Chloride ion ( Cl- ) content is one of the key indicators of deliquescence, dehalogcnation and efflorescence in the Magnesium Oxychloride Cement (MOC). An optimized pretreatment for determination of Cl ~ is proposed in this paper. The influence of grinding process of MOC specimens (ground by hand and milled by machine) and leaching conditions (nitric acid concentration,nitric acid volume and leaching time) on analysis results of Cl- content was investigated in detail. Comparisons of results obtained by the new pretreatment with those obtained by the standard CNS14164 of Cl" were carried out for five MOC specimens from factory. The restuts show that the measured value of Cl" in powdered sample gound by hand was higher 0. 37% than milled by machine and the relative deviation was 3. 91% ; the nitric acid concentration had a certain impact on leaching Cl". Under the optimized conditions, the leaching volume reduced to 40 mL and leach liquor was nearly colourless which more conducive to follow-up operations, the relative error for detecting Cl" was less than 0.44% ,the precision and accuracy were better than CNS 14164 method.%氯氧镁胶凝材料的总Cl-含量是衡量产品吸潮、返卤和泛霜性能的关键指标之一.讨论了样品粉碎方式及硝酸酸溶浸取条件对样品中总Cl-测定的影响,并用优化后的预处理方法和台湾标准CNS14164方法对样品中总Cl-含量进行了分析.结果表明,手工研磨样品比机械粉碎样品中的总Cl-测定值偏高0.37％,相对偏差为3.91％；硝酸浓度对总Cl-的浸取有一定影响.经优化后的预处理方法为,取1g用机械粉碎至88μm的粉末样品,用40 mL体积比为15/85的稀硝酸浸取20 min,再过滤洗涤得到待分析液.优化预处理方法后,测定Cl-的相对误差在0.44％以内,且有利于后续的滴定分析操作,精密度和准确度均优于CNS14164方法.
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