1、INTERNATIONAL STANDARD IS0 13321 First edition 1996-07-o I Particle size analysis - Photon correlation spectroscopy Analyse granulom B max c G2) f-2 Nv 77 r ;lo e P 8 P2 maximum value of the intercept B for a given setting of the detection optics; concentration of particulate material, in moles per
2、litre; intensity autocorrelation function; refractive index of the dispersion medium; number of particles in scattering volume V; viscosity of the dispersion medium; decay rate; laser wavelength in vacua (632,8 nm for He-Ne laser); particle volume fraction; particle density; scattering angle; second
3、 cumulant. 4 Principle A monochromatic and coherent laser light beam illuminates a representative sample for particle size analysis, dispersed at a suitable concentration in a liquid. The light scattered by the particles at an angle (typically 90) is recorded by a detector whose output is fed to a c
4、orrelator. The decay of the autocorrelation function of the scattered intensity is interpreted in terms of average particle size and polydispersity index by the so-called cumulants method. Annex C provides some theoreticai background for particle sizing by PCS. Copyright International Organization f
5、or Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 13321:1996(E) is0 5 Apparatus beam is on. Observe local regulations for laser radiation safety. The main components of a typical photon correlation spectrom
6、eter are listed below. NOTE 2 - Commercial or “home-made” instruments that meet the requirements of this International Standard may be used. There are several significant differences, both in hardware and software, not only between instruments from different manufacturers but also between different
7、types from one manufacturer. The instrument specifications do not always give adequate information for proper assess- ment of its specific features. Therefore, annex D has been provided to recommend specifications for PCS instruments. 5.1 Laser, monochromatic, emitting light polarized with its elect
8、ric field component perpendicular to the plane formed by the incident and detected rays (vertical polarization), e.g. a He-Ne laser capable of 2 mW to 5 mW power output. 5.2 Sample holder, allowing control and measure- ment of the temperature to within + 0,3 “C. 53 . Primary beam stop. 5.4 Optics an
9、d detector, to collect and digitize the radiation scattered by the sample at an angle of, e.g., 90”. If a polarization analyzer is included, it shall be positioned in the vertical position, i.e. with a maximum transmission for light polarized with its electrical field perpendicular to the plane of i
10、ncident and scattered beams. 5.5 Correlator. 5.6 Computation unit. 6 Preliminary procedures 61 . Instrument location The instrument shall be placed in a clean environment, free from excessive electrical noise and mechanical vibration and out of direct sunlight. If organic liquids are used (e.g. as a
11、n index-matched liquid and/or as the suspension medium), there shall be due regard to local health and safety requirements, and the area shall be well ventilated. The instrument shall be placed on a rigid table or bench to avoid necessity for fre- quent realignment of the optical system. NOTE 3 - Al
12、ternatively, it may incorporate a rigid optical bench internally. WARNING - PCS instruments are equipped with low or medium power lasers whose radiation can cause permanent eye damage, Never look into the direct path of the laser beam or its reflections. Do not use highly reflecting surfaces when th
13、e laser 6.2 Sample preparation and inspection 6.2.1 Samples shall consist of well-dispersed par- ticles in a liquid medium. The dispersion liquid shall fulfil following requirements: a) b) cl d) d f 1 it shall be transparent (non-absorbing) at the laser wavelength; it shall be compatible with the ma
14、terials used in the instrument; it shall not dissolve, swell or coagulate the particu- late material; it shall have a refractive index different from that of the particulate material; its refractive index and viscosity shall be known with an accuracy better than 0,5 %; it shall be well filtered. Wat
15、er is often used as a dispersion medium. The use of freshly distilled water (the still shall be built from quartz glassware) or of deionized and filtered (pore size 0,2 pm) water is recommended. Since long-range particle interaction may affect the results for strongly charge-stabilized dispersions,
16、a trace of salt c(NaCI) about IO-3 mol/l may be added to such samples to reduce the range of particle interaction. Large fluctuations in recorded scattered time- averaged signals (count rate) on short time scales (e.g. 0,l s intervals) with bursts of high count rates indicate the presence of contami
