Tantalum Substrate Research Articles

Comparisons between the Direct and Indirect Effect of 1.5 keV X-rays and 0-30 eV Electrons on DNA: Base Lesions, Stand Breaks, Cross-Links, and Cluster Damages.

The interaction of low energy electrons (LEEs; 1-30 eV) with genomic material can induce multiple types of damage that may cause the loss of genetic information, mutations, genome instability, and cell death. For all damages measurable by electrophoresis, we provide the first complete set of G-values (yield of a specific product per energy deposited) induced in plasmid DNA by the direct and indirect effects of LEEs (GLEE) and 1.5 keV X-rays (GX) under identical conditions. Low energy photoelectrons are produced via X-rays incident on a tantalum (Ta) substrate covered with DNA and placed in a chamber filled with nitrogen at atmospheric pressure, under four different humidity levels, ranging from dry conditions to full hydration (Γ = 2.5 to Γ = 33, where Γ is the number of water molecules/nucleotide). Damage yields are measured as a function of X-ray fluence and humidity. GLEE values are between 2 and 27 times larger than those for X-rays. At Γ = 2.5 and 33, GLEE values for double strand breaks are 27 and 16 times larger than GX, respectively. The indirect effect contributes ∼50% to the total damage. These G-values allow quantification of potentially lethal lesions composed of strand breaks and/or base damages in the presence of varying amounts of water, i.e., closer to cellular conditions.

Thermovoltaic response in two-layered thin-film zinc oxide structures

A method of measuring the thermovoltaic effect in heterogeneous media with gradient doping impurity distributions producing gradient carrier distributions has been proposed. Iron doped zinc oxide specimens have been produced using ion beam sputtering on thin foil tantalum substrates for thermovoltaic effect measurements, glass-ceramic substrates for Hall measurements and silicon substrates for structural study. The doping impurity concentration хFe in the specimens has been varied from 0.34 to 4.18 at.%. X-ray phase analysis has shown that all the specimens have a hexagonal zinc oxide crystal structure. The films have preferential [002] orientation. The carrier concentration in the experimental specimen layers according Hall data obtained on an ECOPIA 5500 measurement system in a 0.5 T DC magnetic field has varied in the 1016–1020 cm-3 range. The specimens have an n-type conductivity. Thermovoltaic measurements have been carried out for two-layered iron doped zinc oxide specimens with different carrier and iron doping impurity concentrations using the method proposed. The maximum thermovoltaic response (U ~ 80 μV) has been observed in the two-layered thin-film specimen with the carrier concentration difference between the layers (Δn ≈ 2∙103 cm-3). The observed saturation of the thermovoltaic response has been attributed to the establishment of dynamic equilibrium between carrier diffusion from the high carrier concentration layer to the low carrier concentration layer and carrier drift due to internal electric field.

Fretting wear mechanism of bones against a plasma-sprayed hydroxyapatite/copper coating on a tantalum substrate

A hydroxyapatite (HAp)/copper (Cu) coating was deposited on a Ta substrate by plasma spraying to mitigate the fretting wear of bones. It was found that the HAp/Cu coating significantly reduced the fretting slip of Ta at the Ta-bone interface. The friction coefficient of the HAp/Cu coating-bone frictional pair (1.14) was much higher than that of the Ta-bone frictional pair (0.71). The HAp/Cu coating significantly mitigated the fretting wear of bones by forming a protective layer on the fretting interface and reduced the wear rate from 0.031 mm3/N·mm to 0.0029 mm3/N·mm.

