Pressurized melt growth method

All these samples, except No. 7, were powders of 5-7 /n grain size, which had been elutriated in toluene. Sample 7 was prepared by simple grinding in an agate mortar (this sample was used simply to check the presence of a second phase in a method for growing stoichiometric crystals from a melt which was enriched with mercury in order to establish an equilibrium vapor pressure durii growth). 

Solid state recrystallisation methods are particularly applicable to the elements and intra-rare earth alloys while melt growth techniques have found application for certain of the elements, but most particularly for intermetallic compounds use of the vapour-solid approach has been limited to the higher vapour pressure... 

Many solids occur in different crystal structures that from a thermodynamic point of view are distinct phases. Transitions from one solid phase into another one obey the same laws as do solid hquid phase changes, for example. Most solid-solid phase transitions occur at high temperatures and pressures, far from normal ambient conditions, so the modification of many materials we observe is only one of many possible structures. Sometimes, phase transitions in the sohd state prevent the apphcabihty of an otherwise desirable crystal-growth method. As an example, it should be remembered that the sohdification of a silica melt leads to the cristobalite modification of Si02 and not to the desired a-quartz modification. 

Most types of polymerizations can be performed in liquid and supercritical C02. The two major types of polymerizations, chain-growth and step-growth, have been demonstrated in C02. Reviews in the literature (Canelas and DeSimone, 1997b Kendall et al., 1999) have described numerous polymerizations in C02, many of which will not be discussed in this chapter. Since only amorphous or low-melting fluoropolymers and silicones show appreciable solubility at relatively mild temperatures and pressures (T< 100 °C, P<400 bar), only these two classes of polymers can be synthesized by a homogeneous polymerization in C02. All other types of polymers, including semicrystalline fluoropolymers and lipophilic or hydrophilic polymers, must be made by heterogeneous methods, such as precipitation, dispersion, emulsion, and suspension, since the polymers are insoluble in C02 (when T< 100 °C and P<400 bar). Some semicrystalline fluoropolymers and hydrocarbon polymers can be dissolved at more extreme temperatures and pressures and are discussed in Chapter 7 of this book. 

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