On the structural integrity of the spinel block in the β"-alumina structure.
The β''-alumina structure is examined in detail and an analysis is presented of the three-dimensional integrity of the lattice. The layer structure that is responsible for the very high sodium conduction rate is the specific focus. Rigid layers that are derived from the cubic spinel structure are interleaved by more open honeycomb pathways where rapid ion diffusion takes place. The three-dimensional rigidity of the spinel block in this structure makes it possible to accurately quantify the conduction layer thickness based only on the hexagonal unit-cell dimensions, as suggested originally by Harbach [(1983), J. Mater. Sci. 18, 2437-2452]. His calculation is tested rigorously against the many single-crystal structure determinations that have been made on the β''-alumina family compounds and excellent correlation is found.
Sol–gel synthesis of Mg2+ stabilized Na-β″/β-Al2O3 solid electrolyte for sodium anode battery
Abstract Mg 2+ stabilized Na-β″/β-Al 2 O 3 powder was successfully synthesized by a sol–gel method using PVP-10000 as complexing agent and metal nitrates as corresponding metal sources. The thermal decomposition of the xerogel and the evolution of crystallization behavior of Na-β″/β-Al 2 O 3 were studied. The obtained powders have been unambiguously characterized using X-ray diffraction (XRD), N 2 adsorption, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The Mg 2+ stabilized Na-β″/β-Al 2 O 3 crystallized gradually from amorphous phase to metastable intermediate phases and further formed the major phase at 1000 °C. The results showed that the large surface area of the amorphous intermediate phase with mesoporous structure followed by the generation of intermediate phases named as m-Al 2 O 3 and MgAl 2 O 4 with spinel structure to a great extent promoted the formation of Na-β″/β-Al 2 O 3 phase. The Na-β″/β-Al 2 O 3 nano-powders exhibited a plate-like two dimensional structure with clear crystallographic plane for Na + diffusion. The transformation from m-Al 2 O 3 only required the shift of Na + from alternate layers of oxygen and the accommodation of every fifth layer since the structure of m-Al 2 O 3 is only slightly different from that of Na-β″/β-Al 2 O 3 . The relative density of the sintered ceramic was approximately 98.8% and the ionic conductivity can reach 0.24 S cm − 1 at 350 °C.
Traceability strategy for gear-pitch-measuring instruments: development and calibration of a multiball artifact
There is a strong demand to ensure the traceability of gear-measuring instruments (GMIs). We propose a multiball artifact (MBA) for the evaluation of pitch-measuring accuracy. The aim of the MBA is to transfer the minimum uncertainty from a calibrated value at the National Metrology Institute of Japan (NMIJ) to a measured value of GMIs at a shop floor. The MBA is composed of equally spaced high-accuracy balls around an axis. The pitch-measuring accuracy of GMIs is evaluated by measuring the angular pitch deviation of the balls instead of the angular pitch deviation of a gear. We calibrated the angular pitch deviation using a coordinate measuring instrument (CMM) at the NMIJ and adapting a multiple-orientation technique. We proposed a calibration strategy of the angular pitch deviation. The calibration value of the pitch deviation for the MBA at the NMIJ was obtained with a measurement uncertainty (U95) of 0.2 µm. We evaluated the pitch-measuring accuracy of a GMI using the calibrated MBA. Each value of U95 for the cumulative and single pitch deviations for the left and right flanks was less than or equal to 0.5 µm. The small uncertainty was transferred from the NMIJ to the GMI.