Zr（OH）₄ Gel Effects On The Properties Of MgO-CaO-ZrO₂ Ternary Refractories

High performance demand and environmental protection have been raised on production of refractories due to technology development in iron and steel, cement and other industries as well as enhancement in environmental protection since 1970s. With the need of elimination of "chromium pollution", development of chromium-free refractories is becoming to the major trend. To find new high-performance chromium-free alternative is becoming both theoretical and practical problems to be solved for the current widespread use of magnesia-chrome brick.Magnesia-zirconia and doloma-zirconia bricks are“hot research subjects”for developing chromium-free refractories. The ZrO₂ used as raw material for preparing magnesia-zirconia and doloma-zirconia bricks usually in form of monoclinic ZrO₂ and/or zircon. However, it is difficult to obtain denser product due to ZrO₂ particles size, so as to deteriorate corrosion resistance of materials and decreasing hydration resistance of doloma-zirconia brick. Zr（OH）₄ gel is selected as source of ZrO₂ because of its attractive advantages, such as low processing cost, high dispersion, uniform and reactive. In the present study, the effects of method of adding ZrO₂ derived from Zr（OH）₄ gel on the properties of magnesia–zirconia, and doloma-zirconia bricks are investigated. In additional, from the CaO preparation point of view, how to improve the hydration resistance of doloma-zirconia brick are also studied. Experimental results indicate that:（1） For magnesia-zirconia material, among the three ZrO₂ addition approaches, adding monoclinic ZrO₂ can improve the corrosion performancea, however, clinker adhesions are worse. Although adding of zircon can greatly improve clinker adhesion of material, its corrosion resistance is worse. Samples added Zr（OH）₄ gel have good corrosion resistance and clinker adhesion, which have the highest modulus of rupture and compressive strength. In addition, the properties of samples with 95% fused magnesia as aggregates and 96% fused magnesia fines are superior to that of samples with 95% fused magnesia as aggregates and 95% fused magnesia fines.（2） As for doloma-zirconia materials, the ZrO₂ was introduced by either ZrO₂ nano particles or Zr（OH）₄ gel by using the same sintering temperatures （1610℃）. It was found the addition of nano ZrO₂ and Zr（OH）₄ gel can not only improve hydration resistance but also improve thermal shock resistance and corrosion resistance. Furthermore, we found a serious experimental results: the sample will have the highest hydration resistance by adding 12% of Zr（OH）₄ gel and highest thermal shock resistance and corrosion resistance by adding 15% nano ZrO₂ particles.（3） The improvement in hydration resistance of CaO materials is mainly through by adding MgO additives as well as“core-shell”thin film coating technology. Experimental results indicate:①Samples by using FZT、FCT composite additives with can obviously improve sintering of CaO and effectively increase hydration resistance of materials. It was found that the proper sintering temperature is 1650℃, and the proper addition amount is about 2.5%; The hydration resistance of adding of FCT is superior to FZT.②The hydration resistance of CaO clinker coated with MgO is superior to that CaO contained additives, and that of CaO clinker coated with fused MgO fine particles is superior to clinker coated with light burned MgO fine particles. Coating with 0.1⁰.25mm thickness on CaO clinker can be obtained with coated fused MgO fine particles with ZrO₂ additives, and intermediate layer thickness is in the range of 0.15⁰.3mm. It was expected to protect internal CaO from hydration by decreasing layer crack resulting from mismatch of thermal expansion between MgO and CaO, and samples have the better hydration resistance.