Electrochemically structured tantalum surfaces via anodization for core-shell nanostructures: Optimization and characterization of Zn-ZnO nanoparticle deposition using magnetron sputtering

This study explores the electrochemical anodization of tantalum surfaces to create nanostructured substrates for the deposition of Zn-ZnO nanoparticles (NPs) through magnetron sputtering. The anodization process, conducted at different potentials (25 V and 50 V), resulted in tantalum surfaces with distinct dimple structures. The formation of these nano-level dimples is attributed to the dynamic equilibrium between the continuous formation and dissolution of the anodic TaOx layer. The dimple diameter is observed to increase with applied potential, correlating with the dissolution rate of the anodic oxide. The NP deposition parameters were studied in two steps. First, the effect of the deposition conditions on the nanoparticle size and distribution was evaluated and optimized on silicon substrates. Second, the conditions that resulted in the optimum size and distribution of the nanoparticles were utilized in tantalum substrates and evaluated to which extent these conditions were reproduced onto the anodized Ta substrate. Comparisons of Zn-ZnO nanoparticle depositions on silicon and tantalum substrates reveal similar island growth trends, with differences in nanoparticle size and distribution attributed to substrate properties. Further investigation involves anodized tantalum substrates with varying dimple sizes, and deposition conditions are adjusted with bias voltage, pressure, and deposition time to control nanoparticle characteristics. Characterization of the Zn-ZnO nanoparticles deposited on anodized tantalum surfaces is performed using scanning electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The resulting core-shell structures are confirmed through structural analysis, revealing a core of hexagonal close-packed Zn and a shell of ZnO. The study demonstrates the influence of substrate properties and deposition conditions on the morphology and composition of Zn-ZnO nanoparticles, providing insights for applications in nanoelectronics and catalysis.

Ultra-high temperature oxidation resistance of a MoSi2 composite coating with TaB2 diffusion barrier on tantalum alloy

High-temperature elemental inter-diffusion is an important cause of failure for high-temperature antioxidant coatings on tantalum substrate, yet little research has been reported on improving this phenomenon. A new MoSi2 composite coating with TaB2 diffusion barrier was prepared on a tantalum substrate surface by three steps of embedding/slurry sintering/embedding to solve the failure of silicide coating on tantalum substrate due to elemental diffusion under a high-temperature oxidation environment. The composite silicide coating showed excellent oxidation resistance at 1700 ℃, and the protection time was more than 14 h before failure. This may be due to the prevention of diffusion of Si atoms at the initial stage by the TaB2 with many B atoms in a solid solution. The Mo5SiB2 layer with a low diffusion coefficient will be formed with the slow release of B atoms. The diffusion of Si atoms is further hindered by the formation of a new diffusion barrier between the TaB2 phase and the main layer, and thus slowing down the depletion of Si elements in the main coating. In addition, the coating successfully passed 1021 thermal cycles from room temperature to 1700 ℃, which may be because of the alleviation of thermal mismatch between the ceramic coating body and the tantalum substrate by a diffusion layer thus reducing the cracking trend of coating.

Effect of Argon Glow Plasma Pretreatment of Pure Ta on Hf Coating Preparation

In order to enhance the bonding strength between coatings and substrates, argon glow plasma pretreatment with various times was conducted on tantalum substrates, followed by hafnium coating deposition. The coating, consisting of deposition and a diffusion layer with nanocrystalline grains of dimensions ranging from 10 to 20 nm, obtained on the substrate pretreated for 1 h, manifested the optimal structure, with a maximum thickness of approximately 14 μm and the best adhesion performance of approximately 9.5 N. The study found that the pretreatment led to grain refinement at a depth of approximately 150 nm and an increase in the crystal face spacing of substrate and high-energy defects. In addition, the crystal defects and lightly increased surface roughness enhanced the surface energy, while the Ta (200) and Ta (211) crystal faces, which had a lower combination energy and a more stable state with Hf atoms than the Ta (110) crystal face, were considerably increased on pretreated substrates with a decrease in the Ta (110) crystal face. Consequently, coating elements exhibited enhanced diffusion within the substrate, leading to the better formation of a gradient structure, which effectively improved the adhesion of coatings. Further, this study offers an efficacious approach to enhance coating adhesion and provides a deeper understanding of plasma pretreatment.

Ferroelectric Polarization in BaTiO3 Nanocrystals Controls Photoelectrochemical Water Oxidation and Photocatalytic Hydrogen Evolution.

