激光粒度法测试结果与库尔特法、沉降法的比较

分别采用马尔文激光粒度仪、库尔特颗粒粒度计数仪、岛津离心粒度分析仪对玻璃微珠、聚苯乙烯微球、钨粉、氧化铝微粉、二氧化硅微粉等6种不同类型的粉末进行了测试,并对几种测试方法所得的结果进行比较。结果表明:激光法测试的结果重复性较好;对于粒径范围窄的球形粉体,几种仪器测得的中位径具有可比性,粒度分布曲线也相似;对于粒径范围较宽的球形粉体和不规则形状粉体,测得的中位径和粒度分布曲线一般没有可比性。     

Segregation due to particle shape of a granular mixture in a slowly rotating tumbler

Using DEM particle simulations we consider segregation of a binary granular particle mixture in a slowly rotating cylindrical tumbler where the particles differ only in their shape—spherical versus more cubical particles. We find that the more cubical particles segregate to the inner core of the particle bed while the spherical particles segregate to the curved walls of the tumbler. The main mechanism for this segregation is different energy dissipation rates for the different particle shape types when avalanching down along the free surface. The cubical particles, due to their sharper corners, dissipate energy much faster than the spherical particles. This results in spherical particles reaching the bottom end of the sloped, free surface which are then transported around the cylinder adjacent to the cylinder wall, as rigid body motion. In contrast to size or density segregation, the segregation due to shape is much weaker and takes longer to reach its equilibrium or steady state. In addition, the segregation occurs along the top surface rather than through the top surface (as occurs for size and density segregation). In general, in situations where two particles differ in their ease of flow (viz flowability) the more rapidly flowing particle will segregate to the base of the free surface (which in the case of the tumbler results in spherical particles near the periphery) and the more slowly flowing particle will segregate underneath.     

由 Mie 散射光强反演颗粒粒度分布的一种改进正则化法

基于Mie散射的激光粒度仪广泛地应用在颗粒粒度测量中,其中由光强分布演算出粒度分布的计算方法一直是关注的热点。此反演问题属于第一类Fredholm算子方程,具有不适定性,难以得出准确的稳定解,需要用高效的数值算法。本文提出一种应用于该类仪器颗粒粒度分布反演问题的改进正则化法,采用广义交叉验证法(GCV)来选择正则参数,并引入松弛技术,将迭代值加工成一种松弛值以改善精度,得出了稳定的正则拟解(近似解)。经标准颗粒的验证和计算机模拟证实,此算法是可行和有效的。     

Size distribution measurement of floating particles in the Allen region by a buoyancy weighing-bar method

The particle size distributions of spherical or cylindrical solid particles in the Allen region were measured using a buoyancy weighing-bar method. The particle size distribution obtained in the buoyancy weighing-bar method agrees with those measured by a laser diffraction/scattering method and a sieving method. The present study demonstrates that a buoyancy weighing-bar method is suitable for measuring the particle size distribution of a floating solid in the Allen region.     

Heterogeneous and homogenized models for predicting the indentation response of particle reinforced metal matrix composites

In this study, three-dimensional heterogeneous and homogenized finite element models are used to predict the indentation response of particle reinforced metal matrix composites (PRMMCs). The matrix is assumed to have elasto-plastic behavior whereas the particles (uniform in size and spherical in shape) are assumed to be harder than the matrix, and possess linear elastic behavior. The particles (25 % by volume) are randomly distributed in the metal matrix. Two modeling approaches are used. In the first approach, the PRMMC is fully replaced by an equivalent homogenous material, and its material properties are obtained through homogenization using representative volume element approach under periodic boundary conditions. In second approach, a small cubical volume under the indenter is modeled as heterogeneous material with randomly distributed particles, whereas the remaining domain is assigned equivalent material properties obtained through homogenization. The elastic material properties obtained through simulations are found within Hashin–Shtrikman bounds. A suitable size cubical volume consisting of heterogeneities under the indenter is established by considering different cubical volumes so as to capture the actual indentation response. The simulations are also carried out for different particle sizes to establish a suitable particle size. These simulations show that the second modeling approach yields harder indentation response as compared to first modeling approach due to the local particle concentration under the indenter.     

