WO2017008092A1 - Metal filter - Google Patents

Abstract

The invention relates to a filter, which is formed, at least in some regions, from powder particles containing at least 50 at.% of molybdenum or tungsten. The filter comprises at least a region A and a region B, wherein the average particle size is smaller in region A than in region B. The filter is characterized by excellent filter effectiveness and mechanical stability and is suitable in particular for filtering metal melts.

Description

 METAL FILTER

The invention relates to a filter that at least partially

Powder particles is formed, the at least 50 at% molybdenum (Mo) or

Tungsten (W) included. In addition, the invention relates to a method for

Production of a filter and its use.

Metal or molten salts often need to be cleaned prior to processing by pouring or spraying insoluble contaminants. Such impurities may consist of unmelted or undissolved particles having a higher melting point than the melt, but may also be other solid constituents such as oxides or carbides from constituents of the melt. These insoluble particles then lead to unwanted inclusions in the solidified component. In the case of splashing of the melt, the solid components may cause clogging of the nozzle. A common method for the purification of melts is filtration. For this, the melt is passed through a filter, are retained on the solid components from a certain size. Particles containing the

Filter size are not affected.

The prior art often uses ceramic filters to remove these undesirable components. The use of metal filters is less common because it is too chemical in a variety of cases

Reactions between the metal filter and the melt comes. Ceramic filters offer the advantage of excellent chemical stability over most molten metals (eg aluminum or magnesium melts).

In addition, ceramic filters also offer temperatures close to

Melting point of the molten metal to be processed sufficient compressive strength. The most common filter ceramic is alumina, but other oxides, nitrides and carbides can be used.

However, such ceramic filters also have certain disadvantages. In so-called priming, the molten metal must first be forced through the open-porous structure of the filter. Here it plays Wetting behavior of the molten metal with the filter material

decisive role. It is known that oxidic compounds

(Ceramics) can be badly wetted by liquid metal melts. The wetting behavior can be improved by increasing the temperature of the melt, but this is due to the thermal stability of other components exposed to the process temperature (e.g.

Melting tank) is not always possible. In this case, the required pressure for the starter injection must be increased to allow the flow of the molten metal.

Alternatively, the melt may also be in a closed,

pressurized system through the filter. In such systems, metals are preferably used as boiler wall materials due to the required fracture toughness. The filter must be an integral part of the container. However, ceramic filters often can not be connected directly to the metallic container. direct

Welding by laser or electron beam technology is not possible. Soldering is only possible if the ceramic was previously provided with an activator. The soldering itself represents a critical process step. So special attention must be paid to the selection of a suitable process

 Lotmaterials be placed. In many cases, common metal solders do not show good resistance to molten metals. The same applies to the aforementioned activators. It must also be ensured that, during soldering, the solder material does not penetrate into the filter provided and thus makes it unusable.

In addition to ceramic filters and filters from the refractory metals Mo and W are known because these materials have a high resistance to many metallic melts. So is a filter from W in the

No. 3,565,607 A and from Mo in JP 10168505 A.

If one uses coarse particles of Mo or W for the production of the filter, then the achievable filter effect (smallest filterable impurity) is limited. Is used for the production of a very fine powder, so you can produce only very thin filter elements, otherwise the necessary Filter pressure is too high. With thin-walled filter elements, however, it is disadvantageous that the strength is not sufficient for many applications. In addition, the brittleness of the refractory metals adversely affects the

mechanical stability of the filter.

It is an object of the subject invention to provide a filter which does not have the disadvantages described above. In particular, it is an object of the invention to provide a filter which can separate fine particles from melts, preferably metal melts, at low filter pressure.

The object is solved by the independent claims.

The filter is at least partially, preferably completely off

Formed powder particles containing at least 50 at% Mo or 50 at% W. The filter preferably has> 70 At% Mo or W, in particular> 90 At% Mo or W. The highest corrosion resistance can be achieved if the Mo or W content is> 95 at%, in particular> 99 at%. Also, Mo-W alloys in the entire concentration range are suitable in

excellent as a filter material. Thus, Mo-W alloys have excellent resistance to zinc melting.

