Nanostructure in a Ti alloy processed using a cryomilling technique

A nanocrystalline Ti alloy with a uniform distribution of grains was synthesized using cryogenic mechanical milling. The effects of cryomilling parameters, such as milling time and ball to powder ratio (BPR), on the particle size, grain size, chemistry, and structure of cryomilled Ti powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The experimental results show that nanocrystalline Ti powders with a grain size of about 20 nm can be prepared using the cryomilling technique. Compared to SPEX milling at room temperature, cryomilling led to lower contamination levels of oxygen, nitrogen, and iron in the cryomilled Ti powder. The average particle size initially increased from the original 55 μm to a maximum value of 125 μm after 2 h of milling, and then decreased to 44 μm after 8 h of milling. Both the average particle size and the grain size decreased as the BPR increased.     

机械合金化制备FeSiAl合金粉末的研究

采用机械合金化的方法制备了FeSiAl合金粉末样品。以硅钢粉和铝粉为原料,按摩尔分数Fe3Si0.4Al0.6配比,研究其机械合金化过程,并对机械合金化的机制进行探讨。用激光粒度仪、X射线衍射(XRD)和扫描电子显微镜分析材料的粒度、形貌和结构。研究表明,Fe3Si0.4Al0.6混合粉末球磨30h后,粉末粒径可达18μm;Fe3Si0.4Al0.6混合粉末经高能球磨20h后,形成具有bcc结构的α固溶体;球磨继续进行,合金化的粉末和晶粒不断细化。     

Micromeritic Properties of Nitrofurantoin Microcapsules

In our previous study, we have prepared nitrofurantoin microcapsules using carboxymethylcellulose (CMC) and aluminium sulphate by a coacervation technique. In the present study, the micromeritics of these microcapsules were investigated in terms of standardization of the crude materials employed, the microcapsules product and the dosage forms prepared from these microcapsules. The microcapsules were prepared with a 1:1 core: wall ratio and sieved into three particle sizes. Both the micromeritic properties of the pure drug and the polymer were studied by determining their bulk volume and weight, tapping volume and weight, fluidity, angle of repose, weight deviation, particle size distribution, density and porosity, The particle size range went from approximately 250μm to 3000μm with a peak between 900μm and 1350μm. The results indicate that the flowability and the particle size of the resultant microcapsules were much increased compared with the raw materials. As the microcapsule size increases the porosity also increases but the density decreases.

The weight deviation of the microcapsules first sieved then filled into hard gelatin capsules was carried on according to the USP XXII. Hard gelatin capsule size was found by Lindenwald-Tawashi nomogram as number 3. The geometric mean diameters and the geometric standard deviation of microcapsules were calculated as 750 pm for number distribution and 1275μm for weight distribution and 1.52 for number and weight distribution respectively.

In addition to evaluate whether some kind of glidant will be needed during tableting of microcapsules and filling of them into hard gelatines, “Hausner ratio and consolidation indexes” were calculated.

The results obtained suggest that sustained release dosage forms of nitrofirantoin can be prepared from the obtained microcapsules as far as the micromeritic properties is concerned and the microencapsulation changed the micromeritic properties of the crude materials significantly.     

球磨工艺对太阳能电池正面银浆用玻璃粉的影响

研究了球磨时间、固液比、料球比和磨球尺寸与级配对太阳能电池银浆用玻璃粉粒度及形貌的影响,并将其与一定比例的银粉、有机载体配制成导电银浆,印刷、烧结在硅片上形成晶体硅太阳能电池片,测试了其电学性能。实验结果表明,将玻璃粉用作正面银浆粘接剂时,其最佳的行星球磨工艺参数:球磨时间为4h,固液质量比为1∶0.8,料球质量比为2.5∶1,磨球级配w(大)∶w(中)∶w(小)为3∶2∶1。此时,制备的多晶硅太阳能电池串联电阻为7.15mΩ,光电转换效率可达16.56%。     

Deposition and structural characterization of poly-Si thin films on Al-coated glass substrates using hot-wire chemical vapor deposition

