Copper ⇌ Alkali Ion Exchange of Alkali Aluminosillcate Glasses in Copper-Containing Molten Salt: I, Monovalent Copper Salt, CuCl

Cu⁺⇌ R⁺ (R = Li, Na, and K) ion exchange experiments were conducted for 20R₂O·10Al₂O₃·70SiO₂ glasses in molten CuCl at 550°C in air and nitrogen atmospheres. The depth profiles of the copper incorporated into glasses were determined with an electron microprobe X-ray analyzer. The total amount of diffusing copper, M _t, strongly depended on the type of alkali ion in the glass and the ion-exchange atmosphere; i.e., M _t increased with increasing cationic size in the order Li < Na < K and M _t was greater in air than in nitrogen. The Cu ⇌ R⁺ ion exchange kinetics are discussed in detail.     

Tribological Characteristics of SiC Ceramics in High-Temperature and High-Pressure Water

The effects of temperature and sliding speed on the tribological behavior of a SiC ceramic by sliding on the same material in deoxygenated water were investigated from room temperature to 300°C under the corresponding saturated vapor pressures. The friction coefficient and specific wear rates of both plates and disks increased at elevated temperatures at all sliding speeds, but decreased with increasing sliding speed at 120° and 300°C. Fine mirrorlike worn surfaces were observed without wear debris under all sliding conditions. The wear mechanism appears to consist of hydrothermal oxidation of SiC and dissolution of reaction products such as silica.     

Hydrophobic effects on protein/nucleic acid interaction: enhancement of substrate binding by mutating tyrosine 45 to tryptophan in ribonuclease Tl

Hydrophobic effects on binding of ribonuclease Tl to guaninebases of several ribonucleotides have been proved by mutatinga hydrophobic residue at the recognition site and by measuringthe effect on binding. Mutation of a hydrophobic surface residueto a more hydrophobic residue (Tyr45 – Trp) enhances thebinding to ribonucleotides, including mononucleotide inhibitorand product, and a synthetic substrate-analog trinudeotide aswell as the binding to dinucleotide substrates and RNA. Enhancementson binding to non-substrate ribonucleotides by the mutationhave been observed with free energy changes ranging from –2.2 to – 3 .9 kJ/mol. These changes are in good agreementwith that of substrate binding, –2.3 kJ/mol, which iscalculated from Michaelis constants obtained from kinetic studies.It is shown, by comparing the observed and calculated changesin binding free energy with differences in the observed transferfree energy changes of the amino acid side chains from organicsolvents to water, that the enhancement observed on guaninebinding comes from the difference in the hydrophobic effectsof the side chains of tyrosine and tryptophan. Furthermore,a linear relationship between nucleolytic activities and hydrophobicityof the residues (Ala, Phe, Tyr, Trp) at position 45 is observed.The mutation could not change substantially the base specificityof RNase Tl, which exhibits a prime requirement for guaninebases of substrates.     

Pervaporation membranes for ethanol–water mixture prepared by plasma polymerization. III. Perfluorocarbon membranes

Pervaporation membranes for the ethanol–water mixture were prepared by plasma polymerization of tetrafluoroethylene, perfluoropropane, and perfluoropropylene onto porous substrates. The influence of the monomers on the elemental ratio (F/C) of the polymer depositions by X-ray photoelectron spectroscopy was rather small compared with that of the W/FM parameter (W = wattage for plasma excitation, FM = mass flow rate of a monomer). The optical emission spectroscopy indicated the similarity of gaseous species formed in the plasmas. The membranes were found ethanol-permselective, showing separation coefficients (α_EtOH) around 4–7 and a wide range of permeation rates (J), 10–10^?2 kg/m² h, for the 4.8 wt % ethanol solution at 40°C. The α_EtOH of the membranes with thicker depositions could be correlated to the F/C ratios as a measure of membrane hydrophobicity. It was thought that, by making a plot α_EtOH against J values for the perfluorocarbon membranes, they could be classified into three groups on thickness of deposition. The ethanol-separation mechanisms for each group, which may contain four kinds of mass transfer schemes, i.e., distillation through larger pores, flow of sorption layer at the liquid–membrane interface, and diffusions through deposition or substrate, were also discussed.     

Thermal Response and Oxidation of Tyranno™-Fiber-Reinforced Si-Ti-C-O Matrix Composites for a Thermal Protection System in High-Enthalpy Dissociated Air

The thermal response and oxidation of Tyranno™ Lox-M fiber-reinforced Si-Ti-C-O matrix composites in high-enthalpy dissociated air was investigated in an arc jet facility (an arc wind tunnel). The maximum surface temperature reached 1310–1670°C. Catalytic recombination of oxygen and nitrogen on the composite surface under dissociated air was not significant. Surface recession was insignificant below 1600°C surface temperatures and above 5 kPa of oxygen partial pressure at the stagnation point. Passive-to-active oxidation transition of the composite agreed with Balat's theory for monolithic silicon carbide. A glass sealant prevented active oxidation of the composite for short-time exposures.     

