Nickel-molybdenum Alloys Research Articles

A MoNi4(312) surface preferred reconstruction enhancing hydrogen evolution

Nickel-molybdenum (Ni-Mo) alloys have garnered significant attention for superior electrocatalytic hydrogen evolution reaction (HER). Generally, catalysts undergo reconstruction during HER, leading to surface structure evolution, which is crucial for catalytic properties. However, the real electroactive sites and mechanisms underlying the structure evolution of Ni-Mo alloys through the electrochemical process remain unclear. Herein, we propose a Ni-Mo alloy with enriched MoNi4(312) plane exposure after electrochemical reconstruction due to its preferential growth during the HER. The atomic interaction within the MoNi4(312) plane facilitates the electron transfer from Ni to Mo and optimizes the electronic configuration, accelerating the release of gaseous hydrogen and smoothing the HER process. The reconstructed Ni-Mo alloy demonstrates exceptional HER performance, achieving an ultrasmall overpotential of 23 mV at 10 mA cm–2. Additionally, by scaling up the electrode by 8 times, the overpotentials required remain similar to a small electrode. This study provides insights into surface reconstruction and orientational crystal plane design of low-cost transition metal-based alloy catalysts for industrial hydrogen production.

Highly Active and Durable Nanostructured Nickel-Molybdenum Coatings as Hydrogen Electrocatalysts via Solution Precursor Plasma Spraying.

The increasing demand for green hydrogen is driving the development of efficient and durable electrocatalysts for the hydrogen evolution reaction (HER). Nickel-molybdenum (NiMo) alloys are among the best HER electrocatalysts in alkaline electrolytes, and here we report a scalable solution precursor plasma spraying (SPPS) process to produce the highly active Ni4Mo electrocatalysts directly onto metallic substrates. The NiMo coating coated onto inexpensive Ni mesh revealed an excellent HER performance with an overpotential of only 26 mV at -10 mA cm-2 with a Tafel slope of 55 mV dec-1. Excellent operational stability with minimum changes in overpotential were also observed even after extensive 60 hour high-current stability test. In addition, we investigate the influence of different substrates over the catalytic performance and operational stability. We also proposed that a slow, but consistent, dissolution of Mo is the primary degradation mechanism of NiMo-based coatings. This unique SPPS approach enables the scalable production of exceptional NiMo electrocatalysts with remarkable activity and durability, positioning them as ideal cathode materials for practical applications in alkaline water electrolysers.

An experimental investigation on copper square electrode wear in electric discharge machining of Hastelloy B2

Hastelloy B2 is a high-performance nickel-molybdenum alloy and has been used in micro reactor, pump, pipe, and corrosion-resistant equipment. Square holes are required in the above application components. Although square holes are easily produced by spending more electrodes wear in Electrical Discharge Machining (EDM). Moreover, the square hole with small electrode wear achieved is a challenging task in thermal machining. Hence, in this work, the effects of EDM process parameters on electrode taper angle, electrode radius, electrode wear length and cutting time of Hastelloy B2 are studied. Taguchi based VišekriterijumskoKompromisnoRangiranje (VIKOR) method is used to find the optimum process parameters and compared with Taguchi based Grey Relational Analysis (GRA) method for validation. The results showed that current and pulse duration greatly affects the electrode wear out surface and edges. The square electrodes with sharp edges and surfaces are fully transformed into hemispherical shapes at electrode ends due to an unstable spark with diffusion of heat. Also, the VIKOR method provides an alternative multi-criteria optimization method that enhances the process performance over the grey relational analysis due to comparability, uniqueness, assessment and prediction.

