Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: yiyo on September 11, 2013, 11:33:16 AM
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I would like to ask some information about synthesis of perovskites.
In this synthesis, we first need to mix the raw materials together with the solvent. Then we need to heat the reaction mixture to dryness on a hot plate. After that, we can put the resulting powders in a furnace for firing. Finally, we can obtain a powder X-ray diffraction pattern of the product.
My question is why do we need to dry the mixture on a hot plate first? Why can't we just put the mixture into a furnace immediately?
My guess about the purpose of drying on a hot plate is to remove water inside the mixture. But if yes, we just put it into a furnace which can also remove the water molecules inside.... Or the furnace is used to compact the molecules inside more regularly, so as to form a clearer diagram in X-ray diffraction?
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Heating the mix while wet will result in fast evaporation, you will end not with a solid, but either with a powder, or with a solid with huge holes inside.
Not that I ever worked with perovskites, but I have seen it in other cases.
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but then is the process of heating forming solid? Is the purpose of putting it into a furnance putting oxygen in the atoms, forming perovskites?
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No idea about details, but sintering is a classical method of preparing solids from powders. What kind of reactions/processes take place during the sintering depends on the mixture composition.
Could be sintering is not the best term to use here, but it was the best one I could think of.
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In general, these sort of syntheses (of crystalline solids, supports, catalysts etc.) are more an art still. The steps mentioned have worked which isn't saying other modifications won't.
Very often the protocols have evolved out of trial and error & some heuristics or long years of experience. Not many people can convincingly say why each step in there needs to be there exactly as it is.