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 (αEtOH) 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 αEtOH 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 αEtOH 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. 相似文献
F−- and OH−-free ZnO-B2O3-SiO2-Al2O3-P2O5 glasses used for semiconductor-device passivation or insulation are investigated with regard to compositional dependencies for thermal expansion, viscosity points, and metal oxide semiconductor (MOS) capacitor properties. The experimental data show that thermal expansion increases, and flow points decrease, when P2O5 is substituted for B2O3. MOS capacitors passivated by OH−- and F−-free ZnO-based glasses exhibit normal capacitance-voltage curves. 相似文献
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. 相似文献
Summary Liquid crystalline side-chain polysiloxanes were prepared without metal complex catalyst. Mesogenic groups such as cholesteryl, 4-cyano-4-biphenyl and 4-methoxy-4-biphenyl group were introduced into polysiloxane by esterification and from DSC measurements they were compatible with other liquid crystalline polysiloxanes reported previously. 相似文献
In this paper, we propose a new video conferencing system that presents correct gaze directions of a remote user by switching among images obtained from multiple cameras embedded in a screen according to a local user’s position. Our proposed method reproduces a situation like that in which the remote user is in the same space as the local user. The position of the remote user to be displayed on the screen is determined so that the positional relationship between the users is reproduced. The system selects one of the embedded cameras whose viewing direction towards the remote user is the closest to the local user’s viewing direction to the remote user’s image on the screen. As a result of quantitative evaluation, we confirmed that, in comparison with the case using a single camera, the accuracy of gaze estimation was improved by switching among the cameras according to the position of the local user.
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. 相似文献
Nitrides of transition metals have good wear- and corrosion-resistant properties because of their high hardness and chemical
stability. Chromium-nitride coatings can be deposited by ion plating; however, the thin thickness due to the slow deposition
rate must be improved for severe wear-resistant applications. The main objective in this paper is to realize good structural
control in the processing of chromiumnitride in situ composite coatings formed at a high deposition rate. They were synthesized
by reactive low-pressure plasma spraying using elemental chromium powder as a spray material. The transferred arc between
the gun electrode and the substrate was used to accelerate the nitriding reaction. The sprayed coatings consist of chromium,
Cr2N, and CrN, which have a composition gradient from the substrate interface to the surface. The volume fraction of Cr2N increases with transferred arc current, and nonreacted chromium concurrently decreases, except close to the substrate. The
CrN phase, however, only exists as a surface layer of 20 to 30 μm because it is decomposed to Cr2N above 1420 K. The hardness of the composite coatings depends on the volume fraction of Cr2N, and it increases to 1300 HV at a Cr2N volume fraction of 0.98. The seizure stress with lubricant depends on the coating hardness. The maximum seizure stress of
24.9 MPa is obtained at a hardness of 1300 HV. The composite coatings also show a superior wear resistance. Hence, the Cr2N in situ composite coatings synthesized by reactive plasma spraying with transferred arc are expected to be good candidates
for wear-resistant applications. 相似文献
The surface nitridation of titanium was carried out at a low pressure in nitrogen atmosphere using a gas tunnel type plasma
jet. The titanium nitride (TiN) film, 10 μm thick and 2000 HV, could be formed in 10 s. The structure of the TiN film was
investigated by XRD. The Vickers hardness on the surface of the film was measured. The effects of deposition conditions on
the properties of TiN films (TiN thickness,Vickers hardness, etc.) were investigated, and the advantage of this deposition
method was identified from those results. 相似文献
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. 相似文献