Experimental investigation of newly designed 3D-printed electrodes for hydrogen evolution reaction in alkaline media

This paper employs a novel approach for fabricating 3D-printed cathodes for hydrogen evolution reaction for alkaline water electrolysis. The approach investigated in this study involves using additive manufacturing to 3D print electrodes with non-conductive PLA followed by nickel conductive paint coating and electrodeposition of various catalysts. The nickel and nickel-copper, nickel-iron, and nickel-molybdenum alloys are electrodeposited. The nickel electrodes tend to have high overpotentials for 3D-printed electrodes. In this study, a low overpotential for the nickel coated electrode is reported. At a current density of 10 mA/cm2, for sample J with a nickel mass density of 0.178 g/cm2, an overpotential of 367 mV for hydrogen evolution reaction (HER) is measured in 1 mol potassium hydroxide (KOH) solution. The electrochemical activity of the electrodes is further enhanced through the incorporation of catalysts. Specifically, the electrode coated with nickel-molybdenum is found to have an overpotential of 337 mV at a current density of 10 mA/cm2 for HER in 1 mol KOH solution.

Surface-sulphurated nickel–molybdenum alloy film as enhanced electrocatalysts for alkaline overall water splitting

Nickel-molybdenum (NiMo) alloys are a kind of promising HER electrocatalysts to supersede precious metal based materials due to their highly active hydrogen evolution reaction (HER) kinetics in alkaline solution. However, the poor stability of NiMo, caused by the Mo dissolution mainly due to the thermodynamically instability of Mo in alkaline media, significantly limits its practical applications. Herein, a facile strategy is developed to modify the surface of the electrodeposited NiMo alloy film via a simple surface sulphuration treatment. Material characterizations show that the NiS homogeneously covers the surface of the NiMo alloy, resulting in a NiS/NiMo heterostructure. Electrochemical measurements show that the NiS/NiMo heterostructure exhibits outstanding HER activity (η-10 mA cm-2 = 77 mV) and good stability for 24 h stability test. Surprisingly, the heterostructure also displays excellent OER kinetics by delivering an ultra-low overpotential of 245 mV (10 mA cm−2). The constructed electrolyzer with NiS/NiMo acted as both cathode and anode needs only 1.547 V to power the water splitting at 10 mA cm−2. The formation of heterostructure and the enhanced electrochemically active surface area are responsible for the exceptional HER/OER electrocatalytic performance. This work offers a simple way to build sulfide/alloy heterostructures to improve the electrocatalytic activity of electrocatalysts.

Accelerating Hydrogen Desorption of Nickel Molybdenum Cathode via Copper Modulation for Pure‐Water‐Fed Hydroxide Exchange Membrane Electrolyzer

AbstractThe more sluggish kinetics of hydrogen evolution catalysts in base as compare to that in acid to some degree restricts hydrogen production performance of hydroxide exchange membrane electrolyzers, especially when using earth‐abundant catalysts. Here a ternary nickel–copper–molybdenum hydrogen evolution catalyst is reported that exhibits ≈5 times higher turnover frequency than without copper doping. The X‐ray absorption near‐edge structure and valence band spectrum demonstrate that the light doping of copper into nickel–molybdenum alloy modulates the electronic structure and downshifts the d‐band center, resulting in accelerated hydrogen desorption, as consolidated by H2 temperature programmed desorption and theoretical calculation. An electrolyzer employing this cathode catalyst and a nickel–iron anode, gives a current density of 1.7 A cm−2 at 2.0 V with a pure‐water feed through the anode, which outperforms the 2025 target proposed by the United States Department of Energy, and even is operated continuously for over 1000 h with a decay rate of as low as 0.5 mV h−1. Post‐mortem analysis discloses that hydroxide exchange ionomer migration is one of the key factors affecting long‐term durability. This work demonstrates the feasibility of a low‐cost, water‐fed hydroxide exchange membrane electrolyzer achieving industrial‐level performance and lifetime.

Efficient NH3-Tolerant Nickel-Based Hydrogen Oxidation Catalyst for Anion Exchange Membrane Fuel Cells.

