High-Pressure Synthesis of Molybdates with the Wolframite Structure

A series of small cation molybdates, MgMoO(4), MnMoO(4), FeMoO(4), CoMoO(4), NiMoO(4), and ZnMoO(4) with the wolframite structure characteristic of the corresponding tungstates have been synthesized at high pressure and temperature. The high-pressure compounds revert to the ambient pressure modifications if heated in air at 600 degrees C.     

Deep ultraviolet light-emitting hexagonal boron nitride synthesized at atmospheric pressure

Materials emitting light in the deep ultraviolet region around 200 nanometers are essential in a wide-range of applications, such as information storage technology, environmental protection, and medical treatment. Hexagonal boron nitride (hBN), which was recently found to be a promising deep ultraviolet light emitter, has traditionally been synthesized under high pressure and at high temperature. We successfully synthesized high-purity hBN crystals at atmospheric pressure by using a nickel-molybdenum solvent. The obtained hBN crystals emitted intense 215-nanometer luminescence at room temperature. This study demonstrates an easier way to grow high-quality hBN crystals, through their liquid-phase deposition on a substrate at atmospheric pressure.     

Kaolinite: synthesis at room temperature

To obtain kaolinite at low temperature and pressure from the system Si(OH)(4)-Al(3+)-H(2)O, the sixfold coordination of aluminum is a necessary prerequisite. Kaolinite was synthesized at pH values from 2 to 9 and with a ratio of SiO(2) to Al(2)O(3) in solution from 1 to 10 by means of the complexation of Al(3+) and fulvic acid.     

Synthesis of RNA-polyadenylic acid by isolated brain nuclei

Nuclei, isolated from mouse brain tissue at various stages of postnatal development and incubated under cell-free conditions, synthesized RNA molecules that were associated with polyadenylic acid [poly(A)]. The RNA synthesized by these nuclei was similar to the poly(A)-associated products described for intact eukaryotic cells. The brain nuclei synthesized a similar proportion of RNA-poly(A) in the presence either of Mg(2+) or of Mn(2+) with (NH(4))(2)So(4). The RNA from neonatal brain nuclei appeared to have a greater proportion of poly(A)-containing RNA than nuclear products obtained from more mature neural tissue.     

压力对稀土元素Sm填充方钴矿化合物热电性能的影响

通过高温高压方法合成出稀土元素Sm填充n型方钴矿化合物SmxCo4Sb12（0〈x〈1）,并考察了在室温下Sm填充率对热电性能的影响规律.结果表明：SmxCo4Sb12化合物表现为n型传导;电阻率和Seebeck系数随着合成压力的增加逐渐增加;晶格热导率随着Sm填充分数的增加而降低,在Sm填充量为0.5时达到最小值.室温下Sm0.5Co4Sb12化合物显示最大热电性能指数,其最大无量纲热电性能指数ZTmax值达到0.16.     

Negative Pressure-Temperature Slopes for Reactions Formign MgSiO3 Perovskite from Calorimetry

A new and sensitive differential drop solution calorimetric technique was developed for very small samples. A single experiment using one 5.18-milligram sample of perovskite, synthesized at 25 gigapascals and 1873 Kelvin, gave 110.1 +/- 4.1 kilojoules per mole for the enthalpy of the ilmenite-pervoskite transition in MgSiO(3). The thermodynamics of the reaction of MgSiO(3) (ilmenite) to MgSiO(3) (perovskite) and of Mg(2)SiO(4) (spinel) to MgSiO(3) (pervoskite) and MgO (periclase) were assessed. Despite uncertainties in heat capacity and molar volume at high pressure and temperature, both reactions clearly have negative pressure-temperature slopes, -0.005 +/- 0.002 and -0.004 +/- 0.002 gigapascals per Kelvin, respectively. The latter may be insufficiently negative to preclude whole-mantle convection.     

Antiferromagnetism in Pressure-Amorphized Fe2SiO4

Amorphous Fe(2)SiO(4) synthesized at elevated pressures exhibits a Néel transition at a temperature identical to that observed in the crystalline form, T(N) = 65 (+/-2) kelvin at zero pressure. This behavior contrasts sharply with observations on other disordered systems, such as spin glasses, which characteristically exhibit strong "frustration" of the spins and consequent marked suppression of the Néel transition.     

