Kinetics of extracting magnesium from mixture of calcined magnesite and calcined dolomite by vacuum aluminothermic reduction

The vacuum aluminothermic reduction of the mixture of calcined magnesite and calcined dolomite was studied. An isothermal reduction method satisfying the vacuum aluminothermic reduction was proposed. The experiments were carried out at 4 Pa. The results indicate that the reduction rate is increased with increasing temperature, content of aluminum and pellet forming pressure. The XRD patterns of pellets at different reduction stages confirm that the reduction process can be roughly classified into three stages：the formation of MgAl2O4, and Ca12Al14O33 phases;the phase transformation from MgAl2O4 and C12A7 to CaAl2O4;the formation of CaAl4O7 phase. The experimental data were divided into three parts according to the kinetic models. The apparent activation energies of the three parts were determined to be 98.2, 133.0 and 223.3 kJ/mol, respectively.

Mechanism of extracting magenesium from mixture of calcined magnesite and calcined dolomite by vacuum aluminothermic reduction

The process of aluminothermic reduction of a mixture of calcined dolomite and calcined magnesite had been developed. The mechanism of the process was studied by SEM and EDS. The reduction process was divided into three stages:0≤ηt/ηf≤0.43±0.06, 0.43±0.06≤ηt/ηf≤0.9±0.02 and 0.9±0.02≤ηt/ηf<1, whereηt andηf are the reduction ratio at time t and the final reduction ratio obtained in the experiment at temperature T, respectively. The first stage included the direct reaction between calcined dolomite or calcined magnesite and Al with 12CaO·7Al2O3 and MgO·Al2O3 as products. The reaction rate depended on the chemical reaction. The CA phase was mainly produced in the second stage and the overall reaction rate was determined by both the diffusion of Ca2+ with molten Al and the chemical reaction. The CA2 phase was mainly produced in the third stage and the reaction process was controlled by the diffusion of Ca2+.

Synthesis of Al_2O_3/WC powder by aluminothermic reduction and carbonization method

Al2O3/WC powder was synthesized by means of aluminothermic reduction-carbonization with metallic Al powder, yellow tungsten oxide and carbon black or graphite as raw materials under the protection of coke granules. The effects of Al2O3 content, temperature, C/WO3 molar ratio, and atmosphere on the synthesis of Al2O3/WC powder were studied. The results show that the relative content of WC and W2C is strongly influenced by the factors mentioned-above. Carbon black has higher reactivity than graphite. Al2O3-WC composite is easier to obtain under the protection of coke granules than under argon atmosphere. The CO in the coke layer can easily react with tungsten to form WC and to transfer from W2C to WC.

Effect of magnesium on the aluminothermic reduction rate of zinc oxide obtained from spent alkaline battery anodes for the preparation of Al–Zn–Mg alloys

The aluminothermic reduction of zinc oxide（ZnO） from alkaline battery anodes using molten Al may be a good option for the elaboration of secondary 7000-series alloys. This process is affected by the initial content of Mg within molten Al, which decreases the surface tension of the molten metal and conversely increases the wettability of ZnO particles. The effect of initial Mg concentration on the aluminothermic reduction rate of ZnO was analyzed at the following values： 0.90wt%, 1.20wt%, 4.00t%, 4.25wt%, and 4.40wt%. The ZnO particles were incorporated by mechanical agitation using a graphite paddle inside a bath of molten Al maintained at a constant temperature of 1123 K and at a constant agitation speed of 250 r/min, the treatment time was 240 min and the ZnO particle size was 450？500 mesh. The results show an increase in Zn concentration in the prepared alloys up to 5.43wt% for the highest initial concentration of Mg. The reaction products obtained were characterized by scanning electron microscopy and X-ray diffraction, and the efficiency of the reaction was measured on the basis of the different concentrations of Mg studied.

