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1.
The mechanical relaxation in binary, ternary, quaternary, and quitary bulk metallic glasses with widely different glass-forming ability, or the critical cooling rate, has been studied. A single-roller melt-spinning apparatus was used for preparing thin specimens. The internal friction Q−1 and the oscillation frequency f of the specimens were measured using an inverted torsion pendulum with the free decay method. The measurements were performed from room temperature, through the glass transition temperature Tg, up to the crystallization temperature Tx. As the temperature is increased, the background Q−1 increases, and peaks can usually be seen near Tg and Tx. The shear modulus, which is proportional to f2, is changed near the Q−1 peak. The experimental data are presented and overall features of the results are discussed.  相似文献   

2.
The evolution with temperature of the elastic constants of the metastable β phase in a Cu-27.96 at.%Al-3.62 at.% Ni shape memory alloy (SMA) has been studied by resonant ultrasound spectroscopy (RUS). The corresponding elastic constants of this cubic phase have been measured near the martensitic transformation temperature in a single crystal. Above the martensitic transformation temperature, an anomalous behavior has been found in the C′elastic constant which shows a softening as the temperature decreases. The internal friction value Q−1 has been obtained in this temperature range from the RUS spectra. The mechanisms associated with the Q−1 increase must be related to {1 1 0} shear.  相似文献   

3.
The change of magnetoelastic properties after thermal treatments has been investigated for two groups of metallic glasses. (Fe79Co21)75+xSi15−1.4xB10+0.4x (x (at.%)=0, 2, 4, 6, 8, 10) has been studied both in the as-prepared state and after thermal annealing in an applied magnetic field, to achieve a particular domain structure, at temperatures well below the crystallization temperatures. Changes in the ΔE effect, magnetomechanical coupling (k) and internal friction coefficient (Q−1) are reported, reaching values of about 60% of the saturation value ES. Fe64Ni10Nb3Cu1Si13B9 alloys annealed in vacuum for 1 h in the temperature range 350–550 °C showed maximum values of the ΔE effect and k of 61% and 0.85, respectively, accompanied by a minimum value of Q of around 2 for the sample annealed at 460 °C. These variations are related to the progress of nanocrystalization. The properties achieved are among the best reported for magnetomechanical applications.  相似文献   

4.
The early electromigration (EM) processes in the Al–Si(Cu) thin films several tens of nanometers thick deposited on Si reed substrates were investigated by means of the simultaneous anelasticity and electrical resistivity measurements below 360 K. The grain growth, the shortening of a and the probable lengthening of a take place during the EM tests at the current density of 108 A/m2, where a and a denote the atomic plane spacing normal to and the one parallel to the film surface, respectively. The activation energy, EGB, for the grain growth is found to be as low as 0.32 eV, possibly suggesting that EGB in very thin nanometer-thick films is much lower than that found in thin micrometer-thick films. The increase in the Young’s modulus of the Al–Si(Cu) thin films takes place during the EM tests, suggesting that the grain growth is responsible for it. The decrease in Q−1 observed at 330 and 360 K may be explained by a decrease in the grain boundary regions too. The increase in Q−1 found during the EM tests at 300 K is possibly associated with an increase in a certain anelastic process in the grain boundary regions.  相似文献   

5.
In order to get an insight into the grain boundaries (GBs) in nanocrystalline (n-) metal, we prepared the high-density n-Au with ρ/ρ0>99% by the gas-deposition method and carried out the vibrating reed measurements, where ρ/ρ0 is the relative density referring to the bulk density. The strain amplitude dependence (SAMD) of the resonant frequency (f) and the internal friction (Q−1) was measured for the strain () amplitude between 10−6 and 2×10−3 and for temperature between 5 and 300 K. No plastic deformations are detected for the present strain range, where f decreases for up to 10−4 and then turns to increase, showing saturation for between 10−4 and 2×10−3. The low temperature irradiation by 2 MeV electrons or 20 MeV protons causes an increase in the Young’s modulus at 6 K, which is surmised to reflect a modification of the anelastic process in the GB regions. In contrast, the SAMD of f is hardly modified by irradiation, suggesting that it is indicative of a collective motion of atoms in n-Au.  相似文献   

6.
The effects of ferrite grain size, notch acuity and notch length on brittle fracture stress and fracture toughness of notched specimens were experimentally studied at −196°C for a low-carbon steel.

