JPH04214836A - Molybdenum material - Google Patents

Abstract

A Mo material, for lamp mfr., is doped with K, Si and Al, the novelty being that the Al content is 80-600 (pref. 100-300, esp. 140-180) wt. ppm. Prodn. of the Mo material involves adding Al as an unstable cpd. (esp. the nitrate) to a pulverised Mo cpd. (esp. MoO3 of more than 99.97 wt. % purity) and then reducing. Pref. the material has an Al/K wt. ratio of 1:0.8-2.0 and an Al/Si wt. ratio of 1:1.8-3.8, the K content being 100-400 (pref. 250-300 or 130-170) wt. ppm and the Si content being 200-700 (pref. 400-600 or 270-320) wt. ppm. After redn., the Mo material is pressed to rod, densely sintered at 1700 deg.C without direct current passage and then worked to form pins, tubes, wires or strip.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to molybdenum materials doped with potassium, silicon and aluminum.

0002

BACKGROUND OF THE INVENTION Molybdenum material is to be understood below as a preliminary material which is used for various purposes, in particular in lamp construction. The end product of molybdenum production, which initially exists as a calcined bar, is subsequently reprocessed only purely mechanically, so that the chemical composition no longer changes. The desired preliminary material is produced by rolling, hammering and drawing. More precisely, this process first produces a wire or pin. The tube or strip material for film production is then produced again as a secondary product from pins or wire.

The doping of molybdenum materials with potassium and silicon in the form of potassium silicate solutions has already been known for some time. For example, US Patent No. 44196
No. 02 describes the use of these elements as additives for molybdenum seal films in order to increase the recrystallization temperature. however,
The material properties of doped molybdenum have a significant scattering width, so that if desired, a material with precisely defined properties could traditionally be obtained by mixing the various components in a very difficult working process. It turned out that I had to adjust it later.

0004

The object of the invention was to achieve an improvement in the material properties of molybdenum semi-finished products, especially for the lamp industry, and to reduce waste.

A further object of the invention was to simplify the process for producing molybdenum materials and to produce them at advantageous costs.

[0006]

[Means for Solving the Problem] The problem is that the molybdenum material contains 80 to 600 ppm of aluminum based on weight.
This can be solved by containing Particularly advantageous configurations of the invention are described in Section 2 below.

In recent years, the demands on the thermal and mechanical load capacity of molybdenum materials have been constantly increasing, especially with regard to the development of halogen incandescent lamps and PAR lamps. First of all, this results in a sufficient specialization of molybdenum materials for different fields of use. For example, various molybdenum materials have been produced for core rods, gas-tight melt pins, supporting wires and sealing films. In the case of supporting wires, the most important properties are high and constant elongation, whereas in the case of sealing films, particularly high ductility and high recrystallization temperatures are of concern. For melting pins and core rods, on the other hand, a suitable combination of high recrystallization temperature and high bending modulus is of decisive importance. Furthermore, in molten pins, the void ratio plays an important role.

[0008] The various required properties were taken into account in each case by means of different dopings with potassium and optionally silicon. This has made the production of semi-finished products extremely complex and inefficient, since machines have to be reequipped and reprogrammed many times. Furthermore, there was a risk of changing the various materials during reprocessing.

Furthermore, there have long been apparently unsolvable problems with the high scattering width of the respective dopings. They were faced with a choice between accepting a high percentage of waste or reprocessing the material, albeit of worse quality. For example, high porosity increases the risk that halogen circulation within the lamp will be disturbed by impurities, leading to premature failure.

By the way, two difficulties have been successfully overcome by moderate additional doping of aluminum. Aluminum chemically combines with potassium and silicon to form a high temperature stable compound, thereby removing potassium that would otherwise uncontrollably evaporate partially (i.e. up to 50%) during the reduction process. Hold. By purposefully adding a certain amount of aluminum, it is now possible to retain the desired precisely defined amount of potassium within the molybdenum material. Particularly advantageous is 1 to 1.5 times more potassium. If aluminum is not added at the same time, potassium evaporates during the manufacturing process in an undeterminable partial amount, so conventionally potassium must first be overdoped, which again influences the material properties. Scattering occurred. This evaporation is now blocked by the addition of aluminum. The same applies to silicon.

