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Virtual poster session
In-situ observation of combustion foaming process for synthesizing porous Al3Ti by X-ray radioscopy
Wednesday (07.10.2020) 19:22 - 19:25 Room 1 Part of:Porous metals include a lot of pores inside the materials. Due to the pores, they exhibit unique properties such as light weight, low thermal conductivity. We developed a combustion foaming process using strong exothermic reactions of elemental powder, which enables us to fabricate closed-cellular porous intermetallic compounds with high melting temperatures. Heating a precursor composed of powder mixture of Al, Ti, and B4C facilitates two chemical reactions occurring at the melting temperature of Al: 3Al + Ti → Al3Ti and 3Ti + B4C → 2TiB2 + TiC. These exothermic reactions significantly rise the sample temperature above the melting point of Al3Ti (approximately 1340C). Concurrently, impurity elements dissolved in the Al powder or absorbed on the Al surface can be released as gases, resulting in foaming of the precursor. The extremely rapid and irreversible process of the combustion foaming makes it much difficult to understand the foaming process, whereas it is required to understand its detailed process for controlling fine and uniform cell structures of the produced foams. In the present study, we made an attempt to in-situ observe the combustion foaming behaviors in synthesizing the porous Al3Ti by X-ray radioscopy. The in-situ observations revealed that the combustion foaming process consisted of four steps: (1) gradual expansion in heating, (2) temporary steady state at a constant volume, (3) a slight shrinkage, and (4) significant foaming. After that, the foam sample was contracted drastically while coarsening bubbles in cooling process, resulting in the formation of inhomogeneous and coarse pore morphologies In order to elucidate the chemical reactions arising at each step, heating of the sample was interrupted at different steps. The results of microstructural observations for the interrupted samples will be presented to discuss a change in microstructure inside the precursor during the combustion foaming process.
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| Presentation | ver.1 | Porous metals include a lot of pores inside the materials. Due to the pores, they exhibit unique properties such as light weight, low thermal conductivity. We developed a combustion foaming process using strong exothermic reactions of elemental powder, which enables us to fabricate closed-cellular porous intermetallic compounds with high melting temperatures. Heating a precursor composed of powder mixture of Al, Ti, and B4C facilitates two chemical reactions occurring at the melting temperature of Al: 3Al + Ti → Al3Ti and 3Ti + B4C → 2TiB2 + TiC. These exothermic reactions significantly rise the sample temperature above the melting point of Al3Ti (approximately 1340C). Concurrently, impurity elements dissolved in the Al powder or absorbed on the Al surface can be released as gases, resulting in foaming of the precursor. The extremely rapid and irreversible process of the combustion foaming makes it much difficult to understand the foaming process, whereas it is required to understand its detailed process for controlling fine and uniform cell structures of the produced foams. In the present study, we made an attempt to in-situ observe the combustion foaming behaviors in synthesizing the porous Al3Ti by X-ray radioscopy. The in-situ observations revealed that the combustion foaming process consisted of four steps: (1) gradual expansion in heating, (2) temporary steady state at a constant volume, (3) a slight shrinkage, and (4) significant foaming. After that, the foam sample was contracted drastically while coarsening bubbles in cooling process, resulting in the formation of inhomogeneous and coarse pore morphologies In order to elucidate the chemical reactions arising at each step, heating of the sample was interrupted at different steps. The results of microstructural observations for the interrupted samples will be presented to discuss a change in microstructure inside the precursor during the combustion foaming process. | 14 MB | Download |
