Method of ceramic molding which produces a porosity gradient and the manufacture of compound moldings using this method

A method of manufacturing a ceramic molding having a progressive and steady change in the composition of suspension therein wherein the porosity of the ceramic molding has a gradual and continuous increase along the axis of molding from less than 20% to more than 70%, said method comprising the steps of:

• selecting a plurality of individual mixtures each having a progressive increase in the level of SiO.sub.2 content;
• introducing each said plurality of individual mixtures into a mold means, substantially preventing the intermixing of said individual mixtures with one another during said introduction step;
• effecting the uniform mixing of the individual layers at the respective boundary surfaces through controlled vibration of the mold;
• allowing the mixtures in the mold to stand in the mold for a predetermined period of time up to about 100 hours whereby the mixtures contained in the mold can be removed therefrom as a single unit;
• removing the mixture from the mold for drying at a temperature between about 80 to 150.degree. C. for a period of time between about 2 to 48 hours;
• and
• firing the dry molded material at a predetermined temperature which is a function of the limit application temperature of the fibers used and the sintering or molding temperature of the fine-grain, fire-resistant or refractory materials contained therein wherein during this firing a reaction takes place between the fine-grain, fire-resistant or refractory materials wherein a so-called fiber ceramic is forced into a matrix by sintering or chemical reaction so that the fibers adhere to one another at their contact surfaces whereby the fiber ceramic comprises 90 to 100 percent fibers and the rest organic binders.