多晶硅表面金属催化化学腐蚀法制绒研究现状

在多晶硅太阳能电池的生产过程中, 金刚线切割技术(Diamond wire sawn, DWS)具有切割速度快、精度高、原材料损耗少等优点, 受到了广泛关注。金刚线切割多晶硅表面形成的损伤层较浅, 与传统的酸腐蚀制绒技术无法匹配, 金属催化化学腐蚀法应运而生。金属催化化学腐蚀法制绒具有操作简单、结构可控且易形成高深宽比的绒面等优点, 具有广阔的应用前景。本文总结了不同类型的金属催化剂在制绒过程中的腐蚀机理及其形成的绒面结构, 深入分析和讨论了具有代表性的银、铜的单一及复合催化腐蚀过程及绒面结构和电池片性能。最后对金刚线切割多晶硅片表面的金属催化化学腐蚀法存在的问题进行了分析, 并展望了未来的研究方向。     

Foam-based cleaning of surfaces contaminated with mixtures of oil and soot

Liquid foams of intermediate stability have been shown to be very efficient in the cleaning of sensitive surfaces because of the synergy between imbibition and foam decay. While we quantified these mechanisms for contaminations with liquid oils in our previous work, we show here their extension to oils containing soot particles in an effort to simulate increasingly realistic contaminations. Using foams with a wide range of liquid fractions and with different stabilities, we show that the main cleaning mechanisms remain very similar, with the oil entraining the soot particles. However, we find much less efficient soot removal when the liquid channels of the foams are small enough to hinder efficient transport of the soot particles.     

人造金刚石填充聚酰亚胺树脂基复合材料防刺性能

为研究树脂材料的防刺性能及防刺机制,利用手糊成型与热压法成型制备了手糊分层结构和均布结构层2种结构的人造金刚石填充聚酰亚胺树脂基复合树脂片,并探讨了人造金刚石粒径、填充体积分数对树脂片防刺性能的影响。研究结果表明:经过人造金刚石填充的聚酰亚胺树脂片的防刺性能得到提高,并且均布结构层分层复合结构的树脂片的防刺性能更好;随着人造金刚石粒径的减小,树脂片防刺性能出现先减小后增加的趋势,故防刺机制基本在于碰撞概率与树脂基的防挡;比较防刺力和消耗功发现,不同填充体积分数的单层防刺树脂片的防刺性能随人造金刚石填充体积分数的增加而逐渐降低,该趋势的成因在于复合树脂片的脆化与破坏;在颗粒等效粒径为300 μm、体积分数为10%时,其防刺性能最好。     

全局力平衡PDC钻头布齿优化设计

针对聚晶金刚石复合片(PDC)钻头在钻井破岩过程中因受力不平衡，导致钻井倾斜、井径扩大、钻头产生横向振动和涡动，造成钻头早期失效的问题，基于已有PDC钻头切削力学知识，构建了PDC钻头弯曲力矩及全局力平衡布齿优化设计模型，并提出模型求解方法。布齿设计实例结果表明，采用全局力平衡布齿设计方法得到的布齿结构可使PDC钻头在不同进尺条件下均能保持全局力平衡状态，尤其低进尺（小于1 mm）时的力平衡状态得到极大改善，提高了PDC钻头的钻井稳定性，对于改善钻头受力、提升钻头使用寿命、提高钻井质量与效率具有重要意义。     

Mechanical Properties of Single-Layer Diamond Reinforced Poly(vinyl alcohol) Nanocomposites through Atomistic Simulation

Low-dimensional carbon nanostructures are ideal nanofillers to reinforce the mechanical performance of polymer nanocomposites due to their excellent mechanical properties. Through molecular dynamics simulations, the mechanical performance of poly(vinyl alchohol) (PVA) nanocomposites reinforced with a single-layer diamond – diamane is investigated. It is found the PVA/diamane exhibits similar interfacial strengths and pull-out characteristics with the PVA/bilayer-graphene counterpart. Specifically, when the nanofiller is fully embedded in the nanocomposite, it is unable to deform simultaneously with the PVA matrix due to the weak interfacial load transfer efficiency, thus the enhancement effect is not significant. In comparison, diamane can effectively promote the tensile properties of the nanocomposite when it has a laminated structure as it deforms simultaneously with the matrix. With this configuration, the interlayer sp³ bonds endows diamane with a much higher resistance under compression and shear tests, thus the nanocomposite can reach very high compressive and shear stress. Overall, enhancement on the mechanical interlocking at the interface as triggered by surface functionalization is only effective for the fully embedded nanofiller. This work provides a fundamental understanding of the mechanical properties of PVA nanocomposites reinforced by diamane, which can shed lights on the design and preparation of next generation high-performance nanocomposites.     

Role of interface on irradiation damage of Cu−diamond composites using classical molecular dynamics simulations

Cu?diamond composites have been proposed as a candidate thermal management material for spacecraft electronics. Nevertheless, irradiation effects on the composites remain poorly understood at present. Here we focus on investigating the influence of Cu?diamond interfaces (CDIs) on energetic displacement cascades using atomistic simulations. Results show that a primary knock-on atom of Cu (PKA-Cu) can induce more significant damage than a PKA-C. Under almost all circumstances, the statistically averaged fraction of surviving interstitials is not only lower than that of vacancies but also no more than 1. Because of the unique nature in the mobility and interactions with CDIs, Cu interstitials exhibit the lowest concentration among all defects in most cases. The high residual rate of displaced defects in diamond makes it relatively difficult to heal. The structural damage is mainly manifested in a short-range disorder of diamond and a long-range disorder of Cu after irradiation. At elevated temperatures, the atomic displacement region may form compact chain-like defects to restrain lattice loosening. Despite the above, CDIs could act as effective sinks to facilitate the recombination and/or annihilation of irradiation-induced defects in all scenarios. This study provides an important insight into the understanding of the microscopic evolution of irradiation defects for the composites.     

Drilling machinability of engineering ceramics under low-frequency axial vibration processing by sintering/brazing composite diamond trepanning bit

Thin-wall diamond trepanning bits are extensively used for processing hard and brittle materials such as engineering ceramics. However, it is difficult to achieve high-efficiency processing of engineering ceramics at a constant feed speed, because of high dynamic compressive strength, high hardness, and low density of engineering ceramics. In this study, a novel composite diamond bit combining sintering and brazing has been designed, along with the low-frequency axial vibration technology, to realize the continuous hole processing of engineering ceramics. Drilling experiments have been conducted on Al₂O₃ and SiC engineering ceramics with a constant feed speed. The variation of axial force, micromorphology of hole wall surface drilled, as well as the method of removing nesting during the drilling process were analyzed. According to the results, the novel composite diamond bit fabricated by combining sintering and brazing, can achieve the continuous hole processing of engineering ceramics at a constant feed speed, including Al₂O₃ and SiC. Compared to the conventional drilling (CD), the low-frequency axial vibration drilling (LFVD) can significantly reduce the axial force, and produce fewer plastic scratches on the hole wall surface drilled. In particular, the automatic blanking ratio approaches to 100% by LFVD, and only about 73.58% by CD. It can be concluded that LFVD technology can be used to realize continuous hole processing of engineering ceramics. The research results achieved in this study show that the drilling machinability of engineering ceramics by LFVD and novel composite diamond bit is good. Accordingly, this study provides a useful reference for continuous processing or batch production of engineering ceramics at a constant feed speed.