Boron removal by titanium addition in solidification refining of silicon with Si-Al melt

In order to effectively remove B from Si for its use in solar cells, a process involving B removal by solidification refining of Si using a Si-Al melt with Ti addition was investigated. For clarifying the effect of Ti addition on B removal from the Si-Al melt, TiB₂ solubilities in Si-64.6 at. pct Al melt at 1173 K and Si-60.0 at. pct Al melt at 1273 K were determined by measuring the equilibrium concentrations of B and Ti in the presence of TiB₂ precipitates. The small solubilities of TiB₂ in the Si-Al melt indicate the effective removal of B from the Si-Al melt by Ti addition. Further, solidification experiments of Si-Al alloys containing B by Ti addition were performed, and the effect of Ti addition on the solidification refining of Si with the Si-Al melt was successfully confirmed.     

Fragmentation of faceted dendrite in solidification of undercooled B-doped Si melts

The fragmentation of the faceted dendrite of B-doped Si solidified from the undercooled melt was investigated using an electromagnetic levitator. The 〈110〉 dendrites, which grew at ΔT <∼100 K, never fragmented because they were composed of {111} planes with the lowest interface energy. On the other hand, the 〈100〉 dendrites, which grew at ΔT>∼100 K, showing fourfold axial symmetry, broke up into small pieces at undercoolings of more than 200 K. It was suggested that the capillary force acts on the interface with a relatively high energy to break up the dendrite into small pieces, since the 〈100〉 dendrites are composed of {110} and {100} planes with interface energies larger than that of the {111} plane. Moreover, striations of concentric circles formed by the segregation of B revealed that the remaining melt solidifies from the surface toward the center to engulf the fragmented dendrites. This solidification process seems different from those of typical metallic materials, in which the fragmented dendrites are randomly distributed throughout the sample and the remaining liquid solidifies from the fragmented dendrites. This solidification characteristic was discussed in relation to the influence of electromagnetic force on the microstructure of Si.     

Physical refining of steel melts by filtration

The removal of nonmetallic inclusions from steel melts prior to casting has significant merit. Laboratory prepared steel melts containing carefully prepared alumina inclusions have been successfully filtered at 1600 °C. Two distinct types of filters were used: (i) tabular alumina packed bed (0.2 to 0.5 cm nominal diameter) and (ii) extruded monolithic alumina (400 cells per square inch). The kinetics of the filtration process have been modeled, and inclusion removal efficiency of up to 96 pct has been achieved in laboratory melts. The results show that inclusion removal efficiency is a strong function of melt velocity in the range of 0.08 to 0.68 cm per second and is weakly dependent on filter length. The type of filter utilized affects inclusion removal efficiency significantly. The inclusion capture kinetics and the filtration characteristics of the filter media tested are discussed. Formerly with Drexel University, Philadelphia, PA.     

Removal of phosphorus from synthetic oxide melts

The behavior of phosphorus in FeO-Fe₂O₃-CaO-MgO-SiO₂-Al₂O₃-P₂O₅ oxide melts is experimentally studied. To determine the factors affecting the removal of phosphorus from the oxide melt to the gas phase, experiments are conducted with different melt basicity (CaO/SiO₂) and with different CO/CO₂ ratios in injection. The removal of phosphorus is greatest when the basicity is 0.5. At higher basicity, thermodynamic factors hinder the removal of phosphorus; at lower basicity, the viscosity of the melt is a hindrance. In kinetic calculations, the apparent activation energy of the process is found to be E = 140 ± 56 kJ/mol. That suggests that the process is limited by the diffusional mass transfer of phosphorus pentoxide in the liquid phase.     

Viscosity and nonequilibrium solidification of Co-P melts

The concentration dependences of the viscosity and solidification of Co-P melts containing from 16 to 25 at % P are studied by viscosimetry, differential thermal analysis, and metallography. A maximum near 20 at % P in the concentration dependence of the viscosity is observed for the first time. The maximum is associated with a composition short-range Co₄P-type order present in this composition range. On cooling the melts at rates of 20–100 K/min in the concentration range from 18 to 22 at % P, a metastable phase with a composition close to the eutectic composition (20 at % P) can form. This metastable phase decomposes on cooling to form equilibrium phases (Co and Co₂P).     

