Answer:
1.
According to 5-586 PDF card, the first 15 strongest d spacings datas are found in powder diffraction data of unknown materials. The match datas indicated in red below.
| d (Å) | I (%) | FWHM(°) | d (Å) | I (%) | FWHM(°) | d (Å) | I (%) | FWHM(°) | ||||
| 4.27 | 28 | 0.27 | 2.237 | 4 | 0.23 | 1.700 | 5 | 0.35 | ||||
| 3.86 | 12 | 0.30 | 2.128 | 8 | 0.23 | 1.672 | 6 | 0.23 | ||||
| 3.343 | 82 | 0.25 | 2.102 | 6 | 0.35 | 1.659 | 2 | 0.24 | ||||
| 3.035 | 100 | 0.28 | 2.095 | 18 | 0.27 | 1.626 | 4 | 0.29 | ||||
| 2.845 | 3 | 0.28 | 1.980 | 4 | 0.23 | 1.604 | 8 | 0.28 | ||||
| 2.742 | 12 | 0.35 | 1.939 | 2 | 0.37 | 1.587 | 2 | 0.29 | ||||
| 2.503 | 2 | 0.36 | 1.927 | 5 | 0.29 | 1.541 | 12 | 0.23 | ||||
| 2.495 | 15 | 0.28 | 1.913 | 17 | 0.28 | 1.525 | 5 | 0.28 | ||||
| 2.458 | 10 | 0.22 | 1.875 | 17 | 0.28 | 1.518 | 4 | 0.30 | ||||
| 2.284 | 29 | 0.43 | 1.817 | 15 | 0.22 | 1.510 | 4 | 0.42 |
2.
To confirm that other phases exist in the unknown material, the peak width (FWHM) information has been used. The next stage is to search the powder diffraction data of unknown material, the largest FWHM 0.43 with d(Å) = 2.284 is choosen. Then, it is to find out match data (d = 2.284(Å)), which is based on Page 13, 14, 15, 16 of the Hanawalt search manual. If several the same d = 2.284(Å) datas with different formula materials are found, it must also be thought that if other datas of substances choosen in database can find matches in powder diffraction data of unknown material and the formula of choosen substances in database contain Ca, Si or Mg elements. Lately, other phase SiO2 with code 5-490 is confirmed.
3.
The second larger width peak with d = 1.939(Å) is left in the table of powder diffraction datas of unknown materials. The same method which is mentioned above is carried out, other phase MgCO3 with code 8-479 is also found in the Hanawalt search manual.
4.
This stage is to compare these first 12 lines with those of the full pattern for SiO2 and MgCO3 in the PDF database (see below).
Click here to see PDF entry for SiO2 and Click here to see PDF entry for MgCO3
The comparison reads as follows:
(1). SiO2
| here: | 4.27 | 3.343 | 2.458 | 2.284 | 2.237 | 2.128 | 1.980 | 1.817 | 1.672 | 1.659 | 1.604 | 1.541 | PDF: | 4.26 | 3.343 | 2.458 | 2.282 | 2.237 | 2.128 | 1.980 | 1.817 | 1.672 | 1.659 | 1.608 | 1.541 |
The general agreement with both the d spacings is convincingly good and we can be confident that the unknown second phase is SiO2.
(2). MgCO3
| here: | 2.742 | 2.503 | 2.102 | 1.939 | 1.700 | 1.510 | |||||||
| PDF: | 2.742 | 2.503 | 2.102 | 1.939 | 1.700 | 1.510 |
The general agreement with both the d spacings is convincingly good and we can be confident that the unknown third phase is MgCO3.
Therefore, the ancient plaster has been identified and contain calcite (CaCO3), Silicon Oxide (SiO2) and Magnesium Canbonate (MgCO3).
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yuan@img.cryst.bbk.ac.uk School of Crystallography Birkbeck College, University of London Malet Street, London WC1E 7HX, UK |
©Zhanhui Yuan |