SiC_P/Al水平连铸电磁搅拌结晶器的设计

所设计的水平连铸电磁搅拌结晶器由电磁搅拌装置和结晶器两部分构成 .电磁搅拌装置安装在中间包和结晶器之间 ,可对碳化硅铝基复合材料液在结晶前和结晶过程中进行充分搅拌 .通过对水平连铸电磁搅拌结晶器基本参数计算 ,并结合实验研究 ,在理论上简要分析了水平连铸过程中金属液的形态和传热特征及其对所得到铸坯质量的影响     

电磁搅拌技术

连铸过程采用电磁搅拌的主要作用是提高连铸坯的质量，例如去除夹杂物、消除皮下气泡、减轻中心偏析、提高连铸坯的等轴晶率．因此，在浇铸断面较大的铸坯如大方坯、大板坯以及浇铸质量要求较高或易出现质量问题的钢种时，电磁搅拌技术便成为首选．按照搅拌的位置不同，连铸电磁搅拌可分为结晶器电磁搅拌(M—EMS)、二冷区电磁搅拌(S—EMS)、凝固末端电磁搅拌(F—EMS)．目前，方坯连铸应用较多的是结晶器电磁搅拌，有时为进一步提高质量，增加凝固末端电磁搅拌，即结晶器与凝固末端联合搅拌．板坯连铸应用较多的是二冷区电磁搅拌．近年来，板坯结晶器电磁搅拌技术的应用逐渐为各国钢铁企业所重视，特别是日本在这方面的开发与应用十分活跃．     

小方坯连铸结晶器电磁搅拌磁场和流场的耦合分析

借助有限元方法,对小方坯结晶器电磁搅拌过程进行了磁场和流场耦合数值分析,得出了不同频率下钢液内部磁感应强度和电磁体积力及搅拌速度的分布规律.结果表明,在结晶器电磁搅拌时,随着频率的增加,钢液内部磁感应强度降低,电磁体积力在钢液内部分布不均匀;在电流频率为3 Hz时,钢液搅拌速度最大.在现场对结晶器电磁搅拌器的磁场强度进行了冷态测试,实验值和模拟值基本相符.     

高碳钢连铸圆坯碳元素偏析的控制

分析了圆坯连铸工艺的特点及高碳钢圆坯中碳元素分布特征,并对碳元素偏析形成原因进行分析和讨论。结合连铸圆坯的工艺特点和设备条件,从结晶器电磁搅拌、浇铸钢水过热度以及连铸冷却制度三个方面提出了优化改善措施,并进行工业对比试验,得出如下结论:采用结晶器电磁搅拌电流控制在200A左右、浇铸钢水过热度控制在20℃左右、适当增加连铸冷却强度能够有效地改善高碳钢圆坯中C元素偏析。     

板坯结晶器电磁制动过程的三维流场数值模拟

针对板坯连铸结晶器内的钢液流动特征,利用流场商业软件Fluent,建立了描述板坯结晶器内区域电磁制动过程的三维有限体积数学模型,进行了流场的三维数值模拟研究.通过数值计算,研究了磁场强度、磁场和流场的相互作用位置、拉速和水口侧孔倾角对电磁制动效果的影响,为优化结晶器内的钢液流场,设计合理的电磁制动装置及指导实际生产提供了依据.     

包钢大方坯电磁搅拌器磁场特性测试分析

对包钢大方坯连铸电磁搅拌器进行了在线静态磁场测试,通过测试结果分析,对跨结晶器电磁搅拌器有了更深刻的认识,其结果对跨结晶器电磁搅拌器的搅拌工艺制定具有指导意义。     

电磁铸造实验和数值模拟

通过实验室小型电磁铸造铝及其合金的冷、热态的实验和数值模拟并经工业装置的验证,研究了电磁结晶器内的磁场分布,液体金属柱成型特性.电磁结晶器及屏蔽罩结构的优化,铸造过程中金属液的温度场与流场并进行数值模拟.研究表明:为了稳定进行铸造,液柱的成型特性(液柱高度、形状和稳定性)必须达到一定要求.为了保证电磁铸造时金属液顺利成型,选择适当的功率,确保合适的磁场强度形成一定的推力是必要的.温度场的研究可以看出电磁铸造具有一系列特点,如强烈水冷、电磁搅拌、感应加热,使得电磁铸造中的凝固过程大大不同于普通的直接铸造法的凝固过程.流动场的分析说明,电磁铸造条件下应控制搅拌强度,以便获得良好的铸坯内部组织.     

