铝成分对EDTA法测定水泥中氧化钙和氧化镁的影响

Effect of Aluminum on Determination of Calcium Oxide and Magnesium Oxide in Cement by EDTA

水泥作为工程材料的主体其质量对建筑安全有直接作用。水泥材料中如果存在许多游离氧化钙和氧化镁成分,在胶凝硬化过程里会发生不均匀体积变化,如龟裂、松脆、弯曲及崩溃等不良状况继而破坏混凝土稳定。现行国家标准《水泥化学分析方法》(GB/T176—2017)中EDTA检测CaO与Mg O成分时测试结果并不稳定。“掩蔽”效果常不理想,并使得反应终点延迟、放大和反复。标准梯度Al^(3+)溶液等效测试结果显示0~12%的Al2O3质量分数(以占0.5 g,250 mL计)在掩蔽充分时并不会影响测试终点,在掩蔽效果不充分时两性铝成分会重新进入溶液,引发新的配位反应,EDTA造成标准溶液消耗增多、Ca O测量结果偏大。溶液p H范围对测试结果有明显影响,并应该控制(HOCH2CH2)3N加入顺序,确保Fe^(3+)、Al^(3+)等金属离子被完全结合掩蔽提高试验结果准确度。

As the main body of engineering materials,the cementquality has direct effect on building safety.If there are many free calcium oxide and magnesium oxide components in the cement material,volume changes will occur during the cementation and hardening process,and adverse conditions such as cracking,bending,brittleness and collapse will then destroy the stability of the concrete.In the current national standard"Chemical Analysis of Cement"(GB/T176—2017),the test results of EDTA in detecting CaO and MgO components are not stable.The"masking"effect is often suboptimal and results in delayed,amplified,and repeated reaction endpoints.The equivalent test results of the standard gradient Al^(3+)solution show that the Al2O3 mass fraction of 0~12%(accounting for 0.5 g,250 mL)will not affect the test end point when the masking effect is sufficient.The new coordination reaction,EDTA caused the consumption of the standard solution to increase and the CaO measurement results to be too large.The pH range of the solution has significant impact on the test results,and the order of adding(HOCH2CH2)3N should be controlled to ensure that Fe^(3+),Al^(3+)and other metal ions are completely combined and masked to improve the accuracy of the test results.