Fabrication of Fe-Al Intermetallic Foams via Organic Compounds Assisted Sintering

Abstract

The influence of the addition of organic compounds, such as palmitic acid and cholesteryl myristate, on the porous structure of Fe-Al intermetallics formation has been investigated in detail in this paper. It was found that additives have a significant effect on the final porosity of the obtained sinters. Formed gaseous products from combustion play the role of the foaming agent during Fe-Al intermetallic alloy sintering. The influence of these additives is also clearly noticeable in chemical composition changes of the final products through the increase of carbon content in the porous structure. This is attributed to the thermal decomposition, namely combustion, of the organic additives.

Amino Acids Aided Sintering for the Formation of Highly Porous FeAl Intermetallic Alloys

“…Surprisingly, compared to the foam formed without any additives [ 34 ], the foam formed with the use of phenylalanine showed a much greater flow resistance during the permeability experiments. With an overpressure of 20 kPa applied there was no air flow through the foam, meaning that pore interconnection in the samples was not appropriate for the devised application.…”

“…Organic compound assisted sintering is currently being explored and provides chemically ambient products like carbon dioxide and water steam. During sintering of elemental powders, the added organic compounds—e.g., oxalic acid [ 32 ], eosin [ 33 ], stearic acid [ 34 ] or cholesteryl myristate [ 34 ]—combust to those compounds. Nonetheless, this approach also provides an issue that has to be solved: at low air (oxygen) admission, namely that the added organic does not combust to carbon dioxide but to carbon monoxide or simply to carbon.…”

“…Nonetheless, this approach also provides an issue that has to be solved: at low air (oxygen) admission, namely that the added organic does not combust to carbon dioxide but to carbon monoxide or simply to carbon. At the decomposition sites, much carbon is being found [ 32 , 33 , 34 ], which at elevated temperatures may result in the formation of brittle carbides, spoiling the performance of the intermetallic foam material. The carbon content may be minimized by thermal post-treatment, like annealing at high temperatures in air.…”

“…The major motivations of the use of the amino acids as gas releasing agents are the volume of the in situ produced gases ( Table 1 ) and the formation of gaseous nitrogen, diluting remaining gaseous products including carbon dioxide, and thus decreasing the chemical interaction between the formed sinter and produced gas. Moreover, amino acids as well as other organic compounds [ 32 , 33 , 34 ] work as mentioned gas releasing agent, but first they act as space holders in the same way as e.g., NaCl [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ].…”

“…Table 1 compares various organic compounds suitable to be applied as gas-releasing foaming agents. Chemical compounds used up to date release only carbon dioxide and water steam, as well as bromine [ 32 , 33 , 34 ] ( Table 1 ). In this study we have selected amino acids that also form chemically inert nitrogen.…”