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Chem. Interfacial Electrochem 150 201, 1983. (1 184) Zelez, J., RCA Rev., 43, 685, 1082. (1185) Zelez, J., J . Vac. Sci. Technol. A , 1, 305, 1983. (1186)Zemek, J., and Koc, S., Sol. Energy Mater.. 9 , 183,1983. (1187) Zhang, Q.J., Gomer, R., and Bowman, D. R., Surf. Scl., 129. 535,
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(1189) Zhou, S.Y., and Olander, D. R., Surf. Sci., 138, 82,1984. (1190) Zhou, Y. X., McMahon, Jr., C. J., and Plurnrner, E. W., J . Vac . Scl. Technol. A . 2 . 1 I la. 1984. (1191) Zhu, Y:,-and Schmidt, L. D., Surf. Scl., 129, 107. 1983. (1192) Zurcher, P., and Bauer, R. S.,J . Vac. Scl. Technol. A , 1 1983. (1193) Zwlcker, G.,and Jacobl, K.. Surf. Scl., 131, 179, 1983. (1194) Kane, P. F., and Larrabee, 0.B., Anal. Chem., 49, 221R, 1977. (1195) Kane, P. F., and Larrabee, G. B., Anal. Chem., 5 1 , 308R. 1979. (1196) Larrabee, G. B., and Shaffner,T. J., Anal. Chem., 53. 163R. 1991. (1197) Bowling, R. A., and Larrabee, G. B., Anal. Chem.. 5 5 , 133R, 1983.
Particle Size Analysis Howard G. Barth* and Shao-Tang Sun Hercules Incorporated, Research Center, Wilmington, Delaware 19894
INTRODUCTION Particle size analysis is a specialized area of analytical chemistry which is required in a great number of industries where the product’s end-use is affected by particle size distribution. Particles can be in the form of solids, liquids, (emulsions and dispersions), or gases (bubbles) or an aggregation of molecules as in the case of micelles. In some instances, especially in areas of pharmaceuticals and electronics, analyses are done to ensure the absence of particulate matter. To monitor the environment accurately for particulate matter requires knowing particle size distributions, as well as concentrations, to fully assess health hazards. In view of the growing interest in particle size analysis, especially among analytical chemists, the subject is covered in this issue of Application Reviews. The number of techniques available for particle size analysis is staggering. According to Scarlett (15A),about 400 methods have been reported. Because of the broad scope of this area in terms of techniques and analytical approaches (see Table I), products (see Tables I1 and 111), and size ranges, the authors focused on two major technique areas which have received the most attention in recent years: radiation scattering and chromatographic techniques. These relatively new and growing areas are rapidly becoming techniques of choice especially for the rapid analysis of submicrometer particles. Also included in this review are recent developments involving the more classical techniques listed in Table I as well as a number of related topics (Data Handling and Analysis, Comminution Theory, and Particle Size Generators). Papers published from late 1981 to the end of 1984 (Chemical Abstracts 1982, 96 (1) to 1984 101 (20)) were searched for relevant papers published in English, French, German, and Russian. Polymers in solution were excluded even though they can be classified as particles. Because of the enormous breadth of topics, in terms of sample type, technique, and particle size range, a number of different search strategies were tried in an attempt to include as many pertinent articles as possible. To this end, we gratefully acknowledge the work of Ruth Curtiss, Hercules Technical Information Division, for her excellent search routines.