The growth of polycrystalline Si films onto Al-coated Corning 7059 glass substrates using hot-wire chemical vapor deposition (HW-CVD) was investigated. The crystalline fraction, grain structure and average grain size of the films were compared as a function of the growth rate and the Si/Al thickness ratio. Micrometre-size Si grains were achieved with a Si/Al ratio of 2 and Si thickness of 2 μm at a growth rate of 1 μm h⁻¹. It was found that the films had a bimodal grain size distribution, which included nanocrystalline Si, and that the growth of micrometre-size crystallites does not continue as the thickness of Si film increases. At a growth rate of 5 μm h⁻¹, films are similar to those grown on glass with an average grain size less than 60 nm and crystalline fraction of 75%.     

超细碳化钨介质球磨工艺的研究

对介质球磨法制取超细碳化钨粉末进行了研究。实验探讨了不同线速度、磨球尺寸、分散剂的添加对初始粒径约1μm的碳化钨粉末的介质球磨工艺的影响。根据W=P·t,在保持能耗不变的情况下得到了粒度与线速度之间的关系,从而在一定粒度范围内选择最有效的线速度。同时,采取分阶段球磨的球磨效率要高于单一线速度球磨,可实现用更少的成本达到相同粒度。此外,球磨时添加羧甲基纤维素钠分散剂,粉末粒度越小时分散效果越明显,实验中在输出功率不变时,与不添加分散剂对比,其时间效率提高了13%,最终的粉末也呈现很好的分散性。最后,磨球尺寸的大小可决定最终粒度的大小。因此,根据目标粒度采用合适的磨球尺寸和球磨工艺才能达到最高的球磨效率。     

Synthesis of nanocrystalline SiC at ambient temperature through high energy reaction milling

This study investigated the in-situ synthesis of nanosized crystalline SiC powders at room temperature through high energy ball milling of elemental silicon and carbon mixtures. Milling conditions including the mill design, the milling speed, the milling time and the ball-to-powder weight ratio (i.e. the charge ratio) necessary for the in-situ synthesis were studied. It was found that uniform formation of nanosized crystalline SiC powders within the powder charge could be achieved with a correctly designed attritor and the contamination could be minimized with proper selections of milling conditions. The crystalline β-SiC powders synthesized were themselves in nanosize scale, quite different from many previous studies which have shown that it is the internal grain structure of milled powders that is the “nanocrystalline” component of the powders (typically 5–20 nm), while the powders are themselves typically 0.1 μm to > 1 μm in size. Furthermore, it was found that the product structures generated by high energy reaction milling depended strongly on the milling speed, the charge ratio and the milling time.     

Ductile Regime Mirror Finish Grinding of Ceramics with Electrolytic In-process Dressing (ELED) Grinding

Advanced structural ceramics, such as silicon nitride based materials, are of interest owing to their unique physical and mechanical properties. However the cost of grinding these ceramics, which is an integral part of their fabrication, is very high. Moreover, grinding can result in surface and sub-surface damage in the material and these defects can significantly reduce the strength and reliability of the finished components. Grinding damage is sensitive to grinding parameters. Two types of silicon nitride based ceramic materials were ground with Electrolytic In-Process Dressing (ELID) using different grit sized metal bonded diamond grinding wheels. With the application of ELID technology, mirror surface finish was realized with a #4000 mesh size wheel (average grain size = 4μm). Differences in ground surface topography caused by wheel grain size were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM studies reveal that material was predominantly removed in the ductile mode when ELID grinding was performed with a #4000 grit size wheel or finer.     

