铝硅熔体超重力凝固提纯硅(英文)

研究超重力场下铝硅过共晶熔体凝固精炼提纯冶金硅。实验结果表明:超重力作为一种强化分离手段,可以实现铝硅合金中初晶硅颗粒的富集分离。在超重力作用下,铝硅合金中精炼硅颗粒沿超重力方向富集在铝硅合金下部。用王水溶解其中的铝,得到初晶硅颗粒。通过分析初晶硅中杂质含量可知,与冶金硅原样相比,精炼后的硅纯度由99.59%提高到99.92%,硼和磷的质量分数分别由8.33×10-6和33.65×10-6降低到5.25×10-6和13.50×10-6,表明该提纯方法可行。     

CaCl2-NaCl-CaO熔盐中电解精炼Si的研究

以冶金级Si和电解Cu为原料,制备了Cu-31Si（摩尔分数,%）合金.以Cu 31Si合金为阳极、Mo为阴极和参比电极,采用循环伏安和计时电位方法研究了1173 K下熔盐81CaCl₂ 8.0NaCl 8.5CaO-2.5Si（摩尔分数,%）的阴极行为,讨论了熔盐中Si电解精炼过程的还原步骤.用SEM,EDS和电感耦合等离子原子发射光谱仪（ICPAES）分析和表征了Si晶体的形貌和组成.电解精炼后得到了多晶Si,与冶金Si原料相比,主要杂质含量都显著降低,特别是对太阳能级Si危害较大的杂质B和P去除效果明显,分别从42×10^-6和25×10^-6降至4.5×10^-6和8.2×10^-6.电解精炼过程的电流效率为84.4%.     

冶金级硅吹Ar-H2O混合气精炼除

通过吹高纯氩气和水蒸汽混合气体的方法除去冶金级硅中的杂质磷。采用自行设计的吹气精炼装置,研究喷嘴类型、精炼时间、精炼温度、精炼气温度、精炼气流速等因素对除磷效果的影响。研究表明：使用侧壁和底部多孔型喷嘴,精炼时间3 h,精炼温度1793 K,精炼气温度373 K,精炼气流速2 L/min作为最优吹气精炼条件时,冶金级硅熔体中的磷元素质量分数由94×10-6降低到11×10-6。表明吹气精炼是一种有效的去除冶金级硅中磷的方法。     

高纯铬电解技术的研究进展

从不同角度分类介绍了高纯铬电解的技术和方法及电化学原理，具体包括溶液电解（三价铬的水溶液电解和有机溶液中的电解）和熔盐电解（熔盐电沉积、高温电精炼和低温电精炼）。重点介绍了熔盐电解法这一领域的最新动态。     

Na_3AlF_6-LiF体系下Al的水平电解精炼

在纯氟化物电解质体系下,以原Al为阳极,利用杂质与Al析出电位的差别,采用水平电解槽进行了Al的电解精炼提纯研究.结果表明:水平电解槽导致的电流密度分布不均没有对精炼过程造成不利影响,电解过程槽电压平稳;预电解对电解质净化效果明显,预电解后电解质中Cu,Si和P的含量分别降低到3.2×10~(-6),14×10~(-6)和1.5×10~(-6).与三层液精炼Al相比,水平精炼阴极Al是沉底的,受上层电解质保护从而减少了烧损,电流效率最高达98.6%.最后得到的精炼Al与原Al相比,Fe,Si,Zn和Cu等杂质的含量明显降低,特别是Cu含量由14.5×10~(-6)减少到0.9×10~(-6),精Al纯度达到99.99%.     

CaO-SiO_2熔渣精炼去除冶金级硅中杂质硼(英文)

利用CaO-SiO2熔渣去除冶金级硅(MG-Si)中的杂质硼。热力学分析和实验结果表明:纯SiO2基本上不能去除冶金级硅中的杂质硼。通过建立硼的分配系数与熔渣中SiO2和CaO活度之间的关系,从热力学上对CaO-SiO2熔渣的除硼能力进行表征。结果表明:随着渣中CaO配比的升高,硼的分配系数和去除效率大大提高。当熔渣组成为60%CaO-40%SiO2(质量分数)时,硼的分配系数达到最大值1.57。当渣硅比为2.5,精炼温度为1600°C以及精炼时间为3 h时,利用60%CaO-40%SiO2熔渣可以将冶金级硅中的硼含量从18×10-6降低至1.8×10-6,去除效率达到90%。     

