Properties of Bulk Materials

The striking size-dependent colours of many nanocrystal samples are one of tlieir most compelling features detailed studies of tlieir optical properties have been among tire most active research areas in nanocrystal science. Evidently, tire optical properties of bulk materials are substantially different from Arose of isolated atoms of tire... 

Statistical mechanics is the mathematical means to calculate the thermodynamic properties of bulk materials from a molecular description of the materials. Much of statistical mechanics is still at the paper-and-pencil stage of theory. Since quantum mechanicians cannot exactly solve the Schrodinger equation yet, statistical mechanicians do not really have even a starting point for a truly rigorous treatment. In spite of this limitation, some very useful results for bulk materials can be obtained. 

In many cases of traditional tribology, friction and wear are regarded as the results of surface failure of bulk materials, the solid surface has severe wear loss under high load. Therefore, the mechanical properties of bulk material are important in traditional friction and wear. However, in microscale friction and wear, the applied load on the interactional surface is light and the contact area is also under millimeter or even micrometer scale, such as the slider of the magnetic head whose mass is less than 10 mg and the size is in micrometer scale. Under this situation, the physical and chemical properties of the interactional surface are more important than the mechanical properties of bulk material. Figure 1 shows the general differences between macro and micro scale friction and wear. 

Experiments using the DCC approach aimed at the discovery of improved phosphor materials have also been described. [9] In this case, samples are evaluated optically, an approach well suited to direct comparisons of large numbers of samples, although it is somewhat difficult to compare the results to the optical properties of bulk materials. Further spectroscopic evaluations of individual elements of the sample array are also easily accomplished by a variety of approaches including scanning fiber techniques. One concern in studies of phosphors is the sensitivity of the optical behavior including fluorescence intensity to processing effects such as details of the microstructure or surface preparation. 

Compositional homogeneity may strongly impact the observed properties of bulk material. Often the fact that Tc is a sensitive function of composition (the maximum Tc for BaPb1 xBixOs is observed at 13K (13) for x = 0.25, and a Tc of 34K is found for x =. 6 in Ba K BiOg (11)) means that the width of the resistive transition can be used to determine the uniformity of the product. Use of the resistive Tc onset to characterize these solid solutions, especially in bulk form can lead to errors due to stoichiometric nonuniformity. The results of Tomeno and Ando (50) who have reported that Tc remains constant at 29K for x values from 0.28 to 0.44 in Ba RbjjBiOg, are... 

This paper is a tutorial overview of the techniques used to characterize the nonlinear optical properties of bulk materials and molecules. Methods that are commonly used for characterization of second- and third-order nonlinear optical properties are covered. Several techniques are described briefly and then followed by a more detailed discussion of the determination of molecular hyperpolarizabilities using third harmonic generation. 

While our theoretical understanding of the NLO properties of molecules is continually expanding, the development of empirical data bases of molecular structure-NLO property relationships is an important component of research in the field. Such data bases are important to the validation of theoretical and computational approaches to the prediction of NLO properties and are crucial to the evaluation of molecular engineering strategies seeking to identify the impact of tailored molecular structural variations on the NLO properties. These issues have led to a need for reliable and rapid determination of the NLO properties of bulk materials and molecules. 

Of the thirty-two crystal classes, twenty-two lack an inversion center and are therefore known as non-centrosymmetric, or acentric. Crystalline and polycrystalline bulk materials that belong to acentric crystal classes can exhibit a variety of technologically important physical properties, including optical activity, pyroelectricity, piezoelectricity, and second-harmonic generation (SHG, or frequency doubling). The relationships between acentric crystal classes and physical properties of bulk materials are summarized in Table 9.1.1. 

The collective properties of bulk material typically reflect the behavior of tens of thousands of molecules in a volume of at least 106 A3 [123], The description of the electrostatic and response properties of such volumes is obviously beyond any discrete approach and one has to resort to experimental information, i.e., the dielectric constant. In the Introduction we argued that if sufficient solvation shells are included in a calculation, the effect of an enveloping continuum can be neglected. Nevertheless we give here, for completeness sake, an explicit formulation of the coupling between a set of point charges and polarizabilities and a dielectric continuum. 

Three kinds of properties are considered here rheological properties of solutions, properties of bulk materials and Uquid crystallinity. 

