Controlled grain size metal oxide varistor and process for makin

Details Controlled grain size metal oxide varistor and process for makin Controlled grain size metal oxide varistor and process for makin

1973-11-12

1976-04-27

Padgett, Benjamin R.

Compositions

Electrically conductive or emissive compositions

Free metal containing

252518, 252520, 264 61, 338 20, 428538, H01B 108

Patent

active

039533719

ABSTRACT:
Disclosed is a metal oxide varistor consisting primarily of metal oxide with a small percentage of preselected additives distributed substantially evenly therethrough. A grain growth inhibitor is combined with the metal oxide powder forming a final mix with peripheral regions having a high concentration of the inhibitor that surround and separate interior regions that have a low concentration of the inhibitor. Varistor bodies are formed from the final mix and the peripheral and interior regions retain their identities in the varistor bodies. The bodies can be pressed and sintered in the conventional manner. During sintering the grains within each interior region tend to combine and grow. However, growth is stopped at the peripheral regions due to the high concentration of inhibitor. Thus, the grain size in the processed pellet is dependent upon the size of the interior regions which can be controlled. If desired, one of the additives can be chosen to stimulate grain growth so as to promote the combination and growth within the interior regions. One preferred method of forming the interior regions is to coalesce the metal oxide powder by techniques such as spray drying and then coat the agglomerates thus formed with grain growth inhibitor.

REFERENCES:
patent: 3652378 (1972-03-01), Mistler
patent: 3663458 (1972-05-01), Masuyama et al.

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