马尔文激光粒度仪简介

马尔文激光粒度仪简介 laParticle size analysis-Laser diffraction methods (ISO-13320-1) Introduction Laser diffraction methods are nowadays widely used for particle sizing in many different applications. The success of the technique is based on the tact that it can be applied to various kinds of particulate systems, is fast and can be automated and that a variety of commercial instruments is available. Nevertheless, the proper use of the instrument and the interpretation of the results require the necessary caution. Therefore, there is a need for establishing an international standard for particle size analysis by laser diffraction methods. Its purpose is to provide a methodology for adequate quality control in particle size analysis. Historically, the laser diffraction technique started by taking only scattering at small angles into consideration and, thus, has been known by the following names: - fraunhofer diffraction; - (near-) forward light scattering; - low-angle laser light scattering (LALLS). However, the technique has been broadened to include light scattering in a wider angular range and application of the Mie theory in addition to approximating theories such as Fraunhofer and anomalous diffraction. The laser diffraction technique is based on the phenomenon that particles scatter light in all directions with an intensity pattern that is dependent on particle size. All present instruments assume a spherical shape for the particle. Figure 1 illustrates the characteristics of single particle scattering patterns: alternation of high and low intensities, with patterns that extend for smaller particles to wider angles than for larger particles[2-7,10,15 in the bibliography]. Within certain limits the scattering pattern of an ensemble of particles is identical to the sum of the individual scattering patterns of all particles present. By using an optical model to compute scattering for unit volumes of particles in selected size classes and a mathematical deconvolution procedure, a volumetric particle size distribution is calculated, the scattering pattern of which fits best with the measured pattern (see also annex A). A typical diffraction instrument consists of a light beam (usually a laser), a particulate dispersing device, a detector for measuring the scattering pattern and a computer for both control of the instrument and calculation of the particle size distribution. Note that the laser diffraction technique cannot distinguish between scattering by single particles and scattering by clusters of primary particles forming an agglomerate or an aggregate. Usually, the resulting particle size for agglomerates is related to the cluster size, but sometimes the size of the primary particles is reflected in the particle size distribution as well. As most particulate samples contain agglomerates or aggregates and one is generally interested in the size distribution of the primary particles, the clusters are usually dispersed into primary particles before measurement. Historically, instruments only used scattering angles smaller than ?14,which limited the application to a lower size of about 1μm. The reason for this limitation is that smaller particles show most of their distinctive scattering at larger angles (see also annex Z).Many recent instruments allow measurement at larger scattering angles, some up to about 150?,for example through application of a converging beam, more or larger lenses, a second laser beam or more detectors. Thus smaller particles down to about 0.1μm can be sized. Some instruments incorporate additional information from scattering intensities and intensity differences at various wavelengths and polarization planes in order to improve the characterization of particle sizes in the submicrometre range. Particle size analysis – Laser diffraction methods- Part 1: General principles 1 scope This part of ISO 13320 provides guidance on the measurement of size distributions of particles in any two-phase system, for example powders, sprays, aerosols, suspensions, emulsions and gas bubbles in liquids, through analysis of their angular light scattering patterns. It does not address the specific requirements of particle size measurement of specific products. This part of ISO13320 is applicable to particle sizes ranging from approximately 0.1μm to 3μm. For non-spherical particles, an equivalent-sphere size distribution is obtained because the technique uses the assumption of spherical particles in its optical model. The resulting particle size distribution may be different from those obtained by methods based on other physical principles (e.g. Sedimentation, sieving). 3,terms, definitions and symbols For the purposes of this part of ISO 13320, the following terms, definitions and symbols apply. 3.1 terms, definitions 3.1.1 absorption introduction of intensity of a light beam traversing a medium through energy conversion in the medium 3.1.2 coefficient of variation (变异系数) Noative measure(%) for precision: standard deviation divided by mean value of population and multiplied by 100 or normal distributions of data the median is equal to the mean 3.1.3complex refractive index(,,) Refractive index of a particle, consisting of a real and an imaginary (absorption) part. Np=n-ik pp 3.1.4 relative refractive index (m) complex refractive index of a particle, relative to that the medium。 3.1.5 deconvolution Mathematical procedure whereby the size distribution of a particle ensemble is inferred from measurements of their scattering pattern. 3.1.6 diffraction Spreading of light around the contour of a particle beyond the limits of its geometrical shadow with a small deviation from rectilinear propagation 3.1.7 extinction Attenuation of a light beam traversing a medium through absorption and scattering . 3.1.8 model matrix Matrix containing light scattering vectors for unit volumes of different size classes, scaled to the detector’s geometry, as derived from model computation. 