【作者】 雷云；

【导师】 谢兵；

【作者基本信息】 重庆大学 ， 冶金工程， 2009， 硕士

【摘要】 保护渣润滑铸坯和控制铸坯凝固传热的功能主要是通过填充于铸坯与结晶器壁间的渣膜来实现。提高渣膜的结晶性能可以降低渣膜中玻璃体的辐射传热和晶体的传导传热,但渣膜结晶性能的提高也容易恶化铸坯润滑状况。本文在国家自然科学基金项目《低红外辐射非晶态保护渣生成机理的研究》(项目编号为50474024)和重庆市自然科学基金项目《过渡族金属氧化物对连铸保护渣析晶及红外透射性能的影响研究》(项目编号为2006BB4200)的资助下,利用实验室条件,研究结果如下:过渡族金属氧化物对保护渣物化性能的影响表明:①少量(2wt%)的MnO、TiO2、NiO和ZnO能使保护渣熔化温度降低的能力大小为TiO2>MnO>ZnO>NiO;②加入少量的MnO、TiO2、NiO和ZnO均能使保护渣的粘度和结晶温度降低;③当过渡族氧化物组分含量为0～8%时,MnO和ZnO含量越高,粘度越低;随着TiO2和NiO含量的增加,保护渣的粘度先降低后增加;④在相同的过渡族组分条件下,保护渣的结晶温度随着碱度的增加而提高。TiO2和MnO对保护渣结晶性能的影响表明:①两者均能使保护渣的结晶率显著降低;②XRD衍射结果表明,TiO2和MnO均能抑制保护渣晶体的析出;③由矿相分析可知,TiO2和MnO含量的增加均能使保护渣析出的枪晶石晶粒数量逐渐变少,形态由最初典型的矛头状变得更加纤细。本文利用热丝法研究TiO2对保护渣结晶动力学的影响:①在等温条件下时,TiO2能使保护渣的最佳形核速率和结晶速率随TiO2含量的增加而降低;②在非等温条件下,且降温速率相同时,当TiO2=0～4wt%,保护渣的结晶速率逐渐降低,到TiO2=6wt%时略微升高,当TiO2=8wt%时,保护渣析出钙钛矿,结晶速率在钙钛矿析出的高温区域比较慢,而在枪晶石的析出低温区域比较快;③保护渣晶体析出的机理是非均匀形核,枪晶石呈球团状向三维空间长大,而钙钛矿呈十字形或枝状向二维空间长大;④当TiO2=8wt%,且温度在1200℃以上时,虽然析出高熔点钙钛矿,但由于其生长速度很慢,与基础渣相比,还是降低了保护渣的结晶速率,从而表现为抑制保护渣的析晶。本文利用DSC研究MnO对保护渣结晶动力学的影响,结果表明:①在相同的降温速率条件下,随着MnO含量的增加,保护渣的结晶速率逐渐降低;②由Jeziorny模型分析可知,含MnO保护渣的形核及长大机理是先非均匀形核,随后晶核向二维或三维空间长大,随着MnO含量的增加,结晶速率变得越来越低;由Liu模型可知,在相同的转化率下,结晶能力的强弱顺序为J4>M3-1>M3-2>M3-3;③在相同的转化率条件下,保护渣的MnO含量越高,其结晶活化能也越高,结晶变得困难。综上所述,少量过渡族金属氧化物对保护渣一般起着降低其熔化温度、粘度和结晶温度的作用,但随着其含量的增加,有可能导致熔化温度、粘度和结晶温度的回升。加入少量MnO和TiO2就能使保护渣的结晶率大大降低,结合相关动力学分析,MnO和TiO2对保护渣起着抑制其结晶的作用。虽然当TiO2=8wt%时能析出钙钛矿,但因为在1200～1350℃之间其生长速率不高,对保护渣的总结晶速率和结晶率贡献不大。因此,在保护渣中加入含量为0～8wt%的MnO和TiO2,能提高保护渣的玻璃性能,改善铸坯与结晶器壁之间的润滑;另外,由于两者均没有提高保护渣的总结晶率,所以能在不提高保护渣结晶性能的条件下控制铸坯与结晶器之间的传热。更多还原