Converting hydrogen chemical energy into electrical energy by fuel cells offers high efficiencies and environmental advantages, but ultrapure hydrogen (over 99.97%) is required; otherwise, the electrode catalysts, typically platinum on carbon (Pt/C), will be poisoned by impurity gases such as ammonia (NH3). Here we demonstrate remarkable NH3 resistivity over a nickel-molybdenum alloy (MoNi4) modulated by chromium (Cr) dopants. The resultant Cr-MoNi4 exhibits high activity toward alkaline hydrogen oxidation and can undergo 10,000 cycles without apparent activity decay in the presence of 2 ppm of NH3. Furthermore, a fuel cell assembled with this catalyst retains 95% of the initial peak power density even when NH3 (10 ppm)/H2 was fed, whereas the power output reduces to 61% of the initial value for the Pt/C catalyst. Experimental and theoretical studies reveal that the Cr modifier not only creates electron-rich states that restrain lone-pair electron donation but also downshifts the d-band center to suppress d-electron back-donation, synergistically weakening NH3 adsorption.

A Low‐Cost Ni–Mo Electrocatalyst for Highly Efficient Hydrogen and Oxygen Evolution Reaction

Electrocatalytic water splitting provides an effective way to store electrical energy (i.e., solar and wind energy) intermittently. It is believed that developing electrocatalysts with excellent stability, high catalytic efficiency, and abundant natural reserves is the key to the industrialization of electrochemical water splitting. Herein, nickel–molybdenum electrocatalyst formed on the surface of a low‐cost etched stainless‐steel mesh via a one‐step electrodeposition method exhibits a low hydrogen evolution overpotential of 53 mV and oxygen evolution overpotential of 261 mV at a current density of 10 mA cm−2 due to the synergistic effect of nickel and molybdenum. Moreover, the as‐prepared catalyst demonstrates superior hydrogen evolution reaction (HER) catalytic performance than commercial Pt/C at current density exceed 200 mA cm−2. The electrocatalyst also shows excellent HER and oxygen evolution reaction stabilities at high current density attribute to the tightly bond between electrocatalyst and the etched stainless‐steel mesh, as well as the surface reconstruction of catalyst during the cycle test. The facile electrodeposition method has lower requirements on production equipment, using stainless steel mesh as the basement reduces the production cost, the nickel–molybdenum alloy possesses excellent electrolytic water splitting performance and stability. These results indicate that this work can provide an idea for the industrialization of electrochemical water splitting.

Solid–Liquid–Gas Management for Low-Cost Hydrogen Gas Batteries

Aqueous nickel-hydrogen gas (Ni-H2) batteries with excellent durability (>10,000 cycles) are important candidates for grid-scale energy storage but are hampered by the high-cost Pt electrode with limited performance. Herein, we report a low-cost nickel-molybdenum (NiMo) alloy as an efficient bifunctional hydrogen evolution and oxidation reaction (HER/HOR) catalyst for Ni-H2 batteries in alkaline electrolytes. The NiMo alloy demonstrates a high HOR mass-specific kinetic current of 28.8 mA mg-1 at 50 mV as well as a low HER overpotential of 45 mV at a current density of 10 mA cm-2, which is better than most nonprecious metal catalysts. Furthermore, we apply a solid-liquid-gas management strategy to constitute a conductive, hydrophobic network of NiMo using multiwalled carbon nanotubes (NiMo-hydrophobic MWCNT) in the electrode to accelerate HER/HOR activities for much improved Ni-H2 battery performance. As a result, Ni-H2 cells based on the NiMo-hydrophobic MWCNT electrode show a high energy density of 118 Wh kg-1 and a low cost of only 67.5 $ kWh-1. With the low cost, high energy density, excellent durability, and improved energy efficiency, the Ni-H2 cells show great potential for practical grid-scale energy storage.

