High Purity Argon Research Articles

Thermal properties and decomposition of perovskite energetic materials (C6H14N2) NH4 (ClO4)3

(C6N2H14) NH4 (ClO4)3 (DAP-4) have attracted an increasing focus recently as an ammoniumperchlorate-based molecular perovskite energetic material with outstanding features. Microscopy, variable temperature X-ray diffraction, in situ infrared spectroscopy, differential scanning calorimetry-thermogravimetry simultaneous thermal analysis coupled with infrared spectroscopy and mass spectrometry (DSC-TG/FTIR/MS) techniques were used to systematically investigate DAP-4 thermal properties from -40 °C to 550 °C. The results revealed that DAP-4 have two solid-solid crystallization phase transitions with a non-characteristic melting process. The generated activation energies of HCN, CO, CH2NH2, CO2 and NO2 gas products are all lower than the macroscopic decomposition's of DAP-4. This finding strongly proves that DAP-4 is easy to form these gas products during thermal stimulus. The two stages decomposition mechanism accompanying a large of CH2NH2 and NH2C2H4 gases and kinetic model of DAP-4 were proposed under the condition of high-purity argon gas. This study provides new insight into the in-depth and accurate description thermal decomposition mechanism of DAP-4 as a potential energetic material.

Отримання жароміцного гомогенного сплаву методом пресування та спікання суміші порошків (Nb-21Ti-5Al-10Cr-7Mo) ат. %

Multicomponent high temperature strength alloys of the Nb-Ti-Al system, alloyed with Cr, Zr, Mo and Si, with a specific gravity of 6.3 - 7.4 g/cm3, have proven extremely promising in aviation and space technology. However, their physical and chemical features are associated with the high activity of the components, with a significant difference in melting temperatures (from Tmel. Mo – 2617 °C to Tmel. Al – 660 °C) and different specific gravity (from 10.2 g/cm3- Mo up to 2.7 g/cm3- Al), is a big problem for their production. The long crystallization interval of cast alloys of this system, thermophysical features of their crystallization, determine the possibility of formation of dendritic structures, the development of dendritic liquation and segregation of low- or high-temperature intermetallics and eutectics, the tendency to the formation of crystallization cracks, which reduces the operational characteristics of cast alloys. In this regard, it became necessary to investigate the possibilities of obtaining an alloy by the method of powder metallurgy. The purpose of this work was to obtain a homogeneous alloy, to study changes in the grain structure, phase transformations and mechanical properties of the material at various stages of processing in the process of obtaining a homogeneous alloy structure by powder metallurgy methods. The need to protect powder components from oxidation, formation of nitrides, carbides during technological operations at temperatures above 200 °C (high-purity argon) has been established. The optimal duration of intensive grinding of a mixture of powders and granules of raw materials has been worked out, which makes it possible to control the uniformity of the size of the particles of the mixture components, porosity and homogeneity of the alloy. The optimal duration of grinding is 30 minutes, during which the most homogeneous mixture in terms of particle size is formed. The optimal annealing mode was established, which ensures the achievement of homogenization of the alloy, phase transformations at the boundaries of the contact of component particles, and changes in grain sizes. Microstructural and X-ray structural analysis of the samples was carried out, their microhardness and grain dispersion were determined. Keyword: high-temperature strength niobium alloys, physical and chemical features, powder metallurgy, homogeneity, microstructure, mechanical properties, phase composition.

