1、Designation: B827 05 (Reapproved 2014)Standard Practice forConducting Mixed Flowing Gas (MFG) Environmental Tests1This standard is issued under the fixed designation B827; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides procedures for conducting envi-ronmental tests involving exposures to controlled quantities of
3、corrosive gas mixtures.1.2 This practice provides for the required equipment andmethods for gas, temperature, and humidity control whichenable tests to be conducted in a reproducible manner. Repro-ducibility is measured through the use of control couponswhose corrosion films are evaluated by mass ga
4、in, coulometry,or by various electron and X-ray beam analysis techniques.Reproducibility can also be measured by in situ corrosion ratemonitors using electrical resistance or mass/frequency changemethods.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement a
5、re included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet (MSDS)
6、 for this product/materialas provided by the manufacturer, to establish appropriatesafety and health practices, and determine the applicability ofregulatory limitations prior to use. See 5.1.2.4.2. Referenced Documents2.1 ASTM Standards:2B542 Terminology Relating to Electrical Contacts and TheirUseB
7、765 Guide for Selection of Porosity and Gross Defect Testsfor Electrodeposits and Related Metallic CoatingsB808 Test Method for Monitoring ofAtmospheric CorrosionChambers by Quartz Crystal MicrobalancesB810 Test Method for Calibration ofAtmospheric CorrosionTest Chambers by Change in Mass of Copper
8、CouponsB825 Test Method for Coulometric Reduction of SurfaceFilms on Metallic Test SamplesB826 Test Method for Monitoring Atmospheric CorrosionTests by Electrical Resistance ProbesB845 Guide for Mixed Flowing Gas (MFG) Tests for Elec-trical ContactsD1193 Specification for Reagent WaterD2912 Test Met
9、hod for Oxidant Content of the Atmosphere(Neutral Ki) (Withdrawn 1990)3D2914 Test Methods for Sulfur Dioxide Content of theAtmosphere (West-Gaeke Method)D3449 Test Method for Sulfur Dioxide in Workplace Atmo-spheres (Barium Perchlorate Method) (Withdrawn 1989)3D3464 Test Method for Average Velocity
10、in a Duct Using aThermal AnemometerD3609 Practice for Calibration Techniques Using Perme-ation TubesD3824 Test Methods for Continuous Measurement of Ox-ides of Nitrogen in theAmbient or WorkplaceAtmosphereby the Chemiluminescent MethodD4230 Test Method of Measuring Humidity with Cooled-Surface Conde
11、nsation (Dew-Point) HygrometerE902 Practice for Checking the Operating Characteristics ofX-Ray Photoelectron Spectrometers (Withdrawn 2011)3G91 Practice for Monitoring Atmospheric SO2DepositionRate for Atmospheric Corrosivity Evaluation3. Terminology3.1 Definitions relating to electrical contacts ar
12、e in accor-dance with Terminology B542.4. Significance and Use4.1 Mixed flowing gas (MFG) tests are used to simulate oramplify exposure to environmental conditions which electricalcontacts or connectors can be expected to experience in variousapplication environments (1, 2).41This practice is under
13、the jurisdiction ofASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved Oct. 1, 2014. Published October 2014. Originallyapproved in 1992. Last previous edition approved in 2009 as B827 05
14、(2009)2.DOI: 10.1520/B0827-05R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version o
15、f this historical standard is referenced onwww.astm.org.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.2 Test samples which have been e
16、xposed to MFG testshave ranged from bare metal surfaces, to electrical connectors,and to complete assemblies.4.3 The specific test conditions are usually chosen so as tosimulate, in the test laboratory, the effects of certain represen-tative field environments or environmental severity levels onstan
17、dard metallic surfaces, such as copper and silver couponsor porous gold platings (1, 2).4.4 Because MFG tests are simulations, both the test con-ditions and the degradation reactions (chemical reaction rate,composition of reaction products, etc.) may not always re-semble those found in the service e
18、nvironment of the productbeing tested in the MFG test. A guide to the selection ofsimulation conditions suitable for a variety of environments isfound in Guide B845.4.5 The MFG exposures are generally used in conjunctionwith procedures which evaluate contact or connector electricalperformance such a
19、s measurement of electrical contact resis-tance before and after MFG exposure.4.6 The MFG tests are useful for connector systems whosecontact surfaces are plated or clad with gold or other preciousmetal finishes. For such surfaces, environmentally producedfailures are often due to high resistance or