Preparation of Composites by Nitro Aluminothermic Processes, over β–SiAlON Matrix in the SiAlON-SiC-Al2O3 System

Goal: The goal of the research is preparation of SiAlON-containing composite through nitro aluminothermic processes, by the methods of reactive sintering and hot compaction. Method: The composite CH-6 was obtained by the method of reactive sintering, with further grinding and hot compression in vacuum furnace at 16000°C, under 30 MPa pressure and 10-12 min standing at the final temperature. Precursor was prepared in a thermostat at 150°C temperature by double compression. Pressure equaled to 20-25 MPa. Results: Physical-technical properties of specimens prepared via hot compaction were investigated. Mechanical strength at compression is 1940 MPa;mechanical strength at bending is 490 MPa;elastic module is 199.5 GPa, HV-11.6 GPa. X-Ray diffraction analysis, electron microscopic and X-ray diffraction Microspectral analysis were used to investigate composite microstructure and phase composition. Composite formulation was defined, the main phases of which were: β-SiAlON, corundum and silicium carbide. Conclusion: Composite CH-6 has been selected from the obtained composites, which is characterized by relatively high physical-technical properties: strength, density and hardness. Materials can be used for making high refractory articles, such as jackets to secure thermocouples, furnace bedding, cutting tools for metal and wood treatment, in rocket spatial technology and others.

Aluminothermal reaction to prepare Al-Ti-C master alloy

An investigation was carried out on the reaction process and mechanism between K 2TiF 6, graphite powder and aluminum melt with the common Ti concentration of 5%～7% in the grain refiner Al Ti C master alloys and the reaction temperature of 750～950 ℃, aiming at understanding their reaction mechanism and putting forward the aluminothermal reduction reaction method to practical use. During experimental investigation, K 2TiF 6 and graphite wrapped in aluminum foils were introduced into the aluminum melt at 850 ℃. Samples of alloy and slag were investigated by chemical analysis, XRD examination, SEM observation, and EDS analysis as well. It was found that the reaction was very vigorous at the beginning of the process and then reached a dynamic equilibrium. There were 3 particular reactions during the aluminothermal reaction process. At the beginning stage of the reaction, there emerged the phases of TiC and one type of metastable intermetallic phase TiAl 9 as well as TiAl 3 in aluminum melt. At the late stage of the reaction, the metastable phase TiAl 9 disappeared and another phase of Al 4C 3 emerged.

影响工业还原罐内铝热法炼镁过程还原效率的因素

在工业还原罐内进行铝热还原炼镁试验,分析影响还原效率的因素。结果表明:结晶镁的氧化和燃烧以及原料混合不均匀是导致还原效率降低的主要原因;原料混合不均匀导致贫铝区和MgO剩余,促进生成12CaO·7Al_(2)O_(3)和CaO·Al_(2)O_(3);对于富铝区域,MgO和CaO同时被还原,生成Mg_(2)Ca相。辐射传热和化学反应吸热是影响还原速率的关键因素;提高加热温度能够迅速提高球团层的温度,进而使球团获得足够的反应速度;此外,球团中含镁量越高,需要的反应时间越长。

固溶和时效处理对铝热法制备Cu-Ti合金组织和性能的影响

Cu-Ti合金作为导电弹簧,互联接插件等重要元器件的制备材料,其大规模工业制备方法和热处理工艺仍是当前铜合金领域亟需开发和推进的重点。采用具有工艺简单、环保节能、成本低廉等优点的铝热法制备了Ti含量分别为1%、4.5%、10%,即成分区间较大的Cu-Ti合金,且进一步采用固溶和时效处理调控合金的综合性能。结果表明,时效态的Cu-1%Ti和Cu-4.5%Ti合金中Ti元素主要呈固溶状态,只有非常少量尺寸较小的析出相,而Cu-10%Ti合金中存在大量尺寸较大的Cu 4 Ti相析出。随着Ti含量的增加,合金的导电率有明显降低的趋势,而硬度和强度则呈现与之相反的趋势。对于成分相同的合金,相较于固溶状态,时效后导电率先略微下降然后上升,450°C时效4 h后,三个成分合金的导电率均高于固溶态合金;450°C时效2 h后,Cu-1%Ti和Cu-4.5%Ti合金均获得了硬度、强度和延伸率的最大值,Cu-10%Ti合金的硬度和延伸率也获得了极大值,其屈服强度和抗拉强度则是随着时效时间呈略微下降的趋势。

