Crystalline component

Starch is made thermoplastic at elevated temperatures ia the presence of water as a plasticizer, aHowiag melt processiag alone or ia blends with other thermoplastics (192—194). Good solvents such as water lower the melt-transition temperature of amylose, the crystalline component of starch, so that processiag can be done well below the decomposition—degradation temperature. 

Typically, a semicrystalline polymer has an amorphous component which is in the elastomeric (rubbery) temperature range - see Section 8.5.1 - and thus behaves elastically, and a crystalline component which deforms plastically when stressed. Typically, again, the crystalline component strain-hardens intensely this is how some polymer fibres (Section 8.4.5) acquire their extreme strength on drawing. 

The retarding influence of the product barrier in many solid—solid interactions is a rate-controlling factor that is not usually apparent in the decompositions of single solids. However, even where diffusion control operates, this is often in addition to, and in conjunction with, geometric factors (i.e. changes in reaction interfacial area with a) and kinetic equations based on contributions from both sources are discussed in Chap. 3, Sect. 3.3. As in the decompositions of single solids, reaction rate coefficients (and the shapes of a—time curves) for solid + solid reactions are sensitive to sizes, shapes and, here, also on the relative dispositions of the components of the reactant mixture. Inevitably as the number of different crystalline components present initially is increased, the number of variables requiring specification to define the reactant completely rises the parameters concerned are mentioned in Table 17. 

Another possibility is that one of the reactants is particularly mobile, this is apparent in certain solid—gas reactions, such as the reduction of NiO with hydrogen, which is a well-characterized nucleation and growth process [30,1166]. Attempts have been made to use the kinetic equations developed for interface reactions to elucidate the mechanisms of reactions between the crystalline components of rocks under conditions of natural metamorphism [1167,1168]. 

The nature of the solidification process in these cements has received little attention. Rather, attention has focussed on the crystalline components that form in cements which have been allowed to equilibrate for some considerable time the nature of such phases is now quite well understood. Gelation is reasonably rapid for these cements and occurs within a significantly shorter time than does development of crystalline phases. The conclusion may be drawn that initial cementition is not the same as crystallization, but must occur with the development of an essentially amorphous phase. Reactions can continue in the amorphous gelled phase, but are presumably limited in speed by the low diffusion rates possible through such a structure. However, reactions are able to proceed substantially to completion, since in many cases X-ray diffraction has demonstrated almost quantitative conversion of the parent compounds to complex crystalline mixed salts, though several days or weeks of equilibration are required to bring this about. 

Na-cefazolin is instable in its amorphous state. Takeda [1.32J described a method to ensure complete crystallization in which micro crystalline Na-cefazolin were added to at 0 °C supersaturated Na-cefazolin solution, frozen and freeze dried. The product did not contain amorphous or quasi-crystalline components. 

Termine, J. D. and Posner, A. S. (1966). Infrared analysis of rat bone age dependency of amorphous and crystalline components. Science 153 1523-1525. 

ET40)/PET blends, and in the 100/0 wt% P(HB80-ET20)/PET blend. This is because of either (a) a high content of rigid rod-like liquid crystalline component, or (b) an enthalpy which was too small to detect. The dependence of Tg on the blend composition can be evaluated by using the Gordon-Taylor Equation [37],... 

The lattice energy of an ionic crystal is the amount of energy required at absolute zero temperature to convert one mole of crystalline component into constituent ions in a gaseous state at infinite distance. It is composed of the various forms of energies, as shown above. The calculation is in fact somewhat more complex because of the presence of various ions of alternating charges in a regular tridimensional network. 

Table 3.5 Comparison of simple additivity of oxide constituents (column II) and exchange method of Helgeson et al. (1978) (column I), as methods of estimating heat capacity for crystalline components. Experimental values are shown for comparison in column III. Lower part of table adopted exchange reactions (for which it is assumed that ACp reaction = 0). Data in J/(mole X K) (adapted from Helgeson et ah, 1978).

The molar enthalpy of molten components in the standard reference conditions of r = 298.15 K and P = bar is usually obtained indirectly, by adding first the molar enthalpy of fusion to the molar enthalpy of the crystalline component at its melting point (see also figure 6.10) ... 

Table 6.13 Thermodynamic parameters of crystalline components in Ghiorso-Carmichael model. Heat capacity function Cp = Ki + K2T + K2.T +...

For a given value of P, there is only one T condition at which equation 6.90 is satisfied. Hence, once the activity of the component in the two phases is known, the P-Ploci of equilibrium are also known. This concept can be generalized for solid phases whose crystalline components (M) are stoichiometric combinations of melt components (C) according to... 

Introducing the masses of exchanging isotopes (m and m°, respectively), the ratio of partition functions for crystalline components can be related to that of the primitive unit cell (Kieffer, 1982), thus defining reduced partition function ratio / (whose formulation is equivalent to that obtained by Bigeleisen and Mayer, 1947, and Urey, 1947, for gaseous molecules) ... 

Fig. 2.18 illustrates the nature of the intensity profiles in pure polyetheretherke-tone (PEEK) and carbon fiber reinforced PEEK composites in the transmission and reflection modes, respectively. The quenched amorphous and slowly cooled crystalline components from PEEK can be separated. The three prominent diffraction peaks from the crystalline components in Fig. 2.18(a) correspond to the three uniform rings which can be detected in X-ray photographs. In contrast, no clearly measurable signal is identified from the PEEK amorphous phase independent of the carbon fiber content. 

Neither catalyst showed any evidence of crystalline components by X-ray diffraction. The permanganate on silica gel apparently remains as permanganate. The permanganate on activated carbon appears from the spectrum to have been reduced to Mn02 or to some other hydrous manganic oxide. 

The majority of samples (15 out of 23) were shown to contain no or less than ca. 2 vol% of crystalline inclusions and have a low specific surface area (5spec = 300-600 cm2/g for material ground to 100-125 pm) these samples are considered to be vitreous. The other samples contain higher amounts of crystalline components, either homogeneously or heterogeneously dispersed in a vitreous matrix they are considered to be vitrocrystalline (labelled with an asterisk) and are expected to exhibit a lower resistance to corrosion because of their higher specific surface area. The latter typically varies between 400 and 1000 cm2/g, but may be as high as 8200 cm2/g. None of the HT materials studied was entirely crystalline. 

Although the role of crystalline phases in the leachability of HT materials is unclear and must be examined from case to case, the identified silicates and oxides are overall more resistant to corrosion than silicate glass and residues of incineration (Scholze 1991). Thus, a clear assessment of the durability of HT materials as a function of crystalline components must take into account the combined effects of their enrichment or depletion in trace metals, their individual leachability, the increase (but sometimes decrease) in overall reactivity due to local heterogeneities and increased Sspec (Jacquet-Francillon et al. 1982 Bickford Jantzen 1984 Jantzen Plodinec 1984 Scholze 1991 Adams 1992 Sproull et al. 1994 Sterpenich 1998). 

Figure 2. Glow curves of various polyethelenes with different ratios of crystallinity-amorphous components. Temperature rises from left to right. Peaks 0, y, where a is caused hy crystalline component, and y by amorphous...

D>. Referring to Column 5, Table II, it is seen that Dmln for the glass population is 4.6/, and Dmax for the crystalline population is 37/. If we take 6 a equal to the particle size range and use subscripts 1 and 2 to denote glass and crystalline components respectively, then... 

---