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1.
We analyze the effect of co-segregation on the mobility of grain boundaries within the framework of the impurity drag theory originally proposed by Cahn and Lücke and Stüwe for an ideal solution. The new derivation extends this model to the case where there are two types of impurities (or three components in the alloy). Since the resultant expression for the boundary mobility is complicated, numerical solutions were obtained for several cases to show how co-segregation affects the boundary mobility. Depending on the relative diffusivities of the two impurities which are both attracted to the boundary, the mobility may either increase or decrease with increasing concentration of one of the impurities. When one of the impurities is attracted to the boundary and the other repelled from the boundary, increasing the concentration of the attractive impurity can lead to a sharp decrease in the boundary mobility. 相似文献
2.
Summary We report on neutron emission in palladium and titanium electrolitically charged with deuterium. The detection of neutrons
is observed after thermal treatment of the electrode. In the hypothesis that neutrons came from cold fusion processes, we
estimate a fusion rate as high as 1.3·10−21 fusions/deuteron pair/second. 相似文献
3.
Utilizing forward recoil spectrometry (FRES), we have determined the segregation isotherm which describes the interfacial excess zi* of diblock copolymers of poly (d8-styrene-b-2-vinylpyridine) (dPS-PVP) at the interface between the homopolymers PS and PVP as a function of ?∞, the volume fraction of diblock copolymer remaining in the host homopolymer. All the samples were analyzed after annealing at temperatures and times sufficient to achieve equilibrium segregation. The effect of the degree of polymerization of both the diblock copolymers and the host homopolymers on the segregation isotherm is investigated. When the degree of polymerization of the homopolymer is much larger than that of the diblock copolymer, the normalized interfacial excess (zi*/Rg), where Rg is the radius of gyration of an isolated block copolymer chain, is a universal function of that portion of the block copolymer chemical potential due to chain stretching. The existence of such a universal function is predicted by theory and its form is in good agreement with self-consistent mean field calculations. Using these results, one can predict important aspects of the block copolymer segregation (e.g., the saturation interfacial excess) without recourse to the time-consuming numerical calculations. © 1994 John Wiley & Sons, Inc. 相似文献
4.
Bruce J. West Raoul Kopelman Katja Lindenberg 《Journal of statistical physics》1989,54(5-6):1429-1439
The conditions for macroscopic segregation ofA andB in a steady-stateA+B 0 reaction are studied in infinite systems. Segregation occurs in one and two dimensions and is marginal ford=3. We note the dependence of these results on the precise experimental conditions assumed in the theory. We also note the difference between these results and our earlier ones for finite systems where the critical dimension isd=2. 相似文献
5.
Atomistic simulations of segregation to (100) free surface in Ag–Au, Au–Pd, and Cu–Ni alloy systems have been performed for a wide range of temperatures and compositions within the solid solution region of these alloy phase diagrams. In addition to the surface segregation profiles, surface free energies, enthalpies, and entropies were determined. These simulations were performed within the framework of the free energy simulation method, in which an approximate free energy functional is minimized with respect to atomic coordinates and atomic site occupation. The effects of the relaxation with respect to either the atomic positions or the atomic concentrations are discussed. For all alloy bulk compositions (0.05 C 0.95) and temperatures (400 T(K) 1,100) examined, Ag, Au, and Cu segregates to the surface in the Ag–Au, Au–Pd, and Cu–Ni alloy systems, respectively. The present results are compared with several theories for segregation. The resultant segregation profiles in Au–Pd and Ag–Au alloys are shown to be in good agreement with an empirical segregation theory, while in Cu–Ni alloys the disagreement in Ni-rich alloys is substantial. The width of the segregation profile is limited to approximately three to four atomic planes. The surface thermodynamic properties depend sensitively on the magnitude of the surface segregation, and some of them are shown to vary linearly with the magnitude of the surface segregation. 相似文献
6.