Si-Sn合金精炼-定向凝固过程硅的分离和提纯

采用Sn-Si熔析体系,利用工业规模多晶硅铸锭炉通过控制温度梯度和热场上移速率进行定向凝固处理,研究硅锭的形貌特征、组织结构和提纯效果。结果表明:在定向凝固过程中析出了连续密实的硅晶,且晶体硅与金属熔析剂之间形成了平坦稳定的相界面,实现晶体硅与金属熔析剂的有效分离。晶体硅经过混酸酸洗后,总金属杂质含量由58.3×10-6降低为7.6×10-6,去除率可以达到87%;非金属P含量由50.12×10-6降低为8.48×10-6,去除率大于80%。因此,Si-Sn合金精炼与定向凝固过程复合,解决了硅与金属熔析剂的有效分离问题,同时也实现了杂质的高效去除。     

SiO_2-CaO-MnO熔渣氧化精炼除硼提纯多晶硅的研究

熔渣精炼是制备太阳能级多晶硅过程中最为成熟和广泛应用的除硼手段。为了去除硼杂质,本文选用SiO_2-CaO-MnO熔渣进行熔渣精炼研究,并考察了熔渣的光学碱度与除硼效果的关系。结果表明,经精炼后,渣硅分界明显,精炼硅易于分离,精炼硅存在Si-Ca、Si-Mn金属间析出相,且析出相中富集B、P等杂质;随着熔渣中MnO含量的增加,硅中的B含量先降低后升高,当MnO含量为5%时,硅原料中B含量从23.91×10~(-6)wt降低到4.40×10~(-6)wt,去除效率达到81.60%。     

应用电磁感应造渣法去除冶金级硅中杂质硼(英文)

提出一种新的提纯工艺即通过造渣与电磁感应熔炼相结合的方法来去除冶金级硅中的杂质硼。采用自行设计的真空感应熔炼炉进行不同造渣系条件下除硼的研究。结果表明,SiO2-CaO-Al2O3渣系的除硼效果优于其它渣系,在1823K经过2h精炼后,冶金级硅中的硼含量由原来的1.5×10-5降到0.2×10-5。同时冶金级硅中的Al,Ca和Mg杂质得到了精炼,去除率分别达到85.0%,50.2%和66.7%。表明电磁感应造渣法是一种非常有效的去除冶金级硅中的硼和其他一些金属元素杂质途径。     

熔盐电解共渗铝硅及渗层的抗高温腐蚀性能

在渗铝涂层中加入少量硅可进一步提高涂层的抗高温氧化和热腐蚀性能。本文作者采用一种新的方法—高温熔盐电解法,在熔融氯化物盐浴中进行电解共渗铝硅,在铁和铁—铬合金上获得了渗铝硅涂层。 用氯化物作为电解质主要优点是无毒和价廉。高温熔盐电解渗铝硅可获得表面光洁、厚度均匀、与基体结合良好的致密渗层。通过控制电解温度、时间和电流密度可容易地控制渗层厚度,所得到的渗层不需随后热处理。 1000℃氧化试验和900℃热腐蚀(盐膜法)结果表明渗铝硅涂层比单纯渗铝涂层具有更好的保护性能。     

In-situ synthesis of silicide coatings on molybdenum substrates by electrodeposition in chloride-fluoride molten salts

Silicide coatings including MoSi₂ and Si-MoSi₂ were prepared on molybdenum substrates by electrodeposition in NaCl-KCl-NaF-K₂SiF₆ molten salt. The experimental was conducted under different cathodic current densities at the temperature of 1073 K. The effect of the current density on the microstructure, phase composition, cross-section morphologies and elemental distribution of the as-prepared coatings were investigated by means of SEM, XRD and EDX. The results revealed that the type of the silicide coatings was strongly dependent on the current density and the relevant deposition mechanism was discussed. Besides, the electrochemical behavior of silicon ion in the chloride-fluoride molten salts was also studied using cyclic voltammetry and chronopotentiometry to reveal the electroreduction mechanism. The reduction of Si(IV) to Si was proved to be a quasi-reversible or irreversible diffusion-controlled single-step reaction and the diffusion coefficient of Si(IV) calculated from chronopotentiograms was (1.28 ± 0.25) × 10⁻⁵ cm²·s⁻¹.     

Effect of annealing on properties of lithium aluminum germanium phosphate electrolyte thick films prepared by aerosol deposition

Li_1.5[Al_0.5Ge_1.5(PO₄)₃] glass-ceramic powder was used for the deposition of thick films on silicon substrate by aerosol deposition. The deposited films were annealed at 873 K and 1023 K for 6 h in air. The thickness of the films was 10–12 m and the relative density was 78%–82%. As-deposited films had nano-scale grains and amorphous regions while in the annealed films, the grain growth and improved crystallinity were observed. The grain size was increased from 12 nm to 25 nm and 97 nm after annealing at 873 K and 1023 K, respectively. The ionic conductivity of the as-deposited film was 8.49 × 10^?9 S cm^?1, which increased to 1.06 × 10^?5 S cm^?1 and 1.16 × 10^?4 S cm^?1 after annealing at 873 K and 1023 K, respectively. The increased ionic conductivity is explained in terms of the increased grain size as well as the improved crystallinity.     

