Heterogenic materials

Thermal Conductivity. More information is available relating thermal conductivity to stmctural variables of cellular polymers than for any other property. Several papers have discussed the relation of the thermal conductivity of heterogeneous materials in general (187,188) and of plastic foams in particular (132,143,151,189—191) with the characteristic stmctural variables of the systems. 

Zvi Hashin, The Elastic Moduli of Heterogeneous Materials, Journal of Applied Mechanics, March 1962, pp. 143-150. 

List three heterogeneous materials not given in Section 5-2.1. 

The other major problem concerned with sampling is that of the sample size. The size of the sample taken from a heterogeneous material is determined by the variation in particle size, and the precision needed in the results of the analysis. 

Indeed, one often observes a more or less direct relationship between the rheological properties of melts and the mechanical strength of the condensed material. This is a commonplace statement in regard of, say, stiffness, since the equations relating the viscosity of heterogeneous materials with their composition... 

The median diameter is a measure of the general size level, whereas the standard geometric deviation is a measure of the degree of uniformity. A completely uniform material (all particles the same size) would show up as a horizontal line in Fig 3 and have a standard geometric deviation of 1,0. A completely heterogeneous material would be represented by a vertical line which would have a standard geometric deviation of infinity... 

The exposure of heterogeneous materials to humid environments induces different morphological changes of the polymeric structure, depending on the affinity and mode of sorption of the water. Moy and Karasz 16) presented sorption experiments of... 

The GA is a heterogeneous material having both hydrophilic and hydrophobic affinities. GA physicochemical responses can be handled depending on the balance of hydrophilic and hydrophobic interactions. GA functional properties are closely related to its structure, which determines, for example, solubility, viscosity, degree of interaction with water and oil in an emulsion, microencapsulation ability, among others. 

These models are discussed later in this chapter. The final subject is an introduction to moisture uptake in heterogeneous materials. 

The moisture uptake models we have discussed have been concerned with pure components. The deliquescing material could be a drug substance or an excipient material. In pharmaceuticals, however, mixtures of materials are also important. One possible situation involves mixing nondeliquescing and deliquescing materials that are formed into a porous tablet or powder blend. The obvious question is, Do the models for pure components apply to porous heterogeneous materials For pure components we have assumed that the mass and heat limiting transport... 

Sampling archaeological materials for analytical purposes may sometimes be the most difficult stage in an analytical procedure (Bellhouse 1980 Cochran 1977). Since rock, ceramics, and cement are heterogeneous materials, obtaining a representative sample of them may be the most difficult step in a whole analytical procedure. 

Figure 2.5 illustrates the state of affairs, and shows that heterogeneous material may be characterized by an inhomogeneous (C) or homogeneous (D) concentration function dependent on the relation between the total variation of concentration and the uncertainty of measurement on the one hand and the sample amount (or microprobe diameter in case of distribution-analytical investigations) on the other. 

Figure 3. Detail of the plane at 50 weight percent diblock content in Fig. 2 including various data points from previous studies (1, 4, 26J. Key > 1,41/1,4B O, 1,2B/1,4B solid points, homogeneous materials open points, heterogeneous materials half solid point, a blend for which contradictory results were obtained in various experimental modes (26).

The Murchison meteorite shown in Figure 6.7, like all meteorites, is named after the place from which it was recovered and in this case it is the town of Murchison, Victoria in Australia about 100 km north of Melbourne. The fall occurred in 1969 and was followed by an analysis of the chemical composition in some considerable detail. The Murchison meteorite is a carbonaceous chondrite containing about 2 per cent carbon, some as inorganic carbonates, and some as soluble compounds such as amino acids but the bulk as a macromolecular heterogeneous material referred to as kerogen. 

Magnetic Relaxation Dispersion in Porous and Dynamically Heterogeneous Materials... 

In general, sol-gel catalysts are heterogeneous materials employing solid-liquid or solid-gaseous interphases. A mobile and a stationary component penetrate each other at the molecular level with the catalytic species being well-defined, highly mobile and homogeneously distributed... 

It is clear from our knowledge of material science that the physical properties of materials are dependent upon the nature of the chemical bonding and also upon the type of defects which are present. Paper is a heterogeneous material and its properties are... 

S. Torquato, Random Heterogeneous Materials Microstructure and Macroscopic Properties,... 

Sample Size Another major problem associated with the sampling process is that of the sample size. In fact, the sample size withdrawn from a heterogeneous material is solely guided by two factors, namely ... 

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