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Diamond foils are exceptionally strong yet brittle. One approach to make ceramic foils less susceptible to brittle fracture is to introduce interfaces into the material that provide pathways for crack deflection. In this study, we were able to produce strong yet tough diamond/metal laminates (DMLs) from freestanding diamond foils using a brazing process. The mechanical behavior was characterized via three-point bending (3PB) where the laminates exhibit step-like fracture. Crack deflection at interfaces induces toughening within the laminates. At approx. 3.0 MJ/m3 diamond/metal laminates exhibit more than twice the fracture energy of monolithic diamond foils while maintaining 90 % stiffness and about 70 % nominal strength. Classical laminate theory (CLT) supports the assessment of the deformation behavior and step-like fracture of diamond/metal laminates. We find that the diamond-to-metal interface plays a critical role: it must be strong enough to enable the transfer of shear stress, while being weak enough to deflect a crack.

Electrochemical production of hydrogen peroxide (H2O2) constitutes a cost-effective and alternative method to the complex and energy-intensive anthraquinone oxidation process. The two-electron water oxidation reaction pathway, while unconventional, is an attractive option for H2O2 generation as it can be combined with suitable reduction reactions to effectuate simultaneous electrosynthesis of valuable chemicals at a large scale. In this work we demonstrate that a carbon-based catalyst, boron-doped diamond (BDD), achieves an H2O2 concentration and production rate of 29.0 mmol dm-3 and 19.7 μmol min-1 cm-2, respectively, illustrating the capability of BDD as a suitable electrocatalyst for H2O2 formation from water.

Electrochemical synthesis of hydrogen peroxide (H2O2), via the two-electron water oxidation reaction (2e– WOR), is an attractive method for the sustainable production of valuable chemicals in place of oxygen during water electrolysis. While the majority of 2e– WOR studies have focussed on electrocatalyst design, little research has been carried out on the selection of the supporting electrolyte. In this work, we investigate the impact of potassium carbonate (K2CO3) electrolytes, and their key properties, on H2O2 production. We find that at electrolyte pH values (> 9.5) where the carbonate anion (CO32–) is prevalent in the mixture, a 26.5% increase in the Faraday efficiency (%FE) for H2O2 production is achieved, compared to bicarbonate (HCO3–) dominant solutions. Utilising boron-doped diamond (BDD) in highly concentrated K2CO3 solutions, current densities of up to 511 mA cm-2 (in 4 M) and %FEs of 91.5% (in 5 M) can be attained. The results presented in this work highlight the influence of CO32– on electrochemical H2O2 generation via the 2e– WOR and provide novel pathways to produce desirable commodities at the anode during electrochemical water splitting.

Diamond coatings applied by chemical vapor deposition (CVD) provide extraordinary properties concerning hardness and wear resistance, which enables an increase of the performance or lifetime of highly stressed components. In particular, the combination of steel substrates and diamond coatings allows for numerous applications in several sectors of industry. However, there are significant challenges considering the coating adhesion strength. For example, the mismatch concerning the thermal expansion of steel and diamond commonly leads to a delamination of the coating. Thus, a suitable pre-treatment of the substrate surface is compulsory. With the aim of improving CVD diamond coating adhesion, ultrasonic vibration superimposed machining (UVSM) is applied when doing face milling on steel X46Cr13 specimens. The vibration direction is parallel to the tool axis and perpendicular to the feed direction. The tool wear and the surface microstructure are determined by 3D laser scanning microscopy. The investigations show, that predefined microstructuring of the substrate surface by UVSM contributes to an enhancement of the CVD diamond coating adhesion, especially regarding coatings with a thickness up to 10 µm. This can be referred to a better distribution or a reduction of thermally induced residual stresses in the diamond layer. However, a reliable generation of deterministic microstructures by UVSM significantly depends on the wear behavior of the tool. Uncoated cemented carbide grades exhibit considerable deficits reflecting in rapid tool wear. Therefore, adapted tool coatings are experimentally investigated, which result in an increase of the tool life and a reduction of the geometrical deviations of the microstructures. With an appropriate system of surface microstructure and coating, for example for tribological applications substantial improvements in terms of wear resistance and coefficient of friction are expected.

In the present work, we investigate the efficiency of TiO2 photoelectrode layers on boron doped diamond foil (BDDF) in comparison with a classic conducting glass (FTO) back contact. Crystalline thin TiO2 layers were prepared on the substrates by two different methods: (i) deposition of metallic Ti thin films followed by thermal oxidation to form TiO2 (TO-TiO2), (ii) reactive sputter deposition of TiO2 thin films and crystallization of these layers (SP-TiO2). Optimized layers show that TO-TiO2 films on BDDF deliver a significantly higher incident photon to current efficiency (IPCE) compared to directly sputtered SP-TiO2 layers and these layers on BDDF also outperform conducting glass (FTO) as a back contact. We ascribe this beneficial effect of the BDDF back contact to the formation of an intermediate conductive phase of Ti-carbides at the TO-TiO2/BDDF interface.

