ASTM F21 Standard Test Method for Hydrophobic Surface Films by the Atomizer Test

The ASTM F21 test method is used to detect the presence of hydrophobic (nonwetting) films on surfaces and hydrophobic organic materials in processing environments. This test enables detection of fractional molecular layers of hydrophobic organic contaminants. The sensitivity of the test may vary significantly on very rough or porous surfaces. As specified in this check technique, the atomizer test is quick and non-destructive and can be used to modify and evaluate techniques for removing hydrophobic impurities. The ASTM F21 test method (Standard Test Method for Hydrophobic Surface Films by the Atomizer Test) is used to detect and control hydrophobic contaminants in processing environments, used in cement and soil industries, and research manufacturing plants. 

A simple Hydrophobic surface that can repel water is required for the ASTM F21 test. The ASTM F21 test procedure uses the atomizer test technique. A water-break method happens where running water is allowed to form a sheet across the surface, and breaks in the water indicate the presence of hydrophobic residues. A mist of distilled water is atomized onto the surface. If the water droplets tend to merge into large lenses lasting for 25 s without flashing out, the surface is considered to have satisfactorily passed the water-break test. If the water gathers into droplets within 25 s (if the surface shows a “water break” within that time), the surface is considered to have failed the test. 

This test technique is not quantitative, and it is usually limited to tasks where a pass/fail evaluation of cleanliness is sufficient. This test method is not appropriate where line-of-sight evaluation is not possible, or for assembled hardware where there is a risk of water entrapment in faying surfaces or complex structures where it is not be properly removed.

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