A highly pure ultra-fine SiOx (wherein x is from 0.6 to 1.8) powder having a specific surface area of at least 10 m.sup.2/g and a total content of Na, Fe, Al and Cl of at most 10 ppm is provided. The SiOx powder is produced by reacting a monosilane gas with a gas capable of oxidizing the monosilane gas in a non-oxidizing gas atmosphere under a pressure of from 10 to 1000 kPa at a temperature of from 500 to 1000.degree. C. In this case, the amount of the non-oxidizing gas is preferably larger than the total amount of the monosilane gas and oxygen participating in the oxidation of the gas capable of oxidizing the monosilane gas.

Coated article, e.g., a brake disc, comprising a carbon-carbon composite component or a carbon-carbon-silicon carbide component coated at least with a phosphorus-containing antioxidant undercoating, the undercoating being covered by a silicon carbide particle-containing overcoating of alkali or alkaline earth metal silicate, pH modifier, and silicon carbide particles. Also, method of protecting a carbon-carbon composite brake disc or a carbon-carbon-silicon carbide composite brake disc against oxidation, by: coating the composite brake disc with a first phosphoric acid-based penetrant system; curing the penetrant coating at a temperature of 200.degree. C. or above to form a first coating on the composite brake disc; applying the ceramic coating composition of claim 1 over the first coating and curing the ceramic coating at a temperature below 200.degree. C. to form a second coating on the composite brake disc; and optionally coating the coated composite brake disc so obtained with a second phosphoric acid-based penetrant system; and curing the penetrant coating at a temperature of 200.degree. C. or above to form a third coating on the composite brake disc.