Hydriding properties of Mg–xNi alloys with different microstructures

The hydriding properties of Mg–xNi (x = 13.5, 23.5 and 33.5 wt%) alloys with different microstructures produced by various processing routes were evaluated in this study. The hydrogen storage capacity and kinetics of hydriding of Mg–xNi alloys were strongly dependent on their microstructures. The capacity and kinetics of hydriding were larger and faster when the average size of the hydriding phase was smaller and the volume fraction of the phase boundary was larger.     

Synthesis and characterization of TRITON™ X‐based surfactants with carboxylic or amino groups in the oxyethylene chain end

This paper describes the synthesis and characterization of a series of TRITON™ X‐based surfactants with a predominantly alkyl phenol ethoxylate (APE) backbone and carboxylic or amino chain ends. Three carboxylic acid‐containing TRITON X (or APE)‐derivatives, [OPE2‐COOH], [OPE5‐COOH], and [OPE10‐COOH], were prepared from commercially available octyl phenol ethoxylate (OPE) of different oxyethylene units (i.e., n = 2, 5, and 10) and ethyl bromoacetate via a simple etherification reaction followed by saponification. Two amine‐containing TRITON X ‐derivatives, [NPE10‐NH₂] and [NPE10‐imidazole], were prepared based on modifications of mesylate of nonyl phenol ethoxylate (NPE) of 10 oxyethylene units reacted with ammonia and imidazole, respectively. Depending on their composition and chain length of oxyethylene units used in the reaction, the surfactants show different thermal degradation behaviors. The carboxylic acid‐containing surfactants give no char at high temperatures under air condition. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 162–170, 2007     

Growth mechanism of monodispersed TiO2 fine particles by the hydrolysis of Ti(OC2H5)4

In order to investigate the growth mechanism of TiO₂, the monodispersed TiO₂ fine particles were prepared by hydrolysis of Ti(OC₂H₅)₄ using the seed preparation method. Although it was impossible to grow TiO₂ particles to more than 1 μm with conventional liquid phase reaction method, we obtained monodispersed T1O₂ fine particles of up to 2.5 urn. Nielsen’s chronomal analysis and Overbeek’s theory were applied to clarify the particle growth mechanism. The particle growth mechanism was found out as a first-order polynuclear layer growth mechanism and the growth rate constant, k_P was about 6.45X10^-6 cm/s.     

New method for evaluating the kinetic constant of thermal protection materials

Thermal protection material (TPM) is used to protect rocket structures from extreme conditions created by the hot exhaust of the rocket. Designing TPM is an important step in the rocket design process. Considering that an increase in the system weight decreases the overall performance of a rocket, the amount of TPM is carefully determined during the design process. Therefore, the precise properties of TPM guarantee an accurate thermal analysis and the successful design of the rocket. Among the many properties of TPM, the kinetic constant and activation energy, which govern the thermochemical reaction of the TPM, are the most important. Thus, an experiment to measure the kinetic constant and activation energy is conducted as part of this research. A theoretical approach to deduce the properties from measured data is discussed, and a method to apply the theory to experimental data, termed the R² method, is developed. Compared to a previous method which was difficult to apply, the R² method reduces unclear selections of the reaction time and does not require intervention by an interpreter. The properties deduced by the R² method show good agreement with the other method despite the limited number of experimental results.     

Nanotribological Properties of Fluorinated, Hydrogenated, and Oxidized Graphenes

Recently, the tribological properties of graphene have been intensively examined for potential applications in micro- and nano-mechanical graphene-based devices. Here, we report that the tribological properties can be easily altered via simple chemical modifications of the graphene surface. Friction force microscopy measurements show that hydrogenated, fluorinated, and oxidized graphenes exhibit, 2-, 6-, and 7-fold enhanced nanoscale friction on their surfaces, respectively, compared to pristine graphene. The measured nanoscale friction should be associated with the adhesive and elastic properties of the chemically modified graphenes. Density-functional theory calculations suggest that, while the adhesive properties of chemically modified graphenes are marginally reduced down to ~30 %, the out-of-plane elastic properties are drastically increased up to 800 %. Based on these findings, we propose that nanoscale friction on graphene surfaces is characteristically different from that on conventional solid surfaces; stiffer graphene exhibits higher friction, whereas a stiffer three-dimensional solid generally exhibits lower friction. The unusual friction mechanics of graphene is attributed to the intrinsic mechanical anisotropy of graphene, which is inherently stiff in plane, but remarkably flexible out of plane. The out-of-plane flexibility can be modulated up to an order of magnitude by chemical treatment of the graphene surface. The correlation between the measured nanoscale friction and the calculated out-of-plane flexibility suggests that the frictional energy in graphene is mainly dissipated through the out-of-plane vibrations, or the flexural phonons of graphene.     

