The invention discloses a composite gradient
hydrogen-resistant
coating for a high-temperature evacuated collector tube and a preparation method thereof. The preparation method comprises the following steps of carrying out Ni-Cr-Al
transition layer preparation by a low-pressure
plasma spraying device under the conditions of current of 300-800A,
voltage of 40-100V, H2 flow of 5-100L / min, Ar flow of 5-100L / min,
chamber pressure of 1000-10000Pa, a spraying speed of 1-20mm / s and a spraying distance of 10-100mm, putting a cleaned sample into a
quartz glass tube, carrying out sealing, carrying out vacuum-pumping until pressure is <10Pa, feeding
argon into the
quartz glass tube until pressure is 100000Pa, carrying out vacuum-pumping, carrying out circulation twice, stopping
argon feeding, feeding
hydrogen into the
quartz glass tube until pressure is 100000Pa, carrying heating under the condition of a preset
furnace temperature of 500-1200 DEG C, carrying out heating in water bath having a temperature of 5-60 DEG C when the
furnace temperature is in a range of 500-1200 DEG C, feeding H2 into H2O and then into a
reaction zone to provide low-
oxygen partial pressure of 10<-24> to 10<-16>Pa, and keeping the temperature for 1-20h under the conditions of the
furnace temperature of 500-1200 DEG C and the water-bath temperature of 0-60 DEG C to obtain the Al2O3-Cr2O3 composite gradient
hydrogen-resistant
coating having the thickness of 0.1-20 microns. The
coating is a double-layer structure comprising an
alumina inner layer and a chrome
oxide external layer. The hydrogen-resistant coating has a high bonding degree with the base and has hydrogen resistance improved by 100-120 times. The preparation method has simple processes and a low cost.