Energy dissipation in collision of two balls covered by fine particles

A new fine particle impact damper (FPID) is composed of a spherical impactor and a small quantity of fine particles as damping agent. The model of energy dissipation in the collision between two balls covered by fine particles is necessary to investigate the mechanism and performance of FPID. In this study, a simplified model verified by FEA simulations is proposed to estimate the energy dissipation in collision between two balls covered by fine particles. In addition, the energy dissipation in the collision between two balls covered by fine particles is compared with that in the impact between two balls without fine particles, by means of theoretical predictions. FEA simulations are also carried out to discuss the effects of diameter ratio of particle to ball, particle material and particle amount on the energetic expression of the elastic–plastic loading (EPL) index (EPL_E). The results from the FEA simulations agree well with the estimations from the model proposed in this paper. It is concluded that the energy dissipation in the collision between two balls covered by fine particles can be predicted by classical collision models of two particles through the substitution of several parameters from balls; the plastic deformation of fine particles affixed on balls can exhaust much more energy than that of the two balls without particles, which is the reason for the good performance of FPID; the diameter ratio of particle to ball and the material of particles do not have significant effects on the EPL_E when the ratio is limited to the range of [1/200 – 1/10]. A correlation of the EPL_E and dimensionless initial relative velocity is also found for the collisions between two balls, which is independent not only of the particle size and material properties but also of the particles presence.     

Size-controlled synthesis of highly dispersed silver particles

Silver particles were easily synthesized in the presence of PVP by quickly adding concentrated ascorbic acid solution into the silver complex solution ([Ag(NH₃)₂]⁺). By varying the addition of organic solvents to the reaction system, it was found that highly dispersed spherical silver particles with different sizes were obtained. The effects of different kinds of silver seeds on the size-controlled synthesis of silver particles were also discussed. The as-prepared silver particles were investigated by electron microscopy and X-ray diffraction. A mechanism explaining the size-controlled formation of silver particles was proposed.     

Size-controlled hydrothermal synthesis of monodispersed BaZrO3 sphere particles by seeding

Monodispersed barium zirconate (BaZrO₃) fine particles with a spherical shape have been synthesized by hydrothermal reactions using barium hydroxide and a Zr-triethanolamine (TEOA) complex. The particle mean diameter was gradually controlled in a range from 0.20 μm to 3.5 μm by change in the added amount of seed nanoparticles. The mechanistic characterization of the seed-mediated BaZrO₃ sphere synthesis revealed that the particle growth obeyed a simple seed growth mechanism. In the present system, utilization of the Zr-TEOA complex played an important rule to prevent uncontrollable nucleation to form the uniform BaZrO₃ fine particles with narrow size distributions.     

Synthesis and characterization of uniform fine particles of copper oxalate

Copper oxalate particles were synthesized in various shapes and sizes by mixing appropriate volumes of known concentration of oxalic acid and copper nitrate at 25 and 85 °C. Temperature and reactants concentration had significant effect on the morphology of the precipitated particles and therefore extensive optimizations of the experimental parameters were carried out in order to obtain maximum uniformity in particles' morphological features. Selected batch of the copper oxalate particles was characterized by various physical methods.     

Particle size tuning in scalable synthesis of anti-oxidized copper fine particles by polypeptide molecular weights

Size tuning of metallic copper fine particles is highly important for their application to conductive pastes. Uniformly sized metallic copper fine particles could be successfully obtained by a chemical reduction of CuO micro powders using hydrazine in the presence of polypeptides as the stabilizing regent. Easy tuning of their particle sizes was successfully achieved via controlling the molecular weight of polypeptides. The obtained particles were covered by polypeptide capsules which were approximately 2 wt% of total mass. They are highly stable even under ambient conditions.     

Nickel and copper deposition on fine alumina particles by using the chemical vapor deposition-circulation fluidized bed reactor technique

A Chemical Vapor Deposition-Circulation Fluidized Bed Reactor technique has been developed to deposit metallic Ni and Cu onto alumina particles of 45 m diameter. The furnaces consisted of upper and lower zones, and the deposition precursors were produced both in situ and by vaporization of chlorides. X-ray diffraction, metallographical examination, and compositional analysis were used to analyze the deposition layers. For both Ni and Cu deposition, the deposition rates increased with higher temperatures of the lower furnace. The rates increased with greater amounts of chloride addition as well, but they reached plateaus when the amounts of addition were more than 40%.     

