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61.
Miha Drofenik 《Journal of the American Ceramic Society》1992,75(9):2383-2389
The influence of the initial grain morphology on the anomalous grain growth in donor-doped barium titanate has been studied. The results show that powders with aspherically shaped grains exhibit a much lower critical donor-dopant concentration, inhibiting anomalous grain growth during sintering, than powders with equisized spherically shaped grains and a similar, or even a lower, initial specific surface area. 相似文献
62.
Darja?LisjakEmail author Simona?Ovtar Miha?Drofenik 《Journal of Materials Science》2011,46(9):2851-2859
We have studied suspensions of hard-magnetic BaFe12O19 particles in water, ethanol and 1-butanol. The surfaces of these particles were previously modified with the surfactant dodecylbenzylsulphonic
acid. The stabilities of the suspensions were estimated from their saturation concentrations and zeta potentials. We found
that the 1-butanol suspensions were more stable than the ethanol-based suspensions and much more stable than the water-based
suspensions. We analyzed the suspensions and the dispersed particles using gravimetry, conductometry and transmission electron
microscopy, measured their zeta potentials, and calculated the interparticle-attraction interaction energies due to the van
der Waals and magnetic dipole–dipole forces. The magnitudes of the attraction energies varied significantly with the particles’
sizes and the separation distances between the particles, and we found that the contribution of the van der Waals attraction
energy can be neglected with respect to the magnetic dipole–dipole attraction. The observed differences in the stability of
the suspensions were explained on the basis of the calculated electrostatic and steric repulsion energies. Electrosteric stabilization
was possible in the 1-butanol and the ethanol for particles with radii and thicknesses up to 15 nm, while a too small electrostatic
repulsion and the absence of steric repulsion in the water resulted in rapid agglomeration. 相似文献
63.
Experimental Study of the Radial and Tangential Forces in a Whirling Squeeze Film Damper 总被引:1,自引:0,他引:1
Cyril Defaye Mihaï Arghir Olivier Bonneau Philippe Carpentier Charles Debailleux Frédéric Imbourg 《摩擦学汇刊》2013,56(2):271-278
The present work introduces the main results of a detailed experimental program aimed at investigating the influence of the design parameters and of the working conditions on the global characteristics of squeeze film dampers (SFD) for serial aircraft engines. The SFD is sealed at both ends and is executing circular centered orbits. The results are presented for the tangential and the radial global force in the SFD and the leakage flow rate. The pressure field inside the SFD could also be measured and shows the influence of the inertia force, of the cavitation, and probably of the turbulence regime, as well as the interaction of these effects with the feeding groove. The limits of the existing theoretical models are also demonstrated. 相似文献
64.
In order to reduce the embarked mass, the new designs of turbojet engines use softened rotors working with higher speeds. Following this trend, the use of intershaft bearings in dual-spool turbojets is then recommended for reducing weight. However, due to residual unbalances present in both rotors, the intershaft bearing is submitted to hard working conditions. A supplementary damping might then be necessary in order to enable working to rotation speeds higher than the critical ones. The adopted solution consists of introducing a thin fluid film between the intershaft bearing and one of the two rotors in order to provide the necessary damping. However, due to the rotation of the inner and of the outer rings, fluid film instabilities similar to those met in classical hydrodynamic bearings can appear. This paper is focused on the experimental investigation of several designs of the intershaft bearing damper and of their influence on the dynamic behavior of a double spool rotor. First, a double spool rotor test rig integrating an intershaft bearing is presented. Subsequently, the experimental results are discussed for two dynamic configurations of the double spool rotor and for three intershaft bearing damper designs. For co- and counterrotating shafts, the tests show that the integration of a fluid film on the intershaft bearing makes it possible to attenuate the vibrations on both rotors. Furthermore, the tests confirm that instabilities appear under certain conditions depending on the type of the crossed mode and on the design of the intershaft bearing damper. 相似文献
65.
Assessment of brown rot decay is one of the most important issues within remedial treatment of attacked wood constructions. Pilodyn is a well-established tool for the assessment of density of several commercially important plantation species, therefore the authors were interested in its suitability to evaluate rate of decay as well. The Pilodyn measurements performed on Norway spruce wood exposed to several brown rot fungi clearly indicate correlations between needle penetration and mass loss. 相似文献
66.
Waxes are used for treatment of wood surfaces for several decades predominately as surface treatments because they weakly penetrate into the wood. In order to overcome this issue, water emulsions were applied in the present experiment. Five water emulsions of various concentrations were used, namely montan wax, polyethylene, ethylene copolymer and oxidized polyethylene wax. Performance of wax treated beech (Fagus sylvatica) and Norway spruce (Picea abies) against white rot, brown rot and blue stain fungi was tested. In parallel, sorption properties of wax treated wood were determined. The treated specimens were more resistant to wood decay fungi. Polyethylene and oxidized polyethylene wax were found to be particularly efficient. Although this treatment does not improve resistance to blue stain fungi, it reduces the sorption of water. 相似文献
67.
