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Laser Particle Size Analyzer |
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| 1. | absorption |
| reduction of intensity of a light beam traversing a medium through energy conversion in the medium. | |
| 2. | coefficient of variation |
| relative measure for precision:standard deviation divided by mean value of population and multiplied by 100(for normal distributions of data the median is equal to the mean) | |
| 3. | complex refractive index |
| refractive index of a particle,consisting of a real and an imaginary(absorption) part. | |
| 4. | relative refractive index |
| complex refractive index of a particle,relative to that of the medium | |
| 5. | deconvolution |
| mathematical procedure whereby the size distribution of a particle ensemble is inferred from measurements of their scattering pattern. | |
| 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. | |
| 7. | extinction |
| attenuation of a light beam traversing a medium through absorption and scattering. | |
| 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. | |
| 9. | multiple 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). | |
| 10. | obscuration(optical concentration) |
| percentage or fraction of incident light that is attenuated due to extinction(scattering and/or absorption) by the particles. | |
| 11. | optical model |
| theoretical model used for computing the model matrix fro optically homogeneous spheres with,if necessary,a specified complex refractive index,e.g.Fraunhofer diffraction,anomalous diffraction,Mie scattering. | |
| 12. | reflection |
| return of radiation by a surface,without change in wavelength. | |
| 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. | |
| 14. | scattering |
| general term describing the change in propagation of light at the interface of two media. | |
| 15. | scattering pattern |
| angular or spacial pattern of light intensities originating from scattering,or the related energy values taking into account the sensitivity and the geometry of the detector elements. | |
| 16. | single scattering |
| scattering whereby the contribution of a single member of a particle population to the scattering pattern of the entire population is independent of the other members of the population. | |
| 17. | width of normal size distribution |
| standard deviation(absolute value) or coefficient of variation(relative percentage) of the size distribution. | |
| 18. | What is a particle |
| A particle is a minute object with a certain size and shape. Macroscopically it is very small, but microscopically, a particle contains numberous molecules and atoms. | |
| 19. | What is particle size |
| Although this simply implies particle size is the size of an individual particle, determing absolute particle size can be difficult. | |
| 20. | What is particle size distribution |
| The number of particles that fall into each of the various size ranges given as a percentage of the total number of all sizes in the sample of interest. | |
| 21. | How to describe particle size distribution |
| -Table: percentage of particles from the total within a size range;it includes differential distribution and cumulative distribution -Figure: particle distribution by histogram and curves, etc -Function: particle distribution functionally including R-R distribution and normal distribution |
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| 22. | What is particle diameter |
| It is the diameter of a particle normally expressed either in microns or nanometers. | |
| 23. | What is equivalent particle diameter |
| The equivalent particle diameter is divided into the following meanings: -Equivalent projected area diameter -Equivalent surface area diameter -Equivalent volume diameter -Equivalent sieve (near-mesh) diameter -Stokes diameter |
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| 24. | Why introduce equivalent particle diameter |
| In practice, particles are not uniformly shaped therefore they are difficult to define in a signle number. By correlating the particle to a sphere, one number can describe the size of a geometrically complicated particle. | |
| 25. | What is D50 |
| Also known as the median diameter or the medium value of the particle size distribution, it is the value of the particle diameter at 50% in the cuculative distribution. It is one of an important parameter for representing particle size. For example, if D50=5um, then 50% of the particles in the sample are larger than 5um, and 50% smaller than 5um. | |
| 26. | What is average diameter |
| It is the weighted averaghe of particle size. | |
| 27. | What is D97,What is the purpose of it |
| It is the particle diameter value where 97% of the sample is smaller than that value. It is useful for determining the upper limit to the particle size distribution | |
| 28. | What are frequently used methods to test particle size |
| There are microscope imaging methods, sieve analysis, gravity sedimentation, centrifugal sedimentation, Coulter(resistance) analysis, laser diffraction / scattering methods, electron microscope, ultrasonic, gas sorption, etc. | |
| 29. | Advantages and disadvantages of the above methods |
| -Microscope Imaging A: simple, direct test procedure, shape analysis available D: long test cycle, relatively poor representation, testing of ultra fine particles not possible -Sieve Analysis A:simple, direct test procedure, low cost D:samples smaller than 40um can not be tested; test results are subject to deformation of sieve meshes -Sedimentation A:low price, continuous operation, high degree of accuracy and repeatability, relatively broad test range D:long test cycle -Coulter A:easy operation short testing cycle, relatively high accuracy D:narrower size range, easily blocked apertures, electric conductivity of medium necessary -Laser diffraction A:easy operation, broad test range, high degree of accuracy and repeatability on-line test and dry test available. D:test results are subject to distribution pattern, high cost of instrument -Electron Microscope A:capable of measuring particles of nanometer size, high resolution D:possible alternation of particles during sample preparation, small representation of overall sample, and high cost -Ultrasonic A:direct test on highly concentrated liquid D:low resolution -Gass absorption A:low cost of instrument, sample dispersion not an issue, testing on magnetic powders capable D:only average particle size available, particle size distribution unobtainable |
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| 30. | What are differential distribution and cumulative distribution |
| Differential distribution is the percentage of particles from the total that are withiin a specified size range; for example, 30% within 1-10um range, 50% within 10-20um range, and 20% within 20-30um range. Cumulative distribution is the sum of the differential distributions. The cumulative distribution is obtained by accumulation of differential distribution, for instance, 80% of the particles are smaller than 20um. | |
| 31. | What is repeatability |
| It is the relative error among multiple results from the same sample. | |
| 32. | What affects repeatability |
| -Stability of the instrument or test method -Whether dispersion of the sample is fully obtained or not -Whether the sampling is representative of the overall material -Whether the operational procedures are standardized or not -Working condition including voltage, temperature, clean enviroment, etc. |
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33. |
Mean size |
| Arithmetic mean particle size for a given population of particles, weighted according to number, volume, etc. (synonym to average size) | |
| 33 | Median size |
| Particle size at the point in the cumulative size distribution, where 50% of the particles is smaller and 50% larger. | |
| 34 | Suspension |
| Dispersion of solid particles in a liquid, in which they are not soluble | |
| 35 | Cumulative size distribution |
| Distribution of the fraction of material smaller (undersize) or larger (oversize) than given particle sizes against particle size | |
| 36 | Differential size distribution |
| Distribution of fractions of material in given size classes against particle size, either as a histogram or as a smoothed curve. |
| 37 | Equivalent diameter |
| Diameter of equivalent sphere | |
| 38 | Feret diameter |
| distance between two parallel tangents on opposite sides of the image of a randomly oriented particle | |
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