Difference Between Hardness and Friability

Main Difference – Hardness vs Friability

Hardness and friability are two opposite words that are used to express the response of a substance towards an applied pressure on it. Hardness is the resistance of a substance to undergo plastic deformation when a pressure is applied to it. Friability is the condition of being easily crumbled or pulverized. Since hardness is the opposite of friability, there are many differences between these two terms. The main difference between hardness and friability is that hardness is the resistance to scratch or deformation whereas friability is the tendency to crumble.

Key Areas Covered

1. What is Hardness
      – Definition, Different Hardness Tests
2. What is Friability
      – Definition, Use in Pharmaceutical Industry
3. What is the Difference Between Hardness and Friability
     – Comparison of Key Differences

Key Terms: Abrasion, Deformation, Friability, Friction, Hardness, Indentation, Scratch

What is Hardness

Hardness is the resistance of a substance to plastic deformation when a pressure is applied on it. This term explains the resistance to scratch, deformation, abrasion or cutting. In macroscopic scale, the hardness of a substance occurs mainly due to the presence of strong intermolecular forces between atoms or molecules.

In mineralogy, the hardness of a material is the scratch resistance of a mineral. This hardness is measured using the Moh’s scale. According to the Moh’s scale, the Moh’s hardness of talc is 1 and the Moh’s hardness of diamond is 10.

Figure 1: Diamond is the Hardest Mineral on Earth

Testing Hardness

Different tests can be done to get a measurement for the hardness of a substance in macro-scale, micro-scale or in Nano-scale. The technique that should be used depends on the type of substance, type of force applied on the substance and the displacement that can be observed. There are three main measurements of hardness as:

Scratch Hardness

The scratch hardness is expressed by how resistant a substance is towards scratching or fracture due to friction applied by a sharp object. The technique uses two types of materials: a harder material and a softer material.

The hardness of a coating is measured as the force required to cut the coating (or film) and expose the substrate (on which the thin film is present). Ex: A sclerometer can be used for this testing. The scratch hardness is measured by Moh’s scale.

Indentation Hardness

Indentation hardness is the resistance to deformation towards a constant pressure applied on a substance. Indentation hardness is measured by scales such as Rockwell, Shore, and Brinell.

Rebound Hardness

Rebound hardness can be defined as the height of the “bounce” of a diamond-tipped hammer dropped from a certain height onto a material. A scleroscope is used for the measurement.

What is Friability

Friability is the condition of being easily crumbled or pulverized. This term explains the tendency of a solid substance to break into fine particles (or fibers) when a pressure is applied on it. This pressure can be friction; for example, it can be just a contact such as rubbing.

This term is used in pharmaceutical applications to express the tendency of a tablet to crumble following compression. Therefore, testing friability can be used to determine poor tablet designing, the low moisture content of a tablet and to check whether the binder used is insufficient.

Figure 2: Friability also refers to the tendency of tablets to crumble following compression

However, tablets should be hard enough to not to crumble when packaged, and also friable enough dissociate inside the gastrointestinal tract.

Difference Between Hardness and Friability

Definition

Hardness: Hardness is the resistance of a substance to plastic deformation when a pressure is applied on it.

Friability: Friability is the condition of being easily crumbled or pulverized.

Principle

Hardness:  Hardness is the resistance to scratch, deformation, abrasion or cutting.

Friability: Friability is the tendency to crumble.

Uses of Measurement

Hardness: Measurements are used in testing the hardness of a coating, hardness of metals, minerals, etc.

Friability: Measurement is used in pharmaceutical applications to express the tendency of a tablet to crumble following compression.

Conclusion

Hardness and friability are two terms used to explain physical properties related to the strength of substances. Hardness is the opposite of friability. The main difference between hardness and friability is that hardness is the resistance to scratch or deformation whereas friability is the tendency to crumble.

Reference:

1. “Friability.” The Free Dictionary, Farlex, Available here.
2. “Hardness.” Wikipedia, Wikimedia Foundation, 24 Jan. 2018, Available here.
3. “Introduction to Friability Testing.” Copley Scientific, Available here.

Image Courtesy:

1. “807979” (CC0) via Pixabay
2. “384846” (CC0) via Max Pixel