T. Danny Xiao

The dependency of microstructure and properties of nanostructured coatings on plasma spray conditions

Abstract In this paper, Al2O3-13 wt.% TiO2 coatings formed via a plasma spray approach using reconstituted nanosized Al2O3 and TiO2 powder feeds are described. Effects of various plasma spray conditions on the microstructure, grain size, phase content and microhardness of the coatings have been evaluated. It is found that phase transformation of nanosized Al2O3 and TiO2 during heat treating, sintering and thermal spraying is, in general, identical to that of micrometer-sized counterparts. Furthermore, the particle temperature during thermal spray could be divided into three regimes, i.e. low, intermediate and high temperature regimes, according to the characteristics of the coating produced from the nanopowder. The hardness and density of the coating increase with the spray temperature. The phase content and grain size of the coating also exhibits a strong dependency on the spray temperature. The coating sprayed using nanopowder feed displays a better wear resistance than the counterpart sprayed using commercial coarse-grained powder feed. The observed phenomena are discussed in terms of physics of thermal spraying, mechanisms of coating growth and phase transformation of the oxides.

Abrasive wear characteristics of plasma sprayed nanostructured alumina/titania coatings

Abstract In this paper, the plasma spray technique was used to deposit coatings with reconstituted nanostructured Al 2 O 3 /TiO 2 powders. The abrasive wear resistance of the ceramic coatings was evaluated using diamond abrasives. The result showed that the abrasive wear resistance of the coatings produced using the nanostructured Al 2 O 3 /TiO 2 powders is greatly improved compared with the coating produced using the conventional Al 2 O 3 /TiO 2 powder (Metco 130). The highest abrasion resistance of the coating sprayed with nanostructured Al 2 O 3 /TiO 2 powder is about four times that of the coating sprayed with the conventional Al 2 O 3 /TiO 2 powder. Both as fabricated and after wear Al 2 O 3 /TiO 2 coatings were investigated by X-ray diffraction, SEM and indentation tests. The abrasive wear mechanism is also discussed.

Nickel hydroxide and other nanophase cathode materials for rechargeable batteries

Abstract The staff of US Nanocorp, Inc. are developing unique nanostructured materials for a wide range of applications in the areas of energy storage (batteries and ultracapacitors) and energy conversion (fuel cells and thermoelectric) devices. Many of the preparations of these materials exploit a wet synthesis process (patent pending) that is scaleable to large volume manufacturing and anticipated to be low in cost. Specifically, both the β -form of nickel hydroxide and the hollandite form of manganese dioxide have been synthesized. The hexagonal Ni(OH) 2 is anticipated to significantly boost energy densities in nickel-alkaline batteries, including nickel/cadmium, nickel/metal hydride and nickel/zinc. The nanophase MnO 2 microstructure exhibits an unusual tunnelled tubular geometry within a ‘birds nest’ superstructure, and is expected to be of interest as an intercalation cathode material in lithium-ion systems as well as a catalyst for fuel cells. Characterization of these materials has been by the techniques of high resolution SEM and TEM, as well as XRD. Both Hg porosimetry and BET surface measurements for conventional and spherical nickel hydroxides are summarized. Pore distribution and electrochemical activity for the nanophase materials will be examined in the future.

Novel Design and Fabrication of Thermal Battery Cathodes Using Thermal Spray

Li-Alloy/FeS 2 thermal batteries are the predominant thermal battery chemistry today. Conventional electrodes are fabricated by cold pressing of powders. A better means of providing thin electrodes would dramatically increase volumetric and gravimetric energy densities and cost efficiency of thermal batteries. In this study, experiments were conducted on fabricating the cathode via high-velocity oxygen-fuel (HVOF) and dc-arc plasma thermal spray technique. The deposited films were characterized by cross-section examination using Scanning Electron Microscopy (SEM) and X-ray Diffraction. The thermal decomposition of pyrite was suppressed by a proprietary additive. The electrochemical test results showed that pyrite cathodes prepared by dc-arc plasma spraying with additives demonstrated better performance compared traditional pressed-powder electrodes.