Measurement of grain size and size distribution in engineering materials

Abstract

Methods to characterise grain size distribution in engineering materials are evaluated, and compared with measurements on two representative materials, an equiaxed aluminium alloy and a heterogeneous nickel alloy. Computer simulations from a model tetrakaidecahedron structure have also been obtained using a personal computer program to rotate and section the model randomly, generating distribution data on section area and intercept lengths. Comparisons have been made between the model distribution data and intercept distribution data from the material microstructures.

It is recommended that size distributions of area plotted against size (intercept) or normalised size provide an effective method for discriminating between different grain size distributions. An estimate of area can be used indirectly by squaring intercept values rather than making direct measurements of grain areas.     

Grain size statistics

A method for the computation of spatial grain size distributions from intercept data based on a tetrakaidecahedron grain model is developed. The necessary inverse matrix is presented. The method is applied to a range of metallic and ceramic specimens. The derived distributions are analysed to show that they are not necessarily log-normal. Statistical techniques are applied to determine the minimum sample sizes and these are shown to increase as the distributions become more dispersed. The constant relating the average grain size to the average intercept length is also shown to be sensitive to the grain size distribution.     

Diffusion size effect

On the basis of the fact that the mean square displacement of atoms in the vicinity of the surface is higher than that in the bulk, a thin film diffusion size effect is introduced. In films of the order of 100 Å thick it leads to a marked increase in the diffusivity as the film thickness decreases. The size effect introduced is used to explain experimental data on the high diffusivity in thin films. The approach developed should also be taken into account when consideration is given to other thermally activated processes in thin films as well as in the vicinity of free surfaces, interfaces and grain boundaries (segregation, vacancy distribution and migration to the surface, phase formation etc.).     

From pore size distribution to an equivalent pore size of cement mortar

An experimental and theoretical study has been performed with the aim of quantifying pore size distribution curves and correlating them with water and oxygen permeability. Twenty mortars have been investigated which contained Portland cement, blast-furnace slag cement and silica fume as a binder. Admixtures have been used as well. The water-cement ratio varied between 0.4 and 0.75 and two curing conditions were applied. By the use of mercury intrusion porosimetry, the pore size distribution was determined. Water and oxygen permeability have been measured in the steady state. Equivalent pore sizes have been calculated which quantify the pore size distribution by a single number. This number is not a constant but depends on the physical transport mechanism. It is shown that equivalent pore size and porosity together are sufficient to predict the physical properties with an acceptable accuracy.     

Particle size measurement of standard reference particle candidates with improved size measurement devices

In order to prepare standard reference particles, experimental and theoretical studies have been conducted on particle size measurement of two kinds of spherical glass beads. The sheath flow- type electrical sensing zone method and the revised sedimentation balance method were used for the measurement. The data were compared with those obtained by the microscopic method with a sample size greater than 10 000. The particle size distributions obtained by use of the sheath flow- type electrical sensing zone method and microscopic method are nearly equal for the two kinds of glass beads. However, deviations of less than 5% were observed between the improved sedimentation balance and microscopic methods. The experimental data of the microscopic method are within the 95% reliability region of the sheath flow-type electrical sensing zone method.     

Primary particle size and agglomerate size effects of amorphous silica in ultra-high performance concrete

Silica fume is widely used in ultra-high performance concrete (UHPC). However, it is a by-product in the industrial silicon production and therefore far from an optimized additive. Silica fume improves the compressive strength, but its detailed reaction mechanisms in concretes with low water/cement ratios are not yet fully understood. This study focuses on the influence of primary particle sizes and sizes of agglomerates of different amorphous silicas in UHPC. As a reference system, wet-chemically synthesized silica was used with very high purity, defined particle sizes, narrow primary particle size distributions and controllable agglomerate sizes. The obtained data were compared to silica fume. The results indicate that non-agglomerated silica particles produce the highest strength after 7 d, but a clear dependence on primary particle sizes, as suggested by calculations of packing density, was not confirmed. UHPC may be improved by incorporating an ameliorated dispersion of silica e.g. through commercial silica sols.     

