Diffusion in Metals, Quasicrystals, and Intermetallic Compounds

1998 ◽  
Vol 527 ◽  
Author(s):  
H. Mehrer ◽  
Th. Zumkley ◽  
M. Eggersmann ◽  
R. Galler ◽  
M. Salamon
Keyword(s):  
Temperature Regime ◽  
Diffusion Problem ◽  
Solute Diffusion ◽  
General Mechanism ◽  
Repulsive Interaction ◽  
Transition Elements ◽  
Self Diffusion ◽  
Number Of Factors ◽  
Recent Developments ◽  
Exponential Factors

ABSTRACTIn this paper recent developments of diffusion in three related areas will be reviewed: The first part is devoted to self- and solute diffusion in metals with particular emphasis on Al. Contrary to most other metallic solvents, diffusion of transition elements in Al is anomalous in several respects: diffusion is very slow, activation enthalpies, pre-exponential factors and activation volumes are unusually high. By contrast, non-transition elements in Al show more or less normal solute diffusion behaviour. The anomalous behaviour is attributed to a strong repulsive interaction between transition metal solutes and vacancies. Ab-initio calculations could help to understand this well-documented diffusion problem in detail.In the second part very recent diffusion studies on single crystals of the Al-base quasicrystalline intermetallic compound Al-Pd-Mn will be discussed. Diffusion of Zn, Ge, Mn, Fe, Co, Pd and Au has been studied by various groups. At least in the high-temperature regime diffusion in the quasicrystal – despite some differences in detail – shows striking similarities to diffusion in Al, for which a vacancy-type mechanism is generally accepted. The activation volumes of +0.67 and +0.74 atomic volumes measured for Mn- and Zn-diffusion in Al-Pd-Mn strongly favour a vacancy mechanism as well. For the low temperature regime of Pd and Au diffusion the possibility of a phason-related mechanism is discussed.The third part deals with recent investigations of iron-aluminides and iron-silicides for which Fe self-diffusion and diffusion of selected foreign elements (Ge in Fe–Si, In and Zn in Fe–Al) has been investigated. There is no doubt that vacancies mediate the diffusion process. Within this general mechanism a number of factors like the crystal structure, the state of order, the composition, and the type of bonding have strong influence on diffusion. Such factors are discussed also in connection with results from positron annihilation and M6ssbauer spectroscopy.

scholarly journals New Developments in Understanding Harper-Dorn, Five- power Law Creep and Power-law Breakdown

2020 ◽  
Author(s):  
michael kassner
Keyword(s):  
Stress Exponent ◽  
Power Law ◽  
Dislocation Network ◽  
Creep Equation ◽  
Self Diffusion ◽  
Wide Range ◽  
Recent Developments ◽  
Initial Dislocation Density ◽  
Power Law Creep ◽  
Edge Dislocations

This paper discusses recent developments in creep, over a wide range of temperature, that mqy change our understanding of creep. The five-power law creep exponent (3.5 to 7) has never been explained in fundamental terms. The best the scientific community has done is to develop a natural three power-law creep equation that falls short of rationalizing the higher stress exponents that are typically five. This inability has persisted for many decades. Computational work examining the stress-dependence of the climb rate of edge dislocations we may rationalize the phenomenological creep equations. Harper-Dorn creep, “discovered” over 60 years ago has been immersed in controversy. Some investigators have insisted that a stress exponent of one is reasonable. Others believe that the observation of a stress exponent of one is a consequence of dislocation network frustration. Others believe the stress exponent is artificial due to the inclusion of restoration mechanisms such as dynamic recrystallization or grain growth that is not of any consequence in the five power-law regime. Also, the experiments in the Harper-Dorn regime, which accumulate strain very slowly (sometimes over a year) may not have attained a true steady state. New theories suggest that absence or presence of Harper-Dorn may be a consequence of the initial dislocation density. Novel experimental work suggests that power-law breakdown may be a consequence of a supersaturation of vacancies which increase self-diffusion.

Part III Where to Arbitrate? Distinctive Features of Maritime Arbitral Seats, 11 Maritime Arbitration in China: Strive for a Bigger Presence

2016 ◽  
Author(s):  
Yu Guo
Keyword(s):  
New York ◽  
Foreign Language ◽  
Ad Hoc ◽  
Standard Form ◽  
Chinese Mainland ◽  
Distinctive Features ◽  
Number Of Factors ◽  
Default Options ◽  
Recent Developments ◽  
Maritime Disputes

This chapter discusses recent developments in the resolution of maritime disputes in China. It explores the strengths and weaknesses of the litigation and arbitration services provided in arbitration centres on the Chinese mainland. Efforts to strengthen the appeal of arbitration in China have borne only modest fruit. This is due to a number of factors, including the wider accessibility of courts as compared to arbitration centres; the default options in standard form contracts adopted by BIMCO and others, which tend to refer to the centres in London, New York, and Singapore; and the lack of an ad hoc option in Chinese arbitration services. The tendency to arbitrate abroad can have significant consequences for Chinese companies, who have to make their case in a foreign language, following an unfamiliar procedure, and at a much higher cost than they would have to bear locally. The chapter concludes by proposing ways to address these issues.

scholarly journals Influence of Size and Construction Schedule of Massive Concrete Structures on Its Temperature Regime

2018 ◽  
Vol 251 ◽  
pp. 02014 ◽  
Author(s):  
Nikolay Aniskin ◽  
Chuc Nguyen Trong ◽  
Long Hoang Quoc
Keyword(s):  
Temperature Regime ◽  
Temperature Effects ◽  
Concrete Columns ◽  
Maximum Heat ◽  
Massive Concrete ◽  
Massive Structure ◽  
Number Of Factors ◽  
Maximum Heat Release ◽  
Maximum Temperatures ◽  
Construction Schedule

Cracking is an important problem in the process of building a concrete massive structure. The overwhelming majority of cracks occurring in the concrete are usually caused by temperature effects. Because of this, it is essential to control and regulate temperature, it is necessary to prevent cracking. The formation of the temperature regime of a massive structure is affected by a large number of factors: its size; cement consumption and its maximum heat release; temperature of the concrete to be laid; ambient temperature, etc. In this paper, we consider the influence of the size and construction schedule of a massive concrete structure on its temperature regime. Using the computer program Midas civil 2011, the temperature regime was calculated, maximum temperatures were obtained in massive concrete and massive concrete columns with different sizes. The analysis of possible fracture for different values of the factors are considered.

