超重力在冶金和金属材料领域的研究进展及展望

超重力作为一种外场强化新技术,基于其优越的传质和相际分离特性,引起了广泛的关注。本文着重介绍了我国超重力技术在金属熔体提纯、冶金固废中有价物质的富集提取分离、金属材料凝固组织细化、非金属夹杂物的去除以及矿石气基还原等冶金和金属材料领域的研究进展和成果,提出了其应用过程中存在的科学问题,并展望了超重力技术的发展前景。虽然,目前还以实验室研究阶段为主,并未实现普适化。但作为一种外场强化新技术,其在冶金和金属材料凝固控制等相关研究体系中已突显出强大的熔体提纯、有价组分富集提取、组织细化、夹杂物去除等作用效果,这为进一步拓展超重力技术在冶金和金属材料领域的研究和开发应用提供了参考价值。超重力有望凭借自身的优点成为冶金和金属材料领域生产过程中一种新的外场技术。随着超重力设备的发展及相关科学问题的研究探索,相信在不久的将来,超重力技术必会在冶金和金属材料研究领域得到广阔的应用前景。     

Material removal profile prediction and experimental validation for obliquely axial ultrasonic vibration-assisted polishing of K9 optical glass

K9 optical glass is one of the typical components in optical systems. However, because of its poor fracture resistance, it is difficult to polish it with ultra-precision and high-efficiency and without any surface damage simultaneously. The emergence of the obliquely axial ultrasonic vibration-assisted polishing (UVAP) method can solve this problem which encounters in polishing efficiency and shape accuracy. However, due to the unclear material removal profile (MRP) mechanism, obliquely axial UVAP is not widely used in the processing field. This paper introduces the obliquely axial UVAP method in research processes, mainly focusing on the fixed point MRP analysis of the obliquely axial UVAP. Based on Hertz's contact theory, polishing pressure, the length of the semi-long axis (LLA) and the length of the semi-short axis (LSA) of the contact area are calculated under ultrasonic vibration conditions. Meanwhile, the relative linear velocity distribution of the oblique polishing tool in the instantaneous contact area is modeled by mathematical geometry method. A novel model of the MRP distribution for obliquely axial UVAP is proposed following the Preston equation. Subsequently, a series of polishing experiments were carried out to verify this model. The results show that the numerical model has good agreement with the experimental results on MRP, LLA, LSA, material removal depth and material removal rate (MRR). In addition, the material removal capability can be significantly improved by larger ultrasonic amplitude and larger oblique angle. This model not only more clearly elucidates the processing mechanism of obliquely axial UVAP, but also provides theoretical support for the polishing of free-form optical lenses.     

Evaluation of the localized corrosion on Mg electrode surface by electrochemical noise technique

The symmetrical and asymmetrical electrodes made of Mg were studied in 0.1-M NaCl electrolyte adjusted at pH 12. The statistical and wavelet methods were employed for analyzing the electrochemical current noise (ECN) signals. The asymmetric configuration was used for electrochemical detection of filiform corrosion on Mg electrode. The real time scale of the dominant transients of the asymmetric electrodes was detected on the basis of the maximum peak in the SDPS plots. The SDPS values of the real time scale crystals of the ECN signals resulting from asymmetrical electrodes increased with the increase in immersion time due to the onset of filiform corrosion.     

A novel approach for bulk micromachining of 4H-SiC by tool-based electrolytic plasma etching in HF-free aqueous solution

Bulk micromachining of single-crystal SiC has been challenging due to its extreme stability both mechanically and chemically. To address this issue, a novel tool-based electrolytic plasma etching method is proposed, with which micropatterns and micro-holes are fabricated in SiC in a hydrofluoric acid-free aqueous solution with no need for masks. The material removal is the result of the combined effects of electrolytic plasma chemistry and physics. The chemistry refers to the reaction of Si with hydroxyl radical to form various SiO_x and with H to form silanes, and the reactions of C to form volatile carbon oxides or hydrocarbons, all of which are accomplished and enhanced under the electrolytic plasma atmosphere. Besides, the local high temperature of plasma thermally promotes the evaporation or dissolution of SiO₂ in NaOH solution. The tool-based electrolytic plasma etching method provides alternative approaches for the fabrication of SiC-based MEMS and devices.     

