Low friction states for thin solid lubricant film of MoS2

2018 ◽  
Vol 70 (4) ◽  
pp. 639-644 ◽  
Author(s):  
Kwang-Hua R. Chu
Keyword(s):  
Thin Films ◽  
Solid Lubricant ◽  
Activation Volume ◽  
High Vacuum ◽  
Low Friction ◽  
Friction Behavior ◽  
Stick Slip ◽  
Content Type ◽  
Term Operation

Purpose During the operation of Wendelstein 7-X (W7-X), any mechanical disturbance such as stick-slip may cause quenching of superconducting (SC) coils. The friction behavior of MoS2 lubrication (thin film) for narrow support elements between the SC coils in W7-X is rather important, as there is a design requirement for a coefficient of friction (COF) 0.05 between the sliding surfaces to control the stress contribution (from friction). Design/methodology/approach The author has carried out intensive calibrations or verifications using verified models considering previous friction tests on various samples which measured the COF in 4.2 K, 77 K and room temperature conditions (at high vacuum) to simulate the actual working condition. Findings The author has given useful explanations and diagnosis for previous anomalous scattered data. To improve the performance of MoS2, the author has predicted its better COF (0.002 via tuning of the activation volume), which could be a superlubricating state for MoS2 thin films considering the long-term operation requirement W7-X. Originality/value In this paper, the author has adopted Eyring’s approach to predict the low COF (0.002 via tuning of the activation volume), which could be a superlubricating state for MoS2 thin films considering the long-term operation requirement W7-X. Finally, some recent progresses about the possible few-layer MoS2 role in the electromagnetic loads have been provided.

scholarly journals Evaluation of Friction Behavior and Surface Interactions of Cyano-Based Ionic Liquids under Different Sliding Contacts and High Vacuum Condition

Lubricants ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 69 ◽  
Author(s):  
Shouhei Kawada ◽  
Seiya Watanabe ◽  
Shinya Sasaki ◽  
Masaaki Miyatake
Keyword(s):  
Mass Spectrometry ◽  
Ionic Liquids ◽  
High Vacuum ◽  
Mass Spectrometry Analysis ◽  
Low Friction ◽  
Friction Behavior ◽  
Friction Coefficients ◽  
Spectrometry Analysis ◽  
Worn Surface ◽  
Nascent Surface

The friction coefficients of ionic liquids were evaluated by many investigations. Most investigations used fluorine-based ionic liquids as lubricants. However, these ionic liquids produce the corrosion wear. This investigation focuses on the use of cyano-based ionic liquids as lubricants. Compared to fluorine-based ionic liquids, cyano-based ionic liquids exhibit high friction coefficients against steel material. This work examines how the friction coefficients of cyano-based ionic liquids are influenced by the type of sliding material used (AISI 52100, TiO2, and tetrahedral amorphous carbon). TiO2 lubricated with 1-ethyl-3-methylimidazolium tricyanomethanide, and ta-C lubricated with 1-butyl-1methylpyrrolidinium tetracyanoborate exhibited very low friction coefficients, smaller than fluorine-based ionic liquids. Time-of-Flight Secondary Ion Mass Spectrometry analysis showed that anions adsorb onto the worn surface, suggesting that anion adsorption is a critical parameter influencing friction coefficients. Quadrupole Mass Spectrometry measurements revealed that cations decompose on the nascent surface, preventing adsorption on the worn surface. These results suggest that low friction coefficients require the decomposition of cations and adsorption of anions. The reactivity of nascent surface changes with the sliding material used due to varying catalytic activity of the nascent surfaces.