GENERAL BOOKS AND REVIEWS During the past several years there has been only a handful of general books on particle characterization. (Books on light scattering are reviewed in the Scatterin section.) By far, the most popular is T. Allen’s book f2A), “Particle Size Measurement”, which is considered the authoritative text on particle size analysis. The book deals in depth with a wide range of topics. Included are chapters on sampling handling,
Table I. Common Particle Size Analysis Techniques Centrifugal Sedimentation Techniques Disk Centrifuge photosedimentometry Ultracentrifugation Chromatographic Techniques Field-flow fractionation Hydrodynamic chromatography Classification/Collection/SamplingTechniques (mainly for
aerosol particles) Cyclone/centrifugal separators Elutriators Impactors Electrical Sensing Zone Methods (Coulter Principle) Gravitational Sedimentation Techniques Photosedimentometry Microscopy Optical and electron (Image analysis for data processing) Scattering Techniques Classical light scattering (time-averagelight scattering) Doppler anemometry and related velocimetry methods Electric birefringence Fraunhofer diffraction Single-particle counting techniques Neutron scattering Photon correlation spectroscopy (time-dependentlight scattering, quasi-elastic light scattering) Turbidimetry X-ray scattering Sieving/Filtration Surface Area Measurements data treatment and analysis, and on-line particle size analysis. Most particle size analysis techniques are comprehensively treated including sieving, microscopy, gravitational and sedimentation size analysis, centrifugal methods, Coulter principle, light scattering, and surface area and porosity measurements. “Direct Characterization of Fineparticles”, by B. H. Kaye (2A),represents a comprehensive treatment of well-established particle characterization techniques, including sieve fractionation, gravity and centrifugal sedimentation, and elutriation. Also summarized are single particle counting methods. The chapters on particle sampling, image analysis, and particle
0003-27001a510357-15 I~ $ 0 6 . 5 ~ 0 0 1985 American Chemical Society
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PARTICLE SIZE ANALYSIS
shape characterization are also excellent and well written. “Modern Methods of Particle Size Analysis”,edited by H. G. Barth (3A),focuses on newer techniques of particle analysis including photon correlation spectroscopy, Fraunhofer diffraction, hydrodynamic chromatography, and field flow fractionation. Also covered are chapters on commercially available instrumentation and a thorough treatment of methods used to characterize submicrometer dispersions and emulsions. Although not specifically a particle size analysis book, J. K. Beddow’s text (4A),“Particulate Science and Technology”, which deals with the nature and behavior of particles, is an excellent source book for all those involved in particle characterization. This book discusses the nature of single particles, particle formation and production, processing and handling of particulate matter, an extensive coverage of particle characterization in terms of shape and distributions, physical and chemical properties of particles, and hazards associated with particles (dust explosions and fires, health hazards, and desertification). The Proceedings of the 4th Particle Size Analysis Conference, edited by Stanley-Wood and Allen (16A),contains a wealth of information on major areas of particle size analysis including papers on surface area/porosimetry measurements, the Coulter principle, particle shape and morphology, sedimentation, particle statistics and in-stream analysis, and light scattering techniques. C. H. Murphy’s book (12A),“Handbook of Particle Sampling and Analysis Methods”,includes chapters on particle characterization and behavior and contains comprehensive coverage of particle sampling instrumentation (impactors, cyclones, and centrifugal separators), filtration, condensation nuclei counters and diffusion devices, particle electric mobility techniques, and optical particle samplers. The last section covers various particle analytical methods including an excellent discussion on data interpretation. Another book is “Particle Size Analysis” by G. Butters and A. L. Wheatley (6A). “Air/Particulate Instrumentation and Analysis”, edited