Orel B Jese R Vuk AS Jovanovski V Perse LS Zumer M 《Journal of nanoscience and nanotechnology》2006,6(2):382-395
A dialkylsubstituted imidazolium iodide ionic liquid (1-methyl-3-[3-(trimethoxy-lambda4-silyl)propyl]imida-zolium iodide, MTMSPIm+I-) was prepared with the intention of using it as a quasi-solid-state electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of Gr?tzel design, while the analogous electrolyte in a gel state was made by the addition of tetramethoxysilane (TMOS) in the molar ratio MTMSPIm+I-:TMOS = 1:1. The structure of the MTMSPIm+I- in its non-hydrolyzed and hydrolyzed states and in its fully condensed form, obtained after ageing the sols for various times (from a few hours to a few weeks) and heating them at 200 degrees C (fully condensed form), was studied employing time-dependent infrared attenuated total reflection (ATR) and 29Si NMR spectroscopic measurements. The structure of the condensed species was correlated with the viscosity and the specific conductivity measurements of MTMSPIm+I- sols and TMOS/MTMSPIm+I- gels during their ageing. The final product of the condensation of MTMSPIm+I- sols was described as a positively-charged ladder-like polysilsesquioxane with Tn end groups exhibiting a single T3 signal in 29Si NMR spectra and characteristic doublet bands at 1138 and 1049 cm(-1) in IR. This structure was retained to a large extent in TMOS/MTMSPIm+I- gels, confirming their nanocomposite structure. The results of the ATR infrared time-dependent spectroscopic studies showed that in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to shifts in the vibrational band positions in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined and the results applied in this work. 相似文献
68.
Miha Drofenik Darko Makovec Igor Zajc Hans T. Langhammer 《Journal of the American Ceramic Society》2002,85(3):653-660
Grain growth and semiconductivity of donor-doped BaTiO3 ceramics with an excess of BaO and additions of SiO2 or B2 O3 were studied. The microstructures and electrical measurements on sintered samples revealed that their electrical properties are related to the microstructure development of the sintered samples. Samples heated with an excess of BaO developed a normal microstructure during sintering, as a consequence of normal grain growth (NGG), and were yellow and insulating. In contrast, samples with an excess of BaO and an addition of SiO2 or B2 O3 exhibited anomalous grain growth (AGG) and were dark blue and semiconducting after sintering. When some BaTiO3 seed grains were embedded in a sample of donor-doped BaTiO3 with an excess of BaO (without SiO2 or B2 O3 ), AGG was observed, i.e., some seed grains grew into large grains and were blue and semiconducting. An explanation is given for why AGG is responsible for the oxygen release and the formation of semiconducting grains in donor-doped BaTiO3 and not NGG. 相似文献
69.
Structural and mechanical properties of diamond-like carbon films deposited by an anode layer source
Markus Kahn Miha ?ekada Roswitha Berghauser Christoph Bauer Elmar Brandstätter 《Thin solid films》2009,517(24):6502-680
An anode layer source is a special ion gun, which can be fed with carbon precursors like acetylene to deposit hard and highly defect-free hydrogenated diamond-like carbon films at room temperature. The present study focuses on the influence of the process parameters — discharge voltage, process pressure and acetylene flow — on structure and mechanical properties of the deposited films. Raman spectra show that an increased discharge voltage yields decreased structural disorder, i.e. a lower C-C sp3 hybridised fraction of carbon atoms in the films. By an elevation of the discharge voltage from 1 to 3 kV the full width at half maximum of the G-band decreases from 194 ± 0.2 cm− 1 to 183 ± 0.7 cm− 1. Films deposited at the lowest discharge voltage show in accordance to the spectroscopic data the highest nanohardness (36 ± 1 GPa), stress (− 2.34 ± 0.2 GPa) and reduced elastic modulus (180 ± 4 GPa). 相似文献
70.
Microstructural changes occurring during oxidation of the reduced form of donor-doped BaTiO3 (Ba1− X D X . Ti1− X 4+ Ti X 3+ O3 ) and during reduction of the oxidized form of donor-doped BaTiO3 (Ba1− X D X . Ti1− X /4 4+ ( V Ti ) X /4 O3 ) were studied using TEM. Samples of both types of solid solutions, containing different La concentrations (from 2 to 20 mol% La), were prepared by sintering under reducing conditions and in air, respectively. The reduced form of donor-doped BaTiO3 was oxidized by annealing at high temperatures (1150° and 1350°C) in air, while the oxidized form was reduced by annealing under reducing conditions. Because of oxidation of the reduced phase of donor-doped BaTiO3 , the Ti-rich phases Ba6 Ti17 O40 and BaLa2 Ti4 O12 were precipitated. Reduction of the oxidized form caused precipitation of the Ba-rich phase Ba2 TiO4 preferentially inside the matrix grains. All precipitates had well-defined orientational relationships with the perovskite matrix. 相似文献