材料期刊网

总结讨论了熔锍及熔融金属中元素选择性氧化的行为,举出镍锍中 Ni 与 S,铁液中 Cr,V,Nb,Mn 或 P 与 C 作为应用的实例.利用热力学分析提出氧化的转化温度的概念,并指出二步及一步计算该温度的方法.在排除新相生成的晶核能的条件下,氧化的转化温度与氧的存在形式(无论是气态 O_2,溶于金属液中的[O]或炉渣中的 FeO)以及氧的压力或活度无关,而只决定于参加反应的物质及产物的本质及活度(压力).同时,转化温度不是一成不变的温度,而是随着熔池组成的改变而不断地在变化.降低气体氧化产物的分压将有助于降低氧化的转化温度.理论计算的转化温度可提供使熔池中一个元素的优先氧化而使另一元素保留不变的最佳条件.小型实验和工业上实践证明,转化温度的概念可以成功地控制吹炼操作,作到按意图进行选择性氧化.影响熔池内元素氧化顺序的动力学因素也作了简略的分析.对镍锍脱 S、不锈钢脱 C 以及高碳锰铁降 C 的吹炼,熔池温度永远要高于相应熔池组成的转化温度.而对铁水脱 Cr 和铁水提 V 或 Nb,熔池温度则应保持低于相应熔池组成的转化温度.P,C 在铁水中的氧化顺序,除与转化温度有关外,还取决于熔渣组成以及 CO 承担的压力.

The selective oxidation of elements in molten matte and metals is reviewed and discussed from thermodynamic viewpoint,Ni vs S in nickel matte,Cr,V,Nb, Mn or P vs C in iron melts being taken as examples of practical application.On grounds of thermodynamical analysis,a concept of transition temperature of oxi- dation has been introduced,and methods of calculating the transition temperature with either the two-steps- or the one-step-method are presented.On the assumption that no nucleation energy is required for the formation of new phases (gas bub- bles and the condensed oxidation products),the transition temperature of oxida- tion is independent of the forms of oxygen present,be it gaseous oxygen,dissolved [O] in metal melts or FeO from the slag,and also independent of the pressure or activity of oxygen,but it depends solely upon the nature and activity (pressure) of the reactants and products taking part in the reaction.Furthermore,the transi- tion temperature of oxidation is not a fixed temperature,it varies continuously with the composition of the bath as the oxidation process goes on.Reducing the pressure of the gaseous product would help to lower the transition temperature of oxidation. With the transition temperature of oxidation theoretically calculated,it is possible to deduce the optimal conditions for allowing one element preferentially oxidized while leaving the other element practically intact in the bath.Small- scale experiments and industrial practices show that the concept of the transition temperature of oxidation does successfully serve as a guide to control the blowing (smelting) operation,with the result that the desired element could be oxidized selectively.The kinetic factors which influence the sequence of oxidation of ele- ments in the bath are also briefly discussed. For the desulphurization of nickel matte,the decarburization in the 18-9 stainless steel manufacture (including the AOD process)and the decarburization of high-carbon ferromanganese,the blowing operation should be run so that the temperature of the bath should always be higher than the transition temperature of oxidation corresponding with the composition of the bath.But for the dechro- mizing of pig iron,and the extraction of V or Nb from the pig iron,smelting operation should be carried on,so that the temperature of the bath should be kept always lower than the transition temperature of oxidation for the respective com- position of the bath.As regards the sequence of oxidation of P with respect to C,besides the effect of the transition temperature of oxidation,the basicity and the FeO-content of the slag for holding P_2O_5 as well as the pressure exposed to or sustained by the CO-bubbles should be both considered.