Study Set Content:
Methods based on Sedimentation:
Pipette method
• Balance method
• Hydrometer method
operates on the particle that when a particle suspended in a conducting liquid pass through a small orifice on either side of which are electrodes, a change in electric resistance occurs.
Coulter counter
A change in resistance, which is related to the particle volume, causes a voltage pulse that is amplified and fed to a pulse-height analyzer calibrated in in terms of
particle size
affects the flow and packing properties of a powder as well as well as having some influence on the surface area.
Particle Shape
adsorption and dissolution rate studies.
Surface area per unit weight or volume
has minimum surface area per unit volume.
Sphere
Spherical particle is characterized by completely by its
diameter
The more asymmetric a particle, the (blank) is the surface area per unit volume.
greater
As the particle becomes more asymmetric, it becomes increasingly difficult to assign a meaningful (blank) to the particle
diameter
Methods of determining surface area
Adsorption method
Air permeability method
Pore size
– Particles with a large specific surface are good adsorbents for the adsorption of gases and of solutes from solution.
Adsorption method
– high permeability low surface area
Air permeability method
In determining the surface of the adsorbent, the volume in cubic centimeters of gas adsorbed per gram of adsorbent can be plotted against the pressure of the gas at constant temperature to give a
type II isotherm
The adsorbed layer is (blank) at low pressure
monomolecular
The adsorbed layer is monomolecular at low pressure and becomes (blank) at higher pressure.
multi-molecular
he principal resistance to flow of a fluid such as air through a plug of compacted powder is the
surface area of the powder
The greater is the surface area per gram of powder, Sw, the greater is the
resistance to flow
For a given pressure drop across the plug, (blank) to specific surface
permeability is inversely proportional
Relatively insoluble powdered drugs may dissolve more or less rapidly in aqueous medium depending on their adsorption of
moisture or air.
DERIVED PROPERTIES OF POWDERS
Porosity
Density -
Bulkiness
Compressibility
Fluidity
