硅砂原料对无碱铝硼硅玻璃熔化特性的影响

研究了硅砂原料对无碱铝硼硅酸盐玻璃(即TFT-LCD基板玻璃)熔化特性的影响。结果表明:玻璃熔制过程中"富硅氧层"的出现与石英砂颗粒粒径有关,当粒径小于75微米时,玻璃熔化质量良好;石英砂颗粒形态对于熔解特性也很重要,最佳的颗粒形态为圆形,并且粒径分布范围要相对集中,处于较窄区域。     

Effect of microstructure and grain size on the thermal conductivity of high-pressure-sintered diamond composites

We have studied the effect of the particle size of diamond (several microns to 500 μm) on the thermal conductivity of high-pressure-sintered diamond composites. The results demonstrate that the thermal conductivity of diamond-matrix composites prepared at 8 GPa in the presence of copper rises steeply with increasing diamond particle size, reaching a maximum, 9 W/(cm K), at a particle size of 200–250 μm. In the case of the samples prepared at 2 GPa and containing isolated diamond grains in a Cu-Ti binder, the grain size has a weaker effect on the thermal conductivity of the material, which can be accounted for by the low thermal conductivity and key microstructural features of the binder.     

Variation of mechanical properties of WC-Co alloys with microstructure

K_Ic values of various grades of WC-Co alloys seem to correlate with the single microstructural parameter, thickness of the binder phase. The correlation holds well for cobalt-layer thicknesses ranging from 0.02 to 1.0 μm, which covers almost all commercial grades. The K_Ic values reported by some other researchers fit this curve just as well. Hence K_Ic may be predicted from the thickness of the binder phase in the final product, irrespective of grain size and cobalt content. The correlation between cobalt-layer thickness and hardness, however, is not unique, and there are different curves for different grain sizes or cobalt contents.     

Relationship Between Particle Size and Dissolution Rate of Bulk Powders and Sieving Characterized Fractions of two Qualities of Orthoboric Acid

Abstract

We have carried out a study of the particle size distribution and aqueous dissolution rate of two commercially available qualities of orthoboric acid, labeled “crystal” (ABC) and “powder” (ABP). In a previous work, we have shown that the two commercial qualities of orthoboric acid chosen as model compound (“powder” and “crystal”) are related to the same crystal network in spite of their dvferent names. However, these two qualities have very different size particle distributions, as previously determined by sieving and confirmed by the present laser light scattering study. Dissolution testing is performed under sink conditions and show that the bulk ABC quality dissolves far more rapidly that the bulk ABP quality, For each quality, dissolution rates of four sieved particle size fractions (0-90 μm; 90-125 μm; 125-180 μm; 180-250 μm) were compared. Concerning the ABC quality, comparisons were also done with three other particles size fractions: 250-355 μm, 355-500 μm, and 500-710 μm. This study used the dQ/dt versus t profile. Dissolution profiles of the fractions enclosing particles with a size superior to 125 μm are very close. On the other hand, fractions enclosing particles with a size smaller than 90 μm present a different profile and a slower rate of dissolution.     

Aluminum matrix composites based on preceramic-polymer-bonded SiC preforms

Polymethylsiloxane (PMS) was used as a binder to make self-supporting SiC preforms for pressurized aluminum melt infiltration. The SiC particles were coated with preceramic polymer by spray drying; this ensured a fine and homogeneous distribution coupled with a high yield of the binder. The conditioned SiC powder mixtures were processed into preforms by warm pressing, curing and pyrolysis. A polymer content of 1.25 wt.% conferred sufficient stability to the preforms to enable composite processing. Using this procedure, SiC preforms with various SiC particle size distributions were prepared. The resulting Al/SiC composites with SiC contents of about 60 vol.% obtained by squeeze casting infiltration exhibit a 4-point bending strength of ∼500 MPa and Young’s moduli of ∼200 GPa. These values are comparable to those of compositionally identical, but binder-free composites. It is thus shown that the PMS-derived binder confers the desired strength to the SiC preforms without impairing the mechanical properties of the resulting Al/SiC composites.     

