Comminution lecture 18 Flashcards Preview

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Flashcards in Comminution lecture 18 Deck (18):
1

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

2

what are the different particle size ranges?

coarse: >350um
medium/fine powder: 100 - 350um
fine powder: 50 - 100um
very fine powder: 10 - 50um
micronised powder: <10um

3

what is the particle size of inhaled powders?

0.5-1um

4

What is the 'equivalent sphere' for?

to reduce the 3D nature to a single number so easier to know particle size

5

determining equivalent sphere is based on what?

surface, volume, sieve aperture, sedimentation charecteristics

6

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)

7

what are the different methods used to analyse particle size?

sieve, microscope, sedimentation, laser diffraction

8

Why is the mean better than mode/median?

as it's determined when size distribution is complete and determines upper and lower size limits

9

define comminution:

the reduction of solid materials from a bigger mean particle size to a smaller mean particle size

10

what is the difference between milling and prolonged milling?

milling = normal --> fine particles (bimodal)
prolonged milling = finer --> finer particles (unimodal)

11

what are the size reduction method particle sizes ranges?

cutting: 100um-100mm
compression: 10um - 100mm
impact: 1um - 10mm
attrition: 1um - 100um
combination of impact and attrition: 1um - 10mm

12

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

13

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

14

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

15

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

16

What are the different sieving methods?

1. agitation
2. brushing
3. centrifugation

17

define separation efficiency:

the effectiveness of a given process in separating particles into oversize and undersize fractions

18

What are the different size separation methods?

sieving (wet is better than dry)
sedimentation
elutriation
cyclone