METHOD AND DEVICE FOR FILTERING A PLATINUM BATH BY ELECTRODIALYSIS

Abstract

Method for filtering a platinum bath by electrodialysis, including consecutive steps of extracting fluid from the platinum bat by an extraction current; filtering the fluid extracted during the extraction step, carried out by electrodialysis in a filtering device having an electrodialysis reactor; supplying the platinum bath with the fluid from the filtering step, by a filtered bath current; all of these steps being carried out in a continuous flow.

Claims

1. Method for filtering a platinum bath by electrodialysis, the platinum bath containing Cl.sup. ions and Na.sup.+ ions, the method comprising consecutive steps of: extracting fluid from the platinum bath by means of an extraction current; filtering the fluid extracted during the extraction step, carried out by electrodialysis in a filtering device comprising an electrodialysis reactor; supplying the platinum bath with the fluid from the filtering step, by means of a filtered bath current; all of these steps being carried out in a continuous flow, and the filtering step being carried out when the concentration of Cl.sup. ions in the platinum bath is greater than or equal to a first predetermined threshold value, or the concentration of Na.sup.+ ions in the platinum bath is greater than or equal to a second predetermined threshold value.

2. Method according to claim 1, wherein the filtering device further comprises a filtering current and an electrode current, the fluid extracted from the platinum bath, the filtering current and the electrode current flowing separately in the electrodialysis reactor, the electrodialysis filtering step being performed in the electrodialysis reactor.

3. Method according to claim 1, wherein the temperature of the extraction current in the electrodialysis reactor is between 40 and 65 C.

4. Method according to claim 1, wherein the concentration of Cl.sup. ions in the platinum bath is continuously maintained at a value within a range of 0 to 200 g/L.

5. Method according to claim 1, wherein the concentration of Na.sup.+ ions in the platinum bath is continuously maintained at a value within a range of 0 to 200 g/L.

6. Method according to claim 1, wherein the pH of the platinum bath is continuously maintained at a value in the range of 6.10 to 6.30.

7. Method according claim 1, wherein the filtering step is carried out when the pH of the platinum bath increases by a predetermined value.

8. Method according to claim 1, wherein the filtering step is carried out when at least one regeneration of the platinum bath has been carried out.

9. Device for filtering a platinum bath by electrodialysis, comprising: a platinum bath comprising Cl.sup. ions and Na.sup.+ ions and concentration measuring means for continuously measuring the concentration of Cl.sup. ions and Na.sup.+ ions, the device for filtering being configured to be implemented when the concentration measuring means detect that either Cl.sup. or Na.sup.+ concentration exceeds a predetermined threshold value; a filtering bath and an electrode bath; an electrodialysis reactor fed by an extraction current from the platinum bath, by a filtering current from the filtering bath and by an electrode current from the electrode bath; a filtered bath current from the reactor, which supplies the platinum bath.

10. Method according to claim 1, wherein the temperature of the extraction current in the electrodialysis reactor is 64 C.

11. Method according to claim 1, wherein the pH of the platinum bath is continuously maintained at a value of 6.20.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The invention and its advantages will be better understood by reading the detailed description below of different embodiments of the invention, which are given as non-limiting examples. This description refers to the appended pages of figures, wherein:

[0045] FIG. 1 shows a block diagram of a platinum bath filtering system according to the present disclosure;

[0046] FIG. 2 shows a detailed schematic diagram of the electrodialysis reactor of FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0047] FIG. 1 is a block diagram of a platinum bath filtering device 1 according to the present disclosure. The device 1 comprises a platinum bath B filled at least partially with a fluid comprising one or more platinum complexes to form a metallic bond coat. Under the influence of the electrical current flowing through the bath, the platinum complexes are deposited on the metal part, for example a turbomachine blade part, to form the metallic bond coat.

