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A cement compound CaO.Al2O3.10H2O gives certain peaks when using the powder diffraction method. The compound now increases its water of crystallization to become CaO.Al2O3.11H2O. Will the diffraction pattern obtained be basically the same as the former, with only a slight difference, which corresponds to a slight increase in the d spacing? Or will the diffraction pattern be an entirely different pattern?
Answer 1:

I looked through the scientific literature for calcium aluminates and I did not find any evidence that monocalcium aluminate decahydrate(CaO.Al2O3.10H2O) will add water to become monocalcium aluminateundecahydrate (CaO.Al2O3.11H2O), so I'm not sure there is an answer to your question. The only undecahydrate I found in this chemical family was Ca4Al2O7.11H2O which is not the same compound you asked about.

Most calcium aluminate hydrates have a hexagonal structure. The powder diffraction patterns for any hexagonal structure will be very similar with only, as you say, a slight difference corresponding to differences in d spacings. If changing the hydration of the compoundchanges the overall crystal structure, then you will get an entirelydifferent pattern, as in the case of Ca3Al2(OH)12 which has a cubicstructure.

References:
Edmonds, R.N.; Majumdar, A.J. "The Hydration of Monocalcium Aluminateat Different Temperatures." Cement and Concrete Research. 1988, 18,311-329.
Jensen, T.R.; Christensen, A.N.; Hanson, J.C. "Hydrothermal transformation of the calcium aluminum oxide hydrates CaAlsO4.10H2O and Ca2Al2O5.8H2O to Ca3Al(OH)12 investigated by in situ synchrotronX-ray powder diffraction." Cement and Concrete Research, 2005, 35,2300-9.



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