Boron Doped Diamond Coatings Research Articles

Enhancing electrochemical production of peroxophosphates using new boron doped diamond coatings

Two boron doped ultrananocristallyne diamond (UNC) electrodes were manufactured and compared with a standard microcrystalline commercial electrode, to clarify how their differences may affect to the production of oxidants in the electrolysis of solutions containing phosphoric acid or phosphate salts. Effects of the current density and electrolyte pH were evaluated. Significant differences were found in the production of oxidants, being the production of oxidants favored, at high current densities and alkaline pHs. The effect of the pH was explained in terms of the higher stability of the peroxodiphosphate anion in comparison with the monoperoxyphosphate acid produced at low pHs. As well, because of the improved electrostatic attraction of the anion with the anode. Despite not exhibiting the largest electrochemical surface area, the flat UNC electrode shows the best performance for this process, except for the operation at low current densities and alkaline pHs in which the porous UNC outperforms it. Better efficiencies are obtained operating at mild current densities which was explained in terms of the great significance of direct processes in the production of oxidants by electrolysis of phosphoric acid or phosphate solutions

Advances in RF Glow Discharge Optical Emission Spectrometry Characterization of Intrinsic and Boron-Doped Diamond Coatings

Accurate determination of the effective doping range within diamond thin films is important for fine-tuning of electrical conductivity. Nevertheless, it is not easily attainable by the commonly adopted techniques. In this work, pulsed RF glow discharge optical emission spectrometry (GD-OES) combined with ultrafast sputtering (UFS) is applied for the first time to acquire elemental depth profiles of intrinsic diamond coatings and boron content bulk distribution in films. The GD-OES practical advances presented here enabled quick elemental profiling with noteworthy depth resolution and determination of the film interfaces. The erosion rates and layer thicknesses were measured using differential interferometric profiling (DIP), demonstrating a close correlation between the coating thickness and the carbon/hydrogen gas ratio. Moreover, DIP and the adopted semiquantification methodology revealed a nonhomogeneous bulk distribution of boron within the diamond crystalline structure, i.e., boron doping is both substitutional and interstitial within the diamond framework. DIP measurements also showed that effective boron doping is not linearly correlated to the increasing content introduced into the diamond coating. This is a finding well supported by X-ray diffraction (XRD) Rietveld refinement and X-ray photoelectron spectroscopy (XPS). This work demonstrates the advantage of applying advanced GD-OES operation modes due to its ease of use, affordability, accuracy, and high-speed depth profile analysis capability.

Boron Doped Diamond for Real-Time Wireless Cutting Temperature Monitoring of Diamond Coated Carbide Tools.

Among the unique opportunities and developments that are currently being triggered by the fourth industrial revolution, developments in cutting tools have been following the trend of an ever more holistic control of manufacturing processes. Sustainable manufacturing is at the forefront of tools development, encompassing environmental, economic, and technological goals. The integrated use of sensors, data processing, and smart algorithms for fast optimization or real time adjustment of cutting processes can lead to a significant impact on productivity and energy uptake, as well as less usage of cutting fluids. Diamond is the material of choice for machining of non-ferrous alloys, composites, and ultrahard materials. While the extreme hardness, thermal conductivity, and wear resistance of CVD diamond coatings are well-known, these also exhibit highly auspicious sensing properties through doping with boron and other elements. The present study focuses on the thermal response of boron-doped diamond (BDD) coatings. BDD coatings have been shown to have a negative temperature coefficient (NTC). Several approaches have been adopted for monitoring cutting temperature, including thin film thermocouples and infrared thermography. Although these are good solutions, they can be costly and become impractical for certain finishing cutting operations, tool geometries such as rotary tools, as well as during material removal in intricate spaces. In the scope of this study, diamond/WC-Co substrates were coated with BDD by hot filament chemical vapor deposition (HFCVD). Scanning electron microscopy, Raman spectroscopy, and the van der Pauw method were used for morphological, structural, and electrical characterization, respectively. The thermal response of the thin diamond thermistors was characterized in the temperature interval of 20–400 °C. Compared to state-of-the-art temperature monitoring solutions, this is a one-step approach that improves the wear properties and heat dissipation of carbide tools while providing real-time and in-situ temperature monitoring.