Liquidity hedging with futures and forward contracts

2019 ◽  
Vol 36 (2) ◽  
pp. 265-290 ◽  
Author(s):  
Yong Jae Shin ◽  
Unyong Pyo
Keyword(s):  
Firm Value ◽  
Minimal Amount ◽  
Forward Contracts ◽  
Content Type ◽  
Term Operation ◽  
Futures Contract ◽  
Hedging Strategies ◽  
Parameter Values ◽  
Risky Debt

Purpose This paper aims to develop hedging strategies using both futures and forward contracts and issuing risky debt when financially constrained firms are forced to operate in long horizon. Design/methodology/approach The authors present a model for developing hedging strategies using both futures and forward contracts and issuing risky debt. A theoretical model employing stochastic differential equations for forward hedging is illustrated with a numerical example over parameter values consistent with the literature. Findings A financially constrained firm with limited cash balance must hedge its liquidity with both future and forward contracts and issue risky debt to support its long-term operations. The firm can issue a minimal amount of risky debt by adding forward contracts into hedging and can increase its value higher than that when hedging with only futures contracts. We show numerically that hedging with both futures and forward contracts allows the firm to issue minimal risky debt in increasing its firm value. Practical implications When Metallgesellschaft nearly collapsed in 1993, it offered long-term forward contracts to its customers and attempted to hedge its risk by rolling over series of short-term futures contract. It created the situation of inherent mismatch in maturity structure. A financially constrained firm operating in a long horizon appears to commit its liquidity as long-term forward contracts, which cannot be fully hedged with series of futures contacts. The firm should hedge its liquidity with both futures and forward contracts and avoid liquidation with deadweight costs in its long-term operation. Originality/value This is the first study examining hedging strategies with both futures and forward contracts.

LONG-TERM OPERATION TESTS OF ORGANIC SOLID-STATE SOLAR CELLS

2007 ◽  
Vol 14 (04) ◽  
pp. 539-542 ◽  
Author(s):  
HIROKI SHIOKAWA ◽  
MASAAKI YOKOYAMA ◽  
MASAHIRO HIRAMOTO
Keyword(s):  
Solid State ◽  
Short Circuit ◽  
High Vacuum ◽  
Organic Photovoltaic ◽  
Organic Layer ◽  
Term Operation ◽  
Organic Solid ◽  
Initial Decrease ◽  
Junction Type

The long-term operation tests of two types of solid-state organic photovoltaic (OPV) cells, p–n heterojunction type cells and p–i–n junction type cells, were performed. In both cells, a drastic decrease in photocurrent within 1 h was observed in air. This rapid decrease was revealed to be caused by oxygen molecules which act as a electron trap in the electron transporting organic layer. Initial decrease of photocurrent was effectively suppressed under high vacuum (10-7 Torr). In the case of a p–n type cell, the decrease in short-circuit photocurrent was only 15% even under prolonged light irradiation of 260 h.

scholarly journals Geochemical and Temporal Influences on the Enrichment of Acidophilic Iron-Oxidizing Bacterial Communities

2016 ◽  
Vol 82 (12) ◽  
pp. 3611-3621 ◽  
Author(s):  
Yizhi Sheng ◽  
Kyle Bibby ◽  
Christen Grettenberger ◽  
Bradley Kaley ◽  
Jennifer L. Macalady ◽  
...  
Keyword(s):  
Community Structure ◽  
Microbial Community ◽  
Microbial Communities ◽  
Temporal Distance ◽  
Fed Batch ◽  
Content Type ◽  
Term Operation ◽  
Geochemical Conditions ◽  
Suspended Growth

