FIELD: products made of carbon, graphite or ceramic materials having low thermal expansion and coated with stoichiometric composition of pyrolytic PB(Si)N and method of preparing coated product. SUBSTANCE: method comprises feeding vapors of reagents under suitable conditions of sedimentation into interior of the heated furnace chamber in which product to be coated is placed. Vapors of reagents include ammonia, gaseous sources of boron and silicon and also diluent gas. They are fed at such rate of gas streams that total rate of boron and silicon streams is less than rate of ammonia stream. Coatings have thermal resistance at temperature up to 1900 C for longer than 20 hours. In this case, coating comprises up to 25 % of silicon and is resistant to oxidation in the air at temperatures from 100 to 1500 C. EFFECT: more efficient coating formation method. 11 cl, 2 dwg, 10 ex, 2 tbl
