Precious Alloys Research Articles

Gold and Gold Alloys Electropolishing in Choline Chloride-Glycerol Deep Eutectic Solvents

Electropolishing (EP) is a finishing technique used to reduce the roughness of metallic surfaces while enhancing their brightness. This process enables the treatment of complex shaped parts and reduces processing time compared to conventional mechanical polishing methods. Electropolishing of precious metals typically requires the use of electrolytes containing cyanides and other toxic compounds, which reduces its attractiveness from an industrial perspective. Deep Eutectic Solvents (DES) are emerging as a good alternative for the chemical and electrochemical dissolution of valuable metals, like gold, silver and copper. However, their use in the specific context of electrochemical polishing of precious alloys has not been considered so far. This work aims to evaluate the effectiveness of choline chloride-based DES in electropolishing 18K gold alloys. Their performance will be assessed in terms of roughness reduction, brightness enhancement and color preservation, all characteristics associated with the presence of a uniform dissolution.

Effect Of Surface Treatment on The Shear Bond Strength Between Nickel-Chromium Alloy and Veneering Porcelain

Nickel–chromium (Ni–Cr) alloys, have been used widely, due to their superior physical properties and economic issues in relation to other precious alloys. Many studies have been carried out on porcelain fused to metal restorations to enhance the bonding quality of the porcelain to Ni-Cr alloy, such as mechanical treatment by air abrasion particles or chemical treatment by acid etching to increase the longevity of the restoration. The purpose of this study is to investigate the effect of surface treatments sandblasting with Aluminum Oxide (Al2O3), acid etching with Potassium hydrogen difluoride acid (KHF2) and combination treatment on the shear bond strength between Nickel-chromium alloy substructure and porcelain veneer. Twenty-one cylindrical shaped samples have base of 5 mm in diameter and 1 mm in thickness and a cylinder with 4 mm in diameter and 4 mm in length were prepared from Ni – Cr alloy. The samples were divided into 3 groups (n=7) according to surface treatment: Nickel -chromium treated with sandblasting with 50μm Al2O3 group (c), Nickel – chromium etching with KHF2 group (k), and Nickel – chromium sandblasting with 50μm Al2O3 followed with acid etching with KHF2 group (comb). Then ceramic build up (opaque, dentin, enamel, and glaze Vita VMK Master opaque, dentin, enamel, and glaze Vita VMK Master) and sintering was performed according to manufacturer's instructions and the final dimension of porcelain cylinder (4 X 4X 1) were checked with a metal gauge. All samples were subjected to shear force in a universal testing machine at cross head speed 0.5 mm/min. and recorded in MPa. The fractured samples were checked under (DIGITAL MICROSCOPE) (X50) to evaluate the mode of failure, it was adhesive, cohesive and mixed failure modes. The shear bond strength values were analyzed with one-way ANOVA and LSD. The results showed that the highest mean of shear bond strength values was in Ni – Cr combination surface treatment group (26.11 ± 1.85), while the lowest mean was for Ni- Cr acid etched group (22.02 ± 1.5) and Nic group (20.85 ± 1.5). Within the limitation of the present study, the following conclusion can be drawn: Combination surface treatment produced the highest shear bond strength between Ni – Cr surface and veneering porcelain, followed by etching with KHF2, so combination method would increase longevity of porcelain fused to metal restorations.

Coupling Glycerol Conversion with Hydrogen Production Using Alloyed Electrocatalysts.

