Molybdenum Sheet Research Articles

Improvement of Thermal Stability of Charges in Polylactic Acid Electret Films for Biodegradable Electromechanical Sensors.

Eco-friendly sensors fabricated from biocompatible and biodegradable materials are promising candidates for wearable and implantable electronics due to their environmental sustainability and biosafety. This article reports a fully biodegradable electromechanical sensor (FBES) utilizing a sandwich structure with macro ripple structured polylactic acid (PLA) electret films acting as sensitive layers and molybdenum (Mo) sheets serving as electrodes for a wearable device application. The stability of the space charge stored within the PLA film has been enhanced by introducing an internal cellular structure and improving the polarization process. A macro ripple structure of the PLA layer with higher deformation is a great guarantee for boosting the pressure sensitivity. The results indicate that inserting cell microstructures and optimizing the polarization process significantly improve the charge storage stability of PLA films by nearly 55%. This enhancement is attributed to several factors, including the extended charge drift path of the charges in cellular films, a synergy effect of surface charges, and "macroscopic" dipole charges distributed in the cells. The fabricated sensor achieves a high sensitivity of 1000 pC/kPa, a wide pressure detection range of 0.03-62.4 kPa, and satisfactory stability. Such sensors are not only sensitive to body movements but also to subtle physiological signals, satisfying the diverse needs of wearable healthcare. Importantly, all the composition materials of the sensor can be completely degraded after their service, aligning with the environmentally friendly principles of green development.

Towards the fabrication of flexible thin film CdTe solar cells: The significance of substrate surfaces

Thin film CdTe solar cells have been recognized as reliable alternative for the manufacture of cheap photovoltaic solar cells of the future, due to its excellent absorber characteristics and simple, low-cost manufacturability. However, for the attainment of higher cell performances, additional studies are needed to increase cell efficiency through further development of better quality films and new fabrication processes. In the substrate-structured CdTe thin film solar cells, the CdTe absorber layer is deposited directly onto the substrate or through a back contact layer. But the quality of deposited film is believed to depend on the type and smoothness of the substrate. In this work CdTe was deposited on different substrates by RF sputtering and the effects on the deposited films were studied in terms of their structural and morphological forms. The substrates used were: pure molybdenum sheets (Mo), molybdenum-sputtered on molybdenum (Mo/Mo), molybdenum-sputtered polyimide (PI/Mo) and molybdenum-sputtered glass (glass/Mo). The characterization tools used included XRD, SEM and AFM. The results showed that all surfaces produced uniform, compact and pinhole-free films; however, those on smoother surfaces produced larger as-deposited grain sizes of up to1.7μm as against 1.3 for rougher surfaces. Non-uniformities such as overgrowth and voids were observed, but only films on PI showed evidence of cracking and peel-offs.

The Effect of Heat Treatment and Different Degrees of Deformation on the Microstructure and Mechanical Properties of Pure Mo Sheets

Molybdenum has a broad application and good prospect in the field of nuclear energy, aerospace, electronics, etc., due to its high melting point, high hardness, corrosion resistance and other excellent performances. In this paper, an isothermal and isochronous annealing heat treatment, at the temperature of 800–1300 °C for 0.5–2 h, was applied to pure molybdenum (PM) sheets with deformation of 70%, 80%, 90%, and 95%. The initial deformation of the PM sheet was increased from 70% to 95%. After annealing at 900–1200 °C for 1 h, the recrystallized grain size gradually decreased. The Goss texture ({110}<001>) was always present in the pure molybdenum sheet with 95% deformation during heat treatment, but its strength decreased with the increase of the temperature. The copper texture ({112}<110>) deflected to a cubic texture, and its orientation changed from {001}<110> to that of cube texture {110}<100>. With the increase of the temperature, the cubic texture was obtained more easily in the pure molybdenum sheet. The recrystallization nucleation mechanism of the pure molybdenum sheet with 95% deformation was mainly in situ nucleation and orientation nucleation. The Avrami index of the pure molybdenum sheet with 95% deformation was calculated by the JMAK equation and found to be 3.6.

Molybdenum as a Potential Biocompatible and Resorbable Material for Osteosynthesis in Craniomaxillofacial Surgery-An In Vitro Study.

Titanium and stainless steel are commonly known as osteosynthesis materials with high strength and good biocompatibility. However, they have the big disadvantage that a second operation for hardware removal is necessary. Although resorbable systems made of polymers or magnesium are increasingly used, they show some severe adverse foreign body reactions or unsatisfying degradation behavior. Therefore, we started to investigate molybdenum as a potential new biodegradable material for osteosynthesis in craniomaxillofacial surgery. To characterize molybdenum as a biocompatible material, we performed in vitro assays in accordance with ISO Norm 10993-5. In four different experimental setups, we showed that pure molybdenum and molybdenum rhenium alloys do not lead to cytotoxicity in human and mouse fibroblasts. We also examined the degradation behavior of molybdenum by carrying out long-term immersion tests (up to 6 months) with molybdenum sheet metal. We showed that molybdenum has sufficient mechanical stability over at least 6 months for implants on the one hand and is subject to very uniform degradation on the other. The results of our experiments are very promising for the development of new resorbable osteosynthesis materials for craniomaxillofacial surgery based on molybdenum.

