Molybdenum Wire Research Articles

Hot‐wire vapor deposition of amorphous MoS2 thin films

AbstractAmorphous, as shown by X‐ray diffraction measurements, MoS2 films (a‐MoS2) were deposited by heating a molybdenum wire at temperatures between 500 and 700 °C in H2S at 1 Torr. As shown by Scanning Electron Microscopy measurements, the morphology of samples depends significantly on the filament temperature; at low temperature samples are homogeneous and smooth, at intermediate temperatures they exhibit a granular microstructure and at high temperatures a columnar one. X‐ray photoelectron spectroscopy measurements have shown S/Mo ratios in films varying between 2.5 and 1.5 dependent on filament temperature. Films also contain oxygen at atomic contents of 8 to 12%. As shown by XPS and Raman spectroscopy, at a filament temperature of 600 °C films are mainly composed of MoS2 also containing oxygen at an atomic ratio of 8%. Spectroscopic ellipsometry measurements made on a‐MoS2 films have shown that their band gap is of the order of 1.4 eV, slightly higher than that for the bulk crystalline material. Photoluminescence spectroscopy measurements have shown that samples exhibit a doublet of peaks at 2.8 and 3 eV blue shifted relatively to MoS2 samples composed of one or two mono‐layers. The above indicate that the electronic structure of crystalline atomic‐layer thick MoS2 is preserved in a‐MoS2 films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modeling of the K and L x-ray line structures for molybdenum ions in warm dense Z-pinch plasma

For molybdenum wire implosions on the Z-machine at Sandia National Laboratories the high-resolution measurements of x-ray spectra have been recently published. The K and L x-ray spectra modeled here within the framework of Collisional-Radiative Model using the Flexible Atomic Code package reproduce well the published data to show that such model is a reasonable one.

Characteristics of a molybdenum X-pinch X-ray source as a probe source for X-ray diffraction studies.

X-ray emission from a molybdenum X-pinch has been investigated as a potential probe for the high pressure states made in dynamic compression experiments. Studies were performed on a novel 300 kA, 400 ns generator which coupled the load directly to a low inductance capacitor and switch combination. The X-pinch load consisted of 4 crossed molybdenum wires of 13 μm diameter, crossed at an angle of 62°. The load height was 10 mm. An initial x-ray burst generated at the wire crossing point, radiated in the soft x-ray range (hυ < 10 keV). This was followed, 2-5 ns later, by at least one harder x-ray burst (hυ > 10 keV) whose power ranged from 1 to 7 MW. Time integrated spectral measurements showed that the harder bursts were dominated by K-alpha emission; though, a lower level, wide band continuum up to at least 30 keV was also present. Initial tests demonstrated that the source was capable of driving Laue diffraction experiments, probing uncompressed samples of LiF and aluminium.

Fabrication of 3D surface model with environmental materials for architectural modeling by hot cutting system

With the development of the society, green and sustainable manufacturing becomes an important issue. Also, the need for architectural modeling’s diversity becomes more urgent. To ensure environmental protection and low cost, the five-axis hot cutting system independently designed and developed by the authors is applied to the processing of EPS model. During the fabricating process, there is an interference problem between molybdenum wire and the blank. To solve this problem, the optimized algorithm is proposed in this paper. As to equipments, advanced servo motors are used to replace the existing stepper motors to ensure effective and accurate fabrication. The research is mainly composed of four parts: first, analyzing the local topological relationship with algorithm of grouping matrix; second, obtaining section contours by defining a group of discriminant conditions and outside normal vectors; third, acquiring all the cutting paths by summing every section contour in the same direction; and finally, fabricating the 3D model by using the algorithm researched. The experimental results show that EPS can be efficiently applied to fabricate architectural model with the algorithm we proposed.

