The nanostructure of soot-in-oil particles and agglomerates from an automotive diesel engine

The characteristics of soot particles and agglomerates of particles extracted from samples of lubricating oil drawn from the sump of a diesel engine have been investigated. The engine was a high pressure common rail, direct injection diesel designed for light duty automotive applications. Soot from the samples was prepared for imaging by sample dilution with heptane, followed by washing in diethyl ether and in some cases, sample centrifugation. The size and shape of agglomerates were defined from measurements of projected length and width allowing for chain contortion. When used, centrifugation is shown to alter the size and shape of agglomerates, increasing the proportion of chain agglomerates and reducing clusters. Without centrifugation, roughly half of the soot in oil exists in long-chain agglomerates with average length of 130 nm and 50 nm in width. Clusters with modest branching account for the remaining 46%. The average aspect ratio (L/W) was of 2.9. The diameter of spherical primary particles that form the agglomerates ranges between 10 and 35 nm grouped in a Gaussian distribution with a mean value of 20.2 nm. All primary particles exhibit an inner core and an outer shell. The inner core is composed by several nuclei of around 4 nm diameter. Inner core is of around 8–15 nm in diameter and outer shell 4–12 nm thick.     

Third body effects in the wear of polyamide: Micro-mechanisms and wear particles analysis

The wear micro-mechanisms at a frictional interface between a polyamide 4,6 (PA 46) substrate and a spherical sapphire counterface have been investigated using in situ contact observation. Experiments were carried out under reciprocating sliding conditions with varying values of the overlap ratio, Δ, defined as the ratio of the displacement amplitude to the contact diameter. Using this procedure, it was found possible to vary the extent of wear particles accumulation within coherent third body agglomerates. For low overlap ratios (Δ < 0.2), particles detached from the PA 46 substrate were extensively agglomerated within distinct third body corrugations. In this regime, the rate limiting process regarding the wear degradation was found to be the extrusion of fibril-like wear particles from the extremities of sheared third body agglomerates. On the other hand, no substantial debris accumulation was found to occur when the overlap ratio was greater than 0.2. Additional infrared thermal contact imaging showed that these wear mechanisms were induced under essentially isothermal conditions. From differential scanning calorimetry (DSC) and size exclusion chromatography (SEC) analysis, micro-structural changes within wear particles were found to be associated with a strong reduction in the molecular weight of the PA 46 molecules by virtue of stress-induced chain scission mechanisms.     

Solid particle erosion studies on biomorphic Si/SiC ceramic composites

Solid particle erosion tests were conducted on four different types of silicon carbide ceramic composites. The composites are cotton fabric based Si/SiC with and without chemical vapour infiltration, fine teak wood powder based Si/SiC and coarse teak wood powder based Si/SiC. The erodents used are angular SiC particles of average size 80, 250 and 450 μm. The velocities with which particles impacted on the target materials were varied from 20 to 50 m/s. Similarly the angle of impact was varied from 20° to 90°. Scanning electron microscopic observations on the eroded surface show brittle and cleavage like fracture. Fine teak wood powder based Si/SiC ceramic shows better erosion resistance than the other ceramics. Homogenous distribution of SiC grains with the presence of very fine grains of silicon and carbon is responsible for the improved erosion resistance. The higher erosion rate in cotton fabric based SiC arises from its microstructure. Here, the free carbon and free silicon grains are large in size and the SiC phase has very low hardness as compared to the erodent.     

Microstructure,mechanical properties and tribological behavior of tribofilm generated from natural serpentine mineral powders as lubricant additive

Surface-modified serpentine powders with an average size of 1.0 μm were dispersed into mineral base oil to improve the lubricating properties of oil, as well as to generate a thin tribofilm on the worn surface. SEM, TEM, nano-indentation and Stribeck testing were performed to study the morphology, microstructure, micromechanical properties and tribological behavior of the tribofilm, respectively. Results show that a nanocrystalline tribofilm, with a thickness of 500–600 nm, is formed on the worn surface under the lubrication of oil with 1.5 wt% serpentine. The film is mainly composed of Fe₃O₄, FeSi, SiO₂, AlFe and Fe-C compound (Fe₃C). A phenomenological model of the tribofilm generated by serpentine was developed based on the experimental results. The excellent mechanical properties, reinforced phase of embedded particles and porous structure of the tribofilm contribute to the reduction of friction and wear, especially in the case of boundary and mixed lubrication.     

