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

Krzysztof Karczewski,Marco Salerno,Wojciech Stepniowski

doi:10.3390/ma10070746

Abstract

Fabrication of metallic foams by sintering metal powders mixed with thermally degradable compounds is of interest for numerous applications. Compounds releasing gaseous nitrogen, minimizing interactions between the formed gases and metallic foam by diluting other combustion products, were applied. Cysteine and phenylalanine, were used as gas releasing agents during the sintering of elemental Fe and Al powders in order to obtain metallic foams. Characterization was carried out by optical microscopy with image analysis, scanning electron microscopy with energy dispersive spectroscopy, and gas permeability tests. Porosity of the foams was up to 42 ± 3% and 46 ± 2% for sintering conducted with 5 wt % cysteine and phenylalanine, respectively. Chemical analyses of the formed foams revealed that the oxygen content was below 0.14 wt % and the carbon content was below 0.3 wt %. Therefore, no brittle phases could be formed that would spoil the mechanical stability of the FeAl intermetallic foams. The gas permeability tests revealed that only the foams formed in the presence of cysteine have enough interconnections between the pores, thanks to the improved air flow through the porous materials. The foams formed with cysteine can be applied as filters and industrial catalysts.

Highlights

Iron aluminides, including FeAl intermetallic alloys, are well-known materials for their remarkable mechanical properties and excellent corrosion resistance at room and elevated temperatures [1,2,3,4]. These materials are often used as protective coatings for exploitation in high temperature aggressive environments due to the formation of the protective oxide layer on their surface [5,6,7,8,9,10]. For this reason, application of FeAl intermetallic alloys can be a key for the development of filtrating elements in chimneys, where extremely hot outlet gasses are being ejected
1, one can. see that the addition of amino acids resulted in a significant increase of Figure 1, 1,of one can see that that the the addition addition of of amino amino acids acids resulted resulted in in aa significant significant increase increase of of 2 see In Figure one can porosity of the FeAl intermetallic alloys: from 28 of whenacids sintering without upincrease to 42 ± 3%
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Summary

Introduction

Iron aluminides, including FeAl intermetallic alloys, are well-known materials for their remarkable mechanical properties and excellent corrosion resistance at room and elevated temperatures [1,2,3,4]. The formation of FeAl intermetallic foams with the use of amino acids as gas releasing agents was studied. The major motivations of the use of the amino acids as gas releasing agents are volume of the in situ produced gases (Table 1) and the formation of gaseous nitrogen, diluting remaining the in in The situ produced gases carbon. Amino acids as well well asholders other organic compounds gaseous products including carbon dioxide, and the chemical interaction between work as mentioned releasing agent, but first they actdecreasing space in thecompounds same way as e.g., the formed sinter produced gas. Chemical compounds used up to date release only carbon dioxide steam, volume of formed gases estimated atimportant ambient conditions from combustion of 1and g of water the additive. 2.and eosin Y (0.9 dm3 /g), significantly more gas is produced by previously used oxalicofacid relatively large amounts of

Discussion

Porosity

Materials and Methods