The Heat Capacity of Sulfur from 25 to 450°, the Heats and Temperatures of Transition and Fusion<sup>1,2</sup>

West, E. D.

doi:10.1021/ja01510a008

Cited by 108 publications

(42 citation statements)

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“…Specifically, there are ranges of temperatures in which the viscosity of Sulphur exhibits anomalous temperature dependence. In the liquid state, just above melting (T m =119 o C), eight-membered rings (S8) are the most abundant species, and the viscosity slightly decreases with temperature as normally expected, reaching values as low as 0.01 Pa·s at T = 157 o C. Further increase of temperature causes a dramatic increase of viscosity [1], accompanied by gross changes in optical [2,3,4] and thermodynamic [5,6] properties, which, at T ≈185 o C, reaches a maximum value of 100 Pa·s. Beyond this temperature, a gradual viscosity decrease is observed.…”

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confidence: 60%

Origin of theλTransition in Liquid Sulfur

et al. 2007

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Developing a novel experimental technique, we applied photon correlation spectroscopy using infrared radiation in liquid Sulphur around T λ , i.e. in the temperature range where an abrupt increase in viscosity by four orders of magnitude is observed upon heating within few degrees. This allowed us -overcoming photo-induced and absorption effects at visible wavelengths -to reveal a chain relaxation process with characteristic time in the ms range. These results do rehabilitate the validity of the Maxwell relation in Sulphur from an apparent failure, allowing rationalizing the mechanical and thermodynamic behavior of this system within a viscoelastic scenario. PACS numbers: 62.60.+v,64.70.Ja,62.10.+s, Common wisdom holds that liquids become less viscous as the temperature is raised. On a microscopic ground, indeed, viscosity can be regarded as arising from continual brushing of molecules which are close to each other. On increasing temperatures the more vigorous thermal motion of the molecules is expected to render such mutual friction progressively less effective. This naive description provides a qualitative interpretation of the decrease in viscosity normally observed in almost all substances as the temperature increases. There exist, however, a few remarkable exceptions exhibiting complex behavior, which can be regarded as extreme examples of how critically viscosity depends upon molecular interactions. Specifically, there are ranges of temperatures in which the viscosity of Sulphur exhibits anomalous temperature dependence. In the liquid state, just above melting (T m =119 o C), eight-membered rings (S8) are the most abundant species, and the viscosity slightly decreases with temperature as normally expected, reaching values as low as 0.01 Pa·s at T = 157 o C. Further increase of temperature causes a dramatic increase of viscosity [1], accompanied by gross changes in optical [2,3,4] and thermodynamic [5,6] properties, which, at T ≈185 o C, reaches a maximum value of 100 Pa·s. Beyond this temperature, a gradual viscosity decrease is observed. Although this phenomenon, known as λ-transition (T λ = 159 o C), has been tackled for more than 150 years, its comprehension is still far from being reached: to rationalize this puzzling temperature dependence of viscosity, indeed, a liquid-liquid transition from a monomeric (i.e. a S8 rings liquid) to a polymeric phase has been invoked [7,8]. The temperature dependence of the mass fraction of S atoms participating in the polymeric component turns out to be a central parameter for extracting information on many thermodynamic aspects of the λ-transition [9,10]. This phenomenon has been classified as a living polymerization [11] transition that essentially involves two steps, the initiation (formation of diradicals through opening of S8 rings) and propagation (concatenation of species to form long polymeric chains). Thermo-chemical models were developed in the past [12,13,14] to relate the transport properties of liquid sulphur to the underlying polymerization phenomenon. T...