Determination of particle impacts and impact energy in the erosion of X65 carbon steel using acoustic emission technique

An in-situ acoustic emission (AE) monitoring technique has been implemented in a submerged jet impingement (SIJ) system in an effort to investigate the effect of sand particle impact on the degradation mechanism of X65 carbon steel pipeline material in erosion conditions.A detailed analysis of the acoustic events' count rate enabled the number of impacts per second to be quantified for a range of flow velocities (7, 10, 15 m/s) and solid loadings (0, 50, 200, 500 mg/L) in a nitrogen-saturated solution at 50 °C. The number of impacts obtained from acoustic signals showed a strong agreement with theoretical prediction for flow velocities 7 and 10 m/s. A deviation between practical readings and theory is observed for flow velocity of 15 m/s which may be due to error from detected emissions of multiple rebounded particles.Computational fluid dynamics (CFD) was used in conjunction with particle tracking to model the impingement system and predict the velocity and impact angle distribution on the surface of the sample. Data was used to predict the kinetic energy of the impacts and was correlated with the measured AE energy and material loss from gravimetric analysis. The results demonstrate that AE is a useful technique for quantifying and predicting the erosion damage of X65 pipeline material in an erosion–corrosion environment.     

Co-precipitation synthesis of nanocrystalline SnO2: Effect of Fe doping on structural,morphological and ethanol vapor response properties

The present study describes undoped and Fe-doped tin dioxide thick films as selective ethanol vapor sensors. The undoped and Fe doped SnO₂ powders were synthesized by using a facile co-precipitation route. The thick films of undoped and Fe-doped SnO₂ were deposited by screen-printing technique and then sintered at 650 °C for 2 h. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) techniques. The XRD studies reveal formation of nanocrystalline structure. The particle size of undoped and Fe (2 and 4 mol%) doped SnO₂ sintered powders were 17, 10 and 8 nm, respectively. It was found that the response of SnO₂ improved on addition of Fe. The 2 mol% Fe doped SnO₂ exhibits highest response toward ethanol at the operating temperature of 300 °C with response and recovery time of 15 and 32 s, respectively.     

Thermogravimetric analysis of carbon black and engine soot—Towards a more robust oil analysis method

This work examined the thermal behaviour of diesel engine produced soot and commercial carbon black using thermogravimetric analysis (TGA). It was found that during TGA analysis of the carbon matrices (at a temperature range commonly used for soot-in-oil content determination), a gradual mass loss occurred. This was attributed to pyrolysis effects and combustion processes occurring due to poor hydrodynamic design of some commercial thermobalances. This process resulted in a significant mass loss of the carbon during TGA. This finding may strongly effect soot-in-oil analysis conducted using current methods. Experiments were conducted using a range of soot-in-oil mixtures according to the widely used thermogravimetric standard method ASTM 5967-08 which showed a significant underestimation of the soot content in the oil as a result of carbon mass loss due to combustion and/or pyrolysis effects. An improved oil analysis method is proposed which provides a significantly increased accuracy of soot determination in lubricant oils.     

Fabrication of a resin-bonded ultra-fine diamond abrasive polishing tool by electrophoretic co-deposition for SiC processing

A resin-bonded ultra-fine diamond abrasive polishing tool is fabricated by electrophoretic co-deposition (EPcD), and the processing performance of the tool is evaluated in this study. The dispersion stability of suspensions is characterized by a laser particle size analyzer and settlement ratio. The cathodic EPcD of composite powder is realized by adding Al³⁺ into the suspension. The sintering temperature of composite coatings is determined by differential thermal analysis/thermogravimetry. The surface morphology of the composite coating is observed under a confocal microscope. Results show that uniform, dense, and smooth coatings with diamond and resin particles distributed homogeneously are obtained from the steel substrate. A large (Φ150 mm) polishing tool with a 20 μm-thick coating is successfully prepared using the above process. A smooth mirror surface of SiC wafer with a nanoscale roughness (4.3 nm) is achieved after processing with the ultra-fine diamond abrasive polishing tool.     

