# ASTM E128 Maximum Pore Diameter and Permeability of Rigid Porous Filters for Laboratory Use

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. This test method establishes a uniform designation for maximum pore diameter and also provides a means of detecting and measuring changes that occur through continued use.... Read More

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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.

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