Ultrahigh-pressure (4.5–5.5 GPa) experimental research on pyroxene-garnet transition and its significance

Conclusions The transition from natural Al-enstatite to garnet and Al-poor pyroxene has taken place under the condition of about 1000°C and 4.5–5.5 GPa, and new phases of garnet and corundum have formed when 15% Al₂O₃ was added to the initial natural Al-enstatite. This experimental result has explained the ultrahigh pressure (3.5–5.0 GPa) and relatively low temperature (< 1000°C) genesis of the ultramafic rock of high-pressure metamorphic zone in Dabieshan-northern Jiangsu-Jiaodong and of red corundum garnetite coexisting with garnet peridotite. From the genetic mineralogy, petrology andP-T equilibrium conditions of garnet peridotite of the high-pressure metamorphic zone, kimberlite and Cenozoic basalt and the ultrahigh pressure experimental result, it is inferred that the upper mantle garnet peridotite is transformed with the increase of depth from Al-rich pyroxene garnet peridotite (80–120 km) to Al-poor pyroxene garnet peridotite (greater than 120–150 km).     

Two different illites in Luochuan loess,Northern Shaanxi Province

Illite is the dominant clay mineral in loess and pa-leosol of China accounting for over 50% in content. Ac-cording to the latest mica group nomenclature issued bythe International Mineral Association (IMA), illite is de-fined as a dioctohedron-textured mi…     

Subsolidus phase relations in the system MgO-ZnO-SiO2 at high pressure

The subsolidus phase relations were determined experimentally in the system MgO-ZnO-SiO2 at 1.0 GPa and 1 200℃, by use of the high-pressure apparatus "piston-cylinder". The results showed characteristics of the phases assemblage different from that in similar ternary systems. It is impossible to form complete Mg2SiO4-Zn2SiO4 olivine and Mg2Si2O6-Zn2Si2O6 pyroxene solid solution. This is controlled by the properties of Zn2+ with an outer layer of electron (Ar)3d10, different from others transition metal ions, like Fe2+ , Ni2+ , Co2+ .     

Down-conversion characteristics of Eu3+ doped M2Y2Si2O9 (M = Ba,Ca, Mg and Sr) nanomaterials for innovative solar panels

Down-conversion properties of Eu³⁺ doped M₂Y₂Si₂O₉ (M = Ba, Ca, Mg, Sr) phosphors have been investigated in detail. These phosphors were synthesized via the simple, fast and cost-effective sol-gel technique at a temperature of 950 °C. Color coordinates and emission color can be altered by the varying concentration of dopant ion in Ca₂Y₂Si₂O₉ phosphor. Optimum luminescence intensity was obtained when doping 0.03 mol of Eu³⁺ ion. Using the excitation wavelength of 395 nm, these silicates showed strong red color, pure and sharp spectral peaks in visible region due to ⁵D₀→⁷F_1-3 transitions of Eu³⁺ present in the lattice. Effect of reaction temperature on luminescence was also analyzed for these phosphors. The sharp peaks in the X-ray diffraction pattern indicated the high crystallinity of prepared phosphors. Ca₂Y₂Si₂O₉ has shown an orthorhombic crystal structure. The FTIR results confirmed the metal-oxygen vibrational modes available in the range of 400–1600 cm^?1. Transmission electron microscopy images have revealed that the variation of alkaline earth metal provided a very different crystal structure. Excellent down conversion response of these phosphor materials can provide a great significance in the application of the coming solar devices.     

Synthesis characterization and improved electrochemical performance of Li_2FeSiO_4/C as cathode for lithium-ion battery by metal doping

In this paper, Li_2FeSi_(0.98)M_(0.02)O_4/C(M = Mg, Zn, Co, Mn, Ni) was synthesized as cathode material for lithium ion battery by solid-state method. The results show that the materials doped with Mg and Zn at the Si-sites have good initial discharge capacity. Then Li_2FeSi_(1-x)M_xO_4/C(M = Mg, Zn; x = 0.01, 0.02, 0.03, 0.05) were also synthesized via solid-state method. It is concluded that Li_2FeSi_(0.99)Mg_(0.01)O_4/C and Li_2FeSi_(0.98)Zn_(0.02)O_4/C have better initial discharge capacity which is 125 mAh/g and 166.2 mAh/g, respectively. The capacity of Li_2Fe_(0.98)Zn_(0.02)SiO_4/C is 157.3 m Ah/g after 10 cycles at 0.1 C, and the capacity retention rate is 94.6%. The Li~+ diffusion coefficient of Li_2FeSi_(0.98)Zn_(0.02)O_4/C is higher than that of pure phase materials by one order of magnitude. The Li_2FeSi_(0.99)Mg_(0.01)O_4/C and Li_2FeSi_(0.98)Zn_(0.02)O_4/C were tested by XRD and SEM. XRD patterns indicate that the crystal structure of Li_2FeSiO_4 is not changed after being doped with metal ion at the Si-site. The SEM image indicates that no obvious agglomeration is detected in these materials. Li_2FeSi_(0.98)Zn_(0.02)O_4/C processes better electrochemical performance analyzed by EDS、XPS and FT-IR spectra. The data prove that Si~(4+) is successfully replaced by Zn~(2+) in the crystal structure of Li_2FeSiO_4.     

