Academic literature on the topic 'MoS2 doped coating'

A WC-Co coating with self-lubricating property was deposited by detonation gun (D-gun) process, using a WC-Co powder doped with a MoS2-Ni powder, under a proper spray condition. It is proved that the MoS2 composition was kept in the resulting coating by SEM, XRD and EPMA. Evaluation on sliding wear property indicates that the MoS2 composition plays an important role in lowering both coefficient of friction and wear rate for the resulting coating, which is confirmed by observations on wear track. It suggests that the deposition of WC-Co coating with self-lubricating property by D-gun spray is feasible by controlling lubricant powder and spray conditions, which can exhibit higher sliding wear resistance.

ABSTRACTWe report a simple and scalable process to synthesize the core–shell nanostructure of MoS2@N-doped carbon nanosheets (MoS2@C), in which polydopamine is coated on the MoS2 surface and then carbonized. Transmission electron microscopy reveals that the as-synthesized MoS2@C possesses a nanoscopic and ultrathin layer of MoS2 sheets with a thin and conformal coating of carbon layers (∼5 nm). The MoS2@C demonstrates a superior electrochemical performance as an anode material for lithium ion batteries compared to exfoliated MoS2 sample. This unique core–shell structure is capable of excellent delivery of Li+ ion in charging–discharging process: a specific capacity as high as 1239 mA h g−1, a high rate of charging-discharging capability even at a high current rate of 10 A g−1 while retaining 597 mA h g−1, and a good cycle stability over 70 cycles at a high current rate of 2 A g−1.

The paper presents an analysis of the friction and wear processes of a composite coating based on molybdenum disulphide doped by tungsten and titanium, taking into account the impact of load and temperature in the contact zone. The tribological tests were performed at room temperature and at 300°C and 350°C in non-lubricated sliding contact with an Al2O3 ball. The characterization of the micromechanical properties and the adhesion of coatings to steel substrates were done by scratch testing. The analysis of the coatings wear and the sliding tribolayer formation was conducted by the observation of the friction track using light microscopy (LM) and scanning electron microscopy (SEM). The low hardness of the MoS2(Ti,W) coating, equal to 6 GPa, with the predominantly amorphous structure, allows for quick formation of the tribological contact and the sliding tribolayer creation. Due to self-lubricating properties, the coating has a high wear resistance and a low friction coefficient (below 0.1), both at room and elevated temperatures. The study allowed the determination of the operating temperature limit of the coating-substrate system in sliding point contact, which helped to specify the application area of such material.

Determination of the location and quantity of poison or promoter elements on catalyst surfaces is an ideal application for the high spatial resolution available on the analytical electron microscope (AEM). However, these elements are often unstable under an electron beam making them difficult to detect consistently. This paper describes a method to enhance the stability of cesium, a mobile alkali metal, on the surface of a catalyst using a thin coating of chromium.The catalyst in this study was MoS2 doped with 5.3 wt% CsOOCH (4.8 mol% Cs) which is used for alcohol synthesis. After grinding with a mortar and pestle and spreading between glass slides, the Cs/MoS2 was supported on a carbon coated Cu grid. The Cs/MoS2 particles were coated with 10nm of Cr using a VCR Group, Inc. ion beam sputterer model IBS/TM200. During sputtering, the vacuum produced by a turbo pump and LN2 cold trap was better than 10-5 torr and the sample was continuously rotated and tilted.

