Carbonaceous Films Research Articles

Enhancing lubrication of electrified interfaces by inert gas atmosphere

Abstract Considering the growing interest in increasing performance and efficiency of driveline components of modern electric vehicles, this work aims to analyze and report the wear mechanisms and notable enhancement of the lubrication of electrified contact interfaces by inert gas atmospheres. Systematic tribological studies were conducted on AISI 52100 steel test pairs using driveline lubricants under unelectrified and electrified conditions in ambient air and dry N2. Test results showed that in ambient air and electrification, the formation of iron oxides (in particular hematite) was most dominant and gave rise to severe abrasive wear regardless of the lubricant type being used. In dry N2, however, the tribo-oxidation was suppressed but the formation of a carbon-rich tribofilm was favored (especially under electrified conditions). Such a shift from surface oxidation to carbonaceous film formation resulted in dramatic reductions (by factors of 8 to 10) in the wear of test pairs.

Carbon-based thin films as a suitable alternative to metallized films for the preparation of radioactive sources

A new method for radionuclide labeling by the use of graphene thin films was previously presented. In this work, a comparison among low energy radioactive sources supported on carbonaceous thin films on polyvinyl chloride-polyvinyl acetate copolymer (VYNS), based on the use of aqueous solutions is investigated as a feasible alternative to the traditional metallized films avoiding the downside of the loss of many broken films. Graphene-based materials were prepared by both oxidation-exfoliation-reduction and direct graphite exfoliation routes. In addition, multiwalled carbon nanotubes (MWCNTs) thin films were also evaluated. The stability of both carbonaceous materials aqueous dispersions were studied by using ionic and non-ionic surfactants. Solid carbon-based materials were characterized by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) whereas the colloidal nature of the aqueous dispersions was verified by the measurement of Tyndall effect and the morphology of thin films was evaluated by Scanning Electron Microscopy (SEM). 55Fe solutions were used to prepare the radioactive sources on the thin films by quantitative drop deposition. The quality of spectra was measured in a pressurized proportional counter. Results showed a resolution higher than 0.9 keV for all the tested sources. However, MWCNT-based along with non-surfactant sources presented non-adequate escape peaks and low energy tails. On the contrary, all the graphene-based sources prepared using surfactants to stabilize aqueous solutions presented an energy resolution comparable to that of the metallized source while offering notable advantages in terms of cost efficiency and reliability of the as-prepared supports.

Nano-etching of carbon nanofiber surface and subsequent Fe–N–C thin film coating for enhancement of oxygen evolution reaction

The oxygen evolution reaction (OER) is involved in many electrical–chemical energy conversion systems; however, the slow reaction rate of the OER leads to a high overpotential (η) and low energy efficiency. Recently, an extremely low-η OER phenomenon was observed at a carbonaceous Fe–N-doped thin film with enriched step edges on highly oriented pyrolytic graphite and the carbon fiber surface in an alkaline electrolyte, although the activity was limited. In this study, multi-walled carbon nanotubes (MWCNTs) were used as substrates to utilize their high specific surface areas to develop an active OER catalyst. Nanoscale etching of the MWCNT surface was performed by Fe3O4 nanoparticle loading and subsequent heat treatment in an inert atmosphere, followed by acid washing. Afterwards, a carbonaceous thin film containing Fe and N was coated on the surface via sublimation, deposition, and pyrolysis of Fe phthalocyanine (Pc). A roughened surface was observed for the FePc-derived thin film coated on the nano-etched MWCNT, in contrast to the smooth surface observed for the film coated on the MWCNT without nano-etching. The combination of the nano-etching and the thin-film coating enhanced the OER, which was analyzed by parallel Tafel processes.