No proper treatment option for peri-implantitis exists yet. Based on previous studies showing the in vitro effectiveness of electrochemical disinfection using boron-doped diamond electrodes, novel double diamond electrodes (DDE) were tested here. Using a ceramic carrier and a laser structuring process, a clinically applicable electrode array was manufactured. Roughened metal discs (n = 24) made from Ti-Zr alloy were exposed to the oral cavities of six volunteers for 24 h in order to generate biofilm. Then, biofilm removal was carried out either using plastic curettes and chlorhexidine digluconate or electrochemical disinfection. In addition, dental implants were contaminated with ex vivo multispecies biofilm and disinfected using DDE treatment. Bacterial growth and the formation of biofilm polymer were determined as outcome measures. Chemo-mechanical treatment could not eliminate bacteria from roughened surfaces, while in most cases, a massive reduction of bacteria and biofilm polymer was observed following DDE treatment. Electrochemical disinfection was charge- and time-dependent and could also not reach complete disinfection in all instances. Implant threads had no negative effect on DDE treatment. Bacteria exhibit varying resistance to electrochemical disinfection with Bacillus subtilis, Neisseria sp., Rothia mucilaginosa, Staphylococcus haemolyticus, and Streptococcus mitis surviving 5 min of DDE application at 6 V. Electrochemical disinfection is promising but requires further optimization with respect to charge quantity and application time in order to achieve disinfection without harming host tissue.

A boron doped diamond (BDD) electrode was employed in an electrochemical reactor to oxidize the phenolic content of Jordanian olive mill wastewater. The BDD anode was fabricated using hot filament chemical vapor deposition on niobium and the morphology of the BDD electrode was characterized using an atomic force microscope. Then, electrolysis batch runs were carried out at laboratory scale to test the effect of different process parameters, namely, initial chemical oxygen demand (COD) load (72.9, 33.8, and 0.18 g/L), the addition of Na2SO4 as supporting electrolyte, and adding NaCl along with Na2SO4, on the efficiency of the treatment process. The results were reported in terms of COD, color and turbidity removal, and pH variation. The experiments revealed that electrochemical oxidation using BDD significantly reduced the COD by 85% with no supporting electrolytes. It was observed that adding Na2SO4 with NaCl brought the COD removal to higher than 90% after 7 hours of treatment for COD loads of 72.9 and 33.8 g/L, and after 2 hours for a COD load of 0.18 g/L. Likewise, color was completely removed regardless of the initial COD load. The turbidity for samples with 72.9 and 33.8 g/L as COD load reached a minimal value of 2.5 and 1 NTU respectively.

Disinfection and prevention of re-infection are the decisive treatment steps in endodontic therapy. In this study, boron-doped diamond (BDD) electrodes have been fabricated and used for disinfecting the root canals of extracted human teeth, which had been covered with bacterial biofilms formed by Bacillus subtilis and Staphylococcus epidermidis. The growth of B. subtilis could be successfully impaired, achieving a complete disinfection after 8.5 min treatment time with the success of disinfection depending on the insertion depth of the electrode in the root canal. S. epidermidis could completely be removed after 3.5 min treatment time. A clinically applicable electrode array led to complete disinfection after treatment times of 10 min for S. epidermidis and 25 min for B. subtilis. BDD electrode application allowed for the improved disinfection of root canals and dentin tubules based on a continuous production of reactive oxygen species and their enhanced penetration of dentin tubules most likely due the formation of a continuous stream of small gas bubbles. The treatment times that are required here will be shortened in clinical application, as mechanical shaping of the canal system would precede the disinfection process.

Reactive Blue 19 (RB-19) dye has low fixation efficiency, a long half-life and high toxicity. It is easily loss during the cleaning of textiles and can remain in the environment for long time causing serious environmental problems if not removed. This study reports the degradation of RB-19 by: 1) the electrochemical direct degradation with Boron-Doped Diamond (BDD) electrodes and 2) a combined processes using BDD and Reticulated Vitreous Carbon (RVC) electrodes that generates H2O2. The direct degradation uses different current densities and concentrations. High currents densities, longer electrolysis time and low volumetric flow rates, favour RB-19 degradation removing total colour and 100 % TOC at 5 and 60 min respectively. At 41 mA cm-2 current density and 20 dm3 h-1 volumetric flow rate, the energy consumption to degrade 20 mg dm-3 of RB-19 was 279 kWh kg-1. The TOC removal of RB-19 dye combining BDD and RVC at a current density of 41 mA cm-2 was below 72% during 90 min and the energy consumption increased to 612 kWh kg-1. The higher energy consumption obtained during the combined process suggested that the direct degradation process at low volumetric flow rates is more efficient than the combined process.

