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.