Orthorhombic Sulfur Research Articles

Raman Studies of Sulfur Crystal (α-S8) at High Pressures and Low Temperatures

We have studied the temperature and pressure dependence of the vibrational energy levels of orthorhombic sulfur. Spectroscopic measurements were performed using standard Raman equipment; high pressure experiments made use of a diamond anvil cell (DAC). In general all external modes are sensitive to temperature variation in the range 50−300 K; internal modes exhibit a different behavior. It was found that mode energies were more influenced by pressure (0−5 GPa) than by temperature (12−300 K). In addition it was found that the intensities of prominent features of the Raman spectrum were pressure dependent.

The anthracite smokers of eastern pennsylvania: $$P_{S_2 (g)} $$ -T stability diagram by TL analysis

Coal seams and culm banks associated with mine fires in the anthracite region of eastern Pennsylvania have been burning for decades. Many of the fires may have ignited by spontaneous combustion or by the burning of trash. Minerals associated with the combustion of anthracite form by the condensation of gas exhaled through surficial gas vents or “anthracite smokers.” A Pressure-Temperature (P-T) stability diagram is constructed for the condensation of orthorhombic sulfur from anthracite gas using “Thermodynamic Loop Analysis” (TL analysis). This method of analyzing chemical systems incorporates Kirchhoff's Law into a four step procedure structured around a closed thermodynamic cycle or “thermodynamic loop.” The four steps, referred to us “The Four S ′S of Thermodynamic Loop Analysis,” include: (1) “Set Up”—graphical characterization of the problem. (2) “Sum”—the application of thermodynamic principles. (3) “Substitute”—the use of materials data available from the literature, and (4) “Solve”—computation of one or more variables. The example presented demonstrates that thermodynamic loops can incorporate any number of polymorphic phase transformations. In addition, thermodynamic loop analysis is applicable to any geologic process involving the condensation of minerals from a gas. The stability diagram derived by TL analysis may have applicability in monitoring the release of sulfur gas into the atmosphere.

Raman spectrum of sulfur under high pressure

The phase diagram of sulfur has been studied in a diamond anvil cell (DAC) up to about 20 GPa at room temperature by Raman spectroscopy using a 590 nm dye laser as well as the 488.0 and 514.5 nm lines of Ar + lasers. Two reversible phase transitions have been observed: (1) from an original orthorhombic sulfur with S 8 ring molecules to a high pressure unknown (HPU) phase at 5.2 GPa; and (2) to a high pressure, high temperature (HPHT) phase with S 6 ring molecules at about 10 GPa. These reversible phase transitions are observed in the Raman spectrum only through excitation by a laser whose photon energy and power are sufficiently large.

Colloidal properties of a microbiologically produced sulphur suspension in comparison to a LaMer sulphur sol

The colloidal characteristics of a biotechnologically produced hydrophilic sulphur suspension have been compared to those of a synthetically formed LaMer sulphur sol. Biologically produced sulphur is the end-product of microbiological sulphide oxidation, a process carried out by mixed cultures of Thiobacillus-like bacteria. Electrophoretic mobility measurements and flocculation experiments revealed differences in the colloidal properties of the two sols. This observation was explained by the assumption that negatively charged (bio)polymers are attached to the microbiologically produced sulphur particles, which have an orthorhombic sulphur nucleus, while a LaMer sol has a vesicle structure which is built up of long-chain polythionates. As shown by dynamic light scattering measurements, the diameter of the biological sulphur particles decreases with increasing salt concentration, indicative of an inward shift of the adsorbed polymers at high electrolyte concentrations.

Pressure-induced structural phase transition in sulfur at 83 GPa.

The pressure-induced phase sequence of sulfur up to 90 GPa has been studied by an angle-dispersive x-ray-diffraction method. The orthorhombic sulfur (S-I) with ${\mathrm{S}}_{8}$ cyclic molecules transforms to a high-pressure crystal phase (S-II) between 6 and 55 GPa. The second structural phase transition takes place at 83\ifmmode\pm\else\textpm\fi{}2 GPa. The highest-pressure phase (S-III) can be explained as a base-centered orthorhombic lattice. This lattice is isomorphous to that in the metallic high-pressure phase of selenium. Metallization for sulfur reported by Luo et al. is ascribed to the second transition.

