The correlation between the strength factor and the true tensile strength of agglomerate spheres

Spheres were produced from an iron-ore concentrate by balling and subsequent shaping, and cylinders were cut from these spheres. Experimental data are presented, correlating the factor L/D² for the spheres with the failure stress of the cylinders. The latter was measured by the diametral compression (Brazilian) test. The results confirm the direct proportionality between the two, but only above a minimum level of agglomerate matrix strength. At less than 120 kPa the relationship may become complex. A qualitative explanation is offered in terms of the stress-deformation behaviour of the spheres and cylinders.     

Effect of agglomerate size on extrudability of titania pastes

Pastes prepared from three high surface area titania powders were tested via torque and capillary rheometry to explain the different flow behaviour during mixing and extrusion processing. The Benbow analysis was used to calculate the main extrusion parameters, including bulk yield and shear stresses, and to compare the processability of the extrudable pastes. A critical water fraction was found for all powders and related to extrudability. The results show that the flow properties of the pastes are strongly influenced by the particle size distribution and the shear stability of large aggregates of different dimensions in the paste microstructure.     

超细粉在声场导向管喷流床中的聚团尺寸预测模型

超细粉的流化性能与聚团尺寸密切相关。通过分析超细粉聚团在声场导向管喷流床中的形成过程,提出了高速射流的剪切作用和聚团间的碰撞作用是决定聚团尺寸的主要原因。在此基础上,结合聚团在射流剪切过程和聚团间碰撞过程中的力平衡分析,建立了声场导向管喷流床中聚团尺寸分布的预测模型;并运用这一模型成功预测了不同射流气速下,超细TiO₂颗粒在声场导向管喷流床中的聚团平均直径和聚团尺寸分布。     

The physicochemical parameters determining the size of agglomerate prepared by the wet spherical agglomeration technique

Lactose samples of five different particle sizes from 31 to 261 μm dispersed in chloroform were agglomerated with a small amount of saturated aqueous lactose solution which acted as a bridging liquid to wet the particles preferentially. The effects of raw particle size and the amount of bridging liquid on the average size of resultant agglomerate were investigated.

The agglomerate size increased with decreasing size of lactose. This effect was enhanced by increasing the amount of bridging liquid for lactose less than 79 μm. A linear correlation on a log—log plot was observed between the agglomerate size and the saturation ratio of bridging liquid. The slope increased with decreasing particle size of lactose. The size distribution of agglomerates was also determined for the particle size of lactose and the amount of bridging liquid used. The physicochemical properties of the bridging liquid, i.e. contact angle and interfacial tension, were also taken into account for interpreting the agglomerate size. The correlation between the agglomerate size and the above parameters was represented quantitatively by eqn. (10) in the text. The parameter n, which varies directly with agglomerate size, increased with increasing saturation ratio, or with decreasing lactose particle size.     

石灰石水泥颗粒分布与其强度的灰色关联分析

将石灰石和水泥熟料按不同比例混合共同粉磨,运用灰色关联分析方法,研究了石灰石水泥颗粒分布对强度的影响,并建立了28d抗压强度与0~40μm颗粒含量的GM(1,2)灰色模型。研究结果表明:石灰石水泥粉体中10~20μm的颗粒含量与3d强度的关联度最大,20~30μm对28d强度影响最大。     

A new derivation of the agglomerate size distribution for a constant coagulation kernel

The agglomerate size distribution for an assembly of primary particles coagulating with constant kernel K is usually derived from the solution of the relevant deterministic equations. We present an alternative stochastic approach to the problem.     

Effect of agglomerate properties on agglomerate stability in fluidized beds

Fluidized bed agglomeration is used to stabilize particulate mixtures and reduce dust emissions. This technology is applied to a variety of production processes for the pharmaceutical, chemical, fertilizer and food industries. In most of these applications, agglomerate stability is an essential criterion. Agglomerates and granules that do not conform to size and shape specifications may create problems in downstream processes, such as tableting, thus compromising process efficiency and product quality. When an agglomerate is formed in a fluidized bed, it can grow by incorporating other bed particles, split into smaller fragments, or be eroded by fluidized bed solids. The objective of the present study is to determine the critical agglomerate liquid content at which the rates of agglomerate growth and shrinkage are balanced when artificial agglomerates made from glass beads and water are introduced into a fluidized bed. This study examined the effects of agglomerate size, agglomerate density, liquid viscosity, binder concentration, and fluidizing gas velocity on the critical initial liquid content. This study found that small agglomerates and low density agglomerates displayed higher critical initial moisture contents. When the viscosity was increased by using sugar solutions, agglomerates were very stable and had very low critical initial moisture contents. The study also found that as the superficial gas velocity increased, the agglomerates started to fragment, rather than erode.     

