Solid sphere (1D radius describes size, shape, SA, volume), solid geometrical particles (2-3D required to describe size, shape, SA, volume)
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What is the particle shape in reality?
Solid irregular particles (size and shape can only be approximated, SA and volume can be measured). Porous irregular particles (size, shape, SA and volume can only be approximated)
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Describe features of particle sizing powders
Large geometric objects (size is described in 3D). Small irregular particles (3D size description is impractical, only 1D/average diameter is used)
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Describe features of the ESD (1)
ESD of an irregularly shaped object is the diameter of the sphere of an equivalent volume
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Describe features of the ESD (2)
Equivalent diameter of non-spherical particle is equal to diameter of spherical particle that exhibits identical properties (e.g. optical electrical) to that of the non-spherical particle e.g. dmax, dsec, dsieve, ds, dv, dw, dmin
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What are the two ways to plot size distributions?
Incremental (how many particles fall within given size band) and cumulative (how much material lies above or below particle size)
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Do I need to know what % of the powder falls into a specific size increment? Do I want quick information on the particle size distribution?
Incremental
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Do I need to know what % of the powder is smaller or larger than a specified size?
Cumulative
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Describe features of incremental histograms (more common)
Normal, bimodal, + skewed or - skewed. Reflects distribution of particle sizes. Presents interpretation of particle size distribution. Enables determination for % of particles having equivalent diameters. Compare different particle distributions
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Describe features of cumulative size distributions
Undersize (shows relative amount at or below particular size). Oversize (shows the relative amount at or above particular size)
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Describe features of micromeritics - characterising the particle size and distribution
Normal distribution (bell curve, very common continuous probability distribution). Lognormal distribution (continuous probability distribution in which logarithm of variable is normally distributed)
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When is the arithmetric mean and arithmetic SD used?
For normal distributions (for all samples and randomly selected samples)
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When is the geometric mean and geometric SD used?
For lognormal distributions
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What if the powder shows neither a normal or lognormal distribution?
Powders not milled long enough to slow ideal normal or lognormal distribution model (multimodal). If you continue to mill powder longer enough, it should show a lognormal distribution
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When is the median used instead of the mean?
Data set contains small number of outliers (affects mean). Data set contains 0 as a value (affects mean). Data is unimodal/skewed but had no normal or lognormal distribution. End values of data set of known - all unaffected by median
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How do you calculate the arithmetic SD from probability graphs?
D50 - D16 or D84 - D50
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How do you calculate the geometric SD from probability graphs?
Square root of D84/D16
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What is used to describe the polydispersity of powders?
D90/D10 ratio. Useful measure of dispersion for multimodal distributions. No units, expressed in 2 d.p. - closer to 1.00 (more narrow dispersion around median value)
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How do you calculate the CV% (or RSD)?
SD/mean x 100 - used to compare degree of variance between multiple sample populations (uniformity of dosage form studies, quality control of tableting equipment)
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Other cards in this set
Card 2
Front
What is the particle shape in reality?
Back
Solid irregular particles (size and shape can only be approximated, SA and volume can be measured). Porous irregular particles (size, shape, SA and volume can only be approximated)
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