Electrodeposited Ni–Mo coatings as electrocatalytic materials for green hydrogen production

In this work, nanocrystalline nickel and nickel-molybdenum alloys were electrodeposited from electrolytes based on deep eutectic solvents. Eutectic mixtures of choline chloride with ethylene glycol (ethaline) and urea (reline) were used as typical representatives of deep eutectic solvents. The deposited Ni and Ni–Mo films were evaluated as potential electrocatalytic materials for green hydrogen production via electrolysis of alkaline aqueous solutions. The electrodeposited samples were characterized by XRD, SEM and EDX techniques, and the electrochemical behavior was evaluated by means of linear voltammetry and Tafel analysis. It was shown that the deposition of nickel (without molybdenum) from the electrolytes based on ethaline provides a higher electrocatalytic activity of the material with respect to the hydrogen evolution reaction than the material deposited from the reline-based electrolytes. The reline-based plating electrolytes contribute to a greater inclusion of molybdenum in the fabricated Ni–Mo alloys and therefore ensure increased electrocatalytic activity as compared with the ethaline-based electrolytes. The electrocatalytic behavior well correlates with the molybdenum content in the coatings. Ni and Ni–Mo electrodeposits produced from the deep eutectic solvent-mediated plating baths exhibit improved electrocatalytic performance and can be considered as promising catalytic materials for water electrolysis in green hydrogen energy.

Effect of Y2O3 nanoparticles on the microstructure and corrosion resistance of electrodeposited Ni-Mo-Y2O3 nanocomposite coatings

In this study, a composite coating for corrosion protection was successfully prepared on Q235 steel under neutral conditions by means of the DC electrodeposition technique. According to the results of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electrochemical tests, the effects of different additions of yttrium oxide nanoparticles in the electrolyte on the surface morphology, phase structure and corrosion resistance of nickel-molybdenum alloys were analyzed, and the deposition mechanism of yttrium oxide nanoparticles in the bath was proposed. The average grain size of the composite coating was reduced from 6.9 nm to 4 nm due to the grain refining effect of yttrium oxide nanoparticles in the coatings. The content of yttrium oxide in the coating increased with its concentration in the electrolyte, while the content of Mo atoms increased first and then decreased, reaching a peak when the addition of Y2O3 reached 2 g/L. To facilitate the study of the corrosion behavior of the coating after the introduction of the added phase, an equivalent series circuit was also proposed to fit the EIS test results, and it was hypothesized that a corrosion microcell was formed between the nanoparticles and the Ni-Mo alloy when the electrolyte solution uniformly penetrated the film. Based on the results of the electrochemical tests in 3.5 wt% NaCl solution, it was shown that it was not the case that the higher the amount of yttrium oxide added was, the better the corrosion resistance of the coating. Among all samples, Ni-Mo-Y2O3-2 g/L had the most positive corrosion potential (−0.54 V) and the best corrosion current density of 2.452 μA cm−2, which was 52.8 % lower than that of the Ni-Mo alloy coating.

A salt-baking ‘recipe’ of commercial nickel-molybdenum alloy foam for oxygen evolution catalysis in water splitting

Ni-based metal foam holds promise as an electrochemical water-splitting catalyst, due to its low cost, acceptable catalytic activity and superior stability. However, its catalytic activity must be improved before it can be used as an energy-saving catalyst. Here, a traditional Chinese recipe, salt-baking, was employed to surface engineering of nickel-molybdenum alloy (NiMo) foam. During salt-baking, a thin layer of FeOOH nano-flowers was assembled on the NiMo foam surface then the resultant NiMo-Fe catalytic material was evaluated for its ability to support oxygen evolution reaction (OER) activity. The NiMo-Fe foam catalyst generated an electric current density of 100 mA cm−2 that required an overpotential of only 280 mV, thus demonstrating that its performance far exceeded that of the benchmark catalyst RuO2 (375 mV). When employed as both the anode and cathode for use in alkaline water electrolysis, the NiMo-Fe foam generated a current density (j) output that was 3.5 times greater than that of NiMo. Thus, our proposed salt-baking method is a promising simple and environmentally friendly approach for surface engineering of metal foam for designing catalysts.

