Synthesis of nanometric molybdenum disulphide particles and evaluation of friction and wear properties

Nanometric molybdenum disulphide particles of about 30 nm diameter have been prepared by the hydrodesulphurisation of molybdenum trisulphide obtained from acidifying a mixed solution of Na₂MoO₄ and Na₂S at ambient temperature using a quick homogeneous precipitation method (QHPM). Using X‐ray diffraction and transmission electron microscopy (TEM), the size and crystallisation of the nano‐MoS₂ obtained by hydrodesulphurisation at different temperatures have been investigated. In addition, the tribological performance of nano‐MoS₂ has been investigated by means of a block‐on‐ring tribometer, X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results show that base oils with nanometric MoS₂ as an additive provide higher wear resistance than other oils containing commercially available common MoS₂. However, the friction reduction is not obviously improved. SEM characterisation reveals a worn, smooth surface when using the nano‐MoS₂ additive, and XPS analysis indicates a greater amount of molybdenum oxide and iron sulphide in the antiwear thin film formed on the rubbed surface.     

Tribological Properties of Films Formed by the Reaction of Carbon Tetrachloride with Iron

The tribological properties of halide films grown on iron by reaction with carbon tetrachloride vapor at a temperature of 617 K and a pressure of 1.7 Torr are compared, in ultrahigh vacuum, with FeCl₂ films evaporated onto the surface. It is found that the reactively formed film has a slightly lower limiting friction coefficient than the evaporated layer (~0.06 compared to ~0.08), which may be due either to the diffusion of some carbon into the substrate or the formation of a more oriented layer when this is formed reactively. The major difference between the reactively grown and evaporated film is that the evaporated layer attains the minimum friction when ~40 ? of FeCl₂ has been evaporated, while the reactively formed layer has a minimum friction coefficient when a film of 6±2 ? has been deposited. In the case of the evaporated FeCl₂ film, the growth of second and subsequent layers proceeds before the first layer is complete. It has been shown that the friction coefficient reaches its minimum value after completion of the first monolayer, a process that is complete after the evaporation of ~40 ? of FeCl₂. In the case of the film formed by reaction with CCl₄, the halide film grows directly on the surface implying that the FeCl₂ monolayer thickness is ~6 ?. This value is in good agreement with the layer thickness in bulk ferrous chloride.     

The surface chemistry of chloroform as an extreme-pressure lubricant additive at high concentrations

Carbon tetrachloride is an extremely good extreme-pressure (EP) lubricant additive at low concentrations (<3 wt% chlorine) since it can react to form a high-melting-point Fe₃C antiseizure layer. In contrast, small hydrogen-containing additive molecules (CH₂Cl₂, CHCl₃) decompose to form FeCl₂ which melts at ~940 K and limits the maximum seizure load to ~3500 N as measured hi a pin and v-block apparatus. However, both thermodynamic calculations and results of a Mössbauer analysis of an iron foil heated in CHCl₃ at 830 K indicate that iron carbide can be formed from chloroform. In addition, it is also found in that case that a plot of seizure load versus concentration, after initially forming a plateau, once again increases with higher additive concentrations (>4 wt% chlorine) in accord with the idea that a higher melting point carbide film can be formed. It has been shown previously that asymptotes in the plot of removal rate versus applied load correspond to melting of the interfacial anti-seizure film. When using 9.0 wt% chlorine from chloroform as the additive, a drastic increase in removal rate is found at an interfacial temperature of ~940 K corresponding to the melting of FeCl₂ and an additional asymptote is evident at ~1500 K due to the melting of Fe₃C in accord with the thermodynamic and Mössbauer results.     

Iron enhances generation of fibrin fibers in human blood: Implications for pathogenesis of stroke

Stroke is associated with the intracerebral formation of fibrin clots which may lead to irreversible brain damage. Thrombolytic therapies employ a variety of natural and/or recombinant plasminogen activators to initiate fibrinolytic degradation of cerebral thrombi. However, such therapies when installed beyond 4‐ to 6‐h window, may fail to achieve the expected outcome. This is due to the hydroxyl radical‐induced modification of fibrin(ogen) molecules rendering them refractory to fibrinolytic degradation, but no cause of the increased free radical generation in stroke was offered. Here, we show by means of electron microscopy that iron ions added to human blood dramatically enhances fibrin fibers formation with thrombin, and significantly delays fibrinolysis during spontaneous clotting of native blood. Iron ions caused the appearance dense matted fibrin deposits, similar, if not identical, to those observed in plasma of patients with stroke. These results may explain a known relationship between thrombotic diseases and the increased body concentrations of free iron and/or hemoglobin derivatives. We conclude that any action resulting in the inhibition of hemostatic abnormalities, as well as in the reduction of body free iron and scavenging of hydroxyl radicals (e.g., by polyphenols) can potentially prevent pathological reactions associated with consequences of stroke. Microsc. Res. Tech. 75:1185–1190, 2012. © 2012 Wiley Periodicals, Inc.     

