试论沉降法测定颗粒粒度及其分布

颗粒的粒度及其分布显著影响粉末的性质和用途，为了掌握生产中产品的质量，必须对粉末进行粒度分布的检测。详细介绍了沉降法的基本原理，实验方法、步骤和结果处理。试验和生产应用表明，粒度测定的方法多种多样，沉降法以其原理简单、易于操作而被广泛采用。     

The distribution of brownian motion on linear stopping boundaries

We consider Brownian motion with drift and stopping boundaries: linear upper and lower boundaries, and possibly a vertical boundary at a truncation point, all under conditions assuring a finite stopping time. T. W. Anderson (Ann. Math. Statist. 31, 1960) derived formulas for the distributions of the stopped process along these boundaries and for the associated expected stopping times. We present simpler formulas, and briefer derivations.     

Deconvolution of fractional brownian motion

We show that a fractional Brownian motion with H'∈(0,1) can be represented as an explicit transformation of a fractional Brownian motion with index H ∈(0,1). In particular, when H'=½, we obtain a deconvolution formula (or autoregressive representation) for fractional Brownian motion. We work both in the `time domain' and the `spectral domain' and contrast the advantages of one domain over the other.     

重力沉降原理在微粉和超细粉粒度分析中的应用

探讨了利用重力沉降原理对粉体颗粒粒度分布进行测试时 ,颗粒的布朗运动对测定精度的影响。并推导出常见的耐火材料粉体最小的测试颗粒粒径范围应为 0 .6～ 0 .95 μm。同时介绍了采用国产KCT - 1型沉降天平进行微粉与超细粉的粒度分布测定时的操作要点与技巧。并对测试过程中出现的异常现象和解决的方法进行了阐述     

The effect of particle size distribution on packing density

The packing density of a multi-particle system is found to increase if the particle size distribution is extended. Results are reported for Gaussian and log-normal size distributions using dense random packing of two sands with particle sizes of front <0.07 to 8.0 mm. Packing density is shown to be a function only of size distribution represented by a dimensionless standard deviation, and of particle shape. It is independent of particle size. Packing densities of binary mixtures of continuously distributed systems are found to depend upon the composition of the mixture, the mean-size ratio of the components of the binary, and upon the packing density of the individual components. Maxima occur at compositions of 55 to 75% larger component, and increasing mean-size ratios result in greater packing densities. The “increase in packing density” factor is a useful function for comparing, and setting limits to, packing densities of binary mixtures. The results should allow improved prediction and control of packing densities of many commonly encountered particle systems.     

气力输送装置对原料颗粒度的影响

在玻璃工业中,气力输送装置作为一种运输机械,专门用来输送散状物料.这种输送设备以其易管理、密封性好,设备简单,便于布置等优点被许多玻璃厂所采用.然而在使用过程中,它也表现出了较多弊端.其中在产生超细粉方面对产品质量所起的副作用就不可忽略.气力输送不同于其他输送装置,它不仅用来作为单纯的输送,还可作为生产工艺的一环,在输送过程中同时对物料进行粉碎、分级、干燥、加热等作用.就它的粉碎作用来说,影响具体有多大,恐怕被大多数厂家所忽略.下面是我厂在使用气力输送装置走过的曲折路程,供大家参考.     

A new particle size effect

The sintering effect of highly dispersed metals is the reason for the following phenomena: thermal deactivation, particle size effect, separable or non-separable kinetics and the isokinetic relationship ( = compensation effect). A comparison of these phenomena reveals a contradiction which can be reconciled by a new particle size effect. This effect is characterized in the following way: The dependence of specific activity on particle size is always connected with a variation of the activation energy, caused by the particle size distribution. Therefore, this effect is referred to as the partical size and distribution effect, P.S.D.E. This new concept describes all the observed phenomena of the conventional partical size effect. Moreover, it is consistent with similar effects such as non-separable kinetics and the isokinetic relationship. In consequence, the method of isothermal measurement of specific activity is inadequate.     

