Sol-gel bonding

Abstract

Preexisting elements are bonded by placing a sol-gel solution between juxtapositioned surfaces of the elements and sintering a gel formed from the solution at a temperature, which does not damage the elements, to form a sol-gel derived bonding material. The elements may be constructed of glasses, metals, infrared transmissive materials, or diamond, and bonded by sintering at about 300.degree. C. The bonding material may be resistant to high temperature and may have properties, such as refractive index, selected by varying the composition of the sol-gel solution. Optical and electronic articles are constructed by preparing a mandrel conforming to a substrate, which may be of arbitrary shape; depositing a coating on the mandrel; bonding the coating to the substrate with a sintered sol-gel; and removing the mandrel, as by etching. Diamond films formed by chemical vapor deposition at temperatures destructive to optical and microelectronic materials are thus mounted on variously shaped elements of these materials for protection against erosion and high temperatures and to provide low friction and high thermal conduction. Tetraethyl orthosilicate used as a sol-gel precursor gives a silica bonding layer effective at up to 800.degree. C. Other precursors may be used, and a titania sol-gel precursor provides a matching index of refraction for zinc sulfide or zinc selenide substrates. An intermediate layer, as of sputter deposited metal selected to accommodate thermal expansion differences, may be disposed between an element to be bonded and the bonding material.