Designation:B827–97(Reapproved2003)
Standard Practice for
Conducting Mixed Flowing Gas(MFG)Environmental Tests1 This standard is issued under thefixed designation B827;the number immediately following the designation indicates the year of original adoption or,in the ca of revision,the year of last revision.A number in parenthes indicates the year of last reapproval.A superscript epsilon(e)indicates an editorial change since the last revision or reapproval.
1.Scope
1.1This practice provides procedures for conducting envi-ronmental tests involving exposures to controlled quantities of corrosive gas mixtures.
1.2This practice provides for the required equipment and methods for gas,temperature,and humidity control which enable tests to be conducted in a reproducible manner.Repro-ducibility is measured through the u of control coupons who corrosionfilms are evaluated by mass gain,coulometry, or by various electron and X-ray beam analysis techniques. Reproducibility can also be measured by in situ corrosion rate monitors using electrical resistance or mass/frequency change methods.
1.3The values stated in SI units are to be regarded as the standard.
1.4This standard does not purport to address all of the safety concerns,if any,associated with its u.It is the responsibility of the ur of this standard to become familiar with all hazards including tho identified in the appropriate Material Safety Data Sheet for this product/material as pro-vided by the manufacturer,to establish appropriate safety and health practices,and determine the applicability of regulatory limitations prior to u.See5.1.
2.4.
2.Referenced Documents
2.1ASTM Standards:
B542Terminology Relating to Electrical Contacts and Their U2
B765Guide for Selection of Porosity Tests for Electrode-posits and Related Metallic Coatings3
B808Test Method for Monitoring of Atmospheric Corro-sion Chambers by Quartz Crystal Microbalances2
B810Test Method for Calibration of Atmospheric Corro-sion Test Chambers by Change in Mass of Copper Cou-pons2
B825Test Method for Coulometric Reduction of Surface Films on Metallic Test Samples2
B826Test Method for Monitoring Atmospheric Corrosion Tests by Electrical Resistance Probes2
B845Guide for Mixed Flowing Gas(MFG)Tests for Electrical Contacts2
D1193Specification for Reagent Water4
D1607Test Method for Nitrogen Dioxide Content of the Atmosphere(Griess-Saltzman Reaction)5
D2912Test Method for Oxidant Content of the Atmo-sphere(Neutral KI)6
D2914Test Methods for Sulfur Dioxide Content of the Atmosphere(West-Gaeke Method)5
D3449Test Method for Sulfur Dioxide in Workplace At-mospheres(Barium Perchlorate Method)6
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D3464Test Method for Average Velocity in a Duct Using a Thermal Anemometer5
D3609Practice for Calibration Techniques Using Perme-ation Tubes5
D3824Test Methods for Continuous Measurement of Ox-ides of Nitrogen in the Ambient or Workplace Atmosphere by the Chemiluminescent Method5
D4230Test Method of Measuring Humidity With Cooled-Surface Condensation(Dew-Point)Hygrometer5
E902Practice for Checking the Operating Characteristics of X-Ray Photoelectron Spectrometers7
G91Practice for Monitoring Atmospheric SO2Using Sul-fation Plate Technique8
3.Terminology
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3.1Definitions relating to electrical contacts are in accor-dance with Terminology B542.
4.Significance and U
4.1Mixedflowing gas(MFG)tests are ud to simulate or amplify exposure to environmental conditions which electrical
1This practice is under the jurisdiction of ASTM Committee B02on Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee B02.11on
Electrical Contact Test Methods.
Current edition approved June10,2003.Published July2003.Originally approved in1992.Last previous edition approved in1997as B827-97.
2Annual Book of ASTM Standards,V ol02.04.
3Annual Book of ASTM Standards,V ol02.05.
4Annual Book of ASTM Standards,V ol11.01.
5Annual Book of ASTM Standards,V ol11.03.
6Discontinued;e1990Annual Book of ASTM Standards,V ol11.03.
7Annual Book of ASTM Standards,V ol03.06.
8Annual Book of ASTM Standards,V ol03.02.