Tunable amorphous carbon films formed on ultralow wear, Pt–Au alloys

The mechanocatalytic formation of carbonaceous films at the interface between sliding metallic contacts is simultaneously advantageous for reducing friction and adhesion in several tribological applications and detrimental for electrical contacts as they can induce device failure by increasing the contact resistance. Yet, remarkably little is still known about the chemistry, structural and mechanical properties, and tunability of these interfacial layers. In this study, we performed contact pressure-dependent tribological experiments in dry nitrogen containing trace organics on four, nanocrystalline Pt–Au alloys ([Au] from 0 at.% to 10 at.%) – a promising class of alloys for ultralow wear and electrical contact applications. The ex-situ, multi-technique characterization results did not only provide insights into the chemical nature and mechanical behavior of the mechanocatalytic, carbon-rich films formed on Pt–Au surfaces, but also revealed the interplay between catalytic and mechanochemical tribofilm formation controlled by the composition-dependent electronic structure of the Pt–Au substrate and the applied contact pressure. The results of this work provide guidelines for tailoring nanocrystalline alloys to control their mechanocatalytic activity on the basis of variations of the alloy mechanical properties and element's electronic structure with the alloy stoichiometry.

Carbon gas sensors synthesized using acacia auriculiformis tree branches to detect methanol, ethanol, acetone vapors and ammonia gas

Metal oxides and carbon are the prime candidates of gas sensor devices. For the inaugural instance, carbonaceous particulate matter was meticulously derived from the branches of Acacia auriculiformis tree indigenous to Sri Lanka to detect vapor and gas. It is worth noting that biomass derived carbon had hitherto remain unexplored in the realm of vapor and gas detection. Carbon films were fabricated via the doctor blade method. The resistivity characteristic of these carbon samples exhibited discernible variations upon exposure to methanol, ethanol, acetone vapors, and ammonia gas. Notably, the gas-sensing properties of sample derived from the central core and the outer shell of Acacia auriculiformis tree branches were independently assessed in these vapors and gas at ambient temperature. Various analytical techniques, including X-ray diffraction (XRD), UVvisible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), were judiciously employed to scrutinize the structural attribute, optical band gap, chemical composition and surface morphology of the aforementioned carbon film samples, respectively. XRD analyses unequivocally confirmed the successful formation of carbonaceous films. FTIR spectra conspicuously delineated the presence of oxygen within the carbon films. Importantly, the optical band gap of our carbon films manifested within the range characteristic of organic carbon. Furthermore, the resistance of the carbon films demonstrated a significant reduction upon adsorption of each vapor. It is noteworthy that while gas sensitivities and response times were superior for carbon derived from the central core of the Acacia tree branches, the recovery times were notably expedited for carbon synthesized from the outer shell of these branches. The zenith of gas sensitivity, an impressive 187%, was recorded in response to 1000 ppm of methanol vapor, when employing carbon sourced from the central core of the acacia tree branches.

Influence of Atmosphere on Carbonaceous Film Formation in Rubbing, Metallic Contacts

Many previous researchers have reported the formation of carbonaceous tribofilms from organic lubricants on rubbing metallic surfaces. This paper shows that a very important factor in the formation of such tribofilms is the presence or absence of molecular oxygen. When steel surfaces are rubbed in saturated hydrocarbon lubricants in the absence of oxygen, for example in nitrogen or hydrogen gas, carbonaceous films form very readily, resulting in low friction and wear. However, when a significant amount of oxygen is present, as is the case in air, carbonaceous tribofilms are not generally formed, so friction and wear are very high, with values comparable to those seen when no lubricant is present. In situ Raman analysis combined with gas-switching experiments show that the carbonaceous films formed during rubbing when no oxygen is present are rapidly removed during rubbing in air, while tests in which lubricant is removed during a test in N2 indicate that the films are quite weak. This suggests that these carbonaceous films are being continually removed and replenished during rubbing in oxygen-free conditions. It is proposed that these carbonaceous films are formed from hydrocarbyl free radicals that are generated mechanochemically from hydrocarbon molecules during rubbing. In the absence of oxygen, these free radicals then react together to form a carbonaceous film. However, when oxygen is present, the hydrocarbyl free radicals react extremely rapidly with oxygen molecules to produce hydroperoxyl free radicals and so are no longer available to generate a carbonaceous tribofilm.Graphical abstract