Theoretical treatment of the solidification of undercooled Fe-Cr-Ni melts

The solidification behavior of undercooled Fe-Cr-Ni melts is analyzed with respect to the competitive formation of body-centered cubic (bcc) phase (ferrite) and face-centered cubic (fcc) phase (austenite). The activation energies of homogeneous nucleation and growth velocities for both phases as functions of undercooling of the melt are calculated on the basis of current theories of nucleation and dendrite growth using data of thermodynamic properties available in the literature. As model systems for numerical calculations, the alloys Fe-18.5Cr-11Ni forming primary ferrite and Fe-18.5Cr-12.5Ni forming primary austenite under near-equilibrium solid-ification conditions are considered. Nucleation of the bcc phase is always promoted in the under-cooled primary ferrite alloy, whereas the barrier for bcc nucleation falls below that for fcc nucleation for large undercooling in primary austenite alloys. With rising undercooling, tran-sitions of the fastest growth mode were found from bcc to fcc and subsequently from fcc to bcc for the primary ferrite forming alloy and from fcc to bcc for the primary austenite forming alloy. The results of the calculations provide a basis for understanding contradictory experi-mental findings reported in the literature concerning phase selection in rapidly solidified stainless steel melts for different process conditions. Formerly Visiting Scientist at the Institut fur Raumsimulation     

Removal of a sulfur impurity from complex nickel melts in vacuum

Various methods of removing sulfur from a complex nickel melt are considered. They are based on the use of slags based on CaO or metallic calcium and the introduction of a rare-earth metal (La, Y) during melting in a vacuum induction furnace. Some properties of alloys (high-temperature strength, long-term strength, ductility) are improved after decreasing the sulfur content.     

High-Speed imaging and analysis of the solidification of undercooled nickel melts

Rapid solidification of undercooled pure nickel has been imaged at sufficiently high spatial resolution (64 ×X 64 pixels) and temporal resolution (40,500 frames/s) to observe interface shape and motion at solidification velocities exceeding 45 m/s. Imaging was of 8 g, quartz-enclosed melts at undercoolings of 70 to 300 K. Dendrite velocities within the melt were calculated from the surface velocities observed employing a simple geometric model of growth. Solidification was found to proceed invariably from a single nucleation point; growth velocity then followed an approximate power-law relationship with respect to undercooling up to some critical value ΔT*, where 150 K < ΔT* < 180 K. At higher undercoolings, velocity increased less rapidly than predicted by the power-law relationship and the interface morphology changed in appearance from angular to macroscopically smooth.     

A kinetic model for the vacuum refining of inductively stirred copper melts

An experimental investigation into the removal of impurities (bismuth, lead, arsenic, and antimony) from baths of molten copper (blister, anode and cathode type copper) under vacuum was carried out. A pilot scale vacuum induction melting facility was used for these tests. The effects of (1) vacuum levels of 8.0 to 40.0 Pascals, (2) melt temperatures of 1150 to 1350 °C, (3) melt surface area to volume ratios of 6 to 10 m⁻¹, (4) a water cooled condenser placed within a distance of two centimeters above the melt surface, and finally, (5) different levels of dissolved oxygen and/or sulfur contained in the melt, were studied. Kinetic data were obtained for evaluating the potential of a full scale vacuum melting facility. A mathematical model was also developed for the proper interpretation of the experimental results and for making projections for lower pressure and higher temperature levels. The rate of removal of bismuth and lead increased as the chamber pressure was lowered and the melt temperature increased, while removal of arsenic and antimony was negligible. Neither the melt surface area to volume ratio nor the distance of the condenser to melt surface had any significant effects on the rate constants governing the rate of removal of impurities. The rate of elimination of bismuth and lead over the range of 1150 to 1350 °C and 40.0 to 8.0 Pa followed first order kinetics. Removal rates were largely controlled by mass transport in the gas phase. Formerly Graduate Student at McGill University, Montreal, PQ, Canada     

Heterogeneous nucleation of solidification of Si by solid AI in hypoeutectic Al-Si alloy

