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991.
The present study concerns the effect of copper additions on the microstructural evolution and mechanical properties of directly
quenched Ti–B steels. Ti and B are added as microalloying elements with an aim of achieving adequate austenite hardenability
and Cu is added to retard the austenite (γ) → ferrite (α) transformation. Therefore, the microalloying and Cu additions together allow the transformation of austenite to occur at
a lower temperature, resulting in a finer microstructure containing martensitic constituents. The direct-quenching route is
adopted with an aim of facilitating the nucleation of the constituent phases from the deformed austenite. In order to circumvent
the hot-shortness due to the Cu addition, 0.79 wt% Ni has been added to one of the 1.5 wt% Cu microalloyed steels. The present
study has demonstrated that the Ni-containing 1.5Cu–Ti–B steel is capable of providing an attractive combination of strength
and ductility comparable to the high strength varieties of HSLA steels in directly quenched condition. 相似文献
992.
On structural and high temperature electrochemical properties of ZrO2 thin film coating on Zr metal produced by carbonate melt 总被引:1,自引:0,他引:1
Melt of NaCO3 can favor oxidation of Zr to form ZrO2 thin film on Zr surface, which is used to make Zr/ZrO2 oxidation/reduction electrode of pH sensor for testing elevated temperature aqueous solutions. Using SEM, EPMA, XPS, EXAFS
and HRTEM, we found that ZrO2 film is tightness and solid with 20 μm thickness composed by nanometer-sized monoclinic crystals. Zr/ZrO2 interface is characterized of zoning structure according to topography and chemical composition in five zones: oxygen-rich
ZrO2, ZrO2, oxygen-rich Zr metal, oxygen-bearing Zr and Zr from outmost to center. Melt oxidation process of Zr involved oxidation time,
air and temperature. The air is important effect on structural and electrochemical properties of ZrO2 thin film for making elevate temperature electrochemical sensor. If oxygen air largely presented in carbonate melting process,
ZrO2 thin film is not tightness and not for oxidation/reduction electrode. 相似文献
993.
Alexander Chroneos Nicholas J. Ashley Kaajal H. Desai John F. Maguire R. W. Grimes 《Journal of Materials Science》2007,42(6):2024-2029
The structures of a number of hydroxide and oxyhydroxide minerals have previously been reported without the hydrogen positions
explicitly defined. Here we use two atomic scale computer simulation techniques, one based on classical ionic potentials,
the other on density functional theory (DFT), to predict these positions. The aim is not only to provide data that can be
used as the basis for future experimental structure optimizations but also model parameters that can be used to predict complex
hydroxide structures. The efficacy of the approach is demonstrated through the comparison of predicted and experimental data
for minerals whose hydrogen positions are known. 相似文献
994.
Z. Ferhat-Hamida H. Phuong-Nguyen P. Bernazzani A. Haine G. Delmas 《Journal of Materials Science》2007,42(9):3138-3154
LLDPE samples synthesized with Ziegler–Natta (ZN) and Metallocene (MT) catalysts have been analyzed to investigate a potential
catalyst-dependent morphology and to find an explanation for the difficult processing of MT. Slow calorimetry at v = 0.02 K/min and IR at RT and in the melt are used. The differences between MT and ZN are assigned to their different composition,
MT not having the linear segments, which are present in ZN. Slow calorimetry is effectively a drawing process of the melt
with chain orientation followed by decay. The later event, characterized by an endotherm, ΔH
network, occurs at higher temperatures for MT, the presence of a regular distribution of methyl groups slowing down the process.
The rocking, gauche, bending and stretching regions of the IR spectra are analyzed. The nascent MT has more strained bands
in the rocking region. The wagging region reveals the more homogeneous environment of MT through the maximum absorbance at
1,368 cm−1. Decomposition of bands is made for the rocking and wagging regions. The orthorhombic crystallinity, αc (FTIR), measures the sum of long- and short-range orthorhombic order, the latter being obtained by αc (FTIR)-αc (X-rays). The values of αc (FTIR) for MT and ZN are very similar in conditions of equilibrium. The justifications for the molecular origin of ΔH
network are presented: (i) the slow relaxation of long chains strained and oriented in the melt measured by other techniques, (ii)
The correlation, for gels of a linear sample, made in different solvents, between the maximum drawability, λmax, and ΔH
network in a slow T-ramp. The range is 80–270 for λmax and 40–120 J/g for ΔH
network. (iii) The comparison of two traces of the same sample, between 140 °C and 270 °C, show that comparable events in the melt
appear in the integrated absorbance and in the slow calorimetry signal. Analysis on thin films of the little-studied CH2 stretching region reveals that their extinction coefficient, ε, and the shape of the bands are highly sensitive to the sample
history, ε diminishing by a large factor in slowly crystallized samples. Events in the slow T-ramp, followed by a fast crystallization, on the other hand, leads to materials with standard characteristics. Slow calorimetry
traces display more events (endothermic and exothermic) for MT than for ZN, a finding consistent with more flow irregularities
during processing. Equilibrium conditions and better processing could be reached for MT by extending time in the melt or using
higher temperatures. 相似文献
995.
