硅砂对高碱铝硅酸盐玻璃熔解特性的影响研究(英文)

通过固定熔制工艺制度,研究了硅砂原料粒径大小、分布情况、颗粒形态对高碱铝硅酸盐玻璃熔解特性的影响关系。研究结果表明:在玻璃配合料熔制过程中,白色未熔物的产生与石英砂密切相关,石英砂粒径处于45-150μm范围熔化效果最好,石英砂粒度分布为正态分布的熔化效果优于均匀分布,经过粒化处理的石英砂比破碎处理的熔化特性更优,可促进玻璃的熔化。     

Optimization of Parameters for Synthesis of MFI Nanoparticles by Taguchi Robust Design

MFI‐type zeolite was successfully synthesized by hydrothermal crystallization of clear synthesis mixtures. A statistical experimental design method (the Taguchi method with an L8 orthogonal array) was implemented to optimize the experimental conditions for the preparation of MFI nanocrystals with respect to particle size and distribution as the desirable properties. In the Taguchi experimental design, crystallization temperature, water content, template/silica molar ratio, aluminum content, as well as the presence of alkaline cations were chosen as significant parameters affecting the properties. It was shown that water and aluminum content of the synthesis solution were the most important parameters affecting particle size and distribution. The MFI nanocrystals with an average particle size of 95 nm and the narrow particle size distribution of ± 8.5 nm were synthesized under optimum conditions.     

Dispersion viscosity of aluminum trihydroxide of various particle size distributions in an unsaturated polyester resin

The effect of filler particle size distribution on the viscosity of an aluminum trihydroxide/unsaturated polyester resin dispersion was studied. Four basic aluminum trihydroxides with distinctively different particle sizes were combined to generate various particle size distributions systematically. The particle size distribution producing the minimum viscosity was determined by employing a modified extreme vertices experiment design for mixtures to establish a quadratic model which was then optimized. The predicted viscosities in general as well as the particle size distribution corresponding to the minimum viscosity agreed well with the observed data.     

Influence of erodent particle types on solid particle erosion of polyphenylene sulphide composite under low particle speed

The influence of erodent particle types on solid particle erosion of randomly oriented short glass fiber and mineral particle reinforced polyphenylene sulphide (PPS) was investigated. The solid particle erosion studies were carried out using low speed solid particle erosion test rig with 150 to 212‐μm brown fused aluminum oxide (Al₂O₃), 150 to 200‐μm silica sand and 150 to 250‐μm glass bead. Glass bead eroding particles appear spherical in shape whereas aluminum oxide and silica sand eroding particles have sharp and angular edges. The erosion tests were conducted at six different contact angles of 15, 30, 45, 60, 75, and 90°, respectively. The results showed a strong dependence of the eroding particle types on the erosive wear behavior of PPS composite. The peak erosion rate occurred at 45° contact angle for silica sand eroding particles while the peak erosion rate occurred at 30° contact angle for aluminum oxide and glass bead particles. The morphologies of eroded surfaces were characterized by the scanning electron microscopy. In case of aluminum oxide and silica sand, the erosive wear mechanism occurs firstly by the erosion of matrix, followed by the fracture of un‐supported fibers and their detachment; however, the erosive wear mechanism occurs different for glass bead particles. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Influence of particle size distribution on rheology and particle packing of silica-based suspensions

The effect of particle size, particle size distribution and milling time on the rheological behaviour and particle packing of silica suspensions was investigated using slurries containing total solids loading of 46 vol.%. Three silica powders with different average particle sizes (2.2, 6.5 and 19 μm), derived from dry milling of sand, and a colloidal fumed silica powder with 0.07 μm were used. Different proportions of colloidal fumed silica powder were added to each of the coarser silica powders and the mixtures were ball-milled for different time periods. The influence of these factors and of the particle size ratio on the rheological behaviour of the suspensions and densities of green slip cast bodies was studied.The results show that the flow properties of slips are strongly influenced by the particle size distribution. The viscosity of suspensions increases with the addition of fine particles, imposing some practical limitations in terms of volume fraction of fines that can be added. On the other hand, increasing the size ratio enhanced the shear thinning character of the suspensions, while decreasing the size ratio led to an accentuation of the shear thickening behaviour. For all mixed suspensions, green densities increased with increasing milling time, due to size reduction of silica powders and a more efficient deagglomeration of fumed silica. Increasing amounts of fumed silica led to a first increase of particle packing up to a maximum, followed by a decreasing trend for further additions. Good relationships could be observed between rheological results and packing densities.     