Evolution of nano-pores during annealing of technically pure molybdenum sheet produced from different sintered formats

Molybdenum is a refractory metal with no phase transformation in the solid state and a high melting point. It is therefore an excellent structural material for various high temperature applications. Especially in this field of operation, significant creep resistance is essential. To achieve this, a microstructure with grains in the range of millimeters is desired. However, as demonstrated in the present study, the onset temperature for secondary recrystallization, which would lead to a beneficial grain size, is among other things dependent on the initial dimensions of the sintered part. One possible reason for the different microstructural evolutions is the influence of residual pores in sub-micrometer size. Sheets were thus fabricated via three different production routes employing the same initial Mo powder to exclude chemical variation as an influencing factor. The samples were investigated by in-situ small-angle X-ray scattering at a synchrotron radiation source with two different heating rates. Additionally, selected annealed samples were studied ex-situ with high energy X-rays. The apparent volume fraction of pores is compared to a volatilization model for the vaporization of typical accompanying elements and the induced thermal expansion.

Laser-assisted growth of hierarchically architectured 2D MoS2 crystals on metal substrate for potential energy applications

Recently, there has been substantial interest in the large-scale synthesis of hierarchically architectured transition metal dichalcogenides and designing electrodes for energy conversion and storage applications such as electrocatalysis, rechargeable batteries, and supercapacitors. Here we report a novel hybrid laser-assisted micro/nanopatterning and sulfurization method for rapid manufacturing of hierarchically architectured molybdenum disulfide (MoS2) layers directly on molybdenum sheets. This laser surface structuring not only provides the ability to design specific micro/nanostructured patterns but also significantly enhances the crystal growth kinetics. Micro and nanoscale characterization methods are employed to study the morphological, structural, and atomistic characteristics of the formed crystals at various laser processing and crystal growth conditions. To compare the performance characteristics of the laser-structured and unstructured samples, Li-ion battery cells are fabricated and their energy storage capacity is measured. The hierarchically architectured MoS2 crystals show higher performance with specific capacities of about 10 mAh cm−2, at a current rate of 0.1 mA cm−2. This rapid laser patterning and growth of 2D materials directly on conductive sheets may enable the future large-scale and roll-to-roll manufacturing of energy and sensing devices.

A Ka-Band Angular Log-Periodic Meander-Line SWS Supported by Diamond Rods

The angular log-periodic meander-line traveling wave tube (TWT) is a kind of low voltage, small-sized, high power, low cost, on chip amplifiers, and considered as a key part of the advanced communication systems, the future biomedical applications and the next electronic counter measure (ECM) instruments <i>et al.</i> Here, an angular log-periodic meander-line TWT is presented in this article. The angular log-periodic meander-line slow wave structure (SWS) is supported by two diamond rods. The dispersion and the impedance characteristics are analyzed in detail. In order to reduce the reflection loss, a gradual ridged waveguide is connecting the input&#x2013;output standard rectangular waveguide to the meander-line SWS. The particle in cell (PIC) simulations show that the output power of the TWT can reach 55 W at 34 GHz with the operation voltage of 1800 V and the beam current of 0.2 A. The SWS is manufactured by a laser machine with Molybdenum sheet. The assembled TWT is tested and the results show that the <inline-formula> <tex-math notation="LaTeX">${S}_{{11}}$ </tex-math></inline-formula> is less than &#x2212;10 dB at 30&#x2013;39 GHz. The <inline-formula> <tex-math notation="LaTeX">${S}_{{21}}$ </tex-math></inline-formula> mismatch between the simulated and the measurement is discussed at the end.

Improved quality of resistance spot welded joints for molybdenum sheets in lap configuration by adding titanium interlayer

Resistance spot welding (RSW) exhibits low heat input and high efficiency. However, because Mo exhibits low resistivity and high hot strength, it is difficult to effectively combine the resistance spot welded joints of Mo. The lap joint of 1-mm-thick Mo sheets was welded using RSW. Moreover, the welding parameters (current, welding duration, and electrode force) were optimised. Using Ti foil as the interlayer, the influence of the alloying element on the resistance spot welded joint of the Mo sheets was explored. The results indicate that the success rate of welding can be improved by utilising a high current and short welding duration, and increasing the electrode force causes reduced contact resistance and further failure of the welding. In addition, an excessively high electrode force may result in electrode adhesion. Here, a current of 20 kA, welding duration of 0.4 s, and electrode force of 3726 N were used as the optimised parameters. The joint obtained under the parameters can withstand the highest shear load (about 2.20 kN); the shear load of the joint obtained after adding the Ti interlayer (thickness: 0.03 mm) increases by approximately 54%. After adding the Ti foil, the heat input on the interface increased and Ti melted to form metallurgical bonding with Mo. Under these conditions, the interfacial strength increased significantly. During the tensile–shear test, the heat-affected zone of Mo is fractured, in which the shear fracture is subjected to brittle failure.