Mass Transport of Multicomponents Solute in Bentonite Clay

2000 ◽  
Vol 663 ◽  
Author(s):  
Y. Ichikawa ◽  
K. Kawamura ◽  
M. Nakano ◽  
K. Kitayama ◽  
N. Saito ◽  
...  
Keyword(s):  
Md Simulation ◽  
Chemical Species ◽  
Bentonite Clay ◽  
Diffusion Problem ◽  
Radioactive Waste Disposal ◽  
Inhomogeneous Material ◽  
Solute Diffusion ◽  
Diffusion Behavior ◽  
Molecular Behavior ◽  
High Level

ABSTRACTA fundamental concept combining a molecular behavior and macro-continuum phenomenon is presented for a multicomponent solute diffusion problem in bentonite clay, which is a key component of the Engineering Barrier System (EBS) of high-level radioactive waste disposal (HLRW). Bentonite is a micro-inhomogeneous material. Properties of the saturated bentonite are characterized by the constituent clay mineral (montmorillonite) and water, namely montmorillonite hydrate. We analyze its molecular behavior by applying a molecular dynamics (MD) simulation to inquire into the physicochemical properties such as diffusivity of chemical species. For extending the microscopic characteristics of constituent materials to a macroscopic diffusion behavior of the micro-inhomogeneous material we apply a homogenization analysis (HA).

Calculation of The Diffusion Parameters in an Ordered Ni3Al-Alloy for A Relaxed Lattice

1998 ◽  
Vol 527 ◽  
Author(s):  
C. Schmidt ◽  
J.L. Bocquet
Keyword(s):  
Activation Energy ◽  
Gradient Algorithm ◽  
Al Alloy ◽  
Self Diffusion ◽  
Barrier Heights ◽  
Diffusion Parameters ◽  
Exponential Factors ◽  
Diffusion Mechanisms ◽  
Body Potential ◽  
Semi Empirical

ABSTRACTUsing atomistic computer simulations, we calculate the diffusion parameters of an Ll2-ordered Ni3Al-alloy. A conjugate gradient algorithm under constant zero pressure and a semi-empirical N-body potential are applied to evaluate potential barrier heights and pre-exponential factors. We focus our investigation on those diffusion mechanisms that have been proposed to account for the experimentally observed but theoretically still disputed fast self-diffusion of Al in Ni3Al: antisite bridge mechanisms and correlated six-jump cycles. Our results demonstrate that the most competitive jumps or jump sequences involve AlNJ-antistructure atoms which are shown to play a key role in the diffusion process by either actively or passively lowering the activation energy of migration.

Uranium Diffusion in Metals Used in Nuclear Facilities - A New Approach

2017 ◽  
Vol 375 ◽  
pp. 3-17 ◽  
Author(s):  
Rodolfo A. Pérez
Keyword(s):  
Base Material ◽  
Formation Enthalpy ◽  
Nuclear Facilities ◽  
Normal Behaviour ◽  
Self Diffusion ◽  
The Matrix ◽  
Order Of Magnitude ◽  
Temperature Ranges ◽  
Exponential Factors ◽  
Similar Temperature

Diffusion at infinite dilution of U in metals, with particular emphasis in those used in nuclear facilities, is revisited. Early works present some particularities such as activation enthalpies lower than the vacancy formation enthalpy in the matrix, large differences with self-diffusion in the base material, up to four orders of magnitude differences between measurements performed by different authors in similar temperature ranges, etc. In particular U self-diffusion was qualified as abnormal when compared with other metals. Recent studies by means of α-spectrometry reveal a normal behaviour: activation enthalpies and pre-exponential factors similar to the self-diffusion one and diffusion coefficient values in the same order of magnitude than self-diffusion. The possible influence of short circuits, impurities and/or uncertainties in the techniques used in the early works is discussed in order to explain the differences obtained.

Socially Inclusive Processes: New Opportunities with New Media?

2012 ◽  
Vol 142 (1) ◽  
pp. 74-86 ◽  
Author(s):  
Robyn Penman ◽  
Sue Turnbull
Keyword(s):  
New Media ◽  
Conceptual Framework ◽  
Social Inclusion ◽  
Media Theory ◽  
Good Effect ◽  
Open Collaboration ◽  
Number Of Factors ◽  
Recent Developments ◽  
The Government ◽  
Inclusive Processes

The tools of Web 2.0 and its culture of open collaboration offer a number of new opportunities to individuals, communities and governments. At first glance, many of these opportunities appear to lend themselves to fostering socially inclusive practices, and the report of the Government 2.0 Taskforce in 2009 certainly claimed this. However, while there has been much discussion of social inclusion in policy terms, there has been little consideration of what it means in practice, and no evidence to link the efficacy of new media in enhancing that practice. We develop a conceptual framework to account for the practice of social inclusion, drawing on recent developments in media theory focused on the themes of hospitality and listening. This framework is used to analyse the government's Social Inclusion website and the online forum. Our analysis suggests new media may offer the potential for new opportunities for social inclusion, but there are a number of factors militating against these opportunities being taken up to good effect.

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