ASTM B825-13
在金属试样上表面薄膜的电量滴定减少的标准试验方法

Standard Test Method for Coulometric Reduction of Surface Films on Metallic Test Samples

被代替

标准号

ASTM B825-13

发布

2013年

发布单位

美国材料与试验协会

替代标准

ASTM B825-19

当前最新

ASTM B825-19

 

 

引用标准

ASTM B808 ASTM B809 ASTM B810 ASTM B827 ASTM D1193

适用范围

4.1 The present trend in environmental testing of materials with electrically conductive surfaces is to produce, under accelerated laboratory conditions, corrosion and film-forming reactions that are similar to those that cause failures in service environments. In many of these procedures the parts under test are exposed for days or weeks to controlled quantities of both water vapor and pollutant gases, which may be present in extremely dilute concentrations.

Note 2—Descriptions of such tests can be found in Practice B827.

4.2 Many of these environmental test methods require monitoring of the conditions within the chamber during the test in order to confirm that the intended environmentally related reactions are actually taking place. The most common type of monitor consists of copper, silver, or other thin metallic coupons of a few square centimeters that are placed within the test chamber and that react with the corrosive environment in much the same way as the significant surfaces of the parts under test.

4.3 In practice, a minimum number of control coupons are placed in each specified location (see Test Method B810) within the chamber for a specified exposure time, depending upon the severity of the test environment. At the end of this time interval, the metal samples are removed and analyzed by the coulometric reduction procedure.

4.4 Other corrosion film evaluation techniques for metallic coupons are also available. The most common of these is mass gain, which is nondestructive to the surface films, but is limited to the determination of the total amount of additional mass acquired by the metal as a result of the environmental attack. The most common is weighing using high performance microbalances or for purposes of real-time monitoring, quartz crystal microbalances (see Specification B808).

Note 3—Detailed instructions for conducting such weighings, as well as coupon cleaning and surface preparation procedures, are included as part of Test Method B810.

Note 4—Some surface analytical techniques (such as X-ray methods) can provide nondestructive identification of some compounds in the films, but such methods, for example, X-ray diffraction, can miss amorphous compounds and compounds present in quantities less than 58201;% of the tarnish film volume.

4.5 With the coulometric technique, it is possible to resolve the complex total film into a number of individual components (Fig. 1) so that comparisons can be made. This resolving power provides a fingerprint capability for identifying significant deviations from intended ......

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