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US 4,048,294 AGranted
Preparation of stannic oxide
AssigneeM&T Chemicals Inc.
InventorsCarl R. Gloskey, Stanley Littman
Life of this patent
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Abstract
An improved method is provided to reproducibly obtain stannic oxide of a type suitable for polishing plastic lenses. The optical density, bulk density and color of the oxide are within specified limits.
Claims1
A method for preparing particulate stannic oxide exhibiting an optical density of between 200 and 400, a bulk density of between 6.3 and 9.0 grams per cubic inch, and a Gardner color of between 3 and 6, said method comprising the steps of
- a. maintaining a uniformly agitated aqueous solution of sodium stannate exhibiting a pH of between 8 and 9,
- b. gradually adding to said uniformly agitated solution over a period of between 5 and 15 minutes a stoichiometric amount of an aqueous solution containing an alkali metal bicarbonate, thereby precipitating hydrated stannic oxide, and isolating said stannic oxide,
- c. washing the precipitated oxide with an aqueous solution of sodium carbonate,
- d. washing the precipitated oxide with aqueous sulfuric acid exhibiting a pH between 3.5 and 4,
- e. calcining the hydrated stannic oxide at a temperature between 950.degree. and 1050.degree. C. for a period of time sufficient to convert the hydrated stannic oxide to an anhydrous form exhibiting a Gardner color of between 3 and 6, and
- f. classifying the anhydrous oxide as required to remove a first fraction wherein 90% of the particles are larger than about 4 microns,
- g. recovering the remaining fraction of said anhydrous oxide.
4 more elements
Dependencies are inferred from the claim text.