Shan Qin

Progress and records in the study of endogenetic mineralization during collisional orogenesis

To develop and perfect the theory of plate tectonics and regional metallogeny, metallogenesis during collisional orogenesis should be thoroughly studied and will attract increasing attention of more and more scientists. This paper presents the main aspects of research and discussions on metallogenesis during collisional orogenesis after the development of plate tectonics, and accordingly divides the study history into two stages, i.e. the junior stage during 1971–1990 and the senior stage after 1990. Beginning with the negation of mineralization in the collision regime by Guild (1971), the focus of study was put on whether there occurred any mineralization during collisional orogenesis at the junior stage. At the senior stage, which is initiated by the advance of metallogenic and petrogenic model for collisional orogenesis, scientists begin to pay their attention to the geodynamic mechanism of metallogenesis, spatial and temporal distribution of ore deposits, ore-forming fluidization, relationship between petrogenesis and mineralization in collisional orogenesis, etc. Abundance of typical collisional orogens such as Himalayan, China has best natural conditions to study collisional metallogenesis. Great progress in the study of metallogenesis during collisional orogenesis has been made by Chinese geologists. Therefore, we hope that the’ Chinese geologists and Chinese governments at various levels to pay more attention to the study of collisional metallogenesis. Some urgent problems are suggested to be solved so as to bring about breakthroughs in the aspects concerned.

Cryptomelane(KxMn8−xO16): Natural active octahedral molecular sieve(OMS-2)

The Xiangtan manganese deposit (XTM) used to be considered a supergene oxide manganese ore in South China. We reported a new identification of the naturally outcropping cryptomelane by examining the physical, chemical and structural features of the XTM supergene oxide manganese ore. The MnO2 content was over 90%, K2O more than 3%, and water from 2.2%–3.1% which is similar to one in zeolite. The cell parameters of the cryptomelane were given as a0 = 0.9974 nm, b0 = 0.2863 nm, c0 = 0.9693 nm and β = 91.47 °. There was a larger pseduotetragonal tunnel in the natural cryptomelane that was formed by [MnO6] octahedral double chains with aperture of 0.462 × 0.466 nm2, filled with K cations resulting in some Mn3+ substituting for Mn4+ to balance the negative charges of structure. The finding is important not only for prospecting manganese resources in South China, but also in application of octahedral molecular sieve of natural cryptomelane as that developed in the tetragonal molecular sieve of natural zeolite over the past century. The XTM cryptomelane (OMS-2) may be the real mineral of the active octahedral molecular sieve in nature.

High-Pressure and High-Temperature in situ X-Ray Diffraction Study of FeP2 up to 70 GPa

The high-pressure and high-temperature structural behavior of FeP2 is investigated by means of synchrotron x-ray powder diffraction combined with a laser heating technique up to 70GPa and at least 1800 K. No phase transition of FeP2 occurs up to 68 GPa at room temperature. While a new phase of FeP2 assigned to the CuAl2-type structure (I4/mcm, Z = 4) is observed at 70 GPa after laser-heating. This new phase presents a quenchable property on decompression to ambient conditions. Our results update previous experimental data and are consistent with theoretical studies.

Compressibility of a natural smithsonite ZnCO3 up to 50 GPa

Natural smithsonite (ZnCO3) has been investigated by synchrotron radiation X-ray diffraction and X-ray absorption spectroscopy combined with diamond anvil cells up to 50 GPa at room temperature. At ambient pressure, smithsonite adopts as calcite phase with a=4.6557(11) Å and c=15.072(12) Å. Both experimental results demonstrate that no phase transition occurs in the present examined pressure range. Isothermal pressure–volume relationship of smithsonite can be well described by the third-order Birch–Murnaghan equation of state with V0=284.6(7) Å3, B0=126.8(6) GPa and (fixed). The axial compressibility of smithsonite presents clear anisotropy with αc=3.60×10−3 Å GPa−1>αa=1.21×10−3Å GPa −1. ZnCO3-smithsonite is proposed to approach the NaCl rocksalt structure on compression.

Application of vermiculite and limestone to desulphurization and to the removal of dust during briquette combustion

Abstract Small domestic cooking furnaces are widely used in China. These cooking furnaces release SO2 gas and dust into the atmosphere and cause serious air pollution. Experiments were conducted to investigate the effects of vermiculite, limestone or CaCO3, and combustion temperature and time on desulphurization and dust removal during briquette combustion in small domestic cooking furnaces. Additives used in the coal are vermiculite, CaCO3 and bentonite. Vermiculite is used for its expansion property to improve the contact between CaCO3 and SO2 and to convey O2 into the interior of briquette; CaCO3 is used as a chemical reactant to react with SO2 to form CaSO4; and bentonite is used to develop briquette strength. Expansion of vermiculite develops loose interior structures, such as pores or cracks, inside the briquette, and thus brings enough oxygen for combustion and sulphation reaction. Effective combustion of the original carbon reduces amounts of dust in the fly ash. X-ray diffraction, optical microscopy, and scanning electron microscopy with energy dispersive X-ray analysis show that S exists in the ash only as anhydrite CaSO4, a product of SO2 reacting with CaCO3 and O2. The formation of CaSO4 effectively reduces or eliminates SO2 emission from coal combustion. The major factors controlling S retention are vermiculite, CaCO3 and combustion temperature. The S retention ratio increases with increasing vermiculite amount at 950ºC. The S retention ratio also increases with increasing Ca/S molar ratio, and the best Ca/S ratio is 2 -3 for most combustion. With 12 g of the original coal, 1 to 2 g of vermiculite, a molar Ca/S ratio of 2.55 by adding CaCO3, and some bentonite, a S retention ratio >65% can be readily achieved. The highest S retention ratio of 97.9% is achieved at 950ºC with addition of 2 g of vermiculite, a Ca/S ratio of 2.55 and bentonite.

