Studies on development of highly basic fluxes with large refining capacity

测定了CaO-Al_2 O_3、CaO-CaF_2、BaO-BaF_2、CaO-SiO_2-CaF_2和CaO-SiO_2-CaF_2-Na_2O等渣系的CO_2溶解度，并计算了这些渣系的碳酸盐容量。在一定的炉渣成分范围内，CO_2溶解度可以作为炉渣碱度的一个很好的指标。碳酸盐容量与磷、硫容量之间存在良好的相关性，它们是衡量炉渣脱磷、脱硫能力的指标。以碳酸盐容量作为衡量各种熔剂精炼能力的指标，研制出了具有高精炼能力的新型熔剂。结果表明，在CaO-CaF_2-SiO_2系熔剂中加入少量Na_2O可显著提高精炼能力。用该熔剂进行了铁水中各种杂质的去除试验。在熔剂中加入少量Na_2O，除去铁水中的钒、铌、钛和磷、硫，保留铁水中的锰。由于BaO-BaF_2系的精炼能力与碳酸盐容量相差很大，本文研究了在CaO-CaF_2-SiO_2系熔剂中加入BaO对磷分配的影响。磷的分区。即磷酸盐容量随熔剂中BaO含量的增加而增加。由于根据常规方法从熔融硅中去除硼是困难的，因此进行实验以研究高碱性熔剂是否有效地去除熔融硅中的硼。MgO-CaO-SiO_2和BaO-CaO-SiO_2熔剂处理降低了硅中的硼含量。发现有可能开发一种新的精炼工艺，从粗金属硅中提供比传统工艺更便宜的太阳能电池用硅。

The CO_2 solubilities were measured for the various kinds of slag systems such as CaO-Al_2O_3, CaO-CaF_2, BaO-BaF_2, CaO-SiO_2-CaF_2 and CaO-SiO_2-CaF_2-Na_2O etc. and carbonate capacities of these slags were calculated. It is found that the CO_2 solubilities can be a good measure of slag basicity in the limited range of slag composition. The good relationships between carbonate capacities and phosphate or sulfide capacities, which are the measure of dephosphorization or desulfurization capability of slag, were observed. Using the carbonate capacity as a index of refining capability for various fluxes, new fluxes whith refining capacities are very high were developed. As a result, a addition of a small amount of Na_2O to CaO-CaF_2-SiO_2 fluxes increases the refining capacity significantly. Experiments for the removal of various impurities from hot metal were conducted by using this flux. Vanadium, niobium and titanium as well as phosphorus and sulfur were removed from hot metel to flux with a addition of a small amount of Na_2O, retaining the manganese in the hot metal. Since the refining capacities for the BaO-BaF_2 system are estimated to be vary large from the carbonate capacities, the effect of a BaO addition to CaO-CaF_2-SiO_2 fluxes on the phosphorus partition was investigated. The phosphorus partitions. namely phosphate capacities, increase with increasing BaO content in flux. Since the removal of boron from molten silicon is difficult according to the conventional method, experiments were conducted in order to investigate whether the highly basic fluxes are effective for removing boron in molten silicon or not. The treatments with MgO-CaO-SiO_2 and BaO-CaO-SiO_2 fluxes decrease the boron content in silicon. It is found that there is a possibility to develop a new refining process which provide cheaper silicon for solar cell from crude metallic silicon than that refined by the conventional process.