Spray-dry synthesis of β-Cu1.8Zn0.2V2O7 ceramic fine particles showing giant negative thermal expansion

We used spray-dry method to synthesize fine powder of β-Cu_1.8Zn_0.2V₂O₇ showing large negative thermal expansion (NTE) linearly to temperature over a wide temperature range. The NTE of β-Cu_1.8Zn_0.2V₂O₇ is produced by microstructures consisting of voids and anisotropic thermal deformation of crystal grains in ceramics. By reducing the size of the microstructures that produce NTE, large NTE equivalent to that of bulk was realized, even for ceramic particles of about 2 μm size. Comparison with particles produced using a conventional method demonstrates that the particle size distribution is narrow and that the particles are nearly spherical. This achievement is expected to pave the way to use of NTE materials in micrometer-scale control of thermal expansion.     

Effect of Sliding History on Super-Low Friction of Diamond-Like Carbon Coating in Water Lubrication

Water lubrication using diamond-like carbon (DLC) coatings is regarded as being a promising eco-friendly technology. However, it has been reported that delamination of DLC coatings occurs in water. The authors clarified that the application of friction in ambient air prior to self-mating DLC water lubrication, in addition to the suppression of DLC delamination, caused the friction coefficient to decrease more than when no processing is performed in the boundary lubrication region. When compared to the case when there was no pre-sliding, in terms of the wear scar, in this case, a much more hydrophilic and smoother surface was formed. Therefore, the friction-reducing process in water due to the presence of a sliding history (pre-sliding in ambient air) was clarified by an analysis of the DLC geometry, structure, chemical state and an in situ analysis that can measure the friction properties and the chemical state of DLC. We clarified that the process in which the oxidation and structural changes of the DLC proceed at the time of pre-sliding in ambient air using in situ Fourier transform infrared spectroscopy–attenuated total reflection. It was also revealed that the OH termination subsequently accelerated rapidly due to the friction in water after pre-sliding process. In addition, a time-of-flight secondary ion mass spectrometry analysis revealed that this OH group was derived from the lubricating water and unlike the case in which there was no pre-sliding in ambient air, the rate at which OH terminates increased considerably.     

Effective resistance of current-carrying superconducting wire in oscillating magnetic fields 1: Single core composite conductor

The influence of oscillating magnetic fields on the dc transport current in a single core superconducting wire has been studied by observing the terminal voltage of the wire. The voltage versus oscillating field characteristics can be explained quantitatively by a theoretical analysis based on the critical state model. The analysis shows that the voltage measurement gives detailed information on the change of the distribution of the magnetic induction inside the superconductor. An effective resistance appears in the transport current loop when the amplitude of the oscillating field exceeds a certain threshold value. The dependence of the effective resistance on the amplitude and frequency of the oscillating field and on the conductor diameter is discussed.     

Copolymerization of glycidylmethacrylate–methylmethacrylate–divinylbenzene in cyclohexane

The copolymerization of glycidylmethacrylate–methylmethacrylate–divinylbenzene in cyclohexane was studied as an example of crosslinking precipitation copolymerization. The resultant copolymer is fine spheroidal. The copolymerization proceeds acceleratively at first, then steadily, and gradually slows down. The larger the divinylbenzene concentration, the smaller is the copolymerization rate. Glycidylmethacrylate is preferentially incorporated in the copolymer.     

Deposition and structural analyses of molybdenum-disulfide (MoS2)–amorphous hydrogenated carbon (a-C:H) composite coatings

In this study we developed composite coatings consisting of amorphous hydrogenated carbon (a-C:H) and molybdenum-disulfide (MoS₂), and clarified their microstructure. In addition, we interpreted the tribological properties of the composite coatings in the viewpoint of a deposition-induced microstructural modification. The coatings were produced by the hybrid deposition technique of RF-generated methane and argon plasma and DC magnetron co-sputtering of MoS₂ target. The deposition parameter investigated in this study was methane flow rate. Structural analyses were performed using a transmission electron microscope (TEM) and an atomic force microscope (AFM). Friction tests were conducted using a ball-on-disk type tribometer. From an electron micrograph, it was confirmed that nano-clusters were embedded into an amorphous carbon host matrix. Surface roughness of the composite coating was ～ 0.25 nm in R_a compared to 5.0 nm in R_a of sputtered MoS₂. The concentration measurements were performed, and the results show that the sulfur and molybdenum concentration ratio, [S]/[Mo], is ～ 0.9, which indicates that the amount of sulfur was reduced due to the discharged plasma. In friction tests, composite coatings showed high friction in a vacuum condition. It was considered that lubricant MoS₂ lamellar structures showing super-low friction in a vacuum condition during friction could not be formed between ball and coating during friction because of the lack of sulfur in embedded clusters.     

