Oxide melts viscosity

When sulphur is melted viscosity changes occur as the temperature is raised. These changes are due to the formation of long-chain polymers (in very pure sulphur, chains containing about 100 (X)0 atoms may be formed). The polymeric nature of molten sulphur can be recognised if molten sulphur is poured in a thin stream into cold water, when a plastic rubbery mass known as plastic sulphur is obtained. This is only slightly soluble in carbon disulphide, but on standing it loses its plasticity and reverts to the soluble rhombic form. If certain substances, for example iodine or oxides of arsenic, are incorporated into the plastic sulphur, the rubbery character can be preserved. 

Termination. The conversion of peroxy and alkyl radicals to nonradical species terminates the propagation reactions, thus decreasing the kinetic chain length. Termination reactions (eqs. 7 and 8) are significant when the oxygen concentration is very low, as in polymers with thick cross-sections where the oxidation rate is controlled by the diffusion of oxygen, or in a closed extmder. The combination of alkyl radicals (eq. 7) leads to cross-linking, which causes an undesirable increase in melt viscosity. 

Borides are relatively inert, especially to non-oxidizing reagents. They react violently with fluorine, often with incandescence. Reaction with other halogens is not as violent and may require some heat. Resistance to oxidation, acids, and alkalis is summarized in Table 17.5. In oxidation conditions, a layer of boric oxide is formed on the surface which passivates it to some degree. Boric oxide melts at 450°C and vaporizes at 1860°C. It offers good protection up to 1500°C in a static environments but it has low viscosity at these temperatures and tends to flow under stress and the protection it offers is limited.f k l... 

Melt-state testing, of polymers, 19 575 Melt-to-mold thermoforming, 18 49 Melt viscosities (MVs), 21 712-714 of ethylene oxide polymers, 10 680 of FEP resin, 18 306, 308 Membrane-based reactive separation processes, 15 848... 

Brings down the viscosity of a liquid polymer. Also, lowers the melt viscosity of a thermoplastic polymer. Thus it improves the workability and enhances the loading capability of a polymer with explosives, fillers or oxidizers. This is of special interest in the field of explosives or propellants where the amount of an explosive or oxidizer ingredient considerably increases leading to improvement in their performance. 

Oxidation during processing of polypropylene is principally accompanied by chain scission made evident by a reduction in melt viscosity. The oxidation during processing of polyethylene on the other hand is accompanied mainly by crosslinking. The following two tests are, therefore, used ... 

FIGURE 9.7 Melt viscosity stability of polyamide 6,6 containing Firebrake ZB vs. antimony oxide (PyroChek 68PBI is a brominated PS). 

Oxide melts on solid substrates. Contrary to metals for which the viscosity tj changes little with temperature or from one metal to the other, the viscosity of... 

Teramoto, a., and H. Fujita Temperature and molecular weight dependence of the melt viscosity of polyethylene oxide in bulk. Makro. Chemie 85, 261 (1965). 

The effects of composition and temperature on the viscosity of oxide melts suitable for use as casting fluxes is discussed. A relation to express the temperature dependence of viscosity for oxide melts based on the Clausius-Clapeyron Equation is evaluated, viz.,... 

Several recent publications have discussed the effects of compositional variables on the viscosity of oxide melts for use as mold fluxes. Lanyi ( 1) measured the viscosity of several continuous casting fluxes and found that the viscosity correlated well with the combined silica and alumina content of the flux. The fluxes... 

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