全麻加颈丛神经阻滞对复杂性甲状腺手术麻醉的效果观察

目的 :观察全麻加颈丛阻滞用于复杂性甲状腺手术是否优于全麻。方法 :68例复杂性甲状腺手术分为全麻复合颈丛神经阻滞组 (A组 ) 4 2例和全麻组 (B组 ) 2 6例 ,观察两组患者术前、术中和术毕的血压、心率、血糖变化及清醒拔管时间。结果 :两组间术前血压、心率和血糖无明显差异 ,但在手术开始和分离甲状腺时血压、心率及术中血糖变化差异非常显著 (P<0 .0 1 )。A组在气管插管时的血压和心率较术前、术中和术毕明显升高 (P<0 .0 1 ) ;而 B组在气管插管时的血压和心率与术中比较无差异 ,但比术前和术毕明显升高 (P<0 .0 1 )。结论 :复杂性甲状腺手术选择全麻复合颈丛神经阻滞 ,在术中血流动力学稳定、减轻应激反应及缩短术毕清醒气管导管拔除时间等方面明显优于单纯全麻。     

An asymmetric membrane of polyimide 6FDA-BDAF and its pervaporation desulfurization for n-heptane/thiophene mixtures

Polyimide(PI) is a type of important membrane material. A soluble polymer was synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride(6FDA) and 2,2-bis[4-(4-aminophenoxy) phenyl] hexafluoropropane(BDAF) by the two-step polymerization method. The polymer was proved to be polyimide 6FDA-BDAF by the Fourier transform infrared(FT-IR), the 1H-NMR and ~(19)F-NMR spectra. An asymmetric membrane was prepared with the synthesized polyimide 6FDA-BDAF, it was porous in the 50 μm height bulk and dense in a 3–5 μm height surface. The membrane was used to separate n-heptane/thiophene mixtures by pervaporation with sulfur(S) contents from 50 to 900 μg g~(–1). The total flux was enlarged from 7.96 to 37.61 kg m~(–2) h~(–1) with temperature increasing from 50 to 90°C. The membrane's enrichments factor for thiophene were about 3.13 and dependent on the experimental conditions. The experimental results demonstrated that polyimide 6FDA-BDAF would be a potential membrane material for desulfurization and controlled release of the S-containing fertilizer.     

北五味子多糖对小鼠抗疲劳和耐缺氧的作用

将160只昆明种小鼠随机分成4组,即空白组(蒸馏水)、高、中、低剂量组(多糖含量分别为40、20、10 mg·kg-1·d-1).每组40只,每日以10 mL/kg剂量给小鼠连续灌胃30 d.然后测定其负重游泳时间、常压耐缺氧时间,并测定其血清中乳酸、乳酸脱氢酶活性、血清尿素氮(血清尿素氮)浓度和肝糖原质量分数.结果表...     

Synthesis of todorokite

Todorokite of chemical composition (Mg(0.77)Na(0.03))(Mg(0.18)Mn(2+)(0.60)Mn(4+)(5.22)22) O(12).3.07 H(2)O was synthesized by a two-step procedure. First, sodium birnessite was synthesized and magnesium was exchanged for sodium to form magnesium birnessite, which was autoclaved under a saturated steam pressure at 155 degrees C for 8 hours to form well-crystallized todorokite. Synthesized todorokite particles consisted of fibers extending from a central plate. The plate itself was made of twinned fibers forming a trilling pattern. The infrared spectra and x-ray diffraction patterns were similar to those of natural todorokite samples. Calcium birnessite and nickel birnessite, when autoclaved under conditions similar to those for magnesium birnessite, yielded a todorokite structure. However, the formation of todorokite from calcium and nickel birnessite was less extensive.     

Modified spinel, Beta-manganous orthogermanate: stability and crystal structure

A new high-pressure polymorph with a modified spinel structure, beta-Mn(2)GeO(4), is stable in a pressure range intermediate between the field of the polymorph with the olivine structure and that of another high-pressure polymorph. Oxygen atoms are located approximately in cubic close packing with manganese and germanium atoms in octahedral and tetrahedral interstices, respectively, as in the spinel structure; however, germanium atoms form Ge(2)O(7) groups instead of isolated GeO(4) groups.     

Filled Skutterudite Antimonides: A New Class of Thermoelectric Materials

A class of thermoelectric materials has been synthesized with a thermoelectric figure of merit ZT (where T is temperature and Z is a function of thermopower, electrical resistivity, and thermal conductivity) near 1 at 800 kelvin. Although these materials have not been optimized, this value is comparable to the best ZT values obtained for any previously studied thermoelectric material. Calculations indicate that the optimized material should have ZT values of 1.4. These ternary semiconductors have the general formula RM4X12 (where R is lanthanum, cerium, praseodymium, neodymium, or europium; M is iron, ruthenium, or osmium; and X is phosphorus, arsenic, or antimony) and represent a new approach to creating improved thermoelectric materials. Several alloys in the composition range CeFe4-xCoxSb12 or LaFe4-xCoxSb12 (0 < x < 4) have large values of ZT.     

Comment on "Synthesis of ultra-incompressible superhard rhenium diboride at ambient pressure"

Chung et al. (Reports, 20 April 2007, p. 436) reported the synthesis of superhard rhenium diboride (ReB2) at ambient pressure. We show that ReB2, first synthesized at ambient pressure 45 years ago, is not a superhard material. Together with the high cost of Re, this makes the prospect for large-scale industrial applications of ReB2 doubtful.     

