水泥粒度分布的分维评价研究

对比分析了7种水泥样品的粒度分布实测值与Fuller曲线计算值，结果表明：所研究的水泥样品中较细颗粒的含量与较粗颗粒的含量均偏少，而中间段颗粒的含量偏多；测算了水泥样品实测粒度分布分维与Fuller曲线计算粒度分布分维，将两者分维的差值作为表征水泥粒度分布偏离最佳粒度分布程度的参数。研究发现：7种水泥样品的粒度分布均偏离了最佳粒度分布，随着分维差值的减小，样品空隙率降低。     

Bimodal particle size distribution polymer/oligomer combinations for printing ink applications

This paper describes a study in which anionically stabilised acrylic latices with a bimodal particle size distribution, produced by blending polymer particles of 50 and 350 nm in different blend ratios, are blended with oligomers. Reversibility, rheology, drying behaviour, film formation and blocking resistance of these systems were studied Reversibility appears to show two regions of linear dependence on the total particle surface area. The lower the surface area, the lower the amount of oligomer needed for good reversibility. The rheological data was fitted by the Krieger–Dougherty equation and it appeared that both in the presence and absence of oligomer an 80/20 large/small blend exhibited the highest maximum packing fraction. Short drying times were obtained with bimodal blends at high solids content and the drying profiles could be explained by the Croll model. The presence of oligomer was shown to exhibit a positive effect on film formation and when the oligomer is hard, the blocking resistance is already very good at low oligomer content, resulting in a very good MFT/blocking resistance balance. The latter can also be obtained when as well the size as the T_g of the polymer particles is varied.     

Random particle packing with large particle size variations using reduced-dimension algorithms

We present a reduced-dimension, ballistic deposition, Monte Carlo particle packing algorithm and discuss its application to the analysis of the microstructure of hard-sphere systems with broad particle size distributions.We extend our earlier approach (the “central string”algorithm) to a reduced-dimension, quasi-3D approach. Our results for monomodal hard-sphere packs exhibit a calculated packing fraction that is slightly less than the generally accepted value for a maximally random jammed state. The pair distribution functions obtained from simulations of composite structures with large particle size differences demonstrate that the algorithm provides information heretofore not attainable with existing simulation methods, and yields detailed understanding of the microstructure of these composite systems.     

An improved estimation of size distribution from particle profile measurements

Several methods are available to measure particle size. The majority of them, such as sieving, are off-stream techniques where samples must first be separated from the main stream for analysis.Therefore, the search for on-line particle size analysis systems has provided the impetus for the introduction of image-based particle size analysers to the mineral industry in the past three decades. Generally, the estimation of particle size distribution on the basis of image analysis depends on measuring a single parameter of particle profile. For example the equivalent area diameter (d_A) or mean Feret's diameter (d_F) distributions, then transforming this data to the equivalent size distribution. However, due to the irregularity of particles being analysed, it is believed that this kind of analysis may increase the error in estimation of particle size distribution since profiles of irregular particles carry more information than can be represented by a single parameter.In this paper, a proposed technique which measures two parameters, equivalent area diameter (d_A) and mean Feret's diameter (d_F), for each particle profile has been developed. The accuracy of the technique has then been investigated in the laboratory by successfully estimating (unfolding) the size distribution, where size refers to sieve size, of three samples of different particle shapes with known size distribution.     

A particle packing algorithm for pellet design with a predetermined size distribution

In this paper a particle packing algorithm is proposed which is to be used to predict the behaviour of pellets in the blast furnace on a first principal basis. Pellets consist of particles of various mineralogical composition and the structure in which they pack together to form a pellet is dependant on the size distribution of the particles and the pellet porosity. This packing structure can result in isolated volumes within the pellet where the local composition deviates from the overall average composition. This can result in, for example, melt formation at lower temperatures than expected, which will have a detrimental effect on the pellet strength. These local compositions result from the contacts between particles of different minerals and can thus be quantified by the coordination number of the particles. By using a validated coordination number model, which is unique for a particle packing algorithm, virtual pellets were created for a range of particle size distributions and porosities. The algorithm used the Monte Carlo method combined with the simulated annealing minimisation algorithm to solve the pellet simulations. The objective function is a combination of two functions, one describing the deviation from the target coordination number of the particles and the other the average fraction of overlapping volume of the particles per contact. In this way a realistic pellet structure was maintained while at the same time controlling the coordination number of the particles.     

