PHYPHAR LEC - Micromeritics of Solids

Micromeritics

Science and technology of small particles

• Involves properties such as size, shape, surface properties, density and porosity, among others

Sieving

• USP Method

• Uses a series of sieves calibrated by the National Bureau of Standards (NBS)

• The particle size may be estimated by calculating the relative abundance of particles in each sieve

• Variables causing sieving errors Sieve loading, duration and intensity of agitation

Very Coarse

All particles pass through a No. 8 sieve and not more than 20% through a No. 60 sieve.

Coarse

All particles pass through a No. 20 sieve and not more than 40% through a No. 60 sieve.

Moderately Coarse

All particles pass through a No. 40 sieve and not more than 40% through a No. 80 sieve.

Fine

All particles pass through a No. 60 sieve and not more than 40% through a No. 100 sieve.

Very Fine

All particles pass through a No. 80 sieve. There is no limit to greater fineness.

Microscopy

• Ordinary Microscope

• Particle Range: 0.2 um - 100 um

• Electronic Scanners

• Disadvantages:

  • Diameter is obtained only from the particle’s length & breadth

  • Slow & Tedious: Number to be counted is 300-500 in order to obtain a good distribution estimation

Martin’s Diameter

Length of a line that bisects the particle image

Feret’s Diameter

Distance between two tangents on opposite sides of the particle parallel to some fixed directions

Projected Area Diameter

Area of a circle with the same area as that of the particle observed perpendicular to the surface on which the particle rests

Particle Volume Measurement

• Determining the particle volume distribution in suspended particles

• Uses a Coulter Counter (Light Diffractor Analyzer)

Sedimentation Method

• This method employs the settling of particles in a liquid of a relatively low density under the influence of a gravitational or centrifugal field

• Uses the Andreasen Apparatus

• Utilizes Stoke’s law

Gas Adsorption Method

• Particles with a small particle size have larger surface areas, and are good adsorbents

• ↓ Particle Size = ↑ Adsorption = ↑ Surface Area

Air Permeability Method

• Based on the principle that the resistance offered to the flow of a fluid, such as air, through a plug of compacted powder is proportional to the surface area of the powder

• ↑ Air Permeability = ↓ Resistance = ↓ Surface Area

Porosity

Percentage expression of voids

Excellent

Carr’s Index

• 1-10

Hausner Ratio

• 1.00-1.11

Good

Carr’s Index

• 11-15

Hausner Ratio

• 1.12-1.18

Fair

Carr’s Index

• 16-20

Hausner Ratio

• 1.19-1.25

Passable

Carr’s Index

• 21-25

Hausner Ratio

• 1.26-1.34

Poor

Carr’s Index

• 26-31

Hausner Ratio

• 1.35-1.45

Very Poor

Carr’s Index

• 32-37

Hausner Ratio

• 1.46-1.59

Very, Very Poor

Carr’s Index

• > 37

Hausner Ratio

• > 1.59

Angle of Repose

Maximum angle possible between the surface of a pile of powder and the horizontal plane

Good Flow

Low Angle of Repose = ____ Flow

Poor Flow

High Angle of Repose = _____ Flow