High-Temperature Oxidation Behavior of Vanadium, Titanium-Bearing Magnetite Pellet

 By means of isothermal oxidation and chemical analysis, great importance was attached to the parameters that made effects on the oxidation degree of vanadium, titanium-bearing magnetite pellet in high-temperature processing (1073-1323 K). Based on the experimental data, oxidation kinetics of pellet was analyzed according to shrinking unreacted-core model subsequently. Experiment results display that the oxidation degree of pellet increases with increasing of oxidation time, oxidation temperature and oxygen content, as well as shrinking of pellet diameter. Under the condition of oxidation time 20 min, oxidation temperature 1223 K, oxygen content 15%, and pellet diameter 12 mm, oxidation degree of pellet reaches 92.92%. The analysis of oxidation kinetics indicates that oxidation process of pellet is controlled by chemical reaction with activation energy 68.64 kJ/mol at a relatively lower temperature (1073-1173 K). Oxidation process of pellet is mixed-controlled by chemistry reaction and diffusion with activation energy 39.66 kJ/mol in the temperature range of 1173-1273 K. When oxidation temperature is higher than 1273 K, the limited link of oxidation reaction is the diffusion control with the activation energy 20.85 kJ/mol. These results can serve as a reference to the production of vanadium, titanium-bearing magnetite pellet.     

PMC精矿配加司家营矿粉球团焙烧机理

 针对PMC矿的利用问题,对PMC精矿与司家营矿粉以7[∶]3配矿比例造球的氧化焙烧行为进行了研究。研究结果表明,当预热时间为10 min、焙烧温度为1 275 ℃、焙烧时间为20 min时,球团抗压强度随预热温度的升高呈现先升高后降低的趋势,当预热温度为925 ℃时,球团抗压强度达到最大为2 765.75 N/个;当预热温度为925 ℃、焙烧温度为1 275 ℃、焙烧时间为20 min时,球团抗压强度随预热时间的延长由2 64升高到2 833.61 N/个;当预热时间为15 min、预热温度为925 ℃、焙烧时间为10 min时,球团抗压强度随焙烧温度的升高由674.96升高到2 503.83 N/个;当预热时间为15 min、预热温度为925 ℃、焙烧温度为1 300 ℃时,球团抗压强度随焙烧时间的延长由2 503.83升高到2 872.52 N/个。     

钨酸钙球团碳化硅还原试验研究

采用高温炉恒温试验对不同时间、温度及还原剂配比条件下钨酸钙与碳化硅球团还原情况进行研究,结合熔点测试结果分析了球团在升温过程中的物理变化行为,得到各影响因素对球团还原的作用关系及钨直接合金化炼钢工艺的优化条件。结果表明,在1 400～1 500℃时,钨酸钙球团可以被碳化硅还原,还原产物为W、WC、Ca3(Si3O9)及SiO2,球团还原反应可能由固—固、固—液反应共同组成,在升温过程中亦发生碳化硅相变和分解、还原剂的氧化及钨金属的二次氧化;在1 400～1 500℃和10～30min时,低温条件下适当延长反应时间、时间较短条件下适当增加反应温度及适当提高还原剂配比有利于提高球团还原反应率;钨直接合金化电炉炼钢工艺中,采取钨酸钙快速还原,防止钨金属二次氧化措施,可以实现钨酸钙在冶炼早期大部分被还原。     

低碳钢固态相变过程的原位观察

利用共焦激光扫描显微镜（CSLM）原位观察了低碳钢升温及降温过程中的固态相变,直接观测出升温时低温铁素体（α）到奥氏体（γ）以及奥氏体（γ）到高温铁素体（δ）的相变温度,和降温时δ到γ以及γ到α的相变温度。结果表明,随着升温速率从75℃／min升至130℃／min,α—γ相变开始温度从961．6℃升至1014．0℃、γ→δ相变开始温度从1351℃升至1386．9℃;降温时随着降温速率的增大（70℃／min增至530℃／min）,γ—α相变开始温度从871．6℃降至858．4℃。在升温速率为130℃／min的情况下,随着升温最大值的提高（1300℃至1480℃）,γ—α相变温度降低,相变开始温度从895．2℃降至858．4℃。     