半固态触变成形制备高硅铝基电子封装盒体的组织与性能

利用半固态触变成形工艺制备高硅铝电子封装盒体,分析盒体中Si相的分布特征.采用金相显微镜和扫描电镜观察盒体不同部位的显微组织,并测定其热物理性能及力学性能.结果表明,Al-25％Si(质量分数)合金在半固态触变成形中Si相和液相产生分离流动,液相从盒体中流出,Si相在盒体中聚集,其体积分数从盒体底面向四壁逐渐降低.盒体底面中心和四壁的热导率分别为107.6和131.5W/(m.K),热膨胀系数分别为7.9×10-6和10.6×10-6 K,抗弯强度由167MPa缓慢增加至180MPa.组织和性能呈现梯度变化.     

Thermal properties of pressureless melt infiltrated AlN–Si–Al composites

Thermal properties of AlN-Si-Al composites produced by pressureless melt infiltration of Al/Al alloys into porous α-Si₃N₄ preforms were investigated in a temperature range of 50-300 °C. SEM and TEM investigations revealed that the grain size of AlN particles was less than 1 μm. In spite of sub-micron grain size, composites showed relatively high thermal conductivity (TC), 55-107 W/(m.K). The thermal expansion coefficient (CTE) of the composite produced with commercial Al source, which has the highest TC of 107 W/(m.K), was 6.5×10^?6 K^?1. Despite the high CTE of Al (23.6×10^?6 K^?1), composites revealed significantly low CTE through the formation of Si and AlN phases during the infiltration process.     

Thermal expansion of the V5Si3 and T2 phases of the V–Si–B system investigated by high-temperature X-ray diffraction

The thermal expansion anisotropy of the V₅Si₃ and T₂-phase of the V–Si–B system were determined by high-temperature X-ray diffraction from 298 to 1273 K. Alloys with nominal compositions V_62.5Si_37.5 (V₅Si₃ phase) and V₆₃Si₁₂B₂₅ (T₂-phase) were prepared from high-purity materials through arc-melting followed by heat-treatment at 1873 K by 24 h, under argon atmosphere. The V₅Si₃ phase exhibits thermal expansion anisotropy equals to 1.3, with thermal expansion coefficients along the a and c-axis equal to 9.3 × 10^?6 K^?1 and 11.7 × 10^?6 K^?1, respectively. Similarly, the thermal expansion anisotropy value of the T₂-phase is 0.9 with thermal expansion coefficients equal to 8.8 × 10^?6 K^?1 and 8.3 × 10^?6 K^?1, along the a and c-axis respectively. Compared to other isostructural silicides of the 5:3 type and the Ti₅Si₃ phase, the V₅Si₃ phase presents lower thermal expansion anisotropy. The T₂-phase present in the V–Si–B system exhibits low thermal expansion anisotropy, as the T₂-phase of the Mo–Si–B, Nb–Si–B and W–Si–B systems.     

Microstructural evolution of Al-20Si-5Fe alloy during rapid solidification and hot consolidation

Al-20Si-5Fe melt was rapidly solidified into particles and ribbons and then consolidated to near full density by hot pressing at 400°C/250 MPa/1 h. According to the eutectic-growth and dendritic-growth velocity models, the solidification front velocity and the amount of undercooling were estimated for the particles with different sizes. Values of 0.43−1.2 cm/s and 15–28 K were obtained. The secondary dendrite arm spacing revealed a cooling rate of 6 × 10⁵ K/s for the particles with an average size of 20 μm. Solidification models for the ribbons yielded a cooling rate of 5 × 10⁷ K/s. As a result of the higher cooling rate, the melt-spun ribbons exhibited considerable microstructural refinement and modification. The size of the primary silicon decreased from approximately 1 μm to 30 nm while the formation of iron-containing intermetallic compounds was suppressed. Supersaturation of the aluminum matrix in an amount of ∼7 at.% Si was noticed from the XRD patterns. During the hot consolidation process, coarsening of the primary silicon particles and precipitation of β-Al₅FeSi phase were observed. Evaluation of the compressive strength and hardness of the alloy indicated an improvement in mechanical properties due to the microstructural modification.     

