The dissolution rate of dense lime specimens in calcium aluminosilicate based melts was measured at 1430°C to 1600°C in air, using a rotating disk/cylinder technique. The measured dissolution rates were strongly dependent on the rotation speed with the results indicating mass transfer in the slag phase to be a rate-limiting step. At a given rotation speed, the slag chemistry and temperature had strong effects on the dissolution rate. The diffusivity of CaO in the slag was calculated from the dissolution rate and solubility data, using known mass-transfer correlations. Addition of CaF 2 MnO x , FeO x , and TiO 2 to the slag increased the CaO diffusivity, while SiO 2 had an opposite effect. Addition of CaF 2 had the strongest effect and increased the diffusivity by a factor of 3 to 5 in the temperature range of 1500°C to 1600°C. The deduced activation energy for diffusion of CaO in these slags ranged from about 53 to 246 kJ/mole, depending on the concentration of additives used.
Static dissolution of CaO into a CaO-SiO 2 -Al 2 O 3 slag with fluxing agents (fluorspar, ilmenite and nepheline syenite) was studied using two experimental techniques. In one method, the slag was packed into dense CaO crucibles, and heated to 1 500°C/1 600°C. After reaction, the crucible was air cooled and cross-sectioned. In the second technique, slag with a piece of lime was heated in a platinum capsule. The development of the Ca 2 SiO 4 phase at the lime/slag interface and the CaO dissolved in the slag from the lime specimen were examined by Electron Probe Micro Analysis and Scanning Electron Microscopy. Ilmenite and nepheline syenite were found to be effective substitutes for fluorspar, increasing the CaO dissolution rate in the slag.KEY WORDS: lime; dissolution; slag; fluorspar; nepheline syenite; ilmenite.The current study examines the dissolution of lime at steelmaking temperatures in calcium alumino-silicate slags with basicity of 1. The aim of this study is to examine the effect of addition of 10 wt% fluxing agents: fluorspar, nepheline syenite and ilmenite on the rate of lime dissolution in the slag. While acknowledging that in industry, the burnt lime is porous (more than 50% porosity for softburnt lime and about 25% porosity for hard-burnt), it was decided to use a low porosity lime (8.4 %). This was to ensure a sharp lime/slag boundary and consequently better control of experimental conditions.
ExperimentalStatic dissolution of CaO into slag was studied by two experimental techniques. Firstly, holding slag in a dense lime crucible, varying reaction time, temperature and slag chemistry. Secondly, by reacting a piece of lime with slag in a small platinum crucible, varying temperature.
MaterialsManufacture of the lime crucibles included the following operations. The limestone powder with 50-70 mm particle size was milled with alumina balls producing 0.8-1 mm particles that were then calcined to CaO and pressed in a mould and subsequently fired to provide the necessary density and strength. This technique allowed a close control of bulk density and apparent porosity by precisely varying compacting pressure, sintering temperature, rate of heating and cooling and sintering time.The experimental slags were prepared in a platinum crucible by melting a mixture of slag components, quenching the melt and then re-melting to ensure slags' homogeneity. The master slag was a three component CaO-SiO 2 -Al 2 O 3 system with 45 wt% CaO, 45 wt% SiO 2 , and 10 wt% Al 2 O 3 . Flux additions were made by adding 10 wt% of fluorspar and fluorspar replacement candidates to the master slag. The flux compositions used in the present work are presented in Table 1 and the chemical composition of slags studied in the present work are tabulated in Table 2. In the case of the CaF 2 addition, subsequent analysis revealed that the CaF 2 content of the resultant slag was only 5.7 wt% indicating a loss of fluorine. The fluorine loss and oxidation of calcium of fluorspar was previously reported by Shimizu et al.
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Experimental Proce...
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