利用四氯化硅制备二氧化硅粉体的研究

以多晶硅副产物四氯化硅和硅酸钠为硅源,以低浓度的非离子表面活性剂聚乙二醇和无水乙醇为添加剂成功合成了二氧化硅粉体。讨论了硅酸钠浓度、反应温度和表面活性剂的加入对二氧化硅颗粒粒径和形貌的影响。利用透射电子显微镜、扫描电子显微镜、Fourier红外光谱仪、X射线粉末衍射仪、激光粒度分析仪等测试工具对所制备的二氧化硅的结构、粒径、表观形貌进行了测试与表征。结果表明：在最佳试验条件下,可制得平均粒径为150nm的二氧化硅粉体;非离子表面活性剂的加入可使二氧化硅颗粒分散均匀;二氧化硅颗粒粒径随硅酸钠浓度的增大而增大,故控制硅酸钠的浓度是本实验的关键。     

Particle shape effects on particle size measurement for crushed waste glass

Recently, narrow particle size distributions, as measured by sieve analysis, of crushed waste glass were used as a replacement for Portland cement in concrete. Their chemical reactivity was successfully studied as a function of this measure of particle size. Differences between sieve analysis and laser diffraction measures of particle size prompted this current re-analysis. Extremely careful sieving was used to divide the crushed waste glass particles into 0–25 μm, 25–38 μm, and 63–75 μm sieve size ranges, but laser diffraction did not agree with these particle size cutoffs. We use these same materials to try and understand the discrepancies between particle size as measured by laser diffraction and sieve analysis by using X-ray computed tomography followed by spherical harmonic analysis to measure the three-dimensional particle shape and size, as well as the length (L), width (W), and thickness (T) of each particle. We show how laser diffraction and X-ray CT results, along with sieve analyses, can be quantitatively related for these crushed waste glass particles in the approximate size ranges considered. In contrast to previous speculation, the particle width W does not have to correspond closely to the sieve opening – the correspondence depends on overall particle shape. In addition, we demonstrate how many particles are needed to analyze in order to achieve stable averages and distributions of the L/W, W/T, and L/T aspect ratios, which approximately define particle shape. These results have implications for how particle size is measured and interpreted in the cement and concrete and other industries.     

A combined physical and DEM modelling approach to investigate particle shape effects on load movement in tumbling mills

The discrete element method (DEM) which is used to simulate granular flows often assumes spherical shape for particles. This assumption is legitimized by the added complexity of non-spherical shape representation, contact detection and computational cost. In this work, the difference between the dynamics of non-spherical and spherical particles was studied in detail by a combined physical and DEM modeling approach. An in-house developed DEM software called KMPC_DEM©, which was coded to handle non-spherical particles, was used to simulate the behavior of particles. To calibrate the model parameters, a model tumbling mill (100 cm diameter and 10.8 cm length) with one transparent end was used which made accurate photography possible. The tests were performed at filling of 20% and mill speed of 85% of critical speed with steel balls and wood cubes. In the simulation, each cubical particle was represented with clusters of spheres (with identical size) by particle packing algorithm for contact detection and contact-force calculation. Comparison of the simulation and experimental results showed that the difference between the measured and predicted impact toe, shoulder angle and bulk toe angle were 3, 4 and 5°, respectively. The significant change in the charge movement and structure on account of non-spherical particles was reflected in the amount of in-flight charge, and positions of shoulder, impact toe and bulk toe. It found that there was a 17% difference in the amount of in-flight of charge between cubical and spherical particles. The marked difference was attributed to higher interlocking of non-spherical particles in comparison to spherical balls. The results showed that cubical particles participated 5% more in the high energy impact action compared to that of the spherical particles. The simulation computation time increased by 35 times when the shape of particles changed from spherical to cubical.     

NiO包覆Ni纳米颗粒的制备及其氧化特性研究

通过对直流电弧等离子体制备的Ni纳米颗粒钝化处理得到NiO包覆Ni纳米颗粒。并对试样的组成成分、形貌、晶体结构、粒度和氧化特性采用高分辨透射电子显微镜(HRTEM)、X射线衍射(XRD)、透射电子显微镜(TEM)和选区电子衍射(SAED)、热重和差示扫描量热分析仪(TGA/DSC)等手段进行分析。结果表明:经过表面钝化处理的NiO包覆Ni纳米颗粒具有明显的核-壳结构,内核为纳米Ni,外壳为NiO氧化物。颗粒呈球形,粒度均匀,分散性良好,粒径分布在20~70nm范围内,平均粒径为44nm,壳层氧化膜的厚度为5~8nm。壳核结构防止了纳米Ni颗粒的进一步氧化和团聚。     

Sizes influences of weighing bar and vessel in the buoyancy weighing-bar method on floating particle size distribution measurements

To evaluate the influences of particle migration lengths as well as the sizes of the weighing bar and vessel on the particle size distribution measured by the buoyancy weighing-bar method, we experimentally measured the size distribution of hollow glass beads as floating particles. The buoyancy weighing-bar method, microscopy, and laser diffraction/scattering method give similar particle size distributions. The variation coefficient of the buoyancy weighing-bar method is close to the value determined by the laser diffraction/scattering method. Moreover, the accuracy of the buoyancy weighing-bar method is equal to that of the laser diffraction/scattering method. For vessels with identical sizes, the particle sizes measured by the buoyancy weighing-bar method increase when the weighing bar is too thick or too thin. Additionally, the influence of the weighing bar length on the particle size distribution is not confirmed in the case of the hollow glass beads. Thus, to effectively employ the buoyancy weighing-bar method, the sectional area ratio of the rod/vessel must be 0.02–0.2.     