Synthesis of nano-sized Co<Subscript>3</Subscript>O<Subscript>4</Subscript> powder by spray conversion method for anode material of lithium battery

A nano-sized Co₃O₄ powder was prepared using a spray conversion method that could be applied for mass production. The spray-conversion process consisted of spray drying of a metallic liquid solution, a calcination treatment, and a ball milling process. The calcined Co₃O₄ powder consisted of agglomerated spherical clusters with nano-sized particles. After milling for 24 h, agglomerated powders were fragmented into fine powders sized below 60 nm. The lithium/cobalt oxide cell was charge-discharged at a constant current density of 0.2 mAcm⁻² and showed a first discharge capacity of 1100 mAhg⁻¹. The discharge capacity of the Li/Co₃O₄ cell drastically decreased with cycle number. By increasing the carbon content of the anode, the cycle life was improved. For a Co₃O₄ electrode containing 40 wt.% carbon, the discharge capacity was over 400 mAhg⁻¹ after 50 cycles. The spray conversion method might be a useful method to prepare nano-sized Co₃O₄ powder for the anode material of lithium batteries.     

Transmission Electron Microscopy Microstructure of 0.95(Na0.5K0.5)NbO3–0.05BaTiO3 Ceramics

Microstructural characterizations using transmission electron microscopy on 0.95(Na_0.5K_0.5)NbO₃–0.05BaTiO₃ ceramics sintered at 1030°–1150°C for 2 h were carried out. The liquid phase was found at the triple junction of the grains in all specimens and abnormal grain growth occurred in the presence of the liquid phase. Abnormally grown grains whose shapes were cuboidal were well developed. Anisotropically faceted amorphous liquid phase pockets were observed inside the grain in a specimen sintered at 1060°C for 2 h. The interface between the grain and the liquid matrix was flat and some were identified to be {100} planes of the grains. A certain amount of liquid at the sintering temperature of 1060°C enhanced the abnormal grain growth and contributed to the improvement of the piezoelectric properties.     

Effect of Post Weld Heat Treatment on Cryogenic Mechanical Properties of Electron Beam Welded Cast Inconel 718

Electron beam welding of pre-aged cast 718 produced a slender Laves phase, while welds from solutionized cast 718 exhibited a blocky Laves phase with an initial stage of δ precipitation and formation of γ′+γ″ strengtheners after post weld heat treatment (PWHT). The presence of primary strengthener and coarse Laves particles in PWHT weld may cause reduction of the micro-plastic zone ahead of a crack, leading to a significant decrease in Charpy impact toughness at 77 K (?196 °C).     

Optical Properties of Polydispersed Atmospheric Aerosols Following Wet Removal

It is well known that size distributions of aerosols influence their optical properties. Many previous studies have focused on the optical properties of aerosols with particular weather conditions, such as haze, fog, or pollution. However, few studies have investigated the influence of precipitation on the optical properties of aerosols. In this study, the optical properties of polydispersed atmospheric aerosols following a wet removal process were investigated. For these calculations, a lognormal distribution was used to represent the raindrop size distribution and the tri-modal aerosol size distributions. Variations in aerosol size distributions and the corresponding changes an extinction coefficient caused by the wet scavenging process were quantified with different compositions of aerosols as a function of rain intensity. The results showed that the extinction coefficient decreased and the corresponding visibility was enhanced with the precipitation duration because of the precipitation scavenging. It was also shown that the rain intensity and the refractive index and size distribution of aerosols influenced the calculations of extinction coefficient of aerosols.