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

The paper presents the results obtained by in situ observation of Al-based foams formation at heating of powder compacts with calcium carbonate (CaCO3) by comparing with those prepared with conventional titanium hydride (TiH2). 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 identiFIed that expansion and stability of foams with CaCO3 are much superior to those with TiH2. 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 CaCO3 is explained on the base of stabilizing models developed by Kaptay by assuming an interfacial force, the disjoining pressure, which efFIciency is variable and dependent on the distribution and wetting behaviour of the clustered oxide network/solid particles in foamy melt.