空气中氮气或氩气浓度对锆粉尘层着火温度的影响

为了探索抑制锆包壳剪切过程中锆粉着火的方法,采用粉尘层最低着火温度测定仪、红外热成像仪、真空手套箱等测定了不同粒径的锆粉尘层在空气和含不同浓度氮气、氩气的空气中的最低着火温度和火焰温度。结果得出:锆粉的中位粒径从2.4 μm升至71.7 μm,粉尘层最低着火温度从200 ℃升至390 ℃,表明粒径越小的锆粉着火敏感性越高;4种粒径的锆粉燃烧火焰最高温度都在1 776～1 913 ℃范围内,锆粉粒径较大时,燃烧的剧烈程度较低;氮气或氩气体积分数从60%～65%升至70% 85%时,锆粉尘层最低着火温度升至400 ℃,表明空气中高浓度的氮气或氩气对锆粉燃烧有抑制作用,且浓度越高,抑制作用越强,锆粉粒径越小,抑制效果越好。氩气的抑制效果强于氮气。     

不同粘结剂对碳纳米管红外吸收涂层性能的影响

碳纳米管涂层已在低温工作环境中大量应用,所选用的粘结剂在很大程度上影响其红外吸收性能及与基体的结合性能。分别用水玻璃粘结剂和磷酸盐粘结剂与碳纳米管、镍粉混合制成涂料,并将其涂覆在铜基体表面。采用XRD和SEM对涂层的红外吸收性能、物相、晶体结构及形貌进行了表征;测试了涂层的抗热震性能。结果表明:当粘结剂为磷酸盐、含量为90%~85%时,1 400~3 570 cm~(-1)(2.80~7.14μm)波段内涂层的平均光吸收度达1.992~2.084,红外吸收性能最佳,抗热震次数可达35次(25~120℃),满足了用户要求(10次)。     

三七超微粉体与细粉、不同目数范围粉体的粒度分布和显微形貌特征的比较

通过比较三七超微粉体、细粉(三七常规饮片)以及不同目数范围粉体(三七细粉经多次筛分得到的粉体)在粒度分布、显微形貌特征方面的差异,探讨了超微粉碎技术应用于中药三七加工的优势。应用激光粒度分析仪对三七超微粉体与细粉、不同目数范围粉体的粒度及其分布进行表征,观察其显微形貌特征。粒度分布测试和显微形貌观察的结果表明,超微粉粒度分布在0.30～24μm,大部分粉体达到了10μm以下,呈对称的单峰分布,引起团聚的作用力为各种表面力,说明超微粉体均匀度高质量易控。三七细粉及不同目数范围的粉体粒度分布范围在2～190μm,分布不对称,引起团聚的作用力为重力的等质量力,说明其均匀度差,质量难以控制。     

Drainage phenomenon of pastes during extrusion

The effects of elemental powder characteristics, binder content and its composition, as well as some additives on pressure change and drainage phenomenon of pastes during extrusion have been mainly investigated. The pastes consisted of a powder, zirconia or stainless steel, and a water-based binder, an aqueous solution of water-soluble polymer (hydroxypropyl methylcellulose). The drainage phenomenon has been found in extrusion of the stainless steel pastes with lower binder contents, while the zirconia pastes show a small probability of drainage in the range of the binder contents used in this investigation. It is shown that broadening particle size distribution by mixing powders with different average particle sizes has a significant effect on decreasing extrusion pressure and restraining occurrence of the drainage phenomenon, thus improving the extrudability of pastes. It is effective to increase the binder content in pastes, raise the mixing fraction of HPMC in binder and add plasticizer like glycerol, in order to reduce occurrence of the drainage phenomenon during extrusion of the stainless steel pastes.     

Effects of Powder Activated Carbon Particle Size on Activated Carbon Monolith's Properties

Methyl cellulose as organic binder and bentonite as clay binder were simultaneously used to prepare activated carbon monolith (ACM) using powder activated carbon (PAC) and by means of extrusion process. To study the effects of PAC particle size on porosity, adsorption, and mechanical properties of the ACMs, four broad types of PAC including powder with particle size less than 150, 90, 50 µm, and powder without screening were prepared and used. Actually, it was tried to improve the adsorption capacity, surface area, and mechanical strength (both compression and impact strength) of the ACMs by screening the PAC microparticles to certain particle sizes. The results showed that arranging and decreasing the PAC particle size significantly improved the above-mentioned properties.     

