Bonding by Hydroxide-Catalyzed Hydration and Dehydration
- Thursday, 03 January 2008
Room-temperature process can be varied to suit optical and non-optical applications.
A simple, inexpensive method for bonding solid objects exploits hydroxidecatalyzed hydration and dehydration to form silicatelike networks in thin surface and interfacial layers between the objects. (Silicatelike networks are chemical-bond networks similar to, but looser than, those of bulk silica). The method can be practiced at room temperature or over a wide range of temperatures.
The method was developed especially to enable the formation of precise, reliable bonds between precise optical components. The bonds thus formed exhibit the precision and transparency of bonds formed by the conventional optical-contact method and the strength and reliability of high-temperature frit bonds. The method also lends itself to numerous non-optical applications in which there are requirements for precise bonds and/or requirements for bonds, whether precise or imprecise, that can reliably withstand severe environmental conditions. Categories of such non-optical applications include forming composite materials, coating substrates, forming laminate structures, and preparing objects of defined geometry and composition.
In this method, a silicatelike network that bonds two substrates (see figure) can be formed either by a bonding material alone or by the bonding material together with material from either or both of the substrates. In preparation for bonding, the mating surfaces of the substrates should be cleaned to render them maximally hydrophilic or at least minimally hydrophobic. Typically, an aqueous hydroxide bonding solution is dispensed and allowed to flow between the mating surfaces by capillary action. If at least one of the substrates can form a silicatelike network and if the surface figures of the substrates match with sufficient precision, then a suitable bonding solution would be one that contains a suitable concentration of hydroxide ions but substantially or completely lacks silicate material. If neither substrate material can form a silicatelike network through hydroxide catalysis or if the degree of mismatch between the surface figures of the substrates is such that silicatelike network cannot be formed at a sufficient rate, then a silicate material should be included in the bonding solution.