Effect of CaCO₃ Foaming Agent at Formation and Stabilization of Al-Based Foams Fabricated by Powder Compact Technique

Abstract

The paper presents the results obtained by in situ observation of Al-based foams formation at heating of powder compacts with calcium carbonate (CaCO 3 ) by comparing with those prepared with conventional titanium hydride (TiH 2 ). Foamable precursors comprising powder of either pure aluminium or AlZnMg-alloy were used for detailed investigation of foam evolution and stability. High temperature X-ray furnace was applied for in situ visualization of foam formation. It was identi ed that expansion and stability of foams with CaCO 3 are much superior to those with TiH 2 . Distribution and size of solid inclusions (network of oxide remnants, particles of foaming agent, secondary reaction products, and solid oxide skin) in the cell wall materials of studied foams as well as relevant wetting data were determined to clarify the difference in foams stability. Improved stability of foams with CaCO 3 is explained on the base of stabilizing models developed by Kaptay by assuming an interfacial force, the disjoining pressure, which ef ciency is variable and dependent on the distribution and wetting behaviour of the clustered oxide network/solid particles in foamy melt.

High porosity micro- and macro-cellular copper foams with semi-open cell microstructure toward its physical and mechanical properties

“…In this study, the optimal strength value of the foam was higher than the one reported by Michailidis et al [17] in which sugar and dissolution were applied as a foaming agent and foaming agent removal method, respectively. It is noteworthy that the optimal amount of strength value obtained in the present study is remarkably higher than those reported by other studies that worked on melting or dissolution route and other foaming agents such a polymer (PMMA), TiH 2 , and K 2 CO 3 [3,4,14,18]. This may possibly be the result of a higher amount in compacting pressure, as well as applying CaCO 3 as a foaming agent.…”

“…This was due to a higher diffusion, more interfaces between copper particles (low amount of foaming agent) during the solid-state sintering process and the higher strength of cell walls [15]. Figure 7(e) shows that the rise of compacting pressure from P2 to P5 (250 MPa to 624 MPa) upgrades the compressive strength of the samples from 324 MPa to 526 MPa because of the lower number of the pores and the strain hardening of copper particles [18]. When preform compacted below 250 MPa, the deficient bonding strength between Cu particles prompted the collapse of the green compact amid handling.…”

“…Some efforts have so far been made to investigate the properties of copper foams produced by different space holders such as NaCl, K 2 CO 3 , and sugar [17]. Moreover, other studies have employed lost carbonate sintering (LSC) method for foaming process [14,18,19]. Zhao et al [3] used the LSC method to produce high-porosity copper foams by potassium carbonate space holders.…”

“…Koizomi [19] developed the PM method for fabrication of the Al-Cu alloy foam with CaCO 3 and TiH 2 foaming agents and the effect of these different foaming agents on pores characteristics have been investigated. In the previous study [18], the effects of different foaming agents (CaCO 3 and TiH 2 ) on the foaming process of Al-Cu alloy produced by a melting method have been investigated. Here, we have introduced a simple and easy pathway for the fabrication of copper metal foam with semi-open cell microstructure along with the investigation of pores formation, microstructure characterization, porosity type, and pore morphology, mechanical and physical properties.…”

Obtención de espumas metálicas utilizando como metal principal aluminio comercial y reciclado con diversos agentes espumantes

“…En algunas patentes tempranas (Nakamura et al, 2002) y en el trabajo reciente de Nakamura y colaboradores (Byakova, Nakamura et al, 2017) se encontró que el uso de CaCO 3 es potencialmente adecuado como agente espumante para la obtención de espumas mediante el método de fundición del metal base. Además, Bryat (Bryat et al;2008) informó que el CaCO 3 actúa como agente espumante cuando se encuentra en contacto con el aluminio en estado líquido y, al mismo tiempo, a través de los productos de descomposición tiene un efecto sobre la estabilidad de la espuma, permitiendo la formación de "espumas de aluminio autoestabilizadas".…”