Advanced Certificate in Powder Diffraction On the Web - Assignment 4 - Kennedy Miller

The three powder diffraction patterns were identified as Calcite (Calcium carbonate), Magnetite (Magnesium carbonate) and a-Quartz (Silicon Dioxide). From the original set of data, intensities of the expected signals were subtracted from the relevant d-spacings: The first three columns down the left are the original data Columns 4 and 5 are the d-spacings and Intensities assigned to calcite and as provided on Data Card 5-586. Column 6 represents the remaining d-spacing that have not been assigned and column 7 shows the relevant Intensity ratios. Column 8 Ratios the highest intensity peak to 100 and the remaining intensities are ratioed to the same value. I.e. The highest intensity unassigned was a d-spacing of 3.343Å and a % ratio of 82. This was multiplied by 100/82 to produce a % ratio of 100. All the remaining ratio were multiplied by the same factor and rounded up/down to the nearest relevant figure. The three highest intensity peaks were identified (bold figures in column 6) and these were searched for in the ICCD-PDF manual.

Peaks from Original spectra     Peaks assigned to calcite   Remaining peaks    
1 2 3 4 5 6 7 8
d I FWHM D I D I Ratioed I
4.27 28 0.27 0 0 4.27 28 35.0
3.86 12 0.3 3.86 12 0 0 0.0
3.343 82 0.25 0 0 3.343 82 100.0
3.035 100 0.28 3.035 100 0 0 0.0
2.845 3 0.28 2.845 3 0 0 0.0
2.742 12 0.35 0 0 2.742 12 15.0
2.503 2 0.36 0 0 2.503 2 2.5
2.495 15 0.28 2.495 15 0 0 0.0
2.458 10 0.22 0 0 2.458 10 12.0
2.284 29 0.43 2.284 18 2.284 11 12.0
2.237 4 0.23 0 0 2.237 4 6.0
2.128 8 0.23 0 0 2.128 8 9.0
2.102 6 0.35 0 0 2.102 6 7.0
2.095 18 0.27 2.095 18 0 0 0.0
1.98 4 0.23 0 0 1.98 4 6.0
1.939 2 0.37 0 0 1.939 2 2.5
1.927 5 0.29 1.927 5 0 0 0.0
1.913 17 0.28 1.913 17 0 0 0.0
1.875 17 0.28 1.875 17 0 0 0.0
1.817 15 0.22 0 0 1.817 15 17.0
1.7 5 0.35 0 0 1.7 5 6.0
1.672 6 0.23 0 0 1.672 6 7.0
1.659 2 0.24 0 0 1.659 2 3.0
1.626 4 0.29 1.626 4 0 0 0.0
1.604 8 0.28 1.604 8 0 0 0.0
1.587 2 0.29 1.587 2 0 0 0.0
1.541 12 0.23 0 0 1.541 12 15.0
1.525 5 0.28 1.525 5 0 0 0.0
1.518 4 0.3 1.518 4 0 0 0.0
1.51 4 0.42 1.51 3 1.51 1 1.0


Comment: This is all correct and well set out. The anomalous intensities/FWHMs might be pointed out.
3.5 Marks

The best solution was identified as Data Card 5-490. This returned the data card for silicon dioxide (a-Quartz). The d-spacings associated with this data card were checked against the spacings from the original data. All the d-spacings down to 1.500Å were accounted for


Comment: A correct solution and search logic. The weakest lines in the database were not evident but this is not unreasonable (see model answer).
7 Marks

and the same process as the first data card was followed using the newly calculated ratio's. The same logic as the first data card has been applied here except the ratioed intensities have been used. The first three columns down the left are the original data and the fourth is the ratioed Intensities from the first calculation Columns 5 and 6 are the d-spacings and Intensities assigned to a-quartz and as provided on Data Card 5-586. Column 7 represents the remaining d-spacing that have not been assigned and column 8 shows the relevant Intensity ratios. Column 9 Ratios the highest intensity peak to 100 and the remaining intensities are ratioed to the same value. i.e. The highest intensity unassigned was a d-spacing of 2.742Å and a % ratio of 15. This was multiplied by 100/15 to produce a % ratio of 100. All the remaining ratio were multiplied by the same factor and rounded up/down to the nearest relevant figure. The three highest intensity peaks were identified (bold figures in column 7) and these were searched for in the ICCD-PDF manual.

