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1、BS 8471:2007 Guide to particle sizing methods ICS 17.040; 19.120 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BRITISH STANDARD Licensed Copy: London South Bank University, London South Bank University, Thu Dec 20 02:42:01 GMT+00:00 2007, Uncontrolled Copy, (c) BSI Publishin
2、g and copyright information The BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2007 ISBN 978 0 580 53047 0 The following BSI references relate to the work on this standard: Committee reference LBI/37 Draft for comment 06/19987355 DC Publication histo
3、ry First published November 2007 Amendments issued since publication Amd. no.DateText affected BS 8471:2007 Licensed Copy: London South Bank University, London South Bank University, Thu Dec 20 02:42:01 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BSI 2007i BS 8471:2007 Contents Foreword ii 0Introduct
4、ion 1 1Scope 1 2Normative reference 1 3Definitions 1 4General 1 5Particle size distribution 2 6Methods of particle size determination 3 7Aggregation 4 8Size and shape 4 9Sampling and dispersion 5 10Factors affecting the choice of sizing method 7 11Cost 13 12Calibration, traceability, validation and
5、verification 13 13Particle sizing techniques 14 Annexes Annex A (informative) Flow diagrams to aid the choice of dispersion technique 18 Bibliography 20 List of figures Figure A.1 Powder dispersion procedures 18 Figure A.2 Decision trees 19 List of tables Table 1 Most commonly used particle sizing t
6、echniques 15 Table 2 Less commonly used particle sizing techniques 16 Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 21 and a back cover. Licensed Copy: London South Bank University, London South Bank University, Thu Dec 20 02:42:01 GMT+00:0
7、0 2007, Uncontrolled Copy, (c) BSI BS 8471:2007 ii BSI 2007 Foreword Publishing information This British Standard was published by BSI and came into effect on 30 November 2007. It was prepared by Technical Committee LBI/37, Sieves, screens and particle sizing. A list of organizations represented on
8、this committee can be obtained on request to its secretary. Hazard warnings The guidance contained in this British Standard is of a general nature. It cannot take account of hazards associated with specific materials which, when subjected to recommended treatments may be dangerous. Information about
9、 this document Users of this guide are directed to relevant Health and Safety (e.g. COSHH 2002 1) regulations, which require potential users of any procedure to assess hazards associated with it and to document the precautions appropriate to the risk. Contractual and legal considerations This public
10、ation does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Licensed Copy: London South Bank University, London South Bank University, Thu Dec 20 02:
11、42:01 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BSI 20071 BS 8471:2007 0 Introduction This 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 which are
12、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 emulsions.
13、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 choi
14、ces 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 illustrated.
15、 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 Scope This British Standard guide discusses the techniques commonly used for particle sizing, in the context of the physical and
16、 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 reference The following referenced document is indispensable for the applicat
17、ion of this document. BS 2955:1993, Glossary of terms relating to particle technology 3 Definitions For the purposes of this British Standard, the definitions given in BS 2955 apply. 4 General Particle size is an important determinant in particle behaviour and its measurement can be achieved by many
18、 methods. 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
19、 with shape descriptions. Licensed Copy: London South Bank University, London South Bank University, Thu Dec 20 02:42:01 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS 8471:2007 2 BSI 2007 Direct visual comparison of specific particles is not possible for particles the size of which is insufficient f
20、or 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 of 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
21、value, as information is usually required on the size distribution of a population of particles. Obtaining this information by recording the dimensions of individual particles without the use of automation can be tedious and slow. Without automation, individual measurement is rarely the method of ch
22、oice even with large sized particles. A comparator method involves the segregation of particles through a mesh of finite size. Those particles that 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 appropr
23、iate to the sizes of the particles present, the population can be fractionated into classes whose contribution to the whole may be estimated by the weight of each fraction. Detailed information, by assessing the proportions of the population falling within channels defined by a series of size limits
24、 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 upon each particle being measured and the distribution is thus derived from a process whereby individual particle data are sorted into size categories. So
25、me methods depend, not upon the measurement of individual particles, but upon the measurement of a characteristic of the entire particle assembly, for example the scattering of light by a dispersed cloud of particles. 5 Particle size distribution A particle size distribution can be described as: a f
26、unctional relationship between the quantity of particles and some measure of particle size, or a description of the size and frequency of particles in a population (BS 2955:1993, 6 029). Particle size distributions can be expressed as a fraction, which indicates the proportion of the total populatio
27、n occurring in size channels defined by a continuous range of upper and lower limits. These limits are usually chosen between zero and a magnitude greater than the largest particle present, or an arbitrarily defined maximum. In particle size distributions the quantity axis may be measured and expres
28、sed in terms of number, surface, volume or mass. Significant numerical differences occur when the quantity of particles in a particle size distribution 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 pa
29、rticles. 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 diameter. Licensed Copy: London South Bank University, London South Bank University, Thu Dec 20 02:42:01 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BSI 2007
30、3 BS 8471:2007 The 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 optical and e
31、lectron 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 the effect
32、iveness 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 distinguisha
33、ble 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 the techn
34、iques discussed in this standard can be found in 2 and 3. 6 Methods of particle size determination 6.1General Particle size analysis methods can be divided into three basic approaches: direct (6.2); classification (6.3) and indirect (6.4). 6.2Direct methods These examine and estimate the size of eac
35、h particle separately and individually. These methods include: microscopy; electrical sensing zone; light blockage; and single particle light scattering. 6.3Classification methods With these methods, the assembly of particles is separated into size groups based upon a physical parameter of the parti
36、cle. Such methods include: sieving; sedimentation; field flow fractionation; and hydrodynamic chromatography. Licensed Copy: London South Bank University, London South Bank University, Thu Dec 20 02:42:01 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS 8471:2007 4 BSI 2007 6.4Indirect methods These ar
37、e the methods that utilize a property of the particle. The particles are presented as an ensemble from which a size distribution is inferred from the measured property. Such methods include: laser diffraction; dynamic light scattering; ultrasound; and specific surface. 7 Aggregation It is important
38、to determine whether the particle size distribution is to be obtained from examination of the fundamental particles or whether to measure them 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 seed
39、s or the berry? Aggregated particles can be reduced to individual particles by de-aggregation prior to analysis. Conversely, prior treatment can cause individual particles to aggregate into groups which are so stable that they are subsequently measured as individual particles. It is important that t
40、he potential for aggregation or de-aggregation occurring in particular samples is assessed. Examination by microscopy can be invaluable for determining changes in the degree of aggregation, even if alternative methods are to be used for the quantitative analysis. 8 Size and shape The shape of partic
41、les is an extremely important factor in measuring particle size as it can influence the perception of size by the methods discussed in this guide. In sieving, for example, the method discriminates the size of irregular particles according to the second largest dimension of the particle. Shape also i
42、nfluences the sedimentation of particles, causing them to appear smaller by mass than their actual mass. Difficulties in interpretation of results 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 th
43、e shape or range of shapes present, allowing the choice of method or methods adopted to be matched to the predicted behaviour of particles under conditions of measurement. Licensed Copy: London South Bank University, London South Bank University, Thu Dec 20 02:42:01 GMT+00:00 2007, Uncontrolled Copy
44、, (c) BSI BSI 20075 BS 8471:2007 It 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 types of diameter ha
45、ve 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 diameter all of which
46、are defined in BS 2955. 9 Sampling and dispersion 9.1Sampling As 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 results to be
47、 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 difficult since the
48、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 level of accord, o
49、r 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 the 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 preparation Licensed Copy: London South Bank University, London South Bank
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