Coatings for the protection of diamond in high-temperature environments

Diamond is an ultra-durable material with high thermal conductivity and good transmission in the visible, near-infrared and far-IR (8-12 mu m) wavebands. Recent advances in the development of synthetic diamond made by chemical vapour deposition promise an expanding range of applications for the material. An example is in advanced airborne windows and domes for highspeed flight, either as a window or as a protective coating for other infrared window materials, where the diamond has sufficient durability to withstand high-speed impact by particles and raindrops, and a high level of thermal conductivity to minimise the effect of thermal shock due to frictional heating. However, diamond is subject to oxidation in air at temperatures greater than 750 degrees C, After only a few seconds of exposure, the diamond surface becomes severely etched, and the optical transmission is degraded. Very high-speed flight can lead to temperatures in excess of 800 degrees C, For this and other high-temperature applications, therefore, it is essential to protect the diamond surface from exposure to air. We have demonstrated that CVD diamond can be protected from oxidation for extended exposure (greater than or equal to 10 s) in air at temperatures up to 1000 degrees C by a single-layer anti-reflection coating of d.c. magnetron-sputtered aluminium nitride. The coatings have excellent mechanical durability. (C) 1999 Elsevier Science S.A. All rights reserved.