Tribological properties of nano‐calcium borate as lithium grease additive

Nano‐calcium borate (NCB) with an average particle size of about 70 nm was synthesised via ethanol supercritical fluid drying technique, and the morphology and microstructures of as‐prepared particles were characterised by means of scanning electron microscope (SEM, JEOL LTD., Tokyo, Japan) and X‐ray powder diffraction. The friction and wear behaviour of the NCB as additive in lithium grease were evaluated with an Optimol‐SRV IV (Optimol Instruments Prüftechnik GmbH, Munich, Germany) oscillating friction and wear tester (SRV tester). The morphology and surface composition of the worn surfaces of lower discs after SRV test were analysed by SEM and X‐ray photoelectron spectroscopy (XPS, Physical Electronics, Inc., USA). The result demonstrated that the anti‐wear and load‐carrying capacities of the lithium grease were significantly improved, and the friction coefficient of the lithium grease decreased with the addition of NCB additive. The analytical results of XPS indicate that the good tribological performance of NCB is attributable to the formation of a boundary lubrication film composed of deposited NCB and the tribochemical reaction products such as B₂O₃, CaO and iron oxides on the rubbing surface. Copyright © 2013 John Wiley & Sons, Ltd.     

Clinical relevance of hypercoagulability and possible hypofibrinolysis associated with estrone and estriol

Estrone (E₁) and Estriol (E₃) are endogenous female hormones, present in increased concentrations during female specific physiological processes (menopause and pregnancy respectively) that are associated with increased venous thrombotic risk. These hormones are also used as hormone therapies that are also associated with increased thromboembolism risk. Viscoelastic analysis revealed no significant difference to clot formation after hormone addition, however morphological analysis showed that the addition of both E₁ and E₃ result in fibrin clots composed of thinner fibrin fibers arranged in dense matted networks. These changes to the fibrin network ultrastructure are indicative of a prothrombotic state but may also indicate hypofibrinolysis. We therefore conclude that the increased risk of venous thrombosis during pregnancy and menopause may originate from a combination of hypercoagulation and a possible hypofibrinolytic mechanism of these hormones. Therefore females with a hypercoagulable tendency that fall pregnant or enter menopause need to be monitored to prevent venous thrombotic events. The decision to use hormone therapies during and after menopause should not be taken lightly and the risk‐reward scale should be closely examined to ensure it does not tip towards thrombosis and subsequent thrombotic events that ultimately could have been prevented.     

Sample preparation and microscopical investigation techniques for metal and ceramics containing graphite and graphene‐like layered particles

Scanning electron microscopy (SEM) techniques are widely used in microstructural investigations of materials since it can provide surface morphology, topography, and chemical information. However, it is important to use correct imaging and sample preparation techniques to reveal the microstructures of materials composed of components with different polishing characteristics such as grey cast iron, graphene platelets (GPLs)‐added SiAlON composite, SiC and B₄C ceramics containing graphite or graphene‐like layered particles. In this study, all microstructural details of gray cast iron were successfully revealed by using argon ion beam milling as an alternative to the standard sample preparation method for cast irons, that is, mechanical polishing followed by chemical etching. The in‐lens secondary electron (I‐L‐SE) image was clearly displayed on the surface details of the graphites that could not be revealed by backscattered electron (BSE) and Everhart–Thornley secondary electron (E‐T SE) images. Mechanical polishing leads to pull‐out of GPLs from SiAlON surface, whereas argon ion beam milling preserved the GPLs and resulted in smooth surface. Grain and grain boundaries of polycrystalline SiC and B₄C were easily revealed by using I‐L SE image in the SEM after only mechanical polishing without any etching process. While the BSE and E‐T SE images did not clearly show the residual graphites in the microstructure, their distribution in the B₄C matrix was fully revealed in the I‐L SE image.     