Boron-doped diamond electrodes can be used to generate reactive oxygen species directly at the electrode's surface. This property was used in this study for in-situ electrochemical oxidation to eliminate different bacteria, i.e. Escherichia coli, Pseudomonas fluorescens and Pseudomonas aeruginosa, as well as Bacillus subtilis spores from water samples. Application of low voltages in the rage from 4 to 10 V and short incubation times in the range of minutes allowed a complete disinfection of water contaminated with enterobacteria and freshwater microbes including nosocomial pathogens as well as a significant reduction of spores. A pilot reactor was constructed, which allowed to decrease microbial contamination of sewage plant effluent drastically. Boron-doped diamond electrodes allow efficient reduction of bacterial contaminations in water samples.

To investigate the growth and the thermoelectric properties of nitrogen-doped diamond, samples were grown by microwave plasma chemical vapor deposition with varying nitrogen flows as well as with a high nitrogen flow and varying methane flows. The samples were characterized according to their morphology, phase composition, electrical conductivity, and Seebeck coefficient. It was found that an increased nitrogen flow leads to a higher fraction of sp2-bond carbon. Furthermore, a structure consisting of graphene nanowalls which exhibits many cavities is created. For nitrogen flows above 70 sccm, the electrical conductivity increases abruptly and significantly from less than 0.3 s m to more than 4.3 s m . A lower methane flow inverts this development. It was not possible to find a clear dependency of the Seebeck coefficient on the nitrogen flow. Seebeck coefficients were measured between − 17 μ V K at 23 °C and − 34 μ V K at 110 °C.

Here we report a novel structuring technique for diamond coatings using a copper masking on a previously deposited diamond layer to epitaxially grow a subsequent diamond layer only at the exposed areas of the mask. An 8 μm thick copper mask is applied onto the substrate using physical vapor deposition and structured by standard photolithographic methods. Hot filament chemical vapor deposition is used to grow the 14 μm thick structured diamond layer on the diamond coated silicon wafer. Micro and nano crystallinity of the diamond layers are varied, as well as the doping with boron to verify the applicability of the new structuring method for different kinds of diamond qualities. It is shown that four-inch wafers can be fully structured with this high temperature masking technique and the resolution was mostly affected by the quality of the printed mask used for the photolithographic structuring of the copper mask. This diamond structuring method could pave the way for diamond being used in electronics or adding additional functionalities to diamond coated tools.

Nano- and micro-crystalline diamond foils with a thickness of at least 30 μm are manufactured by hot-filament chemical vapor deposition (HFCVD) in an industrial coating machine. Some of them are doped with trimethylborate. The diamond foils are exposed to air at 450 °C and 500 °C and oxidized for up to 738 h. At these temperatures all investigated diamond foils exhibit a substantial weight loss, which is measured with a high precision balance. Nanocrystalline diamond foils show a high weight loss rate compared to microcrystalline diamond foils. At 500 °C the weight loss rate is two to seven times higher than that at 450 °C. Grain boundaries and small diamond crystals are etched much faster than larger diamond crystal. The incorporation of boron does not significantly affect the oxidation of the diamond foils.

For the continuous development of ultra high temperature ceramic matrix composites manufactured using reactive melt infiltration (RMI), the influence of three different melt alloys and two preform ...

Nanocrystalline diamond foil (NCDF) is a self supporting, detached diamond layer with a thickness in the range of several 10 μ. Its freestanding character allows the investigation of the surface energy considering the growth as well as the nucleation (seeding) side. This is shown here for the first time. Contact angles of different liquids on the NCDF were measured and the surface energies were calculated using the Owens–Wendt–Rabel–Kaelble (OWRK) method. A compulsive cleaning process with liquid substances like acetone has no effect on the surface energy. Nevertheless it is recommended to clean the surface before contact angle measurements to prohibit distractions by dirt. The polar surface energy component of a NCDF after cleaning is 3 mN/m and the nonpolar component is 44 mN/m. The NCDF's surface morphology which is induced by the choice of a template's structure does not influence the surface energy. A surface oxidation by hot air or oxygen plasma is resulting in a higher surface energy and more polar components on the nucleation side of the NCDF. This effect can be used to activate the surface for applications like gluing.

A tensile testing method to directly determine the elastic as well as the fracture properties of self-supporting nanocrystalline diamond foil (NCDF) is introduced. NCDF is the strongest ceramic foil material known, offering a bending strength of more than 4 GPa [1] . The previously presented bending test reflects the influence of the surface morphology on the mechanical properties well, but is limited to a small near-surface volume. Hence only a small number of different flaws in the material can be detected. To investigate the bulk properties of this novel material a tensile testing method, where the stress is evenly distributed over the whole cross-section of the sample, was developed and validated. The interpretation of the tensile strength by the statistical Weibull approach resulted in values of ∼535 MPa and 470 MPa for NCDF grown on silicon and copper templates, respectively. The combination of tensile testing with digital image correlation allows for the direct determination of Young’s modulus. As compared to methods using resonance frequencies this technique does not have limitations regarding the thickness of the specimen. Young’s modulus was found to yield 624 ± 88 GPa for NCDF synthesized on polished silicon and 536 ± 65 MPa for NCDF from an etched silicon template. Furthermore, by stressing the double-edge-notched specimen in this set-up, the fracture toughness was determined to be 3.5 ± 0.7 MPa m .