Selective collection of fine particles by water drops

This study was concerned with the interaction between a gaseous dispersion of fine particles travelling in the horizontal direction and discrete drops of water falling vertically through the dispersion. A simple analytical model of the particle–drop collision was developed to describe the particle recovery by the drops as a function of the water flux, covering two extremes of relative velocity between the particles and drops. The Discrete Element Method was used to validate the analytical model. Further validation of the model and insights were obtained through experimental studies. The physical process of wetting was observed to be important in influencing the tendency of particles to become engulfed by the drops of water, or to either adhere to the drops or by-pass the drops altogether. Hydrophilic particles were readily engulfed while hydrophobic particles, at best, adhered to the surface of the drop, or failed to attach. Moreover, the recovery of the hydrophilic silica particles was significantly higher than the recovery of hydrophobic coal particles, with the selectivity ratio approximately 1.5. Spherical ballotini particles were the most sensitive, with a notable increase in recovery when cleaned, and evidence of increased recovery with increasing particle size. The recovery of irregular shaped silica flour particles, however, was largely independent of the particle size. A similar result was observed for irregular coal particles, though the recoveries were all lower than relatively more hydrophilic ballotini or silica flour.     

Morphology of iron fine particles

The process of formation of iron fine particles from goethite microcrystals was investigated by means of powder X-ray diffraction, gas adsorption, and electron microscopy. In the first process, microporous hematite particles were prepared by decomposing goethite particles. The pores formed in hematite particles were slit-shaped (width : 0.9 nm). In the second process, microporous hematite particles were reduced at 250-350°C under the flow of hydrogen gas, and the reduction degree R (%) was determined. In the sample of R=8%, mesopores of 4 - 8 nm were formed by aggregation of slit-shaped micropores, but the skeleton of acicular particles was not significantly altered. With the progress in reduction, a number of crystallites were formed in the parent particles together with growth of pore size. In the sample of R=72%, the crystallites were separated from the parent particles. Finally, the separated crystallites sintered to give granular iron particles having low coercivity of 375 Oe. It was found that alumina or silica gel coated on the surface of goethite particles was remarkably effective for preventing the separation and sintering of crystallites formed in the parent particles. The silica-coated iron fine particles consisting of the crystallites which were as large as single domain particles showed excellent acicular shape and high coercivity of 1600 - 1700 Oe.     

纳米粒子包覆杂化改性室内涂料

将正钛酸丁酯、醋酸锌和正硅酸乙酯复合醇溶胶作为前驱体配置出稳定的纳米TiO2/ZnO/SiO2复合体系,在紫外光的照射下添加到成膜物质中充分搅拌,制备纳米复合涂料.测定其黏度、甲醛含量、抗茵性能、TVOC含量等,通过透射电子显微镜观察微观形态,分析纳米粒子在涂料中的分散性和杂化机理;结果表明,杂化后的纳米粒子改变了原来的结晶形态和粒径,在涂层中的分散性得到改善,改性后的纳米复合涂料能够降低室内的TVOC含量,甲醛降解率为70%,抗菌圈半径由原来0.75cm提高到2.3cm,比加入单一纳米粒子具有更优越的性能.     

Modification of electrostatic charge on inhaled carrier lactose particles by addition of fine particles

Triboelectrification affects particle adhesion and agglomeration and hence the formulation, manufacture, and use of dry powder inhaler (DPI) devices. Electrostatic charge measurement of two component mixes of spray-dried or crystalline lactose fine particles (< 10 microns) 0, 5, 10, 15, 20, and 30% w/w with spray-dried or crystalline lactose 63-90 microns, respectively, has been undertaken using a system incorporating pneumatic transport of the mixed powders to a stainless steel cyclone charging device. The magnitude of charge on the mixes was shown to decrease with increased fine particle content, and there was no significant difference in charge for each concentration between spray-dried and crystalline lactose. Both the variation of charge and powder adhesion to the cyclone surface increased with increase in fine particle content. The proportion of fine particles in carrier systems in DPIs may thus have an important role where triboelectrification is involved.     

Patterning of fine particles by means of supercritical CO2

A new method for positioning fine particles on surfaces has been developed. Supercritical CO₂-assisted printing (SCAP) was utilized to spray and deposit the prepared particles on solid substrates. By means of masks, regular arrays of the particles were successfully created in designed patterns. Typical size of the particles employed was in the range of submicrometers to micrometers. Supercritical CO₂ (sc-CO₂) acted as an effective dispersion and transportation medium in this process. Good dispersion state of the particles was achieved by stirring in sc-CO₂. Fabrications of fine patterns of solder particles and other ceramic powders on smooth plates were demonstrated. Under optimum operation conditions, fine structures of 30 μm in width can be formed in a minimal pitch of 60 μm. Ultra high yield of the patterning was obtained since the deposition rate could be as high as 100 μm per second. Main factors affecting the process were discussed. The research results indicate that the SCAP is a potential approach to the organization of fine particles into microstructures. Hopefully, it may find wide industrial applications where lithography is needed, such as solder printing in surface mounting technology for higher density electronics and thick film fabrication for miniature systems.     