3.1.9multiple scattering Subsequent scattering of light at more than one particle, causing a scattering pattern that is no longer the sum of the patterns from all individual particles (in contrast to single scattering ) 3.1.10 obscuration Optical concentration Percentage or fraction of incident light that is attenuated due to extinction (scattering and/or absorption) by the particles 3.1.11 optical model Theoretical model used for computing the model matrix for optically homogeneous spheres with, if necessary, a specified complex refractive index, e.g. Frauhofer diffraction, anomalous diffraction, Mie scattering 3.1.12 reflection Return of radiation by a surface, without change in wavelength 3.1.13 refraction Change of the direction of propagation of light determined by change in the velocity of propagation in passing from one medium to another, in accordance with Snell’s law Nsinθ=nsinθ mmpp 3.1.14 scattering General term describing the change in propagation of light at the interface of two media 3.1.15 scattering pattern Angular or spatial pattern of light intensities[I(θ) and I(r) respectively] originating from scattering ,or the related energy values taking into account the sensitivity and the geometry of the detector elements 3.1.16 single scattering Scattering whereby the contribution of a single member of variation (relative percentage) of the size distribution NOTE for normal distributions about 95% of the population falls within ,2 standard deviations from the mean value and about 99.7% within ,3 standard deviations from the mean value. 3.2 symbols 4 principle A representative sample, dispersed at an adequate concentration in a suitable liquid or gas, is passed through the beam of a monochromatic light source, usually a laser. The light scattered by the particles at various angles it measured by a multi-element detector and numerical values relating to the scattering pattern are then recorded for subsequent analysis. These numerical scattering values are then transformed, using an appropriate optical model and mathematical procedure, to yield the proportion of total volume to a discrete number of size classes forming volumetric particle size distribution. , Laser diffraction instrument In the conventional set-up, a light source(typically a laser) is used to generate a monochromatic, coherent, parallel beam. This is followed by a beam processing unit, usually a beam expander with integrated filter, producing a extended and nearly ideal beam to illuminate the dispersed particles. A representative sample, dispersed at an adequate concentration is passed through the light beam in a measuring zone by a transporting medium (gas or liquid); this measuring zone should be within the working distance of the lens used. Sometimes, the particle stream in a process is illuminated directly by the laser beam for measurement, as in the case of sprays, aerosols and air bubbles in liquids. In other cases (such as emulsions, pastes and powders), representative samples can be dispersed in suitable liquids (see annex C). Often dispersants (wetting agents: stabilizers) and /or mechanical forces (agitation; ultrasonication) are applied for deagglomeration of particles and stabilization of the dispersion. For these liquid dispersions a recirculating system is most commonly used, consisting of an optical measuring cell, a dispersion bath usually equipped with stirrer and ultrasonic elements, a pump and tubing. Dry powders can also be converted into aerosols through application of dry powder dispersers, which apply mechanical forces for deagglomeration. Here a dosing device feeds the disperser with a constant mass flow of sample. The disperser uses the energy of a compressed gas or the differential pressure to a vacuum to disperse the particles It outputs an aerosol that is blown through the measuring zone, usually into the inlet of a vacuum pipe that collects the particles. There are two positions in which the particles can enter the laser beam. In the conventional case the particles enter the parallel beam before and within the working distance of the collecting lens [see Figure 3-a]. In the so-called reversed Fourier optics case the particles are entered behind the collecting lens and, thus, in a converging beam [see Figure 3-b]. The advantage of the conventional set-up is that a reasonable path length for the sample is allowed within the working distance of the lens. The second set-up allows only small path lengths but enables measurement of scattered light at larger angles, which is useful when submicrometre particles are present. The interaction of the incident light beam and the ensemble of dispersed particles results in a scattering pattern with different light intensities at various angles (see annex a for theoretical background of laser diffraction), the total angular intensity distribution I(θ),consisting of both direct and scattered light, is then focused by a positive lens or an ensemble of lenses onto a multi-element detector. The lens(es) provide(s) for a scattering pattern which, within limits, is not dependent upon the location of the particles in the light beam. So, the continuous angular intensity distribution I(θ) is converted into a discrete spatial intensity distribution I(r) on a set of detector elements. It is assumed that the recorded scattering pattern of the particle ensemble is identical to the sum of the patterns from all individual single scattering particles presented in random relative positions. Note that only a limited angular range of scattered light is collected by the lens(es) and, thus, by the detector. The detector generally consists of a number of photodiodes; some instruments apple one photodiode in combination with moving slits. The photodiodes convert the spatial intensity distribution I(r) into a set of photocurrents I, subsequent electronics then convert and digitize the n photocurrents into a set of intensity or energy vectors L. Representing n the scattering pattern. A central element measures the intensity of the non-scattered light and, thus, with a calculation, provides a measure of optical concentration or obscuration. Some instruments provide special geometries of the central element in order to automatically re-centre or re-focus the detector by moving the detector or the lens. It is desirable that the detector elements are positioned so as to prevent the light reflected from the surface from re-traversing the optical system. A computer controls the measurement and is used for storage and manipulation of the detected signals, for storage and/or calculation of a proper form of the optical model (usually as a model matrix containing light scattering vectors per unit of volume per size class, scaled to the detector’s geometry and sensitivity) and calculation of the particle size distribution (see annex a for theoretical background of laser diffraction). Also it may provide automated instrument operation. Several significant differences exist, both in hardware and software, not only between instruments from different manufacturers but also between different types from one company. The instrument specifications should give adequate information for proper judgement of these differences. In annex B recommendations are presented for the specifications of laser diffraction instruments. 