TW201706033A - Metal filter - Google Patents

Abstract

The invention comprises a filter which is formed at least in regions of powder particles which contain at least 50 At% molybdenum or tungsten. The filter has at least a region A and a region B, wherein in the region A, the average particle size is less than in the region B. The filter is distinguished by an excellent filter effect and also mechanical stability and is suitable, in particular, for filtering metallic melts.

Description

Metal filter

The present invention relates to a filter formed from at least 50 At% of molybdenum (Mo) or tungsten (W) powder particles in the form of zones. Additionally, the invention relates to a method for producing a filter, and to the use of a filter.

The metal melt or salt melt must often be purified by removing insoluble impurities prior to processing by casting or spraying. Such impurities may be composed of non-melted or non-dissolved particles having a higher melting point than the melt, but may also be solid components such as oxides or carbides of the constituents of the melt. These insoluble particles thus cause unwanted inclusions in the solidified component. In the case of injection molding of the melt, the solid component may cause clogging of the nozzle. The current method for purifying the melt is filtration. For this purpose, the melt is passed through a filter where a solid component above a certain size is retained. Particles smaller than the filter size are not affected.

In the prior art, ceramic filters are often used for removing such unwanted components. The use of metal filters is less common because, in many cases, a chemical reaction occurs between the metal filter and the melt. Ceramic filters offer the advantage of excellent chemical stability for most metal melts (eg, aluminum or magnesium melts). In addition, the ceramic filter provides sufficient pressure stability even at temperatures close to the melting point of the molten metal to be treated. Sex. The most common filter ceramics are alumina, but other oxides, nitrides, and carbides can also be used.

However, such ceramic filters also have certain disadvantages. In the so-called priming, the molten metal must be forced through the open structure of the filter for the first time. In this case, the wetting behavior of the molten metal with the filter material plays a key role. It is well known that oxidized compounds (ceramics) can only be poorly wetted by liquid metal melts. The wetting behavior can be improved by increasing the temperature of the melt, however, due to the thermal stability of the additional components exposed to the process temperature (e.g., the melt bath), increasing the temperature of the melt is not always possible. In this case, it is necessary to increase the pressure required for the priming to enable the flow of the molten metal.

As an alternative, it is also possible to force the melt through the filter in a closed pressurization system. In such systems, metal is preferred as the wall material for the fracture due to the required fracture toughness. In this case, the filter must be the integral component of the vessel. However, ceramic filters are often not directly bonded to metal vessels. Direct fusion by laser or electron beam technology is not possible. Welding is only possible if the ceramic previously had an activator. Welding itself is a key process step. Therefore, special care must be taken to select the right solder material. In many cases, conventional metal solders do not exhibit good stability against metal melts. The same applies to the above activators. Likewise, it must be ensured that the solder material does not penetrate into the provided filter during soldering and thus renders the filter unusable.

In addition to ceramic filters, filters made of refractory metals Mo and W are also known because of their high stability relative to many metal melts. For example, a filter made of W is described in US Pat. No. 3,565,607, and a filter made of Mo is described in JP 10168505 A.

If coarse particles made of Mo or W are used for the production of the filter, the achievable filtration effect (minimum filterable impurities) is limited. If very fine-grained grade powders are used for this production, only very thin filter elements can be produced, which is otherwise too high because of the necessary filtration pressure. However, in the case of thin walled filter elements, it is disadvantageous that the strength is insufficient for many applications. In addition, the brittleness of the refractory metal is also detrimental to the mechanical stability of the filter.

One object of the present invention is to provide a filter that does not have the disadvantages described above. In particular, it is an object of the present invention to provide a filter that separates fine particles from a melt, preferably a molten metal, at low filtration pressures.

This target is achieved by an independent entry in the scope of the patent application.

In this case, the filter is formed at least in the form of a zone, preferably completely formed from powder particles containing at least 50 At% Mo or 50 At% W.

Preferably, the filter has >70 At% Mo or W, especially >90 At% Mo or W. The highest corrosion resistance is achieved when the Mo content or W content is >95 At%, especially >99 At%. Mo-W alloys in the total concentration range are also significantly suitable as filter materials. For example, Mo-W alloys have significant stability relative to zinc melts.

