Thermodynamics of phosphorus in carbon-saturated manganese-based alloys

The interaction coefficient of phosphorus with silicon in a Mn-Si-C_sat alloy has been measured at 1573 K, equilibrating CaC₂, C, and Ca₃P₂ in a quartz capsule to keep the phosphorus partial pressure as high as 33.7 Pa. The activity coefficient of phosphorus in the melts increases with increasing silicon content, and the interaction parameter between silicon and phosphorus in the melts at carbon saturation ε^Si_P, C_sat was found to be 10.4. The activity of phosphorus in a carbon-saturated Fe-Mn alloy was also determined at temperatures of 1573 to 1673 K using a chemical equilibration technique between BaO-BaF₂ fluxes and Fe-Mn-C_sat with manganese mass contents ranging from 0 to 85.3 %. A slight decrease in the activity coefficient of phosphorus in Fe-Mn-C_sat alloys was observed with increasing manganese content, as a reflection of a stronger interaction between manganese and phosphorus than that between iron and phosphorus. The value for e^Mn_P,Csat was found to be -0.0029 between 1573 and 1673 K.     

Sintering behaviour of the diamond-cobalt system at high temperature and pressure

A powder mixture of diamond—8.9 vol % Co was consolidatedin situ on a WC-10 wt % Co base at temperatures of 1300 to 1500° C under a pressure of 5.8 GPa. The sintered body obtained at 1300° C, which is below the diamond—cobalt eutectic point, was not hard, and the surface of the diamond particle was partially graphitized. On the other hand, the sintered body obtained at 1400 to 1500° C was fairly hard. A strong correlation was also observed between hardness and the cobalt content found in the sintered body. The cobalt content in the harder sintered body was clearly lower compared with that of the softer one. The surface graphitization of the diamond particles is necessary to the transfer of cobalt during the sintering of diamond. In sintering the diamond-cobalt system, the sinterability of diamond was closely related to the feasibility of transformation from diamond to graphite.     

Deposition characteristics and properties of iron nitride films by CVD using organometallic compound

Iron nitride films were prepared by chemical vapour deposition from the gas mixture of Fe(C₅H₅)₂-NH₃-H₂-CO₂. The effects of deposition parameters on the deposition characteristics were investigated. Iron nitride films were deposited above 500 ° C and the films of -Fe₄N single phase were deposited above 700 ° C. At 700 ° C and under the total gas flow rate from 1 to 8 l min^–1, the deposition rate of the film may be controlled by the transport of Fe(C₅H₅)₂ molecules to the surface of the deposits. At 700 °C and under the total gas flow rate of 4 l min^–1, the phases and nitrogen contents of the films were determined bypNH₃/pH₂ ^3/2, the controlling factor of the nitrogen contents of the films. Decreasing of the total gas flow rate and increasingpCO₂ increased the nitrogen contents of the films and phases with higher nitrogen were deposited. On the other hand, increasingpFe(C₅H₅)₂ and the absence ofpCO₂ increases the carbon contents of the films, and the phase with a greater solubility in carbon, i.e. -Fe₂N, was codeposited with -Fe₄N. The saturation magnetization of the films deposited at 700 ° C was in good agreement with that reported for the bulk iron nitride, which depended not on the deposition conditions but on the nitrogen contents of the films.     

Formation of amorphous Al-Cr alloys by mechanical alloying of elemental aluminium and chromium powders

Mechanical alloying (MA) of elemental aluminium and chromium powders has been performed using a conventional ball-mill. The MA process produces composite metal powders and homogeneously alloyed powders. During continuous heating at the rate of 0.33 K sec^–1 Al-15 at% Cr samples ball-milled for 800 and 1000 h showed two exothermal peaks. The first peak which appeared at the lower temperature corresponds to amorphization of the MA powders. It was confirmed by X-ray and transmission electron microscopy that the heattreated powders, quenched from a temperature just above the first peak, were amorphous phase. Amorphous Al-Cr alloys were formed using elemental powders by MA and subsequent heat treatment.     

