共查询到20条相似文献,搜索用时 15 毫秒
1.
V. V. Skorokhod V. P. Titov M. M. Churakov 《Powder Metallurgy and Metal Ceramics》1999,38(11-12):608-609
The kinetics of WS2 layer growth at the interface of tungsten with molten metals saturated with silicon is studied. Research is performed at 1200°C using melts based on copper, silver, and tin. It was established that WSi2 layer growth in these melts obeys a “parabolic” rule but the corresponding growth rate constants differ markedly, i.e., from 3.4·10?11 m2/sec (melt based on copper) to 1.5·10?13 m2/sec (melts based on silver and tin). The reasons for this difference are discussed. 相似文献
2.
A. O. Volkhonskii I. V. Blinkov Yu. V. Levinsky E. A. Skryleva 《Russian Journal of Non-Ferrous Metals》2017,58(6):678-683
The thermal stability of multilayered nanostructured coatings is evaluated by analyzing the diffusion mobility of layer components. The possibility of increasing the thermal stability of multilayered coatings based on mutually soluble Ti–Al–N and Cr–N layers due to the introduction of an additional barrier layer based on Zr–N into a multilayered nanostructure is investigated in detail. Calculated diffusivities of basic metallic elements of the coating into corresponding nitride layers upon heating in a temperature range of 800–1000°C evidence the absence of noticeable diffusion spread of layer boundaries in the presence of the Zr–N-based barrier layer. For example, their values lower upon its introduction (it is found at t = 1000°C, cm2/s: DCr/TiN = 5 × 10–17, Dcr/ZrN = 2 × 1018, \({D_{Ti/C{r_2}N}}\) = 9 × 10–18, and DTi/ZrN = 3 × 10–18). The physicomechanical properties of coatings do not vary upon their vacuum annealing at t < 900°C; however, they noticeably lower with a further increase in temperature due to the degradation of a multilayered coating structure during annealing. 相似文献
3.
The assembling of a coating of time-resolved fluorescent chelator BSPDA ( abbreviated for 4, 7-bis ( sulfhydrylphenyl)-1, 10-phenanthroline-2, 9-dicarboxylic acid) onto a nano-gold layer was demonstrated. First, BSPDA was synthesized by simple procedures, and then an approach was developed to immobilize BSPDA onto the nano-gold layer deposited on a silane modified glass substrate, whereby europium ion (Ⅲ, Eu^3+ ) was captured and released owing to the interactive process of complexation and dissociation between BSPDA functionalized coating and Eu^3+ solution. The fluorescence spectra and related lifetimes were determined. Also, the BSPDA functionalized coating's specific complexation with Eu^3+ on the BSPDA assembly layer and the nonspecific adsorption of Eu^3+ on the nano-gold layer were compared. These results allowed a selective complexation of Eu^3+ by assembling a BSPDA chelating layer on the nano-gold layer; thus, a tunable time-resolved fluorescent layer was covalently attached, The results of the nanoparticle assembling and probing (or labeling) processes to specific bio-systems were very interesting and had significant implications to time-resolved-fluorescence-based detection on biosensor surfaces such as DNA chip and to arrayed light display devices. 相似文献
4.
《中国稀土学报(英文版)》2020,38(5):531-538
The mismatch between the photovoltaic(PV) cells absorption and the solar irradiance on earth is one of the major limitations towards more efficient PV energy conversion.This aspect was addressed by downshifting the solar irradiance on Earth through luminescent down-shifting layers based on lanthanidedoped surface-functionalized ionosilicas(ISs) embedded in poly(methyl methacrylate)(PMMA) coated on the surface of commercial Si-based PV cells.The IS-PMMA hybrid materials exhibit efficient solar radiation harvesting(spectral overlap of ~9.5 × 10~(19) photons/(s·m~2)) and conversion(quantum yield~52%).The direct solar radiation and the down-shifted radiation are partially guided and lost through total internal reflection to the layer edges being unavailable for PV conversion of the coated PV cell.By tuning the down-shifting layer thickness,it also acts as luminescent solar concentrator enabling the collection of the guided radiation by flexible PV cells applied on the borders of the down-shifting layer leading to an enhancement of the PV energy conversion from ~5%(in the case of the single-use of the luminescent down-shifting layer) to~13% comparing with the bare PV cell.The overall electrical output of the device resulted in an absolute external quantum efficiency increase of~32% for the optimized Eu~(3+)-based films in the UV spectral region(compared with the bare PV device,which is among the best values reported so far). 相似文献
5.