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contacts or connectors can be expected to experience in various application environments (1,2).9
4.2Test samples which have been expod to MFG tests have ranged from bare metal surfaces,to electrical connectors,and to complete asmblies.
4.3The specific test conditions are usually chon so as to simulate,in the test laboratory,the effects of certain repren-tative field environments or environmental verity levels on standard metallic surfaces,such as copper and silver coupons or porous gold platings (1,2).
4.4Becau 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-mble tho found in the rvice environment of the product being tested in the MFG test.A guide to the lection of simulation conditions suitable for a variety of environments is found in Guide B 84
5.
4.5The MFG exposures are generally ud in conjunction with procedures which evaluate contact or connector electrical performance such as measurement of electrical contact resis-tance before and after MFG exposure.
4.6The MFG tests are uful for connector systems who contact surfaces are plated or clad with gold or other precious metal finishes.For such surfaces,environmentally produced failures are often due to high resistance or intermittences caud by the formation of insulating contamination in the contact region.This contamination,in the form of films and hard particles,is generally the result of por
e corrosion and corrosion product migration or tarnish creepage from pores in the precious metal coating and from unplated ba metal boundaries,if prent.
4.7The MFG exposures can be ud to evaluate novel electrical contact metallization for susceptibility to degradation due to environmental exposure to the test corrosive gas.4.8The MFG exposures can be ud to evaluate the shielding capability of connector housings which may act as a barrier to the ingress of corrosive gas.
4.9The MFG exposures can be ud to evaluate the susceptibility of other connector materials such as plastic housings to degradation from the test corrosive gas.
4.10The MFG tests are not normally ud as porosity tests.For a guide to porosity testing,e Guide B 76
5.
4.11The MFG tests are generally not applicable where the failure mechanism is other than pollutant gas corrosion such as in tin-coated parable contacts.
5.Apparatus
5.1Apparatus required to conduct MFG tests are divided into four major categories,corrosion test chamber,gas supply system,chamber monitoring system,and chamber operating system.
5.1.1Corrosion Test Chamber :
5.1.1.1The chamber shall consist of an enclosure made of nonreactive,low-absorbing,nonmetallic materials contained within a cabinet or oven capable of maintaining the tempera-
ture to a maximum tolerance of 61°C with a preferred tolerance held to 60.5°C within the usable chamber working space accordance with 7.3,with a means to introduce and exhaust gas from the chamber.
5.1.1.2The chamber isolates the reactive gas from the external environment.Chamber materials that are not low-absorbing can affect test conditions by absorbing or emitting reactive gas,leading to control and reproducibility problems.The chamber construction shall be such that the leak rate is less than 3%of the volume exchange rate.
5.1.1.3The chamber shall have provision for maintaining uniformity of the average gas flow velocity within 620%of a specified value or of the chamber average when the chamber is empty.For chamber
s with a dimension of more than 0.5m,measurement points shall be in accordance with Test Method B 810.For chambers with all dimensions of less than 0.5m,a minimum of five points shall be measured at locations in the plane of sample exposure (perpendicular to the expected flow direction)that are equidistant from each other and the walls of the chamber.After all five or more data values are recorded,all measurements shall be repeated a cond time.After the two ts of measurements are recorded,a third complete t shall be recorded.The arithmetic average of the 15or more measure-ments shall be the chamber average.See 7.5and 7.
6.8.If a hot wire anemometer is ud for gas velocity measurements,it shall be made in accordance with Test Method D 3464,with the exception that sample sites shall be in accordance with Test Method B 810.
5.1.1.4A sample access port is desirable.This should be designed such that control coupons can be removed or replaced without interrupting the flow of gas.Corrosion test chamber corrosion rates have been shown to be a function of the prence or abnce of light (3,4).Provision for controlling the test illumination level in accordance with a test specification shall be made.