An investigation on component and formation of tribochemical film in Si3N4-white iron sliding pair lubricated with distilled water

A tribofilm was formed during wear tests of a Si₃N₄-white iron pair lubricated with distilled water. In order to clarify the formation of the film, the wear tests for Si₃N₄-white iron pair with different sliding distances were carried out on a ring-block tester, using distilled water as lubricant. The worn surfaces of white iron specimens were observed under SEM. Furthermore, the component and structure of the film were analyzed by using AES, XPS, FTIR and XRD. From the investigation, the following results are presented. During the wear tests of Si₃N₄-white iron pair lubricated with distilled water, the oxidation and hydrolysis of Si₃N₄ occur on the wearing surfaces, and a tribochemical film, which mainly consists of silica gel, is formed on the wearing surface. The reason for the film formation is that the carbides in cast iron spall off during the wearing tests and the spalling pits are left on the wearing surface of the white iron. Then, the debris of Si₃N₄ or its oxidized product are embedded into the pits, and are further oxidized and hydrolyzed. The products of reactions are concentrated in the pits and polycondensed into silica gel, and a silica gel film is formed on the wearing surface. The film protects both Si₃N₄ and white iron, and makes the paired surfaces smooth. Therefore, the friction coefficient of the pair is down to 0·02, and the wear rates of Si₃N₄ and iron are near zero. However, because the resultants of oxidation and hydrolysis of Si₃N₄ can not be enriched on the wearing surface of carbon steel to form an effective tribofilm, both friction coefficient and wear rate of Si₃N₄-carbon steel pair lubricated with distilled water are still high in value.     

The effects of osmium tetroxide post‐fixation and drying steps on leafy liverwort ultrastructure study by scanning electron microscopy

Leafy liverwort is one of the most abundant and diverse plants in Indonesia. Their high variation and beneficial secondary metabolites contained in the oil bodies have attracted researchers' attention. The ultrastructural analysis of leafy liverworts is important as a means of species identification and also for further exploration of their oil bodies. However, the optimization of the preparation steps for observing leafy liverworts by SEM is necessary to avoid sample destruction. Fixation and drying play important roles in maintaining a sample's structure as close to its natural state as possible. Thus, in this study, we evaluated the effect of 4% Osmium tetroxide (OsO₄) and drying on leafy liverworts ultrastructure. Microlejeunea, Acrolejeunea, and Frullania were fixed with 2.5% glutaraldehyde. Some samples were then post‐fixed with 4% OsO₄, while the rest were directly dehydrated with an ethanol series and then subjected to different drying methods, i.e. air drying, freeze drying, and drying with hexamethyldisilazane (HMDS). According to the data obtained, post‐fixation with 4% OsO₄ could better maintain the integrity of the samples and enhance the contrast of leafy liverwort SEM images. In addition, samples dried with HMDS showed more detailed structures compared to those that were air dried. Different ultrastructure were found among the different leafy liverworts observed by SEM. Our data suggested the advantages of SEM in providing ultrastructure information on leafy liverworts as well as the optimum conditions to observe them with less deformation. OsO₄ post‐fixation could enhance the contrast of leafy liverwort SEM images and maintain the structure of the samples. Drying with HMDS provided a convenient way for rapid SEM preparation with less structural distortion.     

The deintercalation effect of FeCl3–graphite intercalation compound in paraffin liquid lubrication

The weld load of graphite and FeCl₃–graphite intercalation compound as an additive in paraffin liquid were evaluated with a Four-ball tester. The analytical tools, such as X-ray diffractometer, X-ray photoelectron spectrometer, and electron spin resonance spectrometer were used to investigate the reaction between steel and graphite intercalation compound. FeCl₃–GIC was found to exhibit over a twofold increase in weld load relative to graphite. Deintercalated FeCl₃ surrounding the contact favours the reaction of steel and graphite intercalation compound, which leads to an increase of weld load.     

Physicochemical and triboengineering properties of melted iron using a pulsed-plasma jet

The results are presented of studies on how plasma jets affect the physicochemical and triboengineering properties of Fe specimens melted and alloyed with a plasma jet. The microhardness of the molten specimens increased by 2.5 times compared with the original specimens and their wear during friction by cylinder-on-plane pairs turned out to be two times less than that of the original specimens. The subsurface iron is alloyed with elements that the electrode contains, such as W, Co, and Cu. In addition to α-Fe, finely dispersed Fe₆W₆C carbides and, possibly, W₆Co₆C form in the subsurface layers. After wear tests, up to ≈ 1.2 at. % were found at a depth of 15 μm beneath the friction surface of the alloyed Fe. Original Russian Text ? A.D. Pogrebnyak, S.N. Bratushka, A.D. Mikhalev, N.K. Erdybaeva, O.V. Kolisnichenko, O.P. Kul’men’tyeva, Yu.N. Tyurin, 2007, published in Trenie i Iznos, 2007, Vol. 28, No. 5, pp. 457–464.     

