BS 8471-2007 Guide to particle nsizing methods《颗粒筛分法指南》.pdf

1、BS 8471:2007Guide to particle sizing methodsICS 17.040; 19.120NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2007ISBN 978 0

2、580 53047 0The following BSI references relate to the work on this standard:Committee reference LBI/37Draft for comment 06/19987355 DCPublication historyFirst published November 2007Amendments issued since publicationAmd. no. Date Text affectedBS 8471:2007 BSI 2007 iBS 8471:2007ContentsForeword ii0

3、Introduction 11 Scope 12 Normative reference 13 Definitions 14 General 15 Particle size distribution 26 Methods of particle size determination 37 Aggregation 48 Size and shape 49 Sampling and dispersion 510 Factors affecting the choice of sizing method 711 Cost 1312 Calibration, traceability, valida

4、tion and verification 1313 Particle sizing techniques 14AnnexesAnnex A (informative) Flow diagrams to aid the choice of dispersion technique 18Bibliography 20List of figuresFigure A.1 Powder dispersion procedures 18Figure A.2 Decision trees 19List of tablesTable 1 Most commonly used particle sizing

5、techniques 15Table 2 Less commonly used particle sizing techniques 16Summary of pagesThis document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 21 and a back cover.BS 8471:2007ii BSI 2007ForewordPublishing informationThis British Standard was published by BSI and came i

6、nto effect on 30 November 2007. It was prepared by Technical Committee LBI/37, Sieves, screens and particle sizing. A list of organizations represented on this committee can be obtained on request to its secretary.Hazard warningsThe guidance contained in this British Standard is of a general nature.

7、 It cannot take account of hazards associated with specific materials which, when subjected to recommended treatments may be dangerous.Information about this documentUsers of this guide are directed to relevant Health and Safety (e.g. COSHH 2002 1) regulations, which require potential users of any p

8、rocedure to assess hazards associated with it and to document the precautions appropriate to the risk.Contractual and legal considerationsThis publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a Briti

9、sh Standard cannot confer immunity from legal obligations. BSI 2007 1BS 8471:20070IntroductionThis British Standard provides simple advice for those wishing to obtain particular information on the size distribution of particles in a sample of particulate material. Various methods of sizing exist whi

10、ch are based on several principles. The advice given is aimed at enabling users to select methods appropriate to their needs.Particles exist as powders or as suspensions in solid, liquid or gaseous media. In the context of this document particles might also be in the form of liquid droplets or emuls

11、ions. Methods are available for sizing them in all these conditions. In some cases it might be desirable, or indeed essential, to examine them in their original condition. In other instances it can be advantageous to change the condition of suspension.The standard provides a listing of the practical

12、 choices available and offers a logical approach to decision making. Principal features of each method are available at a glance in tabulated form. Important criteria that should be borne in mind when an analysis is discussed and some variables that might influence the choice of approach are illustr

13、ated. Although many methods of particle sizing are ingenious, sensitive, reliable and repeatable, no method can be regarded as perfect and compromise is frequently necessary. 1 ScopeThis British Standard guide discusses the techniques commonly used for particle sizing, in the context of the physical

14、 and chemical properties of the sample on which the information is required, and the purpose for which the information is to be used. This information is primarily relevant to particles in the sub-millimetre range.2 Normative referenceThe following referenced document is indispensable for the applic

15、ation of this document.BS 2955:1993, Glossary of terms relating to particle technology3 DefinitionsFor the purposes of this British Standard, the definitions given in BS 2955 apply.4 GeneralParticle size is an important determinant in particle behaviour and its measurement can be achieved by many me

16、thods. The simplest involve determination of particle dimensions by comparison with a standard scale, calliper gap or two-dimensional figure, such as a circle. Single, two- and three-dimensional measurements can be of value on occasions and their usefulness might be enhanced by being complemented wi