by Cheresmisinoff (7A), focuses on the analysis of particles contributing to air pollution. Chapters include an overview of particle measurement techniques, characterization of atmospheric particles, and collecting and sampling methods. The American Institute of Chemical Engineers ( I A ) have issued a booklet describing procedures for conducting and interpreting performance evaluation tests on particle classifications equipment (sieving,air and liquid sedimentation and elutriation, particle counting, and surface area measurements). Although not directly related to particle size analysis, Svarovsky (17A)was written a handbook on solid-gas separation which deals with the removal of particles from gases. In 1984, Verlag Chemie introduced a new journal, Particle Characterization, which is devoted to the measurement and description of particle and bulk properties in disperse systems. The editors are K. Leschonski, G. Jimbo, B. H. Kaye, and B. Scarlett. As of this writing three issues (July, October, and November, 1984) have appeared. Scarlett (14A) presented an interesting and informative discussion on particle science and technology. Included is a brief, but excellent, overview of particle properties. This author (15A) also discussed classification of particle sizing methods and calibration approaches. The advantages and problem areas of on-line methods for particle size analysis were presented by Leschonski (10A)who considered methods of sampling and analysis times. The ”Kirk-Othmer Encyclopedia of Chemical Technology” (13A)contains an excellent review of particle size analysis by C. Orr which includes data treatment and an overview of major techniques. Bunville (5A)provided a comprehensive coverage of commercial instrumentation for particle size analysis. Techniques presented were those based on the Coulter principle, transport properties (gravitational and centrifugation sedimentation, hydrodynamic chromatography, and aerodynamic transport), and nonimaging optical methods (optical blockage techniques, time-averaged light scattering, and photon correlation spectroscopy). Groves (8A)wrote an excellent survey of methods used to characterize submicrometer dispersions and emulsions, including advantages and limitations of each technique. A review of particle size analysis in coating systems was presented by Lloyd (1IA). 152 R
ANALYTICAL CHEMISTRY, VOL. 57, NO. 5, APRIL 1985
SCAllER ING TECHNIQUES Light, neutron, and X-ray scattering techniques have been used extensively to study the structure and dynamics of particles and macromoleculesin multicomponent systems. In a typical experiment an incident beam probes the medium of interest and the scattered radiation is analyzed with a suitable spectrometer. The momentum and energy differences between the scattered and the incident radiations characterize the structure and dynamics of the medium with a spatial and temporal resolution of q-’ and u-’,respectively, where q is the wave vector and w is the frequency. In the case of light scattering, the ranges of the respective length and time scales are 10-1to lo4 cm and lo-’ to s. Neutron scatterin and X-ray scattering cover a similar range of 4-l 10-~-105 cm, but different d amic ranges, w-l 10*-10-16 s for the former and w-l 10-K10-’7 s for the latter. Two techniques that have attracted a great deal of recent attention for particle size determination are quasi-elastic light scattering (QELS), also referred to as photon correlation spectroscopy (PCS) or time-dependent light-scattering, and small-angle neutron scattering (SANS). Active research using these two methods has increased because of the commercial availability of the instrumentation and the accessibility of neutron scattering facilities. In this section, the emphasis will be placed on the application of these two relatively new approaches to particle size analysis. In the case of classical light scattering, the radius of gyration of the particle is determined from the q dependence or angular dependence of the time-averaged scattering intensity. However, with PCS, the size information is obtained from the time dependent fluctuations of scattered intensity due to concentration fluctuations resulting from Brownian motion of particles. The diffusion coefficient of the Brownian particles is determined