Morphology examples

Fig. 6. TEM micrographs of apatite crystals in burned bone (a) at the outside showing higher crystal size and a polygonal apatite morphology, (b) at the inside of the sample with smaller crystal size with an irregular or acicular morphology. Example burned bone from HK layer, station 19 of Chalain lake. (Reproduced by permission of I. Reiche et a/., J. Trace Microprobe Tech. 20 (2) (2002) 211-231.)...

Nucleation sites, preferential (film formation) Positions on a surface that have a high chemical reactivity and will react with mobile adatoms more readily than most of the surface. The site may be due to chemistry or morphology. Examples Steps in the surface providing a high coordination at the base of the step inclusion of tin in one surface of float glass. 

There are also more complex virus assemblies where the capsid is neither purely helical, nor purely icosahedral, presenting a combination of icosahedral and heUcal shape. Extra features may be present, like a complex outer wall or a head-tail morphology. Examples of viruses with a complex structure are (i) the variola virus (which causes smallpox) presenting a unique outer wall and capsid (Fig. 15.1C) and (ii) bacteriophages, which (most of them) present a head-tail morphology structure—this is unique to viruses that only infect bacteria (Fig. 15.1D). 

Qualitative examples abound. Perfect crystals of sodium carbonate, sulfate, or phosphate may be kept for years without efflorescing, although if scratched, they begin to do so immediately. Too strongly heated or burned lime or plaster of Paris takes up the first traces of water only with difficulty. Reactions of this type tend to be autocat-alytic. The initial rate is slow, due to the absence of the necessary linear interface, but the rate accelerates as more and more product is formed. See Refs. 147-153 for other examples. Ruckenstein [154] has discussed a kinetic model based on nucleation theory. There is certainly evidence that patches of product may be present, as in the oxidation of Mo(lOO) surfaces [155], and that surface defects are important [156]. There may be catalysis thus reaction VII-27 is catalyzed by water vapor [157]. A topotactic reaction is one where the product or products retain the external crystalline shape of the reactant crystal [158]. More often, however, there is a complicated morphology with pitting, cracking, and pore formation, as with calcium carbonate [159]. 

Lamellar morphology variables in semicrystalline polymers can be estimated from the correlation and interface distribution fiinctions using a two-phase model. The analysis of a correlation function by the two-phase model has been demonstrated in detail before [30,11] The thicknesses of the two constituent phases (crystal and amorphous) can be extracted by several approaches described by Strobl and Schneider [32]. For example, one approach is based on the following relationship ... 

The physical structure of a surface, its area, morphology and texture and the sizes of orifices and pores are often crucial detemrinants of its properties. For example, catalytic reactions take place at surfaces. Simple... 

In some cases it may be advantageous to deviate from the classical technology. For example, in wet-chemical preparation better chemical and morphological control may be achieved by starting from salt solutions. 

A weU-known feature of olefin polymerisation with Ziegler-Natta catalysts is the repHcation phenomenon ia which the growing polymer particle mimics the shape of the catalyst (101). This phenomenon allows morphological control of the polymer particle, particularly sise, shape, sise distribution, and compactness, which greatiy influences the polymerisation processes (102). In one example, the polymer particle has the same spherical shape as the catalyst particle, but with a diameter approximately 40 times larger (96). 

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