Madej Dominika, Tyrała Karina
Department of Ceramics and Refractories, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland.
Materials (Basel). 2020 Mar 19;13(6):1403. doi: 10.3390/ma13061403.
The hydration of an equimolar mixture of MgO and AlO nano-powders has been proven to be an effective way to synthesize MgAlCO(OH)∙4HO as a component of a nano-structured matrix and magnesia-alumina spinel precursor for high-performance cement-free corundum-spinel refractory castables. (Mg)-OH-brucite sites (417 °C) formed initially within the magnesia-alumina hydrating blended paste were replaced with (MgAl)-OH and (Mg)-OH hydrotalcite sites, which were dehydroxylated at 420 °C and 322 °C, respectively. This reorganization was connected with the incorporation of anions and water molecules in the interlayer spacing of hydrotalcite, which was dehydrated at 234 °C. Hence, the thermal decomposition of a nano-structured matrix system containing mainly MgAlCO(OH)∙4HO consists of a complex sequence of dehydration, dehydroxylation and decarbonization, and this finally leads to the formation of inverse spinel MgAlO and periclase MgO through many intermediate stages containing the mixed tetrahedral-octahedral Al phase and MgO-like structure. Hence, the hydraulic bond that primarily existed was replaced by a ceramic bond at a relatively low temperature, i.e., 700 °C, where a spinel was formed. Important changes in oxygen coordination polyhedra around Al in the dehydrated-dehydroxylated hydrotalcite occurred between 600 and 1100 °C.
氧化镁和氧化铝纳米粉末的等摩尔混合物水合已被证明是一种有效的方法，可合成碱式碳酸镁铝（MgAlCO(OH)∙4H₂O），作为纳米结构基体的组成部分以及用于高性能无水泥刚玉-尖晶石耐火浇注料的氧化镁-氧化铝尖晶石前驱体。氧化镁-氧化铝水合混合浆料中最初形成的（Mg）-OH水镁石位点（417℃）被（MgAl）-OH和（Mg）-OH水滑石位点取代，它们分别在420℃和322℃脱羟基。这种重组与水滑石层间间距中阴离子和水分子的掺入有关，水滑石在234℃脱水。因此，主要包含碱式碳酸镁铝（MgAlCO(OH)∙4H₂O）的纳米结构基体系统的热分解包括一系列复杂的脱水、脱羟基和脱碳过程，最终通过许多包含混合四面体-八面体Al相和MgO类结构的中间阶段形成反尖晶石MgAl₂O₄和方镁石MgO。因此，主要存在的水硬性结合在相对较低的温度（即700℃）下被陶瓷结合所取代，此时形成了尖晶石。在脱水-脱羟基水滑石中，Al周围的氧配位多面体在600至1100℃之间发生了重要变化。
