Transparent non-vitreous ceramic particulate
AssigneeMinnesota Mining and Manufacturing Company
InventorRoger W. Lange
Life of this patent
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Abstract
Solid, transparent, non-vitreous, ceramic particles useful as lens elements in retroreflective pavement markings characterized by having: A. at least one metal oxide phase; and B. an average minimum dimension of more than 125 micrometers. These particles are formed by various sol gel techniques, one example of which is the chemical gelation of titania sols by first mixing with glacial acetic acid, then with ammonium acetate, followed by formation of microspheres in 2-ethylhexanol. Microspheres of this ceramic composition can have relatively large diameters (e.g. over 200-1000 micrometers) making them quite useful as retroreflective lens elements in pavement marking sheet materials.
Claims25
Solid, transparent, non-vitreous, dense, ceramic microspheres comprising at least one crystalline phase comprising at least one metal oxide other than titanium dioxide, although titanium dioxide may be present in minor amounts, and having an average particle size of more than 125 micrometers, said microspheres being useful as lens elements.
Solid, transparent, non-vitreous, ceramic microspheres comprising polycrystalline titanium dioxide and having an average particle size greater than 200 micrometers, said microspheres being useful as lens elements.
A formed mass of discrete, solid, dense, transparent, non-vitreous, ceramic microspheres averaging at least 125 micrometers in diameter and useful as lens elements in retroreflective pavement markings, said microspheres comprising an amorphous, grainy silica matrix filled with zirconia crystallites less than about 1000 angstroms in size.
Solid, transparent, non-vitreous, ceramic microspheres consisting essentially of silica, having an average particle size of more than 125 micrometers, and being fully dense, said microspheres being useful as lens elements.
A pavement marking containing solid, transparent, non-vitreous, dense ceramic microspheres averaging greater than 125 micrometers in diameter and which consist essentially of grains less than about 1000 angstroms in size.
A chemical gelation process for making solid, non-vitreous ceramic particles comprising the steps of:
- (i) mixing a sol comprising a source of a metal oxide selected from the group consisting of titania, silica, zirconia and mix;tures of the foregoing with a gelling agent comprising ammonium acetate;
- (ii) adding the composition from step (i) to a forming fluid in which particles form;
- (iii) separating the gel particles from the forming agent;
- (iv) drying the gel particles from step (iii);
- (v) firing the particles at temperatures between about 500.degree. and 1200.degree. C. in order to form fired, ceramic particles;
- and
- (vi) allowing the fired, transparent, ceramic particles from step (v) to cool.
Dependencies are inferred from the claim text.