Mo Rod Research Articles

In-situ redox conditions in hydrothermal diamond-anvil cell experiments using various metal gaskets

Hydrothermal diamond-anvil cells (HDACs) have been widely used in various research fields since they were introduced in 1993. Unlike temperature (T) and pressure (P), the redox states of the samples in HDAC experiments were poorly controlled or measured; they were usually estimated by observing the reduction/disappearance of redox-sensitive mineral(s) (e.g., Mo metal) and corresponding formation and growth of such mineral(s) (e.g., MoO2) without in-situ redox measurement. In this study, we demonstrated the generation of H2 during experiments using various metal gaskets, including inert (Re) and chemically more reactive metals (Ni, Co, Mo, and W), in the pure H2O system under various P-T conditions. A technique for quantitative Raman spectroscopic analysis of H2 in HDAC is designed. Based on this technique, the oxygen fugacity (fO2) values of Mo-MoO2 buffer at the experimental P-T conditions were then calculated from these measured H2 pressures. We demonstrated that steady-state redox control can be maintained at a fixed T between 400 and 500 °C in HDAC experiments using a Mo gasket for durations of up to two hours and for those using a Re gasket with an additional Mo rod in the sample between 400 and 800 °C for durations of up to 90 min, regardless of the considerable changes in sample pressure. This demonstration was established by the balance between the rates of H2 generation and H2 loss from the sample chamber. The loss of H2 enhanced the consumption of H2O and therefore reduced the sample pressures during the experiments.We believe that hydrogen contents in every HDAC experiment, which attempt to control the redox state, need in situ measurement, then estimate the real redox state and compare it to thermodynamic equilibrium prediction. To enhance in situ redox control and measurements, modifications of HDAC are required for improving the quantitative Raman spectroscopic analysis technique in both sensitivity and accuracy.

Preparation of zirconium metal through electrolysis of zirconium oxycarbonitride anode

• A single phase zirconium oxycarbonitride was prepared through carbothermal reduction route using ZrO 2 and graphite powder as raw materials. • The zirconium oxycarbonitride has good chemical stability in NaCl-KCl melt and also exhibits good anodic dissolution. • Zirconium metal was produced by electrolysis using zirconium oxycarbonitride as anode in NaCl-KCl melt, which indicated that zirconium oxycarbonitride was a suitable consumable material for the electrolytic preparation of zirconium. A single phase zirconium oxycarbonitride was prepared through a carbothermal reduction route at 1600 °C in nitrogen atmosphere using ZrO 2 and graphite powder as raw materials. The hot-pressed zirconium oxycarbonitride block has good stability in the NaCl-KCl melt. The anodic dissolution behavior of zirconium oxycarbonitride and the reduction mechanism of zirconium ion in NaCl-KCl melt were studied by linear sweep voltammetry, electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The results show that zirconium in the anode is oxidized to Zr 2+ ions and dissolved in the molten salt. The zirconium ions diffuse to the cathode and are reduced to zirconium metal by transferring two electrons in one step. Potentiostatic electrolysis at −2.9 V was performed between a Mo rod cathode and ZrC x O y N z anode. The cathode product was detected to be zirconium metal, which indicated that zirconium oxycarbonitride was a suitable consumable anode for the electrolytic preparation of zirconium metal.

Fatigue wear test comparing vitamin-E-blended crosslinked polyethylene and conventional polyethylene in a Posterior Dynamic Stabilization System of the spine in the laboratory

