High-efficiency metal membrane element, filter, and process for making

Abstract

A high-porosity metallic membrane element comprising a sintered element having at least about 55% porosity, the sintered element comprising a matrix of substantially interconnected pores, each of the pores being defined by a plurality of dendtritic metallic particles. A preferred form is made from pure nickel, preferably filamentous nickel powder. The high-porosity metallic membrane element, comprising the aforementioned sintered element having at least about 55% porosity, can be sealed within a filter housing to produce a highly porous filter device with a filtered fluid flow path through the metal membrane element. Also disclosed is a method of making the high-porosity metallic membrane element which includes depositing by air-laying techniques a substantially uniform low-density bed of a sinterable dendritic material into a mold suitable for applying compressive force thereto, compressing the low-density bed of sinterable dendritic material to form a green form, and sintering the green form. The present filter devices exhibit superior porosity and face velocities, negligible outgassing and limited particle shedding when compared to the devices of the prior art.

I claim: 
     
       1. A high-porosity metal filter comprising: a membrane element formed by . .sintering.!. .Iadd.increasing the density of .Iaddend.a mass of dendritic metal particles .Iadd.and then sintering said mass .Iaddend.in the absence of any extraneous material cohesively binding or supporting said dendritic particles forming said mass. .;   each of said metal particles having intertwined appendages and the intertwined appendages between adjacent sintered dendritic metal particles forming a matrix of substantially interconnected pores;.!. .Iadd.whereby .Iaddend.   the porosity of said membrane element . .being defined by said intertwined appendages and being.!. .Iadd.is .Iaddend.at least 55%.   
     
     
       2. The metal filter of claim 1 wherein said porosity is from about 55% to about 70%. 
     
     
       3. The metal filter of claim 1 wherein said metal comprises nickel. 
     
     
       4. The metal filter of claim 1 wherein said element is sintered at a temperature of from about 675° C. to about 725° C. 
     
     
       5. The metal filter of claim 1 wherein a substantially uniform low-density bed of said dendtritic metal particles is formed prior to sintering by air-laying said particles into a mold. 
     
     
       6. A high-porosity membrane filter comprising: a membrane element formed by sintering a mass of dendritic metal particles in the absence of any extraneous material cohesively binding or supporting individual dendritic particles forming said mass;   each of said metal particles having intertwined appendages and the intertwined appendages between adjacent sintered particles forming a matrix of substantially interconnected pores within said membrane element, the porosity of said element being at least 55%;   a filter housing defining a fluid conduit, said housing comprising a casing for retaining said membrane element in said fluid conduit, said casing having an anterior and a posterior with said element being located therebetween and being sealably joined to said casing, said housing thereby defining a filtered fluid flow path; and   means for sealably connecting said casing to a fluid to be filtered.   
     
     
       7. The high-porosity membrane filter of claim 6 wherein the porosity of said membrane element is from about 55% to about 70%. 
     
     
       8. The high-porosity membrane filter of claim 6 wherein said metal particles are nickel particles. 
     
     
       9. The high-porosity membrane filter of claim 8 wherein said membrane element is sintered at a temperature of from about 675° C. to about 725° C. 
     
     
       10. The high-porosity membrane filter of claim 6 wherein a substantially uniform low-density bed of said dendtritic metal particles is formed prior to sintering by air-laying said particles into a mold. 
     
     
       11. A method of making a high-porosity metallic membrane element comprising the steps of: air-laying a substantially uniform low-density bed of a sinterable dendritic material into a mold in the absence of any extraneous material, said mold being suitable for applying compressive force thereto, said bed having a density less than the apparent density of said sinterable dendritic material;   compressing said low-density bed to form a green form; and   sintering said green form.   
     
     
       12. The method of claim 11 wherein compressing said substantially uniform low-density bed of sinterable dendritic material occurs at a pressure below about 500 psi. 
     
     
       13. The method of claim 11 wherein compressing said substantially uniform low-density bed occurs at a pressure below about 1000 psi. 
     
     
       14. The method of claim 11 wherein said sinterable dendritic material comprises nickel. 
     
     
       15. The method of claim 11 wherein said metallic membrane element has a porosity of from about 55% to about 70%. 
     
     
       16. The method of claim 11 wherein said green form is sintered at a temperature of from about 675° C. to about 725° C. 
     
     
       17. The method of claim 11 wherein said membrane element is compressed at a second higher pressure after sintering, thereby imparting additional structural rigidity to said element. 
     
