC), thermogravimetry (TG), thermomechanical analysis (TMA) and thermodilatometry (TD) have been carried out recently. The results are discussed in this short review. The DSC applications tested were not only for determination of transition temperature but also for measurements of the transition heat and heat capacity. The TG task group did not aim at longterm thermal endurance studies, but relative thermal stability in molding and estimation of filler content, residual solvent content, etc. TMA was found to be a useful tool for measuring softening temperature and heat distortion temperature, especially for high-temperature engineering plastics, instead of the Vicat test which has temperature limitations. For temperature calibration of DSC and TG, ICTA-NIST certified reference materials were used together with other potential temperature standards; some inorganic substances and alloys were not found to be preferable to pure metals. For TMA and TD metal plates were found to be very useful for temperature calibration. Analysis of the round-robin test results also clarified present status of practical applications of thermal analysis, such as reproducibility and causes of errors.
By expanding the initial equation, it is shown that the Friedman method for estimating the activation energy of chemical reactions by using both the conversion and the rate in the thermoanalytical data has wide applicability to crystal growth from pre-existing nuclei, diffusion and other processes in which a single unit process is involved.
Abstract
Now we can use several temperature control modes, i.e., the isothermal run including stepwise heating and cooling, constant rate heating (or cooling), temperature control for sample thermal history, sample controlled thermal analysis (SCTA or controlled-rate thermal analysis, CRTA), temperature jump, rate jump, temperature modulation and repeated temperature scanning. Their advantages and drawbacks are reviewed with some illustrative examples, especially for application to kinetic analysis. The combined use of these varieties of temperature control mode is recommended by showing examples. Temperature modulation and repeated temperature scanning are discussed in comparison with temperature modulated DSC, and common and analogous points are elucidated. In relation to this, the possibility that an imaginary part of overall reaction rate constant in complex reaction is postulated. Finally,these modes are classified and tabulated from two viewpoints and other possible modes are shown.
Abstract
Temperature oscillation has been used in various applications of thermal analysis, such as relaxation, non-stoichiometry and chemical reactions. However, there are common essential points in these applications, and these are discussed in this short communication for further understanding significance of the temperature oscillation in thermal analysis.
Abstract
Repeated temperature scanning method was applied to observe non-stoichiometry of YBa2Cu3O7-d, and interesting results were obtained. Two simultaneously occurring processes were separately observed in mass change; one is a fast process and the other is slow, so that their responses to the temperature change are quite different from each other. The fast process follows the cyclic temperature change, but the slow process is observed to be a gradual mass change. Kinetic behaviors of these two processes are also made clear by plotting the mass vs. the temperature. Furthermore, a hysteresis loop was observed in the plot of the mass vs. the temperature in a high temperature range presumably due to the third process, and it depends on the heating and cooling rates.