BackgroundAlthough artificial joints using polyethylene have been developed for various joints, the development of Posterior Dynamic Stabilization system of the spine using polyethylene has proceeded at a much slower pace. There are no studies which compare the abrasion resistance of vitamin-E-blended crosslinked polyethylene (VE) and conventional polyethylene (Virgin) in the spinal region. The purpose of this study was to compare the wear resistance of VE and Virgin in a Posterior Dynamic Stabilization System of the spine. MethodsPosterior Dynamic Stabilization System of the spine uses a polyethylene ball as a sliding surface. A fatigue wear test was repeated up to 1 million cycles at a speed of ±5°, 1 Hz while the rod was being pulled at a load of 50 N. Balls were compared using VE and Virgin in 6 samples each. Ti-6AL-4 V (Ti 64) and Co–Cr–Mo (CoCr) rods were used. Abrasion loss and shape change of the polyethylene balls were compared. ResultsWhen Ti 64 was used as the rod, the average wear amount was −0.01 mg (0.02 mg, 0.01 mg, −0.06 mg) for VE, and 0.23 mg (0.18 mg, 0.13 mg, 0.38 mg) for Virgin. When CoCr was used as the rod, the average wear amount was 0.42 mg (0.71 mg, −0.06 mg, 0.61 mg) for VE, and 0.73 mg (0.72 mg, 0.70 mg, 0.76 mg) for Virgin. Most polyethylene samples showed indentations of 0.1 m or less at the contact point with the set screw. In the combination of Virgin and CoCr, a white patch was observed on the inner side of the polyethylene samples, with a maximum depression of 0.1 mm. ConclusionsA fatigue wear test showed VE to be more efficient in abrasion resistance than Virgin in a Posterior Dynamic Stabilization System of the spine in the laboratory.

Synthesis and kinetic study of Mo(Si,Al)2 coatings on the surface of molybdenum through hot dipping into a commercial Al-12 wt.%Si alloy melt

Mo(Si, Al)2 coatings were synthesized through hot dipping of Mo rods into a commercial Al-12 wt.% Si alloy melt in the temperature range of 750 to 950 °C for 15 to 150 min. The structure of the coatings was characterized by X-ray diffraction analysis. In addition, optical and scanning electron microscopes along with energy dispersive spectroscopy were employed for microstructural and chemical analyses, respectively. For the sample treated at 750 °C, Mo(Si, Al)2 layers were only formed at high dipping times. An increase in the temperature up to 850 °C facilitated the formation of the coatings and a uniform layer of Mo(Si, Al)2 with 40 to 60 µm thickness was obtained after 60 min. However, a two-layer coating was observed after processing at 950 °C for 60 min. The first layer attached to the substrate mainly consisted of nano-sized Mo5Si3 particles dispersed in an Al8Mo3 matrix. The second layer had a microstructure containing Al8Mo3 and Mo(Si, Al)2 phases. Furthermore, some transverse cracks were detected across the coatings obtained at both 850 °C and 950 °C. The rate of the formation of the coating obeyed the linear law and its activation energy was estimated by the Arrhenius equation as 110 kJ/mol.

Al Electrodeposition in Molten CaCl2 with Various Calcium Aluminates

An innovative production process of Al metal is desired to reduce CO2 and perfluorocarbon gas generation. Our previous study showed that calcium titanate and silicate dissolved in molten CaCl2. Ti and Si metals could be electrodeposited, and it was indicated that Ti and Si reductions depended on the molar ratio of CaO to TiO2 or SiO2. In this study, direct production of liquid Al metal was attempted in molten CaCl2 with various calcium aluminates.Molten CaCl2 at 1373 ~ 1573K in an Ar atmosphere was used as a bath. Calcium aluminate (molar ratio of CaO to Al2O3, RCaO/Al2O3 =1.0, 12/7 or 3.0) was prepared by sintering a molded mixture of CaO and Al2O3, and it was added in CaCl2 beforehand. Mo and graphite rods were used a working and counter electrode, respectively. Mo wire was used as a quasi-reference electrode. The cathodic reaction was investigated by cyclic voltammetry, and potentio-static electrolysis was carried out. The electrodeposit was analyzed by XRD and SEM-EDX.Although no sharp current peak was seen, cathode current increased overall with calcium aluminate addition. The shape of CVs slightly changed with RCaO/Al2O3, but RCaO/Al2O3 seemed not to affect Al reduction significantly.Al and Al-Mo alloy were detected in the electrode after the electrolysis at -1.8V at 1573K regardless of RCaO/Al2O3, but the Al amount was very small. So, a Mo cathode with BN receiver in the bottom shown Fig.1 was used to prevent deposited Al metal from running down from the cathode. Al metal covered the surface by electrolysis, and a thick Al-Mo alloy layer was found in its cross section. It was shown that calcium aluminate dissolved in molten CaCl2 above 1573K, and that Al metal could be deposited electrochemically. The molar ratio of CaO to Al2O3 slightly affected the Al deposition though its influence have not clarified well.

