1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58methods Part 1: Concepts and procedures in ultrasonic attenuation spectroscopyICS 19.120Measurement
2、 and characterization of particles by acoustic BRITISH STANDARDBS ISO 20998-1:2006BS ISO 20998-1:2006This British Standard was published under the authority of the Standards Policy and Strategy Committee on 29 September 2006 BSI 2006ISBN 0 580 49269 9Amendments issued since publicationAmd. No. Date
3、Commentscontract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations. National forewordThis British Standard was published by BSI. It is the UK implementation of ISO 20998-1:2006.The UK participation in its preparation w
4、as entrusted to Technical Committee LBI/37, Sieves, screens and particle sizing.A list of organizations represented on LBI/37 can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a Reference numberISO 20998-1:2006(E)INTERNATIONAL ST
5、ANDARD ISO20998-1First edition2006-08-01Measurement and characterization of particles by acoustic methods Part 1: Concepts and procedures in ultrasonic attenuation spectroscopy Mesurage et caractrisation des particules par des mthodes acoustiques Partie 1: Concepts et modes opratoires en spectroscop
6、ie dattnuation ultrasonique BS ISO 20998-1:2006ii iiiContents Page Foreword iv Introduction v 1 Scope . 1 2 Terms and definitions. 1 3 Sampling and reference materials 3 3.1 Sampling considerations . 3 3.2 Reference materials 4 4 Methods . 4 4.1 Principles. 4 4.2 Apparatus 5 4.3 Preparation 6 4.4 Me
7、asurement. 8 4.5 Interpretation of measurement data . 9 5 Reporting of results 10 5.1 Reports for laboratory testing . 10 5.2 Results for in-process and control applications . 10 Annex A (informative) Techniques . 11 Annex B (informative) Application examples 17 Annex C (informative) Inversion of at
8、tenuation spectrum. 18 Bibliography . 20 BS ISO 20998-1:2006iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical com
9、mittees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
10、 International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft Internatio
11、nal Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be t
12、he subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 20998-1 was prepared by Technical Committee ISO/TC 24, Sieves, sieving and other sizing methods, Subcommittee SC 4, Sizing by methods other than sieving. ISO 20998 consists of the follow
13、ing parts, under the general title Measurement and characterization of particles by acoustic methods: Part 1: Concepts and procedures in ultrasonic attenuation spectroscopy The following parts are under preparation: Part 2: Guidelines for linear theory Part 3: Guidelines for non-linear theory BS ISO
14、 20998-1:2006vIntroduction It is well known that ultrasonic spectroscopy can be used to measure particle size distribution (PSD) in colloids, dispersions, and emulsions (see 6789). The basic concept is to measure the frequency-dependent attenuation or velocity of the ultrasound as it passes through
15、the sample. This attenuation includes contributions due to scattering or absorption by particles in the sample, and the size distribution and concentration of dispersed material determines the attenuation spectrum (see 101112). Once this connection is established by empirical observation or by theor
16、etical calculations, one can in principle estimate the PSD from the ultrasonic data. Ultrasonic techniques are useful for dynamic on-line measurements in concentrated slurries and emulsions. Traditionally, such measurements have been made off-line in a quality control laboratory, and constraints imp
17、osed by the instrumentation have required the use of diluted samples. By making in-process ultrasonic measurements at full concentration, one does not risk altering the dispersion state of the sample. In addition, dynamic processes (such as flocculation, dispersion, and comminution) can be observed
18、directly in real time (see 13). This data can be used in process control schemes to improve both the manufacturing process and the product performance. ISO 20998 consists of three parts: Part 1 introduces the terminology, concepts and procedures for measuring ultrasonic attenuation spectra; Part 2 p
19、rovides guidelines for determining particle size information from the measured spectra for cases where the spectrum is a linear function of the particle volume fraction; Part 3 addresses the determination of particle size for cases where the spectrum is not a linear function of volume fraction. BS I
20、SO 20998-1:2006blank1Measurement and characterization of particles by acoustic methods Part 1: Concepts and procedures in ultrasonic attenuation spectroscopy 1 Scope This part of ISO 20998 describes ultrasonic methods for determining the size distributions of one or more material phases dispersed in
21、 a liquid. Colloids, dispersions, slurries and emulsions are within the scope of this part of ISO 20998. The typical particle size for such analysis ranges from 10 nm to 3 mm, although particles outside this range have also been successfully measured. Measurements can be made for concentrations of t
22、he dispersed phase ranging from 0,1 % by volume up to 50 % or more by volume, depending on the density contrast between the continuous and the dispersed phases. These methods can be used to monitor dynamic changes in the size distribution, including agglomeration or flocculation in concentrated syst
23、ems. 2 Terms and definitions For the purposes of this document, the following terms apply: 2.1 absorption direct reduction of incident ultrasonic energy by means other than scattering 2.2 attenuation extinction total reduction of incident ultrasonic energy, including both scattering and absorption.