Thermal fluctuation of fine ferromagnetic particles

Fine ferromagnetic particles jump spontaneously from one locally stable state to another; they surmount intervening energy bartiers with the aid of thermal agitation. A theory of this phenomenon has as its primary goal the calculation of time constants. The elements of such a theory are presented. The emphasis is on calculations that require only elementary methods and on results that are simple enough to be easily applicable. The reader is assumed to be acquainted with the basic properties of ferromagnetic materials but not necessarily with Brownian-motion theory, on which the present theory is based.     

Morphology of ultra fine iron particles

Variation in morphology of the silica thin film coated ultra fine goethite particles(length:140 nm, aspect ratio:11/1, surface area:95 m²/g, SiO2/Fe:3.4 wt%) in the process of decomposition and subsequent reduction was examined by means of gas adsorption and electron microscopy. Microporous hematite particles, prepared by decomposition of the silica-coated ultra fine goethite particles at 250°C in vacuo, were subjected to heat-treatment at 700°C in air to form the nonporous hematite particles without degradation of the acicular shape. The highly acicular and nonporous ultra fine iron particles(length:110 nm, aspect ratio:10/1, surface area: 80 m²/g) were obtained as a result of shrinkage of the particles in the reduction process of the nonporous hematite particles at 400°C in hydrogen gas. Coercivity of the ultra fine iron particles was 1660 Oe.     

Preparation of fine particles of carnegieite by a mist decomposition method

A mist of a hydrosol consisting of silica, alumina/NaAlO₂ and sodium hydroxide was produced by a supersonic atomization, and treated successively in three furnaces of different temperatures. The temperatures of the furnaces were adjusted for the evaporation of water, the dehydration and the crystallization of the mixed oxide, respectively. The spherical particles ( 0.5m) of carnegieite were found to be formed in a narrow composition range of the raw materials at temperatures of 650 to 900° C. The factors affecting the properties of the particles were investigated.     

Restraint of fatigue crack growth by wedge effects of fine particles

This paper presents some experimental results which demonstrate restraint of fatigue crack growth in an Al–Mg alloy by wedge effects of fine particles. Fatigue test specimens were machined from a JIS A5083P‐O Al–Mg alloy plate of 5 mm thickness and an EDM starter notch was introduced to each specimen. Three kinds of fine particles were prepared as the materials to be wedged into the fatigue cracks, i.e. magnetic particles and two kinds of alumina particles having different mean particle sizes of 47.3 μm and 15.2 μm. Particles of each kind were suspended in an oil to form a paste, which was applied on the specimen surface covering the notch zone prior to the fatigue tests. In order to make some fracture mechanics approaches, in situ observations of fatigue cracks were performed for the two cases using a CCD microscope, with a magnification of ×1000. The crack length and the crack opening displacement (COD) at the notch root, δ, were measured. First it was ensured by control tests that the wedge effect of the oil itself was negligible. Then it was found that the large size alumina particles were not effective in restraining crack growth because the paste was difficult to make due to the large particle size and the particles could not enter the cracks properly. However, both of the magnetic particles and the small size alumina particles effectively restrained crack growth, especially the latter which produced 143–350% increase in the lifetime to failure. From the in situ observations, in the case of the small size alumina particles, a pronounced retardation of crack growth was observed immediately after the crack length exceeded 0.4 mm, and this is considered to be due to the range of COD value, δ_max ? δ_min , being strongly affected by the wedge effects of the particles. The crack retardation effect continues almost through the entire lifetime if the alumina paste is re‐applied at specified intervals, while the effect is apparently lost after the crack length exceeds ～2 mm when such re‐painting is not continued. After the fatigue tests, some macro‐ and microfractographic analyses were performed using a CCD microscope, a SEM and an EPMA (electron probe microanalyser), in order to examine the mechanism of fatigue crack restraint by the wedge effects of the fine particles. From those analyses, it was reasoned that the fine particles that entered a fatigue crack are subjected to cyclic pressures between the crack faces and then form a kind of wedge which causes significant levels of crack closure that restrain crack growth.     

超音速微粒轰击45钢表面纳米化的研究

采用超音速微粒轰击技术(SFPB)对由铁素体和珠光体组成的45钢进行表面纳米化处理,在材料表面制备了纳米结构表层,利用X射线衍射、扫描电镜、透射电镜等分析技术研究了表面纳米结构层不同深度的微观组织结构特征.研究表明:经SFPB处理后,材料表层发生了严重的塑性变形,形成了由铁素体和渗碳体组成的纳米结构层;随着处理时间的增加纳米结构层的厚度由几微米增加到15 μm(晶粒尺寸＜100 nm);在材料的最表层形成了晶粒尺寸约15 nm的具有随机取向的等轴晶,纳米晶粒尺寸随着距表面距离的增加增大;在距表面约为15 μm处,存在平均晶粒尺寸约100 nm的等轴晶和具有相近尺寸的胞状结构;在约30 μm处,大量的高密度位错墙分别将铁素体相和珠光体相分割成尺寸在200～500 nm的胞状结构.分析表明45钢表面纳米化主要是位错运动的结果.