Herein, uniform precious alloys including PtAg, PdAg, and PtPdAg nanoparticles were synthesized as electrocatalysts for glycerol oxidation reaction (GOR). The structures of the samples were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectrometry. The catalytic performance of the samples was evaluated in both alkaline and acidic electrolytes. Among the samples, PtPdAg exhibited superior activity with the largest current density of 3.77 mA cm-2 in alkaline solutions, which is 4.1 and 7.7 times those of Pd/C and Pt/C, respectively. In acidic solutions, the PtPdAg catalyst shows the highest current density of 0.58 mA cm-2, which is 1.8 times that of the Pt/C catalyst. The products of GOR were analyzed by high-performance liquid chromatography. Eight products including oxalic acid, tartronic acid, glyoxylic acid, glyceric acid, glyceraldehyde (GLAD), glycolic acid, lactic acid, and dihydroxyacetone were detected. Notably, in acidic solutions, PtAg and PtPdAg yielded the largest GLAD selectivity of 92.2% at 0.6 and 0.8 V, respectively. Using the alloyed catalysts, electrolysis processes coupling the GOR with the hydrogen evolution reaction were conducted. The conversion of glycerol and production of hydrogen were determined. To highlight the energy efficiency, a solar-panel-powered electrolysis process was conducted for the simultaneous production of hydrogen and high-valued products.

Can we use the translucency parameter to predict the CAD/CAM ceramic restoration aesthetic?

To evaluate the effects of background color, ceramic type and coping thickness on masking ability (ΔE) and translucency parameter (TP) of CAD/CAM lithium disilicate glass-ceramic/monolithic zirconia and, to determine the correlations between coping thickness, TP and ΔE. A total of 120 ceramic specimens (2mm, 1mm and 0.5mm thickness; n=10) of four CAD/CAM ceramics: IPS e.max, IPS ZirCAD, Upcera Li CAD and Upcera TT CAD, were studied. Specimens were tested over nine fabricated backgrounds: A1, A2, A3.5, ND2 and ND7 shade resin-based composites, cobalt-chromium alloy (CC), medium precious alloy (MPA), black (B) and white (W). CIELab values (L*, a* and b*), color difference (ΔE) and translucency parameter (TP) were measured and calculated using a digital spectrophotometer (color i7, X-Rite, Pantone®). Data were analyzed using the Shapiro-Wilk test, one-way ANOVA, three-way ANOVA, independent t-tests and Tukey post-hoc tests (p<0.05). 2mm CAD/CAM ceramics showed ideal color matching (ΔE<2.6) over different backgrounds, except for CC, B and W backgrounds. Monolithic zirconia had lower ΔE values than lithium disilicate glass-ceramics. ΔE and TP values significantly reduced with the increased coping thickness (p<0.05). Regardless of ceramic type and thickness, a strong TP-SD of ΔE correlation was observed. CAD/CAM ceramic restoration color was significantly affected by background color, ceramic type and coping thickness. TP is a promising predictor for appropriate ceramic selection to receive an acceptable CAD/CAM ceramic restoration aesthetic.

Indirect repair of saliva-contaminated materials using veneering ceramics.

To analyze the in vitro efficacy of a surface conditioning liquid facilitating ceramic repairs of saliva-contaminated metal-ceramic and all-ceramic restorations. Specimens constructed from nonprecious alloy (NPA), precious alloy (PA), lithium-disilicate (LD), zirconia (ZI), veneering ceramics for zirconia (VZI), veneering ceramics for lithium-disilicate (VLD), and veneering ceramics for metal alloys (VM) were manufactured (total: n= 168; each material n= 24). Veneering ceramic cylinders (thickness: 2mm) were hand-layered on top of the specimens. Shear bond strength (SBS) tests were performed, measuring the maximum bond strength (MBS) of the cylinders on the specimens. Following this, the specimens were artificially aged and stored in artificial saliva for 30 days at 37°C. After physical cleaning using aluminum oxide air abrasion, a new surface conditioning liquid was applied (test, n= 84) or not (control, n= 84). New ceramic cylinders were hand-layered followed by a second SBS test. Descriptive statistics, linear regression analyses, and a one-sample t-test (α= 0.05) were used to ascertain the differences within (prerepair vs. postrepair) and between the groups. All specimens in the test group could be repaired, whereas 18 repairs in the control group failed. After the repairs, an MBS decrease was observed for the NPA specimens of the control group (-15.5MPa, p= 0.004) but not among any of the test groups. Comparing the change in MBS between the test and control groups, the reduction was significantly higher in the repaired NPA specimens of the control group (mean difference 11.8MPa, p= 0.017). Using the analyzed surface conditioning liquid, metal-ceramic and all-ceramic materials can be repaired, while some repairs failed without the liquid. The initial bond strengths between core and veneering materials could be restored in all specimens when the new surface conditioning liquid was applied.

