1、Designation: B 827 05Standard Practice forConducting Mixed Flowing Gas (MFG) Environmental Tests1This standard is issued under the fixed designation B 827; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 ofcorrosive gas m
3、ixtures.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 gain, coulometry,
4、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 as thestandard.1.4 This standard does not purport to addre
5、ss 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 for this product/material as pro-vided by the manufacturer, to establish appr
6、opriate safety andhealth practices, and determine the applicability of regulatorylimitations prior to use. See 5.1.2.4.2. Referenced Documents2.1 ASTM Standards:2B 542 Terminology Relating to Electrical Contacts andTheir UseB 765 Guide for Selection of Porosity and Gross DefectsTests for Electrodepo
7、sits and Related Metallic CoatingsB 808 Test Method for Monitoring of Atmospheric Corro-sion Chambers by Quartz Crystal MicrobalancesB 810 Test Method for Calibration of Atmospheric Corro-sion Test Chambers by Change in Mass of Copper Cou-ponsB 825 Test Method for Coulometric Reduction of SurfaceFil
8、ms on Metallic Test SamplesB 826 Test Method for Monitoring Atmospheric CorrosionTests by Electrical Resistance ProbesB 845 Guide for Mixed Flowing Gas (MFG) Tests forElectrical ContactsD 1193 Specification for Reagent WaterD 2912 Test Method for Oxidant Content of the Atmo-sphere (Neutral KI)3D 291
9、4 Test Methods for Sulfur Dioxide Content of theAtmosphere (West-Gaeke Method)D 3449 Test Method for Sulfur Dioxide in Workplace At-mospheres (Barium Perchlorate Method)3D 3464 Test Method forAverage Velocity in a Duct Using aThermal AnemometerD 3609 Practice for Calibration Techniques Using Perme-a
10、tion TubesD 3824 Test Methods for Continuous Measurement of Ox-ides of Nitrogen in the Ambient or Workplace Atmosphereby the Chemiluminescent MethodD 4230 Test Method of Measuring Humidity With Cooled-Surface Condensation (Dew-Point) HygrometerE 902 Practice for Checking the Operating Characteristic
11、sof X-Ray Photoelectron SpectrometersG91 Practice for Monitoring Atmospheric SO2Using Sul-fation Plate Technique3. Terminology3.1 Definitions relating to electrical contacts are in accor-dance with Terminology B 542.1This practice is under the jurisdiction of ASTM Committee B02 on NonferrousMetals a
12、nd Alloys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved May 1, 2005. Published June 2005. Originallyapproved in 1992. Last previous edition approved in 2003 as B 827 - 97 (2003).2For referenced ASTM standards, visit the ASTM websit
13、e, 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.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Un
14、ited States.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).44.2 Test samples which have been exposed to MFG tes
15、tshave 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 onstandard metallic sur
16、faces, 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 environment of the
17、 productbeing tested in the MFG test. A guide to the selection ofsimulation conditions suitable for a variety of environments isfound in Guide B 845.4.5 The MFG exposures are generally used in conjunctionwith procedures which evaluate contact or connector electricalperformance such as measurement of
18、 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 intermittencesc
19、aused 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 base metalbounda
20、ries, 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 which may act as
21、 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 porosity testing, se
22、e Guide B 765.4.11 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, gas supplysyst
23、em, 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 tolerance of 61C w
24、ith 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 affect test co
25、nditions 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 flow velocity w
26、ithin 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 MethodB 810. For chambers with all dimensions of less than 0.5 m, aminimum of five points shall be measured at locatio
27、ns 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 recorded, a third c
28、omplete 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 D 3464, withthe exception that sample sites shall be in acc
29、ordance with TestMethod B 810.5.1.1.4 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 light (3, 4)
30、. 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 RequirementsThe gas supply
31、 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 minimum num
32、ber 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 with gas con
33、centra-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 chamber equil
34、i-brates within several hours after sample loading and start of the4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.B827052corrosive gas supply. Times longer than 2 h shall be reported inthe test report; see Section 8. A guide to estimating supplyrequir
35、ements is provided in Appendix X1.NOTE 1Guidance: when inlet to outlet concentrations vary by morethan 615 %, it usually indicates an overloaded chamber.5.1.2.2 Clean, Dry, Filtered Air Source Gases other thanoxygen and nitrogen that are present in the dry air source shallbe less than or equal to th
36、ose defined by OHSA Class D limitswith the following additional constraint. Gases 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 Hum
37、idity SourceThe humidity source shall usedistilled or deionized water, Specification D 1193, Type 1 orbetter, and shall introduce no extraneous material. The humid-ity source shall be maintained equivalent to SpecificationD 1193 Type II or better, with the exception that electricalresistivity shall
38、be maintained equivalent to SpecificationD 1193 Type IV. The time averaged value of 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,such as
39、 nitrogen dioxide, hydrogen sulfide, chlorine, sulfurdioxide, etc. shall be of chemically pure5grade or better. Suchgases are frequently supplied in dry carrier gas such as nitrogenor air. (WarningThis practice involves the use of hazardousmaterials, procedures, and equipment. The gas concentrations
40、in the test chamber may be within permissible exposure limits(PEL). However, concentrations 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 associatedw
41、ith MFG testing.)5.1.2.5 Gas Delivery SystemThe gas delivery system iscomprised of three main parts: gas supply lines, gas controlvalves and flow controllers, and a mixing chamber. The gasdelivery system shall be capable of delivering gases at therequired concentrations and rates within the test cha
42、mber.(1) All materials used for the gas transport system must notinteract with the gases 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 e
43、nsure absence of aerosolformation in the mixing chamber whereby gases are consumedin 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
44、the presence of a visiblefilm or deposit on the interior surface of the gas system wherethe 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 ins
45、ide a separate area of, or as close as possibleto, the test chamber so as to ensure 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
46、.5.1.2.6 Corrosive Gas Concentration Monitoring SystemStandard measurement systems for 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 character
47、ized for interferencewith the gases specified, both individually and mixed.(2) Depending 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 main
48、tained andcalibrated electronically in accordance with the manufacturersrecommendations. Standard gas sources shall also be calibrated5Chemically Pure and Pre-Purified are designations of Matheson Gas Co., EastRutherford, NJ, for specific grades of purity of gas. Other vendors such as AIRCOhave equi
49、valent gas purities available sold under different terminology.FIG. 1 Schematic Flow-Through Mixed Flowing Gas (MFG) TestSystemB827053in accordance with the manufacturers specifications, or inaccordance with Practice D 3609. 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 i
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