氧化球团微波加热煤基直接还原过程微观机制

为了解决常规加热煤基直接还原的反应时间长、还原温度高、产品质量差等问题,基于微波加热特性结合直接还原理论提出了采用微波加热进行氧化球团煤基直接还原的新工艺。通过采用扫描电镜、能谱分析仪和显微硬度计等检测手段对常规加热和微波加热煤基直接还原过程进行了深入研究,探究氧化球团微波加热煤基直接还原过程微观机制。研究结果表明,微波加热不仅改变了球团矿的微观结构和能量分配,而且在某种程度上表现出微波加热的“非热效应”,常规加热时,在还原温度1050℃下还原150 min,球团金属化率仅为89.38％;氧化球团煤基直接还原过程采用微波加热,从室温上升到1050℃后再等温14 min,球团金属化率达到92.67％。     

Nonisothermal gravimetric investigation on kinetics of reduction of magnesia by aluminum

An investigation of the reduction of magnesia by aluminum was carried out using a nonisothermal gravimetric technique under an argon atmosphere, in the temperature range from 1273 to 1873 K. The mixture of magnesia and aluminum powders was formed into a pellet under various isostatic pressures. It was found that magnesia is reduced by aluminum to form magnesium and spinel at first, and then the excess aluminum reacts with spinel slowly. The temperature at which the reaction starts increases with an increasing heating rate. The reaction rate is also affected by pellet-forming conditions. A kinetic model is proposed to explain the experimental results. The activation energy of the reduction of magnesia by aluminum is 151.2 kJ/mol. Good agreement between calculated and experimental results is obtained.     

Changes in Effective Thermal Conductivity During the Carbothermic Reduction of Magnetite Using Graphite

Knowledge of the effective thermal diffusivity changes of systems undergoing reactions where heat transfer plays an important role in the reaction kinetics is essential for process understanding and control. Carbothermic reduction process of magnetite containing composites is a typical example of such systems. The reduction process in this case is highly endothermic and hence, the overall rate of the reaction is greatly influenced by the heat transfer through composite compact. Using Laser-Flash method, the change of effective thermal diffusivity of magnetite-graphite composite pellet was monitored in the dynamic mode over a pre-defined thermal cycle (heating at the rate of 7 K/min to 1423 K (1150 °C), holding the sample for 270 minutes at this temperature and then cooling it down to the room temperature at the same rate as heating). These measurements were supplemented by Thermogravimetric Analysis under comparable experimental conditions as well as quenching tests of the samples in order to combine the impact of various factors such as sample dilatations and changes in apparent density on the progress of the reaction. The present results show that monitoring thermal diffusivity changes during the course of reduction would be a very useful tool in a total understanding of the underlying physicochemical phenomena. At the end, effort is made to estimate the apparent thermal conductivity values based on the measured thermal diffusivity and dilatations.     

冶金尘泥在转炉中的应用技术研究与实践

在实验室对冶金含铁尘泥在冶炼工序实现直接回收利用的热力学和动力学条件进行了研究,得出C-FeO反应的工况条件必须控制在温度大于950℃,金属化率随加热温度的升高和加热时间的延长而增加,并指出转炉是添加铁碳球的最佳位置。同时,开展转炉加铁碳球工业验证性试验,得出铁碳球对转炉终渣TFe含量没有显著影响,平均金属铁收得率约50%,加铁碳球的经济价值取决于废钢和铁水的价格差、铁碳球加入量及S含量3个主要因素。     

润磨对制备硫酸渣氧化球团的影响

为了提高硫酸渣的成球性能,试验采取润磨方式对其进行了预处理。结果表明:润磨时间4 min,润磨水分(质量分数)10%,造球时间10 min时,所得生球的落下强度较之未润磨的由1.5次/0.5 m增至3.7次/0.5 m,抗压强度由3.12 N/个增至15.61 N/个,且生球爆裂温度达到828 K。焙烧试验显示,硫酸渣经润磨后所制备的氧化球团的抗压强度达到3 332 N/个,能满足高炉生产的要求。     

Composite Pre-Reduced Pellet (CPR) — A New Way for Fines Utilisation

Composite pre-reduced pellet has a metallised core encased in a sintered shell of iron ore. It is produced under oxidizing atmopsphere and degree of reduction obstained is as high as 91%. Non-coking coal, charcoal, coke and char fines are used as reducing agent. The physical properties of this pellet make it suitable for use in blast furnace/steelmaking processes.

In this paper an attempt has been made to present a review of the work done in this area as well as ore: coal mixed pellet. The effect of process variables like, temperature, time, Fe₂O₃/C ratio, heating rate and heating conditions on degree of reduction has been discussed. Attempt has also been made to judge the suitability of the pellet for use in iron and steel industries.     