Electrogalvanism in Oral Implantology: A Systematic Review.

Purpose The objective of this work is to study galvanic corrosion of different couples of prosthetic and implant alloys through the realization of a systematic review. Materials and Methods An electronic search was performed on Pubmed, Google Scholar, Scopus, ScienceDirect, EbscoHost, and Web of Science for published studies related to electrogalvanism in oral implantology. The keywords used were “dental implants” and “galvanic corrosion.” Two independent readers read the scientific articles. Results From 65 articles initially identified, only 19 articles met the eligibility criteria. The evaluation of the selected articles allowed us to determine the parameters compared, such as the resistance to galvanic corrosion, the influence of fluorine and pH on the electrochemical behavior, and the release of metal ions and their cytotoxicity. Indeed, Ti6Al4V and precious alloys coupled to titanium were found to be the most resistant to galvanic corrosion, followed by cobalt-chromium alloys and nickel-chromium alloys which were least resistant. This resistance decreases with increasing fluorine concentration and with decreasing pH of the environment. Discussion. The implant-prosthetic system's galvanic resistance is influenced by many intrinsic factors: alloy composition and surface condition, as well as extrinsic factors such as pH variations and amount of fluorine. The effects of oral electrogalvanism are essentially the result of two main criteria: effects due to electric currents generated by corrosion and effects due to the release of metal ions by corrosion. Conclusion To avoid this phenomenon, it is wise to follow the proposed recommendations such as the use of the minimum of distinct metals as much as possible, favoring the commercially pure titanium implant of Ti6Al4V, opting for the choice of couples, titanium/titanium, favoring daily mouthwashes of 227 ppm of fluoride, and avoiding fluorinated acid solutions.

Development of Special Magnetic Separator to Recover Precious Metal-Bearing Alloy from High-grade Nickel Matte and Its Magnetic Field Simulation

Development of Special Magnetic Separator to Recover Precious Metal-Bearing Alloy from High-grade Nickel Matte and Its Magnetic Field Simulation

MRI and Its Implications in Dentistry

Magnetic Resonance imaging (MRI) has become one of the most powerful diagnostic tools in radiology and diagnostic sciences. It is non-invasive and non-ionizing and the images are highly sensitive and specific with excellent soft tissue contrast. It gives excellent images of anatomic structures differing in proton density and other tissue characteristics. It can be used to assess intracranial and extracranial lesions particularly those involving the soft tissues.&#x0D; MRI has the shortcoming of being prone to magnetic susceptibility difference artefacts, caused by the presence of metallic materials such as dental restorative materials, implants and orthodontic appliances. All substances when placed in a magnetic field are magnetized to a degree which varies according to their magnetic susceptibility. Non precious dental alloys have the potential of causing image deformation or image voids. &#x0D; Dentists are not the only professionals implanting metal devices. Heart pacemakers and defibrillators, aneurysm clips, cochlear implants, insulin pumps, vascular stents and artificial joints are widely used in various branches of medicine. In some cases, it is not possible to carry out MRI due to extensive dental hardware with a high ferromagnetic content. Severe image distortion or an inability to perform the MRI scan due to dental restorations is a rare problem, but cannot be completely eliminated. This article has been written to educate the dentists on the implications of metallic dental restorations on MRI scans.&#x0D; Keywords: Magnetic resonance imaging, MRI, Dentistry, Dental materials, artefact, artifacts.

