Prediction of Size Distribution of Particles Penetrating Dry Cyclone Separators

The efficiency of cyclones varies widely with the size of particles and complex mathematic formulations are used for predicting the collection efficiency of a single particle size. Numerical integration of the latter, in conjunction with the appropriate in each case input particle size distribution, or direct use of nomographs if lognormal input particle size distribution can be assumed, yields the overall efficiency. In either case, no information is available regarding the size distribution of the penetrating particles. As shown in this paper, lognormal input particle size distributions yield lognormal output particle size distributions. Based on this and on the analysis of functional relations, a set of nomographs is developed directly yielding the mean diameter and standard deviation of penetrating particles as a function of the input particle size distribution parameters and key cyclone design and operating conditions. The above set the stage for the rigorous computation of the size-specific emissions from cyclones and the overall and size-specific efficiencies of secondary control systems that may follow. This analysis is in line with current trends, which, on the basis of health considerations, place emphasis on the size-specific rather than on the overall particle emissions.     

Character of porosity of compact materials obtained from metalorganics

The possibility of obtaining highly porous (60–80% pores) materials by combining techniques of powder metallurgy with chemical-metallurgical processes of formation of nanodimensional activators of sintering during the thermal destruction of metalorganics is shown. It is noted that, irrespective of the composition of starting charges, the surface porosity of such materials is represented by pores <30 μm, the fraction of which does not exceed 1%. The basis (86–89%) is represented by pores <4 μm. The character of porosity inside the sintered articles is determined by the sizes and shape of the powderlike skeleton material introduced into the starting charge to prevent the outflow of metalorganics during thermal treatment. When using powders with highly developed particle surfaces as such, the character of the internal porosity is similar to the surface porosity. The combination of scale particles up to 100 μm in size and highly dispersed (<10 μm) particles promotes the formation of long porous channels (100–350 μm) 10–50 μm in width.     

Comparative Fractional Efficiency Predictions by Selected Cyclone Simulation Models

The recently introduced ambient air quality standards for fine particulates expand the use of available control system simulation models, from the prediction of total particulate matter removal efficiencies, to the prediction of PM2.5 and PM10 (particulate matter with diameters less than 2.5 and 10?μm) ones. In order to assess the suitability of cyclone simulation models for this task, the fractional efficiency predictions of six prominent models (Lapple, Leith and Licht, Dietz, Mothes and Loffler, Iozia and Leith, and Mothes and Loffler with the turbulent dispersion coefficient of Salcedo and Coelho) are compared for a number of “standard” cyclone design configurations under a wide range of cyclone diameters and pressure drops. The results reveal a significant discrepancy among model predictions, suggesting that at least some of the models considered are unsuitable for predicting size-specific (e.g., PM2.5 and PM10) cyclone efficiencies. They also show that the sensitivity of fractional efficiencies to changes in the configuration ratios, diameter, and gas pressure drop varies widely, and in some cases even in opposite directions, among models. The above-noted results demonstrate the need for a systematic model validation against credible and sufficiently extensive experimental data sets.     

细磨对矿粉特性和造球性能的影响

 为了研究细磨对矿粉特性和造球性能的影响,利用球磨机对某种粒度较粗的矿粉进行不同程度的细磨,然后按照不同的配比进行混合,制成11种不同粒度组成的矿粉试样,对11种矿粉进行物理性能测试和造球试验。结果表明,随着磨矿时间的延长,细磨后矿粉颗粒形貌变化不大,但细颗粒质量分数增多,矿粉的比表面积增加,毛细水质量分数增加,而分子水质量分数无明显变化规律。矿粉的比表面积与矿粉中细微颗粒（小于10 μm）的质量分数有很大关系。生球的落下强度由比表面积和粒度组成共同决定,当矿粉比表面积为1 500～2 500 cm2/g时,矿粉中大于76. 33和小于10 μm粒级的质量分数为10%～15%,有利于造球和生球落下强度的提高。     

Fabrication of high-alloy powders consisting of spherical particles from ultradispersed components

It is shown that powders of a model high alloy consisting of spherical particles 25–50 μm in size can be synthesized from a starting ultradispersed powder, which is made of a mixture of the alloy components and is fabricated by the magnesiothermal reduction of metal chlorides in the potassium chloride melt. The synthesis includes the stages of microgranulation of an ultradispersed powder, heat treatment of microgranules, classification of the microgranules with the separation of microgranule fraction of 25–50 μm, spheroidization of the separated fraction in a thermal plasma flow, and classification with the separation of a fraction of micro- and submicrometer-sized particles.     