Noncalcified dasyclad algae from the Vasalemma Formation, late Sandbian (Late Ordovician) of Estonia

The Vasalemma Formation, late Sandbian, Late Ordovician in Estonia contains a previously unknown flora of noncalcified dasyclad algae. The Vasalemma Formation is a locally restricted limestone unit, which is predominantly composed of an echinoderm grainstone. The formation, in its central areas, contains bryozoa- and echinoderm-rich reefs, and associated with these reefs, small patches of dolomitic lime-mudstone with an algal-Lagerstätte occur. The macroalgae are preserved as thin carbonaceous film associated with pyrite without any micro-structures evident. Three taxa could be distinguished: Chaetocladus vasalemmense Kröger, et Tinn spec. nov., Chaetocladus sp., Eocladus estoniense Kröger, et Tinn spec. nov. All three taxa have simple monopodial morphologies and delicate laterals. Remarkable is the occurrence of branched laterals in E. estoniense, which to our knowledge, is among the earliest occurrence of this morphotype. The Vasalemma algae flora can be compared with roughly contemporaneous occurrences in North America, which show similarities in depositional environments and associated fauna but differ in morphological and taxonomical diversity.

Fabrication of HAp/rGO nanocomposite coating on PEEK: Tribological performance study

Polyetheretheretherketone (PEEK) is a prominent alternative material in medical applications because of its lower stress shielding impact than metal. Friction and wear characteristics have a large impact on the long-term in vivo performance of load-bearing implants. As a result, orthopaedic polymer implants have been subjected to a myriad of surface changes to increase their biofunctionality. In this study, wear resistant coatings, including hydroxyapatite (HAp) and reduced graphene oxide (rGO) as HAp/rGo, rGo/HAp and HAp+rGO nano composites were applied to the polyetheretherketone (PEEK) sample through dip coating method. The characterization of various coating combinations and patterns was accomplished by FESEM, XRD, AFM, and FT-IR. It was observed that the inclusion of rGO with HAp enhanced the friction and wear behaviour, with the HAp+rGO composition achieving the best wear resistance. In addition, carbonaceous films formed between the composite surfaces and counter body operated as solid lubricating films, resulting in a drop in the coefficient of friction (COF) from to 0.23 r min−1 on the coating and even helps to increase hydrophobicity state of the coating. Nevertheless, because rGO functions as an interstitial bonding agent between PEEK and HAp, bond strength increases, with the HAp+rGO combination having the highest bond strength of 35 MPa.

A new specimen of the Early Cretaceous long-necked choristodere Hyphalosaurus from Liaoning, China with exceptionally-preserved integument

Although the highly specialized long-necked Early Cretaceous choristodere Hyphalosaurus is well known from the Jehol Biota of China, the integument of this genus has been only partially described. A new specimen from Liaoning Province, China, attributed to the species H. lingyuanensis, reveals additional details. The integumentary remains demonstrate a variety of scale shapes including rhomboid, square, rectangular, polygonal, and round-to-ovoid scales. The latter are arranged in parasagittal rows along the flanks and tail, but not along the neck. These rows of enlarged scales resemble the pattern seen in the contemporaneous short-necked Chinese Monjurosuchus splendens and may be a shared derived trait. In addition, carbonaceous films between the phalanges support the view that the manus and pes were partially webbed in Hyphalosaurus, as in Monjurosuchus and many other aquatic reptiles. The new specimen thus provides further insights into the life appearance of Hyphalosaurus.

Adsorption and corrosion inhibition performance of rice bran extract on carbon steel in aqueous chloride solution: Experimental, computational and theoretical studies

In this study, an ecofriendly corrosion inhibitor made of waste rice bran was produced to reduce corrosion caused by chloride on reinforcement. Electrochemical results revealed that with increasing inhibitor concentration the inhibition efficiency of the rice bran extract (RBE) reached the maximum value of 98% at an optimum concentration of 4.5%. The existence of carbonaceous passive film over the steel surface was established by X-ray photoelectron spectroscopy (XPS). Quantum mechanics and Molecular simulations evidenced the adsorption of phytochemicals onto the steel surface thus, affirming the inhibition action of the rice bran extract.

