Preformulation - Powder Flow

Question 1

What are the different time of powders?

Answer 1

Coarse
Moderately coarse
Moderately fine
Fine
Very fine
Microfine
Superfine

Question 2

What are powders?

Answer 2

Complex fluid compromising a mixture of solid particles + air

Question 3

What do driving forces do?

Answer 3

Promote flow

Question 4

What do resistive forces do?

Answer 4

Inhibit flow

Question 5

What are the driving forces?

Answer 5

Gravity

Mechanical agitation

Question 6

What are the resistive forces?

Answer 6

Cohesion/adhesion

Friction

Question 7

What is adhesion?

Answer 7

Attractive forces between 2 chemically different surfaces

Question 8

What is cohesion?

Answer 8

Attractive forces between 2 chemically similar surfaces

Question 9

What are adhesion + cohesion result of?

Answer 9

London forces
Electrostatic attraction
Mechanical interlocking

Question 10

How do you calculate gravitational force?

Answer 10

Mass X particle acceleration

Question 11

What are London forces?

Answer 11

Induced dipole-dipole interactions

Question 12

When are London forces greater?

Answer 12

Larger + closer together

Question 13

What does electrostatic force depend on?

Answer 13

Magnitude of charge + separation distance between surfaces

Question 14

When do mechanical interlocking happen?

Answer 14

Physical obstruction 
Rough surface texture
Sharp edges
Angular edges
One particle stops movement of another

Question 15

When is friction present?

Answer 15

At contact surfaces where at least one surface is in motion

Question 16

How does friction inhibit movement?

Answer 16

Acts in opposite direction to direction of movement

Question 17

How do you calculate friction force?

Answer 17

Coefficient of friction X reaction force

Question 18

What size should the particle be to favour powder flow?

Answer 18

Large

Question 19

What density should the particle be to favour powder flow?

Answer 19

High

Question 20

What shape should the particle be to favour powder flow?

Answer 20

Spherical

Question 21

What specific surface area should the particle be to favour powder flow?

Answer 21

Small

Question 22

What packing geometry should the particle be to favour powder flow?

Answer 22

Loose

Question 23

What moisture content should the particle be to favour powder flow?

Answer 23

Moderate

Question 24

What do smaller particles have compared to larger particles?

Answer 24

Smaller SA per particle
Larger total SA
Larger specific SA

Question 25

How do you calculate specific SA?

Answer 25

Total SA ------------ Mass

Question 26

What does a larger specific SA have?

Answer 26

``` Greater surface free energy More bonding interactions More cohesive Greater resistive forces Powder flow ability ```

Question 27

Why should the particles be spherical?

Answer 27

Smallest specific SA of any particle shape | Less likely to mechanical interlock

Question 28

What does a more spherical particle have?

Answer 28

``` Smaller specific SA Lower surface free energy Fewer bonding interactions Less cohesive Smaller resistive forces Better flow ability ```

Question 29

What is packing geometry?

Answer 29

Position of solid particles relative to one another

Question 30

What is packing fraction?

Answer 30

Vol fraction of solid particles

Question 31

What is porosity?

Answer 31

Vol of air

Question 32

What is bulk density?

Answer 32

Density of solid particles plus entrapped air when powder is allowed to settle naturally under gravity

Question 33

How do you calculate bulk density?

Answer 33

Mass/ bulk vol

Question 34

What is trapped density?

Answer 34

Density of solid particles with minimal amount of entrapped air, after consolidation using a pharmacopeial method

Question 35

How do you calculate trapped density?

Answer 35

Mass/ trapped vol

Question 36

What is true density?

Answer 36

Density of solid particles only (discounting air)

Question 37

How do you calculate true density?

Answer 37

Bulk density/ packing fraction

Question 38

What does it mean if there is a denser particle?

Answer 38

Greater mass at same vol Greater gravitational force Better flowability

Question 39

Why do denser particles have better flowability?

Answer 39

Lower specific SA Less cohesive Smaller resistive forces

Question 40

What makes particles stick together?

Answer 40

Binding properties

Question 41

What are dry particles most likely to experience?

Answer 41

Friction + generate statics

Question 42

Why do we need a moderate moisture content?

Answer 42

Balance between lubrication + cohesion

Question 43

What do liquid bridges between particles provide?

Answer 43

Lubrication

Question 44

What are the different powder flow patterns?

Answer 44

Mass flow | Funnel flow

Question 45

Describe mass flow

Answer 45

First in, first out | Good flowability

Question 46

Describe funnel flow

Answer 46

Last in, first out Arching, ratholing Poor flowability

Question 47

Describe flow through orifice

Answer 47

Powder discharged from hopper through orifice under gravity

Question 48

How do you calculate flow rate?

Answer 48

Amount of powder discharged --------------------------------------------- Discharge duration

Question 49

What is method 1 of measuring flow rate?

Answer 49

Measure amount of powder discharged over fixed duration

Question 50

What is method 2 of measuring flow rate?

Answer 50

Measure time taken to discharge fixed amount of powder

Question 51

Describe more cohesive powder flow rate

Answer 51

Flows less readily Takes longer to flow through orifice Lower flow rate

Question 52

What is flow rate influenced by?

Answer 52

Hopper shape Orifice shape Orifice diameter

Question 53

What has no effect on flow rate?

Answer 53

Height of powder in hopper

Question 54

What does the compressibility index + Hausner ratio measure?

Answer 54

Measures degree of vol reduction upon powder consolidation

Question 55

How is compressibility index + Hausner ratio measured?

Answer 55

Measure bulk vol of graduated cylinder Consolidate powder on tapped vol tests to a standardised set of parameters Measure tapped col in graduated cylinder

Question 56

What are the units of Hausner ratio?

Answer 56

NONE

Question 57

What does a smaller value of Hausner ratio mean?

Answer 57

Better flowability

Question 58

What is the equation for Hausner ratio?

Answer 58

Bulk vol Tapped density ------------ = ---------------------- > 1 Tapped vol Bulk density

Question 59

What are the units of compressibility index?

Answer 59

%

Question 60

What does a smaller value of compressibility index mean?

Answer 60

Better flowability

Question 61

What is the equation for the compressibility index?

Answer 61

100 (Vf-Vt) 100(Pt-Pf) ----------------- = ----------------- <100 Vf Pt ``` Vf = bulk vol Vt = tapped vol Pf = bulk density Pt = tapped density ```

Question 62

What is the angle of repose?

Answer 62

Angle between slope + horizontal

Question 63

What does the steepness of the slope represent?

Answer 63

Eqm of driving + resistive forces

Question 64

What does cohesion cause particles to do?

Answer 64

Pile up (stop flowing)

Question 65

What does gravity cause particles to do?

Answer 65

Slope (flow), reducing angle

Question 66

What will happen if you have a more cohesive powder?

Answer 66

Greater angle of repose = poorer flowability

Question 67

How do you calculate the angle of repose?

Answer 67

tan-1 (h/r)