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30 Cards in this Set
- Front
- Back
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What are the six consequences of powder flow? |
-Uneven mix into feed -Risks of segregation -Non-uniformity of dose -Problems with reproducibility of dosage forms -Risks of capping and lamination -Increase in particle-die-wall friction and risks of dust contamination |
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What causes resistance of powder flow? |
-Cohesion -Adhesion -Small particle size (less than 10micrometres) -Less dense particles |
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What causes cohesion between like molecules? |
-Cohesive forces -Van der Waals (electrostatic) forces -Moisture (when above critical humidity) |
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What causes particle adhesion? |
Adhesive forces between two unlike surfaces |
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What increases the cohesion of particles? |
Electrostatic forces on particle surfaces |
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What is the bulk density? |
The density of a powder sample |
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What is the minimum bulk density? |
The maximum volume occupied by powder |
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What is the poured bulk density? |
The volume of powder measured after pouring into a cylinder |
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What is the tapped bulk density? |
The maximum bulk density (in theory) that can be achieved without deformation of particles |
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What is the equation for relative density, k? |
bulk density k= ---------------------- true density |
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What is the relative density? |
Packing fraction or fractional solids content |
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What is the equation for porosity of powder bed? |
Bulk density Porosity= 1- --------------------- True density |
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What are the two requirements for powder flow in the hopper? |
-Controlled and constant flow rate -Uniformity of flow (no segregation of powder) |
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What are the two main types of flow? |
-Mass flow -Core flow |
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What is mass flow? |
-All material is in motion during discharge -Whole bulk of powder moves downwards -Generally Ɵ of around 20° (Need to consider wall friction angle, Ø) |
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What is core flow? |
-Materials outside the falling region do not move -Some powders remain undisturbed -Dead space occurs during discharge -Generally Ɵ around 50°: Need to consider wall friction angle, Ø |
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What are the problems of core flow? |
-Flow from hopper can suddenly stop -Sudden rapid discharge of powder -Segregation of powder |
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What happens when the flow from hopper suddenly stops? |
Arching: -Formation of arch between the hopper walls -Arch strong enough to support material above it Piping, rat holing or funnelling |
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What happens when there is a sudden rapid discharge of powder? |
-Collapse or the arch or pipe, rate hole or funnel results in flooding |
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What happens if there is segregation of powder? |
-Loss of mixing quality -Non-uniformity of flow-dose irregularities |
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What happens when powder travels through an orifice? |
-Particles just above the orifice flow freely -A depression forms at the upper surface and spreads outwards to side of the container -A 'tongue' is formed above the orifice |
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What is a good flow angle of response? |
< 30° |
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What is a problematic flow angle of response? |
• > 40° |
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What is the Hausner ratio? |
The ratio of the poured bulk density and tapped bulk density of powder |
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What is the equation for the Hausner Ratio? |
Tapped bulk density (Df) Hausner Ratio= ------------------------------------ Poured bulk density (D0) |
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What ratio value represents free flowing powder? |
Around 1.2 |
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What ratio value represents cohesive powder? |
>1.6 |
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What is the equation for Carr Index? |
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What is the measure of tendency of arch formation using the Carr Index? |
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What is the tapped density tester? |
-BP: Carry out 10,500 and 1250 taps and read the corresponding volumes (V10, V500, V1250) to the nearest mL. -Mechanically tapped at a constant speed -Allow measurements of D0 and Df |