The mechanical and tribological properties of pure MoS2, pure Au, Au-MoS2 and Ti-MoS2 coatings were evaluated and examined at a microscopic scale. The metal doped MoS2 coatings had varying metal content, 5-10at% for Ti and 10-90% for Au. Reciprocating sliding wear tests were performed with a range of initial Hertzian contact pressures from 0.41 to 3.5 GPa and in air at two humidity levels (i.e. "low" being 3-5%RH and "high" being 30-40%RH). Titanium and gold were chosen for this study as metal additives due to their positive influence on the mechanical properties of the coating. The friction and wear behavior at the micro-scale were directly compared to tribological properties at the macro-scale, which were performed using an in situ tribometer. Reciprocating micro- and macro- wear tests were performed with spherical diamond tip (with 10 and 50 µm radii) and a sapphire tip (with a radius of 3.175 mm), respectively. The range of initial Hertzian contact pressures for macro-scale (i.e. between 0.41GPa and 1.2GPa) overlapped with that for micro-scale. However, the initial Hertzian contact diameters (2*a) were very different (i.e. 0.8-2.3 µm for micro-scale and 60-180 µm for macro-scale). It was observed that the small addition of Ti or Au to MoS2 improved the microtribological properties (i.e. lower friction and less wear) compared to pure MoS2 coatings. The improved microtribological properties with metal additions were attributed to an increase in the mechanical properties, decrease in adhesion, and a decrease in the interfacial shear strength. In terms of the different length scales, lower steady state friction was observed for macrotribology compared to microtribology. The higher friction at the micro-scale was explained by the greater adhesion effects and additional velocity accommodation modes (e.g. microplowing or plowing). The microplowing or plowing at the microscopic scale was attributed to the tip roughness and the inability to sustain a stable transfer film throughout the tests at high humidity. In addition, using in situ and ex situ techniques, three different stages for solid lubrication were identified based on differences in contact area, tip shapes, and environmental conditions. The first stage has been previously observed with macrotribology on MoS2 coatings at low humidity levels. The second stage, on the other hand, was observed for micro-tribology where the contact size is significantly smaller compared to stage one. The main wear mechanism is still adhesion, but there is also some micro-plowing. The final stage was observed for humid sliding in microtribology, where no transfer films were observed and therefore the main wear mechanism was plowing.
Les propriétés mécaniques et tribologiques de revêtements de MoS2 pur, d'Au pur, de Au-MoS2 et de Ti-MoS2 ont été évaluées et examinées à l'échelle microscopique. Les revêtements nanocomposites étudiés contenaient 5-10 % at. de Ti et 10-90 % at. d'Au. Des tests d'usure par glissement alternatif ont été mis en œuvre, l'échelle de pression Hertzienne de contact initiale variant de 0.41 à 3.5 GPa, dans une atmosphère d'air avec deux niveaux d'humidité contrôlée (le niveau le moins élevé se situant entre 3 et 5 % HR et le plus élevé entre 30 et 40 % HR). Pour cette étude, le titane et l'or ont été choisis comme additifs métalliques pour leur influence positive sur les propriétés mécaniques des revêtements. Les comportements de friction et d'usure des revêtements à l'échelle microscopique ont été directement comparés à leurs propriétés tribologiques à l'échelle macroscopique, dont les tests étaient effectués à l'aide d'un tribomètre in situ. Des tests sclérométriques alternatifs ont été réalisés aux échelles microscopiques et macroscopiques avec des pointes de diamant sphérique (10 et 50 µm de rayon) et une pointe de saphir (ayant un rayon de 3.175 mm). La gamme de pression Hertzienne de contact utilisée à l'échelle microscopique (entre 0.41 GPa et 1.2 GPa) était très proche de celle utilisée à l'échelle macroscopique. Cependant, le diamètre de contact Hertzien initial (2*a) était très différent, soit 0.8 – 2.3 µm à l'échelle microscopique et 60 – 180 µm à l'échelle macroscopique. Les résultats montrent que l'ajout de faibles quantités de Ti ou d'Au au MoS2 améliore les propriétés micro-tribologiques (comportements à la friction et à l'usure atténués) en comparaison avec des revêtements de MoS2 pur. L'amélioration des propriétés micro-tribologiques due à l'addition de métaux a été attribuée au renforcement des propriétés mécaniques, une adhésion plus faible et une baisse des contraintes de cisaillement interfaciales. Si l'on compare des tests micro- et macro-tribologiques effectués sur des étendues de longueur variées, ces derniers étaient caractérisés par une friction en régime permanent moins élevée. Le comportement de friction plus accentué dans le cas des tests réalisés à l'échelle microscopique s'explique sur la base d'effets d'adhésion plus importants et des modes additionnels de compensation de vitesse (labourage ou micro-labourage). Les tendances au labourage ou micro-labourage observées à l'échelle microscopique ont été attribuées à la rugosité de la pointe de diamant et à la difficulté de maintenir une couche de film de transfert en place lors de tests effectués dans des conditions d'humidité élevée. L'utilisation de techniques in situ et ex situ a également permis de déterminer trois stades de lubrification solide, en se basant sur des différences observées à la zone de contact, dues aux formes des différentes pointes et aux conditions environnementales appliquées. Le premier stade, avait été identifié auparavant, lors de tests de macro-tribologie sur des revêtements de MoS2, à un niveau d'humidité faible. Par contre, le deuxième stade n'a été observé que lors de tests de micro-tribologie où la taille de la zone de contact était bien plus petite que dans le cas du premier stade. A ce stade, le mécanisme d'usure est principalement relié au comportement d'adhésion du revêtement, avec une influence possible de l'effet de micro-labourage. Le stade final de lubrification a été observé lors de tests de micro-tribologie réalisés dans des conditions d'humidité élevée et caractérisés par l'absence du film de transfert. De cette observation, il a été déduit que le principal mécanisme d'usure du film à ce stade de lubrification correspondait au labourage.

