The existence of ceramic oxide, e.g. alumina and zirconia, powders and fibers is known to those skilled in the art.
U.S. Pat. No. 3,180,741 discloses a conventional process for the preparation of ceramic (refractory) fibers. The conventional process involves the steps of forming a dilute solution of a ceramic oxide precursor such as zirconium acetate followed by concentrating the solution to the desired viscosity. The concentrated solution of desired viscosity is then fiberized with the resulting fibers subsequently heated in an oxygen containing atmosphere to form an oxide fiber. A difficulty encountered in this process is the required concentration of the ceramic oxide precursor solution. This is because the typical modes of concentration, e.g. vacuum evaporation and solids precipitation, are not only time consuming and cumbersome but also if they are not properly controlled can lead to solutions of either too high or too low of viscosities to subsequently fiberize. If the resulting viscosity is too high, the solution is difficult to spin into fibers. A solution of too low of viscosity yields inferior fibers, if any.
U.S. Pat. No. 4,159,205 discloses that fibers made by such conventional methods had insufficient strength and flexibility for many applications.
In recent years, attempts have been made to viscosify the solution by the addition of certain organic acids. U.S. Pat. No. 4,159,205 discloses that the addition of acetic acid to spinning solutions results in fibers which were still too brittle for many applications because of the lack of control of nucleation, grain size, phase stabilization, and crystallization behavior. Although the use of lactic acid is disclosed as an alternative, it is possible that fibers of non-uniform cross sections, poor reproducibility, and relatively poor physical properties can result.
As disclosed by U.S. Pat. No. 4,619,817 there are five main methods that have been reported to date for producing partially stabilized zirconia powders (granules): (1) powder mixing, (2) coprecipitation and decomposition, (3) vapor phase decomposition, (4) sol-gel processing, and (5) hydrothermal processing. As disclosed by U.S. Pat. No. 4,619,817 difficulties lay in utilizing the methods in that each is specilized and therefore has its own distinct drawbacks and disadvantages.
From the foregoing discussion, it is readily apparent that each known method for the production of ceramic oxide powders and fibers has disadvantages and drawbacks. Because of the continuing demand for ceramic oxide powders and fibers, improved methods which eliminate any of the drawbacks of the conventional methods and which are practical and economical to utilize would be highly advantageous.