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.

Comment: You have got the right idea and you have clearly written this by yourself. The large peak widths with the 2.284 and 1.510 lines are well worth noting at this early stage (see model answer).
3 Marks

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.

Comment: This is the correct solution. It seems you used the peak width to guide you in identifying 2.284 as a line to consider. Although peak widths have relevance (see model answer) it is intensities that should guide you in selecting lines for searching. NOTE: The whole concept of search match is based around using the intensities of the observed d spacings. The widths simply help you sometimes to distinguish phases or to indicate peak overlap.

Also note that ideally you must explain that there are no lines missing in the sample that are present in the data file - in fact there are 1 or 2 missing (see model answer) but this can be explained on account of their weak intensities.
5 Marks

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.

Comment: Again this is the correct solution but the same comments made above apply to your answer.
5 Marks

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).

Comment: Good clear comparisons of the data. You might also point out the final agreement with the elemental information and make some conjecture about the relative amounts of phases (see model answer).
3 Marks

Comment: Correct solutions but note the various comments I have made. The English is bit difficult to follow in places but I am glad to see that you have made a real effort to write it yourself rather than just copy material. If it helps I would be happy to personally show you where the text can be improved.