Metallurgical Transactions B

The dissolution of a copper cylinder in molten tin-lead alloys was studied at 673 K under static and dynamic conditions in the peripheral velocity range 1.9 to 75.4 cm per second using an immersion method. The dissolution rate of copper increased with increasing tin concentration and peripheral velocity. The solution rate constant increased with peripheral velocity and with diffusion coefficient of copper in the melt. The constant decreased with kinematic viscosity of the melt and diameter of the specimen. The dissolution of copper in molten tin-lead alloys was mixed control. Flow of the melt under forced convection was turbulent flow with Taylor vortices. Natural convection occurred in dissolution of stationary copper in tin rich alloys due to hydrodynamic instability from density differences in the melt.

The possibility of using steady uniform rotation about a vertical axis to suppress the onset of buoyancy-driven convection during solidification of a binary alloy is considered using a linear stability analysis. For Pb-Sn alloys, our results clearly show that the onset of convection in a horizontally unbounded layer can be suppressed significantly at modest rotation rates. Specifically, “plane-front” solidification is linearly stable at higher Sn concentrations in a rotating configuration than in a nonrotating one. The predicted inhibitory effects of rotation on convection are discussed in terms of previous experimental and theoretical studies of the effect of rotation on the onset of buoyancy-driven convection in single-component fluids heated from below and in binary fluids subject to thermal and solutal stratification.

Nitrogen solubility in liquid Fe, Fe-V, Fe-Cr-V, Fe-Ni-V and Fe-18 pct Cr-8 pet Ni-V alloys has been measured using the Sieverts’ method for vanadium contents up to 15 wt pct and over the temperature range from 1775 to 2040 K. Nitrogen solution obeyed Sieverts’ law for all alloys investigated. Nitride formation was observed in Fe-13 pet V, Fe-15 pet V and Fe-18 pet Cr-8 pet Ni-10 pet V alloys at lower temperatures. The nitrogen solubility increases with increasing vanadium content and for a given composition decreases with increasing temperature. In Fe-V alloys, the nitrogen solubility at 1 atm N2 pressure is 0.72 wt pet at 1863 K and 15 pct V. The heat and entropy of solution of nitrogen in Fe-V alloys were determined as functions of vanadium content. The first and second order interaction parameters were determined as functions of temperature as: $$e_N^V = \frac{{ - 463.6}}{T} + 0.148 and e_N^{VV} = \frac{{17.72}}{T} - 0.0069$$ The effects of alloying elements on the activity coefficient of nitrogen were measured in Fe-5 pet and 10 pet Cr-V, Fe-5 pet and 10 pet Ni-V and Fe-18 pet Cr-8 pct Ni-V alloys. In Fe-18 pet Cr-8 pet Ni-10 pet V, the nitrogen solubility at 1 atm N2 pressure is 0.97 wt pet at 1873 K. The second order cross interaction parameters, e N Cr,V and e N Ni,V , were determined at 1873 K as 0.00129 and − 0.00038 respectively.

Several anthracites were calcined at temperatures ranging from about 1100 to 2300°C and bench scale cathodes fabricated, baked, and tested for electrical resistivity and expansion during electrolysis. Cathode electrical resistivity did not decrease much with increasing anthracite calcination temperature to about 1800°C but decreased sharply there-after. Cathode expansion during electrolysis was inversely proportional to anthracite calcination temperature to about 2000°C. Electrical resistivity generally decreased during test cell operation. A correlation between anthracite properties and cathode properties for anthracites calcined at 2100°C could not be made. With a commercial electrically calcined anthracite, the finer of two aggregate sizings resulted in cathodes with superior properties, and properties generally optimized at a binder level producing about a zero volume change during baking.

The dissolution of synthetic samples of zinc ferrite in aqueous hydrochloric acid is stoichiometric. The rate appears to be controlled by a chemical reaction on the solid surface, and dependence of the dissolution rate on hydrochloric acid activity is of the first order. Activation energy of 83 kJ mol-1 was found. Zinc ferrite leaching is a slow solubilization process in the hydrochloric acid treatment of dead-roasted Iberian pyrite ashes. The most favorable conditions are 0.5-1 M HC1 at 90 to 100 ‡C, when preferential solubilization of the spinel phases takes place on the hematitic matrix. Extensive extraction of zinc (~90 pct of total zinc) in one to two hours and low solubilization of iron (~8 pet of total iron) results under these conditions.

A mathematical model has been developed to predict the internal stresses generated in a steel ingot during thermal processing. The thermal history of the ingot has been predicted by a finite-element, heat-flow model, the subject of the first part of this two-part paper, which serves as input to the stress model. The stress model has been formulated for a two-dimensional transverse plane at mid-height of the ingot and is a transient, elasto-viscoplastic, finite-element analysis of the thermal stress field. Salient features of the model include the incorporation of time-temperature and temperature-dependent mechanical properties, and volume changes associated with nonequilibrium phase transformation. Model predictions demonstrate that the development of internal stresses in the ingot during thermal processing can be directly linked to the progress of the phase transformation front. Moreover, the low strain levels calculated indicate that metallurgical embrittlement must be very important to the formation of cracks in addition to the development of high tensile stresses.

A diffusion bridge apparatus has been used to measure diffusivities for the gas pairs CO2−N2, CO2−Ar, and CH4−N2 at temperatures ranging from 300 to 1000 K. The apparatus measured effective diffusivities which were transformed into ordinary diffusivities after calibration with a gas pair (CO2−N2) of known diffusivity. The apparatus was also used to measure the viscosities of the four gases over the same temperature range. The results were compared with the predictions of the Chapman-Enskog correlation (ordinary diffusivities and viscosities) and predictions for diffusion rates in porous solids developed in Monte Carlo simulations. Additional experiments examined the effect of changing pore structure on the diffusivities of gases.