I have need of a sealed crucible to melt titanium (in the absence of a vacuum/inert environment), and have been considering using Alumina or Zirconia powders in a suspension (alcohol or water), and attempting to slip cast a crucible. I'm not sure of any methods or materials that may be more air tight with regards to porosity, so any information will help.
Dear Tristan Harding
Titanium has a melting point of above 1670oC
So the crucible should be made of the material that has three main properties:
1. High refractoriness point (above 1900oC)
2. Gas permeability resistant
2. Corrosion (and wetting) resistant against titanium melt
Both latter properties need lower porosity level and lower pore size
The oxide relation about corrosion resistance against (reduction with) titanium melts:
Y2O3, CaO, ZrO2, Al2O3 and MgO
Therefore, alumina is not a good choice for corrosion resistance against titanium.
ZrO2 crucible with 6 Wt% of pure CaO sintered at 1750oC (to obtain porosity level of under 2%) is a well choice for your goal. Specially, if it is isostatically pressed or it is sintered at vacuum condition and in the best condition, if it is coated from inside with 200 micrometer thickness of Y2O3 slurry before sintering process