One of the main trends in the past decades is the reduction of wastage and the replacement of toxic compounds in industrial processes. Some soft metallic particles can be used as nontoxic solid lubricants in high-temperature processes. The behavior of bismuth metal particles, bismuth sulfide (Bi2S3), bismuth sulfate (Bi2(SO4)3), and bismuth oxide (Bi2O3) as powder lubricants was studied in a range of temperatures up to 580 °C. The mechanical behavior was examined using a high-temperature pin-on-disc setup, with which the friction force between two flat-contact surfaces was recorded. The bismuth-lubricated surfaces showed low coefficients of friction (μ ≈ 0.08) below 200 °C. Above the melting temperature of the metal powder at 271 °C, a layer of bismuth oxide developed and the friction coefficient increased. Bismuth oxide showed higher friction coefficients at all temperatures. Bismuth sulfide exhibited partial oxidation upon heating but the friction coefficient decreased to μ ≈ 0.15 above 500 °C, with the formation of bismuth oxide-sulfate, while some bismuth sulfate remained. All surfaces were studied by X-ray diffraction (XRD), confocal microscopy, high-resolution scanning electron microscopy (HR-SEM), and energy-dispersive X-ray spectroscopy (EDS). This study reveals how the partial oxidation of bismuth compounds at high temperatures affects their lubrication properties, depending on the nature of the bismuth compound.
In view of their possible application as high temperature solid lubricants, the tribological and thermochemical properties of several organosilica networks were investigated over a range of temperatures between 25 and 580 °C. Organosilica networks, obtained from monomers with terminal and bridging organic groups, were synthesized by a sol-gel process. The influence of carbon content, crosslink density, rotational freedom of incorporated hydrocarbon groups, and network connectivity on the high temperature friction properties of the polymer was studied for condensed materials from silicon alkoxide precursors with terminating organic groups, i.e., methyltrimethoxysilane, propyltrimethoxysilane, diisopropyldimethoxysilane, cyclohexyltrimethoxysilane, phenyltrimethoxysilane and 4-biphenylyltriethoxysilane networks, as well as precursors with organic bridging groups between Si centers, i.e., 1,4-bis(triethoxysilyl)benzene and 4,4′-bis(triethoxysilyl)-1,1′-biphenyl. Pin-on-disc measurements were performed using all selected solid lubricants. It was found that materials obtained from phenyltrimethoxysilane and cyclohexyltrimethoxysilane precursors showed softening above 120 °C and performed best in terms of friction reduction, reaching friction coefficients as low as 0.01. This value is lower than that of graphite films (0.050 ± 0.005), a common bench mark for solid lubricants.
The effect of water addition during preparation of a CH NH PbI layer on the photodynamics is studied by femtosecond transient absorption. Both the regular perovskite and the aqueous analogue show charge thermalisation on a timescale of about 500 fs. This process is, however, less pronounced in the latter layer. The spectral feature associated with hot charges does not fully decay on this timescale, but also shows a long-lived (sub-ns) component. As water molecules may interfere with the hydrogen bonding between the CH NH cations and the inorganic cage, this effect is possibly caused by immobilisation of cation motion, suggesting a key role of CH NH dipole reorientation in charge thermalisation. This effect shows the possibility of controlling hot charge carrier cooling to overcome the Shockley-Queisser limit.
strategy for conventional transparent conducting oxides (TCOs) is to resort to degenerately dope wide-bandgap semiconductors to achieve the two key properties: electrical conductivity and optical transparency. Wide bandgap semiconductors are selected as host materials, which have the interband transitions above the visible spectrum, whereas dopants increase carrier density and thus electrical conductivity. Tin-doped indium oxides (ITOs) have been widely used because of its best balance of high electrical conductivity and optical transparency in the visible spectrum. [3] However, the increasing use of ITO as TCOs has resulted in the increase in the cost of ITO due to the limited availability of indium ore. [4] Meanwhile, many other applications, such as solar blind detection, ultraviolet (UV) lithography, UV light-emitting diodes, and UV curing, require transparent conductors in the UV spectrum. [5][6][7][8] However, conventional TCOs with high conductivity present low transmittance on the UV side of the spectrum. [1] Recently, an alternative design strategy has been proposed to use correlated metals with the intrinsic high carrier density exhibiting strong electron correlations to achieve both high electrical conductivity, thus low resistivity, and optical transparency in the UV-visible spectral range, overcoming the limitations of conventional TCOs. [9][10][11][12][13][14][15][16][17][18][19] It has been shown that as correlated metal films on single crystal substrates get thin, they maintain low resistivity and thus low sheet resistance at room temperature (RT) whereas their optical transmittance is comparable to (or higher than) conventional TCOs in the visible (or UV) spectrum. [9,10,17] However, the epitaxy so far required expensive and size-limited single crystal substrates, which impedes the application of correlated metals as TCOs.Meanwhile, oxide nanosheets drew attention because they can be used as buffer layers to promote the growth of highquality and thus high-performance transition metal oxide films regardless the supporting substrates. [20][21][22][23][24][25][26] Almost full coverage of oxide nanosheets can be obtained on virtually any flat substrates without the limitation of the substrate size by using Langmuir-Blodgett method. [21,24,25] Boileau et al. showed that correlated CaVO 3 and SrVO 3 (SVO) films with a thickness of 40 nm on Ca 2 Nb 3 O 10 (CNO) nanosheets on glass had the RT Correlated metals with high carrier density and strongly correlated electron effects provide an alternative route to achieve transparent conducting materials, different from the conventional degenerately doped wide-bandgap transparent conducting oxides (TCO). The extremely low electrical resistivity and high optical transparency in the ultraviolet-visible spectral range shown in 4d correlated metals present an advantage over conventional TCOs. However, most of the 4d correlated metals are grown epitaxially on single crystal substrates. Here, it has been shown that Ca 2 Nb 3 O 10 nanosheets with different buffer laye...
The potential of the electrospray deposition technique as new method to make nanosheet-based multilayer films is evaluated. Densely packed nanosheet-based films with thicknesses of 1–20 nm with rms roughnesses of 2.1–2.4 nm were fabricated on samples of 1 cm2 size with a growth rate of 0.5 nm/min. Electrosprayed Ti0.87O2 nanosheet films were successfully used as oriented growth templates for 40 nm perovskite SrRuO3 thin films grown by pulsed laser deposition. The electrospray method provides a fast and easy alternative to the more commonly used Langmuir–Blodgett (LB) deposition method for nanosheet films.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.