The surface tension of pure Zn measured by means of the maximum bubble pressure method

The surface tension σ of pure Zn and its temperature coefficient have been measured by means of the maximum bubble pressure technique over the temperature range [Tm, Tm+250 °C], where Tm is the melting temperature. Alumina and quartz capillaries of various radii were used. Alumina capillaries were coated with boron nitride to discard possible wetting and high purity argon was used as bubbling gas. In addition, σ was measured while heating, cooling, or introducing the capillaries in the melt at several chosen temperatures. All measurements with alumina capillaries showed a negative temperature coefficient while those with quartz capillaries gave a positive temperature coefficient. These results are compatible with Nogi et al. conclusion in the sense that positive temperature coefficients reported in the literature should be ascribed to oxygen and/or impurity effects enhanced in volatile metals. In particular we argue that the positive temperature coefficient is a consequence of the concomitant action of several factors, namely, vaporization of Zn, oxygen traces in the bubbling gas, and the oxygen and Si produced in the chemical reactions involving quartz and liquid zinc.

Crystal structure and thermodynamic properties of the new compound Sc4Sb2.52 in the Sc-Sb system

The new compound Sc4Sb2.52 was first discovered, which was synthesized by the arc-melting under high purity argon. The composition of the new compound was examined by energy dispersive X-ray spectroscopy (EDS). Its crystal structure was first determined using X-ray powder diffraction data by Rietveld method. In order to further verify its structure, it was also observed by transmission electron microscope (TEM). The compound crystallized in a cubic Th3P4-type structure with the space group I4¯3d (No. 220) and the lattice parameter is a = 8.65454(9) Å. Its atomic positions are Sc at 16c (0.0736(3), 0.0736(3), 0.0736(3)), and Sb at 12a (0.375, 0, 0.25). The heat capacity (Cp) of the new compound Sc4Sb2.52 was reported for the first time, which were measured using differential scanning calorimetry (DSC) in a temperature range from 105 K to 450 K. The curve of Cp shows the normal sigmoidal temperature dependence with no evidence of transitions and other anomalies, and which was fitted using Debye function from 0 K to 77 K and using Maier-Kelley type expression from 77 K to 450 K. The entropy, enthalpy and free-energy values were derived with integration of the heat capacities based on the relations of thermodynamic properties with Cp.

Influence of Film Thickness on Nanofabrication of Graphene Oxide

Nanofabrication of two-dimensional materials through mechanical machining is normally influenced by not only process parameters such as load and velocity but also intrinsic properties such as strength and thickness. Herein, we examined the effects of graphene oxide (GO) film thickness on nanofabrication on the plane surfaces and at the step edges using scanning probe microscope lithography. The material removal of GO initiates at the load above a critical value, which strongly depends on film thickness and locations. With the increase in film thickness, the critical load decreases monotonically on the plane surfaces but increases gradually at the step edges. Further, the critical load for the GO monolayer at the step edges is at least 25 times lower than that on the plane surfaces, and the gap decreases to around 3 times when GO thickness increases to four layers. Then, mechanical nanofabrication initiating from the GO step edge allows producing various nanopatterns under extremely low loads around 1 nN. Finally, the GO nanostructures are deoxidized by annealing at 800 °C in high-purity argon to restore their highly functionalized conjugated structures, which are supported by X-ray diffraction and Raman characterizations. This work provides a novel approach to fabricating graphene-like nanostructures by deoxidizing GO after nanofabrication, which holds significant potential for applications in graphene-based devices.Graphical

The Four-Sinker Densimeter: A New Instrument for the Combined Investigation of Accurate Densities and Sorption Phenomena of Pure Gases and Gas Mixtures

