高铁赤泥煤基直接还原中铁晶粒成核及晶核长大特性

讨论了高铁赤泥煤基直接还原特性及还原过程中金属铁晶粒成核及晶核长大特征。研究结果表明，由于还原过程中生成了铁橄榄石和铁尖晶石，使得金属铁晶核更加难成；新相一旦形成后，铁橄榄石和铁尖晶石充当了成核剂，使得金属铁晶粒成核位垒降低，成核进度加快，其过程系“吸附－固相反应－自动催化”。

低品位赤铁矿直接还原过程中铁晶粒的长大行为

采用光学显微镜、莱卡图像分析软件对低品位赤铁矿煤基直接还原产品中金属铁晶粒尺寸进行检测。利用Hillert晶粒长大动力学模型对低品位赤铁矿煤基直接还原过程中铁晶粒的长大行为进行研究。结果表明：在还原温度为1200℃、还原时间为5~120 min时，金属铁晶粒的生长速率常数k为1.155μm2/min；在1200℃时，球团还原过程中，金属铁晶粒的平均尺寸D（μm）与还原时间t（min）的关系式为D=exp（0.565ln T＋0.072）。在还原时间为120 min时，还原球团金属铁晶粒的平均尺寸D（μm）与还原温度T（K）的关系式为D=exp（-8995845ln T＋8.899）。在还原温度1000~1200℃范围内，还原球团的金属铁晶粒生长表观活化能为132.53 kJ/mol。

微波还原鲕状赤铁矿中铁晶粒的形核生长机理

采用Avrami-Erofeyev模型对微波还原鲕状赤铁矿含碳球团过程中铁晶粒的形核与生长动力学进行了研究,并采用XRD、SEM、EDX对还原样物相组成、铁晶粒形貌尺寸、元素组成分布等进行了测试分析。研究结果表明,在1173~1473 K下20 min时间内可获得金属化率77.6%~92.6%;微波还原鲕状赤铁矿球团过程中铁晶粒形核速率与铁晶粒生长速率与模型拟合度高,1173~1473 K下置信度R2范围分别为0.9411~0.9977与0.9484~0.9848。拟合得出了动力学参数,获得铁晶粒形核活化能为51.21 kJ/mol、生长活化能为18.05 kJ/mol,还原速率受形核速度控制。通过与常规加热对比发现,微波场中铁晶粒形核与生长速率更快。扫描电镜观察发现铁晶粒的生长形态部分为球形熔滴状、部分为蠕虫状链晶,视域内最大单个铁晶粒尺寸约为10μm。

高硅铁废渣直接还原铁晶粒形成与长大

冶金工业每年会产生大量的高硅铁废渣,铜渣作为一种典型的高硅铁废渣,目前主要以露天堆积方式处理,为了提取铜渣中有价元素,并进行资源化利用,以某厂铜渣为例进行煤基直接还原试验,采用XRD衍射、扫描电镜等分析手段,探究铜渣在直接还原过程中不同阶段以及加入形核剂条件下铁晶粒的形成、长大及分布规律。结果表明,还原时间为30 min时,金属化率最高为78.40%,铁晶粒生长情况最为良好,铁元素分布最集中;还原过程中加入磁铁矿能明显提高金属化率,有利于铁晶粒的生长,当磁铁矿配比为20%时,金属化率最高,为87.59%;磁铁矿作为形核剂加入可降低形核位垒,促进铁晶粒的长大与铁元素的集中分布。

钙基提钒尾渣强化还原-磁选分离钛铁技术研究

采用直接还原-磁选方法从钒钛磁铁矿直接提钒尾渣中回收Fe,在还原温度1250℃、还原时间2 h、还原剂用量为尾渣质量的20%的条件下,球团的金属化率为92.71%。在球团中加入5%CaCO_(3)并延长保温时间至6 h后,Fe晶粒的平均直径从14.53μm增加至25.39μm。通过对Fe晶粒的生长速率拟合发现,加入CaCO_(3)后,晶粒生长速率常数从0.26μm^(2)/min提高至1.45μm^(2)/min。加入CaCO_(3)的直接还原球团经过磁选后,可以得到TFe含量为90.72%的直接还原铁和TiO_(2)含量为41.75%的含钛渣,Fe的回收率达到了91.05%,大幅提高了钒钛磁铁矿的资源利用率。