from the intensity autocorrelation function measured experimentally with a digital correlator. The hydrodynamic radius is then calculated from the diffusion coefficient using the Stokes-Einstein relation. Because the temporal resolution of PCS is of the order of lo-’ to lo4 s, this method is used to probe particle sizes ranging from lo-’ to cm. The power of PCS lies in its relative ease of use, rapid determination of diffusion coefficienb with high precision (0.7 pm and separated su micrometer particles into two fractions by diffusion. The errors in recovered particle size distributions caused by impactor sampling with bent nozzles were discussed by Felix and McCain (IOR).In flue gas sampling, analyses with straight nozzles resulted in higher particulate masses than those with curved nozzles. Cascade Impactors. An important factor that affects the accuracy of cascade impactor data is the type of substrate used for collecting aerosol particles. In view of this, Barr et al. (3R) described the calibration of a cascade impactor using different uncoated substrates. Stainless steel, silver membrane filters, and cellulose acetate membrane filters showed collection characteristics that closely fit theoretical predications while fiber-type substrates showed the most deviation. A parallel-stage impactor consisting of a set of single-stage impactors operating in conjunction with a total particle collection filter was developed by Lee and Esmen (16R).Each stage consists of a jet, an impaction surface, and a backup filter, which collects particles not collected on the impaction surface. This procedure provides bounce-loss-free and wall-loss-free analysis of particle size distributions. Sporenberg et al. (25R) compared the separation efficiencies of an annulus-orifice nozzle-impactor and an Andersen impactor and found that the separation efficienciesof the stages of the former were more variable and wall losses greater than those of the latter. Multislot and multiorifice cascade impactors were compared with an inertial spectrometer in evaluating the particle size distribution of iron oxide and sodium chloride aerosols (9R). The instruments agreed well in the smaller size ranges but for larger aerosols, the multislot impactor overestimated the median size. Boulaud et al. (7R)evaluated a Mark I1 Andersen cascade impactor used for measuring particle size distribution of 0.5-10 pm. The influences of the type of collection surface, electric charge of the aerosol, and mass loading of the collection surface on efficiencywere investigated. Effects of particle bounce and blow-off were reduced by using grease-coated plates. Boesch (5R) compared the distribution curves for Berner, Andersen, and Marple impactors. Virtual Impactors. Because of the particle-surface interaction problems associated with inertial impactors such as particle bounce, reentrainment, and collection surface overload, virtual impactors have been designed in which the solid impaction surface has been replaced with a slowly pumped stagnant air void (11R).Farney et al. (11R)described and evaluated a two-dimensional virtual impactor. A single-stage, rectangular-jet virtual impactor was described by Overcamp and Taylor (2OR). The impactor was calibrated with a nearly monodisperse methylene blue aerosol produced by a spinning top generator. A high-volume dichotomous virtual impactor for the fractionation and collection of particles according to aerodynamic size was designed by Solomon et al. (24R). An in-stack virtual impactor, consisting of a series of cascade particle-size sepa-
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 5, APRIL 1985
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PARTICLE SIZE ANALYSIS
Table 111. Selected Applications of Other Techniques application alloys alumina aluminum atmosphere pollutants artic haze
method' DSC XRD RADTR GD IMP
atmosphere aerosols
IMP XRE IMP
lead
IMP IMP IMP IMP, SED IMP IMP MIC, RAD
marine aerosols nuclear reaction plutonium radionuclides
IMP, RAD IMP smog traffic-derived aerosols
uranium mines urban aerosols
IMP IMP IMP IMP IMP IMP XRE IMP
IMP IMP EM workplace aerosols (also OPT, IMP see dusts) OPT LS GD GD bubbles carbon
catalysts
cement ceramics (also see kaolin) 164R
ref 7u 32U 39u 58U 3v
coal particles/dust
