Technology Offer

Ref: 07 CH RAEP 0I6B

Date: 29/06/2007 20:29:23

Title: Replication process for manufacture of highly porous metallic foams

Abstract: A research laboratory from a Swiss engineering school has patented a process for manufacture of highly porous metallic foams. The pre-form, obtained by mixing salt (NaCl), flour and water, is easy to shape, non-toxic and rapidly removed by contact with water. The porosity of the metallic articles can be tuned up to 40 to 90 %vol. and presents a high degree of interconnectivity. Industrial partners are requested for joint development, integration of the process and license agreement.

Description: The expertise of a Swiss research laboratory is focused on science and engineering of structural metallic materials, in particular on advanced metallic material, including metal matrix composites and metal foams. Several methods exist for production of highly porous metallic material; among them, the replication processing is well adapted for open-pore microcellular structures. For example, NaCl-based replication methods are promising for fine pore sizes, but present difficulties for large pore sizes and variable pore shapes. Moreover, this process lacks industrial scalability, particularly in large components due to the long time required for the dissolution step. The development of the replication method described here uses a paste that is made by mixing salt (NaCl), flour and water. This paste can be shaped, by hand or by any conventional shaping process commonly used in (for example) the food industry, into a pre-form with the desired shape. The size, the shape and the volume of the porosity can be tuned in the final porous metal article. This pre-form is then baked to harden while retaining this shape. During the thermal treatment, the pre-form loses organic components (flour) and water, leaving a moulded salt pre-form that contains many fine pores. It is placed in a mould and metal is cast to penetrate the spaces around baked paste elements. After solidification and machining (if required), the pre-form is rapidly removed by contact with water, due to interconnectivity of the small holes and the NaCl small grain size. The porosity obtained in the resulting metallic article can vary from 40 to 90 %vol., with a high degree of interconnectivity. This replication method has been validated at laboratory scale with 99.99% pure aluminium and aluminium alloys. Metallic foams can be interesting in a variety of applications: - Core materials for sandwich or energy absorbing structures. - Solid metal reinforcing phase. - Baffles. - Filters. - Wicks. - Catalyst support. - Heat exchanger (gas or fluid). . The foams produced by the current process are especially suitable for the last five applications. Innovative Aspects: - Ease of shaping pre-form to whatever required form. - Ease to tune the pore microstructure. - Interconnected porosity in metal. - Sufficient strength of the pre-form at liquid metal temperature. - Chemical inertness of the pre-form in contact with metal. - Non-toxicity and low cost of all materials involved in the pre-form. - The pre-form is removed rapidly and easily.