Deposition of ceramic layers using liquid organometallic precursors

1. A method of depositing a metal or ceramic layer comprising a metal selected from the group consisting of Zr, Hf, Nb, Ta, W, V, Ti, and mixtures thereof by chemical vapor deposition, comprising:

a. introducing particles to a fluidized bed reactor, wherein the particles comprise nuclear fuel kernels;

b. heating the fluidized bed reactor to a desired operating temperature T 1 ;

c. initiating a flow of a carrier gas through a vaporizer;

d. injecting a non-halogenated liquid organometallic metal precursor into the vaporizer and vaporizing the non-halogenated liquid organometallic metal precursor,

wherein the non-halogenated liquid organometallic metal precursor is a compound of the metal selected from the group consisting of Zr, Hf, Nb, Ta, W, V, Ti, and mixtures thereof;

e. allowing a first mixture of the carrier gas and the vaporized non-halogenated liquid organometallic metal precursor to leave the vaporizer;

f. optionally mixing the first mixture with a gaseous carbon source, a gaseous nitrogen source, a gaseous oxygen source, or a mixture thereof to produce a second mixture; and

g. either:

causing the first mixture to flow into the fluidized bed reactor at operating temperature T 1 , allowing deposition of a desired metal coating on the particles; or

causing the second mixture to flow into the fluidized bed reactor at operating temperature T 1 , allowing deposition of a desired ceramic coating on the particles.

2. The method of claim 1 , wherein the particles are nuclear fuel kernels selected from the group consisting of oxides, carbides, oxycarbides, and nitrides of a metal selected from the group consisting of uranium, plutonium, and thorium, and mixtures thereof.

3. The method of claim 1 , wherein the particles are nuclear fuel kernels selected from the group consisting of uranium oxides, uranium carbide, uranium nitrides, uranium oxycarbide, and mixtures thereof.

4. The method of claim 1 , wherein the nuclear fuel kernels comprise:

a core of a ceramic uranium material, a ceramic plutonium material, a ceramic thorium material, or a mixture thereof; and

at least one coating of porous or non-porous pyrolytic carbon.

5. The method of claim 1 , wherein each particle comprises a nuclear fuel kernel, a porous carbon buffer layer on the kernel, and a dense layer of pyrolytic carbon on the buffer layer.

6. The method of claim 1 , wherein:

step (g) is the step of causing the second mixture to flow into the fluidized bed reactor; and

the method further comprises:

a step of depositing an inner carbon layer on the nuclear fuel kernels, prior to step (d); and

a step of depositing an outer carbon layer on the desired ceramic coating.

7. The method of claim 1 , wherein the non-halogenated liquid organometallic metal precursor has a formula M +n L n , M +n L 1 (n-m) L 2 (m) , or (L 3 =) p M +n L (n-2p) , wherein:

M is Zr, Hf, Nb, Ta, W, V, Ti, or a mixture thereof;

L and L 1 are independently selected from C1-C4 alkyl groups, C1-C4 alkoxy groups, bis(C1-C4 dialkyl)amido groups, or a combination thereof;

L 2 is a cyclopentadienyl anion;

L 3 is O═ or RN═, wherein R is alkyl;

m is 1 or 2,

p is 1 or 2, and

n is the valency of the metal M.

8. The method of claim 1 , wherein the non-halogenated liquid organometallic metal precursor is:

a metal alkoxide selected from the group consisting of titanium(IV) isopropoxide, titanium(IV) isobutoxide, hafnium(IV) butoxide, niobium(V) t-butoxide, niobium(III) t-butoxide, and zirconium(IV) butoxide; or

a metal amine selected from the group consisting of:

(tert-butylimino)tris(diethylamino)tantalum(V);

(tert-butylimino)tris(diethylamino)niobium(V);

(tert-butylimino)tris(methylethylamino)niobium(V);

tris(diethylamino)niobium(III);

tris(methylethylamino)niobium(III);

tris(diethylamino)niobium(III);

tris(dimethylamino)cyclopentadienyl zirconium(IV);

tetrakis(isopropylmethylamino)zirconium(IV);

tetrakis(ethylmethylamino)zirconium(IV);

tetrakis(diethylamino)zirconium(IV);

tris(dimethylamino)cyclopentadienyl hafnium(IV);

bis(methylimino)bis(dimethylamino)tungsten(VI); and

bis(tert-butylimino)bis(dimethylamino)tungsten(VI).

9. The method of claim 1 , wherein:

step (f) comprises mixing the first mixture with the gaseous carbon source to produce the second mixture; and

step (g) comprises causing the second mixture to flow into the fluidized bed reactor at operating temperature T 1 , allowing deposition of a desired metal carbide coating on the particles.

10. The method of claim 9 , wherein the gaseous carbon source is methane, ethane, ethylene, propylene, acetylene, natural gas, or a mixture thereof.

11. The method of claim 1 , wherein:

step (f) comprises mixing the first mixture with the gaseous nitrogen source to produce the second mixture; and

step (g) comprises causing the second mixture to flow into the fluidized bed reactor at operating temperature T 1 , allowing deposition of a desired metal nitride coating on the particles.

12. The method of claim 11 , wherein the gaseous nitrogen source is nitrogen gas, ammonia, or a mixture thereof.

13. The method of claim 1 , wherein:

step (f) comprises mixing the first mixture with the gaseous oxygen source to produce the second mixture; and

step (g) comprises causing the second mixture to flow into the fluidized bed reactor at operating temperature T 1 , allowing deposition of a desired metal oxide coating on the particles.

14. The method of claim 13 , wherein the gaseous oxygen source is ozone, oxygen, nitric oxide, nitrous oxide, or a mixture thereof.

15. A method of depositing a metal or ceramic layer by chemical vapor deposition, comprising:

a. introducing nuclear fuel kernels to a fluidized bed reactor;

b. heating the fluidized bed reactor to a desired operating temperature T 1 ;

c. initiating a flow of a carrier gas through a vaporizer;

d. injecting a non-halogenated liquid organometallic metal precursor into the vaporizer and vaporizing the non-halogenated liquid organometallic metal precursor;

e. allowing a first mixture of the carrier gas and the vaporized non-halogenated liquid organometallic metal precursor to leave the vaporizer;

f. optionally mixing the first mixture with a gaseous carbon source, a gaseous nitrogen source, a gaseous oxygen source, or a mixture thereof to produce a second mixture; and

g. either:

causing the first mixture to flow into the fluidized bed reactor at operating temperature T 1 , allowing deposition of a desired metal coating on the nuclear fuel kernels; or

causing the second mixture to flow into the fluidized bed reactor at operating temperature T 1 , allowing deposition of a desired ceramic coating on the nuclear fuel kernels.

16. The method of claim 15 , wherein the nuclear fuel kernels comprise:

a core of a ceramic uranium material, a ceramic plutonium material, a ceramic thorium material, or a mixture thereof; and

at least one coating of porous or non-porous pyrolytic carbon.