Particle size reduction of RDX by sequential application of solvent–antisolvent recrystallization and mechanical methods

ABSTRACT

Solvent–antisolvent recrystallization produced ~8 µm average size RDX particles (UF-RDX) that were subsequently subjected to mechanical methods of ultrasonication and ball-milling to find further achievable reduction in particle size. Long duration ultrasonication for 20 h and 300 rpm ball milling for 4 h of UF-RDX decreased its average particle size to ~2 µm. RDX produced by all the three processes (solvent–antisolvent recrystallization, ultrasonication and ball-milling) was similar to coarser RDX in structure and thermal decomposition behavior. However, UF-RDX produced by solvent–antisolvent recrystallization was significantly less impact sensitive than that produced by ball-milling and ultrasonication. The issues of residual solvent and the metal contamination during RDX processing were addressed by process parameter optimization. Solvent–antisolvent recrystallization and mechanical methods even when used sequentially could not bring average particle size of RDX to nano-scale.     

铁基粉末齿环材料的制备

采用高能球磨法制备Fe-2Mn-2Cu-Mo-C-P粉末．研究了粉末形态的变化规律，以及压坯密度、烧结密度与球磨时间的关系．结果表明，球磨8h的粉末经压制烧结，材料密度为7．21g／cm^3。退火后Hv5值为230-240。该材料具有良好的热塑性及硬度，适合粉末热锻法生产齿环．     

Additive-free superhard B4C with ultrafine-grained dense microstructures

A unique combination of high-energy ball-milling, annealing, and spark-plasma sintering has been used to process superhard B₄C ceramics with ultrafine-grained, dense microstructures from commercially available powders, without sintering additives. It was found that the ultrafine powder prepared by high-energy ball-milling is hardly at all sinterable, but that B₂O₃ removal by gentle annealing in Ar provides the desired sinterability. A parametric study was also conducted to elucidate the role of the temperature (1600–1800 °C), time (1–9 min), and heating ramp (100 or 200 °C/min) in the densification and grain growth, and thus to identify optimal spark-plasma sintering conditions (i.e., 1700 °C for 3 min with 100 °C/min) to densify completely (>98.5%) the B₄C ceramics with retention of ultrafine grains (∼370 nm). Super-high hardness of ∼38 GPa without relevant loss of toughness (∼3 MPa m^1/2) was thus achieved, attributable to the smaller grain size and to the transgranular fracture mode of the B₄C ceramics.     

Influence of two-step ball-milling condition on electrical and mechanical properties of TiC-dispersion-strengthened Cu alloys

TiC-dispersion-strengthened Cu alloys were prepared by a two-step ball-milling (BM) process followed by sparks plasma sintering (SPS), heat treatment and hot rolling in sequence. The two-step BM process is composed of a pre-ball-milling (pre-BM) on both Ti and graphite powders as well as a subsequent homogenizing by BM together with Cu powder. Microstructure evolution analysis was performed to evaluate the effects of BM conditions on the electrical and mechanical properties of Cu-based alloys. The X-ray results revealed that titanium carbide (TiC) formed from Ti and C under high impact energy BM. Moreover, the formation of TiC during the SPS and heat treatment processes was found to more beneficial in enhancing the mechanical properties of alloy. The residual Ti in Cu matrix was found to be the predominant factor lowering the electrical conductivity of Cu–Ti–C alloys.     

NaNH2–NaBH4 hydrogen storage composite materials synthesized via liquid phase ball-milling: Influence of Co–Ni–B catalyst on the dehydrogenation performances

The composite NaNH₂–NaBH₄ (2/1 molar rate) doped with different amount Co–Ni–B catalyst was synthesized via liquid phase ball-milling method in the cyclohexane agent. The composition evolution and dehydrogenation performance of the as-prepared sample were characterized by means of XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy) and TG–DTA–MS (Thermogravimetric–differential thermal analysis–mass spectroscopy) measurements, respectively; and the activation energies were calculated by the Achar differential and Coats–Redfern integral method. The composite NaNH₂–NaBH₄ (2/1) with 5 wt% Co–Ni–B catalyst (the sample C5) generated Na₃(NH₂)₂BH₄ successfully after the liquid phase ball-milling. Due to the interaction between functional groups of NaNH₂–NaBH₄ (2/1) with catalyst, Co–Ni–B catalyst not only benefits improving the thermodynamical performance, that is, the initial dehydrogenation temperature is as low as 200 °C and the weight percentage of hydrogen is about 5.05 wt% obtained from TG–DTA-MS curves; but also promoting the kinetics property that the activation energy of the major dehydrogenation stage is only 68.2 kJ mol^?1. Furthermore, it is revealed that the kinetics mechanism of the dehydrogenation performance depends on the synthesis methods and adding catalyst.     

