May-Ying Chu

Effect of temperature on the densification/creep viscosity during sintering

Abstract The densification and creep rates of polycrystalline zinc oxide and of alumina powder compacts have been measured simultaneously in a loading dilatometer, under constant heating rate and constant temperature conditions. The data show that the ratio of the densification to the creep rate is remarkably constant within a wide temperature range for densification, from the earliest stages of densification to at least the onset of the final stage. As a consequence, the ratio of the densification to the creep viscosity is nearly independent of temperature or sintered density. The analysis leads to a simple method for determining the simultaneous densification over the creep rate ratio. The implications of the result for the processing of heterogeneous ceramics and composites are discussed.

Wear Behavior of Ceramic Sliders in Sliding Contact with Rigid Magnetic Thin-Film Disks

This study identifies factors that affect slider performance and reports the effect of the nature of slider materials on wear behavior. Three factors relating to wear behavior are discussed: slider shape, wear data reproducibility and patterns of wear behavior. First, the performance of various sliders shows a strong correlation to the slider crown shape. Second, wear behavior is more reproducible when unlubricated disks replace lubricated disks. With lubricated thin-film disks, slider failure is reasonably reproducible, but when the failure occurs it is erratic. Although unlubricated disks show more reproducible wear data, the wear life of the disks is roughly an order of magnitude shorter than lubricated disks. It is important to recognize these factors before evaluating material differences in slider performance. Finally, multi-phase slider materials have more variation in failure patterns than single-phase slider materials; the difference is attributed to more flaws present in the multi-phase material...

Pore Size Distribution, Grain Growth, and the Sintering Stress

The effects of a pore size distribution and of the pore separation on the sintering stress is examined using a simple model. The sintering stress is found to be proportional to the mean of the pore sizes weighted according to the Voronoi cell pertaining to each pore, rather than to the simple pore size average. Large heteropores are shown to have little effect on the mean effective sintering stress. Decreases in pore coordination number of such pores, resulting from grain growth can significantly increase the stress intensification factor. The near-constancy of the sintering stress, observed experimentally for many powders over a wide range of sintered densities, does not directly follow from the simple model. It is argued that this constancy results from pore shrinkage, due to densification, which is compensated by pore growth due to coarsening.

Processing of diamond/alumina composites for low wear applications

A simple hot-pressing procedure for fabricating composites of diamond particulates in an alumina matrix at moderate applied pressures is described. Dense composites with up to 33 vol. % diamond particles are made by pressure-sintering at applied stress of 35 MPa in vacuum atmosphere. Preliminary wear tests of these composites on magnetic thin-film rigid disks show a low friction comparable to that of single crystalline diamond. Diamond/alumina composites can be an economical alternative to diamond or diamond coated materials for abrasion resistant applications.

High specific power lithium polymer rechargeable battery

PolyPlus Battery Company (PPBC) is developing an advanced lithium polymer rechargeable battery based on its proprietary positive electrode. This battery offers high steady-state (>250 W/kg) and peak power densities (3000 W/kg), in a low cost and environmentally benign format. This PolyPlus lithium polymer battery also delivers high specific energy. The first generation battery has a energy density of 100 Wh/kg (120 Wh/l) and subsequent generations increases the performance in excess of 500 Wh/kg (600 Wh/l). The high power and energy densities, along with the low toxicity and low cost of materials used in the PolyPlus solid-state cell make this battery exceptionally attractive for both hybrid and electric vehicle applications.

High performance S-type cathode [for Li-polymer battery]

The PolyPlus Battery Company (PPBC) is developing an advanced lithium polymer rechargeable battery based on proprietary positive electrode chemistry. In one formulation, this electrode contains elemental sulfur, either free or in association with secondary materials that promote its utilization. Batteries based on this cathode chemistry offer high steady-state (>250 W/kg) and high peak power densities (3000 W/kg), in a low cost and environmentally benign format. High energy density, in excess of 500 Wh/kg (600 Wh/l) can also be achieved. The high power and energy densities, along with the low toxicity and low cost of materials used in the PolyPlus solid-state cells make this battery exceptionally attractive for both hybrid and electric vehicles, and for consumer electronic applications.