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101.
C. Popov W. Kulisch S. Boycheva K. Yamamoto G. Ceccone Y. Koga 《Diamond and Related Materials》2004,13(11-12):2071
Nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films have been prepared by microwave plasma chemical vapor deposition (MWCVD) from methane/nitrogen mixtures. The complex nature of the coatings required the application of a variety of complementary analytical techniques in order to elucidate their structure. The crystallinity of the samples was studied by selected-area electron diffraction (SAED). The diffraction patterns revealed the presence of diamond crystallites within the films. From the images taken by transmission electron microscopy (TEM) the crystallite size was determined to be on the order of 3–5 nm. The results were confirmed by X-ray diffraction (XRD) measurements exhibiting broad (111) and (220) peaks of diamond from which the average size of the crystallites was calculated. The grain boundary width is 1–1.5 nm as observed by TEM images which corresponds to a matrix volume fraction of about 40–50%. This correlates very well with the crystalline phase content of about 50% in the films estimated from their density (2.75 g/cm3 as determined by X-ray reflectivity). The bonding structure of the composite films was studied by electron energy loss spectroscopy (EELS) in the region of carbon core level. The spectra were dominated by a peak at 292 eV indicating the diamond nature of the investigated films. In addition, the spectra of NCD/a-C films possessed a shoulder at 284 eV due to the presence of a small sp2 bonded fraction. This phase was identified also by X-ray photoelectron spectroscopy (XPS). The sp2/sp3 ratio was on the order of 10% as determined by deconvolution of the C1s XPS peak. 相似文献
102.
Heinz Buschatz Birgit Dagefrde Kai Jakoby Klaus‐Viktor Peinemann Dieter Paul 《化学,工程师,技术》2001,73(4):297-303
Membrane processes are able to separate liquid mixtures as well as mixtures of gases or vapours according to the sizes, solubilities, rates of diffusion or charges of the components. A separation is also possible using membranes in which the transport is coupled to a specific chemical reaction between the permeand and the membrane (facilitated or carrier mediated transport). This paper discusses aspects related to carrier‐mediated separation processes such as the transport mechanisms, the choice of appropriate carriers, the incorporation of carriers in the polymeric membrane material, the coating of porous support membranes with thin selective layers of the carrier‐polymer and, finally, the choice of appropriate parameters for the separation process. The separation of gas mixtures by carrier‐membranes appears very promising from a technical point of view. Experimental membrane samples often show excellent separation factors, but they have not met the permeability requirements for an economic use so far. 相似文献
103.
104.
105.
Yu. M. Milekhhin A. N. Kluchnikov V. S. Popov 《Combustion, Explosion, and Shock Waves》2013,49(5):575-582
A physicomathematical formulation of the coupled gas-dynamic and geometric problem of modeling intrachamber processes and calculating the internal ballistics of nozzleless solid rocket motors is given, and a method and algorithm for solving the problem are developed. The parameters in the forward section of the motor are calculated using averaged unsteady equations of internal ballistics, and the parameters of the grain channel and the exit cone are determined using one-dimensional gas-dynamic equations in a quasi-steady formulation. The software package is verified by calculating the internal ballistics of a motor which is utilized without nozzle cluster and simulates intrachamber processes in a nozzleless solid rocket motor during the full-duration firing. The design features, motor operating parameters, and the composition characteristics influencing the energetics of propellants in nozzleless solid rocket motors are calculated. It is shown that, depending on comparison conditions (identical expansion ratios and identical profiles of the nozzle and exit cone), the specific impulse of nozzleless solid rocket motors (the main energy parameter) is slightly smaller than or nearly comparable to that of conventional solid rocket motors. 相似文献
106.
Imad Ibrahim Yang Zhang Alexey Popov Lothar Dunsch Bernd Büchner Gianaurelio Cuniberti Mark H Rümmeli 《Nanoscale research letters》2013,8(1):265
All-carbon single-walled carbon nanotubes (SWCNTs) were successfully synthesized, nucleated using a fullerene derivative. A systematic investigation into the initial preparation of C60 fullerenes as growth nucleators for the SWCNTs was conducted. Enhancement in the yield of the produced SWCNT has been achieved with exploring different dispersing media for the fullerenes, the period, and environment of the initial thermal treatment of the fullerenes in addition to the use of different fullerene-based structures. The systematic studies significantly advance our understanding of the growth of the all-carbon catalyst-free single-walled carbon nanotubes. Field-effect transistors were fabricated using the catalyst-free SWCNT and then electrically characterized, showing current capacity as high as the well-studied catalyst-assisted nanotubes. 相似文献
107.
