Zinc Foam Research Articles

Investigation of metal foam formation by microscopy and ultra small-angle neutron scattering

Zinc foams were prepared by applying the powder compaction method which comprises mixing zinc powder with a small fraction of a blowing agent, compacting this mix and creating a foam by heat treatment above the melting temperature of the metal. The foaming process which normally leads to a volume expansion of some 500% was artificially stopped in very early stages by quenching. The resulting samples with porosities below 20% were then characterised by microscopy and ultra small-angle neutron scattering (USANS). Foam microstructures, pore morphologies, the locations of the blowing agent particles, pore and particle size distributions and total pore volume fractions were determined. Two mechanisms for pore formation could be identified by microscopy. The pore growth behaviour for different size regimes could be obtained from the USANS distribution curves, thus giving insight into the early stages of metal foam formation.

Deformation characteristics of metal foams

The deformation behaviour of a series of aluminium and zinc foams was investigated by uniaxial testing. Because the deformation behaviour of metal foams is expected to be anisotropic owing to the existence of a closed outer skin and with respect to the foaming direction, a series of measurements was carried out where the orientation of the outer skin and the foaming direction were varied. Stress–strain diagrams and corresponding compression strengths were determined for aluminium- and zinc-based foams. The influence of an age-hardening heat treatment was investigated. Finally, the axial deformation behaviour of aluminium tubes filled with aluminium foam was tested under uniaxial loading conditions. The results of the measurements are discussed in the context of possible applications of metal foams as energy absorbers. © 1998 Chapman & Hall

The removal of zinc from solutions by foam separation, I. Foam separation of complex zinc anions

The effectiveness of zinc foam separation by cetyltrimethylammonium collector increases with increasing chloride, bromide, iodide, and thiocyanate concentration and in relation to the nature of the ligands it follows the order: Zn(Cl) 4 2− <Zn(Br) 4 2− <Zn(SCN) 4 2− ≤Zn(I) 4 2−. Moreover, the experiments show the separation sequence: Co(SCN) 4 2− <Zn(SCN) 4 2− <Cd(SCN) 4 2−. In the presence of acids, the zinc thiocyanate complex removal (and the amounts of zinc in the sublate) decrease with increasing acid concentration in the following sequence: HClO 4<H 3PO 4<HCl<H 2SO 4< no acid. The surface tension of zinc foam separation media decreases with increasing bromide or chloride concentration while it increases with increasing thiocyanate or iodide concentration and changes as follows: Br −<Cl −<SCN −<I −. Moreover, measurements in the presence of different metals and thiocyanate show the surface tension sequence: Co<Zn<Cd. The interpretation of the effectiveness of zinc complex removal as well as the changes in interface phenomena are based on the analysis of interactions in the foam separation medium. The results of foam separation are compared with those of solvent extraction and paper chromatography.

Deformation characteristics of zinc foam

The temperature dependence of the yield stress and energy absorbing capacity of zinc foam, having a density between 0.05 and 0.07 of that of zinc, was determined over a range of temperatures from 0.1 Tm to 0.7 Tm approximately. With increase in temperature over this temperature range, the yield stress and energy absorbing capacity of the foam at first increased, and then subsequently decreased, above room temperature. At low temperatures,e.g. 0.1 Tm, the foam disintegrated into powder, and the energy absorbing efficiency parameters were high and independent of the foam density. In contrast, at the highest temperatures,e.g. 0.7 Tm, the energy absorbing efficiency parameters were lower and decreased with increase in density. The results are interpreted on the basis of the change in deformation mode which occurs in the zinc matrix of the foam over this temperature range,i.e. the transition from cleavage at the low temperature to plastic flow at the high temperature of deformation.