Melt-spun Al-3 wt pct Si with and without ternary additions of Na and Sr has been heat-treated above the Al-Si eutectic temperature in a differential scanning calorimeter to form a microstructure of Al-Si eutectic liquid droplets embedded in the α-Al matrix. During subsequent cooling in the calorimeter, the heterogeneous nucleation temperature for solidification of Si in contact with the surrounding Al matrix depends sensitively on the alloy purity, with a nucleation undercooling which increases with increasing alloy purity from 9 to 63 K below the Al-Si eutectic temperature. These results are consistent with Southin’s hypothesis that low levels of trace P impurities are effective in catalyzing Si nucleation in contact with the surrounding Al matrix. With a low Al purity alloy, 0.1 wt pct Na addition increases the Si nucleation undercooling from 9 to 50 K, 0.15 wt pct Sr addition does not affect the Si nucleation temperature, and 0.3 wt pct Sr addition decreases the Si nucleation undercooling from 9 to 3 to 4 K. The solidified microstructure of the liquid Al-Si eutectic droplets embedded in the Al matrix depends on the Si nucleation undercooling. With low Si nucleation undercooling, each Al-Si eutectic liquid droplet solidifies to form one faceted Si particle; however, with high Si nucleation undercooling, each Al-Si eutectic droplet solidifies to form a large number of nonfaceted Si particles embedded in Al. Formerly with the Oxford Centre for Advanced Materials and Composites, Department of Materials, Oxford University     

Undercooling and solidification of Al-50 at. pct Si Alloy by electromagnetic levitation

Electromagnetic levitation is applied to achieve containerless solidification of 10-mm-diameter droplets of Al-50 at. pct Si. A maximum undercooling of 320 K is obtained. Phase morphologies on the droplet surfaces and on the deeply etched sections of the samples solidified at different undercoolings are examined by scanning electron microscopy. The primary silicon shows well-developed faceted dendrites at a small undercooling, but a fine granular form at a large undercooling. Stratified deposits of aluminum are found within the primary silicon plates, arising from solute pileup during growth. The microstructural refinement at a large undercooling has its origins in solute restriction of crystal growth and in fragmentation of the primary silicon dendrites. The form of the Al-Si eutectic is also found to be changed into an anomalous form at a large undercooling.     

Selective removal of iron contaminations from zinc-chloride melts by cementation with zinc

An investigation into the cementation of iron chloride from a zinc-chloride melt at 400 °C has been carried out with zinc powder. The variables studied include preparation of the chloride melt and the amount of zinc added. The effect of lead, copper, and cadmium on cementation of iron has also been investigated. According to the results, it is possible to reduce the iron concentration in zinc-chloride melts to 20 ppm with a small excess of zinc. The preparation of the melt proved to be very important. Insufficient purification of the melt with respect to oxides, hydroxides, and water resulted in a low reaction rate and high residual iron concentration.     

混合型铝土矿浮选脱硅试验研究

试验以俄罗斯某一水软铝石、三水铝石和一水硬铝石三种铝石混合型低品位铝土矿为研究对象,其关键技术是有效脱除非目的矿物如高岭石、绿泥石和伊利石。研究以矿石性质人手,结合以前的经验,以中国铝业郑州研究院开发的BKS-1为捕收剂,采用正浮选脱硅工艺技术提高矿石的铝硅比。通过多因素条件试验优化了适宜的工艺条件,当综合磨矿细度为90％,pH为9．5,六偏磷酸钠用量100g／t,BKS-1捕收剂用量为800g／t时,获得精矿铝硅比7．31,氧化铝回收率68．61％的工艺指标。     

Interaction of oxyfluoride melts of Ca,Si, Mg,Al, and Na with steels: I. Chromium-carbon-containing melts

The interaction of a mixture of Ca, Si, Mg, Al, and Na oxides and fluorides with two chromium-carbon-containing iron-based melts are experimentally studied at 1600°C and p _Ar = 0.1 MPa. The equilibrium concentrations of the components in the slag at a holding time of 500 s are determined. The chromate capacities of the oxyfluoride melts are calculated and related to the composition of the melted slag using its optical basicity.     

高拉碳法冶炼82B系列钢的生产实践

根据首都钢铁股份有限公司第二炼钢厂生产的实际情况,初步分析了高拉碳法冶炼82B系列钢的过程控制。在分析了复吹转炉脱磷的热力学与动力学条件的基础上,利用吹炼前期低温的有利条件实现钢-渣充分脱磷、前期双渣后进行少渣冶炼、高碳出钢,以实现复吹转炉吹炼前期高效脱磷。出钢碳质量分数由原来的平均0.10%左右提高到0.34%左右,大于0.40%者达到50%。