The recovery of lead from scrap lead acid batteries by pyrometallurgical processes is generally accompanied by emissions of sulphur dioxide and lead-containing particulates into the atmosphere. The latter two products are undesirable as they lead to serious environmental problems. In an effort to overcome these difficulties, a sodium carbonate leaching process was investigated. In the present contribution, the leaching reactions of pure lead sulphate in sodium carbonate solutions are discussed from both a thermodynamic and kinetic aspect based on the experimental results obtained on leaching rates, stoichiometry of the reaction and X-ray diffraction analysis of the reaction products. A mass transfer model based on the diffusion of CO32? ions through a solution boundary layer is proposed to account for the leaching rates. 相似文献
6.
The electrochemical reduction of CuFeS2 mineral electrodes has been investigated by performing cathodic polarization curves, constant potential experiments, and cyclic polarization curves in various electrolytes. The effects of H2SO4, Fe2+ and Cu2+ concentrations have been examined as well as the effects of various dissolved gases, air, O2, H2S and N2. Decreasing H2SO4 only shifts the curve to more negative potentials but initial concentrations of 0.36 M Fe2+ cause up to a ten-fold enhancement in the observed current. The presence of oxygen or Cu2+ also leads to an increase in the reduction current but in either case further increases in current are observed when Fe2+ is added to the electrolyte. Chalcocite (Cu2S) or djurleite (Cu1.96S) have been identified as products of reaction, although it is possible that a thin layer of a different copper-iron sulfide may form as an intermediate based on the color changes which appear after cathodic excursions. In addition, scanning Auger microprobe analyses of these surfaces show an increasing Cu:Fe ratio as the time at potential is increased. The results also indicate that the solid product layer is porous. A mechanism which accounts for the observed current increase in the presence of Fe2+ is proposed which involves a redox reaction between dissolved Fe2+ and cupric ion in the copper sulfide product layer. 相似文献
7.
Michael F. Amsterdam 《Metallurgical and Materials Transactions B》1970,1(3):643-646
When Schottky barrier diodes are used to evaluate lightly dopedn type (n~1015 per cu cm) epitaxial GaAs onn + substrates, the diodes do not always have the expected varactor characteristics. The capacitance variation with bias is sometimes too small, and the voltage intercept on the 1/C 2 vsV plot too high. This behavior has been attributed either to a thin intrinsic semiinsulating layer between substrate and epi layer,1 or to deep trap impurities in the epi layer.2 The effects seen in this work are shown to be due to traps by the dependence of diode characteristics on heat, light, and frequency. These diodes also have conductances which decrease with reverse bias. The model of Sah and Reddi3 leads to a reduction in high frequency junction capacity and capacitance-bias variation range. The large, bias dependence conductance observed in our diodes must also be explained, however. A schematic model is proposed in which a series resistancer, due to the resistance of the undepleted epi layer at high frequency, is shunted by a capacitanceC u, also due to the undepleted layer. A junction conductance 1/R is in parallel with the junction capacitanceC. The equivalent circuit seen by the capacitance bridge, used for obtaining data, is a measured capacitanceC m in parallel with the measured shunt resistanceR m. Much of the observed diminution of capacity and varactor action can be accounted for in terms of this model. The series resistancer seems to be large only at high frequencies, and is associated with the traps in the epi layer. 相似文献
8.
M. S. Koval’chenko A. V. Paustovskii V. P. Botvinko A. P. Tamarov 《Powder Metallurgy and Metal Ceramics》1998,37(9-10):495-498
The effect of electrospark alloying with refractory compounds based on WC, TiC, TiN, and TiB2 on the mechanical and service properties of high-speed steel R6M5K5 cutters was investigated. Increasing the electrospark discharge energy by increasing the current strength to 3 A, and the specific alloying time to 1.2–1.8 Msec/m2, increased the alloyed layer depth, but decreased the microhardness. Further increase of alloying time did not produce further increase in layer depth. The optimal regimes of electrospark alloying were determined from durability tests of the hardened cutting tool. The greatest increase in durability (by 1.3–1.4 times) was obtained at I=1.5–2 A, τ=0.9–1.5 Msec/m2, at which values the optimal combination of hardness and coating depth was attained. 相似文献
9.