Based on thermodynamic analysis of interfacial segregation, the segregation enthalpy H
o of a solute I in a given matrix was found to depend linearly on two mutually independent terms reflecting the type of interface and the solid solubility limit X
infI
sup*
at temperature T and can be written as In this equation, the structural dependence of interfacial segregation is contained in H
*() which corresponds to the extrapolated segregation enthalpy of a solute with unlimited solubility in the matrix. The product [Tln(X
infI
sup*
)] is essentially constant with temperature, and can therefore be obtained from data for maximum solid solubility, [Tln(X
infI
sup*
)]max. The parameter v>0 represents the relationship between the activity a
infI
sup*
of a solute at the bulk solid solubility limit in a given matrix and X
infI
sup*
, a
infI
sup*
=(X
infI
sup*
)
v
, and is characteristic for the matrix. Using recent experimental data for silicon, phosphorus, and carbon segregation at well-characterized grain boundaries in oriented bicrystals of -iron, the averaged value
was determined. Values of H
*() range from -8 kJ/mol (general grain boundaries) up to +8 kJ/mol (special grain boundaries). These values are discussed and used for a more precise and generalized construction of grain boundary segregation diagrams of -iron. 相似文献
7.
Manfred Leisch 《Mikrochimica acta》1992,107(3-6):95-104
The atom probe field ion microscope (AP-FIM) is a combination of a field ion microscope and a time-of-flight mass spectrometer with a single ion detection sensivity. With the field ion microscope topology of a surface, surface reactions and surface modifications can be studied in atomic detail. By time-of-flight measurements surface layers and interface layers can be chemically analyzed atom by atom and atomic layer by atomic layer. Compositional variations according to surface or interface segregation, precipitations, or surface changes in corrosion or in electrochemical layer formation etc. can be studied quantitatively on a subnanometer scale. Some of our studies on related problems will be decribed briefly. 相似文献
8.
利用金属有机物化学气相淀积(MOCVD)方法不同生长条件下在c面蓝宝石衬底上制备了InN薄膜,通过不同的物理表征手段研究了InN薄膜的物理性质,结果表明:合适的生长温度可以抑制InN薄膜表面分凝现象。研究认为较低的生长温度使作为N源的NH3分解率较低,In—N的成键可能性小,导致In在表面聚集出现分凝;而较高生长温度时,InN薄膜中In—N键能较小,易发生断裂,反应活性较强的N和H原子逸离薄膜表面,In滞留在薄膜表面也导致In分凝现象的出现。相对于表面分凝的样品,未出现表面分凝的样品的薄膜晶体质量和表面形貌也得到了提高。同时,通过Raman散射谱研究了晶格振动E2声子模的应力效应。 相似文献
9.
Abstract Solid solutions Ca1-xGdxF2+x for 3 × 10?7≤ x ≤10?1 have been studied by electron paramagnetic resonance (EPR) and ionic thermal currents (ITC). The EPR experiments show the presence of two single-ion sites a cubic and a tetragonal Gd3+ center which co-exist with comparable abundances for intermediate impurity concentrations. The cubic center predominates at very low and high concentrations. Seven different relaxation processes have been identified from the ITC spectra and the variation of their intensity vs. x was measured. The absolute concentrations of the cubic and nn Gd3+ dipoles were calculated. The scavenging of interstitial fluorines by the neutral clusters explains both the abundance of cubic sites at high concentration and the variety of orientable clusters detected by ITC. 相似文献
10.
The airborne transport of particles on a granular surface by the
saltation mechanism is studied through numerical simulation of
particles dragged by turbulent air flow. We calculate the
saturated flux qs and show that its dependence on the wind
strength u* is consistent with several empirical relations
obtained from experimental measurements. We propose and explain
a new relation for fluxes close to the threshold velocity ut,
namely, qs=a(u*-ut)α with α≈2. We
also obtain the distortion of the velocity profile of the wind due to the
drag of the particles and find a novel dynamical
scaling relation. We also obtain a new expression for the dependence of
the height of the saltation layer as function of the strength of the wind. 相似文献