Experimental research of the fine foil explosion dynamics

The work is devoted to studying of substances properties at high specific deposit energy using double-frame pulsed backlighting system. The high specific deposit energy was reached at electrical conductor explosion (ECE). Fast mode of ECE was investigated. Fine foils of aluminum, cooper, titanium and nickel were used as conductors. Experiments were carried out on the experimental complex consisting of three current generators. The first generator WEG-' was used for explosion of the fine conductors. This generator represents fast capacitor with capacity 250 nF, which was charged to voltage 10 to 30 kV. The investigated conductor was mounted in special holder and the foil contacts with the electrodes were soldered. Two other generators - radiographs XPG-1 and G2 with x-pinch load were used two frame X-ray backlighting imaging. The generators current pulses had amplitude 300 kA and rising time 180 ns with a low inductance load. Four crossed molybdenum wires with diameter of 25 μm were used to form an x-pinch. Using of the x-pinches soft x-ray radiation the images of exploded foil were registered with temporal resolution of 2 ns. The images were detected by a photo film located behind the filter. The x-ray imaging, together with the measurements of the current flowing through a conductor and voltage on the exploded conductor had allowed inferring of the energy deposited into the conductor, delay time of the bubbles formation relative to the moment of current- cutoff and the time dependence of the vapor bubbles quantity.

Experimental study of the neck formation in an X pinch

X-pinch experiments have been performed on a compact 250 kA, 180 ns pulsed power generator specially designed for this purpose at the Institute of High Current Electronics (Tomsk, Russia). The X pinches were composed of two molybdenum wires of diameter 25 μm making an angle of 36° with the z-axis. The X-pinch dynamics was recorded with a 3 ns exposure time using an HSFC Pro four-frame camera. Axial plasma jets propagating toward both the anode and the cathode were observed. The jets became noticeable within 10 ns after the onset of current flow, which approximately corresponded to the time at which the electrical explosion of the X-pinch wires occurred. The velocity of the anode-directed jet reached 107 cm/s, which was about 1.5 times the velocity of the cathode-directed jet. These high jet velocities are inconsistent with the plasma temperature resulting from the wire explosion. Hence, these jets seem to develop due to implosion of the light plasma layer stripped by magnetic forces from the wire surface, and the increase in their velocities is perhaps due to cumulative effects taking place at the X-pinch axis. The X-pinch neck formed as a rule above the initial wire cross point (closer to the anode). In this region, the plasma diameter gradually increased with time and then drastically decreased 10-15 ns prior to the x-ray pulse. Immediately before the x-ray pulse, in the (250-300 μm long) plasma neck, a lower scale constriction developed, forming a "hot spot". It has been confirmed that the anode-directed plasma jet could take some part of the X-pinch wire current because of the evident jet pinching in the anode region. This process seems to determine the neck length.

Study of the termination phase of plasma production and the formation of magnetic flux breakthroughs during wire array implosion

The phenomenon of magnetic flux breakthrough into a wire array during its implosion was studied experimentally at the Angara-5-1 facility. It is shown that breakthroughs develop in the final stage of plasma production from the wire material and occur near the initial wire position. The spatial distributions of the azimuthal magnetic field within tungsten, molybdenum, copper, and aluminum wire arrays were studied using magnetic probes. The distributions of the azimuthal magnetic field B φ(z, t) along the array height in different stages of implosion were measured, and the characteristic dimensions of regions with a nonuniform magnetic field that appear during magnetic flux breakthroughs at the outer boundary of the wire array plasma were determined. The dimensions of these regions are compared with those of the regions with depressed plasma radiation observed in frame and time-integrated X-ray images. The dynamics of the distribution B φ(z, t) in regions with a nonuniform magnetic field during breakthroughs of the azimuthal magnetic flux is compared with that of the spatial distribution of pinch radiation in the frame X-ray images in different stages of implosion. The experimental data on the characteristics of spatially nonuniform breakthroughs of the magnetic flux into the wire array are analyzed using the plasma rainstorm model proposed by V.V. Aleksandrov et al. (JETP 97, 745 (2003)). The plasma density in the region of magnetic flux breakthrough is estimated.