Effect of Iron Particles on the Coke Solution Loss Reaction.

The coke solution loss reaction was investigated by using a well-type Si–Mo rod electric furnace. The effects of the CO2 flow rate, reaction time, loading mode, and loading amount of iron particles on the coke solution loss reaction were investigated. By comparing the SEM and EDS before and after the reaction of loaded iron particle coke, the reasons for the influence of loading mode on the coke solution loss reaction were explored, and the mechanism behind it was further explored. The experimental results show that there is a positive proportional relationship between the CO2 flow rate and reaction time with coke solution loss reactivity. The adsorption and addition of iron oxide play an important role in promoting the coke solution loss reaction, but when the saturation point of iron oxide loading is exceeded (1%), the adsorption load of iron particles has little effect on the coke solution loss reaction. At the same reaction temperature, the carbon conversion of the adsorption method is 10% larger than that of the addition method. From the analysis of SEM, it can be seen that the mechanism of iron particles affecting the coke solution loss reaction is different under the two loading modes. In the addition method, some iron particles are wrapped in a coke pore wall matrix, so they cannot play a role. In the adsorption process, iron particles are uniformly distributed on the coke surface, which provide more effective catalytic active centers. In addition, when iron particles are loaded by the addition method, they participate in coke formation, which affects the coke structure and then affects the coke solution loss reaction. The iron particles in the adsorption method play a catalytic role in the coke solution loss reaction.

Direct alloying of immiscible molybdenum-silver system and its thermodynamic mechanism

Direct alloying is difficult to be realized in an immiscible Mo-Ag system with a positive formation heat due to the absence of thermodynamic driving force at equilibrium. In this work, a direct alloying method is developed to realize the direct alloying between Mo and Ag and construct Mo-Ag interface. The direct alloying method was mainly carried out through a direct diffusion bonding for Mo and Ag rods at a temperature close to the melting point of Ag (TmAg). Then the microstructure and phase constitution of the as-constructed Mo-Ag interface are characterized. The results show that Mo-Ag metallurgical bonding interface has been constructed successfully, indicating that a direct alloying in the immiscible Mo-Ag system has been realized. Additionally, mechanical tests are carried out for the Mo-Ag joints prepared through the direct alloying method. The test results show that the average maximum tensile strength of the joints is about 107 MPa. The effect of alloying parameters on the tensile strength is also discussed, which shows that there is an effective temperature range for the direct alloying between Mo and Ag. Lastly, an improved thermodynamic model that considers the formation of Mo-Ag crystalline and amorphous phase is presented to reveal the thermodynamic mechanism of the direct alloying. Combining the calculation and differential scanning calorimetry (DSC) tests results, the Gibbs energy diagram for the direct alloying is obtained. It is confirmed that the co-release of storage energy and surface energy can serve as the thermodynamic driving force to overcome the effect of positive formation heat and lead to direct alloying for Mo-Ag systems.