Smart coatings based on polymer matrix doped with carbon nanoparticles, such as carbon nanotubes or graphene, are being widely studied. The addition of carbon nanofillers into organic coatings usually enhances their performance, increasing their barrier properties, corrosion resistance, hardness, and wear strength. Moreover, the developed composites provide a new generation of protective organic coatings, being able to intelligently respond to damage or external stimuli. Carbon nanoparticles induce new functionalities to polymer coatings, most of them related to the higher electrical conductivity of nanocomposite due to the formation of percolation network. These coatings can be used as strain sensors and gauges, based on the variation of their electrical resistance (structural health monitoring, SHM). In addition, they act as self-heaters by the application of electrical voltage associated to resistive heating by Joule effect. This opens new potential applications, particularly deicing and defogging coatings. Superhydrophobic and self-cleaning coatings are inspired from lotus effect, designing micro- and nanoscaled hierarchical surfaces. Coatings with self-healable polymer matrix are able to repair surface damages. Other relevant smart capabilities of these new coatings are flame retardant, lubricating, stimuli-chromism, and antibacterial activity, among others.

In all conducting polymers (CPs), polyaniline (PANI) is one of the most thoroughly studied CPs. An essential feature of PANI is that its repeating units have two different moieties in different weights: oxidized and reduced state. In light of this element, PANI might be doped to get new molecular structures with various properties. It is considered as a (p-type) material, since it has excellent mechanical flexibility and environmental stability, and its conductivity could be controlled with acid/base (doping/undoping), it has potential applications in numerous fields, for example, lightweight battery electrodes, electromagnetic shielding devices, anti-corrosion coatings, and sensors. This chapter is focused on PANI as a leading polymer and brief synthesis of PANI thin films by the diverse strategies pursued by various applications in different fields.

In this study, magnesium (Mg) disks were coated with β-tricalcium phosphate (β-TCP) doped with different mass percent of silver (Ag) (0 wt%, 1 wt%, 5 wt% and 10 wt%) in an effort to modulate the detrimental osteoimmunomodulatory properties and colonization of bacteria on Mg disk, due to the reported favorable osteoimmunomodulatory properties of β-TCP and antibacterial properties of Ag. This paper describes the growth, characterization and corrosion analyses of β-TCP doped with different compositions of Ag thin film coatings. The phase composition and microstructure analyses were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The SEM images showed that varying the percentage of Ag dopant affects the surface morphology of the β-TCP coatings. The corrosion protection behavior of the coated samples were evaluated using electrochemical measurement techniques, such as potentiodynamic polarization (PD) and electrochemical impedance spectroscopy (EIS). The corrosion tests were performed in Hank’s Balanced salt solution using a three-electrode electrochemical cell. The results showed that the β-TCP coating and β-TCP doped with Ag coatings on the Mg disks exhibit a much superior stability and lower corrosion rate compared to bare Mg. It was observed that increasing the mass of the Ag dopant increases the corrosion protection, but 10 wt% Ag doping in β-TCP reduces the corrosion protection behavior. The SEM images of the samples after corrosion show that the β-TCP and β-TCP doped with 10 wt% Ag suffered the most corrosion attack compare to β-TCP doped with 1 wt% and 5 wt% Ag. In conclusion, we have developed β-TCP and β-TCP doped with 1 wt%, 5 wt% and 10 wt% Ag coating with tunable corrosion protection efficiency above 88%.

