Effect of structure and phase equilibria on crystallization of fluoride free mould fluxes
- 作者：SHU QifengWANG ZhenZHOU Guozhi
- 会议时间：2013-06-01
- 关键词：mould fluxes ; crystallization ; phase equilibria ; structure
- 母体文献：第五届宝钢学术年会论文集
- 会议名称：第五届宝钢学术年会
- 会议地点：上海
- 主办单位：中国金属学会
- 语种：chi
摘要
Mould fluxes play a crucial role in continuous casting process.During casting operation,fluorine in mould fluxes tends to react with moisture to form HF evaporation,which is harmful to human health and cause pollution to environment.Therefore,there are recent increasing demands for developing fluoride free mould fluxes due to environmental concerns.Crystallization behavior is one of key properties of mould fluxes to fulfil important function of heat transfer control.In the present work,crystallization behavior of a base system of CaO-B2O3-TiO2- SiO2 as fluoride free fluoride were investigated using Differential Thermal Analysis ( DTA),X-ray diffraction (XRD) and Scanning Electron Microscopy equipped with Energy Dispersive Spectrometry ( SEM-EDS).The crystallization behavior was further explained by investigation of phase equilibria and structure.Crystallization products were distinguished using XRD and SEM-EDS technique on heat treated samples.The crystallization products for slags with TiO2 content less than 18% were CaSi03 and CaTiSiO5 with CaSiO3 as main product.CaTiSiO5 become the sole crystallization product for slags with content of TiO2 large than 22%.Phase equilibria of slags were also studied using DTA curves at heating rate of 10K/min.Vertical section of CaO-SiO2 ( CaO/SiO2 = 1) - 10% B2O3 and TiO2 join was constructed.It was found that crystallization product could be predicted according to information of phase equilibria.DTA measurements with various heating rates are carried out to investigate non-isothermal crystallization kinetics of the CaO-B2O3-SiO2-TiO2 system in glass state.The non isothermal kinetics data was dealt with by employing a wide employed methods named Matusita-Sakka model.Activation energy of crystal growth was extracted through kinetic analysis.It was found that,with the increase of TiO2content to 18%,activation energy for growth increases and retards of crystallization procedure,while further increase of TiO2content would lead to decrease of activation energy for growth and accerelation of crystallization procedure.Structure of slags was also studied in the present workusing Raman spectroscopy.Deconvolution results on Raman spectral showed that Ti02 exist in structure as[ TiO4 ] and degree of polymerization increase with TiO2 increases.It was found that crystallization ability of slag could be partly explained by structure information of slag.The decrease of activation energy for growth of CaSiO3 could be attributed to increase of polymerization degree.The crystallization could be mainly control by one-dimensional growth of crystals.The present study has provided an example of impact of phase equilibrium and structure knowledge on crystallization for mould fluxes.The fundamental phase equilibrium and structure investigation on mould fluxes would be critical to rationalize the development of new type mould fluxes.