Comparison of Machining Responses Using Multiple Regression Analysis and Group Method Data Handling Technique of EN-19 Material in WEDM

Wire Electrical Discharge Machining (WEDM) is a specialized thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. This study outlines the development of model and its application to estimation and comparison of machining responses using Multiple Regression Analysis (MRA) and Group Method Data Handling Technique (GMDH). Experimentation was performed as per Taguchi’s L’16 orthogonal array for EN-19 material. Each experiment has been performed under different cutting conditions of pulse-on, pulse-off, current and bed speed. Among different process parameters voltage and flush rate were kept constant. Molybdenum wire having diameter of 0.18 mm was used as an electrode. Four responses namely accuracy, surface roughness, volumetric material removal rate and electrode wear have been considered for each experiment. Estimation and comparison of responses was carried out using MRA and GMDH.

Volumetric flame synthesis of one-dimensional molybdenum oxide nanostructures

A laminar counter-flow diffusion flame formed with methane/acetylene and oxygen enriched-air was used for the controlled synthesis of 1-D molybdenum oxide nanostructures directly in the gas phase. Raw material was introduced into the oxidizer side of the flame in the form of solid molybdenum wires with ∼99% purity. Molybdenum oxide vapors formed in the gas phase were transported by the gas flow in the flame environment possessing strong thermal and chemical gradients. The generated nanostructures were collected thermophoretically from the flame volume. Essential morphological variations of generated nanomaterials were observed depending on sampling position within the flame volume and probe parameters. The mechanism behind the synthesis of the spherical and 1-D nanoforms is analyzed and modeled numerically. The nanorod growth model involves monomer transport, nucleation and growth. The monomer formation is through the oxidation and vaporization of the probe material. The nucleation model is based on the classical nucleation theory. The model predicts the trajectory and growth of the formed nuclei as they are transported in the flame volume. It is considered that the ends of the cylindrical 1-D nanorods grow by the phenomenon of rough growth while the lateral faces exhibit layered growth. The growth model also considers the contribution of the monomers diffusing on the nanoparticle surface as well as the effect of the atoms impinging directly onto the growth sites and compares their relative contributions. The model qualitatively predicts the variation of aspect ratio of the formed nanomaterials with increase of monomer concentration as observed in the experiments.

Comparative Study of Electrode Wear Estimation in Wire EDM using Multiple Regression Analysis and Group Method Data Handling Technique for EN-8 and EN-19

Wire Electrical Discharge Machining (WEDM) is a specialized thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. In WEDM a specific wire run-off speed is applied to compensate wear and avoid wire breakage. Since the workpiece generally stays stationary and short discharge durations are applied, the relative displacement between wire and workpiece during one single discharge is very small. This study outlines the development of model and its application to optimize WEDM machining parameters using the Taguchi's technique which is based on the robust design. Present study outlines the electrode wear estimation in the wire EDM. EN-8 and EN-19 was machined using different process parameters based on L'16 orthogonal array. Among different process parameters voltage and flush rate were kept constant. Parameters such as bed speed, current, pulse-on and pulse-off was varied. Molybdenum wire having diameter of 0.18 mm was used as an electrode. Electrode wear was measured using universal measuring machine. Estimation and comparison of electrode wear was done using multiple regression analysis and group method data handling technique. From the results it was observed that, measured electrode wear and estimated electrode wear correlates well with respect to MRA than GMDH.

Signatures of hot electrons and fluorescence in Mo Kα emission on Z

Recent experiments on the Z accelerator have produced high-energy (17 keV) inner-shell K-alpha emission from molybdenum wire array z-pinches. Extensive absolute power and spectroscopic diagnostics along with collisional-radiative modeling enable detailed investigation into the roles of thermal, hot electron, and fluorescence processes in the production of high-energy x-rays. We show that changing the dimensions of the arrays can impact the proportion of thermal and non-thermal K-shell x-rays.

Comparison of Machining Performances Using Multiple Regression Analysis and Group Method Data Handling Technique in Wire EDM of Stavax Material

Wire Electrical Discharge Machining (WEDM) is a specialized thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. This study outlines the development of model and its application to estimation of machining performances using Multiple Regression Analysis (MRA) and Group Method Data Handling Technique (GMDH). Experimentation was performed as per Taguchi's L’16 orthogonal array for Stavax (modified AISI 420 steel) material. Each experiment has been performed under different cutting conditions of pulse-on, pulse-off, current and bed speed. Among different process parameters voltage and flush rate were kept constant. Molybdenum wire having diameter of 0.18mm was used as an electrode. Four responses namely accuracy, surface roughness, volumetric material removal rate and electrode wear (EW) have been considered for each experiment. Estimation and comparison of responses was carried out using MRA and GMDH.