[0048] For example, to produce one litre of platinum bath B at 8 g/litre of platinum, proceed as follows: [0049] preparation of a solution B: in 300 mL of distilled water (<500 ) at 30 C., put 44.0 g of diammonium hydrogen phosphate of chemical formula (NH.sub.4).sub.2HPO.sub.4 (0.33 mol) and 75.0 g of ammonium dihydrogen phosphate of chemical formula NH.sub.4H.sub.2PO.sub.4 (0.65 mol). The molar ratio between the amount of ammonium dihydrogen phosphate and the amount of diammonium hydrogen phosphate is 2. Once the salts are dissolved, cover the solution and heat to 50 C. for 4.5 hours. [0050] Preparation of solution A: in 300 mL of distilled water at 45 C., add 5 g of sodium hydroxide of chemical formula NaOH (0.080 mol) and 18.3 g of platinum diammonium hexachloroplatinate salt of formula (NH.sub.4).sub.2PtCl.sub.6 (0.040 mol). The molar ratio between the amount of soda and the amount of diammonium hexachloroplatinate salt is 2. Dissolve the platinum salts in solution A; [0051] Once solution B is ready and hot, solution A is prepared and added to solution B previously heated to 60 C. [0052] Finally, the mixture A+B (whose pH is first adjusted to 6.3 by adding a basic solution such as, for example, soda, potash, sodium triphosphate) is heated to 85 C. for 3 hours. All solutions are covered during the heating steps. [0053] More generally, with this solution B comprising diammonium hydrogen phosphate of chemical formula (NH.sub.4).sub.2HPO.sub.4 and ammonium dihydrogen phosphate of chemical formula NH.sub.4H.sub.2PO.sub.4, the pH of the mixture of solutions A+B is fixed between 6 and 10 and preferably between 6 and 7.

[0054] The device 1 also includes an extraction current 10a flowing through a first pipe, a filtering current 20a flowing through a second pipe, and an electrodialysis reactor R. The platinum bath B and the electrodialysis reactor R are connected to each other by the extraction current 10a. The extraction current 10a takes part of the platinum B bath to be filtered and supplies it to the electrodialysis reactor R. A filtered bath current 10b flows through a third pipe and connects the electrodialysis reactor R and the platinum B bath. The filtered fluid, from the electrodialysis reactor R, is then conveyed to the platinum bath B by means of the filtered bath current 10b.

[0055] The combination of the platinum bath B, the extraction current 10a, the electrodialysis reactor R and the filtered bath current 10b forms a circulation loop of the platinum bath, changing from a bath to be filtered state, in the extraction current 10a, to a filtered bath state, in the filtered bath current 10b.

[0056] In addition, the platinum bath B may include concentration measuring means 70 to continuously measure the concentration of elements to be filtered in the platinum bath B. The elements to be filtered can be Cl.sup., Na.sup.+ and NO.sub.3.sup. ions.

[0057] A filtering bath D is connected to the electrodialysis reactor R by the filtering solution current 20a. The filtering bath D contains a fluid that can be, for example, water from the public network. The filtering current 20a takes part of the fluid contained in the filtering bath D and conveys it to the electrodialysis reactor R and then, after passing through the electrodialysis reactor, the fluid returns to the filtering bath D by means of a filtering return current 20b.

[0058] An electrode bath E is connected to the electrodialysis reactor R by the electrode current 30a. The electrode bath E contains a fluid that can have a Na.sub.2SO.sub.4 concentration between 9 g/L and 11 g/L, preferably between 9.5 g/L and 10.5 g/L, more preferably 10.0 g/L. The electrode current 30a takes part of the fluid contained in the electrode bath E and conveys it to the electrodialysis reactor R and then, after passing through the electrodialysis reactor R, the fluid returns to the electrode bath E by means of an electrode return current 30b.