This advantageous property is due to the fact that aluminum 80-6
This is achieved by adding 0.00 ppm by weight. Particularly good results are shown when 100 to 300 ppm is used. If significantly large amounts of aluminum (in the permil and percent range) are added, the potassium stabilizing effect of aluminum is overshadowed by its getter properties, especially for O2 (Mikrochimica Ac
ta, 1987. I. S. 437-444). that time,
At the same time, the thermal and mechanical properties are also deteriorated, and in particular the material is no longer suitable for the lamp industry.

However, it has surprisingly been found that the properties of molybdenum materials can be significantly improved with slight doping of the aluminum. A molybdenum material superior to all previously available special molybdenum materials can be obtained. Furthermore, it makes it possible to replace the various molybdenum materials mentioned above with homogeneous and even more improved molybdenum types, which reduces manufacturing costs. Furthermore, in the case of such new molybdenum types, energy savings of up to 25% are possible, since it is now possible to use direct current firing (
This is because high-temperature firing) can be abandoned.
Framund Molybdaen, Akademi
e-Verlag, Berlin, 1959, especially chapter 6). Instead, it now has significantly lower temperatures (approximately 20
The calcination process can be carried out in an extrusion furnace at a temperature of about 1700°C relative to 00°C.

[0013]

EXAMPLES The present invention will be explained in detail below using two examples.

The first molybdenum type contains approximately 160 ppm aluminum, 275 ppm potassium and 500 ppm silicon.
Doped with ppm. The void ratio was less than 1% and the bending modulus was 11.5. This value was measured on wires each having a diameter of 600 μm.

The second molybdenum type contains approximately 150 ppm aluminum, 150 ppm potassium and 30 ppm silicon.
Doping was 0 ppm. The void ratio was approximately 8% and the bending modulus was 6, again measured on a wire having a diameter of 600 μm.

The two examples are each only suitable for capturing the wide variety of uses hitherto covered by the various molybdenum types.

However, the present invention, on the contrary, also intentionally
It can be used to optimize the crystal structure of molybdenum materials for very specific applications. This is because such a structure primarily determines the material properties.

The particularly advantageous molybdenum materials described in the two examples (column I) have, as wires, the following properties compared to conventional materials (column II shows the best measurements of conventional materials in each case). list possible values):
I
II Scattering width of potassium content
±20% / ≧±50% Elongation rate △l/l1
21.5% / 21.0% Elongation constant 1

2% / >4.5% Recrystallization temperature 2
170
0℃ / 1600℃ Gap absence rate 2
≦10%
/ 50% Number of bends 2
6 to 11.5 /
6 1 For a wire diameter of 100 μm 2 For a wire diameter of 600 μm This table clearly shows the improvement in properties, especially the reduction in the scattering width of the potassium content.

The method for producing the molybdenum material is basically carried out by the Coolidge method. The starting material for producing molybdenum products is Mo with a purity of 99.97% by weight.
It is O3. MoO3 in two stages, about 500-60
It is reduced to Mo via MoO2 at a temperature of 0°C (first stage) to 1000-1100°C (second stage). The reduction of the molybdenum oxides is carried out in a manner known per se using H2/N2 mixtures and pure H2 gas. Instead of an extrusion furnace equipped with a boat, a rotary tube furnace is preferably used. Before the first reduction (carried out in the case of Example 2) to molybdenum trioxide, which is initially present as a powder,
Alternatively, later (as carried out in the case of Example 1), potassium and silicon are added as doping substances in a manner known per se as an aqueous potassium silicate solution. At the same time, aluminum is added as nitrate (Al(NO3)3). The use of other unstable aluminum compounds, such as AlCl3, is also conceivable. In contrast, compounds with high stability, such as Al2O3, are unsuitable. This is because the aluminum is not liberated during reduction despite the high temperatures.

[0020] In order to be able to produce a material with the desired ductility,
Molybdenum powder is pressed in a steel mold using a hydraulic press. Optionally, a pre-firing is advantageously carried out at this location. A conventional high-temperature calcination is then carried out in a sintering bell at temperatures up to 2000° C. with direct current (5000 A). This process applies rather to high doping (Example 1). This step can optionally be carried out in an extrusion furnace to increase capacity and save energy, which applies in particular to low doping rates (Example 2). The fired bar thus formed is subsequently processed into a molybdenum wire by rolling, hammering and drawing. This wire can now be used as a lead wire, support pin or so-called electrode (for example in halogen incandescent lamps for automobiles) or as a core rod for producing tungsten filaments. The strip material for the film is obtained from molybdenum wire by further rolling, while the tube can be produced by rolling the wire and subsequent longitudinal bending to form the tube.

