摘要
为了减缓海绵铁的高温再氧化,在以含碳球团制备海绵铁的过程中,在含碳球团表面包覆一层约0.25mm厚的Al2O3-MgO-CaO-SiO2陶瓷料浆作为保护层,研究了有无防护层的海绵铁在制备过程中的金相组织及微观形貌,分析了氧化产物的物相组成,测试了球团的金属化率,考察了包覆层对含碳球团还原过程的影响,探讨了涂层防护含碳球团的还原行为和防护机理。研究结果表明,含碳球团"自还原"过程中表层还原产物FeO在高温下通过塑性变形进入包覆层,并包裹其中的功能组元MgO颗粒,两者发生固溶反应生成主要成分为(MgO)0.239(FeO)0.761的致密层,该致密层可进一步氧化生成内层为"针状"的Fe2.95Si0.05O4、外层为"补丁"状的MgFe2O4尖晶石结构的防护层,防护层的总厚度为0.20mm,可通过挤压形变处理的方式使其从海绵铁基体上完整剥落。涂层防护改变了海绵铁疏松多孔的氧化皮结构,致密的防护层很好地维持含碳球团内部的还原性气氛,防止生成的海绵铁被高温氧化性炉气二次氧化,在富氧炉况下取得了80%的金属化率(与无防护涂层的含碳球团相比,金属化率提高了59.5个百分点)。
To reduce sponge iron reoxidation at high temperature, as a protective coating, a 0.25-mm-thick Al2O3-MgO-CaO-SiO2 ceramic slurry was coated on the surface of carbon-containing pellet. The metallographic tissue and micro-morphology of the sponge iron with and without protective coating were observed during preparation, the phase composition of oxidation product was analyzed and the metallization rate of the pellet were tested. The influence of the coating layer on the reduction process of pellet as well as the reduction behavior and anti-oxidation mechanism of the carbon-containing pellet with protective coating were studied. The results indicated that the reduction product FeO on surface layer is able to penetrate into the coating layer and encase functional MgO particles through plastic deformation at high temperate during the self- reducing course of carbon-containing pellet, and a dense layer with （MgO）0.239（FeO）0.761 as main composition was produced through solid solution reaction of FeO and MgO, which can be oxidized further to a 0.20-mm-thick protective layer with an inner layer containing ＂needle-like＂ Fe2.95Si0.0504 and an outer layer with ＂patch-shaped＂ MgFe204 spinel structure. The protective layer can be fully removed from sponge iron substrate by extrusion deformation treatment. The coating protection changes the loose and porous scale structure of sponge iron, and a dense protective layer can effectively maintain the reducing atmosphere inside the carbon-containing pellet, which prevents the formed sponge iron from being reoxidizing by high-temperature gas. As a result, an 80% metallization rate is obtained in oxygen-rich environment, which increases by 59.5 percentage points as compared with that of the carbon-containing pellet without protective coating.
出处
《电镀与涂饰》
CAS
CSCD
北大核心
2013年第6期51-56,共6页
Electroplating & Finishing
基金
2011年吉林省与中国科学院合作长吉图开发开放先导区科技创新合作专项资金(2011CJT0008)
国家自然科学基金(51202249)
关键词
海绵铁
含碳球团
再氧化
防护
陶瓷涂层
sponge iron
carbon-containing pellet
reoxidation
protection
ceramic coating