An apparatus for high-accuracy gas density and adsorption measurements over the range of temperature from (193 to 423) K and pressure from (0 to 15) MPa is described. This instrument is based on the two-sinker densimetry principle and incorporates a magnetic suspension balance. In addition to the two “density sinkers”, two “sorption sinkers” are weighed to investigate density and adsorption of a gas sample simultaneously. The design of the sinkers increases the resolution of density and adsorption investigations and enables the correction of sorption effects on density measurements. The complete apparatus, including the sinkers, the temperature and pressure measuring systems, and the measurement procedure, is described. For the density range investigated, the uncertainty (k = 2) is between (0.0034 to 0.019) kg·\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\cdot$$\\end{document}m−3, corresponding to (0.060 to 0.011)%. The uncertainty (k = 2) in adsorption load is (0.16 to 0.26) μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}g·\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\cdot$$\\end{document}cm−2. Density measurements at T = (283 and 293) K and pressures up to 10 MPa of high-purity argon and nitrogen validate the instrument for density. Adsorption measurements of high-purity carbon dioxide and propane on a gold surface validate the instrument for adsorption investigation at T = (283 and 293) K and up to the saturation pressure of the investigated gas. The apparatus was used to measure the binary mixture (0.75 CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{CO}_2$$\\end{document} + 0.25 C3H8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{C}_3\ ext{H}_8}$$\\end{document}). In the future, the apparatus will also be used to accurately determine dew-point densities and pressures of pure gases and gas mixtures.

Formation of Extended Tubular Plasma in Argon at Low Pressure and in a Weak Longitudinal Magnetic Field

The results of experimental studies on the formation and subsequent evolution of extended (l = 300 mm) and thin-walled (Δr ≈ 10 mm) tubular (2r ≈ 110 mm) plasma in a weak longitudinal magnetic field (B = 175 G) without the use of a thermionic cathode are presented. The cylindrical chamber in which the tubular plasma was formed was pumped with high purity argon (99.998%) at an average velocity of about 1 m/s at a pressure of P = 10–3–10–2 Torr. Two methods of creating seed electrons initiating the development of ionization avalanches were used. The difference inherent to these methods has been established in the dynamics of breakdown, completing in the formation of a tubular discharge. In the first of them, a pulsed discharge preceding the high voltage supply of the main discharge created gas preionization in a small area around the sectioned cathodes. In the second method, seed electrons were created in the entire working area of the discharge chamber by an RF discharge with a frequency of 85 kHz and duration of about 1 s. High-speed shooting with a 4-frame ICCD camera allowed us to establish the dynamics of tubular discharge formation at all its stages. Measurements of the longitudinal and radial discharge current were carried out. The results we obtained showed the possibility of spatial isolation of an extended tubular plasma from the close located metal wall of the discharge chamber by using a weak longitudinal magnetic field.

Tailoring microstructures and properties in Co-free FeNiCrCuAl high entropy alloys by Al addition

In this study, a series of Co-free FeNiCrCuAlx (x = 0.1, 0.3, 0.5, 0.8 and 1.0) high entropy alloys (HEAs) were developed by vacuum arc melting and casting method in high-purity argon atmosphere. The effects of Al addition on the microstructure and properties were investigated using X-ray diffraction, scanning electron microscopy, Vickers hardness tester, tensile test, wear test and electrochemical experiment. It was found that with the increase in the large atomic-sized Al content, the closely-packed FCC structure was destabilized for a transition to the loosely-packed BCC structure at x = 0.3. As x increased up to 1.0, the structure was mainly composed of BCC phase. The hardness of HEAs was enhanced by the influence of the contiguous atomic planes in BCC structures due to the relatively lower inter-planar spacing and higher lattice friction for dislocation motion, with the potential to increase the yield strength of the HEAs by 93.5 %. The friction coefficient decreased with increasing Al content, as indicated by stable profiles of Al0.8 and Al1.0 under progressive wear in comparison to those of Al0.1, Al0.3 and Al0.5 while the associated minimal wear depth and lower capacity for debris accumulation of the higher Al content HEAs confirmed their superior wear resistance. As FeNiCrCuAl0.5 presented the most superior corrosion resistance due to high resistance to ionic transport via the steady oxide film and the indication of a comparatively wider capacitive semicircle, undue Al additions would not be beneficial to improving plasticity or enhance corrosion resistance. Thus, FeNiCrCuAlx HEAs with Al contents in the range of 0.5–1.0 were found to possess optimized comprehensive properties, and can be suitably recommended as nuclear structural materials. This study will shed light on advancing the development of cutting-edge HEAs.

