Formation of glasses

Alumina trihydtate is also used as a secondary flame retardant and smoke suppressant for flexible poly(vinyl chloride) and polyolefin formulations in which antimony and a halogen ate used. The addition of minor amounts of either zinc borate or phosphoms results in the formation of glasses which insulate the unbumed polymer from the flame (21). 

Unsaturated polyesters The formation of the coating occurs in situ by the reaction between polyester resin and styrene, activated by a catalyst such as organic peroxide. The main use as coatings is in the formation of glass fiber or glass flake, reinforced plastics. 

C. A. Angell, Formation of glasses from liquid and biopolymers, Science, 267, 1924 (1995). 

Zone melting is a possibly generic approach to IL purification. The solidification of ILs often resulfs in the formation of glass. However, it is possible to determine/choose conditions under which single crystals of ILs with a melting point down to -25°C (but not all) can be grown [39]. Where crystallization is seen, then separation of impurities can be demonstrated. 

Absorption of hydrogen by titanium metal above 400 °C gives a solid whose stoichiometry approaches TiH2, but a true dihydride does not appear to exist. This hydride has been used for the formation of glass-to-metal and ceramic-to-metal seals.1 Thermal desorption above 600 °C provides a source of very pure hydrogen.2... 

However, in materials consisting of large molecules (e.g., polymers) or covalently bonded liquids (e.g., siliceous materials), the growth rate may be controlled by the rate at which the molecules can assemble into crystalline form. In this case crystallization may be suppressed with the resulting formation of glass (see Chapter 15). 

Zachariasen and co-workers formulated four requirements for formation of glass from oxides. The requirements are ... 

The formation of glass is a kinetically controlled phenomenon and is directly associated with atomic or ioiric diffusion within the melt. This controls the formation and growth of microcrystals when the temperature of the liquid reaches the solidus line (i.e. the crystallization temperature). 

One of the very important processes for the formation of glasses and ceramics is the sol-gel process. The first publications, by Ebetmen, appeared in 1844. The focus until today has been on the preparation of silicate ceramics. Mostly alcoxysilanes such as Si(OR)4 (R = CHj, CH2CH3,. ..) or RSi(OR)3 are used as molecular precursors. Remarkably, sol-gel processing allows for the formation of ceramic bulk materials, fibers, and coatings. ... 

Above 2000°F the authors observed the presence of beta-alumina. In the higher alumina products, the amount was still on the increase at the highest test temperature. Unexplainably the quantity of beta-alumina decreased above the 2300°F in the 70% alumina sample. Furthermore, a decrease in beta-alumina occurred above this temperature in the superduty product. This was due to the increased formation of glass. The magnitude of these decreases was not discussed by the authors. However, their plot of relative XRD peak intensity vs. temperature clearly indicates that the decrease is greater for the 70% alumina product than the superduty sample. 

One of the chemical reactions that occurs in the formation of glass is the combining of calcium carbonate (CaCOf) and silica (Si02) to form calcium silicate (CaSiOj) and carbon dioxide (CO2) ... 

Fig. 3. Arrhenius plot of the viscosity of several supercooled liquids. The horizontal dotted line, where the viscosity reaches 10 P, is commonly used as a definition of the glass transition. (Reprinted with permission from C. A. Angell. Formation of glasses from liquids and polymers. Science (1995) 267 1924. Copyright (1995), American Association for the advancement of Science.)...

Evidently in such multi-component glasses of simple halides, significant lowering of the eutectic temperatures and of course, the confusion principle, together assist formation of glasses. 

Figure 2. Schematic representation of the specific volume Vsp of a glass-forming liquid as a function of temperature T. The dependence of the glass transition temperature Tg on the cooling rate is shown. A slower cooling rate was applied for the formation of glass 2 as compared to that of glass 1. (This figure is reproduced from Ref. 11.)...

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