Synthesis, Structure, and Physical Properties of Bulk Material... 

Electric and thermal properties of bulk materials have been calculated to examine reliability of our calculation. Figures 2(a) and (b) indicate temperature dependence of calculated electron mobility for bulk Sio.7Geo.3 and PbTe, respectively. The mobility of SiGe is almost inversely proportional to temperature, while that of PbTe is almost proportional to T. It is notable that strong temperature dependence of PbTe, which is experimentally obtained, is successfully achieved. 

X ray processing is now a practicable and economically competitive technique. X ray processing is a relatively new irradiation method which can be used for various applications where greater penetration would be beneficial, such as sterilizing medical devices, preserving foods, curing composite structures and improving the properties of bulk materials. 

Many of the measured properties of bulk materials are dominated by structures at a scale somewhere between millimetres and micrometers, called the microstructure of the material (Figure 3.5c). For example, good-quality ceramics have a microstructure that is a mixture of crystallites in glass. Much of materials processing is centred on the production of the correct microstructure in the finished product. The architecture of older silicon chips were somewhere between macrostructure and microstructure. Modern chips have architecmre at a smaller... 

In general, one should not suppose that the properties of bulk materials will apply to materials at the nanoscale level. With respect to the mechanical properties of small-scale solids, it is known that the elastic behaviour, due to bond stretching and twisting, does not vary significantly in nanoparticles compared with that in the bulk. Other properties are more sensitive. For example, the rate of diffusion creep (Nabarro-Herring and Coble creep) is dependent on grain size. Hence, creep will be enhanced in compacts of nanoparticles and in thin films. 

In the final chapter of Part IV, we tackle a very new and exciting field called nanotechnology. In this area of study, the size and shape of materials is often of paramount importance. At the size scale of living matter (bacteria are 20 nanometers (nm) in size, DNA is 1-2 nm wide) inorganic chemists can make exquisite materials with near-atomic precision. The advantage of nanotechnology is realized in many different applications for example, it can be used to enhance catalytic processes, in biomedical applications, and to enhance the mechanical properties of bulk materials. 

The SAW device has potential for use in the characterization of polymeric materials. It has several advantages over existing methods, including small sample requirements (1 yg or less), sensitivity, versatility, and low cost. It must be stressed that these SAW data were collected using very thin films. The ability to extrapolate from thin film data to determine the properties of bulk materials must be verified by studying well-characterized materials. In addition, uniform, contiguous films and/or thicker films should be studied to aid in the identification of transition temperatures. 

Statistical mechanics is the mathematical means to extrapolate thermodynamic properties of bulk materials from a molecular description of the material [14]. Statistical mechanics computations are often performed at the end of ab initio calculations for gas-phase properties. For condensed-phase properties, often molecular dynamics calculations are necessary in order to do a computational experiment. Thermodynamics is one of the best-developed physical theories and it gives a good theoretical starting point for the analysis of molecular systems. 

The purpose of sampling is to estimate the amount or properties of bulk material. Samples are taken... 

In this chapter, the physical and mechanical properties of bulk M +iAX phases are summarized. The chapter is subdivided into six sections, in the first two of which the structure and bonding (including theoretical) characteristics of these materials are reviewed. Their elastic properties are summarized in Section 7.3., while in Sections 7.4 and 7.5 their electrical properties and thermal properties are reviewed, respectively. The mechanical properties are dealt with in Section 7.6. What is not detailed in this chapter are the MAX-phase thin films, for which several excellent groups, especially in Europe [6-9], have provided details. Another topic that has encouraged much activity, but which will not be reviewed here, is that of the processing of the MAX phases rather, at this point emphasis is placed on the properties of bulk materials. 

Table VI. Properties of bulk materials suitable for rapid evaluation by LCVD in the form of continuous, low diameter, single crystal fibers for ultrahigh temperature composites...

Polymerization of adsorbed monomers on solid surfaces results in the formation of ultrathin coating layers. Obtained thin polymer layers are attractive coating materials for many applications due to their wide range of chemical, mechanical, electrical, and optical properties that can be engineered to fit specific needs. Therefore, the GASP method is very suited to the modification of surface properties of bulk materials. 

Basing safety strategies on properties of bulk materials ... 

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