Crystal structure change in magnetocaloric compounds (Er,Nd)2Fe17

Numerous research studies have documented materials exhibiting a significant magnetocaloric effect (MCE) at elevated temperatures. However, there is a scarcity of materials displaying both intriguing MCE and a second-order transition phase from a ferromagnetic state to a paramagnetic state at approximately 300 K. In this current study, we provide an account of the structural, magnetic, and magnetocaloric characteristics of the (Er,Nd)2Fe17 system. (Er,Nd)2Fe17 compound was prepared by arc melting under high pure argon and homogenized at 1073K to minimize the amount of other possible impurity phases. X-ray diffraction (XRD) coupled with Rietveld analysis with FullProf computer code was used for the structural study. This compound crystallizes in the rhombohedral Th2Zn17 and Th2Ni17 type structure.the Er2−xNdxFe17 compounds adopt the hexagonal Th2Ni17-structure type and extends for x = 0, 0.4, 0.7, while for x = 1.75, 1.85 and 2 adopts the rhombohedral Th2Zn17-structure type. Hence, the temperature dependence of the magnetization is determined. The Curie temperature increases from 294K to 335K after the total Er substitution by Nd. The magnetic entropy changes ΔSM, and the relative cooling power and temperature-averaged entropy change (TEC) are reported. Based on these results, the compounds under investigation exhibit an intriguing magnetocaloric effect in the vicinity of room temperature.

Wetting of Graphite and Platinum Substrate by Oxide System with Graded B2O3 Content

This work focuses on wetting two types of substrates (a platinum substrate and a polished graphite substrate) by molten polycomponent oxide system CaO–MgO–SiO2–Al2O3–B2O3 to test the level of interaction at high temperatures. The tested systems were subjected to high-temperature wetting tests in the temperature range from liquidus temperature to 1550 °C using the sessile drop method. A total of four oxide systems were tested with graded boron oxide contents ranging from 0 to 30 wt%. The experiments were conducted in a CLASIC high-temperature resistance observation furnace and an inert atmosphere of high-purity argon. Droplet silhouettes were obtained with a CANON EOS 550D high-resolution camera during heat treatment, with reactive and non-reactive wetting occurring depending on the substrate type. The dependence of the average wetting angles on temperature and time was evaluated, and it was found that boron oxide decreased the average wetting angles of molten oxide droplets. The analyses were accompanied by the SEM/EDX analysis of the substrate and FTIR analysis of the droplets after high-temperature experiments. The phase composition of the oxide systems was evaluated by XRD analysis.

Study on Hot Deformation Behavior and Microstructure Evolution of MgAlCuZnMnCe Alloy

The Mg79Al12.5Cu2.5Zn4MnCe multi-principal element alloys was prepared by induction melting under a high-purity argon. The true stress-strain curves at deformation temperatures of 250-350°C and strain rates of 0.001-1s−1 were used to establish the constitutive equations as well as the thermal processing map. The optimal hot processing parameters for the alloy were determined as a deformation temperature of 320-350°C and a strain rate of 0.1-1s−1. Further investigation into the impact of various deformation parameters on the microstructure and macrotexture of the alloy during hot compression was conducted. The findings indicate that at a deformation rate of 1s−1, the second phase of the alloy is broken and deformed. The texture intensity follows a pattern of initially decreasing and then increases as the temperature rises. The change in grain size is influenced by the deformation crushing effect, initiation of the non-substrate slip system, and grain growth. When the strain rate increases, the changes in texture intensity and distribution are not pronounced, indicating that the strain rate has minimal influence on the macro texture.

