Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Abstract

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many cases validated experimentally, for light weight or impact energy absorbing structures, as high surface area heat exchangers or electrodes, as implants to the body, and many more. Although great progress has been made in understanding their structure-properties relationships, the large number of different processing techniques, each producing material with different characteristics and structure, means that understanding of the individual effects of all aspects of structure is not complete. The replication process, where molten metal is infiltrated between grains of a removable preform material, allows a markedly high degree of control and has been used to good effect to elucidate some of these relationships. Nevertheless, the process has many steps that are dependent on individual "know-how", and this paper aims to provide a detailed description of all stages of one embodiment of this processing method, using materials and equipment that would be relatively easy to set up in a research environment. The goal of this protocol and its variants is to produce metal foams in an effective and simple way, giving the possibility to tailor the outcome of the samples by modifying certain steps within the process. By following this, open cell aluminum foams with pore sizes of 1-2.36 mm diameter and 61% to 77% porosity can be obtained.

A comparison of the manufacture and mechanical performance of porous aluminium and aluminium syntactic foams made by vacuum-assisted casting

“…Creating shaped or sandwich-type products requires additional specialist equipment and processing steps, and careful process control is vital to achieve accurate products with acceptable reproducibility. Porous aluminium structures, with interconnected porosity, are commonly made by pressurised casting methods that either replicate the cavity left behind after removal of a reticulated polymer foam template from a plaster mould, or fill the gaps within a packed bed of sacrificial salt particles [1,[4][5][6][7][8]. Specialist casting apparatus and protracted additional processing steps, to remove the mould or the salt particles, are required.…”

“…Previous work [9] has shown the potential to adopt an alternative, novel approach to creating syntactic metal foams (SMFs) as alternatives to conventional metal foams and porous metals, by incorporating weak, highly porous, large, expanded glass particles (EGP). The manufacturing technology used to make these novel materials is essentially the same as that to produce microcellular aluminium [5][6][7][8][9], using a pressure differential to infiltrate a packed bed of particles with molten metal. The large particle size enables vacuum casting methods with simple, low cost apparatus, to be utilised.…”

Ceria-coated replicated aluminium sponges as catalysts for the CO-water gas shift process

“…However, no systematic dependence has been found on pore density [31]. On the other hand, the effective thermal conductivity of open cell replicated aluminium metal sponges [32], with a porosity (expressed as a fraction of the whole volume) from 0.57 to 0.77 and pore size between 0.7 mm and 2.4 mm, decreases with increasing porosity, while no pore size influence was found [33]. Another critical issue related to the preparation of structured catalysts is the loading of the active species on the structured carrier.…”

Assessment of the flow behavior and structural performance of open-cell aluminum foams at critical flow conditions of pressure and temperature

“…Depending on the desired structural and mechanical properties, there are different methods for metallic foam fabrication. Some of them are metal deposition [2], the powder metallurgy method [3,4], and the liquid-state processes, i.e., the replication casting technique and the foaming by blowing agent [5][6][7][8][9]. Recently, an unconventional technique to produce metallic foams without foaming agents or space holders has been reported.…”