Abstract The development of temperature sensing Thermal Barrier Coating (TBC) systems by phosphor thermometry has significant potential to achieve accurate non-destructive temperature measurement in the coating. The doping of coatings using rare earth elements is a viable option to enable the temperature measurement by the virtue of their luminescence. While facilitating the temperature sensing, however, the thermo-mechanical and thermo-chemical stability of the coating must be maintained under extreme operating conditions. In this work, TBC configurations including a doped layer placed at the top or the bottom of the top coat have been fabricated via Air Plasma Spray (APS) using Yttria-Stabilized Zirconia (YSZ) that contains Europium (Eu) dopant. The TBC configurations have been characterized using high energy synchrotron X-ray diffraction (XRD) at both room temperature and high temperature. The TBC samples have been subjected to a single cycle thermal load during XRD data collection. The residual strain in the top coats of the TBCs have been quantified using XRD data. Residual strain in the top coat of the regular TBC configuration has been measured to be in the range of −0.8 × 10−4 to −1.0 × 10−4 for out-of-plane strain (e11) and 0.5 × 10−4 to 2.0 × 10−4 for in-plane strain (e22). The doped layer above the top coat was found to most significantly affect the spatial strain distribution across depth in the YSZ layer by increasing the strain magnitudes closer to the bond coat. However, the difference in strain distribution due to doped layers was found to be less than 1.0 × 10−4, which is close to the experimental limit. Thus, the doped layer did not significantly alter the overall residual strain states of the coating.

By adapting existing thermal barrier coatings a sensor coating has been developed to enhance their functionality, such that they not only protect engine components from the high temperature gas, but can now also measure the material temperature accurately and the health of the coating e.g. ageing, erosion and corrosion. The sensing capability is introduced by embedding optically active materials into the thermal barrier coating and by illuminating these coatings with excitation light phosphorescence can be observed. The phosphorescence carries temperature and structural information about the coating. Knowledge of the exact temperature could enable the design of advanced cooling strategies in the most efficient way using a minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of thermal barrier coatings to be realized due to improved accuracy in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. Application: The work carried out included the successful implementation of a sensor coating system on a Rolls-Royce Viper engine. The system consists of three components: industrially-manufactured robust coatings, advanced remote detection optics and improved control and readout software. The majority of coatings were based on yttria stabilized zirconia doped with Dy, although other coatings made of yttrium aluminium garnet were manufactured as well. Coatings were produced on a production line using atmospheric plasma spraying. Parallel tests at Didcot power station revealed the durability of specific coatings in excess of 4,500 effective operating hours. It is expected that the capability of these coatings is in the range of normal maintenance schedules of industrial gas turbines of 24,000hrs or even longer. An optical energy transfer system was designed and developed permitting scanning of coated components and also the detection of phosphorescence on rotating turbine blades (13,000 RPM) at probe-to-target distances of up to 400mm. The online measurement system demonstrated precision (around ±5K) comparable to commercial thermocouples and has shown calibration accuracy of ±4K. Transient temperatures were tracked at maximum at 8Hz which is fast enough to follow a typical power generation gas turbine. Repeatable measurements were successfully taken from the nozzle guide vanes (hot), the combustion chamber (noisy) and the rotating turbine blades (moving) and compared with thermocouple and pyrometer installations.