高压断路器用CuW触头材料研究进展

CuW合金已作为触头材料被广泛用作高压SF6断路器和气体绝缘组合电器中,其抗侵蚀性能决定着开关设备的使用寿命。CuW触头材料主要的制备工艺包括熔渗法和粉末烧结法,最新的研究进展发现熔渗CuW合金的关键点在于W骨架的连接强度,而液相烧结CuW合金的关键在于熔融Cu与W颗粒之间的润湿性,明确了两种工艺的研究方向;对基于铝热还原工艺制备CuW合金的研究进行概述,提出思路是进行前驱体的烧结,降低反应物的活化能,从而促进自蔓延反应的进行;同时总结了目前CuW合金的改性研究在于增强相的添加和变形加工,旨在对工业上技术改进提供指导,但如何更好地应用于工业上仍需要一定时间的探索;最后着眼于弧触头的整体研究,明确CuW和CrCu之间的结合强度是弧触头整体材料的关键因素,也对后续整体材料的改进与发展提供新的方向。

聚合物基Al/CuO纳米铝热剂的制备及表征

为研究聚合物基铝热剂的性能,制备了以GAP-ETPE和F2311作为黏结剂的Al/CuO纳米铝热剂。然后利用油墨直写技术(DIW)配制出固含量高达80%的含能油墨GAP/F2311-MICs(GF-MICs),在此基础上加入高氯酸铵(AP),探索AP/GF-MICs模型推进剂的可打印性,并研究了AP含量对于AP/GF-MICs模型推进剂燃烧性能的影响规律;采用FTIR方法测试了混合黏结剂的相容性和稳定性,通过TG-DSC和静态拉伸研究了GF-MICs纳米铝热剂的热性能,并测试了其流变性和聚合物的力学性能。结果表明,GAP-ETPE与F2311质量比为1∶4时,混合黏结剂的相容性、稳定性和力学性能最好;纳米Al/CuO的加入使得F2311和GAP-ETPE的热分解温度分别提前89.0℃和32.9℃;随着模型推进剂中Al/CuO含量的增加,AP高温分解温度最高提前101.58℃,预先点火反应提前29.68℃,放热量提升135%;GF-MICs能够很好地提高模型推进剂的反应活性和燃烧速率,且当模型推进剂中Al/CuO质量分数由10%增至40%时,到达P max时间缩短了71%,平均燃烧速率提升了293%。

考虑焊接残余应力的钢轨铝热焊焊缝滚动接触应力分析

铝热焊焊缝的滚动接触应力是钢轨滚动接触疲劳问题的关键影响因素。本文开展了静力拉伸试验研究母材与焊缝材料的基本力学性能,采用Chaboche塑性本构方程描述两种材料在塑性阶段的力学响应。利用ABAQUS计算了铝热焊焊接过程的温度场和残余应力场。建立了轮轨滚动接触应力分析的有限元计算模型,并将焊接残余应力分析与焊缝滚动接触应力相结合,提出了考虑焊接残余应力的轮轨滚动接触应力计算方法。最后,分析了焊缝局部应力场的特点。研究结果表明:(1)焊缝边缘处相比中心处承受更大的接触压力,残余应力的存在会增加焊缝的滚动接触应力以及焊缝边缘处的接触压力;(2)随着车轮滚动次数的增加,焊缝的塑性应变会不断累积,进而影响钢轨疲劳伤损的演化。

钢轨铝热焊接过程传热传质行为计算流体力学数值分析

铝热焊在道岔焊接、既有线钢轨维修与断轨抢修中有着广泛的应用。由于铝热焊过程的封闭性,其温度与材料流动难以通过试验的方式进行测量。为此,运用计算流体力学的方法,采用k-ε湍流模型,结合流体体积法,并考虑液态金属的重力、浮力、表面张力与马兰戈尼效应,建立数值分析模型,对浇注和冷却过程不同时刻的传热传质行为进行定量分析,通过相分布特征研究凝固顺序,为后期优化浇注体系、构建新焊剂成分和砂型型式提供基础数据。结果表明:浇注过程中空气被裹挟进入熔池,浇注时间约为11 s,接头冷却至固相线1641 K以下的时间约为58 s;浇注开始后,不同区域最大温差约为1400 K,高温区位于轨底,低温区位于轨头;随着浇注的进行,轨头温度升高,轨腰温度先升后降,轨底温度降低;在浇注的最后阶段,不同区域温差缩小,最大约为400 K,高温区位于轨头,低温区位于轨底;在冷却过程中,轨头温度始终最高,轨底温度始终最低,按照轨底、轨腰、轨头的顺序发生凝固。