Mn-ion-enhanced red spectral emission from yttrium aluminum garnet doped cerium phosphor

Mnions were co-doped in yttrium aluminum garnet doped cerium(YAG:Ce) phosphors as a co-activator and host lattice element using the co-precipitation method.These ions broadened the emission spectra of the pure YAG:Ce phosphor,which is caused by the 2E-4A2,5E-5T2 or 1T2-5T2 transition.From our X-ray diffraction results,we observed that Ce3+(1.032 ) was substituted at the Y3+(0.900 ) site,and Mn4+(0.538 ) and Mn3+(0.67 ) were substituted at the Al3+(0.535 ) site.The chromaticity color co-ordinates of YAG:Ce0.06 is(0.203,0.167),and the indices of YAG:Ce0.06,Mn0.04 and YAG:Ce0.06,Mn0.08 are(0.249,0.181) and(0.233,0.194),respectively.The manganese co-doped yttrium aluminum garnet doped cerium blended with the YAG:Ce phosphor showed improved white light emission.     

Structural investigation and luminescent properties of BaZr(BO<Subscript>3</Subscript>)2:Eu<Superscript>3+</Superscript> phosphors containing Si

Si⁴⁺-doped BaZr(BO₃)₂:Eu³⁺ phosphors are prepared by a conventional solid-state reaction. The influence of Si⁴⁺ addition on the charge transfer state of Eu³⁺-O^2– and photoluminescence (PL) properties of BaZr(BO₃)₂:Eu³⁺ are discussed. Room temperature PL spectra indicated that efficient emission is obtained by Si doping. Increased values for the peak-peak ratio (PPR) of BaZr(BO₃)₂:Eu³⁺ at higher Si doping concentrations implied that the Eu³⁺ ion is located in a more asymmetric environment in BaZr_0.8Si_0.2(BO₃)₂:Eu³⁺ than in the undoped samples. The Judd-Ofelt parameters Ω_λ (λ=2,4) were calculated from the PL data, giving results that were consistent with those from the PPR. The maximum radiative quantum efficiency was achieved at a Si doping concentration of 20 mol%.     

Reaction mechanism for in-situ β-SiAlON formation in Fe3Si-Si3N4-Al2O3 composites

In this work, Fe₃Si-Si₃N₄-Al₂O₃ composites were prepared at 1300℃ in an N₂ atmosphere using fused corundum and tabular alumina particles, Al₂O₃ fine powder, and ferrosilicon nitride (Fe₃Si-Si₃N₄) as raw materials and thermosetting phenolic resin as a binder. The effect of ferrosilicon nitride with different concentrations (0wt%, 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%) on the properties of Fe₃Si-Si₃N₄-Al₂O₃ composites was investigated. The results show that the apparent porosity varies between 10.3% and 17.3%, the bulk density varies from 2.94 g/cm3 and 3.30 g/cm3, and the cold crushing strength ranges from 67 MPa to 93 MPa. Under the experimental conditions, ferrosilicon nitride, whose content decreases substantially, is unstable; part of the ferrosilicon nitride is converted into Fe₂C, whereas the remainder is retained, eventually forming the ferrosilicon alloy. Thermodynamic assessment of the Si₅AlON₇ indicated that the ferrosilicon alloy accelerated the reactions between Si₃N₄ and α-Al₂O₃ fine powder and that Si in the ferrosilicon alloy was nitrided directly, forming β-SiAlON simultaneously. In addition, fused corundum did not react directly with Si₃N₄ because of its low reactivity.     