Thermal barrier coatings are used to reduce the actual working temperature of the high pressure turbine blade metal surface and hence permit the engine to operate at higher more efficient temperatures. Sensor coatings are an adaptation of existing thermal barrier coatings to enhance their functionality, such that they not only protect engine components from the high temperature gas, but can also measure the material temperature accurately and determine the health of the coating e.g. ageing, erosion and corrosion. The sensing capability is introduced by embedding optically active materials into the thermal barrier coatings and by illuminating these coatings with excitation light phosphorescence can be observed. The phosphorescence carries temperature and structural information about the coating. Accurate temperature measurements in the engine hot section would eliminate some of the conservative margins which currently need to be imposed to permit safe operation. A 50K underestimation at high operating temperatures can lead to significant pre-mature failure of the protective coating and loss of integrity. Knowledge of the exact temperature could enable the adaptation of the most efficient coating strategies using the minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of thermal barrier coatings to be realised due to improved accuracy in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. Application: This paper describes the implementation of a sensor coating system on a Rolls-Royce jet engine. The system consists of three components: industrially manufactured robust coatings, advanced remote detection optics and improved control and readout software. The majority of coatings were based on yttria stabilized zirconia doped with Dy (dysprosium) and Eu (europium), although other coatings made of yttrium aluminium garnet were manufactured as well. Coatings were produced on a production line using atmospheric plasma spraying. Parallel tests at Didcot power station revealed survivability of specific coatings in excess of 4,500 effective operating hours. It is deduced that the capability of these coatings is in the range of normal maintenance schedules of industrial gas turbines of 24,000 hours or even longer. An advanced optical system was designed and manufactured permitting easy scanning of coated components and also the detection of phosphorescence on rotating turbine blades (13k RPM) at stand-off distances of up to 400mm. Successful temperature measurements were taken from the nozzle guide vanes (hot), the combustion chamber (noisy) and the rotating turbine blades (moving) and compared with thermocouple and pyrometer installations for validation purposes.

7YSZ (yttria stabilized zirconia) was co-doped with metal oxides of different valence, ionic radius and mass in order to investigate microstructural and property changes as a result of co-doping. Mechanical alloying process was used to produce the powder blends which were subsequently sintered at 1500°C for 120 hours. The results from SEM, XRD and DSC showed that the microstructures of the co-doped ternary oxides were affected by the amount of oxygen vacancies in the system, the co-dopant cation radius and mass. Increasing the number of oxygen vacancies by the addition of trivalent co-dopant (Yb2O3 and Sc2O3) as well as the use of larger cations promoted the stabilization of cubic phase. The tetravalent co-dopant (CeO2), on the other hand, had the effect of stabilizing tetragonal phase which may transform into monoclinic phase during cooling, depending on the concentration of tetravalent co-dopant and the mass. Smaller cation mass had the effect of reducing the transformation temperature from tetragonal to monoclinic phase. Pentavalent co-dopants (Nb2O5 and Ta2O5) were found to stabilize the tetragonal phase at high temperature; however, the stability of the tetragonal phase upon cooling was determined by the mass and ionic radius of the co-dopants. Cation clustering was observed during cooling in trivalent oxide co-doped 7YSZ while clustering of trivalent and pentavalent cations in pentavalent co-doped 7YSZ was not detected. Additionally, from the thermal conductivity measurement results, it was found that trivalent oxides exhibited the most significant effect on reducing the thermal conductivity of ternary oxides; this trend was followed by pentavalent co-doping oxides whereas the tetravalent CeO2 co-doped 7YSZ showed marginal effect. A semi-empirical thermal conductivity model was established based on defect cluster model and the predicted room temperature thermal conductivity values were found to be consistent with that measured experimentally. Furthermore, the incorporation of co-dopant oxide in 7YSZ was observed to substantially modify the elastic modulus of the ternary oxides. More specifically, the addition of co-dopant with larger cation radius was found to reduce the elastic modulus of 7YSZ due to the increase in lattice parameter(s).

Titania doped YSZ ceramic samples were subjected to calorimetric, thermal and microstructural analyses to assess the value of titania as a dopant for use as thermal barrier coating in modern gas turbine engines. The primary objective of titania addition was to effectively stabilize the tetragonal phase at operating temperatures while lowering the thermal conductivity. Powder blends with 5, 10, and 15 wt% titania added to standard 7YSZ powder were sintered at 1200°C for 325hrs after plasma spraying. Basic physical properties related to the thermal conductivity of the material such as bulk densities and Young’s modulus were determined. Phase analysis of all samples was performed using x-ray diffraction techniques so the percentage of monoclinic, tetragonal, and cubic phases could be determined. For all titania samples, it was shown that the composition was predominantly tetragonal with slightly decreasing amounts of monoclinic phases present with increasing titania content. The results of calorimetric analysis showed a marginal decrease in the specific heat capacities of the sintered titania doped samples. Similarly, thermal diffusivities were lowered by the addition of titania, though only slightly, since it has been previously shown that diffusivity is more strongly linked to sample porosity. Using these results, the experimental thermal conductivities for all titania doped samples were determined and compared to theoretical conductivities based solely on the mechanical properties of the ceramic. The results showed a decrease in thermal conductivity with the addition of titania, though with higher values than that predicted from the theoretical model. Experimental thermal conductivities were also shown to decrease with temperature initially, while increasing slightly at higher temperatures, which is most probably due to the radiation effect.

