呋咱并［3,4-e］-1,2,3,4-四嗪-1,3-二氧化物(FTDO)分子结构及性质的理论研究

采用密度泛函方法在B3LYP/6-31+G(d,p)水平上对呋咱并[3,4-e]-1,2,3,4-四嗪-1,3-二氧化物(FTDO)的结构进行了优化,并分析了其红外振动吸收,计算得到FTDO密度为1.860 g.cm-3,氧平衡为-10.25%,生成焓为661.0 kJ.mol-1。以FTDO为单质炸药计算得到其爆容为718 L.kg-1,爆速达9493 m.s-1,爆压达40.76 GPa。与现有的高能量密度材料HMX比较,密度和爆容小于HMX,其余性能均优于HMX。     

Injection‐molded porous hydroxyapatite/polyamide‐66 scaffold for bone repair and investigations on the experimental conditions

Hydroxyapatite/polyamide‐66 (HA/PA66) composite scaffolds were prepared using injection‐molding technique and also analyzed by means of scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, and mechanical testing. Compared with common methods to fabricate scaffolds, this process can fabricate composite scaffolds in a rapid and convenient manner by adjusting the experimental conditions of foaming agent and shot size. The interactions between PA66 and HA particles affect the crystallization behavior of PA66 and the pore structure of scaffolds. HA particles can increase the stiffness of composite scaffolds accompanied by the reduction of impact strength, pore size and porosity. The obtained 40 wt% HA/PA66 composite scaffolds with a pore size ranging from 100–500 μm and a porosity more than 65% can simultaneously meet the requirements of porous structure and mechanical performance. POLYM. ENG. SCI., 54:1003–1012, 2014. © 2013 Society of Plastics Engineers     

Low-temperature reactive hot-pressing of cerium-doped titanate composite ceramics and their aqueous stability

Reactive hot-pressing was scarcely applied to fabricate titanate ceramic waste forms designed for immobilizing high-level radioactive waste (HLW). However, compared with non-reactive processes, there is an advantage of producing high-density ceramics at reduced temperatures by reactive hot-pressing. Ce^IV-doped titanate composite ceramics with relative densities in excess of 99% were prepared by reactive hot-pressing at temperature as low as 1150 °C and pressure of 30 MPa for 1–4 h. The results show that low-temperature densification of the composite ceramics might be attributed to the plastic deformation under hot-pressing condition. In addition, aqueous stability testing was carried out using the standard MCC-1 static leach test method. The results demonstrate that the normalized elemental leach rate of Ca, Ce and Zr were fairly constant in a low value below 5 × 10⁻² g m⁻² d⁻¹, 7 × 10⁻⁶ g m⁻² d⁻¹ and 6 × 10⁻⁶ g m⁻² d⁻¹ after 21 d.     

Low-temperature sintering of (K,Na)NbO3-based lead-free piezoceramics with addition of LiF

Dense Li/Ta-codoped KNN-based piezoceramics with d₃₃^* up to 375 pm/V were successfully fabricated by conventional sintering at a temperature as low as 900 °C by using LiF as a sintering additive. The reduction of densification temperature up to 200 °C was realized by a transient liquid phase sintering mechanism, consequently no grain boundary phase was observed in the sintered samples. It was found that the addition of LiF could further shift down the tetragonal–orthorhombic transition point (T_T-O), indicating that a small amount of Li⁺ could diffuse into the A-site of KNN matrix. The introduction of LiF enhanced the linearity of strain curves of the ceramics, which is unambiguously in favor for the actuator application. The present work reveals that low-temperature sintered LiF-doped KNN-based piezoceramics demonstrates promising potential in multilayer-structured actuator applications.     

Effect of steam content and O2 pretreatment on the catalytic activities of Au/CeO2–Fe2O3 catalysts for steam reforming of methanol

The Au/CeO₂–Fe₂O₃ prepared by deposition–precipitation were studied by steam reforming of methanol at a reaction temperature range of 200–400 °C. Complete methanol conversion was obtained at the optimal steam/methanol ratio of 2 at 400 °C. A high steam content strongly depressed both methanol conversion and hydrogen concentration since this led to a complex mechanism and the formation of carbonate and formate species. After pretreating with oxygen, the catalytic activity dramatically decreased with the presence of an inhomogeneous Ce_xFe_1−xO₂ solid solution phase; the covering Au sites by the free α-Fe₂O₃ particles; and an agglomeration of both free α-Fe₂O₃ and Au particles.     