Solidification Calculations of Precious Alloys and Al-Base Alloys for Additive Manufacturing

In this paper, we report two cases studies where solidification processes were successfully investigated with CALPHAD-based methodologies. The first one refers to the use of thermodynamic databases to describe the solidification processes of a precious Au-base alloy containing Ir as a grain refiner. The second one concerns the development and use of a quaternary database for Al-Mg-Si-Er alloys for additive manufacturing, where Er is added as a nucleating agent. While in the former case, the solidification process was investigated by running the Thermo-Calc software with a specific TCNOBL1 commercial database, in the latter, the necessary database was first constructed, using available thermodynamic assessments in the literature and experimental data, and then applied to investigate the solidification behavior of selected alloys.

Features of design, construction and technology of manufacturing galvanoplastic jewellery

The features of design, construction and manufacturing technology of electroplated jewellery are considered. The classification of jewellery made by the method of electroforming, based on their areas of application, is presented. The technological features of the formation of the surface of products with a “posi-tive” and “negative” build-up of the deposited metal, ways of reducing the roughness of the deposited coat-ings with an increase in their thickness are considered. Methods of creating suspension and fastening ele-ments of the product structure are described. The main modern trends in the development of technology and design of products made by the method of electroforming are considered: the use of 3D technologies in the development and creation of models, the use of conductive polymer compositions for the manufacture of models, computerization of the technological process of forming metal deposits of precious alloys of a cer-tain carat and colour. Modern technological methods allow raising the level of electroplated jewellery de-sign to a new level.

Identification of white jewelry alloy based on silver and platinum for testing purposes

The procedure for the identification of white jewelry alloys based on precious metals, in particular, silver, platinum and platinum group metals with different contents of alloying components, by testing on an assay stone and by the method of X-ray fluorescence analysis has been considered. The methodology for assessing the compliance of silver and platinum fineness in white jewelry alloys of different component composition with the requirements of regulatory documents and the procedure for their identification has been improved. It has been established that the silver fineness in precious alloys of the AgCu, AgZnCu system, determined using the potassium dichromate reagent on the test stone, depends on the manifestation of the contrast of the qualitative reaction from the standard sample (assay needle). It has been proven that for testing silver alloys containing palladium, the "Acid reagent for gold 750" is effective, which works to determine the qualitative and approximate content of silver in alloys. It was determined that the reagent "Ferrous-cyanide potassium" is very sensitive to changes in the alloy composition of silver alloys and makes it possible to establish the silver content with an accuracy of 5 %. The presence in silver alloys of such impurities as zinc, cadmium, nickel, gold, palladium and others increases the error in determining the fineness of silver and forms a different color and shade. It has been proven that testing of silver alloys on an assay stone with silver nitrate is effective only for the СрМ system. The presence of zinc in 925 sterling silver alloys visually increases the color intensity of the sediment, which indicates a higher overestimated fineness. It has been found that the identification of the content of precious alloys based on platinum for the presence of ligature components is carried out with a potassium iodide reagent at t=120 °C by the color and shade of the sediment. The procedure for using potassium iodide during testing of precious platinum-based alloys has been optimized

Retention forces between primary and secondary CAD/CAM manufactured telescopic crowns: an in vitro comparison of common material combinations

