bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular‐Dynamics Simulation of Surface Phenomena
Authors: Rahman Talat S. 
Published: October 2003

AbstractMolecular‐dynamics (MD) simulation is a well‐developed numerical technique that involves the use of a suitable algorithm to solve the classical equations of motion for atoms interacting with a known interatomic potential. This method has been used for several decades now to illustrate and understand the temperature and pressure dependencies of dynamical phenomena in liquids, solids, and liquid‐solid interfaces.MD simulation techniques are also well suited for studying surface phenomena, as they provide a qualitative understanding of surface structure and dynamics. This article considers the use of MD techniques to better understand surface disorder and premelting. Specifically, it examines the temperature dependence of structure and vibrational dynamics at surfaces of face‐centered cubic (fcc) metals—mainly Ag, Cu, and Ni. It also makes contact with results from other theoretical and experimental methods.While the emphasis in this article is on metal surfaces, the MD technique has been applied over the years to a wide variety of surfaces including those of semiconductors, insulators, alloys, glasses, and simple or binary liquids. A full review of the pros and cons of the method as applied to these very interesting systems is beyond the scope of this article. However, it is worth pointing out that the success of the classical MD simulation depends to a large extent on the exactness with which the forces acting on the ion cores can be determined. On semiconductor and insulator surfaces, the success ofab initiomolecular dynamics simulations has made them more suitable for such calulations, rather than classical MD simulations.
Magnetism in Alloys
Authors: Pinski F.J. , Staunton J.B. , Razee S.S.A. , Johnson D.D. 
Published: October 2003

AbstractMagnetism in transition metal materials can be described in quantitative detail by spin‐density functional theory (SDFT). At low temperatures, the magnetic properties of a material are characterized in terms of its spin‐polarized electronic structure. It is on this aspect of magnetic alloys that is focused on here. From this basis, the early Stoner‐Wohlfarth picture of rigidly exchange‐split, spin‐polarized bands is shown to be peculiar to the elemental ferromagnets only. Shown are the origins of two commonly occurring features of ferromagnetic alloy electronic structures, and the simple structure of the Slater‐Pauling curve for these materials (average magnetic moment versus electron per atom ratio), can be traced back to the spin‐polarized electronic structure.The details of the electronic basis of the theory can, with care, be compared to results from modern spectroscopic experiment.Although SDFT is “first‐principled,” most applications resort to the local approximation (LSDA) for the many electron exchange and correlation effects. This approximation is widely used and delivers good results in many calculations.The LDA in magnetic materials fails when it is straightforwardly adapted to high temperatures. This failure can be redressed by a theory that includes the effects of thermally induced magnetic excitations, but which still maintains the spin‐polarized electronic structure basis of standard SDFT.Although not spin‐polarized “globally”—i.e., when averaged over all orientational configurations—the electronic structure is modified by the local‐moment fluctuations, so that “local spin‐polarization” is evident. A mean field theory of this approach and its successes for the elemental ferromagnetic metals and for some iron alloys are discussed. The dynamical effects of these spin fluctuations in a first‐principles theory remain to be included.Also emphasized is how the state of magnetic order of an alloy can have a major effect on various other properties of the system, and effect upon atomic short‐range order by describing case studies of NiFe,FeV, andAuFe alloys is dealt with at length. The results of our calculations with details of “globally” and “locally” spin‐polarized electronic structure are linked. The relativistic generalization of SDFT and covered its implication for the magnetocrystalline anisotropy of disordered alloys, with specific illustrations for CoPt alloys are discussed.In summary, the magnetic properties of transition metal alloys are fundamentally tied up with the behavior of their electronic “glues.” As factors like composition and temperature are varied, the underlying electronic structure can change and thus modify an alloy's magnetic properties. Likewise, as the magnetic order transforms, the electronic structure is affected and this, in turn, leads to changes in other properties. Here the focussed is the effect on ASRO, but much could also have been written about the fascinating link between magnetism and elastic properties—“Invar” phenomena being a particularly dramatic example.
Kinematic Diffraction of X Rays
Authors: Chen Haydn 
Published: October 2003