Al2O3夹杂物在钢-渣界面处的运动特性及去除率

通过理论计算和分析,研究了夹杂物颗粒在钢-渣界面处夹杂物去除层内的运动特性及去除率。结果表明:在夹杂物去除层内,Al2O3夹杂物颗粒的布朗扩散上浮临界尺寸为1.33μm,直径小于临界尺寸的夹杂物颗粒很难上浮去除;布朗碰撞的优势区域主要是直径为2.5μm以下的夹杂物颗粒之间以及直径为2.5～5μm夹杂物颗粒与0.5μm以下的微小颗粒之间的碰撞;直径为20～150μm的夹杂物颗粒在钢-渣界面去除层中9min内很容易完全上浮去除,而直径小于10μm的夹杂物颗粒去除率很低且升高缓慢,是提高钢液洁净度的主要控制对象。     

Transformation of Chlorinated Methanes by Nanoscale Iron Particles

This paper examines the potential of using laboratory-synthesized nanoscale iron particles to transform chlorinated methanes. The iron particles have diameters on the order of 1–100 nm (0.001–0.1 μm). Palladized iron particles were prepared by depositing palladium (0.05–1% Pd by weight) on the surface of iron. Batch experiments were conducted to compare reactions of chlorinated methanes with palladized nanoscale iron, nanoscale iron, and commercial grade iron particles (～10 μm). Rapid transformations of tetrachloromethane (CT) and trichloromethane (CF) were achieved with the palladized nanoscale iron particles. Typically 0.1 mM CT or CF was reduced below detection limits within 1 h. Methane and dichloromethane (DCM) were the major end products. Yields of methane and DCM from CT were 52% and 23%, respectively. Little degradation of DCM was observed within 72 h. With the nanoscale iron and commercial-grade iron particles, much slower reactions of chlorinated methanes were observed. Kinetic analyses indicated that the surface area-normalized rate coefficients kSA of the nanoscale iron and commercial grade iron particles were one to two orders of magnitude lower than those of the palladized nanoscale iron.     

Analysis of softening alloys of the Al-Ni system containing particles of variable dispersity

Regularities of the deformation strengthening and softening of aluminum alloys containing second-phase Al₃Ni particles 0.3 to 2.2 μm in size with a volume fraction from 0.03 to 0.1 are investigated during cold deformation and subsequent annealing at 0.6t _m. It is shown that the largest hardness increment is observed for alloys with a maximal fraction of fine particles (d = 0.3 μm) after rolling deformation larger than 0.4. Fine particles prevent the development of crystallization upon true deformation up to 2.3, thereby effectively inhibiting softening. An increase in the particle size to 1.2–2.2 μm stimulates nucleation during recrystallization, substantially accelerating this process. For example, in order to ensure recrystallization uniformly over the entire sheet volume at d = 2.2 μm, cold deformation with ? = 0.4 is sufficient.     

钼镧合金表面FeCrAl涂层耐腐蚀性能

采用非平衡磁控溅射工艺在Mo–La合金表面沉积FeCrAl涂层,研究所制备涂层的耐腐蚀性及涂层的腐蚀机理。结果表明：FeCrAl涂层样品在360℃、18.6 MPa、纯水的高压釜中腐蚀72 h,平均腐蚀速率为3.8 mg·dm_?²,低于同条件下锆合金以及未沉积涂层的钼镧合金的腐蚀速率,且涂层中的Al与外界环境介质中的氧发生反应,在涂层表面形成致密的Al₂O₃薄膜,在一定程度上减缓了涂层的腐蚀速度,有效保护了基体材料。FeCrAl涂层样品在1200℃、0.1 MPa的高温水蒸气环境下腐蚀8 h,Al₂O₃氧化膜厚度在4.0μm左右,涂层维持保护效果,钼镧合金基体未暴露在腐蚀环境中;经淬火后,Al₂O₃氧化膜厚度减小至2.5μm左右,涂层依旧维持结构完整性,没有出现贯穿性脱落,满足Mo–La合金表面耐腐蚀性的使用要求。     