煤粉超细化技术及设备研究

根据双向旋转球磨机的超细粉碎原理,研究开发制备超细煤粉的技术及设备,并采用该设备进行煤粉的超细粉碎实验,分析各种工艺参数对超细煤粉产品粒度影响。结果表明:采用双向旋转球磨机制备超细煤粉的最佳工艺条件为:筒体及搅拌器转数25r/min,球料质量比为8,研磨时间为4～5h,磨球尺寸为10～20mm,制备出超细煤粉产品的粒度为d50=1.15μm,d90=2.67μm。     

硬质木炭、竹炭超细粉碎技术研究

采用双向旋转球磨粉碎技术制备了超细木炭、竹炭粉,研究了工艺参数对粉碎效果的影响,并对普通球磨粉碎、双向旋转球磨粉碎原理进行了分析、比较,研究结果表明:对于此两种物料,球的大小级配是不同的,应根据粉碎物料的性质而定,球料比按8:1,粉碎腔内装填系数为50%~70%,球磨机的转数与内搅拌器转数之比为1:3时对粉碎效果有利。与普通球磨机、普通搅拌磨进行了对比试验,在相同条件下,双向球磨机粉碎效果好,效率高。     

Influence of dry and wet grinding conditions on fineness and shape of particle size distribution of product in a ball mill

The influence of grinding conditions on the production of fine particles and the width of the particle size distribution produced during ball mill grinding was investigated. The grinding experiments were carried out varying the grinding ball diameter under dry and wet conditions. The relation between the weight passing size observed in an arbitrary cumulative undersize fraction and the grinding time was expressed by modifying Tanaka’s semi-theoretical equation for the grinding limit. The fineness of the product was evaluated by the median particle size in undersize distribution, and the shape of the particle size distributions by three different size ratios calculated using 10%, 20%, 50%, 80% and 90% cumulative weight passing sizes, that showed the width of the particle size distribution. The median particle sizes of product obtained for the grinding limit in wet and dry conditions were around 0.5–0.6 μm and 2 μm, respectively. The width of the particle size distribution in wet grinding decreased with decreasing median particle size of the ground product, and the size distribution in dry grinding became nearly constant. The particle size distribution width was lowered by using smaller grinding balls in wet condition and larger grinding balls in dry condition.     

球磨促进碳热还原反应合成氮化铝研究

研究了高能球磨氧化铝和细化和机械力化学作用及球磨对碳热还原反应合成氮化铝（ＡｌＮ）的影响。结果表明：经高能球磨细化后的氧化铝（Ａｌ２Ｏ３）,相对于原始粉末,反应生成的ＡｌＮ 较大提高,且随着球磨时间增加,ＡｌＮ生成量增大。用灰色关联分析方法比较了几种球磨效应对碳热还原反应的作用,发现粉末的晶粒尺雨与反应的关联度最大,表明球磨晶粒细化作用是球磨促进碳热还原反应的最主要原因。     

Mechanical properties of WC/Co cemented carbide with larger WC grain size

The mechanical properties of WC/Co cemented carbide with WC grain size of up to 30 μm are investigated through compressive and transverse rupture tests, because it is now to produce WC/Co cemented carbide of which grain sizes are from 20 to 30 μm. From testing specimens with a WC grain size of 3–30 μm and Co content of 5–20 wt.%, it is found that WC/Co cemented carbide with larger WC grains (20–30 μm) exhibit ductility, whereas smaller-grained materials are characteristically brittle.     

搅拌式球磨机细磨磁铁矿的工艺研究

研究了搅拌式球磨机细磨磁铁矿的工艺,试验了主要操作参数对搅拌磨效果的影响。结果表明,当矿浆浓度为55%、搅拌速度为1200r/min、球矿比为4、研磨时间为2h,研磨介质为3mm钢球时,能达到最佳值。分析和探讨了产生这种影响的原因。     

Jet mill grinding of portland cement,limestone, and fly ash: Impact on particle size,hydration rate,and strength

