Metal membrane filter, and method and apparatus for the production thereof

#The invention relates to a metal membrane filter and to a method and apparatus for the production thereof, in accordance with the preambles of the independent claims.

#Plastics membrane filters having small pores are produced from plastics films by bombarding the plastics films with ion beams. Such bombardment results in discrete ion beam tracks, which can subsequently be dissolved out from the plastics film so that filter pores of uniform diameter are formed and the plastics membrane filters can be used for separating particles of defined average diameter. That method cannot, however, be applied to metal foils or metal membranes because, on passing through thin metal foils, ion tracks do not leave behind ion tracks that can be etched out as in the case of plastics films.

#The problem of the invention is to provide a metal membrane filter, and a method and apparatus for the production thereof, which metal membrane filter corresponds geometrically to a plastics membrane filter formed by means of an ion beam and a technique of dissolving out the ion beam tracks, wherein the method should transfer the structure of a plastics membrane filter to a metal membrane filter at reasonable cost and wherein the apparatus for the production thereof should be capable of rapid adaptation to different metal membrane filter materials.

#The invention will now be described in greater detail on the basis of embodiments with reference to the accompanying drawings.

#FIG. 1 shows, in diagrammatic form, a cross-section through a portion of a metal membrane filter having a filter pore.

#FIG. 2 shows, in diagrammatic form, a cross-section through a portion of a metal membrane filter having a further filter pore.

#FIG. 1 shows, in diagrammatic form, a cross-section through a portion of a metal membrane filter 1 having a filter pore 2. Reference numeral 3 denotes a metal membrane filter surface, it being possible for the density of the filter pores 2 to be between a single filter pore per cm2 up to 107 filter pores per cm2 of metal membrane filter surface 3. Reference numeral 4 denotes the top of the filter pore 2, which in the embodiment according to FIG. 1 has a rounded-off aperture-rim 5. The filter pore 2 extends from the metal membrane filter surface 3 to the reverse side 30 of the metal membrane filter and has a rectilinear and cylindrical form with smooth internal walls 8, the thickness L of the metal membrane filter being between 5 μm and 200 μm, preferably between 8 μm and 50 μm.

#The diameter d of the filter pore 2 is between a few tens of nanometres and several micrometres. Reference numeral 7 denotes a sharp-edged aperture-rim on the reverse side of the filter pore 2. That sharp-edge aperture-rim 7 is achieved by polishing the reverse side 30 of the metal membrane filter 1. The material of the metal membrane filter 1 consists preferably of gold, platinum, copper, nickel or alloys thereof. A precious metal embodiment in gold was produced at room temperature in a thickness of from 10 to 12 μm. By way of comparison, a further metal membrane filter was produced from gold at 55° C., which differed from the metal membrane filter produced at room temperature in that it had better ductility. The positive pressure for the liquid that is inactive with respect to electrodeposition, for which water was used in this instance, was set at 100 Pa.

#In the case of deposition of a metal membrane filter 1 from platinum, a higher hydrostatic pressure of about 300 Pa was set, with, on the one hand, an acidic platinum electrolyte being used, which yielded a brittle metal membrane filter and consequently limited the thickness to a few micrometres, the brittleness being attributable to a high degree of hydrogen inclusion.