Primary amorphous phase

Although Equation (4) is conceptually correct, the application to experimental data should be undertaken cautiously, especially when an arbitrary baseline is drawn to extract the area under the DSC melting peak. The problems and inaccuracy of the calculated crystallinities associated with arbitrary baselines have been pointed out by Gray [36] and more recently by Mathot et al. [37,64—67]. The most accurate value requires one to obtain experimentally the variation of the heat capacity during melting (Cp(T)) [37]. However, heat flow (d(/) values can yield accurate crystallinities if the primary heat flow data are devoid of instrumental curvature. In addition, the temperature dependence of the heat of fusion of the pure crystalline phase (AHc) and pure amorphous phase (AHa) are required. For many polymers these data can be found via their heat capacity functions (ATHAS data bank [68]). The melt is then linearly extrapolated and its temperature dependence identified with that of AHa. The general expression of the variation of Cp with temperature is... 

In the course of cooling commercial aluminosilicate fly ash, phase separation is often followed by partial crystallization of the alumina-rich amorphous phase. Primary crystallization at... 

On dehydration of sodium dihydrogen monophosphate in a normal atmosphere it first passes over completely to the acid diphosphate, Na2H2P207, without forming amorphous phases. From this at temperatures above 240°C trimetaphosphate I and Maddrell s salt are formed in proportions which appear to depend in the first place on the water vapor pressure 229). Usually the low-temperature form of Maddrell s salt is the primary prod-... 

According to a dynamic mechanical study by Saba, Sauer, and Woodward (1963) for PPO and a dilatometric study by Daane and Barker (1964) for cellulose acetate, the high-temperature relaxations of PPO, CDA, and CTA are primary relaxations which arise from segmental motion in the amorphous phase and the low-temperature relaxations are presumably ascribed to a more local motion in the amorphous phase. 

Plasticized PVC has the same structures as rigid PVC, except that plasticizer enters the amorphous phase of PVC and makes the he molecules elastomeric. The grains break down to l- rnr primary particles winch become the melt flow units. The crystallites are not destroyed by plasticizer. Table 2 provides a list of the PVC physical parameters. 

Here Dv is the volume diffusion coefficient of the solute atoms and C, is the solute content of the residual amorphous phase (C, C0 at an early stage of primary crystallization). Here, dr/df is proportional to f1/2 and the growth rate decreases progressively with time. An in-situ time-resolved x-ray... 

It has therefore been concluded that (i) the most common process of zeolite nucleation relies on a primary nucleation mechanism and (ii) the most probable primary nucleation mode is heterogeneous and centred upon the amorphous phase of the reaction mixture (which for most clear solution syntheses is colloidal in nature). 

The non-equilibrium condition of most groundwater systems with respect to many primary minerals, or similarly the metastability which exists with respect to many semi-crystalline or amorphous phases are common problems, especially for silicates. Some clear identification is needed for system reaction time, or the rate at which equilibrium is approached, and similarly identification is needed for metastable plateaus of pseudo-equilibrium, especially for compounds such as amorphous silica, cristobalite, quartz, clay minerals, etc. The likely magnitude of saturation indices which could apply to a given mineral could be specified for a variety of conditions. In this volume, Glynn, and elsewhere others, have recently shown that some error occurs in the calculated saturation values for trace elements when pure end member minerals are assumed to be present, when actually the phases are solid solutions. The consensus among modelers appears to be that error is present and significant the challenge is to develop procedures that quantify the error, so models become tools that provide realistic and interpretable results. 

In some cases, a primary consideration in freeze drying is the production of the amorphous phase of the drug so that rapid and complete... 

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