Ferroelectric (FE) semiconductors such as BaTiO3 support a remnant polarization after the application of an electric field that can promote the separation of photogenerated charge carriers. Here, we demonstrate FE-enhanced photocatalytic hydrogen evolution and photoelectrochemical water oxidation with barium titanate nanocrystals for the first time. Nanocrystals of the ferroelectric tetragonal structure type were obtained by a hydrothermal synthesis from TiO2 and barium hydroxide in 63% yield. BaTiO3 nanocrystal films on tantalum substrates exhibit water oxidation photocurrents of 0.141 mA cm-2 at 1.23 V RHE under UV light (60 mW cm-2) illumination. Electric polarization at 52.8 kV cm-1 normal to the film plane increases the photocurrent by a factor of 2 or decreases it by a factor of 3.5, depending on the field polarity. It also shifts the onset potential by -0.15 or +0.09 V and it modifies the surface photovoltage signal. Lastly, exposure to an electric field increases the H2 evolution rate of Pt/BaTiO3 by a factor of ∼1.5, and it raises the selectivity of photodeposition of silver onto the (001) facets of the nanocrystal. All FE enhancements can be removed by heating samples above the Curie temperature of BaTiO3. These findings can be explained by FE dipole-induced changes to the potential drop across the space charge layer of the material. The ability to use the ferroelectric effect to enhance hydrogen evolution and water oxidation is of potential interest for the development of improved solar energy for fuel conversion systems.

In vitro tribological behavior and corrosion resistance of SiO2/TiO2/ZrO2 coatings formed on the tantalum substrate using plasma electrolytic oxidation for orthopedic implant applications

Tantalum (Ta) is widely used in orthopedic and dental implants due to its remarkable stability, biocompatibility, and mechanical properties. However, in physiological environments, even stable and noble metals can form harmful complexes. This study aimed to enhance the surface mechanical, topographical features, and biocompatibility of Ta by applying a coating of ZrO2, SiO2, and TiO2 nanoparticles using the plasma electrolytic oxidation (PEO) technique. A composite layer was formed on the Ta substrate through PEO at a constant voltage of 500 V with duty cycles of 20% and 40% for 10 min. Evaluation of the coated samples revealed significant improvements in various properties. The nanohardness of the Ta surface at a 40% duty cycle was found to be 6.7 times higher than that of the uncoated Ta sample. The stiffness of the coated Ta at a 40% duty cycle was 2.4 times higher than the uncoated Ta. However, the surface roughness of the 40% duty cycle-coated Ta was higher compared to other samples. The coated Ta at a 40% duty cycle exhibited a higher surface roughness and wettability, which can potentially enhance cell adhesion and proliferation. The surface morphology properties were analyzed using FESEM, which revealed the presence of a composite layer composed of ZrO2, SiO2, and TiO2 nanoparticles on the Ta substrate. Additionally, the contact angle test demonstrated that the coated Ta samples had decreased contact angles from 86° to 9°, indicating increased hydrophilicity compared to the uncoated Ta. Corrosion resistance was assessed through potentiodynamic polarization test and electrochemical impedance spectroscopy. The corrosion resistance of the coated Ta at 20% and 40% duty cycles increased from 0.78 × 103 Ω cm2 to 8.85 × 103 and 9.4 × 103 Ω cm2, respectively, indicating the formation of a nobler layer on the Ta surface. Biocompatibility studies using MG-63 cells showed enhanced cell adhesion and viability on the surface of the 40% duty cycle-coated Ta, attributed to its higher surface roughness and hydrophilicity. The cell viability for the coated samples (Ta-20 and Ta-40) after 3 days of culture was 95% and 98%, respectively, compared to 89% for the uncoated Ta sample. These findings demonstrate that the SiO2/TiO2/ZrO2 ceramic coatings significantly improve the mechanical properties, corrosion resistance, surface morphology, and hydrophilicity of Ta implants. Such enhancements have the potential to extend the lifetime of Ta implants in dental and orthopedic applications.