Fe-Si-B非晶带材高温氧化行为及回收工艺

??In order to reduce the oxidative burning loss of Fe78Si9B13 amorphous ribbon in the recovery process?? the oxidation behavior of Fe78Si9B13 amorphous ribbon was studied. The results show that the oxidation of Fe78Si9B13 amorphous ribbon at high temperature is related to the heating rate. The oxidation weight gain of Fe78Si9B13 amorphous ribbon at 5 and 10K/min from room temperature to 1223K are 44% and 31% respectively. There is an oxide layer with loose texture and a small amount of microcrack at the interface between the sample and atmosphere by SEM. The oxide layer contains a large amount of Fe2O3 and a little SiO2 by XRD. Oxidation kinetics curve shows that the oxidation weight gain of the samples follows a linear rule within 5hours at 1073 and 1173K?? then a parabolic rule. At 1273K?? however?? it only follows a linear rule?? meanwhile the oxidation speed is very fast?? with the oxidation weight gain reaches 40% in 12min. The oxidation weight gain in the amorphous ribbon recycling process can be reduced through cutting down the furnace gas temperature?? compressing the waste ribbon and unqualified products in the packaging process and blowing argon to reduce the partial pressure of oxygen in the furnace. Thus the slag decreases to 9-10g when 1kg waste ribbon is recovered?? and the Si content of liquid alloy increases to 8. 9%.     

Temperature Rise Characteristics of Carbon-Containing Chromite Ore Fines in Microwave Field

To avoid the nonuniform phenomena of heat and mass transfer of metallurgical powdery materials caused by conventional heating method,the temperature rise characteristics of carbon-containing chromite ore fines in the microwave field were investigated using microwave heating in a microwave metallurgical furnace.The experimental results show that the carbon-containing chromite ore fines have better temperature rise characteristics in the microwave field at a frequency of 2.45 GHz.After heated in the microwave field of 10 kW,the temperature of 1 kg carbon-containing chromite ore fines rose up to 1 100 ℃ in 7 min,at a temperature rise rate of 157.1（℃·min-1·kg-1）,whereas the temperature of 1 kg carbon-containing magnetite ore fines rose only up to 1 000 ℃ in 10 min,at a temperature rise rate of 100（℃·min-1·kg-1）.With increasing carbon-fitting ratios and by adding calcic lime,their heating effects changed regularly.     

CuO氯化过程动力学研究

铜渣中含有30 %~40 %的Fe, 对铜渣中的Fe进行回收, 有利于缓解中国依赖进口铁矿石的压力.基于热力学分析氯化除铜的可行性, 在823 K、873 K、923 K、973 K温度下, 通过热重分析研究CuO-FeCl₂体系的氯化过程动力学, 并考察反应温度和Ar气流量对反应的影响: CuO-FeCl₂体系的氯化率随温度的升高而增大, 当Ar流量为50 mL/min时, 氯化率达到最大值为62.46 %.通过推导氯化反应动力学公式, 确定CuO-FeCl₂体系的氯化反应为0级反应, 并且在873 K时由氯化过程动力学区过渡到扩散区, 动力学区的反应速率取决于CuCl₂的挥发速率, 扩散区的反应速率取决于FeCl₂向CuO表面扩散的速率.      

VOD精炼316L不锈钢吹氮合金化的研究

用0.8 kg钢水石墨坩埚的硅钼棒炉研究了常压下氮气分压(33～100 kPa) 、吹氮时间(0～50 min) 、吹氮流量(0.3 L/min) 、钢液温度(1 773～1 833 K)对316L钢(%:0.031C、16.13Cr、10.12Ni、2.12Mo、0·028N)中氮含量的影响,并试验了在前期真空条件下1 853～1 833 K吹氮40 min、2 kPa、0.1 L/min,中期吹氮40 min、100 kPa、0.3 L/min,后期吹氮50 min、100 kPa、自然冷却至1 773 K时316L钢水的增氮行为。结果表明,钢中氮含量随着吹氮时间、氮分压的增加而增大,常压下吹氮10 min,钢液含氮量即可超过0.10%,随吹氮流量增加钢液达到饱和的时间缩短,氮的溶解度随着钢液温度的降低而升高。应用热力学和动力学模型进行了分析。     

铁矿石含碳球团中碳的气化反应速度对球团熔融的影响

 利用气化反应速度不同的焦炭和石墨作为还原剂,考察了铁矿石含碳球团在高温加热时还原铁的渗碳、熔融及球团结构的变化规律。根据研究的结果,得到以下结论：①碳的气化反应速度对铁的渗碳及熔融有重要影响;②气化反应速度较快的焦炭混合球团在1 350 ℃加热9 min时球心部首先出现熔融铁粒,而气化反应速度较慢的石墨混合球团在1 250 ℃加热9 min时在球团表面首先出现熔融铁粒;③反应中物料混合状态的变化以及反应后球团内部空洞的大小都受到碳的气化反应速度的影响。     

