Pressure and photo-induced phase transitions in sulphur investigated by Raman spectroscopy

Abstract

The phase transition of orthorhombic sulphur α-S₈ to a high pressure amorphous sulphur allotrope (a-S) has been investigated by Raman spectroscopy. The conversion is found to be induced by the absorption of laser light and can be discussed in terms of ring opening followed by cis-trans conversion of the dihedral angle of S₈ molecules. Laser energy and transition pressure are correlated due to the pressure tuned red shift of the absorption edge of α-S₈. The amorphous (a-S) phase is observed up to 15 GPa at laser intensities below 30μW/μm² at 514.5 and 488.0 nm. Above this threshold power a-S transforms into a second photo-induced phase (p-S), whose discrete Raman spectrum implies an ordered molecular and crystalline structure. By further increasing pressure crystalline S₆ can be created which is found to be the dominant molecular species at pressures above 10 GPa and low temperatures. A phase diagram in the range T < 300 K and p < 15 GPa is also presented.     

Synthesis and chemical structure of natural rubber adduct with SO2 and study of the thermal stability

Natural rubber (NR, cis-1,4-polyisoprene) was reacted in solution with SO₂ at room temperature in different solvents (tetrahydrofuran, CHCl₃, CH₂Cl₂ and tetralin). The reaction product consisted of an adduct between NR and SO₂. The chemical structure of the adduct was studied by FT-IR spectroscopy, by thermogravimetry coupled with FT-IR (TGA-FT-IR), by differential thermal analysis (DTA) and by derivative thermogravimetry (DTG). The maximum SO₂ uptake from NR was 21% as determined by TGA. The TGA of the NR-SO₂ shows that the adduct decomposes in two steps initially releasing SO₂ at lower temperature and then decomposing at higher temperature like common NR. It is proposed that the chemical structure of the NR-SO₂ adduct consists of SO₂ molecules added to the double bonds of the isoprene units forming a sulfone derivative with three-membered rings known as thiirane-1,1-dioxide. On heating the thiirane ring decomposes releasing SO₂ in an extrusion reaction giving back the NR macromolecule.The possible potential applications of the NR-SO₂ adduct which is cheap and easy to prepare are outlined.     

原子吸收光谱法间接测定铁矿及锌精矿中的硫

本文研究了铬酸钡沉淀置换－原子吸收光谱法间接测定铁矿、锌精矿中硫时大量共存元素的影响，采用数学校正方法消除大量铁的干扰。建立的方法简便、快速，特征浓度为０．１６μｇ·ｍｌ￣－１／１％，线性浓度范围为０～４０μｇ／ｍｌ。试样分析的结果表明准确度及精密度均符合要求。     

Kinetics of formation of sulfur dimers in pure SF6 and SF6-O2 discharges

The emission band spectra of S, molecule (B³ _u ^– X³ _g ^– transition) and of SO molecule (A³ X^3–) were detected in SF₆ and SF₆-O₂ rf discharges. It has been observed that the presence of a material which can be etched by SF₆ products considerably enhances the density of S₂ in the reactor. By means of mass spectrometry it has been shown that the m/e =83 mu signal assigned to S₂F⁴ ions evolves exactly in the same manner as the S₂ band intensity during the etching of Si or W in SF₆-O₂ discharge. A reaction scheme involving S₂F radicals is proposed to explain these experimental results.     

Solvothermal Synthesis of two 2‐D Thioantimonates(III) with Metal Complexes as Template Ions, [M(dap)3]Sb4S7 (M = Ni2+ and Co2+)

Two new thioantimonates [M(dap)₃]Sb₄S₇ (M = Ni²⁺ ( 1 ) and Co²⁺ ( 2 )) were synthesized under solvothermal conditions by the reaction of NiS (or Co metal), Sb and S in an aqueous solution of 1,2‐diaminopropane (dap). Compounds 1 and 2 are isostructural. The polymeric [Sb₄S₇^2?]_n anion is composed of two SbS₃ trigonal pyramids and two SbS₄ units. The SbS₃ and SbS₄ units are interconnected by corners and edges to build a 2‐D puckered layer with Sb₄S₄ and Sb₁₆S₁₆ heterorings. The apertures of the large Sb₁₆S₁₆ hetero‐rings are filled by two [M(dap)₃]²⁺ complex cations which serve as template ions. The band gaps of 2.44 eV for 1 and 2.43 eV for 2 have been estimated from optical absorption spectra.     

The mechanical properties of radiation-vulcanized NR/BR blending system

The effect of radiation dose on the mechanical properties of NR/BR blending system is reported in this paper. A comparison was made between sulphur vulcanization and radiation vulcanization for an optimal nature rubber (NR)/ butyl rubber (BR) blending ratio (60/40) at dose range from 10 to 150 kGy. The result shows that the mechanical properties, especially, tensile strength, elongation at break, and tear strength have been improved significantly by radiation–vulcanization. This finding was also proved by thermal aging experiment on a selected NR/BR blend at 70°C for up to 168 h.     

化学气相沉积对Pt/KL沸石芳构化性能的影响

PT／KL沸石催化剂对正己烷芳构化有很高的活性及选择性，但是至今为止人们对于其中沸石载体是否起到重要作用仍众说不一．为了深入探讨这一问题，有必要了解Pt粒子在KL沸石孔道内的分散状态．但是要测定小于1nm的Pt粒子需要高分辨电镜，受到实验条件的限制．我们知道，化学气相     

Determination of sulphur in liquids obtained by thermal cracking of waste polymers and commercial fuels with different analytical methods

Low sulphur concentration in hydrocarbon products as fuels or lubricants is an important requirement for the high quality standards of refineries. A non-polarised energy dispersive X-ray fluorescence spectroscopy (EDXRFS) and sample combustion technique (ASTM D6428-99) was compared. A new application of energy dispersive X-ray spectrometry as analytical method for the determination of sulphur in fuels and fuel-like fractions was investigated. Low sulphur containing fuels and hydrocarbon mixtures obtained by thermal cracking of waste polymers were measured and the influence of C/H ratio on accuracy was studied. The concentration of sulphur in samples was measured with calibration graphs of different hydrocarbon matrices (commercial gasoline, diesel oil and white oil were used). Good correlation was observed between the different methods, but the correlation was depending on the characteristics of the matrices. Detection limits of 1.0 ppm, 1.1 ppm and 0.9 ppm were obtained for S in gasoline, diesel oil and white oil, respectively.     

HCS-140碳硫仪故障检修

介绍了几例HCS-140高频红外碳硫仪故障检修方法.