Study On Synthesis And Hydration Resistance Of Doloma Clinker

In recent years, with the demand of high-end steel products, such as clean steel and special steel, the research and production of MgO-CaO refractories has attracted more and more attention at home and abroad. MgO-CaO refractories have the widespread application prospect because of the characteristics of high refractoriness, high basicity, excellent slag resistance and strong spalling resistance, especially the internal free CaO, which can purify molten steel. But the biggest disadvantage of MgO-CaO refractories is hydration reaction of CaO, causing the materials powdering, so that application MgOCaO refractories has been greatly limited.Hydration resistance of MgO-CaO refractories have been researched a lot by many scholars at home and abroad, including two-step calcination method, introducing additives, surface treatment and other methods. The research direction of this dissertation is to improve the hydration resistance of MgO-CaO refractories by two-step calcination method and introducing composite additives composing Fe2O3+ZrO2.Research of this topic includes three steps: First, after crushing and grinding them into powders, which particle size was less than 100μm, light burned natural dolomite and natural magnesite at different temperatures for 2h, then the activities of the firing products were tested so that the best firing temperatures can be selected. Second, composed the powders respectively according to the composite ratios of CaO content 45%, 50% and 55% after burned them on chosen temperatures. Then Fe2O3 and ZrO2 were introduced into the powders as two kinds of additives according to three composite ratios, which are 0.5%Fe2O3+1%ZrO2, 0.75%Fe2O3+2%ZrO2 and 1%Fe2O3+3%ZrO2. Then aluminum dihydrogen phosphate powders were introduced in powders as binder, the powders were pressed into cylindrical specimens with the size of Φ50mm×50mm under 100 MPa after dry mixing for 6 hours, then respectively sintered at 1500℃ and 1600℃ for 3 hours. Third, the best introducing quantity of additives was determined according to the apparent porosities, the bulk densities, the hydration rates and the microstructures of samples.The results showed that:(1) The best light-burn temperature of dolomite was 1100℃, and the best light-burn temperature of magnesite was 800℃.(2) Samples with a certain amount of active MgO showed better performance in the hydration resistance and sintering properties than that without MgO.(3) Introducing Fe2O3+ZrO2 composite additives can promote the improvement of the sintering properties of MgO-CaO refractories and the grain growth, the apparent porosities, the bulk densities and the hydration rates of samples with composite additives were much better than the blank samples. Where the hydration rate of the sample with w(CaO)=50%, sintering at 1600℃, adding additives ratio of 1%Fe2O3+3%ZrO2 fell down to 4.3% from 10.8% of the blank sample, shows that the introduction of additives can effectively improve the hydration resistance of MgO-CaO refractories.(4) Samples sintered at 1600 ℃ showed significantly better hydration resistance and sintering properties than that sintered at 1500℃, indicating that the hydration resistance and sintering properties improved more obvious when the sintering temperature is higher.