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Cabinet testing refers to tests conducted in closed cabinets where the conditions of exposure are controlled and mostly designed to accelerate specific corrosion situations while trying to emulate as closely as possible the corrosion mechanisms at play. Cabinet tests are generally used to determine the corrosion performance of materials intended for use in natural atmospheres. In order to correlate test results with service performance, it is necessary to establish acceleration factors and to verify that the corrosion mechanisms are indeed following the same paths.
Modern surface analysis techniques can be quite useful to ascertain that the corrosion products have the same morphologies and crystallographic structures that are typically found on equipment used in service. There are basically four types of cabinet tests: (reference)
Controlled humidity test: there are fifteen ASTM standards relating different variations of creating and controlling fog and humidity in cabinets for corrosion testing of a broad spectrum of products, from decorative electrodeposited coatings to the evaluation of the corrosivity of solder fluxes for copper tubing systems. The basic humidity test is most commonly used to evaluate the corrosivity of materials or the effects of residual contaminants. Cyclic humidity tests are conducted to simulate exposure to high humidity and heat typical of tropical environments. The cabinet performing such tests should be equipped with a solid-state humidity sensor reading the current humidity condition and a feedback controller. The mechanism used to control the humidity moves chamber air via a blower motor and passes it over a heater coil in the bottom of the chamber with an atomizer nozzle fogging into this air stream.
Corrosive gas test: in these tests, controlled amounts of corrosive gases are added to humidity to replicate more severe environments. Some of these tests are designed to reveal and amplify certain characteristics of a material. The ASTM B775 (Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor) and B 799 (Test Method for Porosity in Gold or Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor) employ very high concentrations of corrosive gases to amplify the presence of pores in gold or palladium coatings. The moist sulfur dioxide test (ASTM G 87) is intended to produce corrosion in a form resembling that in industrial environments. A very sophisticated variation of these tests is the flowing of mixed gas test (ASTM B 827), that consists in introducing parts per billion levels of pollutants such as chlorine, hydrogen sulfide and nitrogen dioxide in a chamber at controlled temperature and humidity. This test is particularly adapted to the needs of the electronics industry.
Salt spray testing: the oldest and most wildly used cabinet test is ASTM B 117 (Test Method of Salt Spray [Fog] Testing), a test that introduces a spray in a closed chamber where some specimens are exposed at specific locations and angles. The concentration of the NaCl solution has ranged from 3.5 to 20%. There is a wide range of chamber designs and sizes including walk-in rooms that are capable of performing this test. Although used extensively for specification purposes, results from salt spray testing seldom correlate well with service performance. Hot, humid air is created by bubbling compressed air through a bubble (humidifying) tower containing hot deionized water. Salt solution is typically moved from a reservoir through a filter to the nozzle by a gravity-feed system. When the hot, humid air and the salt solution mix at the nozzle, it is atomized into a corrosive fog. This creates a 100% relative humidity condition in the exposure zone. For a low humidity state in the exposure zone of the chamber, air is forced into the exposure zone via a blower motor that directs air over the energized chamber heaters.