Optimization of Ni-Mo-Coated Stainless Steel as a High-Performance Cathode in Alkaline Water Electrolysis

Considering the widespread use of alkaline water electrolysis (AWE) in the chemical industry and the growing need to design and manufacture low-cost and efficient electrodes, the optimization of a Ni-Mo-coated stainless steel substrate is investigated in the present work to use this substrate as a cathode of an alkaline water electrolyzer. The crystallographic structure, surface morphology, and composition of the optimized coating are characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and surface elemental mapping. The electrocatalytic activity for the hydrogen evolution reaction (HER) is evaluated by making electrochemical measurements. In addition, the optimization of the electrodeposition bath is investigated to promote the HER activity. The results show that nickel-molybdenum (1:2) alloy exhibits a higher HER activity, and a current density of 180 mA cm−2 is achieved at −1.7 V vs. Ag/AgCl using this coating. Also, the polarization curves of the electrolysis cell demonstrate that using the optimized cathode, the cell operates at 1.9 V at a current density of 1.5 A.cm−2 and the operating temperature of 60 °C, which is suitable for use in large-scale industrial AWE units.Graphical Abstract

Insights into alloy/oxide or hydroxide interfaces in Ni-Mo-based electrocatalysts for hydrogen evolution under alkaline conditions.

Nickel-molybdenum (Ni-Mo) alloys are promising non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) in alkaline water; however, the kinetic origins of their catalytic activities still remain under debate. In this perspective, we systematically summarize the structural characteristics of Ni-Mo-based electrocatalysts recently reported and find that highly active catalysts generally have alloy-oxide or alloy-hydroxide interface structures. Based on the two-step reaction mechanism under alkaline conditions, water dissociation to form adsorbed hydrogen and combination of adsorbed hydrogen into molecular hydrogen, we discuss in detail the relationship between the two types of interface structures obtained by different synthesis methods and their HER performance in Ni-Mo based catalysts. For the alloy-oxide interfaces, the Ni4Mo/MoO x composites produced by electrodeposition or hydrothermal combined with thermal reduction exhibit activities close to that of platinum. For only the alloy or oxide, their activities are significantly lower than that of composite structures, indicating the synergistic catalytic effect of binary components. For the alloy-hydroxide interfaces, the activity of the Ni x Mo y alloy with different Ni/Mo ratios is greatly improved by constructing heterostructures with hydroxides such as Ni(OH)2 or Co(OH)2. In particular, pure alloys obtained by metallurgy must be activated to produce a layer of mixed Ni(OH)2 and MoO x on the surface to achieve high activity. Therefore, the activity of Ni-Mo catalysts probably originates from the interfaces of alloy-oxide or alloy-hydroxide, in which the oxide or hydroxide promotes water dissociation and the alloy accelerates hydrogen combination. These new understandings will provide valuable guidance for the further exploration of advanced HER electrocatalysts.

Interface Catalysis of Nickel Molybdenum (NiMo) Alloys on Two-Dimensional (2D) MXene for Enhanced Hydrogen Electrochemistry.

Development of efficient bifunctional nonprecious metallic electrocatalysts for hydrogen electrochemistry in alkaline solution is of importance to enable commercialization of a low-cost alkaline hydrogen fuel cell and water electrolyzer, but it is very challenging. Two-dimensional (2D) MXene-based electrocatalysts hold tremendous potential for the applications of hydrogen fuel cell and water electrolyzer. Here, we successfully immobilized transition-metal-based NiMo nanoparticles (NPs) on 2D Ti3C2Tx (Tx: surface terminations, such as O, OH, or F) surfaces by a wet chemical method. Our results demonstrate that the NiMo NPs are monodispersed on Ti3C2Tx with surface functionalization. These monodisperse NPs resulted in superior hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) activities in an alkaline media. The NiMo NPs/Ti3C2Tx in 1.0 M KOH yielded an HER current of -10 mA cm-2 at -0.044 V vs reversible hydrogen electrode (RHE), nearly 232 mV smaller than that of the parent NiMo NPs. The NiMo NPs/Ti3C2Tx produced an HOR current density of 1.5 mA cm-2 at 0.1 V vs RHE. Density functional theory (DFT) results further reveal that Ti3C2Tx support can facilitate the charge transfer to metallic NPs and tailor the electronic structure of catalytic sites, resulting in optimized adsorption free energies of H* species for hydrogen electrochemistry. This work provides a facile and universal strategy in the development of 2D Ti3C2Tx with nonprecious metals for low-cost bifunctional hydrogen electrocatalysts.