骨料粒径对混凝土动态拉伸强度及尺寸效应影响分析

骨料粒径是影响混凝土力学性能及破坏机理的重要因素。从细观角度出发,将混凝土看作由骨料颗粒、砂浆基质及界面过渡区组成的三相复合材料,考虑细观组分的应变率效应,建立了混凝土动态拉伸破坏行为研究的细观力学分析模型,模拟研究了不同骨料粒径下混凝土动态拉伸破坏行为,并揭示了动态拉伸强度的尺寸效应规律。研究表明:低应变率下骨料不发生破坏,骨料粒径对混凝土动态拉伸破坏模式及拉伸强度影响显著,且拉伸强度的尺寸效应随骨料粒径的减小而削弱;高应变率下裂缝将贯穿骨料,骨料粒径的大小对混凝土动态拉伸强度及尺寸效应影响可忽略。最后,结合应变率效应的影响机制,建立了混凝土拉伸强度的"静动态统一"尺寸效应理论公式,该公式可以较好描述各骨料粒径下混凝土动态拉伸强度与试件尺寸的定量关系。     

Effect of ultrasound radiation on the size and size distribution of synthesized copper particles

The effect of ultrasound radiation on the size and size distribution of synthesized copper particles was investigated under various concentrations of ethylene glycol (E.G.) as a capping agent. Monodispersed copper particles were produced by the reduction of an aqueous copper (II) sulfate solution at the presence of hydrazine monohydrate. X-ray diffraction and scanning electron microscopy analysis revealed that the morphology, size, and size distribution of produced particles were influenced by the reducing agent injection rate, capping agent concentration, and sonication. Increasing the injection rate of reducing agent to an amount higher than a critical value decreases the size of copper particles and also converts the monodispersed particles to polydispersed particles. Results of using a sonifier at the reduction stage revealed that finer monodispersed copper particles can be achieved at higher injection rates related to the critical value. Increasing the concentration of E.G. as a capping agent decreases the size of copper particles, while applying ultrasound radiation along with increasing the concentration of E.G. increases the size of copper particles. Morphology of particles varies by the concentration and type of the capping agent. Higher reducing agent injection rates and the application of a sonifier at the instance of reduction result in smaller spherical particles at various capping agent concentrations.     

Influence of particle size and particle size distribution on MICA filled nylon 6 composite

Particulate reinforced thermoplastic composites are designed to improve the properties and to lower the overall cost of engineering plastics. In this study the effects of particle size and particle size distribution on the properties of mica filled nylon-6 was investigated. Composites of nylon-6 with varying concentrations (viz. 5 to 40 wt%) of mica were prepared by twin screw extrusion. The composite showed improved mechanical, thermal as well dielectric properties on addition of filler.     

Particle size determination of a three-component suspension using a laser-scattering particle size distribution analyzer

In this study, a rapid and accurate particle size determination method using a light-scattering particle size analyzer was developed to measure the particle size and size distribution of a suspension containing three solid components: clotrimazole, triamcinolone, and sarafloxacin, which have different refractive indices. To ensure that data represent the size distribution of the primary particles of the suspension, the optimal sonication prior to and during measurement was determined. It was found that the results obtained using the average relative refractive index (RRI) of the three components agreed with the results obtained using three individual RRIs. In addition, the results from two analysts demonstrated good reproducibility of this method. The size distribution data of the suspension were also compared to those of the bulk drugs. The results showed that the median particle size of this three-component suspension is relatively close to that of clotrimazole, which accounts for 80% of solid particles in the suspension. Furthermore, the results obtained using the light-scattering technique were comparable to those obtained using a polarized light microscope equipped with an image analyzer, indicating acceptable accuracy of this technique.     

Influence of particle size and particle size distribution on toughening mechanisms in rubber-modified epoxies

The principal toughening mechanism of a substantially toughened, rubber-modified epoxy has again been shown to involve internal cavitation of the rubber particles and the subsequent formation of shear bands. Additional evidence supporting this sequence of events which provides a significant amount of toughness enhancement, is presented. However, in addition to this well-known mechanism, more subtle toughening mechanisms have been found in this work. Evidence for such mechanisms as crack deflection and particle bridging is shown under certain circumstances in rubber-modified epoxies. The occurrence of these toughening mechanisms appears to have a particle size dependence. Relatively large particles provide only a modest increase in fracture toughness by a particle bridging/crack deflection mechanism. In contrast, smaller particles provide a significant increase in toughness by cavitation-induced shear banding. A critical, minimum diameter for particles which act as bridging particles exists and this critical diameter appears to scale with the properties of the neat epoxy. Bimodal mixtures of epoxies containing small and large particles are also examined and no synergistic effects are observed.