粒度分布对超低水泥刚玉质浇注料流变性的影响

用浇注料流变仪研究了粒度分布对超低水泥刚玉质浇注料流变性的影响。结果表明 :粒度分布对超低水泥浇注料的流变性影响较大。随着粒度分布系数 (q)的减小 (从 0 .2 9、0 .2 6到 0 .2 3) ,浇注料的剪切应力、粘度和屈服应力增加 ,需水量上升 ,说明流变性变差。以 2 %的SiO2 微粉等量替代q =0 .2 3的浇注料中的Al2 O3微粉后 ,试样的流变性得到明显改善 ,更适合用于泵送施工 :浇注料的需水量减少 ,自流值提高。     

Variation of particle size and its distribution during the synthesis of silicalite-1 nanocrystals

Recent studies imply that the external surface area of the nanozeolite product may, at least in some cases, be related to the average size of the particle population participating in aggregative nucleation, a population which itself is a product of aggregation of even smaller primary nanoparticles. This possibility puts more importance on our understanding of the variation of particle size and its distribution during the crystallization of zeolite nanoparticles. Variation of the particle size and PSD during nanoparticle silicalite-1 crystallization was followed with respect to time by a laser light scattering device with a scattering angle of 173°, for several starting synthesis compositions. Effects of varying TPAOH and water contents in the starting synthesis mixtures on the variation with time of the particle sizes and PSDs, especially across the two distinct aggregation events, were investigated. The products were also analyzed by XRD and AFM. Parallel to the decrease in the average particle size of the final product population with increasing alkalinity and organic template content, its PSD was observed to become narrower too. A reversal in the dependence on TPAOH content, of the average size of the population formed by aggregation, with respect to that of the population participating in aggregation, was observed across both aggregation events, implying that smaller particles aggregated to form larger particles, while larger particles aggregated to form smaller particles during these processes, and this was also seen from the AFM images, to be reflected to the surface features of the final product particles.     

Effect of wet screening on particle size distribution and coal properties

Wet screening is one of the methods used to remove fine material from the coal feed to gasification. Sasol Synfuels in South Africa undertook an investigation to quantify fine coal generation in the coal supply to gasification. Coal samples were wet screened in the laboratory and results compared to the normal dry screening procedure. It was found that the fines (−0.5 mm) increased almost five times when the coal was wet screened compared to dry screening. This study was subsequently initiated by Sasol Technology R&D to establish the mechanism of fine coal generation during wet screening, as well as the effect of wet screening on particle size distribution (PSD) and chemical properties of coal. Changes in the PSD and chemical properties of coal from individual coal sources used at Sasol Synfuels were compared. Composite coal samples with a predetermined PSD of all individual coal sources used at Sasol Synfuels were screened under wet and dry conditions. The PSD was again determined after screening, as well as the mineral composition (by X-ray diffraction) of the fines. Results indicated that wet screening caused clay minerals to be removed from the coal structure leading to an increase in the fines. This removal of minerals weakened the coal structure causing further size degradation of coarser fractions.     

Challenges in particle size distribution measurement past, present and for the 21st century

The field of particle size distribution (PSD) characterization and measurement has experienced a renaissance over the past ten years. This revitalization has been driven by advances in electronics, computer technology and sensor technology in conjunction with the market pull for PSD methods embodied in cost effective user friendly instrumentation. The renaissance can be characterized by at least four activities. (1) End user innovation exemplified by techniques such as hydrodynamic chromatography (HDC), capillary hydrodynamic fractionation (CHDF) and field flow fractionation methods (SdFFF, FlFFF, and ThFFF). (2) Revitalization of older instrumental methods such as gravitational and centrifugal sedimentation; (3) Evolution of research grade instrumentation into low cost, routine, user friendly instrumentation exemplified by dynamic light scattering (DLS). (4) The attempt to meet extremely difficult technical challenges such as: (a) providing a single hybrid instrument with high resolution over a very broad dynamic range (4+ decades in size; e.g., Fraunhofer/Mie; photozone sensing/DLS); (b) PSD measurement of concentrated dispersions (acoustophoretic, dielectric measurements, fiber optic DLS (FOQELS)); (c) in-situ process particle size sensors (in-line or at line, e.g., FOQELS); (d) routine measurement of particle shape and structure (e.g., image analysis). Instrumental methods resulting from these activities are discussed in terms of measurement principles and the strengths and weaknesses of these methods for characterizing PSDs. Business and societal driving forces will impact customer perceived instrumentation and knowledge needs for the 21st century and the ability to meet the specific difficult technical challenges in particle size distribution characterization mentioned above. Anticipated progress toward meeting these technical challenges is discussed in conjunction with the associated anticipated advances in required technologies.     

On the role of an unconventional rigid rodlike cationic surfactant on the styrene emulsion polymerization. Kinetics, particle size and particle size distribution

An unconventional amphiphile (1-[ω-(4′-methoxy-4-biphenylyloxy)octyl]pyridinium bromide, PC8) was used as surfactant in the emulsion polymerization of styrene. At low surfactant concentration (6, 12 or 36 mmol l⁻¹), curves of polymerization rate versus conversion obeyed the typical behavior characterized by intervals I, II and III. However, at high concentration (48 or 72 mmol l⁻¹) the interval II was not observed. The particle size distribution curves showed two families of polymer particles, indicating the participation of at least two mechanisms of particle formation, one being the simple micellar nucleation and the other probably the coagulative nucleation of precursor particles. The latter was considered to occur during the nucleation interval.     

