Papers by Keyword: Tungsten

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Authors: Shun Myung Shin, Jei Pil Wang
Abstract: Stainless steel materials (FeCr and FeCrNi-based alloys) are employed in a wide range of modern applications due to their ability to withstand corrosive environments while maintaining good mechanical properties. Their corrosion resistance originates from Cr-rich oxide layer which serves as a barrier against ion diffusion between the alloy and the ambient phase. Custom steel grades can be designed for specific applications by optimizing their properties throughout alloy composition [1].
Authors: Ming Li, Qing Qing Liu, Xiao Li Xi, Zuo Ren Nie
Abstract: In this study, a new green approach has been developed for the recovery of tungsten by using tungsten carbide (WC) scrap material as consumable anode in LiCl-KCl molten salts at 773 K to produce metallic tungsten. The feasibility of the direct electrochemical dissolution of WC anode into metallic tungsten was evaluated based on the experimental verifications and electrochemical methods. The effects of the main technical parameters, including the cell voltage, electrolysis time and electrolysis temperature, on the dissolved condition of anode were studied and the optimal anode parameters were obtained. It was found that a large electrolytic voltage, high electrolytic temperature and long electrolysis time would be favorable for the dissolved state of the tungsten carbide anode under the same conditions. The cathode product was analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the tungsten particles with a diameter of 100 nm could be prepared by this process in a molten salt bath. Linear sweep voltammetry was applied to investigate the dissolution of WC anode, and showed that the WC scrap material could be used as consumable anode to produce tungsten powder. Other electrochemical techniques including cyclic voltammetry , square-wave voltammetry and chronopotentiometry were employed to explore the electrochemical properties of tungsten ion derived from WC anode in LiCl-KCl melts. These results confirmed that electroreduction of tungsten ion in the melts proceeded in one step with four exchanged electrons.
Authors: Wei Li, Cheng Ge Wu, Qiang Han Fang
Abstract: The iron-based composite ceramic powder Fe-WC is produced by ball milling with synthetic tungsten mine and graphite. The process is accomplished through mechanical activation and reductive diffusion of the reactant powders during the milling process. The products are analyzed by means of XRD, DTA and EPMA. The results approved that the reaction does not carry through completely when the milling time is less than 8h. However, the composite powder of Fe and WC is gained by annealing from powders milled under 180V of the milling machine. The apparent activation energy of the reductive reaction is gradually decreased with the extending of milling time by mechanical activation.
Authors: Sebastien Mercier, Denis Boivin, Marie Pierre Bacos, Pierre Josso
Abstract: A diffusion barrier between a 4th generation superalloy (MC-NG) and a β-(Ni, Pt)Al has been studied. The used coating process combines Re and NiW electrolytic deposits followed by thermal treatments. The diffusion barrier is composed of a continuous 3 &m thick ReWNi layer under a 10 &m thick β-(Ni, Pt)Al containing W rich precipitates. EDS analysis on as coated samples and on 50h-1100°C-Ar aged samples showed that the Re-NiW layer works as a diffusion barrier. The Al reservoir in the bond coat after aging is higher with the diffusion barrier than without. The concentrations of alloying elements are also lower in the bond coat with the diffusion barrier than without.
Authors: Cheng Wei Kang, Han Huang
Abstract: Tungsten based products are extensively used in engineering practices. However, there exist some controversies in deformation behaviour between polycrystalline tungsten and its bulk counterpart. In this work, elastic modulus, hardness and removal characteristics of polycrystalline tungsten (poly-W) were investigated by use of nanoindentation and nanoscratch. Atomic Force microscopy (AFM) and Scanning Electron Microscopy (SEM) were employed to characterize the surfaces prior to and after indenting/scratching. The elastic modulus and hardness of the poly-W obtained were 323.6 and 7.1 GPa, respectively. Elastic recovery was barely observed in poly-W after indenting and scratching, indicating that the material was dominantly deformed in plastic regime. The plastic deformation of the poly-W was found to be somehow different from the bulk W, but similar to that of single crystal W nanowhiskers. In multi-scratch test, the pitch distance and scratching speed demonstrated to affect the roughness of the scratched surfaces.