Properties of magneto-rheological fluids based on amorphous micro-particles

To improve the magneto-rheological (MR) properties of magneto-rheological fluids, self-made amorphous alloy particles, the composition of which was Fe76Cr2Mo2Sn2P10B2C2Si4, were used as the disperse phase to replace traditional carbonyl iron (CI) particles to prepare amorphous based magneto-rheological fluid (AMRF). Soft magnetic properties and densities of the amorphous particles and the CI particles were tested and compared. The results indicate the amorphous particles present a lower density but larger magnetization intensity and larger permeability at lower field levels. Properties of the AMRF with 20% particles in volume fraction were tested and compared with the CI based MR fluid (CMRF). The AMRF presents a saturation yield stress of 41 kPa at ~227 kA/m and a sedimentation ratio of 80%. The results indicate the magneto-rheological fluid based on amorphous micro-particles has better MR properties and sedimentation stability than that based on CI particles at lower field levels (0-200 kA/m).

Grain refinement process of pure iron target under hypervelocity impact

The structure of ultrafine grain is formed at the crater bottom of pure iron target under hypervelocity impact. The microstructures of different layers at the crater bottom were characterized by optical microscopy （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The cross-section observation was performed to reveal the grain refinement process driven by plastic deformation. Firstly, low energy dislocation structures （LEDS） such as dense dislocation walls （DDWs） and dislocation tangles （DTs） refine the original grains and form intersecting lamellar structures. With increasing strain, DDWs and DTs transform into subboundaries with small misorientations to separate lamellar structure to cells. Subboundaries are converted to high misorientation grain boundaries, so ultrafine grains are formed. The formation of ultrafine grains was discussed in the dynamic recrystallization process due to the large strain and strain rate induced by spherical shock wave.

FE-based coupling simulation of Ti60 alloy in isothermal upsetting process

A constitutive equation was proposed to describe the effect of grain size on the deformation behavior.And a coupling simulation of deformation with heat transfer and microstructure was carried out in isothermal upsetting process of Ti60 alloy.The effects of processing parameters on the equivalent strain,the equivalent stress,the temperature rise and the grain size distribution in isothermal upsetting process of Ti60 alloy were analyzed.It is concluded that the uniformity of equivalent strain and equivalent stress increases with the increase of deformation temperature.However,the temperature rise and the grain size decreases with the increase of deformation temperature.The non-uniformity of equivalent strain,equivalent stress,temperature field and grain size increases with the increase of height reduction.And the calculated grain size using simulation is in good agreement with the experimental one.

Swelling behavior of hot preheated pellets in reduction roasting process

One kind of facile coal-based direct reduction process is using hot preheated pellets for reduction in grate kiln. In this work, effects of reduction parameters on swelling index of hot preheated pellets were investigated by photographic technique under isothermal conditions. Experimental results show that swelling index of pellets is firstly increased then gradually decreased with increasing reduction time, while that is found to be an obvious decrease from 175 % to 30% with the variation of temperature from 900℃ to 1100℃. Results of XRD combined with SEM reveal that swelling behavior of pellets is decided by structure of newly formed metal iron grains. The formation and growth of fibers iron grains promote the increase in volume. Low temperature and low CO content are favored to the formation and orientated growth of metal iron grains in the one step process.