While the majority of commercial ordinary portland cement (OPC) is ground using a ball mill or a vertical roller mill, other industries have shown that jet mill grinding can be an alternative approach for grinding materials. This paper investigates the potential application of jet mill grinding for two systems. The first system is a blend of OPC and 15% limestone, and the second system is a blend of OPC and 40% fly ash. It was observed that when jet mill grinding is used, the average particle size of the powders is decreased to approximately 4 μm or less with a narrower particle size distribution than that achieved using ball milling. In addition to evaluating the size and shape of the particles obtained from the jet mill grinding process, this paper focuses on evaluating, using isothermal calorimetry, the effect these changes in particle size and distribution have on the extent and rate of hydration as well as their effect on the compressive strength of cement pastes or mortars.This study also investigated differences between inter-grinding and blending separately ground materials to form an OPC/limestone mixture. Both inter-ground and separately ground OPC/limestone mortars demonstrated an accelerated hydration at early ages accompanied by an increase in early age strength. This appears to be primarily due to the increased surface area of the finer particles that provides more available surface for the hydration reaction. The inter-grinding appeared to be more effective than grinding the materials separately because an improved graded particle size distribution was obtained. The inter-ground OPC/limestone mixture shows accelerated initial hydration at water to powder ratios (w/p, where powder = cement + limestone) of 0.50 and 0.35 when compared with the samples before grinding. At the lower w/p of 0.35, the OPC/limestone mixture appears much more efficient. In the OPC/fly ash mixture, jet mill grinding also accelerates the rate of hydration and strength development.     

Nanostructured materials by mechanical alloying: new results on property enhancement

Mechanical attrition—the mechanical alloying or milling of powders—is a very versatile and potent method of obtaining nanocrystalline or ultrafine grain structures with enhanced properties. This article presents three examples of enhanced properties obtained by materials in which the grain size has been reduced to the nanoscale or ultrafine scale by ball milling and consolidation of powders. Very high strength/hardness—the highest hardness yet reported for crystalline Mg alloys—for a ball milled Mg₉₇Y₂Zn₁ alloy is due in part to the nanocrystalline grain structure, along with nanoscale precipitates. A ternary Cu-base alloy with a low stacking fault energy was found to have both high strength and good ductility in a nanocrystalline material synthesized by the in situ ball milling consolidation method. This is another example that shows nanocrystalline materials need not be brittle. It is shown that bulk thermoelectric materials with superior properties can be produced by the ball milling and consolidation of powders to provide an ultrafine grain structure.     

Milling as a pretreatment method for increasing the reactivity of natural zeolites for use as supplementary cementitious materials

This work examined the effects of milling using a gravity ball mill on the reactivity of natural zeolites used as supplementary cementitious materials (SCMs). Six different particle size distributions of zeolites, created by milling the as-received zeolite in a ball mill for a specified amount of time, were characterized using x-ray fluorescence, quantitative x-ray diffraction, particle size analysis, pore size distribution and surface area analysis. Following material characterization, the pozzolanic reactivity of the zeolites was determined by measuring the quantity of calcium hydroxide in paste after 28 or 90 days and by tracking the compressive strength of zeolite-cement mortars. Results showed that a critical milling time exists, corresponding to a d₅₀ of 7–9 μm, after which reductions in particle size can no longer be achieved and zeolite performance can no longer be improved through ball milling.     

Synthesis and characterisation of polymer-coated metallic magnetic materials

Polymer-coated magnetic microspheres can be used for bioengineering applications; hence, the synthesis and characterization of such materials was studied. Cobalt and iron powders were ball milled and subsequently characterized by scanning electron microscopy (SEM) and XRD methods. The average size of the ball milled Co powders was 7.4 μm after 1 h of milling; for Fe, the smallest average size was 808 nm after 10 h of milling. These milled powders were then coated, using the solvent evaporation technique with the polymer poly-l-lactic acid (PLLA) to form microspheres. The process parameters to form microspheres with the smallest diameter, spherical morphology and a narrow size distribution was determined. The stirring speed and polymer viscosity were found to control the size and shape of microspheres. The Co and Fe microspheres had an average size of 105 and 125 μm, respectively. The VSM results showed that saturation magnetization decreased with polymer coating thickness.     

Ball Milling Synthesis and Property of Nd_(0.7)Sr_(0.3)MnO_3 Manganites

Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw materials are 4 h and 10:1, respectively. The grain size of as-milled Nd0.7Sr0.3MnO3 ceramics ranges from 51 to 93 nm, and the fine particles contain two phases of crystalline phase and amorphous phase. For the Nd0.7Sr0.3MnO3 synthesized by ball milling and sequent heat treatment, a remarkable...     

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。