Magnesium aluminate spinel with the alumina rich composition MgO · 1.5 Al2O3 has been prepared as a transparent polycrystalline ceramic with average in‐line transmission at 550 nm of 83.3 ± 0.9% and >80% throughout the visible spectrum. This finding significantly increases the compositional range over which polycrystalline magnesium aluminates can be prepared as fully dense ceramics with high transparency to visible light. Starting powders are prepared from combinations of high purity Mg(OH)2 and γ‐Al2O3 thoroughly mixed in an aqueous slurry, and the solids are collected, dried, calcined, mixed with LiF sintering aid, and sieved. The powders are sintered into dense ceramics by hot pressing at 1600°C under vacuum and 20 MPa uniaxial load, followed by hot isostatic pressing at 1850°C under 200 MPa Ar. The crucial parameter for forming highly transparent MgO · 1.5 Al2O3 ceramic from this procedure is to hold the amount of LiF to 0.25 wt%.
Many U.S. Army systems, such as ground vehicles and fully equipped soldiers, are comprised of multiple subcomponents which each typically perform unique functions. Combining these functions into single, multifunctional components could reduce mass and improve overall system efficiency. In particular, creating structural materials that also provide power generating or energy storing capacity could provide significant weight savings over a range of platforms. In this study, structural composite batteries, fuel cells, and capacitors are proposed. To ensure performance benefits, these multifunctional composites are designed so that the materials involved in power and energy processes are also load bearing, rather than simply packaged within monofunctional structural materials. Fabrication and design details for these multifunctional systems, as well as structural and power/energy performance results, are reported. Critical material properties and fabrication considerations are highlighted, and important technical challenges are identified. Structural lithium-ion batteriesMater. Res. Soc. Symp. Proc. Vol. 851
It has long been known that a relation exists between a material's hardness and its gross impact performance; however, the nature of this relationship has not been understood to a degree useful in materials development. Many studies have shown that harder ceramics tend to display better ballistic performance. In addition, some research has suggested that a material's potential for inelastic deformation (or its "quasi-plasticity"a bulk property) may also play an important role in its resistance to penetration. Methods of quantifying the bulk plasticity of a ceramic material are, however, extremely limited. The current study continues an investigation into a recently proposed technique to (1) quantify bulk quasi-plasticity in SiC materials, and (2) use the "plasticity" value along with a hardness value to predict the transition velocity of potential armor ceramics. The transition velocity values predicted by this approach generally show excellent agreement (within 5% in most cases) with experimentally determined velocities. In addition, the robustness of this predictive technique is demonstrated through the use of multiple operators and multiple hardness testing units. †
The U.S. Army has investigated a variety of multifunctional designs in order to achieve system level mass and/or volume savings. One of the multifunctional devices developed is the multifunctional fuel cell (MFC)—a fuel cell which simultaneously provides a system with structural support and power generation. However, there are no established methods for measuring how well a particular design performs or its multifunctional advantage. The current paper presents a metric by which multifunctional fuel cell designs can be characterized. The mechanical aspect of the metric is based on the specific bending stiffness of the structural cell and is developed using Frostig’s high-order theory. The electrical component of the metric is based on the specific power density achieved by the structural cell. The structural systems considered here display multifunctional efficiencies ranging from 22% to 69%. The higher efficiency was obtained by optimizing the contact pressure at the gas diffusion layer (GDL) in a model cell design. The efficiencies obtained suggest the need for improved multifunctional designs in order to reach system level mass savings.
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