Diamond coatings are used in heavily stressed industrial applications to reduce friction and wear. Hot-filament chemical vapour deposition (HFCVD) is the favourable coating method, as it allows a coating of large surface areas with high homogeneity. Due to the high temperatures occurring in this CVD-process, the selection of substrate materials is limited. With the desire to coat light materials, steels and polymers a new approach has been developed. First, by using temperature-stable templates in the HFCVD and stripping off the diamond layer afterwards, a flexible, up to 150 μm thick and free standing nanocrystalline diamond foil (NCDF) can be produced. Afterwards, these NCDF can be applied on technical components through bonding and brazing, allowing any material as substrate. This two-step process offers the possibility to join a diamond layer on any desired surface. With a modified scratch test and Rockwell indentation testing the adhesion strength of NCDF on aluminium and steel is analysed. The results show that sufficient adhesion strength is reached both on steel and aluminium. The thermal stress in the substrates is very low and if failure occurs, cracks grow undercritically. Adhesion strength is even higher for the brazed samples, but here crack growth is critical, delaminating the diamond layer to some extent. In comparison to a sample directly coated with diamond, using a high-temperature CVD interlayer, the brazed as well as the adhesively bonded samples show very good performance, proving their competitiveness. A high support of the bonding layer could be identified as crucial, though in some cases a lower stiffness of the latter might be acceptable considering the possibility to completely avoid thermal stresses which occur during joining at higher temperatures.

Electrochemical technologies are a promising alternative for the Oil Industry, for the treatment of formation water containing organic and inorganic contaminants. The main advantages of these technologies include environmental compatibility, versatility, energy efficiency, health & safety and selectivity. However, the effectiveness of the electrochemical approaches depends significantly on the electrode material and the cell parameters. Recently, BDD electrodes have shown a growing interest due to their unique ultra-wide electrochemical window with highest O2 and H2 over-potentials. The current approach based on the application of boron doped diamond (BDD) electrode to treat electrochemically production water (PW) coming from a heavy oil field, was investigated in one-compartment electrolytic batch cell. Formation water is increasing more and more with the depletion of pressure and the age of many oil and gas fields. This formation water is characterized by high initial chemical oxygen demand (COD) due to their high level of organic content. Proper elimination of the high COD content from PW to be re-usable water streams for beneficial purposes such as irrigation water or correct disposal is becoming increasingly important for an environmental and human health in the Oil Industry. The influence of primary settling treatment step and several operating parameters such as applied current density, supporting electrolyte (NaCl or Na2SO4), agitation and temperature on the COD removal efficiency from PW were investigated and the corresponding energy consumption value was also evaluated. The estimated COD removal efficiency was achieved with and without settling step between 90 and 100 % within treatment time of 5h - 7h by using applied current in the range of 5 - 12.5 mA/cm2, but the minimum absolute value of COD for the resulting water with and without settling step was achieved to be less than 0.09 mg/l and 75 mg/l, respectively by adding 3.5 g/l NaCl. However, the energy requirement for high removal efficiency without adding NaCl was 2.5 more than with NaCl into PW. Adding NaCl into PW decreases the energy consumption and increases the oxidation efficiency by promoting the electro-generation of active chlorine species in addition to hydroxyl radical. On the other hand, only 67 % removal efficiency of COD was achieved by adding 5.1 g/l Na2SO4 into PW which affect negatively the COD removal efficiency compared to PW without any supporting electrolyte. The integration of electrochemical treatment step based on BDD electrodes after settling primary step, which is commonly used in industry, as a novel secondary treatment step will create a hybrid stable electrochemical system combining different electrochemical removal mechanism by BDD electrode as anode and cathode such as electro-oxidation, - reduction [1], -flotation, - coagulation and -disinfection simultaneously.

In this study, the cracking of a brittle diamond coating on a titanium substrate under tensile straining was investigated by micro-Raman spectroscopy and analytical modelling. The in-situ micro-Raman investigations showed that the fracture strength of the coating is ∼1.5 GPa, and it contains an initial compressive residual stress of ∼−5.4 GPa which can be reduced by the application of uniaxial tensile strain. At higher strains, the compressive stress was transformed into the tensile regime and cracks appeared in the coating, followed by a reduction in crack spacing and finally delamination. The stress measurements across different cracked coating segments, using Raman spectroscopy, indicated tensile stresses at the middle and compression near the edges of the segment under tensile load. Coating fragmentation leads to a relaxation of the stress within the cracked coating segment. Further cracking of the smaller segments requires larger strains. Here, the classical shear lag model was extended to derive the stress distribution in the coating bonded to the substrate, considering both residual stress and cracking using a fracture criterion. The effect of substrate plasticity on the evolution of residual stress and on the cracking behaviour of the coating is also introduced. A good agreement is found between the modelling approach and the measured failure behaviour as well as the stress distributions in the fractured diamond segments.