Effect of carbide volume fraction on erosive wear behaviour of hardfacing cast irons

The present work reports the effect of carbide volume fraction on erosive wear behaviour of hardfacing cast irons. Five different grades of weld hardfacing cast irons were selected for the present investigation. The solid particle erosion experiments were carried out with blast furnace sinter, silica sand and alumina particles under mild (53–75 μm, 25 m s⁻¹), moderately severe (125–150 μm/100–150 μm, 50 m s⁻¹) and under severe erosion conditions (300–425 μm, 90 m s⁻¹) at impingement angles of 30 and 90°. The variation in erosion rate with carbide volume fraction was observed to be strong function of the erodent particle hardness, impingement angle and the impact velocity. Under mild erosion conditions, erosion rate decreased with increasing carbide volume fraction (CVF), whereas erosion rate increased with CVF under moderately severe erosion condition with alumina particles. With silica sand particles under moderately severe erosion conditions the beneficial effect of large volume fraction of carbides could only be observed at 30°, whereas at normal impact erosion rate increased with increasing CVF. The erosion rate showed power law relationship with ratio of hardness of erodent particle to that of the target material (H_e/H_t) and expressed as E=c(H_e/H_t)^p.With increasing severity of erosion conditions erosion rate showed stronger dependence on H_e/H_t as compared to those under mild and moderately severe erosion conditions. The mechanism of materials removal from the carbides involved Hertzian fracture with softer sinter particles, whereas harder alumina particles could plastically indent and cause gross fracture of the carbides.     

Friction and wear behavior of laser composite surfaced aluminium with silicon carbide

The present study concerns the wear behavior of laser composite surfaced Al with SiC and Al + SiC particulates. A thin layer of SiC and Al + SiC (at a ratio of 1:1 and dispersed in alcohol) were pre-deposited (thickness of 100 μm) on an Al substrate and laser irradiated using a high power continuous wave (CW) CO₂ laser. Irradiation leads to melting of the Al substrate with a part of the pre-deposited SiC layer, intermixing and followed by rapid solidification to form the composite layer on the surface. Following laser irradiation, a detailed characterization of the composite layer was undertaken in terms of microstructure, composition and phases. Mechanical properties like microhardness and wear resistance were evaluated in detail. The microstructure of the composite layer consists of a dispersion of partially melted SiC particles in grain refined Al matrix. Part of the SiC particles are dissociated into silicon and carbon leading to formation of the Al₄C₃ phase and free Si redistributed in the Al matrix. The volume fraction of SiC is maximum at the surface and decreases with depth. The microhardness of the surface improves by two to three times as compared to that of the as-received Al. A significant improvement in wear resistance in the composite surfaced Al is observed as compared to the as-received Al. The mechanism of wear for as-received vis-à-vis laser composite surfaced Al has been proposed.     

Thermogravimetric analysis of carbon black and engine soot—Towards a more robust oil analysis method

This work examined the thermal behaviour of diesel engine produced soot and commercial carbon black using thermogravimetric analysis (TGA). It was found that during TGA analysis of the carbon matrices (at a temperature range commonly used for soot-in-oil content determination), a gradual mass loss occurred. This was attributed to pyrolysis effects and combustion processes occurring due to poor hydrodynamic design of some commercial thermobalances. This process resulted in a significant mass loss of the carbon during TGA. This finding may strongly effect soot-in-oil analysis conducted using current methods. Experiments were conducted using a range of soot-in-oil mixtures according to the widely used thermogravimetric standard method ASTM 5967-08 which showed a significant underestimation of the soot content in the oil as a result of carbon mass loss due to combustion and/or pyrolysis effects. An improved oil analysis method is proposed which provides a significantly increased accuracy of soot determination in lubricant oils.     

Drop swarm analysis in dispersions with incident-light and transmitted-light illumination

The new developed Optical Multimode Online Probe (OMOP) can process images from either incident-light illumination (also called epi-illumination) or transmitted-light illumination (also called trans-illumination). The probe has an outer diameter of 38 mm and the illumination is achieved by high performance Light Emitting Diodes (LEDs) with specifications of 1.96 mm² and 493 lm (251.53 lm/mm²) at an angular deviation of 0.37°. A camera probe is used with either an object-space telecentric (telecentricity <0.2°, 2437 mm virtual pupil distance) or entocentric objective (Köhler based illumination, 6238 mm virtual pupil distance). Using the telecentric mode, the particle distance independency is located within 20 mm while the focal depth is approximately 5 mm. The local resolution is between 20 and 30 μm, according to the used optics, with a standard deviation less than 4.5%. Maximum particle diameter is up to 5 mm while particles can reach up to 2 m/s as function of exposure. The basic distance transform approach with watershed segmentation for analysis of transmitted-light images gives deviations less than 5% at high particle densities and less than 2% at low ones. The error of false positives typically is below 5% while the error of wrong radiuses is below 1% for up to 90% of all droplets and below 5% otherwise. Up to five images per core and second (trans-illumination) can be analyzed automatically and online at densities up to 25% (trans-illumination, gap width less than 5 mm) 40% (object side telecentric epi-illumination, single probe) respectively.The advanced pre-segmentation approach based on the Random Forest Classifier (RFC) is used to perform the more complex image analysis with epi-illumination. As long as the quality of pre-segmentation is high enough, the classification results in images, which can be analyzed in the following distance transform approach. This is considerably depending on the quality of training the algorithm and recurring image features. Compared to the distance transform analysis at low densities the deviation increases. The RFC pre-segmented image gives an additional deviation of 1.1% (both in regard to the total amount of evaluated pixels) and a deviation of 12.9% in regard to the mean particle diameter. Below a particle size of 50 pixels the image analysis overestimates the actual number of particles due to the sensitivity of the Euclidian distance approach.     

