I hope the enclosed article (and references therein) can help.

Note that:

1) The best preparation method of choice will depend on whether you want a highly sintered (dense) ceramic material or a high surface area (porous) solid.

2) The 1:2 Ni to Al ratio is needed to satisfy the right stoicheometry: NiAl(2)O(4).

Best wishes,

Carlos

The classical way of making spinels is choosing your starting materials (e.g. nickel nitrate and aluminium sulphate). These are decomposable materials leaving no rest of sulphur or nitrate. Since these starting materials can contain different amounts of crystal water you have to weigh a certain amount of these materials and decompose these first into Al2O3 and NiO and weigh them again so you exactly know how many mole of Al you have in a certain amount of weighed Al2(SO4)2*XH2O material. You need to do this otherwise the composition will not be exact what you think it is based on the molar weight of the starting material. Once you know the conversion, you can mix both starting materials and do some thorough ball mixing. Then you slowly decompose the materials in air gradually raising the temperature, first loosing the crystal water and then heating above the decomposition temperature of the sulphates and nitrates (>500C). The material will shrink and again you do some thorough ball mixing to make sure you get a homogeneous mix of small particles. This mixture you can press into pellets or bars and you need to sinter the material at the right temperature to form stoichiometric NiAl2O4. For this you need to know what partial oxygen pressure you need to set at the chosen sinter temperature so no phase seggregation will take place (look up the NiO-Al2O3-P02 phase diagram). Usually the sinter temperatures are above 1000C, certainly when the concentration of Al is high, as in your case. Usually after ca. 8-10 hours you should have a homogeneously sintered spinel and the quality can be checked with powder XRD to check for phase segregations

sir how 1:2 satisfy the right stoichiometry and why this specific ratio?

i want to make a stable at high temperature, surface area spinel?

1) Because in the chemical formula of nickel aluminate spinel there is 1 Ni and 2 Al.

2) The article that I enclosed in my answer (yesterday) decribes the preparation of a high-surface-area stable nickel aluminate spinel.

Best wishes,

Carlos

You do not necessarily need to stick to 1:2 ratio. You can make mixseries Ni1-xAl2-2/3xO4 and I'm sure there is literature about this spinel mixseries.