6 operational procedures 6.1 requirements 6.1.1 instrument location The instrument should be located in a clean environment that is free from excessive electrical noise, mechanical vibration, and temperature fluctuations and is out of direct sunlight. The operating area should be well ventilated. The instrument should either contain a rigid internal optical bench or be installed on a rigid table or bench to avoid realignment of the optical system at frequent intervals. Warning:the radiation of instruments equipped with a low power laser can cause permanent eye damage. Never look into the direct path of the laser beam or its reflections. Avid cutting the laser beam with reflecting surfaces. Observe the local laser radiation safety regulations. 6.1.2 dispersion liquids Any optically transparent liquid of known refractive index may be used. Thus, a variety of liquids is available for preparation of liquid dispersions of powders. Annex c provides requirements for the dispersion liquids. If an organic liquid is used for dispersion, observe the local health and safety regulations. Use a cover for the ultrasonic bath when using liquids with a high vapour pressure in order to prevent the formation of hazardous vapour concentrations above the bath and/or the generation of low-temperature zones with fluctuating refractive indices in the fluid by evaporation. 6.1.3 dispersion gases For dry dispersion and spray applications a compressed gas is sometimes used. If used, it is essential that it is free from oil, water and particles. To achieve this, a dryer with a filter is required. Any vacuum unit should be located apart from the measurement zone, so that the output of the hot air does not reach the measuring zone, draught should be avoided in order to avoid unstable particulate streams. 6.2 Sample inspection, preparation, dispersion and concentration 6.2.1 sample inspection Inspect the material to be analysed, visually or with the aid of a microscope, firstly to estimate its size range and particle shape and later to check whether the particles have been dispersed adequately. The size distribution measured in a sample is only valid for a batch of material if the sample is representative for that batch and dispersed adequately. 6.2.2 preparation For dry powders, prepare a representative sample of suitable volume for the measurement by an adequate sample splitting technique, for instance a rotating riffler. If very small samples are required, or in the case of wet powders, it is also possible to take fractional samples out of a well-mixed sample paste. The consistency of the paste then avoids segregation errors. The pastes are formed by adding dispersant to the sample drop by drop while mixing it with a spatula. As long as the mixture forms lumps, single drops should be added while continuing the mixing after each drop. A good consistency for the paste is one like honey or toothpaste. If the paste becomes too fluid by mistake, it shall not be used, and a new preparation should be initiated. If the maximum size exceeds the measuring range, remove the material that is too coarse, e.g. by presieving. In this case determine and report the amount/percentage removed. Sprays, aerosols and gas bubbles in liquid should be measured directly, provided that their concentration is at an adequate level (see 6.2.3 and 6.2.4) ，since sampling or dilution is generally impossible without altering the particle size distribution. 6.2.3 Dispersion 6.2.3.1 Dry powders can be dispersed either in air or in liquid. The dispersion procedure shall be adjusted to the purpose of the measurement, e.g. It has to be decided whether agglomerates should be detected or broken down to the primary particles 6.2.3.2 An adequate dry disperser should be applied; here, generally compressed air or vacuum is applied for dispersion by shear stress with the assistance of mechanical de-agglomeration by particle-particle or particle-wall collisions(see figure 4). For dry dispersion, the complete fractional sample shall be used for the measurement. Note that the use of large sample quantities can overcome the poor statistical representation of coarse particles in a wide size distribution. It is necessary to check that comminution of the particles does not occur and conversely that a good dispersion has been achieved. This is usually done by direct comparison of dry dispersion with a liquid one: ideally, the results should be the same. Another possibility for checking the degree of dispersion or comminution is by changing the dispersing energy (e.g. The primary air pressure) and monitoring the change of the size distribution. Usually upon increasing the dispersing energy the amount of fines is increased at first, due to improved dispersion, until a plateau is reached, where the size distribution is nearly constant with increasing energy. At still higher energies the amount of fines may rise again as a result of comminution. On some occasions, agglomeration has been found at high flow rates through a cascade. The centre of the plateau define the optimum dispersing energy. Note, however, that a plateau is not always found (for instance for highly aggregated or fragile particles). 6.2.3.3 For the preparation of liquid dispersions a variety of liquids is available. Annex C presents requirements and some advice. Generally, pasting, stirring and ultrasonication can be used to facilitate proper dispersion of particles in the liquid. A preliminary check on the dispersion quality can be made by visual/microscopic inspection of the suspension. Also, it is possible to perform some measurements of the suspension in the laser diffraction instrument, with intermediate ultrasonication: the measured size distribution should not change significantly if the sample is well dispersed and the particles are neither fragile nor soluble. The minimum volume of sample , required for repeatable measurement, increases as the width of the size distribution becomes greater in order to allow a sufficient number of large particles to be present. Accordingly, the volume of the dispersion fluid required to suspend these samples also increases if the limits of optical concentration are to be observed. For example, for a sample with particles in the approximate size range of 2μm to 200μm, a sample volume of at least 0.3 ml is needed. This will require at least 500ml of suspension fluid for its dispersion. Also, the measurement time or the number of detector readings within one measurement should be sufficient to reach a reasonable precision. Appropriate measurement conditions should be established experimentally, in relation to the desired precision. 