Method of making open cell material

Details Method of making open cell material Method of making open cell material

2001-08-27

2003-12-09

Jenkins, Daniel J. (Department: 1742)

Powder metallurgy processes

Powder metallurgy processes with heating or sintering

Making porous product

C264S628000, C075S252000

Reexamination Certificate

active

06660224

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of porous materials, and in particular to a method of making an open cell metal or ceramic material.
2. Description of Related Art
Porous metal or ceramic materials are currently used for the fabrication of devices such as filters, heat exchangers, sound absorbers, electrochemical cathodes, fuel cells, catalyst supports, fluid treatment units, lightweight structures and biomaterials. The structures (open/closed porosity, pore size distribution and shape, density) and properties (permeability, thermal, electrochemical and mechanical properties) required greatly depend on the application. Closed porosity is generally sought for lightweight structure while open porosity is particularly sought when surface exchange are involved or when permeability or pore connectivity is required.
Different approaches have been proposed for the fabrication of such porous materials. Good reviews of manufacturing methods and characterization of porous metal or ceramic material are given in Porous and Cellular Materials for Structural Applications, Materials Research Society Symposium Proceedings Vol. 521, Apr. 13-15, 1998, San Francisco, D.S. Schwartz et al. Ed., Materials Research Society; Metal Foams, Fraunhofer USA Metal Foam Symposium, J. Banhart and H. Eifert, ed. Stanton, Delaware, Oct. 7-8, 1998, and R. Soria, “Overview on Industrial Membranes”, Catalysis Today, 25, pp. 285-290 (1995).
Deposition techniques have been used for the fabrication of metal foam. U.S. Pat. No. 4,251,603 and Japanese Patent Laid-Open Patent Application No. 5-6763 describe processes consisting of plating a sponge-like resin and then burning the resin to obtain a metal foam. Deposition may also be done from salts (U.S. Pat. No. 5,296,261) or gas (U.S. Pat. No. 4,957,543). Those processes provide low-density materials having open-cell porosity.
Direct foaming of melts is described in various patents, for example, U.S. Pat. Nos. 3,794,481; 4,713,277; 4,973,358; 5,112,696 and WIPO publications Nos. WO 91/03578, WO 92/03583, WO 94/172218, WO 91/01387, WO 91/19823, WO 94/09931, WO 92/21457, European Pat. No. 0 210803 and Norwegian Pat. PCT/NO90/00115. In techniques described in these patents, foaming is carried out by blowing gases in the melt or adding chemical foaming agents such as titanium hydride which release gas when heated and creates bubble in the melt. Melt viscosity is generally adjusted using additives such as silicon carbide, aluminum oxide, magnesium oxide or calcium. These processes provide foams with good mechanical properties. The resulting foams have closed porosity.
An alternative approach to produce metal foams from liquid metals is the solid-gas eutectic solidification (Gasars) method such as described in U.S. Pat. No. 5,181,549. The method utilizes an enclosed vessel in which a base material is melted. A gas, whose solubility in the base material decreases with decreasing temperature and increases with increasing pressure, is dissolved into the base material. The metal is then cooled at a predetermined pressure to precipitate the gas and form pores in the solidified material.
Investment casting is also known for the fabrication of metal foams. A polymer foam having open pores is filled with a slurry of heat resistant material. The impregnated foam is then dried and heated at moderate temperature to eliminate the polymer. The resulting heat resistant porous structure is then impregnated with a liquid metal. After solidification, the mold is removed using pressurized water. The final metal foam has the original polymer foam structure. The material has good mechanical properties and large interconnected porosity.
Powder metallurgy has also been extensively used to produce porous materials using different approaches. Some techniques use a combination of solid and liquid state processing to produce metal foam from powders. U.S. Pat. No. 3,087,807 by B. C. Allen, M. C. Mote and A. M. Sabroff describes a method to produce lightweight, porous metal structure comprising the step of compacting a mixture containing aluminum powder and a foaming agent, selected from the group consisting of calcium carbonate, zirconium hydride and titanium hydride, which releases a substantial amount of gas at about the melting temperature of aluminum, extruding the resulting compact below the melting point of aluminum to form a rod, progressively heating the extruded rod to at least the melting temperature of aluminum to produce a foam, and rapidly cooling the resulting foamed material to form a lightweight porous structure having a uniform close cell porosity and density of about 0.45 to 0.58 g/cm
3
.
A modified approach, described in U.S. Pat. No. 5,151,246 by J. Baumeister and H. Schrader, consists of manufacturing foamable metal bodies in which a metal powder and a foaming agent powder is hot-compacted to a semi-finished product at a temperature at which the joining of the metal powder particles takes place primarily by diffusion and at a pressure which is sufficiently high to hinder the decomposition of the foaming agent in such fashion that the metal particles form a solid bond with one another and constitute a gas-tight seal for the gas particles of the foaming agent. The foamable metal body can also be produced by rolling.
An approach described in U.S. Pat. No. 5,865,237 by F. Schorghuber, F. Simancik and E. Hartl involves providing compacts of a powder of a metal to be foamed and a gas-evolving foaming agent; heating a volume of said compacts in a heatable chamber communicating with a mold having a mold cavity of a shape complementary to the casting to be made which, upon complete foaming, corresponds at least to the volume of said mold cavity, the heating of said compacts being sufficient to at least partially foam the metal of said powder; while said metal of said powder is being foamed in said chamber, forcing the entire contents of said chamber, formed by foaming of said compacts, into said mold cavity; and permitting residual foaming of said contents in said cavity to distribute the foaming metal to all parts of said cavity and produce a foamed metal body conforming completely to said cavity.
Techniques involving the deposition of powders on polymer medium (foams or granules) have also been developed. Those techniques consist in deposing metal or ceramic particles on a polymer and burning the polymer to obtain porous metal or ceramic materials. U.S. Pat. No. 5,640,669 by K. Harada, M. Ishii, K. Watanabe and S. Yamanaka describes a process for preparing a metal porous body having a three-dimensional network structure by deposing a layer comprising Cu, a Cu alloy, or a precursor thereof on a skeleton composed of a porous resin body having a three-dimensional network; heat-treating the resin body with the layer formed thereon to remove the heat-decomposable organic component, thereby forming a porous metal skeleton of Cu or a Cu alloy. U.S. Pat. No. 5,759,400 by C. E. Fanning describes the fabrication of metal foams by cutting a polyethylene foam to form a substrate having a desired size and shape, submerging the polyethylene substrate into a solvent for a period of time effective to provide a substrate with a tacky surface, coating the tacky surface of the polyethylene with a slurry of copper powders admixed with a binder, drying the impregnated polyethylene foam, burning the polyethylene in a furnace to produce a foam structure consisting of copper and sintering the final product to obtain a rigid structure.
U.S. Pat. No. 5,881,353 by Y. Kamigata, T. Yoshida, K. Susa, T. Uchida and H. Hiratsuka discloses a method for producing a porous body with high porosity by coating a resin foam, such as urethane foam, with an adhesive to impart stickiness to the surface of the foam, and thereafter a powder such as copper oxide powder is applied thereto, followed by heating to remove the substrate and sinter the powder. Thus, a porous body to which the pattern of the base material has been transferred is produced. The powder may be appropri

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