MgO活性对氯镁石材料开裂和耐水性的影响

EFFECT OF CHEMICAL ACTIVITY OF MgO ON CRACKING AND WATER-RESISTANCE OF MAGNESIUM OXYCHLORIDE MATERIALS

讨论了菱镁矿烟烧过程中MgO晶体结构的形成过程以及对MgO活性的影响,当菱镁矿的煅烧温度低于800℃时,由菱镁矿的晶体结构逐渐转变形成的MgO晶体结构中存在较多的缺陷,赋予MgO高的化学活性,这些缺陷位置是其与MgCl_2水溶液进行化学反应形成5.1.8相的物化活性点。由于5.1.8相或3.1.8相在水中高的溶解度和水化放热,使得氯镁石材料易于开裂和耐水性差,造成氯镁石磨削材料在抛光过程中掉渣,实验表明,粉煤灰和磷酸二氢钙的复合外加剂能有效地改善开裂情况和提高耐水性。

On the view of crystallography, the forming process of crystal structure of MgO during the burning of magnesite and the effect on its chemical activity were discussed. When the burning temperature of magnesite is lower than 800°C, MgO is of high chemical activity due to lots of defects in crystals caused by the gradual change of crystal structure from magnesite to MgO. The chemical reaction of MgO with MgCl2 solution takes place at defect sites of MgO to produce 5Mg(OH)2&middot MgCl2&middot8H2O (5.1.8 phase). Because of the high hydration heat and solubility of 5.1.8 phase or 3Mg(OH)2&middot MgCl2&middot8H2O (3.1.8 phase), magnesium oxychloride materials are easy to be cracked and of poor water-resistance. The results show that the additives of fly ash and calcium diacid phosphate can effectively improve the water-resistance and eliminate the cracking.