结晶性芳香聚酯高压结晶行为研究进展

运用高压极限手段研究聚合物的结构、形态和性能是20世纪60年代以来兴起的一项聚合物前沿课题。本文主要结合作者自己的研究工作，重点叙述聚对苯二甲酸乙二醇酯(PET)的高压结晶行为研究，包括温度、压力、时间及分子量对PET高压结晶行为的影响，高压结晶PET的形态。以及对PET伸直链晶体结晶机理的探讨，同时简要介绍了对其它结晶性芳香聚酯诸如聚对苯二甲酸丁二醇酯(PBT)及聚对萘二甲酸乙二醇酯(PEN)的高压结晶行为研究，反映了该领域的研究概况和最新进展。并对今后的研究提出了展望。     

高压后EuI2的结构及光谱性质研究

研究了高压后ＥｕＩ２的结构及光谱性质，发现高压后其结构由单斜转化为正交，对称性和Ｅｕ＾２＋配位数均有增加，４ｆ＾６５ｄ能级间距加大，能级重心降低。还讨论了发射光谱的红移现象，指认了新出现的４４９ｎｍ处的发射峰，并报道了ＥｕＩ２新的正交结构（ＥｕＩ２－Ｖ）。     

超临界CO2+碳酸二乙酯二元体系高压气-液相平衡

在带有石英视窗的可变体积高压釜内,于333,353,373和393K等4个温度下,测定了3.0～15.0MPa范围内超临界CO2与碳酸二乙酯(DEC)二元体系的气-液平衡数据.结果表明,当温度恒定时,随着压力的增大,液相中超临界CO2的浓度急剧增大,气相中碳酸二乙酯的浓度缓慢增加.根据实验结果推测出了体系的pc,Tc,xc和Vc等临界性质.     

Synthesis, characterization and gas permeation properties of a silica membrane prepared by high-pressure chemical vapor deposition

Cylindrical silica membranes with dead-end structure were prepared by an extended counter-diffusion chemical vapor deposition (CVD) method, in which a tetramethylorthosilicate (TMOS) silica source was fed from the outside of a cylindrical membrane support with γ-alumina interlayer (the membrane side), and oxygen gas was fed from the inside (the support side). Extended counter-diffusion CVD is a method of depositing silica films under highly pressurized conditions applied to the membrane side where TMOS is supplied. Two silica membranes were deposited for 10 h at 573 K under differential pressures of 0.1 MPa and 0.0 MPa applied between the cylindrical membranes. The hydrogen permeances for these silica membranes were unaffected (5 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ at 573 K), although the methane and carbon dioxide permeances were greatly reduced for dense silica films prepared by high-pressure CVD (HPCVD). Therefore, the selectivity of hydrogen over methane and carbon dioxide was 24,000, and 1200, respectively. It is suggested from energy dispersive X-ray microanalysis (EDX) observations in scanning electron microscopy (SEM) and scanning probe microscopy (SPM) results that this high selectivity was due to the reduced number of defects and/or pinholes formed in the dense silica membranes by HPCVD.     

High-pressure preparation, crystal structure, and properties of the new rare-earth oxoborate β-Dy2B4O9

In this work we report about a new rare-earth oxoborate β-Dy₂B₄O₉ synthesized under high-pressure/high-temperature conditions from Dy₂O₃ and boron oxide B₂O₃ in a B₂O₃/Na₂O₂ flux with a walker-type multianvil apparatus at 8 GPa and 1000°C. Single crystal X-ray structure determination of β-Dy₂B₄O₉ revealed: , a=616.2(1) pm, b=642.8(1) pm, c=748.5(1) pm, α=102.54(1)°, β=97.08(1)°, γ=102.45(1)°, Z=2, R1=0.0151, wR₂=0.0475 (all data). The compound exhibits a new structure type which is built up from bands of linked BO₃- (Δ) and tetrahedral BO₄-groups (□). The Dy³⁺-cations are positioned in the voids between the bands. According to the conception of fundamental building blocks β-Dy₂B₄O₉ can be classified with the notation 2Δ6□:Δ3□=4□=3□Δ. Furthermore we report about temperature-resolved in situ powder diffraction measurements and IR-spectroscopic investigations on β-Dy₂B₄O₉.     