 Preferred alloying elements for Mo or W are rhenium (Re), tantalum (Ta), niobium (Nb), chromium (Cr), zirconium (Zr), hafnium (Hf), titanium (Ti) or

Rare earth metals. Particularly advantageous materials are pure W, W - 0.1 to 3% by mass rare earth oxide, pure Mo, Mo - titanium (Ti) - zirconium (Zr) - C (common name: TZM), Mo - hafnium (Hf) - C (common name: MHC), Mo - 0.1 to 3 Ma% rare earth oxide, Mo to 48 Ma% Re and W to 26Ma% Re. As a particularly suitable rare earth oxide La ₂ 0 _{3 is to} strike out. Pure-W or Rein-Mo are to be understood as meaning the metals of the usual technical purity.

The filter has at least two different regions A and B. The regions A and B differ in their average particle size, the particle size in the region A being smaller than in the region B. The particle size is in accordance with conventional methods in cross-section (Cu-infiltrated) based on (instead Grain boundary uses particle boundary) to ASTM E112-13. In the region A, the average particle size is preferably smaller by at least 25%, in particular by at least 50%, particularly preferably by at least 70%, than in the region B.

Expressed in terms of values, the particle size in the range A is preferably 0.1 to 10 μm and in the range B 0.2 to 30 μm.

The area B has the function of a permeable support body. The filtration of the molten metal takes place in the area A.

The filters according to the invention have an improved filter effect compared with the prior art and in particular also a higher heat resistance and mechanical stability, in particular at high use temperatures. The filters according to the invention are furthermore free of macroscopic oxides which would cause a worse wetting behavior. Therefore, the behavior in the starter injection compared to the prior art filter is significantly improved. Another advantage of the present solution is that the filters according to the invention can be joined in a simple manner integrally with other components. The joining can be done by common methods such as electron beam welding, laser welding or resistance welding. This can be dispensed with solder materials or activator materials. This also unwanted reactions of the filter material are excluded with the molten metal

In an advantageous embodiment, the area A and the area B are connected to one another in a material-locking manner. Cohesive connections are all compounds in which the

Connection partners are held together by atomic or molecular forces. Preferably, the cohesive connection between the region A and B is realized by a sintering process. The particles of the filter are preferably at least partially cohesively by a

Sintering process connected. The connection zone between the Particles are also called sinter neck. By the cohesive

Connection of the individual particles ensures that the filter is a

Minimum strength. The non-sintered areas between the particles form an openly porous network of channels, the one

Penetration of the molten metal allows. This is reproduced by way of example in FIG. 1a, wherein the particle size in the region B is X and the

Particle size in the area A is denoted by Y. From Figure 1 b it can be seen how the molten metal penetrates through the open-pore network of channels through the filter, wherein the area A takes over the filter function and the area B the carrier function.

Furthermore, the filter preferably has a porosity in the range A of 10 to 30% and in the range B of 15 to 80%. The determination of the porosity is carried out by mercury porosimetry.

An advantageous use of the filter is in the filtering of metallic melts. The filter of the invention is characterized by a very good resistance to a variety of molten metal. For example, in molten form, aluminum, lead, cesium, gallium, gold, potassium, copper, lithium, magnesium, sodium, mercury, bismuth, tin and rare earth metals can be filtered. The maximum temperature at which sufficient resistance is still present can be taken from Table 1. In particular, the filter is suitable for filtering tin melts in an EUV plant. EUV (Extreme Ultra Violet) is a photolithography technique that uses very small wavelength (13.5 nm) electromagnetic radiation. This method enables structure reduction in

Semiconductor components for smaller, more efficient, faster and cheaper integrated circuits can be made. The EUV radiation is released when generating a plasma. The plasma is generated, for example, by focusing laser radiation. Tin is used as the medium because of the higher conversion efficiency. The tin melt is filtered to ensure a corresponding purity. However, the filter according to the invention is not only suitable for molten metals, but it can also be used to filter other liquids, especially at higher operating temperatures advantageous.