ABSTRACTTwo acid mine drainage (AMD) sites in the Appalachian bituminous coal basin were selected to enrich for Fe(II)-oxidizing microbes and measure rates of low-pH Fe(II) oxidation in chemostatic bioreactors. Microbial communities were enriched for 74 to 128 days in fed-batch mode, then switched to flowthrough mode (additional 52 to 138 d) to measure rates of Fe(II) oxidation as a function of pH (2.1 to 4.2) and influent Fe(II) concentration (80 to 2,400 mg/liter). Biofilm samples were collected throughout these operations, and the microbial community structure was analyzed to evaluate impacts of geochemistry and incubation time. Alpha diversity decreased as the pH decreased and as the Fe(II) concentration increased, coincident with conditions that attained the highest rates of Fe(II) oxidation. The distribution of the seven most abundant bacterial genera could be explained by a combination of pH and Fe(II) concentration.Acidithiobacillus,Ferrovum,Gallionella,Leptospirillum,Ferrimicrobium,Acidiphilium, andAcidocellawere all found to be restricted within specific bounds of pH and Fe(II) concentration. Temporal distance, defined as the cumulative number of pore volumes from the start of flowthrough mode, appeared to be as important as geochemical conditions in controlling microbial community structure. Both alpha and beta diversities of microbial communities were significantly correlated to temporal distance in the flowthrough experiments. Even after long-term operation under nearly identical geochemical conditions, microbial communities enriched from the different sites remained distinct. While these microbial communities were enriched from sites that displayed markedly different field rates of Fe(II) oxidation, rates of Fe(II) oxidation measured in laboratory bioreactors were essentially the same. These results suggest that the performance of suspended-growth bioreactors for AMD treatment may not be strongly dependent on the inoculum used for reactor startup.IMPORTANCEThis study showed that different microbial communities enriched from two sites maintained distinct microbial community traits inherited from their respective seed materials. Long-term operation (up to 128 days of fed-batch enrichment followed by up to 138 days of flowthrough experiments) of these two systems did not lead to the same, or even more similar, microbial communities. However, these bioreactors did oxidize Fe(II) and remove total iron [Fe(T)] at very similar rates. These results suggest that the performance of suspended-growth bioreactors for AMD treatment may not be strongly dependent on the inoculum used for reactor startup. This would be advantageous, because system performance should be well constrained and predictable for many different sites.

The problems of resistance to scuffing of heavily loaded lubricated friction joints with WC/C-coated parts

2014 ◽  
Vol 66 (3) ◽  
pp. 434-442 ◽  
Author(s):  
Remigiusz Michalczewski ◽  
Witold Piekoszewski ◽  
Waldemar Tuszynski ◽  
Marian Szczerek
Keyword(s):  
Design Methodology ◽  
Solid Lubricant ◽  
Vapour Deposition ◽  
Friction Pair ◽  
Low Friction ◽  
Friction Zone ◽  
Content Type ◽  
Steel Coating ◽  
Uncoated Steel ◽  
Practical Implications

Purpose – The purpose of this paper was to explore the mechanisms of scuffing propagation of heavily loaded lubricated friction pair elements coated with low-friction WC/C coating for various material combinations. Design/methodology/approach – The investigations were performed for low-friction coatings WC/C (a-C:H:W) deposited by the reactive sputtering physical vapour deposition (PVD) process. Experiments were carried out using a four-ball tester with continuously increasing loads. Tests were conducted for the following four material combinations: steel/steel tribosystem (all balls uncoated); steel/coating tribosystem (one upper ball uncoated/three lower balls WC/C-coated); coating/steel tribosystem (one upper ball WC/C-coated/three lower balls uncoated); and coating/coating tribosystem (all balls WC/C-coated). Findings – The better scuffing resistance is achieved by coating only one element (coating/steel tribosystem) than all elements (coating/coating tribosystem). The description of scuffing propagation for all investigated tribosystems was done. The high scuffing resistance of the coating/steel tribosystem resulted from reducing the adhesion between rubbing surfaces due to low chemical affinity (similarities) between the steel and the coating material and the presence of solid lubricant in the friction zone. Practical implications – In all cases, when a coating is applied, an increase in scuffing resistance is observed. However, it is better to coat only one element than all. Furthermore, the scuffing resistance for the coating/steel tribosystem is significantly higher than for the steel/coating tribosystem. Originality/value – The main value of this paper is description of scuffing propagation and revealing the new aspects in application of low-friction WC/C coating for heavily loaded lubricated friction pair elements. The overlapping ratio has been defined as an important factor influencing the scuffing resistance of the coated tribosystems.

