Effect of Cu Content on the Structure,and Performance of Substoichiometric Cr–N Coatings

Cu–Cr–N coatings with Cu contents between 3 and 65 at.%, Cu/Cr ratios in the 0.04–4.5 range and 21–27 at.% N, synthesized by twin electron-beam Physical Vapor Deposition at 450 °C, were investigated and compared against substoichiometric Cr–N reference samples. The main objective of this study is to study the influence of Cu on the structure, and the subsequent effects on the mechanical properties, room (22 °C) and high temperature (500 and 840 °C) tribological performance of Cu–Cr–N coatings. Using X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and scanning electron microscopy, in combination with nanoindentation mechanical property measurements and laboratory-controlled ball-on-disc sliding experiments, it is shown that Cu–Cr–N coatings with low Cu content (3 at.%) possess sufficient wear resistance for high-temperature demanding tribological applications. The lubricious effect of oxide formation at high temperatures is also evaluated.     

Tribological investigation of cast iron air-conditioning compressor surfaces in CO2 refrigerant

Tribological investigations of air-conditioning compressors have been a topic of great interest in recent years and gray cast iron has been a commonly used material by various compressor manufacturers. The scope of this paper is to determine the role of oxygen and in particular carbon dioxide refrigerant (R744) in cast iron samples tribologically tested using an Ultra High Pressure Tribometer that is suitable for tribological testing of compressor contact interfaces that operate with carbon dioxide refrigerant. A series of experiments was performed in environments of air, nitrogen (N₂), oxygen (O₂) and carbon dioxide (CO₂). While it was found that the presence of oxygen is beneficial, CO₂ has a more positive effect on the surfaces than in the case of pure O₂ suggesting that the use of CO₂ promotes a different wear mechanism. Also, it was found that CO₂ has better tribological performance over a range of pressures between 100 psi (0.69 MPa) to 600 psi (4.1 MPa), compared to lower pressures. Furthermore, CO₂ was compared with tetrafluorethane (R134a), a common hydrofluorocarbon refrigerant and found to have superior tribological performance. Two surface chemical analysis techniques were utilized to examine the surfaces after tribological testing. Auger electron spectroscopy (AES) was used to track changes in the elemental composition while X-ray photoelectron spectroscopy (XPS) was utilized to detect the different chemical states resulting from compound formation on the tribologically tested surfaces. It was found that CO₂ leads to better tribological performance of the interface due to the formation of carbonates on the surface, which reduce friction and prevent wear.     

Metadata requirements for digital museum environments

We describe a system which addresses all the processes involved in digitally acquiring, modelling, storing, manipulating and creating virtual exhibitions from 3D museum artefacts. More specifically, we examine the significance of metadata in enabling and supporting all of these processes and describe the extensive facilities provided for authoring, maintaining and managing metadata. The development of the system has been heavily influenced by factors relating to interoperability, standards, museum best practice and feedback from two museum pilot sites. Finally, we briefly consider the system in the wider context of applications such as virtual learning environments and distributed repositories of archives.     

Tribological Effects of BN and MoS2 Nanoparticles Added to Polyalphaolefin Oil in Piston Skirt/Cylinder Liner Tests

We report in this article the friction and wear results of polyalphaolefin (PAO 10) base oil with the addition of 3 wt% boron nitride (BN) and molybdenum disulfide (MoS₂) nanoparticles with nominal size of 70 and 50?nm, respectively. The formulations were tested using cast iron cylinder liner segments reciprocating against aluminum alloy piston skirt segments at 20, 40, and 100?°C. The results showed that, at a load of 250?N and a reciprocating frequency of 2?Hz, BN did not lower friction whereas MoS₂ nanoparticles were very effective at reducing both friction and wear, compared with the base oil. The viscosities of both formulations were similar to the base oil, which allowed for a direct comparison between them. Raman spectroscopy showed the formation of an aligned MoS₂ layer on the cast iron liner surface, which most likely functions as a tribofilm. In the case of the cast iron liner tested with BN nanolubricant, no traces of BN were found. The effect of surfactants was also studied, and it was found that some surfactants were not only beneficial in dispersing the nanoparticles in oil, but also in producing some reduction in friction and wear, even when used as stand-alone additives in PAO 10.     

Tribological Study Comparing PAG and POE Lubricants Used in Air-Conditioning Compressors under the Presence of CO2

Polyalkylene glycol (PAG) and polyolester (POE) synthetic lubricants are good candidates for air-conditioning systems that work with alternative refrigerants such as carbon dioxide (CO₂). Both synthetic lubricants are widely used in air-conditioning compressors and have been optimized for use with hydrofluorocarbon (HFC) refrigerants. However, it is still not clear which lubricant is more suitable for use in compressors operating with CO₂ as a refrigerant. This study compares the performance of PAG and POE lubricants of the same viscosity (ISO VG 68) used in air-conditioning compressors. The materials used were Al390-T6 disks and hardened steel SAE 52100 pins. The tests were performed using a high pressure tribometer (pin-on-disk configuration) in the presence of CO₂. The results showed that scuffing and wear resistance of Al390-T6 tested with PAG were superior compared to the samples tested with the POE lubricant. Chemical analysis using X-ray photoelectron spectroscopy showed that PAG tends to promote the formation of carbonate layers on the surface, leading to improvement in the tribological performance of the interface.     

