超音速等离子喷涂的射流特性

采用非局域热力学平衡条件,考虑等离子喷涂过程中的电离及复合反应,研究超音速等离子喷涂过程中的流场特性。结果表明,氩氢混合气体中氢气的体积分数为15%时,喷枪内部的最大速度达到3 200 m/s,最高温度达到18 000 K。采用氩氢混合气体比纯氩情况下的速度和温度都有所提高。等离子体的最大速度随电流增大而增大,最高温度在470 A出现拐点,当电流大于470 A时,气流温度开始升高。加入粉末后,气流速度增大。流场速度随载气量增大而减小。氩氢混合气体中氢气的最佳含量为体积分数15%。     

全玻璃等离子体炬管的研制

自六十年代以来,低温等离子体作为光源,已经在光谱分析中得到了广泛应用。其优点是背景浅,灵敏度高,基体影响小,由于等离子体焰温度高达6000～10000度,比电弧和火花具有更好的前景。等离子体光源主要由高频发生器产生5～50兆周的高频电流,经过负载(感应线圈)     

高温还原性气氛下TiOx-SiO2-MgO系结晶过程的研究

实验通过定组成的H2/CO2混合气控制氧分压,在温度为1873 K、1673 K、1473 K,氧分压为1.22×10-8~2.18×10-12 Pa、4.92×10-8~8.79×10-12 Pa的范围内,研究了TiOx-SiO2-MgO 系的析出相.结合XRD和EDS分析并对比汪大亚等人的研究可知,当氧分压较高（PCO∶PCO2=5∶1）时,对于初始成分TiO2∶MgO∶SiO2摩尔比为60∶25∶15的试样,在1873 K 和1673 K 时的析出相为TiO2,在1473 K 时其析出相为MgTi2O5;对于初始成分TiO2∶MgO∶SiO2摩尔比为60∶15∶25的试样,在1873 K时其析出相为TiO2,在1673 K和1473 K时析出相为MgTi2O5.而当氧分压较低（PH2∶PCO2=600∶1、300∶1、150∶1）时,2种不同成分的试样在不同温度下的析出相均为黑钛石,并且随着氧分压的降低,黑钛石中的Mg 含量逐渐减少.     

TiC含量对钨基材料性能的影响

用热压烧结法制备了TiC含量 (体积分数 )分别为 0、10 %、2 0 %、30 %和 40 %的五种钨基材料 (TiC/W )。材料的硬度及弹性模量随TiC含量的增加而增大 ,分别由W基体的 3 4GPa、313GPa ,提高到 40 %TiC/W的 11 2GPa和 392GPa。随TiC含量的增加 ,材料的室温横向断裂强度和断裂韧度呈上升趋势 ,均在 2 0 %TiC/W时达到峰值 ,分别为 845MPa和 10 1MPa·m1/ 2 。随TiC含量增加 ,材料的热膨胀系数和比热容都增加 ,而热扩散率和热导率则显著下降。材料的热扩散率和热导率分别由W基体的 0 6 2 9× 10 -4 m2 /s和 15 3W / (m·K) ,提高到 40 %TiC/W的 0 110× 10 -4 m2 /s和 2 7 9W/ (m·K)     

氢等离子体还原 SiHCl_3的一些工艺参数的研究

一、前言用氢等离子还原金属氯化物制取金属或其化合物近来被人们广泛重视。金属氯化物沸点一般都较低(如TiC1_4、SiHCl_3),易于挥发,便于用载气输送到等离子体放电区或加入到等离子体尾焰中去。氢等离子体具有能量集中、热焓值高、导热性强等特点,在高温下氢的还原能力也大为提高。所以它在冶金中应用是很有前途的。用氢等离子体还原气相SiHCl_3制取硅是新工艺,目前国内外在这方面研究得不多,也多处于探索性阶段。文献〔1〕报道了在中性或还原性等离子体中分解SiCl_4之理论计算,指出分解成硅的温度是3500K,而在4500K时分解率达100％。Л.C.Πoπak对高温氢还原SiCl_4     

