INDEX nucleation effects

Since the HDPE resin may have a refractive index similar to that of the film base resin, it may have a nucleating effect, and/or may disturb the normal crystallization of the film base resin, the clarity and the gloss of the film may be improved. In addition, since the HDPE resin may have a melt viscosity lower than that of the film base resin, may have a relatively soft surface, and may melt at about the same time as the film base resin, the extmsion will be easier without... 

Although the Langelier index is probably the most frequently quoted measure of a water s corrosivity, it is at best a not very reliable guide. All that the index can do, and all that its author claimed for it is to provide an indication of a water s thermodynamic tendency to precipitate calcium carbonate. It cannot indicate if sufficient material will be deposited to completely cover all exposed metal surfaces consequently a very soft water can have a strongly positive index but still be corrosive. Similarly the index cannot take into account if the precipitate will be in the appropriate physical form, i.e. a semi-amorphous egg-shell like deposit that spreads uniformly over all the exposed surfaces rather than forming isolated crystals at a limited number of nucleation sites. The egg-shell type of deposit has been shown to be associated with the presence of organic material which affects the growth mechanism of the calcium carbonate crystals . Where a substantial and stable deposit is produced on a metal surface, this is an effective anticorrosion barrier and forms the basis of a chemical treatment to protect water pipes . However, the conditions required for such a process are not likely to arise with any natural waters. 

The parameters indexed with a are connected with the nucleation step or other effects occurring only once per triple helix. Parameters denoted by s are related with the equilibrium constants of the propagation steps and are ordered to be independent of the position of the reacting chain segment. This implies that end effects are neglected. Since the same dependences are valid for AH° and AS, with the help of their chain length dependence we can determine AG by extrapolation up to 3 n - 2 = 0, and thus, a can be estimated it depends neither on temperature nor on the chain length. 

When the value of index ( ) is closer to 100%, it the more effective is the base to heterogeneous nucleation of inoculated metal. 

Figure 7.9 Effect of mean residence time on mean crystal size parameter i = bjg, the relative nucleation to growth order index)...

The value of for ammonium alum has been determined and the points in Fig. 12 for ammonium alum can be replotted as log g versus the reciprocal of log p jp). Surprisingly a straight line is obtained (Fig. 13), in agreement with the form of Eq. (12) when r is taken as effectively independent of p. This agreement may mean that the growth of patches takes place by Volmer nucleation. Volmer nucleation would only be necessary if the interface between the patch and the parent crystal were flat and parallel to a low index plane. Acock et al [( ), p. 510] mention that patches on ammonium alum and other hydrates tend to have crystallographic interfaces. The patches on chrome.alum appear to be hemispherical in shape two-dimensional nucleation would not be necessary for curved interfaces. 

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