Structural studies on a high-pressure polymorph of NaYSi2O6

High-pressure synthesis experiments in the system Na₂O-Y₂O₃-SiO₂ revealed the existence of a previously unknown polymorph of NaYSi₂O₆ or Na₃Y₃[Si₃O₉]₂ which was quenched from 3.0 GPa and 1000 °C. Structural investigations on this modification have been performed using single-crystal X-ray diffraction data collected at ambient conditions. Furthermore, unpolarized micro-Raman spectra have been obtained from single-crystal material. The high-P modification of NaYSi₂O₆ crystallizes in the centrosymmetric space group C2/c with 12 formula units per cell (a=8.2131(9) Å, b=10.3983(14) Å, c=17.6542(21) Å, β=100.804(9)°, V=1481.0(3) Å³, R(|F|)=0.033 for 1142 independent observed reflections) and belongs to the group of cyclo-silicates. Basic building units are isolated three-membered [Si₃O₉] rings located in layers parallel to (010). Within a single layer the rings are concentrated in strings parallel to [100]. The sequence of directedness of up (U) or down (D) pointing tetrahedra of a single ring is UUU or DDD, respectively. Stacking of the layers parallel to b results in the formation of a three-dimensional structure in which yttrium and sodium cations are incorporated for charge compensation. In more detail, four non-tetrahedral cation positions can be differentiated which are coordinated by 6 and 8 oxygen ligands. Refinements of the site occupancies did not reveal any indication for mixed Na-Y populations on these positions. Finally, several geometrical parameters of rings occurring in cyclo-trisilicate structures have been compiled and are discussed.     

Interpenetrated structure and compressibility studies in pressure frozen pentafluoropyridine crystals at 0.3 and 1.1 GPa

Pentafluoropyridine has been pressure frozen in situ in a diamond-anvil cell (DAC) and its structure determined at 0.30(5) and 1.10(5) GPa and at room temperature by single-crystal X-ray diffraction. The freezing pressure of pentafluoropyridine has been determined to be 0.10(5) GPa. The crystals are monoclinic, space group P2₁/c. The crystal packing is governed by F?F and C/N?F van der Waals contacts, but no ring stacking is observed. The intermolecular interactions are non-directional, and the crystal compresses nearly isotropically between 0.3 and 1.1 GPa.     

Synthesis of the novel perovskite-type oxyfluoride PbScO2F under high pressure and high temperature

We synthesized a novel perovskite-type oxyfluoride, PbScO₂F, and investigated its crystal structure, thermal stability and dielectric properties. PbScO₂F has a cubic perovskite-type structure with Pb ions displaced from the ideal A-site positions along the 〈110〉 direction. By thermal gravity and differential thermal analyses, we found that this compound is stable up to 963 K (690 °C) under ambient atmosphere. The dielectric permittivity of PbScO₂F is approximately 80, at room temperature, which is almost the same as KTiO₂F and smaller than that of PbFeO₂F. Furthermore, an anomaly in the dielectric permittivity was observed in the vicinity of 100 K that seems to be related to the displacement of the Pb ions.     

Cation-dependent anomalous compression of gallosilicate zeolites with CGS topology: A high-pressure synchrotron powder diffraction study

The high-pressure compression behaviour of 3 different cation forms of gallosilicate zeolite with CGS topology has been investigated using in situ synchrotron X-ray powder diffraction and a diamond-anvil cell technique. Under hydrostatic conditions mediated by a nominally penetrating pressure-transmitting medium, unit-cell lengths and volume compression is modulated by different degrees of pressure-induced hydration and accompanying channel distortion. In a Na-exchanged CGS (Na₁₀Ga₁₀Si₂₂O₆₄·16H₂O), the unit-cell volume expands by ca. 0.6% upon applying hydrostatic pressure to 0.2 GPa, whereas, in an as-synthesized K-form (K₁₀Ga₁₀Si₂₂O₆₄·5H₂O), this initial volume expansion is suppressed to ca. 0.1% at 0.16 GPa. In the early stage of hydrostatic compression below ∼1 GPa, relative decrease in the ellipticity of the non-planar 10-rings is observed, which is then reverted to a gradual increase in the ellipticity at higher pressures above ∼1 GPa, implying a change in the compression mechanism. In a Sr-exchanged sample (Sr₅Ga₁₀Si₂₂O₆₄·19H₂O), on the other hand, no initial volume expansion is observed. Instead, a change in the slope of volume contraction is observed near 1.5 GPa, which leads to a 2-fold increase in the compressibility. This is interpreted as pressure-induced rearrangement of water molecules to facilitate further volume contraction at higher pressures.     

Dynamics of hydrogen-bonded water networks under high pressure: Neutron scattering and computer simulation

Abstract

Molecular dynamics simulation of proton-ordered high pressure ice modifications II and IX was performed. Dynamics of both isotope varieties, H₂O and D₂O, was simulated. Rectangular simulation box of ice II contained 576 and that of ice IX 768 molecules. The average kinetic energy corresponded to 82 and 201 K for ice II and to 87 and 203 K for ice IX. One-phonon densities of states were calculated via Fourier transformation of velocity autocorrelation functions and compared with those found experimentally from inelastic incoherent neutron scattering. This characteristic was calculated for all the molecules, as well as for the molecules of a particular crystallographic type. Both simulated ice modifications contain molecules of two different structural types. Dynamic characteristics of molecules of different types are slightly different. Splitting of the librational peak at about 60–70meV observed in the ice II experimental spectrum is mainly due to such difference. In the case of ice II simulated spectra reproduce experimental ones quite reasonably in the whole range of energies, while in the case of ice IX agreement with the experiment is worse.