Derived Properties of Powders

Derived properties of powders refer to characteristics that are not inherent to the powder itself but are calculated or inferred from its behavior and interactions. These properties are important in various applications, from pharmaceuticals to material science. Here are some key derived properties:

1. Bulk Density: This is the mass of a powder per unit volume, including the space between particles. It's calculated by dividing the mass of the powder by the total volume it occupies. It provides insight into how the powder will pack and flow.

2. Tapped Density: This is the density of a powder after it has been subjected to tapping or vibration to remove air gaps and settle the particles. It's usually higher than bulk density and helps in understanding how the powder will behave in processes like tablet compression.

3. Hausner Ratio: This is the ratio of tapped density to bulk density. It indicates the flowability of the powder. A Hausner ratio greater than 1.25 suggests poor flowability, while a ratio close to 1 indicates good flowability.

4. Compressibility Index: This is derived from bulk and tapped densities and provides information about the powder's compressibility. It's calculated using the formula:

   $$\text{Compressibility Index}=\frac{\text{Tapped Density}-\text{Bulk Density}}{\text{Tapped Density}}\times 100\mathrm{\%}$$

   Higher values indicate higher compressibility and potential for easier compaction.

5. Powder Flow Function: This measures the flowability of the powder under different conditions and is used to predict how the powder will behave during processing. It's often assessed using a powder rheometer.

6. Particle Size Distribution: Derived from various methods like laser diffraction or sieve analysis, this property describes the range and distribution of particle sizes in the powder, affecting its flow, mixing, and dissolution characteristics.

7. Specific Surface Area: This measures the total surface area of the powder per unit mass. It's often determined by techniques such as BET (Brunauer-Emmett-Teller) adsorption. A higher specific surface area can affect the reactivity and solubility of the powder.

8. Powder Flow Rate: This indicates how quickly the powder flows through a given orifice under specific conditions, which is crucial for processes like filling and blending.

9. Cohesion and Adhesion Properties: These are derived from interactions between particles and can affect how powders handle moisture, stick to surfaces, or clump together.

Understanding these derived properties helps in optimizing the processing and application of powders in various industries.