Date of Award

Summer 1980

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)


Mechanical Engineering


The thermal conductivity of ZnO based ceramic varistors was characterized under steady state conditions. Studies were performed as a function of grain size at constant composition, as a function of composition at constant grain size, and as a function of post sintering heat treatment. In order to maintain constant composition, the starting additives to ZnO were varied such that the final composition of the samples, in terms of the metallic constituents, was about 2.02% Sb, 1.95% Bi, 1.69% Co, 1.45% Ni, 0.8% Cr, and 0.64% Mn, plus 91.45% Zn. Composition variations at constant grain size were obtained by progressively increasing the constituents other than ZnO, and decreasing the concentration of ZnO accordingly. Thus, the amount of boundary phase material could be increased without appreciably varying the composition of this material. The grain size of these specimens was held constant by sintering at constant temperature for varying the intervals. Post sintering heat treatments consisted of reheating the samples to a temperature of 600°C for a period of one hour. These studies reveal that the thermal conductivity of ZnO- based ceramic varistors increased with an increase in grain size, and with a decrease in the amount of boundary phase material and specimen porosity. The post sintering heat treatment led to an increase in the thermal conductivity.



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