4. Other Novel Synthesis Techniques
Besides “wet-synthesis” methods, another two novel methods have been used to
synthesize MA spinel powders. These are mechanochemical alloying and molten
salt synthesis (MSS).
In mechanochemical alloying, the appropriate raw materials (oxide,
hydroxides, or carbonates) are mixed and co-milled by a high-energy milling
machine. On milling a spinel-forming precursor forms from which fine spinel
powders can be obtained by crystallization usually below _12008C. Kim and
Saito (12) investigated the effect of dry milling of a powder mixture of
Mg(OH)2 and Al(OH)3 on spinel formation and found that MA spinel crystallized
in a mixture ground for only 15 min at as low as 7808C.
The MSS technique uses low-melting salts as the reaction medium and/or
reactants, thus permitting atomic-scale mixing of the reactants in the liquid phase.
This, along with the quicker diffusion of species in the liquid medium, means the
spinel formation reactions can be completed at a relatively low temperature and
in a short time. Zawrah and Kheshen (13) co-melted Al(NO3)3 . 9H2O and
Mg(NO3)2 . 6H2O at 5008C for 2 hr and later calcined the resulting mixture at
500–10008C to prepare MA powders. They found that pure nanocrystalline
(with a maximum size of _10 nm) spinel powders can be obtained by calcining
the mixture at 10008C.
4. Other Novel Synthesis Techniques
Besides “wet-synthesis” methods, another two novel methods have been used to
synthesize MA spinel powders. These are mechanochemical alloying and molten
salt synthesis (MSS).
In mechanochemical alloying, the appropriate raw materials (oxide,
hydroxides, or carbonates) are mixed and co-milled by a high-energy milling
machine. On milling a spinel-forming precursor forms from which fine spinel
powders can be obtained by crystallization usually below _12008C. Kim and
Saito (12) investigated the effect of dry milling of a powder mixture of
Mg(OH)2 and Al(OH)3 on spinel formation and found that MA spinel crystallized
in a mixture ground for only 15 min at as low as 7808C.
The MSS technique uses low-melting salts as the reaction medium and/or
reactants, thus permitting atomic-scale mixing of the reactants in the liquid phase.
This, along with the quicker diffusion of species in the liquid medium, means the
spinel formation reactions can be completed at a relatively low temperature and
in a short time. Zawrah and Kheshen (13) co-melted Al(NO3)3 . 9H2O and
Mg(NO3)2 . 6H2O at 5008C for 2 hr and later calcined the resulting mixture at
500–10008C to prepare MA powders. They found that pure nanocrystalline
(with a maximum size of _10 nm) spinel powders can be obtained by calcining
the mixture at 10008C.
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