Peaks from Original spectra       Peaks assigned to quartz   Remaining peaks    
1 2 3 4 5 6 7 8 9
d I FWHM Ratioed I D I D I Ratioed I
4.27 28 0.27 35.0 4.27 35 0 0.0 0.0
3.86 12 0.3 0.0 0 0 0 0.0 0.0
3.343 82 0.25 100.0 3.343 100 0 0.0 0.0
3.035 100 0.28 0.0 0 0 0 0.0 0.0
2.845 3 0.28 0.0 0 0 0 0.0 0.0
2.742 12 0.35 15.0 0 0 2.742 15.0 100.0
2.503 2 0.36 2.5 0 0 2.503 2.5 18.0
2.495 15 0.28 0.0 0 0 0 0.0 0.0
2.458 10 0.22 12.0 2.458 12 0 0.0 0.0
2.284 29 0.43 12.0 2.282 12 0 0.0 0.0
2.237 4 0.23 6.0 2.237 6 0 0.0 0.0
2.128 8 0.23 9.0 2.128 9 0 0.0 0.0
2.102 6 0.35 7.0 0 0 2.102 7.0 45.0
2.095 18 0.27 0.0 0 0 0 0.0 0.0
1.98 4 0.23 6.0 1.98 6 0 0.0 0.0
1.939 2 0.37 2.5 0 0 1.939 2.5 12.0
1.927 5 0.29 0.0 0 0 0 0.0 0.0
1.913 17 0.28 0.0 0 0 0 0.0 0.0
1.875 17 0.28 0.0 0 0 0 0.0 0.0
1.817 15 0.22 17.0 1.817 17 0 0.0 0.0
1.7 5 0.35 6.0 0 0 1.7 6.0 35.0
1.672 6 0.23 7.0 1.672 7 0 0.0 0.0
1.659 2 0.24 3.0 1.659 3 0 0.0 0.0
1.626 4 0.29 0.0 0 0 0 0.0 0.0
1.604 8 0.28 0.0 1.608 0 0 0.0 0.0
1.587 2 0.29 0.0 0 0 0 0.0 0.0
1.541 12 0.23 15.0 1.541 15 0 0.0 0.0
1.525 5 0.28 0.0 0 0 0 0.0 0.0
1.518 4 0.3 0.0 0 0 0 0.0 0.0
1.51 4 0.42 1.0 0 0 1.51 1.0 4.0

At this point, the ICCD-PDF manual was searched on the three highest intensity ratios of the remaining d-spacings. The best solution was identified as Data Card 8-479. This returned the data card for magnesite (Magnesium Carbonate). The d-spacings associated with this data card were checked against the spacings from the original data. The majority of the d-spacings down to 1.500Å were accounted for and the same process followed using the newly calculated ratio's. There were some extra d-spacings on the magnesite, that could not be accounted for in the original set of data. These d-spacings have relatively low intensities on the data card. If these intensities are ratioed down to the intesities that would be expected in the original set of data, then the peaks would be less than 1%, which is negligible in the scheme of things.

Peaks from Original spectra     Remaining peaks after 2 subtractions     Peaks assigned to magnesite   Remaining peaks  
d I FWHM d I Ratioed I d I d I
4.27 28 0.27 0 0.0 0.0 0 0 0 0.0
3.86 12 0.3 0 0.0 0.0 0 0 0 0.0
3.343 82 0.25 0 0.0 0.0 0 0 0 0.0
3.035 100 0.28 0 0.0 0.0 0 0 0 0.0
2.845 3 0.28 0 0.0 0.0 0 0 0 0.0
2.742 12 0.35 2.742 15.0 100.0 2.742 100 0 0.0
2.503 2 0.36 2.503 2.5 18.0 2.503 18 0 0.0
2.495 15 0.28 0 0.0 0.0 0 0 0 0.0
2.458 10 0.22 0 0.0 0.0 0 0 0 0.0
2.284 29 0.43 0 0.0 0.0 2.318 4 0 -
2.237 4 0.23 0 0.0 0.0 0 0 0 0.0
2.128 8 0.23 0 0.0 0.0 0 0 0 0.0
2.102 6 0.35 2.102 7.0 45.0 2.102 45 0 0.0
2.095 18 0.27 0 0.0 0.0 0 0 0 0.0
1.98 4 0.23 0 0.0 0.0 0 0 0 0.0
1.939 2 0.37 1.939 2.5 12.0 1.939 12 0 0.0
1.927 5 0.29 0 0.0 0.0 0 0 0 0.0
1.913 17 0.28 0 0.0 0.0 0 0 0 0.0
1.875 17 0.28 0 0.0 0.0 0 0 0 0.0
1.817 15 0.22 0 0.0 0.0 1.769 4 0 -
1.7 5 0.35 1.7 6.0 35.0 1.7 35 0 0.0
1.672 6 0.23 0 0.0 0.0 0 0 0 0.0
1.659 2 0.24 0 0.0 0.0 0 0 0 0.0
1.626 4 0.29 0 0.0 0.0 0 0 0 0.0
1.604 8 0.28 0 0.0 0.0 0 0 0 0.0
1.587 2 0.29 0 0.0 0.0 0 0 0 0.0
1.541 12 0.23 0 0.0 0.0 0 0 0 0.0
1.525 5 0.28 0 0.0 0.0 0 0 0 0.0
1.518 4 0.3 0 0.0 0.0 0 0 0 0.0
1.51 4 0.42 1.51 1.0 4.0 1.51 4 0 0.0

 


Comment: Similar comments to above except you did make explicit comments about the weak peaks.
8.5 Marks

As can be observed, all the peaks have been accounted for and the there are two peaks with d-spacings of 2.318Å and 1.769Å that would be expected to be observed in the original set of data/spectra. Due to the rationalising of the intensity peaks, it could be suggested that the sample has a high percentage of calcite, a slightly less percentage of quartz and a significantly smaller percentage of magnesite. The three components are confirmed by the presence of Calcium (from the calcite), Silicon (from the quartz) and magnesite (from the magnesite) being revealed by the electron microprobe analysis.


Comment: Yes I wanted a mention of the confirmation by the microprobe data. The large FWHMs and anomalous intensities could be mentioned here.
3 Marks


Overall Comment: Correct solutions and good methodology used in the searching. I hope this assignment was useful in giving you some further grasp of the procedures involved in search/match analysis.


Total Mark 22