DE1621264A1 - Refractory metal objects coated with platinum metals or alloys thereof - Google Patents

Description

Dipl.-Phys. W. Kemp

IC ö i π - L 5 η ds π t π α Ι
S-ad.-waia'süricl 20-22

April 17, 1967

JOHNSON, MATTHEY ε CO. LIMITED 78, Hatton Garden, London. E "C1" Bigland

Refractory metal objects covered with platinum metals or alloys thereof

The invention relates to the plating of refractory metals with metals of the platinum group or with at least one metal platinum group alloys. These alloys are referred to as platinum-based alloys in the following description designated.

In particular, but not exclusively, the invention relates to this Plating of objects by means of these metals or alloys, which are used in the glass manufacturing industry, for example, as stirring arms, Crucibles, spinnerets, dies for making pipes and the like. be used.

Among the metals of the platinum group, platinum, rhodium, palladium and iridium in particular have proven to be particularly suitable plating metals Highlighted · Among the alloys composed predominantly of one or more platinum group metals, satisfactory ones have become Results obtained with the following cladding alloys:

109818/028 4 bath original

16 * 1264

Rhodium-iridium, platinum-iridium, palladium-iridium and platinum-rhodium-iridium.

In use, such objects must be exposed to the influence of molten material. Glass at temperatures of up to 1100 ⁰ C and sometimes up to 1500 ⁰ C can withstand. In addition, they should not introduce any measurable impurities into the molten glass with which they come into contact.

Platinum metal and certain rhodium-platinum alloys, for example, have good resistance to molten glass and good strength behavior when in a hot state. Therefore, while it would be possible to manufacture the above items directly from platinum or rhodium-platinum alloys, the cost would be totally uneconomical. A typical iShrarm, for example, has the shape of an inverted ¹ T ', the vertical shaft being approx. 180 cm long and approx. 38 mm in diameter, and the horizontal part approx. 125 cm long and 38 mm in diameter. Normally these and similar parts are made from a core made of a metal, for example molybdenum, which is significantly cheaper than platinum and also has good warm strength behavior, but quickly and completely oxidizes at the temperature of the liquid glass in air; this core is plated with a thin, continuous layer of platinum or an alloy based on platinum. In practice, it has been found that such an object is not only cheaper than a ganzlich made of platinum, but also solid in the temperature range of 1400 ⁰ C, since molybdenum at this temperature-resistant than platinum.

1098Ί8 / Π2Β /,

■ ■. -3-

The sheathing of platinum or rhodium-platinum is usually used so applied * that appropriately shaped parts. made of platinum or Platinum-rhodium alloy wiggled around the object to be plated or be applied to these and then welded together so that they have a well-fitting covering or Form relation to the core. Usually the plating has one or more small Ehtgasungsrohifcen with the border area are in communication between the cladding and the core, but is otherwise gas-tight.

The bid stage of plating involves reducing the pressure of the flow medium (e.g. gas or steam) in the interface between the cladding and the core through the degassing tube or tubes up to a low pressure, whereupon the tube or tubes are sealed by squeezing off. The pressure in this border area is reduced in such a way as to prevent the oxidation of the molybdah core during Prevent use or reduce it to a minimum and improve the fit of the cladding. The fourth, on soft the pressure in this space is reduced, depends, among other things, also depend on the geometry of the core, and can be within some Microns are 2 Torr.

It has been found, however, that such palttiert molybdenum objects fail soon in use. These failures generally take the form of a fracture or bite in the plating, so Molten glass can get through the plating to the underlying motydank. Originally it was believed that this Failures are due to molybdenum being transferred from the core to the Platinum plating diffused into it, u.zw. in the contact zone between

BATH ORIGINAL 10 98 18 / ft? R '=

■ -4- ItSZI

the cladding and the core. For this reason, there is provides at least minimize this effect by allowing to prevent a boundary layer of a refractory material "for example Aluminiuraoxyd, einbraqhte between the Plattxerung and the core to direct contact · Better results were at the lower operating temperatures of about 125O ⁰ C. achieved. when the aluminum oxide was applied to the core by flame spraying, but the improvement was not particularly noteworthy, although this process could extend the useful life of the dysentery arm.

It has now been found that, although the failure of the platinum plating on the diffusion of the moi ^ d'an into the platinum of the platinum is due, the molybdenum passes to the platinum plating in the vapor phase as one or more oxides of molybdenum, wherein it is assumed that the trioxide is the main component. At the working temperature of the agitator arm, the molybdic oxides evaporate, due to the interaction of the core material with the oxygen- rest in the space and become on contact with the inner surface the platinum plating is reduced back to the metal, which can be combined with the Alloyed platinum · The oxygen released in this way is then available available to oxidize further parts of the molybdenum core so that this effect is continuous and after a few hundred hours of work the inner zones of the cladding begin to fail what eventually leads to collapse.