Phase transitions of sulfur at high pressure: Influence of temperature and pressure environment

Abstract Phase transitions of orthorhombic sulfur were investigated above 10 GPa by Raman spectroscopy using red light excitation. Transitions into several phases that have been reported in previous studies using green light excitation, are confirmed. The phase behaviour is observed to depend strongly on the preparation method. In the presence of a pressure transmitting medium (methanol/ethanol, 4:1), a sequence of phases α-S8 → [intermediate phase (“ip”) + S6] → [S6 + high pressure-low temperature phase (“hplt”)] is described and characterized. Without the use of a pressure transmitting medium, the phase sequence α-S8 → [“ip” + “hplt”] + “hplt” is observed. In addition, contributions of amorphous sulfur are detected around 10 GPa, i.e. at pressures below the transformation of α-S8 into the above-mentioned phases. Characteristic Raman spectra of the different phases are extracted and documented over a wide pressure range.

Comparison between the optical constants obtained by the Kramers–Kronig analysis and the maximum entropy method: infrared optical properties of orthorhombic sulfur

The optical constants of orthorhombic sulfur computed by the Kramers-Kronig phase-shift analysis were recently reported by Fuller et al. The results obtained by Fuller et al. are compared with the ones obtained by a novel maximum entropy procedure.

Raman Spectroscopic and X-Ray Diffraction Study of Sulfur under High Pressure

Raman spectrum and X-ray powder pattern of orthorhombic sulfur have been examined at pressures up to about 10 GPa. The Raman spectrum shows reversible phase transition at 5.2 GPa, while the X-ray diffraction pattern shows no sign of phase change up to 8.3 GPa. These contradictory results are explained as follows. A high-pressure phase exists above 5.2 GPa. In this pressure region, the metastable orthorhombic phase can also exist. The argon ion laser (λ=514.5 nm) used for Raman measurement induces a structural transformation from the orthorhombic phase to the high-pressure phase. The Raman spectrum suggests that the high-pressure phase is composed of chain molecules. In addition, evidence for interference between inter- and intramolecular bondings has been observed in this phase.

Temperature dependence of vibrational relaxation processes in sulfur crystals: Effect of isotopic impurities

We have studied phonon relaxation processes in orthorhombic sulfur crystals, for several lattice and internal vibrations. Bandwidths were measured as a function of temperature using a tandem Fabry–Perot spectrometer instrument with a limiting resolution of 0.001 cm−1. In order to obtain a basis for the study of the effect of isotopic impurities, we have grown single crystals of isotopically pure 32S. We have measured the bandwidths of six lattice phonons and eight internal vibrons. For most of the bands the width showed a linear variation with temperature in the classical regime, and in these cases we have interpreted the widths in terms of three-phonon decay processes. In some cases, however, a nonlinear temperature variation was observed, which we interpreted in terms of four-phonon and pure dephasing mechanisms. We have measured the widths of the same phonons and vibrons in single crystals of natural sulfur, which contains 4.2% 34S. The widths are in many instances larger when the impurity is present, and the increase is temperature-dependent. This difference is interpreted as being the sum of two contributions. One is temperature-independent, and reflects the simple scattering process, controlled by a harmonic term in the Hamiltonian, in which a phonon is dephased within its own dispersion curve. The second contribution is temperature-dependent, and is interpreted as being due to the same anharmonic processes observed in the pure crystal, scaled by a factor which takes into account the coupling of resonant scattering and anharmonic relaxation processes.

Infrared optical properties of orthorhombic sulfur

Because of recent developments in planetary astronomy, there has been a resurgence of interest in the optical and thermodynamic properties of elemental sulfur. An encounter between the space probe Galileo and the Jovian moons, particularly Io, is expected to contribute further to this interest. A thorough investigation of the optical properties of orthorhombic sulfur from 2 to 56 microm (5000-180 cm(-1)) is presented. Since less care was taken in many past studies of this element than was warranted, a critical review of some of the relevant literature is included. The near-normal specular reflectance of the (111) face of an orthorhombic sulfur crystal has been measured in both polarized and unpolarized radiation at room temperature. The reflectance of a cryptocrystalline melt freeze has also been obtained. Associated optical constants are determined from a Kramers-Kronig phase shift analysis of the reflectance data. The average reflectance and absolute refractive index n were found to vary with polarization from 0.100 to 0.125 and from 1.92 to 2.09, respectively. Between eight and eleven mostly weak absorption bands of the cyclo-S(8) molecule were discernible, but the attenuation index k remains small throughout most of the region studied. The crystal spectra were found to be quite sensitive to polarization in the neighborhood of the v(4) fundamental. Extrapolation of n to other temperatures and to the liquid phase through the use of the Lorentz-Lorenz relation is discussed.

Phase transformations and the spectral reflectance of solid sulfur: Can metastable sulfur allotropes exist on Io?

