Manufacturing lightweight aggregate (LWA) (ie, porous ceramics) by means of a sintering technique requires a delicate balance among three conditions: (a) forming a sufficient amount of molten liquid phase during sintering, (b) reaching an appropriate viscosity for solid‐liquid suspension, and (c) emitting a sufficient amount of gas that can be entrapped by the liquid phase to form pores. This study evaluates these three conditions in the production of LWAs made from two types of waste coal bottom ash (low‐calcium and high‐calcium), and relates them to the formation of LWA pore structure. A thermochemical analytical approach, including thermodynamic modeling and the Browning viscosity model, was used to quantify the extent of the liquid phase and calculate its viscosity. In conjunction with thermochemical analysis, an experimental approach including quantitative x‐ray diffractometry, thermogravimetric analysis, and x‐ray computed tomography was also used to identify the candidate chemical compounds that contribute to gas emission during sintering and to evaluate the LWA pore structure. The results indicated that a mass fraction of at least 50% for the liquid phase is required for a successful entrapment of emitted gaseous phases during sintering. Larger pores were observed in the microstructure of LWA samples made using high‐calcium bottom ash in comparison to those made with low‐calcium bottom ash. This observation was mainly attributed to the high‐calcium samples forming liquid phases with lower viscosities and emitting higher amounts of gaseous phase during sintering than did the low‐calcium samples. It was found that the gaseous phase was generated by hematite reduction and anhydrite decomposition, which led to the release of O₂ and SO₂.

中文翻译：

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用废煤底灰生产轻质骨料的热化学原理

通过烧结技术制造轻质骨料（LWA）（即多孔陶瓷）需要在以下三个条件之间达到微妙的平衡：（a）在烧结过程中形成足够量的熔融液相；（b）达到适当的固相粘度-液体悬浮液，以及（c）散发足以被液相截留而形成孔的气体。这项研究评估了由两种类型的废煤底灰（低钙和高钙）制成的LWA的生产中的这三个条件，并将它们与LWA孔结构的形成相关。使用热化学分析方法（包括热力学模型和布朗宁粘度模型）来量化液相的程度并计算其粘度。结合热化学分析，还使用了包括定量X射线衍射仪，热重分析和X射线计算机断层扫描在内的实验方法来鉴定在烧结过程中有助于气体排放的候选化学化合物，并评估LWA孔结构。结果表明，在烧结过程中，要成功截留排放的气相，需要液相的质量分数至少为50％。与用低钙底灰制成的LWA样品相比，在用高钙底灰制成的LWA样品的微观结构中观察到较大的孔。该观察结果主要归因于高钙样品在烧结过程中形成了粘度较低的液相，并且与低钙样品相比，在烧结过程中散发了更多的气相。₂和SO ₂。