Tribological performances of a-C films tested on dry nitrogen environment with various Hertz pressures: Failure mechanisms and in-situ formation graphene

The tribological properties of hydrogen-free amorphous carbon (a-C) films are affected by the test environment and load condition. The wear mechanisms of a-C films sliding against Si3N4 ball under inert atmosphere exhibits different mode during different sliding cycles. The results show that the tribological behaviors for a-C films exhibit adhesive wear and it did not wear out even after sliding test 40,000 cycles when the normal load is 1 N. As the normal load increases, the wear mechanisms mainly show fatigue wear and three-body wear induced by fatigue wears due to the increasing of alternating stress. The emergence of three-body wear will drastically change the local stress distribution of a-C film. The position obtaining maximum Von-Mises stress shifts from the subsurface of substrate to subsurface of a-C film, and the maximum Von-Mises stress and Hertzian contact pressure increases sharply. The structures of in-situ formation graphene originated from the transformation of amorphous carbonaceous structure are detected on the wear scars. The formation of carbonaceous transfer film is beneficial to facilitate the graphitization transition with increasing Hertz pressure from 0.65 GPa to 1.35 GPa. On the other hand, the transition temperature of graphitization is sharply reduced to the flash temperature of contact zone due to the emergence of three-body wear obtaining the instantaneous Hertz pressure reached to 29.5 GPa. These conclusions possibly provide valuable references for designing film thicknesses, reveal tribological mechanism for a-C films under dry inertness atmosphere and broaden industrial application.

The role of cermet interlayer on tribological behaviors of DLC/Cr3C2–NiCr duplex coating from the perspective of carbonaceous transfer film formation

The effect of applied load on the tribological behaviors of single DLC coating and DLC/Cr3C2–NiCr duplex coating was explored in the paper experimentally, and the role of cermet interlayer on the duplex coating tribological behavior was analyzed from the perspective of carbonaceous transfer film formation. Results proved that the duplex coating wear rate under 20 N was the lowest, about 1/6 of that of the single coating. The existence of Cr3C2–NiCr interlayer can prevent the top DLC film from being damaged in high load friction, reduce the fluctuation and vibration of the friction interface, and help the friction-induced graphitized carbonaceous transfer film to maintain on the friction counterpart, thus realizing the low-friction of the duplex coating. Furthermore, the critical conditions under which the friction-induced carbonaceous transfer film of a single coating maintains on the friction counterpart are explored by designed experiments. Results show that the carbonaceous transfer film derived from the single coating can only maintain on the friction counterpart under conditions of low load, low sliding frequency, and high humidity, which indirectly confirms the excellent tribological performance of the duplex coating.

Effect of Ti/Si and Ti/TiN/Si interlayers on the structure, properties, and tribological behavior of an a-C film deposited onto a C17200 copper-beryllium alloy

