Preparation of TiFe based alloys melted by CaO crucible and its hydrogen storage properties

Abstract

The carbon contamination of alloys prepared by the electro graphite crucible is impossible to avoid due to the inherit reaction between the melt and the crucible. In this study, the TiFe-based alloy is prepared by VIM process using CaO crucible as well as the electro graphite crucible. The samples are examined by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Energy Dispersive Spectrometer (EDS), and the PCT curves are also measured. It is resulted that, the oxygen content of alloys melted by CaO crucible is almost equal to the one melted by graphite crucible and without the carbon contamination, meanwhile the carbon content of alloys obtained by the electro graphite crucible is 1860ppm, which exceeds the tolerance of the commercial alloy (1000ppm). The microstructure of the alloy melted by CaO crucible is dendrite, while it is composed of the equiaxed crystal with the lamellar structure and the spherical TiC particles distributed along grain boundaries or within the grain when melted by the graphite crucible; the interfacial reaction of the electro graphite crucible with TiFe alloy melt is serious and the interaction layer is formed up to 200μm in thickness, the carbon in TiFe-based alloys forms TiC. The hydrogen desorption plateau pressure of alloys melted by CaO crucible is (0.11–0.4)×105Pa, and that by the graphite crucible is (0.6–1)×105Pa. This may imply that the CaO crucible may be the promising candidate for melting the high performance TiFe based hydrogen storage alloys.