Electron bridging based on ternary AgNPs/MoS2/NaTaO3 heterojunction films enhanced photocatalytic activity

The exceptional cyclic utilization performance of fixed-state thin film photocatalysts has garnered significant interest, yet their industrial application remains constrained by their low photocatalytic efficiency. In this investigation, MoS2/NaTaO3 thin films were synthesized in situ on tantalum substrates utilizing a facile hydrothermal approach. The resulting heterojunction architecture serves to facilitate efficient separation of electron-hole pairs while also notably expanding the photoresponse range. Furthermore, the incorporation of Ag nanoparticles (AgNPs) via photochemical reduction engendered the establishment of Schottky contacts (MoS2-Ag), which considerably expedited the photoinduced charge separation process. Within the context of the ternary system, the construction of electron bridges accelerates the rate of electron transfer. Hence, the designed ternary AgNPs/MoS2/NaTaO3 heterojunction films showed enhanced photocatalytic activity and degraded more than 94.6% of methylene blue (MB) after 50 min of irradiable light. Also, the composite exhibits notable antibacterial efficacy (99.99%) against S. aureus and E. coli owing to the synergistic influence of photo-induced ROS and AgNPs. Moreover, cyclic photocatalytic degradation/sterilization experiments demonstrated the proficient stability of the film.

Orthogonal Experimental Optimization of Preparation and Microstructural Properties of a Diffusion Barrier for Tantalum-Based Silicide Coatings.

To solve the problem of silicide coatings on tantalum substrates failing due to elemental diffusion under high-temperature oxidation environments and to find diffusion barrier materials with excellent effects of impeding Si elemental spreading, TaB2 and TaC coatings were prepared on tantalum substrates by the encapsulation and infiltration methods, respectively. Through orthogonal experimental analysis of the raw material powder ratio and pack cementation temperature, the best experimental parameters for the preparation of TaB2 coatings were selected: powder ratio (NaF:B:Al2O3 = 2.5:1:96.5 (wt.%)) and pack cementation temperature (1050 °C). After diffusion treatment at 1200 °C for 2 h, the thickness change rate of the Si diffusion layer prepared using this process was 30.48%, which is lower than that of non-diffusion coating (36.39%). In addition, the physical and tissue morphological changes of TaC and TaB2 coatings after siliconizing treatment and thermal diffusion treatment were compared. The results prove that TaB2 is a more suitable candidate material for the diffusion barrier layer of silicide coatings on tantalum substrates.

The high temperature oxidation and thermal shock behavior of a dense WSi2–TaSi2 coating on Ta substrate prepared by a novel two-step process

In order to improve the oxidation resistance of the Ta substrate, a novel two-step process including molten salt electrodeposition (Na2WO4-WO3 system) and halide activated pack cementation was adopted to prepare a WSi2–TaSi2 coating on tantalum substrate. During the electrodeposition process, dense tungsten coatings were fabricated at current densities of 30 mA/cm2, 40 mA/cm2 and 50 mA/cm2. It was observed that the grain size exhibited a log-normal distribution. When the current density was 40 mA/cm2, the grain size and flattest surface of the tungsten coating reached 9.50 ± 0.23 μm and 6.792 μm, respectively. When performing the static oxidation test, the WSi2–TaSi2 coating could effectively protect the Ta substrate oxidized at 1600 °C for 30 h. This is attributed to the presence of dense SiO2 and Ta2O5, which acted as a protective layer and suppressed the further penetration of oxygen. Furthermore, due to the matching thermal expansion coefficient between each layer and the sealing ability of semi-molten SiO2, the four-layer SiO2–W5Si3–WSi2–Ta5Si3 coating could successfully pass 721 thermal shock tests from 1600 °C to room temperature.

