P. C. Hayes

Predicting slag viscosities in metallurgical systems

Slag viscosity is a major process variable for most pyrometallurgical smelting and refining process operations. While extensive measurements have been made of slag viscosities, it is not practicable to provide data on all the possible combinations of compositions and process conditions encountered in metallurgical practice. This article reviews the mathematical models that have been developed to predict slag viscosities and provides some advice on the factors to be considered in their selection and use.

Microstructural changes on the reduction of hematite to maanetite

The microstructures resulting from the reduction of hematite to magnetite have been examined for a wide range of temperatures and gas conditions. A transition in product morphology from plate or lath magnetite to porous magnetite was found to occur at a constant free energy difference between the reducing gas mixture and the hematite over a range of reaction temperatures. Direct observations of lath nucleation and growth are reported and show the self-accelerating effect of the Fe2O3 → Fe3O4 transformation. The limits of porous growth are discussed in terms of established theories of discontinuous precipitation and a mechanism for the formation of lath magnetite is proposed.

Characterisation of protective surface films formed on molten magnesium protected by air/SF6 atmospheres

Abstract Magnesium metal in its molten state will oxidise rapidly in air, leading to burning on the melt surface. In order to process molten magnesium safely, the melt is protected from oxidation by blanketing the surface with a cover gas. The cover gas reacts with the metal and forms a protective film on the melt surface. Sulphur hexafluoride (SF 6 ) is widely used by the magnesium industry as a component of cover gas mixtures. However, the use of SF 6 has come under increased scrutiny due to its high cost and, more importantly, its significant impact on the greenhouse effect. To optimise the use of SF 6 , a detailed knowledge of its role in protecting molten magnesium is required. This paper describes the characterisation of the surface films formed on molten magnesium protected by cover gas mixtures containing SF 6 . Sensitive surface analysis techniques have been used to quantitatively determine the chemical attributes of the films. XPS showed that the film contains only MgO and MgF 2 . No sulphur compounds were detected. AES depth profiling indicated film thickness to be in the range 0.1–1 μm.

The kinetics of formation of h2o and co2 during iron oxide reduction

AbstractThe kinetics of the chemical reaction-controlled reduction of iron oxides by H2/H2O and CO/CO2 gas mixtures are discussed. From an analysis of the systems it is concluded that the decomposition of the oxides takes place by the two dimensional nucleation and lateral growth of oxygen vacancy clusters at the gas/oxide interface. The rates of decomposition of the oxides under conditions of chemical reaction control are dependent not only on the partial pressures of the reacting gases at the reaction temperature but also on the oxygen activity of the prevailing atmosphere. Application of this model to the kinetic data leads to the determination of the maximum chemical reaction rate constants for the decomposition of the iron oxide surfaces. Assuming the reactions H2(g) + O(ads) → H2O(g) andCO(g) + O(ads) → CO2(g) to be rate controlling the maximum chemical reaction rate constants for the reduction of iron oxides are given by % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqefavySfgDP5% 2BGWuAU9gD5bxzaGqbaiaa-z6adaWgaaWcbaGaaeisamaaBaaameaa% caqGYaaabeaaaSqabaGccqGH9aqpcaaIXaGaaGimamaaCaaaleqaba% GaaiOlaiaaicdacaaIWaaaaGqaaOGaa4xzaiaa+HhacaGFWbGaa4hi% amaabmaabaWaaSaaaeaacaGFTaGaa4Nnaiaa+LdacaGFSaGaa43mai% aa+bdacaGFWaaabaacbiGaa0Nuaiaa9rfaaaaacaGLOaGaayzkaaGa% a4xBaiaa+9gacaGFSbGaa4hiaiaa+1gadaahaaWcbeqaaiaa+1caca% GFYaaaaGqabOGaaW3CamaaCaaaleqabaGaaWxlaiaa8fdaaaGccaGF% HbGaa4hDaiaa+1gadaahaaWcbeqaaiabgkHiTiaaigdaaaaaaa!5D53!

The Breakdown of dense iron layers on wustite in CO/Co2 and H2/H2O systems

\Phi _{{\text{H}}_{\text{2}} } = 10^{.00} exp \left( {\frac{{ - 69,300}}{{RT}}} \right)mol m^{ - 2} s^{ - 1} atm^{ - 1}

The mechanism of protection of molten magnesium by cover gas mixtures containing sulphur hexafluoride

and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqefavySfgDP5% 2BGWuAU9gD5bxzaGqbaiaa-z6adaWgaaWcbaGaa83qaiaa-9eaaeqa% aOGaeyypa0JaaGymaiaaicdadaahaaWcbeqaaiaaisdacaGGUaGaaG% inaiaaicdaaaGcciGGLbGaaiiEaiaacchadaqadaqaamaalaaabaGa% aGymaiaaicdacaaIZaGaaiilaiaaiMdacaaIWaGaaGimaaqaaiaadk% facaWGubaaaaGaayjkaiaawMcaaGqaaiaa+1gacaGFVbGaa4hBaiaa% +bcacaGFTbWaaWbaaSqabeaacaGFTaGaa4Nmaaaakiaa+nhadaahaa% Wcbeqaaiaa+1cacaGFXaaaaOGaa4xyaiaa+rhacaGFTbWaaWbaaSqa% beaacaGFTaGaa4xmaaaaaaa!5D50!

Mechanisms of porous iron growth on wustite and magnetite during gaseous reduction

\Phi _{CO} = 10^{4.40} \exp \left( {\frac{{103,900}}{{RT}}} \right)mol m^{ - 2} s^{ - 1} atm^{ - 1}