carbon impurities
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Metals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 159
Author(s):  
Nicholas Olynik ◽  
Bin Cheng ◽  
David J. Sprouster ◽  
Chad M. Parish ◽  
Jason R. Trelewicz

Exploiting grain boundary engineering in the design of alloys for extreme environments provides a promising pathway for enhancing performance relative to coarse-grained counterparts. Due to its attractive properties as a plasma facing material for fusion devices, tungsten presents an opportunity to exploit this approach in addressing the significant materials challenges imposed by the fusion environment. Here, we employ a ternary alloy design approach for stabilizing W against recrystallization and grain growth while simultaneously enhancing its manufacturability through powder metallurgical processing. Mechanical alloying and grain refinement in W-10 at.% Ti-(10,20) at.% Cr alloys are accomplished through high-energy ball milling with transitions in the microstructure mapped as a function of milling time. We demonstrate the multi-modal nature of the resulting nanocrystalline grain structure and its stability up to 1300 °C with the coarser grain size population correlated to transitions in crystallographic texture that result from the preferred slip systems in BCC W. Field-assisted sintering is employed to consolidate the alloy powders into bulk samples, which, due to the deliberately designed compositional features, are shown to retain ultrafine grain structures despite the presence of minor carbides formed during sintering due to carbon impurities in the ball-milled powders.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Katherine A. Cochrane ◽  
Jun-Ho Lee ◽  
Christoph Kastl ◽  
Jonah B. Haber ◽  
Tianyi Zhang ◽  
...  

AbstractAtomic spin centers in 2D materials are a highly anticipated building block for quantum technologies. Here, we demonstrate the creation of an effective spin-1/2 system via the atomically controlled generation of magnetic carbon radical ions (CRIs) in synthetic two-dimensional transition metal dichalcogenides. Hydrogenated carbon impurities located at chalcogen sites introduced by chemical doping are activated with atomic precision by hydrogen depassivation using a scanning probe tip. In its anionic state, the carbon impurity is computed to have a magnetic moment of 1 μB resulting from an unpaired electron populating a spin-polarized in-gap orbital. We show that the CRI defect states couple to a small number of local vibrational modes. The vibronic coupling strength critically depends on the spin state and differs for monolayer and bilayer WS2. The carbon radical ion is a surface-bound atomic defect that can be selectively introduced, features a well-understood vibronic spectrum, and is charge state controlled.


Author(s):  
Colin K Swee ◽  
Benedikt Geiger ◽  
Ralph Dux ◽  
Santhosh Kumar ◽  
Fernando Castillo ◽  
...  

Abstract The transport of carbon impurities has been studied in the helically symmetric stellarator experiment (HSX) using active and passive charge exchange recombination spectroscopy (CHERS). For the analysis of the CHERS signals, the STRAHL impurity transport code has been re-written in the python programming language and optimized for the application in stellarators. In addition, neutral densities both along the NBI line of sight as well as for the background plasma have been calculated using the FIDASIM code. By using the basinhopping algorithm to minimize the difference between experimental and predicted active and passive signals, significant levels of impurity diffusion are observed. Comparisons with neoclassical calculations from DKES/PENTA show that the inferred levels exceed the neoclassical transport by about a factor of four in the core and more than 100 times towards the plasma edge, thus indicating a high level of anomalous transport. This observation is in agreement with experimental heat diffusivites determined from a power balance analysis which exhibit strong anomalous transport as well.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Lilla Fijołek ◽  
Joanna Świetlik ◽  
Marcin Frankowski

AbstractIn water treatment technology, activated carbons are used primarily as sorbents to remove organic impurities, mainly natural organic matter, but also as catalysts in the ozonation process. Commercially available activated carbons are usually contaminated with mineral substances, classified into two main groups: alkali metals (Ca, Na, K, Li, Mg) and multivalent metals (Al, Fe, Ti, Si). The presence of impurities on the carbon surface significantly affects the pHpzc values determined for raw and ozonated carbon as well as their acidity and alkalinity. The scale of the observed changes strongly depends on the pH of the ozonated system, which is related to the diffusion of impurities from the carbon to the solution. In an acidic environment (pH 2.5 in this work), the ozone molecule is relatively stable, yet active carbon causes its decomposition. This is the first report that indirectly indicates that contaminants on the surface of activated carbon (multivalent elements) contribute to the breakdown of ozone towards radicals, while the process of ozone decomposition by purified carbons does not follow the radical path in bulk solution. Carbon impurities also change the distribution of the reaction products formed by organic pollutants ozonation, which additionally confirms the radical process. The study showed that the use of unpurified activated carbon in the ozonation of succinic acid (SA) leads to the formation of a relatively large amount of oxalic acid (OA), which is a product of radical SA degradation. On the other hand, in solutions with purified carbon, the amount of OA generated is negligible.


Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1620
Author(s):  
Robert Köhler ◽  
Domenico Hellrung ◽  
Daniel Tasche ◽  
Christoph Gerhard

The chemical composition of ground and polished fused silica glass surfaces plays a decisive role in different applications of optics. In particular, a high level of carbon impurities is often undesirable for further processing and especially for gluing or cementing where adhesion failure may be attributed to carbonic surface-adherent contaminants. In this study, the surface carbon content at different stages of classical optics manufacturing was thus investigated. Two different standard processes—grinding and lapping with two final polishing processes using both polyurethane and pitch pads—were considered. After each process step, the chemical composition and roughness of the surface were analysed using X-ray photoelectron spectroscopy and atomic force microscopy. An obvious correlation between surface roughness and effective surface area, respectively, and the proportion of carbon contamination was observed. The lowest carbon contamination was found in case of lapped and pitch polished surfaces.


Author(s):  
Thomas Pelini ◽  
Christine Elias ◽  
Ryan Page ◽  
James H. Edgar ◽  
Pierre Valvin ◽  
...  

2021 ◽  
Vol 7 (2) ◽  
Author(s):  
Arti Yadav ◽  
Noushin Moharrami ◽  
Steve Bull

AbstractModification of the chemomechanical behaviour of the surface of sapphire by ion implantation to improve its near-surface mechanical properties has been investigated. 300 keV Ti+ ions at various doses were implanted and the concentration and damage profiles characterised using Rutherford Backscattering (RBS). At high doses (≥ 3 × 1016 Ti+ cm−2), a surface amorphous layer is formed due to implantation-induced damage. Nanoindentation was used to determine the hardness behaviour of the ion-implanted layer. Hardness increases at low implantation doses, associated with implantation-induced damage, but it is also observed that chemomechanical softening of the surface is reduced due to the removal of adsorbed water. In situ Raman scattering measurements demonstrate this removal at low doses and the re-establishment of the adsorbed water layer at high doses. The adsorption process is changed due to the introduction of carbon into the sapphire surface during implantation. For the optimum-implanted dose, the water readsorption does not recur even several years after the implantation treatment was first carried out. The loss of water adsorption is related to the formation of a non-polar carbonaceous layer on the sapphire surface by cracking of back-streamed diffusion pump oil deposited on the sample surface by inelastic collisions with the ion beam. Based on this study, it is concluded that ion implantation with an appropriate ion species and dose can control the chemomechanical effect and improve the hardness of ceramics, such as sapphire.


2021 ◽  
Vol 141 (2) ◽  
pp. 133-138
Author(s):  
Masaaki Takezawa ◽  
Kenji Sakakura ◽  
Jun Tanaka ◽  
Hiroaki Machida ◽  
Teruhiko Fujiwara

2021 ◽  
Vol 6 ◽  
pp. 28-37
Author(s):  
V. I. Silaev ◽  
◽  
L. P. Vergasova ◽  
V. N. Filippov ◽  
A. F. Khazov ◽  
...  

The results of studies of metal-carbon composites, unique in composition and origin, in which the metal component is a tin-aluminum alloy with an admixture of In, Cu, Fe, Cr, Se, are discussed. The morphology and internal structure of particles, variations in the chemical composition, and the isotopic of carbon impurities are analyzed. Based on the diagram of the eutectic type, a conclusion was made about the crystallization of alloys in the temperature range 650—150 °С. The question of the indium content of volcanic products in Kamchatka as a new and possibly industrially promising type of phase-diverse indium mineralization is discussed.


2020 ◽  
Author(s):  
Katherine Cochrane ◽  
Jun-Ho Lee ◽  
Christoph Kastl ◽  
Jonah Haber ◽  
Tianyi Zhang ◽  
...  

Abstract We demonstrate the creation of a spin-1/2 state via the atomically controlled generation of magnetic carbon radical ions (CRIs) in synthetic two-dimensional transition metal dichalcogenides. Hydrogenated carbon impurities located at chalcogen sites introduced by chemical doping are activated with atomic precision by hydrogen depassivation using a scanning probe tip. In its anionic state, the carbon impurity exhibits a magnetic moment of 1 μB resulting from an unpaired electron populating a spin-polarized in-gap orbital. By inelastic tunneling spectroscopy and density functional theory we show that the CRI defect states couple to a small number of vibrational modes, including a local, breathing-type mode. The electron-phonon coupling strength critically depends on the spin state and differs for monolayer and bilayer WS2. These carbon radical ions in TMDs comprise a new class of surface-bound, single-atom spin-qubits that can be selectively introduced, are spatially precise, feature a well-understood vibronic spectrum, and are charge state controlled.


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