Effect of ball size on milling efficiency of zinc oxide dispersions

Zinc oxide (ZnO) was wet milled using inert Al₂O₃-ceramic balls having different diameter at different milling intervals and the milling efficiency of the resultant dispersion was followed through particle size analysis and zeta potential measurements. The results indicated that small-sized balls improved the milling efficiency. The highest share (%) of lower-size particles was obtained after 24?h of ball milling.     

CaCO3粉体气流粉碎/静电分散粒径分布规律研究

气流粉碎是近年来发展起来的一种新型微纳米粉体制备技术,然而采用该方法制备的粉体在一定程度上会自发团聚形成团聚体。将静电分散与气流粉碎相结合,研究了不同粒径的原始粉料经气流粉碎/静电分散方法处理后的粒径分布以及粒径随时间的变化关系,得到了气流粉碎/静电分散中荷电电压对所制备粉体粒径分布的影响规律和颗粒荷电分散的时效性,结果表明荷电电压越高粉体分散性越好,经J/E处理后粉体粒径随时间变化关系满足d=Aet/B+d0。     

粒度搭配对水雾化铁粉工艺性能的影响

为了研究粒度组成对水雾化铁粉松装密度、流动性、压缩性及压制过程的影响,将-80+100目和-325目两种粒径的水雾化纯铁粉以不同比例搭配进行研究.结果表明:通过控制不同的粒度组成,铁粉松装密度在2.84～3.42 g/cm3内变化、铁粉流动性在20～31 s/50 g内变化;与纯粗粉样品A相比,在粗粉中添加质量分数25%细粉的样品B在低压(300 MPa)下压坯密度增加,高压(≥300 MPa)时压坯密度减少;细粉质量分数为75%时的样品D与样品C相比,压坯密度均增加;全部采用-325目细粉的样品E与样品D相比,压坯密度均降低.当压制压力低于300 MPa时,压坯致密化主要由颗粒的滑移、重排决定;当压制压力高于300 MPa时,压坯致密化主要以粉末的塑性变形为主.     

Effect of the milling method and particle structure on the color tone of (Cr,Fe)2O3 inorganic black masterbatch pigment

(Cr, Fe)₂O₃ pigment was milled using different techniques into the same particle sizes to investigate the influence of milling processes on its properties. The research showed that milling type resulted in significant color differences, accompanied by the pigment color changing from intense reddish-brown to dark brown. Differences in the morphology of the particles embedded in the plastic matrix led to different light scattering, which is observed as a decrease in the color saturation of the pigment. Particle size distribution (PSD) was characterized by measuring with a laser diffraction particle size analyzer. Pigments were milled down to 4 µm in all milling methods. The very small particles in the pigment affected the light scattering and the color tone. The particle size of the pigment milled by the planetary mill was D₁₀ = 0.035 μ ± 0.1. Color values of the plastic plates were measured according to CIE laboratory analysis. The pigment milled with the planetary mill was lighter, greener, and yellower (ΔL*=4.15, Da*=3.68, Db*=2.96). The pigment milled with the jet-mill was closest to the pigment color after calcination. The pigment milled with ball mill was slightly greener than the values after calcination (Da*=1).     

Effect of powder particle size on green properties and stress wave

In the powder metallurgy (PM) industry, high velocity compaction (HVC) technique is a new way to obtain higher density parts. In this study, three reduced pure iron powders with different particle sizes were pressed by HYP35-2 High Velocity Compaction Machine. A computer controlled universal testing machine was used to measure the bending strength of the green body. The relationships among the particle size, the impact velocity, the green density, the stress wave, the bending strength and the radial springback were discussed. The results show that the powder of −200 mesh is the best option among the three powders for the HVC process. At the identical impact velocity, the green density for the powder of −200 mesh is higher than the other two types of powders, while the bending strength and the radial springback for the powder of −300 mesh is the highest. In addition, the stress waves exhibit similar, pulsed waveforms. As the impact velocity rises up, the duration of the first peak decreases gradually, while that of the stress wave increases slowly. The response time for the powder of −200 mesh is shorter than the other two types of powders.     

颗粒尺寸及温度对羰基铁粉磁化性能的影响

为了揭示颗粒尺寸及温度对羰基铁粉磁化性能的影响规律,利用振动样品磁场计分别测试了两种不同粒径羰基铁粉在室温条件下的磁化特性曲线,并以粒径为7μm的颗粒为对象,研究了温度对其磁化性能的影响。结果表明,粒径较大的颗粒具有更为优良的磁化性能,相同磁场作用下,其磁化强度较大而矫顽力却较小;温度升高将导致颗粒达到相同磁化强度所需磁场强度减小且对应磁化强度值降低,并且这种影响随温度的升高而逐渐加剧;当长期处于高温下工作后,由于表面氧化层的形成,颗粒磁性将会出现较大程度的减弱。     

Effect of ball milling time on the structural characteristics and mechanical properties of nano-sized Y2O3 particle reinforced aluminum matrix composites produced by powder metallurgy route

Mechanical milling presents an effective solution in producing a homogenous structure for composites. The present study focused on the production of 0.5 wt% yttria nanoparticle reinforced 7075 aluminum alloy composite in order to examine the effects of yttria dispersion and interfacial bonding by ball milling technique. The 7075 aluminum alloy powders and yttria were mechanically alloyed with different milling times. The milled composites powders were then consolidated with the help of hot pressing. Hardness, density, and tensile tests were carried out for characterizing the mechanical properties of the composite. The milled powder and the microstructural evolution of the composites were analyzed utilizing scanning and transmission electron microscopy. A striking enhancement of 164% and 90% in hardness and ultimate tensile strength, respectively, were found compared with the reference 7075 aluminum alloy fabricated with the same producing history. The origins of the observed increase in hardness and strength were discussed within the strengthening mechanisms' framework.     