Pressure-induced phase transformations of PbCO3 by X-ray diffraction and Raman spectroscopy

ABSTRACT By employing synchrotron radiation, X-ray diffraction and Raman spectroscopy, the high pressure structural transformations of lead carbonate PbCO3 was investigated in diamond anvil cells up to ∼50 GPa at room temperature. Three pressure-induced transitions have been observed at ∼8.5, ∼15 and ∼26 GPa, respectively. The transition from PbCO3-I to PbCO3-II is a displacive transformation featured with anti-rotation of [CO3]2− triangles. PbCO3-II is a metastable phase because the [CO3]2− groups are in a unfixed state until they reach the equilibrium positions in PbCO3-III. PbCO3-III adopts a monoclinic symmetry with primitive lattice, and tendentiously exhibits a more compressible b-axis relative to c-axis. Isothermal pressure–volume relationship of PbCO3-III is well described by the Birch–Murnaghan equation of state with K0 = 131(4) GPa, (fixed) and V0 = 246(1) Å3. However, little information on the crystal structure of PbCO3-IV can be extracted from the present experiment. The transformation process of PbCO3 exhibits similarity to that of calcite and dolomite.

Pressure-induced phase transformation of CsPbI3 by X-ray diffraction and Raman spectroscopy

ABSTRACT The structural transformation of cesium lead iodine (CsPbI3) has been investigated in diamond anvil cells up to ∼15 GPa at room temperature by employing synchrotron radiation X-ray diffraction and Raman spectroscopy. One reversible transformation from orthorhombic (Pnma) to monoclinic (P21/m) phase has been observed at 3.9 GPa. Isothermal pressure–volume relationship of orthorhombic CsPbI3 is well fitted by the third-order Birch–Murnaghan equation of state with K0 = 14(3) GPa, K′0 = 6(2) and V0 = 891(7) Å3. The ultralow value of bulk modulus K0 demonstrates the high compressible nature of CsPbI3, similar to those of organic–inorganic metal halide perovskites. The present results provide essential information on the intrinsic properties and stability of CsPbI3, which may be applied in photovoltaic devices.

Pressure-induced structural and spin transitions of Fe 3 S 4

Greigite (Fe3S4), isostructural with Fe3O4 has recently attracted great scientific interests from material science to geology due to its complicated structure and electronic and magnetic configurations. Here, an investigation into the structural, magnetic and electronic properties of Fe3S4 under high pressure has been conducted by first-principle calculations based on density functional theory. The results show that a first-order phase transition of Fe3S4 would occur from the inverse spinel (SP) structure to the Cr3S4-type (CS) structure at 3.4 GPa, accompanied by a collapse of 9.7% in the volume, a redistribution of iron cations, and a half-metal to metal transition. In the CS-Fe3S4, Fe2+ located at octahedral environment firstly undergoes a transition from high-spin (HS) state to low-spin (LS) state at 8.5 GPa and Fe3+ subsequently does at 17 GPa. The Equation of State for different phases of Fe3S4 are also determined. Our results not only give some clues to explore novel materials by utilizing Fe3S4 but also shed light on the fundamental information of Fe3O4, as well as those of other SP-AB2X4 compounds.

Enhanced visible-light response of natural V-bearing rutile by annealing under argon

Like synthetic V-doped TiO 2 , natural semiconducting V-bearing rutile (TiO 2 ) has potential capability for visible-light absorption. The traditional modification for the synthetic V-doped TiO 2 was to enhance the sample’s visible-light absorption by increasing the doping concentration. This paper demonstrates that the visible-light absorption of natural rutile with low V doping concentration (1.0 mol%) is significantly enhanced simply through annealing under argon. In the visible-light region of 400–750 nm, the integral absorbance of rutile treated at 1173 K increased by around 63 % compared to untreated rutile. Electronic paramagnetic resonance (EPR) measurements indicated that argon annealing induced a substantial increase of V 4+ as an active state of V doping ions for the visible-light absorption. This argon annealing can provide a simple modification method for enhancing the visible-light absorption of V-doped TiO 2 .

Stability and anisotropy of (FexNi1−x)2O under high pressure and implications in Earth’s and super-Earths’ core

Oxygen is thought to be an important light element in Earth’s core but the amount of oxygen in Earth’s core remains elusive. In addition, iron-rich iron oxides are of great interest and significance in the field of geoscience and condensed matter physics. Here, static calculations based on density functional theory demonstrate that I4/mmm-Fe2O is dynamically and mechanically stable and becomes energetically favorable with respect to the assemblage of hcp-Fe and