Surface tension of melts of СаО – SiO 2 – Al 2 O 3 – В 2 O 3 system

Using the method of experiment planning by simplex, the surface tension of the melts of СаО – SiO 2 – Al 2 O 3  – В 2 O 3  system was researched. The local part of the system was explored which covered the process of ferrosilicon, silicochrome, cement clinker, ceramics, glass, and sittals production. The amount of oxides in it was (%): 9.8 – 52.0 CaO; 0 – 70.4 SiO 2 ; 0 – 51.5 Al 2 O 3  and 0 – 20 B 2 O 3 . A mathematical model of surface tension dependence on the melts composition has been created and diagrams in the form of tetrahedron sections in B 2 O 3 have been constructed. It was found that, in the CaO – SiO 2 – Al 2 O 3 system, which is basic for metallurgy, melts with a high surface tension adjoin the binary side of CaO – Al 2 O 3 in the area of calcium aluminates crystallization which have small sizes, high charge and due to this bond to melt volume. With the introduction of SiO 2 , σ of melts decreases due to the formation of large aluminosilicon formations of the [Al 2 Si 2 O 8 ] 2– type, rankinite groups Si 2 O 7 6- , and ring complex [Si 3 O 9 ] 6- pseudo-wollastonite anion. The complication of anions due to polymerization leads to a drop of surface tension because of a decrease in charge ratio of the latter to the radius and, consequently, the strength of bond with cations. Boron anhydride injection causes a decrease in surface tension of melts СаО – SiO 2 – Al 2 О 3 which can be explained by boron transition at high temperature from four oxygen-coordinated (BO 4 5- ) to three oxygen-coordinated state (BO 3 3- ). Formed flat triangles BO 3 3-  or complexes with them are loosely related to the melt’s volume, they are forced out to the surface and reduce surface tension. Mostly this affects the main aluminate melts, rather than acid ones. The latter can be explained by the closeness of the capillary activity of boron – and silicon-oxygen anions. The surface phenomena between the products of blast-furnace smelting of titanomagnetite iron ores have been studied experimentally using the method of lying drop. It was noted that the highest adhesion forces (work of adhesion) take place between slag and grenal (cast iron with a high titanium and silicon content), which is the reason for the loss of metal at the outlet with slags during the processing of such ores. Boron loaded into the blast furnace (in the form of natural ores) is redistributed under reduction conditions between cast iron, grenal and slag. Experiments have shown that the presence of boron in slag at the level of microconcentrations reduces the work of adhesion from 688 to 436 MN/m (by 37 %). Industrial experiments have shown that this helped to reduce the loss of valuable vanadium-containing cast iron with slags by 1.2 – 1.5 times with a simultaneous improvement in smelting performance.