Process of forming a sol-gel/metal hydride composite
An external gelation process is described which produces granules of metal hydride particles contained within a sol-gel matrix. The resulting granules are dimensionally stable and are useful for applications such as hydrogen separation and hydrogen purification. An additional coating technique for strengthening the granules is also provided.
1. A process of forming a sol-gel matrix containing therein a hydrogen storage material comprising the steps of:
providing a supply of particulates of a hydrogen storage material;
blending said hydrogen storage material with a pore former, thereby forming an agglomeration of said hydrogen storage particles and said pore former;
dispersing said agglomeration into a colloidal silicate/solvent suspension;
introducing drops of said suspension into a supply of heated silicon oil;
evaporating said solvent from said drops while in the presence of said heated silicon oil, thereby forming substantially spherical granules of a metal hydride within a silica matrix; and,
separating said granules from said silicon oil.
2. The process according to claim 1 wherein said hydrogen storage material is selected from the group consisting of metal hydrides, complex alloys of B, Ti, La, Ni, Zr, Co, Al, and combinations thereof.
3. The process according to claim 1 wherein said supply of particulates of a hydrogen storage material have an average particulate size of about 20 microns or less.
4. The process according to claim 1 wherein said pore former is abietic acid.
5. The process according to claim 4 wherein said abietic acid is present at a ratio of about 1:4 per wt % relative to said hydrogen storage material.
6. The process according to claim 1 wherein said solvent within said colloidal silicate/solvent suspension is selected from the group consisting of water and ethanol.
7. The process according to claim 1 wherein said heated silicon oil has a viscosity of between about 500 centistokes to about 3,000 centistokes.
8. The process according to claim 1 wherein said silicate used in said colloidal suspension is a fumed silica.
9. The process according to claim 8 wherein said fumed silica has an average particle size of about 14 nanometers.
10. The process according to claim 1 wherein said colloidal silica/solvent suspension further comprises about a 40 wt % of silica.
11. The process according to claim 1 wherein said hydrogen storage material is a lanthamum-nickle-aluminum alloy.
12. The process according to claim 1 wherein said heated silicon oil is at a temperature of between about 60° C. to about 95° C.
13. The process according to claim 1 wherein said step of introducing drop of said suspension further comprises placing said drops in a first supply of heated silicon oil and subsequently introducing said drops in said first supply of heated silicon oil into a second supply of heated silicon oil, said second supply of heated silicon oil being warmer than said first supply of silicon oil.
14. The process according to claim 1 wherein following said separating step, said granules have applied thereto a protective coating.
15. The process according to claim 14 wherein said protective coating is tetraethoxysilane (TEOS).
16. The process according to claim 1 comprising the additional step of heating said granules to a temperature of between about 200° C. to about 300° C. in the presence of an inert gas thereby evaporating said pore former.
17. A porous sol-gel matrix containing therein a hydrogen storage material made according to the process of claim 1 .
18. A process of strengthening a sol-gel matrix containing therein a hydrogen storage material comprising the steps of:
providing a particulate comprising a sol-gel matrix containing therein a hydrogen storage material;
coating an exterior of said sol-gel particulate with tetraethoxysilane; and,
reacting said tetraethoxysilane with water, thereby providing an exterior protective layer of tetraethoxysilane to said sol-gel.
19. The process according to claim 18 wherein said sol-gel matrix further defines a plurality of cracks created by the absorption and desorption of hydrogen by the hydrogen storage material therein.