Improving the electrochemical properties of Ti3C2Tx MXene for H2S electrochemical sensor by calcination

The existence level and metabolic mechanism of hydrogen sulfide (H2S) have been proved to have an important impact on organisms, even affecting the generation and development of many neurological diseases. Therefore, it is essential to develop sensitive and accurate H2S sensors to detect H2S concentration at trace level and provide effective research tools for studying the mechanism of action of H2S on organisms. MXene is a class of two-dimensional transition metal carbonitrides with a graphene-like structure, which indicating great application prospects as a biosensor due to its large specific surface area and good conductivity. In this work, the properties of multilayer Ti3C2Tx MXene materials are optimized concerning their physical structure and functional groups. Based on the Li + intercalation method, SL-Ti3C2Tx MXene is prepared by a mild route, and its electrochemical performance is optimized by high temperature calcination under high purity argon conditions. The change in material properties at high temperature is discussed through structural and chemical analysis, and the optimal calcination temperature is determined to be 700 °C. The constructed H2S electrochemical sensor exhibits high stability and reproducibility in applications, with a detection range of 0.1–500 μM, and the detection limit is reduced to 5.77 nM.

Effects of carbon doping on annealing behavior of a CoCrFeNiMn high-entropy alloy

A 1 at% carbon non-equiatomic doped Co19Cr5Fe38Ni19Mn19 high-entropy alloy was synthesized by vacuum arc-melting in a high-purity argon atmosphere, followed by homogenization, cold rolling, and annealing under various conditions. The evolutions of microstructure and mechanical properties during annealing were systematically studied and compared with the carbon free alloy. Results showed that nano-sized fibrous deformation grains were formed in the 90% cold rolled alloys, resulting in high strength but low plasticity. Recovery sub-structures and recrystallized grains gradually formed with increasing annealing temperature, leading to a significant decrease in defect density, thereby softening the materials and increasing their plasticity. The early stage of recovery was mainly related to the migration of vacancy and interstitial carbon atoms, while dislocation climb became the main recovery mechanism in the late recovery stage. The carbon-doped alloy exhibited a higher recovery activation energy compared with the carbon free alloy. Therefore, 1 at% interstitial carbon effectively increased the recovery and recrystallization resistance of the Co19Cr5Fe38Ni19Mn19 alloy.

ELECTROLYTIC CATALYSTS BASED ON TUNGSTEN AND CARBON COMPOUNDS FOR THE HYDROGEN EVOLUTION REACTION

The hydrogen evolution reaction (HER) is one of the most promising methods of obtaining high-purity hydrogen. However, the high cost and limited resources of materials with low cathodic hydrogen evolution overvoltage values, such as platinum group metals, are the main obstacles to the use HER for obtaining hydrogen on an industrial scale. Therefore, it is necessary to develop new alternative materials and methods of their production. One of the promising materials are catalysts based on refractory metals, in particular tungsten carbides. Metal tungsten can also be used for these purposes. In our opinion, high-temperature electrochemical synthesis (HTES) in molten salts can be a promising method of obtaining materials with properties that meet the requirements for effective catalysts, namely: ultra-dispersity, high specific surface area, mesoporosity and defective structure, high chemical and electrochemical stability. Therefore, the purpose of this work is to evaluate the electrocatalytic activity of a group of materials for HER, which are obtained by HTES in melts. Four samples of electrolytic materials were chosen for the study: tungsten, carbon, tungsten mono- and semi-carbides (WC and W2С). All samples were characterized in detail using X-ray diffraction (phase composition), SEM (morphology), Raman spectroscopy (structure of carbon phases), DTG (free carbon content).
 Based on the analysis of the obtained data, it was established that all samples can be used as catalysts: crystallites have a nanometer size and a large number of structural defects; morpho­logy provides increased surface area; tungsten carbide particles are covered with a layer of free carbon, which prevents oxidation of carbide to WO3, which has a lower catalytic acti­vity; carbon particles are nanosized (20–30 nm) and contain a large number of structural defects; tungsten carbide-based samples contain free carbon, which increases the specific surface area, but does not cause clogging of pores.
 Polarization measurements were carried out at room temperature at a polarization rate of 5 mV/s in a standard three-electrode cell with an Ag|AgCl reference electrode. 1N H2SO4 was used as a base solution, which was bubbled with high-purity argon. Onset potentials for all samples are -0.05 – -0.25 V (in order WC/C – W2C/WC/C – C – W). The overvoltage and Tafel slope were calculated and WC/C composite was shown to have the lowest values of -0.2 V and -75 mV, respectively.
 Electrolytic composite of tungsten carbide/carbon have demonstrated the best characteristics, so we plan to continue the development of synthesis method of carbide compounds, which will allow us to reveal even greater potential of carbide catalysts and pave the way for their wide application in catalytic processes.

