共查询到20条相似文献,搜索用时 23 毫秒
1.
Andrey M. Abyzov Sergey V. Kidalov Fedor M. Shakhov 《Journal of Materials Science》2011,46(5):1424-1438
Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about
430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral
analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W2C–WC. The average roughness, R
a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal
conductivity (TC) as high as 900 W m−1 K−1 are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper
or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness
the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 107 W m−2 K−1. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation
process and on the TC of the composites are considered. 相似文献
2.
Measurements of pyroelectric currents and coefficients of poled sintered discs of ferroelectric solid solutions, potassium-cesium
vanadate and potassium-lithium vanadate have been investigated in the temperature range covering their transition points.
In these solid solutions, K
x
Cs1−x
VO3 and K
x
Li1−x
VO3, pronounced peaks have been observed at the ferroelectric curie temperatures. The peak values of pyroelectric currents and
coefficients change with change in potassium concentration in both the solid solutions. 相似文献
3.
D. K. Dwivedi Vipin Kumar M. Dubey H. P. Pathak 《Journal of Materials Science: Materials in Electronics》2012,23(3):675-680
Cd1−xZnxTe (where x = 0.02, 0.04, 0.06, 0.08) thin film have been deposited on glass substrate at room temperature by thermal evaporation
technique in a vacuum at 2 × 10−5 torr. The structural analysis of the films has been investigated using X-ray diffraction technique. The scanning electron
microscopy has been employed to know the morphology behaviour of the thin films. The temperature dependence of DC electrical
conductivity has been studied. In low temperature range the thermal activation energy corresponding to the grain boundary—limited
conduction are found to be in the range of 38–48 μeV, but in the high temperature range the activation energy varies between
86 and 1.01 meV. The built in voltage, the width of the depletion region and the operating conduction mechanism have been
determined from dark current voltage (I–V) and capacitor-voltage (C–V) characteristics of Cd1−xZnxTe thin films. 相似文献
4.
Three sources of errors in the extended dynamic plane source (EDPS) method caused by the discrepancy between experiment and
model are analyzed. The source effect is eliminated by introducing the nuisance parameter R
0 and the surface effect by a surrounding vacuum. The original model assumes a constant heating power but a constant current
is used in the experiment. Suppression of this effect leads to a new solution of the heat equation designated as the constant-current
model. The measurements on polymethylmetacrylate (PMMA) in vacuum, evaluated by the constant-current model, provided results
of λ = 0.191 W.m−1.K−1 and a = 0.118 ×10−6
m
2.s
− 1, which are in good agreement with published values. The total standard uncertainty was estimated as 1.5 % for both thermophysical
properties. 相似文献
5.
Daisuke Watanabe Keishi Nishio Yoshio Sakka Masataka Ohgaki Ian J. Davies Tomohiro Umeda Seiichiro Koda Kiyoshi Itatani 《Journal of Materials Science》2011,46(6):1956-1962
High-density β-calcium orthophosphate (β-Ca3(PO4)2, also called β-tricalcium phosphate: β-TCP) ceramics with submicrometer-sized grains were fabricated using a pulse-current
pressure firing route. The maximum relative density of the β-TCP compacts was 98.7% at 1050 °C and this was accompanied by
a translucent appearance. The mean grain size of the β-TCP compacts increased slightly with temperature to reach 0.78 μm at 1000 °C. However, upon further increasing the firing
temperature to 1050 °C the mean grain size increased significantly to 1.6 μm. The extent of plastic deformation during tensile
testing was examined at temperatures between 900 and 1100 °C using a strain rate in the range 9.26 × 10−5 to 4.44 × 10−4 s−1. The maximum tensile strain achieved was 145% for a test temperature of 1000 °C and strain rate of 1.48 × 10−4 s−1 and this was attributed to the relatively high density and small grain size. 相似文献
6.
