an open - pored body , in particular a carbon component of an aluminum production cell , which is to be exposed to oxidizing conditions or chemical attack at high temperatures is treated to protect the body against oxidation or corrosion at high temperature by impregnating the surface of the body at about ambient temperature with a hot non - saturated liquid . this liquid contains a treating agent at a temperature above the temperature of the body . the concentration of treating agent in the hot liquid is such that when the liquid is cooled , before it reaches the temperature of the body , the liquid saturates and treating agent precipitates . a pressure differential is applied to cause the liquid to impregnate into the surface pores of the body and precipitate a layer of the treating agent from the liquid inside the body by cooling as it impregnates the pores of the body . the treating solution preferably comprises soluble boron compounds and , when the body is exposed to high temperature oxidizing conditions , the precipitated layer of the treating agent inside the body forms a protective , vitreous layer in the surface pores which protects the body against oxidation .