Mixing Flashcards
What is a homogeneous system?
a particle system where the concentration of all elements is uniform
Which parameters should be tested during the mixing process?
the degree of mixing, efficiency of mixer and time necessary to achieve required degree of mixing & the components and their properties
What is meant by a positive mixture?
Components mix spontaneously and irreversibly by diffusion (almost perfect mix is achieved) e.g. miscible liquids
What happens in a negative mixture?
Components tend to separate, and they need a constant input energy to maintain the desired dispersion
Positive mixtures require a high degree of mixing efficiency. True or false?
false, negative mixtures do
What happens in a neutral mixture?
The components have no tendency to either mix or to separate spontaneously.
It is possible to separate a neutral mixture, but energy is required to do this. True or false?
false, no energy is required
What is meant by a random mixture?
The components are perfectly mixed, hence the probability of selecting x type of particle is the same in all positions in the mixture
During the manufacturing process, mixtures can change due to physical modification. True or false?
True
If you decrease the solvent viscosity, a negative suspension will shift to a neutral mixture. True or false?
False, if you increase viscosity this will happen
What happens in ordered mixing?
The components are not independent of each other, resulting in a “spontaneous” degree of order in the mix
Which type of mixture is driven by adhesive and cohesive forces
ordered mixture
What is the scale of scrutiny?
The amount of material (in weight or volume) used to test the quality of a mixture
What is the most appropriate scale of scrutiny to guarantee the strength of a 200mg tablet?
200mg
The higher the concentration of active drug in the mixture, the harder it is to test to quality of the mixing process. True or false?
false, the lower the conc the harder it is
An already formed random mix is capable of changing to a non-random mix. True or false?
True
What are the 3 types of mixers?
Batch, Semi-batch & continuous
What factors cause segregation to occur?
particles differing in size, shape, density
What are the 3 types of mixing for solids?
- convective: involves bulk movement or gross displacement of particles within mixture
- shear: happens when particles have different velocities
- Diffusion: caused by random motion of particles
Which type of mixing is preferred with potent/active drugs?
diffusive mixing
Which type of mixing is preferred with particles with a tendency to aggregate?
High shear mixing
Which mechanism of mixing is macroscopic and relatively quick, involving the transfer of a large group of powder through the powder bed?
Convection
Which mechanism of mixing is known as interface mixing and involved the flow of one layer of material over another layer, resulting in moving layers at different speeds?
Shear
Which mechanism of mixing allows a true movement of individual particles to achieve a true random mix, where the powder bed is forced to move and the movement generates space between particles?
Diffusion
In a mixing process, more than one mechanism is likely to occur. True or false?
True
What are the 3 mechanisms of mixing liquids?
bulk transport, turbulent mixing & diffusion
Which components are used to mix liquids?
to achieve an acceptable degree of mixing (i.e. random mix) all these three mechanism are required
What is the typical powder weight that is used in a tumbling mixer?
50g to 100kg
A tumbling mixer is generally used in the blending of excipients prior to tabletting. True or false?
True
There is high risk of “deep spot” with non-mixed materials in propeller mixers. True or false?
false, in planetary mixers
What is the importance of mixing?
– to ensure the quality of pharmaceutical products, provide an even distribution of active components and other ingredients, guarantee drug release with the desired rate, give an even appearance to dosage forms
Turbine mixers are suitable for viscous fluids.
True
Segregation can be minimised by using a similar size of drug and excipient. True or false?
True