MoS_2-CaO-O_2系热力学分析及应用

通过热力学计算得出温度为800,900 K时,不同Mo S2,Ca O,O2初始物质量条件下对应Mo S2-Ca O-O2体系的热力学平衡,确定辉钼矿石灰焙烧的反应机制。热力学分析表明,800 K时体系初始摩尔量Mo S2∶Ca O=1∶3时,随着氧用量的增加Mo(VI)优先与石灰、氧气结合生成CaMoO_4,然后S(II)被氧化生成CaSO_4,体系氧化最终热力学平衡产物为CaSO_4,CaMoO_4;800 K时体系初始摩尔量Mo S2∶Ca O=1∶2时,随着氧用量的增加,约70%的Mo S2首先生成CaMoO_4,Ca S,然后Ca S氧化为CaSO_4,最终CaMoO_4作为固硫剂与残余的Mo S2反应生成Mo O3和CaSO_4,最终对应热力学平衡产物为CaSO_4,Mo O3。理论上证明可以实现辉钼矿选择性钙化焙烧;温度从800 K提高至900 K时,不影响全钙化焙烧过程;对于选择钙化焙烧高温不利于CaMoO_4固硫,而富氧益于固硫。验证试验采用100 g辉钼矿与55 g氧化钙混匀,在温度为800 K的马弗炉中焙烧2 h,焙砂钼、硫固定率分别为98.36%,91.44%,X射线衍射(XRD)分析表明钼硫分别以Mo O3,CaSO_4存在,与热力学分析结论一致。     

微量热法测定二钼酸铵比热容

用Micro-DSCⅢ微热量仪的连续比热容模式分别测定了普通ADM(二钼酸铵)和非团聚ADM的比热容,结果表明,298.15 K时的标准摩尔比热容分别为278.997 J·mol-1·K-1和281.940 J·mol-1·K-1,相对偏差1.04%,两种晶形的宏观比热容热力学性质基本一致.同时,研究发现非团聚ADM存在着可逆晶形转变,转变Te、Tp分别为52.054 ℃和53.351 ℃,转变焓为7.411 J·mol-1.     

La(C7H5O3)2·(C9H6NO)的合成及热化学研究

研究由七水氯化镧与水杨酸、8-羟基喹啉反应合成镧与水杨酸、8-羟基喹啉多元混合配合物,并对该配合物进行表征.测定该合成反应的标准摩尔反应焓以及配合物的标准摩尔生成焓.通过红外光谱、元素分析、摩尔电导率、差热热重分析以及化学分析等方法来确定配合物的组成.应用溶解量热法分别测定了七水氯化镧、水杨酸、8-羟基喹啉和配合物在298.15 K、混合量热溶剂(VDMFVEtOHVHClO4=110.5)中的标准摩尔溶解焓.通过设计热化学循环,根据盖斯定律计算了合成反应的标准摩尔反应焓以及配合物的标准摩尔生成焓.该配合物的分子式是La(C7H5O3)2·(C9H6NO).各物质的溶解焓分别为△sH(I○)mLaCl3·7H2O(s),298.15 K]=-96.45±0.18 kJ·mol-1,△sH(I○)m[2 C7H6O3(s),298.15 K]=14.99±0.17 kJ·ml-1,△SH(I○)m[C9H7NO(s),298.15 K]=-3.86±0.06kJ·mdl-1及△S(I○)m[La(C7H5O3)2·(C9H6NO)(s),298.15K]=-117.78±0.11kJ·mol-1.反应LaCl3·7H2O(s)+2C7H6O3(s)+C9H7NO(s)=La(C7H5O3)2·(C9H6NO)(s)+3HCl(g)+7H2O(1)的标准摩尔反应焓为91.57±0.33 kJ·mol-1.La(C7H5O3)2·(C9H7NO)(s)的标准摩尔生成焓为△sH(I○)m[La(C7H5O3)2·(C9H6NO)(s),298.15 K]=-2076.5±3.9 kJ·mol-1.     

