【作者】 熊建华；

【导师】 蔡舒； 张立明；

【作者基本信息】 天津大学 ， 材料工程， 2008， 硕士

【摘要】 采用天然白云石为起始原料,以低成本制备钢铁冶炼用高钙镁钙质耐火材料为目的,系统研究了白云石粒径、烧结助剂种类及添加比例、烧结温度等对合成镁钙砂致密度及抗水化性的影响;在此基础上,通过在较细粒径的商业白云石中添加烧结助剂的方法,工业规模合成了高钙镁钙砂,并制备了高钙镁钙砖;采用真空感应炉浸棒法和静态坩埚法两种抗渣试验方法,研究了镁钙砂中烧结助剂对高钙镁钙砖抗渣性能的影响,研究结果表明:白云石粒径对合成镁钙砂致密度影响较大。当白云石粒径较粗时烧结性能极差,在1650℃,3h条件下,添加少量烧结助剂虽能迅速提高镁钙砂的体积致密度,但仅通过添加烧结助剂不能实现粗白云石粉的致密烧结;当白云石充分磨细后(D50≈5μm),无需添加任何烧结助剂,在1650℃,3h条件下即可烧结合成CaO含量约为56%、体积密度超过3.39g/cm3的高钙镁钙砂。在较低温度下由白云石中MgCO3、CaCO3分解出来的MgO、CaO有较高的反应活性,有利于烧成时的致密化。烧成温度对合成镁钙砂的致密度影响较大,但超过1650℃时,烧成温度的影响不再显著,同时添加少量烧结助剂后不同温度下合成镁钙砂致密度的差异极小,过度提高烧结助剂的加入比例,将降低液相形成温度或增加液相量,试样表面玻璃化造成表面气孔的过早封闭,在低温阶段未完全分解的CaCO3高温分解的CO2逸出阻力增大,导致镁钙砂体积密度降低。对于充分磨细后的白云石粉,添加烧结助剂、提高烧成温度只是促进镁钙砂中MgO、CaO的晶粒长大,对合成镁钙砂的致密度、抗水化性的影响均不明显;合成镁钙砂水化速率的控制因素为水蒸气通过颗粒表面向内部的扩散控制。高钙镁钙砂中的烧结助剂都使镁钙砖抗渣侵蚀性出现不同程度的降低,其中以Fe2O3为烧结助剂时更为明显。静态坩埚法抗渣试验时,尽管熔渣碱度不同,但渣蚀产物层次相同,自渣层到原砖层组成依次为渣层、方镁石富集层、裂隙、原砖层;镁钙砖抗渣性能主要取决于其中玻璃相数量、粘度,当玻璃相数量较多或粘度较低时,镁钙砖抗渣性能明显降低;同时试验过程中镁钙试样内方镁石富集层的形成也对试样抗渣性能产生显著影响。采用真空感应浸棒法时,试样内不出现方镁石富集层,熔渣对试样的侵蚀程度显著提高,含有较多TiO2的4号试样抗熔渣侵蚀能力稍好,可能因TiO2进入熔渣,提高了玻璃相粘度,并在试样表面形成了包含高粘度玻璃相的过渡层,缓冲了钢、渣对试样的冲刷,并从一定程度上抑制了熔渣对试样的熔蚀、渗透,从而使试样抗渣性能有所改善。更多还原

【Abstract】 Natural dolomite was selected as the starting materials to prepare the MgO-CaO refractories for steel refining with a low price, and the effects of dolomite powder size, sintering temperature and additives on the density and hydration resistance of synthesized doloma clinker were also studied in this paper. Doloma bricks were prepared with clinker which was synthesized from industrial dolomite powders with sintering aids, and the slag resistance of the doloma bricks was investigated by two test methods. The results were list as following:Dolomite powder size has major effects on the density of synthesized doloma clinker. When sintered at 1650℃, 3h, dense doloma clinker can’t be obtained from coarser dolomite powders containing additives which can enchance sintering by providing a path for rapid material transfer. After grinding, the fine dolomite powder can be decomposed completely at a lower temperature. And the high reactivity of the produced MgO and CaO resulting from the decomposition of dolomite would accelerate the densification of doloma clinker. As a result, the doloma clinker with 56% CaO and a density of 3.39g/cm3 can be prepared without aids(additives) at 1650℃, 3h.Sintering temperature also has some effects on the density of synthesized doloma clinker. However, the effects are no longer notable when sintering temperature over 1650℃Adding a few sintering aids into dolomite powder, there is little difference for doloma clinker sintered at different temperature, but high aids would result in much liquid at relatively low temperature, which would produce closed pores, prevent the release of CO2 from the decomposition of dolomite powder and inhibit the densification of doloma clinker.For the ground dolomite powder, sintering aids and increasing temperature just promote the growth of CaO and MgO crystal grains, but have little influence on the density and hydration resistance of synthesized doloma clinker. The hydration rate of doloma clinker is controlled by the vapor diffusion from the surface to the interior of the clinker.Sintering aids for the synthesis of doloma clinker decrease the slag resistance of doloma bricks to some extent, and the deterioration of the slag resistance is more notable when Fe2O3 was selected as sintering aid. For static crucible slag corrosion test, the eroded crucibles showed the same reactive layers for the slags with different basicity, and the layer sequence is slag layer, enriched MgO layer, cranny layer and origin layer. The slag resistance of doloma brick is mainly determined by the amount and the viscosity of the liquid at high temperature, and doloma bricks with more low-viscosity melt at high temperature will have worse resistance to slag corrosion. However, the enriched MgO layer formed in doloma bricks during slag corrasion also has notable effects on improving slag resistance.In the dynamic slag corrosion experiment conducted in vacuum induction furnace, there is no enriched MgO layer in doloma bricks, and the slag erodes doloma samples more severely than that in static crucible slag corrosion experiment. 4# samples containing more TiO2 have a bit better slag resistance than other samples. This might be contributed to the entrance of TiO2 in the melted slag and the increase of the slag viscosity in the transition layer between the sample and slag, which cushion the scouring of steel and slag against the sample surface, and prevent slag corrosion and infiltration into the samples.更多还原