Thermodynamics of the Si-C-O system for the production of silicon carbide and metallic silicon

The predominance diagrams of the Si-C-O system for 1350 to 2200 °C have been constructed thermodynamically by taking into account the presence of liquid silicon monoxide. The high-temperature behavior of various feeds, such as the SiO₂-C and SiO₂-SiC systems, have been calculated as functions of mixing ratio and reaction temperature by using the method of equilibrium mass-balance. For an efficient SiC-making, a charge having a C/Si ratio of 2.91 should be heated between 2035 and 2045 °C, where SiC crystals can be grown mainlyvia gas-phase reactions of SiO(g). Metallic silicon cannot be produced unless a charge of the Si-C-O system is heated above 2037 °C. In Si-making, liquid SiO plays an important role in that the yield can be improved substantially by enhancing the condensation of SiO gas in the upper cooler part of the furnace. This work also lends thermodynamic proof and support to the double-reactor model, in which a greater fixation of ascending SiO gas on carbon as SiC is considered essential for obtaining a higher silicon yield in industrial furnaces. Some fundamental strategies useful to the improvements of commercial Si- and SiC-making operations have been described quantitatively.     

Impact of ethanol addition on the solubility of various soybean isoflavones in supercritical carbon dioxide and the effect of glycoside chain in isoflavones

Solubilities of glycoside isoflavones (daidzin, genistin and glycitin) and their aglycons (daidzein, genistein and glycitein) in supercritical carbon dioxide (SCCO₂) were measured. In the SCCO₂-only system, the solubility of glycoside isoflavones was very low. Adding over 0.1 molar fraction of ethanol to SCCO₂ increased the solubility of glycoside isoflavones. The solubility was almost proportional to the third power of the molar fraction of ethanol. Adding ethanol significantly affected the solubility of glycoside isoflavones. In particular, the solubility of daidzin was remarkably increased by ethanol addition. The solubility of six tested isoflavones in SCCO₂ with ethanol was correlated with the second virial coefficient. The solubility depended on seventh power of the molar fraction of ethanol in SCCO₂. This suggested that the addition of ethanol facilitated cluster formation of CO₂ molecules in the supercritical phase, enhancing the solubility of isoflavones. A SCCO₂ and ethanol binary system was especially effective in extracting glycoside isoflavones.     

A holonic control system based on a universal learning network

A new control method is presented using the holonic concept on a universal learning network (ULN). The holonic concept was proposed by Arthur Koestler in 1905. Its aim is to harmonize entire systems with partial systems that have hierarchal structures. On the other hand, a ULN that models and controls large-scale complicated systems such as industrial plants and, economic, social, and life phenomena is proposed. In this paper, a holonic control system based on the holonic concept and ULN is presented. From simulation results from a nonlinear crane system, it has been proved that holonic control can harmonize the system rather than optimize it, which used to be the conventional method in control engineering.     

Volatilization of bismuth in copper matte converting — computer simulation

A computer model has been developed to simulate the behavior of bismuth in copper matte converting at 1100 to 1300 ‡C. The rate equation is integrated numerically by dividing a continuous process of matte converting into a great number of microsteps, in each of which the volatilization of Bi-bearing gases is thermodynamically calculated by assuming a steady state. The bubbles of offgas consisting of SO₂ and N₂ are assumed to be saturated with the vapors of BiS, Bi, BiO, and Bi₂. However, the partial pressures of BiO and Bi₂ are found to remain negligible at all stages of converting. BiS is the most volatile species over the slag-making stage with low grade mattes, but its volatility decreases markedly, becoming negligibly low over white metal. When the copper content of the initial matte is known together with the weight of matte, converting temperature and blowing rate of tuyere air, the present computer model can predict the Bi contents in all the phases involved (gas, slag, matte, copper) at any given time. The predictions by the present computer model are compared with the known commercial data from various smelters around the world. The agreements between the computer predictions and the commercial data are excellent in all cases, so that the present computer model can be used to monitor and optimize the bismuth elimination in the actual industrial operations of copper matte converting. Formerly Associate Professor, Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112     

Activities of CoS and FeS in copper mattes and the behavior of cobalt in copper smelting

The distributions of cobalt and iron between metallic copper and high copper mattes were measured at 1400 and 1500 K. A value of 0.40 ±0.02 was found as the Raoultian activity coefficient of CoS at infinite dilution in the Cu₂S-FeS-CoS mattes. The present activities of FeS in the Cu-saturated Cu₂S-FeS mattes were found to deviate more positively than those reported by Krivsky and Schuhmann at 1623 K, and the positive deviation from the Temkin’s ideality was greater at 1400 K than at 1500 K. Using the activity coefficient of CoS, the partitions of cobalt between copper mattes and fayalitic slags were calculated for various conditions of copper smelting. It was found that cobalt exhibits, in the matte-slag equilibria, chemical properties intermediate between nickel and iron, but much closer to iron than to nickel. The overall recovery of cobalt in blister copper depends on matte grade, and is as low as 3 pct at best. When a high cobalt recovery is desired, therefore, a copper concentrate rich in cobalt must not be processed by conventional pyrometallurgical technology in view of the inevitably high loss to slag. M. NAGAMORI, formerly Associate Professor, Department of Metallurgical Engineering, University of Utah, Salt Lake City, Utah.     

Thermodynamics of copper matte converting: Part I. Fundamentals of the noranda process

This paper presents a computer-oriented thermodynamic method to analyze copper matte smelting and converting, the system of which was ideally defined as consisting of five major components: Cu, Fe, S, O and SiO2. As an example of its application, the method was demonstrated in establishing a steady-state model for the Noranda Process producing either metallic copper or high grade matte. Process variables such as temperature, oxygen enrichment, charge (or concentrate) composition, matte grade and magnetite content of slag are integrated into one computer model. The model gives the chemical composition of metallic copper, matte and slag phases for any specified condition. Mathematical formulae accounting for physical entrainment in the melts are also presented to correlate the computed melt composition with that observed. The computer model can provide predictions as to the effects of operating and chemical parameters and can contribute to improved metallurgical control.     

Enhanced and prolonged production of plantlets regenerated from carrot callus in a viscous additive-supplemented medium

To reduce the hydrodynamic stress in plant cell culture and enhance the production of regenerated plantlets, a liquid medium containing a viscous additive was newly designed and plantlet production from embryogenic carrot callus cultivated in the medium was examined. Na-alginate or carboxymethyl cellulose (CMC) was used as the viscous additive. The viscosity of the medium increased with increasing additive content and the number of regenerated plantlets also increased. When carrot calli were cultivated in the medium containing 0.4% CMC, designated as N medium (viscosity, 3 mPa.s), the maximum enhancement of plantlet regeneration, approximately 2.5 times higher than that in the control medium, was obtained. Enlargement of callus size observed in N medium is considered to be the main reason for the enhanced plantlet regeneration. Regeneration enhancement was sufficiently induced after calli were cultivated once in N medium, but this regeneration ability rapidly disappeared after once cultivation in the conventional medium. In repeated batch culture using N medium, plantlet production continued at a high level for 18 batches (250 d) with no significant decrease, while in the control culture without CMC the number of plantlets produced dropped to almost zero by the sixth batch (84 d).