Lars-Erik Briggner, Assignment 5

The results from XRPD mesurements were as follows (with suggestions for interpretation in the "Phase columns"):

d (Å) I (%) FWHM(°) Phase d (Å) I (%) FWHM(°) Phase d (Å) I (%) FWHM(°) Phase
4.27 28   0.27 B 2.237 4   0.23 B 1.700 5   0.35 C
3.86 12   0.30 A 2.128 8   0.23 B 1.672 6   0.23 B
3.343 82   0.25 B 2.102 6   0.35 C 1.659 2   0.24 B
3.035 100   0.28 A 2.095 18   0.27 A 1.626 4   0.29 A
2.845 3   0.28 A

1.980

 4   0.23 B 1.604 8   0.28 A
2.742 12   0.35 C 1.939 2   0.37 C 1.587 2   0.29 A
2.503 2 0.36 C 1.927 5   0.29 A 1.541 12   0.23 B
2.495 15   0.28 A 1.913 17   0.28 A 1.525 5   0.28 A
2.458 10   0.22 B 1.875 17   0.28 A 1.518 4   0.30 A
2.284 29   0.43 A+B 1.817 15   0.22 B 1.510 4   0.42 A+C

1. From the PDF entry for Calcite (5-586) it was most likely that the three largest peaks for Calcite were those denotet with A in the table above. All of the next five peaks and several of the even weaker peaks could also be identified, A. The peaks at 2.284 and 1.510, being broader, most likely contain contribution from other phases as well. This is also supported by the fact that the 2.284 peak has a higher intensity than expected (compared to 2.095 which shoud be about equal).


Comment: You have got the right idea; I like the summary table. You have correctly noted the potential problems with the 2.284/1.510 lines and I am pleased to see you bringing in intensity considerations into the analysis.
5 Marks

2. Assuming that the largest of the remaining peaks belong the second phase gives B for the three strongest. From the Hanawelt search manual it can be seen that SiO2 (5-490) is a likely candidate with these three being the largest. The next five largest from the PDF entry are also used to verify this phase, B, and all that are within the range of this solution are idenetified. The broader and unexpectedly high peak at 2.284 is explained here since also the second phase has a peak here. Finally, several of the even weaker peaks for phase B were identified, B.


Comment: This is the correct solution. Note that the agreement should be in both positive and negative senses; i.e. you must also explain that there are no lines missing in the sample that are present in the data file - in fact there are 2 missing (see model answer) but this can be explained on account of their weak intensities. Also the intensities of the SiO2 lines are reasonable.
8 Marks

3. The three strongest of the remaining peaks were denoted C. From Hanawelts search manual the MgCO3 (8-479) fits very well with these peaks and all of the remaining could also be found in this PDF entry among the five next strongest, C. The broader peak at 1.510 is due to the presence of both A and C.


Comment: This is also correct. Again note that a missing line in the sample (compared to the data file) needs to be excused and the intensities must be reasonable.
8 Marks

4. All three of the major heavier elements Ca, Si and Mg were present in plausible compounds for this type of material in this solution. All  peaks from the powder diffraction pattern could be accounted for and even the two odd peaks could be explained. For the peak at 1.510 there were no real gain in intensity since this was a very small contribution from C (peaks of similar intensity were not detected at all!) but was merely seen as a broadening of the peak from phase A. Even though no quantitative calibration were done I would estimate that there are much less present of phase C than A and B (which are more similar in quantity).


Comment: This is the kind of information I wanted to see - confirmation with the elemental information given; the rough estimate of amounts (personally I would put the quartz quantity as intermediate); I also point to the historical feasibility in the model answer.
3 Marks


Overall: Correct solutions; clear explanation and noted the most important features.