La0.9Sr0.1Ga0.8Mg0.2O3-δ电解质材料的合成及性能研究

对合成La0.9Sr0.1Ga0.8Mg0.2O3-δ(LSGM)电解质的制备过程做了TG-DTA分析,然后采用固相法合成LSGM电解质材料。利用XRD、粒度分析、交流阻抗谱等检测技术,对LSGM电解质结构及性能进行表征。XRD分析表明,在1 000℃烧结后,粉体开始形成钙钛矿结构,随着温度的升高,粉体中杂相含量越来越少,经1 000℃和1 450℃两次烧结后,形成了单一的钙钛矿结构相;粒度分析表明,合成电解质粉体的粒径较为合理;交流阻抗谱检测表明,烧结样品具有稳定的离子电导性能,在800℃时,电导率约为1.2S/m。     

Determination of fracture toughness and bridging tractions from crack-opening displacement measurements in particulate composites of diamond in zinc sulfide

The fracture toughness of zinc sulfide ceramic and a series of ZnS diamond particle composites was studied through measurements of crack opening displacement profiles. Five composites were fabricated using weight fractions of 10, 20 and 30% of 0–1 μm diamond particles, and 10 and 20% of 1–3 μm particles in a ZnS matrix. The cracks were grown using a novel specimen geometry and a loading technique that permitted stable crack growth even in small specimens. The fracture toughness of each material was calculated on the basis of the displacement profiles and the material properties, as opposed to the applied loads and the specimen geometry. The pure zinc sulfide material exhibited nearly ideal brittle behavior, and the toughness measurements agreed closely with other methods. The greatest toughening occurred in the 1–3 μm particle size composites, in which weak bridging tractions (⩽ 100 MPa) over a short distance along the crack (50–100 μm) could explain the reduced displacements near the crack tip. Even smaller size bridging zones (5–10 μm) may have been present in the 0–1 μm particle size composites, but elastic shielding alone can explain the observed toughening. The specimen geometry used here permitted toughness measurements using small specimens (< 5 mm) but is limited to materials having bridging zones that are less than about 250 μm.     

Structure and phase composition of composite pellets based on the ALTEK heat-resistance aluminum alloy with boron-containing filler

Composite pellets based on the ALTEK heat-resistant aluminum alloy (Al-Cu-Mn-Zr system) and reinforced with B₄C particles in a volume fraction of ～11% and 1–10 μm in size are produced by mechanical alloying. The pellet structure includes a significant amount of inclusions of the Al₁₅(Fe, Mn)₃Si₂ phase, which have a globular shape and an average size of about 2 μm. It is suggested that both the inclusions and B₄C can be considered a reinforcing filler.     

Dusting and fluidity of alumina with different physicochemical properties

The objects of investigation were metallurgical aluminas from different manufacturers and with different physicochemical properties varying in wide limits: the content of the fraction ?45 μ m was 4–60%, the losses during calcination were 0.5–1.2%, the content of the α phase was 2.5–23.0%, and the specific surface was 55–120 m²/g. The outflow time t _out of the aluminas was measured using funnels with standard (2.4 mm) and increased (4 and 5 mm) orifices; the outflow time was 2–20 min. The correlations for the values of t _out for the funnels with mentioned orifices were obtained. The outflow time decreased as the content of the fraction ?45 μ m decreased and the water content in alumina increased. The dusting factors (DF) of aluminas were measured with the help of the developed dust counter, and the variation range was 0.5–8.0 mg/g. The dusting factor increased as the content of the fraction ?45 μm and water content in aluminum increased. The main factor determining t _out and DF is the granulometric composition of alumina. The effect of the form of alumina particles and moisture content in alumina on the t _out and DF is established. The mechanism explaining the interrelation between the moisture and these values is suggested.     

