Growth process of iron whiskers and mechanism of CaO influence on precipitation morphology of metallic iron at the gas-solid interfaces was studied. Analytical reagents of Fe（NO3）3 and Ca（NO3）2 aqueous solution we...Growth process of iron whiskers and mechanism of CaO influence on precipitation morphology of metallic iron at the gas-solid interfaces was studied. Analytical reagents of Fe（NO3）3 and Ca（NO3）2 aqueous solution were used to prepare sheet film sample of Fe2 O3-CAO by thermal decomposition at high temperature. In-situ observation was con-ducted using a stereo optical microscope and a hot-stage. And reduction kinetics of samples was studied by thermo gravimetrie （TG） method. Some samples after reduction were analyzed by using the scanning electron microscope （SEM）, energy dispersive spectrometer （EDS） and fourier transform infrared （FT-IR） spectrometer. Results indi-cate that during the reduction of iron oxides with CO, metallic iron is mostly precipitated as whisker and the precipi- tation behavior mainly depends on reduction rate. Doping CaO can significantly increase the reduction rate and effec-tively change the precipitation morphology of metallic iron after the reduction. When CaO doping concentration is less than 4% （mass percent）, CaO can promote whisker formation of reduced iron; as it reaches 6% （mass per- cent）, CaO inhibits iron whiskers growth; as it is more than 8% （mass percent）, no whiskers could be observed. Therefore, controlling the quantity of Ca^2＋ is effective to control the formation and growth of iron whiskers during gaseous reduction and thus eliminating ore grain sticking caused by intertexture of iron whiskers.展开更多
基金Item Sponsored by National Natural Science Foundation of China ( 50834007 )National Basic Research Program of China ( 2012CB720401 )
文摘Growth process of iron whiskers and mechanism of CaO influence on precipitation morphology of metallic iron at the gas-solid interfaces was studied. Analytical reagents of Fe（NO3）3 and Ca（NO3）2 aqueous solution were used to prepare sheet film sample of Fe2 O3-CAO by thermal decomposition at high temperature. In-situ observation was con-ducted using a stereo optical microscope and a hot-stage. And reduction kinetics of samples was studied by thermo gravimetrie （TG） method. Some samples after reduction were analyzed by using the scanning electron microscope （SEM）, energy dispersive spectrometer （EDS） and fourier transform infrared （FT-IR） spectrometer. Results indi-cate that during the reduction of iron oxides with CO, metallic iron is mostly precipitated as whisker and the precipi- tation behavior mainly depends on reduction rate. Doping CaO can significantly increase the reduction rate and effec-tively change the precipitation morphology of metallic iron after the reduction. When CaO doping concentration is less than 4% （mass percent）, CaO can promote whisker formation of reduced iron; as it reaches 6% （mass per- cent）, CaO inhibits iron whiskers growth; as it is more than 8% （mass percent）, no whiskers could be observed. Therefore, controlling the quantity of Ca^2＋ is effective to control the formation and growth of iron whiskers during gaseous reduction and thus eliminating ore grain sticking caused by intertexture of iron whiskers.
文摘硼铁矿是中国含硼原料的主要来源,其加工利用的关键在于硼和铁的分离。研究了不同条件下硼铁矿在直接还原过程中金属铁颗粒的生长特性,可为硼铁矿中硼和铁的有效分离提供理论支撑,从而达到硼铁矿资源化利用的目的。采用Leica DMI5000M光学显微镜获得还原球团中金属铁颗粒的显微图像后,通过Image-Pro Plus 6.0图像软件对显微图像进行金属铁颗粒粒径的分析统计,并采用化学分析的方法对还原产品中铁的金属化率进行检测,同时利用扫描电镜研究了Na_(2)CO_(3)促进铁氧化物还原的作用机理和金属铁颗粒的生长行为。结果表明,Na_(2)CO_(3)作用下硼铁矿球团中的铁氧化物能有效被还原,随着还原时间的延长,还原球团中铁的金属化率和金属铁颗粒的平均粒径均有效增大,在还原温度为1100℃、还原时间为60 min的条件下,不添加Na_(2)CO_(3)的焙烧产物中铁的金属化率和金属铁颗粒的平均粒径分别为84.36%和8.55μm,而在添加15%Na_(2)CO_(3)后于同样条件下焙烧,产物中铁的金属化率和金属铁颗粒的平均粒径分别为91.72%和14.07μm;SEM-EDS分析结果说明,Na_(2)CO_(3)不仅有促进金属铁和其他物质分离的作用,而且还会影响金属铁颗粒在还原焙烧过程中的迁移行为;在直接还原过程中,金属铁颗粒先由“点”接触变为“颈”接触,然后重新相交形成新的晶界成为多边形颗粒,最后多边形颗粒间互相连接形成致密化集合体。
