Improved target for X-ray tubes

This invention pertains to improvements in rotary anode X-ray tube targets which are composed either partially or substantially of graphite. The invention markedly reduces the problems formerly occurring with use of graphite targets by subjecting the graphite substrate or target disk to pyrolytic carbon infiltration (PCI). This treatment results in deposition of a thin impervious coating of pyrolytic carbon on all internal and external surfaces of the graphite target substrate and effectively prevents escape of any adsorbed gases from the target in the high vacuum of an X-ray tube. Surface voids or microscopic cavities between graphite crystallites are coated with pyrolytic carbon to serve, not only as a sealant, but to increase the strength of the graphite body at its surface by coating any minute flaws, cracks or other potential failure sites. Very importantly, the pyrolytic carbon coating prevents loss of graphite particles through thermal cycling, rubbing, abrasion or other mechanical action. The coating does not diminish surface roughness which is desirable because a rough surface has better emissivity than a smooth surface. (Auth.)