20、 intermittencescaused by the formation of insulating contamination in thecontact region. This contamination, in the form of films andhard particles, is generally the result of pore corrosion andcorrosion product migration or tarnish creepage from pores inthe precious metal coating and from unplated
21、base metalboundaries, if present.4.7 The MFG exposures can be used to evaluate novelelectrical contact metallization for susceptibility to degradationdue to environmental exposure to the test corrosive gases.4.8 The MFG exposures can be used to evaluate theshielding capability of connector housings
22、which may act as abarrier to the ingress of corrosive gases.4.9 The MFG exposures can be used to evaluate thesusceptibility of other connector materials such as plastichousings to degradation from the test corrosive gases.4.10 The MFG tests are not normally used as porosity tests.For a guide to poro
23、sity testing, see Guide B765.4.11 The MFG tests are generally not applicable where thefailure mechanism is other than pollutant gas corrosion such asin tin-coated separable contacts.5. Apparatus5.1 Apparatus required to conduct MFG tests are dividedinto four major categories, corrosion test chamber,
24、 gas supplysystem, chamber monitoring system, and chamber operatingsystem.5.1.1 Corrosion Test Chamber:5.1.1.1 The chamber shall consist of an enclosure made ofnonreactive, low-absorbing, nonmetallic materials containedwithin a cabinet or oven capable of maintaining the tempera-ture to a maximum tol
25、erance of 61C with a preferredtolerance held to 60.5C within the usable chamber workingspace accordance with 7.3, with a means to introduce andexhaust gases from the chamber.5.1.1.2 The chamber isolates the reactive gases from theexternal environment. Chamber materials that are not low-absorbing can
26、 affect test conditions by absorbing or emittingreactive gases, leading to control and reproducibility problems.The chamber construction shall be such that the leak rate is lessthan 3 % of the volume exchange rate.5.1.1.3 The chamber shall have provision for maintaininguniformity of the average gas
27、flow velocity within 620%ofaspecified value or of the chamber average when the chamber isempty. For chambers with a dimension of more than 0.5 m,measurement points shall be in accordance with Test MethodB810. For chambers with all dimensions of less than 0.5 m, aminimum of five points shall be measu
28、red at locations in theplane of sample exposure (perpendicular to the expected flowdirection) that are equidistant from each other and the walls ofthe chamber.After all five or more data values are recorded, allmeasurements shall be repeated a second time. After the twosets of measurements are recor
29、ded, a third complete set shall berecorded. The arithmetic average of the 15 or more measure-ments shall be the chamber average. See 7.5 and 7.6.8.Ifahotwire anemometer is used for gas velocity measurements, itshall be made in accordance with Test Method D3464, with theexception that sample sites sh
30、all be in accordance with TestMethod B810.5.1.1.4 A sample access port is desirable. This should bedesigned such that control coupons can be removed or replacedwithout interrupting the flow of gases. Corrosion test chambercorrosion rates have been shown to be a function of thepresence or absence of
31、light (3, 4). Provision for controlling thetest illumination level in accordance with a test specificationshall be made.5.1.1.5 Examples of test chamber systems are diagrammedin Figs. 1-3. They are not to be considered exclusive examples.5.1.2 Gas Supply System:5.1.2.1 Description and RequirementsTh
32、e gas supply sys-tem consists of five main parts: a source of clean, dry, filteredair; a humidity source; corrosive gas source(s); gas deliverysystem; and corrosive gas concentration monitoring system(s).Total supply capacity must be such as to meet requirements forcontrol of gas concentrations.The
33、minimum number of volumechanges is determined by the requirement that the concentra-tion of corrosive gases be maintained within 615 % betweengas inlet and outlet. This is verified by measurement of the gasconcentrations near the gas inlet upstream of the usablechamber working volume and comparing w
34、ith gas concentra-tions measured downstream of the usable chamber workingvolume just prior to the chamber exhaust; these values shall bewithin 615 % (see 7.6). Alternative methods of demonstratingcompliance with the maximum allowable concentration gradi-ent are acceptable. Normally, a conditioned ch