A new process for producing rapidly solidified bulk alloys was developed based on the hammer- and-anvil concept. In the process,
an A1-12 wt pct Si alloy slab was built up layer by layer and then hot worked to get a solid and integral sheet. The oxygen
content of the layer-deposited alloy is less than the typical value of powder metallurgy (PM) alloys by one order, and the
cooling rate can reach 104 K/s, which is higher than that of the spray deposition process. In comparison with the ingot-processed Al-12 wt pct Si alloy,
layer-deposited alloy exhibits su- perior mechanical properties. This is attributable to the fine and uniform silicon-particle
distri- bution which not only brings on dispersion hardening effect but also raises the elongation and fracture strain. The
mechanisms responsible for this enhancement were discussed in terms of particle size and effective volume fraction. 相似文献
10.
Agitation of the electrolyte by gas sparging was studied as a means of intensifying the electrowinning of copper. Diffusion
layer profiles at the cathode were quantitatively measured using a new technique based on the mass transfer controlled codeposition
of a tracer metal ion. Smooth, good quality cathodes were produced in a prototype cell at current densities up to 30 A/dm2 (270 asf).
B. V. TILAK, formerly also with the J. Roy Gordon Research Laboratory is now with the Hooker Research Center, Niagara Falls,
N.Y. 14302. This paper is based on the presentation made at the 102nd Annual Meeting of AIME, Chicago, 1973. 相似文献
11.
《粉末冶金学》2013,56(4):296-300
AbstractFunctionally graded materials consisting of two different materials with a graded interlayer have attracted much interest for their ability to exhibit the characteristics of the individual materials plus new functionality. This concept was applied to the field of hard materials. The developed material consists of a titanium based ceramic surface layer, a tough cemented carbonitride core containing Bl type and WC phases, and an intermediate layer with graded composition. The surface region is characterised by a high compressive residual stress of 0·8 GN m?2. When applied in the form of cutting tools, the material was found to have an abrasion resistance and fracture toughness much higher than those of a conventional cermet of uniform composition. Because of the graded composition, the ceramic surface layer has high adhesive strength, providing longer life than coated tools when spalling of the film can occur easily. The new material is produced by controlled sintering of a green compact of uniform composition. PM/0743 相似文献
12.
V. V. Skorokhod V. P. Titov M. M. Churakov 《Powder Metallurgy and Metal Ceramics》2005,44(11-12):523-526
Growth kinetics for a layer of W6Co7 at the interfaces tungsten-cobalt and tungsten-melts based on copper and tin containing cobalt at 1200 °C are studied. It is established that rate constant for growth of this layer in the system with participation of tin (kSn) is much greater than in the system with copper (kCu). Dependences are determined for these constants on cobalt activity in the melt (aCo): kCu(m2/sec) = = 1.72 · 10?15(aCo ? 0.221) + 2.99 · 10?14 (aCo ? 0.221)2; kSn(m2/sec) = 1.8 · 10?14 (aCo ? 0.221) + + 9.077 · 10?12 (aCo ? 0.221)3. 相似文献
13.
C. B. Solnordal F. R. A. Jorgensen R. N. Taylor 《Metallurgical and Materials Transactions B》1998,29(2):485-492
A mathematical model of the heat flow to a Sirosmelt lance is presented, which predicts lance wall and air temperatures and
the thickness of the slag layer on the lance. By measuring the distribution of wall temperature and slag thickness on an operating
Sirosmelt lance, the model was used to determine both the heat-transfer coefficient between the vessel contents and the lance
and the thermal conductivity of the slag layer. The slag layer thermal conductivity was found to be within the range of 0.5
to 1.1 W m−1 K−1, while the outside heat-transfer coefficient varied from 80 to 150 W m−2 K−1, both of which are smaller than quoted in the literature for metal/slag systems. The discrepancy was attributed primarily
to the large quantities of combustion gases that envelop the lance and reduce convection and conduction from the melt to the
lance. Other factors causing low thermal conductivity and a low heat-transfer coefficient include the thermal resistance at
the slag/lance interface and the mushy region on the outside of the slag layer. 相似文献
14.
Experiments have shown that the sorption of uranium from strong phosphoric acid solutions onto four D2EHPA/TOPO based ion exchange resins and one aminophosphonic acid resin is particle diffusion controlled in the uranium concentration range 42–780 μM. Interdiffusion coefficients of about 10?12 m2s?1 were obtained for D2EHPA/TOPO resins and 0.14 × 10?12 m2s?1 with the aminophosphonic acid exchanger at 20°C in 3 M H3PO4. Both homogeneous particle diffusion, based on Fick's Law, and the ash layer diffusion model fitted the kinetic measurements. 相似文献
15.
