Titanium Cathode Research Articles

Electrochemical degradation of Azo-dye Acid Violet 7 using BDD anode: effect of flow reactor configuration on cell hydrodynamics and dye removal efficiency

The electrochemical oxidation of synthetic textile effluent containing Azo-dye Acid Violet 7 (200 mg L−1) was investigated using planar disk electrodes placed in a one inlet–outlet (I–O) cylindrical reaction chamber. Two different I–O configurations were studied, one parallel and the other perpendicular to the electrodes. Both reactors were equipped with boron-doped diamond (BDD) anodes and titanium cathodes. The effect of cell design on the hydrodynamic characteristics and efficiency of the reactors in terms of colour and chemical oxygen demand (COD) removal was studied. Mass transfer coefficient (Km) values of 1.86 × 10−5 m s−1 and 2.56 × 10−5 m s−1 were obtained for the parallel and perpendicular I–O flow reactors, respectively, using the limiting current technique. The degradation results indicated that the colour elimination was quite efficient regardless of the type of reactor used and that complete colour removal could be reached in less than 80 min at applied current density of 30 mA cm−2 and above. However, higher COD removal efficiency was always achieved in the parallel I–O flow cell compared to perpendicular I–O flow reactor at all of the current densities studied, which can be attributed to the possibility of some stagnation in the lateral regions of the electrodes. These favour a longer contact time between the pollutants and the anode, also favouring its removal. Besides, similar electric energy consumption per g COD removal was observed during the treatment with either reactors; thus demonstrating the suitability of the parallel I–O flow cell for the efficient and economic treatment of textile effluent.

Phosphorus removal from domestic wastewater in electrocoagulation reactor using aluminium and iron plate hybrid anodes

The aim of this study was to investigate the effects of initial pH (pHi = 4.0–7.0), current density (j = 10–40 A/m2), initial phosphorus (P) concentration (Ci of 5.01–52.13 mg/L) and electrocoagulation (EC) time (tEC = 10–100 min) on phosphorus removal from domestic wastewater by a batch EC reactor using hybrid aluminium (Al)-iron (Fe) anodes and titanium cathode. Phosphorus removal from domestic wastewater containing 52.13 mg/L PO4-P was obtained to be 99.99% at optimum conditions (pHi = 4, j = 20 A/m2 and EC time = 80 min). The energy and electrode consumptions at optimum conditions were calculated as 3.422 kWh/m3 and 0.328 kg/m3, respectively. The amount of removed P per electrochemically dissolved total metal electrode (qe) was calculated as 55.69 mg P/g, while the dissolved metal to removed phosphorus ratio (Me/P, mol/mol) was 4.40 (Fe/P = 2.63 and Al/P = 1.77) at optimum conditions. It can be concluded that phosphorus removal by hybrid Al-Fe anodes is as effective as using only Fe or Al anodes as per the results present in literature. In addition, the effluent pH after EC treatment process at optimum conditions was 8.8, hence requiring no pH adjustment before discharge.

Controllable synthesis of hydroxyapatite-supported palladium nanoparticles with enhanced catalytic activity

A multi-stage electrochemical method was developed to synthesize palladium (Pd) nanoparticles supported on hydroxyapatite (HA) coatings. In the first stage, a dense coating of HA nanocrystals was synthesized from an aqueous electrolyte solution onto a titanium cathode surface through a galvanostatic process. The HA-coated titanium electrode was then used as the cathode for the electrochemical reduction of Pd2+ from aqueous solution. A synthesis approach using two sequential electrochemical reduction reactions was found to be more effective in producing uniform coatings of Pd nanoparticles than a single stage reduction. In the first step, a higher voltage was applied to the cathode for a short time to promote the nucleation of Pd nanoparticles. A lower voltage was then applied for a longer time in the second stage to promote the growth of the Pd nanoparticles. The size and size distribution of the Pd nanoparticles were controlled by adjusting the duration of the first and second stages of electrochemical reduction. The resulting HA supported Pd nanoparticles demonstrated significantly higher catalytic activity than commercial Pd nanoparticles in the degradation of methyl orange by NaBH4. The high surface area and the complex oxidation states of the HA-supported Pd nanoparticles are believed to account for the enhanced catalytic activity.