Process Optimization and Estimation of Machining Performances Using Artificial Neural Network in Wire EDM

Wire Electrical Discharge Machining (WEDM) is a specialized thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. This study outlines the development of model and its application to optimize WEDM machining parameters using the Taguchi's technique which is based on the robust design. Experimentation was performed as per Taguchi's L’16 orthogonal array. Each experiment has been performed under different cutting conditions of pulse-on, pulse-off, current, and bed speed. Among different process parameters voltage and flush rate were kept constant. Molybdenum wire having diameter of 0.18mm was used as an electrode. Three responses namely accuracy, surface roughness, volumetric material removal rate have been considered for each experiment. Based on this analysis, process parameters are optimized. ANOVA is performed to determine the relative magnitude of the each factor on the objective function. Estimation and comparison of responses was done using artificial neural network.

Влияние параметров ВЧ-разряда и параметров нагревателя на температуру подложки в плазмохимическом реакторе «Алмаз» для синтеза углеродных алмазоподобных пленок

The paper presents the research results on the device for obtaining diamond-like films from gas phase, constructed and tested in the Institute for Nuclear Research of the National Academy of Sciences. The device is based on a high-frequency (HF) discharge (13,56 MHz) into controlled crossed magnetic and electric fields. The discharge is excited in H2+CH4 or H2+CH4+Ar mixtures in different proportions. Working pressure in the chamber is 10–1—10–2 Torr. From the obtained results, the authors determine the time period for establishing of equilibrium substrate temperature at different HF discharge and main heater parameters. HF discharges, in the conditions of this study, at substrate temperatures above 600°C have virtually no influence on the temperature rise of the substrate. In addition, a new heater is proposed in order to increase the attainable temperature and reduce the time for establishing the equilibrium substrate temperature. A fehral heater can not heat the substrate to temperatures above 650°C. A molybdenum wire as a material of the heater can ensure the substrate holder temperature above 1000°C in a hydrogen atmosphere, but it has a short lifespan of a few months at the maximum temperature under daily use.

Estimation of Machining Performances Using MRA, GMDH and Artificial Neural Network in Wire EDM of EN-31

Wire Electrical Discharge Machining (WEDM) is a specialized thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. This study outlines the development of model and its application to estimation of machining performances using Multiple Regression Analysis (MRA), Group Method Data Handling Technique (GMDH) and Artificial Neural Network (ANN). Experimentation was performed as per Taguchi's L’16 orthogonal array. Each experiment has been performed under different cutting conditions of pulse-on, pulse-off, current and bed speed. Among different process parameters voltage and flush rate were kept constant. Molybdenum wire having diameter of 0.18mm was used as an electrode. Three responses namely accuracy, surface roughness, volumetric material removal rate have been considered for each experiment. Estimation and comparison of responses was carried out using MRA, GMDH and ANN.

Research of Composite Coating Composed of Mo Wire and High-Cr Cast Iron Made by Laser Cladding Technology

The experiments of laser cladding on the surface of H13 steel were made. Molybdenum (Mo) wire and high-chromium (Cr) cast iron powder were used as cladding material. The microstructure and hardness of laser cladding layer were studied. The experiments showed that Mo wire and high-Cr cast iron cladding layer had better properties such as minute crystals, high density, no crack, no gas cavity and good metallurgical bonding with base metal. There was a slight melting on the surface of Mo wire which would greatly increase the binding force between Mo wire and high-Cr cast iron. Mo wire could make grain refine and limit the growing of carbide. The average hardness of junction zone of Mo wire and high-Cr cast iron was 750HV0.2 which was higher than that of cladding zone composed of high-Cr cast iron (650HV0.2).

