Optimum preparation of silanes for steel pretreatment

The Ministry of Defence requires equipment which is reliable and available for instant use in a world-wide environment. This imposes very stringent requirements when considering service life. Adhesives are crucial components in many systems, and moisture degradation is often a key factor in their application. This work investigates the use of a silane coupling agent in a rocket motor bonding process. It is concerned with the rate of hydrolysis of the silane in aqueous and ethanolic solutions, which is thought to be a key process in the application of the silane coupling agent during fabrication. The rate of hydrolysis of gammaglycidoxypropyltrimethoxysilane has been measured by 1H NMR spectroscopy. Results are presented for aqueous solutions, and a range of ethanolic solutions with various amounts of water. The dependence of the rates on pH and concentration is investigated. It is concluded that the rates are very pH dependent, and adequate control of pH is essential for a reproducible manufacturing process. This is particularly true for ethanolic solutions, where the reaction rates are considerably slower than in pure water, and the rates in nearly neutral solutions can be very slow.