Fast-cooling

Amorphous or "plastic" sulfur is obtained by fast cooling of the crystalline form. X-ray studies indicate that amorphous sulfur may have a helical structure with eight atoms per spiral. Crystalline sulfur seems to be made of rings, each containing eight sulfur atoms, which fit together to give a normal X-ray pattern. 

Fig. 10.4. Room temperature microstructures in the Al + 4 wt% Cu alloy, (a) Produced by slow cooling from 550°C. (b) Produced by moderately fast cooling from 550°C. The precipitates in (a) are large and far apart. The precipitates in (b) are small and close together.

The polymer is liable to depolymerisation at temperatures just above T. In the case of pure polymer there is a tendency for the few spherulites to grow to sizes up to 1mm diameter. Spherulite size may be reduced by the use of nucleating agents and by fast cooling. 

Fumed silicas have an amorphous nature probably caused by the fast cooling during the manufacturing process. It is an important benefit because it does not cause silicosis. 

Figure 8.29 Entropy of a supercooled liquid and glasses formed by fast and slow cooling of this liquid (the different dashed lines). The short dashed line represents slow heating of a glass first prepared by fast cooling.

Metastable phases and equilibria may be obtained by fast cooling. 

The desorption of ions and neutrals into the vacuum upon irradiation of a laser pulse onto a surface proceeds as a jet-like supersonic expansion. [38] a small, but initially hot and very rapidly expanding plume is generated. [49] As the expansion is adiabatic, the process is accompanied by fast cooling of the plume. [38]... 

For example, at a ratio of molecular iodine to tetrathiatetracene (TTT) of 1 2, mixtures of iodides (TTT)i(I)i and (TTT)2(I)3 can be obtained on fast cooling. Slow cooling of the same component mixture in the same proportion leads to the single product (TTT)2(I)3. The latter is just the product that possesses metallic properties. Sometimes, even at nonstoichiometric ratio, salts of the 1 1 composition are formed. Interaction between TTF and TCNQ can be exemplified. To obtain the 2 1 composition, an indirect synthesis is appropriate. The synthesis is based on an exchange reaction of the following type ... 

The macromolecular nature provides an interesting feature of LC polymeric cholesterics, namely the possibility of obtaining monochromic films. Thus for polymeric liquid crystals the helix pitch is practically not altered with temperature below Tg, when a cholesteric phase is frozen in a glassy matrix (Fig. 23a). This implies that fast cooling of polymeric films from a mesomorphic state (shown with arrows) fixes their optical properties, which makes it possible to use them at ordinary temperatures as selective monochromic reflectors. On the other hand, such polymeric films display the extraordinary polarizing properties of cholesterics, i.e. the different absorption... 

The panel also examined samples irradiated at — 196°C. using various warming and cooling rates for texture variation. Some samples fast-cooled to — 196°C. were described as having a texture similar to dry turkey... 

In the fast cooling method, two different samples were heated and cooled very rapidly. The first was B2 (same composition in powder lamination method) the second was B4, obtained from B2 by sintering in an A1N BN powder bed. The surface of B2 was ground until 70% P-SiAlON was obtained before fast cooling treatment. Then, the specimens were inserted in a furnace with high-speed cooling. They were heated to 1600°C at a rate of 15°C/min and cooled rapidly by immediate removal from the furnace. 

Change in P-SiAION ratio in B1 sample ground up to 70% 0-SiAION content as a function of fast cooling. 

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