The mechanical characterization of self-supporting nanocrystalline diamond foils (NCDFs) using the “ball on three balls test” is introduced. This mechanical testing method is validated for the measurement of fracture strengths of NCDFs of a thickness down to 50 μm. NCDFs manufactured by a hot-filament chemical vapor deposition (HFCVD) process on rolled copper sheets, oxidized and polished silicon wafers as templates, were characterized in regards to their surface morphology by scanning electron microscopy, 3-D surface imaging and atomic force microscopy. The effects of the different template materials on the mechanical properties of the NCDFs are presented by means of a statistical Weibull approach. Thus a mechanical characterization method is provided to measure the impact of different manufacturing parameters on the fracture strength of self-supporting NCDFs. This is a crucial milestone on the way to applying NCDFs on substrate materials which cannot sustain the HFCVD environment, thus exploiting the excellent properties of diamond for protection against friction and wear. In comparison with state-of-the-art ceramic foils it could be shown that NCDFs can be manufactured with high reliability, and offer fracture strengths far greater than those of conventional technical ceramics.

Standard heat-treatable C35 (1.0501) steel specimens were pre-coated with diffusion chromium carbide interlayer and in second step a crystalline diamond film was applied by Hot-Filament Chemical Vapour Deposition. This study investigates the tribological properties of specimens that were treated mechanically in a different way before the coating in order to achieve a different roughness. The tests were performed in a water lubricated ring-on-disc configuration while the coefficient of friction was measured. Wear analysis was done by light microscope. The wear development was obtained by several stops during testing. The friction and wear developments are compared and discussed for different surface roughness. Pre-treatment of the steel surface has a great influence on the tribological properties of the CVD diamond coating, especially the evenness of the surface determines the real contact area and therefore the wear behavior.

The manufacturing and application of self-supporting nanocrystalline diamond foils is introduced. The high temperature manufacturing of nanocrystalline diamond foils by hot-filament chemical vapour deposition (HFCVD) is separated from the low temperature application, allowing the coating of temperature sensitive materials, which cannot be coated by HFCVD conventionally. By coating appropriate template materials and stripping-off after the CVD-process, self-supporting, flexible nanocrystalline diamond foils with high hardness (> 70 GPa) and very low thermal conductivity (< 1 W/mK) with thicknesses of up to 100 µm can be produced. Lasercutting is an appropriate method for machining any desired geometry. Thus the possibility to use the extreme properties of diamond for protection against friction and wear on new substrate materials, e.g. steels, light metals and polymers, is generated.

In order to reduce wear and therewith enhance the microelectrical discharge machining (µ-EDM) results, a coated electrode was used. The paper presents the results of investigations into the influence of grain size of the boron-doped CVD diamond coating on the wear behavior in microsinking EDM. Experimental investigations show that nanocrystalline coatings exhibited smaller discharge craters compared to those for microcrystalline diamond coatings, and microcrystalline coating showed melted material around the discharge crater. The finding will be subjected to further investigations.

CVD-diamond deposition onto steel substrates has been an important aim of research projects. The combination of the unique surface properties of diamond with steel as the most common substrate material would generate a new solution for machine parts with extreme loads by friction and wear. In this work the influence of diamond deposition temperature in a Hot-Filament Chemical Vapour Deposition (HFCVD) process onto the adhesion of the diamond layer is presented.

Electrochemical zircon dioxide oxygen sensors were applied to measure oxygen in diamond hot-filament CVD (HFCVD) coating atmospheres. These low-pressure hydrogen environments are highly reductive and methane containing. Under industrial coating conditions there is the possibility that oxygen from ambient air enters the reactor by leakages. This leads to a tremendous influence on coating conditions by lowering the active carbon content in the gas phase and by decarburizing the gas activating filaments in HFCVD. In order to ensure process stability, a monitoring of an oxygen-related value is desired. This work displays the possibility to measure oxygen in HFCVD with potentiometric and amperometric ZrO 2 sensors. The dependency of the sensor signals on process parameters is investigated and the possibility of monitoring an oxygen-related value during a coating process is shown. The sensor signals allow a comparison of plants and processes regarding the seal tightness condition. The employed zircon dioxide sensors offer a cost effective and feasible method to monitor air leakage and ensure process reproducibility.

We designed a new hot-filament plant which features some new operating states for chemical vapor infiltration with diamond. Complete infiltration of porous substrates with diamond by using standard hot filament plants is not possible. Chemical vapor infiltration with diamond is limited by the overgrowing diamond layer at the surface primarily caused by high recombination rates of atomic hydrogen on surfaces. As a consequence, the pore mouth is closed before the pore is completely infiltrated (“bottleneck” effect). Porous substrates were infiltrated by using a forced flow through the substrate. In order to achieve good infiltration results, it was necessary to use very low methane concentrations.