ApoA1 Deficiency Reshapes the Phenotypic and Molecular Characteristics of Bone Marrow Adipocytes in Mice

In the present study, we studied the effect of apolipoprotein A-1 (APOA1) on the spatial and molecular characteristics of bone marrow adipocytes, using well-characterized ApoA1 knockout mice. APOA1 is a central regulator of high-density lipoprotein cholesterol (HDL-C) metabolism, and thus HDL; our recent work showed that deficiency of APOA1 increases bone marrow adiposity in mice. We found that ApoA1 deficient mice have greatly elevated adipocytes within their bone marrow compared to wild type counterparts. Morphologically, the increased adipocytes were similar to white adipocytes, and displayed proximal tibial-end localization. Marrow adipocytes from wild type mice were significantly fewer and did not display a bone-end distribution pattern. The mRNA levels of the brown/beige adipocyte-specific markers Ucp1, Dio2, Pat2, and Pgc1a; and the expression of leptin were greatly reduced in the ApoA1 knock-out in comparison to the wild-type mice. In the knock-out mice, adiponectin was remarkably elevated. In keeping with the close ties of hematopoietic stem cells and marrow adipocytes, using flow cytometry we found that the elevated adiposity in the ApoA1 knockout mice is associated with a significant reduction in the compartments of hematopoietic stem cells and common myeloid, but not of the common lymphoid, progenitors. Moreover, the ‘beiging’-related marker osteopontin and the angiogenic factor VEGF were also reduced in the ApoA1 knock-out mice, further supporting the notion that APOA1—and most probably HDL-C—regulate bone marrow microenvironment, favoring beige/brown adipocyte characteristics.     

Fast screening of municipal wastewater components by reversed-phase chromatography coupled to ultraviolet-diode array detection

The screening of ingredients in municipal wastewater samples was studied, by reverse‐phase high‐performance liquid chromatography (RP‐HPLC) implemented with a ultraviolet (UV)‐diode array detector, in an effort to establish a quick screening method for finding the main UV‐absorbing components of the wastewater that enters the biological treatment plant. For the purposes of direct comparison of the chromatograms obtained, a single sample taken from the inlet of municipal biological treatment plant was used for all experimental tests and the optimal elution conditions were established by detailed investigation through isocratic and gradient elution techniques. The optimal column resolution was reached by testing a broad range of capacity and selectivity factor values. The criterion used for validating the complete separation of solutes was based on the spectral purity of eluted chromatogram peaks and on the stability of retention time of a peak in real‐time chromatograms taken at different wavelengths during the elution process. From this research work, it was found that the overall chromatogram peak pattern was sensitive to the mobile phase composition and solvent system but under fixed elution conditions, the pattern of the major peaks was stable and depended on the composition of the wastewater sample. By testing different types of elution modes, it was found that the best column resolution was obtained under programmed isocratic‐gradient elution using a binary mobile phase. Finally, a relatively high column resolution method is reported for fragmentation of municipal wastewater samples.     

Tribological evaluation of piston skirt/cylinder liner contact interfaces under boundary lubrication conditions

The friction and wear between the piston and cylinder liner significantly affects the performance of internal combustion engines. In this paper, segments from a commercial piston/cylinder system were tribologically tested using reciprocating motion. The tribological contact consisted of aluminium alloy piston segments, either uncoated, coated with a graphite/resin coating, or an amorphous hydrogenated carbon (a‐C : H) coating, in contact with gray cast iron liner segments. Tests were conducted in commercial synthetic motor oils and base stocks at temperatures up to 120°C with a 2 cm stroke length at reciprocating speeds up to 0.15 m s⁻¹. The friction dependence of these piston skirt and cylinder liner materials was studied as a function of load, sliding speed and temperature. Specifically, an increase in the sliding speed led to a decrease in the friction coefficient below approximately 70°C, while above this temperature, an increase in sliding speed led to an increase in the friction coefficient. The presence of a coating played an important role. It was found that the graphite/resin coating wore quickly, preventing the formation of a beneficial tribochemical film, while the a‐C : H coating exhibited a low friction coefficient and provided significant improvement over the uncoated samples. The effect of additives in the oils was also studied. The tribological behaviour of the interface was explained based on viscosity effects and subsequent changes in the lubrication regime, formation of chemical and tribochemical films. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of magnetic inhomogeneity in β-Cu3Fe4V6O24

The temperature dependence of dc magnetization and electron paramagnetic resonance (EPR) spectra of the ??-Cu₃Fe₄V₆O₂₄ multicomponent vanadate were investigated. Dc magnetic measurements showed the presence of strong antiferromagnetic interactions (Curie-Weiss temperature, ?? ?? 80 K) at high temperatures, while zero-field-cooled (ZFC) magnetization revealed a cusp-like maximum in low fields at T _f1 = 4.4 K, which coincides with the splitting of the ZFC and FC curves. Another maximum was registered at T _f2 = 3.0 K. These two temperatures (T _f1 and T _f2) could be regarded as freezing temperatures in the spin glass state of two magnetic sublattices of Fe1 and Fe2 ions. The EPR spectrum of ??-Cu₃Fe₄V₆O₂₄ is dominated by a nearly symmetrical, very intense and broad resonance line centered at g _eff ?? 2.0 that could be attributed to iron ions. Below 10 K, an additional EPR spectrum with g ₁ = 2.018(1) and g ₂ = 2.175(1) appears, as well as a very weak line at g_eff = 1.99(1). The former spectrum is probably is due to divalent copper ions, and the latter line due to vanadium V⁴⁺ complexes. The temperature dependence of EPR parameters (g-factor, linewidth, integrated intensity) was determined in the range of 3?C300 K. Two low-temperature maxima in the temperature dependence of the integrated intensity (at 40 and 6 K) were fitted with a function suitable for pairs of exchange-coupled Fe³⁺ ions. A comparison of dc magnetic susceptibility and EPR integrated intensity indicates the presence of spin clusters, which play an important role in determining the low-temperature magnetic response of _??-Cu₃Fe₄V₆O₂₄.