Computational Fluid Dynamic Modeling of a Flame Reaction Process for Silica Nanopowder Synthesis from Tetraethylorthosilicate

The process of synthesizing silica nanopowder by the gas phase thermal oxidation of tetraethylorthosilicate in a diffusion flame reactor was simulated using a commercial computational fluid dynamic code. The fuel combustion process and silica particle formation and growth in the flame were modeled. The temperature, velocity, and particle size distribution (PSD) fields inside the reactor were computed. Chemical reaction rate and a population balance model were used to calculate the particle formation and growth and PSD. Satisfactory results were obtained for the temperature profile and PSD. Computed values of the average size of the final products were consistent with those obtained in a previous experimental work.     

Size distribution for periclase particles below 40 microns

The distribution of particles of size below 40 μm was determined for seven fractions of an electrically fused and crushed magnesite. This was accomplished by muscopic counting attar sedimentation analysis. The log-normal distribution law was applicable in all cases. Tile mean particle diameters and the standard deviations were evaluated from the data of the normal-distribution and log-probability plots. For every fraction, the particle size distribution curates were sharp showing only one maximum and indicating a homogeneous distribution (uni-modal). The sizes obtained from both determinations were in good agreement. The specific surface areas were determined by low-temperature nitrogen adsorption, and evaluated from the size distribution data. The calculated surface roughness factors were found to range between 4.1 and 5.1.     

Mesoporous carbon confined conversion of silica nanoparticles into zeolite nanocrystals

A novel synthesis method has been developed to synthesize zeolite nanocrystals with controllable size and size distribution through conversion of colloidal silica nanoparticles in a mesoporous carbon matrix. Colloidal silica nanoparticles serving as the silica source as well as the hard template were embedded in the mesoporous carbon via in situ polymerization of furfuryl alcohol in the presence of tri-block copolymer (Pluronic P123), and then reacted with an alkaline aqueous solution (Na₂O–Al₂O₃–H₂O) infiltrated through the mesoporous channels of the carbon matrix. The synthesis of zeolite NaA nanocrystals is demonstrated. SEM images reveal that the sizes of the zeolite NaA nanocrystals obtained are similar to those of the starting silica nanoparticles. As a result, this synthesis method shows the potential for controlling the nanocrystal size and size distribution of silica-containing zeolites by choosing colloidal silica nanoparticles with a desired particle size distribution.     

不同pH环境下CMS改性纳米铁在异质多孔介质中的迁移

纳米铁在污染土壤和地下水的修复中受到广泛关注。为进一步探究其在多孔介质的迁移行为,本研究采用羧甲基淀粉钠（CMS）对纳米零价铁（nZVI）进行包覆,进行了改性纳米零价铁的沉降试验,测量zeta电位与粒径分布探究其分散性;进行了不同pH条件下改性纳米零价铁在酸洗砂与水洗砂的柱实验,分析了化学异质性与pH对纳米铁在多孔介质迁移的影响。结果表明,CMS包覆纳米铁不仅使纳米颗粒本身稳定,而且还减少其在多孔介质表面沉积,大大提高了迁移性。pH=6～8时,nZVI的zeta电位由18.3mV减小到2.9mV,有效粒径由685nm增大到880nm,稳定性变差;而CMS-nZVI的zeta电位值由-19.7mV增大到-53.5mV,颗粒间静电排斥力增强稳定性变好。经能量色散X射线光谱（EDS）分析,水洗砂表面存在碳、铝、铁等氧化物杂质,这些杂质带有正电荷,会增强与带负电的CMS-nZVI的吸附作用,不利于其迁移;而经过酸洗后的石英砂,其表面杂质大大减少,在pH=8时,CMS-nZVI在酸洗砂最大迁移率为77.0%要好于水洗砂的63.0%。此外较高pH环境有助于增加石英砂介质的表面负电荷,减少颗粒与介质的吸附,促进纳米颗粒的迁移。     

Computational fluid dynamic modeling of a chemical vapor synthesis process for aluminum nanopowder as a hydrogen storage precursor

A chemical vapor synthesis (CVS) process for synthesizing nano-sized aluminum powder as a precursor for various hydrogen storage materials was simulated by the use of computational fluid dynamic modeling. The fluid flow, heat transfer and chemical reaction phenomena taking place inside the reactor were analyzed together with particle formation and growth in the CVS process. The temperature, velocity and particle size distribution fields inside the reactor were computed. Chemical reaction rate and population balance model were used to calculate the particle formation and growth. The particle size computed by the program was compared with the experimental data, and the calculated average size of the final product particles was consistent with those obtained in the experimental work.     

