Inaug.-diss.--Technische hochschule, Karlsruhe.

Inaug.-diss.--Technische hochschule, Karlsruhe.

No description available.

Rare earth ferrosilicon is a versatile alloy mainly used to control the detrimental effects of sulfur in steel and to modify graphite structures in cast iron. The aim of this study was to optimize the experimental conditions for the production of rare earth ferrosilicon alloy by using a preconcentrate prepared from a bastnasite type of ore present in the Beylikahir-EskiSehir region of Turkey. After unsuccessful initial tests realized with this preconcentrate, however, two batches of rich-rare earth oxide concentrates with different compositions, that were supplied from the Turkish glass producer SiSecam A.S. were utilized in order to investigate the effects of several variables like temperature, duration, amount of reducing agents etc. on the recovery of rare earth metals and the alloy compositions. The findings of these tests were then tested again on the bastnasite preconcentrate. There was no difficulty in obtaining rare earth ferrosilicon alloys containing 35-55 wt % rare earths, 25-40 wt % silicon and 5-25 wt % iron, with about 80 % rare earth metal recovery in the tests made with rich rare earth oxide concentrates, while alloys containing up to 44 wt % rare earths, with 48 % rare earth metal recovery could be produced with the bastnasite preconcentrate.

Rare earth ferrosilicon alloy is an important additive for ferrous metallurgy. It is mainly used to control the detrimental effects of sulfur in steel and to modify graphite structures in cast iron. The aim of this study was to optimize the conditions for the production of rare earth ferrosilicon alloy by metallothermic reduction process using a preconcentrate prepared from a bastnasite type of ore present in the Beylikahir-EskiSehir region of Turkey. In this study, the rare earth preconcentrate was reduced by aluminum together with ferrosilicon and rare earth ferrosilicon alloys were produced. The optimum conditions of reduction, which are time, temperature, reducer amounts and the basicity of the slag phase, were investigated by smelting in an induction furnace. At the end of the study, a rare earth ferrosilicon alloy containing 39.3 % rare earths, 37.5 % silicon, 19.3 % iron and 3.9 % aluminum was produced under the optimum conditions determined with 57.7 % rare earth metal recovery.

M. Tech. / The separation of minerals such as coal, diamonds and others have involved the use of a heavy medium. The heavy medium separation technique, used in the diamond industry as a primary concentrator, is a physical process that separates minerals of different specific densities based on their relative movement and resistance to motion in a viscous fluid. It is made up of a suspension of finely ground solid particles constituting a stable suspension. There is a wide range of materials that are used to prepare suspension media in Heavy Medium Separation (HMS), but Ferrosilicon has found a wider usage. Major demand for dense medium Ferrosilicon powder is from the diamond industry which accounts for 77 percent of milled sales. In HMS, either dynamic or static separators can be used, even though; dynamic separators are widely used because they give higher separation efficiencies. A number of accounts have been reported on the effects of stability and viscosity to the medium. It is, however, observed that the effect of ore mineralogy, which is a major contributing factor during ore and medium interaction, during separation, has not been properly taken into account, apart from the fact that ore mineralogy form a basis for HMS efficiency. The literature, however, does not cover a thorough investigation of the relationship between the recovery of diamond bearing ores and stability of Ferrosilicon grades media, as a function of physicochemical properties of ferrosilicon. Eight samples of Ferrosilicon, four milled and four atomized were used to prepare media to recover value from kimberlitic ore, alluvial ore and synthetic ore in a laboratory set-up HMS. Both Ferrosilicon and ore samples were characterized with the following techniques before use: XRD, XRF, SEM-EDAX and Screening, to investigate physico-chemical properties of ferrosilicon and ore mineralogy. The used Ferrosilicon was also characterized to investigate any v changes as Ferrosilicon medium interacted with the ores. Settling tests were performed on each Ferrosilicon grade to investigate media stability before and after recovery exercise. The stability of the media was then related to the recovery of each ore. In-circuit sample of ferrosilicon was collected from Letšeng diamonds to compare any changes with Ferrosilicon used in the laboratory, and also used to study the effects of contamination on the degradated medium. All recovery results were done in a static HMS, but in practice dense medium cyclones are widely used. The screening characterization technique revealed that there was a loss of finer particles size fraction, predominant in sieves 75 microns and 45 microns and that loss was highest with atomized grades than milled ferrosilicon grades. Minimal changes in density and chemical compositions were observed for each ferrosilicon grade. The loss of the finer fraction was found to effect changes in the settling rate of each ferrosilicon grade differently, hence changes in the stability of their media. The efficiency (Ep) of separation was found to vary with each grade of Ferrosilicon used, accompanied by a shift in cut point density indicating the influence of grade on the separation efficiency. The effects of medium stability on recovery for both ores showed that although both ores percentage recoveries differ, the trend of medium stability to recovery, with each Ferrosilicon grade, is the same. However, the recovery was found to be more dependent on the density of the medium, as the effects of loss of finer particle size fraction did not show any significant contribution to recovery, but rather on the medium loss. The mineralogy of the ores also had been observed to give a minimal or no contribution to the separation efficiency, if related to recovery. Milled Ferrosilicon is further recommended over atomized Ferrosilicon, based on cost and stability. The highest loss of atomized Ferrosilicon could escalate the operating costs and affect the stability of the medium. It should be remembered that the purchasing costs of atomized grades is higher than that of milled grades.

