Particle refinement of ZrB2 by the combination of borothermal reduction and solid solution

Flexible synthesis of ultra‐fine ZrB₂ powders was achieved by borothermal reduction in a mixture of ZrO₂, boron, and TiO₂. Without TiO₂ additive, coarse ZrB₂ powders with particle size of 0.81 μm were obtained, presumably due to good wettability and solubility of ZrB₂ in the byproduct B₂O₃. It was found that the particle growth of ZrB₂ was effectively inhibited by the solid solution of TiB₂ (≥1 mol%). The refinement mechanism was that the solid solution of in situ formed TiB₂ presumably lowered the wettability and solubility of ZrB₂ in the B₂O₃ liquid and significantly inhibited the coarsening of ZrB₂. The average particle size of resulting powders decreased to 0.37 μm with the addition of 10 mol% TiO₂.     

Raman spectroscopy and TEM characterization of solid particulate matter emitted from soot generators and aircraft turbine engines

To obtain reliable mass concentrations of solid particulate matter (PM) in the exhaust emissions from engines using optical instruments, it is essential that the solid PM used for instrument calibration has similar optical properties to the solid PM emitted from the engines being tested. The solid PM emitted from combustion engines is predominantly soot. The optical properties of soot are dictated by its chemical structure, size, and morphology. In this work, the chemical bond structure, primary-particle diameters, aggregate sizes, and morphological parameters of the soot emitted from two laboratory soot generators, widely used for calibrating instruments, are compared to those of soot emitted from three aircraft turbine engines using Raman spectroscopy and transmission electron microscopy. The Raman spectral properties, size, and morphology of soot emitted from aircraft engines are distinctly different from the properties of soot emitted from the soot generators operating under globally near-stoichiometric and fuel-rich conditions. These differences can be attributed to the variations in the size and orientation of the graphitic crystallites, amorphous-carbon content, amount of polyacetylene compounds, deposition of organic material, and extent of oxidation. Conversely, general agreement is observed between the chemical structure, size, and morphology of soot emitted from aircraft engines and the soot emitted from the soot generators operating at globally fuel-lean conditions. The findings of this investigation can be useful for identifying suitable soot particles for the calibration of instruments to measure the mass concentration of solid PM emissions from engines, and for other types of soot.

Copyright © 2017 Crown Copyright     

Synthesis of osmium borides by mechanochemical method

Transition metal osmium borides were synthesized by mechanochemical method using high‐energy ball‐milling with Os (Osmium) and B (Boron) powders as raw materials. The formation process, reaction mechanism, and thermal stability of the mechochemically synthesized osmium borides were studied. Almost pure Os₂B₃ phase was obtained when the Os‐to‐B molar ratio was 1:2; while ReB₂‐type hexagonal OsB₂ with a small amount of RuB₂‐type orthorhombic OsB₂ was obtained when the Os‐to‐B molar ratio was 1:3. Stoichiometry OsB₂ was obtained from boron rich starting mixture powders due to the B loss during the high‐energy ball‐milling process. It was also found that WC and osmium oxide were present as contaminants after ball milling for 40 hours. Heat treatment results revealed that the as‐synthesized Os₂B₃ powders are thermally stable in flowing Ar up to 800°C, but a transformation from hexagonal to orthorhombic structure partially occurred for the OsB₂ powders as low as 600°C.     

Hydroelastic response of a box-like floating fuel storage module modeled using non-conforming quadratic-serendipity Mindlin plate element

Presented herein are the hydroelastic responses of a floating fuel storage module under wave action. The box-like fuel storage module is modeled by an equivalent solid plate. For the analysis, a non-conforming quadratic-serendipity (NC-QS) element based on the Mindlin plate theory was developed. In this element, we make use of the reduced integration method and the superposition of non-conforming modes onto the basis function of the 8-node element in order to prevent spurious modes and shear locking phenomena. Thus the element may be applied for both thick and thin plates. The solution for the hydroelastic response involves solving the coupled plate–water equation and the water equation numerically using the hybrid finite element–boundary element (FE-BE) method. The coupled plate–water equation is derived by equating the force term in the Mindlin plate equation with the wave pressure distribution obtained from the linearized Bernoulli equation; whereas the boundary integral equation relates the displacement of the plate and water velocity potential using the free-surface Green’s function. Results of the displacement and water velocity potential are found to be more accurate when compared with existing solutions for special cases. Moreover, the stress resultants computed are significantly more accurate than previous results as spurious modes are eliminated.     