Recovery and recrystallization in molybdenum studied by positron annihilation and X-ray methods

The study investigated the recrystallization and induced changes in positron annihilation characteristics and the crystallographic texture of rolled molybdenum sheets as a function of annealing temperature. After deformation, the positron lifetime spectrum revealed dislocations and divacancies, however, above 200 °C where the recovery process of the deformed material began clusters with five vacancies were detected. Above 500 °C the step-like dependence of the mean positron lifetime on temperature was registered which is associated with recrystallization as was proofed by XRD measurements. This type of dependency can be well described using the positron diffusion model, which allows determining the activation energy of the grain boundary migration. This energy was determined as equal to 1.41 ± 0.23 eV. Variation of positron lifetime with temperature can be linked with changes in the texture. The rotated cube {100} 〈110〉 component dominates in the rolled material texture. The {111} <110> − {111} 〈112〉 fiber, typical for the recrystallization texture were registered for the samples annealed at 800 °C and 1050 °C.

Modeling and Experimental Verification of Induction Heating of Thin Molybdenum Sheets

This paper deals with the issues relevant for precise finite element method (FEM) modeling of thin molybdenum plates’ induction heating. The proposed methodology describes the step-by-step Multiphysics (electro-thermal) design approach, verified by the experimental measurements. Initially, it was observed that the relative error between model and experimental set-up is within the 1.2% up to 2.5% depending on the location of the measuring points. Further research was focused on the enhancement of the simulation model in the form of its parametrization. It means that it is easy to define the induction coil’s operational parameters and geometrical properties (ferrite shape, operating frequency, the distance between plate and heating element, the value of coil current, etc.). The target of this approach is to be able to determine the optimal operational settings targeting the required heating performance of thin molybdenum plates. One of the main requirements regarding the optimal heating process is temperature distribution within the molybdenum plate’s surface. The proposed model makes it possible to obtain information on optimal operational conditions based on the received results.

Manufacturing features, structure, and properties of high-purity Mo-Re thin sheets

Manufacturing features, structure and properties of low-alloyed molybdenum sheets 0.5 mm thick made from the experimental Mo-3 wt.% Re single crystal are described and discussed in the present work. The developed technological scheme includes warm rolling of the initial ingot at a temperature of 1150 °C, with heating in the argon protective atmosphere, subsequent annealing at 850 °C for 2/3 h in a vacuum, no less than 1 ·103 mmHg, cold rolling at a temperature of 400 °C, and post-deformation annealing at 800 C for 1/2 h. The results of micro structure analysis, physical and mechanical studies show that thin sheets are characterized by simultaneously high strength and plasticity, as well as the required temperature coefficient of linear expansion (TCLE), necessary for bonding with a glass by a thermo-compression welding. Obtained results reveal perspectives for the development of the application of thin Mo-3 wt.% Re sheets in vacuum engineering for the vacuum-tight metal-glass parts.

Molybdenum strip test experiments and simulations at various temperatures to determine friction coefficients

The aim of the presented study was to perform the strip test of 0.5 mm thick molybdenum strip specimens by various simulated drawbead heights from 2 mm up to 6 mm and various temperatures from 20 °C up to 320 °C to obtain friction coefficients between the molybdenum strip and steel cylinders built-in the developed test device simulating the drawbead. The friction coefficients between the dry and lubricated molybdenum strip and the steel cylinders simulating the drawbeads were obtained by changing its value in the bilinear friction model and matching the holder drawing force and the drawbead restraint force curves achieved during the tests and the simulations. The increasing temperature of molybdenum strip led to reduced holder drawing force and drawbead restraint force and increased friction coefficient because of the decrease of molybdenum strip yield strength and the increase of surface contact between molybdenum sheet and the testing tool at elevated temperature.

The microstructure and texture evolution of pure molybdenum sheets under various rolling reductions

Pure molybdenum sheets were prepared by powder metallurgy and unidirectional rolling process. The microstructure, texture, grain orientation, mechanical properties and fracture mechanism of sintered samples were investigated. The results show that tensile strength and microhardness of 95% rolled sheet are 1028.095 ± 19.32 MPa and 323.2 ± 11.68 HV. The main texture components of (011)〈110〉 is Goss texture with reduction in the range of 70–95%. Two grain orientations of 〈111〉 fiber & 〈100〉 fiber and 〈100〉 fiber & 〈110〉 fiber are formed in the 47% and 95% rolled molybdenum sheets, respectively. Meanwhile, the fiber structure become more refined and oriented in the rolled molybdenum sheets when the rolling reduction is >87%. Brittle characteristics show typical cleavage failure.

