Volatilization Mechanism And Influence Of Electroslag Refining With High Fluoride Slag

In the metallurgical industry,smelting temperatures,chemical reactions,metal solidification,and removal of inclusions are all closely related to slag performance.Studies have shown that the high-fluorine slag used in electroslag remelting has volatilization in the heating process and high-temperature holding stage.When the physicochemical properties of the slag are measured in the laboratory,the high temperature stage will be experienced,and the slag composition will inevitably change.Due to the volatilation and the difference between the actual slag composition and the slag preparation composition,how to match the measured physicochemical properties and corresponding slag composition lacks systematic research.Therefore,it is of great significance to study the volatilation mechanism of high fluoride containing slag at high temperature and its influence to determine slag performance under high temperature conditions.In this paper,the research of our group on physicochemical properties of fluorine-containing slag for electroslag refining and the research results of fluorine-containing slag volatilization was summarized.With reference to the high-fluorine slag actually used in the factory,the experimental components of high-fluorine slag were selected and orthogonal experiments designed.The basic physic-chemical properties of high-fluorine slag,including melting point,viscosity and phase equilibrium,were calculated by Factsage software.The Gibbs free energy of each volatilization reaction was calculated and the influence of alkalinity on the volatilization of volatiles was analyzed.The melting point and viscosity were measured.The volatilization mechanism of high-fluorine slag were studied by thermogravimetry,thermogravimetry-thermal mass spectrometry,slag heating test and the actual composition of slag was measured to make it in accordance with the measured physic-chemical properties.The main conclusions are as follows:（1）SiO₂ and MgO promote the volatilization process,CaO inhibit the volatilization process,and Al₂O₃ has no obvious effect on volatilization;（2）The volatiles of the high fluorine residue for electroslag remelting are SiF₄,MgF₂,AlF₃,and CaF₂.The order of volatilization is SiF₄,MgF₂,AlF₃,CaF₂;（3）Within the range of selected slag components,the weight loss during the melting point determination process can reach2.11%-12.37%,and the slag weight loss during the viscosity measurement process can reach 9.85%-29.52%;（4）The weight loss curve of the five-element slag system is divided into three stages:decomposition of Ca（OH）₂,Mg（OH）₂ between 200℃and450℃,and the volatile matter is H₂O;For the reaction of CaF₂ with SiO₂ and MgO between 550℃and 800℃,the volatile matter is SiF₄ and MgF₂ gas;between 1300℃and 1500℃,the volatile matter is mainly CaF₂.The weight loss range is 8%-14%.The more CaF₂,CaO,SiO₂ and MgO content,the greater the weight loss rate;the more Al₂O₃ content,the smaller the weight loss rate;（5）Based on thermogravimetric experiments,high temperature sampling and XRF analysis,the true composition of slag with high fluorine slag at 1000℃-1500℃was obtained.According to the new method proposed by our research group,make the melting point and viscosity corresponding to the slag real component obtained.