In general, the doping of molybdenum with potassium, silicon, aluminum (eg K275 ppm) according to the present invention has no relation to the coincidentally similar doping of tungsten with the same materials. While in the case of molybdenum according to the invention the doping leads to a series of improvements in the overall properties, in the case of tungsten this doping particularly helps the formation of grain length growth, which eventually leads to the sagging of the tungsten wire. It is intended to prevent this. The powder metallurgical suppression of both elements is also not comparable (
Tungsten is fired at a high temperature of 2800°C). The reaction of molybdenum in doping and reduction is fundamentally different from that of tungsten. A possible cause is the bonding energy of the molybdenum compound, which is significantly weaker than that of the corresponding tungsten compound. For example, in the case of molybdenum, as opposed to tungsten, during reduction no stable beta phase is formed that allows the introduction of potassium into the crystal lattice as occurs in the case of tungsten. Therefore, the doping effect in the case of molybdenum can rather be characterized as a surface effect on the crystal lattice. On the other hand, in the case of tungsten, it can be said that there is a volume effect.

The results obtained in the case of tungsten regarding doping with potassium, silicon and aluminum cannot therefore be transferred to individual problems in molybdenum production.

The molybdenum wire rod according to the present invention has a cylindrical bulb made of, for example, hard glass or quartz glass, and a halogen for automobiles has a light emitting body such as a low beam and a high beam held within the bulb by three lead wires. Used for incandescent light bulbs. Optionally, a light reduction plate is also provided. Such a lamp is described, for example, in DE 28 29 677 A1. In a particularly advantageous embodiment, the lead wire and optionally also the light-reducing plate are manufactured from molybdenum wire with additions of 150 ppm aluminum, 150 ppm potassium and 300 ppm silicon. In the case of a bulb made of quartz glass, a molybdenum wire can be used as the support pin and film, but in the case of a hard glass bulb, it is used as a lead wire (electrode) passing through the wire.

Another field of use is high-pressure halogen incandescent lamps with a long axial illuminant, sealed on one or both sides, or with a U-shaped or V-shaped bent illuminant, sealed on one side. It is a halogen incandescent light bulb. In order to support the illuminant, in the first case it is possible to reinforce the lead wire that has separated from the base within the bulb, as described in German Utility Model No. 88 12 010. In the case of tube lamps, a support for the luminous body can also be provided (for example as described in European Patent Publication No. 150
503 Specification). Finally, in the third case, U-shaped or V-shaped
The shaped light emitter may be supported by a frame at the end remote from the base (for example as described in European Patent Publication No. 1
73995). In these cases too, the advantageous embodiments described above are used.

In the case of filament production, the filament is wound around a core made of molybdenum, and the core is finally immersed in acid to dissolve it again.

Claims (8)

[Claims] Claim 1: A molybdenum material doped with potassium, silicon and aluminum,
Aluminum content is 80 to 600 ppm by weight
A molybdenum material characterized by being [Claim 2] Al/K weight ratio is about 1:0.8 to 1:
2. The molybdenum material of claim 1. [Claim 3] Aluminum/silicon weight ratio is about 1:1.
．． 8. The molybdenum material according to claim 1, wherein the ratio is 8 to 1:3.8. Claim 4: Aluminum content is 100 to 300p
The molybdenum material according to claim 1, which is pm. [Claim 5] Aluminum content is 140 to 180p
The molybdenum material according to claim 4, which is pm. [Claim 6] Potassium content is 100 to 400 ppm
Molybdenum material according to any one of claims 1 to 5, having a silicon content of 200 to 700 ppm (in each part by weight). [Claim 7] Potassium content is 250 to 300 ppm
and a silicon content of 400 to 600 ppm.
Molybdenum material listed. [Claim 8] Potassium content is 130 to 170 ppm
and a silicon content of 270 to 320 ppm.
Molybdenum material listed.