ObjectivesTo analyze the retention forces between primary and secondary telescopic crowns milled from various materials and to compare them with the retention forces between cast telescopic crowns made of precious metal alloys.Materials and methodsPrimary and secondary crowns (N = 60; n = 10 per group) were fabricated using various material combinations (1: zirconia [ZIR]/polyether ether ketone [PEEK]; 2: titanium grade IV [TI]/PEEK; 3: PEEK/PEEK; 4: non-precious alloy [NPA]/PEEK; 5:NPA/NPA), while precious alloy (PA) was used for the control group (6: PA/PA). The retention forces at 10, 1000, 5000, and 10,000 connection and disconnection cycles and the relative weights were analyzed, applying nonparametric repeated measures ANOVA and post hoc Mann–Whitney and Wilcoxon signed-rank tests (α < 0.05).ResultsGlobally, significant differences in the retention forces among the materials (p < 0.0001), time points (p < 0.0001), and wear resistance for the various materials (p < 0.0001) were observed. No significant changes in retention forces compared to baseline were observed in groups 2, 4, 5, and 6. A significantly higher weight loss for both primary and secondary crowns was observed in groups 4 and 6.ConclusionsThe material combination in telescopic attachments influences retention forces and wear. Interactions between materials and time were evident, indicating that the change in retention forces differs among the materials. The combinations of milled TI/PEEK and NPA/NPA qualify for further preclinical testing in a more clinically realistic setup, determining a material-specific double-crown design.Clinical relevanceThe design of precious alloy telescopic crowns cannot be directly transferred to other milled material combinations due to different retention behaviors.

Biocompatibility assessments of 316L stainless steel substrates coated by Fe-based bulk metallic glass through electro-spark deposition method

Metallic materials made of rather precious alloys are widely used in orthopedic surgery, circulatory system, and dentistry fields. Stainless steel coated by alloys with a variety of physiochemical properties can be an excellent candidate for making economical devices with superior biomedical compatibility. In this study, a Fe- based metallic glass alloy was applied on 316L stainless steel (316L SS) using the electro-spark deposition (ESD) method as an economic and easy handling method. The coated samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). It was found that a metallic glass coating was uniformly formed on the stainless steel substrate. Cytocompatibility (MTT assay), hemocompatibility, and cell attachment assays of the fabricated biomaterials were carried out using bone and connective tissue cell lines. The samples with optimized coating were shown to exert lower cytotoxicity, better cell attachment, and higher blood compatibility than the stainless steel substrates.

Corrosion Susceptibility and Allergy Potential of Austenitic Stainless Steels.

Although called stainless steels, austenitic steels are sensitive to localized corrosion, namely pitting, crevice, and intergranular form. Seventeen grades of steel were tested for localized corrosion. Steels were also tested in general corrosion and in galvanic couplings (steels–precious alloys) used in watchmaking applications. The evaluations have been carried out in accordance with the ASTM standards which specifically concern the forms of corrosion namely, general (B117-97, salt fog test), pitting (G48-11, FeCl3), crevice (F746-87) and intergranular (A262-15, Strauss chemical test and G108-94, Electrochemical potentiodynamic reactivation test). All tests revealed sensitivity to corrosion. We have noticed that the transverse face is clearly more sensitive than the longitudinal face, in the direction of rolling process. The same conclusion has been drawn from the tests of nickel release. It should be pointed out that, despite the fact that the grade of steel is in conformity with the classification standards, the behavior is very different from one manufacturer to another, due to parameters dependent on the production process, such as casting volume, alloying additions, and deoxidizing agents. The quantities of nickel released are related to the operations involved in the manufacturing process. Heat treatments reduce the quantities of nickel released. The surface state has little influence on the release. The hardening procedures increase the quantities of nickel released. The quantities of released nickel are influenced by the inclusionary state and the existence of the secondary phases in the steel structure. Another aspect is related to the strong dispersion of results concerning nickel release and corrosion behavior of raw materials.

Influence of thermo-mechanical history on the ordering kinetics in 18 carat Au alloys

Precious alloys are subjected to a series of mechanical and thermal operations during manufacturing. For 18 carat gold alloys the processing operations can induce L10 ordered nanodomains, known to lead to the build-up of residual stresses, which are the prime cause for shape distortion. Here, in situ high-energy synchrotron X-ray diffraction experiments in combination with electron microscopy observations reveal the influence of the thermo-mechanical history and chemical composition on the ordering kinetics during isochronal heating. Initially, during heating, the elastic lattice strain in the ordered nanodomains increases. The ordering rate and accumulation of lattice strain depend on the cooling rate, predeformation and chemical composition. Above a given temperature, which depends on the deformation state and chemical composition, the lattice strain in the ordered domains relaxes which is ascribed to the formation of a tweed structure.

