Thermochemical Characterization of Fine Ceramic Powders

热力学研究的目的是表征陶瓷的细粉末，如<TiO_2>和ZnO。基于一个适用于三种仪器的统一模型，对经典差热分析、功率补偿差热分析和热通量差热分析进行了理论分析。给出了一阶相变时实际温度的估计方法。给出了确定转变焓的基线绘制原则。由于转变的理论峰值高度表示为热容量，热阻和加热（冷却）速率的函数。采用四异丙醇钛水解法制备了<TiO_2>粉体样品。扫描电镜检测颗粒尺寸为0.1 ~ 0.3 <微>。该结构经x射线衍射鉴定。比表面积采用氮吸附法测定。用热通量式量热计测量了浸水热。TG-DTA实验表明，样品在650 K以下加热时可逆脱水，在650 K以下冷却时可逆水化，在650 K以下由无定形结晶到锐钛矿，出现了一个明显的放热峰。对不同温度下处理的样品进行了比表面积和浸没热的测量。讨论了颗粒的表面性质。采用草酸锌热分解和氧化锌水解法制备氧化锌粉体。对制备的氧化锌粉末的分解过程和微观结构进行了研究。研究了颗粒表面的物理化学性质。

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.