Powders & Granules Flashcards
List differences between crystalline and amorphous solids.
Crystalline
- Have an orderly arrangement of the lattice units
– Have higher purity
– Are more physically and chemically stable
– Have LOWER solubility
– Have a NARROW melting point range
– Are LESS compressible
– Have BETTER FLOW
– Are LESS hygroscopic
Amorphous solids:
– have no order of arrangement
– are less physically and chemically stable (due to the weakness of the interaction
between molecules)
– Have glass transition (Tg) temperature (and not a narrow melting point)
– Are usually more soluble
Define enantiotropic polymorphism
More stable form exists and it is a reversible transformation
In polymorphic forms why do we use a metastable form with lower melting point?
Lower melting point = weak lattice = more soluble = faster dissolution rate
Which are more soluble: anhydrous crystals or hydrate crystals.
Anhydrous crystals
Which powder properties can particle size affect?
- Flow
- Powder packing and compaction
- dissolution rate
- Sedimentation
What are advantages of having an amorphous dispersion?
- In amorphous dispersions, the amorphous drug is stabilized by a presence of a polymer.
- The polymer helps to stabilize the drug in the solid state and prevents the drug crystallization on
dissolution. - This results in increased solubility of the amorphous material and increased physical
stability. - Itraconazole is practically insoluble in water, and by making an amorphous dispersion
with HPMC, its solubility was increased, and its bioavailability was increased by 30%.
Define micromeritics
The science and technology of small particles
- particle size measurements
- size distribution
- packing arrangements
What are importance of particle size?
- Affect flow and packing properties
- Facilitate drying
- Improve penetration in lungs
Which type of density will have the highest inter particulate spaces?
bulk density
Which densities are related to the porosity of powder particles
Bulk density and true density
Which particle size has the biggest mesh opening size and smallest mesh size number?
Coarse
Explain the methods for determining particle size distribution
1. Microscopy
Optical microscope
Scanning electron microscope
Transmission electron microscopy
Dynamic image analyses
Optical microscope
- powder dispersed on microscope slide
Scanning electron microscope
- powder are fixed to aluminum stubs
Transmission electron microscopy
- powder is set in resins
Dynamic image analyses
- automated image analyses for light and electron microscopy
which particle size has the most mesh size number
very fine
Explain the methods for determining particle size distribution
Sieving method
Predetermined weight of dry powder is passed through wire mesh screens, having openings of different sizes and the weight of powder that is retained on each sieve is measured
What does a LARGE sieve # (mesh) indicate for sieve opening
Small sieve opening (small particle size)
Advantages and Disadvantages of Sieving method
Advantages
- Technique is well adapted for bulk materials
Disadvantages
- Smallest practical sieve size 400 mesh is 38um
- amount of energy is empirically determined
Sedimentation Method
Settling of a single particle in a liquid medium under the influence gravitational and centrifugal forces
Explain crack propagation
Material breaks along cracks, so most effective size reduction would be to focus force on cracks
Explain the bulk powder properties (including, excluding)
True density
True volume
Void/%porosity
Particle density
Bulk density
Tapped density
True density
- ratio of mass of particle to its actual volume
- (excludes pores and gaps)
True volume
- weight over true density
Void/%porosity
- bulk volume - true volume over bulk volume
Particle density
- Ratio of mass to volume of particle
- including intraparticule air volume (pores), excluding gaps
Bulk density
- Ratio of bed mass to volume of loose powder bed
- includes pore and gap volumes
Tapped density
- ratio of powder bed mass to volume trapped (or compacted)
- includes pore and gap volumes
Explain Void types of air volume
Pores
Gaps
Pores: intRAparticule air volume
Gaps: intERparticule air volume
What do light/heavy powders indicate in terms of bulk density and bulk volume
Light
- low bulk density and large bulk volume
Heavy
- high bulk density and small bulk volume
What are factors affecting powder flow?
- Adhesion/Cohesion
- Size, shape, density
Differentiate between adhesion vs. cohesion
Adhesion: tendency of DISSIMILAR particles to cling one another
Cohesion: tendency of SIMILAR particles to cling one another
What particle size flow better?
Bigger particle size flow better (250 um +)