On the comparable activity in plasmonic photocatalytic and thermocatalytic oxidative homocoupling of alkynes over prereduced copper ferrite

Despite of extensive attention on the copper-based heterogeneous oxidative homocoupling of alkynes(OHA)to 1,3-diynes,the photocatalytic OHA is scarcely investigated.By screening copper-containing spinel catalysts,we discovered that a prereduced copper ferrite(CuFe2O4)not only can catalyze the thermocatalytic OHA but also is efficient for the photocatalytic OHA under visible light irradiation.It is found that the sol-gel combustion(SG)method and the partial reduction at 250 ℃ can result in the optimal CuFe2O4-SG-250 catalyst showing high activity and stability.Surface oxidized Cu2O is evidenced to be the active species for the thermocatalytic OHA,whereas metallic copper nanopaticles(CuNPs)are identified as the active sites for the photocatalytic OHA.The efficiency of photocatalytic OHA at ambient temperature is comparable to that of thermocatalytic OHA at 120 ℃,and the CuFe2O4-SG-250 catalyst can be magnetically separated and reused at least five times.The localized surface plasmon resonance effect of CuNPs contributes to visible light-induced photocatalytic OHA.

Effect of mechanical activation on alkali leaching of chromite ore

Mechanical activation was used to improve the extraction of chromium in molten NaOH.It is observed that the extraction ratio reaches 97% after leaching for 200 min when chromite ore is mechanically activated for 10 min,but only 34% if not activated.Mechanical activation can decrease the particle size,increase the surface area,and enhance the lattice distortion.Further,the mechanisms for mechanical activation were exposed.The results show that the mechanical activation mainly focuses on chromite ore particle size decrease and the lattice distortion.The formation of aggregation weakens the strengthening effect of mechanical activation for releasing high surface energy.

生物质对钒钛磁铁矿还原行为影响及过程强化

为了缓解冶金行业严重的污染和温室气体排放,生物质作为清洁能源的应用迫在眉睫。从还原速率、矿物相变和铁晶粒长大等方面,对生物质和无烟煤还原钒钛磁铁矿特性进行了对比研究。结果表明,生物质具有较好的反应活性,促进了黑钛石和金红石的形成,避免了钛铁尖晶石的形成,从而提高还原速率。但由于生物质的持久性较差,还原产物金属化率较低且铁晶粒尺寸较细。以一定比例的生物质和无烟煤作为复合还原剂,既保证了还原速率和金属化率,又促进了铁晶粒的生长,达到协同作用的目的。

某低品位铁矿回转窑还原结圈物特性及其形成机制

回转窑结圈一直以来是制约煤基回转窑直接还原工艺发展的重要因素,以某低品位铁矿回转窑还原结圈物为研究对象,深入研究回转窑结圈物的特性及其形成机制.从结圈物的宏观形貌、物化性能、软熔特性和微观结构入手对某低品位铁矿球团回转窑结圈物的特性进行分析,并结合热力学相图、化学物相及能谱分析研究了结圈物的形成机制.结果表明：结圈物由熔融物包裹球团形成,接近窑壁,其熔融包裹物增多,结圈物中MFe、Ca O含量明显增大,软熔温度越低;由球团粉末中Fe O与Si O2形成的铁橄榄石及煤灰带入的Ca O而形成的钙铁辉石低熔点相是造成结圈的主要原因;低熔点相的存在同时也促进了金属化球团间铁晶粒的相互扩散与迁移,从而加剧了结圈现象.

Complex Permeability of Ferrites as Intrinsic and Extrinsic Properties

CIP （complex initial permeability） spectra of PF （polycrystalline ferrite） are studied both as intrinsic and extrinsic properties. In the former case, main steps of modeling, based on effects coming from polycrystal grain sizes distribution and defects, are described. The obtained relations work well in practice for PF with more or less normal MS （microstructure） and no size effects. Besides, fundamental connection between parameters of CIP and MS is found. Another case--PF with possible size effects （MnZn-ferrites） are studied experimentally for different sizes of cores, unveiling the dependence of phenomena on： dimensions of cross-section, number of turns, width of nonmagnetic gap.