Regeneration of Sn4+ from Sn2+ solution during electrowinning process using anion exchange membrane

ABSTRACTElectrowinning process to regenerate Sn4+ from Sn2+ in HCl solution using an electrowinning cell with anion exchange membrane was proposed to suggest a novel recycling process to recover Sn. During the tests, the effects of initial Sn2+ concentration on the regeneration of Sn4+ were investigated under the following condition; 7,000 mg/L, 10,000 mg/L, and 13,000 mg/L of Sn2+, 1 M HCl, 250 A/m2 of current density, graphite anode, titanium cathode, room temperature, and 2 h. Electro-deposited Sn on the cathode showed dendritic structure regardless of the Sn2+ concentration and no change of Sn concentration was observed in the anolyte. Leaching tests were performed using the anolyte, obtained from the electrowinning tests, to examine the amount of regenerated Sn4+ concentration during electrowinning process. Based on the results of Sn leaching tests, it was found that 84.44%, 81.03%, and 79.43% of Sn4+ were regenerated from 7,000 mg/L, 10,000 mg/L, 13,000 mg/L initial concentration of Sn2+ solution, respectively. Consequently, it was found that the regeneration of Sn4+ can occur during the electrowinning process at the same time with Sn recovery and Sn4+ can be reused as an oxidant to leach Sn successfully.

Optimization of solar-driven photo-electro-Fenton process for the treatment of textile industrial wastewater

This work deals with the evaluation of a solar-driven Photo Electro-Fenton (SPEF) process as an alternative for the effective degradation of an industrial textile wastewater sample. Experiments were carried out in a laboratory scale batch cell reactor, using boron-doped diamond (anode) and titanium (cathode) electrodes in monopolar configuration. The effect of the main operational parameters (pH, current density (j), conductivity (ơ), Fe2+ concentration and anode area to effluent volume ((A/V) ratio) on the COD removal and energy consumption were studied using a Box-Behnken experimental design. The SPEF process was optimized using the Response Surface Methodology. At optimum operational conditions (pH = 4, j = 40 mA/cm2, ơ = 5768 μS/cm and Fe2+ = 0.3 mM), the solar-driven process achieved total discoloration, COD reduction of 83% and TOC mineralization of 70%, after 15 min of electrolysis. The process yielded a highly oxidized (AOS = 2.24) and biocompatible (BOD5/COD > 0.4) effluent. Additionally, the most suitable effective surface area of the electrodes (A/V ratio) was determined (3.75 m−1). The analysis of operational costs was also performed. The SPEF process demonstrated to be an efficient alternative for the treatment of industrial wastewater effluent, allowing to achieve Colombian permissible discharge limits.

Competition between local lattice strains and distribution of metallic species in Ti1−xAlxN coatings with fluctuating [Ti]/[Al] ratio

The effect of a locally fluctuating [Ti]/[Al] ratio in the Ti1−xAlxN coatings on the formation of the lattice strains at the (Ti,Al)N/(Al,Ti)N interfaces and the influence of these interfaces on the stabilization of metastable (Al,Ti)N with face centered cubic structure were investigated using glancing angle X-ray diffraction, transmission electron microscopy and X-ray spectroscopy. A series of Ti1−xAlxN coatings with different [Ti]/[Al] ratios was deposited using cathodic arc evaporation from a titanium and an aluminum cathode. The overall chemical composition was controlled by the position of the respective sample in the deposition chamber and ranged from x = [Al]/([Ti] + [Al]) = 0.06 to 0.64. The local fluctuations of the [Ti]/[Al] ratio were produced by interrupting the deposition from the titanium cathode. It was shown that such local fluctuations of the [Ti]/[Al] ratio generate large contrary residual stresses at the respective side of the (Ti,Al)N/(Al,Ti)N interface. These stresses were almost completely relieved after annealing at 750 °C. The stress relaxation after annealing was accompanied by an equalization of the [Ti]/[Al] ratio and by a decay of the composition fluctuations in the Ti1−xAlxN coatings. The stress relaxation and the reduction of the local composition gradients were concluded from measured residual stresses, stress-free lattice parameters and local concentration profiles.

Electrocatalytic degradation of rice straw lignin in alkaline solution through oxidation on a Ti/SnO2–Sb2O3/α-PbO2/β-PbO2 anode and reduction on an iron or tin doped titanium cathode

A novel procedure for selective production of biomass-based compounds by electrochemical conversion has been developed in this work.