Subgrains, Texture Evolution, and Dynamic Abnormal Grain Growth in a Mo Rod Material

The roles of subgrains, texture, and surface energy during dynamic abnormal grain growth (DAGG) were examined in a commercial-purity Mo rod material. DAGG was observed in this material during tensile deformation at 2023 K (1750 °C). Cooling of specimens after tensile testing was sufficiently rapid to preserve both subgrain structures developed during deformation and several abnormal grains at early stages of growth. These and other microstructural features were characterized to evaluate how subgrains and boundary character influence the early stages of DAGG. Subgrains were observed in the deformed polycrystalline material but were generally absent in newly formed abnormal grains. This was identified as the cause of the sudden drop in flow stress observed at the initiation of DAGG. It is proposed that subgrain intersections with abnormal grain boundaries provide a driving pressure for DAGG. Subgrains within the deformed polycrystals were observed to locally change the boundary curvature at their intersections with abnormal grain boundaries, which likely encouraged growth of the abnormal grains into the deformed polycrystals. Abnormal grains produced by DAGG retained crystallographic orientations and boundary characters that closely resembled those of the polycrystalline material from which they grew. This suggests that neither differences in orientation nor boundary character were important to DAGG in this material.

Localized surface plasmon resonance H2 detection by MoO3 colloidal nanoparticles fabricated by the flame synthesis method

Beside the noble metal nanoparticles (NPs), plasmonic semiconductors are being developed nowadays for a variety of applications such as catalyst, phototherapy and sensing technologies. In the present study, colloidal plasmonic MoO3 NPs with <20 nm mean size are prepared by flame synthesis as a rapid, cost effective, catalyst-free and atmospheric route. A Mo rod was converted to oxide nanopowder in an oxyhydrogen flame and collected on a water-cooled rotating substrate. Colloidal solutions of these particles were made by dispersing the MoO3 NPs into DI water. As a palladium precursor, solutions of aqueous PdCl2 were added to the colloidal NPs to make them sensitive to hydrogen. Formation of cubic Pd NPs in among the MoO3 NPs were recognized in TEM images for hydrogen-exposed samples. Upon hydrogen injection, a localized surface plasmon resonance (LSPR) absorption band was appeared in the UV–Vis absorption spectra at 700–800 nm region, which began to decline by further exposure time. Within few seconds of gas exposure, samples turned blue and longer exposure made them brownish. The LSPR peaks exhibited a spectral blue shift with a more hydrogenation, in agreement with the existing plasmonic model. In addition, a correlation between optical band gap and LSPR intensity was found. The colloidal Pd-MoO3 solutions then were employed for LSPR sensing of hydrogen at a concentration range of 0–5%. A pronounced LSPR linear sensitivity toward low concentration (<2.5%) of hydrogen was observed.

Variations of the field of view depending on the Si deflector shape in a microcolumn

A microcolumn is widely investigated as one of the strong candidates for multiple electron beam systems. In the microcolumn, one or two octupole deflectors are usually adopted to scan the electron beam, and the octupole deflector is assembled by placing eight deflector electrodes symmetrically around the electron beam path. The deflector electrodes are composed either of Mo rods or of Si electrodes fabricated through appropriate micro electro mechanical systems processes. Usually, to expand the field of view and reduce the electron beam distortion, the double-deflector method is used. However, the wiring for electrical connection to each electrode and the operation of the octupole deflector are rather complicated. In order to improve the assembly and performance of the octupole deflector, the authors devised a modified Si deflector and tested its performance.

Fatigue pre-cracking and fracture toughness in polycrystalline tungsten and molybdenum

