ASTM D6376 Standard Test Method for Determination of Trace Metals in Petroleum Coke by Wavelength Dispersive X-ray Fluorescence Spectroscopy
7. Apparatus
7.1 Balance, capable of weighing 50 g +/- 0.01 g.
7.2 Hydraulic Press, capable of exerting a force of not less than 276 MPa (40 000 psi).
7.3 Mill or Grinder, capable of reducing 20 g of petroleum coke to a sample passing 75 µm (U.S. No. 200 mesh) in less than 10 min, without introducing contamination.
7.4 Mixer/Mill, for blending sample and binder.
7.5 Pellet Cup, Aluminum (optional), tapered to hold pressed pellets.
7.6 Pelletizing Die, for forming pellets of a diameter suitable for use in the spectrometer.
7.7 Sieves, 75 µm (U.S. No. 200 mesh) as specified in Specification E11.
7.8 Drying Oven, capable of maintaining a minimum temperature of 110 °C +/- 10 °C.
7.9 X-ray Spectrometer, equipped for soft X-ray detection of the K-alpha spectral lines for all of the elements determined by this test method. For increased sensitivity, this instrument shall be equipped with the following:
7.9.1 Analyzing Crystals - This choice is made based on the element to be determined. The crystal selected should yield optimal sensitivity with minimum interferences. The same crystal shall be used for both standards and unknowns. See Table 2 for recommended crystals.
7.9.2 Detector, suitable for the determination of elements in question. Choices include gas-flow proportional, sealed proportional, and scintillation detectors.
7.9.3 Optical Path, in a vacuum.
7.9.4 Pulse-Height Analyzer, or other means of energy discrimination.
7.9.5 Suitable X-ray Tube - Chromium, molybdenum, platinum, rhodium, or tungsten target and dual targets have been found suitable. The scandium tube is very advantageous for light elements.
8. Reagents and Materials
8.1 Purity of Reagents - Reagent grade chemicals shall be used 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. Other grades may be used, provided they are of sufficiently high purity to permit use without diminishing the accuracy of the determination.
8.2 Detector Gas - P-10 gas (90 % argon, 10 % methane) is used with gas-flow proportional detectors.
8.3 Pellet Binder Material - Stearic acid, or other suitable binder, providing no spectral interferences shall be used.
8.4 Reference Samples, of petroleum coke bracketing the element ranges of the analytical samples. Commercial reference samples of this type are available from several sources.
