HAN-TEAN-H_2O 三元体系的相变及其相图

用ＤＳＣ研究了ＨＡＮ－ＴＥＡＮ－Ｈ２Ｏ三元体系的低温热行为，建立了该体系低温下相变与组分关系的相图。考察了玻璃化转化温度随ＨＡＮ／ＴＥＡＮ比例的变化规律。发现了三元体系的溶液性质在ＨＡＮ－ＴＥＡＮ比率较大时，与ＨＡＮ－Ｈ２Ｏ二元体系相似，而在ＨＡＮ／ＴＥＡＮ比率较小时，则与ＴＥＡＮ－Ｈ２Ｏ二元体系相似。     

二氧化钛相变研究现状

综述了二氧化钛由锐钛矿型向金红石型转变的影响因素,重点研究了温度调控与添加剂调控对二氧化钛锐钛矿型向金红石型转变的影响和作用机理。结果表明：温度调控能直接有效地促进二氧化钛锐钛矿型向金红石型转变;掺杂熔点低于TiO2的金属氧化物V2O5、SnO2等,离子半径与Ti4+半径相近的Fe3+、V4+、Ce4+等,以及体积小的低价阴离子Cl-、F-等都能促进TiO2由锐钛矿型向金红石型转变。     

Isotope effect of H2/D2 and H2O/D2O for the PROX reaction of CO on the FeOx/Pt/TiO2 catalyst

The oxidation reaction of CO with O₂ on the FeOx/Pt/TiO₂ catalyst is markedly enhanced by H₂ and/or H₂O, but no such enhancement occurs on the Pt/TiO₂ catalyst. Isotope effects were studied by H₂/D₂ and H₂O/D₂O on the FeOx/Pt/TiO₂ catalyst, and almost the same magnitude of isotope effect of ca. 1.4 was observed for the enhancement of the CO conversion by H₂/D₂ as well as by H₂O/D₂O at 60 °C. This result suggests that the oxidation of CO with O₂ via such intermediates as formate or bicarbonate in the presence of H₂O, in which H₂O or D₂O acts as a molecular catalyst to promote the oxidation of CO as described below.      

Dilatometric studies of phase transition in NaNH4SeO4·2H2O single crystal

Thermal expansion of NaNH₄SeO₄SeO₄2H₂O crystal was measured by means of dilatometric method along three crystallographic axes in the temperature range of 300-140 K. Anomalies of relative expansion and thermal expansion coefficients related to ferroelectric phase transition were observed and confirmed its continuous character.     

Faraday effect aid birefringence in orthorhombic Li2Ge7O15 near the ferroelectric phase transition

The tensor of the Faraday effect and its temperature derivatives were determined from the temperature dependence of Faraday rotation and indices of refraction of orthorhombic Li₂Ge₇O₁₅ between 120K and 340K, wave length 633nm. A strong anomaly of the Verdet constant V₃₃ and of the index n₃ was observed passing through the transition at 284K. The ratio of the slopes of the Verdet constant V₃₃ above and below the transition is about -2. This value corresponds to a second-order ferroelectric phase transition.     

Use of T1ρH as a probe for polymer blend phase structure

T_1ρH′ the proton spin-lattice relaxation time in the rotating frame, can be used as a probe for polymer blend miscibility in the same way the glass transition temperature (T_g) is used. T_1ρH has some advantages over T_g. It is indicative of the separate phases at a level of a few nanometers, below what T_g can distinguish. Also, T_1ρH is the only parameter related to the local proton density in a sample. This paper shows a few examples of T_1ρH investigations, including thermally reversible blends, phase separated composites, and mixtures of polymers with small molecules.     

