JP2002030479A - Method for producing a plate made of a refractory metal plated with platinum on one side and use of the plate thus produced - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plate made of a refractory metal plated with platinum on one side and an expanded metal grating produced therefrom, which is suitable for use as an electrode in an electrolytic process and an electroplating process. SOLUTION: Plates of refractory metal of predetermined dimensions are tightly bonded to one another back-to-back, form-fitting, which is coated with platinum on their free surface using molten salt electrolysis, and Then they are separated from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a plate made of a refractory metal whose one surface is plated with platinum and an expanded metal lattice.

[0002]

BACKGROUND OF THE INVENTION Plates or sheets of refractory metal coated with platinum and expanded metal grids made therefrom are often used as anodes in electrolytic and electroplating processes. A typical field of use is, for example, as an inert anode in the electrodeposition of metal and alloy layers, in particular in the production of decorative and / or functional layers made of noble metals or noble metal alloys. Further fields of use are for the electrolytic production of chromic acid from dichromate, for the treatment of chromic acid (oxidation of Cr ³⁺ to Cr ⁶⁺ ), for the oxidation of cyanide, for the recovery of metals by electrolysis, for electrodialysis, for the cathode It is an electrode for corrosion protection and the like.

[0003] The conventional method of producing plates made of refractory metal coated with platinum is based on roll-bonding, wherein a thin platinum foil is roll-coated on one or both sides of the refractory metal. The roll-bonded strips and sheets may then be processed into expanded metal in a known manner by making cuts in the plate and drawing them into an expanded metal grid. This method requires a minimum thickness of platinum foil of at least about 3 μm for mechanical and processing technical reasons. Further reductions in thickness to save expensive platinum are not possible.

[0004] The electrodeposition of platinum on refractory metals is possible in principle and in practice with any smaller thickness. Of course, refractory metal plates suspended in a platinum electrolytic bath are generally coated with platinum. However, platinum plating on one side is sufficient for use as an electrode, which can save expensive platinum on the other hand. However, effective partial resists on refractory metal plates are almost impossible for use in aggressive conditions in platinum electrolytes, and in addition they are associated with considerable special material and processing costs.

[0005] Electroplating of refractory metals from aqueous electrolytes is extremely difficult due to the spontaneous formation of protective films in aqueous solutions. Due to the pre-roughening in an expensive pickling process, a moderate adhesion of the coating can be achieved primarily by mechanical adhesion. Adhesion may be somewhat increased by heat treatment in a reducing atmosphere. Simultaneous deposition of hydrogen during platinum deposition embrittles the platinum layer due to the incorporation of hydrogen into the platinum.

[0006] Poor adhesion to refractory metals and slight ductility of the platinum layer which has been deposited in a substantially aqueous manner, due to its use with severe mechanical loads and deformations, in particular for plates or plates which are coated. Eliminate use in the production of expanded metal from sheets.

[0007]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to find and develop a method by which a plate made of a refractory metal plated on one side with platinum can be produced. It is then suitable that the expanded metal grid can be manufactured, for example, for use as an electrode in electrolytic and electroplating processes.

[0008]

Means for Solving the Problems Incidentally, the above-mentioned problems are as follows.
Plates of refractory metal of predetermined dimensions are tightly bonded together back to back formschluessig, which is coated with platinum on their free surface using molten salt electrolysis and the plates are then It has been found that it can be achieved when separated from each other.

In the method according to the invention, the form-fitting tight connection of the refractory metal plate to be coated with platinum is advantageously achieved by screwing or welding in the edge region of the plate. The plate has dimensions intended for its intended use. Typically, for example, dimensions 400 × 600
mm plate. For the screwing of two plates each, a sufficient number of assembly holes are provided jointly in the edge area, through which the plates are joined together back to back, through which the assembly screwing is performed.
In the case of joining by welding, point-like or full-surface (vollflaec
hig) welds may be provided in the edge gaps of the combined plates.

The applicable refractory metals are titanium, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum, tungsten or alloys of these metals. Titanium is particularly preferred.

Prior to the bonding and coating of the plate, it may be advantageous to remove and activate the oxide from its surface, especially the surface to be coated with platinum. Pickling in sandblasting and acid, for example in a nitric acid / hydrofluoric acid mixture, is advantageous.

For platinum coating on their free surfaces using molten salt electrolysis, the mounted plate pairs are housed in a conventional electroplating apparatus suitable for a molten salt electrolysis process and there as a cathode. It is connected.
Platinum plating is carried out in a melt of sodium cyanide and potassium cyanide at a temperature between 500 and 600 ° C., wherein a sheet of pure platinum serves as a soluble anode as a plate of refractory metal to be coated. Is connected in reverse. The molten electrolyte preferably consists of about 50% by weight of sodium cyanide and about 50% by weight of potassium cyanide and has a platinum content of about 0.5 to 3% by weight during operation. It is preferably adjusted to a current density of 1 to 5 A / dm ² . The platinum layer thickness to be achieved is controlled by the current density and the duration of the coating process. A coating thickness of 0.5-2.5 μm preferably results. In each case, for example, 1
Larger layer thicknesses of up to 0 μm can easily be achieved.

