the composition is in the formula. the hexaaluminate is formed via the reaction:
LA2O3 + 2 MgO + 11 Al2O3 => 2 LaMgAl11O19
so you need to mix and mill the oxides in the above molar ratio.
Of course you cannot just spray the mixture of oxides but make the powder by reaction sintering. the annealing temperature to get the ternary composung strongly depends on the homogeneity of the mixture and the grain size of your starting powders.
it is known that magnesia evaporates during coating and and application so it may be helpful to start with a slight excess in MgO.
If you do not work using a glovebox, you should also check your lanthanum oxide before use, as it rapidly reacts with water when stored in air to form La(OH)3. If so, you should heat your precursor around 1000°C in air and use it rapidly.
La2O3 + 2 MgO + 11 Al2O3 ---- 2 LaMgAl11O19
La2O3 should be pre heated in a furnace at 973K and weighed just after taking out of furnace as it absorbs moisture. MgO is volatile at high temperature. It is advisable to use 5% mol % excess of MgO. Mix all the powders maintaining the above condition and start heating from 1073K. Continue to increase the temperature of the reaction by 100 K till phase pure product is obtained. But dont try to go above 1473K.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry