| http://www.w3.org/ns/prov#value | - Alternatively, water washing is sufficiently performed in a water washing step of the aforementioned step, to synthesize a preliminary powder (complex aggregate of zinc oxide and base powder) not substantially containing impurities other than a base powder and zinc oxide, and the powder is immersed in an aqueous solution containing an alkali metal salt, and dried, whereby, an alkali metal salt can
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