     
       18. The method of claim 11 wherein said membrane element is cut into individual filter elements of a predetermined size. 
     
     
       19. The method of claim 18 wherein said membrane element is cut by wire electrical discharge machining. .Iadd.20. The high-pososity metal filter of claim 1, wherein the density of said mass of dendritic particles is increased by compressing said mass at a pressure below about 500 psi. .Iaddend..Iadd.21. The high-porosity metal filter of claim 20, wherein the density of the mass of dendritic particles of the mass is increased by 
     
     
        applying a pressure to said mass of about 150 psi. .Iaddend..Iadd.22.  The high-porosity metal filter of claim 1 wherein the density of the mass of dendritic particles is increased by applying compression to said mass of dendritic particles. .Iaddend..Iadd.23. The high-porosity metal filter of claim 1, wherein the density of the mass of dendritic particles is sufficiently increased to form a self-supporting green form. .Iaddend..Iadd.24. The high-porosity metal filter of claim 1, wherein the porous membrane filter is formed by sintering said dendritic mass of a temperature of up to about 950° C. .Iaddend..Iadd.25. The high-porosity metal filter of claim 1, wherein the density of said mass of dendritic particles is increased by compressing said mass at a pressure below about 1000 psi. .Iaddend..Iadd.26. The high-porosity metal filter of claim 1, wherein the membrane element is formed by further including the step of compressing the mass of dendritic particles after said mass has been sintered. .Iaddend..Iadd.27. The high-porosity metal filter of claim 26, wherein the membrane element is compressed at a pressure of about 500 psi. .Iaddend..Iadd.28. The high-porosity metal filter of claim 1, wherein the membrane element is compressed at a pressure in a range of between about 600 and about 1100 psi. .Iaddend..Iadd.29. The high-porosity metal filter of claim 1, wherein the membrane element is compressed at a pressure greater than about 1000 psi. .Iaddend..Iadd.30. The high-porosity metal filter of claim 1, wherein the pores of said filter are 
     
     
        substantially interconnected. .Iaddend..Iadd.31.  The high-porosity metal filter of claim 1, wherein the average diameter of pores of said filter is in a range of between about 2 and about 10 μm. .Iaddend..Iadd.32. The high-porosity metal filter of claim 5, wherein the dendritic particles are air-laid through a sieve at least 25 cm above a mold in which said mass of dendritic particles is formed. .Iaddend..Iadd.33. The high-porosity metal filter of claim 32, wherein the metal comprises a metallic material. .Iaddend..Iadd.34. The high-porosity metal filter of claim 33, wherein the metallic material includes nickel. .Iaddend..Iadd.35. The high-porosity metal filter of claim 34, wherein the density of the membrane element is between about 2.75 and 3.0 g/cc. .Iaddend..Iadd.36. The high-porosity metal filter of claim 1, wherein the porosity of said membrane element is greater than about 65%. .Iaddend..Iadd.37. The high-porosity metal filter of claim 36, wherein the porosity of said membrane element is between about 67% and about 72%. .Iaddend..Iadd.38. The high-porosity metal filter of claim 36, wherein the porosity of said membrane element is in a range of between about 70 and about 80%. .Iaddend..Iadd.39. The high-porosity metal filter of claim 6, wherein said mass of dendritic particles is sintered at a temperature of up to about 950° C. .Iaddend..Iadd.40. The high-porosity metal filter of claim 6, wherein said anterior and posterior define a casing wall, and wherein said membrane element is 
     
     
        bonded to said casing wall. .Iaddend..Iadd.41.  The high-porosity membrane element of claim 6, wherein the porosity of said membrane element is between about 67% and about 72%. .Iaddend..Iadd.42. The method of claim 11, wherein said green form is sintered at a temperature of up to about 950° C. .Iaddend..Iadd.43. A method of filtering particulates from a gas, comprising the step of directing the gas through a filter element, said filter element having been formed by sintering, at a temperature of up to about 800° C., a mass of dendritic particles in the absence of any extraneous material cohesively binding or supporting said dendritic particles, whereby said filter element has a porosity of at least about 55%. .Iaddend..Iadd.44. The method of claim 43, wherein the filter element through which the gas is directed is comprised of nickel. .Iaddend..Iadd.45. The method of claim 43, wherein the filter element through which the gas is directed is formed from dendritic particles having an average particle size in a range of between about 2 and about 3 μm. .Iaddend..Iadd.46. The method of claim 43, wherein the filter element through which the gas is directed defines pores having an average diameter in a range of between about 2 and about 10 μm. .Iaddend..Iadd.47. The method of claim 43, wherein the filter element through which the gas is directed has a density in a range of between about 2.75 and about 3.0 g/cc. .Iaddend..Iadd.48. The method of claim 43, wherein the filter element through which the gas is directed is formed by sintering said dendritic mass at a temperature in a range of between about 675° C. and about 725° C. .Iaddend..Iadd.49. The method of claim 43, wherein the filter element through which the gas is directed is formed by air laying said dendritic particles into a mold to form a substantially uniform bed of said dendritic particles prior to sintering. .Iaddend..Iadd.50. The method of claim 43, wherein the filter element through which the gas is directed is formed by increasing the density of said bed of dendritic particles prior to sintering. .Iaddend..Iadd.51. The method of claim 43, wherein the filter element through which the gas is directed is formed by compressing said bed of dendritic particles at a pressure below about 500 psi. .Iaddend..Iadd.52. The method of claim 43, wherein the filter element through which the gas is directed is formed by compressing said bed of dendritic particles at a pressure below about 1000 psi. .Iaddend..Iadd.53. The method of claim 43, wherein the gas being filtered is a semiconductor process gas. .Iaddend.