Investigation of the Corrosion Resistance of Nickel-Molybdenum Alloys in the Eutectic LiF–NaF–KF

Investigation of the Corrosion Resistance of Nickel-Molybdenum Alloys in the Eutectic LiF–NaF–KF

Catalytic conversion of enzymatic hydrolysis lignin into cycloalkanes over a gamma-alumina supported nickel molybdenum alloy catalyst

The efficient depolymerization and hydrodeoxygenation of enzymatic hydrolysis lignin are achieved in cyclohexane solvents over a gamma-alumina supported nickel molybdenum alloy catalyst in a single step. Under initial 3 MPa hydrogen at 320 °C, the highest overall cycloalkane yield of 104.4 mg/g enzymatic hydrolysis lignin with 44.4 wt% selectivity of ethyl-cyclohexane was obtained. The reaction atmosphere and temperature have significant effects on enzymatic hydrolysis lignin conversion, product type and distribution. The conversion of enzymatic hydrolysis lignin was also investigated over different nickel and molybdenum-based catalysts, and the gamma-alumina supported nickel molybdenum alloy catalyst exhibited the highest activity among those catalysts. To reveal the reaction pathways of alkylphenol hydrodeoxygenation, 4-ethylphenol was tested as a model compound. Complete conversion of 4-ethylphenol into cycloalkanes was achieved. A two-step mechanism of 4-ethylphenol dihydroxylation – hydrogenation is proposed, in which the benzene ring saturation is deemed as the rate-determining step.

Electrodeposited Transitional Metal-Based Electrocatalysts for Hydrogen Evolution Reaction

As the fossil fuel is continuously declining, the necessity of a sustainable and clean source of energy is increasing. Hydrogen has been considered as a potential alternative due to its “zero emission” when reacting with oxygen in electrochemical cells. In addition, hydrogen is also a promising energy carrier/ storage to compensate the intermittent nature of other renewable energy sources (e.g. sunlight, wind, and tides). However, majority of hydrogen production comes from the combustion of fossil fuel which doesn’t make hydrogen a practical sustainable energy. Electrocatalytic hydrogen evolution reaction (HER) in water electrolysis therefore has drawn considerable attention owing to water and oxygen as the “green” reactant and by-product respectively.Early works with electrocatalytic HER involved noble metals (e.g. Pt) which is not cost-effective for industrial scale production. Therefore, transitional metal-based electrocatalysts (TMEs) have been intensively studied owing to the affinity of unpaired d-band electrons for chemisorption of hydrogen atoms. Among different strategies to improve the intrinsic properties of TMEs, coupling with other materials synergistically promotes the kinetics of HER. Nickel with minimum energy for hydrogen adsorption among various nonprecious metals exhibits the most efficient catalytic activities as a binary alloy with molybdenum in alkaline HER. Hydrogen spillover and averaging effect between the hydrogen adsorption energies of nickel and molybdenum facilitate the catalytic activity of nickel molybdenum alloy. On the other hand, transitional metal phosphides, especially cobalt with similar energy for hydrogen adsorption as nickel, have been considered as promising TMEs for acidic HER. With high electronegativity, phosphorus atoms can trap the positively charged protons and consequently enhance the dissociation of hydrogen. Moreover, dissolution of phosphorus-doped cobalt is less thermodynamically favored than that of cobalt, resulting in better electrocatalytic stability. To further enhance the HER catalytic performance, both types of electrocatalysts are synthesized at non-equilibrium by electrodeposition techniques to introduce chemical disorders and metaphases as well as to widen the range of composition. Different properties of deposits (e.g. composition, morphology, and grain size) can be tuned by controlling electrolyte composition and electrodeposition parameters.

