纳米/微米碳酸钙的结构表征和热分解行为

采用棕榈酸对纳米碳酸钙进行有机表面改性, 运用SEM﹑TEM、XRD、FTIR 及TG-DTG 对表面改性前后的纳米碳酸钙进行表征, 并与微米碳酸钙的微晶结构及热分解特性进行比较. FTIR 分析结果确证了棕榈酸与纳米碳酸钙表面是以化学键合和物理吸附方式相结合, 粒子表面存在羧基等有机官能团的红外吸收特征. 对比研究发现, 碳酸钙微晶纳米化后, 其红外V3特征吸收峰出现约35 cm-1 的蓝移现象, 并且明显窄化. 初步解释了纳米碳酸钙红外吸收峰蓝移的原因, 认为尺寸效应和晶体场效应是影响纳米碳酸钙红外光谱特征的主要因素. 微晶结构的变化使得纳米碳酸钙的热分解反应表现出反常特性, 热分解温度较微米碳酸钙下降了40.6 ℃.

Structural Characterization and Thermal Decomposition Behavior of Microsized and Nanosized CaCO3

The surface organic modification of nanosized CaCO3 with palmitic acid was carried out. The prepared samples were characterized by SEM, TEM, XRD, FTIR, and TG-DTG techniques. A comparative study on the crystal structure and thermal decomposition characteristics of nanosized CaCO3, modified nanosized CaCO3, and microsized CaCO3 was made. According to the spectra of FTIR, it was inferred that the chemical binding and the physical adsorption between palmitic acid and nanosized CaCO3 have happened during the modification reaction. The results also revealed that the infrared absorption peaks of C—O bond of modified and unmodified nanosized CaCO3 shifted to a higher frequency by 35 cm-1 compared with that of microsized CaCO3. The mechanism of blue shift in nanosized CaCO3 was discussed, and it was believed that crystalline electric field effect and size effect influenced their infrared spectra. TG-DTG analysis showed that nanosized CaCO3, modified nanosized CaCO3, and microsized CaCO3 decomposed at 735.0, 764.7, and 775.6 ℃, respectively. The decrease of the decomposition temperature was supposed to be related to the lattice expansion and crystallographic deformation of nanosized CaCO3.