Fatigue pre-cracking performance and fracture toughness in polycrystalline tungsten (W) and molybdenum (Mo) have been investigated in relation to grain boundary (GB) configuration with respect to the crack advance direction. Sub-sized, single edge notched bend (SENB) specimens with three different orientations, R-L (ASTM notation) for a forged Mo rod and L-S and T-S for a rolled W plate, were pre-cracked in two steps: fully uniaxial compression fatigue loading to provoke crack initiation and its stable growth from the notch root, and subsequent 3-point bend (3PB) fatigue loading to extend the crack. The latter step intends to minimize the influence of the residual tensile stresses generated during compression fatigue by moving the crack tip away from the plastic zone. It is shown that fatigue pre-cracking performance, especially pre-crack extension behavior, is significantly affected by the specimen orientation. The R-L orientation, giving the easiest cracking path, permitted crack extension completely beyond the plastic zone, while the L-S and T-S orientations with the thickness cracking direction of the rolled plate sustained the crack lengths around or possibly within the plastic zone size due to difficulty in crack advance through an aligned grain structure. Room temperature fracture toughness tests revealed that the 3PB fatigued specimens exhibited appreciably higher fracture toughness by about 30% for R-L, 40% for L-S and 60% for T-S than the specimens of each orientation pre-cracked by compression fatigue only. This indicates that 3PB fatigue provides the crack tip front out of the residual tensile stress zone by crack extension or leads to reduction in the residual stresses at the crack tip front. Strong dependence of fracture toughness on GB configuration was evident. The obtained fracture toughness values are compared with those in the literature and its strong GB configuration dependence is discussed in connection with the appearance of pop-in.

Compatibility studies on Mo–coating systems for nuclear fuel cladding applications

To improve the safety factor of nuclear power plants in accident scenarios, molybdenum (Mo), with its high-temperature strength, is proposed as a potential fuel-cladding candidate. However, Mo undergoes rapid oxidation and sublimation at elevated temperatures in oxygen-rich environments. Thus, it is necessary to coat Mo with a protective layer. The diffusional interactions in two systems, namely, Zircaloy-2 (Zr2) on a Mo tube, and iron-chromium-aluminum (FeCrAl) on a Mo rod, were studied by aging coated Mo substrates in high vacuum at temperatures ranging from 650 °C to 1000° for 1000 h. The specimens were characterized using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and nanoindentation. In both systems, pores in the coating increased in size and number with increasing temperature over time, and cracks were also observed; intermetallic phases formed between the Mo and its coatings.

High-Speed Observation of Electrolytic Deposition of Liquid Lithium Droplets in LiCl-KCl Melt

In the case of metallothermic reduction of oxide XOx-1(s) (X=Ti, Ta, etc.) by electro-deposited liquid metal Me(=Ca, Li or their alloys), the it accompanied with dissolved Me at the vicinity of the cathode is essential, where the oxide is placed close to the cathode. In this mechanism, the dissolved Me works effectively to reduce XOx-1, even if these solids do not have any direct electronic contact with the cathode. In the case of Li-LiCl-KCl-Li2O system at 723 K, colloidal microparticle dissolution of Li occurs in addition to true dissolution. Recently, the in-situ Raman spectroscopy was carried out, and obtained from colloidal Li were in agreement with the lithium cluster, Li8. The colloidal Li formation strongly depends on the linear current density and that the current concentration should cause its formation. Although colloidal Li occurs at the liquid Li and molten salt interface, the morphology of liquid Li on the electrochemically precipitated cathode surface has not been well understood as root cause. High-speed photography with high-resolution image quality has been becoming possible by recent C-MOS image sensor which has been improved by recent digital optical technology. In this study, we investigated the morphology of liquid Li in molten LiCl-KCl-Li2O by recording electrode surface image obtained with digital microscope at high speed. To elucidate the mechanisms of interfacial morphology on the basis of three-dimensional shape observations, the electric resistance furnace was designed to allow the phenomena occurring within to be observed directly. The changes induced in the interface of electrodes were recorded at a rate of 500 frames per a second (fps) and a resolution of 640 × 480 pixels using a high-speed microscope (the field of view of 610 μm × 460 μm, and the length per pixel of 1.04 μm) was employed. LiCl (>99.0%) and KCl (>99.5%) were used for the melt. The eutectic mixture of LiCl–KCl (= 59:41 mol%, m.p. = 625 K) contained in a borosilicate glass crucible with flat surface was dried under vacuum at 573 K for more than one night to remove residual water and then melted. Li2O (>99.5%) was directly added to the melt as an O2-ion source in the concentration range of 0.1–1.0 mol%. The experimental temperature was 723 K. The interface temperature was measured with a K–type thermocouple with a glass protection tube. All the experiments were conducted in an Ar atmosphere (>99.9995%). The working electrode was a Mo rod (ϕ 1.5 mm, 99.95%) for cyclic voltammetry and it was used as a cathode for electrodeposition of liquid lithium. The counter electrode was a graphite rod (ϕ 10 mm). The Ag+/Ag reference electrode was employed, i.e. a silver wire (ϕ 1.0 mm, 99.99%) was immersed in the LiCl–KCl eutectic melt containing 0.5 mol% AgCl (>99.5%), which was set in a borosilicate tube. Electrochemical measurements were performed using an automatic polarization system (Hokuto Denko Corp., HZ-5000). From the snapshots corresponding to each potential in cyclic voltammograms, blue “fog” was observed are observed at about −2.46 V (vs. Ag+/Ag) with the electrodeposited Li, notably during Li dissolution reaction. The amount of colloidal Li generation decreased by Li2O addition. Chronoamperometry was conducted at -2.55 V vs. Ag+/Ag using a Mo rod electrode for 1.0 s. Photographs of the transient behavior of electrode surface in LiCl-KCl melt are shown in Fig. 1. It can be seen that droplets are formed and grow on the surface of the Mo electrode as the current is generated. It should be noted that the liquid phase precipitates grow heterogeneity on the Mo surface. Considering the “electrocapillary” theory, due to the electrostatic attraction between the droplets charge and charge in the electrode, the energy of their interface is reduced, and the wetting of the electrode should be enhanced. Nevertheless, metal droplets do not wet and spread on the electrode surface completely. Figure 1

