碱性氧化物对煤灰熔融特征行为的影响

利用分析纯试剂制备了酸碱比为0.82，但Na₂O、CaO、MgO和Fe₂O₃含量不同的合成灰，并在815℃下在马弗炉中进行灼烧后，对其熔融温度进行测定。同时利用扫描电子显微镜-能谱仪（SEM-EDS）和X射线衍射仪（XRD）对样品微观形貌和矿物组成进行表征。结果表明：随着Na₂O质量分数从4%升高到12%，合成灰变形温度（DT）、软化温度（ST）、半球温度（HT）和流动温度（FT）分别从1225℃、1233℃、1255℃和1297℃下降为1162℃、1174℃、1181℃和1189℃，意味着Na₂O对合成灰具有较强的助熔效果；随着CaO和MgO含量在合成灰中分别增加，DT、ST和HT均单调上升，而FT则呈先下降后上升趋势，说明二者含量变化与合成灰熔融温度呈非线性关系；随着Fe₂O₃质量分数由5%增加至30%，FT由1215℃上升至1308℃，而其他3个熔融特征温度并无显著变化。通过SEM-EDS和XRD表征发现，合成灰中耐熔矿物（SiO₂和CaAl₂Si₂O₈等）和助熔矿物（CaMgSi₂O₆和NaAlSiO₄等）的比例变化和含钠矿物、含钙矿物之间低温共熔反应程度是影响其熔融温度的主要原因。综合对比所有合成煤灰熔融特征温度和化学组成发现，对于具有相同酸碱比的煤灰，DT主要与样品中Na₂O含量和碱土金属总量（CaO+MgO）密切相关影响，而FT主要受Na₂O和Fe₂O₃含量影响。

Effects of basic oxides on ash fusion characteristic of coal ash

The fusion characteristics of twenty-three synthetic ashes with the same acidic to basic ratio (R_a/b) of 0.82 but with varying acidic oxides including Na₂O, CaO, MgO, and Fe₂O₃ were investigated. The synthetic ashes were prepared in accordance with the R_a/b of Zhundong coal ash, and then ashed in a muffle furnace at 815℃. These ashes were then subjected to ash fusion analyzer, SEM-EDS and XRD analysis for their fusion temperatures (AFTs), microstructures and mineralogical composition. The results showed that deformation temperature (DT), softening temperature (ST), hemispherical temperature (HT) and flow temperature (FT) of the synthetic ash decreased from 1225℃, 1233℃, 1255℃ and 1297℃, respectively, to 1162°C, 1174℃, 1181℃ and 1189℃ as Na₂O content increased from 4% to 12%, indicating that Na₂O played a significant role in decreasing AFTs. Likewise, as the CaO and MgO contents increased, DT, ST and HT were decreased, while FT was decreased first but increased afterwards, indicating that the effect of CaO and MgO addition on AFTs were non-linear. Furthermore, significant changes in AFTs were not observed as Fe₂O₃ mass fraction varied from 5% to 30%, with the exception that FT increased from 1215℃ to 1308℃. SEM-EDS and XRD analysis revealed that the variation in fusion characteristics of the synthetic ashes were mainly attributed to the proportion of refractory minerals mainly SiO₂ and CaAl₂Si₂O₈ and the fluxing minerals such as CaMgSi₂O₆ and NaAlSiO₄, as well as the degree of eutectic formation between Na- and Ca- bearing minerals. A comprehensive comparison between the measured AFTs and their corresponding basic oxide contents showed that DT was mainly affected by the overall amount of alkaline-earth metal (CaO and MgO) and Na₂O content, whereas FT was closely associated with Na₂O and Fe₂O contents in the synthetic ash.