The Formation of Composite Ti-Al-N Coatings Using Filtered Vacuum Arc Deposition with Separate Cathodes

Ti-Al-N coatings were deposited on high-speed steel substrates by filtered vacuum arc deposition (FVAD) during evaporation of aluminum and titanium cathodes. Distribution of elements, phase composition, and mechanical properties of Ti-Al-N coatings were investigated using Auger electron spectroscopy (AES), X-ray diffraction (XRD), transmission electron microscopy (TEM) and nanoindentation, respectively. Additionally, tribological tests and scratch tests of the coatings were performed. The stoichiometry of the coating changes from Ti0.6Al0.4N to Ti0.48Al0.52N with increasing aluminum arc current from 70 A to 90 A, respectively. XRD and TEM showed only face-centered cubic Ti-Al-N phase with preferred orientation of the crystallites in (220) direction with respect to the sample normal and without precipitates of AlN or intermetallics inside the coatings. Incorporation of Al into the TiN lattice caused shifting of the (220) reflex to a higher 2θ angle with increasing Al content. Low content and size of microdroplets were obtained using coaxial plasma filters, which provides good mechanical and tribological properties of the coatings. The highest value of microhardness (36 GPa) and the best wear-resistance were achieved for the coating with higher Al content, thus for Ti0.48Al0.52N. These coatings exhibit good adhesive properties up to 30 N load in the scratch tests.

Electrochemical Induced Calcium Phosphate Precipitation: Importance of Local pH.

Phosphorus (P) is an essential nutrient for living organisms and cannot be replaced or substituted. In this paper, we present a simple yet efficient membrane free electrochemical system for P removal and recovery as calcium phosphate (CaP). This method relies on in situ formation of hydroxide ions by electro mediated water reduction at a titanium cathode surface. The in situ raised pH at the cathode provides a local environment where CaP will become highly supersaturated. Therefore, homogeneous and heterogeneous nucleation of CaP occurs near and at the cathode surface. Because of the local high pH, the P removal behavior is not sensitive to bulk solution pH and therefore, efficient P removal was observed in three studied bulk solutions with pH of 4.0 (56.1%), 8.2 (57.4%), and 10.0 (48.4%) after 24 h of reaction time. While P removal efficiencies are not generally affected by bulk solution pH, the chemical-physical properties of CaP solids collected on the cathode are still related to bulk solution pH, as confirmed by structure characterizations. High initial solution pH promotes the formation of more crystalline products with relatively high Ca/P molar ratio. The Ca/P molar ratio increases from 1.30 (pH 4.0) to 1.38 (pH 8.2) and further increases to 1.55 (pH 10.0). The formation of CaP precipitates was a typical crystallization process, with an amorphous phase formed at the initial stage which then transforms to the most stable crystal phase, hydroxyapatite, which is inferred from the increased Ca/P molar ratio from 1.38 (day 1) to the theoretical 1.76 (day 11) and by the formation of needle-like crystals. Finally, we demonstrated the efficiency of this system for real wastewater. This, together with the fact that the electrochemical method can work at low bulk pH, without dosing chemicals and a need for a separation process, highlights the potential application of the electrochemical method for P removal and recovery.

Electrodeposition of Nickel on Titanium in Aqueous Acidic Electrolytes

Nickel may be produced in acidic chloride-sulfate based electrolytes. Nickel is initially deposited on stainless steel or titanium cathodes to produce starting sheets while chlorine gas is evolved on DSA anodes. Stress in the nickel deposit may cause bending of the cathode sheet. In addition, irregular growth such as dendrite formation may occur. In extreme cases, short-circuiting of electrodes will happen. Fundamental electrochemical studies of the initial stages of the electrodeposition process may give valuable information for obtaining smooth nickel deposits. Electrochemical experiments of nickel deposition were carried out on titanium substrates using cyclic voltammetry and potential step, and examined with SEM imaging. The measurements were performed at different deposition potentials and times to get an overall picture of the nucleation and growth of nickel on titanium substrates. Further deposition studies have been performed using in situ AFM to study the whole process from single nickel nuclei to a cohesive layer, and determine the nucleation mode and characteristics. The effects of electrolyte composition and pH will be presented. The pre-treatment of the substrate is important for the nucleation and properties of the nickel deposit. The figure illustrates the different nucleation overpotential for a smooth and rough titanium substrate. Figure 1

Effects of electrode gap and electric current on chlorine generation of electrolyzed deep ocean water

Electrolyzed water is a sustainable disinfectant, which can comply with food safety regulations and is environmental friendly. A two-factor central composite design was adopted for studying the effects of electrode gap and electric current on chlorine generation efficiency of electrolyzed deep ocean water. Deep ocean water was electrolyzed in a glass electrolyzing cell equipped with platinum-plated titanium anode and cathode in a constant-current operation mode. Results showed that current density, chlorine concentration, and electrolyte temperature increased with electric current, while electric efficiency decreased with electric current and electrode gap. An electrode gap of less than 11.7 mm, and a low electric current appeared to be a more energy efficient design and operation condition for the electrolysis system.