一种新型多功能附聚剂的制备

以丙烯酸丁酯（BA）、甲基丙烯酸和苯乙烯等为原料合成了一种新型多功能附聚剂。探讨了水油比、引发剂用量、不同乳化剂对附聚剂粒径、粘度和固含量的影响,并对附聚剂共聚物的红外谱图进行了分析,最终得到了附聚剂的最佳工艺配方。     

Mathematical modeling of pigment dispersion taking into account the full agglomerate particle size distribution

The purpose of this work is to develop a mathematical model that can quantify the dispersion of pigments, with a focus on the mechanical breakage of pigment agglomerates. The underlying physical mechanism was assumed to be surface erosion of spherical pigment agglomerates. The full agglomerate particle size distribution was simulated. Data from two previous experimental investigations were used for model validation. The first concerns two different yellow organic pigments dispersed in nitrocellulose/ethanol vehicles in a ball mill and the second a red organic pigment dispersed in a solvent-based acrylic vehicle in a three-roll mill. When the linear rate of agglomerate surface erosion was taken to be proportional to the external agglomerate surface area, simulations of the volume-moment mean diameter over time were in good quantitative agreement with experimental data for all three pigments. The only adjustable parameter used was an apparent rate constant for the linear agglomerate erosion rate. Model simulations, at selected values of time, for the full agglomerate particle size distribution were in good qualitative agreement with the measured values. A quantitative match of the experimental particle size distributions could be obtained using time-dependent fragment distributions, but this resulted in a very slight improvement in the simulated transient mean diameter only. The model provides a mechanistic understanding of the agglomerate breakage process that can be used, e.g., in the development of novel dispersion principles and for analysis of dispersion failures. The general applicability of the model, beyond the three pigments considered, needs to be confirmed.     

Taylor-expansion moment method for agglomerate coagulation due to Brownian motion in the entire size regime

Through applying the Taylor-expansion technique to the particle general dynamic equation, the newly proposed Taylor-expansion moment method (TEMOM) is extended to solve agglomerate coagulation due to Brownian motion in the entire size regime. The TEMOM model disposed by Dahneke's solution (TEMOM–Dahneke) is proved to be more accurate than by harmonic mean solution (TEMOM–harmonic) through comparing their results with the reference sectional model (SM) for different fractal dimensions. In the transition regime, the TEMOM–Dahneke gives the more accurate results than the quadrature method of moments with three nodes (QMOM3). The mass fractal dimension is found to play an important role in determining the decay of agglomerate number and the spectrum of agglomerate size distribution, but the effect decreases with decreasing agglomerate Knudsen number. The self-preserving size distribution (SPSD) theory and linear decay law for agglomerate number are only applicable to be in the free molecular regime and continuum plus near-continuum regime, but not perfectly in the transition regime.     

Fabrication of yttria-stabilized-zirconia coatings using electrophoretic deposition: Effects of agglomerate size distribution on particle packing

Yttria-stabilized-zirconia (YSZ) particles with various size distributions have been electrophoretically deposited (EPD) on Fecralloy substrate to investigate the particle size effect on EPD coatings. The deposition rates, as-deposited particle packing densities, green densities and sintered (for 2 h at 1250 °C in air) coating hardnesses are dependent on particle size. The particle packing arrangement in EPD coatings can be affected by further electric field densification (EFD) of the as-deposited coating in which the wet EPD coating is immersed in pure solvent (acetylacetone) with the application of a constant electric field. The effect of EFD was found to be most effective on small particles (<0.5 μm) when they are co-deposited with large particles (>1 μm). The improvements are reflected in increased mechanical hardness of sintered coatings.     

Statistical size scaling of ceramic strength

This work is based on the belief that the uniform spatial distribution of flaws underlying Weibull statistics is not necessarily always true for all ceramics. The weakest-link statistics for a power-law spatial distribution of flaws is adopted to synchronize the size dependence and random variation of ceramic strength. Three sets of published strength data of ceramics from different sized specimens are used for this purpose. The assumption of power-law spatial distribution of flaws in ceramics is validated, with both uniform and nonuniform spatial distributions being showcased possible. For all the three case studies, there exists a master curve to correlate a compound parameter encompassing cumulative failure probability and size effect with the nominal fracture strength.     

