ASTM D4048 test method for detection of copper corrosion from lubricating grease
6. Apparatus
6.1 Test Jars - Cloud and pour jars, cylindrical jars of clear glass with flat bottoms, 30 mm to 33.5-mm (1 3/16 in. to 1 5/16 in.) inside diameter, and 115 mm to 125 mm (4 1/2 in. to 5 in.) in height as described in Test Methods D97 and D2500.
6.2 Test Jar Covers - Beakers, 50-mL; borosilicate glass, approximately 40 mm (1.6 in.) by 50 mm (2.0 in.) suitable for covering individual test jars. Small porcelain or glazed silica crucibles or crucible covers or watch glasses or vented corks that lightly cover the test jars, allowing pressure equalization between the inside and outside of the jars, yet minimizing exposure of the inside of the jars to foreign vapors present in the oven will also be satisfactory.
6.3 Oven - A circulating air oven or liquid bath capable of maintaining a temperature of 100 more or less 1°C (212 more or less 2°F) or other desired temperatures with the same precision.
6.4 Polishing Vise - For holding the copper strip firmly without marring the edges while polishing. Any convenient type of holder (see Appendix X1 of Test Method D130) may be used, provided that the strip is held tightly and that the surface of the strip being polished is supported above the surface of the holder.
6.5 Viewing Test Tubes - Flat glass test tubes may be used to protect corroded strips for close inspection or storage. (See the Appendix X1 of Test Method D130.)
6.6 Copper Strip Corrosion Standard - consists of reproductions in color of typical strips representing degrees of tarnish and corrosion, the reproductions being encased in plastic in the form of a plaque.
6.6.1 Keep the plastic-encased printed Copper Strip Corrosion Standard protected from light to avoid the possibility of fading. Inspect for fading by comparing two different plaques, one of which has been carefully protected from light (new). Observe both sets in diffused daylight (or equivalent), first from a point directly above and then from an angle of approximately 45°. If any evidence of fading is observed, particularly at the left end of the plaque, it is suggested that the one that is the more faded with respect to the other be discarded.
6.6.1.1 Alternatively, place a 20-mm (3/4 in.) opaque strip (masking tape) across the top of the colored portion of the plaque when initially purchased. At intervals, remove the opaque strip and observe. If there is any evidence of fading of the exposed portion, it is suggested that the standard be replaced.
6.6.1.2 These plaques are full-color productions of typical strips. They have been printed on aluminum sheets by a four-color process and are encased in plastic for protection. Directions for their use are given on the reverse side of each plaque.
6.6.2 If the surface of the plastic cover shows excessive scratching, it is suggested that the plaque be replaced.
7. Reagents and Materials
7.1 Acetone - American Chemical Society Reagent Grade acetone is suitable. (Warning - Extremely flammable. Harmful if inhaled. Vapors may cause flash fires.)
7.2 Copper Strips - Use strips 12.5 more or less 2 mm (1/2 more or less 1/16 in.) wide, 1.5 to 3.0 mm (1/16 to 1/8 in.) thick, cut 75 more or less 5 mm (3 more or less 1/4 in.) long from smooth-surfaced, hard-temper, cold-finished copper of 99.9 + % purity; electrical bus bar stock is generally suitable. (See Appendix X1 of Test Method D130.) The strips may be used repeatedly but should be discarded when the surfaces become deformed on handling.
7.3 Polishing Materials - Silicon carbide grit paper of varying degrees of fineness, including 65-µm (240-grit) paper or cloth, also a supply of 105-µm (150-mesh) silicon carbide grain and absorbent cotton (cotton wool).
7.4 Wash Solvent - Volatile, sulfur-free hydrocarbon solvent may be used provided that it shows no tarnish at all when tested at 50 more or less 1°C (or 122 more or less 2°F). Knock test-grade isooctane (Warning - see 8.1.2) or American Chemical Society Reagent Grade n-heptane (Warning - see 7.1) are suitable solvents. Because of possible toxic effects, the use of benzene should be avoided.
8. Preparation of Strip
8.1 Mechanical Cleaning of Strips:
8.1.1 Surface Preparation - Remove all surface blemishes from all six sides of the strip with silicon carbide paper of such degrees of fineness as are needed to accomplish the desired results efficiently. Finish with 65-µm (240-grit) silicon carbide paper or cloth, removing all marks that may have been made by other grades of paper used previously. Immerse the strip in wash solvent (Warning - see 7.1.) from which it can be withdrawn immediately for final polishing or in which it can be stored for future use.
8.1.1.1 As a practical manual procedure for surface preparation, place a sheet of the paper on a flat surface, moisten it with wash solvent, and rub the strip against the paper with a rotary motion, protecting the strip from contact with the fingers or by wearing impervious gloves (see Note 1). Alternatively, the surface of the strip may be prepared by use of motor-driven machines using appropriate grades of dry paper or cloth.
NOTE 1 - Disposable polyethylene is one type of glove that has been found to be satisfactory. However, any type of glove that is impervious to the reagents and materials used in this test method, while preventing fingers from contacting the strip directly, may also be used.
8.1.2 Final Polishing - Remove strip from the wash solvent. Holding it in the fingers protected with the ashless filter paper, polish first the ends and then the sides with the 105-µm (150-mesh) silicon carbide grains picked up from a clean glass plate with a pad of cotton (cotton wool) moistened with a drop of wash solvent. Wipe vigorously with fresh pads of cotton (cotton wool) and subsequently handle only when wearing impervious gloves (see Note 1) or with stainless steel forceps; do not touch with naked fingers. Clamp the strip in a vise, and polish the main surfaces with silicon-carbide grains on absorbent cotton. Rub in the direction of the long axis of the strip, carrying the stroke beyond the end of the strip before reversing the direction. Clean all metal dust from the strip before reversing the direction. Clean all metal dust from the strip by rubbing vigorously with clean pads of absorbent cotton until a fresh pad remains unsoiled. When the strip is clean, immediately immerse it in the prepared sample. (Warning - Forceps can scratch copper, affecting the results.)
8.1.2.1 It is important to polish the whole surface of the strip uniformly to obtain a uniformly stained strip. If the edges show wear (surface elliptical), they will likely show more corrosion than the center. The use of a vise will facilitate uniform polishing.