氟化石墨粒度测试分散条件优化

采用激光粒度分析仪,对氟化石墨样品的粒度及粒度分布进行测试研究,获得测试样品最佳分散条件。结果表明:采用质量分数为5%的乳化剂OP-10的水溶液作为氟化石墨的分散剂,超声振荡分散时间为3 min,悬浮液质量浓度为46.67～53.33 mg/L,可使样品粒度分布重现性好,由此表明悬浮体系具有良好的稳定状态。     

Unfolding Particle Size Distributions

This paper treats the unfolding problem of estimating the density distribution of particles dispersed in a three-dimensional specimen. A general framework is set in terms of a probabilistic model for the distribution of a discrete number of particle sizes with prescribed shapes which are sampled and observed by processes capable of being modeled. The general formulation allows density estimates and standard deviation estimates for each particle size in the distribution to be made with data from observational processes that may distort or truncate the sampled information. The method is related to the earlier works on unfolding or estimating the density distribution of spherical particles sectioned by planar probes. The method is also used to develop a more accurate estimate for the density distribution of spherical voids where the observational process is the indirect microscopy of a replicated surface.     

聚氨酯预聚体分散体胶粒的形成与扩链

以聚丙二醇(PPG)、异佛尔酮二异氰酸酯(IPDI)、二羟甲基丙酸(DMPA)、乙二胺(EDA)为原料合成了固含量40%的聚氨酯分散体。采用激光粒度分析仪测试了预聚体分散体胶粒形成和扩链过程中的平均粒径和粒径分布,透射电镜(TEM)表征了胶粒的形态结构。结果表明,预聚体分散体中可能存在理想胶粒、活性胶粒、可再分散胶粒,理想胶粒中的NCO处于胶粒内部,活性胶粒中的NCO处于胶粒的内部和表面;分散和扩链反应中活性胶粒之间的反应使胶粒粗化和呈双峰分布;提高预聚体nNCO/nOH、COOH%,预聚体分散体中活性胶粒增加;TEM显示聚氨酯分散体胶粒主要呈球形,部分呈不规则形态。     

Estimation of particle size distribution from cross-sectional particle diameter on the cutting plane

To control highly functional sintered materials, it is necessary to evaluate particle size segregation within materials. In the present study, a new method for estimating particle size distribution is proposed; this method considers the occurrence probability of the cutting diameter. The proper particle size distribution in a particle bed was estimated by calculating a matrix consisting of the occurrence probability and the distribution of particle diameters measured on a cutting plane. The estimated particle size distribution was smoothed using the Phillips–Twomey method. A cavity-filling simulation was carried out to verify the validity of the proposed method using the Distinct Element Method. The particle size distribution estimated by this method correlated well with the actual particle size distribution. The effect of particle size distributions with various geometrical standard deviations on the accuracy of estimated values was also investigated. The accuracy increased as the geometric standard deviation increased, and there was an optimum particle size bin number for a specific particle distribution. It was found that a large bin number and a large number of measured particles were required to obtain a higher accuracy for narrow size distributions.     

激光粒度仪颗粒联测的结果与评价

为了解不同激光粒度仪的硬件、软件等方面差异对粒度测量结果的影响,用4种颗粒形状不同的粉末在不同公司生产的激光粒度仪上进行测试。结果表明:激光粒度仪测试结果重复性很好;对于球形粉末和形状较规则的粉末,大部分激光粒度仪测得的中位径值之间可以比较;而粒径范围较宽和不规则形状粉末,个别仪器测量的中位径值有差异。     

Combination of Different Size Distributions for Mineral Particles by Applying Experimentally Determined Apparent Mean Shape Factor

As is well known, the behavior of systems of fine particles is strongly dependent on the size of the individual particles, and the size effects become increasingly important as the particles become progressively smaller. This study covers two different size analysis techniques, sieving and laser diffraction measurement, and constructs whole size distribution for different mill (ball and rod) products of some industrial minerals: barite and quartz minerals. A smooth overlap of corrected laser diffraction size distribution and sieve size distribution was obtained by applying the particle size with the apparent mean shape factor shifting to the right side of the curve for the rod-milled barite and ball- and rod-milled quartz. The apparent mean shape factors determined from the corrected particle size distributions were found to be 1.02 and 1.39 for ball- and rod-milled barite and 1.29 and 1.25 for ball- and rod-milled quartz, respectively. The results indicate that the ball-milled products of barite mineral have more regular (rounder in shape) particles than those of rod-milled barite, but there are not significant differences between the shape factors of ball- and rod-milled products of quartz mineral, i.e., both of them have irregular particles that deviate from spherical shape, as evident from the SEM pictures taken.     