Preferred alloying elements for Mo or W are ruthenium (Re), tantalum (Ta), niobium (Nb), chromium (Cr), zirconium (Zr), hafnium (Hf), titanium (Ti), or rare earth metals. Particularly advantageous materials which may be mentioned are pure W, W-0.1 Ma% to 3 Ma% rare earth oxide, pure Mo, Mo-titanium (Ti)-zirconium (Zr)-C (common name: TZM), Mo-铪(Hf)-C (common name: MHC), Mo-0.1 Ma% to 3 Ma% rare earth oxide, Mo- to 48 Ma%Re, and W- to 26 Ma%Re. As a particularly suitable rare earth oxide, La ₂ O ₃ must be emphasized. In this case, pure W or pure Mo is considered to mean a metal having a conventional technical purity.

The filter has at least two distinct zones A and B. Zones A and B differ in their average particle size, wherein the particle size in zone A is smaller than in zone B. The particle size is determined here by a conventional method (Cu infiltration) in cross section as specified in ASTM E112-13 (instead of grain boundaries, using grain boundaries). Preferably, in zone A, the average particle size is at least 25% smaller than zone B, especially at least 50% less, particularly preferably at least 70% less.

Expressed numerically, the particle size in the region A is preferably from 0.1 μm to 10 μm, and the particle size in the region B is from 0.2 μm to 30 μm.

Here, the zone B has the function of permeable support. Filtration of the metal melt continues in zone A.

The filter according to the invention has an improved filtration effect compared to the prior art, and in particular also has a high thermal strength and mechanical stability, especially at high service temperatures.

Additionally, the filter according to the present invention does not have a macroscopic oxide which will result in a poor wetting behavior. Therefore, the behavior during the priming is also significantly improved compared to prior art filters. A further advantage of the solution of the invention is that the filter according to the invention can be integrally joined to other components in a simple manner. This bonding can be continued by a common method such as electron beam welding, laser welding or resistance welding. Thereby solder material or activator material can also be dispensed with. The undesired reaction of the filter material with the metal melt is thus also excluded.

In an advantageous embodiment, zones A and B are joined to each other using material joining. Material connections include connecting connections that are held together by atomic or molecular forces. Preferably, the material connection between zone A and zone B is achieved by a sintering process. Over The particles of the filter are also preferably joined to each other at least partially on the material by a sintering process. The junction zone between the particles is also referred to as a sintered neck. The material connections of the individual particles ensure that the filter has minimal strength. The non-sinter zone between the particles forms an open channel network that achieves penetration of the metal melt. This situation is shown as an example in Figure la, where the particle size in zone B is denoted as X and the particle size in zone A is denoted as Y. It can be seen from Figure 1b how the metal melt penetrates through the filter via the open channel network, where zone A takes over the filtration function and zone B takes over the support function.

Further, the filter preferably has a porosity of from 10% to 30% in the zone A and a porosity of from 15% to 80% in the zone B. Here, the porosity is determined by mercury porosimetry.

This filter is advantageously used to filter metal melts. The filter according to the invention is distinguished by its excellent stability against many metal melts. For example, aluminum, lead, bismuth, gallium, gold, potassium, copper, lithium, magnesium, sodium, mercury, bismuth, tin, and rare earth metals can thus be filtered in molten form. The maximum temperature at which the filter still has sufficient strength can be taken from Table 1.

In particular, the filter is suitable for filtering tin melt in an EUV system. Extreme ultra violet (EUV) is a photolithography process that uses extremely short wavelength (13.5 nm) electromagnetic radiation. This process permits the reduction in the structural dimensions of the semiconductor components and thus permits the production of smaller, more efficient, faster and more advantageous integrated circuits. EUV radiation is released when plasma is produced. The plasma is produced, for example, by focusing laser radiation. As a medium, tin is used due to high conversion efficiency. The tin melt is filtered to ensure proper purity.

However, the filter according to the invention is not only suitable for metal melts, but it is also advantageous for the filter to filter other liquids, especially at high service temperatures.

