particle science final

Question 1

What is comminution?

Answer 1

The mechanical reduction of large solid particles into smaller particles (a defined size range) by applying force.

Question 2

How does comminution break particles?

Answer 2

Crack formation and crack propagation within the particle.

Question 3

Why is comminution important in pharmacy?

Answer 3

Most dosage forms (tablets, capsules, suspensions, creams) are made from powders and raw materials are initially too large.

Question 4

What manufacturing processes are affected by particle size?

Answer 4

Powder flow, mixing, die filling, and content uniformity.

Question 5

What biopharmaceutical properties are affected by particle size?

Answer 5

Dissolution rate, absorption, and bioavailability.

Question 6

What is specific surface area?

Answer 6

Surface area per unit mass of particles.

Question 7

What happens to surface area when particle size decreases?

Answer 7

Surface area increases.

Question 8

Why do smaller particles dissolve faster?

Answer 8

More drug surface is exposed to the solvent.

Question 9

Relationship between particle size and bioavailability?

Answer 9

Smaller particles lead to faster dissolution and improved bioavailability.

Question 10

Which dissolution principle explains this relationship?

Answer 10

The Noyes-Whitney dissolution principle.

Question 11

How does particle size reduction improve tablet content uniformity?

Answer 11

Smaller particles mix more evenly and reduce segregation.

Question 12

Effect of comminution on bulk density?

Answer 12

Often increases bulk density due to improved packing.

Question 13

Why does increased bulk density help manufacturing?

Answer 13

Improves handling, transport, and die filling.

Question 14

What is particle size distribution?

Answer 14

The range and spread of particle sizes within a powder.

Question 15

Why is a narrow particle size distribution desirable?

Answer 15

Improves mixing, die filling, and dose uniformity.

Question 16

What does Griffith’s theory state about particle fracture?

Answer 16

Particles contain microscopic cracks that propagate when force is applied, causing fracture.

Question 17

Why do brittle materials mill easily?

Answer 17

Cracks propagate rapidly under stress.

Question 18

How do material properties affect milling?

Answer 18

Brittle materials mill easily, hard materials damage equipment, and tough materials are difficult to mill.

Question 19

What type of materials are most pharmaceutical crystals?

Answer 19

Brittle.

Question 20

What are the four main mechanisms of size reduction?

Answer 20

Cutting, compression, impact, and attrition.

Question 21

What is cutting?

Answer 21

Blades slice material.

Question 22

What is compression?

Answer 22

Material crushed between surfaces.

Question 23

What is impact?

Answer 23

High-velocity collision breaks particles.

Question 24

What is attrition?

Answer 24

Particles rub or shear against surfaces or each other.

Question 25

Which mill uses cutting?

Answer 25

Cutter mill.

Question 26

Which mills use compression?

Answer 26

Runner mill and roller mill.

Question 27

Which mills use impact?

Answer 27

Hammer mill and vibration mill.

Question 28

Which mills use impact and attrition?

Answer 28

Ball mill, fluid energy mill, and pin mill.

Question 29

Which mill produces very fine particles (~1 µm)?

Answer 29

Fluid energy mill (micronizer).

Question 30

How does a cutter mill work?

Answer 30

Rotating knife blades cut particles as they pass through a screen.

Question 31

How does a runner mill work?

Answer 31

Compression crushing using heavy rollers, similar to a mechanised mortar and pestle.

Question 32

How does a roller mill work?

Answer 32

Two rollers compress and shear material as it passes between them.

Question 33

How does a hammer mill work?

Answer 33

High-speed rotating hammers impact particles causing brittle fracture.

Question 34

How does a ball mill work?

Answer 34

A rotating drum contains balls that cascade and collide with particles, causing impact and attrition.

Question 35

How does a fluid energy mill (microniser) work?

Answer 35

High-velocity air jets cause particles to collide with each other, producing extremely fine particles (~1 µm).

Question 36

How does a pin mill work?

Answer 36

Two rotating discs fitted with pins create impact and shear between particles.

Question 37

What determines choice of milling method?

Answer 37

Desired particle size, material properties, and cost.

Question 38

Which mills are used for coarse vs fine particles?

Answer 38

Coarse particles use runner or roller mills; very fine particles use a fluid energy mill.

Question 39

Material properties affecting milling?

Answer 39

Hardness, brittleness, toughness, abrasiveness, and stickiness.

Question 40

Relationship between particle size and energy requirement?

Answer 40

Smaller particles require more energy.

Question 41

Why is micronisation expensive?

Answer 41

Producing extremely fine particles requires very high energy.

Question 42

Why is micronisation used despite cost?

Answer 42

Necessary for poorly soluble drugs to improve dissolution.

Question 43

What problems can excessive size reduction cause?

Answer 43

Electrostatic charging, aggregation, poor flow, and oxidation instability.

Question 44

Key trade-off with very fine powders?

Answer 44

Better dissolution but worse flow.

Question 45

How does particle size affect powder flow?

Answer 45

It affects die filling.

Question 46

How does particle size affect dose accuracy?

Answer 46

It affects uniformity.

Question 47

How does particle size affect dissolution and bioavailability?

Answer 47

Increased surface area increases dissolution and therapeutic effect.

Question 48

How does particle size affect compaction?

Answer 48

It affects packing density and tablet strength.

Question 49

What is the main effect of comminution?

Answer 49

Increase in specific surface area.

Question 50

Define comminution in an exam answer.

Answer 50

Mechanical reduction of particle size by applied force.

Question 51

Why is comminution important for tablets?

Answer 51

Improves dissolution, uniformity, density, handling, and bioavailability.

Question 52

What overall pharmaceutics relationship does comminution demonstrate?

Answer 52

Particle size controls flow, compression, dissolution, bioavailability, and therapeutic effect.