AbstractDiffraction by x rays, electrons, or neutrons has enjoyed great success in crystal structure determination. For a perfectly ordered crystal, diffraction results in arrays of sharp Bragg reflection spots periodically arranged in reciprocal space. Analysis of the Bragg peak locations and their intensities leads to the identification of crystal lattice type, symmetry group, unit cell dimensions, and atomic configuration within a unit cell. On the other hand, for crystals containing lattice defects such as dislocations, precipitates, local ordered domains, surface, and interfaces, diffuse intensities are produced in addition to Bragg peaks. The distribution and magnitude of diffuse intensities are dependent on the type of imperfection present and the x‐ray energy used in a diffraction experiment.Diffuse scattering is usually weak, and thus more difficult to measure, but it is rich in structure information that often cannot be obtained by other experimental means. Since real crystals are generally far from perfect, many properties exhibited by them are therefore determined by the lattice imperfections present. Consequently, understanding of the atomic structures of these lattice imperfections and of the roles these imperfections play is of paramount importance if these materials properties are to be exploited for optimal use.This article addresses the fundamental principles of diffraction based upon the kinematic diffraction theory for x rays. (Nevertheless, the diffraction principles described here unit may be extended to kinematic diffraction events involving thermal neutrons or electrons.). In practice, most x‐ray diffraction experiments are carried out on crystals containing a sufficiently large number of defects that kinematic theory is generally applicable.This article is divided into two major sections. In the first section, the fundamental principles of kinematic diffraction of x rays are discussed and a systematic treatment of theory is given. In the second section, the practical aspects of the method are discussed; specific expressions for kinematically diffracted x‐ray intensities are described and used to interpret diffraction behavior from real crystals containing lattice defects. Neither specific diffraction techniques and analysis nor sample preparation methods are described in this article.
Mechanical Testing
Authors: Abbaschian Reza 
Published: October 2003

Abstract
Basic mechanical property and materials strength measurements are obtained by standardized mechanical tests, many of which are described in this category. Each article in this category not only covers details, principles, and practical aspects of the various tests, but also provides comprehensive reference to the standard procedures and sample geometries dictated by the ASTM or other standards agencies. Also covered are additional mechanical testing techniques such as high‐strain‐rate testing, measurements under pressure, and tribological and wear testing. As such, the group of articles covers a broad spectrum of techniques used to assess materials behavior in a variety of engineering applications.
High‐Strain‐Rate Testing of Materials
Authors: Gray George T. (Rusty) 
Published: October 2003

Abstract
Experimental methods of probing material behavior at high rates of strain are concerned with measuring the variation of mechanical properties, such as strength and ductility, that can vary with strain rate. Interest in the high‐rate mechanical behavior of materials has continued to expand during the last four decades, driven by demands for increased understanding of material response in impact events. High‐rate tests also provide the data critically needed to create predictive constitutive model descriptions of materials. These descriptions strive to capture the fundamental relationships between the ways that each of the independent variables—stress, strain rate, strain, and temperature—independently affect the constitutive behavior of materials.

Measurements of the mechanical properties of materials are normally conducted via loading test samples in compression, tension, or torsion. Mechanical testing frames can be used to achieve nominally constant loading rates for limited plastic strains and thereby a constant engineering strain rate. Typical screw‐driven or servohydraulic testing machines are routinely used to measure the stress‐strain response of materials up to strain rates as high as 1 s
−1
. Specially designed testing machines, typically equipped with high‐capacity servohydraulic valves and high‐speed control and data acquisition instrumentation, can be used during compression testing to achieve strain rates as high as 200 s
−1
. Above this strain rate regime,

> 200 s
−1
, alternative techniques using projectile‐driven impacts to induce stress‐wave propagation have been developed.

Chief among these techniques is the split‐Hopkinson pressure bar, which is capable of achieving the highest uniform uniaxial stress loading of a specimen in compression at nominally constant strain rates of the order of 10
3
s
−1
. Stress is measured by using an elastic element in series with the specimen of interest. Stress waves are generated via an impact event and the elastic elements utilized are long bars such that the duration of the loading pulse is less than the wave transit time in the bar. Utilizing this technique, the dynamic stress‐strain response of materials at strain rates up to 2 × 10
4
s
−1
and true strains of 0.3 can be readily achieved in a single test.
Hardness Testing
Authors: Klansky Janice 
Published: October 2003

