DE1034446B - Molten bath and process for the galvanic deposition of firmly adhering coatings of titanium, zirconium, hafnium, vanadium, tantalum, niobium, chromium, molybdenum or tungsten - Google Patents

Description

GERMAN

The invention relates to a bath composition and method for coating Base rivets with corrosion-resistant metals by electrolysis in the salt bath will.

Although a number of metals are easily obtained by electrolysis from aqueous solution as adherent, thin coating can be deposited on a base metal, this leads to the metals Titanium, zirconium, hafnium, niobium and tantalum did not produce a satisfactory result.

The classic electrolytic process. Deposition of these metals uses a bath molten halides, but a, on the cathode only relatively loosely adhering, granular Coating arises.

One non-prior art suggestion is a method of coating Base metals with the aforementioned coating metals described, in which the electrolytic deposited layer is metallically connected to the base metal and adheres firmly. This procedure requires compliance with specified, relatively high temperatures and certain current densities, that is to be deposited Metal is supplied by a solid anode, which the plating metal in either soft Contains shape. However, some difficulties arise from the high bath temperature, such as evaporation of the bathroom.

According to the invention, a base metal is coated with a corrosion-resistant metal at significantly lower temperatures by using a molten bath which contains the metal to be deposited in the form of an alkali fluoride-metal fluoride double salt, hereinafter referred to as double fluoride, and also ¹ U to 10 percent by weight of water.

The salt bath is composed

a) from a larger amount of a single or a mixture of the alkali and alkaline earth metal halides,

b) about 15 to 50 percent by weight of a double fluoride,

c) to about ¹ U to 10 percent by weight of water.
The electrolysis is carried out at an elevated temperature in the

molten salt bath carried out between a solid anode and the base metal as the cathode, whose melting point is significantly higher than the melting temperature of the salt bath.

The coating can be reworked afterwards.

Using the abovementioned molten bath, all can according to the method according to the invention Metals with a melting point above 600 ° C are coated, e.g. B. iron, steel, non-

Weld pool and process

for galvanic deposition

firmly adhering coatings of titanium, zirconium, hafnium, vanadium, tantalum, niobium, chromium,

Molybdenum or tungsten

Applicant:

Horizons Titanium Corporation,
Princeton, NJ (V. St. A.)

Representative: Dr. E. Lichtenstein, lawyer,
Stuttgart, Werastr. 14-16

Claimed priority:
V. St. v. America September 30, 1953

Merle Eugene Sibert, Euclid, Ohio,
and John Townsend Burwell Jr.,

Gates Mills, Ohio (V. St. A.),
have been named as inventors

rusting steel, molybdenum-iron alloys, molyb Danish-nickel alloys, nickel-chromium alloys, nickel-copper alloys, nickel and copper,

In addition, a corrosion-resistant metal of titanium that differs from the metal to be deposited, Zircon, tantalum, hafnium, vanadium, niobium, chromium, molybdenum or tungsten. The shape and size the cathode is only limited by the geometric dimensions of the electrolyzer cell.

The choice of alkali and alkaline earth halides for the salt bath depends only on the desired melting point, e.g. B. has a mixture of Sodium chloride, said double fluoride and water have a melting point of about 700 ° C, while a eutectic mixture of sodium chloride and potassium chloride along with the double fluoride and water already melts at 550 ° C. The bath can also contain a mixture of chlorides, bromides,

5 "iodides and fluorides of lithium, sodium, potassium, Contains magnesium, calcium, strontium and barium.

The metal to be deposited must be present as a double fluoride. Although this double salt in the bathroom

809 577/351

could even be produced by electrolysis with an anode containing the corrosion-resistant metal, it is advantageously added to the bath as a double salt, one component being either Naitrium- or potassium fluoride.

That the surface of the base metal, which is connected as a cathode, is covered with a firmly adhering layer. a corrosion-resistant "metal can be coated in a salt bath, the temperature of which is less than the melting point of either alloy of the two metals, is due to the presence of a small but important amount of water in the bath. It has been found that a Water content of ¹ U to 10 percent by weight must be adhered to, preferably ¹ Zs to 5 ^fl / E. The water can be added to the bath either directly or indirectly, e.g. as hydrating water.

