Cu/Co-W nanolayers electrodeposited from single bath and investigations of their nanohardness

For the first time thick (??8 ??m) Cu/Co-W multilayered coatings with individual layers ranging from 5 to 200 nm were electrodeposited from a single bath. The content of tungsten in rich-in Co-W layers was controlled by varying current densities in a citrate-borate bath. Continuous Multi-Cycle (CMC) nanoindentation technique was used to analyze mechanical properties of those deposits. Optical examination of the indented zone revealed the absence of cracks inside and outside the indentation area in the interval of the normal loads used. The hardness of Cu/Co-W multilayers varied with the bi-layer period and the electrodeposition parameters. The Cu/Co-W multilayers showed an increased hardness compared to that of Co-W coatings electrodeposited under the same conditions.     

Strategies to cope with methanogens in hydrogen producing UASB reactors: Community dynamics

Methane occurrence is a common concern in hydrogen producing reactors. This study presents the analysis of the microbial community structure during the application of operational strategies to decrease methane production, in three different up-flow anaerobic sludge blanket hydrogen-producing reactors. Cloning and denaturing gradient gel electrophoresis approach were used to establish the presence of homoacetogens, methanogens and hydrogen producers. The results showed that homoacetogenic organisms related to Blautia hydrogenotrophica and Oscillibacter valericigenes, and the hydrogen producer Enterobacter aerogenes where favored during pH decreasing strategies (5.6 to 4.5). The increment of the organic loading rate from 20 to 30 g chemical oxygen demand/L-d, selected hydrogen producers similar to Clostridium tyrobutyricum, Citrobacter freundii and E. aerogenes; further increments caused inhibition of hydrogen production due to the high undissociated acids concentration. Methane production was inhibited completely only when the biomass of the reactor was heat treated for a second time, this strategy selected hydrogen producers capable to sporulate, but homoacetogens were also favored. In all reactors the methanogenic activity was attributed to hydrogenotrophs related to the genera Methanobrevibacter and Methanobacterium.     

Mechanical and tribological behavior of nanostructured copper–alumina cermets obtained by Pulsed Electric Current Sintering

Nanostructured Cu–Al₂O₃ powders obtained by the reduction of CuO with Al in a high energy ball mill were successfully consolidated by Pulsed Electric Current Sintering (PECS). The effect of the composition and microstructure of these PECS Cu–Al₂O₃ cermets on their strength was investigated. The friction and wear behavior of these cermets were studied under reciprocating sliding against corundum at 23 °C and 50% RH, and compared to the behavior of coarse grained PECS sintered pure copper. The effect of grain size on the coefficient of friction was masked by the formation of a surface tribolayer. The wear depth recorded on Cu–Al₂O₃ is lesser than half the one on coarse grained copper. Surface and subsurface deformation studied through FIB cross-sections showed that delamination and oxidative wear were active on Cu and Cu–Al₂O₃ cermets respectively under the current sliding test conditions. PECS Cu–Al₂O₃ cermets showed a good thermal stability even at 600 °C.     

Electrodeposited composite tin-lead coatings

The structures, morphologies and composition of tin-lead alloy electrodeposits, with and without dispersed silicon carbide particles, were studied using a rotating cathode. The incorporation of silicon carbide particles was found to reduce the rate of reduction of tin ions.     

DFT study of H2 adsorption on Pd-decorated single walled carbon nanotubes with C-vacancies

Carbon nanotubes are considered important materials for hydrogen storage. Although the C–H interaction is very weak at room temperature, the incorporation of highly dispersed Pd nanoparticles increases the H₂ adsorption on carbon surfaces. In this work we performed density functional theory studies of H₂ adsorption on single walled carbon nanotubes (SWCNTs) with C-vacancies and a Pd decoration. We used the VASP and SIESTA codes. Our calculations show that Pd adsorption is favored on the C-vacancies of the (5,5) SWCNT, while H₂ adsorption also occurs preferentially on C-defective sites.     

The Lubricity of Oxides Revised Based on a Polarisability Approach

The lubricity of a wide variety of solid oxides at high temperature is analysed mainly based on the existing polarisability approach. The starting point is that the interaction between ions in an oxide depends on how strongly electrons are interacting in overlapping orbitals. This is related to the polarisability of ions. From this polarisability, the interaction between cation and anion present in an oxide was calculated for binary/mixed oxides and for six new simple oxides (values for 17 oxides collected from literature) and correlated to the coefficient of friction of these oxides below their melting temperature. Based on that correlation, the mechanism of friction of these oxides is proposed.     