Flexible B, N co-doped graphene electrodes for electrochemical detection of serotonin in bodily fluids

Real-time monitoring of neurotransmitters can offer critical information for understanding neural functions and diagnosing diseases. Herein, a flexible electrochemical biosensor suitable for detecting serotonin (5-HT) in different bodily fluids was developed based on vertical graphene co-doped with boron and nitrogen (BNVG). BNVG nanosheets were vertically grown on flexible tantalum substrates via chemical vapor deposition. The electrochemically active sites were regulated by changing the B and N contents in the BNVG film. The BNVG-based biosensor exhibited a quantitative response toward 5-HT in the pH range of 1.5–9.0. The linear concentration range of 5-HT depends on the pH, with the widest measurable concentration ranging from 0.10 to 224.43 μM. The range of 5-HT detection limits (S/N = 3) was 0.009–0.266 μM. The BNVG-based biosensor detected 5-HT in gastric juice, intestinal juice, and blood samples with high sensitivity and stability. The well-designed flexible BNVG-biointerface is an effective biosensor platform for detecting the neurotransmitter 5-HT, which can aid the development of neural electrodes and medical-care products.

Application of Micro-Arc Discharges during Anodization of Tantalum for Synthesis of Photocatalytic Active Ta2O5 Coatings

Ta2O5 coatings were created using micro-arc discharges (MDs) during anodization on a tantalum substrate in a sodium phosphate electrolyte (10 g/L Na3PO4·10H2O). During the process, the size of MDs increases while the number of MDs decreases. The elements and their ionization states present in MDs were identified using optical emission spectroscopy. The hydrogen Balmer line Hβ shape analysis revealed the presence of two types of MDs, with estimated electron number densities of around 1.1 × 1021 m-3 and 7.3 × 1021 m-3. The effect of MDs duration on surface morphology, phase and chemical composition, optical absorption, and photoluminescent, properties of Ta2O5 coatings, as well as their applications in photocatalytic degradation of methyl orange, were investigated. The created coatings were crystalline and were primarily composed of Ta2O5 orthorhombic phase. Since Ta2O5 coatings feature strong absorption in the ultraviolet light region below 320 nm, their photocatalytic activity is very high and increases with the time of the MDs process. This was associated with an increase of oxygen vacancy defects in coatings formed during the MDs, which was confirmed by photoluminescent measurements. The photocatalytic activity after 8 h of irradiation was around 69%, 74%, 80%, and 88% for Ta2O5 coatings created after 3 min, 5 min, 10 min, and 15 min, respectively.

Friction and Wear Properties of Multilayer Films Designed on Tantalum Substrate

In this paper, a titanium nitride film (TiN) monolayer film was deposited on a pure Tantalum (Ta) substrate with Ti as an intermediate layer by magnetron sputtering technique, and a Ta/Ti/DLC (diamond-like carbon)/Ti/TiN/DLC multilayer film was designed. Raman spectroscopy and scanning electron microscopy were used to observe the film structure and morphology. Friction and wear properties of Ta/Ti/TiN monolayer film and Ta/Ti/DLC/Ti/TiN/DLC multilayer film were analyzed by UMT-3 tester. The results show that the surface of multilayer film is denser and better bonded than TiN monolayer film. Under dry friction conditions, the friction coefficient of TiN monolayer film is stable at about 0.45. In contrast, the friction coefficient of DLC multilayer film remains around 0.15 with very small fluctuation during the whole friction process. This is determined by the inherent characteristics of DLC film, which is composed of sp2-C graphite structure and sp3-C diamond structure. From the analysis of the wear mechanism, the Ta substrate mainly undergoes adhesive wear and abrasive wear, however, the TiN monolayer film and Ta/Ti/DLC/Ti/TiN/DLC multilayer films mainly undergo abrasive wear mechanism. The friction coefficient of TiN monolayer fluctuates more than that of dry friction conditions in the body-liquid environment, and finally stabilize at about 0.5. The friction coefficient of DLC multilayer films does not differ much from those of dry friction conditions. This is because the TiN monolayer film generates a large amount of abrasive chips to fill the scratches in the body fluid environment, accompanied by the peeling and flaking of the compacted abrasive chips, thus the friction coefficient fluctuates greatly. The DLC multilayer films also undergoes graphitization transfer. In addition, the free hanging bonds of DLC film are passivated, which reduces the degree of adhesive wear. In summary, the DLC multilayer film has better biocompatibility, wear resistance, and stronger bonding.