Plasmachemical synthesis of coatings using a vacuum arc discharge

Summary In this paper we discuss the issues of applying protective coatings on the copper anodes of powerful generator tubes. As a synthesized material due to its high operational properties was chosen titanium carbide obtained by sputtering a titanium cathode in benzene vapors. Scheme of a vacuum arc device used in this work and also the technological processes for the plasmachemical synthesis of coatings on complex shape anodes are described. For a correct choice of the technological parameters it was considered a model of penetration of the plasma flux into the hollow copper anode that was verified by experiments using a setup with a variable cavity diameter. On the emission spectrum of the discharge in the process of coating deposition shown in this work were recorded spectral lines corresponding to the atoms and ions of titanium and carbon ions. We investigated the distribution of elements across the thickness of the formed coating immediately after deposition and after annealing in vacuum, also the X-ray diffraction pattern and a microsection for the obtained titanium carbide coating are presented. As a result of the work it can be noted that the described sequence of technological processes, subject to the control of plasma flux parameters, allows obtaining a high quality protective coating on parts of complex shape.

H2O2 Assisted Photoelectrocatalytic Oxidation of Ag-Cyanide Complexes at Metal-free g-C3N4 Photoanode with Simultaneous Ag Recovery

A g-C3N4 thin film was synthesized by a liquid-based reaction onto ITO substrate via the calcination treatment. The resultant electrode was used as photoanode for photoelectrocatalytic (PEC) oxidation of Ag cyanide complexes with simultaneous Ag recovery, which was enhanced with the addition of H2O2. Surface variation of the g-C3N4 photoanode and titanium cathode was analyzed using SEM, XRD, and XPS techniques. It was observed that, with the cyanide oxidation, Ag oxides and metal Ag were deposited onto the g-C3N4 photoanode and titanium cathode, respectively. The photoelectrochemical response of the g-C3N4 photoanode was obviously increased after the AgO deposition. ESR and trapping experiments confirmed the existence and roles of •O2– and •OH in the PEC oxidation process. The photogenerated electrons from g-C3N4 could be captured by •O2– and H2O2, generating •OH radicals for oxidizing the Ag cyanide complexes. Meanwhile, the deposition of AgO species onto the g-C3N4 surface increased its electrical condu...

Modelling of process formation of the nanocomposite TiN-Cu layers received by vacuum-arc evaporation of Ti and magnetron sputtering of Cu

Modeling a TiN-Cu layers deposition process on a fused silica substrate under given conditions is carried out in this work. Calculation formulas which allow to determine the films thickness and their uniformity, with a substrate holder being located at an angle of 45 degrees to the normals of mutually perpendicular planes of the evaporated titanium cathode and the magnetron sputtering copper cathode, are given. The results of this work will be used to analyze the distribution velocity of the substance condensation flow and the character of the formed composite layers depending on the geometry of the cathode-substrate system.

Performance Evaluation of a Hard Composite Solid Lubricant Coating When Dry Machining of High-carbon Steel

ABSTRACTA novel hard composite solid lubricant coating combining TiN and MoSx has been developed using pulsed DC closed-field unbalanced magnetron sputtering (CFUBMS). The tribological and mechanical properties together with their interdependencies with the coating microstructures have been assessed and reported elsewhere. This article evaluates the machining performance and correlates the underlying tribological aspects of different TiN-MoSx coating architectures (deposited at titanium (Ti) cathode currents of 1, 3.5, and 5 A) when dry turning AISI 1080 high-carbon steel. A comparative performance study clearly established the supremacy of the composite coating (deposited at 3.5 A Ti cathode current with ∼12 wt% of MoSx) with a hard TiN underlayer over monolayer TiN, MoSx, and other related coating architectures in terms of cutting force, tool wear, and workpiece surface roughness. The superlubricity behavior of the said composite coated tool resulted in a reduction of cutting force (by up to ∼45% compared to the uncoated tool) and exhibited a tool life of 8 min, which was eight times and more than two times longer than that of the uncoated and conventional hard TiN coated counterparts, respectively. The workpiece surface roughness, Ra, also decreased by 13 to 21% when machined with the TiN-MoSx coated tool in comparison to the uncoated cemented carbide.

