Zirconia preparation

Zirconia (ZrO₂) can be prepared from Zircon - ZrSiO₄ - an opacifier used in pottery glazes and obtainable from pottery suppliers.

1 part of fine Zircon powder is fused with 2 parts of KOH for about 30 minutes at medium Bunsen heat. Ideally a nickel crucible is used.

ZrSiO₄ + 4 KOH === > K₂ZrO₃ + K₂SiO₃ + 2 H₂O

After cooling 3 parts of water are added and the wet frit allowed to soften up overnight.

The zirconate and silicate hydrolyse to Zr(OH)₄ and hydrated silica.

The content of the crucible is quantitatively transferred to a mortar and pestle and ground down, then transferred to a glass beaker.

Slowly and with constant stirring the equivalent of 2 parts of KOH of HCl is added as 37 w% HCl. This solution/slurry is simmered for about 1 hour, causing zirconyl chloride - ZrOCl₂ - to enter the solution while hydrated silica does not.

The solution is then decanted or filtered to clarity.

To the filtrate, diluted to twice its original volume, conc. ammonia solution is added, equivalent to the amount of HCl previously used or until pH > 9. This causes zirconium hydroxide - Zr(OH)₄ - to precipitate. Filter this off and wash it profusely with several aliquots of hot water to remove KCl and salmiac.

If better purity is required then re-dissolve the previously obtained Zr(OH)₄ in a minimum of conc. HCl, then reduce the solution's volume by boiling. Allow to cool and gas this solution with HCl: quite pure ZrOCl₂.8H₂O ([1]zirconyl chloride octahydrate) then precipitates. Dissolve this in slightly acidified water and re-precipitate the Zr(OH)₄ from dilute solution with ammonia solution. Filter and wash the filter cake.

Calcine the Zr(OH)₄ to ZrO₂.