ALLOYS OF THE TYPE FE3AITA(RU) AND USE THEREOF AS ELECTRODE MATERIAL FOR THE SYNTHESIS OF SODIUM CHLORATE OR AS CORROSION RESISTANT COATINGS
Disclosed is an alloy of the formula: Fe3−xAl1+xMyTzTat wherein M represents at least one catalytic specie selected from the group consisting of Ru, Ir, Pd, Pt, Rh, Os, Re and Ag; T represents at least one element selected from the group consisting of Mo, Co, Cr, V, Cu, Zn, Nb, W, Zr, Y, Mn, Cd, Si, B, C, O, N, P, F, S, CI, Na and Ti; and Ta represents tantalum. Such an alloy can be used as an electrode material for the synthesis of sodium chlorate. It can also be used as a coating for protection against corrosion.
The present invention relates to new catalytic alloys based on Fe, Al, Ta and catalytic species such as Ru.
The present invention also relates to the use of such catalytic alloys as electrode material for the synthesis of sodium chlorate.
TECHNOLOGICAL BACKGROUNDNanocrystalline alloys of the formula
Fe3−xAl1+xMyTz
wherein
M represents at least one catalytic specie selected from the group consisting of Ru, Ir, Pd, Pt, Rh, Os, Re and Ag;
T represents at least one element selected from the group consisting of Mo, Co, Cr, V, Cu, Zn, Nb, W, Zr, Y, Mn, Cd, Si, B, C, O, N, P, F, S, Cl and Na;
x is a number higher than −1 and smaller than or equal to +1
y is a number higher than 0 and smaller than or equal to +1
z is a number ranging between 0 and +1
have been disclosed recently as efficient cathodic materials for the synthesis of sodium chlorate (see CA 2,687,129 and the corresponding international application WO 2008/138148). These catalytic materials, when use as cathode for the electrosynthesis of sodium chlorate show very low cathodic overpotentials and they do not absorb hydrogen when the H2 evolution reaction takes place on their surfaces. These materials also show good corrosion resistance in the sodium chlorate electrolyte under typical industrial operating conditions (NaClO3: 550 g/l; NaCl: 110 g/l; NaCr2O7: 3 g/l; NaClO: 1 g/l; pH=6.5 and temperatures around 70° C.).
Although corrosion resistance of these Fe3−xAl1+xMyTz alloys is quite good at pH 6.5, it is not the case in acidic conditions. Standard industrial practises use acid wash from time to time to clean electrochemical cells and electrodes. To do so, HCl solutions at concentrations varying between 3% (˜1M) and 9% (˜3M) are often used. When the above mentioned alloys are put in contact with such concentrated acidic solutions, they can be severely damaged. Indeed, the corrosion resistance of these new catalytic alloys in HCl solutions at low pH is not so good.
SUMMARY OF THE INVENTIONTo solve this problem, the inventors of record have search new formulations and have discover surprisingly that the addition of a small amount of Ta to these materials could make these new alloys not only highly resistant to corrosion in chlorate electrolyte but also in acidic (HCl) solutions without loosing any performance regarding the electrochemical synthesis of sodium chlorate.
Fe3Al(Ru) alloys are often single phase solid solutions usually prepared in a nanocrystalline form by mecanosynthesis. A powder mixture of ruthenium and iron aluminide is milled intensively for several hours until the Ru catalytic element enters and gets highly dispersed into the cubic crystalline structure of iron aluminide (Fe3Al). The nanocrystalline Fe3Al(Ru) alloy thus formed is highly active thanks to its high surface area and highly dispersed electrocatalytic element.
The present inventors have actually found by investigating various ternary phase diagrams that Ta (tantalum) which is known to be a good corrosion resistant element, is quite soluble in Fe—Al alloys. Therefore, Fe3Al(Ru)Tat with various Ta concentration “t” can be prepared as a single phase material by mechanosynthesis very easily and these new alloys show not only good electrocatalytic activity towards the electrosynthesis of sodium chlorate but also good corrosion resistance in the sodium chlorate electrolyte as well as in concentrated HCl solutions.
