超重力冶金:科学原理、实验方法、技术基础、应用设计

超重力显著增大两相间的重力差,可用于加速固-液、液-液、液-气高温黏稠混和体的相分离速度;超重力具有定向性,避免搅拌等技术产生的熔体湍流返混,可用于深度脱除金属液中细小夹杂物;超重力条件下固-液界面张力微不足道,可容易实现微孔渗流;超重力条件下进行结晶凝固,按结晶顺序实现固-液分离,可用于制备梯度材料;超重力加速固-液分离,可细化凝固组织晶粒,但对非共晶熔体也易产生宏观偏析.将超重力技术应用于冶金及材料生产过程中,有望解决高温冶金和材料制备的一些难题,如复杂矿冶金渣有价组分的分离提取、冶炼渣中金属液的分离回收、多金属的熔析结晶分离、复杂矿直接还原铁的渣-金分离;在高端金属材料方面,应用超重力技术,有望解决近零夹物金属材料的精炼除杂难题,提高梯度功能材料、金属-陶瓷复合材料、多孔金属材料、器件材料表面电沉积修饰的制造水平.此外,在材料科学研究方面,超重力凝固可作为一种材料基因组高通量制备方法.

钢铁冶金新技术专刊序言

我国钢铁工业支撑了国民经济的持续快速发展,也对世界经济发展作出了重要贡献.但同时,我国钢铁工业的发展承载着巨大的节能减排压力,面临着严重的铁矿资源短缺问题,存在着产品质量进一步提升和生产过程智能化、绿色化的迫切技术需求.解决这些制约我国钢铁工业可持续发展的问题,必须加强基础理论研究与创新技术研发,形成具有自有知识产权的新工艺、新技术.

Flow Behavior in Z-Path Fluidized-Moving Bed with Inclined Perforated Plate

Much researches on the operation and structure of tundish were carried out at Xiangtan Iron and Steel Co Ltd to increase the yield of grade 20 carbon steel on the continuous casting production line. Through analyzing formation mechanism of pinholes and non metallic inclusions in billets and describing pattern of the flow of molten steel in tundish by a mathematic model, it was shown that the structure and operation of tundishes play an important part in product quality. So some measures were taken as follows: (1) Optimizing the tundish construction to decrease the impact of liquid steel and lengthening the residence time of liquid steel for homogenization of liquid steel; (2) Improving the influent and effluent operation of liquid steel to avoid the contact of liquid steel with air in order to decrease reoxidation; (3) Reducing over heat during continuous casting. After above measures being taken, the yield of grade 20 carbon steel and the service life of equipment were improved remarkably.

Conversion Excess Coal Gas to Dimethyl Ether in Steel Works

The centrifugal casting of compound HSS/nodular cast iron roll collar was studied, and the factors affecting transition zone quality were analyzed. The pouring temperature and interval in pouring are the main factors affecting transition zone quality. By controlling process parameter and flux adding during casting, high quality roll collar was obtained. The cause, why in the casting of HSS part, segregation appears easily, was analyzed and the countermeasure eliminating segregation was put forward, the measure eliminating heat treatment crackling was also put forward.

Morphology and Magnetic Properties of Electrodeposited Iron and Nickel Based Alloy Foils

An alternative to conventional process for the preparation of soft magnetic metal foils of Fe,Fe-Ni,Fe-Co and Fe-Ni-Co by electroforming was described.The microstructure and magnetic properties were observed.The results showed that the crystal size of the iron-based alloy foil is less than 10μm,while that of nickel-based alloy foil is about 2μm.Moreover,the electroformed Fe-Ni foil has better magnetic properties than the conventional milled permalloy 1J79 foil.

Reduction Behavior With CO Under Micro-Fluidized Bed Conditions

To process optimization and improve the degree of reduction, a two-step experiment was designed. The experiment was carried out in the micro-fluidized bed. The reactor in the micro-fluidized bed is operated as a differential reactor to ensure an equal temperature and residence time with the reactor volume. The experiment used Brazilian iron ore and reducing gas of CO. The operating temperature was 400 to 800 ℃ and the residence time was between 10 and 60 min. In correspondence with experiment, microscopic technique was applied too. The test shows that temperature and residence time of the pre-reduction stage have an important effect on the degree of reduction. By using two-step experiment, the maximum value of reduction degree increases by 44.1% compared with the maximum value of traditional reduction experiment. Microscopic analysis shows that the specific surface area, surface morphology and texture of reduced iron ore after pre-reduction stage have an important effect on the degree of final reduction too.

Kinetics of Reduction Reaction in Micro-Fluidized Bed

Micro-fluidized bed reactor is a new research method for the reduction of iron ore fines. The reactor is op- erated as a differential reactor to ensure a constant gas concentration and temperature within the reactor volume. In order to understand the dynamic process of the reduction reaction in micro-fluidized bed, a series of kinetic experi- ments were designed. In the micro fluidized bed, the use of shrinking core model describes the dynamic behavior of reduction of iron ore. And the apparent activation energy is calculated in the range of 700--850 ~C while the initial atmosphere is 100% content of CO.

Effects of CaO on Precipitation Morphology of Metallic Iron in Reduction of Iron Oxides Under CO Atmosphere

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.

Intensifying Gaseous Reduction of High Phosphorus Iron Ore Fines by Microwave Pretreatment

Gaseous reduction kinetics of the high phosphorus iron ore fines from Hubei in China and effect of microwave pretreatment on the gaseous reduction behavior were studied. Gaseous reduction kinetics were investigated by TG （Thermogravimetric） methods using LINSEIS STA PT 1600 thermal analysis equipment. Microwave pretreatments to the ore fines with four power levels were performed using a high temperature microwave reactor. Its effect was examined by TG methods and its mechanism was analyzed by SEM （scanning electron microscope） and EDS （energy dispersive spectrometer）. Gaseous reduction tests were carried out using a tubular furnace. Results of kinetic study indicate that controlling step of the gaseous reduction of the ore fines is a mixing control of gas internal diffusion and interface chemical reaction when reduction fraction is less than 0.8 and is solid state diffusion when reduction fraction is more than 0.8. Microwave pretreatment of the ore fines could change the pore structure of the oolitic unit to generate cracks, fissures and loose zones, which promotes reduction in the early stage and delays the occurrence of sintering. Gaseous reduction tests show in the condition that the ore fines are pretreated with a microwave power of 450 W for 4 min and reduced under temperature of 1 273 K, the gaseous reduction of the ore fines could be apparently intensified. Using CO or H2 as a reductant and ore fines being reduced for 1.5 to 2 h , increase of metallization rate of the ore fines is 10% to 13%.