On the correlation of minimum porosity with particle size distribution

It has long been recognised that the major factors which influence the density of cohesionless material are the type of distribution of particle size, and particle shape. However, the difficulty of measuring particle shape and of expressing a particle size distribution comprehensively has proved a stumbling block to the determination of a successful correlation with porosity. None of the correlations so far has yielded an empirical relationship which can be employed with confidence to a wide range of types of particle size distribution.This paper examines some of the difficulties which are encountered with such correlations when attempting to describe the particle size distribution by Gaussian measures, and develops a new method of expression, by a single ‘offset‘ value, of a particle size distribution. A good empirical relationship is found between minimum porosity and this value, having taken due account of particle shape. It is suggested that the method will give engineers greater appreciation of the grading curve of cohesionless materials.     

An investigation of the parameters effecting the agglomerate size of a PZT ceramic powder prepared with a sol–gel technique

This paper describes the production of Pb_1.0Zr_0.9Ti_0.1O₃ ceramic powder, by using metal organic precursors as starting materials and a polyvinylpyrrolidone (PVP) as an agglomeration control agent. In this study, the effects of water content, aging time and polyvinylpyrrolidone molecular weight on the agglomeration behaviour of the powders were investigated. Least agglomerated powder, with size population ranges 60–200 nm and 200–800 nm, was produced from gel which contained the lower molecular weight of polymer and was unhydrolysed and unaged.     

Design of the spherical agglomerate size in crystallization by developing a two-step bridging mechanism and the model

Spherical agglomeration technology can produce high-performance spherical particles in a single crystallization unit, although it is still challenging to control the particle size and shape. To solve this issue, a two-step bridging (TSB) mechanism containing a preconditioning period, size period, and shape period is proposed. The dynamic balance among the forces of adhesion, dispersion, and capillary action in the multi-liquid phases plays a key role. This is fully considered to establish the TSB-based thermodynamic size model and particle design framework by weighting the force action regions in multi-liquid phases with dynamic composition. The spherical agglomerates of benzoic acid, celecoxib, and salicylic acid with narrow particle size distributions and tunable particle size ranges of 2000–5000, 800–3500, and 1500–4500 μm, respectively, were designed and prepared successfully, showing good correlation with the calculation, which is superior to the reported methods and indicates that the mechanism has certain universality and guiding significance.     

用非均匀团聚体模型模拟燃料电池老化过程

在燃料电池老化过程中,催化层中催化剂的迁移和粒径增加会造成燃料电池的性能下降。本文提出了一种新型的团聚体分层分布模型,且分层界面可沿膜厚方向发生线性变化。通过宏观电极模型和团聚体亚尺度模型的耦合,用有限元法分析了团聚体不均匀分布对质子交换膜燃料电池性能的影响。研究表明,靠近团聚体外侧的催化剂的流失对电池性能影响很大,当没有催化剂的外侧区域达到0.1倍半径时,输出电压为0.2V时的电流密度下降89.8%;当没有催化剂的内侧区域达到0.1倍半径时,输出电压为0.2V时的电流密度下降25%左右。相比于向质子交换膜方向的催化剂迁移,向气体扩散层方向的催化剂迁移对电池性能影响更大,其中分层递增分布的团聚体模型的电池电流密度是均匀分布团聚体模型的60%左右,分层递减分布模型的电流密度是均匀分布团聚体模型的10%左右。此外,铂负载量增加一倍对递增分布模型的电池性能有所提高。     

The densification and strength of porous Y-TZP materials with a bimodal particle size distribution for dental applications

In this study the densification behavior of bimodal Y-TZP powder compacts consisting of nano/sub-micron-sized particles was studied and an explanation for their improved flexural strength while biscuit-sintered is provided. An in situ-heating TEM analysis revealed that up to 800 °C only the nanoparticles sinter in a bimodal mixture without any densification. By increasing the temperature to 900 °C the densification of the nanoparticles begins and partially densified nanoparticle clusters migrate into the contact area between the core particles. Consequently, the driving force for the sintering of the powder-blend compacts is reduced and this is reflected in a slower densification compared to that of the core material. At 1000 °C the sintered nanoparticle clusters begin to incorporate into the core material, resulting in a sharp increase in the strength due to the increased neck area. Biscuit-sintered powder-blend compacts reached a plateau of strength at 670 MPa, which was reached at a relative density of 70%.