Therefore, the first object of the present invention is an alloy characterized by the following formula:
Fe3−xAl1+xMyTzTat
wherein:
M represents at least one catalytic specie selected from the group consisting of Ru, Ir, Pd, Pt, Rh, Os, Re and Ag;
T represents at least one element selected from the group consisting of Mo, Co, Cr, V, Cu, Zn, Nb, W, Zr, Y, Mn, Cd, Si, B, C, O, N, P, F, S, Cl, Na and Ti;
x is a number higher than −1 and smaller than or equal to +1
y is a number higher than 0 and smaller than or equal to +1
z is a number ranging between 0 and +1
and t is a number higher than 0 and smaller than or equal to +1, preferably lower than 0.4 and more preferably lower than or equal to 0.2
The alloy of the invention is preferably in a nanocrystalline state. If nanocrystalline, the crystallites are smaller than 100 nm. The alloy is also preferably a single phase material with a cubic crystallographic structure but can also be multiphase depending on the x, y, z and t composition. Most of the time, these alloys are metastable. In other words, they decompose or transform into a different state when heated at high temperatures. But again, they can also be thermodynamically stable depending on the x, y, z and t composition.
A second object of the present invention is the use of such alloys as electrode material for the synthesis of sodium chlorate. In order to prepare an electrode of these alloys, several methods can be used. A preferred one is thermal spray such as the high velocity oxyfuel (HVOF) technique using the alloy in powder form as feedstock for the spray gun. If the method of preparation involves a rapid quenching process, the alloy can be prepared in a nano crystalline state.
Even though, the preferred application of these new materials is sodium chlorate, several other electrochemical processes can take advantage of these alloys such as industrial and swimming pool water treatment.
Moreover, since the corrosion resistance of these new alloys is very good in various conditions, a third object of the present invention is the use of these alloys as coating for the protection against corrosion. If the targeted application is a coating for protection against corrosion, there may be no advantage of adding a large amount of expensive catalytic element to the alloy. In these cases, the molar content “y” can be chosen small to reduce costs. Moreover, it may be advantageous to add some Ti (titanium) to the alloy since Ti is also known for its good corrosion resistance and the inventors of the present invention found that Ti like Ta is quite soluble in iron-aluminium alloys.
The invention and its associated advantages will be better understood upon reading the following more detailed but not limitative description of preferred modes of achievement of it, made with reference to the enclosed drawings.
As it can be seen,
Claims
1. An alloy of the formula: wherein:
- Fe3−xAl1+xMyTzTat
- M represents at least one catalytic specie selected from the group consisting of Ru, Ir, Pd, Pt, Rh, Os, Re and Ag;
- T represents at least one element selected from the group consisting of Mo, Co, Cr, V, Cu, Zn, Nb, W, Zr, Y, Mn, Cd, Si, B, C, O, N, P, F, S, Cl, Na and Ti;
- x is a number higher than −1 and smaller than or equal to +1
- y is a number higher than 0 and smaller than or equal to +1
- z is a number ranging between 0 and +1
- Ta represents tantalum and t is a number higher than 0 and smaller than or equal to +1.
2. The alloy according to claim 1, characterized in that t is a number lower than 0.4.
3. The alloy according to claim 2, characterized in that t is a number lower or equal to 0.2.
4. The alloy according to any one of claims 1 to 3, characterized in that it is a material with a nanocrystalline structure.
5. The alloy according to any one of claims 1 to 4, characterized in that it is a material with a single phase metastable structure.
6. A method of fabrication of an alloy as claimed in any one of claims 1 to 5, in powder form, which consists of milling intensively a mixture of an iron aluminide powder with powders of the M, T and Ta species.
7. A coating of an alloy as claimed in any one of claims 1 to 5, which is prepared by using the powder according to claim 6 and a thermal spray technique to project the powder on a substrate thus producing a coated electrode or a corrosion resistant coating.
8. A corrosion resistant coating according to claim 7, characterized in that it is made of an alloy according to claim 1 containing Ti.
9. Use of an alloy according to any one of claims 1 to 5, as an electrode material for the synthesis of sodium chlorate.
10. Use of an alloy according to any one of claims 1 to 5, as a coating for protection against corrosion
Type: Application
Filed: Apr 26, 2013
Publication Date: Apr 9, 2015
Inventors: Robert Schulz (Ste-Julie), Sylvio Savoie (Ste-Julie)
Application Number: 14/403,296
International Classification: C25B 1/26 (20060101); C23F 13/14 (20060101);