Near Net-Shaped, Alkaline-Earth-Bearing Ceramics for Electronic and Refractory Applications Via the Oxidation of Solid, Metal-Bearing Precursors (the VIMOX Process)

In most of the published work on the high-temperature oxidation of bulk metals, the resulting oxides are treated as undesired corrosion products. The opposite paradigm is discussed in this paper: bulk precursors containing alkaline earth metals (AE = Mg, Ca, Sr, Ba) are completely oxidized to produce electrical or refractory ceramics. Relatively dense AE-metal-bearing green bodies can be fabricated by either solid-state deformation processing or liquid metal infiltration processing. Rapid oxidation of the solid AE metals and reaction with other oxides in the green bodies can yield desired compounds. Unlike other oxides, AE oxides possess smaller molar volumes than the corresponding metals. Hence, by adjusting the amounts of AE and non-AE components in a precursor, an all-ceramic body with a shape and volume identical to the precursor can be produced (Volume Identical Metal Oxidation or VIMOX). The syntheses of shaped electronic titanates and cerates, and refractory aluminates and aluminosilicates, are discussed.     

Piezoelectric generators for biomedical and dental applications: Effects of cyclic loading

This paper presents the results of a study of the effect of cyclic loading parameters on the performance of piezo crystals. The output power of the crystals was observed to increase with parameters such as the cyclic frequency and the dynamic load range. However, the output power also decreased with increasing mean load. The efficiency of the crystal was calculated based on the mechanical energy applied to the piezo crystal. The ratio of the electrical output to mechanical energy input was taken as the efficiency of the crystal. This ratio was seen to increase with the cycling frequency, and also with the dynamic load range. However, increasing mean load caused the efficiency to drop significantly. The implications of the results are discussed for possible applications implanted bioMEMS and microelectronics systems.     

The effect of ginger on diabetic nephropathy,plasma antioxidant capacity and lipid peroxidation in rats

Oxidative stress is a major factor in the pathogenesis of diabetic complications. We studied the effects of ginger powder on nephropathy induced by diabetes, and measured changes in plasma antioxidant capacity and lipid peroxidation.     

An investigation of fracture and fatigue in a metal/polymer composite

This article presents the results of a combined experimental and analytical study of the fatigue and fracture behavior of a polymer/metal composite which was developed recently for self-lubricating applications in automotive engines that utilize liquefied natural gas as fuel. For comparison, the microstructure and the fatigue and fracture behavior of a nonpolymer-containing “matrix” material are also presented. Since the crack profiles observed in both systems under monotonic or cyclic loading reveal significant components of ligament bridging, micromechanics models are presented for the modeling of crack bridging. The resulting predictions of resistance-curve behavior are compared with measured resistance curves. The shielding effects of ligament bridging are also quantified under cyclic loading. The implications of the work are also discussed for the modeling of fatigue damage and fracture in polymer/metal coatings.     

An investigation of the effects of thickness on mechanical properties of LIGA nickel MEMS structures

This paper examines the effects of thickness on the mechanical properties of LIGA Ni MEMS structures plated from sulfamate baths. The as-plated LIGA Ni specimens of different thickness (50 m, 100 m and 200 m) were utilized in the microtensile experiments. Optical microscopy, orientation imaging microscopy and scanning electron microscopy were used to characterize the microstructure of the LIGA Ni specimens. Fracture Modes obtained from specimens with different thickness were revealed by scanning electron microscopy. The effects of specimen thickness are then discussed within the context of strain gradient plasticity theories.     

An introduction to mechanical-properties-related issues in MEMS structures

A brief introduction to the issues related to the mechanical properties of MEMS components in terms of their functionality, types of loading and modes of operation is presented. At the microscale, for most cases, some mechanical properties including strength increase. However, surface phenomena such as adhesion/stiction become important as the aspect ratio of the components decreases. Subcritical crack initiation and growth in silicon, as the most common type of material used in MEMS devices under various types of loading is discussed. In addition, fatigue and creep behavior of MEMS components are described.     

Nanoindentation Measurements of the Mechanical Properties of Ni Thin Films: Effects of Film Microstructure and Substrate Modulus

This paper presents the results of nanoindentation measurements of the hardness and moduli of normally and obliquely deposited nanocrystalline Ni films on substrates of SiO₂, Si, and bulk Ni. Following an initial characterization of film microstructure and surface topography with atomic force microscopy (AFM), the paper examines the effects of film microstructure, film thickness, and substrate modulus on the measured film mechanical properties. Obliquely deposited films are shown to have lower hardness values than normally deposited films. The measured hardness values and material pile-up are also shown to depend significantly on the mismatch between the film modulus and substrate modulus. A framework is presented for quantifying the effects of substrate modulus mismatch on basic film mechanical properties.     

High creep exponents in a nearly-lamellar γ-based titanium aluminide intermetallic

Secondary creep data are reported for an extruded nearly-lamellar Ti-48Al-1.5Cr-alloy tested in a temperature range of 700 to 900°C. Within this temperature regime, this alloy exhibits a two-stage creep deformation behavior, with relatively high (approximately 8–12) creep exponents occurring in the high stress/high temperature regime. The high exponents in this regime are explained by dynamic recrystallization phenomena observed ₂ + in the nearly-lamellar microstructure.