Fusion process

Figure 4.3b is a schematic representation of the behavior of S and V in the vicinity of T . Although both the crystal and liquid phases have the same value of G at T , this is not the case for S and V (or for the enthalpy H). Since these latter variables can be written as first derivatives of G and show discontinuities at the transition point, the fusion process is called a first-order transition. Vaporization and other familiar phase transitions are also first-order transitions. The behavior of V at Tg in Fig. 4.1 shows that the glass transition is not a first-order transition. One of the objectives of this chapter is to gain a better understanding of what else it might be. We shall return to this in Sec. 4.8. 

This notation indicates the contribution to the value for the fusion process (subscript f) per mole of repeat units (subscript 1). Entries are discussed by number in the text. 

Solid-State Welding. Sohd-state welding comprises a group of welding processes wherein a bond is made between two base materials upon the apphcation of pressure at a temperature below the soHdus of the base materials (Table 1). Interlayers are sometimes used. By joining materials in the sohd state, many of the difficulties of the fusion processes are avoided. 

In the commonly used Welland process, calcium cyanamide, made from calcium carbonate, is converted to cyanamide by reaction with carbon dioxide and water. Dicyandiamide is fused with ammonium nitrate to form guanidine nitrate. Dehydration with 96% sulfuric acid gives nitroguanidine which is precipitated by dilution. In the aqueous fusion process, calcium cyanamide is fused with ammonium nitrate ia the presence of some water. The calcium nitrate produced is removed by precipitation with ammonium carbonate or carbon dioxide. The filtrate contains the guanidine nitrate that is recovered by vacuum evaporation and converted to nitroguanidine. Both operations can be mn on a continuous basis (see Cyanamides). In the Marquerol and Loriette process, nitroguanidine is obtained directly ia about 90% yield from dicyandiamide by reaction with sulfuric acid to form guanidine sulfate followed by direct nitration with nitric acid (169—172). 

Oxidation of manganese dioxide to higher valence states takes place in the fusion process of Mn02 and KOH. A tetravalent manganese salt identified as K MnO [12142-27-7] (63) which disproportionates spontaneously is formed. 

Fusion Process. In the fusion process, also frequendy referred to as fusion cook, inert gas is continuously sparged from the bottom of the reactor to carry away water vapor from the reaction mixture. The exhaust is then either vented away or sent to a fume scmbber, which is frequendy a small vessel with water atomi2ing no22les. After the reaction is completed, the finished resin may be discharged, filtered, and packaged without solvent. More frequendy, it is cooled to a safe temperature, then dissolved in the desired type and amount of solvent in a thinning tank, filtered, and packaged, or pumped... 

The refluxing solvent provides a constant wash to the reactor and brings back reactants that had escaped from the reaction mixture. The reaction temperature is better controlled by the constant refluxing, and the viscosity of the reaction mixture is lower, which improves the effectiveness of the agitation. The product usually has better color and is more uniform than material made by the fusion process. Ordinarily, the reactor requires no more than... 

In this method, a metal oxide or hydroxide is slurried in an organic solvent, neodecanoic acid is slowly added, and the mixture is refluxed to remove the water. Salts that are basic can be prepared by using less than stoichiometric amounts of acid. This method has been used in the preparation of metal salts of silver (80) and vanadium (81). The third method of preparation is similar to the fusion process, the difference is the use of finely divided metal as the starting material instead of the metal oxide or hydroxide. This method has been appHed to the preparation of cobalt neodecanoate (82). Salts of tin (83) and antimony (84) have been prepared by the fusion method, starting with lower carboxyHc acids, then replacing these acids with neodecanoic acid. 

When calcium aluminate cements are made by the fusion process, the solidified melt must be cmshed and then ground. The material is very hard to grind and power consumption is high. 

MetaUic soaps are manufactured by one of three processes a fusion process, a double decomposition or precipitate process, or a direct metal reaction (DMR). The choices of process and solvent depend on the metal, the desired form of the product, the desired purity, raw material avadabihty, and cost. 

Fusion Process. In the fusion process, a metal oxide, carbonate, or hydroxide reacts with a carboxyUc acid at temperatures up to 230°C. Water is spht out and the resulting metal soap is solubilized ia a hydrocarbon solvent because the metal soaps themselves are generally hard, glassy, and difficult to gtind. 

In recent years, proprietary catalysts for advancement have been incorporated in precataly2ed Hquid resins. Thus only the addition of bisphenol A is needed to produce soHd epoxy resins. Use of the catalysts is claimed to provide resins free from branching which can occur in conventional fusion processes (10). Additionally, use of the catalysts results in rapid chain-extension reactions because of the high amount of heat generated in the processing. 

Schmelz-verfahren, n. melting process, fusion process smelting process, -warme, /. heat of fusion, -wasser, n. water from melting ice or snow, -werk, n. smeltery foundry enameled work. 

Strict control of the fusion process is imperative. In addition to thickness, hardness, continuity and adhesion checks, correct cure may be assessed by differential scanning calorimetry techniques, which are designed to measure any difference in the glass transition temperature of a laboratory-cured powder and the cured coating taken from the factory-coated pipe. 

There is no generally acceptable comprehensive theory of melting. A feature of the fusion process, which is usually regarded as important in theoretical treatments of the subject, is the inability of a solid to superheat, and only a very small number of exceptions to this generalization are known [2], This almost universal onset of liquefaction immediately upon reaching the melting point is in sharp contrast with the reverse process since supercooling of the vast majority of liquids can be demonstrated under appropriate conditions. 

Figure 13.1 Schematic illustrations of vesicle fusion process.

The artificial lipid bilayer is often prepared via the vesicle-fusion method [8]. In the vesicle fusion process, immersing a solid substrate in a vesicle dispersion solution induces adsorption and rupture of the vesicles on the substrate, which yields a planar and continuous lipid bilayer structure (Figure 13.1) [9]. The Langmuir-Blodgett transfer process is also a useful method [10]. These artificial lipid bilayers can support various biomolecules [11-16]. However, we have to take care because some transmembrane proteins incorporated in these artificial lipid bilayers interact directly with the substrate surface due to a lack of sufficient space between the bilayer and the substrate. This alters the native properties of the proteins and prohibits free diffusion in the lipid bilayer [17[. To avoid this undesirable situation, polymer-supported bilayers [7, 18, 19] or tethered bilayers [20, 21] are used. 

---