In hot-filament CVD we synthesized single diamond crystals up to 100 μm in diameter [1]. In order to enhance growth rate and impede growth defects, it is intended to employ a new gas feeding system. This allows CH4 to be separately applied from H2 to the reactor locally at the substrate position. The effect of this concept on the gas phase was analyzed by Infrared Tuneable Diode Laser Absorption Spectroscopy (IR-TDLAS). The changes in species concentrations of CH4, CH3 and C2H2 with the substrate distance from filaments as well as first growth results are shown.

Surface roughness of self-mated CVD diamond coatings have a decisive effect on coefficient of friction (COF) and wear especially under dry ambient conditions. Therefore diamond films with four different grain size domains were deposited onto silicon carbide front faces and tested in unlubricated planar sliding contacts. In accordance to the different growth morphologies, the roughness of the coarsest diamond films is about four times higher in average than that of the nanocrystalline films. The diamond film quality, expressed in terms of sp 3 -hybridised diamond fraction, decreases from nearly 100% to about 73% with falling grain size due to an increase in grain boundaries. The topography of the respective diamond coatings differs also considerable. While the coarse-grained films exhibit a pronounced wedge shape and a strong two-waviness, the fine-grained diamond films display a good flatness with a maximum profile height of only 280 nm. All results obtained from the dry sliding tests are visualised in a tribo map. The best tribological behaviour in terms of low COF and little wear is achieved by the fine-grained diamond coatings. The worst results reveal the nanocrystalline films with Cauliflower structure, mainly due to the highest number of local film delaminations in this test series. For high-end sealing applications, smooth fine-grained microcrystalline CVD diamond coatings therefore seem to be the most promising approach.

Adherent and homogeneous diamond films were deposited on 41Cr4 steel substrates employing c hemical v apor d eposited (CVD) TiBN interlayers. The suitability of CVD-TiBN interlayers for diamond deposition was investigated. The CVD intermediate layers showed excellent barrier properties against the diffusion of iron from the bulk substrate to the surface and against diffusion of carbon from gas phase during diamond deposition. Various growth conditions for interlayers affect their thickness and composition. For these samples different shares in the phases TiB 2 and TiN were analyzed by XRD. The diamond coating onto the TiBN interlayer showed very good adhesion. The measured Raman spectra proved high compressive stresses in the diamond film with a high diamond quality. Sandblasting tests indicated an enormous improvement of the erosion resistance after diamond deposition on 41Cr4 substrates with a 5 μm intermediate layer of TiBN.

and fibre textured diamond films are grown on SSiC sliding rings by hot filament CVD and are tribologically tested in dry planar contact under ambient air. The wear of the self-mated textured diamond coating takes place initially at protruding grains of the as-deposited micro rough diamond surface. After 10 km of dry sliding against textured diamond the respective counterparts with and textures exhibit smoothly polished diamond faces without visible surface failures. After dry sliding against textured diamond as static counterpart {100} diamond faces of isolated grains show Hertzian cone cracks and propagation of cracks preferred along {111} easy cleavage planes whereas {111} diamond faces reveal no crack propagation in substrate direction. The results are visualised in a tribo map in which the linear wear of the dynamic diamond face is plotted against the mean coefficient of friction. The best tribological behaviour in terms of low friction and little diamond wear is achieved for sliding couples with fibre texture on the rotating sliding ring and fibre texture on the static ring as mating diamond faces.

In hot-filament CVD the gas-phase composition is a vital parameter for diamond coating results. Concentrations of carbon-containing species have significant influence on growth rate, quality and morphology of deposited diamond. To learn more about the correlations between process parameters and gas species concentrations we applied the highly sensitive infrared tunable diode laser absorption spectroscopy (IR-TDLAS) technique. With a sophisticated compact IR-TDLAS unit, relative and absolute concentrations of CH4, C2H2 and CO were simultaneously measured. Also, the absolute concentration of the methyl radical was determined in dependence on process parameters. Concentrations of CO2, C2H6 and HCN were investigated but found to be lower than the detection limit. The influence of the typical diamond CVD-process parameters on various species concentrations is discussed. The applicability of IR-TDLAS for hot-filament process monitoring is evaluated. In context with diamond growth results, information for CVD process refinement was deducted from the IR-TDLAS measurements.

Since diamond coating via hot filament chemical vapour deposition (HFCVD) processes is possible, the coating of steel substrates is in the focus of research programs. As the direct deposition onto steel is not possible yet, the role of interlayers is of extraordinary importance. In this work, we deposited diamond onto steel samples with chromium carbide interlayers at temperatures above 800 °C without film delamination after deposition. Further advantages of this process are an improved chemical activation of the surface at high temperatures, a higher growth rate and a higher quality (sp3-ratio) of the diamond film. The mismatch in thermal expansion of diamond, interlayer and steel leads to high residual compressive stresses in the diamond layer, but about 30% less than theoretically expected. We ascribe this stress reduction to the specific thermal expansion characteristics of a certain class of steels, which show a α-γ phase transformation during cooling down from 850 °C. This transformation from closer packed γ-phase (fcc-structure, austenite) to α-phase (bcc-structure, ferrite) comes along with a volume expansion of approx. 1% and enables the reduction of the high residual compressive stresses in the diamond film, analysed via Raman spectroscopy.

