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Significance and Use
Mixed flowing gas (MFG) tests are used to simulate or amplify exposure to environmental conditions which electrical contacts or connectors can be expected to experience in various application environments (1, 2).
Test samples which have been exposed to MFG tests have ranged from bare metal surfaces, to electrical connectors, and to complete assemblies.
The specific test conditions are usually chosen so as to simulate, in the test laboratory, the effects of certain representative field environments or environmental severity levels on standard metallic surfaces, such as copper and silver coupons or porous gold platings (1, 2).
Because MFG tests are simulations, both the test conditions and the degradation reactions (chemical reaction rate, composition of reaction products, etc.) may not always resemble those found in the service environment of the product being tested in the MFG test. A guide to the selection of simulation conditions suitable for a variety of environments is found in Guide B845.
The MFG exposures are generally used in conjunction with procedures which evaluate contact or connector electrical performance such as measurement of electrical contact resistance before and after MFG exposure.
The MFG tests are useful for connector systems whose 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 caused 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 pore corrosion and corrosion product migration or tarnish creepage from pores in the precious metal coating and from unplated base metal boundaries, if present.
The MFG exposures can be used to evaluate novel electrical contact metallization for susceptibility to degradation due to environmental exposure to the test corrosive gases.
The MFG exposures can be used to evaluate the shielding capability of connector housings which may act as a barrier to the ingress of corrosive gases.
The MFG exposures can be used to evaluate the susceptibility of other connector materials such as plastic housings to degradation from the test corrosive gases.
The MFG tests are not normally used as porosity tests. For a guide to porosity testing, see Guide B765.
The MFG tests are generally not applicable where the failure mechanism is other than pollutant gas corrosion such as in tin-coated separable contacts.
1.1 This practice provides procedures for conducting environmental tests involving exposures to controlled quantities of corrosive gas mixtures.
1.2 This practice provides for the required equipment and methods for gas, temperature, and humidity control which enable tests to be conducted in a reproducible manner. Reproducibility is measured through the use of control coupons whose corrosion films 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.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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 become familiar with all hazards including those identified in the appropriate Material Safety Data Sheet (MSDS) for this product/material as provided by the manufacturer, to establish appropriate safety and health practices, and determine the applicability of regulatory limitations prior to use. See 188.8.131.52.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
B542 Terminology Relating to Electrical Contacts and Their Use
B765 Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
B808 Test Method for Monitoring of Atmospheric Corrosion Chambers by Quartz Crystal Microbalances
B810 Test Method for Calibration of Atmospheric Corrosion Test Chambers by Change in Mass of Copper Coupons
B825 Test Method for Coulometric Reduction of Surface Films on Metallic Test Samples
B826 Test Method for Monitoring Atmospheric Corrosion Tests by Electrical Resistance Probes
B845 Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
D1193 Specification for Reagent Water
D2912 Test Method for Oxidant Content of the Atmosphere (Neutral Ki)
D2914 Test Methods for Sulfur Dioxide Content of the Atmosphere (West-Gaeke Method)
D3449 Test Method for Sulfur Dioxide in Workplace Atmospheres (Barium Perchlorate Method)
D3464 Test Method for Average Velocity in a Duct Using a Thermal Anemometer
D3609 Practice for Calibration Techniques Using Permeation Tubes
D3824 Test Methods for Continuous Measurement of Oxides of Nitrogen in the Ambient or Workplace Atmosphere by the Chemiluminescent Method
D4230 Test Method of Measuring Humidity with Cooled-Surface Condensation (Dew-Point) Hygrometer
E902 Practice for Checking the Operating Characteristics of X-Ray Photoelectron Spectrometers
G91 Practice for Monitoring Atmospheric SO2 Deposition Rate for Atmospheric Corrosivity Evaluation
ICS Number Code 71.100.20 (Gases for industrial application)
UNSPSC Code 41114604(Corrosion testers); 39121522(Electrical contacts)