ELECTROREFINING OF URANIUM ALLOYS CONTAINING PALLADIUM AND NEODYMIUM IN 3LiCl–2KCl–UCl<sub>3</sub> MELTS

The technology of pyrochemical processing of mixed nitride uranium-plutonium spent fuel, realizable at the experimental and demonstration energy complex of the site of the Siberian Chemical Plant, includes several operations with the ultimate goal of isolating the target fission products. It’s planned to use the electrofining of the products of the previous stage, metallized spent nuclear fuel, аs the penultimate stage of processing. It’s necessary to determine the processes and technological modes of electrolytic refining of alloys modeling the product of this stage of the processing module to implement electrolytic refining. This paper presents the results of electrofining of model alloys (simulating the raw materials of the stage of electrofining processing) on an enlarged laboratory electrolyzer. The initial parameters of uranium refining processes in melts based on 3LiCl–2KCl–UCl3 were determined earlier. The basic parameters of refining were the use of electrolyte 3LiCl–2KCl–UCl3 (10.1 wt % UCl3) and conducting experiments at 550°C. Uranium alloys containing palladium and neodymium were prepared by direct fusion of uranium metal, PdAP-1 grade palladium metal powders and neodymium metal (99.99%) in a medium of high-purity argon (99.998%). The data obtained showed that at a temperature of 550°C, cathode precipitates are typical dendritic forms of alpha-uranium in rhombic syngony with a tendency to needle formation with an increase in cathode current density. An increase in the company time and cathode current density leads to a decrease in the current output due to short-circuiting of the electrodes with cathode sediment needles or metal shedding from the cathode. The modes of the cathode process have been experimentally refined as a result of electrofining. When electrofining alloys U–Pd(1.59 wt %), U–Pd(1.62 wt %), U–Pd(1.54 wt %), U–Pd(1.58 wt %)–Nd(5.64 wt %), U–Pd(1.84 wt %)–Nd(6.49 wt %), U–Pd(1.79 wt %)–Nd(6.54 wt %), uranium cathode precipitates were obtained, which were subjected to chemical analysis, which showed the high purity of the resulting metallic uranium, as well as the absence of metallic palladium and molybdenum in it. The palladium purification coefficient exceeds 5000, the neodymium purification coefficient exceeds 1000, which meets the requirements for purification from fission products at this stage of pyrochemical processing of spent fuel. Palladium accumulates in anode slime, while the bulk of neodymium passes into the molten electrolyte.

Corrosion of iron–nickel–chromium alloys in high temperature carbonate salt under argon atmosphere

Next generation concentrated solar thermal power can produce receiver temperatures up to 800 °C, however current solar salt based thermal storage is limited to 560 °C. Eutectic salt mixtures with high melting temperatures are potential latent heat energy storage media, and store heat in a solid-liquid phase change. This approach reduces the amount of material required, and therefore physical size of the storage system. This work investigates the compatibility of a binary eutectic mixture of 52.81 wt% K2CO3 and 47.19 wt% Na2CO3 salt with three high temperature alloys (316L, 347H and 800H) was assessed at the maximum proposed temperature of 750 °C under high purity argon cover gas.This salt proved to be very aggressive to the alloys tested, with corrosion rates determined to be approximately 1 mm/year for the 316L and 800H alloys, and up to 10 mm/year for 347H. The corrosion product was found to consist of sodium chromite (NaCrO2) and iron and nickel oxides. After testing niobium was detected in the solidified salt in greater amounts than in the corrosion product, indicating that the niobium corrosion product was soluble in the salt. Additionally, the 800H experienced significant grain boundary oxidation, throughout the test sample.A corrosion mechanism is proposed, based on chemical thermodynamics, which suggests that the salt will dissociate when in contact with metal at a lower temperature than previously determined. Likely corrosion reactions are discussed, and the higher corrosion rate for the niobium containing 347H was attributed to an oxygen producing reaction, which accelerates the attack on the metal.