Authors: Sang Won Lee, Young Shin Lee, Jae Hoon Kim, Yong Woon Bae, Jong Min Park
Abstract: In this paper, the penetration characteristic of tungsten penetrator was studied. Tungsten and aluminum was used as the material of the penetrator and target, respectively. Dimensions of the aluminum target were 100 X 100 X 5 (mm3). The penetrator with cylinder conical tip and flat tip was used in the impact test and simulation. The range of the initial velocity was from 400 to 1600 m/s. The angle of the incidence on the penetrator with cylinder cone tip was 0 ̊. The angle of the incidence on the penetrator with flat tip was 0 ̊, 30 ̊ , 60 ̊ . To obtain results of the simulation, AUTODYN 3D code was used. The residual mass and velocity was obtained to compare with results between the impact test and simulation.
Authors: György Vida, Ildikó Beck, V. Katalin Josepovits, Miklós Győr
Abstract: In the present paper the secondary emission and work function of W covered with different thickness Ba layers are compared. The secondary emission and work function were measured by Work Function Spectroscopy (WFS). It is clearly pointed out that the thin Ba coating causes the the enhancement of electron induced secondary electron emission. In high pressure discharge lamps high secondary emission and high thermionic current are required for reliable operating conditions, i.e., for reaching the nominal burning voltage and current etc. The results prove that the Ba spreading on the W surface from an alkali earth tungstate material is advantageous for lowering the work function and, simultaneously, for increasing the secondary emission yield.
Authors: S.M. Klotsman, G.N. Tatarinova, Alexander N. Timofeev
Abstract: The volume diffusion of nonmagnetic homovalent atomic probes (APs) from the IIIB group of the periodic table of the elements (PTE)Sc, La, and Th in Whas been studied by the method of secondary ion mass spectrometry. The Arrhenius dependences have the following parameters: the coefficients DSc - (D0)Sc = (1.4  0.3)10-4 m2s-1 and QSc = (546±4) kJ/mole; the coefficients D¬La - (D0)La = (1.6  0.8)×10-6 m2s-1 and QLa = (41010) kJ/mole; and the coefficients DTh - (D0)Th = 4.4×10-6 m2s-1 and QTh = 447 kJ/mole. It has been found that the coefficients D5dAP(Tm)W of the bulk diffusion of transition 5d APs in W coincide at its melting point (Tm)W. The enthalpies, QWSc,La,Th, of the volume diffusion of nonmagnetic homovalent APs from the IIIB group of PTE increase linearly with decreasing relaxation volumes, , of these APs, which interact with vacancies in W. The sums, (Q + E)WSc,La,Th, of the bulk diffusion enthalpies, QWSc,La,Th, and the relaxation energy, (E)WSc,La,Th, of the environments of homovalent APs diffusing to W are nearly constant.
Authors: S.M. Klotsman, G.N. Tatarinova, Alexander N. Timofeev
Abstract: The Volume Diffusion of Homovalent Atomic Probes (APs) from the VB Group of the Periodic Ta-Ble of Elements (PTE) – V and Nb in W Single Crystals Has Been Studied by Using the Method of Secondary Ion Mass Spectrometry (SIMS). the Parameters of the Arrhenius Dependence of the Coefficients DV of Vanadium Volume Diffusion in W Have Been Measured: (D0)V = (1.3  0.4) X 10-4 M2s-1 and QV = (564 ± 6) Kj/mol. the Parameters (D0,Q)Nb of the Bulk Diffusion of Nb Aps in W Have Been Estimated with the Help of Several Measured Coefficients Dnb and the Empirical Correlation [1,2]: (D = DWW)(Tm)W: the Diffusion Coefficients of Substitutional Non-Magnetic 5d-Aps Coincide with the Self-Diffusion Coefficients in W at its Melting Point (Tm)W. the Enthalpies Qnb,Ta of the Bulk Diffusion of Non-Magnetic (nm) Homovalent Aps from the VB Group of PTE – Nb and Ta [3] Also Coincide with the Relaxation Volumes vacVBAPs of Complexes “vacancies-VB Aps” in the W Lattice. Electron Contributions (EDN)vacVBAPs to the Energies Evacvbaps of Interaction of Point Defects in Complexes “vacancies- VB Nm- Aps” Are Lower than in Complexes “vacancies-IVB Nm- Aps” [4]. the Dependence of {EDN(n)}vacVBAPs the Electron Contributions (EDN)vacVBAPs on the Difference of N Numbers of Periods of PTE the Deviation of Contributions (EDN)vacVAPs for Vanadium Aps to En-Ergies Evacvaps of their Interaction in Complexes “vacancy-VAP” Has Been Determined. this Devi-Ation Is Conditioned by the Contribution of the Exchange Energy (Eexch)VAP of Vanadium to the En-Ergy Evacvaps of the Point-Defect Interactions in the Complex “vacancy-VAP”.
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