Thermal Barrier Coatings (TBC) are used to reduce the actual working temperature of the high pressure turbine blade metal surface. Knowing the temperature of the surface of the TBC and at the interface between the bondcoat and the thermally grown oxide (TGO) under realistic conditions is highly desirable. As the major life-controlling factors for TBC systems are thermally activated, therefore linked with temperature, this would provide useful data for a better understanding of these phenomena and to assess the remaining lifetime of the TBC. This knowledge could also enable the design of advanced cooling strategies in the most efficient way using a minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of TBCs to be realised due to improved precision in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. The concept of a thermal-sensing TBC was first introduced by Choy, Feist and Heyes in 1998 [1]. The TBC is locally modified so it acts as a thermographic phosphor. Phosphors are an innovative way of remotely measuring temperatures and also other physical properties at different depths in the coating using photo stimulated phosphorescence [2]. In this study the temperature dependence of several rare earth doped EB-PVD coatings will be compared. Details of the measurements, the influence of aging, the composition and the fabrication of the sensing TBC will be discussed in this paper. Temperature detection at ultra-high temperatures above 1300°C is presented using new types of EBPVD TBC ceramic compositions. Multilayer sensing TBCs will be presented, which enable the detection of temperatures below and on the surface of the TBC simultaneously.

The standard yttria-stabilized zirconia (YSZ) has been used as thermal barrier coatings (TBCs) in the hot sections of gas turbine engines for several decades. To achieve further improvement to the thermal insulation capability of current TBCs, doping of alternative oxides to zirconia or co-doping of oxides to YSZ has been employed. In our previous study, it has been shown that doping of 7YSZ with titania (TiO2) reduces thermal conductivity of 7YSZ substantially. As TBCs are susceptible to various failure mechanisms, in this study the erosion resistance of TiYSZ at high impingement speed and angle is evaluated along with measurements of hardness (H) and elastic modulus (E). Specimens with 5 different TiO2 doping amounts (5%, 7.5%, 10%, 12.5% and 15%) are fabricated using plasma spraying and high temperature sintering. The erosion test results show that sample with 5% TiO2 (5TiYSZ) suffers the most erosion damage at high impingement angle due to brittle fracture while 10-15TiYSZ samples exhibit less brittle erosion damage which leads to lower erosion rates under the same test condition. When comparing the erosion rates (defined as the loss of sample mass per mass unit of abrasive particles) to the hardness values, they were found to follow the same trend. The addition of TiO2 (10–15 wt%) had the effect of reducing the erosion rate of 7YSZ at high impingement angle.

Silicon is the most widely used material in the microelectronics and photovoltaics industry. Currently it is used in one of two forms: as wafers of single- or polycrystalline material or as CVD deposited thin film material. While crystalline silicon solar cells achieve high efficiencies, the silicon wafer contributes significantly to the module cost. Thin film silicon solar cells can be produced at much lower cost, but they also feature lower efficiencies. In this presentation, we discuss an alternate route to forming silicon (Si) or germanium (Ge) thin films from solution on flexible substrates. Silicon (germanium) nanocrystals are formed in a nonthermal plasma. In the plasma environment a Si/Ge precursor is broken down by electron impact, leading to the nucleation and growth of Si or Ge crystals. By adding dopant precursors, p- and n-doped as well as intrinsic crystals can be formed. Organic ligands can be attached in the plasma such that nanocrystals become soluble in organic solvents. These “nanocrystal inks” can be used to form Si or Ge films with ultra-low-cost printing or coating techniques. Film properties of Si/Ge-ink processed films will be discussed. Proof-of-concept demonstrations of solar cells produced from silicon inks will be presented.