The inventor has now found that the useful life of one with platinum or a platinum-based alloy plated core can be significantly improved by making the core of a metal

18/0284

• i 6 * 126.4

"whose oxides volatilize less easily at operating temperatures of about 1100 to 140O ⁰ C than that of molybdenum. Two core materials that meet these conditions are niobium and tantalum. The core can also be made from chromium or chromium alloys. Since the niobium or tantalum ^{oxides are not very volatile at these operating temperatures (1100-1400 or 1500 0} C), the platinum or the platinum-based alloy is not attacked by the core metal and the operating life of such an arrangement is significantly less found that an object made of molybdenum, which was loosely provided with a 0.5 mm thick platinum plating, the boundary space between the two metals had not been completely evacuated and therefore still contained oxygen residues, at operating temperatures of 1400 ^° C. in air for 400 hours A similar plating on a nion core gave protection under dense lben conditions for a period of 1000 to 2000 hours · This characterizes the advantages achievable by the non-volatile niobium oxides.

Although certain core metals with which the applicant experiments performed, e.g. titanium, zirconium and vanadium, within the stated Temperature range do not form volatile oxides, they form in one certain composition range with the platinum or the alloy based on platinum phases with low melting points, and these low-melting phases ultimately lead to failure the wrapping. The collapse of the cladding metal as a result of the formation of low-melting phases can be reduced quite significantly and consequently significant the business life of the object by providing an interface between the core and the cladding to allow mechanical contact between the two

109313/028 /, "bad original"

1021264

to prevent.

The invention therefore includes the use of a boundary layer, for example between a molybdenum core or a core Niobium, tantalum, chromium or zirconium plated with platinum

a) refractory oxides (not oxides of refractory metals);

b) refractory carbides (including the rare carbides Earth metals);

c) refractory nitrides {e.g. Boron nitride and silicon nitride);

d) refractory sulphides;

e) other refractory assemblies or connections that are compatible with the two at the operating temperatures that occur Substances with which they come into contact are compatible.

As mentioned earlier, an arrangement that has a molybdenum core used, a shorter useful life appears to be desirable and Try to extend this useful life by taking the pressure off is decreased in the interface between the core and the cladding have so far been unsuccessful. Nonetheless, they show Attempts by the applicant suggest that a further reduction in the pressure in the space between the core and the cladding Can prevent migration of the mblybdane oxides to the plating metal.

It has also been found «that the application of a trapping material or "getter" on the surface of the molybdenum in the form of a refractory job supports evacuation and useful life a molybdenum - platinum (or an alloy based on platinum) - Plating improved.

109818 / (1284

The molybdenum core can be injected with a zirconium metal application which leads to a coating consisting of a mixture of metallic zirconium, zirconium oxide and zirconium nitride leads. Because zircon with platinum or one built on platinum Forming an alloy with a low melting point, there must be direct contact between the metallic zirconium and the alloy Plating metal can be essentially prevented and for this purpose zirconia is iaa flame spraying process on the originally applied zircon injected. The amount of first sprayed zircon is chosen so that the amount of available zircon is only a little larger than the one to pick up of the oxygen present in the space is necessary. Preferably the zirconium oxide is porous to allow the rapid movement of gases

In experiments for the purpose of; determining the effect of the zircon a molybdenum core was used as a "getter" in molybdenum plated with platinum Splashed with metallic zircon to a 0.0 - 6 mm thick Layer to get. This layer was then covered with zirconia and the second cover layer was 0.254 nwu thick This core coated in this way was 0.508 mm thick Platinum jacket sealed without evacuating the gap. The useful life of the core was 2000 hours at a working temperature of 14OO ° C.

If desired, the zirconium can also be incorporated into the molybdenum core so that an alloy of, for example, 0.5 to 1.0 percent by weight Zircon-Mölybdan comes about.

- »- - *

BAD ORiGiNAL

-8- IbZ1264

It is also possible to have an assembled core made of molybdenum to use, which is a first coating made of titanium. Zircon or Vanadium and an outer boundary layer of a rare earth oxide.

109818/0284

Claims (1)

Claims 1. Object for use at high temperatures, with a core made of refractory material and with a metal plating, thereby characterized in that the core is made of a refractory metal or a refractory alloy and the cladding is made of platinum or a consists of at least one metal of the platinum group composed of alloy, and further characterized in that the refractory metal or the refractory alloy at working temperature no volatile Oxide forms and that the refractory metal or alloy core does not form an alloy with the cladding, the melting point of which is below the working temperature. 2. Article according to claim 1, characterized in that the core Niobium, tantalum or chromium or an alloy of niobium, tantalum or chromium includes. 3. Article according to claim 1 and 2, characterized in that the Plating includes platinum or an alloy built on platinum. 4 * item according to one of claims 1 to 3t characterized in that that the core is provided with a boundary layer that is a refractory Compound includes which at working temperature with the core and is compatible with the plating. 5 » Object according to claim 4, characterized in that the boundary layer is selected from the group which comprises refractory carbides, refractory suicides, refractory borides, refractory sulfides, refractory nitrides and refractory oxides BAD ORlGiNM. 109818 / Π28Α Ί621264 -to - 6. The subject of .Anspruch 4 »characterized in that the Boundary layer made of a nitride or an oxide or a carbide of a rare earth metal. 7. Article according to claim 1, characterized in that the core is made of molybdenum and the cladding is made of platinum, and further characterized in that the pressure in the intermediate space between the core and cladding is reduced to less than one thousandth of a Torr. 8. Article according to claim 7, characterized in that the core 'is provided with a boundary layer according to one of claims 4, 5 or 6. ■ ft-}