ASTM D943 method for oxidation characteristics of inhibited mineral oils
5. Apparatus
5.1 Oxidation Cell, of borosilicate glass, as shown in Fig. 1, consisting of a test tube, condenser, and oxygen delivery tube. The test tube has a calibration line at 300 mL (maximum error 1 mL). This calibration applies to the test tube alone at 20°C.
5.2 Heating Bath, thermostatically controlled, capable of maintaining the oil sample in the oxidation cell at a temperature of 95 +/- 0.2°C, fitted with a suitable stirring device to provide a uniform temperature throughout the bath, and large enough to hold the desired number of oxidation cells immersed in the heating bath to a depth of 390 +/- 10 mm and in the heating liquid itself to a depth of 355 +/- 10 mm.
5.2.1 Studies have suggested that direct sunlight or artificial light may adversely influence the results of this test. To minimize effects of light exposure on the lubricant being tested, light shall be excluded from the lubricant by one or more of the following ways:
5.2.1.1 Use of heated liquid baths that are designed and constructed of metal, or combinations of metals and other suitable opaque materials, that prevent light from entering the test cell from the sides is preferred. If a viewing window is included in the design, this viewing window shall be fitted with a suitable opaque cover and be kept closed when no observation is being made.
5.2.1.2 If glass heating baths are used, the bath shall be wrapped with aluminum foil or other opaque material.
5.2.1.3 Bright light entering the test cell from directly overhead can be eliminated by use of an opaque shield.
5.3 Flowmeter, with a capacity of at least 3 L of oxygen/h, and an accuracy of +/- 0.1 L/h.
5.4 Heating Bath Thermometer - ASTM Solvents Distillation Thermometer having a range from 72 to 126°C, and conforming to the requirements for Thermometer 40C as prescribed in Specification E 1, or for Thermometer 70C as prescribed in Specifications for IP Standard Thermometers. Alternatively, temperature–measuring devices of equal or better accuracy may be used.
5.5 Oxidation Cell Thermometer, having a range from 80 to 100°C, graduated in 0.1°C, total length - 250 mm, stem diameter - 6.0 to 7.0 mm, calibrated for 76-mm immersion. Alternatively, temperature–measuring devices of equal or better accuracy may be used.
5.6 Thermometer Bracket, for holding the oxidation cell thermometer, of 18-8 stainless steel, having the dimensions shown in Fig. 2. The thermometer is held in the bracket by two fluoroelastomer O-rings of approximately 5 mm inside diameter. Alternatively, thin stainless steel wire may be used.
5.7 Wire Coiling Mandrel, as shown in Fig. 3.
5.8 Abrasive Cloth, silicon carbide, 100-grit with cloth backing.
5.9 Syringes, glass, with Luer-Lok locking connectors, 10 and 50-mL capacities for sampling, and water additions, respectively.
5.10 Syringe Sampling Tube, Grade 304 stainless steel tubing, 2.11 mm (0.083 in.) in outside diameter, 1.60 mm (0.063 in.) in inside diameter, 559 +/- 2 mm (24.0 +/- 0.08 in.) long, with one end finished at 90° and the other end fitted with a Luer-Lok female connector. The Luer-Lok connector is preferably of elastomeric material, such as polyfluorovinyl-chloride to provide a good seal with the syringe.
5.11 Stopper, for Luer fitting of syringe sampling tube, made of polytetrafluoroethylene or polyfluorovinylchloride.
5.12 Sampling Tube Holder, for supporting the syringe sampling tube, made of methyl methacrylate resin, having the dimensions shown in Fig. 4.
5.13 Sampling Tube Spacer, for positioning the end of the sampling tube above the sampling tube holder, made of a length of plastic tubing polyvinyl chloride, polyethylene, polypropylene, or polytetrafluoroethylene having an inside diameter of approximately 3 mm (1/8 in.) and 51 +/- 1 mm (2.0 +/- 0.04 in.) length.
5.14 Flexible Tubing, polyvinyl chloride approximately 6.4 mm (1/4 in.) in inside diameter with a (3/32-in.) wall for delivery of oxygen to the oxidation cell.
6. Reagents and Materials
6.1 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean reagent water as defined by Type II of Specification D1193.
6.2 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
6.3 Acetone, reagent grade.(Warning - Health hazard; flammable.)
6.4 Catalyst Wires:
6.4.1 Low-Metalloid Steel Wire, 1.59 mm (0.0625 in.) in diameter (No. 16 Washburn and Moen Gage).
6.4.2 Electrolytic Copper Wire, 1.63 mm (0.064 in.) in diameter (No. 16 Imperial Standard Wire Gage or No. 14 American Wire Gage), 99.9 % purity, conforming to Specification B 1. Soft copper wire of an equivalent grade may also be used.
NOTE 2 - Alternatively, suitably prepared catalyst coils may be purchased from a supplier.
6.5 Detergent, water-soluble.
6.6 n-Heptane, reagent grade. (Warning - Flammable. Harmful if inhaled.)
6.7 Hydrochloric Acid, concentrated [36 mass % (relative density 1.19)]. (Warning - Toxic and corrosive.)
6.8 Isopropyl Alcohol, reagent grade. (Warning - Flammable.)
6.9 Oxygen, 99.5 % minimum purity, with pressure regulation adequate to maintain a constant flow of gas through the apparatus. The use of a two-stage pressure regulator on tank oxygen is recommended. (Warning - Vigorously accelerates combustion.)
6.10 Cleaning Reagent, cleaning by a 24–h soak at room temperature either in Nochromix (Warning - Corrosive. Health Hazard.) or in Micro solution.
7. Sampling
7.1 Samples for this test can come from tanks, drums, small containers, or even operating equipment. Therefore, use the applicable apparatus and techniques described in Practice D4057.
7.2 For one single determination the minimum required sample size is 300 mL.