Kinetic study of the II-I phase transition of isotactic polybutene-1

Kinetics of the solid-solid II-I phase transition of isotactic polybutene-1 was investigated. The fraction W_I of phase I as a function of time t_tr during the phase transition was measured by X-ray diffraction at various temperatures T_tr. The Avrami indices n of the W_I-t_tr plots are approximately unity for T_tr > 288 K. A bell-shaped temperature dependence of the transition rate V with the maximum transition rate at 285 K was obtained. The V-T_tr curve and the Avrami index n = 1 suggest that the rate-determining process is primary nucleation. The dependence of V on T_tr for T_tr < 283 K is described by the William-Landel-Ferry (WLF) equation, which shows that the glass transition affects the transition rate. The Avrami index decreases to n < 1 for T_tr < 283 K, indicating a broadened distribution of the transition rate caused by the spatial heterogeneity of the amorphous state at low temperatures near the glass transition. Those evidences at low temperature clearly suggest that the solid-solid phase transition is influenced by the mobility of chain folding, tie chains and cilia in the amorphous between the stacks of lamellar crystals.     

Surfactant chain length effect on the hexagonal-to-cubic phase transition in mesoporous silica synthesis

In this study, silica-based mesoporous materials (the M41S family mesoporous molecular sieves) are synthesized using alkyltrimethylammonium bromide with different chain lengths (C_nH_2n+1N(CH₃)₃Br, n = 10, 12, 14, 16) as templates. The resulting silica structures are characterized by X-ray diffraction and are found to exhibit the phase transformation from the hexagonal mesophase MCM-41 to the cubic mesophase MCM-48 (with the space group of Ia3d). The structural phase transition in our study is controlled by the alkyl chain length of the surfactant: with an increase in the surfactant chain length (from C10 to C16), the structure goes from MCM-41 (synthesized by C10), through an intermediate structure (synthesized by C12), to MCM-48 (synthesized by C14 and C16). The amount of ethanol, which is used as a cosolvent, affects the pore size of the structured mesoporous silica, but only to a small extent. In the mean time, the autoclaving time has some effect, though not distinctively, on the structure integrity as well. With increased surfactant to silica ratio, the phase transformation can be shifted to longer chain template.     

The effect of phase transition of methanol on the reaction rate in the alkylation of hydroquinone

An O-alkylation reaction of hydroquinone with excess methanol was carried out by using alkaline metal ion-exchanged zeolite catalysts at various phases of methanol in a slurry type reactor. The amount of methanol, used as a methylating agent and also a solvent, significantly affected the reaction rate. When the amount of methanol was decreased from 2 mol to 0.6 mol, the reaction rate was increased more than nine times. These changes in the reaction rate could be explained by the pressure change and the phase transition of the reactant, methanol, depending on the temperature and the elimination of a diffusion limitation of reactants through the zeolite pores in a gas phase condition. Thus, higher than 89% selectivity to 4-methoxyphenol was obtained at 80% conversion of hydroquinone at a gas phase reaction condition using 1 mol of methanol for 2 hours.     

1H T2‐NMR monitoring of crosslinked polyolefin aging

This work examines the correlation between the ¹H‐NMR T₂ relaxation constant and the mechanical properties of aged crosslinked polyolefin cable insulation. T₂ experiments on unswollen samples could not differentiate between unaged and highly aged materials; all exhibited ¹H T₂ constants of approximately 0.5 ms. To accentuate the effects of aging, samples were swollen in various solvents. Unaged samples had T₂ values of approximately 15 ms in good solvents. With thermal aging, T₂ values decreased as the ultimate tensile elongation decreased. However, the correlation between T₂ and elongation differed for samples irradiated with high‐energy radiation and for materials aged above versus below the crystalline melting temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2578–2582, 2003     

Titanium effect on phase transformation and sintering behavior of transition alumina

The sintering behavior of doped γ-alumina powders studied by dilatometry and electron microscopy is analysed with a particular emphasis on the role of titanium on the various densification steps. Compared with other doping elements, such as Mg, Y and Zr, which do not improve α-phase densification, titanium enhances this densification step by a fast decrease of internal colony porosity. This internal densification of single crystalline zones is attributed to the lengthening of the elementary bricks in titanium-doped samples. A transient increase in densification rate is also observed, corresponding to the precipitation when during grain growth, grain boundaries become saturated with titanium. Final densities close to the theoretical values are obtained.     