Combination of Different Size Distributions for Mineral Particles by Applying Experimentally Determined Apparent Mean Shape Factor

As is well known, the behavior of systems of fine particles is strongly dependent on the size of the individual particles, and the size effects become increasingly important as the particles become progressively smaller. This study covers two different size analysis techniques, sieving and laser diffraction measurement, and constructs whole size distribution for different mill (ball and rod) products of some industrial minerals: barite and quartz minerals. A smooth overlap of corrected laser diffraction size distribution and sieve size distribution was obtained by applying the particle size with the apparent mean shape factor shifting to the right side of the curve for the rod-milled barite and ball- and rod-milled quartz. The apparent mean shape factors determined from the corrected particle size distributions were found to be 1.02 and 1.39 for ball- and rod-milled barite and 1.29 and 1.25 for ball- and rod-milled quartz, respectively. The results indicate that the ball-milled products of barite mineral have more regular (rounder in shape) particles than those of rod-milled barite, but there are not significant differences between the shape factors of ball- and rod-milled products of quartz mineral, i.e., both of them have irregular particles that deviate from spherical shape, as evident from the SEM pictures taken.     

Real-time shape-based particle separation and detailed in situ particle shape characterization

Particle shape is an important attribute in determining particle properties and behavior, but it is difficult to control and characterize. We present a new portable system that offers, for the first time, the ability to separate particles with different shapes and characterize their chemical and physical properties, including their dynamic shape factors (DSFs) in the transition and free-molecular regimes, with high precision, in situ, and in real-time. The system uses an aerosol particle mass analyzer (APM) to classify particles of one mass-to-charge ratio, transporting them to a differential mobility analyzer (DMA) that is tuned to select particles of one charge, mobility diameter, and for particles with one density, one shape. These uniform particles are then ready for use and/or characterization by any application or analytical tool. We combine the APM and DMA with our single-particle mass spectrometer, SPLAT II, to form the ADS and demonstrate its utility to measure individual particle compositions, vacuum aerodynamic diameters, and particle DSFs in two flow regimes for each selected shape. We applied the ADS to the characterization of aspherical ammonium sulfate and NaCl particles, demonstrating that both have a wide distribution of particle shapes with DSFs from approximately 1 to 1.5.     

Particle morphology and size distribution of plasma processed aluminium powder

Commercially available aluminium powder has been processed in a thermal plasma jet. The processed powder has been characterized by scanning electron microscopy (SEM) for particle size and morphology. Particle size distribution has been determined by laser scattering technique. Results show that, in contrast to the irregular shapes of the particles of the raw material, majority of the processed powder particles bear spherical or near-spherical morphology. The spherical morphology without sharp edges and corners and particle size distribution in a narrow range ensures free flow of the powder through the powder feed lines, and better spray efficiency, making it ideal for thermal spray applications. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Perturbed Talbot patterns for the measurement of low particle concentrations in fluids

Behind periodic amplitude or phase objects, the object transmittance is repeated at the so-called Talbot distances. In these planes perpendicular to the propagation direction, Talbot self-images are formed. In the case of plane wave illumination, the distances between the self-images are equally spaced. A periodic pattern called optical carpet or Talbot carpet is formed along the propagation direction. We show theoretically how the presence of spherical particles (10 to 100 μm in diameter) behind gratings of 20 and 50 μm period affects the formation of Talbot carpets and Talbot self-images at 633 nm illumination wavelength. The scattering of the particles is modeled by the Fresnel diffraction of its geometrical shadow. We analytically calculate the interference of the diffraction orders of rectangular and sinusoidal amplitude gratings disturbed by the presence of particles. To verify our model, we present measurements of Talbot carpets perturbed with both opaque disks and transparent spheres, and discuss the effects for various size parameters. We present an approach to simulate the movement of particles within the Talbot pattern in real time. We simulate and measure axial and lateral particle movements within a probe volume and evaluate the effect on the signal formation in a Talbot interferometric setup. We evaluate the best system parameters in terms of grating period and particle-detector-distance for a prospective measuring setup to determine characteristics of flowing suspensions, such as particle volume concentration or particle size distribution.