5.1.1.5Examples of test chamber systems are diagrammed in Figs.1-3.They are not to be considered exclusive examples.5.1.2Gas Supply System :
5.1.2.1Description and Requirements —The gas supply sys-tem consists of five main parts:a source of clean,dry,filtered air;a humidity source;corrosive gas source(s);gas delivery system;and corrosive gas concentration monitoring system(s).Total supply capacity must be such as to meet requirements for control of gas concentrations.The minimum number of volume changes is determined by the requirement that the concentra-tion of corrosive gas be maintained within 615%between gas inlet and outlet.This is verified by measurement of the gas concentrations near the gas inlet upstream of the usable chamber working volume and comparing with gas concentra-tions measured downstream of the usable chamber working volume just prior to the chamber exhaust;the values shall be within 615%(e 7.6).Alternative methods of demonstrating compliance with the maximum allowable concentration gradi-ent are acceptable.Normally,a conditioned chamber equili-brates within veral hours after sample loading and start of the corrosive gas supply.Times longer than 2h shall be reported in the test report;e Section 8.A guide to estimating supply requirements is provided in Appendix X1.
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The boldface numbers in parenthes refer to the list of references at the end of this
standard.
N OTE 1—Guidance:when inlet to outlet concentrations vary by more than 615%,it usually indicates an overloaded chamber.
5.1.2.2Clean,Dry,Filtered Air Source —Gas other than oxygen and nitrogen that are prent in the dry air source shall be less than or equal to tho defined by OHSA Class D limits with the following additional constraint.Gas other than nitrogen,oxygen,carbon dioxide,noble gas,methane,ni-trous oxide,and hydrogen shall be less than 0.005(ppm)by volume total and shall be High Efficiency Particulate Arrestants (HEPA)filtered.
5.1.2.3Humidity Source —The humidity source shall u distilled or deionized water,Specification D 1193,Type 1or better,and shall introduce no extraneous material.The humid-ity source shall be maintained equivalent to Specification D 1193Type II or better,with the exception that electrical resistivity shall be maintained equivalent to Specification D 1193Type IV .The time averaged value of humidity shall be within 61%relative humidity of the specified value with absolute variations no greater than 63%relative humidity from the specified value.
5.1.2.4Corrosive Gas Sources —Corrosive (test)gas,such as nitrogen dioxide,hydrogen sulfide,chlorine,sulfur dioxide,etc.shall be of chemically pure 10grade or better.Such gas are frequ
ently supplied in a carrier gas such as nitrogen which shall be of Pre-Purified 10grade or better.(Warning —
This practice involves the u of hazardous materials,proce-dures,and equipment.The gas concentrations in the test chamber may be within permissible exposure limits (PEL).11However,concentrations in the compresd gas cylinders or permeation devices are often above the PEL,and may exceed the immediately dangerous to life and health level (IDHL).This practice does not address safety issues associated with MFG testing.)
5.1.2.5Gas Delivery System —The gas delivery system is comprid of three main parts:gas supply lines,gas control valves and flow controllers,and a mixing chamber.The gas delivery system shall be capable of delivering gas at the required concentrations and rates within the test chamber.
(1)All materials ud for the gas transport system must not interact with the gas to the extent that chamber gas concen-trations are affected.
(2)Gas,make-up air,and water vapor must be thor-oughly mixed before gas delivery to the samples under test in the chambers.Care must be taken to ensure abnce of aerosol formation in the mixing chamber whereby gas are consumed in the formation of particulates which may interfer
e with gas concentration control and may introduce corrosion process which are not reprentative of gaous corrosion mechanisms.Aerosol formation may be detected by the prence of a visible film or deposit on the interior surface of the gas system where the gas are mixed.
(3)Any fogging of the tubing walls or mixing chamber walls can be taken to be an indication of a loss of corrosive gas from the atmosphere.Final mixing of the specified gas should occur inside a parate area of,or as clo as possible to,the test chamber so as to ensure thermal equilibration with the test chamber.新年好儿歌
(4)Flow measurement capability is required at the inlet of the chamber and also at the exhaust of negative pressure chambers to ensure the abnce of uncalibrated gas streams.5.1.2.6Corrosive Gas Concentration Monitoring System —Standard measurement systems for very low level gas concen-trations are listed in Table 1,which provides for gas in common u in prent mixed flowing gas systems,for testing electrical contact performance.