煤矿锚杆机除尘马达改进

针对煤矿进口锚杆机除尘马达频繁出现故障的情况,通过排查除尘装置的安装方式和监测马达工作时的压力状态,查找故障原因,并制定解决方案。通过马达外接单向阀,可满足马达进油口最低安全压力限制的要求,解决了马达频繁损坏的问题,保障了设备工作的稳定性,提高了工作效率。     

One-pot synthesis of hematite-alumina hollow sphere composite by ultrasonic spray pyrolysis technique with high adsorption capacity toward PAHs

A hybrid nanocomposite of alumina and hematite was synthesized by ultrasonic spray pyrolysis technique. The study of microscopic images, mapping analysis, and XRD patterns revealed that the Al₂O₃ – Fe₂O₃ nanocomposite was composed of separated spherical particles with a thin layer ball-shaped structure that metal oxides are uniformly distributed in the wall of hollow sphere particles, led to a coherent and monotonous construction. A series of coefficients of equilibrium sorption of polycyclic aromatic hydrocarbons (PAHs) as hazardous materials were measured on the prepared composite material in a batch technique. The free or pure Al₂O₃ or Fe₂O₃ showed negligible removal efficiency for the mentioned analytes. The various significant variables, such as initial analyte concentration, solution pH, adsorbent dose, and contact time to remove analyte, were studied in the aqueous solutions. Adsorption data were modeled to Langmuir, Freundlich, and Temkin isotherms, and a good correlation found in the case of Langmuir isotherm and adsorption capacity for anthracene, phenanthrene, and naphthalene were 370, 333, and 322 mg g^?1, respectively. Investigation of the kinetic models proved a pseudo-second-order, and the prepared adsorbent can be reused more than 7 times without a significant decrease of adsorption performance.     

Effects of microstructure shape parameters on water removal in a PEMFC lotus-like flow channel

To improve the drag reduction performances of the proton exchange membrane fuel cell (PEMFC), a three dimensional numerical investigation about the water removal in a lotus-like PEMFC flow channel is carried out. The effects of the microstructure shape parameters (height, radius and spacing) are investigated. The investigation revealed that the liquid water can be effectively removed by the lotus-like flow channel from the channel wall surface. The appropriate height of lotus-like channel can effectively reduce the water coverage ratio on the top wall of the lotus-like flow channel. As height increases, the average drag reduction ratio increases firstly and decreases finally. When the radiuses are 25 μm and 50 μm, the average drag reduction ratios of these cases are higher than those of the other cases obviously. The spacing of the lotus-like channel has a few effects on the water removal and water coverage ratio. The lotus-like flow channel with the height of 50 μm, the radius of 50 μm and the spacing of 150 μm has a high drag reduction and anti-corrosion performance. The work in this study provides a new choice for the flow channel and has certain guiding significance for the design of the flow channel for anti-corrosion and drag reduction.     

微波作用下硅藻土酸浸除铁过程研究

研究在微波作用下硅藻土酸浸除铁过程的影响因素和工艺条件。结果表明。硫酸浓度、微波功率和浸出时间对硅藻土除铁均有影响，浸出时间是影响浸出的最主要因素，微波功率和硫酸浓度次之。随浸出时间延长。微波功率增加，硫酸浓度加大，硅藻土中的Fe2O3含量减少。Fe2O3浸出率增加。在试验条件下。较佳的工艺条件为硫酸浓度40％，浸出时间45min，微波功率260W。在此条件下获得的硅藻土产品指标为SiO283．50％，Al2O37．18％，Fe2O30．87％，达到了硅藻土助滤剂质量标准SiO2〉80％，Al2O3〈10％。Fe2O3〈2％。     

天然气/液化气先进再燃脱硝特性研究

利用自行研制的可燃气体再燃脱硝实验台，在先进再燃脱硝的典型影响因素条件下比较了两种再燃燃料的脱硝特性.实验燃料先进再燃脱硝时均存在最佳过量空气系数、最佳NH₃/NO摩尔比；1 050,1 150 ℃时脱硝效率随再燃气/NO摩尔比增加而提高，而1 200 ℃时脱硝效率随天然气/NO比增加先升高后降低，实验最佳天然气/NO比为3.63；天然气/液化气先进再燃时再燃区最佳温度分别为1 250 ℃与1 050 ℃，再燃区温度高于1 150 ℃时选择天然气为再燃燃料，反之选择液化气；从停留时间上考虑应优先选择天然气作为再燃燃料.