JPH042657B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lithium-tungsten alloy used in a filament for a light bulb and a method for manufacturing the same.

[Prior Art] Tungsten or tungsten alloy is generally referred to as an ultra-high temperature material and has the highest melting point among metals, reaching a temperature of 3400°C.

In addition, it has excellent mechanical strength even under high temperatures with low vapor pressure, so it can be used in vacuum tubes, incandescent bulbs, fluorescent lights, furnace reflectors, heating elements, X-ray tube targets, rocket parts, etc. It is widely used where it is needed.

However, tungsten or tungsten alloys have the property that their mechanical strength decreases significantly after recrystallization, so once recrystallized materials are processed under normal conditions, brittle fracture will occur. It was hot.

Therefore, in order to prevent such brittle fracture, attempts have been made to manufacture using a doped tungsten powder raw material to which a recrystallization inhibitor or ductility enhancer is added.

That is, in the conventional manufacturing method of tungsten or tungsten alloy using doped tungsten, first, potassium oxide is added to the tungsten oxide powder raw material.
Doped tungsten metal powder containing appropriate equivalent amounts of dopants containing K2O3, silica SiO2, and alumina Al2O3 is made, and this is made into a metal body by powder metallurgy, followed by swaging or processing at a processing temperature of around 1500℃. Initial processing such as rolling and forging is performed.

Here, by swaging, rolling forging, etc., the internal structure of the doped tungsten metal body is crushed along the stress direction during processing, and the internal structure of the doped tungsten metal body is crushed in the direction perpendicular to this stress direction, that is, the length direction of the crushed metal body. The fibers are stretched along the fibers, forming a fibrous texture.

Furthermore, when compression processing is performed, processing is continued while gradually lowering the processing temperature. For example, when compression processing is performed to about 30% of the thickness of the doped tungsten metal body at the initial processing, the processing temperature is approximately 30%. The finishing process is done at a temperature of 1000℃.

At this time, the doped tungsten metal body that has been processed into a plate or rod shape is bent at room temperature or slightly heated, so that the fibrous texture inside the body further develops and becomes tougher. It becomes possible to perform molding processes such as processing. Furthermore, a higher appropriate temperature (400-900
If the temperature is selected, the material can be made to withstand strong processing such as punching, wire drawing, or thin plate rolling.

[Problems to be Solved by the Invention] However, the doped tungsten metal body consisting of a long fibrous texture once developed by the conventional manufacturing method is difficult to process when it is actually used for a filament of a light bulb. Although it varies depending on the amount of strain applied to the inside and the amount of recrystallization inhibitor added, it usually recrystallizes in granular form in the range of 1250 to 1400°C, and under certain temperature conditions, the crystal particles further become
They had the disadvantage that they grew together and became coarse.

For this reason, at room temperature, recrystallized doped tungsten has a strength comparable to that of glass or porcelain, which is completely brittle against external impacts, and there is a problem of deterioration in the yield of products that can actually withstand use such as filaments for light bulbs. I was getting used to it.

Particularly, when filaments for light bulbs containing halogen gas are actually used under conditions exceeding 2800°C, deterioration in sagging resistance and service life have become major problems.

In view of the above-mentioned drawbacks, the technical problem of the present invention is to provide a sagging-resistant material that suppresses grain growth of crystal grains by preventing recrystallization of a doped tungsten metal body at high temperatures during actual use. An object of the present invention is to provide an excellent lithium-tungsten alloy and a method for manufacturing the same.

[Means for Solving the Problems] According to the present invention, a lithium-tungsten alloy with excellent sagging resistance is obtained, which is characterized by comprising 0.001 to 0.5% lithium and the balance tungsten in terms of weight ratio.

Further, according to the present invention, a mixed powder forming step of adding a lithium salt solution to a tungsten oxide powder raw material, mixing and drying to form a mixed powder, and reducing the mixed powder in a reducing atmosphere to form a doped tungsten powder. and a sintering step of sintering the doped tungsten powder in a reducing atmosphere so that 0.001 to 0.5% of the lithium remains by weight after compression molding the doped tungsten powder. A method for producing a lithium-tungsten alloy having excellent sagging resistance is obtained.

Furthermore, according to the present invention, the weight ratio is from 0.001 to
A lithium-tungsten alloy with excellent sagging resistance is obtained, which is characterized by comprising 0.5% lithium, 0.05 to 0.1% metal oxide, and the balance tungsten. Preferably, a lithium-tungsten alloy is obtained in which the metal oxide is an oxide of at least one substance selected from silicon, aluminum, and potassium.

That is, the present invention provides a method for adding lithium (Li), a volatile element, to doped tungsten containing a recrystallization inhibitor, which is an oxide of potassium, silicon, and aluminum, in an amount ranging from 0.001 to 0.5% by weight. It is added so that it remains in the

As a result, due to the formation of a dispersion-strengthened skeleton in the tungsten metal body due to the evaporation of lithium during the sintering process, and the remaining trace amounts of lithium and recrystallization inhibitor in the metal body, the tungsten metal body itself It is possible to raise the recrystallization temperature (1600 to 1800°C), and even when recrystallized, the crystals grow in the form of fibers.

