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Clare's lectures semester 2 > Powder flow > Flashcards

Powder flow Flashcards

1
Q

What are the importance of powder flow?

A
  • For tabletting
  • Granulation
  • Capsulation
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2
Q

What are the wto types of transfers in the manufacturing process?

A
  • Pneumatic transfer

- Hydraulic transfer

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3
Q

What are the consequences of poor powder flow?

A
  • Uneven mix into feed
  • risks of segregation
  • Non-uniformity of dose
  • Problems with reproducibility of dosage forms that require powder flow
  • Risks of capping and lamination (tabletting)
  • Increase in particle die wall friction and risks of dust contamination
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4
Q

What are cohesion forces between particles due to?

A

-Due to van der waals forces (electrostatic)

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5
Q

Cohesion forces between particles due to van der waals forces increases as particle size decreases. TRUE OR FALSE?

A

TRUE

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6
Q

Cohesion in powder flow is due to cohesion and moisture (Relative humidity). TRUE OR FALSE?

A

TRUE

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7
Q

What is adhesion?

A

-Adhesion forces between two unlike surfaces e.g particle with the hopper wall of a tabletting press

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8
Q

What are the factors affecting powder flow?

A
  • Resistance to flow due to cohesion/adhesion
  • Particle size
  • Density of particles
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9
Q

Dense particles are more cohesive. TRUE OR FALSE?

A

FALSE

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10
Q

What range of particles are extremely cohesive, irregular and free flowing?

A
  • Particle size <10 micro - extremely cohesive
  • Particle size <50 micro - Irregular/no flow due to van der waals
  • Particle size >50 micro - free flowing
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11
Q

Spherical particles are less interparticulate contact than other uniform or irregular particle shape. TRUE OR FALSE?

A

TRUE

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12
Q

Smaller particles (>50 um) settle below larger particles and lead to uneven powder flow. TRUE OR FALSE?

A

TRUE

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13
Q

(Particle surface) Electrostatic forces decreases cohesion. TRUE OR FALSE?

A

FALSE

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14
Q

(Particle texture) Rough surfaces have more cohesion. TRUE OR FALSE?

A

TRUE

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15
Q

Humidity causes moisture to be absorbed on the particle surface. TRUE OR FALSE?

A

TRUE

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16
Q

What is powder density?

A

-The rearrangement of particle packing geometry e.gchange in bulk volume, change in density of the powder

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17
Q

Different geometric packing’s can be achieved with particles of same shape. TRUE OR FALSE?

A

TRUE

18
Q

Different geometric packing’s can be achieved with particles of same shape, Give an example for this?

A

-e.g cubic or rhombohedra particle packing (more densed packed) compared with spherical particles

19
Q

Density of a powder sample is referred to as the bulk density. TRUE OR FALSE?

A

TRUE

20
Q

What is minimum bulk density?

A

-The maximum volume occupied by powder

21
Q

What is poured bulk density?

A

-Volume of powder measured after pouring into a cylinder

22
Q

What is tapped bulk density?

A

-The maximum bulk density that can be achieved without deformation of particles

23
Q

What is relative density (K) also known as?

A

-Known as the packing fraction or fractional solids content

24
Q

What is the equation for relative bulk density?

A

K= Bulk density/true density

25
Q

What is the porosity of powder bed?

A

It is a measure of the packing efficiency of the powder

26
Q

What does porosity of powder bed indicate?

A

-It is an indication of the proportion of a powder bed that is occupied by pores

27
Q

What is the equation for porosity?

A

Porosity = 1 - Bulk density/true density

28
Q

Why do we need to formulate powders?

A
  • To get a uniform manufacture to enable flow
29
Q

What is required in the formulation of powders and provide some examples?

A
  • Addition of glidants
  • Anti-adherent properties
    e. g magnesium stearate, colloidal silicon dioxide and sodium bicarbonate
30
Q

What does colloidal silicon dioxide and sodium bicarbonate do?

A
  • colloidal silicon dioxide: Helps reduce bulk density of powder bed
  • sodium bicarbonate: May improve flow of hygroscopic powder
31
Q

What are the requirements for powder flow in the hopper?

A
  • Controlled and constant flow rate

- Uniformity of flow (no segregation of powder)

32
Q

What are the two types of powder flow in the hopper?

A
  • Mass flow

- core flow

33
Q

Describe mass flow and what is the degree of angle?

A
  • All materials in motion during discharge , the whole bulk of powder moves downwards
  • 20 degrees
34
Q

Describe core flow and what is the degree of angle?

A
  • Materials outside the falling region do not move, some powders remain undisturbed
  • Dead space occurs during discharge
  • 50 degrees
35
Q

What are some of the problems involved with core flow?

A
  • Flow hopper can suddenly stop
  • Sudden rapid discharge of powder
  • Segregation of powder
36
Q

Describe what occurs in Flow hopper can suddenly stop

  • Sudden rapid discharge of powder
  • Segregation of powder?
A
  • Flow hopper can suddenly stop: Arching (formation of arch between the hopper walls, arch strong enough to support material above it
  • Sudden rapid discharge of powder: Collapse of the arch or pipe, rate hole or funnel results in flooding

-Segregation of powder: Loss of mixing quality
non-uniformity of low - dose irregularities

37
Q

Partciles just above orifice flow freely. TRUE OR FALSE?

A

TRUE

38
Q

A tongue is not formed above the orifice. TRUE OR FALSE?

A

FALSE

39
Q

What are the characteristics of powder flow?

A
  • Angle of repose
  • <30 degrees (good flow)
  • > 40 degrees (problematic)
40
Q

What is bulk density measurement?

A

It is the ratio of the poured bulk density and tapped bulk density of powder

41
Q

What is the hausner ratio equation?

A

hausner ratio= Tapped bulk density (Df)/Poured bulk density (D0)

42
Q

Free flowing powder (aprox 1.2) and cohesive powder (aprox >1.6). TRUE OR FALSE?

A

TRUE

Clare's lectures semester 2 (10 decks)

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