Long-term clinical outcome of posterior metal-ceramic crowns fabricated with direct metal laser-sintering technology

ObjectivesTo evaluate the long-term clinical outcome of posterior metal-ceramic crowns fabricated with CAD/CAM-based laser-sintering technology (BEGO Medical, Bremen, Germany). Materials and MethodsSixty posterior crowns were placed in 39 patients. After tooth preparation, impression taking and model casting, the stone dies were scanned to create STL data, followed by manufacturing of crown frameworks with laser-sintering technology. A base metal alloy (CoCr) and a precious alloy (AuPt) were used for 31 and 29 posterior crowns, respectively, which were veneered using the layering technique. All crowns were cemented using glass-ionomer cement. ResultsThe mean observation period was 10.5 ± 3.9 years. Six patients with 10 crowns were regarded as dropout. Nine crowns had been removed, three of them were intact but they were removed due to a new prosthetic treatment plan. The cumulative survival rate of all crowns was 81% after 14.7 years. When comparing the survival rates related to the alloy used, the Gehan-Wilcoxon test showed no significant differences between both alloys. Biological complications were most commonly reported, while technical complications did not affect the function of the crowns. ConclusionThe long-term clinical outcome of posterior metal-ceramic crowns fabricated with CAD/CAM-based laser-sintering technology is very promising, so that this novel technique could be an alternative to the traditional lost wax casting process.

Improving a procedure for determining the assay of gold in a precious alloy of different composition using a touchstone

We report testing the and jewelry alloys based on that contains nickel, zinc, palladium, using a touchstone by applying various chemical reagents and XFA (X-ray fluorescence analysis).We have improved the procedure for assessing the conformity of assay of the precious alloys based on considering the content of component composition by using the results from rubbing the alloys on a touchstone.It was established that the magnitude of assay for precious alloys in the system AuAgZnCu, determined under the action of the reagent chloric gold on the touchstone, depends on the manifestation of contrast in the course of quality reaction against a standard sample (touch-needle).Under the influence of the reagent, the alloys demonstrate chloride compounds with silver and copper, being reduced to a metal powder of black and brown color. In this case, copper dissolves while together with silver, forms an intensive residue on a strip that depends on the ligature composition of the alloy. It was established that the lower the assay of a tested sample, the greater the amount of chlorine gold that decomposes, the larger the sediment of silver chloride and the pure reduced from the reagent, and hence the darker the sediment.It has been proven that testing the precious alloys of red color from the system AuAgZnCu 585 with a content of zinc (over 2 %), nickel, indium by using a reagent based on potassium dichromate and copper chloride is not effective.The results of our analysis indicate the increased assay compared with a standard touch-needle.To eliminate this phenomenon, it is recommended that one should first determine the composition of an alloy by the XFA method and construct an algorithm for testing in accordance with the content of the alloy by other reagents.It was determined that the assay defined on a touchstone for alloys from the system AuAgZnCu 585 (a content of zinc is over 2 %) is more contrast under the influence of acidic reagents and depends on the component composition of the alloy.It has been proven that the alloy of white gold, composed of palladium and silver (AuAgPd585), is not affected by the acid reagent for assay 585.Testing the alloy of white gold (AuAgPd585) using an acid reagent for assay 750 yields the dark sediment of a bluish tint.We have established a more contrast effect on the alloys of white gold and yellow gold of assay 750 from the acid reagent for alloys of assay 750.