Long-term water absorption behavior of thermoplastic composites produced with thermally treated wood

Wood plastic composites (WPCs) were produced from thermally treated beech (Fagus orientalis L.) wood and polypropylene (PP) polymer with coupling agent, by using injection molding. The wood chips were thermally treated for 30 or 120 min at three different temperatures (120 °C, 150 °C, or 180 °C) under saturated steam in a digester and then grounded (40-mesh size) by wood mill. Long-term water absorption kinetics of the composites were investigated with water immersion test. It was found that the water absorption decreased with increasing severity of the thermal-treatment and water immersion time as compared to the control composites. Furthermore, the composites produced with wood treated at 180 °C for 120 min exhibited the least water absorption. Microstructures of the composites were examined by SEM analysis to understand the mechanisms for the wood–plastic interaction which affected the water absorption. Further studies were conducted to model the water diffusion of the composites. Diffusion coefficient parameter in the models was obtained by fitting the model predictions with the experimental data. Water absorption of the studied composites was proved to follow the kinetics of a Fickian diffusion process.     

Analysis of impact energy factors in ductile materials using single particle impact tests on gas gun

Wear is surface damage that involves progressive material loss due to relative motion between the contacting surfaces. Removal of material by action of impacting particles is known as erosion. Single particle impact tests were conducted using small particles (95–100 μm) and impact velocity 90 ms⁻¹. A new technique has been developed to measure the impact crater using Laser Scanning Confocal Microscope (LSCM). Depth of craters was calculated based on the impact parameters and the material properties and compared with measured values. The variations are discussed with the high strain-rate deformation and energy loss in the material through strain energy and heating.     

Paraffinic mineral oil lubrication for cold forward extrusion: Effect of lubricant quantity and friction

In this paper, Finite Element (FE) and experimental analyses have been developed on the deformation of aluminium billet over a tool. Effect of friction resulted from the use of additive-free ISO460-compliant paraffinic mineral oil with kinematic viscosity of 455.192 mm²/s at 40 °C in amounts of 0.1, 1, 5, and 20 mg were examined. The time behaviour of displacements on the billet in the experiment was used as inputs for the FE model. The FE analysis results for load–displacement behaviour of the extrusion were compared with the experimental results. It was shown that significant differences exist between the four lubricant quantities on friction and contact pressure distribution.     

Experimental measurement and statistical analysis of the RMS delay spread in time-varying ultra-wideband communication channel

The statistical analysis of the RMS delay spread is achieved based on the results obtained from an outdoor time-varying ultra-wideband (UWB) channel measurement. The paper reports on the RMS delay spread values, the cumulative distribution functions (CDFs) and the probability density functions (PDFs) for the measured channel configurations with their estimated parameters. Findings show how the RMS delay spread values are fluctuating for different channel configurations within the same measurement campaign. For example, 35 ns and 2.5 ns have been obtained for different channels. The differences in the measured instantaneous RMS delay spread leads to obtaining different PDFs that fit the measured data where Generalized Pareto distribution is dominant. The relation between the RMS delay spread and the channel path loss has been studied. Positive correlation is seen for all measured channels with different amounts. The highest correlation value is 0.7675 while the lowest is 0.2951. The coherence bandwidth analysis is also conducted, and the values are fluctuating as the case of the RMS delay spread. The obtained values varies between 325.3 MHz and 5.7 MHz.     