"Weak" ultrasonic pre-treatment on anaerobic digestion of flocculated activated biosolids

This study examined how "weak" ultrasonic pre-treatment affects anaerobic digestion of waste biosolids, treated with a cationic polyelectrolyte flocculant. In relation to pre-treatment, the term "weak" used refers to the fact that the total ultrasonic energy input to biosolids is insufficient to fully disrupt its floc structure or the cell walls, as described in the literature. Methane production potential, floc characteristics (size, morphology and zeta-potential) and process parameters (chemical oxygen demands and oxidative-reductive potentials) were monitored, as the digestion was tested. The presence of polyelectrolyte flocculants enhanced methane production within 6 days of digestion (phase I), but inhibited the digestion thereafter (phase II). Following pre-treatment by sonication (0.33 W/mL, 20 min), the methane productions of both original and flocculated biosolids significantly increased. The underlying mechanisms of weak ultrasonic pre-treatment are discussed.     

Mechanisms and models for anaerobic granulation in upflow anaerobic sludge blanket reactor

Upflow anaerobic sludge blanket (UASB) reactor has been employed in industrial and municipal wastewater treatment for decades. However, the long start-up period required for the development of anaerobic granules seriously limits the application of this technology. In order to develop the strategy for rapid UASB start-up, the mechanisms for anaerobic granulation should be understood. This paper attempts to provide a up-to-date review on the existing mechanisms and models for anaerobic granulation in the UASB reactor, which include inert nuclei model, selection pressure model, multi-valence positive ion-bonding model, synthetic and natural polymer-bonding model, Capetown's model, spaghetti theory, syntrophic microcolony model, multi-layer model, secondary minimum adhesion model, local dehydration and hydrophobic interaction model, surface tension model, proton translocation-dehydration theory, cellular automaton model and cell-to-cell communication model. Based on those previous works, a general model for anaerobic granulation is also proposed. It is expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of the UASB granules.     

Hexagonal Boron Nitride Thin Film for Flexible Resistive Memory Applications

Hexagonal boron nitride (hBN), which is a 2D layered dielectric material, sometimes referred as “white graphene” due to its structural similarity with graphene, has attracted much attention due to its fascinating physical properties. Here, for the first time the use of chemical vapor deposition ‐grown hBN films to fabricate ultrathin (≈3 nm) flexible hBN‐based resistive switching memory device is reported, and the switching mechanism through conductive atomic force microscopy and ex situ transmission electron microscopy is studied. The hBN‐based resistive memory exhibits reproducible switching endurance, long retention time, and the capability to operate under extreme bending conditions. Contrary to the conventional electrochemical metallization theory, the conductive filament is found to commence its growth from the anode to cathode. This work provides an important step for broadening and deepening the understanding on the switching mechanism in filament‐based resistive memories and propels the 2D material application in the resistive memory in future computing systems.     

Development of a new infrared device for monitoring the coefficient of variation in yarns

The coefficient of variation (CV) in yarns is the most important evenness characteristic in textile processing and quality control. This article develops a new infrared device for monitoring the coefficient of variation in yarns, based on on‐line measurement of the yarn diameter, during the yarn manufacturing process. The device is composed of a 555 astable oscillator, four pairs of infrared emitters and receivers, a summing amplifier, an inverting amplifier, an alternating current (AC) to direct current (DC) converter, a unity‐gain second‐order Sallen–Key low‐pass filter, and a data acquisition system. The optimum values of some factors with the circuit, including the oscillator frequency, amplified gain, cutoff frequency of the low‐pass filter, sampling time, and number of sampling data to be averaged in the moving average method, are systematically chosen by the Taguchi method to reduce the variance in the output voltage of the device. The CV based on measured yarn diameter data is transformed to that based on mass profiles. The experimental results reveal that the CVs evaluated by the infrared device are close to those by the Uster Evenness Tester, which is verified by the statistical analysis of variance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007