Effect of Contact Stiffness on Creep-Groan Occurrence on a Simple Caliper-Slider Experimental Model

In this paper, a fundamental mechanism for creep-groan generation is investigated by adopting a simple yet effective caliper-slider experimental model. Contact condition, which is a function of three parameters, namely normal force, contact roughness, and material combination, is connected with the creep-groan phenomenon in terms of contact stiffness. Creep-groan generation is determined by analyzing the frequency characteristic of the generated vibration acceleration when the sliding commences due to a simultaneous application and release of force in the tangential and normal directions, respectively. As per the obtained results, creep-groan occurrence or absence in the employed experimental model may be classified into three regions based upon the value of the contact stiffness, i.e., occurrence, non-occurrence, and mixed regions. The results also indicate that creep-groan occurrence in this caliper-slider experimental model can be avoided by controlling the value of contact stiffness in an effective manner.     

Thermal Stability of Hexaaluminate Film Coated on SiC Substrate for High-Temperature Catalytic Application

A coating of barium hexaaluminate (Ba_0.75Al_11.0O_17.25) on an α-SiC substrate and the thermal stability of the formed film were investigated for a high-temperature catalytic application. The film prepared by sol coating consisted of BaAl₂Si₂O₈ and α-Al₂O₃ phases and always contained many cracks or exfoliations after heating at 1200C. A hexaaluminate porous film was successfully formed by slurry coating without void formation at the interface between the film and the substrate and exfoliation due to the formation of the intermediate layer after heating at 1200°C. The microstructure of the film remained unchanged, even after heating at 1300°C.     

Comparative study on the growth mechanisms of PAHs

The efficiencies of recently proposed, phenyl addition/cyclization (PAC), methyl addition/cyclization (MAC) and a popular hydrogen abstraction/acetylene addition (HACA) mechanisms have been examined experimentally by detecting the gas phase reaction products of pyrolysis of toluene with/without addition of benzene + acetylene by using vacuum ultraviolet (VUV) single photon ionization (SPI) time of flight mass spectrometry (TOFMS). Besides the observation of verities of large polycyclic aromatic hydrocarbons (PAHs), intense mass peaks of indene, phenylacetylene and propyne confirmed a remarkable quenching of the major active species, benzyl, phenyl and methyl radicals by acetylene. In spite of quenching, only benzyl contributed products were diminished while phenyl and methyl contributed products were enhanced. Uniquely observed symmetrical PAHs; corrannulene/coronene; formed by the active involvement of PAC, HACA and/or MAC mechanisms, reflects the interdependencies of these mechanisms. Individually, PAC was found highly efficient for endless growth, HACA for filling triple fusing site and MAC for expanding cyclotetra/pentafused into benzenoid structure, respectively.     

Persistence and partitioning of eight selected pharmaceuticals in the aquatic environment: Laboratory photolysis, biodegradation, and sorption experiments

We selected eight pharmaceuticals with relatively high potential ecological risk and high consumption—namely, acetaminophen, atenolol, carbamazepine, ibuprofen, ifenprodil, indomethacin, mefenamic acid, and propranolol—and conducted laboratory experiments to examine the persistence and partitioning of these compounds in the aquatic environment. In the results of batch sunlight photolysis experiments, three out of eight pharmaceuticals—propranolol, indomethacin, and ifenprodil—were relatively easily photodegraded (i.e., half-life < 24 h), whereas the other five pharmaceuticals were relatively stable against sunlight. The results of batch biodegradation experiments using river water suggested relatively slow biodegradation (i.e., half-life > 24 h) for all eight pharmaceuticals, but the rate constant was dependent on sampling site and time. Batch sorption experiments were also conducted to determine the sorption coefficients to river sediments and a model soil sample. The determined coefficients (K_d values) were much higher for three amines (atenolol, ifenprodil, and propranolol) than for neutral compounds or carboxylic acids; the K_d values of the amines were comparable to those of a four-ring polycyclic aromatic hydrocarbon (PAH) pyrene. The coefficients were also higher for sediment/soil with higher organic content, and the organic carbon-based sorption coefficient (log K_oc) showed a poor linear correlation with the octanol-water distribution coefficient (log D_ow) at neutral pH. These results suggest other sorption mechanisms—such as electrochemical affinity, in addition to hydrophobic interaction—play an important role in sorption to sediment/soil at neutral pH.     

Effect of oxygen content on impact toughness of a fine-grained magnesium alloy

Fine-grained Mg-3Al-Zn alloys with various oxygen contents were prepared by a powder metallurgy process, and the effect of oxygen content on the impact toughness of the fine-grained magnesium alloys was quantitatively investigated. It is found that the impact toughness of magnesium alloys with mean grain size smaller than 3 μm is extremely high when the oxygen content is less than 400 pp, but it becomes very low as the oxygen content is higher than 1000 ppm. Both magnesium oxides and hydroxides are detected in the magnesium alloys. The presence of excessive magnesium oxides and hydroxides deteriorates the dynamic plastic deformation ability of the fine-grained magnesium alloys.