ASTM D7667 Standard Test Method for Determination of Corrosiveness to Silver by Automotive Spark-Ignition Engine Fuel - Thin Silver Strip Method
6. Apparatus
6.1 Silver Strip Corrosion Pressure Vessel (Procedure A), constructed from stainless steel according to dimensions given in Fig. 1, as described in Test Method D130. The vessel shall be capable of withstanding a test pressure of 700 kPa (100 psi). Alternative designs for the vessel's cap and synthetic rubber gasket may be used provided that the internal dimensions of the vessel are the same as shown in Fig. 1, which allow a nominal 25 mm by 150 mm (1 in. by 6 in.) test tube (see 6.2) and the SSCD (see 6.4) to be placed inside the pressure vessel.
6.2 Test Tubes, of borosilicate glass of nominal 25 mm by 150 mm (1 in. by 6 in.) dimensions, preferably graduated at 30 mL volume. The internal dimensions shall be checked as acceptable by use of a silver strip (see 7.4). When 30 mL of sample is added to the test tube with the silver strip in it, a minimum of 5 mm of liquid shall be above the top surface of the strip.
6.3 Test Bath, General, whether liquid or solid, the test bath shall be able to maintain the test temperature to within +/- 1 °C (2 °F) of the required test temperature. It is recommended that baths be placed inside a fume-hood.
6.3.1 Bath, shall be fitted with suitable supports to hold each test tube (see 6.2) in a vertical position to a depth of about 100 mm (4 in.) as measured from the bottom of the test tube to the bath surface.
6.3.2 Bath Medium, as a liquid bath medium, both water and oil have been found to be satisfactory and controllable at the specified test temperature and duration required by the test procedure.
6.3.3 Solid Block Bath, made of aluminum, shall meet the test temperature control, test duration, and immersion conditions required by the test procedure, and shall be verified, at least annually, for temperature measurement (heat transfer) by running tests on tubes filled with 30 mL of product plus a thin silver strip of the given nominal dimensions, plus a temperature sensor.
6.3.3.1 Wells provided in the solid block bath to accommodate pressure vessels (see Fig. 1) shall be of the following dimensions: ~54 mm (2 1/8 in.) diameter from top, up to a depth of ~70 mm (2 3/4 in.) continuing with an opening of ~38 mm (1 1/2 in.) diameter up to a depth of ~140 mm (5 1/2 in.). An opening of ~8 mm (5/16 in.) diameter by ~210 mm (8 1/4 in.) depth shall be provided in the center of the block for immersion of a metal temperature sensor (connected to a suitable 50 °C +/- 1°C (122 °F +/- 2 °F) temperature controller), or thermometer (see 6.5).
6.3.3.2 Wells provided in the solid block bath to accommodate test tubes shall be of the following dimensions: ~20 mm (1 1/16 in.) diameter by ~140 mm (5 1/2 in.) deep. An opening of ~8 mm (5/16 in.) diameter by ~210 mm (8 1/4 in.) depth shall be provided in the center of the block for immersion of a metal temperature sensor (connected to a suitable 50 °C +/- 1 °C (122 °F +/- 2 °F) temperature controller), or thermometer (see 6.5).
6.3.3.3 Provide insulation made of ~25.4 mm (1.0 in.) thick fiberglass with aluminum backing (or, similar insulation) to cover all the four sides of the solid block bath.
6.4 Silver Strip Centering Device (SSCD), made of material which is gasoline-compatible at 50 °C (122 °F) for the duration of the test, such as Acetal Resin, White Nylon 6/6, or PTFE. See details in A1.1(Assembly View) and A1.2 (Individual Parts View). Length of SSCD inside the test tube is such that the lower edge of the assembled silver strip is about 22 mm (7/8 in.) from the bottom of the test tube.
6.5 Temperature Sensing and Monitoring Device (TSMD), capable of sensing and monitoring the desired test temperature in the bath to within an accuracy of +/- 1 °C (2 °F). The ASTM 12C (12F) (see Specification E1) or IP 64C (64F) total immersion thermometer has been found suitable for use in the test. If used, no more than 10 mm (0.4 in.) of the mercury shall extend above the surface of the bath at the test temperature.
6.6 Timing Device, electronic or manual, capable of accurately measuring the test duration within the allowable tolerance.
6.7 Forceps, with inert tips, stainless steel or polytetrafluoroethylene (PTFE) tips, have been found suitable for use in handling the silver strips.
6.8 Polishing Board, 150 mm by 100 mm by 3 mm (6 in. by 4 in. by 1/8 in.) solid plastic piece having a smooth surface, for placement of silver strip during polishing.
6.9 Optional Equipment:
6.9.1 Refrigerator, for cooling samples below 5 °C (41 °F) during storage.
7. Reagents and Materials
7.1 Wash Solvent, 2,2,4-trimethylpentane (iso-octane) of minimum 99.75 % purity. (Warning - Extremely flammable, see 8.1.)
7.2 Surface Preparation/Polishing Material, Scouring-pad, approximately 400 grit, made of polyester material that is free of detergents or spongy material, containing aluminum oxide as a scouring-aid.
NOTE 1 - Some 400-grit pads are commercially available in the form of 229 mm by 152 mm by 9.5 mm (9 in. by 6 in. by 3/8 in.) thick pads. For ease of handling and polishing, it is recommended that the pads be cut so that the dimensions of the scouring-pads are about 114 mm by 38 mm by 9.5 mm (4 1/2 in. by 1 1/2 in. by 3/8 in.).
7.3 Waterproof Aluminum Oxide Cloth Sanding Sheets or Rolls, 150-grit.
7.4 Silver Strips, Use strips 36.0 mm to 40.0 mm (1 7/16 in. to 1 9/16 in.) long, 6.25 mm to 6.35 mm ( 15/64 in. to 1/4 in.) wide and 0.526 mm to 0.541 mm (~1.35/64 in.) thick, assaying at 99.9 % (m/m) Ag minimum. 10,6 When necessary, cut, straight and smooth, using a sharp tin-snip or any other metal-cutting device, (such as a heavy-duty ~152 mm (6 in.) shear) approximately 38.0 mm (1 1/2 in.) long strips from the longer strips supplied. Strips may be used repeatedly, but should be discarded when the original shape becomes deformed, or surface shows pitting, scratches or tarnish that cannot be removed by the specified polishing procedure.
7.5 Ashless Filter Paper or Disposable Gloves or Finger-Tip Protectors, for use in protecting the silver strip from coming in contact with the individual during polishing.
8. Hazards
8.1 Wash Solvent. (Warning - iso-octane: Harmful if inhaled. Vapors may cause flash fire. Keep away from heat, sparks and open flames, and container closed. Use with adequate ventilation. Avoid build-up of vapors and eliminate all sources of ignition, especially non-explosion-proof electrical apparatus and heaters. Avoid prolonged breathing of vapor or spray mist.)
8.2 Gasoline, (Unleaded or Leaded). (Warning - Keep away from heat, sparks and open flames, and container closed. Use with adequate ventilation. Avoid build-up of vapors and eliminate all sources of ignition, especially non-explosion-proof electrical apparatus and heaters. Avoid prolonged breathing of vapor or spray mist. Avoid prolonged or repeated skin contact.)
8.3 Pressure Vessel, heat and pressure will be built-up in the pressure vessel during the test. After the test, cool and depressurize pressure vessel carefully and fully before opening it for inspection of the silver strip.
