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Significance and Use
This test method evaluates, under carefully controlled conditions, the changes in the mass of a test specimen on exposure under vacuum to a temperature of 125°C and the mass of those products that leave the specimen and condense on a collector at a temperature of 25°C.
The 24 h test time does not represent actual outgassing from years of operation, so a higher test temperature shorter time was selected to allow material comparisons with no intent to predict actual outgassing in service. The test temperature of 125°C was assumed to be significantly above the expected operating temperature in service. If expected operating temperatures exceed 65 to 70°C the test temperature should be increased. It is suggested that test temperature be at least 30°C higher than expected maximum service temperature in order to provide material comparisons for TML and CVCM.
Comparisons of material outgassing properties are valid at 125°C sample temperature and 25°C collector temperature only. Samples tested at other temperatures may be compared only with other materials which were tested at that same temperature.
The measurements of the collected volatile condensable material are also comparable and valid only for similar collector geometry and surfaces at 25°C. Samples have been tested at sample temperatures from 50 to 400°C and at collector temperatures from 1 to 30°C by this test technique. Data taken at nonstandard conditions must be clearly identified and should not be compared with samples tested at 125°C sample temperature and 25°C collector temperature.
The simulation of the vacuum of space in this test method does not require that the pressure be as low as that encountered in interplanetary flight (for example, 10−12 Pa (10−14 torr)). It is sufficient that the pressure be low enough that the mean free path of gas molecules be long in comparison to chamber dimensions.
This method of screening materials is considered a conservative one because maximum operating temperatures in service are assumed not to exceed 50 to 60°C for most applications. It is possible that a few materials will have acceptable properties at the intended use temperature but will be eliminated because their properties are not satisfactory at the test temperature of 125°C. Also, materials that condense only below 25°C are not detected. The user may designate additional tests to qualify materials for a specific application.
The determinations of TML and WVR are affected by the capacity of the material to gain or lose water vapor. Therefore, the weighings must be accomplished under controlled conditions of 23°C and 50 % relative humidity.
Alternatively, all specimens may be put into open glass vials during the 24-h temperature and humidity conditioning. The vials must be capped before removal from the conditioning chamber. Each specimen must be weighed within 2 min after opening the vial to minimize the loss or absorption of water vapor while exposed to an uncontrolled humidity environment. While control of humidity is not necessary at this point, the temperature for the weighing should be controlled at 23°C, the same temperature prescribed for the 24-h storage test.
1.1 This test method covers a screening technique to determine volatile content of materials when exposed to a vacuum environment. Two parameters are measured: total mass loss (TML) and collected volatile condensable materials (CVCM). An additional parameter, the amount of water vapor regained (WVR), can also be obtained after completion of exposures and measurements required for TML and CVCM.
1.2 This test method describes the test apparatus and related operating procedures for evaluating the mass loss of materials being subjected to 125°C at less than 7 × 10−3 Pa (5 × 10−5 torr) for 24 h. The overall mass loss can be classified into noncondensables and condensables. The latter are characterized herein as being capable of condensing on a collector at a temperature of 25°C.
Note 1—Unless otherwise noted, the tolerance on 25 and 125°C is ±1°C and on 23°C is ±2°C. The tolerance on relative humidity is ±5 %.
1.3 Many types of organic, polymeric, and inorganic materials can be tested. These include polymer potting compounds, foams, elastomers, films, tapes, insulations, shrink tubings, adhesives, coatings, fabrics, tie cords, and lubricants. The materials may be tested in the “as-received” condition or prepared for test by various curing specifications.
1.4 This test method is primarily a screening technique for materials and is not necessarily valid for computing actual contamination on a system or component because of differences in configuration, temperatures, and material processing.
1.5 The criteria used for the acceptance and rejection of materials shall be determined by the user and based upon specific component and system requirements. Historically, TML of 1.00 % and CVCM of 0.10 % have been used as screening levels for rejection of spacecraft materials.
1.6 The use of materials that are deemed acceptable in accordance with this test method does not ensure that the system or component will remain uncontaminated. Therefore, subsequent functional, developmental, and qualification tests should be used, as necessary, to ensure that the material's performance is satisfactory.
1.7 This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods