Melt formation

Many nylon and polyester assemblies are configured so that there is a continuous progression from the melt formation of the polymer, and without hardening, the melted polymer is melt-spun into fibers. 

Thermotropic behaviour is observed in many polymers that contain rigid-rod units alternating regularly with relatively flexible spacer units. A first requirement for nematic melt formation is that the rigid-rod unit should exceed a certain length and length diameter ratio. The shortest rigid-rod unit so far reported 52) to permit nematic melt formation is... 

Ceramics with a wide sintering interval include, for instance, porcelain for which temperature variations within limits of about 20 ""C have little effect on the final properties. In contrast, for example, with cordierite ceramics a change in temperature of several degrees may damage the ware seriously as a result of excessive melt formation. 

Representation of a section across an advancing interface. Within the interface both chemical reactions and phase transformations may occur. In some decompositions, these processes may be spacially separated. The thickness of the interface may range from molecular dimensions (e.g. in topotactic reactions) to much larger distances when there is melt formation. 

Oxygen in the reaction vessel may influence kinetic behaviour by participating in these equilibria. There is also the possibility that changes in oxidation state of the cation may occur during the decomposition (e.g. FeS04 and CrSOJ. A number of sulfates (e.g. CaS04 and rare earth sulfates) decompose to yield intermediate oxysulfates. The possibility of melt formation before or during reaction cannot always be excluded and is a further factor that complicates the kinetic interpretations. 

It is important to note that both the liquid phase below 450" C and that above 715 C contain NaCl in dissolved form and are potentially highly corrosive. A rule of thumb stated earlier is that SCWO corrosion is highest at subcritical conditions because of ionic corrosion reactions, while at SCWO conditions ionic dissociation is largely absent and corrosion reactions are correspondingly diminished. This generalization does not hold for salt-water systems that are in a region of brine or melt formation, even though temperatures may be well above the critical temperature of water. 

Few studies have been made on transport processes involving concentrated solutions. In the concentrated solutions, in the range of dehydrated melt formation, incompletely hydrated melts and anhydrous salt melts, various structural models are described to define their properties, i.e. the free-volume model, the lattice-model and the quasi-crystalline model. Measured and calculated transport phenomena do not always represent simple ion migration of individual particles, but instead we sometimes find them to be complicated cooperative effects (27). 

Item (4) requires that the steam partial pressure be maintained at all times below the minimum value at which melt formation occurs—i.e.9 13 atm. This is achieved (Figure 1) by recycling the product gas. Likewise, it must be demonstrated that ash fusion is not a problem in the regenerator. 

Phase equilibrium studies were also conducted to obtain a better understanding of the melt formation which introduces important operability limits in the process. 

Melt Formation. The binary system CaO-Ca(OH)2 was studied to determine the equilibria in the following reactions ... 

Melt Formation. The equilibrium steam pressures for Reactions 12, 13, and 14 are shown in Figure 8. The eutectic in the binary system CaO-Ca(OH)2, is at 1454°F. and corresponds to the point where curves... 

In the liquid state (melt) antimony is fully soluble in lead. On cooling the melt, formation of an a-Pb solid—solution starts whose composition depends on temperature and Sb content in the melt. Figure 4.3 presents the equilibrium phase diagram of the Pb—Sb system [13]. It reflects the thermodynamic state of the system when the phases are in equilibrium. 

Fig. 2.43 Enthalpy of elinkering process 1, 3, 5, 7, P heating of raw mix, 2 dehydroxylation kaolinite, 4 decarbonisation of CaCOj, 6 mullite crystallization, 8 melt formation, 10 crystallization of clinker phases, 11 clinker cooling, 12 cooling of gaseous CO 13 eooling of water vapour...

Cause. Inadvertent withdrawal of control rods, leading to core melting, formation of hydrogen and a chemical explosion. 

Dense clinker structure, closed pore system Densification at temperature below melt formation (Fundal, 1980)... 

Klemm, W. A., Jawed, L, and Holub, K.J. (1979) Effect of calcium fluoride mineralization on silicate and melt formation in Portland cement clinker. Cement and Concrete Research 9,489-496. 

At temperatures well above 1000°C a melt starts to be formed, and this process is associated with a distinct shrinkage and loss of strength. The exact temperamre of melt formation will depend on the composition of the cement employed. It will increase with increasing AI2O3 content, whereas the presence of iron oxide has a negative effect on the temperature of melt formation. 

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