ASTM D1934 method for Oxidative Aging of Electrical Insulating Petroleum Oils
ASTM D1934 Standard Test Method for Oxidative Aging of Electrical Insulating Petroleum Oils by Open-Beaker Method
6. Apparatus
6.1 Oven, electrically heated, thermostatically controlled, capable of maintaining a constant temperature of 115 more or less 1°C (239 more or less 2°F). Use an oven with a testing chamber large enough to test the anticipated number of test specimens at one time. A uniformity of temperature within more or less 1 % of the differential between oven and ambient temperatures is required. (See Note 1.) Circulate air in the chamber with a low velocity fan during the aging period. The volume and condition of the circulated air is not considered to be critical. It is recommended that the oven provide several air changes per hour, and that vapors and fumes be removed if present.
NOTE 1 - Refer to Specification E 145 for the measurement of the temperature uniformity of the oven.
6.1.1 Procedure A - For test specimens aged in the absence of a metal catalyst the choice of a suitable oven design is not critical. Either fixed- or rotating-shelf stage ovens of satisfactory thermal quality may be used, although a rotating-shelf oven is preferred. If a fixed-shelf oven is used, it is recommended that test specimen positions within the oven be changed periodically (for example, at daily intervals) to minimize the effects of any temperature differentials that may exist.
6.1.2 Procedure B - When a metal catalyst, such as copper, is used, the rate of oxidation usually is increased, and the procedure becomes sensitive to movement of the oil past the metal surface. An aging oven equipped with a slowly rotating shelf has been adopted for uniformity when a metal catalyst is used. Other oven designs having satisfactory thermal quality and a rotating shelf may be used.
6.2 Beaker, borosilicate glass, low-form, of 400-mL capacity. The approximate dimensions of a suitable beaker are 100 mm in depth and 70 mm inside diameter. Clean the beakers used in the aging test, and thoroughly dry before use. One recommended cleaning procedure is as follows: Remove residual oil from the beaker by rinsing in mineral spirits or equivalent. Rinse thoroughly with an acid cleaning solution consisting of 3 parts nitric acid (HNO3) to 1 part sulfuric acid (H2SO4). Remove traces of cleaning solution by carefully rinsing with distilled water followed by rinsing in acetone and air drying.
7. Reagents and Materials
7.1 Purity of Reagents - Use reagent grade chemicals in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available.
7.2 Hydrochloric Acid, 10 % volume solution from concentrated hydrochloric acid.
7.3 Nitric Acid - Concentrated nitric acid (HNO3).
7.4 Sulfuric Acid - Concentrated sulfuric acid (H2SO4).
7.5 Metal Catalyst with 15 cm2 of clean surface available for exposure to the oil for use in Procedure B. If the metal catalyst is copper wire, it is convenient to wind an appropriate length into a loose hank which is then cleaned to remove oil, oxide, and the other extraneous matter. The metal catalyst may also be used in the form of strips, but the strips require special attention to maintain the desired amount of exposed surface. One good method of cleaning copper hanks is to immerse the hank for 30 s in a 10 % solution of hydrochloric acid (HCl), after which the hank is rinsed three times in distilled water then in acetone and air dried. The cleaned hank should be handled with clean tongs.
