X-ray powder diffraction is a fast method for determining the average size of crystallites. The crystallinity of petroleum coke (expressed as Lc value) is a measure of quality affecting suitability for the end use of the coke, and is a function of the heat treatment of the coke. The ASTM norm D 5187 describes how to obtain the crystallinity of coke by evaluating the shape of a carbon X-ray peak. This peak is scanned over a wide range and the Lc value calculated from the full width of the X-ray peak at half maximum intensity.
A coke powder specimen was prepared according to ASTM D 5187 and measured with the D2 PHASER. Experimental details are summarized in Table 1. Figure 1 shows a typical diffraction scan from petroleum coke. After automatic subtraction of the base line, DIFFRAC.EVA estimates the crystallite size by means of the Scherrer equation from the full width of the peak at half maximum.
Table 1. Experimental settings.
|D2 PHASER, LYNXEYE detector
|Cu radiation (30 kV, 10 mA), Ni filter
|Continuous scan from 14.0 to 38.0° 2Theta
Step width 0.01°
counting time 0.1 sec per step
|Total scan time about 30 sec.
|2.5° Soller collimators, 1.0 mm divergence slit,
|LYNXEYE detector opening 5° 2Theta
Figure 1. Determination of the full width at half maximum of the 002 peak of petroleum coke using DIFFRAC.EVA. The software evaluates the peak shape and automatically calculates the crystallites size (36.5 Å) using the Scherrer equation.
The data presented in figure 1 exceeds the maximum peak intensity (in cps) shown in ASTM D 5187 by a factor of 50. Notably, this data was collected in less than 1 min, compared to 20 min mentioned in the norm. The 1-dimensional LYNXEYE detector makes this intensity and speed gain possible, even for a low powered XRD system.
To conclude, our cost-effective desktop XRD system D2 PHASER allows for extremely fast and precise quality control of anode coke material.
This information has been sourced, reviewed and adapted from materials provided by Bruker X-Ray Analysis.
For more information on this source, please visit Bruker X-Ray Analysis.