Research on the Process Parameters of W-Mo-Dy Co-Diffusion by Plasma

W-Mo-Dy alloying layer were prepared on the surface of different carbon content of steel by plasma alloying technique and the optimum parameters were obtained under the experimental conditions. The optimal process parameters are as follows: Source material is Φ 5mm × 30mm tungsten and molybdenum wire, the number of W:Mo is 2:8, spacing is 10~15mm; Rare earth Dy using an independent plate source and evenly arranged on the Φ 100mm the barrel auxiliary cathode; the source voltage is-850~-900V, the cathode voltage is-700~-750V, the limit vacuum is 2Pa; the working pressure is argon gas, gas pressure is 30pa, the insulation temperature is 1020°C; the holding time is 4.5h. Available to meet the test requirement and obtain the alloying layer thickness is 128um.

Dynamic Abnormal Grain Growth in Molybdenum

A new abnormal grain growth phenomenon that occurs only during continuous plastic straining, termed dynamic abnormal grain growth (DAGG), was observed in molybdenum (Mo) at elevated temperature. DAGG was produced in two commercial-purity molybdenum sheets and in a commercial-purity molybdenum wire. Single crystals, centimeters in length, were created in these materials through the DAGG process. DAGG was observed only at temperatures of 1713 K (1440 °C) and above and occurred across the range of strain rates investigated, ~10−5 to 10−4 s−1. DAGG initiates only after a critical plastic strain, which decreases with increasing temperature but is insensitive to strain rate. Following initiation of an abnormal grain, the rate of boundary migration during DAGG is on the order of 10 mm/min. This rapid growth provides a convenient means of producing large single crystals in the solid state. When significant normal grain growth occurs prior to DAGG, island grains result. DAGG was observed in sheet materials with two very different primary recrystallization textures. DAGG grains in Mo favor boundary growth along the tensile axis in a 〈110〉 direction, preferentially producing single crystals with orientations from an approximately 〈110〉 fiber family of orientations. A mechanism of boundary unpinning is proposed to explain the dependence of boundary migration on plastic straining during DAGG.

Experimental investigations on performance characteristics in wire electro discharge machining of Ti50Ni42.4Cu7.6 shape memory alloy

This article investigates the effect of pulse on time, peak current and pulse off time on wire electro discharge machining characteristics of Ti50Ni42.4Cu7.6 shape memory alloy. A Ti50Ni42.4Cu7.6 alloy was prepared by conventional tungsten arc melting. The machining experiments were performed as per Box–Behnken design on computer control wire electro discharge machining machine using molybdenum wire electrode. The relationships between the process parameters (pulse on time, peak current and pulse off time) and wire electro discharge machining responses (surface roughness and material removal rate) have been established using response surface methodology–based quadratic models. The analysis of variance has been employed to test the significance of the developed second-order mathematical models. The parametric analysis–based results reveal that low peak current with prolonged pulse on duration leads to reduced surface roughness. However, combination of low peak current with low pulse on time is beneficial for achieving better material removal rate for machining of shape memory alloy.

Steam reformation of hydrogen sulfide

A modified version of the Sulfur–Iodine cycle, here called the Sulfur–Sulfur Cycle, offers an all-fluid route to thermochemical hydrogen and avoids implications of the corrosive HI–H2O azeotropic mixture:(1)4I2(l) + 4SO2(l) + 8H2O(l) ↔ 4H2SO4(l) + 8HI(l) (120 °C)(2)8HI(l) + H2SO4(l) ↔ H2S(g) + 4H2O(l) + 4I2(l) (120 °C)(3)3H2SO4(g) ↔ 3H2O(g)+3SO2(g) + 1½O2(g) (850 °C)(4)H2S(g) + 2H2O(g) ↔ SO2(g) + 3H2(g) (900–1500 °C)The key step in the Sulfur–Sulfur cycle is the steam reformation of hydrogen sulfide, which is highly endothermic and has a positive Gibbs free energy change. The steam reformation of hydrogen sulfide was investigated under favorable circumstances (excessive dilution with steam and inert carrier) over a variety of catalytic and non-catalytic settings in a quartz tube. Successful results were obtained by pretreating a molybdenum wire with H2S at high temperature. Apparent Arrhenius parameters for both thermal splitting and steam reformation of hydrogen sulfide were determined.