A numerical model to predict the powder–binder separation during micro-powder injection molding

The micro-powder injection molding (micro-PIM) process has the potential to bridge the gap between the design and manufacturing of micro-components that are often used in small and handy devices. Numerical modeling helps to analyze and overcome various difficulties of micro-PIM. In the present work, a numerical model is developed to predict the powder–binder separation (a common defect in PIM and especially severe in micro-PIM) during the injection of an alumina feedstock. A powder–binder separation criterion is proposed dealing with applied injection pressure and friction force between the powder and binder. An indirect comparison of feedstock travel time between two locations is used to validate the model. The predicted segregation from the simulated result is supported by a qualitative experimental measurement. The developed model can be used to optimize injection parameters to get a defect-free product.     

Reconstruction and hydration of hydrotalcite response to thermal activation temperature: Enhancement of properties for magnesia castables

Optimization binding system for refractory castables is significant to enhance the service performance. Hydrotalcite has been considered a promoter for high-temperature performance of basic castables, however, its binding property remains to be improved before practical application. In this work, the thermal activated Mg–Al hydrotalcites were incorporated in magnesia castables, and the mutual influence of pre-calcination temperature on the hydration, microstructure, and strength of castables was investigated. The obtained results indicated that the reconstruction of calcined hydrotalcite took place in the hydration process and effectively motivated the hydrolysis. Hydrate was thus promoted and a relatively dense microstructure of magnesia castables was confirmed by X-ray computed tomography analysis. Hydrotalcite pre-calcinated at 300 °C contributed to the highest early strength for castable, and the high-temperature properties also performed better than that of other pre-calcinated hydrotalcite-adding. The enhancement mechanisms of calcined hydrotalcite were attributed to the two following reasons: (ⅰ) the modified microstructure of magnesia castables from the early stage by hydration process, (ⅱ) the further enhanced sinterability inspired by the appropriate thermal activation effect.     

Effect of impact angle on wear behavior of Mo2NiB2–Ni cermets with different Ni content

Herein, the influence of the impact angle and Ni content on the wear behavior of Mo₂NiB₂–Ni cermets was studied using an erodent-carrying slurry comprising artificial seawater and SiO₂ sands. The results reveal that the material loss may be attributed to the wear damage caused by SiO₂ sands because cermets are expected to exhibit good corrosion resistance in artificial seawater. The relative density of cermets markedly influences their resistance to wear damage, and the material loss experienced by cermets with poor relative density is 2–4 times higher than that of cermets with good relative density; this occurs because a higher relative density can markedly enhance the mechanical properties and reduce the defects in the cermets. Moreover, the results indicate that as the impact angle increases from 0° to 60°, the manifestation of the wear mechanism changes from damaging the Ni binder phase (caused by single cutting wear) to damaging both the Mo₂NiB₂ ceramic and Ni binder phases due to the combination of cutting wear and impact wear. The wear damage is dominated by the cutting wear and impact wear from SiO₂ sand at the low and high impact angles, respectively. Furthermore, the severe deterioration of the single ceramic skeleton at high impact angles indicates that the synergistic influence of the Mo₂NiB₂ ceramic and Ni binder phases on enhancing the wear resistance of the cermets intensifies at high impact angles.     

Effects of water and carbon dioxide pressure on the adhesion of Na2SiO3 and K2SiO3 binders on silica sand surface: Comparison of experimental data and molecular dynamics simulation

In this study, the effects of different water amounts, CO₂ blowing pressures, Na₂O:SiO₂ and K₂O:SiO₂ ratios were studied on the bonding strength of Na₂SiO₃ and K₂SiO₃ binders. It was concluded that the increase in water content had an adverse effect on the bonding strength of CO₂-hardened Na₂SiO₃ sand. The blowing pressure did not have a linear relationship with the bonding strength, but it was closely related to the diffusion coefficient of CO₂. Based on scanning electron microscopic results, it was inferred that the low strength was caused by the formation of lamellar crystals after the adhesive was hardened. It was found that the low strength was caused by the formation of lamellar crystals after the adhesive was hardened. Based on molecular dynamics simulations, different pressures and water contents had a great influence on the diffusion coefficient of CO₂ in the silicate binder system. This research provides an important theoretical background to improve the technology of CO₂-hardened Na₂SiO₃- and K₂SiO₃-bonded sands during the casting process.     