Promoting the formation of Co (III) electrocatalyst with diamond anodes

In this work, the catalytic effect of electrode substrate on the electrochemical oxidation of cobalt (II) using boron doped diamond (BDD) anodes was studied. A significant increase of the Co (III) formation was observed in using BDD coatings on tantalum substrate (91.43% at around 90 min of galvanostatic electrolysis), with respect to the Si-BDD anode, which only attained a poorer Co (III) conversion (8.33%) after applying the same electric charge. Electrochemical impedance spectroscopy showed that the Ta/BDD electrode has a lower charge-transfer resistance for the Co (II)/Co(III) metallic pair and the process is controlled by diffusion of cobalt towards the electrode surface, due to its rapid adsorption at the interface. This was further confirmed by cyclic voltammetry (CV) where the electrodeposition of Co (II) on the electrode surface is obviously significant if we compare it with that of Si/BDD anode. This difference in the electrode behavior, caused by the substrate on which the diamond coating is deposited, opens a line of research to improve the efficiency of mediated electrolytic treatments based on the use of Co, with important industrial applications in the treatment of many pollutants including volatile organic compounds (VOCs).

Comparative study on stability of boron doped diamond coated titanium and niobium electrodes

The service life of boron doped diamond (BDD) coated electrodes is closely related to the substrate material and preparation process of the BDD coatings. In this paper, the failure process of BDD coated titanium (Ti/BDD) and niobium (Nb/BDD) electrodes prepared by arc plasma chemical vapor deposition method was comparatively studied by accelerated life test. The results showed that the main failure mechanism of the two types of electrodes is delamination of the BDD coatings, accompanied by coatings' corrosion. The delamination of BDD coatings from both the substrates showed an incubation period, with the Ti/BDD electrode having a much shorter incubation period and a higher coating delamination rate than its Nb/BDD counterpart. By comparing growth process of diamond coatings and corrosion behavior of carbides formed on both substrates, it is found that on a Ti substrate, diamond coating is more liable to incorporate pore like defects, and carbide layer formed beneath the diamond coating is more susceptible to corrosion in electrolysis solution. It is believed that these two factors would be responsible for short service life for Ti/BDD electrodes as compared with that for Nb/BDD electrodes.

Investigation on microstructure evolution and failure mechanism of boron doped diamond coated titanium electrode during accelerated life test

For a long time, due to a lack of understanding on microstructure evolution of boron doped diamond (BDD) electrodes in application, there have been controversies on failure mechanism of the electrodes material. In this paper, A BDD coated titanium (Ti/BDD) electrode prepared by arc plasma chemical vapor deposition method was analyzed and accelerated life test (ALT) was carried out in 1 mol/L H2SO4 electrolyte at constant current density of 1A/cm2. Various analyses techniques were combined to track the electrode failure process. The results showed that during the ALT process, the failure process of the Ti/BDD electrodes may be divided into two stages. In the first stage, defects existed in the coatings may lead to penetration of electrolyte into the BDD coatings, resulting in cracking and delamination of the coatings. Then in the second stage, corrosion of BDD grains and dissolution of intermediate titanium carbide layers occur accompanied by slow coatings delamination. Based on these analyses, possible ways to improve the service life of Ti/BDD electrodes are summarized.