For the case of smaller notch root radius, fracture stress and fracture toughness are not so much conspicuously affected by ferrite grain size. The effect of ferrite grain size will increase with increase of notch root radius. Fracture stress and fracture toughness will decrease with increase of d−1/2 (d = grain size diameter) a smaller range of d−1/2, and increase nearly linearly with increase of d−1/2 in larger range of d−1/2, and, thus have minimum at some value of d−1/2.  相似文献   


7.
Solid solutions of Bi3(Nb1−xTax)O7 (x = 0.0, 0.3, 0.7, 1) were synthesized using solid state reaction method and their microwave dielectric properties were first reported. Pure phase of fluorite-type could be obtained after calcined at 700 °C (2 h)−1 between 0 ≤ x ≤ 1 and Bi3(Nb1−xTax)O7 ceramics could be well densified below 990 °C. As x increased from 0.0 to 1.0, saturated density of Bi3(Nb1−xTax)O7 ceramics increased from 8.2 to 9.1 g cm−3, microwave permittivity decreased from 95 to 65 while Qf values increasing from 230 to 560 GHz. Substitution of Ta for Nb modified temperature coefficient of resonant frequency τf from −113 ppm °C−1 of Bi3NbO7 to −70 ppm °C−1 of Bi3TaO7. Microwave permittivity, Qf values and τf values were found to correlate strongly with the structure parameters of fluorite solid solutions and the correlation between them was discussed in detail. Considering the low densified temperature and good microwave dielectric proprieties, solid solutions of Bi3(Nb1−xTax)O7 ceramics could be a good candidate for low temperature co-fired ceramics application.  相似文献   

8.
An organic amorphous semiconductor with unusual electrical switching capability has been synthesized by the direct decomposition of carbon disulfide. Metallic black highly conducting (above 102 Ω−1 cm−1) thin films of approximate composition C3S have been prepared by the simple passage of dilute carbon disulfide vapors over an incandescent tungsten filament. Film growth rates greater than 10 μm h−1 are observed. The coatings are hard, adherent on a wide variety of substrates, thermally stable, and remarkably inert to all but the most severe mineral acid digestion. The carbon sulfide solids behave like varistors, following Ohm's law over many decades of current up to a threshold voltage, typically 1–10 V, beyond which the current surges, independent of applied voltage. The threshold voltage is uniquely temperature dependent, reaching a maximum as the temperature is reduced from room temperature, then decreasing once again at cyrogenic temperatures.  相似文献   

9.
A 60 layer lead-liquid scintillator shower detector, which we call the SLIC, has been used for multiphoton detection in the Fermilab tagged photon spectrometer. The detector has an unimpeded active area which is 2.44 m by 4.88 m and is segmented, by means of teflon coated channels, into 3.17 cm wide strips. The 60 layers in depth are broken into three directions of alternating readouts so that three position coordinates are determined for each shower. At present the readouts are made by 334 photomultiplier tubes coupled to BBQ doped wavelength shifter bars which integrate the entire depth of the detector. It is relatively straightforward to increase the number of readouts to include longitudinal segmentation and to increase the segmentation of the outer region which are at present read out two strips to a readout. The energy and position resolutions of isolated showers are about and 3 mm., respectively. The SLIC has been used to study the Kπ+π0 decay of the D0 [1], as well as for electron and muon identification in ψ → e+e and ψμ+μ plus π0 identification in γp → ψχ [8].  相似文献   