The spectral reflectance of elemental sulfur that has solidified from a melt changes with time after the sulfur has solidified. This temporal variation arises as a result of phase transformations occuring within the solid. In a set of laboratory investigations, we find that variations in the thermal history of the sulfur samples profoundly affect the solid-state transformation rate and the corresponding spectral variation of freshly frozen sulfur. In particular, samples that were heated to 393 and 453 K for various lengths of time (up to 50 hr) and then solidified and aged at various temperatures (from 260 to 318 K) brighten at visible wavelengths on very different time scales. This temporal variation is thought to be due to differences in the amount and type of metastable allotropes present in the sulfur after solidification as well as to the physics of the phase transformation process itself. Our laboratory data have implications for the spectral variation and physical behavior of freshly solidified sulfur, if any exists, on Jupiter's satellite Io. Depending on its thermal history, molten sulfur on Io will initially solidify into a glassy solid or a monoclinic crystalline lattice; these forms may contain polymeric molecules as well as the more abundant S 8 molecules. If freshly frozen sulfur on Io can lose heat rapidly and approach ambient dayside Io temperatures within a few hours, then our laboratory results imply that the metastable monoclinic or polymeric allotropes can be maintained on Io and will take years to convert to the stable orthorhombic crystalline form. We present cooling rate calculations that indicate that metastable allotropes can be preserved in small droplets of sulfur ejected during volcanic plume eruptions on Io. However, sulfur in large lakes or flows on Io might remain warm long enough for the conversion of monoclinic sulfur into orthorhombic sulfur to proceed, and we would expect rapid brightening (on the order of hours or days) in these areas after the liquid sulfur has solidified.

Phase transitions in crystalline sulfur at p>8 GPa, observed by Raman spectroscopy in a diamond anvil cell

Abstract Raman spectra of sulfur have been recorded in a diamond anvil cell, in the pressure range 0 to 40 GPa, using a 0.6 m triple spectrograph and a CCD multichannel detector. When orthorhombic sulfur (S8) is pressurized to 12 GPa, the appearance of either of two distinctly different phases is observed, depending on temperature. When comparatively high temperatures (high laser power. T- 380 K) are used, a phase exhibiting six prominent Raman bands is observed. To establish the identity of this phase, its pressure dependent Raman spectrum is compared with the one of chemically prepared six-ring sulfur (S6). On the other hand, the high pressure-low temperature phase is obtained either by pressurizing S8 at low laser powers, or by unloading S6 after pressurizing to 40 GPa. This phase is tentatively assigned to the sulfur modification Sxii, on the basis of matching Raman spectra.

Electron time-of-flight measurements in sulfur interpreted via an extra surface mobility channel.

Time-of-flight measurements were carried out in orthorhombic sulfur for various fields, ranging from -2 to -20 kV/cm. No dependence of the mobility with the electric field was found but the current, normalized by the initial current, showed an electric field dependence at small times, decaying faster for larger electric field. After the failure of the usual models in explaining the results---including the assumption of depth-dependent density of traps---a model assuming an extra mobility channel near the surface provided a reasonable set of parameters independent of the electric field. The measurements were carried out at 8.5, 29, 53, 68, and 79 \ifmmode^\circ\else\textdegree\fi{}C.

Geothermal prospects in the central region of sucre state, venezuela

In the geothermal area of El Pilar-Mundo Nuevo, Sucre State, sampling was carried out in 36 geothermal manifestations, 18 cold springs and 10 surface runoffs. From the results of water analyses three different systems were identified: 1.(a) El Salvaje-Buena Esperanza system: acid-sulfate-calcium waters and orthorhombic sulfur, gypsum, anhydrite and low quartz deposits.2.(b) El Palmar-Aguas Calientes-Los Chirriaderos system: generally neutral, sodium chloride waters with abundant carbonate deposits.3.(c) Mundo Nuevo-Los Mereyes system: acid-sulfate-calcium waters in the higher temperature springs with low quartz and orthorhombic sulfur deposits. There are also neutral calcium bicarbonate waters, without deposits, and lower temperatures.The highest temperatures assessed from chemical geothermometers for the systems of El Salvaje-Buena Esperanza and El Palmar-Aguas Calientes-Los Chirriaderos, allow us to consider their utilization for electricity generation, exploiting the excess lower temperature fluid in fish meal and timber drying, fast drying of farm products and evaporation in sugar refining.

Electrical conductivity and compressibility of sulfur under shock loading

The authors mathematically and experimentally assess the transition of orthorhombic elementary sulfur from a dielectric to a superconducting regime under the influence of pressure generated by shock wave loading. They also determine its compressibility over a range of 4-38 GPa.