6.2.4 Concentration The particle concentration in the dispersion should be above a minimum level, which for many instruments will correspond to about 5% obscuration, in order to produce an acceptable signal-to-noise ratio in the detector. Likewise, it should be below a maximum level, which for many instruments will correspond to about 35% obscuration for particles larger than about 20μm, in order to avoid multiple scattering (where light is scattered subsequently at more than one particle). For particles smaller than about 20μm, the obscuration value should be kept below about 15% for the same reason. In general, multiple scattering appears at larger scattering angles. Without multiple scattering correction, the amount of fines calculated will exceed the true value. If work at higher concentrations is required, it should be possible to correct for multiple scattering or systematic errors will arise. A first estimate for the concentration can be reserved from figure 5. Figure 5, though only an example, shows that the optimum particulate concentration is nearly proportional to the circle size: smaller particles require lower concentrations. For instance, particles with a diameter of about 1μm fire volumetric concentrations during measurement of about 0.002%, whereas the concentration for 100μm circles should be about 0.2%, in a cell with a 2mm path length. As a consequence, the width of the particle size distribution influences the optimum sample concentration for measurement. Moreover, the range of concentrations, shown in figure 5, is influenced by the laser beam width, the path length of the measurement zone, the optical perties of the particles and the sensitivity of the detector elements. New of the above, measurements should be performed at different particulate concentrations in order to decide be optimum concentration range for any typical sample of material. 6.3 measurement 6.3.1 procedure Optical measurement of a particle size distribution by laser diffraction comprises the following steps: a ) setting up instrument and blank measurement After selection of the appropriate particle size range and proper alignment of the optical part of the instrument. The blank measurement is performed in which a particle-free dispersion medium is used. Detector data are saved in order to subtract them later from the data obtained with that sample in order to obtain net sample signals. b ) measurement the scattering pattern of dispersed sample(s) Generally, a measuring time allowing for a large number of detector scans or sweeps at short time intervals is used: typically some 2 seconds or 1000 sweeps. For each detector element an average signal is calculated, sometimes together with its standard deviation. Data are store in the computer memory. The magnitude of the signal from each detector element depends upon the detection area, the light intensity and the quantum efficiency. The coordinates (size and position) of the detector elements together with the focal distance of the lens determine the region of scattering angles for each element. Generally all these factors are factory determined and stored in the computer. Most instruments also measure the intensity of the central laser beam. The fractional difference between a dispersed sample and a blank experiment is given as an obscuration value, which is indicative of the total amount of scattered light and the particle concentration. c ) selection of an appropriate optical model Most often either the fraunhofer or the Mie theory is used. Sometimes other approximating theories are applied for calculation of the scattering matrix. When using the Mie theory, the refractive indices of particulate and medium, or their ratio, should be brought into the instrument in order to allow calculation of the model matrix (see annex D for the refractive indexes of liquids and solids). Often , small values of the imaginary part of the refractive index (about 0.01-0.1) are applied to cope with the surface roughness of the particles. NOTE: small differences in the assumed complex refractive index may cause significant differences in resulting particle size distributions.. In order to obtain traceable results it is essential that the refractive index values used are reported d ) conversion of scattering pattern into particle size distribution This deconvolution step is the inverse of the calculation of a scattering pattern for a given particle size distribution. The fact that short measured data always contain some random and systematic errors, may cause erroneous size distribution results. Several mathematical procedures have been developed for use in the different instruments available [4, 6, 7, 10, 12, 14]. They contain some weighting of deviations between measured and calculated scattering patterns (e.g. least squares), some constraints (e.g. Non-negativity for amounts of particles) and/or some smoothing of the size distribution curve. A new procedure [5] uses the observed fluctuations of the detector signals to introduce proper weighting of these data and to calculate confidence intervals for the particle size distribution. 6.3.2 Precautions Before starting, and during any measurement, the instructions given in the instrument manual should be followed. The following precautions should be taken. a ) Before switching on the power to the instrument make sure that all components of the system are properly grounded. It is essential that all the particle dispersing and transporting devices, such as the ultrasonic bath, the dry disperser, the vacuum inlets and vacuum hoses, are earthed to prevent ignition of organic solvents or dust explosions caused by electrostatic discharges. b ) After switching the power on, allow sufficient time for the instrument to stabilize. Gas lasers such as the He-Ne laser usually have a warm-up time of more than half an hour. c) Check the instrument status and , if necessary, set up the required measuring range and lens. Ensure, by watching the intensities on the detector, that the detector is properly centred and positioned in the focal plane of the lens. Without particles. the background signal should be below the specified thresholds