Preparation of Zinc Oxide Varistor by a Wet Chemical Method and Its Electrical Properties.

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In attempt to obtain chemically pure and homogenous product, a wet chem ical method has been applied to synthesize zinc oxide varistor, which is marketed by sintering after mixing of powders by a ball mill.Efficient yield was attained for precursors by a precipitation method using zinc acetate and zinc acetyl ace tonate as starting materials with praseodymium oxide and cobalt chloride as additives.Calcination process, crystalline size of zinc oxide, additives distri bution and voltage-current curve were characterized by thermogravimetric analyzer, reflected right microscope, SEM-EPMA and varistor tester.The samples sintering over 1200°C showed a decreasing tendency of the grain size of zinc oxide with the increase of praseodymium content.Uniform distribution of praseodymi um was observed for the samples obtained by the wet chemical method, especially for the samples with calcination before sintering, rather than the samples ob tained from zinc oxide and praseodymium oxide powders by using a ball mill.<BR>Non-linearity of voltage-current curve was observed for the both samples of ZnO-PrO<SUB>2</SUB> obtained by a wet chemical and a conventional ball-mill methods. The non-linearity, however, was not observed for a cobalt-added sample except for a sample containing high cobalt content obtained by a wet chemical method.
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