The effect of boron concentration on the electrical, morphological and optical properties of boron-doped nanocrystalline diamond sheets: Tuning the diamond-on-graphene vertical junction

In this paper, the effect of boron doping on the electrical, morphological and structural properties of free-standing nanocrystalline diamond sheets (thickness ~ 1 μm) was investigated. For this purpose, we used diamond films delaminated from a mirror-polished tantalum substrate following a microwave plasma-assisted chemical vapor deposition process, each grown with a different [B]/[C] ratio (up to 20,000 ppm) in the gas phase. The developed boron-doped diamond (BDD) films are a promising semiconducting material for sensing and high-power electronic devices due to band gap engineering and thermal management feasibility. The increased boron concentration in the gas phase induces a decrease in the average grain size, consequently resulting in lower surface roughness. The BDD sheets grown with [B]/[C] of 20,000 ppm reveal the metallic conductivity while the lower doped samples show p-type semiconductor character. The charge transport at room temperature is dominated by the thermally activated nearest-neighbor hopping between boron acceptors through impurity band conduction. At low temperatures (<300 K), the Arrhenius plot shows a non-linear temperature dependence of the logarithmic conductance pointing towards a crossover towards variable range hopping. The activation energy at high temperatures obtained for lowly-doped sheets is smaller than for nanocrystalline diamond bonded to silicon, while for highly-doped material it is similar. Developed sheets were utilized to fabricate two types of diamond-on-graphene heterojunctions, where boron doping is the key factor for tuning the shape of the current-voltage characteristics. The graphene heterojunction with the low boron concentration diamond sheet resembles a Schottky junction behavior, while an almost Ohmic contact response is recorded with the highly doped BDD sheet of metallic conductivity. The free-standing diamond sheets allow for integration with temperature-sensitive interfaces (i.e. 2D materials or polymers) and pave the way towards flexible electronics devices.

Conductive printable electrodes tuned by boron-doped nanodiamond foil additives for nitroexplosive detection

An efficient additive manufacturing-based composite material fabrication for electrochemical applications is reported. The composite is composed of commercially available graphene-doped polylactide acid (G-PLA) 3D printouts and surface-functionalized with nanocrystalline boron-doped diamond foil (NDF) additives. The NDFs were synthesized on a tantalum substrate and transferred to the 3D-printout surface at 200 °C. No other electrode activation treatment was necessary. Different configurations of low- and heavy-boron doping NDFs were evaluated. The electrode kinetics was analyzed using electrochemical procedures: cyclic voltammetry and electrochemical impedance spectroscopy. The quasi-reversible electrochemical process was reported in each studied case. The studies allowed confirmation of the CV peak-to-peak separation of 63 mV and remarkably high heterogeneous electron transfer rate constant reaching 6.1 × 10−2 cm s−1 for 10 k ppm [B]/[C] thin NDF fitted topside at the G-PLA electrode. Differential pulse voltammetry was used for effective 2,4,6-trinitrotoluene (TNT) detection at the studied electrodes with a 87 ppb limit of detection, and wide linearity range between peak current density and the analyte concentration (0.064 to 64 ppm of TNT). The reported electrode kinetic differences originate primarily from the boron-dopant concentration in the diamond and the various contents of the non-diamond carbon phase.Graphical abstract

Ultra-high temperature oxidation resistance of a novel (Mo, Hf, W, Ti)Si2 ceramic coating with Nb interlayer on Ta substrate