Table 1

The method for producing the filter comprises a pressing step for the preparation of the region B and the application of a suspension for the preparation of the region A. The powder used for the region B preferably has a particle size of 0.2 to 30 μm. The particle size is measured according to Fisher (FSSS ... Fisher Sub-Sieve Sizer). For the suspension for the application of the area A powder with particle size FSSS is preferably used from 0.1 to 10 μιη. In order to achieve the sintering necking between the particles, the filter blank is a

Subjected to heat treatment (sintering) in the range of 1 .000 ° C to 1 .800 ° C. The temperature for the heat treatment depends on the material used and the particle size. In the lower temperature range are Materials with low liquidus temperature or fine powder sintered.

Coarse powder or materials with a high liquidus temperature are sintered in the upper part of the previously specified temperature range. Since the particle size of the region A differs from the particle size of the region B, it is advantageous to subject the region B to a separate heat treatment even before the suspension is applied. For the preferred particle size range of the range B of 0.2 to 30 μιη the preferred heat treatment temperature is 1 .100 ° C to 2,000 ° C. For fine-grained powders, in turn, the lower and for coarse-grained powder the upper area is used. The powder consolidation of the region B is preferably carried out by compacting the powder in a die or

cold isostatic in a flexible container (tube presses).

In the following example, the invention will be described in more detail.

Figure 1 a, b show the schematic structure of the open-pored

 Structure of the two-layer filter.

Figure 2 shows the porous structure of region B. Example

 The filter element was produced by a two-stage process. In a first step, W powder having an average particle size (FSSS) of 6 μm was pressed into a base body by die pressing. Thereafter, the so-called green body (pressed body) in reducing

Atmosphere (hydrogen with a dew point <-20 ° C) sintered at a temperature of 1800 ° C. By a mechanical treatment, the sintered body was brought into the desired shape of the later filter. In a second step were on the porous body over a

Suspension process W particles deposited. For this purpose, the component was immersed in a tungsten suspension and dried. The mean particle size FSSS of the tungsten powder in the suspension was 0.75 μm. In a subsequent heat treatment at a temperature of 1600 ° C in one

Hydrogen atmosphere (dew point <-20 ° C), the open-pore structure of the region A formed. The filter thus prepared was used to filter an aluminum (melt temperature: 700 ° C) and a tin melt (melt temperature: 300 ° C). The filter was characterized by an excellent filtering effect, high mechanical stability and corrosion resistance.

Claims

claims  Filter, which is at least partially formed of powder particles containing at least 50 at% molybdenum (Mo) or tungsten (W), characterized in that the filter has at least two different areas A and B, wherein in area A the mean particle size is smaller than in area B. Filter according to claim 1, characterized in that in the region A the average particle size is smaller by at least 50% than in the region B. Filter according to claim 1 or 2, characterized in that the average particle size in the range A is 0.1 to 10 μm and in the range B is 0.2 to 30 μm. Filter according to one of the preceding claims, characterized characterized in that the powder particles are at least partially interconnected via sintered necks. Filter according to one of the preceding claims, characterized characterized in that the region A has a porosity of 10 to 30% and the region B of 15 to 80%. Filter according to one of the preceding claims, characterized characterized in that the particles of Mo, a Mo alloy with Mo> 90 At%, W, a W alloy with W> 90 At% or a Mo-W alloy. Filter according to one of the preceding claims, characterized characterized in that the areas A and B cohesively connected to each other. 8. Use of a filter according to any one of claims 1 to 7 for filtering molten metal. Use of a filter according to claim 8 for filtering a tin (Sn) melt in an EUV plant. Method for producing a filter according to one of  Claims 1 to 7, characterized in that the production of the region B comprises a pressing step and the production of the region A, the application of a suspension. A method according to claim 10, characterized in that the method comprises at least the following steps:  - Producing area B by pressing particles having a particle size FSSS of 0.2 pm to 30 pm;  - Producing the area A by applying a suspension in the area B, the suspension containing powder particles with a particle size FSSS of 0.1 to 10 pm;  - Heat treatment of area A and B at 1000 to 1800 ° C. A method according to claim 10 or 11, characterized; that the area B is subjected to a heat treatment at 1100 to 2000 ° C before applying the suspension. 13. The method according to any one of claims 10 to 12, characterized  characterized in that the pressing of the area B in one  or cold isostatically done in a flexible container.