Sulfur melting curve

The melting curve of sulfur with respect to metastability and experimental procedures has been critically analyzed by Vezzoli and Walsh [194]. The authors also discussed the previously reported phase boundaries of the sohd high-pressure allotropes in the range up to 4 GPa and from room temperature up to about 670 K [132]. However, the structures of these high-pressure polymorphs are unknown and their probability to exist under equilibrium conditions is still awaiting confirmation. 

Under higher pressures, liquid sulfur shows several additional transitions [195]. Near the melting point at 12 GPa and 1100 K, the melt transforms to a metallic liquid state the pressure of metallization being much lower than in the solid state (-80-90 GPa at room temperature) [196]. The most reliable critical points in the vicinity of the melting curve of sulfur are listed in Table 24. 

Selenium and tellurium have the A8 helicoidal zigzag chain structure at ambient conditions (1). Both show maxima in their melting curves at about 50 kb at 963°K for selenium (32) and at an average p-T of about 12 kb at 743°K (22, 29, 33, 34, 35) for tellurium. These maxima are suspected to be related to the maximum in the melting curve of sulfur at 86 kb at 953°K (12) because at these conditions the sulfur polymorph... 

Gaudette and Coatney [115] reported that primaquine phosphate was unstable when subjected to dry heat of 100 °C in the presence of sodium chloride for 24 h, when boiled in water for 24 h and when heated for 24 h at 100 or 200 °C in melted hydrogenated vegetable oil. These findings exclude the use of primaquine phosphate as a salt additive in cooking. Primaquine phosphate was isolated from the test preparations at alkaline pH by extraction into ethylene chloride, after which primaquine phosphate was returned to an aqueous phase by shaking with 0.1 N sulfuric acid the concentration of primaquine phosphate was then determined spectrophotometrically. The ultraviolet absorption curve of primaquine phosphate has maxima at 224, 266, 282, and 300 nm, and minima at 216, 250, 276, and 310 nm. A solution containing 10 yl/mL has an optical density of 0.375 at 282 nm optical densities were proportional to concentrations. 

Sometimes a transition between two crystalling phases occurs vei7 rapidly. That between orthorhombic sulfur and monoclinic i ulfur is rather slow, however, taking minutes or hours, and it is hence easy to superheat orthorhombic sulfur by heating it rapidly. If-this is done, the vapor pressure of the crystals increases as shown by the curve A, and at the point IP, where this curve crosses the vapor pressure curve of the liquid, the crystals melt. The temperature at P, 112.8° C, is... 

The DTA curve of sulfur, as recorded by Chiu i 2k is shown in Figure 7.22. The enantiotropic change from the rhombic to the monoclinic form is indicated by the 113CC peak, while melting was observed during the 124°C peak. Further transformations in liquid sulfur were observed at 179°C, and finally the boiling peak at 446°C. 

The flow behavior of molten macromolecular substances is generally quite different from that of low-molecular-weight compounds. This is obvious, for example, from the shape of the flow curves. Moreover, flow orientation can be observed. In ideal liquids (water, glycerol, sulfuric acid, etc.), the viscosity is a characteristic quantity which does not depend on the shear rate y ( Newtonian flow ) if the shear force x is plotted vs. y, a straight line is obtained with slope "q (Newtonian viscosity). Macromolecular melts behave differently since their melt... 

The melt processing characteristics of dynamic vulcanized HDPE/NR/TPS blends have been studied from the processing torque-time curve. Figures 10.1(a) and (b) show the processing torque of the melt mixed sulfur and... 

In the linear viscoelasticity regime, the principle of time-temperature superposition that was developed for polymer melts seems to work equally well for unfilled elastomers. Data of /(co), / ( )), and values of tan 5 = / (co)//(cl)) versus co for butyl rubber vulcanized with sulfur to various extents over a wide range of temperature (from -25°C to 50°C) were shown separately to collapse on master curves with a temperature shift factor a-j- obeying the general form of the WLF equation. Figure 9.23 shows the results for tan 5 [42]. Each curve represents the master curve for data of a giveu... 

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