10.
We have studied the basic d.c. electrical properties of evaporated CdSe films in the context of the development of inexpensive solar cells. Earlier measurements have shown significant variations, which depend on the preparation and previous treatment of the films. In the present work Al---CdSe---Al sandwich structures were studied, with the CdSe thickness in the range 0.1–1.0 (μm. D.c. capacitance varied inversely with film thickness, yielding a permittivity of 7.82 × 10−11 F m−1 (relative permittivity 8.83). Current density was proportional to applied voltage at low voltage levels, but followed a power law at higher voltages with exponent typically 2.5; the transitional voltage was directly proportional to the square of the film thickness. The results were interpreted as ohmic conduction at low voltages and space-charge-limited conductivity (SCLC) dominated by an exponential trap distribution, at higher voltage levels. Measurements of current density as a function of inverse temperature for different applied voltages in the SCLC region enabled the derivation of typical mobilities in the range of ( 7.65–10.15) × 10−5 m2 V−1 s−1 using the results of our existing theory. This value of mobility and the derived trapping parameters were in general agreement with some earlier measurements.  相似文献   

11.
In the development of ZnO-based varistors the electrical properties of ZnO/Bi2O3 junctions and of the two individual oxides are being investigated. Following our recent work on a.c. conductivity in Al---ZnO---Al sandwich structures we currently report d.c. measurements. The structures were prepared by r.f. magnetron sputtering in an argon/oxygen mixture in the ratio 4:1. Capacitance-voltage data confirm that the Al/ZnO interface does not form a Schottky barrier and measurements of the dependence of capacitance on film thickness indicate that the relative permittivity of the films is approximately 9.7. With increasing voltage the current density changed from an ohmic to a power-law dependence with exponent n≈3. Furthermore measurements of current density as a function of reciprocal temperature showed a linear dependence above about 240 K, with a very low activation energy below this temperature consistent with a hopping process. The higher temperature results may be explained assuming a room-temperature electron concentration n0 and space-charge-limited conductivity, dominated by traps exponentially distributed with energy E below the conduction band edge according to N = N0exp(−E/kTt), where k is Boltzmann's constant. Typical derived values of these parameters are: n0 = 7.2 × 1016 m−3, N0 = 1.31 × 1045 J−1 m−3 and Tt = 623 K. The total trap concentration and the electron mobility were estimated to be 1.13 × 1025 m−3 and (5.7−13.1) ×10−3m2V−1s−1 respectively.  相似文献   

12.
The amplitude-dependent internal friction (ADIF) of very pure aluminum (99.9999%) and Al dilute alloys (20–100 ppm) has been measured at temperatures between 2 and 240 K. Two universal properties have been found in the temperature dependence of the required stress amplitude for a constant decrement. At relatively low temperatures (or high stress amplitude), the decrease of the stress with increasing temperature is proportional to T2/3 down to 65% of the stress for 0 K, and then deviates from the T2/3 dependence. It is explained that the elementary process is due to unpinning of a dislocation from a single solute atom. The interaction potential has been determined successfully from this region (above 40% of the stress at 0 K). At relatively high temperatures (or stress less than 40% of that for 0 K), we find for the first time that the stress changes as proportional to T−1 for all dilute Al alloys but for a pure Al crystal. It is explained that the elementary process is due to simultaneous unpinning of a dislocation from several solute atoms for dilute alloys.  相似文献   