After the platinum plating of the plate pairs, the plates are separated by loosening the screws and / or trimming the edge areas.

After a conventional cleaning and drying step, which is known per se, a plate or sheet of the refractory metal whose desired one side is plated with platinum is obtained and may be subjected to its intended use or further processed. You may.

In a further processing step, after the coating has been performed, the separated plate may be heat-treated in an oxygen-containing atmosphere at 500 to 650 ° C. in order to oxidize the surface not coated with platinum. The duration of the heat treatment may generally be from 1 minute to 60 minutes. This step firstly passivates the non-platinated surface, which is important for use as an electrode during the electrolytic process, since the only platinum-plated surface is the functional layer Because it is. The heat treatment oxidizes the uncoated surface of the refractory metal, which, on the other hand,
These give a distinctly different appearance than the platinum-plated surface. In the case of titanium as base material, an attractive and well recognizable blue color of the non-functional surface can be achieved. This as a result guarantees the identifiability of the functional and non-functional aspects of the corresponding electrodes in the field.

Another processing step is to cut the plate and pull it into an expanded metal grid with one side plated with platinum. The manufacture of expanded metal is known and need not be described in further detail here. Typical mesh size is about 10 × 5 × 1 × 1mm
It is. For use as an electrode in the form of an expanded metal grid, it is advantageous to carry out a heat treatment for the passivation and identification of the non-functional surface after the expanded metal grid has been manufactured. The expanded metal grid may then be cut and / or shaped into a corresponding electrode geometry, depending on the requirements of use.

Independent of the platinum savings achieved by reducing the layer thickness compared to conventional roll-bonding,
The method according to the invention enables a platinum saving of about 70% compared to the general electroplating of expanded metal grids and about 48% compared to the general electroplating of bulk refractory metal plates. . Platinum plating by molten salt electrolysis imparts excellent adhesion to the platinum layer, especially in the case of a single-sided coating for the purpose. This is particularly illustrated by severe mechanical loads, such as bending stresses and drawing and tensioning processes that typically occur in the production of expanded metal grids.

FIG. 1 is an enlarged view of a cross section of a titanium expanded metal lattice having a platinum plating on one side manufactured according to the present invention. Titanium-based material (dark color)
Crack-free platinum plating (light color) firmly bonded to the surface is clearly identifiable.

The plate made of a refractory metal plated on one side made according to the invention and the expanded metal grid plated on one side made of refractory metal are very advantageously used in electrolytic and electroplating processes. Can be used as

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view of a titanium expanded metal lattice manufactured according to the present invention and having one side thereof plated with platinum.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Thomas Engelt Germany Heubach Boelena-Strasse 62 (72) Inventor Gerhard Steinhilbar Germany Aalen Farbach 76 F-term (reference) 4K024 AA12 AB01 AB06 BA07 BC01 CA04 DA06 DB01

Claims (9)

[Claims] 1. A method of manufacturing a plate made of a refractory metal plated on one side with platinum, the plates made of a refractory metal having a predetermined size are tightly joined to each other in a back-to-back shape connection, and the molten salt electrolysis is performed. A method for producing a plate made of a platinum-plated refractory metal on one side, wherein the plate is coated with platinum on its free surface and then separated from one another. 2. The method according to claim 1, wherein the form-locking of the refractory metal plate is effected in the edge region by screwing or welding. 3. The method according to claim 2, wherein the separation of the plates is performed by cutting edge regions. 4. Titanium, zirconium as a refractory metal,
Using hafnium, vanadium, niobium, tantalum, molybdenum, tungsten or alloys of these metals,
A method according to any one of claims 1 to 3. 5. Coating with platinum at a temperature between 500 and 600 ° C. in a melt of sodium cyanide and potassium cyanide, wherein a sheet of pure platinum is coated as a soluble anode. 5. The method as claimed in claim 1, wherein the plate is reversely connected to a plate made of refractory metal.
The method described in the section. 6. After completion of the coating, the separated plate is
2. A heat treatment at 500 to 650 [deg.] C. in an oxygen-containing atmosphere to oxidize a surface not coated with platinum.
The method according to any one of claims 1 to 5. 7. The method according to claim 1, wherein the plate is subsequently provided with a cut and is drawn into an expanded metal grid with one side plated with platinum. 8. The use of a sheet made of a refractory metal plated on one side with platinum, produced by the method according to claim 1 as an anode in an electrolytic process and an electroplating process. 9. Use of an expanded metal grid made of a refractory metal plated with platinum on one side, produced according to the method of claim 7, as an anode in an electrolytic process and an electroplating process.