Effects of drilling parameters and aspect ratios on delamination and surface roughness of lignocellulosic HFRP composite laminates 下载免费PDF全文
Sikiru Oluwarotimi Ismail Hom Nath Dhakal Eric Dimla Johnny Beaugrand Ivan Popov 《应用聚合物科学杂志》2016,133(7)
Hemp fibre‐reinforced polycaprolactone (HFRP) composite has inherent good mechanical properties and benefits which include remarkably high specific strength and modulus, low density, and renewability. No doubt, these properties have attracted wider applications of HFRP composite in engineering applications. This paper presents an investigation on the influence of drilling parameters and fibre aspect ratios, AR (0, 19, 26, 30, and 38) on delamination damage factor and surface roughness of HFRP composite laminates utilising high speed steel twist drills under dry machining condition. Taguchi's technique was used in the design of experiment. The results obtained show that increase in cutting speed reduces delamination factor and surface roughness of drilled holes, whereas increase in feed rate causes increase in both delamination factor and surface roughness. Feed rate and cutting speed had the greatest influence on delamination and surface roughness respectively when compared with aspect ratio, while an increase in fibre aspect ratios leads to a significant increase in both delamination factor and surface roughness. The optimum results occurred at cutting speed and feed rate (drilling parameters) of 20 mm/min and 0.10 mm/rev, respectively, when drilling sample of AR 19. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42879. 相似文献
108.
William P. Boshoff Viktor Mechtcherine Gideon P.A.G. van Zijl 《Cement and Concrete Research》2009,39(9):787-797
This paper is the second part of a two paper series about the time-dependant behaviour of Strain Hardening Cement-based Composite (SHCC) on the single fibre level. Having dealt with mechanisms of creep in SHCC in the first part, this paper reports single fibre pull-out tests that were done to investigate the effect of the pull-out rate on the mechanical response of the interface between the fibre and the matrix. It was found that not only the pull-out resistance increased with an increase of the pull-out rate but the probability of fibre rupture during pull-out as well. Another important finding was that the interfacial shear resistance and slip-hardening coefficient are not only dependant on the pull-out rate, but also the embedment length. 相似文献
109.
Methods of X-ray diffraction, transmission and scanning electron microscopy, and electron diffraction have been used to study phase composition and structure of an almost stoichiometric alloy Ti50Ni25Cu25. The alloys of the quasi-binary section TiNi-TiCu to be studied, which exhibit in the initial ascast state thermoelastic martensitic transformations B2 ↔ B19 and related shape-memory effects, have been produced by rapid quenching of the melt (melt spinning technique). The chemical composition of the Ti50 + x Ni25 − x Cu25 alloys was varied with respect to titanium and nickel within x ≤ ±1% (from Ti49Ni26Cu25 to Ti51Ni24Cu25). It has been shown that the rapid quenching from the melt at a cooling rate of 106 K/s provides amorphization for all the alloys under consideration. Heating to 723 K or higher temperatures leads to the devitrification of the amorphous alloys with the formation of a polycrystalline structure of the B2 austenite. The mechanical properties of the alloys have been measured in the initial amorphous state and after subsequent heat treatment. It has been established that, depending on the degree of deviation of the alloy from the stoichiometric composition, which leads to solid solution decomposition in the process of nanocrystallization upon heat treatment, there occur regular changes in the mechanical properties and shape-memory effects of the alloys. The characteristic temperatures of the onset and finish of the process of crystallization from the amorphous and amorphous-crystalline states and the critical temperatures of the onset and finish of the forward and reverse thermoelastic martensitic transitions have been determined by measuring temperature dependences of the electrical resistivity of the alloys. The diagram of the dependence of the critical temperatures on the chemical composition of the alloy has been constructed. 相似文献
110.
A. G. Popov A. V. Shitov E. G. Gerasimov D. Yu. Vasilenko M. Yu. Govorkov D. Yu. Bratushev V. P. Vyatkin K. Yu. Shunyaev T. L. Mikhailova 《The Physics of Metals and Metallography》2012,113(4):331-340
Pressless process used for the preparation of sintered Nd-Fe-B magnets has been studied. The effect of the average particle
size D
av, filling density ρf, and powder-texturing conditions for obtaining density ρ and desired magnetic hysteretic properties of sintered magnets has
been investigated for both traditional technology (TT) and low-oxygen technology (LOT). The ρf magnitude ensuring the optimum relation between the density ρ of sintered magnets and their degree of texture was shown to
be 2.5–3.0 and 2.2 g/cm3 for the TT and LOT, respectively. At lower ρf magnitudes, no required density of sintered magnets is reached, whereas at higher filling densities, a low level of texture
and low remanence are realized. Optimum parameters of pulsed field inducing the high degree of texture in powders have been
determined. The following properties were achieved for magnets prepared by pressless LOT: B
r
≥ 14.2 kG, H
c ≥ 8 kOe, and (BH)max ≥ 47.9 MG Oe. 相似文献