AbstractStatic indentation hardness tests such as Brinell, Rockwell, Vickers, and Knoop are frequently used methods for determining hardness. The basic concept utilized in all of these tests is that a set force is applied to an indenter in order to determine the resistance of the material to penetration. If the material is hard, a relatively small or shallow indentation will result, whereas if the material is soft, a fairly large or deep indentation will result.These tests are often classified in one of two ways: either by the extent of the test force applied or the measurement method used. A “macro” test refers to a test where a load >1 kg is applied; similarly “micro” refers to a test where a load of ≤1 kg of force is applied. Additionally, some instruments are capable of conducting tests with loads as light as 0.01 g and are commonly referred to as ultralight or nanoindentation testers. Rockwell and Brinell testers fall into the macro category, whereas Knoop testers are used for microindentation tests. Vickers testers are employed for both macro and microindentation tests. The measurement methods available include a visual observation of the indentation or a depth measurement of the indentation. Rockwell and some nanoindentation testers are capable of determining the depth of the indentation, whereas Brinell, Knoop, and Vickers testers require an indentation diameter measurement. These visual measurements can be automated, and are discussed.Hardness is not a fundamental property of a material, yet hardness testing is considered a useful quality‐control tool. Many properties are predicted from hardness values when combined with additional information such as alloy composition. The following is a list of such properties: resistance to abrasives or wear, resistance to plastic deformation, modulus of elasticity, yield strength, ductility, and fracture toughness. Some of these properties, such as yield strength, have numerical relationships with hardness values, whereas others such as fracture toughness are based on observations of cracks surrounding the indentations. Data analysis and conversions are discussed in detail.
Thermal Analysis
Authors: Dollimore David 
Published: October 2003

Abstract
Thermal analysis is the name given to the measurement of a sample as the sample is programmed through a predetermined temperature regime in a specified atmosphere.
This category of article presents a collection of thermal analysis techniques available for the characterization of the thermal properties of materials. The general nature of the available equipment along with the formal definitions, codes of practice, and nomenclature for each of the principal methods are described early. The most obvious property that can be measured against an imposed temperature regime is the sample mass; this is termed thermogravimetric analysis.
In addition to providing the materials scientist with information on the thermal stability and degradation products of a material under study, thermal analysis methods can reveal the phase properties, mechanical stabilities, thermal expansion coefficients, and electrical or magnetic properties as a function of temperature. While the temperature dependence of the various methods contained throughout this work is presented this category of articles compile the methods whose primary concern is the thermal properties and behavior of the material.
Thermal Analysis‐Definitions, Codes of Practice, and Nomenclature
Authors: Dollimore David 
Published: October 2003

Abstract

Those who practice the techniques of thermal analysis are well advised to notice and use the definitions, conventions, codes of practice, and methods of reporting data advocated by the International Confederation of Thermal Analysis and Calorimetry (ICTAC). These recommendations have been widely circulated and are to be found in the booklet
For Better Thermal Analysis
.

The recommended names and abbreviations of the various techniques in thermal analysis are listed. The classification of thermal analysis techniques is given. The definitions follow. The reporting of thermal analysis data is discussed. Publications on thermal analysis are listed.
Thermogravimetric Analysis
Authors: Dunn J.G. 
Published: October 2003

AbstractThe formal definition of thermogravimetry (TG is the preferred abbreviation, although TGA is also used) has been given by the Nomenclature Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC) as “a technique in which the mass of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature programme”.In the above definition, a controlled temperature program means heating or cooling the sample at some predetermined and defined rate. Although it is common to have just one constant heating or cooling rate, it is also advantageous in some cases to have different rates over different temperature ranges and in some cases even a varying rate over a specific temperature range.An apparatus called a thermobalance is used to obtain a thermogravimetric curve. By means of a thermobalance the temperature range over which a reaction involving mass change occurs may be determined.The sample is usually a solid, or more rarely a liquid.Thermogravimetric data can be presented in two ways. The TG curve is a plot of the mass against time or temperature, with the mass loss on the ordinate plotted downward and mass gains plotted upward relative to a baseline. Alternatively, data can be presented as a derivative thermogravimetric (DTG) curve, which is a plot of the rate of change of masswith respect to timeor temperatureagainst time or temperature. The DTG mass losses should also be plotted downward and the gains upward.Conventionally, thermal analysis experiments are carried out at a constant heating rate, and a property change is measured as a function of time. An alternative approach is to keep the change in property constant by varying the heating rate. For TG, the rate of mass loss is kept constant by variation in heating rate. To achieve this, the mass change is monitored and the heating rate decreased as the mass loss increases, and vice versa. At the maximum rate of mass loss, the heating rate is a minimum. This gives mass losses over very narrow temperature ranges and sometimes enables two close reactions to be resolved. This method has the advantage of using fast heating rates when no thermal event is taking place and then slowing down the heating rate when a mass change is in progress.Thermogravimetry does not give information about reactions that do not involve mass change, such as polymorphic transformations and double‐decomposition reactions. Also, it is not useful for identification of a substance or mixture of substances unless the temperature range of the reaction has already been established and there are no interfering reactions. However, when a positive identification has been made, TG by its very nature is a quantitative technique and can frequently be used to estimate the amount of a particular substance present in a mixture or the purity of a single substance. The types of processes that can be investigated by TG are given.
Combustion Calorimetry
Authors: O'Hare P.A.G. 
Published: October 2003

