ASTM F21-20

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F21 − 14 F21 − 20
Standard Test Method for
Hydrophobic Surface Films by the Atomizer Test
This standard is issued under the fixed designation F21; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the detection of the presence of hydrophobic (nonwetting) films on surfaces and the presence of
hydrophobic organic materials in processing environments. When properly conducted, the test will enable detection of fractional
molecular layers of hydrophobic organic contaminants. On very rough or porous surfaces, the sensitivity of the test may be
significantly decreased.
1.2 Units—The values stated in SI units are to be regarded as the standard. The inch-pound values given in parentheses are for
information only.after SI units are provided for information only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C813 Test Method for Hydrophobic Contamination on Glass by Contact Angle Measurement
D351 Classification for Natural Muscovite Block Mica and Thins Based on Visual Quality
D1193 Specification for Reagent Water
D2578 Test Method for Wetting Tension of Polyethylene and Polypropylene Films
D5946 Test Method for Corona-Treated Polymer Films Using Water Contact Angle Measurements
D7334 Practice for Surface Wettability of Coatings, Substrates and Pigments by Advancing Contact Angle Measurement
D7490 Test Method for Measurement of the Surface Tension of Solid Coatings, Substrates and Pigments using Contact Angle
Measurements
F22 Test Method for Hydrophobic Surface Films by the Water-Break Test
3. Terminology
3.1 Definitions:
3.1.1 contact angle, n—the interior angle that a drop makes between the substrate and a tangent drawn at the intersection
between the drop and the substrate as shown in Fig. 1; this is the angle formed by a liquid at the three phase boundary where a
liquid, gas (air), and solid intersect.
3.1.2 hydrophilic, adj—having a strong affinity for water; wettable.
3.1.2.1 Discussion—
Hydrophilic surfaces exhibit zero contact angle with water. A sessile drop of water applied to the surface will immediately spread
out to form a film.
This test method is under the jurisdiction of ASTM Committee E21 on Space Simulation and Applications of Space Technology and is the direct responsibility of
Subcommittee E21.05 on Contamination.
Current edition approved Nov. 1, 2014April 1, 2020. Published November 2014May 2020. Originally approved in 1962. Last previous edition approved in 20072014 as
F21 – 65F21 – 14.(2007). DOI: 10.1520/F0021-14.10.1520/F0021-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F21 − 20
FIG. 1 Contact Angle
3.1.3 hydrophobic, adj—having little affinity for water; nonwettable.
3.1.3.1 Discussion—
Hydrophobic surfaces exhibit contact angles between a sessile drop of water and the surface appeciably greater than zero.
3.1.4 sessile drop, n—a drop of liquid sitting on the upper side of a horizontal surface.
3.1.5 water-break, n—a break in the continuity of a film of water on a surface on removal from an aqueous bath or on removal
of a flowing water source from the surface.
3.1.5 contact angle, n—the interior angle that a drop makes between the substrate and a tangent drawn at the intersection
between the drop and the substrate as shown in Fig. 1; this is the angle formed by a liquid at the three phase boundary where a
liquid, gas (air), and solid intersect.
4. Summary of Test Method
4.1 The atomizer test is performed by subjecting the dry surface to be tested to a fine water spray. The interpretation of the
test is based upon the pattern of wetting. In the absence of hydrophobic films, the impinging water droplets will wet the surface
and spread immediately to form a continuous water film. Contaminated areas having a surface tension lower than water will cause
the water to bead up at that location. Most common film contaminants such as oils, silicones, or fluorocarbon greases have surface
tensions significantly lower than water. In areas where these hydrophobic materials are present on the surface, the sprayed droplets
will not wet the surface and spread but will tend to remain as fine droplets.
5. Significance and Use
5.1 The atomizer test as described in this test method is rapid, nondestructive, and may be used for control and evaluation of
processes for the removal of hydrophobic contaminants. The test may also be used for the detection and control of hydrophobic
contaminants in processing environments. For this application, a surface free of hydrophobic films is exposed to the environment
and subsequently tested.
5.2 This test method is related to Test Method F22. This test method may be suitable as an alternative to the water-break test
when the surface of interest should not or cannot be immersed or doused with water, or when such immersion or dousing is
impractical.
NOTE 1—This test method is not appropriate where line of sight evaluation is not feasible; or for assembled hardware where there is a risk for
entrapment of water in faying surfaces or complex structures where it may not be effectively removed.
5.3 This test method is not quantitative and is typically restricted to applications where a go/no go pass/fail evaluation of
cleanliness will suffice.
5.4 For quantitative measurement of surface wetting, test methods that measure contact angle of a sessile drop of water or other
test liquid may be used in some applications. Measurement methods based on contact angle are shown in Test Methods C813,
D5946, and D7490; and Practice D7334.
5.4.1 Devices for in situ measurement of contact angle are available. These devices are limited to a small measurement surface
area and may not reflect the cleanliness condition of a larger surface. For larger surface areas, localized contact angle measurement,
or other quantitative inspection, combined with water break testing may be useful.
Linford, H. B., and Saubestre, E. B., “A New Degreasing Evaluation Test: The Atomizer Test,” ASTM Bulletin, May 1953, p. 47.
Feder, D. O., and Koontz, D. E., “Detection, Removal and Control of Organic Contaminants in the Production of Electron Devices,” ASTM STP 246, Am. Soc. Testing
Mats., p. 40 (1959).
F21 − 20
5.5 This test method is only for use on test
...