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Tungsten carbide

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https://www.readbyqxmd.com/read/29316102/selective-production-of-renewable-para-xylene-via-tungsten-carbide-catalyzed-atom-economic-cascade-reactions
#1
Changzhi Li, Tao Dai, Lin Li, Zongbao Kent Zhao, Bo Zhang, Yu Cong, Aiqin Wang
Tungsten carbide was employed as a catalyst in an atom-economic and renewable synthesis of para-xylene with excellent selectivity and yield from 4-methyl-3-cyclohexene-1-carbonylaldehyde (4-MCHCA), the product of Diels-Alder reaction between two readily available bio-based building blocks acrolein and isoprene. Our results suggest that 4-MCHCA undergoes a novel dehydroaromatization-hydrodeoxygenation cascade pathway via intramolecular hydrogen transfer without involving any external hydrogen source, and that the hydrodeoxygenation occurs through the direct dissociation of the C=O bond on the W2C surface...
January 8, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29298034/tungsten-assisted-phase-tuning-of-molybdenum-carbide-for-efficient-electrocatalytic-hydrogen-evolution
#2
Kai Zhang, Gong Zhang, Jiuhui Qu, Huijuan Liu
Phase tuning during crystal phase transformation is an important but challenging step toward the development of effective hydrogen evolution reaction (HER) catalysts. Herein, we report on a feasible approach to achieve effective polycrystalline molybdenum carbides during transformation from α-phase to β-phase through the regulation of additive (tungsten) amount. Benefiting from the optimal Mo-C bond lengths and abundant active sites, molybdenum carbide prepared with a moderate addition of tungsten enhanced electrocatalytic activity and stability compared with pure α-phase and β-phase Mo2C in the HER, and only required an overpotential of 148 and 93 mV to drive 20 mA cm-2 of current density in 0...
January 3, 2018: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/29240116/laser-induced-breakdown-spectroscopy-for-three-dimensional-elemental-mapping-of-composite-materials-synthesized-by-additive-technologies
#3
V N Lednev, P A Sdvizhenskii, M Ya Grishin, V V Cheverikin, A Ya Stavertiy, R S Tretyakov, M V Taksanc, S M Pershin
Three-dimensional multi-elemental mapping of composite wear-resistant coatings by laser-induced breakdown spectroscopy has been demonstrated for the first time, to the best of our knowledge. Individual clads of 1560 nickel alloy reinforced with tungsten carbide were synthesized by a co-axial laser cladding technique. Electron energy dispersive x-ray spectroscopy revealed elemental maps for major elements (W, Ni, Co, Cr, Fe) but failed to measure silicon and carbon. Laser-induced breakdown spectroscopy was utilized for elemental mapping of carbon and all other elements of interest...
December 10, 2017: Applied Optics
https://www.readbyqxmd.com/read/29196873/total-mercury-determination-in-muscle-and-liver-tissue-samples-from-brazilian-amazon-fish-using-slurry-sampling
#4
João Vitor de Queiroz, José Cavalcante Souza Vieira, Izabela da Cunha Bataglioli, Alis Correia Bittarello, Camila Pereira Braga, Grasieli de Oliveira, Cilene do Carmo Federici Padilha, Pedro de Magalhães Padilha
This paper presents a slurry sampling method for total mercury determination by graphite furnace atomic absorption spectrometry (GFAAS) in tissue of fish from the Amazon. The tissue samples were lyophilized and macerated, and then the slurry samples were prepared by putting 20 mg of tissue, added to a solution containing Triton X-100, Suprapur HNO3, and zirconium nitrate directly in sampling vials of a spectrometer. Mercury standard solutions were prepared under the same conditions as the slurry samples. The slurry samples and the mercury standard solutions were sonicated for 20 s...
December 2, 2017: Biological Trace Element Research
https://www.readbyqxmd.com/read/29186228/tungsten-coated-nano-boron-carbide-as-a-non-noble-metal-bifunctional-electrocatalyst-for-oxygen-evolution-and-hydrogen-evolution-reactions-in-alkaline-media
#5
Yan Zhang, Yanhui Wang, Chan Han, Shaopei Jia, Shuyu Zhou, Jianbing Zang
Herein, tungsten-coated nano-boron carbide (W-WB4-WCx/B4C) particles were prepared by heating a mixture of B4C and W powder using a spark plasma coating (SPC) method. During the discharge treatment process, metal W in the mixture is activated and reacts with B4C to form WCx, WB4, and graphite nanoribbons. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance of W-WB4-WCx/B4C is tested in an alkaline solution, and the results show that the W-WB4-WCx/B4C composite electrocatalyst exhibits a low overpotential of 0...