The method for producing the filter comprises a pressing step for the production zone B, and applying a suspension for the production zone A. The powder for zone B preferably has a particle size of from 0.2 μm to 30 μm. In this case, the particle size was measured according to Fisher (FSSS-Fisher Sub-Sieve Sizer). A powder having a particle size FSSS of preferably from 0.1 μm to 10 μm is used for the suspension for application of zone A. In order to achieve a sintered neck formation between the particles, the filter workpiece is subjected to heat treatment (sintering) in the range of 1000 ° C to 1800 ° C. Here, the temperature of the heat treatment depends on the material used and on the particle size. In the lower temperature range, a material or fine powder having a low liquidus temperature is sintered. The coarse-grained grade powder or the material having a high liquidus temperature is sintered within the upper limit of the temperature range specified above. Since the particle size of the zone A is different from the particle size of the zone B, it is advantageous to subject the zone B to the heat treatment of the separation even before the suspension is applied. For zone B from 0.2μm to 30μm A preferred particle size range, preferably a heat treatment temperature of from 1100 ° C to 2000 ° C. For the fine-grained grade powder, the lower zone is used again, and for the coarse-grained grade powder, the upper zone is used. The powder consolidation of zone B is preferably continued by compressing the powder into a matrix or by cold equalization pressing in a flexible container (coiler).

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

Figures 1a and 1b each show a schematic structure of an open cell structure of a two-layer filter.

Figure 2 shows the porous structure of Zone B.

Example

The filter element is produced by a two-stage process.

In the first step, W powder having an average particle size (FSSS) of 6 μm was pressed by matrix pressing to form a matrix. Thereafter, a so-called green body (subjected body) was sintered at a temperature of 1800 ° C in a reducing atmosphere (hydrogen gas having a dew point < -20 ° C). By mechanical processing, the sintered substrate becomes the desired shape of the latter filter.

In a second step, W particles are deposited on the porous substrate via a suspension process. For this purpose, the assembly is dipped into a tungsten suspension and dried. The tungsten powder in the suspension had an average particle size FSSS of 0.75 μm. The open cell structure of the region A is formed during the subsequent heat treatment at a temperature of 1600 ° C in a hydrogen atmosphere (dew point < -20 ° C).

The filter thus produced was used to filter aluminum melt (temperature of the melt: 700 ° C) and tin melt (temperature of the melt: 300 ° C). The filter is excellent in filtration, Famous for its high mechanical stability and corrosion resistance.

Claims (13)

A filter formed from at least 50 At% molybdenum (Mo) or tungsten (W) powder particles in the form of a zone, characterized in that the filter has at least two different zones A and B, wherein In this zone A, the average particle size ratio is smaller in this zone B. A filter according to claim 1, wherein in the zone A, the average particle size is at least 50% smaller than in the zone B. A filter according to claim 1 or 2, wherein the average particle size in the region A is from 0.1 μm to 10 μm, and the average particle size in the region B is from 0.2 μm to 30 μm. A filter according to any one of the preceding claims, characterized in that the powder particles are joined to each other at least in the form of zones by means of a sintered neck. A filter according to any one of the preceding claims, characterized in that the zone A has a porosity of from 10% to 30% and the zone B has a porosity of from 15% to 80%. A filter according to any one of the preceding claims, characterized in that the particles are composed of Mo, Mo alloy with Mo > 90 At%, W, W alloy with W > 90 At% or Mo-W alloy. . A filter according to any one of the preceding claims, characterized in that the zones A and B are joined to each other by means of a material connection. A use of a filter according to any one of claims 1 to 7 for filtering a molten metal. The filter is used to filter a tin (Sn) melt in an EUV system, as described in relation to the filter of claim 8. A method for producing a filter according to any one of claims 1 to 7, wherein the production of the zone B comprises a pressing step, and the production of the zone A comprises applying a suspension. The method of claim 10, wherein the method comprises at least the step of producing the zone B by pressing particles having a particle size FSSS from 0.2 μm to 30 μm; by applying the suspension to the The zone A is produced in zone B, wherein the suspension contains powder particles having a particle size FSSS from 0.1 μm to 10 μm; heat treatment zones A and B at 1000 ° C to 1800 ° C. The method of claim 10 or 11, wherein the zone B is subjected to a heat treatment at 1100 ° C to 2000 ° C before the suspension is applied. The method of any one of clauses 10 to 12, wherein the pressing of the zone B is continued with a matrix or by a cold equalization press in the flexible container.