小方坯连铸结晶器电磁搅拌磁场和流场的模拟仿真

以连铸电磁搅拌器为研究对象,通过建立数学模型,模拟分析了结晶器中磁场、感应电流、电磁力及流场分布,发现结晶器电磁搅拌效果受外加磁场强度、结晶器铜板厚度、材料电导率影响,从而为优化M-EMS工艺提供了理论依据.     

350mm大方坯连铸结晶器电磁搅拌电磁场与流场耦合数值模拟

采用三维有限元技术研究350 mm×350 mm大方坯连铸结晶器电磁搅拌过程电磁场、电磁力和流场的变化规律.在固定电流强度、搅拌器尺寸等参数情况下,研究搅拌频率对铸坯内部磁感应强度、电磁力及钢液流动速度的影响.研究表明:搅拌频率为2,6和8 Hz时,磁感应强度在6 Hz时出现最大磁感应强度,电磁力也出现峰值,钢液流动速度最大,说明350 mm方坯搅拌在2 Hz到8 Hz有一个最优值.从电磁力的分布看,搅拌器的下端出现向上的电磁力,有利于减小钢液的冲击深度.     

结晶器电磁搅拌技术的应用实践

介绍了连铸电磁搅拌器的分类及其对铸坯质量的影响,以及根据不同钢种的冶金质量要求合理选择电磁搅拌器的原则,分析了马钢方坯、圆坯连铸应用结晶器电磁搅拌的冶金效果,并对存在的问题提出了相应的改进建议.     

浅析英语语音教学中的/n//l/发音错误

在大学英语教学过程中,有关/n/与/l/的发音错误很常见,原因是没有完全掌握它们的发音规则。/n//l/发音规则的相似性造成了/n//l/不分的情况,而且局部方言中这两个音也不作区分,使得/n//l/混淆的情况更加严重。在教学过程中,可以通过重点讲解区分/n/与/l/的发音规则及其区别来避免/n//l/发音错误。本文同时也分析了含糊/l/音的发音错误,通过对/n/与/l/相关的发音错误分析找出大学英语语音教学行之有效的途径:在完全把握单音的发音规则的基础上,进一步强调语调的掌握,使学生拥有良好的语音。     

肼类燃料液滴的亚临界——超临界蒸发/分解燃烧理论

对肼、一甲基肼、偏二甲肼的亚临界－－超临界蒸发／分解燃烧进行了研究,计算了肼类燃料滴在不同压力下液滴温度和蒸发速度的变化历程,计算了蒸发常数、传热数和传质数,其结果和实验数据是吻合的。本文不但考虑了肼类燃料滴的亚临界蒸发／分解燃烧,还考虑到了其超临界蒸发／分解燃烧,并对达到超临界工况时的界限参数进行了计算。     

Modification of LiCo1/3Ni1/3Mn1/3O2 cathode material by CeO2-coating

LiCo_1/3Ni_1/3Mn_1/3O₂ was coated by a layer of 1.0 wt% CeO₂ via sol-gel method. The bared and coated LiMn_1/3Co_1/3Ni_1/3O₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammogram (CV) and galvanotactic charge-discharge test. The results show that the coating layer has no effect on the crystal structure, only coating on the surface; the 1.0 wt% CeO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ exhibits better discharge capacity and cycling performance than the bared LiCo_1/3Ni_1/3Mn_1/3O₂. The discharge capacity of 1.0 wt% CeO₂-coated cathode is 182.5 mAh·g⁻¹ at a current density of 20 mA·g⁻¹, in contrast to 165.8 mAh·g⁻¹of the bared sample. The discharge capacity retention of 1.0 wt% CeO₂-coated sample after 12 cycles reaches 93.2%, in comparison with 86.6% of the bared sample. CV results show that the CeO₂ coating could suppress phase transitions and prevent the surface of cathode material from direct contact with the electrolyte, thus enhance the electrochemical performance of the coated material.     

Transport Properties of Polycrystalline La2/3Ca1/3Mn1-xCuxO3

The infuence of Cu dopant (x) and sintering temperature(Ts) on the troansport propeties of La2/3Ca1/3Mn1-xCuxO3 series samples prepared by Sol-Gel technique was investigated.X-ray diffraction patterns show that all the samples with different Cu dopant and sintering temperatures (Ts) are of single phase without obvious latice distortion.Experimental results indicate that the insulator-metal transition temperature is diectly related to the sintering temperature and Cu dopant x.It is interesting to observe that a proper amount of Cu dompant can substantially improve magnetoresistance effects.     