A study on erosion of upper bainitic ADI and PDI

Ductile iron containing ∼3.5 wt.% C and 2.1–4.2 wt.% Si (2.1, 2.8 and 4.2 wt.%) was studied. Three sets of specimens with differing Si contents were made into austempered ductile iron (ADI) and pearlite ductile iron (PDI) through heat treatment. These specimens were then eroded with Al₂O₃ particles and SiO₂ particles of 275–295 μm grit size to understand the relationship between erosion rate and microstructure. The ADI specimens were upper bainitic matrices that were austempered for different periods of time at 420 °C. The heat treatment of PDI was conducted at 870 or 930 °C for 1 h then forced air cooled or oil quenched to room temperature.Two types of wear curves, single peak curves and double peak curves, were found when plotting the erosion rate figures derived from the experimental results. 2.1 wt.% Si and 2.8 wt.% Si ADI tempered for a long period of time, due to their decreased retained austenite content and increased carbide content, had a single peak erosion rate curve. This embrittlement effect caused the impact angle of maximum erosion rate to increase from ∼30 to ∼45°. Decreasing the interspacing of the lamellae cementite promoted the hardness and improved the low-angle erosion wear resistance of PDI. The high hardness and brittleness of the matrix reduces the high-angle erosion resistance and the peak erosion rate occurs at a higher angle.For 2.1Si-ADI and 2.8Si-ADI tempered for a short duration, increasing the volume fraction of martensite in the matrix increases the erosion rate at an impact angle of 30°, but the maximum erosion rate is found at 75°. This results in a curve with a double peak. The double peak curve was also observed for high silicon ADI tempered for a long duration. The high solid solution hardness of 4.2Si-ADI, due to low retained austenite content and the presence of carbide in the matrix, results in poor erosion resistance. When this material is austempered for a long period, the erosion rate curve shifts from a single peak curve (30°) to a double peak curve (30°; 60°).     

Analysis of load-speed sensitivity of friction composites based on various synthetic graphites

The frictional response of a multi-component phenolic-based friction material is highly complex under a set of variable loads and speeds. The present paper discusses the sensitivity of friction coefficient (μ) of friction composites containing synthetic graphite with different particle sizes (with similar crystallinity range) to braking pressure and sliding speed. The friction studies were carried out on a sub scale brake-test-rig, following 4 loads × 3 speeds experimental design. The best combination of performance properties was observed for the composite containing synthetic graphite with an average particle size of 410 μm. Other particle sizes which resulted in good performance were 38 and 169 μm. Very fine particle sizes were not beneficial for desired combination of performance properties. Regression analysis of μ following an orthogonal L₉(3 × 3) experimental design method revealed that the first order influences of sliding speed and braking pressure were significant. When all the combinatorial influences of braking pressure and sliding speed are taken into account together their simultaneous effects would be most effective in the range of graphite particle size ～80–250 μm.     

Digital filtering methodology used to reduce scale of measurement effects in roughness parameters for magnetic storage supersmooth hard disks

Roughness of disk media influences the tribological interaction of head-disk interfaces, especially when the intended flying-height is below 5 nm that is required to achieve extremely high-density recording (EHDR). Roughness parameters such as the root-mean-square (RMS) amplitude, however, are influenced by the scale of measurement, such as the scan size. Effects related to scale of measurement such as varying the scan size were investigated and means to reduce such effects were proposed by establishing an “ad hoc” digital filtering procedure. Two types of magnetic disks intended for EHDR were measured by an atomic force microscope (AFM) at various scan dimensions ranging from 0.5 μm × 0.5 μm to 112 μm × 112 μm. The proposed filtering method used the RMS values as a filter design parameter for choosing the appropriate high-pass cutoff wavelength for each scan size. The study revealed the existence of a unique cutoff wavelength that would identify different wavelength regimes and the associated critical scan size in each disk. To substantiate the effectiveness of the proposed filtering method in reducing the scale of measurement effects related to the scan size, other roughness parameters were also calculated subsequent to the filtering procedure. It was found that the proposed filtering scheme effectively reduced the scale of measurement effects in the amplitude parameters (e.g., RMS and the ten-point height variation) and the functional parameters (e.g., material and core void volumes). These parameters exhibited steady-state trends with respect to increasing scan size, indicating reduced scale of measurement effects.     

Sliding friction induced atom diffusion in the deformation layer of 0.45% C steel rubbed against Tin alloy

Evolution of microstructure and compositions in worn surface and subsurface of 45 (0.45 mass% carbon) steel disc slid against tin-alloy-pin was analyzed by SEM, TEM and SIMS. The mechanical alloying layer and plastic deformation layer were formed in the sliding friction-induced deformation layer (SFIDL) of 45 steel. Ultra-refine and nano grains were detected in the worn surface layer. Elements of Sn, Cu and Sb, originated from the mating tin-alloy-pin, with diffusion depth of 35 μm, 11 μm and 4 μm, respectively, were detected in its SFIDL. Mechanisms accelerating atom diffusion in SFIDL were subsequently propounded.