Crystallization behavior of PVDF/PMMA blends prepared by in situ polymerization from DMF and ethanol
Xuejuan Zhao Jing Cheng Jun Zhang Shuangjun Chen Xiaolin Wang 《Journal of Materials Science》2012,47(8):3720-3728
The crystallization behavior of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends was investigated at
different PMMA content and from two solvents N,N-dimethylformamide (DMF) and ethanol. The PVDF/PMMA blends were obtained by in situ polymerization of methyl methacrylate
(MMA) in the solution of PVDF in DMF. The crystalline phases of PVDF were dependent on crystalline solvents and independent
on PMMA content. For the in situ PVDF/PMMA blends, β phase of PVDF was predominant when they were crystallized from their good solvent DMF, while PVDF exhibited well-defined
α and β phases from non-solvent ethanol. However, the relative fraction of β phase of PVDF in blends crystallized from ethanol varied with PMMA content. The crystallization morphology was related to
crystallization solvent and PMMA content. The in situ blends crystallized from DMF and ethanol presented spherulites morphology
and numerous minute particle structures, respectively. The addition of PMMA could reduce the spherulite size of PVDF. Thermal
properties of in situ blends were also dominated by crystallization solvent and PMMA content. For the blends crystallized
from DMF, their peak melting temperatures and lamellar thickness calculated by WAXD showed a first increasing and then decreasing
tendency. At the same PMMA content, the blends crystallized from ethanol had a higher degree of crystallinity (X
c) of PVDF compared with those from DMF. In addition, the X
c calculated by DSC increased noticeably at PMMA content of 1.0 wt% and afterward it decreased with PMMA content, regardless
of the kind of crystallization solvent. Besides, the hydrophilicity of the PVDF/PMMA blends was improved with PMMA content
based on contact angle measurements. 相似文献
7.
Thermal properties such as thermal diffusivity and thermal conductivity are measured by photoacoustics at room temperature
for various particle sizes, thicknesses and the percentage of mixing of poly (vinyl alcohol) (PVA) in Poly (vinylidene fluoride)
(PVDF)/PVA blends. The results are compared with other experimental reports, which is by laser flash technique for various
temperatures. The agreement is very good at room temperature; in our study, it is 0.20 Wm−1 K−1, whereas by laser flash technique it is 0.18 Wm−1 K−1 for thermal conductivity. The importance of dislocation density and strain is discussed. 相似文献
8.
Hua Wang Xiaodan Huang Jiwen Xu Ling Yang Shangju Zhou 《Journal of Materials Science: Materials in Electronics》2012,23(1):234-237
Bi4Ti3−xNbxO12 ferroelectric thin films were fabricated on p-Si substrates by magnetron sputtering. The effects of Nb doping on microstructure
and properties of Bi4Ti3−xNbxO12 films were investigated. Bi4Ti3−xNbxO12 films had the same structure as Bi4Ti3O12 with smaller and more uniform grains. The dielectric and ferroelectric properties of Bi4Ti3−xNbxO12 films were improved by Nb doping. Bi4Ti3−xNbxO12 films have better dielectric and ferroelectric properties with P
r = 16.5 μC/cm2, E
C < 100 kV/cm, ε
r > 290, low dielectric loss (<0.9%) and clockwise C–V curves with a memory window of 0.9 V when x = 0.03–0.045, while an excessive
Nb doping would lead to bad dielectric and ferroelectric properties. 相似文献
9.
Koji Takahashi Norsyazwan Hilmi Yohei Ito Tatsuya Ikuta Xing Zhang 《International Journal of Thermophysics》2009,30(6):1864-1874
The small size of nanomaterials deposited by either focused ions or electron beams has prevented the determination of reliable
thermal property data by existing methods. A new method is described that uses a suspended platinum hot film to measure the
thermal conductivity of a nanoscale deposition. The cross section of the Pt film needs to be as small as 50 nm × 500 nm to
have sufficient sensitivity to detect the effect of the beam-induced nanodeposition. A direct current heating method is used
before and after the deposition, and the change in the average temperature increase of the Pt hot film gives the thermal conductivity
of the additional deposited material. In order to estimate the error introduced by the one-dimensional analytical model employed,
a two-dimensional numerical simulation was conducted. It confirmed the reliability of this method for situations where the
deposit extends onto the terminals by (1 μm or more. Measurements of amorphous carbon (a-C) films fabricated by electron beam
induced deposition (EBID) produced thermal conductivities of 0.61 W · m−1 · K−1 to 0.73 W · m−1 · K−1 at 100 K to 340 K, values in good agreement with those of a-C thin films reported in the past. 相似文献
10.