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confidence: 60%

Origin of theλTransition in Liquid Sulfur

et al. 2007

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“…The c pg i coefficients of the polynomial for the perfect gas are obtained from spectroscopic data [17], and those for the rhombic solid c sr i come from fitting a third degree polynomial to the experimental heat capacity [18,19]. The values calculated in this way for the coefficients in equation (10) …”

Section: Sublimation Of Rhombic Sulfurmentioning

confidence: 99%

The low-pressure phase diagram of sulfur

Ferreira

Lobo²

2011

The Journal of Chemical Thermodynamics

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“…Of these, the only thermodynamically-stable polymorphs are orthorhombic c~-sulfur, stable at NTP, and monoclinic/~-sulfur, stable only in the narrow temperature range between 95.4 ~ and its melting point [2]. The stability ranges and other thermal properties of e-and fl-sulfur have also been established by modern thermoanalytical methods [3,4].…”

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Thermal behaviour of the monoclinic allotropesγ-sulfur andα-selenium and some structurally related sulfur-selenium compounds

Laitinen¹,

Niinistö²

1978

Journal of Thermal Analysis

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The thermal behaviour of 7-sulfur, monoclinic c~-Se, S6Se2, S~S%, SaSea and $3Se5 has been studied by hot-stage microscopy and differential scanning calorimetry. X-ray diffraction results show that S~,Se~ and SsSe 3 are isostructural with S~/, but S~Sea and $3Se5 are isostructural with monoclinic a-Se. The melting of S~. is accompanied by rapid crystallization of Sa, which often occurs almost simultaneously with melting. The melting of S~;S%, S5S%, SaSe 4 and S:~Sez is irreversible as the compounds decompose on melting. For monoclinic c~-Se no phase transformation to monoclinic fl-Se was observed at 110--120 ~ but it changes to hexagonal ~-Se when the temperature is over 120 ~ .The existence of several crystalline modifications of cyclo-octasulfur has been reported [1 ]. Of these, the only thermodynamically-stable polymorphs are orthorhombic c~-sulfur, stable at NTP, and monoclinic/~-sulfur, stable only in the narrow temperature range between 95.4 ~ and its melting point [2]. The stability ranges and other thermal properties of e-and fl-sulfur have also been established by modern thermoanalytical methods [3,4].The third well-known polymorph of cyclo-octasulfur is monoclinic y-sulfur, which has recently been structurally characterized by X-ray diffraction methods [5]. Although y-sulfur itself is not thermodynamically stable relative to the ~-and//-forms, it has been reported that this structure type is found in sulfur crystals containing approximately 10-45~o selenium [6][7][8][9]. When the selenium content increases to 50 ~ and above, the prevailing structure is that of monoclinic ~-selenium. The nature of these sulfur-selenium crystals was not realized, however, until Hawes [10] showed that definite ring compotmds of type Ss-nSen may be crystallized from melts and solutions containing both these chalcogens.The present investigation was undertaken in order to detect, by the DSC method, possible polymorphic transformations and other thermally induced changes occurring in y-sulfur, in monoclinic e-selenium, and in some of the structurally related compounds of the composition Ss-nS%. Obviously, due to its instability and difficulties involved in preparing larger quantities of 7-sulfur, no such study of the pure phase has been done. It also seems that the thermal behaviour of monoclinic a-selenium has not been studied by modern instrumental methods, in spite of the controversy regarding the existence of a phase transition to the 7*

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The Heat Capacity of Sulfur from 25 to 450°, the Heats and Temperatures of Transition and Fusion^1,2

Cited by 108 publications

References 1 publication

Origin of theλTransition in Liquid Sulfur

Origin of theλTransition in Liquid Sulfur

The low-pressure phase diagram of sulfur

Thermal behaviour of the monoclinic allotropesγ-sulfur andα-selenium and some structurally related sulfur-selenium compounds

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The Heat Capacity of Sulfur from 25 to 450°, the Heats and Temperatures of Transition and Fusion1,2

Cited by 108 publications

References 1 publication

Origin of theλTransition in Liquid Sulfur

Origin of theλTransition in Liquid Sulfur

The low-pressure phase diagram of sulfur

Thermal behaviour of the monoclinic allotropesγ-sulfur andα-selenium and some structurally related sulfur-selenium compounds

Contact Info

Product

Resources

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The Heat Capacity of Sulfur from 25 to 450°, the Heats and Temperatures of Transition and Fusion^1,2