Practical 1 Revision Flashcards
Flowability definition
Degree of easiness of the relative movement of the powder from the stationary to moving condition
Free flowing powder
This powder moves consistently and steadily with particles moving independently of one another
A non free flowing powder contains
Particles moving as agglomerates
What is floodability
Unstable liquid like flow
What can flooding be caused by and what can’t it be aided by
Fluidising a mass of particles by air or other stimuli
Uncontrollable, undesirable
Can’t be aided by the addition of a lubricant
Product bridging or arching
Material that is being discharged forms over a bridge or arch over the discharge point in an hopper
Rat-holing
A condition where the material forms a hole or narrow channel above the feed auger or outlet in a hopper
Whilst remaining stationary against the hopper wall
What is the importance of producing free flowing powders
Improve mixing
Tablet weight uniformity
Reproducible filling of tablet dies and capsule dosalotors improve weight uniformity
Uniformity of dose
Reproducibility of finished product
Uneven powder flow can cause capping or lamination
What is adhesion and the forces s
Unlike surfaces (powder and feed hopper, powder and die wall)
Electrostatic attraction (forces)
Cohesion
Like surfaces such as component particles of a bulk solid
Short range forces (van der waals)
Direct methods - assessment of powder flow
Hopper flow rate or flow meter
Indirect measurements - assessment of powder flow
Angle of repose
Carr’s consolidation index
Hausner ratio
Angle of difference
Angle of spatula
Shear strength
Tensile strength
Angle of repose - how is it measured
When a powder is poured through a funnel, it forms a cone-shaped pile which makes an angle to the horizontal.
The angle between horizontal & slope of a heap of powder dropped from the same elevation is indicative of the degree of cohesion of the particles which reflects the ease with which the powder will flow.
A large angle of repose indicates
Poor flow properties
A small angle of repose indicates
A free flowing powder
How does the poured method work
Performed by flowing powder through a funnel with a defined orifice
If the powder doesn’t flow using the poured method what should you do?
Use the drained method
Making sure the method is consistent when testing multiple powders
Explain the drained method
Allows powder flow by lifting a powder filled cylinder (with a canister inside) allowing the material to drain away
Leaves a come on the canister
How to measure the angle of repose
Tan 0 =(h/r)
Angle of repose indicates the bulk flow properties
Low angle of repose
High flowability
What does carrs consolidation index measure
Compressibility
Rate of packing down
Compares initial and final bulk volumes
Initial density : fluffed poured bulk
Tapped density: density after 50 tap, final, consolidated
One point determination
Doesn’t reflect the ease or speed with which consolidation can occur
How do we measure tapped density
Powder weight/final volume
Weight after 50 taps
Fluff density equation
W/V0
V0= initial volume occupied by the powder in ml
Low consolidation index =
High flowability
