CaO–Al–Al_2O_3–CaCO_3–O_2体系燃烧合成铝酸钙热力学研究

Thermodynamic Analysis of Combustion Synthesis of Calcium Aluminate in CaO–Al–Al_2O_3–CaCO_3–O_2 System

计算了CaO–Al–Al_2O_3–CaCO_3–O_2体系燃烧合成铝酸钙的绝热温度,运用物质自由能函数理论,对主要反应进行了热力学计算,分析了燃烧合成铝酸钙的物相生成过程。结果表明:体系绝热温度随产物中CA_2含量的增加而降低,但均大于1800K,说明反应可自持;在反应初期,C_(12)A7的生成驱动力最大,其次是CA、CA_2的生成驱动力,C_(12)A_7为主要生成物相;随着反应的进行,铝酸钙不同物相间会发生转化,C_(12)A_7转化CA_2的驱动力最大,其次是C_(12)A_7转化为CA;C_(12)A_7和CA2共同转化成CA的驱动力最小,因此形成以CA、CA_2为主要物相的产物,且CA的含量大于CA_2的含量。燃波前端C_(12)A_7特征峰强度最大;反应区C_(12)A_7的特征峰强度减小,而CA、CA_2的特征峰强度增加;产物区C_(12)A_7特征峰强度消失,且CA的特征峰强度大于CA2的特征峰强度,表明产物中CA的含量大于CA2的,与热力学分析结果一致。在反应区有片状CA和颗粒状CA_2生成;在产物区CA_2弥散在CA中。

The phase formation of combustion synthesis of calcium aluminate was analyzed via calculation of the adiabatic temperature of CaO-Al-Al2O3-CaC03-O2 system, and the thermodynamic calculation of the main reactions was based on the theory of Gibbs free energy function. The results show that the adiabatic temperatures of the system are higher than 1 800 K and decrease with the increase of CA2 content in the product, indicating that the reaction can be self-sustaining; In the initial stage of reaction, CI2A7 is the main generating phase due to the maximum generating driving force of C2A7 and the subsequent generating force of CA and CA2. The conversation between different phases occurs as the reaction progresses. The driving force of transformation of C12A7 into CA2 is the maximum, and then the transformation of C12A7 into CA occurs, and the driving force of CA2 and CIzA7 transformed to CA is the minimum. Therefore, it can be deduced that CA and CA2 are the main products, and the content of CA is greater than that of CA2. According to the results of the quenched sample by X-ray diffraction, the peak of C12A7 is the most intense in the product of the combustion wave front. In the reaction zone, the characteristic peak intensity of C12A7 decreases, but the characteristic peak intensity of CA2 and CA increases. In the product zone, the characteristic peak intensity of C12A7 disappears and the characteristic peak intensity of CA is greater than that of CA2, which is in agreement with the thermodynamic analysis. The images by scanning electron microscopy indicate that the flake CA and granular CA2 are formed in the reaction zone. CA2 dispersed in CA appears in the product zone.