ASTM D4308 Test Method for Electrical Conductivity of Liquid Hydrocarbons by Precision Meter
6. Apparatus
6.1 Conductivity Apparatus - Components of the dc conductivity apparatus are shown in Fig. 1.
6.1.1 The conductivity cell shown in Fig. 1 consists of an inner electrode and an outer electrode separated by an insulator. The outer electrode and cap provide a ground path and electrostatic (Faraday) shield.
6.1.2 The electrometer shown in Fig. 1 contains a battery which supplies a voltage to the cell and a bridge circuit which senses the flow of current and converts the output signal directly into conductivity units, that is, pS/m. A pushbutton selector allows selection of zero reading, calibration, and four range selections.
6.1.3 The cell and electrometer are connected by a triaxial cable as shown in Fig. 1.
6.2 Thermometer, general purpose type, having a range of 0 to 60°C (see Specification E1). Temperature measuring devices that cover the temperature range of interest, such as an ASTM 1C thermometer, or liquid-in-glass thermometers, thermocouples, or platinum resistance thermometers that provide equivalent or better accuracy and precision than ASTM 1C thermometers may be used.
7. Reagents
7.1 Cleaning Solvent, The following may be used:
7.1.1 Toluene-Isopropyl Alcohol Mixture - (Warning - Flammable. Vapor harmful. See Annex A1.1.) Mix two volumes of toluene and three volumes of isopropyl alcohol both of reagent grade and distill. Discard the first 20 % and last 5 % fractions.
7.2 n-Heptane - (Warning - Flammable. Harmful if inhaled. See Annex A1.2.) Prepare by percolating ASTM reference fuel grade n-heptane through silica gel as follows:
7.2.1 Activate approximately 2000 g of 100 to 200 mesh silica gel by heating at 180°C for 24 h. Allow it to cool in a desiccator under nitrogen or in vacuum. Soak approximately 0.5 g of glass wool for 24 h in clean n-heptane.
7.2.2 Take a tube of borosilicate glass having an inside diameter of 60 to 70 mm, a length 1500 mm, with a conically shaped lower end provided with a glass cock. Place a perforated porcelain disk (diameter 25 mm) in the lower end of the tube and put the soaked glass wool on top of the disk. Fill the tube with the activated silica gel while tapping to achieve homogeneous filling. The silica gel layer will be approximately 1250 mm high. Wrap the column in black paper to exclude light.
7.2.3 Percolate n-heptane through the column at a rate of about 2 to 3 L/h. Discard the first 3 L. Never allow the column to run dry. The silica gel charge is sufficient for the percolation of 1000 L of n-heptane, provided the conductivity of the untreated n-heptane is below 1 pS/m.
NOTE 2 - If the conductivity of the n-heptane after treatment, measured in accordance with Section 11 in a thoroughly cleaned cell, is higher than 0.1 pS/m, the treatment should be repeated.
7.3 Hydrocarbon, for calibration. The dielectric constant must be known to +/- 5 % at the temperature of calibration.
8. Sampling
8.1 The sample volume should be at least 0.7 L.
8.2 Use a clean epoxy-lined can, or a new glass bottle that has been rinsed successively with hot water, distilled water, acetone, and cleaning solvent then flush with dry nitrogen. Use only non-contaminating caps.
NOTE 3 - Test method results are known to be sensitive to trace contamination from sampling containers. For recommended sampling containers refer to Practice D4306.
NOTE 4 - Bottle samples should be tested immediately, since the glass surface tends to absorb from the fuel the conductive substances that the test method is intended to measure.
8.3 Rinse the container at least three times with portions of the hydrocarbon liquid to be sampled. (When testing diesel or aviation turbine fuels Jet A or A-1, Warning - Combustible. Vapor harmful. See Annex A1.3.) (When testing gasoline, aviation gasoline, or aviation turbine fuel Jet B, Warning - Extremely flammable. Harmful if inhaled. Vapors can cause flash fire. See Annex A1.4.) If possible, fill the container, let stand, then empty and refill. Avoid taking the sample for test by pouring from the container; pipet instead. The sample should be clean and bright when tested.
