Rates of dissolution of solid iron, cobalt, nickel, and silicon in liquid copper and diffusion rate of iron from liquid Cu-Fe alloy into liquid copper

Abstract

Consideration is given to the previously reported data on the observed dissolution rate of the vertical peripheries of cylindrical iron, cobalt, and nickel in liquid copper at temperatures in the range of 1468 to 1653 K under natural convection. The observed steady-state rate is close to the rate calculated from an equation expressed in terms of the activity of solute for dissolution rate controlled by mass transfer through a boundary layer in the liquid. The dissolution rate of the horizontal bottom face of cylindrical cobalt in liquid copper is determined at 1573 to 1574 (±6) K in the absence of fluid flow. The decrease in height of the cylinder, z(m), obeys z = α √t where t is time (s) and α is 4.18 × 10−6 m · s−1/2. This value is in close agreement with the calculated one based on an equation expressed in terms of the activity of solute for dissolution rate controlled by non-steady-state diffusion in the liquid. Experiments have been carried out to explore the dissolution rates of one vertical edge of a square silicon plate and the horizontal bottom face of a silicon disk in liquid copper at ∼1473 K. The rate at the lowest part of the vertical edge ranges from 39 to 69 mol · m−2 · s−1, and the calculated rate based on the former equation is close to the average of the maximum and minimum observed values. The ratios of these observed dissolution rates to those of iron, cobalt, or nickel under natural convection are in the range of 74 to 910. In the dissolution of the horizontal bottom face, the value of α is estimated from another equation in which the densities of solid and liquid different from each other and the activity of solute are taken into account. This estimated value is in the range of the observed ones. The total amounts of iron diffused from liquid Cu-Fe alloy into liquid copper within capillaries at 1574 K are determined. Their average is expressed as a function of the activity of iron.