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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The polycrystalline samples of Dy
x
Bi1−x
FeO3 (x = 1, 0.8, 0.6, 0.4 and 0.2) were synthesized by standard solid state reaction technique. The samples synthesized were characterized
by X-ray diffraction (XRD) technique. Further the samples were characterized by infrared (IR) spectroscopic technique. The
dielectric measurements were carried out as a function of frequency in the range 100 Hz to 1 MHz at room temperature. Also
the dielectric measurements were carried out as a function of temperature at certain fixed frequencies. The ac and dc resistivity
measurements were carried out using two probe method. Also temperature dependence of ac and dc resistivity was noted. These
measurements suggest polaron conduction in the samples. Finally, the data from XRD, IR, dielectric measurements were correlated. 相似文献
992.
A phenomenological model is developed for describing the kinetics of the crystallite size refinement process of Cu powder
under mechanical treatment conditions. Based on the evidence that collisions represent the elementary events of energy transfer,
the rate of crystallite size decrease is related on a statistical basis to the amount of powder trapped at each collision,
to the number of collisions and to the collision energy. The mathematical approach allows for identifying the approximate
functional form of the kinetic curves obtained at largely different impact energies. The values of the apparent kinetic constants
and of the model parameters involved can be thus estimated by fitting the model curves to the experimental data. The results
obtained provide a deeper insight into the details of the crystallite size refinement process. 相似文献
993.
The equilibrium shape and dihedral angles at the solid–liquid–vapor tri-junctions of two-phase alloy small particles containing
a cusp-oriented interface were modeled as a function of phase fraction, surface energy and the interfacial energy. The calculation
was applied to different combinations of surface and/or interfacial energies to demonstrate the various possible particle
shapes and dihedral angles that result for two-phase particles. The dihedral angles at the tri-junction vary with the phase
fraction, due to the coupling between the relative amounts of each phase, interfacial energy relative to the two surface energies
and the equilibrium conditions at the tri-junction. These features can be used to find the ratio of the interfacial energy
to the surface energies of two-phase particles for any state of matter. 相似文献
994.
Reaction models are proposed to quantify the hydration products and to determine the composition of C–S–H from alkali-activated
slags (AAS). Products of the slag hydration are first summarized from observations in literature. The main hydration products
include C–S–H, hydrotalcite, hydrogarnet, AFm phases (C4AH13 and C2ASH8) and ettringite. Then, three stoichiometric reaction models are established correlating the mineral composition of slag (the
glass part) with the hydration products. Using the proposed models, quantities of hydration products and composition of C–S–H
are determined. The models are validated with a number of experimental investigations reported in literature, yielding good
agreement, i.e., these models can successfully predict the hydration reaction of AAS. The models are furthermore applied to
calculate the retained water in the hydration products of AAS in different hydration states and a general hydration equation
of AAS is derived. As an illustration to one of the model applications, chemical shrinkage of the AAS cement paste in different
hydration states are predicted. The chemical shrinkage of AAS is shown to be remarkably higher than OPC. Furthermore, phase
distribution in the hardened AAS paste and the porosity are calculated. 相似文献
995.
The effect of varying normalising and hardening temperatures on the prior austenite grain size in a low alloy Cr–Mo–Ni–V steel
has been examined. An initial relative insensitivity of grain size to increasing austenitising temperature was observed followed
by a sudden growth of grains at approximately 1000 °C. A detailed study of the precipitates in the steel showed the presence
of a bimodal size distribution of vanadium carbides. The grain size increase is attributed to a decrease in volume fraction
and an increase in size of V4C3 particles with increasing temperature. 相似文献
996.
V. Thomas Paul S. Saroja P. Hariharan A. Rajadurai M. Vijayalakshmi 《Journal of Materials Science》2007,42(14):5700-5713
This paper presents the results of a study on the microstructural and microchemical variations in a multipass Gas Tungsten
Arc weld (GTAW) of modified 9Cr-1Mo steel. The changes brought about in the steel due to the heating and cooling cycles during
welding and the subsequent effects due to reheating effects during multipass welding are described. Detailed analytical transmission
electron microscopy has been carried to study the type and composition of the primary and secondary phases in this steel.
The systematic changes in microstructural parameters such as Prior Austenite Grain Size, martensite lath size, number density,
size and microchemistry of carbides, have been understood based on the different transformations that the steel undergoes
during the heating and cooling process. Based on the observed microstructure, an attempt has been made to identify distinct
microstructural zones and possible thermal cycles experienced by different regions of the weldment. 相似文献
997.
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
998.
I. A. Ovid’ko 《Journal of Materials Science》2007,42(5):1694-1708
An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is
presented. The key experimentally detected facts on ductile and brittle fracture processes are discussed. Special attention
is paid to computer simulations and theoretical models of nucleation and growth of nanocracks and nanopores in deformed nanocrystalline
materials. Also, we discuss mechanisms for fracture suppression in such materials showing good ductility or superplasticity. 相似文献
999.
This article will review the development of the Fe–Ga (Galfenol) alloy system for magnetostriction applications including
work on substitutional ternary alloying additions for magnetic property enhancement. A majority of the alloying addition research
has focused on substitutional ternary elements in Bridgman grown single crystals with the intent of improving the magnetostrictive
capability of the Galfenol system. Single crystals provide the ideal vehicle to assess the effectiveness of the addition on
the magnetostrictive properties by eliminating grain boundary effects, orientation variations, and grain-to-grain interactions
that occur when polycrystals respond to applied magnetic fields. In almost all cases, ternary additions of transition metal
elements have decreased the magnetostriction values from the binary Fe–Ga alloy. Most of the ternary additions are known to
stabilize the D03 chemical order and could be a primary contribution to the observed reduction in magnetostriction. In contrast, both Sn and
Al are found to substitute chemically for Ga. For Sn additions, whose solubility is limited, no reduction in magnetostriction
strains are observed when compared to the equivalent binary alloy composition. Aluminum additions, whose effect on the magnetoelastic
coupling on Fe is similar to Ga, result in a rule of mixture relationship. The reviewed research suggests that phase stabilization
of the disordered bcc structure is a key component to increase the magnetostriction of Fe–Ga alloys. 相似文献
1000.
Nina Georgieva Kostova Elka Kraleva Alla A. Spojakina Erika Godocikova Peter Balaz 《Journal of Materials Science》2007,42(10):3321-3325
The Al-MCM-41 has been used as support to prepare Mo-containing catalysts. The 12- molybdophosphoric heteropoly acid (HPMo)
is used as initial compound. The catalysts are synthesized by two different methods: incipient impregnation with aqueous solution
of the acid and mechanochemical synthesis. The samples were tested in the reaction of the thiophene hydrodesulfurization after
activation with mixture H2 + H2S. The effect of the preparation method of the catalysts on their physicochemical and catalytic properties has been studied.
A partial destruction of the loaded compound is observed in mechanochemically treated sample whereas the aggregates are formed
from the particles of different size in the impregnated sample. The specific surface area of the sample prepared by mechanical–chemical
treatment decreases 2–3 times, while the total pore volume is about four times lower. The HDS activity is higher on the impregnated
sample than on the mechanochemically treated one. 相似文献