Control of particle size distribution for the synthesis of small particle size high solids content latexes

A polymerization process to synthesize bimodal latexes with maximum particle diameters below 350 nm and solids content above 65 wt% has been developed.The process is based on an iterative strategy to determine the optimal particle size distribution that gives the maximum packing factor for a given range of particle sizes and at a given solids content. The calculated optimal bimodal PSD was experimentally obtained in a seeded semi-continuous emulsion polymerization reaction as follows: in the first step, a polymer seed latex was loaded in the reactor and grown, under monomer starved conditions, until a given particle size. At this point a fraction of the same seed was added to the reactor and the feed was continued until the desired particle size distribution and solids content were achieved. The point at which the seed was added again to the reactor and the amount of seed required were determined by the iterative strategy and depended on the competitive growth rate ratio of large and small particles that is an input for the iterative strategy.Implementation of the solution obtained from the iterative strategy, and for the first time in the open literature, led to the production of a coagulum free and stable bimodal latex with 70 wt% of solids content and particle sizes below 350 nm.     

A gap-graded particle size distribution for blended cements: Analytical approach and experimental validation

To increase the packing density of blended cement paste, a gap-graded particle size distribution (PSD) was theoretically deduced and modified according to the wet density of actual paste. Then experiments were conducted to validate the hypothesis of improvement of the properties of blended cements by the gap-graded PSDs proposed. The experimental results show that the gap-graded PSD resulted in a decreased water requirement and an increased packing density of blended cement paste, and modified gap-graded PSDs gave further effects. The heat of hydration of gap-graded blended cement pastes released slowly in the first 24 h and increased rapidly afterward. The microstructure of gap-graded blended cements was much more homogeneous and denser than that of reference blended cement, therefore both early and late mechanical properties of low clinker gap-graded blended cements were improved significantly and even higher than those of Portland cement.     

Alkali-activated waste ceramics: Importance of precursor particle size distribution

The waste ceramics belongs to wide range of aluminosilicate materials which can be alkaline-activated to geopolymer cement – possible “green” alternative to conventional Portland cement. The studied ceramic material is generated during the size adjustment of ceramic building blocks by means of grinding. It means that most of the material is very fine, but it contains also some larger shards. This ceramic powder was used as geopolymer precursor “as received” and after removal of particles retained on 1, 0.5 and 0.125 mm sieves. These four types of precursor were activated by sodium silicate (SiO₂/Na₂O = 1) solution. The prepared mortars were tested for strength, basic physical properties, transport parameters and characterized by help of XRD and thermal analysis. It was found that the best mechanical performance provided the precursor after removal of particles retained on 0.5 mm sieve thanks to the highest geopolymerization rate. The presence of coarser particles in precursor gave rise to porosity, what consequently influenced transport parameter of geopolymers towards the lower thermal conductivity and faster moisture transport.     

A particle analyser for measuring particle size distribution and shape,on-line or in the laboratory

Norsk Hydro has developed a Particle Analyser for on-line or laboratory use, which measures particle size, size distribution and the deviation from sphericity (called nonspherical).The principle for this system is that the particles fall in a monolayer curtain in front of a high resolution CCD camera. The computer unit in the analyser measures and calculates the particle size and a sphericity factor for each particle. The data are presented as four real time trend curves, shown simultaneously for the on-line version. These curves show % oversize and fines, d₅₀ and the percentage nonspherical particles. For the laboratory version the data are presented in table and cumulative form.The on-line particle analyser has been installed in two of Norsk Hydro's prilling plants in Norway. The analyser has in both plants improved the product quality during the two years of installation.     

Effect of particle size distribution of raw powders on pore size distribution and bending strength of Al2O3 microfiltration membrane supports

To lower the sintering temperature of Al₂O₃ microfiltration membrane support, Al₂O₃ powders with particle size distribution of tri-modal are chosen. The results show that the function of fine Al₂O₃ grains depends on their agglomeration state: if fine Al₂O₃ grains distribute discretely, the bending strength of the support increases along with a slight increase in porosity; however, the aggregated fine grains are harmful to both bending strength and pore size distribution of the support. The bridging of medium Al₂O₃ grains between coarse grains contributes to increase the bending strength, but has less effect on porosity. The addition of medium (and/or fine) Al₂O₃ powder has less effect on the pore size distribution of the support if only coarse Al₂O₃ grain forms the support's framework, which suggests a new way to prepare the support with both high bending strength and high porosity at low temperature.     