Reference materials of defined particle size certified recently by the community bureau of reference of the european economic community

Some results from an international projects, supported by the Community Bureau of Reference of the European Economic Community, on the certification of five reference materials of defined particle size covering the overall range 0.35 – 650 μm are presented and discussed. Four of the reference materials were certified with respect to the mass distributions of the Stokes' diameters measured by an agreed gravitational sedimentation (Andreasen pipette) method. The coarsest of the reference materials was certified with respect to the mass distribution of the volume diameters of the particles using sieves, the ‘cut sizes’ of which were calibrated with respect to their equivalent volume diameters.Data were also obtained using several other methods, including X-ray gravitational sedimentation, sedimentation balance, centrifugal sedimentation, electrical sensing zone and photo-sedimentation methods. These were not used for certification but are presented for comparison purposes and to indicate the usefulness of the certified reference materials for the checking and calibration of many particle sizing techniques.     

The Effect of Binder Systems on Early Aluminum Reaction in Detonations

The objective of this study was to determine compositional variables that result in early reaction of aluminum in detonations of pressed high explosive compositions, defined as reaction by 7 volume expansions as measured by 2.54 cm diameter copper cylinder expansion tests. In order to accomplish this in an economical fashion, statistical mixture design of experiments (DOE) was used in conjunction with anaerobic detonation calorimetry. The effect of binder type (e.g. energetic vs. inert), binder content, HMX content, aluminum content, and aluminum particle size was investigated. It was determined an energetic binder must be used to obtain significant aluminum reaction at volume expansions less than 7 V/V₀. Aluminum particle size was only a minor factor. Furthermore, the compositional oxygen balance only provides a general indication of which compositions exhibit more aluminum reaction than others.     

Effect of fine aggregate replacement with Class F fly ash on the mechanical properties of concrete

This paper presents the results of an experimental investigation carried out to evaluate the mechanical properties of concrete mixtures in which fine aggregate (sand) was partially replaced with Class F fly ash. Fine aggregate (sand) was replaced with five percentages (10%, 20%, 30%, 40%, and 50%) of Class F fly ash by weight. Tests were performed for properties of fresh concrete. Compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity were determined at 7, 14, 28, 56, 91, and 365 days. Test results indicate significant improvement in the strength properties of plain concrete by the inclusion of fly ash as partial replacement of fine aggregate (sand), and can be effectively used in structural concrete.     

Adsorption of carbon dioxide using polyethyleneimine modified silica gel

To find an ideal adsorbent for carbon dioxide capture, a new polyethyleneimine modified silica gel material was synthesized with a simple procedure. Three silica gel materials with various particle sizes (15, 25 and 40–63 μm) were prepared and functionalized with polyethyleneimine. The carbon dioxide adsorption amounts of modified silica gel and non-modified silica gel were calculated using a mass balance equation at three different temperatures (298.15, 308.15 and 318.15 K), respectively, and the influence of gas pressure and particle size on adsorption was discussed. Experimental data showed that the carbon dioxide adsorption capacity of modified silica gel was better than non-modified silica gel, and the adsorption capacity gradually decreased with increasing particle size. The smaller particle size (15 μm) PEI modified silica gel had the largest adsorption capacity, at 298.15 K, and the adsorption amounts of various particle sizes of PEI-silica better fit the Langmuir isotherm model.     

Real-time analysis of the growth of granular media by an ultrasonic method: Application to the sedimentation of glass balls in water

In this work, we propose a real-time analysis of the growth of a granular material by a high frequency ultrasonic method (around 5 MHz) based on normal incidence reflectometry. This method is non-destructive. It can be applied to the general case of cloudy solutions in optically opaque sedimentation cells. Results were obtained on glass balls used as a model granular material. Glass balls were sedimenting in water. Measurement of the deposit thickness (varying from several dozen of micrometers to several millimeters) leads to morphological and dynamic properties such as the volume solid fraction and the deposit growing rate. The strong influence of the particle size distribution (median diameter, broadness of the size distribution) on the dynamic properties of the particle packing was determined quantitatively. Our results are in good agreement with the classical model of sedimentation for an isolated sphere (Stokes law).     