Thin-Film Oxide Phosphors as Electroluminescent Materials

1999 ◽  
Vol 558 ◽  
Author(s):  
Tadatsugu Minami
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Binary Compound ◽  
Device Structure ◽  
Solution Deposition ◽  
Insulating Layer ◽  
Term Operation ◽  
Full Color ◽  
Color Filters

ABSTRACTIn this paper, we introduce rare earth- or transition metal-activated oxide phosphor thin films prepared by magnetron sputtering and dip-coated solution deposition. Thin-film electroluminescent (TFEL) devices using these oxide phosphor thin films as the emitting layer were investigated with a single insulating layer device structure using a thick ceramic sheet insulating layer. High-luminance multicolor emissions and high luminous efficiencies were obtained in TFEL devices using various oxide phosphors: binary compound, Ga2O3; ternary compound, Zn2SiO4, CaGa2O4 and ZnGa2O4; and multicomponent oxide, Zn2SiO4-Zn2GeO4 system. Luminances above 2000 cd/m2were obtained in CaGa2O4:Mn and Zn2Si1-XGeXO4:Mn TFEL devices driven at 1 kHz. Maximum luminous efficiencies of 2.53, 1.7 and 1.2 Im/W were obtained in Zn2Si0.7Ge0.3O4:Mn, Ga2O3:Mn and ZnGa2O4:Mn TFEL devices, respectively. Stable long-term operation was obtained in dip-coated and sputtered Ga2O3:Mn phosphor TFEL devices even when driven at 10 kHz. Various thin-film oxide phosphors activated with transition metals are suitable for the emitting layer of full-color electroluminescent displays (ELD) without the use of color filters. In particular, Ga2O3 is very promising as a phosphor host material for ELDs.

scholarly journals Structure and Tribo-Mechanical Properties of MoSx:N:Mo Thin Films Synthesized by Reactive dcMS/HiPIMS

2021 ◽  
Author(s):  
Wolfgang Tillmann ◽  
Alexandra Wittig ◽  
Dominic Stangier ◽  
Carl-Arne Thomann ◽  
Jörg Debus ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Mechanical Properties ◽  
Solid Lubricant ◽  
Tribological Behavior ◽  
Sliding Contact ◽  
High Wear Resistance ◽  
Film Material ◽  
Low Friction ◽  
Property Profile

AbstractModifying MoS2 thin films by additional elements shows great potential in order to adjust the property profile and to meet the increasing requirements regarding high wear resistance and low friction properties of industrial components. Within that context, MoSx:N:Mo thin films were deposited by a reactive hybrid dcMS/HiPIMS process. By systematically increasing the Mo target cathode power, an investigation of the structural and the mechanical properties was conducted to understand the evolution of the tribological behavior. A low Mo target cathode power of 1 kW is related to the formation of the preferential (002) MoS2 basal-plane and thus a low friction with µ = 0.2. With an increasing amount of Mo, the film loses its solid lubricant MoS2 properties and a nitride constitution of the thin film is developing due to the formation of crystalline Mo and MoN phases. Related to this transformation, the hardness and elastic modulus are increased, but the adhesion and the tribological properties are impaired. The film loses its plasticity and the generated film material is directly removed from the contact area during the sliding contact.