Effect of Electrode Shape on Lithium Metal Fog in LiCl-KCl

INTRODUCTION Molten salt electrolysis is a common production process of reactive metal. The so-called metal fog formation causes the decrease in current efficiency, whereas it can be used as reductant because of its high reactivity. In our previous research, two types of metal fog were observed in LiCl-KCl; one was dark blue, and considered the dissolution of Li metal. The other had gray color and seemed to start forming at the edge of the electrode. Since this gray fog was seen at high current density, it was suggested that the current concentration at the edge caused its formation. In this paper, the effect of the surface shape of electrode on the gray metal fog formation was investigated in LiCl-KCl. EXPERIMENTAL LiCl-KCl eutectic mixture was melted at 700K. Cyclic voltammetry and potentiostatic electrolysis were performed. Mo rods of various diameters with/without screw cutting were used as working electrode. The surface area of the screw-cut electrode was estimated assuming the series of conic shapes. A carbon rod was used as counter electrode. A reference electrode was an Ag/Ag+couple in a mullite membrane. The appearance around the working electrode was directly observed to confirm the fog formation. RESULT AND DISSCUTION Cyclic voltammograms at the working electrodes of f2.0mm with/without screw cutting surfaces are shown in Fig. 1. The dark blue metal fog was formed at both electrodes, while the gray metal fog was generated only at the screw-cut electrode. The gray metal fog was observed with current decrease as reported in our previous study. It was suggested that edges affected the gray metal fog formation. In the case of f4.9mm electrode, the gray metal fog formation didn’t occur regardless of the electrode shape. The gray metal fog appeared at the screw-cut electrode of f1.5m, and the formation was intenser than the electrode of f2.0mm. To compare the voltammograms at the screw-cut electrode of different diameter, the results were re-plotted with the linear current density (Ia /Acm-1) as shown in Fig. 2, where the linear current density was defined as the division of electrolytic current by the length of the ridge. The linear current density of f2mm and f1.5mm were approximately the same, while that of f4.9mm was very small. In the formers case, the gray metal fog appeared, but its formation didn’t occur in the later. These results suggest that the gray fog formation strongly depends on the linear current density and that the current concentration should cause its formation. The changes in current density during constant potential electrolysis at the screw-cut electrodes of different diameters are shown in Fig. 3. In the electrode of f2.0mm, the gray metal fog was seen for 10 sec from the beginning, and then its formation stopped. Lithium metal deposit was seen after the stop of the formation, and the sphere-like deposit fully covered the surface about 40 sec. The behavior of the electrode of f1.5mm was almost the same, but the time length of the gray fog formation was longer than at the f2.0mm-electrode. In the electrode of f4.9mm, the gray metal fog didn’t appear from the beginning. The gray fog formation occurred at a fine electrode intenser than at a thick electrode, and screw cutting seemed to accelerate the formation. However, lithium metal deposition occurred simultaneously, and the effect by screw cutting was lost by its covering the surface. CONCLUSIONS The effect of the surface shape of electrode on metal fog formation was investigated in LiCl-KCl. Screw cutting accelerated the gray metal fog formation and the formation also depended on the diameters of the electrodes. It is concluded that the shape of electrode strongly affects the gray metal fog formation and the current concentration at the edge causes the formation. Figure 1

