Preparation And Investigation Of Boron-doped Diamond Film Electrode On Ti Substrate

Boron-doped diamond(BDD) is an excellent electrode material to be used in electrochemistry and electrochemical engineering due to its advantages such as wide electrochemical window, low voltammetric background current, high level of mechanical strength and corrosion resistance. One of its potential application is wastewater treatment which has been proposed and is being actively pursued now.In recent years there has been increasing interest in the electrochemical properties of BDD thin films electrode. For the most part BDD thin film has been deposited on silicon substrates, however, the use of other metal discs or meshes as substrate materials is highly desirable for electrochemical applications because of the enhanced electrical conductivity and the increased substrate area. Titanium shows a high conductivity, corrosion resistance, mechanical processing performance and low cost characteristics, which make it a quite promising material for this application. Especially confronted with the poor working conditions for the electrochemical reaction process, the advantages of BDD electrode deposited on Ti substrate is very prominent. For example, the industrial wastewater treatment process. However, the diamond deposition on Ti substrate is accompanied by two bottlenecks,the adhesion and electrode life. On the one hand the coefficient of thermal expansion of Ti and diamond (diamond: 0.84×10^-6℃^-1, Ti: 8.50×10^-6℃^-1, TiC: 7.42×10^-6℃^-1) are quite different. Therefore, residual thermal stress exists duiring the cooling after film deposition process, which directly affects the film adhesion. On the other hand Ti is an active carbide forming element and therefore reacts with the used reaction gases under diamond deposition conditions by forming intermediate layers. The formed TiC-layer is of a rough and porous nature and tends to split off easily, which causes severe adhesion problems of the diamond layers on these substrates and limits the industrialization of Ti/BDD electrodes.In this work, BDD thin films were deposited on titanium substrates using the home-made microwave plasma chemical vapor deposition (MPCVD) equipment. The surface morphologies, residual stress, preferred orientation and TiC-layer were analysed by several experimental apparatus, such as scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffraction (XRD). The result shows the best pretreatment process: firstly grind the Ti substrate with 600#, 800#, 1000#and 1200# sandpaper for 10 min respectively, and then polish it by diamond paste at 200r/min for 10min prior to deposition. The optimum deposition temperature has been found:700⁷50℃。The influences of the boron concentration on BDD growth on Ti were investigated. The experimental results show that the (111) morphology is preferred with increasing boron addition. And the higher boron concentration results in a decrease in the concentration of TiC as well as the grain size, inducing a significantly higher level tensile stress to relieve the compression stress formed in deposition, and thus a greater extent to improve adhesive force.The electrochemical characteristics of BDD film were analyzed in cyclic voltammetry. The results indicated that the BDD film possessed wide electrochemical window about 3.2eV, low voltammetric background current, which are crucially important to oxidation efficiency and energy comsumption. It was believed that the BDD film was a good electrode material. The removal efficiency of COD for wastewaters containing 2,4-Dichlorophenol by BDD is almost 100%, which indicates the BDD on Ti substrate is a promising electrode for the treatment of industrial wastewater. BDD film with a Ta interlayer was also deposited, and the Ti/Ta/BDD electrode shows wide electrochemical window about 3.2eV, low voltammetric background current.