Abstract

In the absence of direct experimental information, one often must rely on a knowledge of thermodynamic properties to predict the chemical behavior of a material under operating conditions. For such applications, the standard molar Gibbs energy of formation

is particularly powerful; it is frequently derived by combining the standard molar entropy of formation

and the standard molar enthalpy of formation

often as functions of temperature and pressure. It follows, therefore, that the standard molar enthalpy of formation,

, is among the most valuable and fundamental thermodynamic properties of a material. This quantity is defined as the enthalpy change that occurs upon the formation of the compound in its standard state from the component elements in their standard states, at a designated reference temperature, usually (but not necessarily) 298.15 K, and at a standard pressure, currently taken to be 100 kPa or 101.325 kPa.

Many methods have been devised to obtain

experimentally. Those include the so‐called second‐ and third‐law treatments of Knudsen effusion and mass‐spectrometric results from high‐temperature vaporization observations, as well as EMF results from high‐temperature galvanic cell studies. Each of those techniques yields

for the studied process at a given temperature. To derive values of

, the high‐temperature results for

must be combined with auxiliary thermodynamic information (heat capacities and enthalpy increments at elevated temperatures).

Alternative procedures involve measurements of the enthalpies (or enthalpy changes) of chemical reactions,

, of a substance and the elements of which it is composed. Experimentally, the strategy adopted in such determinations is dictated largely by the chemical properties of the substance. The most obvious approach involves direct combination of the elements, an example of which is the combustion of gaseous H
2
in O
2
to form H
2
O. In the laboratory, however, it is often impossible under experimental conditions to combine the elements to form a particular compound in significant yield. An alternative, albeit less direct route has been used extensively for the past century or more, and involves measurements of the enthalpy change associated with a suitable chemical reaction of the material of interest. Here, the compound is “destroyed” rather than formed. Such chemical reactions have involved,
inter alia
, dissolution in a mineral acid or molten salt, thermal decomposition to discrete products, or combustion in a gas such as oxygen or a halogen. This last method is the the subject matter of this article.
Simultaneous Techniques Including Analysis of Gaseous Products
Authors: Dollimore David , Lerdkanchanaporn Supaporn 
Published: October 2003

AbstractThe concept of concurrently using two or more techniques of thermal analysis on a single substance has been promoted by advances in microprocessor control. This has made it possible to program and collect the data and process the information in many ways. Strictly speaking, the nomenclature “simultaneous” applied in such circumstance is not always correct. The mass change in thermogravimetry (TG) is generally the first signal received. The signal from the differential thermal analysis (DTA) probe will be received a little later as the heat has to diffuse through the sample and the crucible before reaching the sensing thermocouple. The sample is defined as the material (usually a solid) under investigation. Likewise, in evolved gas analysis (EGA), the gases are sampled but it then takes a finite time for the gas to be analyzed. In the mass spectrometer, there is an interface to allow the gas to be analyzed. In gas chromatography (GC), the signal of gas analysis takes considerable time to process, and consequently the gas analysis signal is intermittent and not received in “real time.”In common with all other thermal analysis techniques, the following parameters must be considered: the sample characteristics, its mass, the sample holder, the temperature range for study, the rate of heating, and the atmosphere.It must be remembered that a single thermal analysis method may not give the investigator sufficient information. Thus DTA will indicate if a transformation is exothermic or endothermic. It needs thermogravimetric analysis to indicate if there is mass change as well as gas analysis to identify any gaseous products involved.Although “simultaneous techniques” is the approved term used by the International Union of Pure and Applied Chemistry (IUPAC), the recommended nomenclature for such simultaneous techniques is to use a hyphen to separate the two techniques, e.g., TG‐DSC. This has led to such techniques being called “hyphenated” techniques.