24、NOTE The recommended measurement unit is the decibel (dB), which is defined as 10 times the common (base 10) logarithm of the ratio of incident intensity to transmitted intensity, or equivalently 20 times the common logarithm of the ratio of incident amplitude to transmitted amplitude. The neper (Np
25、) is a permitted alternative measurement unit based on the natural logarithm, rather than the common logarithm. The conversion factor is 1 Np = 8,686 dB. 2.3 attenuation coefficient extinction coefficient attenuation (extinction) per unit length of ultrasonic propagation through a material, measured
26、 in units of dB/cm or Np/cm. NOTE Attenuation coefficients are sometimes scaled by frequency, or frequency-squared, to identify the dominant attenuation mechanism. For clarity, in this part of ISO 20998, only the attenuation per unit length (in dB/cm) is considered. 2.4 attenuation spectrum attenuat
27、ion coefficient measured as a function of frequency BS ISO 20998-1:20062 2.5 bandwidth range of frequencies contained in an ultrasonic signal, typically measured as the frequency difference between the -3 dB points on a spectrum analyser 2.6 broadband characterized as having a bandwidth that is equa
28、l to at least half of the centre frequency 2.7 digitization act of generating a digital (quantized) representation of a continuous signal NOTE The number of bits determines the resolution (fidelity), and the sampling rate determines the bandwidth (Nyquist criterion). 2.8 excess attenuation increment
29、al attenuation caused by the presence of particles in the continuous phase 2.9 Fourier transform mathematical transform that converts a time-varying signal into its frequency components, which is often implemented in computers as a Fast Fourier Transform (FFT) algorithm 2.10 interference wave phenom
30、enon of cancellation or enhancement observed when two or more waves overlap 2.11 intrinsic response frequency-dependent response of the ultrasonic spectrometer itself NOTE This is not to be confused with the intrinsic absorption of the sample component materials. 2.12 path length distance traversed
31、by the ultrasonic wave between the emitting transducer and the receiver 2.13 pulse wave of sufficiently short duration to contain broadband Fourier components 2.14 reflection return of an ultrasonic wave at an interface or surface 2.15 scattering removal of ultrasonic energy from the incident wave b
32、y redirection 2.16 spectrum frequency components of a signal, typically arranged as magnitude versus frequency 2.17 tone burst short duration of a few cycles of a sinusoidal wave NOTE Typically, a tone burst consists of 5 to 10 cycles of a sinusoidal wave. BS ISO 20998-1:200632.18 transducer device
33、for generating ultrasound from an electrical signal or vice versa NOTE Piezoelectric devices are commonly used for this purpose. 2.19 transmission passage of ultrasound through a sample 2.20 transmission spectrum transmission value measured as a function of frequency 2.21 transmission value amplitud
34、e of an ultrasonic signal (or a component thereof) that has been transmitted through a sample, measured in volts or arbitrary units 2.22 ultrasound high frequency (over 20 kHz) sound waves which propagate through fluids and solids NOTE The range employed in particle characterization is typically 100
35、 kHz to 100 MHz. 2.23 wave fluctuation, e.g. pressure, shear or thermal, which propagates through a physical medium 2.24 waveform shape of the wave when seen on an oscilloscope or digitized display 2.25 wavelength length of a wave, determined by the distance between corresponding points on successiv
36、e waves 3 Sampling and reference materials 3.1 Sampling considerations 3.1.1 Dry powders It is necessary to disperse a dry powder in a liquid before measuring the ultrasonic attenuation spectrum. A representative sample of the powder shall be used in the preparation of the liquid dispersion. It is r
