We obtained a powder through a precipitation process in solution. The powder is expected to be mainly CaCO3 (and sometimes CaCO3 and gypsum). XRD, XRF, FTIR, and EDS ( on the SEM) are available.
How can I find the percentage of CaCO3 (and gepsum) in the dried powder?
If you want to use one of the available equipments then XRD is the right choice.
If the have the thermobalance (TGA) available somewhere, it is a simple tool to get an answer on this. This instrument measures weight changes versus temperature. At low temperatures you might only seen evaporation of humidity and the dehydration of the dihydrates/halfhydrates of calcuim sulfate (all below 300°C). The calcuim carbonate decomposes to Cao and CO2 between 500 and 900°C. The mass loss step you measure in this region can be directly linked to the CaCO3 content (stoichiometrical calculation). If you go higher in temperature (> 1200°C) you might the the sulfate decomposition, as well.
Rietveld refinement on a powder XRD pattern is the most accurate and direct method for getting quantitative phase fractions.
XRF will give only Ca, and S elemental conc....C, O cannot be detected.
Since both are crystalline powder XRD is ideal as Lawrence already stated.
You can try on SEM-EDX (with thin window X-ray detector) in "area mode" data-aq. to get some approximate results if you have a homogeneous mixture,,,and check the stoichiometry with the atomic %
Calculate the carbonate species (CaCO3) by titrating with standard H2SO4 using phenolphthalein indicator and % purity of the sample from the sample taken for analysis.
XRF will not detect carbon and may report CaCO3 as CaO. Though XRF will give you the weight percentage of the identified elements and compounds. XRD will give you the diffraction pattern and identify the peaks appropriately. CaCO3 will be appropriately identified by XRD. You can confirm the result of XRD with TGA as there will be rapid loss in mass between 550 oC and 870 oC when the CaCO3 will be converted to CaO and CO2. FTIR will also be useful as the spectra will show the fingerprints of all the functional groups.
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