Studies on development of highly basic fluxes with large refining capacity

测定了CaO-Al_2O_3、CaO-CaF_2、BaO-BaF_2、CaO-SiO_2-CaF_2、CaO-SiO_2-CaF_2-Na_2O等渣系的CO_2溶解度，计算了这些渣系的碳酸盐容量。研究发现，在炉渣成分有限的范围内，CO_2的溶解度可以很好地衡量炉渣碱度。碳酸盐容量与衡量炉渣脱磷或脱硫能力的磷酸盐或硫化物容量之间存在良好的相关性。以碳酸盐能力作为衡量各种熔剂精炼能力的指标，研制出具有很高精炼能力的新型熔剂。结果表明，在CaO-CaF_2-SiO_2熔剂中加入少量Na_2O可显著提高精炼能力。用该助熔剂对铁水中的各种杂质进行了脱除试验。在铁水中加入少量Na2O，除钒、铌、钛、磷、硫外，还保留了铁水中的锰。由于BaO-BaF_2系统的精炼能力估计与碳酸盐的能力相差很大，因此研究了BaO加入CaO-CaF_2-SiO_2熔剂对磷分配的影响。磷的分隔物。即磷酸盐容量随着助熔剂中BaO含量的增加而增加。由于常规方法难以脱除硅液中的硼，为考察高碱性熔剂对脱除硅液中的硼是否有效进行了实验研究。添加MgO-CaO-SiO_2和BaO-CaO-SiO_2熔剂的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，以粗金属硅为原料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.