November 29, 2017: Nanoscale
https://www.readbyqxmd.com/read/29185145/development-of-a-novel-bioactive-glass-for-air-abrasion-to-selectively-remove-orthodontic-adhesives
#6
Ayam A Taha, Robert G Hill, Padhraig S Fleming, Mangala P Patel
OBJECTIVES: To develop a novel, bioactive glass for removing residual orthodontic adhesive via air-abrasion, following bracket debonding, and to evaluate its effectiveness against a proprietary bioactive glass 45S5(Sylc™)-air-abrasion, and a slow-speed tungsten carbide (TC) bur. MATERIALS AND METHODS: Three glasses were prepared and their bioactivity was proved. One novel glass (QMAT3) was selected due to its appropriate hardness, lower than that of enamel/45S5(Sylc™)...
November 28, 2017: Clinical Oral Investigations
https://www.readbyqxmd.com/read/29140098/surface-roughness-of-methacrylate-and-silorane-based-composites-after-finishing-and-polishing-procedures
#7
M Jacinta Santos, Heleine Maria Chagas Rêgo, Leticia Linares, Amin S Rizkalla, Gildo C Santos
OBJECTIVE: To compare the effect of surface finishing and polishing protocols on the surface roughness (Ra) of methacrylate-based and silorane-based resin composites. METHODS AND MATERIALS: Fifty specimens (5 mm x 2 mm) of each composite material were prepared using a split mold: Filtek™ Supreme Ultra (3M ESPE), Tetric EvoCeram® (Ivoclar Vivadent), Tetric Ceram™ HB (Ivoclar Vivadent), and Filtek™ LS Low Shrink (3M ESPE). Specimens were divided into five groups (n = 10) according to the following procedures: G1 - 15-µm fine diamond bur (FDB); G2 - 15-µm FDB followed by a 20-fluted tungsten carbide bur; G3 - 15-µm FDB followed by diamond-impregnated micropolishing points (D-FINE Double Diamond Polishing System, Clinician's Choice); G4 - 15-µm FDB followed by diamond-impregnated micropolishing points (Flame Point Pre-polisher and Shine, Brassseler USA); and G5 - 15-µm FDB followed by the application of a surface sealer (PermaSeal®, Ultradent Products, Inc...
November 2017: Compendium of Continuing Education in Dentistry
https://www.readbyqxmd.com/read/29139500/self-assembly-of-wo3-3-clusters-on-a-highly-oriented-pyrolytic-graphite-surface-and-nanowire-formation-a-combined-experimental-and-theoretical-study
#8
Xin Tang, Kit H Bowen, Florent Calvo
Tungsten oxide cluster anions (WO3)3(-) produced from a magnetron source were soft-landed on highly oriented pyrolytic graphite (HOPG) surfaces at different temperatures, and the structures formed upon deposition were analyzed using ex situ atomic force microscopy. Under liquid nitrogen cooling conditions of 100 K, the clusters form small branched nanostructures extending over a few nanometers with a height not exceeding 1 nm. At 673 K, nanowires approximately 100 nm long and less than 10 nm in diameter are observed...
November 15, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/29109747/effect-of-finishing-polishing-techniques-and-time-on-surface-roughness-of-esthetic-restorative-materials
#9
Prashanthi Sampath Madhyastha, Shreya Hegde, N Srikant, Ravindra Kotian, Srividhya Sriraman Iyer
Background: Surface roughness associated with improper finishing/polishing of restorations can result in plaque accumulation, gingival irritation, surface staining, and poor esthetic of restored teeth. The study aimed to evaluate the efficiency of various finishing and polishing systems and time using various procedures on surface roughness of some esthetic restorative materials. Materials and Methods: In this in vitro study, samples of two composite materials, compomer and glass ionomer cement (GIC) materials, were fabricated...