In order to solve the challenge of recyclability of tantalum substrates in high temperature oxidation environments, a novel MoSi2-WSi2-HfSi2-TiSi2 composite ceramic coating containing an Nb interlayer was prepared on the surface of tantalum substrate by a three-step method. The mix ceramic silicide coating exhibited superior performance and effective protection for 10.2 h at 1800 °C, possibly due to the formation of an outer SiO2-HfO2-HfSiO4 composite oxide film with low oxygen permeability, moderate viscosity and thermal expansion coefficient, as well as good self-healing ability. Furthermore, the coating successfully passed 537 thermal cycles from room temperature to 1800 °C. The presence of Nb interlayer significantly mitigated the thermal mismatch between the ceramic coating and the tantalum substrate, and the bidirectional diffusion of Nb element during the high temperature oxidation and thermal shock process further reduced the tendency of the coating to crack.

Micro-arc Oxidation Coating Containing Phosphorus on Tantalum Substrates Prepared by Micro-arc Oxidation

Abstract Tantalum has physical and chemical properties that are well suited for use in medical implants. However, a lack of bone induction prevents this biologically inert material from combining well with bone tissue. This study reports the successful preparation of a micro-arc oxidation (MAO) coating on tantalum in phosphate solution. The porous surface of the coating includes uniformly distributed craters. Its constituent elements are evenly dispersed. Tantalum is present in the coating as tantalum pentoxide. In vitro testing of the coating with MG63 osteoblasts showed it has good biocompatibility and can promote cellular adhesion and proliferation. MAO coating on tantalum represents a new and potentially useful method to improve the clinical applicability of tantalum.

Electrophoretic deposition of graphene oxide reinforced hydroxyapatite on the tantalum substrate for bone implant applications: In vitro corrosion and bio-tribological behavior

Tantalum (Ta) is used in dental implantology due to its high biocompatibility and potential clinical applications. Ta has low bone regeneration and low abrasion resistance , which can lead to inflammatory reactions in biological environments. In the present study, the graphene oxide/hydroxyapatite (GO/HA) composite on the Ta substrate was coated using the electrophoretic deposition technique. The deposition process was conducted at a constant voltage of 30 V at two deposition times of 5 and 10 min. Confocal Raman spectroscopy , Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) confirmed GO in the GO/HA composite coating layer. The roughness of samples increased from 35 ± 3 nm for the GO/HA-coated Ta (at 10 min) to 120 ± 4 nm for the uncoated Ta. After coating Ta with the GO/HA at deposition time of 10 min, nanoindentation curve shifted to the left and maximum depth decreased due to an 18-fold increase in the hardness of coated sample in comparison to the uncoated Ta. The GO/HA composite coating improved the bio-tribological behavior, the resistance to plastic deformation , and fracture toughness of Ta substrate. The stiffness of GO/HA-coated Ta (at 10 min) was 8-fold higher than that of the uncoated Ta. Additionally, the friction coefficient of GO/HA-coated Ta (0.3) was lower than the uncoated Ta (0.43). The GO/HA-coated Ta (at 10 min) showed significantly higher corrosion current density (18.6 ± 1.2 vs 4.97 ± 0.23 μA/cm 2 ) compared to the uncoated Ta. The results of antibacterial activity test indicated that the presence of GO in the GO/HA coating decreased the viability of Escherichia coli and Staphylococcus aureus cells on the surface of Ta. Due to higher surface roughness and wettability of the GO/HA-coated Ta compared to the uncoated Ta, the proliferation and viability of MG-63 cells on the surface of GO/HA-coated Ta significantly increased. Our findings demonstrated that the GO/HA composite coating can enhance the lifetime of Ta based dental and orthopedic implants. • The GO/ HA composite coating was successfully prepared and deposited on the Ta surface during EPD process. • The GO/ HA-coated Ta showed the high corrosion protection and antibacterial activity compare to the uncoated Ta. • The GO/ HA coating improved the bio-tribological behavior, resistance to plastic deformation, and fracture toughness of Ta. • The GO/HA caused an increase in the hydrophilicity and roughness, which enhanced the proliferation of cells on Ta surface. • The GO/HA composite coating on the Ta surface could be a promising candidate for dental and orthopedic implants.

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).