Creep and microstructure of electrical discharge machinable Si3N4 composites

The compression creep behaviour of silicon nitride sintered with the aid of Y₂O₃ and Al₂O₃ and containing TiN particles was studied between 1260 and 1340°C at stresses ranging from 100 to 300 MPa. The volume fraction Φ of TiN particles was varied from 0 to about 40 vol % and two particle sizes: 1 μm and 2.5 μm were studied. The dominant creep mechanism of the matrix was viscous creep (n = 1) up to 1340°C and 200 MPa. The effect of the TiN addition on the creep behaviour was marked by a decrease of the creep strength with increasing volume fraction and decreasing particle size of TiN. In the same way, the steady state creep rate increased as the ratio Φ/d. In the microstructure, cavities and microcracks along particle/matrix interfaces show that a cavitational mechanism develop from the particles in the composite.     

球磨时间对钨粉粒度分布及形貌影响

通过改变球磨时间,获得不同粒度分布的钨粉颗粒,分析球磨时间对钨粉粒度分布和形貌特征的影响,提高粒度分布在目标区间（5～11 μm）的钨粉颗粒体积分数。结果表明,球磨的前2 h对原料中大颗粒钨粉的影响较大,钨粉颗粒最大粒径由134 μm迅速下降到20 μm左右。随着球磨时间的增加,钨粉粒度分布指标减缓下降,除粒径变小外,颗粒形貌基本无变化,但是在球磨10 h后开始出现团聚现象。综合分析可知,球磨时间的改变对钨粉粒度分布指标影响较大,球磨时间为8 h时,可获得粒度分布最窄的钨粉颗粒,在目标区间的钨粉颗粒体积分数达到75%。     

Mechanical alloying of Cu–SiC materials prepared with utilisation of copper waste chips

Abstract

The aim of this work was to study the structure and particle size of copper based composite materials reinforced with a high content (15–35 wt-%) of silicon carbide and prepared by mechanical alloying in the high energy planetary mill. Raw materials consisted of grinded copper chips with a size of <5000 μm and reinforcing particles with an initial size of 10 μm. Duration of milling was 20–80 min. It was shown that the formation of Cu–(15–25 wt-%)SiC composites occurred successfully. With an increase in the silicon carbide content of above 25 wt-% (48 vol.-%), the efficiency of mechanical alloying was decreased. The average size of composite particles was ～20 μm.     

应用格子 Boltzmann方法直接数值模拟研究钢中夹杂物上浮及碰撞行为

采用格子Boltzmann方法对钢液中夹杂物上浮及上浮过程中的碰撞行为进行直接数值模拟研究.结果表明,不同尺寸夹杂物颗粒上浮速度的模拟结果和理论值基本一致,表明本文所采用的数值算法能够精确有效地对钢液中固相夹杂物颗粒运动行为进行研究.当钢液中直径为80μm的夹杂物颗粒位于直径为40μm的下方并一起上浮时,直径为80μm的夹杂物颗粒会逐渐追赶上直径为40μm的夹杂物颗粒并发生碰撞形成大尺寸凝聚体,凝聚体的上浮速度显著大于二者单独上浮时的上浮速度.对于直径为40μm的夹杂物来说,形成凝聚体后的上浮速度比单独上浮时的上浮速度增加300%.实际炼钢过程中,采取必要的措施增加夹杂物颗粒之间上浮过程中的碰撞凝聚,对于提高夹杂物颗粒的上浮速度,尤其是小尺寸夹杂上浮去除速度,提高钢液的洁净度具有重要的意义.      