Elevated temperature tensile properties and deformation of directionally solidified NiAl–Mo in-situ composites

Four composition NiAl–xMo (x=7.8, 9, 13 and 16at.%) alloys were directionally solidified by a liquid metal cooling technique at a growth rate of 6μm/s. Perfectly aligned fibrous microstructures were fabricated for all four alloys. Tensile properties at elevated temperature were performed. Damage evolution and fracture characteristics at elevated temperature were also investigated. The fracture behavior of the composites in all tensile tests exhibited a ductile behavior at 1000°C. The high temperature tensile strength was found to increase with the volume fraction of Mo rods. The fibers are expected to bear the greater part of the imposed load due to the strong interface of the constituent phases. The Mo fibers' solid solution strengthened by both Ni and Al also contributes to the strength of composite.

Investigation of mass dependence effects for the accurate determination of molybdenum isotope amount ratios by MC-ICP-MS using synthetic isotope mixtures.

Methodology for absolute Mo isotope amount ratio measurements by multicollector inductively coupled plasma-mass spectrometry (MC-ICP-MS) using calibration with synthetic isotope mixtures (SIMs) is presented. For the first time, synthetic isotope mixtures prepared from seven commercially available isotopically enriched molybdenum metal powders ((92)Mo, (94)Mo, (95)Mo, (96)Mo, (97)Mo, (98)Mo, and (100)Mo) are used to investigate whether instrumental mass discrimination of Mo isotopes in MC-ICP-MS is consistent with mass-dependent isotope distribution. The parent materials were dissolved and mixed as solutions to obtain mixtures with accurately known isotope amount ratios. The level of elemental impurities in the isotopically enriched molybdenum metal powders was quantified by ICP-MS by using both high-resolution and reaction cell instruments to completely resolve spectral interferences. The Mo isotope amount ratio values with expanded uncertainty (k = 2), determined by MC-ICP-MS for a high-purity Mo rod from Johnson Matthey, were as follows: (92)Mo/(95)Mo = 0.9235(9), (94)Mo/(95)Mo = 0.5785(8), (96)Mo/(95)Mo = 1.0503(9), (97)Mo/(95)Mo = 0.6033(6), (98)Mo/(95)Mo = 1.5291(20), and (100)Mo/(95)Mo = 0.6130(7). A full uncertainty budget for the measurements is presented which shows that the largest contribution to the uncertainty budget comes from correction for elemental impurities (∼51%), followed by the contribution from weighing operations (∼26 %). The atomic weight of molybdenum was calculated to be 95.947(2); the uncertainty in parentheses is expanded uncertainty with the coverage factor of 2. A particular advantage of the developed method is that calibration factors for all six Mo isotope amount ratios, involving the (95)Mo isotope, were experimentally determined. This allows avoiding any assumption on mass-dependent isotope fractions in MC-ICP-MS, inherent to the method of double spike previously used for Mo isotope amount ratio measurements. However, data obtained in this study show that instrumental mass discrimination in MC-ICP-MS is consistent with mass-dependent Mo isotope fractionation. This was demonstrated by a good agreement between experimentally obtained and theoretically expected values of the exponent of isotope fractionation, β, for each triad of Mo isotopes.