Coupling phenomena in the transfer of elements between a gas phase and iron melts

The simultaneous transfer of Si and C from a gas phase containing SiO and CO to liquid Fe-C alloys has been investigated. It was found that, although the silicon content of the melt increased with time as expected, the carbon content initially decreased, in spite of the fact that the carbon potential of the gas phase was above that of the liquid alloy. These phenomena are interpreted in terms of irreversible thermodynamics which shows that the overall transfer reactions are comprised of coupled reactions: SiO(g) + CO(g) →Si + CO₂(g) andC + CO₂(g) → 2CO(g). It is also shown that the simultaneous transfer of carbon and oxygen from gas mixtures of CO and CO₂ to liquid iron occurs via the coupled reactions CO₂(g) →O + CO(g) and 2CO(g) →C + CO₂. In each case there is a predominant, or driving reaction which promotes the other.     

Thermodynamics of sulfur in the BaO-MnO-SiO2 flux system

The sulfide capacity of the molten BaO-MnO-SiO₂ system was determined by measuring the sulfur partition ratio between the oxide and an Ag-S alloy in a controlled CO-CO₂-Ar gas mixture at 1573 K for two purposes. One is to develop highly basic fluxes which can extensively desulfurize manganese-based alloys, and the other is to examine the effect of BaO addition on thermodynamic properties of sulfur in the MnO-SiO₂ melts from which MnS precipitates functioning as the nucleus for subsequent γ -α transformation of steel. The sulfide capacity of the BaO-MnO-SiO₂ system strongly depends on the composition, and MnO has been found to enhance sulfide capacity to a greater extent than BaO at less basic compositions.     

The redox equilibria of copper ions in the molten silicate fluxes as a measure of basicity

The redox equilibria of copper ions in the molten NaO_0.5-SiO₂, NaO_0.5-NaF-SiO₂, NaO_0.5-CaO-SiO₂, CaO-CaF₂-SiO₂, CaO-MgO-SiO₂, and CaO-SiO₂ systems have been measured in order to seek a new measure of flux basicity. The Cu²⁺/Cu⁺ ratio decreases with increasing the content of basic oxide. The correlations between the Cu²⁺/Cu⁺ ratio and other refining indexes, such as carbonate, sulfide, and phosphate capacities, CaO activity, and theoretical optical basicity are discussed.     

Thermodynamics of antimony and arsenic in BaO–BaF2 melts

Since the interest in removing tramp elements from steels is increasing, one of the authors has reported the thermodynamic behaviour of P, Sn, As, Sb, Bi, Pb and Cu in CaO–CaF₂ melts under strongly reducing conditions. In this investigation, the BaO–BaF₂ system, which is more basic than the CaO–CaF₂ system, was chosen as a flux and the thermodynamic behaviour of As and Sb in BaO–BaF₂ melts was studied at 1300°C under reducing conditions. The partition ratios of arsenic between Cu–As and BaO–BaF₂ melts and of antimony between Ag–Sb and BaO–BaF₂ melts were measured as functions of the flux composition and the partial pressure of oxygen. Both partition ratios increase with an increase in the BaO content of the flux and with a decrease in the partial pressure of oxygen. The reactions for the removal of arsenic and antimony have been identified. The partition ratios of arsenic and antimony between carbon saturated iron and BaO–BaF₂ melts are estimated and the possibility of the removal of tramp elements from molten iron by using a BaO–BaF₂ flux is discussed.     

Development for 4th generation mobile communications

The great success of the i‐mode service shows that data communication services are becoming accepted in the mobile communication world. Multimedia mobile communication services will be provided by 3rd generation IMT‐2000 systems next year in Japan. Thus, the time has come to begin the research and development for 4th generation (4G) mobile communication systems. There exist many difficult issues for 4G systems, such as frequency resources, additional investment, higher speed wireless transmission technology and so on. Furthermore, a new concept must be discussed for 4G before solving these issues. This paper briefly presents current conditions of cellular systems and the development of IMT‐2000 in Japan. The concept and problems of the 4G system are then described along with new technologies that will be useful in solving technical problems. Copyright © 2001 John Wiley & Sons, Ltd.