1H,1H,2H,2H-全氟烷基丙烯酸酯的自压催化合成

以丙烯酸钾盐和全氟烷基乙烯基加成物(PFOEI)为原料,在反应体系自身产生的压力下,催化合成1H,1H,2H,2H-全氟烷基丙烯酸酯,考察了在原料配比为,n(PFOEI):n(丙烯酸钾):n(叔戊醇):n(PIC):n(阻聚剂)=1:1.5:20:0.06:0.05、反应时间为9 h下,溶剂、相转移催化剂和反应温度对酯...     

Controlling crystal phase transition from form II to I in isotactic poly-1-butene using CO2

Controlling crystal phase transition from modification II to I in isotactic Poly-1-butene (iPB-1) using CO₂ is presented in this article. The intrinsic kinetics of CO₂-induced phase transition from modification II to I in iPB-1 at 40 °C and different CO₂ pressures were detected using in situ high-pressure Fourier transform infrared spectroscopy (FTIR) and correlated by Avrami equation. Sorption of CO₂ in iPB-1 matrix was measured at 40 °C and different CO₂ pressures using both FTIR and magnetic suspension balance (MSB) and the diffusivity was determined by Fick's second law. An algorithm combining the CO₂ diffusion and induced phase transition was subsequently proposed to calculate the CO₂ concentration as well as the phase transition degree in the iPB-1 matrix with different thickness at different saturation time. The calculated phase transition degree in the iPB-1 agreed well with the FTIR results. In addition, the yield stresses of iPB-1 specimens annealed in the air and 6 MPa CO₂ at 40 °C with different durations were also experimentally investigated. The algorithm was applied to predict the phase transition degree of the iPB-1 specimens. The appropriate CO₂ treatment time for getting high yield stress was in consistent with that predicted by the algorithm.     

Magnetocaloric effect in La1-xSrxCoO3 undergoing a second-order phase transition

We have prepared rhombohedral La_1-xSr_xCoO_3-δ (x?=?0.2–0.5) compounds with a mass density ρ?≈?5.5?g/cm³. Their magnetocaloric (MC) effect is studied via the magnetic-entropy change (ΔS_m) and relative cooling power (RCP), which are calculated from initial magnetization data recorded at different temperatures. Results reveal that the ΔS_m magnitude is maximum (ΔS_max) around the ferromagnetic-paramagnetic phase transition and dependent on both the applied-field (H) magnitude and Sr content (x). For H =?50?kOe, |ΔS_max| can be tuned in the range of 1.6–2.7?J/kg?K, corresponding to RCP values of 89–141?J/kg. Among the studied La_1-xSr_xCoO_3-δ samples, the samples with x?=?0.3–0.5 have the largest |ΔS_max| values. If combining these samples as MC blocks in refrigeration application, the working temperature range of a cooling device could range from 204 to ~280?K, with |ΔS_max| stable at ~2.6?J/kg?K and RCP ≈?198?J/kg. We have also assessed the phase-transition type and magnetic order and found La_1-xSr_xCoO_3-δ undergoing a second-order phase transition. Magnetic order tends to change from the long-range type to the short-range one when x varies from 0.2 to 0.5. This is in good agreement with the results obtained from the analysis of critical behavior.     

Permselectivity of cellulose acetate membranes; separation of H2/CO mixtures and the effect of added transition metals

Cellulose acetate membranes permit permeation of H₂ and CO₂ but are relatively impervious to CO and N₂. Permselectivity was demonstrated by effective separation of H₂ from its mixtures with CO. The presence of RuCl₃ in the membrane does not result in any appreciable change in permselectivity. The exposure of RuCl₃- and RhCl₃-modified membranes to H₂/CO mixtures results in the formation of RuCl₂(CO)_x and [RhCl(CO)₂]₂, respectively. However, these complexes are not covalently anchored to the cellulose acetate matrix and apparently function only as additives that block access to the press and channels in the cellulose acetate membrane.     