Simulation study of dynamic heating process of molybdenum for sheet suited for rigid transport components design

Abstract This paper deals with the development of the simulation model of the moving molybdenum sheet, while the molybdenum sheet is heated by direct resistive heating. COMSOL/MATLAB environments are used to create mentioned model. Static model created in COMSOL is compared with measurement and based on this comparison the dynamic model (COMSOL/MATLAB) is adjusted. The dynamic model is created as in-loop simulation for different initial conditions of heating elements position and temperature distribution within molybdenum sheet. The result of dynamic model is temperature distribution within molybdenum sheet for given heating elements shift and speed. For that reason, the proposed model can be used for optimization of direct resistive heating system of molybdenum sheet.

Simulation study of inductive heating of molybdenum sheet suited for rapid prototypes of rigid components of transport systems

Abstract This paper deals with the development of the simulation model of the inductive heating of molybdenum sheet. The proposed model is created in COMSOL environment. The main purpose of proposed model is to determine the optimal shape of magnetic element (ferrite) of inductive heating system, through which the electromagnetic field is enclosed trough molybdenum sheet. Next part of this publication is dedicated to acquisition of thermal-frequency characteristic for given shape of magnetic element of heating system. The result of proposed model can be used for optimization of heating element shape as well as for optimization of control algorithm of inductive heating system based on acquired frequency characteristic.

Reliable Residual Stress Analysis for Thin Metal Sheets by Incremental Hole Drilling

Abstract Sheet metal–forming processes induce characteristic residual stress-depth gradients into technical components. Regarding thin metal sheets with thicknesses of only a few millimeters, or those in the sub-mm range, surface finishing processes, e.g., machining processes like grinding, polishing, lapping, or mechanical post–surface treatments, might cause significant distortions. These may result from intentionally induced one-sided residual stress distributions or residual stress redistributions through one-sided materials removal. For process assessment and control, accurate residual stress analysis is indispensable. However, in sheet metal formation, the residual stress state is often accompanied by pronounced crystallographic textures, which usually cause failure of the standard laboratory procedures. As an example, X-ray residual stress analysis according to the standard sin2ψ-method is not feasible for markedly textured material states because of curved 2θ-sin2ψ distributions. On the contrary, we have already shown that the incremental hole drilling method that uses case-specific calibration data and considers specimen thickness and crystallographic texture provides reliable stress evaluation. Hereby, for thin metal sheets, the appropriate support condition is very important since improper support can lead to significant restraints, i.e., the specimen fixture hinders the strain relaxation on the specimen’s surface during the hole drilling process, and, for nonflat sheets, even assembling stresses can be superimposed. Consequently, stress calculation based on the measured strain relaxation data leads to erroneous residual stress results in application of the incremental hole drilling method. This work is derived from the necessity of measuring residual stress-depth gradients in thin molybdenum sheets. Thereby, an appropriate specimen support strategy for hole drilling application on thin metal sheets is proposed based on a systematic parametric study using 3-D finite element modeling that considers different sheet thicknesses. Based on the simulation results, a support ring with an adequate inner diameter is proposed as the most suitable specimen support. The numerical findings were verified by experimental residual stress analyses with the use of two different specimen supports.

Research on high-temperature properties of the molybdenum sheet doped with 1.0 wt%Al2O3 particles

The high-temperature properties of the molybdenum sheet doped with 1.0 wt%Al2O3 particles were investigated. The Al2O3 particles have a good bond with the Mo matrix and there exists an amorphous transition layer at the interface between Al2O3 particles and Mo matrix in the as-rolled sheet. The tensile strength of the Al2O3-doped Mo sheet is higher 23–62% than that of the pure Mo sheet at room and high temperatures, with its recrystallization temperature increased by about 200 °C than that of the pure Mo sheet. Furthermore, the fracture and strengthening mechanisms were discussed.

Heat distribution in the deep drawing device components working by high temperatures

The subject of the article is a simulation of heat affected components of a device for deep drawing by extreme conditions in vacuum by high temperatures required for forming of crystallization containers made from thin molybdenum sheets. The simulation is focused on the distribution of heat in particular components in relation with their shape. There are presented the design of working components and the boundary conditions of transient thermal simulations with the results.

Modelling of the resistance heating of the moving molybdenum sheet

Modelling of the resistance heating of the moving molybdenum sheet

Molybdenum Sheet Local Resistance Heating Test Device

Molybdenum Sheet Local Resistance Heating Test Device