G. Derge

Note on the Nature of Conduction in Liquid Iron Oxide and Iron Silicates

Current efficiency has been measured for the entire range of melts between iron oxide and the silica saturated slag. All compositions show some ionic conductivity, but the proportion of this type of conductance increases with the concentration of silica.

Surface Tensions of Silicates

The literature dealing with the surface tension of molten silicates with compositions of metallurgical interest has been reviewed. Useful generalizations exist with ionic potentials and types of chemical binding. There are numerous applications to operating problems.

Analysis of Oxygen in Titanium

THE pace of titanium research has been retarded somewhat by the lack of a suitable method of determining oxygen content. Here, the author describes a reliable method of oxygen analysis by a modification of the vacuum fusion techniques which have become conventional for the analysis of gases in steel.

Surface Structure of Nonoxidizing Slags Containing Sulphur

Application of surface tension measurements has been made to molten silicates in order to determine the effect of sulphur upon the surface tensions of synthetic blast furnace slags. In melts with the same molar ratios of Al2O3 + SiO2 to the basic oxides BaO, CaO, and MgO, the surface tensions increase in the order of oxides listed. Sulphur lowers the surface tensions of the basic BaO, basic CaO, acid BaO, acid CaO, and acid MgO slags in that order; and the concentration of excess sulphur at the slag surface increases in this same order of slags. The rate and amount of desulphurization of iron by these slags is favored by a low excess surface sulphur in the slag.

EQUILIBRIUM BETWEEN TITANIUM IN LIQUID IRON AND TITANIUM OXIDES

The amounts of oxygen in liquid iron-titanium alloys up to 50 pet Ti were measured and the oxide phases in equilibrium with these alloys were determined by using Ti02 crucibles. A minimum of about 0.003 pet O occurs at less than 1 pet Ti. The various liquid and solid oxide phases can be arranged on a ternary isotherm.

Conductivity and Sulfur Activity in Liquid Copper Sulfide

The conductivity of liquid copper sulfide has been measured as a function of the mole fraction of sulfur in the melt at three temperatures: 1170°, 1250°, and 1300°C. The results show that a) the conductivity of copper-rich Cu2S is independent of the sulfur pressure in the furnace, and b) the conductivity of sulfur-rich copper sulfide increases rapidly with sulfur pressure. Assuming that the band theory is applicable to liquids leads to the conclusion that copper-rich copper sulfide is an intrinsic semiconductor, in which case electrons act as carriers. The activation energy for conduction in this case has been calculated to be 0.7 ev. On the other hand, sulfur-rich copper sulfide behaves as a p-type semiconductor, positive holes being responsible for conduction.

SELF-DIFFUSION OF IRON IN MOLTEN Fe-C ALLOYS

Self-diffusion coefficients of iron in molten Fe-C alloys have been measured by using the capillary method. In addition, the samples have been autoradiographed and sectioned to insure that no significant convection has occurred during the diffusion. The results can be represented by the equation D = 4.3×10−3 exp (—12.200/RT) for carbon = 4.6 pct and T = 1513° to 1633°K; and D = 1.0×10−2 exp (—15,700/RT) for carbon = 2.5 pct and T = 1613° to 1673°K. The D values are higher and the heat of activation for diffusion lower in alloys containing more carbon. Calculation based on the Einstein-Stokes equation indicates that the diffusing species is iron ion.

Electrical Conduction in Molten Cu-Fe Sulphide Mattes

Using a new alternating-current potentiometer circuit and a specially designed four-terminal cell, the specific conductance of molten Cu2S−FeS mattes was measured as a function of temperature, from the liquidus to 1500°C, over the complete range of composition. The high conductivities, about 1500 ohm−1 cm−1 for FeS and 100 ohm−1 cm−1 for Cu2S, indicate that the conduction is electronic rather than ionic. Molten FeS has a negative temperature coefficient of specific conductance, resembling metallic conduction. Molten Cu2S has a positive temperature coefficient, resembling semiconduction. The binary roughly follows an additive rule of mixtures with respect to both magnitude and temperature coefficient of specific conductance. Metallic bonding in the liquid is postulated to explain these phenomena.

Diffusion in Liquid Lead-Bismuth Alloys

Diffusivity of bismuth in liquid Pb-Bi alloys has been measured by the capillary reservoir method as a function of temperature and composition. Fair agreement between theory and experiment is found for the measured diffusion coefficients and activation energies of diffusivity and viscosity in dilute lead alloys. The measured diffusion coefficients in the high bismuth alloys describe mass transport in special concentration gradients.

IONIC NATURE OF LIQUID IRON-SILICATE SLAGS

Measurements of current efficiency on iron-silicate slags in iron crucibles showed that conduction is about 10 pct ionic in slags with less than 10 pct silica and about 90 pct ionic in slags with more than 34 pct silica, increasing linearly in the intermediate range. The balance of the conduction is electronic in character. Silicate ions are discharged at the anode with the evolution of gaseous oxygen. Transport experiments show that the ionic current is carried almost entirely by ferrous ions, which may be assigned a transport number of one.