A process of obtaining silicon nitride (Si.sub.3N.sub.4) surface coatings on ceramic pieces and components by impregnation of the surfaces of the ceramic pieces with silicon powder suspensions with a particle size preferably less than 200 .mu.m. The thickness of the coatings depends on the impregnation time and on the properties of the slip and the ceramic piece. The subsequent nitridation of the coating by thermal treatment at temperatures between 1300.degree. C. and 1500.degree. C. in N.sub.2 atmospheres leads to a continuous Si.sub.3N.sub.4 coating. The chemical stability and compatibility between Si.sub.3N.sub.4 and molten silicon enables its application in silicon metallurgy, in manufacturing crucibles for silicon fusion or for housing said molten silicon, in manufacturing pipes and chutes for its transport or in manufacturing different components for its subsequent purification.