1. Mixing
Importance:
Ensure an even distribution of the active component(s)
Ensure an even appearance of the DF
Ensure that the DF releases the drug at the correct site and at the desired rate
Mechanisms of Mixing:
1.Diffusion:Movement of single particles
2.Convection:Movement of groups of particles
3.Shear :Sliding of particles in planes over each other

2. Mixing of powders The ideal mixer should
Large-Scale Mixing Equipment
The ideal mixer should
1- produce a complete blend rapidly to avoid product damage.
2- It should be cleaned and discharged easily
3- be dust-tight
4 require low maintenance and low power consumption.

3. Mixers for Powders Tumbling Mixers/Blenders
Barrel blender V-shape blender

4. Tumbling Blenders
Cube blender Double cone blender

5. Tumbling Blenders

6. Factors affecting mixing efficiency by tumbling mixers
1. Too high a rotation speed will cause the material to be held on the mixer walls by centrifugal force, and too low a speed will generate insufficient bed expansion and little shear mixing.
The addition of baffles or rotating bars will also cause convective mixing, for example the V‑mixer with agitator bar.
Presence of significant difference in particle size, as segregation is likely to occur.

7. Extemporaneous Methods 1- Spatulation 2- Trituration 3-Levigation
Mixing of Powders
Extemporaneous Methods
1- Spatulation
2- Trituration
3-Levigation

8. Small-Scale Mixing Equipment
1- Spatulation
The blending of powders with a spatula on a tile or paper used sometimes for small quantities or when the mortar and pestle technique is undesirable.
It is not suitable for large quantities of powders or for powders containing one or more potent substance because homogenous blending may
not occur.

9. 2- Trituration: .
is used to comminute( reduce particle size) & to mix powders.
1-A porcelin preferred than glass morter.
2- A glass morter is preferrable for chemicals that stain a porcelin. When granular or crystalline materials are to be incorporated in to powdered product ,these materials are comminuted individually and then blended together in the morter.

10. 3- Levigation In this process
A- paste is first formed by the addition of a suitable non solvent to the solid material.
B-Particle-size reduction then accomplished by rubbing the paste in a mortar with a pestle or on an ointment’ slab using a spatula.