Tribological performance of an ionic liquid as a lubricant for steel/aluminium contacts

The wear and friction behaviour of an ionic liquid 1‐ethyl‐3‐hexylimidazolium tetrafluoroborate (L206) was investigated as a lubricant for steel/aluminium contacts using an Optimol SRV® oscillating friction and wear tester. The elemental composition and chemical nature of the antiwear films generated on the aluminium surface were analysed using a scanning electron microscope with a Kevex energy dispersive X‐ray analyser attachment (SEM/EDS) and X‐ray photoelectron spectroscopy (XPS). A low friction coefficient (˜0.05) was recorded when lubricating with L206; a small amount of water (5 wt. %) in L206 effectively reduced the wear volume and greatly increased the microhardness of the aluminium alloy, but had little effect on the friction coefficient. The SEM/EDS results showed that severe corrosive wear occurred on the aluminium alloy when lubricating with neat L206, which could be avoided by the addition of water in L206. The XPS results indicated that the species AlF₃, Al₂O₃, AlO(OH), and Al(OH)₃ formed during friction; there was no indication of boron on the worn surfaces.     

Antifriction and Antiwear Properties of an Ionic Liquid with Fluorine-Containing Anion Used as Lubricant Additive

Tribological behavior of trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide [P₆₆₆₁₄][NTf₂] ionic liquid (IL) used as additive in a diester oil at concentrations of 0.25, 0.5 and 1 wt% was studied in this research. The IL solubility in the base oil was measured using the inductively coupled plasma mass spectrometry (ICP-MS) technique, and corrosion analysis was done at room temperature at relative humidity of 49–77%. Tribological tests were conducted for 30 min at room temperature, 15 Hz frequency, 4 mm of stroke length, a load of 80 N (corresponding to 2 GPa of maximum contact pressure) and relative humidity of 35–53%. Friction coefficient was recorded during tests, and the wear scar was measured by confocal microscopy. Worn surface was also analyzed by SEM, EDS and XPS. Results showed that a saturated solution of [P₆₆₆₁₄][NTf₂] in the base oil contains about 30 wt% of IL and corrosion activity for the highest concentration of IL (1 wt%) was not found after a 20-day test. Although the base oil and the mixtures had similar friction behavior, only the 1 wt% sample exhibited slightly lower wear volume than the base oil. SEM images exhibited similar wear track width (707–796 µm) and wear mechanism (adhesive) for all samples tested. In addition, the EDS spectra only showed the elements present in the steel. Finally, the XPS measurements could not detect differences regarding iron chemical state among the samples, which is consistent with the tribological behavior obtained.     

The performance and antiwear mechanism of S-containing organic borate as an oil additive

A sulphur-containing organic borate (BS-2) was prepared. Its friction and wear properties when added to n-tetradecane, and the effect on wear of addition of dodecyl amine to the synthesised S-containing borate oil, were measured using a Timken test machine. The results were compared with those of tridodecyl borate, and a combination of tridodecyl borate and sulphurised cotton seed oil. X-ray Photoelectron Spectroscopy (XPS) was used to examine the rubbed surfaces of the test blocks, while Scanning Electron Microscopy (SEM), Energy Dispersion Analysis of X-ray (EDAX) and X-ray Diffraction (XRD) were used to study the wear debris. It is found that S-containing organic borate exhibits a poorer antiwear property than tridodecyl borate but, with the addition of dodecyl amine to the S-containing borate, its antiwear property can be improved. XPS analyses indicate that sulphur on the rubbed surfaces exists in the forms of organic sulphide and FeSO₄, and the addition of amine reduces the adsorption and reaction of sulphur to the rubbing surfaces. SEM analyses revealed that the wear debris was in powder form, and the EDAX and XRD analyses indicated that iron sulphide, iron oxide and elemental iron were contained in the wear debris. A corrosive wear mechanism of steel test blocks lubricated by S-containing organic borate is proposed.     

Control of charging in low-voltage SEM

Charging of the specimen under electron beam irradiation is a common problem in scanning electron microscopy (SEM). It results in unstable imaging conditions and a loss in resolution due to defocus of the beam. In addition, it can cause permanent changes in some specimens from translocation of mobile ions under the influence of the induced electrostatic field. To minimize charging and its associated problems, the incident beam energy must be carefully chosen to be the value E₂ at which a dynamic charge balance is obtained. This article presents data on E₂ values for a variety of materials and demonstrates how E₂ is affected by the choice of angle of beam incidence.     

A graphite intercalation compound additive in oil

A third-stage FeCl₃-graphite intercalation compound (GIC) with flake graphite has been synthesised by a solvent method. The FeCl₃ deintercalation of GIC forms thick complex film on the metal surface during the friction process, which increases the extreme pressure qualities of the paraffin liquid.     