Sanidine: Predicted and Observed Monoclinic-to-Triclinic Reversible Transformations at High Pressure

High sanidine, (K,Na)AlSi(3)O(8), transforms reversibly to a triclinic phase at high pressure. This is analogous to the high-temperature monalbite transformation. Disordered alkali feldspars of various compositions have unit-cell dimensions which are very similar at the transition (a = 8.30 A, b = 12.97 A, c = 7.14 A, and beta = 116.2 degrees ), indicating that the transformation is structurally controlled. Changes in temperature, pressure, and the sodium/potassium ratio cause similar structural variations: angles between adjacent, rigid tetrahedra vary to accommodate changing effective alkali cation sizes.     

High-throughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture

A high-throughput protocol was developed for the synthesis of zeolitic imidazolate frameworks (ZIFs). Twenty-five different ZIF crystals were synthesized from only 9600 microreactions of either zinc(II)/cobalt(II) and imidazolate/imidazolate-type linkers. All of the ZIF structures have tetrahedral frameworks: 10 of which have two different links (heterolinks), 16 of which are previously unobserved compositions and structures, and 5 of which have topologies as yet unobserved in zeolites. Members of a selection of these ZIFs (termed ZIF-68, ZIF-69, and ZIF-70) have high thermal stability (up to 390 degrees C) and chemical stability in refluxing organic and aqueous media. Their frameworks have high porosity (with surface areas up to 1970 square meters per gram), and they exhibit unusual selectivity for CO2 capture from CO2/CO mixtures and extraordinary capacity for storing CO2: 1 liter of ZIF-69 can hold approximately 83 liters of CO2 at 273 kelvin under ambient pressure.     

Garnet-like structures of high-pressure cadmium germanate and calcium germanate

Crystals of CdGeO(3) grown at a pressure of 65 kilobars are tetragonal and have an ordered, garnet-like crystal structure with cadmium occupying the dodecahedral and octahedral sites, and germanium the octahedral and tetrahedral sites. The crystal structure (a = 12.406 +/- 1 angstroms, c = 12.256 +/- 1 angstroms, and space group 14,/a) has been refined by least-squares analysis to an R (discrepancy index) of 0.073. Two high-pressure phases of CaGeO(3) were synthesized, one isotypic with tetragonal CdGeO(3) (a = 12.514 +/- 3 angstroms, c = 12.358 +/- 3 angstroms), and the other isotypic with perovskite.     

Synthesis and Equation of State of (Mg,Fe) SiO3 Perovskite to Over 100 Gigapascals

Silicate perovskite of composition (Mg(0.88)Fe(0.12)) SiO(3) has been synthesized in a laser-heated diamond-anvil cell to a pressure of 127 gigapascals at temperatures exceeding 2000 K. The perovskite phase was identified and its unit-cell dimensions measured by in situ x-ray diffraction at elevated pressure and room temperature. An analysis of these data yields the first high-precision equation of state for this mineral, with values of the zero-pressure isothermal bulk modulus and its pressure derivative being K(0T) = 266 +/- 6 gigapascals and K'(0T) = 3.9 +/- 0.4. In addition, the orthorhombic distortion of the silicate-perovskite structure away from ideal cubic symmetry remains constant with pressure: the lattice parameter ratios are b/a = 1.032 +/- 0.002 and c/a = 1.444 +/- 0.006. These results, which prove that silicate perovskite is stable to ultrahigh pressures, demonstrate that perovskite can exist throughout the pressure range of the lower mantle and that it is therefore likely to be the most abundant mineral in Earth.     

Pressure-induced enhancement of tc above 150 k in hg-1223

The recently discovered homologous series HgBa(2)Can-1 Cun O2n+2+delta possesses remarkable properties. A superconducting transition temperature, T(c), as high as 133 kelvin has been measured in a multiphase Hg-Ba-Ca-Cu-O sample and found to be attributable to the Hg-1223 compound. Temperature-dependent electrical resistivity measurements under pressure on a (> 95%) pure Hg-1223 phase are reported. These data show that T(c) increases steadily with pressure at a rate of about 1 kelvin per gigapascal up to 15 gigapascals, then more slowly and reaches a T(c) = 150 kelvin, with the onset of the transition at 157 kelvin, for 23.5 gigapascals. This large pressure variation (as compared to the small effects observed in similar compounds with the optimal T(c)) strongly suggests that higher critical temperatures could be obtained at atmospheric pressure.     

Densities of liquid silicates at high pressures

Densities of molten silicates at high pressures (up to approximately 230 kilobars) have been measured for the first time with shock-wave techniques. For a model basaltic composition (36 mole percent anorthite and 64 mole percent diopside), a bulk modulus K(s), of approximately 230 kilobars and a pressure derivative (dK(s)/dP) of approximately 4 were derived. Some implications of these results are as follows: (i) basic to ultrabasic melts become denser than olivine-and pyroxene-rich host mantle at pressures of 60 to 100 kilobars; (ii) there is a maximum depth from which basaltic melt can rise within terrestrial planetary interiors; (iii) the slopes of silicate solidi [(dT(m)/dP), where T(m) is the temperature] may become less steep at high pressures; and (iv) enriched mantle reservoirs may have developed by downward segregation of melt early in Earth history.