Sulfur crystallization

Sulfur crystallizes in at least two distinct systems the rhombic and the monoclinic forms. Rhombic sulfur, Sa, is stable at atmospheric pressures up to 95.5°C, at which transition to monoclinic sulfur, SP, takes place. Monoclinic sulfur is then stable up to its natural melting point of 114.5°C. The basic molecular unit of both of these crystalline forms of sulfur is the octatomic sulfur ring Other forms of sohd sulfur include hexatomic sulfur as well as... 

Several studies confirmed the high-pressure response of sulfur crystals by Raman [109, 119, 120, 135-137] and IR spectroscopy [109,138]. Accordingly, external and torsional vibrations have values for the mode Griineisen parameter around 2, and the parameters of the bending and stretching vibra-... 

The H2S usually escapes and the sulfur crystallizes as a consequence the reaction will always be quantitative after long enough reaction times or in the presence of a catalyst. On the other hand, hquid sulfur and H2S react to give a mixture of long-chain polysulfanes ... 

Electrical and Photoconductive Properties of Orthorhombic Sulfur Crystals... 

FIGURE 20.6 Phase images of ethylene-propylene-diene terpol3mier (EPDM) samples at different scales. Images of the unvulcanized sample are shown in (a, d) and images of samples, which were cross-linked with different amount of sulfur curative—1 phr—in (b, e) and 2 phr—in (c, f). White arrows in (f) most likely indicate locations with small sulfur crystals. 

No element shows as many different structures as sulfur. Crystal structures are known for the following forms S6, S7 (four modifications), Sg (three modifications), S10, S6-S10, Sn, S12, S13, S14, S15, S18 (two forms), S20, (Fig. 11.2). Many of them can be separated by chromatography from solutions that were obtained by extraction of quenched... 

A Sulfur occurs as an element in volcanic areas, and the beautiful sulfur crystals are sought after. Technically, sulfur is increasingly isolated from natural oil. 

These sulfur crystals were found in Sicily, Italy. To a chemist s eye, not only do they look beautiful, but they are perceived as built from many crownlike molecules formed from eight sulfur atoms linked together as shown in the inset. The photographs at the beginning of each chapter throughout this text will illustrate how objects look through chemists eyes. 

V. Makeup of crystals. Soil mineral crystals are made out of ions. However, not all crystals are made out of ions. Exceptions include sulfur crystals (which are made of S atoms), diamonds (which are made out of carbon atoms), and asphalt crystals (which are made out of large organic molecules arranged in a repeating fashion). 

Infiltration of the permeable concrete with molten sulfur yields a matrix which is almost impermeable to water. The freeze-thaw durability tests have indicated this is so, and immersion tests showed that fully infiltrated specimens absorbed less than 0.3% water by volume over several months, although methanol immersion and vacuum poro-simeter measurements revealed that a pososity of over 5% was available for filling. A total shrinkage of about 13% (Table I) occurs when liquid sulfur crystallizes to the stable low-temperature S< form, but much of the volume change appears to be accommodated in closed pores and intercrystal inversion fractures which affect the permeability little. 

Figure 10. (left) Photograph of a flowery exudation of sulfur on concrete immersed in distilled water for 10 months. The basal mound of sulfur crystals is surmounted by a sulfur bloom grown at the tip of a calcite tubule (Magnification X8). (right) Liquid extrusions on dried concrete surface adjacent to earlier sulfur exudation. Same scale. 

Figure 11. Scanning electron micrographs of a calcite tubule, (left) pro-truding from surface of concrete in a mass of sulfur crystals (X44) (right) showing crystal growth in the walls and striae in the conduit (X440)...

Sulfur crystallizes as a monoclinic polymorph which on cooling to room temperature inverts to an orthorhombic form. The most characteristic molecule is an eight-membered, crown-shaped ring (Sx or S8R — cyclooctasulfur), but solids composed of hexatomic sulfur and numerous... 

