Materials science macroscopic properties

Since the macroscopic properties of a material are strongly dependent on its structure, studies of structure/property relationships are among the most important issues in material science. The properties of SiAlON ceramics are strongly influenced by their microstructure and chemical composition. 

There is at present available in the literature on polymers and on materials science a wealth of information regarding measurements of mechanical properties. These properties are dependent upon many relevant physical parameters and most measurements take this into account. There is also available a great deal of information regarding the relations between molecular structure and macroscopic physical properties and many calculations have been made. The bridge between these two extremes (the macro and the micro) is constructed primarily by the use of models of structure. 

An important objective in materials science is the establishment of relationships between the microscopic structure or molecular dynamics and the resulting macroscopic properties. Once established, this knowledge then allows the design of improved materials. Thus, the availability of powerful analytical tools such as nuclear magnetic resonance (NMR) spectroscopy [1-6] is one of the key issues in polymer science. Its unique chemical selectivity and high flexibility allows one to study structure, chain conformation and molecular dynamics in much detail and depth. NMR in its different variants provides information from the molecular to the macroscopic length scale and on molecular motions from the 1 Hz to 1010 Hz. It can be applied to crystalline as well as to amorphous samples which is of particular importance for the study of polymers. Moreover, NMR can be conveniently applied to polymers since they contain predominantly nuclei that are NMR sensitive such as H and 13C. 

The main goal in material science is to provide behaviour laws, i.e. to be able to predict the material properties under given conditions (mechanical, electrical, environmental conditions, temperature, etc.). This requires relating microscopic parameters and local mechanisms to macroscopic behaviours, as there is no other way to express such behaviour laws based on chemical-physical parameters. In other words, the study of materials requires a large part of microstructural observation and analysis. 

No textbook intended for inorganic materials science and engineering students of the twenty-first century could possibly be considered complete without covering nanomaterials (lnm= 10 A). Unfortunately, full justice cannot be done to this subject matter with a single chapter. It has been chosen, therefore, only to present a brief history of nanomaterials, explain why their properties differ from those of the macroscopic counterparts, and to introduce some of the more common preparative techniques. It is hoped that this will be sufficient to motivate the student to pursue further knowledge in this relatively young, but rapidly growing, field. 

Most mechanical tests developed for fats are empirical in nature and are usually designed for quality control purposes, and they attempt to simulate consumer sensory perception (3, 4). These large-deformation tests measure hardness-related parameters, which are then compared with textural attributes evaluated by a sensory panel (3, 5). These tests include penetrometry using cone, pin, cylinder and several other geometries (3, 6-12), compression (13), extrusion (13, 14), spreadability (15, 16), texture profile analysis (2), shear tests (13), and sectility measurements (14). These methods are usually simple and rapid, and they require relatively inexpensive equipment (3, 4, 17). The majority of these tests are based on the breakdown of structure and usually yield single-parameter measurements such as hardness, yield stress, and spreadability, among others (4, 17-20). The relationship between these mechanical tests and the structure of a fat has, however, not been established. The ultimate aim of any materials science endeavor is to examine the relationship between structure and macroscopic properties. 

In this chapter an explanation is presented of certain engineering aspects that are important in understanding the mechanical properties of wood. Individual factors such as growth, environment, chemicals, and use can greatly affect the physical and mechanical properties of the wood material. A theoretical model is presented to explain the relationship between physical properties and chemistry of wood at three distinct levels macroscopic or cellular, microscopic or cell wall, and molecular or polymeric. These three levels and their implications on material properties must be understood to relate both wood chemistry and wood engineering from a materials science standpoint. When this is accomplished, the treatment and processing of wood and wood products can be controlled to yield more desirable and uniform properties. 

Macroscopic properties of ceramic materials are often dominated by localized imperfections such as defects, impurities, surfaces and interfaces. Systematically-doped polycrystalline materials exhibit wider variety of properties as compared with monolithic single crystals. Some of them serve key roles in high-tech society and they are referred to as fine ceramics or advanced ceramics. An ultimate objective of the ceramic science and technology is to understand the nature and functions of the localized imperfections in order to achieve desired performances of materials intellectually without too much accumulation of empirical knowledge. 

In polymer science, an understanding of the relationship between microscopic structure and macroscopic properties is essential for an intelligent design of new improved materials. In this section, we present some case studies that illustrate the role which solid-state NMR can play with regard to the determination of the microscopic structure. It is first necessary to consider how solid-state NMR relates to other methods for structural determination, in particular the established scattering methods. For solids, for which a single crystal of suitable size can be obtained, the ability of X-ray or neutron diffraction methods to determine the complete three-dimensional structure with atomic resolution cannot be matched. 

The principles of spatial resolution and contrast in NMR imaging have been presented in this chapter. An overview of selected applications of NMR to investigations of fluid systems, technical elastomers and rigid polymers has been given. The examples chosen demonstrate the potential of NMR for measurement of macroscopic properties of polymer materials. The importance of developments of NMR methods and equipment for materials science applications was underlined by example of the NMR MOUSE. 

The field of material science is large and diverse. It encompasses many, very different, subjects. Some groups study how materials behave under stress and strain, or under pressure. Other groups manufacture materials that are hard to obtain, such as thin films or pure alloys, and measure properties of these materials. Yet other groups try to formulate theories for how the constituent atoms that make up the materials collaborate to produce the properties of the macroscopic samples that are used in everyday (and perhaps not so everyday) life, and use these models to make experiments with the help of computers. This gives a number of advantages in comparison to real experiments ... 

The directed, non-random, use of atoms and molecules by nanotechniques holds the promise for the production of smaller transistors and wires for the electronics and computer industries. Unusual material strengths, optical properties, magnetic properties, and catalytic properties may be achievable, Higher efficiencies of photo-electronic conversion would be a boon to mankind. There is hope that science will devise nanoparticles that destroy pathogens and repair tissues. See Impact 9.1 for discussion of SPM examination of atom positions on a macroscopic surface and for the current nanotechnological method for positioning atoms on a surface. See Impact 9.2 for discussion of nano-quantum dots that have unusual optical and magnetic properties. 

An underlying principle of materials science is that stmcture (on the atomic or microscopic scale) leads to properties (on the macroscopic scale of real world, engineering appfications). We have already seen that the natures of ceramics and glasses are very different because ceramics have a crystalline atomic arrangement and glasses are noncrystalfine. Similarly, transparent glass... 

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