不同温度下煤灰熔渣的结构演变规律

Structural evolution of coal ash slag at different temperatures

采用热力学计算和分子动力学模拟方法研究了高铁煤灰熔体的结构特征以及结构随温度的变化规律,计算了不同温度下Fe^3+和Fe^2+的含量,分析了径向分布函数、配位数、键角、桥氧与非桥氧、Qn结构单元等结构特征。热力学计算的结果显示温度升高有利于Fe^3+转变成Fe^2+,据此得到了Fe^3+/Fe^2+随温度的变化规律。在采用BMH势函数的基础上,分子动力学模拟显示熔体具有短程有序,长程无序的结构特征。随着温度升高,各离子对的径向分布函数曲线的高度和尖锐度下降,各离子的较高配位状态减少,较低配位状态增加,键角曲线的高度和锐度降低并向较小的方向移动,预示着离子的聚集程度减弱,熔体内部的无序化程度增强。氧的配位状态和Qn的变化是熔体聚合度变化的直观反映,温度升高导致三配位氧和桥氧含量降低,非桥氧和自由氧含量增加,并最终导致较高聚合度的Q4结构单元解体生成较低聚合度的Q3、Q2、Q1和Q0结构单元。

The structural characteristics of high iron coal ash melt and the variation of structure with temperature were studied by thermodynamic calculation and molecular dynamics simulation. The contents of Fe^3+and Fe^2+at different temperatures were calculated, and the radial distribution function, coordination number, bond angle,coordination state of oxygen and Qn structural units were analyzed. The results of thermodynamic calculations show that the increase of temperature is beneficial to the conversion of Fe^3+ to Fe^2+, and the change of Fe^3+/Fe^2+ with temperature is obtained. Based on the BMH potential function, molecular dynamics simulations show that the melt has short-range order and long-range disordered structural features. As the temperature increases, the height and sharpness of the radial distribution function curve of each ion pair decrease, the higher coordination state of each ion decreases and the lower coordination state increases, the height and sharpness of the bond angle curve decrease and the first peak moves in a smaller direction. These phenomena all indicate that the degree of aggregation of ions is weakened, and the degree of disorder inside the melt is enhanced. The coordination state of oxygen and the change of Qn are a direct reflection of the change of melt polymerization degree. The increase of temperature leads to the decrease of tri-coordinate oxygen and bridge oxygen, and the increase of non-bridge oxygen and free oxygen. Q4 structural unit disintegrated to generate Q3, Q2, Q1 and Q0 structural units with lower degree of polymerization.