(1)Each instrument must be characterized for interference with the gas specified,both individually and mixed.
(2)Depending on the exact equipment t ud,it may not be possible to accurately measure the concentration of some gas,such as chlorine,in combination with any of the other gas.
(3)The analytic instruments shall be maintained and calibrated electronically in accordance with the manufacturers’recommendations.Standard gas sources shall also be calibrated in accordance with the manufacturers’specifications,or in accordance with Practice D 3609.Gas concentration analyzers shall be calibrated to standard gas sources in accordance with the manufacturers’recommendations.They shall be calibrated
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Chemically Pure and Pre-Purified are designations of Matheson Gas Co.,East Rutherford,NJ,for specific grades of purity of gas.Other vendors such as AIRCO have equivalent gas purities available sold under different terminology.
11
Pocket Guide to Chemical Hazards,National Institute for Occupational Safety and Health,U.S.Department of Health and Human Service,Publication #85-114,fifth
printing.
FIG.1Schematic Flow-Through Mixed Flowing Gas (MFG)Test
System
before and after each test and whenever the indicated concen-tration changes exceed the allowed variation in the test specification.
(4)Control of the temperature and humidity within the test chamber itlf is part of the chamber monitoring system which is described in 5.1.3
N OTE 2—If the chlorine monitor is not being ud during the test,it need not be calibrated during the test.
5.1.3Chamber Monitoring System —Chamber monitoring systems are required to ensure test reprod
ucibility from one test run to the next.Calibration of monitoring instruments is
required periodically becau the corrosive effects of mixed gas environments can affect instrument nsitivity and accu-racy.The chamber monitoring system must address four test parameters:temperature,humidity,gas concentrations,and corrosivity.
5.1.3.1Temperature Monitoring —Temperature monitoring is usually a simple thermocouple or other temperature mea-surement device capable of the required resolution of 0.2°C and accuracy of 60.5°C within the temperature range required by the test specification.For test temperatures above 40°C,e
7.6.5.
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FIG.2Schematic Vertical Recirculating Mixed Flowing Gas (MFG)Test
System
FIG.3Schematic Horizontal Recirculating Mixed Flowing Gas (MFG)Test
System运动鞋除臭
5.1.3.2Humidity Monitoring —Humidity must be deter-mined by an apparatus with a resolution of 0.5%relative humidity and an accuracy of 61%relative humidity.Test Method D 4230describes a dew point method which meets this requirement.For test temperatures above 40°C,e 7.
6.5.5.1.3.3Corrosive Gas Monitoring —Chamber corrosive gas concentration monitoring must be accomplished by provision of sampling lines from the test chamber to the gas concentra-tion analyzers.The sampling lines must be maintained above the chamber dew point temperature.The interior of the gas concentration analyzers shall also be maintained above the chamber dew point temperature.For test temperatures above 40°C,e
7.6.5.
5.1.3.4Chamber Corrosivity Monitoring —Chamber corro-sivity monitoring can be accomplished by a number of comple-mentary techniques,none of which provide both a comprehen-sive analysis of the corrosion process and an instantaneous indication of the corrosion rate.Five acceptable techniques are as follows:metal coupon corrosion mass gain,corrosion film analysis by coulometric reduction,corrosion film analysis by electron or X-ray beam analysis,quartz crystal microbalance mass gain,and electrical resistance measurement of corroding metal conductors (e Note 3).The first three provide infor-mation subquent to the test whereas the last two can be ud in situ in the test chamber to provide information during the test itlf.See Appendix X2for a discussion of the methods.It is recommended that the test requester specify chamber corrosivity monitoring methods to be ud.
N OTE 3—A potential sixth method utilizing porous gold coupons is under investigation.