17、th shape descriptions.BS 8471:20072 BSI 2007Direct visual comparison of specific particles is not possible for particles the size of which is insufficient for resolution by the naked eye or with the aid of a microscope. To estimate the size of such particles, it is necessary to identify a property o

18、f the particle that varies as a function of size, and to determine that property for the particle concerned.Measurement of a single particle is of limited value, as information is usually required on the size distribution of a population of particles. Obtaining this information by recording the dime

19、nsions of individual particles without the use of automation can be tedious and slow. Without automation, individual measurement is rarely the method of choice even with large sized particles. A comparator method involves the segregation of particles through a mesh of finite size. Those particles th

20、at are small enough to pass through the holes in a uniform mesh are separated from those that are retained on the mesh. By use of a range of meshes appropriate to the sizes of the particles present, the population can be fractionated into classes whose contribution to the whole may be estimated by t

21、he weight of each fraction.Detailed information, by assessing the proportions of the population falling within channels defined by a series of size limits or thresholds, can be achieved by other methods. The upper size limit of one channel forms the lower size limit of the next. Such methods depend

22、upon each particle being measured and the distribution is thus derived from a process whereby individual particle data are sorted into size categories. Some methods depend, not upon the measurement of individual particles, but upon the measurement of a characteristic of the entire particle assembly,

23、 for example the scattering of light by a dispersed cloud of particles.5 Particle size distributionA particle size distribution can be described as: a functional relationship between the quantity of particles and some measure of particle size, or a description of the size and frequency of particles

24、in a population (BS 2955:1993, 6 029). Particle size distributions can be expressed as a fraction, which indicates the proportion of the total population occurring in size channels defined by a continuous range of upper and lower limits. These limits are usually chosen between zero and a magnitude g

25、reater than the largest particle present, or an arbitrarily defined maximum.In particle size distributions the quantity axis may be measured and expressed in terms of number, surface, volume or mass. Significant numerical differences occur when the quantity of particles in a particle size distributi

26、on are expressed on different quantity axes (e.g. number, surface, volume or mass).A single 100 m particle has the same volume as one thousand 10 m particles. The volume of sample in a specific size class is related to the number of particles in that size class and by the cube of the particle diamet

27、er. BSI 2007 3BS 8471:2007The sizing methods discussed in this British Standard depend upon some prior knowledge of the size and nature of the particles present in the sample to be measured. If such knowledge is not available when the sample is supplied, some might be revealed by microscopy. Both op

28、tical and electron microscopy, using calibrated measuring devices, constitute methods of particle sizing, and preliminary examination using a microscope is always recommended, even when it is not chosen as the final method of particle size analysis. Microscopy should also be used as a means to check

29、 the effectiveness of any pre-treatment of the sample prior to analysis.Using appropriate techniques, it is possible to obtain size distributions of populations of particles that are solid, liquid or gaseous. It is necessary that, at the time of analysis, the boundaries of the particles should be di

30、stinguishable from the boundaries of the other particles and from the continuous phase in which they are dispersed. Physical and chemical knowledge is required of the particle population under consideration to select a suspending medium that allows this criterion to be met.A general introduction to

31、the techniques discussed in this standard can be found in 2 and 3.6 Methods of particle size determination6.1 GeneralParticle size analysis methods can be divided into three basic approaches: direct (6.2); classification (6.3) and indirect (6.4).6.2 Direct methodsThese examine and estimate the size

32、of each particle separately and individually. These methods include:microscopy; electrical sensing zone; light blockage; and single particle light scattering.6.3 Classification methodsWith these methods, the assembly of particles is separated into size groups based upon a physical parameter of the p

33、article.Such methods include: sieving; sedimentation; field flow fractionation; and hydrodynamic chromatography.BS 8471:20074 BSI 20076.4 Indirect methodsThese are the methods that utilize a property of the particle. The particles are presented as an ensemble from which a size distribution is inferr