He looked up in dismay, visualizing a thousand ducats subliming away like his sulfur crystals. 

Bright yellow sulfur crystals are formed when 3 g of the sulfur residues from the previous experiments are heated to boiling with 30 mL of p-xylene and the filtrate subjected to shock cooling in the cooling bath. 

X-ray diffraction of sulfur particles excreted by Thiobacillus sp. showed the presence of orthorhombic sulfur crystals. The solubility of crystalline orthorhombic sulfur in water is known to be only 5 /tg 1 [42]. In the solubility test shown in Fig. 7 it was seen that the biologically produced sulfur particles can be dispersed in water but not in hexadecane, whereas crystalline orthorhombic sulfur is soluble in hexadecane but not in water. The reason for the observed hydrophilicity of the biologically produced sulfur particles has to be attributed to the hydrophilic properties of the surface of the sulfur particles. Because of the relatively high stability of the biologically produced sulfur particles at high salt concentrations, it is concluded that the colloidal stability is not merely based on electrostatic repulsion. It is known that hydrophobic sulfur can be wetted by Thiobacillus thiooxidans bacteria due to formation of organic surface-active substances [43, 44]. 

When a mixture of iron filings and sulfur crystals is heated, the elements combine to form iron(II) sulfide. 

Teaching and Learning Suggestions. The scientific particle term has to remain associated to the sub microscopic level, it should not be used for small portions of material. Of course, one can speak of iron filings, small sulfur crystals, tiny water drops or of little gas bubbles at this level it should be no problem to avoid the particle term when talking about matter. Students will thereby realize that the smallest particle is reserved for the invisible area of mental models of matter, i.e. water particles, sugar particles, and ethanol particles (compare Sect. 4.1). 

A method, using differential scanning calorimetry, has been developed to estimate quantitatively orthorhombic and monoclinic sulfur in sulfur materials. Sulfur cooled from the melt at 120°C immediately gives monoclinic sulfur which reverts to orthorhombic sulfur within 20 hr. Limonene, myrcene, alloocimene, dicyclopentadiene, cyclododeca-1,5,9-triene, cycloocta-1,3-diene, styrene, and the polymeric polysulfides, Thiokol LP-31, -32, and -33 each react with excess sulfur at 140° C to give a mixture of poly sulfides and unreacted sulfur. In some cases substantial amounts of this unreacted sulfur may be held indefinitely in a metastable condition as monoclinic sulfur or S8 liquid. Limonene, myrcene, and dicyclopentadiene are particularly effective in retarding sulfur crystallization. 

Tobolsky and Takahashi (7,8) showed that large concentrations of S8 can remain dissolved in a liquid condition in other polymers. In many cases these compositions appear completely stable, i.e., there is no tendency for the dissolved sulfur to crystallize out. The best example is cross-linked polyethylene tetrasulfide polymers which can retain 40% of dissolved sulfur in the form of liquid S8 over long periods of time. The sulfur was shown to be S8 by quantitatively extracting it with carbon disulfide. It was demonstrated that the specific volume of the dissolved sulfur plotted against temperature fits smoothly with the data of specific volume of molten sulfur vs. temperature and finally that the mechanical properties of the cross-linked polymers containing dissolved sulfur are just what would be expected from plasticized, cross-linked, amorphous polymers. Ellis (9) reported the use of resins made by the interaction of 2,3-xylenol and sulfur monochloride as sulfur additives. These resins were added to three times their weight of molten sulfur. There was no indication of sulfur crystallization in the resultant material, which also... 

On cooling from the melt at 120 °C sulfur crystallizes to S/s at a rate too rapid to be determined by differential scanning calorimetry. On storage at ambient temperature the S/s reverts to S (the only allotrope stable under STP conditions). The reversion rate has been measured using differential scanning calorimetry (Figure 2). A 90% reversion rate to S was obtained within 10 hr. 

Figure 19. Layer of sulfur with poorly developed mosaic texture covered with layer of massive sulfur crystals in a cross section...

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