Surface segregation of calcium oxide in wustite and its effects on the reduction
Surface segregation of calcium oxide in wustite and its effects on the reduction
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DOI：
10.1007/bf02663391
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发表时间：
1994-06
期刊：
影响因子：
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通讯作者：
Y. Iguchi;Keisuke Goto;S. Hayashi
中科院分区：
文献类型：
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作者：
Y. Iguchi;Keisuke Goto;S. Hayashi
在973 ~ 1223 K的温度范围内，用原位俄歇能谱研究了氧化钙在浮氏体表面的偏析。氧化钙表现出强烈的偏析倾向，其表面的摩尔分数是体积（xcao体积）的10 ~ 1000倍。分离等温线在中间摩尔分数（XCaObulk= 0.003或0.005）处达到最大值。随着xcao体积的增大，分离焓变从- 43.3 kJ/mol增加到- 5.20 kJ/mol。偏析的主要驱动力可能是钙离子周围产生的应变能的松弛。氧化钙也在与浮士体接触的铁表面分离。由于氧化钙的偏析，使浮思体和铁的表面能降低，而浮思体/铁的界面能升高。氧化钙增强对浮思体的还原作用，主要是由于抑制了新的铁核，使浮思体表面与还原性气体良好而持续的直接接触，并使浮思体/铁核界面面积比浮思体的自由表面积缩小，从而降低了总能量。
The segregation of calcium oxide to the surface of wustite was investigatedin situby Auger electron spectroscopy at temperatures in the range of 973 to 1223 K. Calcium oxide indicated a strong tendency to segregate, with the molar fractions at the surface being 10 to 1000 times the molar fractions in the bulk (XCaObulk). The segregation isotherms showed maxima at intermediate molar fractions in the bulk (XCaObulk= 0.003 or 0.005). The enthalpy change for the segregation increased from −43.3 to −5.20 kJ/mol with increasing XCaObulk. The main driving force of the segregation may be the relaxation of the strain energy generated around calcium ions. Calcium oxide also segregates at the surface of iron in contact with the wustite. By the segregation of calcium oxide, the surface energies of wustite and iron may decrease whereas the wustite/iron interfacial energy may increase. The enhancement of the reduction of wustite by calcium oxide is concluded to essentially occur by the good and continuous direct contact of wustite surface with reducing gases owing to the suppression of new iron nucleus and owing to the contraction of the wustite/iron-nuclei interfacial area compared with the free-surface area of wustite in order to decrease the total energy.