A Low-Binder-Content Ink System for 3D Printing High-Density and Small Feature Size 316L Stainless Steel Parts

Binder ink system is the backbone of binder jet 3D printing (BJ-3DP) technology. Compared with metal injection molding (MIM), BJ-3DP needs much less amount of binder, which means less exhaust gas generation during the debinding process and more environmental friendliness. More than that, low content of binder is also supposed to benefit the structure properties of the printed metal parts. Herein, an ultralow-binder-content ethanol–water–PVP ink system is demonstrated for the BJ-3DP 316 L stainless steel parts by applying thermal bubble inkjet technology. The PVP binder concentration is as low as 80 mg mL⁻¹, which can achieve an ultralow solid content of 0.2 wt% in the printed green part. The two-component solution with water and ethanol provides not only the rheology property adjustment freedom for the ink jetting and infiltration in the metal powders, but also the two boiling points for the step-by-step capillary bridge formation process. By applying the low-binder-content ink, the fully densified 316 L stainless steel parts after sintering can obtain the relative density up to 99.4%, Vickers hardness up to 185 HV, tensile strength up to 542 MPa, 25% elongation at break, and feature size as small as 200 μm.     

Effect of Binder Level and Granulating Liquid on Phenylbutazone Pellets Prepared by Extrusion-Spheronization

Abstract

The effects of type and amount of binding agent and different amounts of granulating liquid on the physical properties of uncoated beads of phenylbutazone were investigated. The binders used were polyvinylpyrrolidone (PVP) and gelatin/starch (G/S) at two levels, and each formulation at two percentages of granulating liquid; water/ethanol at 60/40 ratio. The ability of these binders to produce pellets of phenylbutazone by the extrusion-spheronization method was evaluated by two criteria. The first was physical properties such as particle size, yield between 710 and 1400 μm, friability, and density. The other criterion was the drug release profile. Generally 5% of gelatin/starch with 80% of solvent produced more uniform pellets with a narrower particle size range and a high yield of spheres between 710 and 1000 μm. Changing the type of the binder, its percentage, and the amount of granulating liquid had no significant effect on the pellet density. Changing the type of the binder or/and its percentage and also the effect of granulating liquid in combination with the other mentioned variables had significant effects on the friability of the pellets. The results show that the amount of granulating liquid and binder amount have the same influence on the drug release from pellets. A slower release rate was observed with increased amounts of these two variables. These differences in the release profiles were parallel to the differences in hardness and structure of the pellets. The difference between particle diameter and the percentage of drug released within 30 min was significant in all formulations.     

Preparation and characterization of YBa2Cu3O7−x powder by the ultrasonic spray pyrolysis method

A single-phase YBa₂Cu₃O_7−x powder was prepared in an air flow system by thermally decomposing droplets containing the nitrate salts of yttrium, barium and copper in distilled water. The powder obtained had a mean particle size 0.78 μm and a very narrow particle size distribution. The total porosity of the powder was estimated to be about 63%. It was found that much agglomeration had occurred among the droplets, which would have an adverse effect on the particle size distribution. The bulk density of a sintered specimen using the powder prepared at 950 °C was higher than 97% theoretical density.     

清水营煤超细粉碎过程中的影响因素

为了制备粒度小于10μm的超细清水营煤粉,采用球磨机对煤粉进行研磨,利用激光粒度仪对超细煤粉进行了粒度分析,得出球磨时间、球煤质量比、填充率、转速等主要因素与煤粉碎效果的关系,确立清水煤超细粉碎的最佳工艺条件。结果表明:采用湿磨方式,在球煤质量比为15∶1、填充率为0.45、转速为100 r/min的工艺条件下,经7 h研磨,清水营煤粉的粒度可达到2.596μm。     

Porous polytetrafluoroethylene film

The properties of porous films obtained by sintering a layer of polytetrafluoroethylene (PTFE) powder deposited onto a substrate were studied. The PTFE film porosity was controlled within 50–60% and the maximum pore size was 1–3 μm. The breaking stress of the films reached ～6 MPa at a 100% relative elongation. The influence of the particle size distribution function of the initial PTFE powder on the mechanical properties of sintered films is analyzed.     

