production of fine particle

Question 1

what are the 5 advantages of production of fine particles?

Answer 1

Increase in surface area
increase in dissolution rate 
allow access to the lungs, powder inhalation
promote mixing, interactive mixtures
promote suspension stability
improve properties of the dosage forms

Question 2

what are some of the associated problems with fine particles?

Answer 2

problems with handling and processing
- impaction
-sedimentation
inhaled particles: size/ shape/ density/ charge

Question 3

what are the main methods to produce fine particles?

Answer 3

dry grinding
dissolution> supercritical fluid technique/ spray drying/ precipitation
suspension> wet drying

Question 4

what are the different particle dimensions for gridning?

Answer 4

Coarse grinding 50-500 micrometers
Fine grinding 5-50 micrometers
Micronisation < 5

Question 5

how is particle size and energy related?

Answer 5

energy consumption is related to the particle size achieved- more energy needed for smaller particles

Question 6

what happens when stress is applied to produce fine particles?

Answer 6

1- result in deformation by compression or tensional stress> elastic and brittle fracture OR plastic

OR SHEAR STRESS
- this gieves attrition and wear

Question 7

what is critical particle size?

Answer 7

particle size below which no further fragmentation can take place

Question 8

what is below the critical size?

Answer 8

below the critical size, the energy required to fragment particles is close to infinity

Question 9

what are some of the reasons for particle fracture?

Answer 9

Cracks, flaws inside particles, crystals
Orientation of cracks determines fracture plane and size of fragments Fracture energy = energy to propagate a crack
Cracks with orientation in direction of stress and/or largest crack will propagate first (smallest fracture energy)

Question 10

what is an intermediate between fine particle size distribution and initial particle size distribution?

Answer 10

intermediate( bimodal) particle size distribution

these change during grinding

Question 11

what are some milling mechanisms and examples?

Answer 11

• compression with weight- roller mills, with impact- high speed rotary mills/ fluid energy mills
  with stress- attrition- slow speed tumbling mills

Question 12

what are some compression and impaction methods for size reduction >50um?

Answer 12

roller mills

impact mills high speed rotary type

Question 13

what are the features of roller mills?

Answer 13

rarely used
for herbal powders
mortar and pestle

Question 14

what are the features of impact mills, high speed rotary type?

Answer 14

stator
rotor inside the stator
grinding effect depends on number of hammers and distribution around the rotor
large qt of air inside for cooling effect

Question 15

what are the features of a ball mill?

Answer 15

works mainly by attrition- porcelain balls
grind to 10-50um
some have limited impact
after a long period- 1um 
req optimisation of rotational speed

Question 16

what size does vibration mills produce?

Answer 16

10-50um

Question 17

what size does a fluid energy filled mill produce?

Answer 17

less than or equal to 10um

Question 18

what are some advantages of fluid energy mills?

Answer 18

High speed movement of particles in a high velocity air stream
particles impact each other or the wall of the mill
Grinding and size classification (cyclone)
Large volumes of air pulled through Cooling effect Production of fine particles

Question 19

what are some of the disadvantages of fluid energy mill?

Answer 19

Air contamination with oil
Initial particle size should be small
Low feeding rates
expensive  
large energy expenditure

Question 20

what factors affect the choice of method?

Answer 20

Initial particle size
Target particle size of the powder, final size
Quantity of material to be processed
Mechanical properties
Melting point
Wet or dry powder usable in product manufacture
Sterile products