Development of new Ti50Zr25Nb20Cu5–Ag high-entropy alloys with excellent antibacterial property, osteo-conductivity and biocompatibility in vitro and in vivo

• New Zr–Ti–Nb–Cu–Ag high-entropy alloys(HEAs), especially HEACu 2.5 Ag 2.5 showed better antibacterial ability against Staphylococcus aureus than Ti–6Al–4V. • Excellent osteo-conductivity of HEAs was observed in vitro. • HEACu 2.5 Ag 2.5 can prevent serious bacterial infections peri-implants, with a lower PCT in infection models. A new series of medical antibacterial high-entropy alloys (HEAs) with composition Ti 50 Zr 25 Nb 20 Cu 5– x Ag x ( x = 0 at.%, 1 at.%, and 2.5 at.%) were developed by arc-melting the mixture of pure elements under a high-purity argon atmosphere. The cytotoxicity, osteo-conductivity, and antibacterial properties of these HEAs were systematically investigated in vitro, along with their in-vivo biocompatibility and antibacterial properties. These HEAs, especially Ti 50 Zr 25 Nb 20 Cu 2.5 Ag 2.5 , showed better antibacterial ability against Staphylococcus aureus than Ti–6Al–4V, which has a nearly 99% antibacterial rate in vitro. Moreover, ion release and cytotoxicity tests showed that these HEAs had excellent biosafety, similar to or better than that of Ti–6Al–4V. Osteoblasts were used to evaluate the osteogenic activity of these HEAs, and good osteo-conductivity was observed in vitro. In a Sprague-Dawley rat infection model, Ti 50 Zr 25 Nb 20 Cu 2.5 Ag 2.5 showed remarkable antibacterial properties compared to Ti–6Al–4V. The in-vivo biocompatibility results showed that Ti 50 Zr 25 Nb 20 Cu 2.5 Ag 2.5 did not increase biotoxicity compared to Ti–6Al–4V. The excellent biocompatibility and antibacterial properties of the Ti–Zr–Nb–Cu–Ag HEAs are expected to enable the prevention of periprosthetic/peri-implant infections in the future.

Structural, magnetic and magnetocaloric properties of Laves phase (Gd,Sm)Co[formula omitted] compound

In the present work, the structural, magnetic, and magnetocaloric properties of the intermetallic Gd1−xSmxCo2 (x=0.5,0.6 and 0.7) compounds have been systematically studied. Samples were prepared by arc melting under high pure argon and homogenized at 800 K to minimize the impurity phases. X-ray diffraction (XRD) coupled with Rietveld analysis has shown that all samples crystallize in the cubic MgCu2-type structure (Space group Fd-3 m). Refinement results show that the unit cell parameter increases with increasing Sm content. The magnetic measurement reveals that the Sm content reduces the Curie temperature TC from 404 (for x=0) to 263 K (for x=0.7). The magnetic entropy change of the samples as function of temperature and applied magnetic field were calculated from the isothermal magnetization curves using Maxwell relation. The relative cooling power RCP and the temperature-averaged entropy change (TEC) have been reported. Furthermore, the magnetocaloric behavior is studied using the scaling laws and the phenomenological universal curve.

