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Pharmaceutics > Preformulation - Powder Flow > Flashcards

Preformulation - Powder Flow Flashcards

1
Q

What are the different time of powders?

A 
Coarse
Moderately coarse
Moderately fine
Fine
Very fine
Microfine
Superfine
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2
Q

What are powders?

A

Complex fluid compromising a mixture of solid particles + air

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3
Q

What do driving forces do?

A

Promote flow

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4
Q

What do resistive forces do?

A

Inhibit flow

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5
Q

What are the driving forces?

A

Gravity

Mechanical agitation

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6
Q

What are the resistive forces?

A

Cohesion/adhesion

Friction

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7
Q

What is adhesion?

A

Attractive forces between 2 chemically different surfaces

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8
Q

What is cohesion?

A

Attractive forces between 2 chemically similar surfaces

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9
Q

What are adhesion + cohesion result of?

A

London forces
Electrostatic attraction
Mechanical interlocking

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10
Q

How do you calculate gravitational force?

A

Mass X particle acceleration

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11
Q

What are London forces?

A

Induced dipole-dipole interactions

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12
Q

When are London forces greater?

A

Larger + closer together

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13
Q

What does electrostatic force depend on?

A

Magnitude of charge + separation distance between surfaces

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14
Q

When do mechanical interlocking happen?

A 
Physical obstruction 
Rough surface texture
Sharp edges
Angular edges
One particle stops movement of another
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15
Q

When is friction present?

A

At contact surfaces where at least one surface is in motion

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16
Q

How does friction inhibit movement?

A

Acts in opposite direction to direction of movement

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17
Q

How do you calculate friction force?

A

Coefficient of friction X reaction force

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18
Q

What size should the particle be to favour powder flow?

A

Large

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19
Q

What density should the particle be to favour powder flow?

A

High

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20
Q

What shape should the particle be to favour powder flow?

A

Spherical

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21
Q

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

A

Small

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22
Q

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

A

Loose

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23
Q

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

A

Moderate

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24
Q

What do smaller particles have compared to larger particles?

A

Smaller SA per particle
Larger total SA
Larger specific SA

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25
Q

How do you calculate specific SA?

A

Mass

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26
Q

What does a larger specific SA have?

A 
Greater surface free energy
More bonding interactions
More cohesive 
Greater resistive forces
Powder flow ability
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27
Q

Why should the particles be spherical?

A

Smallest specific SA of any particle shape

Less likely to mechanical interlock

28
Q

What does a more spherical particle have?

A 
Smaller specific SA
Lower surface free energy
Fewer bonding interactions
Less cohesive
Smaller resistive forces
Better flow ability
29
Q

What is packing geometry?

A

Position of solid particles relative to one another

30
Q

What is packing fraction?

A

Vol fraction of solid particles

31
Q

What is porosity?

A

Vol of air

32
Q

What is bulk density?

A

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

33
Q

How do you calculate bulk density?

A

Mass/ bulk vol

34
Q

What is trapped density?

A

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

35
Q

How do you calculate trapped density?

A

Mass/ trapped vol

36
Q

What is true density?

A

Density of solid particles only (discounting air)

37
Q

How do you calculate true density?

A

Bulk density/ packing fraction

38
Q

What does it mean if there is a denser particle?

A

Greater mass at same vol
Greater gravitational force
Better flowability

39
Q

Why do denser particles have better flowability?

A

Lower specific SA
Less cohesive
Smaller resistive forces

40
Q

What makes particles stick together?

A

Binding properties

41
Q

What are dry particles most likely to experience?

A

Friction + generate statics

42
Q

Why do we need a moderate moisture content?

A

Balance between lubrication + cohesion

43
Q

What do liquid bridges between particles provide?

A

Lubrication

44
Q

What are the different powder flow patterns?

A

Mass flow

Funnel flow

45
Q

Describe mass flow

A

First in, first out

Good flowability

46
Q

Describe funnel flow

A

Last in, first out
Arching, ratholing
Poor flowability

47
Q

Describe flow through orifice

A

Powder discharged from hopper through orifice under gravity

48
Q

How do you calculate flow rate?

A 
     Discharge duration
49
Q

What is method 1 of measuring flow rate?

A

Measure amount of powder discharged over fixed duration

50
Q

What is method 2 of measuring flow rate?

A

Measure time taken to discharge fixed amount of powder

51
Q

Describe more cohesive powder flow rate

A

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

52
Q

What is flow rate influenced by?

A

Hopper shape
Orifice shape
Orifice diameter

53
Q

What has no effect on flow rate?

A

Height of powder in hopper

54
Q

What does the compressibility index + Hausner ratio measure?

A

Measures degree of vol reduction upon powder consolidation

55
Q

How is compressibility index + Hausner ratio measured?

A

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

56
Q

What are the units of Hausner ratio?

A

NONE

57
Q

What does a smaller value of Hausner ratio mean?

A

Better flowability

58
Q

What is the equation for Hausner ratio?

A

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

59
Q

What are the units of compressibility index?

A

%

60
Q

What does a smaller value of compressibility index mean?

A

Better flowability

61
Q

What is the equation for the compressibility index?

A

100 (Vf-Vt) 100(Pt-Pf)
—————– = —————– <100
Vf Pt

Vf = bulk vol
Vt = tapped vol
Pf = bulk density
Pt = tapped density
62
Q

What is the angle of repose?

A

Angle between slope + horizontal

63
Q

What does the steepness of the slope represent?

A

Eqm of driving + resistive forces

64
Q

What does cohesion cause particles to do?

A

Pile up (stop flowing)

65
Q

What does gravity cause particles to do?

A

Slope (flow), reducing angle

66
Q

What will happen if you have a more cohesive powder?

A

Greater angle of repose = poorer flowability

67
Q

How do you calculate the angle of repose?

A

tan-1 (h/r)

Pharmaceutics (21 decks)

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