Takeo Ozawa

Estimation of activation energy by isoconversion methods

Abstract There are three isoconversion methods in which relations at a given conversion and at the maximum rate of conversion are used for estimating activation energy. It is shown that they can be derived from a common fundamental equation which includes the reduced time. The wide applicability of these methods is a result of the general form of this fundamental equation. The logical interrelation among these methods is described, and comparison is made of their applicability and accuracy. Further usefulness of the reduced time is discussed.

Thermal analysis — review and prospect

The history of thermal analysis is briefly reviewed, focusing on fundamental aspects, such as quantitative measurement by DTA, kinetics, purity determination, sample-controlled thermal analysis and temperature modulation. Several general trends, commonly seen in the history of thermal analysis, are also pointed out. Among these trends are new techniques, new application fields, diffusion of the techniques from research to quality assurance, computerization and robotics, infrastructure, such as standardization, etc. In this overview, new techniques and methods of thermal analysis are examined and directions of future progress are anticipated for its sound development.

Non-isothermal kinetics and generalized time

Abstract The fundamental equations for non-isothermal kinetics of various processes are reviewed. They are the same in their mathematical form as the isothermal kinetic equation, and time is replaced by generalized time. The independent variables contained in the equations are only generalized times, which determine the conversion of the process. The usefulness of this concept of generalized times is discussed, and they are found to be useful for the systematic description of non-isothermal processes as well as for prediction and control. The essential prerequisites to sound kinetic analysis of thermoanalytical data are briefly discussed.

Kinetic analysis by repeated temperature scanning. Part 1. Theory and methods

A repeated temperature scanning thermal analysis, such as temperature-modulated thermogravimetry, is a useful technique for the kinetic analysis of thermal decomposition in a defined temperature range. In this technique, repeated temperature scanning, i.e., cyclic heating and cooling in a defined temperature range, is introduced into thermal analysis. First, the kinetics for this new mode of temperature change are considered theoretically, and some useful relations for kinetic analysis are revealed. From these relations, methods for estimating kinetic parameters, such as the activation energy, the pre-exponential factor and the conversion functions, are derived. The errors in these parameters are also examined.

Linearity and non-linearity in DSC: A critique on modulated DSC☆

Abstract Recently a new interesting technique, modulated differential scanning calorimetry (MDSC), was published. This technique is based on Fourier transformation, and its sound applicability depends on linearity in thermal processes, because the Fourier transformation is based on linearity or the superposition principle. If a process under observation is a non-linear process, the physical meaning of the Fourier transformation should be closely examined. The DSC output signals of some processes, such as melting and reaction, have been revealed to be non-linear. Therefore, differentiation of linearity from non-linearity in DSC thermal responses is very important for modulated DSC, and they are discussed in this paper. In this discussion, methods to analyze oscillating output signals are also proposed.

Volatility of metal β-diketonates for chemical vapor deposition of oxide superconductors

Abstract For chemical vapor deposition, in which vapors of metallic organic compounds are introduced and decomposed over a substrate to form thin films, data on the volatility of the compounds are of essential importance as basic data. Thermal analysis is a useful tool for observing volatility. The application of thermal analysis, and the results for metal β-diketonates with respect to chemical vapor deposition of oxide superconductors are summarized. Problems to be solved are also pointed out.

The effect of magnetic field on the oxygen reduction reaction and its application in polymer electrolyte fuel cells

Abstract The effect of magnetic field gradients on the electrochemical oxygen reduction was studied with relevance to the cathode gas reactions in polymer electrolyte fuel cells. When a permanent magnet was set behind a cathode, i.e. platinum foil or Pt-dispersed carbon paper for both electrochemical and rotating electrode experiments and oxygen was supplied to the uphill direction of the magnetic field, electrochemical flux was enhanced and the current increased with increasing the absolute value of magnetic field. This magnetic effect can be explained by the magnetic attractive force toward O2 gas. When magnet particles were included in the catalyst layer of the cathode and the cathode was magnetized, the current of oxygen reduction was higher than that of nonmagnetized cathode. A new design of the cathode catalyst layer incorporating the magnet particles was tested, demonstrating a new method to improve the fuel cell performance.

Heat capacity measurements by dynamic differential scanning calorimetry

Abstract Dynamic differential scanning calorimetry (d-DSC) has attracted much attention, and it was postulated that high-precision heat capacity measurements can be made by this technique. However, its applicability, accuracy and precision have not yet been made clear. Because it is based on Fourier transformation, it can be applied to linear thermal responses. The dynamic steady state and the base line, from which the heat capacity is estimated, demonstrate a linear response in DSC, so that the dynamic steady state has been theoretically considered by analytical methods, and analytical solutions have been derived for the dynamic steady state and hence for the heat capacity measurement. For further examination, numerical solutions have also been obtained by taking account of other factors, which may potentially influence the measurements. In conclusion, a few points should be considered in the high-accuracy heat capacity measurements, because some factors, which have not been considered before, affect the dynamic steady state or the base line. Furthermore comparison has been made between d-DSC and conventional DSC in this research.

Investigation of latent heat thermal energy storage materials: V. thermoanalytical evaluation of binary eutectic mixtures and compounds of NAOH with NaNO3 OR NaNO2

Abstract Differential scanning calorimetry was applied to the evaluation of binary eutectic mixtures and compounds of NaOH with NaNO 3 or NaNO 2 as latent heat thermal energy storage materials. There are two compounds and three eutectic mixtures consisting of NaOH and NaNO 3 and one compound and two eutectic mixtures consisting of NaOH and NaNO 2 . The heats of fusion of all compounds and mixtures were more than 200 J g −1 . The thermal behaviour of these materials was observed, and some compounds and mixtures show a great tendency to supercool. The specific heat capacity was also measured. Because the eutectic mixture 18.5 mol.% NaNO 3 -81.5 mol.% NaOH is the most promising material for use in a nuclear power plant, this mixture made from industrial products was examined further. After 1000 cycles of melting and crystallization in bench-scale equipment the material shows little change.

Application of thermal analysis to kinetic study of superconducting oxide formation

Abstract Study of superconducting YBa 2 Cu 3 O 7 oxide formation by TG, DTA, EGA and X-ray diffraction is described. Especially, final stage of forming reaction with evolution of CO 2 from BaCO 3 is investigated by changing starting materials, such as coprecipitated carbonate, coprecipitated oxalate, homogeneous solution of 2-ethylhexanoates and powder mixture of Y 2 O 3 , CuO and BaCO 3 . Phase boundary contracting reaction proceeds for precursors from the coprecipitates, and diffusion controlled reaction for the precorsur from the solution, while multiple parallel processes proceed for the powder mixture.