Sliding Friction Behavior of Sintered Ni-Cr Composites with Solid Lubricants

2021 ◽  
Vol 875 ◽  
pp. 272-279
Author(s):  
Wan Farhana Mohamad ◽  
Amir Azam Khan ◽  
Pierre Barroy ◽  
Olivier Durand-Drouhin ◽  
Clement Puille ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Solid Lubricant ◽  
Sliding Friction ◽  
Solid Lubricants ◽  
Sem Analysis ◽  
Low Friction ◽  
Friction Behavior ◽  
Hardness Tester ◽  
Disc Configuration ◽  
Ball On Disc

High temperature applications of self-lubricated sliding surfaces have gained industrial importance during the recent years. One popular system is based on sintered Ni-Cr composites with addition of solid lubricants. In the present work these composites were prepared under controlled sintering conditions with different combinations of solid lubricants (MoS2, Ag and CaF2) at 1200 °C under flowing argon. The physical properties such as sintered density, relative density and porosity were studied. The microstructures and phase studies of the Ni-Cr based composites were conducted using SEM analysis while the hardness of the composites was measured by Vickers Micro Hardness Tester. The friction tests were conducted with ball on disc configuration following ASTM G-99-95a standard. The MoS2 solid lubricant provides best lubrication at room temperature which is demonstrated by a low friction coefficient compared to pure Ni-Cr composites. The SEM pictures of worn out tracks show solid debris distribution, and filling of pores with solid lubricant phases. The time taken for stabilization of friction coefficient also varies with the type of solid lubricant. Dual and multiple additions of solid lubricants are also able to reduce the friction of coefficient compared to pure Ni-Cr composite.

scholarly journals Effect of Start-Up Strategies and Electrode Materials on Carbon Dioxide Reduction on Biocathodes

2017 ◽  
Vol 84 (4) ◽  
Author(s):  
Soroush Saheb-Alam ◽  
Abhijeet Singh ◽  
Malte Hermansson ◽  
Frank Persson ◽  
Anna Schnürer ◽  
...  
Keyword(s):  
Microbial Community ◽  
Electrode Materials ◽  
Microbial Community Composition ◽  
Community Analysis ◽  
Microbial Community Analysis ◽  
Cathodic Current ◽  
Content Type ◽  
Term Operation ◽  
Start Up

ABSTRACT The enrichment of CO 2 -reducing microbial biocathodes is challenging. Previous research has shown that a promising approach could be to first enrich bioanodes and then lower the potential so the electrodes are converted into biocathodes. However, the effect of such a transition on the microbial community on the electrode has not been studied. The goal of this study was thus to compare the start-up of biocathodes from preenriched anodes with direct start-up from bare electrodes and to investigate changes in microbial community composition. The effect of three electrode materials on the long-term performance of the biocathodes was also investigated. In this study, preenrichment of acetate-oxidizing bioanodes did not facilitate the start-up of biocathodes. It took about 170 days for the preenriched electrodes to generate substantial cathodic current, compared to 83 days for the bare electrodes. Graphite foil and carbon felt cathodes produced higher current at the beginning of the experiment than did graphite rods. However, all electrodes produced similar current densities at the end of the over 1-year-long study (2.5 A/m 2 ). Methane was the only product detected during operation of the biocathodes. Acetate was the only product detected after inhibition of the methanogens. Microbial community analysis showed that Geobacter sp. dominated the bioanodes. On the biocathodes, the Geobacter sp. was succeeded by Methanobacterium spp., which made up more than 80% of the population. After inhibition of the methanogens, Acetobacterium sp. became dominant on the electrodes (40% relative abundance). The results suggested that bioelectrochemically generated H 2 acted as an electron donor for CO 2 reduction. IMPORTANCE In microbial electrochemical systems, living microorganisms function as catalysts for reactions on the anode and/or the cathode. There is a variety of potential applications, ranging from wastewater treatment and biogas generation to production of chemicals. Systems with biocathodes could be used to reduce CO 2 to methane, acetate, or other high-value chemicals. The technique can be used to convert solar energy to chemicals. However, enriching biocathodes that are capable of CO 2 reduction is more difficult and less studied than enriching bioanodes. The effect of different start-up strategies and electrode materials on the microbial communities that are enriched on biocathodes has not been studied. The purpose of this study was to investigate two different start-up strategies and three different electrode materials for start-up and long-term operation of biocathodes capable of reducing CO 2 to valuable biochemicals.

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