35、amber equili-brates within several hours after sample loading and start of thecorrosive gas supply. Times longer than 2 h shall be reported inthe test report; see Section 8. A guide to estimating supplyrequirements is provided in Appendix X1.NOTE 1Guidance: when inlet to outlet concentrations vary b
36、y morethan 615 %, it usually indicates an overloaded chamber.B827 05 (2014)25.1.2.2 Clean, Dry, Filtered Air SourceGases other thanoxygen and nitrogen that are present in the dry air source shallbe less than or equal to those defined by OHSA Class D limitswith the following additional constraint. Ga
37、ses other thannitrogen, oxygen, carbon dioxide, noble gases, methane, ni-trous oxide, and hydrogen shall be less than 0.005 (ppm) byvolume total and shall be High Efficiency ParticulateArrestants(HEPA) filtered.5.1.2.3 Humidity SourceThe humidity source shall usedistilled or deionized water, Specifi
38、cation D1193,Type1orbetter, and shall introduce no extraneous material. The humid-ity source shall be maintained equivalent to SpecificationD1193 Type II or better, with the exception that electricalresistivity shall be maintained equivalent to SpecificationD1193 Type IV. The time averaged value of
39、humidity shall bewithin 61 % relative humidity of the specified value withabsolute variations no greater than 63 % relative humidityfrom the specified value.5.1.2.4 Corrosive Gas SourcesCorrosive (test) gases, suchas nitrogen dioxide, hydrogen sulfide, chlorine, sulfur dioxide,etc. shall be of chemi
40、cally pure5grade or better. Such gases arefrequently supplied in dry carrier gas such as nitrogen or air.(WarningThis practice involves the use of hazardousmaterials, procedures, and equipment. The gas concentrationsin the test chamber may be within permissible exposure limits(PEL). However, concent
41、rations in the compressed gas cylin-ders or permeation devices are often above the PEL, and mayexceed the immediately dangerous to life and health level(IDHL). This practice does not address safety issues associatedwith MFG testing.)5.1.2.5 Gas Delivery SystemThe gas delivery system iscomprised of t
42、hree main parts: gas supply lines, gas controlvalves and flow controllers,6and a mixing chamber. The gasdelivery system shall be capable of delivering gases at therequired concentrations and rates within the test chamber.(1) All materials used for the gas transport system must notinteract with the g
43、ases to the extent that chamber gas concen-trations are affected.(2) Gases, make-up air, and water vapor must be thor-oughly mixed before gas delivery to the samples under test inthe chambers. Care must be taken to ensure absence of aerosolformation in the mixing chamber whereby gases are consumedin
44、 the formation of particulates which may interfere with gasconcentration control and may introduce corrosion processeswhich are not representative of gaseous corrosion mechanisms.Aerosol formation may be detected by the presence of a visiblefilm or deposit on the interior surface of the gas system w
45、herethe gases are mixed.(3) Any fogging of the tubing walls or mixing chamberwalls can be taken to be an indication of a loss of corrosivegases from the atmosphere. Final mixing of the specified gasesshould occur inside a separate area of, or as close as possibleto, the test chamber so as to ensure
46、thermal equilibration withthe test chamber.(4) Flow measurement capability is required at the inlet ofthe chamber and also at the exhaust of negative pressurechambers to ensure the absence of uncalibrated gas streams.5.1.2.6 Corrosive Gas Concentration Monitoring SystemStandard measurement systems f
47、or very low level gas concen-trations are listed in Table 1, which provides for gases incommon use in present mixed flowing gas systems, for testingelectrical contact performance.(1) Each instrument must be characterized for interferencewith the gases specified, both individually and mixed.(2) Depen
48、ding on the exact equipment set used, it may notbe possible to accurately measure the concentration of somegases, such as chlorine, in combination with any of the othergases.(3) The analytic instruments shall be maintained and cali-brated electronically in accordance with the manufacturersrecommenda
49、tions. Standard gas sources shall also be calibratedin accordance with the manufacturers specifications, or inaccordance with Practice D3609. Gas concentration analyzersshall be calibrated to standard gas sources in accordance withthe manufacturers recommendations. They shall be calibratedbefore and after each test and whenever the indicated concen-tration changes exceed the allowed variation in the testspecification.(4) Control of the temperature and humidity within the testchamber itself is part of the chamber monitoring system whichis described in 5.1.35Chemically P