Diamond coated silicon carbide (SiC) bearings can be used in pumps to enable dry running or mixed lubrication conditions. Dependent to different test parameters the coefficient of friction and the wear behaviour shows big differences. In this work α-SiC bearings were coated in a hot filament chemical vapour deposition process (HF-CVD) with a diamond layer thickness of 4 μm. Diamond coated rings were tested in a tribometer under dry running conditions in a ring–ring geometry. During tribological tests under various atmospheres (oxygen, argon, nitrogen, ambient air) the coefficient of friction shows values in a range from 0.1 to 0.4. These values can be ascribed to different chemical and mechanical processes between the mating surfaces. Tribological tests of self mating diamond layers generate wear debris between the mating surfaces. This diamond wear debris can convert from sp 3 hybridized to sp 2 hybridized carbon. Against common expectations tribological tests at ambient air with high sliding velocities and normal loads did not show wear debris, despite of high wear rates. Under inert gas (argon or nitrogen) the sliding surface shows agglomerated areas with sp 2 hybridised carbon. The reason is the absence of oxygen, which is necessary for combustion of carbon species. The coefficient of friction remains nearly constant during the test in oxidizing atmosphere, but shows high fluctuations in inert gas atmospheres. The authors explain this tribological behaviour by a new combustion wear model for self mating diamond coated bearings.

For a more effective heat spreading we deposited thick diamond layers on tungsten copper substrates, which are used as heat sinks in the microelectronic industry. Disadvantages of high growth rate CVD techniques like microwave plasma assisted CVD (MWPACVD) or DC plasma jet CVD are the need for flat and preferable discoidal substrates, the limitation of the total substrate surface and the uniformity of the deposited layers. Thus, the uniform deposition of diamond on a large number of substrates with a rectangular or more complex geometry (like a 3D geometry) is limited. By using hot filament CVD (HFCVD) the reactor size is not limited and it is possible to increase the batch size. Even at typically lower growth rates in HFCVD the total coated surface can over-compensate this disadvantage and renders HFCVD economically more viable. We were able to scale up the number of substrates per HFCVD batch up to 240 pieces which is equal to a coating surface of 480 cm 2 . The substrate temperature was kept between 820 and 870 °C to avoid copper diffusion to the surface and evaporation of copper. An average diamond growth rate of 0.23 μm/h allows the deposition of diamond layers in less than half of the time necessary by using, e.g. microwave plasma assisted CVD at typical process conditions for the same surface (1 μm/h growth rate; substrate temperature of about 850 °C; 45.5 cm 2 coating surface per batch). In spite of the significantly increased coating surface it was possible to deposit uniform diamond layers with a high diamond quality. A further challenge is the bending of the substrates during cooling down caused by the different coefficients of thermal expansion for diamond and WCu. Cooling devices require a planar geometry. It was possible to prevent the substrates from bending after cooling down by using a special pretreatment.

We designed a new hot-filament plant which features some new operating states for chemical vapor infiltration (CVI) with diamond. Most characteristic for the new hot-filament plant is the possibility of a forced flow of the activated gas species through a porous substrate. Separate feeding of hydrogen, methane and oxygen above or underneath the substrate ensures the production of pertinent carbon growth species like CH3 directly at or in the substrate or rather in the pore. We infiltrated porous substrates by using several operating states and compared the results with standard processes. For these first experiments we have set the addition of oxygen aside, which was viable for the infiltration experiments described in Part I of the paper. In order to achieve good infiltration results it was necessary to use very low methane concentrations between 0.2% and 0.3%. We were able to infiltrate at high growth rates (> 0.5 μm/h) combined with a good diamond quality (> 90%). Moreover it was possible to alleviate the “bottleneck” effect which we described in Part I of the paper. Raman spectroscopy and SEM were used to characterize the deposited or rather infiltrated diamond.

Die Abscheidung polykristalliner Diamantschichten auf Stahlwerkzeugen ist seit vielen Jahren Forschungsgegenstand auf der ganzen Welt, aber noch nirgendwo in funktionierende Diamant-Stahlbauteile umgesetzt worden. Durch Fördermittel der Bayerischen Forschungsstiftung ist es am Lehrstuhl Werkstoffkunde und Technologie der Metalle (WTM), Universität Erlangen-Nürnberg, gelungen, eine erfolgreiche Beschichtungsroute für die haftfeste Diamantbeschichtung von Stahlwerkstoffen zu entwickeln. Der Übertrag dieser Ergebnisse in die Produktion bayerischer Unternehmen erfolgt nun im Rahmen eines Neue Werkstoffe Bayern Projekts „DiAlum – CVD Diamant gegen Aluminiumverschleiß“ unter Förderung des Bayerischen Staatsministerium für Wirtschaft. In diesem Projekt werden weltweit erstmalig diamantbeschichtete Stahlwerkzeuge in der Produktion von den beteiligten Firmen getestet.