13.
Enhanced fluoride sorption by mechanochemically activated kaolinites   总被引:1,自引:0,他引:1  
This study investigated the surface modification of photocatalyst and photodecomposition of formaldehyde from indoor pollution source. This study explored the feasibility of the application of the ultraviolet light emitting diode (UVLED) instead of the traditional ultraviolet (UV) lamp to treat the formaldehyde. The photocatalytic decomposition of formaldehyde at various initial concentrations was elucidated according to the Langmuir–Hinshelwood model. The reaction rate constant (k) and adsorption equilibrium constant (KL) over 0.334 g silver titanium oxide photocatalyst (Ag/TiO2) coated on glass sticks with 254 nm ultraviolet lamp (UVC), 365 nm ultraviolet lamp (UVA), and UVLED are 650 ppmv min−1 and 2 × 10−4 ppmv−1, 500 ppmv min−1 and 1.04 × 10−4 ppmv−1, and 600 ppmv min−1 and 2.52 × 10−5 ppmv−1, respectively. A comparison of the simulation results with the experimental data was also made, indicating good agreement. The magnitudes of energy effectiveness (Ee) are in the order of UVLED (0.6942 mg kW−1 h−1) > UVA (0.007 mg kW−1 h−1) > UVC (0.0053 mg kW−1 h−1). The Ee of UVLED is 131 times larger than that of UVC. The UVLED can save a lot of energy in comparison with the traditional UV lamps. Thus, this study showed the feasible and potential use of UVLED in photocatalysis.  相似文献   

14.
Parylene-n (Poly-p-xylylene) (PA-n) [1–3] has a long history of use as a moisture barrier for printed circuit boards and hybrids. This paper evaluates this compound as a candidate vapor-depositable polymer interlayer dielectric for submicron integrated circuit technology due to its low dielectric constant, good step coverage, and high etch selectivity. To apply PA-n on high-density very large scale integrated circuits, its properties, such as deposition rate, deposition yield, and Crystallinity, are investigated as a function of deposition pressure and annealing temperature. The deposition rate was found in the range of 2.66 Pa to 13.3 Pa to be a linearly increasing function of pressure. Good-quality films were obtained when pressure was controlled below 10.64 Pa. Cloudy films, however, were found at 13.3 Pa. The deposition rate could be as high as 3.33 × 10−10 m s−1 when deposited at 10.64 Pa. The plot of PA-n yield vs. pressure showed a constant plateau of 1 × 10−4 m kg−1 from 2.66 Pa to 10.64 Pa. The optimum deposition rate was hence obtained at 10.64 Pa without compromising the deposition yield. The crystallinity-associated properties examined were hardness, dielectric constant, and water permeability. A lower deposition pressure was observed to produce higher Crystallinity that could be further enhanced by thermal annealing. A 5 × 10−8 m hard surface layer was detected with hardness 3.5 GPa, that was 3˜7 times larger than that of bulk hardness which was 0.4˜0.7 GPa. The bulk hardness was found to increase as Crystallinity increased. The dielectric constant tended to increase when the deposition pressure decreased. Furthermore, the dielectric constant was nearly constant when the polymer was heated up to temperatures as high as 698 K. This behavior, together with the formation of the hard layer and a higher Crystallinity, was believed to result from the improved film organization of the deposited films. The competition between the film build-up in the surface region and the monomer diffusion into the bulk region (penetration) was theorized to be responsible for the film organization. The water permeability, which was measured to be as low as 1.2 × 10−15 kg m−1 s−1 Pa−1 and was found to increase as the deposition pressure was increased, further strengthened the film organization claim.  相似文献   

15.
The measurements of the internal friction and dynamic shear modulus as well as differential scanning calorimetry have been performed in order to investigate the structural relaxation and crystallization of Zr41Ti14Cu12.5Ni10−xBe22.5Fex (x=0 or 2) bulk metallic glasses. It is found that the glass transition is retarded and the thermal stability of supercooled liquid is increased by the Fe addition. The experimental results are well analyzed using a physical model, which can characterize atomic mobility and mechanical response of disordered condensed materials.  相似文献   