Combined FTIR and SEM‐EDS study of Bi2O3 doped ZnO–SnO2 ceramics

The effects of Bi₂O₃ addition on the phase composition, microstructure and optical properties of ZnO–SnO₂ ceramics were investigated. Starting powders of ZnO and SnO₂ were mixed in the molar ratio 2:1. After adding Bi₂O₃ (1.0 mol.%) this mixture was mechanically activated for 10 min in a planetary ball mill, uniaxially pressed and sintered at 1300°C for 2 h. Far‐infrared reflection spectra were measured (100–1000 cm^–1). To investigate the occurred differences in FTIR spectra, the Bi₂O₃‐doped sample was examined more carefully with a Perkin–Elmer FTIR spectrometer (Perkin Elmer, Waltham, MA, USA) connected with a Perkin–Elmer FTIR microscope and itemized points of interest were also studied with SEM‐EDS.     

About the role of the various types of secondary electrons (SE1; SE2; SE3) on the performance of LVSEM

The relative weight, δ_Β, of the yield of secondary electrons, SE₂, induced by the backscattered electrons, BSE, with respect to that, δ_P, of secondary electrons, SE₁, induced by the primary electrons, PE, is deduced from simple theoretical considerations. At primary energies E₀ larger than E_M (where the total SE yield δ = δ_P + δ_B is maximum), the dominant role of the backscattering events is established. It is illustrated in SEM by a direct comparison of the contrast between SE images and BSE images obtained at E₀ ～ 5 keV and E₀ ～ 15 keV on a stratified specimen. At energies E₀ less than E_M, the dominant role of SE₁ electrons with respect to SE₂ (and SE₃) is established. It is illustrated by the better practical resolution of diamond images obtained with an in‐lens detection in low voltage SEM E₀ ～ 0.2–1 keV range compared with that obtained with a lateral detector. The present contribution illustrates the improved performance of LVSEM in terms of contrast and of practical resolution as well as the importance of variable voltage methods for subsurface imaging. The common opinion that the practical lateral resolution is given by the incident spot diameter is also reconsidered in LVSEM.     

Label‐free monitoring of inflammatory tissue conditions using a carrageenan‐induced acute inflammation rat model

Although the confirmation of inflammatory changes within tissues at the onset of various diseases is critical for the early detection of disease and selection of appropriate treatment, most therapies are based on complex and time‐consuming diagnostic procedures. Raman spectroscopy has the ability to provide non‐invasive, real‐time, chemical bonding analysis through the inelastic scattering of photons. In this study, we evaluate the feasibility of Raman spectroscopy as a new, easy, fast, and accurate diagnostic method to support diagnostic decisions. The molecular changes in carrageenan‐induced acute inflammation rat tissues were assessed by Raman spectroscopy. Volumes of 0 (control), 100, 150, and 200 µL of 1% carrageenan were administered to rat hind paws to control the degree of inflammation. The prominent peaks at [1,062, 1,131] cm^?1 and [2,847, 2,881] cm^?1 were selected as characteristic measurements corresponding to the C–C stretching vibrational modes and the symmetric and asymmetric C–H (CH₂) stretching vibrational modes, respectively. Principal component analysis of the inflammatory Raman spectra enabled graphical representation of the degree of inflammation through principal component loading profiles of inflammatory tissues on a two‐dimensional plot. Therefore, Raman spectroscopy with multivariate statistical analysis represents a promising method for detecting biomolecular responses based on different types of inflammatory tissues.     

Investigation on the properties of gamma irradiated of polytetrafluoroethylene fibers

The physical, thermal, and chemical properties of gamma‐irradiated polytetrafluoroethylene (PTFE) fibers were investigated using X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) was also used to analyze the surface morphology of irradiated fiber samples. PTFE fiber samples were irradiated by gamma radiation doses ranging from 3 kGy to 40 kGy. The XRD analyses and DSC measurements showed the improvement of crystallinity by gamma irradiation with dose up to 25 kGy reflecting the induced crosslinking with irradiation for PTFE fibers. The crystallinity was found to decrease with higher dose of 40 kGy, reflecting induced amorphization of the polymer sample at the high radiation dose. The calculated crystallite size and XRD parameters showed obvious variations with sample irradiation. The FTIR results showed the liberation of CF₂ groups and the formation of some new chemical bonding with crosslinking‐induced irradiation. The SEM micrographs revealed no variation in the surface morphology of the irradiated fiber samples than the pristine fiber.