The free CaO (FC) in light-burnt MgO due to the impurity of magnesite ores cannot be avoided, and causes the declination of properties of magnesium oxychloride cement (MOC). In order to clearly explain the declination mechanism of MOC properties due to FC, the effect of FC contents on the formation of phase compositions and the compressive strength of MOC pastes were studied in detail. The findings revealed that the addition of FC sharply increased the pH value of MOC pastes, and changed the final compositions of the hardened MOC pastes. Specifically, FC contents more than 4 % could cause the formation of phase 5 by the phase 3 transformation at MgO/MgCl2/H2O molar ratio of 3:1:11, and FC contents more than 2 % could lead to the formation of phase Mg(OH)2 by phase 5 transformation at MgO/MgCl2/H2O molar ratio of 5:1:13. Consequently, the transformation of phase compositions caused the remarkable declination of compressive strength of MOC pastes. The content of FC should be given attention in the MgO/MgCl2/H2O molar ratio, and the permissible contents of FC should be limited to less than 4 % and 2 % relevant to the MgO/MgCl2/H2O molar ratios at 3:1:11 and 5:1:13, respectively.

中文翻译：

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游离CaO含量对三氯镁水泥物相组成的影响


由于菱镁矿的杂质，轻烧 MgO 中的游离 CaO （FC） 是无法避免的，并导致三氯镁水泥 （MOC） 性能的偏角。为了清楚地解释 FC 引起的 MOC 性能的偏角机制，详细研究了 FC 含量对 MOC 浆体相组成形成和抗压强度的影响。结果表明，FC 的添加显著提高了 MOC 浆料的 pH 值，并改变了硬化 MOC 浆料的最终成分。具体来说，FC 含量超过 4% 可通过 MgO/MgCl2/H2O 摩尔比为 3：1：11 的 3 相转变形成第 5 相，而 FC 含量超过 2% 可导致 Mg（OH）2 通过以 5：1：13 的 MgO/MgCl2/H2O 摩尔比形成第 5 相转变。因此，相组成的转变导致 MOC 浆料的抗压强度显着下降。应注意 MgO/MgCl2/H2O 摩尔比中 FC 的含量，在 3：1：11 和 5：1：13 处，FC 的允许含量应分别限制在 4 % 和 2 % 以下，与 MgO/MgCl2/H2O 摩尔比相关。