SPUTTERING BEHAVIOUR OF IRON SILICIDES UNDER LOWENERGY Ar^+ ION BOMBARDMENT

Surface compositions of Fe3Si, FeSi and FeSi2 under 0.1 to 5ke V Ar+ bombaniment have been investigated by using AES method, and the results indicate that the sudece compositions depend strongly on ion enerpy and sample bulk compositions. While in FeSi and FeSi2 only Fe enrichment in the selvage has been observed, in Fe3Si it is Si enriched when the ion enerpy is higher than 31OeV Competition between preferential sputtering and radiation enhanced segmpation is quoted to eoplain this phenomenon.

Investigating the Structurization Process of Iron Monosilicide Powders Obtained by High-Temperature Synthesis from the Preliminarily Mechanoactivated Burden

Raising the efficiency of production, for the most part depends on the use of secondary material resources, particularly such wastes as metallurgical slags of the operating plants. Huge quantity of such slags generates an urgent problem of their reasonable utilization with maximum extraction of valuable metals. The objective of the thesis is the development of an efficient technology for obtaining powder iron-monosilicon alloy by means of processing of iron and silicon containing dump slags on the basis of out-of-furnace aluminothermic reduction. Thus, structure of the obtained alloy strоngly depends on the state of the initial slags, on their correlation and on the amount of components contained in the complement of the burden. The structurization processes of the iron powder-like silicide obtained by the method of self-propagating high-temperature synthesis of the preliminarily mechano activated burden are investigated. The combination of these two methods allows to form unique materials and alloys, significantly reducing the power expenditure by applying the exothermal effect of the reactions, and to obtain a product with special physico-chemical properties. The results of the investigation are to obtain monophase iron silicide by preliminary mechano-chemical activation of the burden, containing a mixture of wastes of a certain composition obtained from metallurgical production—the Alaverdi copper-smelting and the Yerevan molybdenum factories, as well as KNO3 and CaO by combined aluminothermal reduction in the SHS regime. By the X-ray fluorescent method of analysis, the structurization process of the obtained alloy is studied. It is shown that, at the expense of preliminary mechano-chemical activation of the burden, a finer and homogeneous structure of powder-like iron silicide is formed.

Fe-Si particles on the surface of blast furnace coke

This study investigates the surface of unpolished samples of blast furnace （BF） coke drilled from the tuyere zone, which hosts Fe-Si particles （mostly Fe3Si） that vary in size, shape, depth of submersion （penetration） into the coke matrix, and contact features with the surface. Based on the shape of the particles and the extent of their contact with the coke matrix, they have been grouped into three major types： （I） sphere-like droplets with limited contact area, （II） semi-spheres with a larger contact area, and （III） irregular segregations with a spherical surface, which exhibit the largest contact area among the three types of particles. Considering the ratio between the height （h） of the particles and half of their length at the surface level （/） along the cross-section, these three types can be characterized as follows： （I） h 〉/, （II） h ~/, and （1II） h 〈/. All the three types of particles can be found near each other. The shape and the extent of the contact depend on the de- gree of penetration of the material into the matrix, which is a function of the composition of the particles. Type （I） particles were initially saturated with Si at an earlier stage and, for that reason, they can react less with carbon in the coke matrix than type （II） and （III）, thereby moving faster through the coke cone. Thermodynamic calculations have shown that the temperature interval of 1250-1300~C can be consid- ered the starting point for Si entering into molten iron under quartz-dominated coke ash. Accordingly, the initial pick-up of Si by molten iron can be assumed to be mineral-related. In terms of BF practice, better conditions for sliding Fe-Si droplets through the coke cone are available when they come into contact with free SiO2 concentrated into small grains, and when the SiO2/∑MexOy mass ratio in the coke ash is high.