To carry out the method, a cell voltage of at least 4.5 V, preferably from 5 to 8 V, is required, the level of which depends on the dimensions of the cell and the size and shape of the cathode. The voltage is chosen in such a way that current densities of 100 to 500 A / dm ² arise at the KatHöde. Since as far as possible no oxygen, nitrogen or carbon should be present above the bath, the space of the electrolysis cell lying above the bath surface is either pumped empty or flushed with inert gases such as argon. In general, the electrolysis can be continued until the cathode is coated with the desired, dense layer of the corrosion-resistant metal.

If the electrolysis has started in a bath that already has a relatively low water content it is advantageous to readjust the water content continuously or from time to time. The construction and the structure of the cell are of no concern tang, it only has to be used for the cell, a material which during the passage of current is not attacked by the molten salt. Graphite is suitable as a cell material. The graphite cell can either directly connected as an anode, or a graphite rod, a graphite plate or whatever another material that cannot be attacked by free halogen is immersed in the bath as an anode.

After coating, the cathode is removed from the bath and placed in one attached to the cell Cooling chamber cooled in an inert atmosphere. Only the cathode, which is at room temperature, becomes the Exposed to outside air. The salt crust formed on the coating is removed in a conventional manner so that the deposited coating appears.

The following examples illustrate the application of the procedure:

Example I.

600 parts by weight of potassium zirconium fluoride and 12 parts by weight of water are mixed with 1800 parts by weight of sodium chloride. The mixture is heated in a graphite crucible to 750 to 800 ° C and this temperature is maintained in an argon atmosphere. After the salt mixture has melted, the iron workpiece to be coated is completely immersed in the salt bath and a voltage of V is applied between the graphite crucible as anode and the workpiece as cathode in order to generate ^{a cathode current density of approximately 420 A / dm 2.}

After 20 minutes of electrolysis: will removed the cathode from the bath, cooled to room temperature in an argon atmosphere, from the Removed the cooling chamber and washed off the adhering salt crust, leaving a 1.6 mm thick coating metallic zircon is obtained on the iron workpiece. A metallographic study of the workpiece showed that the bond between zirconium and the base metal was uninterrupted proceeded. Adjacent to the bond zone, the base metal had an intermetallic zone of about same thickness as the zirconium coating.

- Example / II

In a salt bath made of ISOCKSE parts by weight of sodium chloride and 400 parts by weight of potassium titanium (IV) fluoride, which contains 20 percent by weight of water of crystallization, is at 770 ° C under the conditions of Example I - carried out an electrolysis. This creates a titanium coating on the cast iron cathode used, which adheres to the base metal with a metallic bond. ".:, :: τ. '■' ::

The degree of purity of the separated layer is relatively insignificant as long as the impurities do not reduce the corrosion resistance of the coating affect. Since the coated workpiece often occurs during the subsequent production process, no more change in shape. experiences, is the ability to change shape the layer insignificant-.

With the method according to the invention Coatings obtained with such properties that the workpieces also ' can be deformed.

Claims (4)

PATENT REVIEW: 1. Molten bath for galvanic deposition of firmly adhering coatings of titanium, zirconium, hafnium, vanadium, tantalum, niobium, chromium; Molybdenum or tungsten, in particular the. metals mentioned as * base metal, characterized in that it contains 15 to 50 weight percent double salt of an alkali fluoride and a fluoride of the corrosion-resistant metal, ¹ U to 10 weight percent water and the remainder an alkali and / or alkaline earth metal halide. 2. Bath according to claim 1, characterized in that; that the water content V2: up to 5 percent by weight amounts to. - 3. Method of galvanic. Deposition of viscous coatings of titanium, zirconium, hafnium, vanadium, tantalum, niobium, chromium, molybdenum or tungsten on in particular the metals mentioned as the basic metal using a bath according to claim 1 or 2, characterized in that the bath is kept under an atmosphere, which are essentially free of oxygen, nitrogen and carbon! and is electroplated with a cathode current density between 100 and 500 A / dm ^2. 4. The method according to claim 3, characterized in that that at a bath temperature of 750 to 800 ° C iron is used as the basic metal. , © 809 577/351 7.58