Vibration damping characteristics of laminated steel sheet 总被引:3,自引:0,他引:3
The use of laminated steel sheets as vibration damping materials was studied. The laminate consisted of a viscoelastic layer
which was sandwiched between two steel sheets. The study sought to identify parameters affecting the damping efficiency of
the laminate. Two viscoelastic materials, a copolymer based on ethylene and acrylic acid (PEAA) and polyvinyl butyral (PVB),
were used. A frequency analyzer was used to measure the loss factor of the laminates. A theoretical analysis of damping efficiency
based on a model described by Ungar[2] was also carried out. The results showed that the loss factor of the PEAA-based laminates increased monotonically with increasing
thickness of the viscoelastic layer and leveled off at 25.9 pct of total thickness. Ungar’s theory predicted a higher loss
factor than the experimental data. This might have resulted from interfacial adhesive bonding, a nonuniform viscoelastic layer
thickness, and the extrapolation of the rheological data from low to high frequencies. The loss factor of the laminate increased
with increasing temperature, reached a maximum value, and then decreased. An optimum temperature for maximum damping was found
for each laminate configuration. The PEAA-based laminates possessed higher damping efficiency than the PVB-based laminates
at room temperature. The symmetric laminate (with the same steel sheet thickness) possessed a better damping efficiency than
asymmetric laminates. The maximum damping peak of the laminates using a polymer blend, when compared to the laminates using
unblended resin, exhibited a lower loss factor value, became broader, and occurred at a temperature between theT
g’s of the individual components of the polymer blend.
This paper is based on a presentation made in the symposium “Acoustic/Vibration Damping Materials” presented during the TMS
Fall Meeting, Indianapolis, IN, October 1–5, 1989, under the auspices of the TMS Physical Metallurgy Committee. 相似文献
16.
Nicholas Ebrill Yvonne Durandet Les Strezov 《Metallurgical and Materials Transactions B》2000,31(5):1069-1079
The effect of substrate preheat temperature on the dynamic wetting of 55Al-43.4Zn-1.6Si hot dip coating melts on low-carbon
steel substrates has been investigated. An experimental apparatus based on the sessile drop technique was developed, which
allowed the substrate to be preheated to a different temperature than that of the droplet. The initial wetting and spreading
of the molten metal droplet on the substrate was recorded at 1000 frames per second using a high-speed digital camera. Wetting
was improved (ϑ decreased from 120 to 25 deg) as the substrate preheat temperature was increased from room temperature and approached the
droplet temperature, beyond which the improvement in wetting was negligible. Immersion experiments using a thermocouple instrumented
substrate dipped into a coating bath were performed for various substrate preheat temperatures. Interfacial heat fluxes and
interfacial resistances were calculated from the temperature responses. The “minimum” interfacial resistance was decreased
by an order of magnitude (1 × 10−4 to 2 × 10−5 m2 K/W) as the substrate preheat temperature was increased from room to bath temperature. The reduction in interfacial resistance
was related to the improvement of the initial wetting and the increase in mass transfer of iron atoms from the substrate across
the interface. There was an apparent increase in the minimum interfacial resistance for substrate temperatures greater than
the bath temperature. This was due to the increased rate of alloy layer formation and the exothermic nature of the Fe-Al interfacial
reactions. The significance of these findings was discussed with respect to the mechanism of alloy layer formation at the
interface during the initial stages of solid-liquid contact.
This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney,
Australia, under the joint sponsorship of ISS and TMS. 相似文献
17.
H. Uzun T. C. Lindley R. D. Rawlings H. B. McShane 《Metallurgical and Materials Transactions A》2001,32(7):1831-1839
Powder metallurgy processing involving cold pressing and hot extrusion has been used to fabricate bulk functionally graded
materials (FGMs) based on the 2124/SiC/10p composite system. Two forms of single-core bulk FGMs with circular cross section were fabricated. One form (designated 10SiC-2124)
had a central core of unreinforced Al-2124 alloy that was surrounded by a 2124/SiC/10p reinforced surface layer: the other (designated 2124-10SiC) had a composite core and an alloy surface layer. These forms
enabled the effect of the radial graded core on fatigue to be investigated with fatigue crack propagation from either (1)
a ductile core to a more brittle region or (2) a brittle core to a ductile region of the FGM. The fatigue crack growth rate
was measured using a constant applied stress intensity factor range (δK=7 MPa
) technique. Two main fatigue crack growth rates were distinguished corresponding to growth in the core and in the surface
layer. The results show that FGMs may exhibit good fatigue crack propagation resistance. For example, when the crack propagated
from the brittle core to the tough surface layer, the average fatigue crack growth rate in the Al-2124 core (3.9×10−6 mm/cycle) was significantly lower than for the Al-2124 alloy (1.5×10−5 mm/cycle) at a similar δK value (7 MPa
), due to the highly tortuous crack path in the 2124/SiC/10p brittle layer. The 2124/SiC/10p brittle layer had a lower fatigue crack growth rate (6.6×10−6 mm/cycle) than the 2124/SiC/10p conventional composite (7.5×10−6 mm/cycle) because of the compressive residual stresses in the surface layer. Thus, FGMs could be more acceptable for critical
applications than their conventional composite counterparts. 相似文献
18.