V. Budhraja X. Wang D. Misra 《Journal of Materials Science: Materials in Electronics》2010,21(12):1322-1326
This paper investigates the electrical characteristics at low temperatures through C–V, I–V and conductance measurements to
understand the interface behavior of HfO2 and p-type GaAs bulk substrate. Room temperature interface state density, D
it
, estimated for as-deposited Ti–Au/HfO2/GaAs capacitors was found to be 3.68 × 1011 cm−2 eV−1. Low temperature measurement suggests that only fast interface states contribute to the conduction process. When the characteristics
of two different metal gates were compared, the accumulation capacitance density observed to be 1.4 and 8.98 fF/μm2 for Be–Au/HfO2/GaAs and Ti–Au/HfO2/GaAs, respectively at 1 MHz. 相似文献
11.
Fei Ai Hong Li Quan Wang Wang Zhang Yuan Xiaoyong Chen Libin Yang Junhong Zhao Yongming Zhang 《Journal of Materials Science》2012,47(12):5030-5040
Poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) membranes have important applications as biomaterials. In
this study, PVDF/PMMA with varying ratios is blown into membranes, the surface property and blood compatibility of which are
thoroughly investigated. Membrane surface characteristics including composition and topography exert considerable influence
on the blood compatibility. Introduction of PMMA disturbs PVDF crystallization, however, favors the β phase crystal formation. PVDF content, crystallization ability, and surface enrichment have decisive effects on the membrane
surface composition. Meanwhile, with increased PMMA fraction, the membrane surface roughness is also increased, and subsequently
results in decreased hemocompatibility. While the membranes with PMMA content lower than 30 wt% show good blood compatibility,
those with higher PMMA fraction exhibit obvious platelet adhesion to the surface. Thermal annealing promotes the formation
of β phase PVDF and generates much smoother surface, thus endowing the membranes with greatly enhanced blood compatibility. These
results show the prospect for optimization of processability, surface property, and blood compatibility of PVDF/PMMA membranes
through facile modulation of PMMA content and fabrication process. 相似文献
12.
Flexible piezo- and pyroelectric composite was made in the thin film form by spin coating. Lead Zirconate Titanate (PZT) ceramic
powder was dispersed in a castor oil-based polyurethane (PU) matrix, providing a composite with 0–3 connectivity. The dielectric
data, measured over a wide range of frequency (10–5 Hz to 105 Hz), shows a loss peak around 100 Hz related with impurities in the polymer matrix. There is also an evidence of a peak in
the range 10–4 Hz, possibly originating from the glass transition temperature Tg of the polymer. The pyroelectric coefficient at 343 K is 7.0×10–5 C·m–2·K–1 which is higher than that of β-PVDF (1×10–5 C·m–2·K–1).
Electronic Publication 相似文献
13.
Frank Hemberger Sebastian Weis Gudrun Reichenauer Hans-Peter Ebert 《International Journal of Thermophysics》2009,30(4):1357-1371
Novel graded carbon aerogels were synthesized to study the impact of different synthesis parameters on the material properties
on a single sample and to test a new, locally resolved thermal-conductivity measurement technique. Two identical cylindrical
aerogels with a graded structure along the main cylindrical axis were synthesized. Along the gradient with an extension of
about 20 mm the densities range from 240 kg·m−3 to 370 kg·m−3 and the effective pore diameter determined via small angle X-ray scattering and SEM increase systematically from 70 nm up
to 11,000 nm. One specimen was cut perpendicular to the cylinder axis into disc-shaped samples; their thermal conductivities
in an argon atmosphere, as determined via a standard laser-flash technique, range from 0.06W·m−1·K−1 to 0.12W·m−1·K−1 at 600 °C. The second specimen, cut to obtain a sample with the gradient in-plane, was investigated with a spatially resolved
laser-flash technique at ambient conditions. The results of the two different techniques are compared and discussed in detail. 相似文献
14.
