Thermal extractive gelation process
AssigneeMinnesota Mining and Manufacturing Company
InventorsThomas E. Wood, Roger W. Lange
Life of this patent
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Abstract
Solid, transparent, non-vitreous, microspheres (zirconia-silica) are formed by extractive gelation (extracting carboxylic acid away from zirconyl carboxylate) of a sol in liquid medium such as hot peanut oil. Zirconyl carboxylate precursor sol is prepared and added in droplet form to the liquid extractant (peanut oil) at an elevated temperature at which a carboxylic acid is liberated from the zirconyl carboxylate. The droplets remain in the extractant for sufficient time to form stable gel spheroids which are separated from the extractant and fired to convert them to durable spheroids useful as lens elements in retroreflective sheeting.
Claims7
A thermal extractive gelation process for making a solid, non-vitreous ceramic article comprising the steps of:
- (i) preparing a zirconyl carboxylate-containing precursor mixture having a concentration sufficient to obtain a convenient density and viscosity for forming droplets;
- (ii) adding the mixture from step (i), by a means which forms droplets of the mixture, to a liquid extractant at a temperature at which carboxylate is liberated from the zirconyl carboxylate as a carboxylic acid and characterized by:
- (a) a substantial solubility, of at least 1 weight percent, for the carboxylic acid at the operating temperature;
- and
- (b) low solubility, of less than 1 weight percent, for the zirconyl carboxylate and other ingredients of the mixture from step (i);
- (iii) allowing the droplets to remain in the extractant for sufficient time to form stable gel spheroids;
- (iv) separating the gel spheroids from step (iii) from the extractant;
- (v) firing the gel spheroids at a temperature in the range of 500.degree.-1350.degree. C.;
- and
- (vi) allowing the fired spheroids from step (v) to cool.
A process for making a solid, non-vitreous ceramic article comprising the steps of:
- (i) preparing a zirconyl carboxylate-containing precursor mixture having a concentration sufficient to obtain a convenient density and viscosity for forming droplets;
- (ii) adding the mixture from step (i), by means which forms droplets of the mixture, to a liquid extractant selected from the group consisting of peanut oil, vegetable oil, corn oil, safflower oil, soybean oil, sunflower oil, derivatives of such oils, and mixtures thereof;
- (iii) allowing the droplets to remain in the extractant for sufficient time to form stable gel spheroids;
- (iv) separating the gel spheroids from step (iii) from the extractant;
- (v) firing the gel spheroids at a temperature in the range of 500.degree.-350.degree. C.;
- and
- (vi) allowing the fired spheroids from step (v) to cool.
Dependencies are inferred from the claim text.