37、ecommended that sampling procedures be carried out in accordance with ISO 14488. Dispersion of the powder should be carried out in accordance with ISO 14887. 3.1.2 Suspensions and slurries The apparent particle size in flocculated or poorly-dispersed systems changes as a function of the applied shea
38、r stress. Therefore, unless floc size or quality of a suspension is to be measured, it is recommended that suspension and slurries be mixed thoroughly before a sample is withdrawn for ultrasonic analysis. The stability of the suspension impacts the results. BS ISO 20998-1:20064 3.1.3 Emulsions Many
39、phenomena affect the homogeneity of emulsions, including creaming, droplet coalescence and phase separation. These changes affect the observed ultrasonic attenuation spectrum. If the initial droplet size distribution is to be measured for unstable emulsions, it is recommended that the sample be prep
40、ared immediately before the measurement. 3.2 Reference materials 3.2.1 Reference liquid The use of a reference liquid is required in order to verify correct operation of the ultrasonic spectrometer itself. De-gassed clean water at ambient temperature has a relatively low attenuation coefficient (see
41、 14). Water is therefore recommended as a reference liquid for determining the intrinsic response of the spectrometer. A procedure for de-gassing water is given in IEC 62127-1. 3.2.2 Reference sample The use of a reference sample is recommended to verify the correct estimation of particle size distr
42、ibution from the observed attenuation spectrum, but no reference material has yet been identified for general use. The user should identify a well-characterized and stable material as a standard sample for monitoring variability in the size distribution results. 4 Methods 4.1 Principles As ultrasoun
43、d passes through a suspension, slurry, colloid or emulsion, it is scattered and absorbed by the discrete phase, with the result that the intensity of the transmitted sound is diminished. The attenuation coefficient is a function of ultrasonic frequency and depends on the composition and physical sta
44、te of the particulate system. The measurement of the attenuation spectrum can be used to estimate the particle size distribution and concentration. The necessary apparatus is described in 4.2. The total measured attenuation is due to the intrinsic absorption of the continuous liquid phase, the intri
45、nsic absorption of the dispersed phase(s), thermal losses, viscous losses and scattering losses (see 67). The relative importance of these loss mechanisms depends on the material system. A theoretical or empirical model of these mechanisms can be used to convert the observed data into an estimate of
46、 the particle size or particle size distribution. There is no single general procedure for determining particle size information from the attenuation spectrum. Different models and procedures are used depending on the application and nature of the sample, as described in ISO 20998-2. The attenuation
47、 spectrum can be measured as long as the signal-to-noise ratio is adequate. However, an a priori theoretical model may not exist due to lack of knowledge about the dispersed or continuous phases. In cases where there is no suitable theoretical or empirical model available to describe the interaction
48、 of ultrasound with the system of interest, the attenuation spectrum can still be used to infer relative changes in particle size (see 13). A variety of techniques (see Annex A) have been used to measure ultrasonic spectra. Some of these methods have been implemented in laboratory instruments and so
49、me have been used in industrial applications. Ultrasonic spectroscopy has been used to measure particle size in a variety of material systems. Example applications are listed in Annex B. BS ISO 20998-1:200654.2 Apparatus 4.2.1 General As a minimum, the spectrometer consists of an excitation source, one or more ultrasonic transducers, a sample cell (or flow cell, in the case of in-process instruments), a preamplifier and a means for acquiring the signal. Each of these components shall be tailored to fit the
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