16.
The purification of municipal incinerator gases generates huge quantities of both fly ashes and used lime, containing high amount of heavy metals (Pb, Cd, Zn and Hg). The used lime is mainly contaminated by Pb and often considered as hazardous waste. This paper is related to a laboratory study on the performance of electrochemical techniques used to recover Pb from leachate produced during used lime decontamination. Two types of electrolytic units (monopolar and bipolar electrode cells) using different electrode materials were studied. Effectiveness was measured in terms of energy consumed, weight of residue sludge produced and reduction in Pb concentration. Results showed that the best performances for Pb removal (in terms of effectiveness and cost) were obtained by initially adjusting the pH of UL leachate to pH 7.5–8.5 with sulphuric acid followed by electrochemical treatment using bipolar electrode (mild steel) system operated at current intensity of 1.5 A through only 5 min. The yield of Pb removal was 98.8 ± 1.3% and an amount of 4.9 ± 1.3 kg trt−1 of metallic sludge was produced. The optimal conditions determined for Pb recovery involved a total cost of CAN$ 1.66 t−1 of dry residue treated, including acid consumption, energy consumption and metallic sludge disposal.  相似文献   

17.
Be diffusion during post-growth annealing has been investigated in InGaAs epitaxial layers. Kick-out mechanisms considering species charges, build-in electric field and Fermi-level effect have been studied. Several forms of Kick-out mechanism have been implemented in our simulation programs. Experimental concentration profiles obtained by SIMS have been compared systematically with the results of simulations. We have deduced that the Kick-out mechanism Bei0 Be + IIII+ is the dominating diffusion mechanism in InGaAs under our experimental conditions (C0 = 3 × 1019 cm−3).  相似文献   

18.
Low cycle fatigue is one of the most important phenomena affecting the lifetime of jet engine blades. In this paper, the effect of aluminide diffusion coating (CODEP-B) on low cycle fatigue properties of René 80 has been studied at temperature of 871 °C, R = 0 and strain rate of about 2 × 10−3 s−1. Experimental results show that the applied cyclic strain is lower than 0.8%, the presence of aforesaid coating increases the fatigue lifetime. In coated specimens, while the total cyclic strain is lower than 0.8%, the nucleation of the cracks occurs merely in substrate, but in cyclic strain more than 1%, as a result of simultaneous nucleation of cracks in the coating surface, diffusion layer and in the substrate, fatigue lifetime of the coated specimens is lower than that of uncoated specimens.  相似文献   

19.
Chromium disilicide (CrSi2) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi2 templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi2 films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi2 film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi2 film is p-type semiconductor having a hole concentration of 1 × 1017cm−3 and Hall mobility of 2 980 cm2 V−1 s−1 at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 1010T−3cm2V−1s−1.  相似文献   

20.
Molecular dynamics simulation using a burchart-DREIDING force field has been employed to determine the self-diffusion coefficients of methane, ethane, propane, n-butane, isobutane, benzene, and pyridine in silicalite at 300 K. In the case of the alkanes, Einstein diffusion was observed early in a 500-ps simulation. Values of the diffusion coefficient for the alkanes ranged from about 9 × 10−4 cm2 s−1 for methane to 2 × 10−6 cm2 s−1 for isobutane at a loading of 0.5 molecule per unit cell (mpuc) or 2 molecules per simulation box. For the alkanes, there is good agreement between the results of simulation and experimental values of the self-diffusion coefficient obtained by microscopic techniques such as pulsed-field gradient NMR measurements. In the case of benzene and pyridine, anomalous diffusion was observed for time scales up to 9 ns and apparent diffusion coefficients (range of 10−11 to 10−8 cm2 s−1) calculated form the Einstein relation increased with increased loading (up to 3.75 mpuc) and, as shown for pyridine, with increasing temperature. In the case of benzene where experimental data was available, the apparent diffusion coefficients calculated at high loadings were within an order of magnitude of experimental values.

Heats of adsorption were calculated by a canonical Monte Carlo method. For the alkanes (methane, ethane, propane, and n-butane), the magnitude of the heats of adsorption linearly increased with the number of alkane carbons in qualitative and quantitative agreement with experimental data. Heats of adsorption calculated for isobutane and benzene also agreed well with experimental values. No experimental values were available for pyridine for comparison.  相似文献   


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