Preparation of Ultra-High Purity Cylindrical Mo Ingot by Electron Beam Drip Melting

A cylindrical Mo ingot with ultra-high purity was obtained by electron beam (EB) drip melting process using a Mo rod. The Mo rod as a bar feeder was prepared from Mo powder by vacuum sintering and swaging processing. Most of impurities excluding W in the Mo ingot were removed down to below ppm level by three-times EB drip melting, where the purity of the Mo ingot except W was improved from the initial Mo powder purity of 3N (99.95%) to 5Nup (99.9998%). Furthermore, the gaseous impurities C, N and O in the Mo ingot were removed to a level below 5 ppm from the initial level of around 460 ppm by repetitive EB drip melting.

Microstructure and room temperature fracture toughness of directionally solidified NiAl–Mo eutectic in situ composites

The microstructure and room temperature fracture toughness of pseudo-binary NiAl–ⅹMo (ⅹ = 7.8, 9, 13 and 16 at. %) in situ composites were investigated. For all four alloys examined, uniform and well-aligned Mo fibrous structures were directionally solidified by the liquid metal cooling process at the growth rate of V = 6 μm/s, respectively. With the increase of the Mo content, the spacing of the Mo fibers decreased and the volume fraction of Mo fibers increased. Significant influence of Mo addition on the toughness was observed for the directional solidification alloys, and the fracture toughness was found to increase with volume fraction of Mo rods. Scanning electron microscopy was used to characterize the fracture behavior. Based on the results of theoretical analysis, the composite structures of these alloys provided improvement in fracture toughness over binary NiAl primarily by crack trapping and crack bridging. Interface debonding, crack deflection and microcrack linkage provided further resistance to crack growth.

Modification of NiAl–Cr(Mo)–0.15Hf alloy by Sc addition

The effect of Sc addition on the microstructure and room temperature compressive properties of NiAl–28Cr–5.85Mo–0.15 (at pct) Hf− x (wt pct) Sc ( x = 0,0.05, 0.1, 0.2, 0.3) alloys was investigated. The results show that appropriate Sc addition (no more than 0.10 wt pct) leads to the refinement of interlamellar and intercellular spacings of the eutectic NiAl/Cr(Mo) cell, and the improvement of the compressive ductility and ultimate compressive strength at room temperature. When the addition of Sc is more than 0.10 wt pct, the typical NiAl/Cr(Mo) cell structure becomes broken. With the fragment of Cr(Mo) rods embedded in NiAl matrix instead of the alternating NiAl and Cr(Mo) plates, which damages the compressive properties. In addition, when the Sc addition content increases to 0.20 wt pct, Sc-containing phase is found and tentatively identified as ScO.

Microstructure study of CVD W coating on Mo single crystal rods with 〈1 1 1〉 axial orientation by EBSD

The morphology and grain orientation of the surface and the cross section of CVD W coating on a single crystal Mo rod with an axial direction of 〈1 1 1〉 have been characterized by SEM and EBSD. An obvious preferred orientation growth has been found in the W coating. About 80% surface area of the W coating is covered by W grains with a normal direction within 10° around 〈1 0 1〉. A strong {1 0 1}〈1 1 1〉 texture has also been observed in the W coating. EBSD studies suggest that a combination of the Mo matrix introducing growth mechanism and the competing growth mechanism should be responsible for the preferred growth and texture formation.