Recently, aspects of colloidal chemistry have been investigated as a starting point for eventually preparing ceramic materials. For example, spherical particles of hydrated basic aluminum sulfate have been formed by a precipitation process utilizing the urea decomposition reaction in aqueous medium. The particles as discussed in "Thermal Decomposition of Spherical Hydrated Basic Aluminum Sulfate" Ceramic Bulletin, Volume 63, No. 2, Pages 301-309, can be calcined to form finely divided particles of aluminum oxide.
In related investigations, monodispersed titanium dioxide powders have been synthesized by the controlled hydrolysis of dilute alcoholic solutions of titanium alkoxides. Thus, as discussed in "Formation, Packing, and Sintering of Monodispersed TiO.sub.2 Powders", Communications of the American Ceramic Society, December 1982, Pages C-199 to C-201, a dilute alcoholic solution such as containing titanium tetraethoxide, by use of special mixing technique, can be used to prepare a very finely divided precipitate. By use of such colloidal chemistry techniques attempts are being made to prepare ideally sinterable powders to produce theoretically dense single-phase ceramics, the powders being of a narrow size distribution and in a non-agglomerated state.
Considering for a moment materials other than oxides, the refractory metal borides, carbides and nitrides have already been discussed for use as components of electrolytic aluminum production cells. Moreover, in the production of such materials, solutions of alcoholic titanium have been suggested as useful. Thus in U.S. patent application Ser. No. 454,718 it has been proposed to initially formulate solutions of a titanium alkoxide plus soluble borate together with a soluble carbon source, such as sugar, as reducing agent. By starting with a combination of ingredients in this manner, and by use of subsequent carefully controlled processing techniques, a finally sintered product of desirable density and purity may be achieved.
It has also been proposed to prepare carbide and nitride alloys, through the carbothermal reduction technique, using inorganic reagents of the metals. Thus in "Fabrication and Characterization of SiC-AlN Alloys", Journal of Material Science, Volume 16, Pages 3479-3488, there has been disclosed the preparation of an aqueous solution of an aluminum chloride in conjunction with a starch dispersion. After the addition of finely divided silica, pH adjustment with ammonia leads to aluminum hydroxide precipitation. The precipitate can be dried and calcined to yield an SiC-AlN ceramic alloy powder.
Considering again the preparation of borides, as well as carbides and nitrides by carbothermal reduction, wherein the use of carbon particulates have been employed, it has been suggested that such can be useful when pressed together with other ingredients. Thus in British Pat. No. 1,004,585, there is disclosed an intimate mixture of boric oxide and titanium dioxide, which includes in the mixture particulate carbon such as graphite, thoroughly blended together, then compressed and sintered. A friable powder prepared by such process can be expected to contain a high yield of titanium diboride.
Thus a variety of reactions and approaches are being made to prepare useful substances for the ceramic industry. Unfortunately, some techniques although providing promise in regard to uniformity and purity of materials have proven to be too expensive and inefficient to be practical. Other, more practical developments in economy of processing, nevertheless rely on expensive ingredients that detract from the overall desirability of the technique.