An approach for matrix densification based on particle packing and its effect on lightweight Al2O3-MgO castables

For lightweight refractory containing lightweight aggregates, the properties of the matrix are decisive to its performance. In the present work, Dinger–Funk equation was adopted to calculate the theoretical packing density of a castables matrix based on Stovall linear packing model and to design its particle size distribution. Four lightweight Al₂O₃-MgO castables with different particle size distribution (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q (>=0.31). For the sample with q=0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favourable compromise among sintering characteristics (apparent porosity=14.8%, bulk density=3.02 g cm⁻³, permanent linear change<0.6%), strength (cold modulus of rapture=12.4 MPa, cold crashing strength=155.5 MPa), and resistance against both slag corrosion (I_c=22.4%) and penetration (I_p=11.5%). The sample with q=0.25 showed the highest strength and resistance against slag corrosion (matrix dissolved in slag), but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.     

Internal particle size distribution of biofuel pellets

Several methods for disintegration of biofuel pellets were tested and compared for their ability to break up the pellets into the original particles of the raw material. Analyses performed on softwood pellets and straw pellets concluded that wet disintegration in water at ambient temperature is insufficient for a determination of the internal particle size distribution of wood- and straw pellets. When the wet disintegration was performed with water heated to the boiling point and coupled with mechanical disintegration in terms of stirring a more complete disintegration of the pellets was obtained. Based on the results obtained in the initial study a round robin was set up including six European laboratories where the selected method was tested. In the round robin test the method combining heated water and stirring of the slurry was tested on solid biofuel pellets produced of comminute straw, deciduous wood and coniferous wood respectively. With the method a satisfactory disintegration was obtained of all three types of pellets.Further wet disintegration of coniferous pellets was compared to a dry disintegration using a hammer mill. The dry disintegration of the coniferous pellets resulted in smaller particle sizes compared to the wet disintegration using heated water and stirring of the slurry indicating a further disintegration of the original particles in the hammer mill process.Overall the wet disintegration combined with mechanical impact was found to be the most suitable method for disintegration of solid biofuel pellets. Combined with sieving analysis the method gives realistic image of the internal particle size distribution of solid biofuel pellets.     

Effects of binary particle size distribution on minimum pick-up velocity in pneumatic conveying

Minimum pick-up velocities (U_pu) for entrainments of particle mixtures having binary particle size distributions (PSD) are measured in a horizontal pneumatic-conveying line using the weight-loss method. Geldart's groups A, B, and C glass beads having diameters of 400, 170, 40, and 5 μm are used. Variations in U_pu as a function of particle mass fraction (m) are examined. The capability of empirical correlations of monodisperse U_pu in predicting U_pu of binary mixtures is investigated. For group B particle mixtures (i.e. 400 & 170 μm), the particles are entrained separately resulting in linear U_pu variations with m, which is accurately predicted by the monodisperse U_pu correlation. For mixtures involving group A and B particles (i.e. 170 & 40, 400 & 40 μm), the two particles are collectively entrained resulting in U_pu that vary non-linearly with m and that cannot be predicted by the correlation. For mixtures involving group B and C particles (i.e. 400 & 5, 170 & 5 μm), U_pu are comparable to that of the monodisperse group B particles, therefore they are accurately predicted by the correlation. The significant impacts of binary PSD on U_pu found presently indicates that PSD effects on particle entrainment process warrants further investigations.     

Measurement methods of particle size distribution in emulsion polymerization

The particle size distribution of polymer always develops in emulsion polymerization systems, and certain key phenomena/mechanisms as well as properties of the final product are significantly affected by this distribution. This review mainly focuses on the measurement methods of particle size distribution rather than average particle size during the emulsion polymerization process, including the existing off-line, on-line, and in-line measurement methods. Moreover, the principle, resolution, performance, advantages, and drawbacks of various methods for evaluating particle size distribution are contrasted and illustrated. Besides, several possible development directions or solutions of the in-line measurement technology are explored     

On-line automatic optical inspection system for coarse particle size distribution

A new online automatic optical inspection system (OAOIS) using digital image processing has been developed to measure the coarse particle size distribution. The OAOIS is composed of particle separation module, image acquisition module, image processing and analysis module and PC/PLC-based electric control module. Experiments were performed with non-uniform particles (1-100 mm). The particle size distribution, number of the particles, and accumulated weight percentages of particles are obtained by using the developed system. The experimental results show that the repeated precision of accumulated weight percentages is around ± 1%. To improve the reliability and accuracy of the OAOIS measuring results, the linear regression equation is applied to mapping the result of OAOIS to that of traditional net sieving system (TNSS). It has been shown that the developed system has a high accuracy and precision for coarse particle sizing distribution.