铝热还原含钛高炉渣制取钛硅铝合金

这是一篇冶金工程领域的文章。在氩气保护下,用铝还原含钛高炉渣制得钛硅铝合金。实验结果显示:在1500℃,氩气保护下,铝粉占高炉渣的30%~40%、石灰占5%~15%、萤石≥5%时,还原得到的合金主要为钛硅相、铝硅相、钛相;合金中钛、硅、铝的含量为分别35%~40%、26%~33%、23%~32%,钛、硅、铝的回收率分别为73%~88%、84%~95%、67%~77%。

加工用高纯钒锭的制备工艺研究

鉴于金属钒具有储氢、高温超导、快中子吸收截面小及对液态钠有耐蚀性等特性,市场对金属钒制品的需求不断增加,而这些钒制品必须使用满足要求的高纯钒锭来加工制作,重点从制备原料、工艺原理及流程、生产影响因素等方面对高纯钒锭的研制工艺进行详细阐述。

钢轨铝热焊轨底角部位伤损波形分析及校对方法

钢轨铝热焊轨底角部位的超声探伤较为复杂,通过研究典型伤损波形,结合金相分析,总结了一套对钢轨铝热焊轨底角部位伤损检测分析及校对的方法,可以更准确、快速地发现钢轨铝热焊轨底角部位的内部伤损,以消除设备隐患,确保行车安全。

铝热还原生产钒铁合金的工艺优化

钒铁是生产工具钢、耐热钢的一种重要中间合金,目前主要采用铝热法生产。本文应用决策树分类方法来分析铝热还原生产铁合金的工艺和技术参数,主要考查了原料品位、发热量、配铝系数、反应时间、喷吹时间、喷吹量等主要工艺参数对产品回收率、铝含量含量的影响,给出各工艺参数对它们的影响模式。由于处理的数据是实际生产数据,数据分析结果可直接用于指导改进生产工艺。

真空铝热还原法制备金属Sr的热力学分析及实验研究

通过热力学计算,得出SrO被Al还原的化学反应自由能和还原反应临界温度,表明造渣反应和真空可有效降低化学反应自由能,由此将还原反应临界温度由标准状态的2244 K降低到1100 K以下.热力学计算、反应产物X射线衍射分析及56%产Sr率测量结果均表明,真空铝热还原法制备金属Sr实际上同时发生了2个反应.反应产物除蒸馏出的金属Sr(纯度为99.0%)外,残留渣团主要为3SrO·Al2O3,并掺有SrO·Al2O3.

底材厚度对铝热反应熔化制备的块体纳米晶Fe_3Al材料的组织和性能的影响

通过铝热反应熔化方法在厚度为5～15mm的铜底材上制备块体纳米晶Fe3Al材料．通过X射线衍射（XRD）研究材料的晶粒尺寸，研究材料室温压缩下的力学性能和硬度．结果表明，所制备材料的晶粒尺寸均约为20nm，且晶粒尺寸随底材厚度的增加而增加．底材厚度为5mm时纳米晶Fe3Al材料的屈服强度和硬度具有最大值，随着底材厚度的增加，屈服强度和硬度急剧减小，最后趋于稳定．5mm时纳米晶Fe3Al材料的屈服强度约是10mm时的1．5倍．

真空铝热还原法制备金属锶的锶还原率

对真空铝热还原法制备金属锶的锶还原率进行了试验研究,分析了SrO的焙烧工艺、原料粒度、混料压制团块压力、原料配比、真空度、加热温度、还原时间等对锶还原率的影响,并对金属锶进行了化学成分分析,对渣相组成进行了XRD定量分析。结果表明:工艺优化前后均制备出优质锶Sr-1,纯度达99.0%以上;综合工艺优化后,实际锶还原率可提高到60%以上;加热温度控制在1050℃较为合适,提高加热温度对提高锶还原率有利。

铝热法制备高钒铝合金的研究

用V2O5粉和Al粉为原料,通过铝热还原法制备了高钒铝合金,研究了反应物配比中Al含量对制备的高钒铝合金纯度和钒回收率的影响。结果表明:当反应物配比中Al欠量5%时,高钒铝合金的纯度最高为98.45%;随着反应物配比中Al含量的增加,高钒铝合金的纯度降低,钒的回收率增加,在Al过量15%时回收率最高为92.4%(质量分数)。高钒铝合金的布氏硬度在Al欠量5%时最低,为213.6 HB;在Al过量15%时布氏硬度最大,为250 HB。可以通过调节原料中Al含量来制备不同纯度的高钒铝合金。