Ferrosilicon containing 50-75% Si and 1.0-5.0% Zr is used as inoculant in the cast iron industry. Zr can be added to liquid ferrosilicon by use of Zr metal or zirconium ferroalloy (FeSiZr). Then the recovery of Zr, i.e. the fraction of Zr transferred from the additive to the ferrosilicon, as well as the hit rate on specification is high. The aim of this study was to investigate the recovery of Zr from zircon sand, ZrSiO4, and zirconia, ZrO2, in comparison to zirconium ferroalloy when added to liquid ferrosilicon with 75% Si at 1600⁰C.  Also the refining effect of the different additives on Al was investigated. The experiments were carried out by stirring samples of controlled amounts of ferrosilicon and Zr additive in a graphite crucible at 1600⁰C and under inert Ar atmosphere for certain amounts of time. The reaction between ferrosilicon and Zr additive was stopped by rapid cooling of the samples. ICP-OES provided the concentration of Zr and Al and LECO O/N the concentration of O. SEM-ESD was used to examine the microstructures of ferrosilicon and Zr additive after experiments. It was found that ZrO2 was reduced by Si at the particle surface to yield dissolved Zr and ZrSiO4. The ZrSiO4 additive decomposed via two simultaneous reactions, one yielding ZrO2, Si and O2 and the other Zr, Si and O2. The recovery of Zr from ZrO2 and ZrSiO4 was significantly lower than from FeSiZr. Of ZrO2 and ZrSiO4, ZrO2 yielded the highest Zr recovery; the difference was much bigger than predicted by thermodynamics. It was discussed if that could be due to a higher reaction rate of the ZrO2, caused by the smaller size (APS 1 µm compared to d50 91 µm) and larger surface area of this addition. It was also found that utilization of density differences to separate the ferrosilicon and Zr additive did not work for zirconia under the same conditions as it worked for zircon sand, although zirconia has a higher density than zircon sand. The reason was the smaller particle size of the ZrO2 powder. No refining of Al was observed.

No / Alpha phase sintering, sinter hardening, and mechanical properties of prealloyed Fe-1.5Mo base powder with and without additions of elemental Si, ferrosilicon, and carbon under various process conditions have been investigated. Liquid paraffin, as a new lubricating agent, was found to be useful in reducing segregation, interparticle and die wall frictions, as well as reducing ejection forces and die and tool wear. It was found that addition of Si to the base powder enhanced the sintering process by stabilisation of the ¿-phase and formation of two kinds of liquid phase at ~1045 and ~1180°C, corresponding to the solidus and liquidus temperatures, respectively. This addition increased the tensile strength of the as sintered Fe-1.5Mo from 174 to 445 MPa owing to massive solid solution strengthening effect of Si. An optimum sinter hardenable alloy, of composition Fe-1.5Mo + 3Si + 1.2C, provided a high sintered density of 7.55 g cm-3, tensile and bend strengths of 764 and 1405 MPa, respectively, with 2.5% elongation, after sintering at 1250°C for 1 h under hydrogen or vacuum using moderate cooling rates of ¿ 20 K min-1. Faster cooling rates caused brittleness and very low UTS for the high carbon steel. Full heat treatment improved the UTS by 200 MPa which was useful only for the high carbon steel with high cooling rates ¿ 30 K min-1. Depending on the cooling rate, the as sintered microstructures consisted of mainly fine or coarse pearlite, bainite, martensite, and some retained austenite with hardness in the range 250-720 HV10. Some proeutectoid grain boundary cementites were also present in the as sintered high carbon steel. This work, therefore, has shown that high densities with acceptable microstructures and good mechanical properties are achievable with single stage compaction and single sintering operations by using the optimum process conditions and alloying composition without the need for a post-sintering heat treatment.