Thermochemical Characterization of Fine Ceramic Powders

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Thermodynamic studies have been performed for the purpose of characterization of fine powders of ceramics such as <TiO_2> and ZnO.Theoretical analysis has been given for classical DTA, power-compensated DSC and heat-flux DSC, based on a unified model which is applicable to all the three types of instruments. The method of estimating the actual temperature was shown in the case of the first-order phase transition. A principle of drawing the base line was given for determining the enthalpy of transition. Theoretical peak height due to the transition was represented as a function of the heat capacity, the thermal resistance and the heating (cooling) rate.The sample of <TiO_2> powder was prepared by hydrolysis of titanium tetraisopropoxide. The size of the particles was 0.1 - 0.3 <micro> which was examined by scanning electron microscopy. The structure was identified by X-ray diffraction. The specific surface area was determined by nitrogen adsorption. The heat of immersion in water was measured by using a heat-flux type of calorimeter. The TG-DTA experiments of the sample showed reversible dehydration on heating and hydration on cooling below about 650 K, at which a sharp exothermic peak was observed due to crystallization from amorphous state to anatase. The measurements of specific surface area and heat of immersion were made on the samples treated at various temperatures. The properties of the surface of the particles were discussed.The samples of ZnO powders were prepared by thermal decomposition of zinc oxalate and by hydrolysis of zinc ethoxide. The process of decomposition and microstructure development of the resulting ZnO powders were examined. The physicochemical properties of the surface of the particles were also studied.