Reduced hardness and wear resistance may limit SAE C17200 copper‐beryllium alloy use in manufacturing applications, such as plunger tips of die casting machines and as cores and inserts for steel dies in injection molding processes. In order to improve the surface properties of Cu—Be alloys, amorphous carbon (a-C) films have been selected since these coatings may show high hardness, low wear rate and low coefficient of friction. However, the adhesion of carbonaceous films on Cu—Be alloys remains a challenge. Two interlayer compositions (Ti/Si and Ti/TiN/Si) were deposited onto Cu—Be disks and silicon wafers to assess amorphous carbon adhesion on substrates made of Cu—Be alloy. The microstructure and topography of the coatings were examined by Field Emission Scanning Electron Microscopy (FESEM) coupled with X-ray dispersive energy spectroscopy (EDS). The chemical composition depth profile was measured by glow discharge optical emission spectroscopy (GDOES), which confirmed distinct coating layers of Ti, Si, a-C (C1 and C2 conditions-pDCMS). A TiN extra layer presence was obtained for the C3 and C4 conditions-pDCMS reactive, confirmed by small angle XRD analysis. Raman scattering spectroscopy showed a higher quantity of sp3 carbon bonds for C3 and C4 coating conditions compared to C1 and C2. Instrumented indentation tests indicated a higher hardness and reduced elastic modulus for C3 and C4 coating systems, corroborating Raman results, in terms of a higher concentration of sp3 bonds. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and coherence correlation interferometry (CCI) were used to characterize the coatings' surface features and scratch tracks after the tests. In addition, ramp load scratch tests were conducted to assess coating adhesion to the Cu—Be alloy substrate by measuring critical loads and the coefficient of friction. The highest critical loads to failure (Lc2) and (Lc3) were found for the Ti/TiN/Si interlayer sample (C4 condition), indicating that this interlayer improved the coating contribution to a gradual increase in the hardness and promotion of an enhanced adhesion strength of the a-C coating.

Neuroanatomy in a middle Cambrian mollisoniid and the ancestral nervous system organization of chelicerates

Recent years have witnessed a steady increase in reports of fossilized nervous tissues among Cambrian total-group euarthropods, which allow reconstructing the early evolutionary history of these animals. Here, we describe the central nervous system of the stem-group chelicerate Mollisonia symmetrica from the mid-Cambrian Burgess Shale. The fossilized neurological anatomy of M. symmetrica includes optic nerves connected to a pair of lateral eyes, a putative condensed cephalic synganglion, and a metameric ventral nerve cord. Each trunk tergite is associated with a condensed ganglion bearing lateral segmental nerves, and linked by longitudinal connectives. The nervous system is preserved as reflective carbonaceous films underneath the phosphatized digestive tract. Our results suggest that M. symmetrica illustrates the ancestral organization of stem-group Chelicerata before the evolution of the derived neuroanatomical characters observed in Cambrian megacheirans and extant representatives. Our findings reveal a conflict between the phylogenetic signals provided by neuroanatomical and appendicular data, which we interpret as evidence of mosaic evolution in the chelicerate stem-lineage.

Physicochemical and statistical characterization of gas-sensing behaviors of resonator sensors with carbonaceous films prepared by rf-sputtering of aromatic and hydrophilic biomolecules

Quartz crystal resonators coated with gas-sorptive films were characterized by analyzing their structures and their organic gas-sorption behaviors, which were then studied using statistics and computational molecular simulations. The films had carbonaceous structures that were prepared by radio-frequency (rf) sputtering of aromatic biomolecules, such as cytosine and lignin. These films had been compared with the rf-sputtered films of hydrophilic biopolymer of lignin and gelatin.The composition and morphology of each film governed the organic gas-sorption characteristics of the resonator sensors used for organic gas-sensing. The cytosine film, which was nitrogen-rich and layered, had a moderate affinity for the larger molecules of normal alcohols and acetate esters. The cytosine film is repulsive to positively-charged moieties of adsorbates. In contrast, the agarose film, which was nitrogen-poor and columnar, had a high affinity for small adsorbates with short hydrocarbon chains. Molecular flexibility of the adsorbate played an important role in the gas-sorption ability of the agarose film. Molecular dynamics simulation clarified that the weakly dipolar adsorbate-aggregate were immiscible in the cytosine adsorbent-aggregate because the collision mixture was prone to be instable. In practice, the cytosine-sputtered film had a higher gas-sorption ability for weakly dipolar species that have the longer hydrocarbon chains.