Oxidation behavior of TiAl coated with a fine-grain Co-30Cr-4Al film

The oxidation behavior of TiAl coupons coated with a fine-grain Co-30Cr-4Al (mass %) film of about 30-m thickness has been studied at 1100–1400 K in a flow of purified oxygen at atmospheric pressure for up to 500 ks. Three oxidation stages were recognized: initial transient, parabolic, and accelerated stages. However, at 1100 K a parabolic stage continues for more than 800 ks. The activation energy for parabolic oxidation agrees with reported values for the oxidation of alumina-former alloys, although the mass gains during the parabolic stages are relatively small at 1200 and 1300 K. Micropores developed mainly at the scale/coating and coating/substrate interfaces as oxidation proceeded. This is attributable to recrystallization of the coating during oxidation and a Kirkendall effect due to preferential diffusion of Co into the substrate. The accelerated oxidation can be explained in terms of the formation of rutile mounds on the scale.     

Oxidation Behavior of Ni-3,6, 10 wt.% Al Alloys at 800°C

The oxidation behavior of Ni and Ni-3, 6, and 10Al alloys at 800°C in an N₂–O₂ gas mixture was investigated. The mass gain of each alloy depended on both the oxidation periods and Al content. NiO scale was formed on all alloy substrates accompanied by internal oxides of Al₂O₃. Many cavities were formed at the NiO/substrate interface at shorter oxidation times, and these cavities were found to be filled by metallic Ni(Al) from the matrix in the internal-oxidation zone by the development of internal oxides. The filling of cavities by Ni(Al) was more significant on higher Al alloys, which had a higher density of internal Al₂O₃. Once metallic Ni(Al) formed along the entire NiO/substrate interface, the oxidation kinetics became the same as pure Ni. It was concluded that pure Ni filling the cavities at the interface provided a diffusion path of Ni from the substrate to the NiO scale, and that controlled the oxidation kinetics.     

Development of new-concept desk top size machine tool

A desktop multiprocess machinery has been designed that has two concepts: miniaturizing of machine tool and multiprocessing with a same machine tool. The prototype of desktop multiprocess machinery is developed in this study. This is tabletop size machine tool that has five changeable machining heads. Outline of main body and machining head are presented.In order to know the basic accuracy of desktop multiprocess machinery, experimental evaluation is carried out. Machining head setting error, stiffness of multiprocess machinery and straightness of X, Y, Z stage is measured. To study the basic performance of desktop multiprocess machinery, a complex machining experiment is carried out with the developed machine tool. The complex machining consists of three steps: electrode machining by milling, hole shaping by EDM, and hole finishing by ECM. These steps are performed in sequence on the same machine tool. The complex machining is successfully carried out. In order to evaluate the desktop multiprocess machinery from environmental point of view, machining energy, volume of machining liquid, and installation space of desktop multiprocess machinery are measured. The measured values are compared with estimated values with conventional machine tools. The machining energy, the volume of machining liquid, and the installation space of desktop multiprocess machinery are smaller than those of conventional machine tool.     

Activity measurement of gallium in the B2 phase of the CoGa–Sb system by the EMF method with zirconia-based solid electrolyte

Gallium activity in the B2 phase regions of both binary Co–Ga and ternary Co–Ga–Sb systems was measured by EMF method with stabilized zirconia solid electrolyte The temperature range was 1073–1273 K and Sb concentrations were 1, 2 and 3 mol fractions. Ga activity at 1173 and 1273 K increases sharply in Ga rich region and the addition of Sb to the CoGa phase increases Ga activity. Activity change corresponds to the lattice parameter change with Sb addition to the CoGa phase.     

Evaluation of hydrogen absorption properties of Ti–0.2 mass% Pd alloy in fluoride solutions

The hydrogen absorption properties of Ti–0.2 mass% Pd (Ti–0.2Pd) alloy in 2.0% and 0.2% acidulated phosphate fluoride (APF) and neutral 2.0% NaF solutions (25 °C) has been evaluated by hydrogen thermal desorption analysis. During the early stage of immersion (120 h) in the 2.0% APF solution, the amount of absorbed hydrogen was lower than 500 mass ppm. A thermal desorption of hydrogen primary appearing with a peak at 500–600 °C and a broad desorption ranging from 100 to 400 °C were observed. In the 0.2% APF solution, the amount of absorbed hydrogen saturated at 100–200 mass ppm; the thermal desorption of hydrogen appeared with a single peak at 550 °C. In the 2.0% NaF solution, hydrogen absorption was negligible even after 1000 h of immersion, although corrosion pits were observed. The results of the present study suggest that the hydrogen absorption of Ti–0.2Pd alloy, as compared with commercial pure titanium, is suppressed in fluoride solutions.