Diffusion mechanism of internal friction in a niobium–titanium alloy

An NT50 alloy of the composition Nb–(48.5 ± 1.5)% Ti is studied after severe plastic deformation and subsequent 100-h annealing. During heating at a rate of 2 K/min, the NT50 alloy subjected to this thermomechanical treatment demonstrates two internal friction peaks at 493 K and 573 K. As the heating rate increases by a factor of three, both peaks shift to higher temperatures and the peak height at 573 K increases. A diffusion mechanism of the temperature-dependent internal friction in the strongly deformed NT50 alloy is proposed. Using this mechanism, the effect of the heating rate on the internal friction in this alloy is explained as the volume titanium diffusion due to the diffusion growth of α-Ti precipitates in subgrains in the alloy. In this case, the first peak is related to the bulk diffusion that accompanies grain-boundary diffusion in subgrains, and the second peak, to usual bulk diffusion in subgrains.     

双层结构对提高含碳球团强度的影响

为了提高含碳球团强度,提出了内层为含碳球团,外层为精矿粉的双层结构复合含碳球团新工艺.研究了不同外层厚度球团的强度和金属化率,分析了球团强度形成的机理.研究结果表明:外层厚度适中的复合含碳球团强度能得到有效提高.该复合球团生球落下强度为普通含碳球团的2倍,400℃预热球抗压强度可达147.6N/个.900℃后,随着温度的增加,球团抗压强度提高,1150℃恒温还原30 min后抗压强度为2 080 N/个.且研究发现复合含碳球团能有效提高碳素利用率,C/O物质的量之比nC/nO为2∶3的复合球团还原后金属化率可达93.90％,其中外层金属化率为92.46％.通过显微结构分析,发现球团还原后外层生成了致密的金属铁外壳,这种外壳的独特力学性能是球团强度提高的主要原因.     

连铸结晶器内含钛无氟保护渣固态渣膜再结晶研究

将Kissinger方程引入到保护渣研究领域,研究了含钛无氟保护渣玻璃体升温结晶(升温速率5～30K/min)、液态降温结晶(降温速率5～30 K/min)的激活能。实验结果表明,保护渣玻璃体的结晶激活能E约为52.75 kJ/mol,保护渣液态降温结晶的激活能E约为61.15 kJ/mol,实验研究的保护渣玻璃体结晶峰温度915～940K,急速冷却形成的玻璃态渣膜在结晶器内存在再结晶,衡量保护渣结晶性能应综合考虑液态降温结晶行为和渣膜在结晶器内再结晶的行为。     

Non-Isothermal Kinetics of Reduction Reaction of Oxidized Pellet Under Microwave Irradiation

 The microwave heating characteristics of the mixture with oxidized pellet and coal was studied, and the non-isothermal reduction dynamics is discussed. The results show that, the slow-heating stage of the temperature rising process can be segmented into two heating temperature curves approximately that have good linear relationship. They can be seen as temperature programming. In the first stage, between 827 and 1073 K, the reaction mechanism obeys diffusion controlled model. In the second stage, between 1093 and 1323 K, the reaction mechanism also obeys diffusion controlled model. The apparent activation energies are found to be 7513 kJ/mol for the first stage and 5317 kJ/mol for the second stage. That is lower than the apparent activation energy under conventional heating. The microstructure of the reduced pellets shows that microwave can improve the kinetics of the reduction. Microwave has anxo-action to the reaction obviously.     

差示扫描量热法测试非晶合金居里温度

从坩埚选择、试样称取量、升温速率等方面摸索了差示扫描量热法(DSC)测试非晶材料 Fe78 Si9 B13居里温度的最佳试验条件,分析了不同升温速率对测试结果的影响,同时与该材料晶化温度、In(标准物质)的熔点随升温速率的变化情况进行了对比分析.研究结果表明：该材料的 DSC 曲线上居里转变过程对应的热信号表现为一个抖动.不同条件下测得的居里温度为399~402℃,与 Hall 效应法测试结果基本一致.最佳的试验条件是：Al坩埚、试样称取量6 mg 左右、20 K/min.在升温速率不小于10 K/min 时可以得到居里转变信号,与该材料晶化温度受热滞后影响而明显随升温速率增大而增大的情况不同,由于居里转变过程相变潜热较小,居里温度测试结果基本不受热滞后的影响.