高能球磨工艺对Ti50Ni22Cu25Sn3组织演变的影响

用高能球磨法制备Ti50Ni22Cu25Sn3非晶粉末,并研究球磨工艺参数对Ti50Ni22Cu25Sn3非晶形成过程的影响。结果表明,球磨转速以及磨球直径对Ti50Ni22Cu25Sn3非晶相的形成效率具有十分重要的影响。较高的转速和合适的球径能有效促进该Ti基合金的非晶化,缩短合金非晶化的时间,当转速为400 r/min,球料比为20:1时,球磨时间约为30 h后,可得到完全的Ti50Ni22Cu25Sn3非晶粉末     

高能球磨对CuCo/ZrO2催化剂合成低碳醇性能的影响

研究高能球磨技术对浸渍法制备CuCo/ZrO2催化剂结构与合成低碳醇性能的影响,借助N2吸附-脱附等温线、扫描电镜、X射线衍射和程序升温还原等测试技术对催化剂进行表征,并以CO加氢合成低碳醇为模型反应对其催化性能进行评价.研究结果表明,催化剂制备过程中引入高能球磨技术可显著提高CuCo/ZrO2催化剂的CO转化率和C2...     

含碳纳米管的Sn-58Bi钎料的制备及其钎焊性

采用球磨—低温冶炼法制备了不同碳纳米管含量的Sn-58B i-CNTs钎料,借助SEM,EDS和DSC等分析手段研究了碳纳米管在钎料合金中的形态以及碳纳米管对Sn-58B i合金焊点拉脱强度的影响.结果表明,经过钎料低温冶炼后,碳纳米管能够部分加入到Sn-58B i合金中形成复合钎料;Sn-58B i-0.03%CNTs复合钎料在焊盘上的润湿性得到了提高,且微量碳纳米管的加入对钎料熔点的影响不大;碳纳米管在焊点中弥散分布使钎料的组织得到细化,并通过对焊点微观断裂机制的影响,提高焊点的可靠性.     

高岭土与膨润土复配填充丁苯橡胶复合材料的性能

以高岭土与不同类型的膨润土JZ-PRT、Na-PRT和Ca-PRT复配,用硅烷偶联剂Si-69进行球磨改性,得到复配黏土K-JZPRT、K-Na PRT和K-Ca PRT,将其作为增强剂填充到丁苯橡胶(SBR)中,制备了复配黏土/SBR复合材料,用X射线衍射仪、傅里叶变换红外光谱仪以及冷场发射扫描电子显微镜对复配黏土及复合材料进行了表征,并考察了复合材料的加工性能、力学性能和气阻隔性能。结果表明,复配黏土中膨润土的特征衍射峰强度都有所降低,高岭土除d001衍射峰外,其他特征衍射峰强度都有不同程度的弱化。与填充K-JZPRT的SBR复合材料相比,填充K-Na PRT和K-Ca PRT的复合材料的硫化速率更快,门尼黏度更低,因而加工性能也更好。填充复配黏土的复合材料的力学性能和气阻隔性能较SBR均有明显改善,其中K-Na PRT的填充效果最好,拉伸强度增加了652%,透气率降低了43%。复配黏土在SBR基体中分散比较均匀,与橡胶分子的结合良好。     

锂硫电池用S/KB复合材料的制备及性能

以科琴碳黑(KB)作为单质硫的载体,分别用球磨法和热处理法制备S/KB复合正极材料。用XRD、循环伏安、电化学阻抗谱(EIS)和恒流充放电测试,对材料进行分析。球磨法制备的材料首次放电比容量较高,1.0 C放电至1.5 V,最高达1 670 m Ah/g;热处理法制备的材料循环性能更稳定,以0.5 C在1.5~2.5 V循环30次,放电容量保持率约为82%。