for that instrument set-up and dispersing device. If this is not the case, inspect and, if necessary, clean the optical components to ensure proper performance. d ) Make sure that the particles are only introduced into the laser beam within the specified working distance of the lens, so that all relevant scattering radiation leaving the particles strikes within the clear aperture of the lens that focuses it on the detector (and thus, vignetting is avoided). Validate the instrument operation with respect to both precision and accuracy at regular time intervals by measuring a control sample of known size distribution (see 6.4 and 6.5.2). e ) In the case of wet dispersion, check that air bubbles are absent in the dispersion liquid. Foaming detergents should be avoided. In the case of dry dispersion, check, visually or by inspection of subsequent obscuration values, that the dosing unit for the disperser generates a steady mass flow. f ) For aerosols and sprays: make sure that no bright daylight is allowed, either directly or via scattering by particles, into the detector and that the flow of particles/droplets is even. Investigate, if possible, the influence of the optical model (relative refractive index) on the resulting particle size distribution, especially if a significant fraction of the particles is smaller than about 10μm. NOTE occasionally a strong dependency of the results on the refractive index has been found whereby even slightly different values resulted in major systematic errors (see further annexes A and D ). 6.4 repeatability For samples where the coefficient of variation of the particle size distribution is equal to or less than about 50%(or fluo of diameter of largest to smallest particle about 10:1(或者最大最小颗粒直径之比为, ,:,)) and for measurements performed on at least five different samples from the same batch in the mid-range of any instrument setting, the repeatability of characteristic particle –es in size distributions should be as follows: for any chosen central value of the distribution, e.g. The median size (x), the coefficient of variation should be smaller than 3%. 0 Values at the sides of the distribution, e.g. X and x, should have a 1090 coefficient of variation not 5%. Below 10μm, these maximum values should be doubled. 6.5 accuracy 6.5.1 calibration User diffraction systems are based on first principles, though with idealized properties of the particles(cf. Annex Z). Thus, calibration in the strict sense is not required. However, it is still necessary and desirable to confirm the correct –ration of the instrument by a validation procedure (see 6.5.2). 6.5.2 validation 6.5.2.1 primary validation can be made with any certified or standard reference material, acceptable to the practice zone end-users’ industries. Here, the total measurement procedure is being examined, including sampling, sample dispersion ,sample transport through the measuring zone, measurement and deconvolution procedure [13]. It is essential that the total operational procedure is adequately described in full detail. Citified or standard reference materials consisting of a known distribution having a range of spherical particles – one decade of size are preferred. They should be certified to mass percentage by an absolute technique, if –lable, and used in conjunction with an agreed, detailed operation procedure. It is essential that the real and –rinary part of the complex refractive index are precisely specified for the material if the Mie theory is applied in the analysis. Response of a laser diffraction instrument is considered to meet this standard if the mean value of the x –ing from at least three independent 50 measurements deviates less than 3% from the certified range of values of the Certified or Standard Reference Material, i.e. The mean value together with its standard deviation; the mean –es for the x and x 1090 should deviate less than 5% from the certified range of values. Through use of spherical reference materials is preferable, non-spherical ones may also be used. Preferably, these should have certified or typical values coming from laser diffraction analyses according to an agreed, detailed –ational procedure. If the Reference values come from other methods than laser diffraction, a significant bias may –t. The reason for this bias is that the different principles applied in the various methods may lead to different sensitivity to the properties of the particles and, thus, to different equivalent-sphere diameters for the same non-rical particle. Addition to the certified reference materials mentioned above, product samples of typical composition and particle distribution for a specified class of products can also be applied for validation of instrument behaviour and operational procedures, provided that their particle size distribution has been proven to be stable over time. Here, the results should comply with previously determined data with the same precision and bias as those for the certified reference materials. Mixtures in ratios of volume of two or more reference materials having the same properties can be applied to test the accuracy of the reported fractional quantities, the size resolution and the sensitivity to fines or coarse material. Representative sampling from the various materials is here, however, even more important than in the normal case, since the fractional quantities can be very small. 6.5.2.2 For secondary validation of a laser diffraction instrument a suitable reference reticle [1, 8, 9] can be used. Thus, only the quality of instrument optics and software is being examined, leaving out the effects of sample dispersion and handling. For instruments with a focal length above 300mm, the application of reticles is not reliable due to speckle effects. Of course, the proper use of a reticle includes the requirement that the illuminating beam diameter allows measurement of the full circular area of the dots deposited. Note that some reverse Fourier applications, where the reticle must be placed close to the detector, may fall within this restriction. The response of a laser diffraction instrument is considered to meet the requirements of this part of ISO13320 if the mean value for the x coming from at least three measurements deviates less than 2% from 50 the quoted value and for x and x less than 3%. 1090 6.6 Error sources; diagnosis 6.6.1 Systematic measurement errors (bias) may arise from improper sample preparation, departure from the theoretical assumptions for the particulate mater and/or improper operation or functioning of the instrument. 