mixing Flashcards
what is a positive mixture?
mixes spontaneously
requires energy to separate
Miscible
what is a negative mixture?
segregates spontaneously
energy required to mix and keep mixed
Immiscible
what is a neutral mixture?
neither mix or segregate spontaneously
energy required to mix or segregate
remains stable when mixed (powders)
3 mechanisms of mixing liquids?
bulk transport
turbulent mixing
molecular diffusion
3 mechanisms of mixing solids?
convective mixing
shear mixing
diffusive mixing
what is bulk transport?
redistribution of large amounts of liquid
large amount of mixing in short period of time
what is turbulent mixing?
group of molecules move with constant velocity changes
what is molecular diffusion?
movement of molecules down conc. gradient
what is convective mixing?
redistribution of large groups of particles
large degree of mixing in short time
what is shear mixing?
velocity differences between layers of particles
mixing at interface of layers
what is diffusive mixing?
powder bed dilation - air added to powder bed during mixing
particles move into air spaces
what is a free flowing powder?
easy to mix, usually low energy mixing sufficient
what is a cohesive powder?
fine particles that stick together
high energy de-agglomeration to mix
consider friability
amount of powder per sample to assess mixing?
amount in 1 dosage unit
what is an ordered mixture?
micro ionised particles adsorbed on surface of carrier particles