Surface chemical structure of titania-silica nanocomposite powder

Titania-silica （TS） nanocomposite powder with three different composite structures, containing 10-30 mol% SiO2 in each structure, have been prepared by sol-gel processes. The surface characteristics of these titania-silica samples have been investigated by X-ray photo-emission spectroscopy （XPS） and high resolution transmission electron microscopy （HRTEM）. The study for all TS oxides annealed at 773 and 1173 K showed： an abnormal surface enrichment in Si increased with increasing annealing temperature; the Ti^3＋, Ti^2＋, Si^3＋ and Si^2＋ oxides coexisted with Ti^4＋ and Si^4＋ oxides, and the contents of these Ti/Si suboxides increased with increasing SiO2 content and annealing temperature; there was a layer rich in O on the topmost surface and the excess O could be attributed to the chem-adsorption of H2O; different composite structures could lead to different contents of Ti/Si suboxides. These results indicated that the surface of TS oxide powder derived by sol-gel process was a double layer with enriched O first and then SiOx/TiOy（x, y〈2）. Ti/Si suboxides could result from the thermal diffusion of Ti^4＋ and Si^4＋, which might be induced by the strong interaction between Ti^4＋ and Si^4＋.     

Thermal degradation of BaAl2Si2O8：Eu2＋ phosphor excited by near ultraviolet light

Eu2+ doped BaAl2Si2O8 phosphor was synthesized by one-step calcination of precursors that were prepared by chemical co-precipitation.The thermal degradation properties of BaAl2Si2O8:Eu2+ were investigated by photoluminescence,lifetime and chromaticity coordinate measurements.BaAl2Si2O8:Eu2+ is efficiently excited by incident light of 250-400 nm,which matches the emission of near ultraviolet LED chips well.BaAl2Si2O8:Eu2+ exhibits broad blue emission at 470 nm because of the 4f65d1-4f7(8S7/2) transition of Eu2+ ions,and the emission band shows an unusual blue shift with bandwidth broadening and emission intensity decreasing as the annealing temperature is increased.The luminescence decay and CIE chromaticity coordinates of BaAl2Si2O8:Eu2+ were determined to investigate its application in white LEDs.     

Phase analysis and thermal conductivity of in situ O′-sialon/β-Si3N4 composites

Typical O??-sialon-based ceramics, with a formula of Si_2?x Al _x O_1+x N_2?x , where x was set as 0.25, were fabricated by in-situ synthesis. Si₃N₄, Al₂O₃, and SiO₂ powders were used as raw materials, and MgO and Y₂O₃ were added as sintering additives. All the samples were sintered at different temperatures under a nitrogen pressure of 0.25?C0.30 MPa, and their microstructure, phase content, and thermal conductivity were evaluated. The effects of O??-sialon and ??-Si₃N₄ on the thermal conductivity were analyzed by numerical calculation in detail. In the case of the similar porosity, the thermal conductivity of O??-sialon-based ceramics decreased with the ratio of O??-sialon/??-Si₃N₄ increasing. When the ratio was 12, the thermal conductivity of O??-sialon ceramics sintered at 1360°C was 1.197 W·m^?1·K^?1.     

Evidence for metasomatic mantle carbonatitic magma extrusion in Mesoproterozoic ore-hosting dolomite rocks in the middle Kunyang rift, central Yunnan, China

The Kunyang rift lying on the western margin of the Yangtze platform is a rare Precambrian Fe-Cu mineralization zone. Wuding- Lufeng basin that is an important part of the zone is located on the west edge in the middle of the rift. The most important ore-hosting rocks are Mesoproterozoic dolomite rocks in the basin controlled by a ring fracture system, which is a fundamental structure of the basin. Plenty of silicate minerals and acicular apatite, feldspar phenocrysts and small vesicular, flown line and flown plane structures, melt inclusion and high temperature fluid inclusion found in most ore-hosting dolomites suggest that this kind of rocks could not be sedimentary dolomite, marble or hydrothermal carbonate rocks. The Zr/Hf and Nb/Ta values of the rocks are identical with those of associated mantle-derived rocks, and vary widely. For the monomineral dolomite, δ^18OSMOW‰=＋5.99 to ＋18.4 and δ^13CPDB‰ = -3.01 to ＋0.94, which fall within the range for all carbonatitic volcanic rocks of the world. As for the accessory minerals, the values of δ^18OSMOW‰ of magnetite （=＋3.47 to ＋5.99‰） are close to that of the mantle （〈5.7%）, and the δ^34S‰ values of sulfides （-5.09 to ＋5.78, averaging ＋1.50） are close to that of meteorite. For all the ore-bearing dolomite rocks, εNd = ＋0.19 to ＋2.27, and the calculated Isr=0.699143, while for the associated mantle-derived rocks, εnd = ＋3.18 to ＋3.72. All the data suggest that the mineral assemblage is not only igneous but also of metasomatic mantle origin. And the presence of acicular apatite indicates that the rocks were formed by magma rapidly cooling. And the phenocryst texture and vesicular, flown and ropy and pyroclastic structures suggest that the igneous rocks were extrusive. Therefore, the ore-bearing dolomite rocks are carbonatitic volcanic rocks. This conclusion implies that most iron and copper ore deposits hosted in the dolomite rocks should be of the carbonatite type.     

