A side‐by‐side comparison of the solidification dynamics of quasicrystalline and approximant phases in the Al–Co–Ni system

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148264/1/aya2gv5001.pd

Investigation of Advanced Cathode Contacting Solutions in SOFC

Contacting solutions for air electrode in Solid Oxide Cells stacks often implement a ceramic paste made of electronic conducting perovskite, comparable or same as the electro-active material. This contacting layer, is applied in a green state by wet-powder-spray or screen-printing, and in situ fired during stack commissioning. The low level of necking between ceramic particles causes increased ohmic losses. Moreover the shrinkage usually observed during long term operation in temperature of this layer, due to sintering effect, lead to cracks and contact losses which hinder the cell performance. Increasing cell’s footprint, performance and lifetime at the stack level requires appropriate contacting solution. In this paper we reports the investigation of a new advanced monolithic contacting solution, easy to handle, soft and flexible, highly porous and highly conductive. Two different compositions have been investigated, with respect of their compatibility with Crofer (SEM, XRD). In addition, solid oxide cells contacted with this solution as well as with a ceramic paste have also been electrochemically tested up to 1000 hours in order to compare and assess the impact of this contacting solution on cell’s performance. Results will be presented and discussed

Tracking the evolution of hot tears in aluminium alloys using high-speed X-ray imaging

Hot tears are detrimental defects forming during the final stage of solidification when the remaining liquid loses the capacity to compensate for liquid to solid volume shrinkage. Although a mature semi-quantitative description of hot tearing has been developed, little is known about the dynamic evolution of hot tears as experimental studies have been conducted mostly post-solidification or in semi-static in-situ conditions. Here, we present a methodology to investigate the evolution of hot tears with high spatial and temporal resolution using synchrotron-based X-ray radiography. We develop a novel hot tear detection and tracking algorithm for quantification of hot tear density, area fraction and merging from the analysis of radiographic sequences of the solidification of thin metal samples. The methodology is demonstrated for an Al-5wt%Cu alloy and examples of the results and new insights that can be achieved are described

The mechanism of Fe-rich intermetallic compound formation and growth on inoculants revealed by electron backscattered diffraction and X-ray imaging

Fe-rich intermetallics affect critically the mechanical properties and recyclability of aluminium alloys. Increasing effort has been spent on the inoculation of these intermetallics, hoping to promote a finer distribution. Recently Al-5Ti-1B (wt.%), originally developed to refine -Al, has been shown to refine Al13Fe4, an intermetallic phase present in a variety of Al alloys. However, mechanisms of the formation and growth of the intermetallics on the inoculants are unclear. In this paper, Ti is added to Fe-containing Al alloys to produce a large number of potent Al3Ti particles, the active inoculant in Al-5Ti-1B. We use a combination of electron backscattered diffraction, in situ synchrotron X-ray radiography and post-solidification X-ray computed tomography to investigate the formation and growth of primary Al13Fe4 on Al3Ti inoculants, first in a model Al-Fe alloy, with key insights then confirmed in a high Fe-containing, recycled 6xxx alloy. Crystallographic orientation relationships between Al13Fe4 and Al3Ti are analysed comprehensively, and the formation and growth dynamics of Al13Fe4 on Al3Ti is also unveiled. A strong link is revealed between the formation of Al13Fe4 on Al3Ti and a twinning-related pseudo-symmetry of Al13Fe4. Finally, a potential strategy to refine both intermetallics and -Al in recycled alloys with elevated Fe concentration is proposed

Dynamic Observation of Dendritic Quasicrystal Growth upon Laser-Induced Solid-State Transformation

We report the laser-induced solid-state transformation between a periodic “approximant” and quasicrystal in the Al-Cr system during rapid quenching. Dynamic transmission electron microscopy allows us to capture in situ the dendritic growth of the metastable quasicrystals. The formation of dendrites during solid-state transformation is a rare phenomenon, which we attribute to the structural similarity between the two intermetallics. Through ab initio molecular dynamics simulations, we identify the dominant structural motif to be a 13-atom icosahedral cluster transcending the phases of matter

Does IT Lead to Urban Agglomeration of Jobs?

Cities have been an important part of the modern economic system where a massive number of people work together to produce diverse goods and services. Some predicted that information technology (IT) would fundamentally change the spatial organization of jobs by eliminating the effects of physical distance. As a result, the “IT revolution” was expected to decrease the advantages of cities. However, cities have prospered despite the rapid technological changes over the past two decades. This study investigates the effect of IT on urban agglomeration from a coordination perspective. Specifically, we examine how IT affects workers’ locations by changing the nature of their jobs and how this effect is moderated by occupational characteristics. We empirically validate our arguments by using occupational-level data from US. This study contributes to the literature on agglomeration economies and routine-biased technical changes by demonstrating that IT facilitates urban agglomeration of jobs, especially for high-skilled workers

Does IT Increase Specialization? An Empirical Analysis

Specialization - the degree of narrowness of task content - has been a foundation for workers\u27 productivity and the prosperity of modern society. Despite the abundance of research on the antecedents to specialization, there has been no research on whether and how IT affects workers’ specialization. The impact of IT on workers’ specialization is not clear since specialization is complexly mingled with occupational roles determined by the structure of organizations. This study examines the impact of IT on workers’ specialization based on organization science and economics literature and panel data from US Bureau of Labor and Statistics. This study contributes to the literature by providing a measure of specialization and clarifying the role of IT in the specialization of workers across different occupations