综采割煤粉尘运移影响因素的数值模拟

为解决综采割煤粉尘质量浓度高的问题,获取粉尘控制的合理参数,改善作业环境,以邢东矿2225工作面为研究背景,依据气固两相流理论,运用Fluent软件对综采工作面割煤粉尘运动规律进行数值模拟,并与现场实测的粉尘质量浓度分布情况进行对比分析,模拟结果与实际数据基本一致.研究结果表明:工作面风速、采煤机滚筒转速、溜子速度以及壁面条件是影响综采工作面粉尘质量浓度分布的几个重要因素.当工作面平均风速在1.4m·s-1,滚筒转速不超过2.5rad·s-1,溜子速度不超过1.5m·s-1,防降尘效果最佳.同时洒水保持煤壁湿润也起到一定的捕尘作用.      

中空、实心电极电炉熔炼钛渣过程中电弧特性的对比研究

为了深入探究中空电极技术在钛渣电炉冶炼工艺中的优势所在,以25.5 MW钛渣电炉实际电极尺寸为基础,分别建立了中空和实心电极电弧的数学模型,模拟得到中空、实心电极电弧的电磁场、温度场和流场分布特性,研究了电流大小和电弧长度对熔池表面温度分布的影响规律。结果表明,电弧内电流密度、焦耳热值、速度和温度的较大值位于阴极斑点附近,中空电极是内外径中心线下方区域,实心电极是中心轴线附近区域。采用中空电极时,周围的电弧会向中轴线汇聚,该现象有利于提高电弧加热物料的效率。当电流值由34 kA增大到54 kA,两种情形下的熔池表面平均温度分别提升了708 K和109 K。当电弧长度由0.3 m缩短到0.1 m,两种情形下的熔池表面平均温度分别提升了2 500 K和46 K。相比于实心电极,中空电极更适合采用大电流和短弧长的运行方式,且合理控制弧长对提高中空电极电弧加热效率的效果更显著。     

On the smelting reduction of iron ores with hydrogen-argon plasma

Investigations of the plasma smelting reduction of iron ore have been carried out on a laboratory scale using a transferred argon-hydrogen plasma arc. Pyrometric measurements show that the surface temperature near the arc foot is about 2600 K when the hydrogen is mixed with the plasma-gas in front of the cathode, about 2250 K when the hydrogen is introduced laterally into the arc and ca. 2150 K when a pure argon plasma is used. With the help of thermodynamic plasma data the corresponding arc temperatures have been estimated to be 13 000 K, 11000 K and 9500 K. It has been shown that the reduction rate after the smelting phase remains constant and is practically independent of the manner of addition of the hydrogen. The measured efficiencies of utilization of hydrogen were 43% and 50% and thus correspond closely to the equilibrium FeO + H₂ = Fe + H₂O. A combination of the rate constants obtained for the plasma smelting reduction with those found in literature for lower temperatures leads to an activation energy of approximately 67 kJ/mol. This value lies in the range of energies reported for the reduction of wustite after precipitation of the iron phase. It is therefore not unlikely, that in the case of plasma smelting reduction also, the rate determining step is the reaction H^ad+OH^ad → H₂O^ad.     

Effects of metal vapor on electron temperature in helium gas tungsten arcs

In order to investigate the effects of metal vapor on the thermodynamic property of arc plasma in the welding process, electron temperatures in the pure helium plasma and in the helium plasma during welding in gas tungsten arcs (GTAs) were measured by using the laser scattering method. The experimental results showed that metal vapor led to a significant decrease in the electron temperature compared with that of pure helium GTA plasma. The temperature difference reached 6000 K in the arc fringe at the maximum.     

Modeling of fluid flow and heat transfer in the plasma region of the dc electric arc furnace

A mathematical model describing the transport processes in the plasma arc in dc electric arc furnaces has been developed. The equations of conservation of mass, momentum, and energy are solved numerically in conjunction with Maxwell's equations of the electromagnetic field to calculate the velocity and temperature distributions in the plasma region. The heat transfer from the arc to a rigid anode surface is calculated. The model is applied to obtain quantitative results on the relative importance of the various modes of heat transfer from the electric arc to the anode surface. Computational results were obtained for varying arc current magnitudes and anode-cathode distances. The model predicts higher arc jet velocity and a broader arc core at higher arc current. The shorter arc length is more efficient for transferring heat to the anode.     