Theoretical study of partial oxidation of ethylene by vanadium trioxide cluster cation

Density functional theory （DFT） study of reaction between vanadium trioxide cluster cation （VO3^＋） and ethylene （C2H4） to yield VO2^＋ ＋ CH3CHO （acetaldehyde） and VO2CH2^＋ ＋ HCHO （formaldehyde） is carried out. Structures of all reactants, products, intermediates, and transition state in the reaction have been optimized and characterized. The results show unexpected barriers in the reaction due to the existence of a η^2-O2 moiety in the ground state structure of VO3^＋. The initial reaction steps combining ethylene adsorption, C=C activation and O-O cleavage are proposed as rate limiting processes. Comparison of reactions of VO3^＋ ＋ C2H4 with VO3 ＋ C2H4 and VO2^＋ ＋ C2H4 in the previous studies is made in detail. The results of this work may shed light on the understanding of C=C bond cleavage in related heterogeneous catalysis.     

Discovery of ultrahighpressure magnesite-bearing garnet lherzolite (>3.8 GPa) in the Altyn Tagh,Northwest China

Magnesite-bearing garnet lherzolite from the Altyn Tagh, associated with garnet pyroxenite, and garnet-bearing felsic gneiss, crops out as lenses in Proterozoic gneiss about 100 km east of the Jianggelasayi River. The garnet lherzolite, together with the eclogite in western Jianggelasayi, composes a high-pressure to ultrahigh- pressure metamorphic belt in the southern margin of the Altyn Tagh. Parageneses of minerals from magnesite-bearing garnet lherzolite indicate that the rock evolved a multi-stage metamorphism. The peak-stage metamorphism produces an assemblage of Grt+Ol+Opx+Cpx±Mgs, in which Al₂O₃ content of Opx is very low (0.30 — 0.66wt%). The calculated P-T condition of the peak stage is 3.8—5.1GPa and 880—970℃, some exsolution rods of clinopyroxene and rutile occur in the Grt and magnesite is rimed by dolomite and orthopyroxene, all implying that the peak stage was a UHP metamorphic process. Together with regional geological studies, isotopic dating and the discovery of coesite inclusions in zircon separates from felsic gneiss from the northern margin of the Qaidam Basin, the presence of a very long UHP metamorphic belt in northwest China is suggested.     

New structure model of oxygen-evolving center and mechanism for oxygen evolution in photosynthesis

So far, many important questions and problems concerning the structure and mechanism of photosynthetic oxygen evolution are still unsolved. On the basis of recent achievements in this field, a new structure model is proposed whereby two H2O molecules bind asymmetrically to two manganese ions (Mn1Ⅱ and Mn4Ⅲ) at the open end of "C" shaped cluster and keep rather large distance. Two histidine residues coordinate to the other two manganese ions in higher oxidation state (Mn2Ⅳ and Mn3Ⅳ ) through their nitrogen atoms of the imidazole. Cl bound as terminal ligand to Mn4Ⅲl is connected to Ca, and the latter is needed to maintain the special configuration of two Mn2O2 units by bridged-oxo and bridged-carboxylate ligands. The whole structure of oxygen evolution center is asymmetry. A new mechanism for oxygen evolution invokes predictions of asymmetric oxidation of two H2O molecules, dynamic structural changes of oxygen e-volving center and indirect proton transport, etc. Only in S2 state, could Mn1Ⅳ = O. intermediate with high oxidation potential be formed. The S2→S3 process occurs with significant structural changes, as well as intramolecular and intermolecular hydrogen transfer. The S3 state corresponds to intermediate of Mn1Ⅳ-O… H… O-Mn4Ⅳ . During S3→ [S4] →S0, the O-O bond is formed only in S4 state. The change of nucleophilic interaction between Cl and manganese ions different oxidation states has consequence for the significant structural changes in H2O oxidation process.     