65U 134U 144U 55u 9ou 121u colloids/micelles (see Scattering Section) 145U 170U 173U dust (also see atmospheric pollutants) 83U, 84U 141U 139U 34u 46U 66U exhausts/emissions 18U auto exhaust 59u 73u coal coinbustion 92U 108U combustion products 109u diesel exhaust 69U 11u l0OU 127U flue gases 132U industrial plants 80U power plants 1ou 13U 23tJ shale oil retorting 31U smelter plumes 54u 56U welding fumes 61U emulsions 120u ferrite particles 42U 86U 88U 94u 138U ferrofluids 147U fibers 179U
155U 40U 60U 166U 8U 19u 29U 33aU 41U 45u 52u 104U EM, XRD 123U EM, XRD 129U EM, SORP EM, XRD, SORP 159U 174U EM, XRD 82U ll0U IMP 3u FILT
COND IMP MIC EM EM, XRD EM, SORP EM, SORP SORP MAG NMR
methodn
application
fire-extinguishing powders flocculants fuel ash iron oxide kaolin
latex particles
ANALYTICAL CHEMISTRY, VOL. 57, NO. 5, APRIL 1985
EM, PS GD SED SED LS, GD GD IMP SED GD
cc
IMP LS LS LS LS IMP LS OPT IMP LS
IMP
ref 21u 106U 114U 2u 43u 95u 105U 122u 151U 163U 164U 178U 6aU 31aU 102aU 6U 74u 91u 148U 162U 165U 166U 180U
176U 64U 128U IMP IMP 9u LS 35u 67U, 68U IMP 152U IMP 188U IMP 181U IMP 98U IMP 20u 62U IMP IMP 53u 25U 12u IMP 71X EM 117U SED 15U 47u SIEV 103U EM, CENT EM, SED, CENT 156U 119u 169U SIEV, OPT 185U 82U SIEV, MIC 183U SED 187U SED 19aU GD 76U IMP 135U EM 14U SED 51U SED lllU GD 138U EM 5u FILT 24U GD 89U CENT 93u GD 96U GD 97u CENT 124U MIC 10T, 161U FC
PARTICLE SIZE ANALYSIS ~
~~
Table I11 (Continued) application
methoda IMP
181U
EM SED PS
182U 184U 186U 50U 133U 63U 26U 48U 89aU
lignite limestone magnesium hydroxide magnetite pharmaceuticals
IMP PS GD
cc
POR SIEV SIEV FILT, PCS, MIC MIC
cc
pigments
potassium chloride proteins quartz
sand sediments/soils
CC, SIEV, LS CENT GD CENT GD SED, COND MIC GD GD
cc SED MIC SED SIEV
application
ref
16U
RAD
SED SIEV SIEV GD silica
sludge
2T 102u 112u 115U 2v 150U 153U
1v 22u 60U 9N 140U 149U 154U 158U 175U 130U 125U 146U 13Q 4N 1u
methodn
smoke/soot
SED SIEV MIC OPT IMP
sprays starch tanning compounds tetrachlorides tungsten carbide
SAUT
EM MIC EM GD
MAG
uranium oxide volcanic ash
wear debris zinc
cc
SIEV SIEV
ref 17U 36U 37u 38U 49u 57u 77u 113U 171U, 172U 72U 137U 168U 44u 78U 75u 87U 107U 160U 4u 79u 99u 189U 85U 142U 167U 27U, 28U 30U 157U 70U 81U 143U 126U l0lU
CC, Coulter counter; CENT, centrifugation; COND, conductometric; DSC, differential scanning calorimetry; EM, electron microscopy; FC, fractional creaming; PILT, filtration; GD, general discussion; IMP, impactor; LS, light scattering; MAG, magnetization; MIC, microscopy; OPT, optical methgds; PCS, photon correlation spectroscopy; POR, porosimetry; PS, photosedimestometry; RAD, radiation track detector/autoradiography;RADTR, radiation transmission; SAUT, Sauter method; SED, sedimentation; SIEV, sieving; SORP, sorption; XRD, X-ray diffraction; XRE, X-ray emission. rators with a light-scattering sensor, was described by Woffinden et al. (28R). A specially designed aerosol generating system was used for evaluation. The four-stage impactor was able to separate polystyrene latex particles ranging from 0.7 to 10 pm. An aerosol concentrator using the virtual impaction principle was described by Barr et al. (4R).Particles larger than a designed aerodynamic diameter cutoff were enriched in a bleed flow. Cyclones. A five-stage cascade cyclone system was described by Smith et al. (23R) for measuring particle size distribution and concentration of particles suspended in process-gas streams. A series of empirical equations were developed for predicting the cyclone cut points over a range of flow rates and temperature. Vrins and Hoffschreuder (26R) reported on the sampling of particles in which particles 6 pm, with a rotation inertial impactor. A particulate mass analyzer was developed by Wang and Libkind (27R) for real time measurement of fluidized bed combustion exhaust. The device consisted of a set of cyclones, each with ita own microbalance. Centrifugal Classifiers. Martoen (18R)developed formulas for predicting operating conditions for aerosol-sizing centrifuges with different winnowing gases using the kinetic viscosity of the actual winnowing gas as a correction factor. Resolution of particle size in spinning duct aerosol centrifuges was optimized by adjusting flow rates and rotational speeds (12R).Lower flow rates and higher rotational speeds favored resolution of particles of