17、nating dust. The appearance of sparkling centres in the beam also usually indicates a dusty sample. Such liquids shall be further cleaned (by filtration and/or distillation) before use. Detailed recommendations for sample preparation are given in annex E. The dispersion liquid alone shall give no (o
18、r very low) scattered signal when checked in the instrument for dust or contaminants. 6.2.2 The concentration of particulate material shall be above some minimum level and shall not exceed a maximum level. The minimum level is determined by the following two requirements: 1) The scattered intensity
19、(count rate) of the sample containing the dispersed particles shall be at least 10 times higher than the signal scattered by the dispersion medium alone. 2) The number NV of particles in the scattering vol- ume shall be at least about 1 000 (any number in the range 500-I 000 is acceptable). 2 Copyri
20、ght International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,- IS0 IS0 13321:1996(E) 3) 4) 5) NOTE 4 -This number can be estimated from the av- erage PCS diameter xpcs, from the particle vol
21、ume frac- tion and from the value Vof the measuring volume by NV = 6qiWlm,$, A typical order of magnitude of V is 1 O-6 cm3 (its value can be found in the specifications provided by the in- strument manufacturer). This equation relates to monosized materials only; for polydisperse samples the actual
22、 number of particles in the scattering volume may be much larger than predicted by this equation. If this larger number density compromises the single- scattering criteria 3) to 5), it may be that further dilution is necessary, leading to a requirement that either the coherence aperture in the recei
23、ver be increased or the incident laser beam made larger to increase the measurement volume. A subsequent reduction in measured intercept will then be incurred. This com- promise is not permitted for the purposes of calibration and verification. The maximum level is mainly determined by the condition
24、 that only single scattering shall be ob- served, i.e. no multiple scattering. The absence of significant contributions from multiple scattering shall be determined by the three following checks. The samples shall not look opaque but shall look clear, or only slightly cloudy or turbid. This shall al
25、- ways be verified before putting the sample into the instrument. The ratio of the measured intercept (see annex A for its determination) to its maximal value (see the specifications of the manufacturer or clause 8 for its determination) shall be at least 0,8. if the instrument allows the laser beam
26、 passing through the sample to be viewed indirectly, a sharp parallel beam shall be observed; a spreading halo around the beam or any apparent absorbance shall not be present. NOTE 5 - If possible, the following additional check is recommended. If a spectrophotometer is available, the optical densit
27、y (O.D.) of the sample at the laser wavelength used for a l-cm path length can be used as an indicator for multiple scattering: for O.D. values larger than 0,04, mul- tiple scattering effects are to be expected. In many applications a volume fraction (I) of dispersed particulate material in the rang
28、e IO-5 to IO-4 fulfils the requirements for particle sizes below about 500 nm. In order to obtain the concentration range (c) in mass of dispersed material per unit volume, multiply the volume fraction by the particle density p (c = p. Switch the instrument on and allow it to warm Typically about 0,
29、5 h is required to stabilize the laser intensity and to bring the sample holder to the desired temperature. 7.2 Check the dispersion medium and record the average count rate scattered by a blank sample of it. 7.3 Place a sample of the dispersion (dispersion medium + particulate sample) in the instru
30、ment and allow temperature equilibrium to be established between sample and sample holder. The temperature shall be controlled and measured with an accuracy of 0,3 “C. NOTE 6 - It can take about 10 min for the liquid in the measurement volume of a l-cm measuring cell to equilib- rate by thermal diff
31、usion for a temperature change of only 3 “C. Errors in particle size determined from aqueous dispersions will be recorded at the rate of 2 % per “C if the temperature of the sample does not reach equilibrium. A possible alternative method is to measure the room temperature and then set the instrumen
32、t to control the sample holder temperature to within 0,3 “C of the room temperature. Samples can then equilibrate at room tem- perature and be measured immediately after insertion in the sample holder. Alternatively, samples can be equilib- rated in a thermostatted bath whose temperature is within 0
33、,3 “C of that of the instrument sample holder. In this case, remove the water from the cell before it contaminates the index-matching fluid. 7.4 The following data shall be recorded: sample identification, laser wavelength and scattering angle if necessary, measuring temperature, refractive index an