6.6.2 Errors made in sample preparation are often a main part of the total error. They can be attributed to the following causes: - Improper sampling technique, leading to a non-representative sample in the measurement zone; this type of error is especially significant when using an inadequate sample splitting technique in the case of a large batch of free flowing material having a wide size distribution, but errors can also be due to selective transport within the instrument, for example, application of too low a pumping speed may lead to sedimentation of the larger particles in the pumping circuit; - Incomplete deagglomeration of particles, due to an improper dispersion procedure (liquid; dispersant; ultrasonication); - Comminution of particles by mechanical forces during dispersion (e.g. Ultrasonication); - Swelling, re-agglomeration, dissolution or evaporation of particles/droplets before or during measurement; - Inclusion of air bubbles due to foaming dispersants and/or vigorous stirring; - Scattering from differences in refractive index in the dispersing liquid or gas due to temperature fluctuations generated by, for example, evaporation of the dispersing liquid or presence of a flame. 6.6.3 Another main source for bias arises from the departure from the theoretical assumptions for the particulate material. Again, the errors can come from different sources. - Firstly, most particles in real life do not fulfil the assumption of sphericity. Non-sphericity of particles leads to different cross- sections in different orientations. since particles are generally measured in all possible orientations, this leads to some broadening of the particle size distribution as compared to the equivalent volume distribution. Moreover, the median and mean diameter may be shifted, often to a larger size. - Secondly, the particle surface may be rough instead of smooth. This causes diffuse light scattering at the boundary, which often has a similar influence as absorption of light within the particle. - Thirdly, the particles may be optically heterogeneous, as is the case for porous particles. This may lead to an apparent presence of significant amounts of very small particles, which are non- existent. - Last but not least, the wrong optical model or parameters may have been chosen. For instance, if the Fraunhofer approximation is applied for samples containing an appreciable amount of small, transparent particles a significantly larger amount of small particles may be calculated (see also annex A ). Generally, the choice of a wrong model also results in a large difference between particulate concentration as calculated by the instrument and from the mass of sample and the volume of dispersion medium (see also 6.6.6). 6.6.4 errors in the operational procedure or in the functioning of the instrument can be specified as follows: - particles with diameters outside the measuring range are present [in this case, adapt the measuring range (change the lens) and/or remove too coarse material, e.g. by presieving ]; - the sample is introduced into the laser beam outside the working distance of the lens; - lens(es) or windows of the measurement cell are dirty and, thus, should be cleaned; - measurements are conducted with excessive levels of background; - the optical system has not been aligned properly; - the particle concentration is too high, causing multiple scattering; - the mathematical procedure for deconvolution of light intensity values to particle size distribution is inadequate (check with the instrument manufacturer). 6.6.5 the absence of maintaining good control on the above points may also lead to errors of a random nature. Moreover, random errors may result from - using insufficient measurement time, or readouts of each detector output - working at too low a concentration, and - instrument imperfections, e.g. fluctuating laser intensity, or noisy detector elements. 6.6.6 errors of specific parts of the procedure can be diagnosed by the following operations. - Measuring the intensity of the laser beam for at least 1h during a blank experiment: it should be stable within the limits given in the instruction manual. - Observing the signals from all detector elements during a blank measurement: the background signal should show a smooth behaviour with only small positive or zero values. Negative or overload (100%) readings indicate faulty detector elements, defects in the electronics or scratched cell windows or lenses. Significant intensities on only localized detector elements are often caused by reflections at damaged optical surfaces of the lens, the cuvette or other parts illuminated by the laser beam; - Observing the detector signals from repeated sample measurements, calculating both mean values for each element and their standard deviations and comparing the measured signals for all detector elements with previously measured ones. Thus, an impression is gained of the precision and accuracy of these signals: large systematic differences or zero values for the signals usually indicate a faulty detector element, a defect in the electronics, dirty windows or lenses, bad alignment, presence of air bubbles or a problem in the sampling and/or dispersion procedure. Moreover, these data enable, after conversion to light intensity values, comparison of the measured light scattering patterns coming from different instruments, to some extent irrespective of the geometry of the detector elements in these instruments (provided that the geometry is known); - Comparing the actual particulate concentration, as calculated from the sample mass and the volume of the dispersion medium, with a calculated one from the obscuration and particle size distribution, while using the same optical model for calculating the extinction coefficients of the particle size fractions as for the deconvolution; a large difference indicates an inadequate optical model or bad sample handling [1]; - Comparing for all detector elements the measured and calculated signals (for the resulting, best-fitting particle size distribution); large systematic differences indicate either a faulty element or an inadequate optical model. 