The effect of coal particle size on pyrolysis and steam gasification

For future power generation from coal, one preferred option in the UK is the air-blown gasification cycle (ABGC). In this system coal particles sized up to 3 mm, perhaps up to 6 mm in a commercial plant, are pyrolysed and then gasified in air/steam in a spouted bed reactor. As this range of coal particle sizes is large it is of interest to investigate the importance of particle size for those two processes. In particular the relation between the coal and the char particle size distribution was investigated to assess the error involved in assuming the coal size distribution at the on-set of gasification. Different coal size fractions underwent different changes on pyrolysis. Smaller coal particles were more likely to produce char particles larger than themselves, larger coal particles had a greater tendency to fragment. However, for the sizes investigated in this study ranging from 0.5 to 2.8 mm, the pyrolysis and gasification behaviour was found not to vary significantly with particle size. The coal size fractions showed similar char yields, irrespective of the different char size distributions resulting from pyrolysis. Testing the reactivity of the chars in air and CO₂ did not reveal significant differences between size fractions of the char, nor did partial gasification in steam in the spouted bed reactor. From the work undertaken, it can be concluded that pyrolysis and gasification within the range of particle sizes investigated are relatively insensitive to particle size.     

Modeling of slurry flow: The effect of particle size

A system of differential equations to obtain concentration and velocity distributions for quasi-uniform particle slurry flows is presented. Numerical solutions for various flow conditions have been obtained using an explicit algorithm. A “supported load” concept is proposed to explain the type of interaction through contact between solid particles in neighboring layers or between particles and the pipe wall. In the analysis, the relative contributions of terms describing turbulent shear stresses, particle interactions, and mixing effects vary with the dimensions of solid particles. The approach is tested for four kinds of sand of narrow size distributions (d = .65 mm, .48 mm, .52 mm and 13 mm), flowing with water in pipelines of various diameters (between 50 and 500 mm), at concentrations below 40% by volume. The coefficients used to estimate local parametes of the two-phase model are related to particle diameter. A comparison of numerical predictions and measurements of concentrations, velocities and headlosses shows the applicability of the model and the possibility of extrapolating available experimental results.     

The effect of particle size distribution on the olefin polymer reactor dynamics

Mass and energy balances in a reactor have been derived to study the effect of particle size distribution (PSD) for each reaction mechanism on the reactor dynamics. It was observed that the PSD affects both bed height and particle volume. A feasible region for reactor operation has been calculated by using physical constraints. In a nonisothermal polymerization system, the reactor temperature does not change appreciably as catalyst injection rate increases. A unique steady state solution is found in a gas-phase continuous stirred-bed propylene polymerization reactor. The eigenvalues of the system of equations indicate that the steady state is unstable. A comparison with published data allows the observation that the actual reactor dynamics may be readily explained by using only the PSD derived from a simple reaction mechanism.     

Multistage latex particle size analysis by disc centrifuge photosedimentometry

Characterization of a heterogeneous latex polymer synthesis requires quantifying the association of successive stage compositions with the previous stage latex seed particles. A new method for performing this analysis is presented for uniform sized latex particles by use of a Joyce Loebl disc centrifuge photosedimentometer. An iterative procedure is employed to solve a problem of unknown particle density when a successive polymerization produces new latex particles. The procedure is applicable regardless of the monomer compositions of the various stages and eliminates problems encountered with electron microscopy of soft deformable latex particles.     

Modelling the effect of particle size on dust explosions

The recent concept of inherent safety uses the properties of a material or process to eliminate or reduce the risk thus removing or minimizing the hazard at the source as opposed to accept the hazard and looking to mitigate the effects. In this framework the control of particle size in dust explosion prevention and mitigation is recognized as a major inherent safety methodology. Indeed, the increase of particle size may allow significant reduction of particle reaction rate eventually reducing the risk.In this paper a novel model is developed to quantify the effect of particle size on dust reactivity in an explosion phenomenon. The model takes into account all of the steps involved in a dust explosion: internal and external heating, devolatilization reaction and volatiles combustion. Varying the dust size can establish different regimes depending on the values of the characteristic time of each step and of several dimensionless numbers (Damköhler number, Da; Biot number, Bi; thermal Thiele number, Th). Results from the model are reported in terms of the deflagration index (K_St) as a function of dust diameter in all regimes and at varying Da, Th and Bi. Comparison with experimental data from polyethylene explosion tests shows promising results. Finally, the results of the model are presented in the form of a dust explosion regime diagram, which is helpful to make a draft evaluation of the role of dust size on explosion behavior and severity.     

