with Nb2Os-bearing slag.In the present study,the equilibrium between slag and molten iron in direct alloying of steel with the Nb2Os-bearing slag was investi- gated.Meanwhile,the activities of oxides in the slag were also measured. 1 The Method of Experiment The experiment was done in a Tamman furnace with alumina and magnesia crucibles.Argon was used as a protection gas for the furnace.The temperature of molten iron was 1600C.200g of high pure iron and 20g of slag composed ◆ of chemical reagent were used for each experiment.Ferro-silicon was added into molten iron according to the requirement of %Si).The results of preliminary- experiment show that the compositions of CSi],CMn],[Nb]and aro)will not change one hour later.This indicates the reaction between the slag and molten iron getting equilibrium.In fact,the time of each experiment took 1.5 to 2h. In the experiment,solid electrolyte oxygen cell was used for measuring the oxygen potential in molten iron.The celf assembly adopted in the experiment is as fo- llows:(+MolMo,MoO211ZrO2 (MgO)COJMo (- The oxygen potential,Pto is calculated with EMF as follows: E-tn(pepe (1)r51 where pMo=e-△G9/RT Mo02=Mo+02△G9=491028-118.40T(J/mo) (2)r81 1ogpe'=-95.67+0.0435T (3) The oxygen activity in molten iron is calculated with formula (4 ) a2o]=plo]e-G9/RT (4) where 02=2〔0)△G9=-274235+15,57T(J/mo1) (5)IB1 2 The Activities of Oxides in the Slag The X-ray diffraction analysis of the slag of this experiment showed that the niobium oxide in the slag is manganoclumbite (Fe,Mn).Nb2Oa.The niobium in slag with five valency can be written as Nb So,can be caleula- ted with formula (9),if ato]is known. 2Nb+号0，=Nb,0。dGg=-1747989+310.89T(dm1) (6)t71 Nb=〔Nb)△G9=23027-52.34T(J/mol) (7)r8J 527一 一 ， ， ，、 王 。 。 一 从 ， 卜 也 · · 从· “ 。 扭 节 一 一 立 〔 〕 一 〔 〕 ， 〔 〕 ， 〔 〕 。 一 ， 五 。 。 饥 公 ， 。 丫 二 ， ， 川 〔 〕 。 一 ， 甲色 二一 影 ，· ，一 ， ‘ ，，‘，一 ‘ 斗 ， 。 ’ ‘ ， 。 二 一 △ 叨 盯 。 △ 全二 一 。 ” ，二 一 了 红 ， 节 。 “ 老 。 二 。 · 一 “ 呈“ 〔 〕 △ 全二 一 “ 气气 一 五 ， · 。 · “ · ， 从 · 切 ， 狄 · 五 令 △口 一 。 。 〔 〔 〕 足“ 一 “ 〕