The dielectric, piezoelectric and elastic coefficients, as well as the electromechanical coupling factors, of NaNbO3 submicron-structured ceramics have been obtained by an automatic iterative method from impedance measurements at resonance.
Poled thin discs were measured from room temperature up to the depoling one, close to 300 °C. Dielectric thermal behaviour
was determined also for unpoled ceramics up to the highest phase transition temperature. Ceramics were processed by hot-pressing
from mechanically activated precursors. Microstructural effects on the properties are discussed. The suppression of the classical
maximum in dielectric permittivity in unpoled ceramics at the phase transition at 370 °C was found when a bimodal distribution
of grain sizes, with a population of average grain size of 110 nm in between much coarser grains, is observed. The appearance
of a phase transition at 150 °C took place when Na vacancies are minimised. The occurrence of a non-centrosymmetric, ferroelectric
phase, in the unpoled ceramic from room temperature to ~300 °C, highly polarisable resulting in high ferro–piezoelectric properties
was also observed in the ceramic which presents grain size below 160 nm. Maximum values of k
p = 14%, d
31 = −8.7 × 10−12 C N−1 and N
p = 3772 Hz m at room temperature, and k
p = 18%, d
31 = −25.4 × 10−12 C N−1 and N
p = 3722 Hz m at 295 °C were achieved in the best processing conditions of the ceramics. 相似文献
15.
T. Ishikawa J. T. Okada P.-F. Paradis Y. Watanabe 《International Journal of Thermophysics》2010,31(2):388-398
Thermophysical properties of liquid gadolinium were measured using non-contact diagnostic techniques with an electrostatic
levitator. Over the 1585 K to 1920 K temperature range, the density can be expressed as ρ(T) = 7.41 × 103 − 0.46 (T − T
m) (kg · m−3) where T
m = 1585 K, yielding a volume expansion coefficient of 6.2 × 10−5 K−1. In addition, the surface tension data can be fitted as γ(T) = 8.22 × 102 − 0.097(T − T
m)(10−3 N · m−1) over the 1613 K to 1803 K span and the viscosity as η(T) = 1.7exp[1.4 × 104/(RT)](10−3 Pa · s) over the same temperature range. 相似文献
16.
T. A. Kompan A. S. Korenev A. Ya. Lukin 《International Journal of Thermophysics》2008,29(5):1896-1905
The artificial material sitall CO-115M was developed purposely as a material with an extra-low thermal expansion. The controlled
crystallization of an aluminosilicate glass melt leads to the formation of a mixture of β-spodumen, β-eucryptite, and β-silica anisotropic microcrystals in a matrix of residual glass. Due to the small size of the microcrystals, the material
is homogeneous and transparent. Specific lattice anharmonism of these microcrystal materials results in close to zero average
thermal linear expansion coefficient (TLEC) of the sitall material. The thermal expansion coefficient of this material was
measured using an interferometric method in line with the classical approach of Fizeau. To obtain the highest accuracy, the
registration of light intensity of the total interference field was used. Then, the parameters of the interference pattern
were calculated. Due to the large amount of information in the interference pattern, the error of the calculated fringe position
was less than the size of a pixel of the optical registration system. The thermal expansion coefficient of the sitall CO-115M
and its temperature dependence were measured. The TLEC value of about 3 × 10−8 K−1 to 5 × 10−8 K−1 in the temperature interval from −20 °C to +60 °C was obtained. A special investigation was carried out to show the homogeneity
of the material. 相似文献
17.