34、ed from the measured property.Such methods include: laser diffraction; dynamic light scattering; ultrasound; and specific surface.7AggregationIt is important to determine whether the particle size distribution is to be obtained from examination of the fundamental particles or whether to measure them

35、 in their aggregated state. For example, a raspberry represents an aggregate of fleshy seeds. Do we wish to determine the size distribution of the fleshy seeds or the berry?Aggregated particles can be reduced to individual particles by de-aggregation prior to analysis. Conversely, prior treatment ca

36、n cause individual particles to aggregate into groups which are so stable that they are subsequently measured as individual particles. It is important that the potential for aggregation or de-aggregation occurring in particular samples is assessed. Examination by microscopy can be invaluable for det

37、ermining changes in the degree of aggregation, even if alternative methods are to be used for the quantitative analysis. 8 Size and shapeThe shape of particles is an extremely important factor in measuring particle size as it can influence the perception of size by the methods discussed in this guid

38、e. In sieving, for example, the method discriminates the size of irregular particles according to the second largest dimension of the particle. Shape also influences the sedimentation of particles, causing them to appear smaller by mass than their actual mass.Difficulties in interpretation of result

39、s are compounded when particles in a population to be measured have a range of both size and shape. Microscopic examination can provide an assessment of the shape or range of shapes present, allowing the choice of method or methods adopted to be matched to the predicted behaviour of particles under

40、conditions of measurement. BSI 2007 5BS 8471:2007It is common to express particle size in terms of an equivalent spherical diameter but, because many principles can be adopted in particle size measurement, there are many different ways in which equivalence can be established. Consequently, many type

41、s of diameter have been defined, to reflect the chosen equivalent property. These include: specific volume diameter; Stokes diameter; projected area diameter (two outcomes according to particle orientation); sieve size of particle; Ferets diameter; Martins diameter; and equivalent diffraction diamet

42、erall of which are defined in BS 2955. 9 Sampling and dispersion9.1 SamplingAs with any type of analysis, it is rarely possible, or even desirable, to perform particle size analysis on an entire bulk particulate material. Consequently it is necessary to create a test sample for the analysis. For the

43、 results to be meaningful in relation to the bulk, steps shall be taken to ensure that the test sample is truly representative of the bulk. In the context of particle sizing, this demands that the sample and the bulk have the same particle size distribution. Demonstrating this conclusively is diffic

44、ult since the bulk cannot usually be analysed. However, there are approaches that offer some reassurance, including: following approved sampling procedures (see e.g. ISO 144881); analysing replicate test samples, each selected according to the approved procedure; comparing them to ascertain the leve

45、l of accord, or differences (i.e. repeatability and reproducibility). The quantity of material constituting the test sample can also have a material influence upon the final precision of the result. It shall be clear that if all the particles are identical then any one will represent the whole. As t

46、he width of the size distribution increases, more and more test sample is required, if precision in the final result is to be maintained (see 4). 1)In preparationBS 8471:20076 BSI 20079.2 Dispersion9.2.1 GeneralDispersion is the separation and distribution of one phase (the dispersed phase) in anoth

47、er (the continuous phase). The physical states (phases) usually measured as particles, constituting the dispersed phase, are liquid, gaseous or solid, and methods exist for measuring each when dispersed in liquid, solid or gas. It is possible to measure gas dispersed as bubbles in liquid or a solid,

48、 but not as a gas dispersed in another gas as for such a measurement to take place it is necessary for a sensible stationary boundary to exist between the dispersed phase and the continuous phase.Facilities for analysing samples vary among methods of particle size analysis. Some methods for analysin

49、g solid dispersed phases require sample presentation as a powder dispersed in gas and others as a suspension in a liquid.NOTE For decision trees showing the steps and decisions to be taken with respect to the type of sample under investigation and the final result required, see Annex A.Converting from one condition to another is simple but retention of the same particle characteristics throughout the transition can be extremely difficult because in changing the state, changes are also broug