Effect of Nickel–Phosphorus and Nickel–Molybdenum Coatings on Electrical Ablation of Small Electromagnetic Rails

The electromagnetic rail catapult is a device that converts electrical energy into kinetic energy, which means that the strength of electrical energy directly affects the muzzle speed of armature. In addition, the electrical conductivity, electromagnetic rails and armature surface roughness, and the holding force of the rail are influencing factors that cannot be ignored. However, the electric ablation on the surface of the electromagnetic rails caused by high temperatures seriously affects the service life performance of the electromagnetic catapult system. In this study, electrochemically deposited nickel-phosphorus and nickel-molybdenum alloy coatings are plated on the surface of electromagnetic iron rails and their effects on the reduction of ablation are investigated. SEM (scanning electron microscopy) with EDS (energy dispersive spectroscopy) detector, XRD (X-ray diffraction), 3D optical profiler, and Vickers microhardness tester are used. Our results show that the sliding velocity of the armature decreases slightly with the increased roughness of the rail coating surface. On the other hand, the area of electric ablation on the rail surface is inversely related to the hardness of the rail material. The electrically ablated surface areas of the rails are in: annealed nickel–molybdenum < nickel–molybdenum < annealed nickel–phosphorus < nickel–phosphorus < iron material. Heat treatment at 400 and 500 °C, respectively for Ni–P and Ni–Mo alloys, significantly increases hardness due to the precipitation of intermetallic compounds such as Ni3P and Ni4Mo phases. Comprehensive data analysis shows that the annealed nickel–molybdenum coating has the best electrical ablation wear resistance. The possible reason for that might be attributed to the high hardness of the heat-treated nickel–molybdenum coating. In addition, the thermal resistance capability of molybdenum is better than that of phosphorus, which might also contribute to the high wear resistance to electric ablation.

Assessment of Electrochemical Compatibility of Structural Materials of some Dental Products

Orthopedic treatment of tooth anomalies in children and adolescents is provided the long-term use of various metal constructions and devices in the oral cavity – braces, retreaders, locks or rings with struts, wire arches, and so on. They are usually made of corrosion-resistant metals and alloys, most often they are made of stainless chromium-nickel austenitic steels of Х18Н9Т type (import analogue – steel 304), martensitic 08Х17 (import analogue – steel 430), nickel-titanium or nickel-molybdenum alloys. The main disadvantage of all metal products is their manifestation of electrochemical properties and participation in electrochemical processes which can flow into the oral cavity and provoke galvanoses, especially for their joint use. In the "in vitro" conditions, according to a specially developed method, investigations of electrode potentials of directly 4 types of very small (2–3 mm) orthodontic products, in recommended for such products environment were carried out: 3 % solution of sodium chloride (pH=6,8), 2 % solution of citric acid (pH=0.5) and 2 % solution of baking soda (pH=8.65). It is found that the considered elements of orthodynamic systems have similar values of electrode potentials in neutral and weakly-alkaline environments and, accordingly, in the absence of other metal inclusions in the oral cavity, can be used jointly without the risk of galvanosis. The most heterogeneous construction is an individual ring with a strut, in which the difference in the values of the potentials between the individual parts in the acidic medium is more than 120 mV, which is a prerequisite for increasing the likelihood of galvanosis. For simultaneous use of other elements, in particular standard doping brackets, the value of EMF can increase up to 160 mV.