ASTM D6376 Standard Test Method for Determination of Trace Metals in Petroleum Coke by Wavelength Dispersive X-ray Fluorescence Spectroscopy
4. Summary of Test Method
4.1 A representative sample of petroleum coke is dried to constant mass at 110 °C +/- 10 °C and then crushed to pass a 75 µm (U.S. No. 200 mesh) sieve. A weighed portion of this analytical sample is mixed with stearic acid, or other suitable binder, and then milled and compressed into a small, smooth pellet suitable for analysis. The pellet is irradiated by an X-ray beam. The characteristic X rays of the elements analyzed are excited, separated, and detected by the wavelength-dispersive X-ray spectrometer. These measured X-ray intensities are converted to elemental concentration through the use of a calibration equation derived from analyses of standard materials. This calibration equation defines the sensitivity and background associated with a particular X-ray spectrometer.
4.2 The K-alpha spectral lines are used for all of the elements determined by this test method.
5. Significance and Use
5.1 The presence and concentration of sulfur and various metallic elements in a petroleum coke are major factors determining the suitability of a coke for various purposes. This test method provides rapid means for measuring sulfur and commercially important metallic elements in coke samples.
5.2 This test method provides a guide for determining conformance to material specifications for use by buyers and sellers in a commercial transfer of petroleum coke.
5.3 Sulfur contents can be used to evaluate the potential formation of sulfur oxides (SOx), a source of atmospheric pollution.
6. Interferences
6.1 Review all potential spectral interferences for the elements listed in Table 2. Follow your manufacturer's operating guide to develop and apply alphas to compensate for these interferences.
6.2 Compensate for inter-element effects by using alphas as part of the regression procedure provided with spectrometer software.
6.3 Changes in the sulfur concentration in the sample affects analyte X-ray intensities. Therefore, determine the magnitude of the sulfur effect on each metallic element and apply in appropriate correction.