Tanu Sharma Sanjeev Aggarwal Shyam Kumar V. K. Mittal P. C. Kalsi V. K. Manchanda 《Journal of Materials Science》2007,42(4):1127-1130
The UV-Visible absorption spectra of virgin and gamma irradiated (20–800 kGy) CR-39 polymer have been deduced by using Shimadzu
Double beam Double Monochromator UV-Visible Spectrophotometer (UV-2550). The existence of the peaks, their shifting and broadening
as a result of gamma irradiation has been discussed. Finally the indirect and direct band gap in virgin and gamma irradiated
CR-39 has been determined. The values of indirect band gap have been found to be lower than the corresponding values of direct
band gap. 相似文献
996.
997.
Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have
been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial
charge model (PCM). For metakaolin powders activated with 5.0 M NaOH, solid-state nuclear magnetic resonance (NMR) spectra
disclose the existence of monomeric [Al(OH)4]− species after two hours of dissolution, consistent with PCM predictions. However, no equivalent monomeric silicate species
were observed for 5.0–10.0 M NaOH activator solutions characteristic of systems with nominal Si/Al ≤ 1. The apparent absence
of monomeric silicate species suggest rapid condensation of silicate units with [Al(OH)4]− to generate aluminosilicate species, as indicated by the evolution of the shoulder at around −87 ppm in the 29Si NMR spectra. Of the two possible stable silicate species [SiO2(OH)2]2− and [SiO(OH)3]−, the latter appears most likely to condense with [Al(OH)4]− to produce aluminosilicate oligomers, from which larger oligomers subsequently form through further condensation with [Al(OH)4]− leading to a gradual build up of aluminosilicate networks and a lowering of system alkalinity. This dissolution and hydrolysis
sequence at the early stages of synthesis suggests a reaction path wholly consistent with predictions of the partial charge
model. 相似文献
998.
I.H. Song 《Thin solid films》2007,515(19):7598-7602
This paper is a report on the effect of a single perpendicular grain boundary on the hot-carrier and high current stability in high performance polycrystalline silicon (poly-Si) thin film transistors (TFTs). Under a hot carrier stress condition (Vg = Vth + 1 V, Vd = 12 V), the poly-Si TFT with a single grain boundary is superior to the poly-Si without any grain boundary because of the smaller free carriers available for electric conduction. The shift of transconductance in poly-Si TFT with a single grain boundary is less than 5% after hot carrier stress during a period of 1000 s. The shift of transconductance is about 25% in the case of the poly-Si TFTs without a grain boundary in the channel. On high current stress, the poly-Si TFT without the grain boundary is less degraded than the poly-Si TFT with the grain boundary because the concentrated electric field near the drain junction is lower. 相似文献
999.
C. B. Winkelmann E. Collin Yu. M. Bunkov H. Godfrin 《Journal of Low Temperature Physics》2004,135(1-2):3-14
We report systematic measurements of the response of a Vibrating Wire Resonator (VWR) in normal and superfluid liquid 3He. Special attention has been paid to the hydrodynamic regime of the superfluid B-phase, where the response parameters of the VWR do not follow a simple law. We show that a simple interpolation between the region where first order slip-corrections can be applied and the ballistic regime is insufficient. Measuring an empirical effective viscosity, we propose a temperature calibration method which allows the use of VWRs as a secondary thermometer at intermediate and high pressures in the temperature range 0.2 T c < T < 50 mK. 相似文献
1000.
Pablo Esquinazi Miguel A. Ramos Reinhard König 《Journal of Low Temperature Physics》2004,135(1-2):27-38
We discuss the strain dependence of the acoustic properties of amorphous metals in both normal and superconducting states, in the temperature range 0.1 mK<T<1 K. A crossover is found when the strain energy is of the order of the effective interaction energy between tunneling systems at the corresponding temperature. Our results provide clear evidence for the interaction between tunneling systems, whose energy is in quantitative agreement with theoretical expectations, and reveal that without the knowledge of the corresponding strain dependences, the measured temperature dependences below ~50 mK of the acoustic properties of disordered solids are rather meaningless. 相似文献