▎ 摘　　要

NOVELTY - The method for preparing a coating on a carbon substrate involves: (S1) mixing hydrogel and organosilane to form a mixture; (S2) applying the mixture to the surface of the carbon substrate to form a first coating layer; (S3) coating an organic tantalum solution on the first coating to form a second coating, where the second coating and the first coating form a composite coating; and (S4) heating and annealing the composite coating. The hydrogel is graphene hydrogel, polyacrylic acid, polymethacrylic acid, polyacrylamide, poly-N-polyacrylamide or chitosan. The organosilane is polysilane, polysiloxane and/or polycarbosilane. The organic tantalum is tantalum ethoxide, tantalum pentamethyl oxide, tantalum isopropoxide, tantalum butoxide and/or tantalum amyl alcohol. USE - Method for preparing a coating on a carbon substrate such as crucible (claimed). ADVANTAGE - The method effectively improve the corrosion of raw materials to a graphite crucible in the growth process of a silicon carbide crystal, effectively solve the problem of thermal mismatch caused by overlarge difference of expansion coefficients of tantalum carbide and the carbon substrate by adopting a composite coating, prevent the coating from peeling off in the use process and improve the adhesiveness of the coating. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for the coating of carbon substrate. DESCRIPTION OF DRAWING(S) - The drawing shows a flow chart of a preparation method of coating of carbon substrate. (Drawing includes non-English language text). Mixing hydrogel and organosilane to form a mixture (S1) Applying the mixture to the surface of the carbon substrate to form a first coating layer (S2) Coating an organic tantalum solution on the first coating to form a second coating, where the second coating and the first coating form a composite coating (S3) Heating and annealing the composite coating (S4)