September 2017: Dental Research Journal
https://www.readbyqxmd.com/read/29058741/electronic-properties-of-single-layer-tungsten-disulfide-on-epitaxial-graphene-on-silicon-carbide
#10
Stiven Forti, Antonio Rossi, Holger Büch, Tommaso Cavallucci, Francesco Bisio, Alessandro Sala, Tevfik Onur Menteş, Andrea Locatelli, Michele Magnozzi, Maurizio Canepa, Kathrin Müller, Stefan Link, Ulrich Starke, Valentina Tozzini, Camilla Coletti
This work reports an electronic and micro-structural study of an appealing system for optoelectronics: tungsten disulfide (WS2) on epitaxial graphene (EG) on SiC(0001). The WS2 is grown via chemical vapor deposition (CVD) onto the EG. Low-energy electron diffraction (LEED) measurements assign the zero-degree orientation as the preferential azimuthal alignment for WS2/EG. The valence-band (VB) structure emerging from this alignment is investigated by means of photoelectron spectroscopy measurements, with both high space and energy resolution...
November 2, 2017: Nanoscale
https://www.readbyqxmd.com/read/29047954/effects-of-interface-thermal-resistance-on-surface-morphology-evolution-in-precision-glass-molding-for-microlens-array
#11
Jiaqing Xie, Tianfeng Zhou, Benshuai Ruan, Yifei Du, Xibin Wang
To study the effects of the interface thermal resistance on surface morphology evolution in precision glass molding (PGM) for microlens array with different mold materials, including Tungsten carbide and heat-resistant stainless steel, the glass-mold interface thermal resistance is calculated, and heat-transfer simulation of PGM based on an interface thermal resistance model at the heating stage is conducted correspondingly. The effect of flattening behavior on the glass-mold interface is explained. Then, experiments evaluating the relationship between heating time and glass surface roughness are carried out, and the glass adhesion phenomenon appearing on the heat-resistant stainless steel mold is observed and analyzed...
August 10, 2017: Applied Optics
https://www.readbyqxmd.com/read/29036935/laser-powder-cladding-of-ti-6al-4v-%C3%AE-%C3%AE-alloy
#12
Samar Reda Al-Sayed Ali, Abdel Hamid Ahmed Hussein, Adel Abdel Menam Saleh Nofal, Salah Elden Ibrahim Hasseb Elnaby, Haytham Abdelrafea Elgazzar, Hassan Abdel Sabour
Laser cladding process was performed on a commercial Ti-6Al-4V (α + β) titanium alloy by means of tungsten carbide-nickel based alloy powder blend. Nd:YAG laser with a 2.2-KW continuous wave was used with coaxial jet nozzle coupled with a standard powder feeding system. Four-track deposition of a blended powder consisting of 60 wt % tungsten carbide (WC) and 40 wt % NiCrBSi was successfully made on the alloy. The high content of the hard WC particles is intended to enhance the abrasion resistance of the titanium alloy...
October 15, 2017: Materials
https://www.readbyqxmd.com/read/28964085/short-pulse-method-for-acoustic-backscatter-amplitude-calibration-at-mhz-frequencies
#13
Gregory W Wilson, Alex E Hay
The short-pulse acoustic backscatter amplitude calibration technique of Dragonette, Numrich, and Frank [(1981), J. Acoust. Soc. Am. 69, 1186-1189] is evaluated for MHz frequency systems, as are used to measure environmental suspended sediment concentration. The technique involves measuring backscatter from a short transmit pulse reflected by a solid spherical target, and treating the first received reflection as equivalent to that from a perfectly rigid sphere. In this implementation, the target sphere is 16 mm diameter tungsten carbide...
September 2017: Journal of the Acoustical Society of America
https://www.readbyqxmd.com/read/28954756/iatrogenic-displacement-of-high-speed-bur-during-third-molar-removal
#14
Jothi Raamahlingam Rajaran, Abd Jabar Nazimi, Rama Krsna Rajandram
Surgical removal of impacted mandibular third molar is a routine procedure in oral surgery. Various iatrogenic complications related to the procedure has been discussed well in the literatures before. Some of these complications are related to the wrong usage of instruments and techniques. Here we discuss a rare complication on a 42-year-old male, related to the use of high-speed handpiece drill in mandibular third molar removal in a general dental office setting. He was referred when a high speed tungsten carbide bur was accidentally broken and displaced into the mandibular bone during surgical procedure...
September 27, 2017: BMJ Case Reports
https://www.readbyqxmd.com/read/28953352/graphene-ingestion-and-regrowth-on-carbon-starved-metal-electrodes
#15
Ming-Sheng Wang, Yong Cheng, Longze Zhao, Ujjal K Gautam, Dmitri Golberg
The interaction between graphene and various metals plays a central role in future carbon-based device and synthesis technologies. Herein, three different types of metal nanoelectrodes (W, Ni, Au) were employed to in situ study the graphene-metal interfacial kinetic behaviors in a high-resolution transmission electron microscope. The three metals exhibit distinctly different interactions with graphene when driven by a heating current. Tungsten tips, the most carbon-starved ones, can ingest a graphene sheet continuously; nickel tips, less carbon starved, typically "eat" graphene only by taking a "bite" from its edge; gold, however, is nonactive with graphene at all, even in its molten state...
