Joseph Lik Hang Chau

Surface modification of silica nanopowders in microwave plasma

In this work, surface modification of nanopowders in microwave plasma process was demonstrated. In order to obtain silica nanopowder with polymeric coating, a two-step microwave process was designed. 3-Aminopropyltrimethoxysilane was used as the surface modifier. Transmission electron microscopy and electron energy loss spectroscopy have been used for the direct microstructural imaging and chemical analysis of surface modified-silica nanopowders. The silica nanopowders were uniformly coated with a thick layer of amino-silane. Surface modification in microwave plasma is a simple, direct and easy to control process without using any solvents. The surface modified-silica nanopowders can be incorporated directly into polymer matrix for the preparation of hybrid nanocomposite materials.

Development of hybrid amorphous barrier coatings on polymer substrates

Flexible hybrid Ta–C–O–F coatings were deposited on polyethylene naphthalate substrates using RF co-sputtering method. The morphologies of the hybrid Ta–C–O–F coatings co-sputtering were strongly dependent on polytetrafluoroethylene (PTFE) sputtering power. By increasing the polymer sputtering power from 20 to 60 W, the water vapor transmission rate increase from 0.015 to 0.030 g/m2day. The water vapor transmission rate remains relatively constant at 0.030 g/m2day with further increasing the PTFE power to 80 W. Coatings prepared by PTFE sputtering power of 20 to 80 W exhibits an average optical transmittance of higher than 70% in the visible range. The Ta–C–O–F coating with a thickness of 577.5 nm was repeatedly flexed back and forth to a radius of curvature of 3 mm. No cracks were observed in the layer after bending. The results show that the hybrid coatings are not only highly flexible, but also with good water vapor barrier property.

Fabrication of high hardness and corrosion resistance coatings from Fe-based alloy powders

ABSTRACT Gas atomized Fe50Cr24Mo21Si2B3 powders were used to form Fe-based alloy coatings by the air plasma spray method. The coatings exhibited high amorphous nature and extremely low porosity of 0.41% in about 200 µm thickness. The Fe-based coating exhibits an average hardness about 1255 Hv. The Fe-based coatings could be potentially applied as functional surface protective coatings.

Zeolite-coated steel fibers for friction materials applications

Zeolite-coated steel fiber used for non-asbestos organic type friction material was studied. High silica zeolite silicalite-1, due to its easy preparation procedures was chosen to be deposited onto the steel fibers. This work shows that the friction material incorporated with zeolite-coated steel fibers exhibit higher coefficient of friction values than the friction material with bare steel fibers. Zeolite-coated steel fibers added friction materials maintain a sufficiently high friction coefficient from 0.332 to 0.514 with the brake discs at high temperature from 150 ℃ to 300 ℃. This kind of friction material with corrosion-resistant property has great potential to be used for vehicle brake pad applications.