Titanium dioxide doped with fluorine and process for the production thereof
A crystalline titanium dioxide containing fluorine atoms within the crystal lattice comprising atoms of titanium and oxygen is described; this titanium dioxide is particularly suitable for the production of solid-state electrolytes, hybrid membranes for fuel cells or electrolysers. A process for producing the aforesaid titanium dioxide is also described.
1. Crystalline titanium dioxide particles having an average particle size of less than 500 nm and having a fluorine content of between 0.5 and 5% by weight, wherein the crystalline titanium dioxide particles include hydroxy groups, ammonium cations and nitrogen oxides.
2. The crystalline titanium dioxide particles of claim 1 wherein the particles have a fluorine content of between 1.0 and 4% by weight.
3. The crystalline titanium dioxide particles of claim 1 wherein the particles have an average particle size of between 10 and 500 nm.
4. The crystalline titanium dioxide particles of claim 1 wherein the particles have a nitrogen content of between 0.2 and 8% by weight.
5. The crystalline titanium dioxide particles of claim 4 wherein the particles have a nitrogen content of between 2.5 and 7% by weight.
6. The crystalline titanium dioxide particles of claim 1 wherein the particles have a hydrogen content of between 0.05 and 4% by weight.
7. The crystalline titanium dioxide particles of claim 1 wherein the particles have at least part of the fluorine content present in a surface layer of the particles.
8. The crystalline titanium dioxide particles of claim 7 wherein at least 80% of the fluorine content is present in a surface layer of the particles.
9. The crystalline titanium dioxide particles of claim 7 wherein the surface layer has a mean thickness of between 0.3 and 20 nm.
10. The crystalline titanium dioxide particles of claim 1 wherein the particles have hydroxy groups present in a surface layer of the particles.
11. The crystalline titanium dioxide particles of claim 1 wherein the particles are in an anatase form.
12. A process for producing crystalline titanium dioxide containing fluorine atoms, comprising the steps of:
(a) reacting a titanium ore with a NH 4 HF 2 aqueous solution to obtain an aqueous dispersion;
(b) filtering the aqueous dispersion to separate the aqueous dispersion into a solid residue and an aqueous solution containing titanium salts;
(c) subjecting the aqueous solution to hydrolysis, the hydrolysis comprising a first stage at a pH between 6.5-8.0 and a second stage at a pH between 9.0-11.0;
(d) filtering the aqueous solution to separate the aqueous solution into an additional solid residue and a filtrate;
(e) subjecting the additional solid residue to pyrohydrolysis at a maximum temperature of around 500° C.; and
(f) obtaining crystalline titanium dioxide containing fluorine atoms from the pyrohydrolysis.
13. The process according to claim 12 wherein the step (a) of reacting a titanium ore with a NH 4 HF 2 aqueous solution is performed at 100-110° C.
14. The process according to claim 12 wherein the step (a) of reacting a titanium ore with a NH 4 HF 2 aqueous solution is performed for a period of time between 40 and 80 minutes.
15. The process according to claim 12 wherein the step (a) of reacting a titanium ore with a NH 4 HF 2 aqueous solution is performed at a pressure of approximately 1-2 bar.
16. The process according to claim 12 wherein the step (a) of reacting a titanium ore with a NH 4 HF 2 aqueous solution is performed at a pH of approximately 6.5-7.0.
17. The process according to claim 12 wherein the NH 4 HF 2 aqueous solution has a concentration of between 10% and 37% by weight.
18. The process according to claim 12 wherein the step (c) of subjecting the aqueous solution to hydrolysis includes adding a solution of ammonium hydroxide to the aqueous solution.
19. The process according to claim 12 wherein the step (e) of subjecting the additional solid residue to pyrohydrolysis includes subjecting the additional solid residue to pyrohydrolysis at a temperature of between 330-470° C.
20. The process according to claim 12 wherein the step (e) of subjecting the additional solid residue to pyrohydrolysis includes subjecting the additional solid residue to pyrohydrolysis for a period of time between 2-6 hours.
21. The process according to claim 12 wherein the step (b) of subjecting the solid residue to pyrohydrolysis includes subjecting the solid residue to pyrohydrolysis at a maximum temperature of 450° C. for a period of time between 2-4 hours.
22. The process according to claim 12 further comprising a step (f) of heating the filtrate of step (d) to a temperature of between 150-170° C. for a period of time of between 0.5 and 2 hours to obtain NH 4 HF 2 .
23. Titanium dioxide particles obtained by the process of claim 12 .
24. The process according to claim 12 wherein the titanium ore is a titanium ore containing iron.