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In the production of zirconia refractories the normal method of stabilizing the ZrO 2 is by electrofiring [1][2][3]. The stabilization is effected in an electric-arc furnace by firing the material into a block [3,4].The published literature contains virtually no data on the effect of the concentration of stabilizing additive on the macro-or microstructure of the block after cooling; on its density; on its strength; or on its thermal-shock resistance. Moreover, these properties may be decisive in the case of milling the fired material and for the properties of the product manufactured from this material In order to study these properties we fired blocks from ZrO 2 stabilized by various amounts of CaO and also without any additive.The blocks were prepared from ZrO 2 with a concentration of up to 99.5% ZrO 2 + HfO2, and as the stabilizer we used chalk with a concentration of 55% CaOo The ZrO 2 was mixed with various amounts of chalk in a ball mill.The samples taken from the central region of the block consisted of crystals of an irregular prismatic shape oriented in the direction of the thermal flow. Depending on the concentration of stabilizing additive, the crystals were from 0.5 to 100 mm long and from 0.1 to 9 mm broad ( Table 1). The crystals in specimens without the stabilizing additive were the largest and present in the maximum amount.The crystals were smallest in specimens containing 2.2-3.0% CaO and consisting of 35-60% of the cubic solid solutions. In these specimens the dense contact between the crystals characteristic of the specimens without additives were destroyed by the formation of cracks whose width increased with an increase in the amount of additive and reached a maximum with a concentration of 5-6% CaO (~ 100% cubic phase).

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Industrial zirconium dioxide is currently used in the USSR for the production of electrosmelted ZrO 2 destined for the production of charging, tamping masses, and other products [1]. In other countries, zirkite, fobas, zircon, baddeleyite, ere, are used for this purpose [2][3][4][5][6][7]; a stabilized material is produced from these materials with the addition of CaO directly to the batch.The Ore-Dressing Works of the Kovdorsk Refractory and Ceramic Board has now started up and it is now possible in the USSR to use baddeleyite for the production of eleetrosmelted ZrO 2. The dressed baddeleyite from the Kovdorsk deposit is characterized by a high concentration of ZrO2 + HfO 2 [8,9] and it is thus pos~ sible to stabilize it by electrosmelting by the method used for producing electrosmelted powders from industrial ZrO 2 [1].The possibility of obtaining electrosmelted baddeleyite products was previously reported in [10] but such products had a low thermal-shock resistance from 1300~ (two or three cycles in water).Studies have been carried out at the Ukrainian Scientific-Research Institute of Refractories with the aim of developing the production methods for thermal-shock resistant products made from electrosmelted 9 Untreated material; contained 0.04% TiO2; 0.13%, R20; and 0.32% calcin, loss. tUntreated material: contains 0.27% TiO2; traces of R20; and 0.76% calcin, loss.