Coatings for the protection of diamond in high-temperature environments

Diamond is an ultra-durable material with high thermal conductivity and goo d transmission in the visible, near-infrared and far-IR (8-12 mu m) waveban ds. Recent advances in the development of synthetic diamond made by chemica l vapour deposition promise an expanding range of applications for the mate rial. An example is in advanced airborne windows and domes for highspeed fl ight, either as a window or as a protective coating for other infrared wind ow materials, where the diamond has sufficient durability to withstand high -speed impact by particles and raindrops, and a high level of thermal condu ctivity to minimise the effect of thermal shock due to frictional heating. However, diamond is subject to oxidation in air at temperatures greater tha n 750 degrees C, After only a few seconds of exposure, the diamond surface becomes severely etched, and the optical transmission is degraded. Very hig h-speed flight can lead to temperatures in excess of 800 degrees C, For thi s and other high-temperature applications, therefore, it is essential to pr otect the diamond surface from exposure to air. We have demonstrated that C VD diamond can be protected from oxidation for extended exposure (greater t han or equal to 10 s) in air at temperatures up to 1000 degrees C by a sing le-layer anti-reflection coating of d.c. magnetron-sputtered aluminium nitr ide. The coatings have excellent mechanical durability. (C) 1999 Elsevier S cience S.A. All rights reserved.