Particle Size Analysis Flashcards
What are the problems with particle size analysis?
Irregular particle shapes = unpredictable
Range of particle sizes
2-dimensional info = lose info on entire dimension
What is the solution to particle size analysis?
Equivalent sphere
Statistics
What is equivalent sphere diameter?
Hypothetical sphere that has an equivalent measurable property (eg. vol, SA) as particle
What is the perimeter diameter?
Diameter of equivalent sphere with same perimeter (circumference)
What is the projected area diameter?
Diameter of equivalent sphere with the same projected area
What are the statistical diameters?
Feret’s diameter
Martin’s diameter
What is Feret’s diameter?
Average length of line across the projected width of particle (dF)
What is Martin’s diameter?
Average length of line bisecting particle into equal areas
What is the hydrodynamic diameter?
Diameter of hypothetical equivalent sphere that diffuses in the same way as the particle under investigation
What is the hydrodynamic diameter affected by?
Ionic strength
Surface structure
Shape
What is convexity?
Convex hull perimeter divided by actual particle perimeter
What is aspect ratio?
Width divided by length
What is circularity?
Circumference of equivalent area circle divided by actual perimeter of particle
What is solidity?
Actual particle area divided by convex hull area
Describe normal particle size distribution on graph
Symmetrical
Mean = median = mode
Standard deviation
Describe bimodal distribution
Suggest 2 distinct populations of different particle size
= 2 peaks = modes
What does it mean when the graph is negatively skewed?
Shifts right
More larger particles than smaller ones
Mean < median < mode
What does it mean when the graph is positively skewed?
Shifts left
More smaller particles than larger ones
Mean > median > mode
What are D-values?
Equivalent sphere diameter at specified percentiles
What is D10?
10% of particles are below this diameter
What is D25?
25% of particles are below this diameter
What is D50?
50% of particles are below this diameter (median)
What is D75?
75% of particles are below this diameter
What is D90?
90% of particles are below this diameter
What does span indicate?
Width of particle size distribution
How do you calculate span?
D50
What numbers is interquartile coefficient of skewness (IQCS)?
-1 to 1
What is IQCS < 0?
Negative skew
What is IQCS > 0?
Positive skew
What is IQCS = 0?
Normal distribution
What is the equation for polydispersity index?
σ
—- *2
μ
Standard deviation
Mean particle size
What happens if polydispersity index is below 0.2?
Narrow particles approx. same size = monodispersed
Describe laser diffraction
Wet or dry samples
Scattered light detected by photodetectors
Particle size determined from angular light intensity
Describe dynamic light scattering
Laser light scattered by particles in Brownian motion
Wet samples only
What do smaller particles do?
Diffuse more rapidly
What happens if the particles move faster?
Different scatter flucuation
How is hydrodynamic diameter of particle determined in dynamic light scattering?
Stokes-Einstein equation
