Lecture 10- Particle Sizing II Flashcards
Number, area & mass distributions
-distribution used needs to be specified
-type of distribution obtained depends on the sizing method used
*sieving & sedimentation= provide the mass of material in a given size band
*coulter counter= measure the number of particles in a given band
Median
Splits the distribution in two halves; 50% of the mass/particle number larger and 50% of the mass/particle number smaller
Symbol= D50
Measures of dispersion
Particles in a sample area= all same size= MONODISPERSED
Range of particle sizes= POLYDISPERSE
Normal distributions
Interest largely= arise when an item is subject to random variation
Found in natural systems such as:
-distribution of heights of people
-distribution of tablet weights in a batch
Normal distribution + log normal distribution activity
Slides 13-17
Particle size analysis
-size range analysis
-wet/dry methods
-manual/auto methods
-speed of analysis
Sieving
-stacking the sieves in order of ascending aperture size + placing the powder on the top sieve whilst agitating it; powder is classified into fractions
Reliever is placed at the bottom to collect the fines and a lid is placed on top to prevent loss of powder
Best to use when;
-separated fraction required for further study
-material must have a good flowability
-material must be handled dry
Avoid when;
-much fine powder is present
-particles are fragile= may break during the process
-material adheres to the sieve/forms clumps
Sieving errors
Sieve may be regarded as a series of gauges which reject/pass particles. Probability that a particle will present itself at an aperture depends on;
-particle size distribution of the powder
-number of the particles on the sieve
-physical properties of the particles
-method of shaking the sieve
Microscopy
-used to analyse particle size; particle sizes are visible therefore the operator can assess easily whether or not they are properly dispersed
Method continued; slide 27-29
Electrical sensing zone; slide 30-33