The anodic dissolution of chalcopyrite in ammoniacal solutions was investigated using electrochemical methods. At low overvoltages,
the formation of a copper deficient sulfide layer, Cu1-xFeS2 through a charge transfer reaction is proposed based upon the dependence of the rest or open circuit potential on solution
composition and the presence of a Tafel region of appropriate slope. In addition, a current peak that occurs at 10−4 A/cm2 is a function of the square root of the voltage scanning speed and is explained in terms of a charge transfer reaction. At
larger overvoltages, constant potential experiments and mass balances performed at various anodic potentials indicate that
the dissolution is consistent with the overall reaction, CuFeS2 + 4NH3 + 9OH- = Cu(NH3)
4
+2
+ Fe(OH)3 + S2O
3
=
+ 3H2O +9e
-, although some copper may be released to solution in the cuprous state and some ferrous iron has been identified in the product
film. Currentvs time data taken during constant potential experiments were found to obey a linear rate relationship. This was interpreted
in terms of the formation of a layer of constant thickness which is corroded at the outer interface at the same rate it is
formed at the inner interface.. The model proposed is typical of the corrosion of some metals. An examination of the polarization
curves shows the dissolution reaction to be first order with respect to [OH-]. The lack of dependence on [Cu2+] indicates that the catalytic effect of cupric ion during oxygen pressure leaching is related only to the cathodic reduction
of O2 in agreement with the results of previous investigations. 相似文献
19.
M. Saqib J. M. Hampikian D. I. Potter 《Metallurgical and Materials Transactions A》1989,20(10):2101-2108
Tantalum was implanted with 180 keV Al+ ions to fluences up to 3×1018 Al+/cm2. Subsequent microchemical and microstructural observations showed that an amorphous layer covered the surface and extended to depths near 3000 Å for fluences above 2.4×1018 Al+/cm2. The layer, comprised of ~70 at. pet Al and ~30 at. pet Ta, crystallized at temperatures above 500°C. Oxidation measurements, performed in one atmosphere of air and at temperatures below 600°C, showed that the layer stopped oxidation of the implanted tantalum, while unimplanted tantalum oxidized rapidly. The protection provided by the implantation deteriorated somewhat by temperatures near 735°C but still reduced the oxidation rate by a factor of 5. The deterioration is caused by localized rupturing of the implanted layer and the resulting oxidation of the underlying tantalum. At 910°C, the implanted tantalum oxidized almost as rapidly as unimplanted tantalum. 相似文献
20.
The refractory absorption bar is inserted into the submersed nozzle by a stopper to absorb the inclusion flowing through the nozzle and increase the cleanness of liquid steel during the continuous casting process. Based on the high-temperature hot-state experiment, the influence of the groove structure of the absorption bar on the inclusion absorption rate in liquid steel is analysed. Experimental result shows that when the groove direction of the absorption bar is perpendicular to the rotating direction, the optimal groove depth is 3?mm, the maximum thickness of the absorption layer is 362.9?μm and the maximum absorption velocity is 0.19?μm?s?1; when the groove direction of the absorption bar is parallel to the rotating direction, the optimal groove depth is 2?mm, the maximum thickness of absorption layer is 404.3?μm and the maximum absorption velocity is 0.22?μm?s?1. When the groove depth is determined, the absorption rate when the groove direction of the absorption bar is parallel to the rotating direction is higher than that when the groove direction of the absorption bar is perpendicular to the rotating direction. In addition, the number of grooves on the absorption bar is positively proportional to the absorption capability. An inclusion absorption capability model is established based on the multiple regression method and the absorption capabilities of different absorption bars are evaluated. This experiment has provided significant data supporting smelting of clean steel. 相似文献