Evaporation of reaction-zone components in the low-temperature plasma treatment of chromium-bearing melts

The evaporation of iron, Fe–Cr, Fe–Ni, and Fe–Cr–Ni melts at the plasma spot in treatment by low-temperature argon plasma is studied. Experiments with different masses of metal and with variation in arc power of the plasmatron are conducted so as to determine the conditions corresponding to stable surface temperature of the metal. The results show that, for experiments in which the plasma flux completely exposes the surface of the metal droplet, arc power no less than 2.0 kW is optimal; the mass of the metal should be 5?10 g. The evaporation process is studied as function of the melt composition, and the evaporation rates are determined. Of the alloys considered, Fe–Cr–Ni melt is characterized by the highest evaporation rate in the neutral atmosphere of a laboratory plasma furnace. The surface temperature of the melt is determined indirectly, on the basis of the evaporation rate. The surface temperature of the plasma-treated melt is found to vary in the range 1950–2100 K with variation in arc power from 1.6 to 2.4 kW.     

Integrated purification of gadolinium and preparation of Gd2O3 nanoparticles by DC arc plasma

The rare-earth metal Gd plays an important role in the energy, information, and national defence fields due to its special optical, electrical, magnetic, and catalytic properties. In this study, Gd was purified by direct current (DC) arc plasma, and Gd₂O₃ nanoparticles were prepared via an integration method using purified Gd. The effects of arc current, melting time, gas pressure, and atmosphere on the purification of Gd by DC arc plasma were investigated. With an increase in the arc current and melting time, the rate of removal of impurities from Gd enhances. Moreover, Gd melting was conducted by H₂–Ar arc plasma, which improves the impurity removal rate by increasing the H₂ content. High thermal conductivity and chemical activity of the activated H atoms generated by the dissociation of H₂ are the main reasons for the significant improvement in the impurity removal rate. The mechanism of Gd purification was analysed based on the above-mentioned experimental results. The as-synthesised Gd₂O₃ nanoparticles have a uniform spherical structure (average diameter of 32.7 nm), appropriate dispersibility, and high purity. This study provides a new strategy for the integrated purification of metals and preparation of metal/metal-based nanomaterials by DC arc plasma.     

直流等离子渗氮法对纯铝耐腐性的改善——时间和温度的影响

为了提高铝的耐腐蚀性能,在氮氢混合物（PN2/PH2=4/1）等离子体中用直流等离子体渗氮法对铝进行了处理。处理温度为673 K和723 K,处理时间为8 h、12 h和20 h。通过利用扫描电子显微镜（SEM）、X射线能量色散光谱仪（EDX）以及X射线衍射仪进行的表面分析发现,随着处理时间的延长和处理温度的升高,样品表面生成层的生长速度增加。为了考察样品的耐腐蚀性,在质量浓度为3.5%的氯化钠溶液中进行了电化学动态极化实验,结果显示,样品的腐蚀行为取决于生成AlN的质量。当处理温度为723 K、处理时间为20 h时,试样的耐腐蚀性最好。     

Spheroidization of Iron Powder in Microwave and Hybrid Plasma Torches

The process of porous iron powder spheroidization with a particle size from 45 to 85 μm is investigated in the microwave discharge and joint microwave and DC discharge modes in nitrogen and helium plasma. The powder was prepared by air spraying and annealed in hydrogen. Spraying in plasma results in hollow spheroidized particles with a wall thickness from 1 to 10 μm. The fraction of spheroidized powder particles in their total number is determined. It is revealed that the degree of spheroidization of iron powder particles linearly increases with an increase in the microwave radiation power from 1.5 to 5 kW. The combination of operational conditions of the microwave radiation with the arc discharge is observed when using the hybrid plasmatron mode, which makes it possible to increase the plasma temperature. An almost 100% spheroidization of iron powder is attained with the power ratio of microwave and arc discharges of 1 : 1. The metallographic investigation of spheroidized particles showed that their finite size differs from the initial one approximately tenfold. It is established that, irrespective of the spheroidization mode, the iron powder oxidizes, which is caused by an insufficient degree of purification of plasma-forming gases. The structure of the particle surface when using nitrogen or helium as a plasma-forming gas is different. The experiments show that the application of helium is preferential because the particles have only insignificant roughness in this case when compared with the particle structure when performing spheroidization with the use of nitrogen.

