These oxides readily absorb moisture from air. As a result, after storage the material transforms into a mixture of RE2O3, REOOH and even RE(OH)3. Annealing leads to the water removal and formation of the stoichiometric oxide.
These oxides readily absorb moisture from air. As a result, after storage the material transforms into a mixture of RE2O3, REOOH and even RE(OH)3. Annealing leads to the water removal and formation of the stoichiometric oxide.
Missyul's comment is a very important one that may cover other systems as well. For instance, when preparing lithium compounds in systems with Li-O it is recommended to start with Li2CO3 in your reaction mixture because LiOH easily forms while the carbonate dissociates to release CO2.
On the whole, never trust the label of your chemical pot. Make a proper phase analysis before using its contents, or you may ruin your synthesis. This may be of value when contacting your supplier of chemicals for a reclamation -- you cannot know how long the material was stored before you got it (and paid for it).
Hi Krishna,
Rare earth oxides are strongly basic and easily form hydroxides, oxyhydroxides, and carbonates when exposed to the atmosphere. It is essential to pre-heat them before they are weighed to prepare a particular compound. If not, the synthesis will lead to nonstoichiometric compounds or other phases. I share here the thermal analyses (TG-DTA) results of La2O3. There are several weight losses with endothermic peaks corresponding to the loss of physisorbed and chemisorbed H2O, decomposition of hydroxides and carbonates. A total of 15% weight loss observed by heating above 900 deg C.
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