The dissolution kinetics of sand as function of particle size

The initial dissolution rate of sand into sodium hydroxide solution (12.5 mol/L) over a wide range of temperatures (150 to 220°C) and pressures (0.47 to 2.29 MPa) has been determined. A semi-empirical equation was found to fit the dissolution data obtained at different temperatures and at different particle sizes. The influence of temperature on the reaction extent led to the activation energy of the dissolution, E_a = 74.41 kJ/mol. Six samples of sieved silica having narrow particle size distribution 38–40, 100–125, 212–200, 400–500 and 850–1000 μm were reacted with 12.5 mol/L sodium hydroxide solution at 220°C. The effect of particle size, i.e., surface area of the grains, on the initial rate of dissolution (denoted v₀) has been described by an empirical equation. Evidence is given here showing that the general assumption of the simple proportionality between the rate of reaction and the exposed surface of solid is not always confirmed.     

The effect of surface modification of aluminum powder on its flowability, combustion and reactivity

Surface modification of aluminum powders for the purpose of flow improvement was performed and several samples were prepared. Correlations between the flowability and reactivity for these powders as well as for the initial untreated aluminum powder were established. The powders were characterized using Scanning Electron Microscope (SEM), particle size distribution, angle of repose flowability test, Constant Volume Explosion (CVE) combustion test, and Thermo-Gravimetric Analysis (TGA). The surface modification of micron-sized aluminum powders was done by: (1) dry coating nano-particles of silica, titania and carbon black onto the surface of spherical aluminum powders and (2) chemically and physically altering the surface properties of the same powders with methyltrichlorosilane. All surface modifications improved flowability of the powders. CVE measurements indicate that powders with an improved flowability exhibit improved combustion characteristics if the powder treatment does not add an inert component to aluminum. The TGA results do not show significant differences in the reactivity of various powders. Based on combined flowability and CVE characteristics, the silane modified material gave the best results followed by the powders dry coated with carbon, titania and silica, respectively.     

Studien zur Korngrößenverteilung von Bleicherden

Studies in Particle Size Distribution of Bleaching Earths The particle size distribution of various German and American bleaching earths was determined to check whether a relation exists between size distribution and technical properties of the earths. The results of determinations obtained by sieving-, sifting-, and sedimentation methods was surprising: the obtained size distribution depends on the method to such a degree that it was impossible to specify the “real” particle size and the functional value of the earths. It is recommended to the consumer to determine as before only these data which concern directly the scope of the earths.     

固体推进剂中铝粉氧化过程及其燃烧效率影响因素

在对铝粉氧化过程和单颗粒燃烧过程分析的基础上,总结了导致铝粉团聚的主要因素,讨论了不同因素对铝粉燃烧效率的影响规律.这些因素包括铝粉粒度及含量、氧化剂种类、氧化剂粒度及级配和环境压力.随着铝粉粒度和含量的提高,铝粉燃烧效率降低;而随着氧化剂热值的提高,气相区的温度随之提高,铝粉的燃烧效率相对较高.对细AP而言,随着粒度...     

Controlling the particle size of spherical silica by adjusting the gas flow environment around the flame

To synthesize silica particles, a dry process consisting of burning an organosilicon compound as raw monomer has been widely studied. Previously, we used six starting materials in the dry process and investigated the effects of monomer species on the particle shape and size of silica. Here, we fixed the raw monomer species and amount of gas supplied from the burner and focused on the relationship between the gas environment around the flame and silica particle size. Specifically, we focused on quaternary gas flowing around the flame as a factor that affected the temperature around the flame. Its flow rate and velocity were expected to directly affect the temperature around the flame. We established the relationship between the temperature environment around the flame, specifically the amount of heat absorbed by the hot water for cooling the reactor and silica particle sizes. The temperature environment around the flame was determined by the balance between the reactor's size and amount of quaternary gas. Simultaneously, it was emitted as the amount of heat absorbed per unit heat transfer area of hot water. Consequently, we concluded that the environment around the flame determined the size of spherical silica particles and successfully controlled the particle size.