The elastic behaviour of orthorhombic sulphur under pressure

Orthorhombic, α -sulphur comprises S 8 rings strongly bound by covalent, intramolecular forces but held together by much weaker intermolecular bonds. To examine the vibrational anharmonicity of the long-wavelength acoustic modes in a molecular crystal of this type, the effects of hydrostatic and uniaxial pressures upon the velocities of ultrasonic modes propagated in a single crystal of orthorhombic sulphur have been measured. From the experimental results at room temperature 19 of 20 third-order elastic constants and also the hydrostatic pressure derivatives of the 9 second-order elastic constants have been obtained. The elastic stiffnesses and their hydrostatic pressure derivatives have also been calculated from an intermolecular potential of the 6-exp variety. Good agreement between the results obtained from this lattice dynamical calculation and the ultrasonic experiments establishes that the potential model provides a reasonable description of the elastic behaviour of this molecular crystal. The compression estimated from the Murnaghan equation of state agrees well with that estimated theoretically from the lattice dynamic calculations. The Debye temperature determined from the ultrasonic-wave velocities is 187.5 ± 2 K. Ultrasonic-wave velocities are linear up to about 100°C; the crystals do not undergo the transition to a monoclinic (β) phase which can take place at 95°C. There is no indication of softening of the long-wavelength acoustic phonon modes. Vibrational anharmonicity is discussed in terms of the long-wavelength acoustic-mode Grüneisen parameters obtained from the generalized Grüneisen theory in the quasiharmonic approximation. The mean high-temperature long-wavelength acoustic-mode Grüneisen parameter γ̄ el H (= 2.72) is much larger than the room-temperature thermal Grüneisen parameter γ th (=0.54). In this molecular crystal the intermolecular volume is much more compressible than the intramolecular volume; the mode Grüneisen parameters for purely internal vibrational modes are small, whereas those for the external modes are large. At room temper­ature all phonon modes contribute so that γ th is made small by the small internal-mode contributions. In contrast, the weak, strongly pressure dependent intermolecular forces dominate the zone-centre acoustic modes and lead to a large mean Grüneisen parameter γ̄ el H .

Determination of the thermal expansion of orthorhombic sulfur

The temperature variation of the lattice parameters of orthorhombic sulfur was determined in the range 100 to 300 K using X-ray powder diffractometry. The following equations represent the results: aT = 10.3506−2.962 × 10−4T + 2.346 × 10−6T2 Å bT = 12.8518 − 1.198 × 10−3T + 4.038 × 10−6T2 Å cT = 24.1986 + 7.952 × 10−4T + 9.902 × 10−7T2 Å. Values are given for the thermal expansion coefficients and the Gruneisen parameter.

Raman spectra of orthorhombic sulfur at 40 K

AbstractHigh–quality Raman spectra of orthorhombic sulfur (S8) have been recorded at 40 K employing multiscanning conditions. Assignments are proposed for the many new features detected, especially binary and ternary overtones and combinations of the SS stretching and SSS bending vibrations. The anharmonicities of these particular modes are shown to be fairly small.

Indirect band gap investigation of orthorhombic single crystals of sulfur

Single crystals of pure and selenium doped orthorhombic sulfur crystal were prepared from carbon disulphide solution. They were investigated at two temperatures (6°C and 85°C) in an optical absorption apparatus. The optical absorption increased with temperature and it was found to be higher for Se doped crystals within the same range of temperatures. The indirect allowed band gap transitions and assisting phonons were observed. Their values were found to shift toward lower energy with increasing temperatures. They are also lower for doped samples. At 6°C, the indirect allowed band gaps are 2.61 eV and 2.56 eV for pure and selenium-doped crystals, respectively. At 85°C, they are 2.44 eV and 2.40 eV for pure and doped crystals, respectively. The phonons associated with the optical transitions could be attributed to the stretching band of S 8 rings.

Optical properties of solid and liquid sulfur at visible and infrared wavelengths

Knowledge of the optical constants of elemental sulfur has potential applications to Venus, Jupiter, Io, Amalthea, and the Earth. The real part, n, of the index of refraction of liquid sulfur (at 133°C) and of solid orthorhombic sulfur (at 25°C) for the wavelength range 0.4–2.0 μm were measured ellipsometrically. The imaginary part, k, of the refractive index of liquid sulfur was obtained by transmittance measurements at the same temperature and wavelength range. The reflectance of semi-infinite slabs of solid and liquid sulfur is calculated using the measured n and k values. We confirm that sulfur melts on Io would be classified as “black” by the Voyager imaging system.