锂离子电池硅基负极黏结剂研究进展

硅在自然界中储量丰富,其理论比容量高达4 200 mA∙h/g,已成为高能量密度锂离子电池负极材料的研究热点。但是Si作为负极材料也存在许多不足,最大的问题是电池充放电过程中,硅体积膨胀（高达300%）,导致Si基负极材料粉化脱落、电池容量迅速衰减,其循环性能尚难以满足实际需求。通过研究开发硅基负极专用黏结剂材料,可以有效抑制循环过程中硅的体积变化,维持硅负极结构稳定,提升电池循环性能。本文综述了近年来硅基负极黏结剂材料的研究进展,主要从合成高分子聚合物黏结剂、天然高分子聚合物黏结剂、导电高分子聚合物黏结剂三个方面进行详细归纳总结,并介绍了本课题组在硅基负极黏结剂方面的部分研究成果,期望能为将来的硅基负极专用黏结剂的研究和应用提供一些思路。     

压力与温度敏感涂料用高分子粘结剂的研究进展

压力敏感涂料(PSP)以及温度敏感涂料(TSP)是通过光学手段研究物体表面压力和温度的功能涂层。简述了气体在聚合物中的渗透机理,发光分子氧猝灭以及热猝灭机理,综述了国内外PSP、TSP中常用的高分子粘结剂,并对PSP、TSP所用高分子粘结剂的未来发展方向进行了展望。这两种涂层均由高分子粘结剂和发光分子探针组成,PSP通过发光探针与氧分子作用产生的光物理行为变化来反映压力大小,TSP是通过发光探针随模型表面温度变化导致光物理行为变化来反映温度高低。目前,已发展的PSP用高分子粘结剂主要为氧透过率较高的含硅聚合物及丙烯酸酯类聚合物;已发展的TSP用高分子粘结剂主要为氧透过率较低的聚苯乙烯、聚丙烯腈、聚氨酯等。高分子粘结剂的主链结构、侧基种类与极性、分子间堆砌密度以及与发光分子相互作用,对涂层光物理性能、力学性能以及与基材结合力产生影响。因此,研究PSP与TSP中的高分子粘结剂对于未来两种技术的优化以及一定特殊要求下的应用有较为重要的意义。     

镀膜金刚石与铜基结合剂间把持力提高方法探讨

在不改变成分的条件下,为了探讨将表面镀覆和表面刻蚀相结合来提高金刚石与金属结合剂把持力的方法和条件,将镀Ti、镀Cr和镀Ni金刚石在1050℃下保温1 h后,用真空热压烧结法制备未镀、高温处理前后镀覆金刚石的铜基结合剂样条。用扫描电子显微镜对金刚石镀层表面形貌进行观测,用金刚石高温热处理前后铜基结合剂样条的抗弯强度来评估金刚石与铜基结合剂的把持力,经1050℃高温处理1 h后,金刚石表面的镍镀层基本上保持完整,而钛镀层和铬镀层则出现脱落;镀覆金刚石的单颗粒抗压强度都下降;镀Ti和镀Cr金刚石铜基结合剂样条的抗弯强度下降,但镀Ni金刚石样条的抗弯强度却大幅度提高,达到833 MPa,增幅为12.1%。结果表明:只有高温处理后镀层保持完整而且镀层能使金刚石表面粗糙度提高的情况下,才能大幅度提高金刚石与金属结合剂之间的把持力。     

基于MATLAB的胶结充填材料BP神经网络质量模型

用BP神经网络的方法建立胶结充填材料质量与主要影响因素胶结剂，浓度，骨料，温度和粒级的关系模型，并用MATLAB实现对该模型的训练和系统仿真，不论用什么样的骨料和胶结剂，只要用一定的试验数据对模型进行训练，然后对拟采用的胶结充填材料进行仿真，均可得到较为可靠的目标参数。     

模糊集合在等强度胶结充填材料优化中的应用

采用模糊集合论方法，通过计算机模拟和试验，合理选择尾砂浓度和胶结剂用量。在等强度和一定料浆浓度的前提下，尾砂浆浓度较大，胶结剂用量则较小，且相对成本较低。尾砂浓度和胶结剂用量两集合交集中的元素，即是矿山可选择的在等强度下较合适的尾砂浓度和胶结剂用量。模糊集合论用于胶结充填材料质量决策系统是可行的。     

有机改性蒙脱土/PVAc纳米复合材料乳液聚合研究

分别以过硫酸铵和氧化还原体系为引发剂,以有机改性蒙脱土为原料,用乳液聚合法制备聚醋酸乙烯酯(PVAc)/蒙脱土纳米复合材料,并采用XRD、SEM、TEM等对所得复合乳液的形态、结构及性能进行了研究。结果表明,氧化还原体系能降低反应温度,提高反应速率,所得纳米复合乳液的黏接强度有了很大提高。