Evolutions of texture and grain boundary plane distributions in a ferritic stainless steel

The grain size, textures and grain boundary plane distributions in a cold-rolled and annealed ferritic stainless steel were investigated by means of EBSD techniques. The results show that, following cold rolling with the thickness reduction of 85%, relatively low temperature （780℃） annealing brings an extremely sluggish grain growth and no grain texture develops when the annealing time varies from 5 min to 480 min. The free energy reduction of the system is mainly caused by the grain boundary plane re-orientation in addition to minor grain growth because the distributions of grain boundary planes are moderately preferred on { 100} according to the five parameter analyses （FPA） concerning the grain boundary plane characteristics. However, in the case of high-temperature （1 000 ℃） annealing, the average grain size does not increase until annealing time is prolonged to 90 min, after which extensive grain growth occurs and strong {100}（hkl） texture emerges whereas nearly random grain boundary plane distributions are observed. The free energy reduction of the system is most likely attributed to the selective growth.

Investigation of the thermal stability of Mn ferrite particles synthesized by a modified co-precipitation method

Manganese ferrite particles with spinel structure were synthesized by a modified co-precipitation method,and then the thermal stability on their structural and magnetic properties was investigated by thermal annealing at different gas ambients.Experimental results showed that decomposition of metal oxides occurred when Mn ferrite particles with spinel structure were annealed under air ambient,while samples annealed in vacuum or argon remained in the spinel structural form.The highest saturation magnetization value of 58 emu/g was obtained when the sample was annealed at 400℃ in argon.The result showed that the thermal stability of MnFe2O4 was better under Ar ambient conditions or in vacuum.

Occurrence andmineral chemistry of chromite and xieite in the Suizhou L6 chondrite

The occurrence and mineral chemistry of chromite and its high-pressure phase xieite in the Suizhou meteorite were studied by different modem micromineralogical techniques. Three types of occurrences for chromite were observed in the Suizhou L6 chondrite： coarse chromite grains, cluster of chromite fragments in molten plagioclase, and exsolution lamellar chromite in oli- vine. All the chromite grains of the first two types are remarkably similar in chemical compositions, but the composition of exsolution chromite is inhomogeneous and variable in A1203 content. Xieite is a post-spinel CT-phase of chromite firstly found in the Suizhou meteorite. Three types of occurrences of xieite have also been revealed in this meteorite： coarse xieite grains, complex three-zone-grains consisting of the inner xieite, the intermediate lamellae-like CF-phase and the outer chromite phase, and two-phase-grains consisting of xieite and one of the high-pressure silicate minerals lingunite, ringwoodite or majorite. The curved boundary between xieite and the silicate half in two-phase grains is indicative of some partial or even full melting of the silicate phase. EPMA and EDS results show that the compositions of xieite inside/contacting the shock veins are also identical to that of chromite outside the veins. However, some element diffusion appeared in between the xieite and the silicate half in the two-phase grains, namely, some of Al^3＋ from lingunite, or Fe^2＋ from ringwoodite migrated to xieite, and some of Cr^3＋ migrated from xieite to lingunite or ringwoodite. Majorite in two-phase grains shows remarkable decrease of SiO2 and MgO, and notable increase of Al2O3 and CaO, indicating that its host mineral pyroxene was fully molten and mixed with the surrounding silicate melt of the vein matrix. The complexity in mineral chemistry of these two-phase grains in shock veins can be explained by the much higher shock peak temperature in shock veins （1800-2000℃） than in unmelted main body （-1000℃）, and by the much lower density of the silicate minerals （2.6-3.3 g/cm3） than that of chromite （4.43 g/cm^3）. Being a refractory and a rela-tively high-impedance material, chromite is chemically more stable and easier to reflect shock wave into the silicate half causing the partial or even full melting of silicate phases, upon which some diffusion of elements between the two phases them-selves, or even mixing of molten pyroxene and the surrounding silicate melt.