The synthesis of diamond volume crystals is of particular interest due to the material's outstanding physical and mechanical properties. Various techniques are pursued by numerous research groups. In hot-filament CVD (HF-CVD) we found a new process parameter window where the growth of single diamond volume crystals can be stabilized. These parameters are far beyond growth conditions for HF-CVD diamond coating processes. Extremely low methane content in the feed gas along with high substrate temperatures allows single diamond nuclei of a certain minimum size to grow stable. Crystals up to 100 μm in diameter were successfully synthesized on ultrasonic pretreated substrates. They were characterized by SEM and Raman spectroscopy. A model for the observed exclusive growth of sufficiently large nuclei is presented. Based on well accepted diamond growth models, an advanced growth theory for the different morphologies and diamond qualities at the {100} and {111} faces of the crystals is postulated. The results give bases on which growing processes can be optimized and upscaled in order to evaluate the applicability of the method for single-crystal diamond growth.

Purpose: The histological differences between the defect and contact areas of the implant surface to bone were tested in 35 New Zealand White rabbits in a standardized model. Microwave plasma chemical vapor-coated implant probes were tested in control and uncoated materials. Material and methods: In each femur of 35 rabbits, cylindrical implant rods with a planed side were inserted. Three groups, divided in coated and uncoated material at half, were observed 42, 84 and 168 days. The probes were examined histologically for bone–implant contact in the curved and plane (defect area) sides. Results: Generally the bone–implant contact seems to be nearly constant in time in the curved area of coated and uncoated probes. Here the implant was inserted in the press-fit mode. Diamond-coated probes showed similar bone–implant contact (51.9% (42 days), 62.5% (84 days), 56.1% (168 days)) compared to uncoated material (56.2%, 65.4%, 62.9%). The defect area (plane side) had no bone–implant contact at the time of insertion and showed increasing values on longer observation times with only significant differences in the 42-day group between coated (17.85%, 35.2%, 47.7%) and uncoated materials (35.5%, 40.55%, 51.81%). Conclusion: The evaluation of the curved side of the implant probe showed no great variation of bone–implant contact within the described observation times. This model simulates the usual implant insertion situation. The diamond-coated material becomes osseointegrated at a later time point. The bone–implant contact was only statistically relevant in one group in comparison to uncoated material.

Diamond/metal or diamond/ceramics penetration structures have a high potential as, e.g. heat sinks in the microelectronic industry and for tribological applications. To learn more about the basic principles in fabricating these new composites, we infiltrated porous structures of silicon carbide with diamond by chemical vapor infiltration (CVI). As a result we get a 3D penetration structures of diamond and substrate. This requires substrates with an open pored structure. An acceptable growth rate, a high amount of sp3-bondings in the coating and the complete infiltration of the substrate are important requirements on the CVI-process. These requirements should be fulfilled with an effective variation of the process parameters gas pressure, gas flow, gas composition of the feed gas and the substrate temperature. The diffusion rate of the important gas species for diamond growth (H, CH3) should be high compared to their durability. With a forced convection the transport rate of the gas species should be improved. For this, we designed a new hot filament apparatus for CVI, which allows some new operating states. Furthermore, we have investigated the fabrication of diamond penetration structures by CVI using a standard microwave plasma deposition reactor (ASTeX AX 6350) and a standard industrial hot filament apparatus (CC800D). Raman spectroscopy and SEM were used to characterize the diamond films.

Well adherent CVD-diamond coatings were deposited onto 41Cr4 steel substrates using chromium carbide diffusion interlayers. The influence of coating parameters on microstructure and composition of chromium carbide layer and substrate was investigated. In situ heat treatment allows for a variation of physical and mechanical properties of the substrate. We assume that the adhesion of CVD-diamond coatings depends inter alia on the carbon concentration on top of chromium carbide layer. This possible effect is discussed as well.

The efficiency of boron doped diamond (BDD) in the electrochemical treatment of synthetically contaminated water with veratric acid (VA), one kind of polyphenolic type compounds, is investigated in this work. A BDD electrode was practically fabricated using hot filament chemical vapor deposition (HFCVD). Later on, the BDD electrode was implemented as an anode in a batch electrolytic reactor. The effect of operating factors such as the initial concentration of VA, NaCl addition, and supporting electrolyte type (H2SO4, H3PO4 and Na2SO4) was studied. The chemical oxygen demand (COD) measurements were conducted to study the VA electrolysis kinetics. The experimental data suggested that sodium sulfate was the best supporting electrolyte as the COD removal reached a percentage of 100% using 1 mmol/dm3 as VA concentration. The kinetics of the COD decay of the VA electrolysis were found to obey the pseudo-first order model. Remarkably, the electrolysis process is significantly speeded up once chloride is added to the reaction. The complete COD removal was achieved in 60 minutes of treatment.