高温时H13钢中初生碳氮化物的分解研究

利用光学显微镜、扫描电镜和电子探针研究了H13钢中初生碳氮化物高温分解时的形貌、尺寸、成分变化规律.原始初生碳氮化物主要为10~30 μm的长条状（V_x，Mo_1-x）（C_y，N_1-y）及少量方形的（Ti_x，V_1-x）（C_y，N_1-y）.在1200℃保温2.5 h后碳氮化物边缘变为凹凸不平的锯齿状，然后形成细小的分解颗粒，10 h后碳氮化物平均长度减小为12.9 μm，主要为（Ti_x，V_1-x）（C_y，N_1-y）.当经过1250℃×5 h保温后87%的碳氮化物发生分解，（V_x，Mo_1-x）（C_y，N_1-y）溶解消失，碳氮化物长度在20 μm以下，当保温时间延长到10 h后碳氮化物长度均在10 μm以下，70%为方形并且93%分解形成细小颗粒，未分解的碳氮化物为（Ti_x，V_1-x）（C_y，N_1-y）.电子探针分析（Ti_x，V_1-x）（C_y，N_1-y）的分解与Fe元素扩散有关，高温时Fe在（Ti_x，V_1-x）（C_y，N_1-y）中含量逐渐增加而Ti、V减少，优先在边部曲率半径较小部位或缺陷处分解，形成0.1~1 μm的细小分解颗粒，并由外向内以区域溶解方式使原始碳氮化物逐渐消失.双亚点阵模型分析两种碳氮化物的平衡溶解温度和组成有关，试样中大部分（Ti_x，V_1-x）（C_y，N_1-y）平衡溶解温度在1200~1246℃之间，与实验吻合较好.      

Crystallization in Polyamide 6/Polysulfone Blends: Effect of Polysulfone Particle Size

By reactive blending of polyamide 6 (PA) with polysulfone (PSU) using a gram-scale mixer (Mini-Max Molder), we prepared a series of PA/PSU (80/20 wt.ratio) with various diameters of PSU particles: 90 nm by using phthalic anhydride-terminated PSU (PSU-PhAH), 0.2 μm by carboxylic acid-grafted PSU (PSU-COOH), and 1.0 μm by nonreactive PSU (nf-PSU). Isothermal crystallization was carried out at 200 degreesC. Light scattering studies showed that spherulites in the blends can grow to more than 10 μm in diameter, as in the case of neat PA. It suggests that crystal growth in the radial direction can be achieved by circumventing the PSU obstacles; i.e., it does not matter how big or small they are in the range of 90 nm to 1 μm. The smaller the PSU particles, the slower was the overall rate of crystallization. The slower rate may be caused by the higher population of brush PA chains attached to PSU particles as block or graft chains, since the brushes may be hard to organize into crystal lamellae, compared with free chains. The blends showed rather broad wide-angle X-ray diffraction profiles. The smaller the PSU particles, the broader was the profile. The scattering from the particles themselves should appear only at extremely low angles (<0.1 degrees) and hardly affects the wide-angle X-ray profiles so that the results may imply that the presence of smaller PSU particles renders the less perfection of the PA crystal. This may be caused also by the higher population of brush chains. Note that the brush chains are formed only in the reactive systems and the population may be higher in the smaller particle systems. Even for the blend with smallest particle size, a small-angle X-ray scattering peak appeared at a magnitude of scattering vector of approximately 0.8 nm-1, suggesting the evolution of interlamellar spacing of 8.7 nm. However, the scattering profile was much broader than that of neat PA. It implies a less ordered lamellar stacking in the blend.     

Physical Characteristics of Urban Roadway Solids Transported during Rain Events

Urban stormwater runoff from paved surfaces transports a wide gradation of solids ranging in size from smaller than 1 μm to greater than 10,000 μm. This study measured physical characteristics of solids transported in lateral pavement sheet flow from a heavily traveled roadway in Cincinnati. Particles smaller than 25 μm were counted and sized using a light obscuration particle counter. Particles larger than 25 μm were separated mechanically to generate particle size distributions. Solids in the 2–8 μm range generated the largest counts and were rapidly washed from the pavement. LPSF rate and duration controlled yield and size of transported solids. Particle transport was mass limited during long duration high intensity events, but flow limited during intermittent low intensity events with high traffic. Particle counts exhibited a first flush from the pavement. Specific surface area generally increased with decreasing particle size, but measured values deviated from the monotonic pattern expected for spherical particles. Particles 425 to 850 μm in size contributed the greatest total surface area. Results provide guidance for assessment of the impact of urban runoff water quality and for design of in situ treatment strategies.