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A novel process for fabricating Mg{sub 2}Ni

Description: The alloy, Mg{sub 2}Ni, has a number of desirable properties for use as a lightweight reversible hydride for hydrogen storage applications. It has relatively good storage capacity (3.6 wt.% H{sub 2} as Mg{sub 2}NiH{sub 4}) and a higher plateau pressure and lower operating temperature than MgH{sub 2}. A novel low temperature (<300 C) process is reported that does not require melting of the alloy constituents to achieve a single phase alloy of Mg{sub 2}Ni. The process results in smaller particle dimensions without sacrifice in product yield and eliminates the need for post processing to achieve homogenization and particle sizing. It can also be implemented in-situ in storage vessels to greatly simplify fabrication while providing more material predictability during the activation process. The process is described and the hydride properties of the product are reported and compared to conventionally formed alloys.
Date: May 1, 1998
Creator: Guthrie, S.E. & Thomas, G.J.
Partner: UNT Libraries Government Documents Department

The development of lightweight hydride alloys based on magnesium

Description: The development of a magnesium based hydride material is explored for use as a lightweight hydrogen storage medium. It is found that the vapor transport of magnesium during hydrogen uptake greatly influences the surface and hydride reactions in these alloys. This is exploited by purposely forming near-surface phases of Mg{sub 2}Ni on bulk Mg-Al-Zn alloys which result in improved hydrogen adsorption and desorption behavior. Conditions were found where these near-surface reactions yielded a complex and heterogeneous microstructure that coincided with excellent bulk hydride behavior. A Mg-Al alloy hydride is reported with near atmospheric plateau pressures at temperatures below 200{degrees}C. Additionally, a scheme is described for low temperature in-situ fabrication of Mg{sub 2}Ni single phase alloys utilizing the high vapor pressure of Mg.
Date: February 1, 1996
Creator: Guthrie, S.E.; Thomas, G.J.; Yang, N.Y.C. & Bauer, W.
Partner: UNT Libraries Government Documents Department

Impurity effects on the adhesion of aluminum films on sapphire substrates

Description: The adhesion of aluminum (Al) films onto sapphire substrates in the presence of controlled contaminants is being investigated. In this study, adhesion strength is evaluated by continuous scratch and nanoindentation tests to induce delamination of the Al film from the sapphire substrate. If delamination blisters or spallations can be induced, then fracture mechanics based models can be used to calculate the fracture energy or work of adhesion based on the radius of the blister. Initial specimens of 178 nm thick Al films were vapor deposited onto (0001) oriented sapphire substrates with a 5--19 nm layer of carbon sputter deposited onto the sapphire surface of selected samples. Continuous scratch tests promoted blistering of the film in specimens with carbon on the sapphire surface. Delamination blisters could not be induced by continuous indentation testing in samples with or without carbon at the interface. An overlayer of sputtered tantalum (Ta) was then used on a second set of 500 nm thick Al films with and without 10--20 nm of sputtered carbon on the sapphire surface to promote delaminations. With Ta overlayers, continuous nanoindentation techniques induced larger diameter delamination blisters in the specimens with carbon, than in the specimens without carbon. Resistance to blistering, or smaller induced blisters, indicates a higher interfacial strength.
Date: May 1, 1998
Creator: Schneider, J.A.; Guthrie, S.E.; Clift, W.M.; Moody, N.R. & Kriese, M.D.
Partner: UNT Libraries Government Documents Department