Living cationic polymerization of 1H,1H,2H,2H perfluorooctyl vinyl ether

Summary Cationic polymerization of 1H,1H,2H,2H perfluorooctyl vinyl ether (CH₂=CH-O-C₂H₄-C₆F₁₃), initiated by the HI/ZnI₂ system in 1,1,2 trichloro trifluoro ethane at-30°C, leads to living polyvinyl ethers bearing a fluoroalkyl group. Results indicate that the polymerization is indeed free from chain transfer and termination reactions and that polyethers of controlled molecular weight and a narrow molecular weight distribution can be made available.     

ZnO包覆TiO_2超微颗粒的制备及相转位研究

采用Ti(SO4)2水解制得纳米级水合TiO2胶粒,并在其表面通过沉积碱式碳酸锌,制备得到ZnO包覆TiO2微粒。采用了SEM、TEM、EDS以及XRD等方法对所制备的粉体进行了表征。通过实验选择了合适的ZnO包覆含量,并对含ZnO摩尔分数为10%的包覆体进行了高温热处理,利用XRD等手段确定了粉体颗粒中锐钛以及金红石的含量,进而进行了相转位动力学研究,得到转化反应的活化能E为99 7kJ/mol,结合热处理过程以及包覆体结构,提出了可能的相转变机制。     

Regulation of Circadian Genes Nr1d1 and Nr1d2 in Sex-Different Manners during Liver Aging

Background: Circadian rhythm is associated with the aging process and sex differences; however, how age and sex can change circadian regulation systems remains unclear. Thus, we aimed to evaluate age- and sex-related changes in gene expression and identify sex-specific target molecules that can regulate aging. Methods: Rat livers were categorized into four groups, namely, young male, old male, young female, and old female, and the expression of several genes involved in the regulation of the circadian rhythm was confirmed by in silico and in vitro studies. Results: Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses showed that the expression of genes related to circadian rhythms changed more in males than in females during liver aging. In addition, differentially expressed gene analysis and quantitative real-time polymerase chain reaction/western blotting analysis revealed that Nr1d1 and Nr1d2 expression was upregulated in males during liver aging. Furthermore, the expression of other circadian genes, such as Arntl, Clock, Cry1/2, Per1/2, and Rora/c, decreased in males during liver aging; however, these genes showed various gene expression patterns in females during liver aging. Conclusions: Age-related elevation of Nr1d1/2 downregulates the expression of other circadian genes in males, but not females, during liver aging. Consequently, age-related upregulation of Nr1d1/2 may play a more crucial role in the change in circadian rhythms in males than in females during liver aging.     

The phase transition of hBN-cBN in the B-N-H-O system

The physical-chemical processes are responsible for hBN-cBN conversion in the B-N-H-O system were studied in region of pressure 3.5–7.2 GPa and temperature up to 1400°C by means of in situ differential thermal analysis (DTA) and the quenched method. The absence of intermediate solid phases in products of the interaction of hBN with melts of anhydrous ammonium borates has confirmed the supposition about the activating effect of these melts on the kinetic of the conversion. A scheme of the part of T,c phase diagram on the (NH₄)₂O-B₂O₃ line was built at 6 GPa. Three peritectics corresponding to the dissociation of proposed NH₄BO₂, (NH₄)₂B₄O₇ and (NH₄)₄B₁₀O₁₇ were found. The connection of the lower-temperature limits of cBN synthesis regions with the found peritectics in the range of 5.5–7.2 GPa was established. The formal critical composition of the melt was 3(NH₄)₂O:7B₂O₃, because the appearance of cBN was fixed in the product beginning with just this composition. However, the question about critical melt composition activating hBN-cBN conversion has no correct solution without information about short-range order structure and relaxation kinetics of the melts. Two unknown anhydrous ammonium borates were found in HPHT products. One of these compounds was determined to be (NH₄)₄B₁₀O₁₇. It crystallizes in a orthorhombic cell with a=12.82 Å, b=11.30 Å, c=9.52 Å, a measured density of 2.10 g cm⁻³, a calculated density of 2.21 g cm⁻³ at Z=4. At normal conditions (NH₄)₄B₁₀O₁₇ is metastable but it can be preserved a long time in a “dry” atmosphere.