Powder flow Flashcards
What are the importance of powder flow?
- For tabletting
- Granulation
- Capsulation
What are the wto types of transfers in the manufacturing process?
- Pneumatic transfer
- Hydraulic transfer
What are the consequences of poor powder flow?
- 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
What are cohesion forces between particles due to?
-Due to van der waals forces (electrostatic)
Cohesion forces between particles due to van der waals forces increases as particle size decreases. TRUE OR FALSE?
TRUE
Cohesion in powder flow is due to cohesion and moisture (Relative humidity). TRUE OR FALSE?
TRUE
What is adhesion?
-Adhesion forces between two unlike surfaces e.g particle with the hopper wall of a tabletting press
What are the factors affecting powder flow?
- Resistance to flow due to cohesion/adhesion
- Particle size
- Density of particles
Dense particles are more cohesive. TRUE OR FALSE?
FALSE
What range of particles are extremely cohesive, irregular and free flowing?
- Particle size <10 micro - extremely cohesive
- Particle size <50 micro - Irregular/no flow due to van der waals
- Particle size >50 micro - free flowing
Spherical particles are less interparticulate contact than other uniform or irregular particle shape. TRUE OR FALSE?
TRUE
Smaller particles (>50 um) settle below larger particles and lead to uneven powder flow. TRUE OR FALSE?
TRUE
(Particle surface) Electrostatic forces decreases cohesion. TRUE OR FALSE?
FALSE
(Particle texture) Rough surfaces have more cohesion. TRUE OR FALSE?
TRUE
Humidity causes moisture to be absorbed on the particle surface. TRUE OR FALSE?
TRUE
What is powder density?
-The rearrangement of particle packing geometry e.gchange in bulk volume, change in density of the powder
Different geometric packing’s can be achieved with particles of same shape. TRUE OR FALSE?
TRUE
Different geometric packing’s can be achieved with particles of same shape, Give an example for this?
-e.g cubic or rhombohedra particle packing (more densed packed) compared with spherical particles
Density of a powder sample is referred to as the bulk density. TRUE OR FALSE?
TRUE
What is minimum bulk density?
-The maximum volume occupied by powder
What is poured bulk density?
-Volume of powder measured after pouring into a cylinder
What is tapped bulk density?
-The maximum bulk density that can be achieved without deformation of particles
What is relative density (K) also known as?
-Known as the packing fraction or fractional solids content
What is the equation for relative bulk density?
K= Bulk density/true density
What is the porosity of powder bed?
It is a measure of the packing efficiency of the powder
What does porosity of powder bed indicate?
-It is an indication of the proportion of a powder bed that is occupied by pores
What is the equation for porosity?
Porosity = 1 - Bulk density/true density
Why do we need to formulate powders?
- To get a uniform manufacture to enable flow
What is required in the formulation of powders and provide some examples?
- Addition of glidants
- Anti-adherent properties
e. g magnesium stearate, colloidal silicon dioxide and sodium bicarbonate
What does colloidal silicon dioxide and sodium bicarbonate do?
- colloidal silicon dioxide: Helps reduce bulk density of powder bed
- sodium bicarbonate: May improve flow of hygroscopic powder
What are the requirements for powder flow in the hopper?
- Controlled and constant flow rate
- Uniformity of flow (no segregation of powder)
What are the two types of powder flow in the hopper?
- Mass flow
- core flow
Describe mass flow and what is the degree of angle?
- All materials in motion during discharge , the whole bulk of powder moves downwards
- 20 degrees
Describe core flow and what is the degree of angle?
- Materials outside the falling region do not move, some powders remain undisturbed
- Dead space occurs during discharge
- 50 degrees
What are some of the problems involved with core flow?
- Flow hopper can suddenly stop
- Sudden rapid discharge of powder
- Segregation of powder
Describe what occurs in Flow hopper can suddenly stop
- Sudden rapid discharge of powder
- Segregation of powder?
- 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
Partciles just above orifice flow freely. TRUE OR FALSE?
TRUE
A tongue is not formed above the orifice. TRUE OR FALSE?
FALSE
What are the characteristics of powder flow?
- Angle of repose
- <30 degrees (good flow)
- > 40 degrees (problematic)
What is bulk density measurement?
It is the ratio of the poured bulk density and tapped bulk density of powder
What is the hausner ratio equation?
hausner ratio= Tapped bulk density (Df)/Poured bulk density (D0)
Free flowing powder (aprox 1.2) and cohesive powder (aprox >1.6). TRUE OR FALSE?
TRUE