Therefore, unlike in the past, the particles do not become granular and grow together and become coarse.
Even at high temperatures (1700 to 2000°C) during actual use, the fibrous texture with excellent sagging resistance can be maintained.

[Example] An example of the present invention will be described with reference to the drawings.

First, in the mixed powder forming step, a solution of metal salts consisting of aluminum, silicon, and potassium, which are usually doping agents, and a chemical solution of lithium are mixed into the tungsten oxide powder raw material, or
After mixing and drying only the lithium compound solution, in the doped tungsten powder forming process,
Doped tungsten powder is formed by heat reduction treatment at approximately 800°C in a hydrogen furnace.

Here, aluminum chloride solution, potassium chloride solution, and potassium silicate solution are generally suitable as the metal salt solution used as the doping agent, and lithium chloride solution is actually suitable as the lithium compound solution.

Note that lithium was contained in an amount of about 0.5% by weight.

Next, in the sintering process, the doped tungsten powder is compacted and pre-sintered at approximately 1100°C in a hydrogen furnace, and then electrically sintered in a hydrogen gas atmosphere to form a rod-shaped ingot. create.

At this time, the so-called direct sintering step in which sintering is normally performed was carried out so that lithium remained in the range of 0.005 to 0.04% by weight. Additionally, in this direct sintering process, most of the aluminum and silicon evaporate, resulting in less than 0.001% potassium and less than 0.001% potassium.
Silicon remained at 0.004% or less.

Next, the obtained ingot was tested for sagging resistance.

First, the obtained ingot has a specific gravity of 17.0~
17.7, and is finished to the specified dimensions (about 0.5 mm in diameter) by rolling, wire drawing, and drawing while the temperature drops from 1600℃ to 200 and 300℃.
A filament was created by coiling. Also,
Filaments made of doped tungsten manufactured using conventional methods that do not contain any lithium were prepared for comparison purposes, and each of these was incorporated into a halogen light bulb simulator to compare the filament lifespan and sagging resistance. , the result is the first
It is shown in Fig. 2 and Fig. 2.

While the lifetime of a filament made of doped tungsten produced using a conventional manufacturing method that does not contain any lithium is approximately 200 to 600 hours, as shown in Fig. The life of the filament (indicated as "tungsten + lithium" in Figure 1) increases significantly from about 300 hours to about 1000 hours as the lithium content increases.
Moreover, from this, an example of the present invention in which tungsten is mixed with a normal dopant except for potassium and lithium is added to this (indicated as "normal dopant except for potassium + lithium" in Fig. 1), and a normal dopant to tungsten is It was observed that the life of the filament was further extended in the example of the present invention (indicated as "normal dope + lithium" in FIG. 1) in which lithium was added to the mixed dopant.

As shown in Figure 2, regarding the sagging resistance of the filament, the remaining lithium content is 0.005
% to 0.03%, improvement in sagging resistance is observed, and it can be seen that as lithium increases, sagging resistance also improves.

[Effects of the Invention] As described above, according to the present invention, by increasing the recrystallization temperature of the doped tungsten structure and preventing recrystallization at high temperatures during actual use, grain growth of crystal grains is reduced. It is possible to provide a lithium-tungsten alloy with excellent sag resistance and a method for manufacturing the same.

Therefore, by using the lithium-tungsten alloy of the present invention in a filament for a light bulb, the life of the filament can be greatly improved and significant economic effects can be obtained.

[Brief explanation of drawings]

FIG. 1 is a correlation diagram showing the relationship between the life of the filament and the remaining amount of lithium, and FIG. 2 is a correlation diagram showing the relationship between the amount of drooping over the life of the filament and the remaining amount of lithium.

Claims (1)

[Claims] 1. A lithium-tungsten alloy with excellent sagging resistance, characterized by comprising 0.001 to 0.5% lithium and the balance tungsten by weight. 2. A mixed powder forming step in which a lithium salt solution is added to a tungsten oxide powder raw material, mixed and dried to form a mixed powder, and a doped tungsten powder forming step in which the mixed powder is reduced in a reducing atmosphere to form a doped tungsten powder. and a sintering step of sintering the doped tungsten powder in a reducing atmosphere so that 0.001 to 0.5% of the lithium remains by weight after compression molding. A method for producing a lithium-tungsten alloy with excellent properties. 3. The method for producing a lithium-tungsten alloy as set forth in claim 2, wherein the step of forming doped tungsten powder includes a heating reduction treatment. manufacturing method. 4. In the method for manufacturing a lithium-tungsten alloy according to claim 2 or 3, the sintering step includes compression molding the doped tungsten powder, pre-sintering it, and then sintering it by electrical current. A method for producing a lithium-tungsten alloy having excellent sag resistance. 5 0.001-0.5% lithium, 0.05-0.5% by weight
A lithium-tungsten alloy with excellent sag resistance, consisting of 0.1% metal oxide and the balance tungsten. 6. The lithium-tungsten alloy according to claim 5, wherein the metal oxide is composed of an oxide of at least one substance selected from boron, aluminum, and potassium. Lithium-tungsten alloy with excellent properties.