6.7 resolution; sensitivity The resolution of the particle size distribution, i.e. the capability to differentiate between different particle sizes, and the sensitivity for small(extra) amounts of particles of certain size are restricted by the following factors: - number, position and geometry of the detector elements; - their signal to noise ratio; - fine structure in the measured scattering pattern; - difference in scattering pattern between size classes; - actual size range of the particulate material; - adequacy of the optical model; - smoothing applied in the deconvolution procedure. These factors prevent the laser diffraction technique in its usual design from being a high resolution technique: the minimum width of each size class is usually about 1.1 to 2 (ratio of upper to lower limit of the size class). Actual values for resolution and/or sensitivity for quality control reasons should be determined by using mixtures of known composition. 7 reporting of results Results should be reported in accordance with ISO 9276-1. Moreover, the following information should be reported in order that the measurements can be readily repeated by different operators in different laboratories. Some of items may be optional for some materials. a ) sample - complete sample identification, such as chemical type, batch number and/or location, date and time of sampling, etc.; - sampling procedure, i.e. sampling method and sample splitting procedure; - sample pretreatment (optional), for instance presieving, type and conditions; - date analysis b ) dispersion - Dispersion type: dry or wet. For dry dispersion - specific details of dispersing device, e.g. Injector diameter, primary pressure; - type of dosing/feeding device; - feeding rate. For wet dispersion - dispersion liquid: identification, volume and, if necessary, temperature; -dispersant(s): type and quantity; - sample concentration; - sonication: type of unit, frequency (energy), duration and pause before starting measurement; - pump speed. c ) laser diffraction measurement - instrument type and number. - software version. - focal length of lens applied. - actual size range used for the measurement. - data of last alignment; - date of last validation. - date and time of measurement. - optical concentration/obscuration. - trigger thresholds for start stop condition (if applied). - threshold for acquisition of valid data (if applied). - type of light scattering model applied. - real and imaginary part of complex refractive index, if the mie theory is applied. - (optional) fit parameter resulting from deconvolution (e.g. log difference, chi-squared). d ) analyst identification - name and place of laboratory. - operator’s name or initials. 粒度分析仪—激光衍射法(ISO13320—1) 简介 如今激光衍射方法已广泛的应用于粒度的测定。这一技术的成功关键在于它可以应用于各种微粒体系，它测定快速，能够实现自动化，并且市场上可获得各种商业仪器。然而，仪器的使用和结果的阐述要求比较谨慎。 因此，对于用激光衍射方法测定粒度需要建立国际。其目 的是在粒度分析中提供质量控制的方法。 原来，激光衍射技术只考虑了小角度的散射，因此有如下的名称: - 弗琅荷费衍射 - (近)寄光散射 - 小角度激光散射(LALLS) 然而，今天这一技术已被扩展到在更大角度范围的光散射和Mie理论的应用(除了如弗琅荷费衍射和不规则衍射的理论)。 激光衍射技术基础是基于在一定强度下粒子能够散射出各个方向的光，强度的形式基于粒子的大小。当前所有的仪器都假定粒子是球型的。图1列出了单个粒子散射图形的特性:在高和低强度下的变化，小粒子图形的延伸要求角度比大粒子大。(2-7，10，15参考文献) 在一定限度内，粒子整体的散射图形认为是所有存在的粒子单个散射图形的总和。通过使用光学模式来推断在所选择的粒度范围粒子的单位体积，数学去卷积过程，计算粒子的体积分布。最好配备一些适当标准散布图案(见附录A)。 一个典型的衍射仪由光束(通常为激光)，粒子分散装置，测定分散图形的检测器和用于控制仪器和计算粒子尺寸分布的计算机组成。激光衍射技术不能区分单一粒子的分散和初始粒子形成的块状物形成的分散。通常，对于块状粒子的尺寸认为是粒子族的尺寸，但有时初始粒子的大小在粒子尺寸分布中也能够反映。大多数粒子样品含有块状粒子或集合体，这对初始粒子的尺寸分布有影响，粒子束在进行测量前通常被分散成初始粒子。 以前仪器所用的分散角小于14度，这限制了对小粒度测定的应用(如1um)。限制的原因是小粒子的大部分的散射是在大角度下的。(见附A)。当前许多仪器能在更大散射角下测量，有些甚至达到了150度。例如，使用聚光束，更多或大的棱镜，第二个激光束或更多的检测器。因此，粒度大约为0.1um的粒子也可被测定。 一些仪器从散射强度和不同波长下强度的不同以及极化位置可获得额外的信息以提高在亚微米范围粒子尺寸的特性。 粒径分析 - 激光衍射法 第一部分:基本原理 1 总则 在这一部分中ISO13320规定了通过测量光衍射角的方法测量任何二相系统例如粉末，泡沫，气溶胶、悬乳剂，乳浊液和液体中的气泡的粒子的粒径分布。 它不涉及具体的产品的粒径测量。该部分的 ISO13320适用的粒径范围是0.1 μm 到3 μm 。 对非球形的粒子来说，可以获得近似球形粒子颗粒分布，其原因在于该技术光学模型里使用球形粒子假设。 由此产生的粒子颗粒分布可能不同于基于其他物理原理(例如沉积，筛分)获得的结果。 3，术语，定义和符号 以下的术语，定义和符号适用与该部分ISO 13320。 3.1 条件，定义 3.1.1 吸收 光束通过介质时能量的变化 3.1.2变异系数 精密度测量(%): 标准偏差除以体均值或者数据的正态分布的中位数然后乘以100。 3.1.3绝对折光率(,,) 粒度的折射率包括实部和虚数部分。 Np=n-ik pp 3.1.4相对折光率(m) 粒度的绝对折光率与介质折光率的比值。 3.1.5 去卷积 凭借测定粒子的散射角度来推断它们的粒径分布的数学程序 3.1.6衍射 光波通过粒子限制而弯曲向后传播的现象。 3.1.7 光的消失 光束通过介质时被吸收和散射而衰减。 3.1.8矩阵模型 模型用光散布向量示不同粒子等级向量。检测器的几何学按比例绘制，是从模型计算派生而来的。 3.1.9 多次散射 在不止一个粒子随后的光散射中，导致散射图案不再是所有单个粒子图形的综合(相对于单个散射)。 3.1.10 消光/光强削弱 入射光的百分含量或分数由于粒子的消光(散射或者吸收)而衰减。 3.1.11光学模型 用于计算光学的单一球形的的理论模型，如有必要，将用特殊的复杂的折射率，例如弗琅荷费衍射，不规则的衍射，Mie 散布。 3.1.12 反射 发射光通过表面返回而波长没有变化 3.1.13 折射 光的折射是由于光在两种介质中传播速度的不同所引起的 。根据斯内尔定律有: nsinθ=nsinθ mmpp 3.1.14 散射 描述了光传播在两种介质的分界面上的变化 3.1.15 散射图样 光强度的角度和空间图形[分别I(θ)和I(r) ]源于散射或考虑到灵敏度的相应能量值，检测器附件的几何元件。 3.1.16单一散射 散射是基于各种尺寸分布的单一成员贡献的散射。 3.1.17粒度分布的宽度 标准偏差(绝对值)或各种尺寸变化的相关系数(相对含量)。 注:颗粒分布的(有关百分比)适合正态分布的大约为总数的95%的数据落在相对平均值2倍标准偏差范围内，大约99.7%的数据落在相对平均值3倍标准偏差范围内。 3.2符号 c 待测粒子浓度 f 透镜焦距 I(θ) 4， 原理 一个具有代表性的样品，溶解在适当溶剂中(气体或液体)，配置成合适的浓度。以单色光源照射样品，通常是激光。光被发散成不同的角度、以多元检测器检测、读出其有效的发散角。这些数学表示的信号通过光学系统和数学模型转换成待测颗粒体积占总体积的比例形式输出。 ,激光粒度仪(图,) 如图(,)所示是一种典型的激光粒度仪的示意图。 在常规装置中，光源(激光)用来产生单色、连续的平行光源。光束通过分光系统，一般上双透镜系统，得到适当的光束来照射待测样品。 将样品溶解成适当浓度，通过传递介质(气体或液体)输送到适宜的光束测量范围内。该测量范围需要在透镜的有效焦距内(工作范围)，有时颗粒可以直接测量，比如:泡沫、气溶胶、液体中的气泡。另外一些样品需要溶解在合适的溶剂中，这些样品是:乳剂，糊状物、粉末等(参见附录,)。经常使用分散剂(湿剂、稳定剂)和(或)机械方法(搅拌、超声)来去除颗粒中的团状物质，并使得分散状态得以保持。在这些液体分散相中，经常使用组合系统，它由下列部件组成:光学测量池、由搅拌和超声单元组成的分散装置、泵和透平机。 使用力学去团的干粉末分散装置也可以把干的粉末制成气溶胶。向装置中加入一定量的物质，它使用的能量是压缩空气或使用不同的压力真空来分散颗粒。将得到的气溶胶从装置的出口注入测量带，在真空管入口处收集颗粒。 离子进入激光范围的装置有两种，在经典的装置中，颗粒进入平行光束，在聚光镜的工作范围内(见图,,,)。在所谓的反转傅立叶光学系统中，颗粒进入聚光镜的后面，在汇聚光束范围内。(见图,,,) 经典装置的优势在于样品在透镜工作范围内有一个合理的光程。第二种装置允许使用短光程。但是它不能测定由超微离子发散的大角度的散射光。 附属光束和所有粒子相互作用导致了在不同角度的不同的光强度的散射图样。(见附录的激光衍射背景理论)。总角强度分配 I(θ)， 由直接和被散布的光组成;然后被凸透镜或者总体透镜聚焦到多元件的检测器上。在限制情况下透镜(组)提供的衍射图样不依赖于粒子在光束中的位置。因此，连续角强度散布I(θ)由一组检测单元的不连续的散布强度I(r)决定。 假定记录散布粒子整体的散射图象和全部个别粒子的散射图象 的总数相同。应当注意到，只有在限定角度范围的散射光能够 被透镜会聚，因此也只有这些光通过检测器。 检测器一般由多个光电二极管组成;一些仪器应用 与移动裂缝集成在一起的光电二极管。光电二极管把空间强度分布，(r)转变成光电流I。然后电子学装置使之转换和数字化而成为强度或者能量n 矢量Ln。用以描述散布的图案。通过一计算模型，提供光学浓度或者暗光的中心元件来测量非散布光的强度。 为了自动再集中和再聚焦，一些仪器通过移动检测器或透镜组为中心元件提供了特殊的几何学方法。 为防止光从表面反射而再次进入光学系统，使检测器位置固定是有必要的。 计算机用于控制测量、存储和识别信号， 存储和/或计算需要有适当形式光学模型(通常是按照各等级的粒径和每计量单位体积和检测器的几何学位置极其敏感性来确定光学模型。)和计算的颗粒分布(已知激光衍射的理论背景值)。 此外它还可以提供使仪器自动化的操作。 不仅来自不同的制造商的仪器之间，即使同一家公司的不同类型的仪器都存在显著的差别，包括硬件和软件两个方面。因此仪器的书应该给这些差别足够的信息，以作出合适的判断。 附件里B里的建议是为激光衍射仪的说明提出的。 6操作程序 6.1要求 6.1.1仪器装置 仪器必须装在一个清洁的环境中，以免过度的电噪音、机械振动、温度波动和阳光直射。操作区域必须有很好的通风。为了防止光学系统频繁振动，仪器需要安装在一稳固的光学工作台或者是稳固的桌子(或实验台)上。 警告:由于仪器的放射性，即使是很少的激光也能引起眼睛的 永久性伤害。禁止激光光束或者是其反射光。避免用反光物切 割激光束。应当遵守激光使用安全规则。 6.1.2制备溶液 因为要使用到一些光学透明的液体的已知折射率。这样，就有许多种液体被用来分散粉末，附录,给出了一些有用的分散液体。 如果在实验中用到有机溶剂来做分散剂，那么就要遵守相应健康和安全规则。如果使用的液体的蒸气压较高，那么在超声是要用盖子(如表面皿)盖上，以防止在低温下流动蒸气在装置的或(和)水浴的表面浓缩而发生危险。 6.1.3制备气溶胶 有时，对于干的分散物或泡沫，需要使用压缩空气。如果使用，那么就要使其中没有油、水、和颗粒物。为了达到这一点，可以使用有过滤功能的干燥器。这些真空单元需要远离测量范围，这样输出的高温空气就不会进入测量带中。为了防止产生不稳定的粒子流，要避免气流进入。 6.2 样品检查、准备、分散和浓缩 6.1样品检查 对所分析样品进行检查，用目测或者借助于显微镜。首先估计 它的粒度范围，粒子形状，然后检查粒子是否被分散完全了， 样品中测量的尺寸分布只对一组材料有效，如果样品在那一组 而且分散完全。 6.2.2 准备 对干的粉末，准备合适体积的具有代表性的样品，需要有快速的技术。比如:旋转曲锉。