【Abstract】 The function of casting strand lubricating and heat diffusion controlling for mold fluxes is depended on the slag film between the strand and the mold. Radiative transfer of glassiness and heat transfer of crystal in the film can be reduced by enhancing its crystalline property; however, the lubrication property might be also deterioritaed.Supported by the project of National Natural Science Foundation of China,“Research on the formed Mechanism of Mold Fluxes film with low infrared Radiation properties”(No.:50474024) and by the project of Natural Science Foundation of Chongqing,“Research on Effects of Transitin Metal Oxides on Crystallization and low infrared Transmition of Mould Fluxes”(No.: 2006BB4200), with equipments in lab, the research results were gotten as following:The effects of transition metal oxides on physicochemical property of mold fluxes:①the capability to reduce the melting point of mold fluxes was arrayed as TiO2>MnO>ZnO>NiO (the content is less than 2wt%);②the viscosity and melting point were reduced by little MnO、TiO2、NiO or ZnO;③with the content of oxides increasing from 0% to 8%, the viscosity of mold fluxes was gradually reduced for MnO or ZnO and firstly reduced and then increased for TiO2 or NiO;④for the same content of the oxides, the crystallization temperature was gradually enhanced with the viscosity increasing.The effects of TiO2 or MnO on crystallization property indicated that:①the crystalline ratio of mold fluxes were greatly reduced by both of them;②from the results of XRD, precipitation of cuspidine was restrained by both of them;③analysis of mineragraphy indicated that both MnO and TiO2 can reduce the amount of cuspidine and the shape become more miniature comparing with original spearhead shape.The effects of TiO2 on crystallization kinetics of mold fluxes:①at the isothermal condition, crystallization rate and optimal nucleation rate increased with the content of TiO2 increasing;②under the condition of nonisothermal process and constant cooling rate, the crystallization rate of mold fluxes was gradually reduced (TiO2=0~4wt%), then became a little quicker (TiO2=6wt%), after the perovskite was precipitated (TiO2=8wt%), the crystallization rate is more quicker at the higher temperature range (perovskite was precipitated) than at lowers’(cuspidine was precipitated);③the research verified that mechanism of nucleation is non-homogeneous, the crystal grain of cuspidine as globularity growths towards three dimensional space comparing with the crystal grain of perovskite as cross shape or arborization growths towards two-dimensional space;④though perovskite was precipitated above 1200℃(TiO2=8wt%), the growth rate was too slow to contribute to accelerate the overall growth rate, comparing with the original samples, the crystallization of mold fluxes was restrained.The effects of MnO on crystallization kinetics of mold fluxes:①at the same cooling rates, the crystallization time was prolonged with the content of MnO increasing;②by Jezinorny model, the mechanism of crystallization is that the grain was non-homogeneously nucleated and then growtht toward two or three dimensional space, the crystallization rate became slower with the content of MnO increasing; by Liu model, at the same relative crystallization x, the crystallization property was arrayed as J4> M3-1> M3-2> M3-3;③at the same relative crystallization, the activation energy of crystallization became higher with the content of MnO increasing, which meant that the crystallization became more difficulty.In conclusion, the melting temperature, viscosity and crystallization time for mold fluxes can be reduced by few transition metal oxides, which, however, might reincrease them with the contents increasing. The crystalline ratio for mold fluxes was greatly reduced by few transition metal oxides and the some result can be gotten by analysis of crystallization kinetics, though the content of TiO2=8wt% can promote perovskite to precipitate, it can’t contribute much to the overall crystallization rate and crystalline ratio because perovskite growthed very slow among the temperature of 1200～1350℃. Therefore, both MnO and TiO2 (0~8wt%) can improve the glass property and the lubrication between casting strand and mold; in addition, as the overall crystalline ratio wasn’t enhanced, the heat transfer between casting strand and mold can be controlled without enhancing the crystallization property.更多还原