Pulsed laser deposition of antifriction thin-film MoSex coatings at the different vacuum conditions

MoSe_x coatings were obtained by pulsed laser deposition in vacuum at the pressure of background Ar gas up to 10 Pa. The deposition temperature was 200 °С. The films were studied by means of X-ray diffraction, scanning and transmission electron spectroscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy of helium ions. The tribological properties of thin-film coatings were investigated by pin-on-disk testing in air with 50% relative humidity. In addition, wear tracks were studied by micro-Raman spectroscopy. Chemical composition, structure, and tribological properties of the coatings were found to be sensitive to the presence of the inert gas. Thus, increasing the gas pressure from 10^− 4 to 10 Pa changes the chemical composition, so that the ratio of the atomic concentrations of Se and Mo (x = Se/Mo) increases from 1.5 to 2.4 in the principal deposition zone. The changing of the structure concerns the accumulation of distortions in the lattice of MoSe_x nano-crystals as increasing the distance between the basal planes and intensive formation of nano-sized inclusions of the amorphous phase and Mo nano-crystals in the volume of the coatings. At the optimal gas pressure (∼ 2 Pa), the composition of the coating was close to the stoichiometric one, and the layer adjacent to the substrate consisted of MoSe_x nano-crystals with the basal planes parallel to the substrate surface or oriented at small angles to the surface. The thickness of the oriented layer in such coatings was greater than the thickness of the similar layer in the coatings deposited in vacuum (10^− 4 Pa). The tribological properties of MoSe_x coatings deposited on substrates of stainless steel type 95 × 18 (18 at.% Cr) depend on the gas pressure. The friction coefficient in air decreases from 0.08 for deposition at the background pressure of 10^− 4 Pa to 0.04 for deposition at the optimal pressure. This change in the deposition conditions has only a marginal effect on the coating durability. Means to increase the durability are also considered.     

Ecological cutting: Feasible or not?

This paper describes the results of a two-year research project on ecological cutting, in which four different applications, namely, cutting, pocket milling, face milling, and drilling, were investigated under dry and lubricated conditions. A traditional cutting fluid and an environmentally friendly cutting fluid were used for the latter. TiN-, Ti (C,N), and (Ti,Al)N-coated tools were tested, together with commercially-available multilayer coated tools, to analyse to what extent the use of coatings could reduce or even eliminate the need for cutting fluids. The machined materials include an unalloyed steel, I.0503, a low alloyed steel, 1.2312, a stainless steel, 1.4306, and cast iron, ADI. End-of- life tests were done in all cases and the wear of the tools was examined with SEM. The research showed that the results are strongly dependent on the application. For cutting, coated tools result in the best tool lives although tools used under lubricated conditions still outperform their dry used counterparts. For milling, dry machining is advantageous. The drilling tests showed better results under lubricated conditions mainly due to the cooling and chip removal capacity of the lubricants. In this case, the (Ti,Al)N-coated drill out-performed the commercially available coated tool.     

In vitro induction of primary, antigen-specific CTL from human peripheral blood mononuclear cells stimulated with synthetic peptides

A protocol for in vitro induction of primary, antigen-specific CTL from human peripheral blood mononuclear cells (PBMCs) was developed. Antigen presenting cells (APCs) consisted of Staphylococcus aureus Cowan-I (SAC-I) activated PBMCs treated with a citrate-phosphate buffer at pH 3 to release endogenous peptides bound to surface MHC. This treatment resulted in transient expression of empty class I molecules which could be subsequently stabilized with peptide and beta 2-microglobulin (beta 2m). SAC-I activated PBMCs from HLA-A2.1 normal donors loaded with HBV core 18-27 peptide following acid treatment were used to stimulate PBMCs depleted of CD4+ T cells, in the presence of recombinant interleukin-7 (rIL-7). After 12 days, cells were restimulated with autologous, peptide-pulsed, adherent cells and tested for CTL activity 7 days later. In 23 independent experiments from 13 different HLA-A2.1 donors, this protocol resulted in induction of primary CTL more than 90% of the time. As indicated by both the frequency and magnitude of the response against peptide-sensitized target cells, SAC-I activated PBMCs treated with acid were the most efficient stimulator APC. Thirteen per cent of the cultures generated were capable of lysing target cells transfected with the HBV core antigen and, in general, these CTL cultures exhibited high avidity for the HBV core peptide. This protocol is generally applicable to different antigens and class I alleles, and thus, may be utilized to screen large numbers of peptides to identify human CTL epitopes.