October 24, 2017: ACS Nano
https://www.readbyqxmd.com/read/28952625/synthesis-of-metastable-chromium-carbide-nanomaterials-and-their-electrocatalytic-activity-for-the-hydrogen-evolution-reaction
#16
Samantha M Schmuecker, Dale Clouser, Theodore J Kraus, Brian M Leonard
Transition metal carbides including chromium, molybdenum, and tungsten are of particular interest as renewable energy catalysts due to their low cost and abundance. While several single metal carbide systems form multiple phases with different compositions and crystal structures, most of these materials are not as well studied due to their limited synthetic approaches and instability. By taking advantage of a low temperature salt flux synthetic method, these unique phases can be more easily synthesized and separated as phase pure materials...
October 10, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28871118/durable-and-self-hydrating-tungsten-carbide-based-composite-polymer-electrolyte-membrane-fuel-cells
#17
Weiqing Zheng, Liang Wang, Fei Deng, Stephen A Giles, Ajay K Prasad, Suresh G Advani, Yushan Yan, Dionisios G Vlachos
Proton conductivity of the polymer electrolyte membranes in fuel cells dictates their performance and requires sufficient water management. Here, we report a simple, scalable method to produce well-dispersed transition metal carbide nanoparticles. We demonstrate that these, when added as an additive to the proton exchange Nafion membrane, provide significant enhancement in power density and durability over 100 hours, surpassing both the baseline Nafion and platinum-containing recast Nafion membranes. Focused ion beam/scanning electron microscope tomography reveals the key membrane degradation mechanism...
September 4, 2017: Nature Communications
https://www.readbyqxmd.com/read/28869256/regioselective-hydrogenolysis-of-aryl-ether-c-o-bonds-by-tungsten-carbides-with-controlled-phase-compositions
#18
Huihuang Fang, Junmou Du, Chenchen Tian, Jianwei Zheng, Xinping Duan, Linmin Ye, Youzhu Yuan
Evenly dispersed tungsten carbides with controlled phase compositions that exhibit an impressive capacity to carry out the regioselective hydrogenolysis of inert aryl ether C-O bonds instead of aliphatic C-O bonds to produce aromatic compounds are reported.
September 14, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28843405/intracanal-temperature-changes-during-bone-preparations-close-to-and-penetrating-the-inferior-alveolar-canal-drills-versus-piezosurgery
#19
József Szalma, László Vajta, Edina Lempel, Ákos Tóth, Sára Jeges, Lajos Olasz
PURPOSE: The aim of this in vitro study was to investigate temperature increases in the inferior alveolar canal (IAC), when different bone preparation methods approximate and penetrate the IAC. MATERIALS AND METHODS: In pig mandible, buccal bone removals were performed until the neurovascular bundle became visible. Temperatures were registered with thermocouple probes and with infrared thermometer. Preparations were performed with diamond drills (DD), tungsten carbide drills (TCD), piezoelectric diamond sphere (PT_D) and saw (PT_S) tips, and a combined preparation method was also performed whereby the superficial three-fourths of the bone was removed with TCD and the deepest one-fourth of the bone with PT_D (TCD + PT_D_7 °C) or PT_S (TCD + PT_S_7 °C), using cooled irrigation (7 °C)...
October 2017: Journal of Cranio-maxillo-facial Surgery
https://www.readbyqxmd.com/read/28832019/anisotropic-electrical-transport-of-flexible-tungsten-carbide-nanostructures-towards-nanoscale-interconnects-and-electron-emitters
#20
Bo Sun, Yong Sun, Chengxin Wang
Due to the coexistence of metal- and ionic-bonds in a hexagonal tungsten carbide (WC) lattice, disparate electron behaviors were found in the basal plane and along the c-axial direction, which may create an interesting anisotropic mechanical and electrical performance. To demonstrate this, low-dimensional nanostructures such as nanowires and nanosheets are suitable for investigation because they usually grow in single crystals with special orientations. Herein, we report the experimental research regarding the anisotropic conductivity of [0001] grown WC nanowires and basal plane-expanded nanosheets, which resulted in a conductivity of 7...
November 3, 2017: Nanotechnology
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