[0059] The three fluids contained in the platinum B bath, the filtering bath D and the electrode bath E respectively circulate separately in the electrodialysis reactor R. To do this, the reactor R has several compartments separated by cationic membranes 44a and anionic membranes 44b parallel to each other, between which the different fluids circulate, without the latter being able to mix with each other. More specifically, as shown schematically in FIG. 2, the reactor R has at least a first compartment 50 in which the extraction current flows, at least a second compartment 60 in which the filtering current 20a flows, and two compartments 42 on either side of compartments 50 and 60, in which the electrode current 30a flows. The reactor R also has two electrodes: a cathode 40a and an anode 40b, arranged on either side of the reactor, along which the electrode current 30a flows. The electrodes, as well as the electrode current 30a, allow the reaction to the electrodes, so that, as they pass through the first and second compartments 50, 60 respectively, the Cl.sup., Na.sup.+ and NO.sub.3.sup. ions contained in the extraction current 10a migrate through the anionic membranes 44b and cationic membranes 44a into the filtering current 20a. More precisely, the Cl.sup. ions contained in the extraction current 10a, cross the anionic membrane 44b to migrate into the filtering current 20a, and are then retained in said filtering current 20a by being blocked by the cationic membrane 44a. Similarly, the Na.sup.+ ions contained in the extraction current 10a, pass through the cationic membrane 44a to migrate into the filtering current 20a, and are then retained in said filtering current 20a by being blocked by the anionic membrane 44b.

[0060] The filtering bath D can also comprise a water supply current 22a, supplying the filtering bath D, and a water extraction current 22b, extracting part of the water contained in the filtering bath D. Indeed, during the filtering steps in the electrodialysis reactor R, the water from the filtering bath D is charged with elements to be filtered, in particular Cl.sup., Na.sup.+ and NO.sub.3.sup. ions from the filtering bath. As the water gradually loses its ability to concentrate in these elements to be filtered, the filtering process loses its efficiency over time. The water supply current 22a and the water extraction current 22b therefore allow the content of the filtering bath D to be continuously renewed. Continuous means that this renewal can be carried out whether or not a filtering process in the reactor R is in progress. Alternatively to the water supply current 22a and the water extraction current 22b, the content of the filtering bath D can be changed when the Cl.sup. concentration reaches a value between 8.0 and 10.0 g/L.

[0061] The filtering method can be implemented when the concentration measuring means 70 detect that either Cl.sup. or Na.sup.+ concentration exceeds a predetermined threshold value. The predetermined threshold value of the Cl.sup. ion concentration in the platinum bath can be for example 11 g/L, and the predetermined value of the Na.sup.+ ion concentration in the platinum bath can be for example 32 g/L.

[0062] The filtering method can also be used when pH measuring means (not shown) detects that the pH of the platinum bath is increasing by a predetermined value. Indeed, during platinum bond coat deposition processes, the pH of the platinum bath tends to decrease. To maintain this pH at a target value, for example 6.20, it is necessary to add soda in the bath. This addition causes the increase in Na.sup.+ ions in the bath. The predetermined value for increasing the pH of the platinum bath is a value to return to the target value. This predetermined value can be, for example, 0.10, allowing to go from a pH of 6.10 to 6.20. Thus, the detection of a 0.10 pH increase characterizes an addition of soda and therefore an increase in the concentration of Na.sup.+ ions in the bath, and thus the need to implement the filtering method.

[0063] The filtering method is also used when at least one regeneration of the platinum bath has been carried out. Indeed, the regeneration process generates an increase in Cl.sup. ions in the platinum bath. Thus, the filtering method is implemented when the pH of the platinum bath increases by the predetermined value, and a regeneration process of the platinum bath has been carried out.

[0064] The different currents (extraction current, filtering current and electrode current) are then circulated by means of pumps (not shown). The elements to be filtered (Cl.sup. and Na.sup.+ ions) contained in the extraction current 10a are then partially transferred to the filtering current 20b, by virtue of the electric current passing through the electrodialysis reactor R. The filtered bath current 10b, which has a lower concentration of elements to be filtered than the extraction current, is then recharged into the platinum bath B. This filtering operation can be performed even when a platinum bond coat deposition process is in progress.

[0065] Although the present invention has been described by reference to specific exemplary embodiments, it is obvious that modifications and changes can be made to these examples without going beyond the general scope of the invention as defined by the claims. In particular, individual features of the different embodiments illustrated/mentioned may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0066] It is also obvious that all the features described with reference to a method can be transposed, alone or in combination, to a device, and conversely, all the features described with reference to a device can be transposed, alone or in combination, to a method.