铝粉粒径对销毁某未爆弹药影响的试验研究

为提高某种新型未爆弹销毁方式的工作效能和操作安全性,基于销毁装置内复合高热剂自蔓延燃烧过程,利用试验分析研究了铝粉粒径大小对销毁该种未爆弹药的影响。结果表明:74~178μm范围内,铝粉粒径越大,金属熔流出口速度达到的峰值越低;同时,铝粉粒径过小(≤89μm),会导致销毁装置内复合高热剂反应过于激烈,容易出现燃爆现象;而124~178μm粒径范围的铝粉适用于榴弹弹丸、破甲弹战斗部、手榴弹、地雷等多种壳体厚度不超过9 mm的猛炸药弹丸的未爆弹销毁工作。为以后提高未爆弹销毁工作效能、保护销毁人员安全提供参考。     

Aluminium powder particles produced by SAMD technique: typical characteristics and correlations between processing conditions and powder size

Abstract

The present paper consists of two parts. In the first part the principles of a new method of metal powder production, termed 'solid assisted melt disintegration (SAMD)' are discussed and the typical characteristics of the produced powder are outlined. In the second part the effects of some processing parameters on the size distribution and mean diameter of the powder are reported. The SAMD method involves mixing solid particles (i.e. alumina) with the liquid aluminium alloy aided by mechanical agitation. The shear force induced by the impeller is transferred to the metal via the non-wetting solid medium and results in melt disintegration. The resulting mixture of aluminium droplets and alumina particles are subsequently cooled in air and screened through 300 μm sieve to separate alumina from solidified aluminium powder particles. The SAMD technique has demonstrated the capability to produce a wide particle size distribution. The small sized particles (i.e. <53 μm) exhibited irregular shapes, but larger ones were mostly spherical. These powder particles were dense (pore free) without attached satellite particles and exhibited a relatively coarse microstructure. The processing parameters investigated include the size of Al₂O₃ particles, Al₂O₃/Al weight ratio, stirring speed and stirring time. It was concluded that there exists an optimum value for each of the aforementioned parameters corresponding to a minimum in the mean particle size.     

Powder Microstructure and Overlay Coating Property ofNiCrAlY Alloy

The microstructural features of NiCrAlY alloy powders with different particle size fractions and their effects on the overlay coating property have been investigated. It is shown that the finer (20~30 μm) powder particles experience rapid recalescence and heat extraction to the surroundings resulting in microcellular structure, whereas the coarser (40~50μm) powder particles exhibit a coarse cellular and dendritic mixed structure because of recalescence followed by slow cooling.In addition, it is also indicated that the finer the powder particle sizes, the higher the mechanical property and the metallurgical thermal stability of the overlay coatings deposited by as-atomized powders, which is presumably attributed to the formation of dense fine grain Structure and oxide layer for the fine size fraction of the powders.     

新拌水泥浆体中邻近胶凝材料粒子表面最近间距分布的解析解

依据Torquato的最邻近表面函数公式, 推导了新拌水泥浆体邻近水泥粒子表面最近间距分布的解析解, 并采用计算机模拟生成了1个水泥浆体结构模型, 选取邻近粒子表面最近间距概率密度分布曲线、 区间概率曲线和累计概率分布曲线这3个函数检验模拟结果与理论结果之间的差别。结果表明, 该解析解与计算机模拟实验结果吻合良好。利用该解析解, 以Rosin-Rammler分布为例, 研究了胶凝材料细度以及水胶比对邻近水泥粒子表面最近间距分布及其平均值的影响。结果显示, 水泥细度对邻近粒子表面最近间距平均值的影响高于水胶比的影响。邻近粒子表面最近间距解析解的获得, 不但为基于不同粒径分布以及尺度范围粉体之间搭配的高粉体初始堆积密度的实现提供了依据, 而且对多尺度模拟方法中选取各级模型的尺度、 量化粉煤灰浆体中粉煤灰颗粒的微集料效应、 了解邻近集料间的交互作用程度以及界面重叠程度等问题具有参考价值。     

Preparation of zirconium diboride nanopowders in a sodium tetraborate ionic melt

Reactions between zirconium powder 10–15 μm in particle size and microcrystalline boron 10–20 μm in particle size in an Na₂B₄O₇ ionic melt have been studied at temperatures from 600 to 850°C and reaction times from 5 to 10 h. The results demonstrate that ZrB₂ forms starting at 750°C. According to scanning electron microscopy data, the ZrB₂ powder consists of particles 90–95 nm in average size. The crystallite size evaluated from X-ray diffraction data is 85 nm.