激光粒度仪测定铝粉粒度

探讨折射率、遮光度、样品质量、采集时间、泵速等因素对铝粉粒度测定的影响,确定了测定铝粉粒度的最佳条件,即折射率为2.5,遮光度在10%~20%之间,采集时间20 s,泵速2 000 r/min,水为分散介质,加入6 m L质量浓度为4 g/L的六偏磷酸钠作分散剂。激光粒度仪测得结果与扫描电镜表征结果基本一致。该方法具有较高的准确性和数据重现性。     

The effect of rubber particle size on the mechanical properties of high-impact polystyrene

Resins having different rubber particle sizes were prepared by polymerizing impact polystyrene using different agitation rates but keeping all other parameters constant. Also, samples were made varying the amount and type of rubber and type of agitation. The impact and tensile properties of the prepared resins are studied in relation to existing theories of rubber particle reinforcement. The particle size dependence of energy absorption in impact (high intensity) and tensile (low intensity) testing appear to be opposite in nature. Energy absorption increases with increasing particle size in the high-intensity mode and decreases in low-intensity testing. Different mechanisms are, therefore, postulated to be operative in each of these two test methods.     

激光粒度仪测定碳酸钙粉体粒度的研究

以蒸馏水为分散介质,加入焦磷酸钠为分散剂,采用百特激光粒度仪测定研磨后的固体碳酸钙粉体的粒度分布,分别从仪器调试,样品处理和测试条件选择等几方面,以测定结果的D50值为参考,探讨引起测试结果误差的可能因素,从而优化了实验操作条件,提高了测定结果的准确度和精密度。     

粒度对高温色料色度的影响

运用离子呈色理论、晶体场理论,较好地解释了颜色釉的呈色机理,并根据色料的晶体结构及在釉中的存在状态,借助粒度分析仪、色度仪研究了色料的粒度大小对色度的影响规律.     

The effect of SiO_2 particle size on iron based F–T synthesis catalysts

The effect of particle size of silica, as catalyst binder, on the chemical and mechanical properties of iron based FT catalyst was studied in this work. The samples were characterized using XRD, BET, TEM, FT-IR, and H2-TPR, respectively. The attrition resistance and the FT activity were tested. Si-8–Si-15 catalysts prepared with 8–15 nm silica sol show good attrition resistance(attrition loss b 4%), especially Si-13 with an attrition loss of 1.89%. Hematite appeared in XRD patterns when silica sol above 15 nm is used. TEM micrographs show that no obvious Si O_2 particles appear when silica sol particle with size less than 8 nm was used, but Si O_2 particles coated with small ferrihydrite particles appear when silica sol above 8 nm was used. Si–O–Si vibration peak in FT-IR spectra increases with increasing silica sol size. Samples prepared with silica sol show good stability of FT reactions, and the average molecular weight of FT products increases with the increase of Si O_2 particle.     

制备条件对碳酸钡沉淀粒度分布的影响

一种功能陶瓷用碳酸钡的制备方法。采用正交试验法考察加料次序、反应温度、加料速度与表面活性剂这4种因素对制备的碳酸钡沉淀颗粒大小及粒度分布的影响。找出了功能陶瓷用碳酸钡制备的较佳条件：慢速反加料、反应温度25℃、添加表面活性剂。     

The particle size distribution effect on the drying efficiency of polymeric fibers containing castables

Refractory castables present several placing methods, defined mainly by the application requirements and material characteristics. Considering the same chemical composition, the particle size distribution (PSD) is the key property related to the large differences in their rheology, creep and corrosion resistance. It also plays an important role on their fluids permeation and drying behaviors. Therefore, it is reasonable to consider that the benefits promoted by polymeric fibers, added as drying agents, would be affected by PSD changes. In this work, the permeability and drying behaviors of fiber containing refractory castables were correlated to their PSD. Typical pumpable, self-flowing and vibrated formulations were tested in combination with polypropylene fibers. Permeability measurements and explosion tests were associated to the maximum paste thickness (MPT) and interparticle separation (IPS) parameters and to the fine/coarse particles ratio. The different classes of castables presented distinct needs of drying additives and the fibers’ efficiency was strongly dependent on castables PSD.