Preliminary NotePreparation and characterization of Ti/Diamond electrodes
Introduction
Oxidative electrochemical processes have continuously growing importance both in selective organic synthesis and in degradation of organic pollutants1, 2, 3. The electrode material is clearly an important parameter when optimizing such processes, since the mechanism and the products of several anodic reactions are known to depend on the anode material. For example the anodic oxidation of phenol yields hydroquinone and benzoquinone at Ti/IrO2 anode and mainly CO2 at Ti/SnO2-Sb2O5 anode4, 5.
Recently synthetic diamond has begun to be investigated as electrode material. Boron-doped synthetic diamond possesses several “electrochemically” desirable properties like corrosion resistance and viable electrical conductivity. The electrochemical behaviour of such diamond thin films deposited on p-Si substrates has been studied with the goal of developing application in electroanalysis[6]electrosynthesis[7]and waste water treatment[8]. The main problem in this configuration where p-Si is used as substrate, are the low mechanical strength of the electrode and the low electrical conductivity of the p-Si substrate.
To overcome this problem a thin layer of synthetic boron-doped diamond has been deposited on Ti base metal (Ti/Diamond). The configuration of this electrode is similar to the DSA® (dimensionally Stable Anodes) electrodes and is supposed to open new possibilities in industrial electrosynthesis, waste water treatment and energy storage devices.
The main problem in the preparation of the DSA® type electrodes is to ensure a good electrical contact between the Ti base metal and the coating. In case of the Ti/Diamond electrodes this has been achieved by the formation of a conductive TiC interlayer between the Ti substrate and the diamond coating.
Section snippets
Experimental
Diamond films of about 3 μm thickness were grown by hot filament chemical vapor deposition7, 9. (HFCVD) on Ti substrates (98,885, Signer titanium AG) at substrate temperatures of 700°C. The Ti substrates, ca 1×1 cm2 and 1 mm thick, were pretreated by polishing with diamond paste, then rinsed with ultrapure water followed by drying. Subsequently, the substrates were placed in the deposition chamber adjacent to 3 pieces of boron oxide (5–6 mg). The chamber first was evacuated to a pressure of less
Results and discussion
Fig. 1 shows a SEM image of polycrystalline diamond films deposited on Ti substrates. The morphological grain size, as observed by SEM, is in the order of 1 μm. The grains are heavily twinned. There is evidence of 〈112〉 fiber texture formation, as inferred from the growth morphology and X-ray diffraction (θ–2θ); i.e. the 〈112〉 axes of the crystallites point preferentially in the direction of the film normal. Diamond growth on the titanium substrate is preceded by the formation of an intermediate
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