Powders Flashcards
what is a powder
pool of solid particles
What are the 3 properties of powders
- Flow like a Liquid
- compressed like a Gas
- resists deformation like a solid
What are powder particles meant to be like?
- heterogeneously redistributed
- irregular shape
Dependent on particle orientation
- martin’s diameter
- Feret’s diameter
Independent on particle orientation
- projected area diameter
- projected perimeter diameter
what is particle size distribution based on?
- no of particles within each class size
- weight of particles within each class size
what happens if all the particles are within the same size class?
-narrow size distribution
what does a higher variety of particle size mean?
-wide size distribution
how is the narrow/wide size detected?
-curve or frequency histogram
what will represent a curve?
-frequency against mean diameter
what will represent a frequency histogram?
-frequency against classes size range
What are the two types of skewed distribution?
-positively and negatively skewed
what does a negative skew mean?
-mode > mean
what does a positive skew mean?
-mean > mode
what does fraction oversized mean?
-anything bigger than 250 retained into the sieve
what does fraction undersized mean?
-anything smaller than 250 goes into the receiver
what is powder fineness based on?
-the median
what will sieving methods generate?
-weight distribution
which forces is flowability dependent on?
- drive flow forces=gravity, particle mass, angle of inclination and applied mechanical force. PROMOTE FLOW.
- resisting flow forces - DRAG FORCES - cohesion and adhesion, surface forces and electrostatic forces.
what will a powder flow on?
-flow promoting forces - drag forces
will large particles flow better than small particles if all is equal?
will spherical particles flow better than irregular particles if all is equal?
will high true density particles flow better than low true density particles?
will powders with a low moisture content flow better than those with a high moisture content?
- yes
- yes
- yes
- yes
what does packing relate to?
- the arrangement of solid particles in a powder bed
- how this will influence volume of powder bed.
what is porosity?
-measure of how tightly or loosely particles are packed.
what is the bulking density?
-property of a powder bed
bulk volume equation?
-true volumes + void volumes
What is the true volume?
-volume of single powder particle
what is the void volume?
-include inter and intra particular pores.
-how is the powder dried (troubleshotting) - POWDER FLOW
- minimum of moisture required
- cohesiveness increased via moisture
-how is the shape changed and roughness controlled - powder flow - troubleshotting
-spray dry to produce more regular shaped particles
-how is flow promoting forces increased?
- mechanical assistance added
- add excipient - lubricant, anti adherent, glidants
-what is the Angle of Repose?
- after powder is left to flow
- cone formed on flat surface
- flatter the cone - smaller AOR - better the flow
-how are powders dispensed?
- bulk - multidosecostainer
- single dose - sachet
How are oral powders dispensed?
- 5ml spoon
- bottle with a wide opening
what are the advantages of oral powders?
- fast absorption
- allows administration of large doses
- shelf life and stability increased
what are the disadvantages of oral powders?
- bulky packaging
- organoleptic properties
- drug degradation can happen
what are topical powders and what are the advantages and disadvantages?
- external use powders - dusting powders
- packaged in bottles with sifter tops
- absorption of skin moisture
- friction reduced
- easy to use
- possible irritation
- risk of pores blocking
- inhalation risk
what are insufflation powders?
- administration in body cavities
- formulated as finely divided powders
what is a eutectic mixture?
-two powder ingredients - mixed - start as solid - liquify at room temperature
What are the two sources of effervescent powders?
- source of co2 - calcium carbonate / sodium bicarbonate
- source of acid - mixture of tartaric acid and citric acid
what happens when effervescent powders are dispersed in h20?
- neutralisation reaction takes place between basic and acidic components
- stored away from moisture - as water interaction will cause neutralisation reaction
where are bulk powders stored?
-cool, dry place in a tightly closed container
what are hygroscopic powders?
-powders that absorb moisture from the env
what are deliquescent powders?
hygroscopic powders that liquify after moisture absorption
what are efflorescent powders?
powders that release moisture into the environment