工艺参数对燃烧合成硼粉的纯度和粒度的影响

以B2O3粉为原料,Mg粉为还原剂,采用燃烧合成法制备硼粉,研究了不同的工艺参数(反应物量、反应配比和压片压力)对燃烧合成制备的硼粉纯度和粒度的影响,并确定了最佳工艺参数。通过扫描电镜(SEM)和能谱对产物进行分析,结果表明,反应物量为100g时产物粒度最小,硼元素的含量最高;反应配比(摩尔比)为1时粒度最小并且硼元素的含量最高;压片压力为5MPa时粒度最小,10MPa时硼元素的含量最高。     

Effect of cement type and limestone particle size on the durability of steam cured self-consolidating concrete

This paper describes a laboratory program to investigate the influence of cement and limestone filler (LF) particle size on the hardened properties and durability performance of steam cured self-consolidating concrete. In addition, the interplay between cement type and LF particle size was investigated. CSA (Canadian Standards Association) Type GU (General Use) and HE (High Early-strength) cements were used with 5% silica fume (SF) [1]. The water-to-cement ratio was 0.34. LF with two nominal particle sizes of 17 μm and 3 μm, which correspond to Blaine fineness of 475 and 1125 m²/kg, respectively, were used. In addition to fresh concrete properties, hardened properties including compressive strength, elastic modulus, ultrasonic pulse velocity and density were measured at 12 h and 16 h, and at 3, 7 and 28 days. Indicators of durability performance including rapid chloride permeability testing (RCPT), sulfate resistance, linear shrinkage, salt scaling resistance and freeze-thaw resistance were evaluated. The results showed that LF improved the 12 and 16-h strength with no influence on later age strength (i.e., 3–28 days). The linear shrinkage and RCPT decreased with the addition of LF. This reduction was linked to the production of calcium mono-carboaluminate. LF did not impact the sulfate resistance, salt scaling resistance or freeze-thaw resistance of concrete.     

Effect of solvents quality on determination of particle size and polydispersity of nanoparticles

Nanotechnology is of great interest to researchers and industrialists and nanocolloidal carrier systems for drug delivery have been studied in great detail, but while much research has been carried out on the preparation of nanoparticles using a variety of techniques employing various solvents, no attention has been given to the quality of solvents used in the process of nanoparticles characterization. The present investigation aimed to study the effect of solvents quality on the chitosan nanoparticles characterization for average particle size (Z) and polydispersity index (P.I.). Particle size distribution study showed that the number of particles contributed by solvents significantly affects both the Z and P.I. of the nanoparticulate suspensions leading to ambiguous results. While the Z decreases upon dilution with organic solvents, the phosphate buffer and water causes a net increase in Z because of the introduction of larger extraneous nanoparticles. The P.I. was found to increase with dilution because of the differences in the size of the polymeric nanoparticles and the nanoparticles introduced by the solvent upon dilution. The study thus recommends use of the highest quality of solvents in nanoparticles manufacturing and characterization process to avoid the generation of erroneous results.     

Effects of particle size and acid addition on the remediation of chromite ore processing residue using ferrous sulfate

A bench-scale treatability study was conducted to assess the effects of particle size and acid addition on the remediation of chromite ore processing residue (COPR) using ferrous sulfate. The remediation scheme entailed the chemical reduction of hexavalent chromium [Cr(VI)] and the mitigation of swell potential. Leaching tests and the EQ3/6 geochemical model were used to estimate the acid dosage required to destabilize Cr(VI)-bearing and swell-causing minerals. The model predicted greater acid dosage than that estimated from the batch leaching tests. This indicated that mass transfer limitation may be playing a significant role in impeding the dissolution of COPR minerals following acid addition and hence hindering the remediation of COPR. Cr(VI) concentrations determined by alkaline digestion for the treated samples were less than the current NJDEP standard. However, Cr(VI) concentrations measured by X-ray absorption near edge structure (XANES) were greater than those measured by alkaline digestion. Greater Cr(VI) percentages were reduced for acid pretreated and also for smaller particle size COPR samples. Upon treatment, brownmillerite content was greatly reduced for the acid pretreated samples. Conversely, ettringite, a swell-causing mineral, was not observed in the treated COPR.     

Surfactant assisted synthesis of precipitated calcium carbonate nanoparticles using dolomite: Effect of pH on morphology and particle size

Synthesis of nanomaterials from readily available minerals for industrial applications is a growing research area. Understanding the causes of their properties becomes handy in utilization. In this study, an effective sucrose solution based method was employed for the extraction of calcium from dolomite to synthesize precipitated calcium carbonate nanostructures with different morphologies and sizes. It was found that 30% (w/v) sucrose solution extracted approximately 91% of calcium from dolomite forming a calcium-sucrate complex. Carbonation was achieved by CO₂ bubbling and aqueous sodium carbonate addition. Precipitation was performed under different pH values of 7.5, 10.5 and 12.5 in the absence of an anionic surfactant and in the template of sodium dodecyl sulfate (SDS)/calcium-sucrate at pH 12.5. It was found that CO₂ bubbling slightly promotes smaller particles. The anionic surfactant enables particle size and agglomeration reduction while introducing some hydrophobicity. The smallest particles were achieved at a range of 40–55 nm in the presence of SDS/sucrose template and were of spherical morphology. By changing the pH, a tendency to form different polymorphs and shapes of calcium carbonate was observed.