Alkali oxide decomposition method:
This is the commonly used chemical process for the preparation of fine and impurity free zirconia powder. The process consists of decomposition of zircon with sodium hydroxide or sodium carbonate as a fusion flux material. When sodium hydroxide is used it reacts with zircon at about 650 to 700.C and forms sodium zirconate and sodium silicate.
When sodium carbonate is used as fusion material the conversion takes place at much higher temperature. The fused material is leached with water to remove the sodium silicate and the sodium zirconate is hydrolysed to zirconia hydrate. The zirconia hydrate is ignited to form impure zirconium oxide.
The impure hydrated zirconia is alternatively dissolved in concentrate sulphuric acid or hydrochloric acid. This will produce corresponding zirconyl sulphate or zirconyl chloride solution. The solutions are then purified by precipitation technique. Further chemical treatment of the formed precipitate by calcination at a temperature of 800 to 1000.C produces very fine and pure zirconia powder.
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