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Crystallizing phosphates


Hi All,

I've hid a roadbump while trying to grow a crystal of copper phosphate and wanted some advice.
Process so far:
-Synthesized copper phosphate by the double replacement of copper sulfate and diammonium phosphate.
-Rinsed the resultant precipitate (aggregates under microscope)to remove the ammonium sulfate ions.
-Suspended in distilled water
-Added minimum amount of phosphoric acid to start dissolving precipitates, leaving some undissolved solids so I know the solution is saturated.
-Decant. Let evaporate.

The issue I am running into is hitting a point where there is no longer any evaporation taking place and no crystals have formed. As I understand it, the solubility of copper phosphate increases with increasing phosphoric acid concentration, and I think I hit a point where as the water evaporated, the concentration of the phosphoric acid went up and the solubility followed. Is this a good line of thinking? Furthermore, I understand that copper phosphate has inverse temperature solubility and I have no way of heating in a slow/controlled enough fashion to get nice crystals.



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