Development of the technology of separated treatment of galvanic bath waste streams with subsequent heavy metals precipitation

Physical-chemical methods of separated decontamination of highly concentrated waste streams from galvanic (electroplating) baths containing nickel, copper, and zinc ions using modified forms of vermiculite have been suggested. At the first stage, decontamination is performed by the method of coagulation using a detergent solution (decontamination degree up to 99%). Thereafter, the produced low-concentration solutions underwent electrochemical treatment with addition of sodium chloride using ruthenium oxide coated titanium anode and cathode. The third stage of extra adsorption decontamination by vermiculite-based sorbents was introduced for nickel- and copper-containing galvanic waste streams. The highest degree of decontamination from nickel and copper was attained using the vermiculite treated by 12% hydrochloric acid and cellulose.

Fabrication and composition control of porous ZnO-TiO2 binary oxide thin films via a sparking method

ZnO-TiO2 binary oxide thin films have been deposited on quartz substrate using sparking of zinc and titanium electrodes. The composition ratio of zinc to titanium in the sparked films is inverse correlated with the emission intensity of Zn/Ti ratio during high voltage discharges across the gap of zinc anode – titanium cathode tips. Interestingly, it exhibited a direct correlation for zinc cathode – titanium anode experiment. Moreover, the Zn/Ti atomic ratio in the deposited films is correlated with Zn/Ti electrode mass loss rate ratio. Meanwhile, the mass loss rate from a metal wire corresponds to an amount of energy required to melt the metal electrodes. Furthermore, structural and optical properties of the as-deposited and the annealed films were investigated. The sparking process is a versatile nano-coating process for metal oxides as well as their binary compounds.

Electrodeposition of Nickel from Aqueous Chloride Electrolytes

Nickel may be produced by electrolysis in acidic chloride based electrolytes. Nickel is initially deposited on stainless steel or titanium starting sheets while chlorine gas is evolved on DSA anodes. Stress in the nickel deposit may cause bending of the cathode sheet. Also irregular growth such as dendrite formation may occur. In extreme cases short circuiting of electrodes will happen. Fundamental electrochemical studies of the initial stages of the electrodeposition process may give valuable information for obtaining smooth nickel deposits. Initial experiments were carried out by using cyclic voltammetry on cathodes of titanium. Ongoing studies are performed by potential step chronoamperometry to study the nucleation and growth of nickel on titanium cathode substrates. Experiments to study the effect of electrolyte composition, pH and temperature on the nickel deposition process are under way. Electrolysis to deposit macroscopic amounts of nickel will be carried out to characterize the deposits by optical methods.

Effects of electrolysis time and electric potential on chlorine generation of electrolyzed deep ocean water

Electrolyzed water is a sustainable disinfectant, which can comply with food safety regulations and is environmentally friendly. A two-factor central composite design was adopted for studying the effects of electrolysis time and electric potential on the chlorine generation efficiency of electrolyzed deep ocean water (DOW). DOW was electrolyzed in a glass electrolyzing cell equipped with platinum–plated titanium anode and cathode. The results showed that chlorine concentration reached maximal level in the batch process. Prolonged electrolysis reduced chlorine concentration in the electrolyte and was detrimental to electrolysis efficiency, especially under high electric potential conditions. Therefore, the optimal choice of electrolysis time depends on the electrolyzable chloride in DOW and cell potential adopted for electrolysis. The higher the electric potential, the faster the chlorine level reaches its maximum, but the lower the electric efficiency will be.

Incorporation of particles into the bulk of expanded polystyrene foam using physical vapour deposition technologies

Expanded polystyrene foam (EPS) is used for various applications because of its significant properties (low weight, low cost, good thermal insulation, etc.). However, some of EPS characteristics should be improved. Because of this, additional materials are incorporated into polystyrene. This article presents the results of particles incorporation into EPS bulk using physical vapour deposition (PVD). TiO2 was used as an additional material, which was incorporated into EPS foam. Non-expanded polystyrene beads were used as a substrate. These beads were treated with argon plasma in order to achieve better surface adhesion. Plasma was generated at 1 × 10–1 mbar pressure using a pulsed DC power source (frequency 20 kHz, voltage 400 V). Particles were deposited on the surface of non-expanded polystyrene beads. Titanium cathode was used as a primary material. The formation of particles was done using magnetron sputtering in reactive atmosphere. The mixture of argon and oxygen gas was used in order to form TiO2 particles (argon 82%, oxygen 18%). Vacuum pressure was 6 × 10–3 mbar during the particles formation process (power during deposition 240 W). Results showed that TiO2 particles were formed on the surface of non-expanded polystyrene beads. These particles remained stable after expansion of beads and compounded in onepiece foam of EPS. Particles were distributed uniformly in all bulk of EPS and remained in place even after flame torch induced heat resistance experiments. The modified EPS also showed photocatalytic activity during the bleaching of methylene blue (MB) aqueous solution under UV-B irradiation.