Hydrogenation Properties of TiFe Doped with Zirconium
The goal of this study was to optimize the activation behaviour of hydrogen storage alloy TiFe. We found that the addition of a small amount of Zr in TiFe alloy greatly reduces the hydrogenation activation time. Two different procedural synthesis methods were applied: co-melt, where the TiFe was melted and afterward re-melted with the addition of Zr, and single-melt, where Ti, Fe and Zr were melted together in one single operation. The co-melted sample absorbed hydrogen at its maximum capacity in less than three hours without any pre-treatment. The single-melted alloy absorbed its maximum capacity in less than seven hours, also without pre-treatment. The reason for discrepancies between co-melt and single-melt alloys was found to be the different microstructure. The effect of air exposure was also investigated. We found that the air-exposed samples had the same maximum capacity as the argon protected samples but with a slightly longer incubation time, which is probably due to the presence of a dense surface oxide layer. Scanning electron microscopy revealed the presence of a rich Zr intergranular phase in the TiFe matrix, which is responsible for the enhanced hydrogenation properties of these Zr-doped TiFe alloys.
Surface TiHn as the catalytically active species for the hydrogen absorption by TiFe; a SX-APS investigation supplemented by AES
Abstract The interaction of hydrogen with the surface of previously cleaned TiFe samples was investigated by means of Soft X-Ray Appearance Potential Spectroscopy (SX-APS) and Auger Electron Spectroscopy (AES). The access of oxygen (air) was carefully prevented by performing all experiments “in-situ” in an UHV-chamber. At about 800°C the hydrogen interaction with the TiFe surface leads to extensive Ti segregation. As observed by SX-APS, iron is displaced by titanium on the whole surface of the sample (about 1.5 cm 2 ). From AES depth profiles the Ti overlayer is estimated to have a thickness of about 100 monolayers. In this region Fe is completely absent. No enrichment of Fe beyond this region could be detected; the Fe concentration increases monotonously from zero to the bulk value. From these results it is obvious that the hydrogen absorption/desorption of TiFe is catalytically activated by Ti species rather than by Fe species. The chemical state of the surface is discussed.
Educating the Educators: Rethinking Subject Matter and Methods
gate? In addition to general requirements in their professional education such as psychological and social foundations and student teaching, what specifically do social studies teachers need to know and be able to do? What, in particular, do they need to study in the subject matters of the social sciences (defined here, for purposes of brevity, to include history and geography), and what should they learn about its effective direction to desired results, that is, method? Usually answers to the first question require reference to the liberal arts component of teacher education and the second to methods in the professional education component. As we shall see, this separation of subject matter and method in the education of social studies teachers, although conventional, poses problems.