EFFECTS OF TITANIUM CARBIDES FORMATION ON INTERNAL HEAT OF WELDING BATH

Problem. At present, precious alloy with alloying elements, which are scarce and expensive in Ukraine, are used to increase the durability of the die tool. In this regard, studies aimed at reducing energy and resource costs while restoring a metalworking tool, enhancing its reliability and durability, are particularly relevant. The goal is to investigate the distribution of the TiC carbide phase in the Cr–Mn–Mo–Ti wear–resistant alloy compounds. Methodologically, the work was carried out in the following way: on the basis of literary sources and industrial research the conditions of the work of dies for hot metal processing were studied. An analysis of existing alloys and their application technologies showed that they all have both advantages and disadvantages. On the basis of this, economically wear-resistant alloys of the Cr–Mn–Mo–Ti system on the basis of iron with a limited content of chromium (up to 3 %) and molybdenum (up to 5%) were developed, as well as the technology of their application with an exhausted additive which is fed to the main part of the welding baths. Results. Application of surfacing with powdered wires with exogenous introduction of carbides into a weld bath promotes a more even distribution of the carbide phase in the volume of metal compared with the endogenous carbide entrance. In this case, increasing the content of Mn and Cr in the welded metal reduces the activity of carbon as a carbide–forming element. An increase in the carbide phase of TiC increases the internal heat of the weld metal when it is exogenously introduced. Practical significance. Warehouses of wear-resistant coatings with limited content of scarce alloying elements have been developed as well as the technology of application. The use of developed wear- resistant alloys and technologies for their application allowed to reduce the concentration of alloying elements, the complexity of the thermal treatment of recovered stamps, the relative weight of flux and the share of electricity consumption, to improve the basic technological parameters of surfacing.

A low-alloy high-carbon martensite steel with 2.6 GPa tensile strength and good ductility

A low-alloy and high-carbon martensite steel (0.66% C) with ultrafine grains is produced by combination of Tempforming (tempering and deforming of a quenched steel) and reheating followed by water quenching and low temperature tempering. The size of prior-austenite grains of the steel is reduced to 2.4 μm through this new technique, and its ultimate tensile strength of 2.6 GPa and elongation of 7% are obtained, which is the highest strength in low alloy high strength steels. The microstructure of the high carbon martensite consists of high density dislocations, undissolved spherical carbides, and dispersed nano-scale Fe3C and Fe5C2 phases precipitated at interior of martensitic after tempering. The strengthening mechanisms of the ultrafine grain martensitic steel are mainly dislocation strengthening and precipitation strengthening and also fine grain strengthening. The tensile strength and ductility of the steel are superior to that of existing maraging steels, such as C350, the highest strength in commercialized level, in which more than 20% precious alloy elements such as Co, Mo, Ni, and Ti are contained, and the cost of our materials is only about 1/50 of the C350. All above advantages are desirable for broad industrial applications at an economic cost.

Enhanced Stability of PtML/MML/WC(0001) Multilayer Alloys under Electrochemical Conditions: A First Principle Study

A platinum (Pt) monolayer catalyst could greatly reduce the use of Pt. However, the core or subsurface transition metal could easily segregate to the surface and eventually selectively dissolve in the working conditions. In this work, a type of PtML/MML/tungsten carbide (WC) multilayer structure catalyst has been designed using the density functional theory method. The results show that the stability of W-terminated core catalysts is lower than that of the corresponding C-terminated one. More importantly, the C-terminated PtML/CoML/WC alloy could also maintain a stable Pt monolayer structure in various electrolyte solutions (e.g., perchloric acid, phosphoric acid, and alkaline solutions) and via different oxygen reduction reaction (ORR) pathways, in addition to the previously well-known precious alloy elements, such as Ru, Ir, and so forth. The segregation of the M metal will be suppressed by introducing a high electronegativity nonmetal element in the core such as C through enhanced interaction between the C and M interlayers. The improved ORR activity and the stability of C-terminated PtML/Co(Ru)ML/WC(0001) multilayer structures highlight the importance of surface chemistry of the substrate in rational design Pt monolayer catalysts.