Deposition of CVD Diamond Coatings on Carbon Fiber Composite Substrates

Boron doped diamond coatings are used in electrochemistry, due to the high overvoltage for oxygen generation. Niobium is often used as bulk material, but also diamond deposition on titanium was demonstrated. For metallic bulk materials corrosion can take place in case of defects in the diamond coating. This problem can be avoided by using carbon based substrates. Diamond deposition on carbon substrates is difficult, because atomic Hydrogen needed for diamond growth attacks graphitic and amorphous carbon. These reactions have the effects that carbon in the substrate is etched and the amount of atomic hydrogen needed for diamond growth is reduced. To reduce the carbon etching on the substrate, the duration till diamond layer formation should be short. By controlling the diamond deposition conditions, boron addition and seeding with diamond prior to deposition, the formation of diamond coatings on carbon fibre composites (CFC) is possible. Electrochemical measurements of the boron doped diamond coatings verified the excellent electrochemical properties of the samples, e.g. good electrical conductivity, high overvoltage for oxygen and hydrogen but also chemical inertness.

Investigations on etching resistance of undoped and boron doped polycrystalline diamond films by oxygen plasma etching

The reactive ion etching (RIE) technique was used to etch the undoped and boron-doped diamond (BDD) polycrystalline films using oxygen plasma. The effect of boron within the BDD coatings on the morphology was investigated. BDD films exhibited much superior etching resistance than the undoped diamond films, wherein the (111) planes of BDD films were more etching resistant than (100) planes due to much higher boron concentration. However, this is in contradiction to undoped diamond films whose (111) planes were etched more quickly. The results would help to better design a particular and efficient etching method for undoped and BDD films to get a well-patterned microstructures.

Is it worth the use of bipolar electrodes in electrolytic wastewater treatment processes?

In this work, it is studied the advisability of the application of bipolar electrodes (consisting of boron doped diamond coatings) for the electrolytic treatment of wastewater. Results are discussed in terms of the success in two different reactions: the depletion of an organic pesticide (2,4-dichlorophenoxyacetic acid) and the oxidation of chlorides to perchlorates. This later reaction should be prevented in an actual environmental remediation process because of the hazardousness of perchlorate, but it has been investigated in this work because it gives valuable information about formation of oxidants during electrolytic processes as chlorates and perchlorates behaves as inert species in the oxidation of 2,4-D. Results pointed out the importance of the optimization of the number of bipolar electrodes to be included in each cell for a given application. Bipolar configuration can help to improve the results obtained in the removal of organic compounds by direct processes and it also influences on the formation oxidizing species that can improve the results of this electrolytic process. However, it increases significantly the cell voltage and hence the power consumption. In this work, it is demonstrate that each bipolar electrode saves around 22% of the electric charge provided by the single cell to deplete 2,4-D and to generate oxidants, although this positive effect is masked by the increase in the cell voltage. Energy required to oxidize organic increases with the number of bipolar electrodes installed in the cell while energy efficiency in the production of oxidants shows a maximum for the cell configuration with 1 bipolar electrode.

Composition profiles and adhesion evaluation of conductive diamond coatings on dielectric ceramics

Sintered silicon nitride (Si3N4) ceramic substrates were investigated as dielectric substrates for the growth of metal-like boron-doped nanocrystalline diamond (NCD) and microcrystalline diamond coatings via the Hot Filament Chemical Vapor Deposition (HFCVD) technique. The structural, electrical and chemical properties of both the ceramic substrates and the diamond coatings may potentiate their applicability in particular in harsh environments and highly demanding situations. Boron doping was achieved via a boron oxide solution in ethanol dragged into the reaction chamber with argon. The coatings were characterized by scanning electron microscopy, UV μ-Raman scattering, X-ray diffraction, time-of-flight secondary ion mass spectroscopy, Brale indentation for adhesion evaluation and two-point contact probe for resistivity measurements. The HFCVD technique led to a maximal growth rate of about 1μm/h. Several metal-like boron doped diamond coatings were obtained. It was found that at lower substrate temperature, lower system pressure and higher methane concentration, the resistivity of the conducting NCD coatings is about 3 orders of magnitude higher when compared with samples obtained with higher substrate temperature, higher system pressure and lower methane concentration. Nevertheless, for every metal-like boron-doped coating the use of the Si3N4 ceramic substrate guaranteed a superior adhesion level.