Scope:

ASTM E128 test method covers the determination of maximum pore diameter and permeability of rigid porous filters used in the laboratory for filtration or diffusion. They are applicable to filters made of sintered glass, ceramic, metal, or plastic. 

Test Procedure:

In ASTM E128, the maximum pore diameter is determined by immersing the filter in a suitable test liquid and applying air pressure until the first bubble of air passes through the filter (Figure 1). The maximum pore diameter is calculated from the surface tension of the test liquid and the applied pressure. Permeability is determined by measuring the flow of air through the filter when subjected to a pressure differential (Figure 2).

Video 01: Explanation of porosity and permeability

Figure 1: Apparatus for determining maximum pore diameter of rigid porous filters

Figure 2: Apparatus for determination of permeability

Specimen size:

Materials for Filters: Glass, Porcelain, Stainless steel, Tetrafluoro-polyethylene, Trifluoromonochloropolyethylene, etc.

Data:

In ASTM E128, the maximum pore diameter is calculated from the following equation:

D = 30γ/p

Where:

D = maximum pore diameter 

γ = surface tension of test liquid in dynes/cm at the temperature of the test, and

p = pressure, mm Hg

Calculate the permeability as follows: 

Permeability = R/Ap 

Where:

R = rate of flow of air, mL/min,

A = effective area of the filter, and

p = observed pressure of water, cm

Conclusion:

ASTM E128 test method covers the determination of maximum pore diameter and permeability of rigid porous filters used in the laboratory for filtration or diffusion.