The insulation barrier is formed of a body of expanded polystyrene which is impregnated with sodium silicate. In addition, a coating formed of a metallic-based inorganic material is applied over at least one surface of the body. The sodium silicate is applied in solution form and maintained within the body by a wetting agent in the solution. The coating is be applied by a coating roller either before or after drying of the impregnated polystyrene body.

An exhaust manifold for conducting heated exhaust gas from an internal combustion engine to an exhaust system. The exhaust manifold includes a preform and a metal layer enclosing the preform. The preform has an inner layer of silicon carbide, a middle layer of insulating material, and an outer layer to seal the middle layer from molten metal used to form the metal layer.

A method is disclosed for making an article, such as a cylinder head, having one or more hollow ceramic tubes, such as ceramic exhaust port liners, cast in-situ therein with reduced cracking or breakage of the ceramic tube from tensile and compressive stresses exerted on the ceramic tube during the casting process. The method involves forming a removable core in the ceramic tube of a core material having a thermal expansion coefficient not exceeding about 10 times that of the ceramic tube to minimize crack-causing differential thermal expansion-induced tensile stresses on the ceramic tube when molten metal is cast therearound, casting the molten metal about the cored ceramic tube in a mold cavity, stress relieving the cast article at an elevated temperature before the cast article cools to a lower temperature at which crack-causing differential thermal contraction-induced compressive stresses are exerted on the cast in-situ ceramic tube, and removing the core from the cast article.

A method of producing a self-supporting ceramic composite body having therein at least one cavity which inversely replicates the geometry of a positive mold of parent metal. The method includes embedding the mold of parent metal within a conformable bed of filler to provide therein a cavity shaped and filled by the mold. The assembly is heated to melt the parent metal mold, e.g., an aluminum parent metal mold, and contacted with an oxidant to oxidize the molten parent metal to form a polycrystalline material which grows through the surrounding bed of filler, the molten metal being drawn through the growing polycrystalline material to be oxidized at the interface between the oxidant and previously formed oxidation reaction product whereby the cavity formerly filled by the mold of parent metal is eventually evacuated of the metal. There remains behind a cavity whose shape inversely replicates the original shape of the mold. The method provides ceramic composite articles having therein at least one cavity inversely replicating the shape of the mold which supplied the parent metal for oxidation.

A casting pattern and process for producing a hollow casting. The casting pattern has a foamed material body and can be constructed to prevent seams or fins from forming at points which are accessible only with difficulty, such as inside points. The contour of the foamed material body is covered on one side with a refractory mold part which is to be molded into the produced casting to form a corresponding part of the contour of the produced casting.