Isothermal reduction experiments are carried out to study carbothermic reduction of hematite in hematite-graphite composite pellets. The carbothermic reduction is dominated by the direct reduction at the initial stage of reduction, and it is determined by the indirect reduction together with the carbon solution loss reaction when the CO partial pressure exceeds a certain value, which is dependent on the temperature. The reduction is greatly promoted due to the increment of the contact area between the hematite and graphite particles and enhancement of heat conduction in the hematite-graphite composite pellets.The indirect reduction together with the carbon solution loss reaction is markedly activated with increasing temperature. At a moderate carrier gas flow rate, the carbothermic reduction rate reaches the highest value. The reduction can also be effectively improved with decreasing the graphite particle size.The relationship of reduction products, heating temperature and holding time has been obtained from the XRD analysis results at the different stages for various temperatures under the present experimental conditions. The SEM observation indicates that the indirect reduction together with the carbon solution loss reaction should dominate the carbothermic reduction of hematite at the later stage of reduction.

The orientation of fibers in a liquid irradiated with ultrasound is studied to realize the noncontact directional control of reinforcing fibers in the molten matrix of a composite material. The equations of translational and rotational motions of a fiber in a standing wave field are derived. The numerical solutions show the movement of the fibers at various initial positions and their stable positions and directions. Experiments are performed using polystyrene fibers of various lengths suspended in an aqueous sugar solution. Both numerical and experimental results indicate that polystyrene fibers shorter than one-fourth of the wavelength are constrained at the pressure node and are oriented in the direction perpendicular to that of wave propagation. On the other hand, fibers ranging from one-fourth to one-half of the wavelength have orientation either parallel to the direction of wave propagation at the pressure loop or perpendicular to that at the pressure node depending on their initial positions and directions.

A new method of desulfurization of molten iron has been developed with magnesium vapor produced insitu by carbothermic reduction of magnesium oxide. Pellets, the main composition of which was magnesium oxide and carbon, were charged into a graphite tube. The tube was immersed into the molten iron to produce magnesium vapor. This process has been studied experimentally and theoretically. The rate of desulfurization depended mainly on the rate of reduction of magnesium oxide. Under the present experimental conditions, the desulfurization rate increased with increasing temperature and Ar carrier gas flow rate. The change in melt mass had little influence on the desulfurization efficiency of magnesium. The effect of pellet composition on the desulfurization has also been investigated. A mathematical model of the desulfurization has been proposed. The calculated results are in good agreement with the experimental results. The rate-controlling step changes with the progress of desulfurization during bubble formation and ascent periods. At the beginning of the formation period, both of the mass transfer of sulfur in the melt and magnesium in the bubble should be considered as rate-controlling steps. At the end of the ascent period, the magnesium partial pressure in the bubble decreases close to the value in equilibrium with the sulfur concentration in the melt. The mass transfer of magnesium in the bubble becomes much slower than that of sulfur in the melt and becomes the rate-controlling step. The desulfurization reaction mainly takes place on the bubble surface. The amount of desulfurization during the bubble formation period is larger than that during the bubble ascent period. Effects of pellet mass and initial sulfur concentration on desulfurization can be reasonably explained by the present mathematical model.

Magnesium vapor produced in-situ by aluminothermic reduction of magnesium oxide was injected directly into the melt with argon carrier gas to desulfurize molten iron to an ultra-low sulfur concentration in a short time.The desulfurization rate increased with increasing temperature in the range from 1 553 to 1 773 K. The desulfurization efficiency of pellet increased with decreasing pellet mass. The effects of initial sulfur concentration and carrier gas flow rate on the desulfurization were also investigated.A mathematical model is developed to calculate the desulfurization rate and good agreement is obtained between calculated and experimental results. The calculated results show that when the initial sulfur concentration is not very high, the mass transfer rate of magnesium in the bubble is faster than that of sulfur in the melt. The amount of desulfurization during the bubble ascent period is 3.5-9.3 times larger than that during the bubble formation period. Effects of the pellet mass and the initial sulfur concentration on desulfurization can be well explained by the present mathematical model.

In recent years, a large number of studies have been published on the use of high intensity ultrasonics in various high temperature technologies. This paper provides an overview of the recent achievements and ongoing works on the application of high intensity sound waves to pyrometallurgy and its related areas. The published results have strongly suggested that ultrasonics has the potential to play a more significant role in such areas as the dedusting of high-temperature exhaust gas, improvement of fuel-combustion efficiency, control of air-pollutant emissions, improvement of the quality of ingots, production of metal powders and ascast composite materials.At higher temperatures, special attractiveness of sound waves is associated with the fact that the waves can propagate through gas, liquids, and solids, and thus supply the acoustic energy from a cooled sonic generator to materials being processed under high temperature conditions. This provides a unique tool, for example, for controlling the rates of interfacial phenomena that is unachievable by any other methods under high temperatures.Industrial competitiveness of the ultrasonic-based technologies is reinforced by the relatively low cost of power-generating equipment and ultrasonic transducers. However, further research efforts are called for to develop new heat-resistant waveguide materials and to integrate the ultrasonic installations with existing industrial facilities in high temperature technologies.KEY WORDS: pyrometallurgy; high temperature; sonoprocessing; high power ultrasonics; non-linear phenomena; air pollutants; continuous casting; melt atomization; cast composites.applications have been summarized in a book by one of the authors of the present review. 4)The following two circumstances make ultrasonics especially applicable to high-temperature technologies: 1) There is a severely limited choice of techniques available for supplying energy under conditions involving higher temperatures. Among these techniques, sonic/ ultrasonic treatment or sonoprocessing should be competitive as regards both technique and cost, because it provides an effective transmission of acoustic energy from the ultrasonic generators to the materials being processed at a relatively low cost for ultrasonic equipment. 2) It is well-known that interfacial phenomena play an important role in governing many high-temperature processes. Examples are mass and heat transfer, crystal growth during the solidification of liquid metals, wetting, and emulsification. Sonic and ultrasonic waves propagate through homogeneous elastic mediums without significant losses. However, when the waves are incident upon an interface, the scattering or reflecting or of the waves from the interface is responsible for a number of nonlinear phenomena that occur at the interfaces. These provide a unique tool for controlling the rates of interfacial phenomena. Such a tool is unachievable by any other methods. Along with improvements in the earlier methods of sonoprocessing, a number of new ultrasonic appl...

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Copper and sulfur are the typical residual elements and impurities in steel. Previously, we reported the precipitation of very fine particles of Cu 2 S in copper and sulfur containing steel by strip casting process. In the present paper, the morphologies of copper sulfides in strip casting low carbon steels were distinguishably investigated by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).Four kinds of copper sulfide with different morphology were observed, namely duplex inclusion of oxide and sulfide (OS), plate-like copper sulfide (PS), shell-like copper sulfide surrounding the inclusions (SS), and nano-scale copper sulfide (NS), and their formation mechanisms were discussed.The OS is considered to firstly form as molten manganese silicate in molten steel, and grow up with the formation of sulfide inside of the silicate after the solidification of steel. The PS is considered to precipitate from the g-Fe phase with plate-like shape due to semicoherency with the g-Fe matrix. The SS is considered to precipitate in lower temperature ranges on the other pre-formed inclusions such as MnS, oxide and also Cu 2Ϫx S. The NS is considered to form in the low temperature range of g-Fe and especially in a-Fe phase as very fine particles due to the high supersaturation, low diffusivity of component elements and the coherency with the a-Fe matrix.Based on this classification, formation stage of oxide, MnS and Cu 2 S was clarified and described as like TTT diagram.

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