Near-infrared to visible up-conversion emissions of Er^3＋ doped Al2O3 powders derived from the sol-gel method

The Er3 doped Al2O3 powders were prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)3]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)3.5H2O]. The different phase structure, including three crystalline types of (Al,Er)2O3 phases, γ, θ, α, and two Er-Al-O phases, ErAlO3 and Al10Er6O24, was obtained with the 1 mol% Er3 doped Al2O3 powders at the different sintering temperatures of 600―1200℃. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the 2H11/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3 , were detected by a 978 nm semiconductor laser diodes excitation. The phase structure and OH content had evident influence on the up-conversion emissions intensity. The maximum intensities of both the green and red emissions were obtained respectively for the Er3 doped Al2O3 powders sintered at 1200 ℃, which was composed mainly of α-(Al,Er)2O3, less of ErAlO3 and Al10Er6O24 phases, and with the least OH content. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er3 doped Al2O3 powders.     

Mineral-phase evolution and sintering behavior of MO-SiO2-Al2O3-B2O3 (M=Ca,Ba) glass-ceramics by low-temperature liquid-phase sintering

In this work, network former SiO₂ and network intermediate Al₂O₃ were introduced into typical low-melting binary compositions CaO·B₂O₃, CaO·2B₂O₃, and BaO·B₂O₃ via an aqueous solid-state suspension milling route. Accordingly, multiple-phase aluminosilicate glass-ceramics were directly obtained via liquid-phase sintering at temperatures below 950℃. On the basis of liquid-phase sintering theory, mineral-phase evolutions and glass-phase formations were systematically investigated in a wide MO-SiO₂-Al₂O₃-B₂O₃ (M=Ca, Ba) composition range. The results indicate that major mineral phases of the aluminosilicate glass-ceramics are Al₂₀B₄O₃₆, CaAl₂Si₂O₈, and BaAl₂Si₂O₈ and that the glass-ceramic materials are characterized by dense microstructures and excellent dielectric properties.     

Preparation of Al-Cu-Fe-(Sn,Si) quasicrystalline bulks by laser multilayer cladding

(Al₆₅Cul₂₀Fe₁₅)_100-x Sn_x (x=0, 12, 20, 30) and Al₅₇Si₁₀Cu₁₈Fe₁₅ powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al₆₅Cul₂₀Fe₁₅ sample were crystalline λ-Al₁₃Fe₄ and icosahedral quasicrystal together with a small volume fraction of θ-Al₂Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al₆₅Cul₂₀Fe₁₅)_100-x Sn_x samples increased owing to the formation of β-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al₅₇Si₁₀Cu₁₈Fe₁₅ sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al₅₇Si₁₀Cu₁₈Fe₁₅ quasicrystalline alloy has the highest value among all the investigated samples.     

In situ reaction mechanism of MgAlON in Al-Al2O3-MgO composites at 1700℃ under flowing N2

The Al-Al₂O₃-MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M₁, M₂, and M₃, respectively, were prepared at 1700℃ for 5 h under a flowing N₂ atmosphere using the reaction sintering method. After sintering, the Al-Al₂O₃-MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M₁ was composed of MgO and MgAl₂O₄. Compared with specimen M₁, specimens M₂ and M₃ possessed MgAlON, and its production increased with increasing aluminum addition. Under an N₂ atmosphere, MgO, Al₂O₃, and Al in the matrix of specimens M₂ and M₃ reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al-Al₂O₃-MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N₂ atmosphere, the partial pressure of oxygen is quite low; thus, when the Al-Al₂O₃-MgO composites were soaked at 580℃ for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al₂O₃ diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al₂O₃ to form MgAl₂O₄. When the temperature was greater than (1640 ±10)℃, AlN diffused into Al₂O₃ and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl₂O₄ at high temperatures because of their similar spinel structures.     

Photoluminescence from Si-based SiNxOy films

B⁺, C⁺, Si⁺, and As⁺ with dose of 5 × 10¹⁶ cm⁻² were implanted into SiN_xO_y, films grown on crystalline silicon by plasma-enhanced chemical vapor deposition. The ion-implanted samples exhibit their photoluminescence with different intensities and different peak wavelengths after thermal annealing. Especially, the C⁺-implanted SiN_xO_y, films show very intense photoluminescence at green-yellow color region.