The Preparation And Properties Of Ca-Co-O Thermoelectric Materials By Spark Plasma Sintering

The preparation, microstructure and properties of Ca2Co2O5 and Ca3Co4O9which was produced by coprecipitating and Spark Plasma Sintering and dopedCa3Co4O9 which was produced by sol-gel method and Spark Plasma Sintering werestudied in this paper. Both microstructure and properties of the products weredetermined respectively. The preparation of Ca2Co2O5 which was produced by coprecipitating and SparkPlasma Sintering was a kind of method that was very simple, fast making and unique.Less time was wasted and more easily produced by this method than by commonmethod—the method of ball milling and sol-gel. ICP was used to determine the pHvalue of the solution which was mixed by the raw materials in stoichiometric ratios.The precursor was dealed with heat treatment under different conditions. The phase ofproduction was determined by XRD method. The mixture of Co3O4, CaO andCa2Co2O5 was get after heat treatment between the temperature from 600°C and900°C. Above 900°C, Ca2Co2O5 was decomposed into Co3O4 and Ca3Co2O6. The production of heat treatment was sintered by SPS method undervarious conditions. When the temperature of heat treatment was between650°C-800°C, Ca2Co2O5 was produced after SPS at 800°C in 5 minutes. When theheat treatment condition was 750°C in 2h, Ca2Co2O5 was produced after SPS atthe temperature between 750°C to 900°C in 5 minutes as well. The microstructurewas scanned by SEM, and the density of the productions was measured byArchimedes method. The result shows that the particles of sintering productions wasincreased when the temperature was rising, while the density was decreased at firstand then, increased a bit. Thermal conductivity was decreased with the temperatureincreasing. ZT figure was increased follow the temperature. Ca3Co4O9 was prepared by coprecipitating and Spark Plasma Sintering. After heattreatment at 750°C in 2h, Spark Plasma Sintering was used to sintering Ca3Co4O9. III北京工业大学工学硕士学位论文The temperature was increased up to 850°C at a rate of 150°C/min by controlling theapplied current, under a pressure of 30MP, and lasted for 5min. La, Ce doped Ca3Co4O9 mass was prepared by sol-gel method and Spark PlasmaSintering. IR was used to determine the condition of heat treatment. The productionphase and suitable doping quantity were determined by XRD method. When x≤0.4(the doping element was La), or x≤0.3 (the doping element was Ce), the rareearth elements which take place of some Ca2+ were get into Ca3Co4O9 crystal tochange the properties of Ca3Co4O9. SEM photo shows that the microstructure of theproduction was plate-like. The thermal conductivity value of Ca3Co4O9 was muchhigher than MxCa3-xCo4O9 (M=La, Ce). The value of thermal conductivity wasincreased follow the increasing temperature, the maximum was at 500°C, and thendecreased. ZT value was increased when Ce doped, whereas decreased when Ladoped.