Abstract: A method and apparatus for making highly pure silica powder by milling the substantially pure SiO2 charge in a ball mill which is made with an interior lining of contiguous silicon nitride plates or tiles and which employs silicon nitride media. The silicon nitride plates and media prevent contamination of the silica charge while minimizing their deterioration. The resulting slip (wet milling) or mix (dry milling) is of a higher purity because there are no substantial impurities contributed by the mill liner material or by the media.

Abstract: A spall shield for armor plate for restraining at least a portion of flying fragments resulting from impact of a projectile with said armor plate, comprises a plasticized resin of the type commonly used as an interlayer of safety plate glass such as for example, plasticized polyvinyl acetal resin or plasticized polyvinyl butyral resin. The novel spall shield replaces nylon cloth, rubber, felt or resin impregnated glass fabric of the prior art while being at least as thin and light as the adhesive commonly used to adhere such prior art spall shield materials to the armor plate. The spall shield of the present invention is substantially lower in weight and substantially more efficient in performance than conventional spall shields.