Browsing by Author "Bhatt, Hemanshu D."

Now showing 1 - 3 of 3
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    Effect of interfacial thermal conductance and fiber orientation on the thermal diffusivity/conductivity of unidirectional fiber-reinforced ceramic matrix composites
    Bhatt, Hemanshu D. (Virginia Tech, 1992-02-06)
    The role of an interfacial barrier at the fiber-matrix interface in the heat conduction behavior of an uniaxial silicon carbide fiber-reinforced reaction-bonded silicon nitride and the effect of fiber orientation on the heat conduction characteristics of carbon fiber-reinforced borosilicate glass was investigated. In the study of the effect of an interfacial thermal barrier, a composite with fibers having a carbon-rich coating of about 3 J.l m was chosen as the reference material. The fiber-matrix interface was then modified by preferential oxidation of the carbon coating on the fibers, using fibers with no carbon coating and using hotisostatic-pressing (HIP) after nitridation. The formation of an interfacial gap at the interface due to thermal expansion mismatch between the fiber and the matrix in reference and HIP'd composites, and removal of carbon coating for oxidized composites, resulted in the dependence of thermal diffusivity/conductivity on the surrounding . atmosphere. This effect was attributed to gaseous heat transfer at the interface. However, no atmospheric effects were observed for composites with fibers without the carbon coating due to very strong bonding between the fiber and the matrix. HIP'ing increased the thermal diffusivity/conductivity of the composites due to densification of the matrix, crystallization of the fibers and increased physical contact at the interface. Removal of the interfacial carbon layer by preferential oxidation lowered the interfacial conductance considerably, due to decrease in the direct thermal contact between the fibers and the matrix. Interfacial contact conductance determined from measurements made in vacuum for reference and HIP'd composites increased rapidly with increasing temperature in accordance with interfacial gap closure. These observations indicate that the heat conduction behavior of all the composites investigated was strongly affected by the existence of an interfacial thermal barrier, for heat transfer transverse to the fiber direction.
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    High temperature electrode-barriers for ferroelectric and other capacitor structures
    (United States Patent and Trademark Office, 1998-08-04)
    A capacitor for use on silicon or other substrate has a multilayer electrode structure. In a preferred embodiment, a bottom electrode situated on the substrate has a bottom layer of Pt--Rh--O.sub.x, an intermediate layer of Pt--Rh, and a top layer of Pt--Rh--O.sub.x. A ferroelectric material such as PZT (or other material) is situated on the bottom electrode. A top electrode, preferably of identical composition as the bottom electrode, is situated on the opposite side of the ferroelectric from the bottom electrode.
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    Simple method of fabricating ferroelectric capacitors
    (United States Patent and Trademark Office, 1998-09-15)
    A ferroelectric capacitor device and method of manufacture. A substrate supports a bottom electrode structure, with an adhesion/diffusion barrier layer sandwiched therebetween. The electrode layer includes a metal or metal alloy and an oxide of the metal or alloy. The adhesion/diffusion barrier layer is a similar oxide. Ferroelectric material is sandwiched between a top electrode. The top layer includes a metal or metal alloy and an oxide of the same; the metal or metal alloy may be the same as the bottom electrode but need not be. The metal and metal oxide electrodes may be deposited by known deposition techniques, or the metal may be deposited and the oxide formed by annealing in oxygen ambient environment.