5.1.4Chamber Operating System —The chamber operating system is comprid of equipment and software necessary to adequately control all of the variables of the test.This will include data logging and alert procedures for operation outside of desired bounds.Some form of computer control is highl
y recommended to assure satisfactory operation during unat-tended periods and for data tracking for failure analysis in ca the test is disrupted.
6.Reagents and Materials
6.1Materials required to conduct flowing mixed gas tests are as follows:
6.1.1Purity of Water —Water for humidity generation shall be equivalent to Type 1or better of Specification D 1193.6.1.2Carrier Gas —Carrier gas such as nitrogen shall not introduce reactive constituents into the test atmosphere to an amount of more than 5%of any specified corrosive test atmosphere constituent.
6.1.3Clean Filtered Air —Clean filtered air as required for makeup to support the necessary exchange rate,in accordance with
7.6.7.1(2)is specified in 5.1.2.2.
6.1.4Corrosive Gas —Corrosive gas shall be chemi-cally pure 9grade or equivalent.
6.1.5Corrosivity Monitor Materials (CMM)—CMM are comprid of the coupons that are expod to t
he test atmo-sphere for mass gain or coulometric reduction in accordance with Test Methods B 810and B 825,respectively,the coated quartz crystals ud for microbalance measurements in accor-dance with Test Method B 808,resistance monitor materials in accordance with Test Method B 826,or other coupons for analytical techniques described in Appendix X2.3.
7.Procedure
7.1The following procedure is comprid of requirements and other comments provided as a general guide to achieving reproducible results with MFG testing.This procedure is compatible with most test facilities;however,differences in apparatus,test conditions,or local safety requirements may necessitate alternative procedures.Any deviations shall be reported with all test results (e Section 8).
7.2The procedure is comprid of the following major activities:test chamber calibration,sample preparation,test chamber t-up,test chamber start-up,test chamber operation during test duration,test chamber shut-down,and reporting requirements.
7.3Test Chamber Calibration —The spatial uniformity of the corrosivity of test chambers larger than 0.5m on a side shall be measured in accordance with Test Method B 810,which describes the requir
ed placement scheme for calibration samples which are ud to determine corrosion rate uniformity over the entire chamber volume.For chambers smaller than 0.5m on a side or chambers of unusual geometry,u sufficient samples for corrosivity characterization so as to clearly delin-eate the usable chamber working volume as defined in this paragraph.This profiling shall be done when the chamber is initially built and after any structural change to the chamber that may affect the flow of test gas over the test samples.Test Method B 810describes a procedure using mass gain.Alter-native means to characterize corrosion rates such as Test Method B 825,Coulometric Reduction,or Test Method B 808,Quartz Crystal Microbalance,in accordance with 5.1.3.4are also acceptable.A minimum of three corrosivity monitors of a given type must be ud,if possible,in each chamber location.The average corrosivity for that location must be within 15%of the average for the entire chamber.When a single monitor has to be ud at a location,due to chamber size limitations or monitor geometry,the average corrosivity for that location must be bad upon three concutive calibration runs.The requirements define the usable chamber working space.
N OTE 4—Profiling does not remove the necessity to provide and
TABLE 1Instrumental Methods for Gaous Components
N OTE 1—Commercial equipment such as Monitor Labs 8770,Hydro-gen Sulfide Converter,in conjunction with Monitor Labs 8850,Sulfur Dioxide Analyzer is suitable for this purpo.
N OTE 2—Commercial equipment such as Monitor Labs 8850,Sulfur Dioxide Analyzer is suitable for this purpo.
N OTE 3—Commercial equipment such as Monitor Labs 8840,Nitrogen Oxides Analyzer is suitable for this purpo.
Gas Suitable Instrumental Method Suitable Procedure
H 2S Photometric or luminescence See Note 1
SO 2
Photometric or luminescence
Test Methods D 2914,G 91,D 3449,e Note 2
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教资面试流程
Chemiluminescence Method D 3824,e Note 3Cl 2Electrochemical or Reflectometric Test Method D 2912
The instrument manufacturer’s instructions for delivering samples to the instru-ments should be
followed.
