Flashcards in Comminution lecture 18 Deck (18):
How does smaller particle size affect bioavailability?
the smaller the particle, the faster the dissolution and the higher the bioavailability
however, v small particles can result in a v rapid absorption/clearance
what are the different particle size ranges?
medium/fine powder: 100 - 350um
fine powder: 50 - 100um
very fine powder: 10 - 50um
micronised powder: <10um
what is the particle size of inhaled powders?
What is the 'equivalent sphere' for?
to reduce the 3D nature to a single number so easier to know particle size
determining equivalent sphere is based on what?
surface, volume, sieve aperture, sedimentation charecteristics
What is the difference between circumscribed and inscribed circle?
circumscribed - absolute outside of circle/rough edges
inscribed - the biggest 'full' circle inside
(see image better explanation lol)
what are the different methods used to analyse particle size?
sieve, microscope, sedimentation, laser diffraction
Why is the mean better than mode/median?
as it's determined when size distribution is complete and determines upper and lower size limits
the reduction of solid materials from a bigger mean particle size to a smaller mean particle size
what is the difference between milling and prolonged milling?
milling = normal --> fine particles (bimodal)
prolonged milling = finer --> finer particles (unimodal)
what are the size reduction method particle sizes ranges?
compression: 10um - 100mm
impact: 1um - 10mm
attrition: 1um - 100um
combination of impact and attrition: 1um - 10mm
what needs to be considered when particle size is reduced to 1-5um?
- that particle to particle forces will be the main comminution stress
- particle agglomeration might happen
Describe the cutting method:
knives/blades on a rotor, causing fracture of particles.
A screen retains the material larger than a specified size (so it's a self classifying method)
- coarse degree of size reduction in dried granules is due to high shear rates
Describe the compression method:
material is compressed by frictional forces between rollers. one roller is mechanically driven, the other is rotated by force
there can be a series of rollers to get smaller sizes
What are the 2 impact methods?
- conventional ball mill (filled to 80% porcelain/steel balls)
- vibrational ball mill (filled with 50-70% porcelain/steel balls) BETTER than conventional
What are the different sieving methods?
define separation efficiency:
the effectiveness of a given process in separating particles into oversize and undersize fractions