ASTM_E_1458_-_12_2016.pdf

Designation:E145812(Reapproved 2016)Standard Test Method forCalibration Verification of Laser Diffraction Particle SizingInstruments Using Photomask Reticles1This standard is issued under the fixed designation E1458;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONThere exists a large variety of techniques and instruments for the sizing of particles and droplets influid suspension.These instruments are based on a number of different physical phenomena andinterlaboratory comparisons of data on,for example,reference liquid sprays have shown significantvariability.This test method evolved in conjunction with efforts to explain the observed variability.The effectiveness of this test method can be traced to the fact it circumvents difficulties associated withproducing,replicating,and maintaining a standard sample of liquid particles in a spray.This testmethod uses a photomask reticle to provide a simulation of some of the optical properties of areference population of spherical particles.This test method is only applicable to optical particle sizinginstruments that are based on measurement and analysis of light scattered in the forward direction byparticles illuminated by a light beam.Since modern optical instruments generally use a laser toproduce a light beam,and since the light scattered in the forward direction by particles can often beaccurately described using diffraction theory approximations,the class of instruments for which thistest method applies have become generally known as laser diffraction particle sizing instruments.Because it is specifically Fraunhofer diffraction theory2,3that is used in the approximation,theseinstruments are also known as Fraunhofer diffraction particle sizing instruments.The diffraction approximation to the general problem of electromagnetic wave scattering byparticles is strictly valid only if three conditions are satisfied.The conditions are:particle sizes mustbe significantly larger than the optical wavelength,particle refractive indices must be significantlydifferent than the surrounding medium,and only very small(near-forward)scattering angles areconsidered.For the case of spherical particles with sizes on the order of the wavelength or for largescattering angles,the complete Lorenz-Mie scattering theory2,3rather than the Fraunhofer diffractionapproximation must be used.If the size and angle constraints are satisfied but the particle refractiveindex is very close to that of the medium,the anomalous diffraction approximation3may be used.A complication is introduced by the fact that the optical systems of most laser diffraction particlesizing instruments can be used,with only minor modifications such as changing a lens or translatingthe sample,for measurement configurations outside the particle size or scattering angle range forwhich the diffraction approximation is valid.In this situation the scattering inversion software in theinstrument would generally incorporate a scattering model other than Fraunhofer diffraction theory,inwhich case the term“laser diffraction instrument”might be considered a misnomer.However,such aninstrument is still in essence a laser diffraction instrument,modified to decrease the lower particle sizelimit.A calibration verification procedure as described by this test method would be applicable to allinstrument configurations(or operational modes)where the photomask reticle accurately simulates therelevant optical properties of the particles.The ideal calibration test samples for laser diffraction particle sizing instruments would becomprised of the actual particle or droplet material of interest in the actual environment of interestwith size distributions closely approximating those encountered in practice.However,the use of suchcalibration test samples is not currently feasible because multi-phase mixtures may undergo changesduring a test and because actual samples(for example,a spray)are not easily collected and stabilizedfor long periods of time.The subject of this test method is an alternative calibration test samplecomprised of a two-dimensional array of thin,opaque circular discs(particle artifacts)deposited ona transparent substrate(the photographic negative,that is,clear apertures in an opaque substrate,maybe used as well).Each disc or particle artifact represents the orthogonal projection of the cross-sectionCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 of one member of a population of spherical particles comprising the reference population.Thecollection of particle artifacts on a reticle represents an orthogonal projection of all the particles in thereference population for one particular three-dimensional arrangement of t