     

Nitrogen Removal and Arc Voltage Increase in EAF Steelmaking by Methane Injection into the Arc

Methane injection into the arcs of electric arc furnaces has been shown on pilot scale to lead to a remarkable arc voltage increase at constant arc current and arc length. Recent investigations have been concerned with the associated metallurgical effects making use of a gas‐tight 150‐kg arc furnace operated with two AC plasma torches. A first test with bored graphite electrodes in this furnace confirmed the power increase observed during methane injection. The carburization slowly occurring when 6 % CH₄ were injected into the argon atmosphere of the furnace could be avoided by adding minor amounts of CO₂. A slag layer decreased mass transfer rates without noticeably affecting heat transfer. Manganese loss by evaporation was measured to investigate the influence of power increase and slag layers. From the results, an increase of 200 K was concluded for the melt surface temperature when CH₄ was added to pure argon. Methane injection into the arcs proved to accelerate nitrogen removal considerably. Starting with an intentionally high nitrogen content of about 200 ppm, the nitrogen removal rate was found to be slowest with pure argon plasma arcs, faster with 90 % Ar + 10 % H₂, and fastest with 95 % Ar + 5 % CH₄ reaching final contents of less than 20 ppm of nitrogen. Based on thermodynamic calculations, the denitrogenation reactions appear to take place via atomic nitrogen in pure argon plasma, via NH₃ in Ar + H₂ and via HCN in Ar + CH₄.     

偏心M-EMS作用下连铸圆坯流动-传热模拟

 为探究偏心结晶器电磁搅拌(M-EMS)对圆坯钢液流动和传热的作用,减轻偏心M-EMS对圆坯的不利影响,通过建立三维耦合模型研究了偏心M-EMS作用下Φ380 mm连铸圆坯钢液流动和传热特点及M-EMS参数的影响。结果表明,在偏心M-EMS(300 A/2 Hz)作用下,由水口进入结晶器钢液流向外弧侧,碰壁后会形成较大回流;外弧侧钢液温度比内弧侧温度高;随着距弯月面距离增加,外弧侧钢液温度先增加后降低,温度最大处在M-EMS中心,为1 779 K;内弧侧钢液温度则一直降低。随着电流强度由100增加到500 A,圆坯下方回流区由1个变为2个;内、外弧侧钢液温差先减小后增加,在300 A时最小,为8.4 K。随着电流频率由1增加5 Hz,外弧侧回流区变小直至消失。当电流频率小于3 Hz时,内、外弧侧钢液温差小于10 K;而当频率大于3 Hz时,温差则大于16 K。Φ380 mm圆坯推荐M-EMS参数为300 A/2 Hz。     

放电等离子烧结制备非连续石墨纤维/Cu复合材料

以磨碎中间相沥青基石墨纤维和铜粉为原料,通过放电等离子烧结(spark plasma sintering,SPS)制备非连续石墨纤维/Cu复合材料,对石墨纤维表面进行镀钛金属化处理,以改善材料的界面结合状况.研究SPS工艺参数、铜粉粒度搭配、石墨纤维表面镀钛以及石墨纤维含量对石墨纤维/Cu复合材料致密度及热导率的影响.结果表明,将平均粒度为12和80 μm的铜粉按1∶2的质量比搭配,再与表面镀钛石墨纤维按1∶1的体积比混合,采用35 MPa先加压后送热的加压方式,于895℃下进行放电等离子烧结,可获得致密度达99.6％、热导率为364 W/(m·K)的石墨纤维/Cu复合材料,是1种很有潜力的电子封装材料.石墨纤维表面镀覆的极薄Ti镀层,可使复合材料在二维平面方向上的热导率从196 W/(m·K)提高到364 W/(m·K).