如果只需要很少的样品，或者粉末样品潮湿时，那么要尽可能的使粉末样品远离易混的糊状样品。糊状物的浓度要避免分隔误差。糊状物被一滴一滴的加入并用刮刀使之成型。在前一滴样品混合形成团时接着加入后一滴样品而使之成型。糊状物中密度合适的样品如蜂蜜和牙膏。如果糊状物变稀的话，那么就不能使用，制备的工作需要重新开始。 如果样品的粒径超出测量范围，需要通过前过滤去除物质中的粗糙杂质。在这一过程测定和记录去除百分率。 泡沫、气溶胶、和液体中气泡能够直接测定，倘若它们的浓度合适(参见6.2.3;6.2.4)。因为采样或者稀释通常不会改变样品的粒度分布。 6.2.3 散射 6.2.3.1干燥的粉末可以分散在空气里或者在液体里。分散过程可依据测定目的调节。例如，确定聚合物是否检测出，或被分散成微小的颗粒。 6.2.3.2 粒子干燥分散器应该使用; 这里，通常压缩空气或者真空施压来分散。辅助粒子与粒子或者粒子与墙(见图4)的碰撞来散布。对于干燥分散碎片样品将用于测定。注意大样品量的使用将克服在宽的尺寸分布范围大颗粒样品存在引起的统计偏差。检查样品是否被粉碎是必要的，样品被粉碎将使样品能够很好的分散。通过 液体样品的干分散的直接对比得到，理想的情况是，所得的结果将一致。检查分散或粉碎的程度的另一种可能性是通过改变分散能量，(例如常压)和检测尺寸分布的改变。通常提高分散能量，细粉的量起初将上升，由于分散度的提高，直到达到一个平台，此时尺寸分布将是一个常数不随能量的提高而改变。当能量更高时，由于粉碎的结果细粉的量将重新上升，在一些情况下，在高流速通过装置时将发现聚合体。平台的中心定义为最佳的分散能量。然而，平台并不是总存在的(例如对于高度聚合或易碎的粒子)。 6.2.3.3对液体分散的准备，需要各种各样的液体。附录C列出了要求和一些建议。总之，过滤，搅拌和超声将被用于在液体中颗粒物的正确分散。通过目测或者显微镜观察对分散质量进行预检查。激光衍射仪也可对悬浮物进行其他测定。中间的超声过程:所测的粒度分布将不会改变很多如果样品分散的很好，样品不易碎或者溶解。 因为为了使存在的大粒子的数量足够多粒度分布范围变宽用于可重复测定所需的最小的样品体积将变大。相应地，如果要达到光学浓度检测线，悬浮这些样品所需的分散液体的体积将变大。 例如，一个样品颗粒它的粒度近似范围为2-200um。所需的样品体积至少0.3ml。那将需要至少500ml悬浮液体用于分散。测定时间或在一次测量中检测读取的数要足够达到可能的精度。在实验过程中相应于所要求的精度，将建立相似的测定条件。 6.2.4 浓缩 分散体系中粒子的浓度应大于最低的范围，最低的范围对于大多数仪器将是大约5%暗光的响应，为了使检测器有较好的信噪比。浓度也应低于最大的范围，对大多数仪器将对粒度大于20um的粒子产生大约35%暗光的响应，为了避免多种散射(在多个粒子中光将持续散射)。 对小于20um的粒子，由于同样的原因暗光值应低于15%。总之，在大散射角度下存在多路散射。没有多路散射校正，所计算的细粉的量将为真实值。如果所需的浓度较高，由于多路散射或者系统误差的存在，所得的值要进行校正。对浓度的最初的估计从图5中看出。 图5，虽然只有一个例子，但表明对于球形尺寸，最佳粒子浓度是几乎成比例的。粒子越小所需的浓度越低。例如，在2mm长的池中，直径大约1um的粒子在测量过程中所占的体积浓度大约0.002%，而对于粒子直径大约100um的浓度为0.2%。结果表明，粒子粒度分布的范围影响在测定过程中最佳样品的浓度。浓度范围 (见图5)，受激光束的宽度，测量区域的长度，粒子的光学特性，检测器元件的灵敏度的影响。 为了测定各种样品最优的浓度范围，要对不同微粒浓度进行测量。 6.3 测量 6.3.1 过程 激光衍射的粒度分布光学测定由以下步骤组成: a) 安装仪器和空白测定 在选择了适宜的粒度范围和仪器光学部分正确的校准之后，将进行空白的测定，测定中将用到粒子随意分散介质。检测器的数据将保留以便在以后获得的数据中减去空白数值，以获得净样品信号。 b) 测定分散样品的散射图 用于检测器扫描的次数或在短时间间隔的扫过次数的测定时间常用:典型的2秒或1000次。对每一个检测元件将计算平均信号，有时加上其标准偏差。数据存储在计算机中。来自每个检测元件的信号的强度依靠检测范围，光强度和量子效率。检测元件和棱镜聚焦位置的协调(尺寸和位置)决定每个元件散射角的范围。总之所有这些因子将被测定，并存于计算机中。 大多数的仪器可测定中心激光束的强度。分散样品和空白实验中碎片的不同认为是暗光值，它被认为是散射光的总量和粒子浓度的反映。 c) 选择适宜的光学模式 大多数用的是弗琅荷费或Mie理论。 有时也有其他的理论用于计算散射矩阵。当用Mie理论时，粒子和介质折射率复数或它们的比率将引入仪器中以便进行矩阵模型的计算(见附录D液体和固体的折射率)。有时，折射率虚部的较小的值(大约0.01-0.1)将用来处理粒子的表面粗糙度。 注:在所假定的复数折射率的微小的不同在粒度分布结果中将产生很大的影响。为了获得获得可靠的结果，应指出所用复数折射率的值。 d) 将散射图转换为粒度分布 去卷积步骤是将散射图计算得到粒度分布图。事实上，所测的数据较少将导致一些随机和系统的误差，可能导致错误的粒度分布结果。在不同的仪器中所用的数学方法有了一定的发展[4，6，7，10，12，14]。在计算和测定散射图之间的偏差的量度(例如平方根)。一些限制和/或粒度曲线的平滑。一个新的方法用于观测检测 器信号的波动以便对这些数据进行正确计量，计算粒度分布的置信区间。 6.3.2 预防 在启动之前，在任何测量期间，指示在手册遵循的仪器内给。 以下的预防应该被采取。 a)在打开仪器前保证系统的全部零部件在正确地位置。全部粒子驱散和运送装置， 例如超音速洗澡， 干燥的分散器，真空进口和真空软管，被覆以防止有机溶剂或者静电的排出物引起的灰尘爆炸的点火，是必要的。 b)在打开电源之后，给足够的时间使仪器稳定。 象He-Ne 激光那样的气体激光通常有超过半小时的预热时间。 c) 检查仪器的状态，如果必要，设定所需测定的范围和棱镜。 通过观察检测器的强度，确定检测器在适当的位置在棱镜的聚 焦处。没有粒子时，背景信号应该低于仪器设置和散射装置的 检测光门。如果不是，进行检查，如果必要，清洗光学部分。 d)确定粒子在棱镜特殊的工作量程内进入激光束中，以便相应的散射辐射离开样品能进入棱镜的狭缝，棱镜的聚焦点在检测器的位置。 通过测定已知粒度的样品评价仪器操作在一定时间段的精确度和准确性。(见6.4和6.5.2)。 e )在湿分散状态，检查在分散液中是否有气泡。避免用泡沫清洁剂。 在干分散状态，检查，目测或通过暗光值，分散物的量产生稳定的质量流。 f)对于气溶胶类物质;确定没有日照光通过，没有直接或者通过粒子散射，进入检测器，粒子流比较稳定。 如果可能，研究一下在粒度分布结果中光学模式(相对折射率)的影响，尤其是粒子碎片的大小小于10um。 注意:有时折射率对结果的影响很大，甚至微小的变化就能导致很大的系统误差。(见附录A和D)。 6(4重现性 对于样品来说，粒度分布变化的相关系数是等于或小于50%(最大粒子的直径是最小粒子的比率大约10:1，在测定过程中从同一个样品容器中要取至少5次不同的样品进行测定，在粒度分布中粒子特性的重现性如下:对于任意选定的分布的中心值，例如中间粒度(X)，相关系数小于3%。关于分布范围的值，例如X1010和X，相关系数小于5%，粒子粒度低于10um，这些值将相应变90 为2倍关系。 6(5精确度 6(5(1校准 衍射体系基于第一个分散原理，把粒子的属性理想化来看待的(附A)。因此，严格将校准并不是必需的，然而通过校准过程(见6。5。2)可以知道仪器的情况。 6(5(2校正 6(5(2(1可用任何一种标准参照物进行初始的校正，这里所有的测定过程都要检查，包括采样，样品的分散，样品的传输，测定和去卷积过程。[13]，对整个操作过程详细的描述是必要的。 标准参照物由已知分布的一定粒度分布的球型粒子组成，他们将用可靠的技术确定质量分布，如果可能和所用的操作过程联系起来。如Mie理论用于分析，对于样品折射率的实部和虚部的精确测定是必要的。 如果来自三次独立测定的平均值X的偏差小于3%，测定所用50 的样品为标准参考物，其值在一定的范围，激光衍射仪能够使用来进行测定。例如平均值加标准偏差，对于一定的范围X和X平均1090值的偏差小于5%。 对球型参考物的使用是可行的，非球型也可以使用。他们可获得根据已知测定过程的激光衍射分析得到的特征值。如果用其他方法的到的值和激光衍射法得到的存在差别，存在差别的原因是在不同方法中所用的原理不同。 此外上面所提到的校准参照材料，有着典型的组分和一定级别的粒度分布，可用于仪器和操作过程的校正。以证明在一定的时间限度内其粒度分布是恒定的。这里所得到的结果与用校正参照物在相同精度和误差下的得到的结果相一致。 具有同样属性的两种或多种参照物体积的比率的混合物可用于检测粒子质量的精度，大小的分辨率和精细或粗糙材料的灵敏度。从各种材料中得到的样品，甚至比常规的更重要，因为碎片的质量是十分小的。 6(5(2(2第二种校准激光衍射仪的方法是用适宜的参考线。这里，只能检测仪器光学元件的质量和软件的质量，不能判断样品分散和处理的影响。对于聚焦长度大约300mm的仪器，由于斑点的影响，运用参考线进行检测是不可靠的。当然，参考线的正确的使用包括要求入射光直径能够对斑点整个圆面积进行测量。注意一些反傅立叶变换的应用，则参考线必须靠近检测器放置。如果所采用的至少三次测量的偏差小于2%的的X值和X和X的偏差小于5010903%的平均值满足要求，激光衍射仪的响应认为符合ISO13320的要求。 6(6误差来源 6(6(1系统测定误差可能来源于不正确的样品制备过程，对粒子的理论假设/对仪器不正确的操作。 6(6(2样品制备过程中的误差常常是误差的重要组成部分。他们可归结为以下原因: , 不正确的采样技术，导致在测量区域样品相关性差;当在可让样品自由流动的大容器内有很大的尺寸分布的情况下使用不完全的样品喷淋技术时这种类型的误差显的尤其重要。，但误差也有可能是所选择的传输方式引起的，例如，所用的泵速过低将导致大颗粒在泵循环中沉淀。 样品粒子不能完全的分散，由于不正确的分散过程(液, 体，分散剂，超声)。 , 在分散过程中通过机械力使颗粒粉碎(例如，超声); , 聚集，不溶或粒子的挥发在测定之前或过程中; , 由于泡沫分散剂或剧烈的搅拌产生气泡; 由于产生温度的波动在分散液或分散气体中折射率会发生变动，例如分散液体的挥发或气泡的存在。 6(6(3对粒子材料的理论假设是产生误差的另一个原因，这种误差可能来源于不同的原因。 , 首先，现实中的大多数粒子不可能完全符合假设的球型。非球型的粒子将导致在不同方向上的不同的交叉。因为不可能对粒子进行各个方向的测定，这将导致粒度分布的扩宽相对于平均体积分布。然而平均直径可能改变，将变大。 , 其次，粒子表面是粗糙的而不是光滑的。这将引起在边缘的光的漫反射，这通常作为粒子吸收光相似的影响。 , 第三，粒子的光学性质要求相似，尤其对多孔的粒子。这对于粒子十分小的情况十分重要。 , 最后，可能是选择错误的光学模式或者参数。例如，如果用弗琅荷费近似，来测定含有一定的微小的透射的粒子的样品，所计算的小粒子的含量将变大。(见附A)。总之，模型选择错误将导致通过仪器所计算出来的粒子的浓度和分散介质的体积和样品的质量得到的粒子浓度存在很大的差别。(参见6.6.6) 6.6.4操作程序错误或者仪器机能错误有如下几点: - 有些粒子的直径超出测量范围 [在这种情况下，可以调整测量范围(改变透镜)和(或)除去太大的粒子，例如 通过预筛分 ]; - 引入激光束的样品在透镜的工作的距离之外; - 透镜(组)或者测量池的窗体被污染。因此，需要清洗; - 测量背景值过高; - 该光学系统没有调整好; - 粒子浓度过高，引起多重散射; - 粒子的分散光强度的去卷积的数学程序不恰当(联系仪器制造商)。 6.6.5缺乏保持上述要点的良好控制可能导致产生随机错误。 而且，随机误差可能起因于: - 测量时间不足或者检测器输出系统能量不足 - 工作浓度太低，以及 - 仪器状态不理想，例如激光强度波动或者检测器噪音。 6.6.6 程序细节的错误可由以下步骤判断: - 测定至少1 h 激光束强度的空白实验: 应该在仪器手册里给出其稳定限制。 - 做空白实验，观测全部检测器的信号: 背景值应该是光滑曲线，其值为零或非常小。 负载或者超载(100%)表明检测器单元有问:电子元件缺陷或者池窗(透镜)有划痕。由于很大的光强只照射检测器的同一部分，使得透镜的光学表面、试管或其它元件损坏。 - 测定重复样品来考察检测器信号， 计算每个成分的平均值和它们的标准偏差并且通过与以前的测量值比较来确定全部检测器单元的测定信号。 这样，可以获得这些信号的准确度和精确度: 大的系统差异或者零值通常表明不良的检测器单元、电子元件缺陷、窗体或者透镜有污染、坏的队列、样品中有气泡或问题和/或分散程序出错。而且，在对光强度值的变换之后， 在不同的仪器上比较散布图案，这些数据能够在某种程度上说明与检测器单元的几何位置;不管在这些文件(如果知道其几何位置)。 - 比较实际粒子浓度， 象从样品的量和散布介质的体积计算的那样， 来自于暗光和粒子颗粒分布的计算， 使用相同的光学模型(去卷积函数)计算粒子尺寸部分的消光系数;如果有较大的差别表明光学模型不适当或者样品操作错误 [1]; - 比较全部检测器单元的测量和计算信号值(针对由此产生，最好适合的粒子颗粒分布);大的系统差异表明一种不良的检测器单元或者是不适当的光学模型。 6.7决定性;灵敏度 粒子粒径分布的决定， 即把不同粒径的粒子尺寸区分开的能力，检测限受以下的因素限制: - 检测器的数目，位置和几何位置; - 它们的信噪比; - 测量散射图样的精细结构; - 分散在尺寸种类之间散射图样的差别; - 微粒的实际尺寸范围; - 合适的光学模型; - 在去卷积程序中滤波的使用。 这些因素用来区别高分辨率技术和普通激光衍射技术: 每个级别粒子的最小宽度通常在大约1，1到2(最小级别尺寸下限的比率)。 结果的实际价值和(或)质量控制灵敏度决定于已知化合物的混剂。 7 结果的报告 结果应该根据ISO 9276-1标准进行报告。 而且，应该给出以下的信息以使在不同的实验室不同的操作人员之间有可比性。下面是一些可选项目。 a )样品 - 完成样品鉴定，例如化学类型，批号和位置，取样的日期与 时间，等等; - 取样程序，即取样的方法和样品粉碎程序; - 样品预处理(可选择)，例如预筛分，类型和条件; - 分析日期 b) 分散 - 分散类型:干法或湿法 干法分散 - 分散装置的具体参数，例如:入射直径，压力; - 定量给料/进样装置的类型 - 进样量 湿法分散 - 分散液体:名称、体积，如果有必要，还要给出温度 - 分散剂:类型和数量 - 样品浓度 - 超声: 类型，频率(能源)，在测量之前持续和暂停的时间; - 泵速度。 c) 激光衍射测量 - 仪器类型和数目 - 软件版本 - 透镜的焦距 - 用于测量的实际尺寸范围 - 上次调整的数据 - 上次生效的日期 - 测量的日期与时间 - 光学常数 - 启闭状态的条件(如果使用) - 获得有效数据(如果使用)的开始 - 光散射模型的使用。 - 如果使用Mie 理论，给出复杂折射率真正和假象部分， - (可选择)从去卷积函数得出的合适的参数(例如对数，开方)。 d) 分析员报告 - 实验室的名称及位置。 - 操作者的姓名或者词首大写首字母。