Within this work we deposited 16 monolayers of stearic acid alternated with 15 monolayers of calix[4]amine to form a non-centrosymmetric Langmuir–Blodgett (LB) thin film onto an aluminized (50 nm coated) glass microscopic slide. Dielectric constant and dielectric loss for the film were determined using C-f and tan (δ-f) measurements. The value of the pyroelectric figure of merit was determined as 1.73 μC m−2 K−1. To elucidate the conduction mechanism of stearic acid/calix[4]amine LB film, DC current–voltage measurements between −4 and +4 V were carried out. The I(V) behaviour shows a symmetrical and highly non-linear behaviour. Analysis of this behaviour of the stearic acid/calix[4]amine LB film showed a conductivity value of 1.12 × 10−13 S m−1 for ohmic region. The exponential part of I(V) dependence obeyed the Schottky conduction mechanism with a barrier height of 1.67 eV. This LB film structure shows a typical insulating behaviour for low voltage values and the Schottky effect becomes dominant when the voltage increases. The frequency dependence of conductivity shows a power law relationship between conductance and frequency. 相似文献
18.
L. Miettinen P. Kekäläinen J. Merikoski J. Timonen 《International Journal of Thermophysics》2009,30(6):1902-1917
The transient fin model introduced recently for determination of the in-plane thermal diffusivity of planar samples with the
help of infrared thermography was modified so as to be applicable to poor heat conductors. The new model now includes a temperature-dependent
heat loss by convective heat transfer, suitable for an experimental setup in which the sample is aligned parallel to a weak,
forced air flow stabilizing otherwise the convective heat transfer. The temperature field in the sample was measured with
an infrared camera while the sample was heated at one edge. The symmetric temperature field created was averaged over the
central fifth of the sample to obtain one-dimensional temperature profiles, both transient and stationary, which were fitted
by a numerical solution of the fin model. One of the fitting parameters was the thermal diffusivity, and with a known density
and specific heat capacity, the thermal conductivity was thus determined. The test measurements with tantalum samples gave
the result (57.5 ± 0.2) W · m−1 · K−1 in excellent agreement with the known value. The other fitting parameter was a temperature-dependent heat loss coefficient
from which the lower limit for the temperature-dependent convection coefficient was determined. For the stationary state the
result was (1.0 ± 0.2) W · m−2 · K−1 at the temperature of the flowing air, and its temperature dependence was found to be (0.22 ± 0.01) W ·m−2 · K−2. 相似文献
19.
S.?I.?Tanase D.?Pinzaru? V.?Georgescu 《Journal of Superconductivity and Novel Magnetism》2011,24(8):2313-2319
The effect of nitrogen addition on the morphology, magnetic anisotropy, and magnetoresistance properties of Co–Ni–N granular
thin films were investigated. The films were grown by electrodeposition onto aluminum substrates at room temperature. By a
complex process of cationic catalysis occurring at the cathode/electrolyte interface, nitrogen is adsorbed in the Co–Ni film.
Finally, a granular film grows by a tridimensional progressive nucleation mechanism. The nature of the grains and of the interface
between them influences exchange interactions between grains, which play an important role in determining the magnetic anisotropy.
From the magnetic measurements, we found that the magnetic anisotropy constant varied in the range K
eff=(−21.5÷36.6)×104 J⋅m−3 and the coercivity varied between H
c=(13÷67) kA⋅m−1 depending on the sodium nitrate content in the plating bath. The Co–Ni–N granular thin films display large values (∼160%)
of magnetoresistance. These large values of magnetoresistance make such structures attractive for applications as sensitive
magnetic field sensors. 相似文献
20.
Yubin Li Jun Yu Jianjun Li Chaodan Zheng Yunyi Wu Yuan Zhao Meng Wang Yunbo Wang 《Journal of Materials Science: Materials in Electronics》2011,22(4):323-327
Bi1.05−xDyxFeO3 (BDFO) (x = 0−0.2) ceramics were synthesized by solid-state reaction method. The influence of Dy dopant on crystal structural,
dielectric and ferroelectric properties was investigated. The lattice parameter and the Curie temperature of BDFO were degraded
continuously with increasing contents of Dy3+ cations. Leakage current density, ferroelectric polarization and dielectric loss were improved by appropriate Dy doping.
When x = 0.1, BDFO showed the best electric properties. At applied electric field of 53 kV/cm, the remnant polarization (2P
r
) was 12.2 μC/cm2.These improvements in electric properties in BDFO ceramics could have resulted from the relatively low oxygen vacancy concentration
and structural distortion. 相似文献