Physicochemical and Statistical Characterization of Gas-Sensing Behaviors of Resonator Sensors with Carbonaceous Films Prepared by Rf-Sputtering of Aromatic and Hydrophilic Biomolecules

Physicochemical and Statistical Characterization of Gas-Sensing Behaviors of Resonator Sensors with Carbonaceous Films Prepared by Rf-Sputtering of Aromatic and Hydrophilic Biomolecules

Comparison of CO and CO2 rf plasma treatment of SnO2 nanoparticles for gas sensing materials

CO and CO2 plasmas were used to modify SnO2 nanoparticles (NPs) to understand the role of key gas-phase species and to explore a potential route for improving these materials as solid-state gas sensors. Excited state species in both plasmas were monitored using optical emission spectroscopy and the NP were analyzed after plasma exposure with x-ray photoelectron spectroscopy. These studies reveal that in the CO2 plasma, CO2 decomposes to CO and O, leading to etching of the SnO2 lattice. Conversely, in the CO plasma, very little O is formed, leading to the deposition of a carbonaceous film on the SnO2 NP. Sensors fabricated with the CO2 modified SnO2 NP demonstrate a higher response to CO, benzene, and ethanol and improved response and recovery behavior when compared with untreated devices. CO plasma modification, however, had a detrimental effect on the gas sensing performance of this material.

Cambrian comb jellies from Utah illuminate the early evolution of nervous and sensory systems in ctenophores

SummaryCtenophores are a group of predatory macroinvertebrates whose controversial phylogenetic position has prompted several competing hypotheses regarding the evolution of animal organ systems. Although ctenophores date back at least to the Cambrian, they have a poor fossil record due to their gelatinous bodies. Here, we describe two ctenophore species from the Cambrian of Utah, which illuminate the early evolution of nervous and sensory features in the phylum. Thalassostaphylos elegans has 16 comb rows, an oral skirt, and an apical organ with polar fields. Ctenorhabdotus campanelliformis has 24 comb rows, an oral skirt, an apical organ enclosed by a capsule and neurological tissues preserved as carbonaceous films. These are concentrated around the apical organ and ciliated furrows, which connect to a circumoral nerve ring via longitudinal axons. C. campanelliformis deviates from the neuroanatomy of living ctenophores and demonstrates a substantial complexity in the nervous system of Cambrian ctenophores.

Fabrication of onion-like fullerene nanostructure film by electrochemical reduction

Onion-like fullerenes possess distinctive physical and chemical performance, and thus are believed to have great significance in theoretical study and engineering applications. In this exploratory research, we introduced a novel way, namely electrochemical reduction method performed in aqueous solution at room temperature and very low voltages, for preparing a film composed of onion-like fullerene nanostructures. The method was discovered by accident. During the preparation of thick Cr coating by electrodepositing from Cr (III) electrolyte, a layer of black film was found at the interface between the steel substrate and Cr coating. XPS analysis shows that the main element contained in the film is C. The results from Raman spectrum, HRTEM and SAED reveal that the carbonaceous film is composed of the nanostructures roughly having onion-like fullerene unit. This means with significant advantages has the potential to develop into a practical technique for fabricating carbonaceous films or coatings.

Enhanced lubrication performance of triethanolamine functionalized reduced graphene oxide on the cold‐rolled surface of strips

Triethanolamine functionalized reduced graphene oxide (rGO‐TEA(s)) nanocomposites have been synthesized by the hydrothermal method. The physical and chemical properties of rGO‐TEA(s) with different degrees of functionalization were characterized by transmission electron microscopy, X‐ray powder diffraction, Raman spectroscopy, and X‐ray photon spectroscopy. The cold rolling lubrication of the rGO‐TEA(s) prepared as nano‐lubricant additives were investigated using a two‐high rolling mill. The microscopic topographies of rolled strips were measured and evaluated by several physical characterizations. The results showed that the increase of functionalization time was favored to the reaction of triethanolamine and C–O–C groups on the GO surface, whereas the defects and disorder in graphene structure were repaired according to the intensity ratio of the D band to G band from 1.154 to 1.130. The cold rolling experiment results demonstrated that rGO‐TEA(s) exhibited excellent lubrication properties, especially the rolled surface lubricated by rGO‐TEA‐10h presented few defects and minimum roughness value. The admirable lubrication performance of rGO‐TEA‐10h was attributed to the formation of absorption film and consecutive carbonaceous protective film.