RDSS/Doppler/GPS/SINS组合导航系统研究

针对双星定位系统(RDSS)存在的定位位置滞后的先天缺陷,根据组合导航定位系统输出速度误差小的特点,给出了一套消除RDSS位置滞后的方案,并对RDSS／SINS组合系统进行了建模,依据联邦滤波器理论,考虑到GPS的实际情况,提出了RDSS／Doppler／GPS／SINS多传感器组合导航系统的设想,仿真结果表明,该组合导航系统具有准确度高、自主性强的特点。     

亚锰酸盐La0.7-xYxCa0.3MnO3的电磁特性和磁电阻效应

研究了用固相反应法制备亚锰酸盐多晶样品La0.7-xYxCa0.3MnO3,并研究了Y的不同掺杂(x=0.1,0.2)对样品的晶体结构、电磁特性和磁电阻效应的影响.实验结果表明,随着温度的降低,x=0.1样品的R-T曲线没有出现峰值,而x=0.2样品出现了峰值,显示了复杂的输运特性.两种样品的磁电阻Rm都随着温度的降低而升高,但都没有出现峰值.x=0.2的样品在较宽的温区内,磁电阻效应都很显著,而且Y掺杂由x=0.1提高至x=0.2,磁电阻效应增强.     

Low temperature properties of organic-inorganic Ag/ p -CuPc/ n -GaAs/Ag photoelectric sensor

A thin organic film of p-type semiconducting copper phthalocynanine (CuPc) was deposited by vacuum evaporation on an n-type GaAs single-crystal semiconductor substrate. The fabricated Ag/p-CuPc/n-GaAs/Ag sensor was carried through an ageing process to stabilize the parameters. Voltage-current characteristics and photoelectrical response of the sensor were investigated at a wide temperature range of 82 to 350 K. Photoelectric characteristics were measured under nonmodulated filament-lamp illumination. It was observed that such sensor parameters as rectification ratio, threshold voltage, junction, shunt and series resistances, open-circuit voltage and short circuit current are temperature-dependent. It was found that wide-range voltage-current characteristics of the sensor may be described similarly to that of a Schottky barrier diode. Using the experimental data on voltage-current characteristics and absorbance of the CuPc films, the energy-band diagram of the p-CuPc/n-GaAs heterojunction was developed. It was shown that data obtained from simulation of an equivalent circuit of photoelectric sensor agreed with experimental results. Supported by the National Engineering and Scientific Commission of Pakistan     

Reliability of Au/PZT/BIT/p-Si ferroelectric diode

A ferroelectric memory diode that consisted of Au/PZT/BIT/p-Si multilayer configuration was fabricated by pulsed laser deposition (PLD) technique. The reliability issues (I-V characteristics, capacitance retention, fatigue and imprint) were investigated. The I-V curve showed the conventional Schottky diode characteristics with a small current density of - 5.3×10 -10 A/cm2 at a voltage of - 4 V and 6.7×10-8 A/cm2 at a voltage of + 4V, and this characteristic can be maintained below 50℃. The capacitance variety of the ferroelectric diode was only 5 % in 10 hours after withdrawing the applied bias of + 5 V or - 5 V, indicating the diode had good capacitance retention. By applying 100 kHz bipolar pulses of 5 V amplitude, the decay in remanent polarization was only 10% after 109 switching cycles, and meanwhile the increase in coercive field was 12%. After being irradiated for 20 min with a 200 W ultraviolet ray lamp, the remanent polarization and coercive field had both varied, and a voltage shift was obse     

用Cr/Au/Ni/Au制备n-GaN欧姆接触

为了获得n-GaN的低接触电阻的欧姆接触,采用Cr/Au/Ni/Au金属化系统与n—GaN形成欧姆接触,并对其不同温度下的接触电阻率进行了测试分析.室温下Cr/Au/Ni/Au的接触电阻率为0.32mΩ·m2。随着温度的升高,接触电阻率略有增加,在300℃时接触电阻率为0.65mΩ·cm2,因此此欧姆接触适合在高温下使用.     

铬/氢/空气/氯体系的焚烧动力学分析

对含铬固体废物焚烧体系进行动力学分析是提出控制六价铬化合物排放措施的基础。本文对铬/氢/空气/氯焚烧体系进行了动力学分析,研究了温度、初始氯含量对产物中六价铬化合物含量的影响。研究表明,六价铬化合物主要以CrO2(OH)2的形式出现,最高含量出现在1700K左右;氯的存在没有导致六价铬化合物CrO2Cl2的大量生成;六价铬化合物CrO2(OH)2的含量随初始氯含量的增大略有下降。建议含铬固体废物实际焚烧过程中,避开1700K左右的温度区域,减少六价铬化合物的排放。