| Popis: |
Chemical vapour deposition (CVD) onto flat substrates has been researched extensively; however, little work has been on done on diamond deposition onto 3-D substrates. Diamond has excellent physical and chemical properties and has considerable potential for use in dental tools and biomedical implants. Since the 1950s sintered diamond burs have been used and are made using diamond particles bonded onto the substrate using a binder matrix material. The binder contains potentially poisonous components such as nickel and CVD technology eliminates the use of such binder materials. Hot Filament Chemical Vapour Deposition (HFCVD) uses a horizontal filament mounted above the substrate. For 3-D substrates the system was modified with the filament mounted vertically and the substrate held concentrically within the coil in a system called vertical filament CVD (VFCVD). Process optimisation was conducted on molybdenum wire and then diamond films were deposited onto metals such as titanium, molybdenum and tungsten carbide (WC-Co) burs. A pre-treatment was required on WC-Co burs using Murakami reagent was used for etching followed by acid etching to remove excess Co from the surface and improve adhesion. The growth rate, adhesion, surface roughness, composition and nucleation densities were all investigated. The substrate temperature influenced the compressive stress of the diamond films due to the thermal gradient, which is related to the position of the substrate within the filament. Machining tests showed that the wear rates of the coated diamond tools were considerably lower than the uncoated burs. These were quantified using a Figure of 5 Merit (F) which was then plotted against the number of holes drilled for uncoated, sintered and VFCVD diamond coated burs to assess the tool performances on human tooth material, acrylic and borosilicate glass. All of the tests showed that the diamond coated dental burs using the new VFCVD process demonstrated a superior performance compared to sintered and uncoated burs. |
