ZIRCONIUM CERAMICS AND ITS FUTURE PROSPECTS IN UKRAINE

Abstract

Ceramics, it seems, are among the first artificial materials created and utilized by people. The range of their application is widening continuously. Considerably novel varieties of ceramics, such as technical or fine ceramics, are becoming more and more significant in our life. They are used not only in households, industry, communications, transport, and agriculture, but in man himself, replacing some parts of his body. According to H. Yanagida [1], the production of technical ceramics based on complex knowledge can determine the prosperity or decline of a country [1]. Zirconia-based materials occupy a special place in the list of the most promising ceramics that can be produced on a large scale. In addition to the high mechanical properties predominantly resulting from the effect known as transformation toughening, the high strength and crack resistance, and the refractoriness and other properties possessed by all ceramics, which are hard, abrasion-resistant, and corrosion-resistant materials, the latter have a unique capacity to be a direct efficient transformer of the energy of organic fuel into electrical energy by the method of fuel elements. The Ukraine Zirconia Company has developed a simple technology for fabricating ceramic (zirconia-based) parts from sand, i.e., zircon of the Volnogorsk deposit. Using zirconium hydroxide produced by the Volnogorsk State mining and metallurgical works (Fig. 1), special milling, cold isostatic pressing, and appropriate sintering regimes, the Ukraine Zirconia Company produces zirconia ceramics with a structure stabilized by yttrium and magnesium oxides (Y-PSZ and Mg-PSZ, respectively). The typical properties of the ceramics are presented in Table 1. At the Hannover Messe-98 exhibition, the company presented such articles as – cutting tools, cutting edges, knives, surgical scalpels; – artificial joints and other biological implants; – friction and frictionless bearings, etc.; – valves, gaskets, and pump parts; – tools for pressure treatment and cutting of metals; – powders for plasma deposition of heat-insulating coats; – ingots for electron-beam spraying; – jewelry; – other articles. The exhibited specimens showed that zirconia ceramics are among the most widespread structural materials. Parts from zirconia ceramics are quite marketable; the demand for them throughout the world increases by 15 – 20% every year. We are convinced that the understanding of the mechanism of transformation toughening and the ability to realize it in the long-term process of the creation of a ceramic part, beginning with the synthesis of the powder and ending with the mechanical treatment of ready ceramics, provide a high level of properties and a wide range of products. After the discovery of the effect of transformation toughening [2], numerous works appeared throughout the world concerning the physical phenomena responsible for the high mechanical properties of ceramics based on ZrO2 and the creation of ceramic materials with record-breaking values of strength and crack resistance exceeding 2 GPa and 15 MPa m 2 (!), respectively, in the system of tetragonalstabilized zirconia polycrystals (Y-TZP). The typical values of the ultimate bending strength and crack resistance (1 GPa and 7 – 10 MPa m , respectively) for ZrO2 partially stabiRefractories and Industrial Ceramics Vol. 41, Nos. 9 – 10, 2000