34、d viscosity of the dispersion medium, particle concentration and any other relevant details. 7.5 Perform a preliminary measurement on the dispersion to check that the particle concentration is not too low less than about 1 000 particles in the scattering volume, see 6.22 check Z) or too high see 6.2
35、2, check 4). Check that the average scattered intensity (count rate) is in the range 5 kcounts/s to 1 000 kcounts/s (5 000 counts/s to 1 000 000 counts/s). if these criteria are not met, repeat a measurement on a sample with a different concen- 3 Copyright International Organization for Standardizat
36、ion Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 13321:1996(E) IS0 tration of particulate material, or use another laser power level if possible. 7.6 For each sample, at least six duplicate measurements of at least 60 s
37、duration shall be performed and results stored. For sample count rates below 20 000 counts/s (20 kcounts/s), the duration in seconds shall be equivalent to at least 1 200 000 counts divided by the count rate in counts per second, or 1 200 kilocounts divided by the count rate in kilo- counts per seco
38、nd. 7.7 Record the average particle diameter xpcs and polydispersity index PI for each of the measurements. Calculate the mean: (x)=$ Xi i=l and the estimated standard deviation: SN-l =$T, f the polydispersity index shall be smaller than 0,l. NOTE 8 - Several suppliers provide traceable latices. A p
39、olystyrene latex (catalogue No. 1963) with a certified diameter of 100,7 nm can be obtained from the National Institute of Standards and Technology (NIST), Gaithersburg, MD, USA. Annex E provides guidelines for the preparation of a suitable sample. The maximal value of the intercept of the autocorre
40、- lation function can be determined as follows: a) select a collecting aperture for which a value of B max is available; b) determine the intercept B (see annex A) with dispersions of polystyrene latex (diameter about 100 nm) with at least two different concentrations meeting requirements I), 2), 3)
41、 and 5) of 6.22; c) if B depends in a systematic way on particle concentration, extrapolate the results to infinite dilution. 9 Repeatability The repeatability of the determination of average particle size, defined as 1 00I/(X), shall be better than 5 %. 10 Test report The average particle size xpcs
42、 and polydispersity index PI shall be reported. These data shall be the mean and standard deviation of at least six repeated measure- ments on a sample and shall be calculated according to the method given in annex A. If the mean values of xpcs and PI are concentration-dependent, their values extrap
43、olated to infinite dilution, or the value obtained at the lowest concentration, shall be reported. 8 Calibration and validation The following details shall also be provided: a) complete sample identification, including available Since particle size determination by PCS is an abso- lute method based
44、upon first principles, calibration as such is unnecessary. However, verification of the instruments performance should be performed with dispersions of particles of certified size after the first information about particle shape and homogen- eity; b) instrument type and number, or its detailed de- s
45、cription if a “homemade” instrument; 4 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-0 IS0 IS0 13321:1996(E) NOTE 9 - The following laser source details should also be
46、provided: type, wavelength, power and that it was vertically polarized; c) dispersion conditions: - dispersing liquid and its cleaning/filtering pro- cedure, - concentration of particulate material, - dispersing agents and their concentration, - dispersing procedure, - sonication conditions: frequen
47、cy and applied power (if necessary); d measurement conditions: - number of concentrations investigated, - number of particles in the measuring volume, as estimated from particle concentration and average particle size xpcs, - maximum value of the intercept B, of the autocorrelation function attainab
48、le for the given optical arrangement of the instrument. NOTE 10 -This value can be determined with a known material (see clause 8 and annex A), a r e) IT available, any other useful results or comments obtained at other scattering angles or from multi- angle results. If available, results obtained b
49、y other data analysis methods and results from other par- ticle sizing methods; value of the intercept B of the autocorrelation function and value of the ratio BIBmax, count rate observed for the dispersion me- dium, viscosity and refractive index of the dispersion liquid, temperature of the sample, average count rate observed for the sample, number of analyses and their duration, the variance of the fit see annex A, equation Mm f) analyst identification: - name and location of laboratory,