Microstructure and properties of high silicon aluminum alloy with 2% Fe prepared by rheo-casting

The morphology changes of both Fe-containing intermetallic compounds and the primary Si phase of Al-20Si-2Fe- 2Cu-0.4Mg-1.0Ni-0.5Mn (mass fraction, %) alloy produced by semi-solid rheo-diecasting were studied. The semi-solid slurry of high silicon aluminum alloy was prepared by direct ultrasonic vibration (DUV) which was imposed on the alloy near the liquidus temperature for about 2 min. Then, standard test samples of 6.4 mm in diameter were formed by semi-solid rheo-diecasting. The results show that the DUV treatment suppresses the formation of needle-like β-Al₅(Fe, Mn)Si phase, and the Fe-containing intermetallic compounds exist in the form of fine Al₄(Fe, Mn)Si₂ particles. Additionally, the primary Si grows up as fine and round particles with uniform distribution in a(Al) matrix of this alloy under DUV treatment. The tensile strengths of the samples at the room temperature and 573 K are 230 MPa and 145 MPa, respectively. The coefficient of thermal expansion (CTE) between 25 °C and 300 °C is 16.052 8×10^?6 °C^?1, and the wear rate is 1.55%. The hardness of this alloy with 2% Fe reaches HB146.3. It is discovered that modified morphology and uniform distribution of the Fe-containing intermetallic compounds and the primary Si phase are the main reasons for reducing the CTE and increasing the wear resistance of this alloy.     

Corrosion Behavior of 9Cr-1Mo Steel in Sulfur Dioxide Environment

Corrosion behavior of annealed 9Cr-1Mo steel was studied in SO₂ environment at 1173 K, at flow rates from 8.33 × 10^?7 to 33.33 × 10^?7 m³/s, and parabolic rate law was followed. The rate constants were found to be independent of flow rate, within the range of flow rate investigated. Corrosion at temperatures from 973 to 1173 K, at a constant flow rate of 16.66 × 10^?7 m³/s, at 1 atmospheric pressure, for 6 h also exhibited parabolic law, however, the rate constants were observed to increase significantly with rise in temperature. The outer layer of the scale formed at 973 K was essentially of iron oxide, with small amount of chromium oxide whereas the inner layer was predominantly of chromium sulphide and chromium oxide. The scale formed at 1173 K was multilayered, in contrast to double layered formed at 973 K and 1073 K. The outer thick layer of the scale formed at 1173 K, consisted of iron oxide followed by thin substrate of chromium sulphide, iron sulphide/iron oxide, and chromium sulphide/chromium oxide toward the substrate. A model is proposed for the process of corrosion of 9Cr-1Mo steel in SO₂ environment, based on the present investigation.     

Crystal structure and thermoelectric properties of β-MoSi2

A powder sample of a metastable phase β-MoSi₂ having the C40-type crystal structure was prepared by heating Mo sheets with a Na–Si melt at 858 K for 12 h to determine details of the crystal structure. The lattice constants (a = 4.6016(3) Å and c = 6.5700(3) Å) and Si atom coordinate (y = 0.1658(2)) of β-MoSi₂ were determined by Rietveld analysis of the X-ray powder diffraction. The thermoelectric properties were refined for a bulk sample prepared by sintering the β-MoSi₂ powder at 773 K and 600 MPa. The electrical resistivity of the sintered β-MoSi₂ sample with a relative density of 65% of the theoretical one was 2.5 mΩ cm at 300 K, and slightly increased with increasing temperature from 300 to 725 K. The Seebeck coefficients changed from +60 to +89 μV/K in the temperature range from 330 to 725 K. The maximum thermoelectric power factor was 2.2 × 10^?6 W cm^?1 K^?2 at 725 K.     

The corrosion of ferritic stainless steels and high-purity Fe-Cr alloys in basaltic lava and simulated magmatic gas

Three ferritic stainless steels, types 410, 430, and 446, containing 12, 17, and 26% Cr, respectively, and two high-purity binary alloys, Fe-19Cr and Fe-24Cr, were subjected to molten tholeiitic basaltic lava with a cover gas simulating magmatic gas at 1150°C for periods up to 400 hr. The oxygen and sulfur partial pressures were 9.8×10^?10 and 7.0×10^?3, respectively. All alloys formed Cr₂O₃ scales. Internal sulfidation occurred in the commercial alloys resulting in the formation of chromium and manganese sulfides. Internal oxidation of silicon also occurred. The extent of internal sulfidation decreased with increasing chromium content. There was a “critical” chromium content between 12 and 17%, above which internal sulfidation did not occur in 96 hr. However, the “critical” chromium level increased with exposure time to nearly 26% for 400 hr. Little internal sulfidation was observed in the high-purity alloys. The different behavior between the commercial and high-purity alloys may be attributed to (i) the formation of more perfect scales on the latter, which inhibited the inward migration of sulfur, and (ii) changes in the sulfur activity gradient across the scale caused by the presence of silicon and manganese.