The decomposition of ammonium metatungstate hydrate at elevated temperatures is a gradual process, and the exact substances produced depend on the temperature and other experimental conditions. The main stages of the process and the substances produced are summarized below in a clear structure:
Low temperature stage (200-300°C):
Ammonium metatungstate hydrate begins to lose its water of crystallization and may shed most of its ammonium ions. At this point, the structure of the compound begins to change, but it is not completely decomposed.
Medium temperature stage (300-350°C):
In this temperature range, ammonium metatungstate undergoes a phase transition to produce stabilized tungsten oxide. The reaction at this stage further drives the decomposition process of the compound.
High temperature stage (400-550°C):
The main decomposition temperature range of ammonium metatungstate hydrate. At this temperature, ammonium metatungstate can decompose more completely and the main product is tungsten oxide.
In addition to tungsten oxide, the decomposition process may also produce reaction products such as ammonia and water.
It should be noted that even if the temperature reaches 500-550 ℃, there may still be a small amount of ammonium root and bound water can not be completely decomposed.
Extremely high temperature stage (above 600℃):
When the temperature exceeds 600°C, ammonium metatungstate can completely decompose into tungsten trioxide (WO3).
At higher temperatures (e.g. 700°C), by controlling the holding time (e.g. 2 hours), products with special structures such as hollow mesoporous tungsten trioxide spheres can be obtained.
To summarize, the main decomposition product of ammonium metatungstate hydrate at high temperature is tungsten oxide, and ammonia and water may also be produced. As the temperature increases, the decomposition reaction is more complete and the products are gradually transformed to the more stable tungsten trioxide. In addition, by controlling conditions such as temperature and time, products with special structures and properties can be obtained.
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