ANODIC PROCESSES OF URANIUM ALLOYS CONTAINING PALLADIUM AND NEODYMIUM IN 3LiCl–2KCl-UCl<sub>3</sub> MELTS

At the reprocessing module of the pilot demonstration power complex site of the Siberian Chemical Combine, a combined technological scheme for the reprocessing of mixed nitride uranium-plutonium spent fuel consisting of pyrochemical operations, hydrometallurgical refining of uranium, plutonium and neptunium is implemented step by step. According to this scheme, the target pyrochemical reprocessing products, purified from the main mass of fission products with actinoid content not less than 99.9%, are sent for hydrometallurgical reprocessing. For pyrochemical reprocessing it is necessary to develop a technology of electrorefining of metallised spent nuclear fuel. To carry out electrolytic refining it is necessary to define processes and regimes of anodic dissolution of alloys simulating product of this head operation “metallization”. In the present work the results of investigations of processes of anodic dissolution of U–Pd and U–Pd–Nd model alloys with different concentrations of palladium and neodymium in melts based on 3LiCl–2KCl–UCl3 (10.1 wt % UCl3) at 550°C using different methods are presented. Uranium alloys containing palladium and neodymium were prepared by direct alloying of uranium metal and palladium metal powders of PdAP-1 grade, and neodymium metal (99.99%) in high-purity argon medium (99.998%). Electrochemical measurements were performed using an Autolab 302N potentiostat/halvanostat equipped with a Booster 20A high-current module. The anodic polarisation curves consist of only one oxidation wave which was attributed to the dissolution of uranium metal. Increasing the palladium content in the alloy from 1.5 to 10.0 wt %, does not affect the shape of the polarisation curves. The increase of neodymium content in the alloy from 1.0 to 10.0 wt % also does not affect the shape of polarization curves. Electrorefining parameters of uranium alloys containing palladium and neodymium were determined. The limiting current density of uranium evolution from uranium alloys containing palladium and neodymium in the electrolyte 3LiCl–2KCl–UCl3 (10.1 wt % UCl3) at 550°C was 0.4 A/cm2. It was shown that palladium does not diffuse into the melt as a result of anodic dissolution and neodymium accumulates in the electrolyte only when the alloy is refined with 10.0 wt % neodymium, which is much higher than the future real concentrations of electrotreated uranium alloy components in the technological chain of spent nuclear fuel processing.

Microstructure and Mechanical Properties of Biomedical Ti-Zr-Nb-Ta-Sn High-Entropy Alloys

Ti(50-x)Zr38NbxTa8Sn4 high-entropy alloys with x = 0, 10, and 20 at.% were produced by vacuum arc melting in a high-purity argon atmosphere. The initial microstructures consisted of equiaxial bcc grains with sizes of 115 ± 30 µm, 250 ± 60 µm, and 280 ± 70 µm for the Ti30Nb20, Ti40Nb10, and Ti50Nb0 alloys, respectively. The Ti30Nb20 and Ti40Nb10 alloys showed untypical mechanical behavior with a short strain-hardening stage followed by a gradual decrease in flow stress after reaching the yield point. Although these two alloys had some inclination toward macroscopic strain localization, their tensile elongation was similar to that obtained in the Ti50Nb0 alloy, which had a more extended stage of uniform deformation. The differences were associated with distinct microstructures observed after deformation to fracture. The formation of dislocation bands and the activation of cross-slip at the microscale, as well as the appearance of kink bands at the mesoscale, can result in plastic instability. In contrast, a lamellar-like microstructure with parallel dislocation bands, such as the one observed in the Ti50Nb0 alloy, can ensure a more stable mechanical behavior. The developed alloys (Ti30Nb20 and Ti40Nb10) have properties that make them highly attractive for biomedical application due to a combination of very high yield strengths (1090 and 930 MPa, respectively), low Young’s moduli (~78 and ~69 GPa, respectively), reasonable ductility, and excellent biocompatibility.