Suppression of high-temperature dielectric loss by designed thermal annealing treatment in (Bi1/2Na1/2)TiO3 ceramics

Dielectrics for automobile applications generally require high temperature reliability. Bi_1/2Na_1/2TiO₃-based materials are excellent high-temperature dielectric candidates with relatively large temperature-insensitive dielectric responses and a maximum dielectric permittivity temperature as high as 300 °C. However, they suffer from a high dielectric loss that increases exponentially above 200 °C due to ionic conduction from thermally activated oxygen vacancy migration. Here, we demonstrate that the impact of ionic conduction on dielectric loss can be effectively suppressed by introducing a sodium deficiency and thermal annealing An appropriate combination of both treatments elevated the temperature insensitivity of the dielectric loss up to ～ 300 °C. A systematic investigation using impedance spectroscopy correlated with microstructure analysis revealed that the sodium deficiency and thermal annealing affected the mobile oxygen vacancy concentration differently.     

Oxidation of graphene-modified HfB2-SiC ceramics by supersonic dissociated air flow

The oxidation resistance of ultra-high-temperature ceramic material (HfB₂-30 vol%SiC)-2 vol%rGO (rGO: reduced graphene oxide) under long-term exposure (2000s) to a supersonic air flow has been studied. The ceramics were obtained by reactive hot pressing of HfB₂-(SiO₂-C)-rGO composite powder at a temperature of 1800°C (pressure 30 MPa, holding time 15 min, Ar). The surface temperature of graphene-modified ceramics under the influence of heating by high-enthalpy air flow (heat flow q reached 779 W·cm^–2) did not exceed 1700°C, which is 650–700°C less than for the HfB₂-30 vol%SiC baseline ceramics. This may be related to an increase in the efficiency of heat transfer from the sample to the water-cooled module, due to the higher thermal conductivity of the rGO-containing material. Thereby, a decrease in the material degradation degree has been noted, i.e. decrease in the recession rate and decrease in the total thickness of the oxidised ceramic layer by tenth. The peculiarities of the oxidised surface and near-surface region microstructure upon aerodynamic heating of the graphene-modified ceramic material, have been shown.     

Insight into t->m transition of MW treated 3Y-PSZ ceramics by grazing incidence X-ray diffraction

The influence of a microwave hybrid heat treatment (MHH) on the surface and in-depth mineralogical transformation of pre-sintered 3Y-PSZ was investigated. 3Y-PSZ samples were prepared by slip casting and sintered by conventional firing (1270 °C). Then, different MHH treatments from 5 to 15 min. at 1200 °C were applied to obtain a fully stabilized 3Y-TZP. The monoclinic fraction depth profiles in the first micrometres (up to 5) of thickness were investigated by means of the grazing incident X-ray diffraction technique (GIXRD). A good sintering degree with practically nil closed porosity and grain growth was achieved after MHH of 15 min. MHH increases the tetragonal phase content both in the surface and in-depth, reducing completely the monoclinic phase shell typically found after conventional sintering. A new parabolic model is proposed for the convoluted monoclinic fraction depth profile, which through the value of its horizontal asymptote allows the determination of the monoclinic shell thickness.     

Role of zirconia phase transformation,interface processes,and Ta2O5 doping on the blistering phenomenon of molten glass in contact with zirconia-based refractories

Bubble formation and removal within the molten glass is an important issue in glass industry. Various sources of bubbles have been identified in glass manufacturing: decomposition of the glass components, air trapping, oxidation/reduction reactions, precipitation resulting from insufficient refining, etc. It has been demonstrated in a previous paper that the blistering phenomenon at the interface between a molten glass and a zirconia-based refractory can be ascribed to the oxygen semipermeability through the zirconia phase. The objective of this study is to clarify the role of temperature on the blistering process, and especially, below and above the phase transition temperature of zirconia (monoclinic/tetragonal transformation) and to evaluate the role of zirconia doping on the blistering level. The influence of the kinetics of the surface processes at the glass/refractory interface is emphasized. Quantitative measurement of the slight blistering ascribed to the so-called “redox shock” is also given.     

Yb doped MgO transparent ceramics generated through the SPS method

Yb doped (0, 0.02, 0.1 and 0.5 at%) MgO transparent ceramics were synthesized through spark plasma sintering (SPS) at the relatively low temperature of 1100 °C for 5–60 min under a pressure of 105 MPa. The effects of dopant concentration and sintering holding time on the densification and microstructure evolution of MgO ceramics were investigated. All ceramics reached a relative density greater than 99.20%. The 0.02% Yb-doped MgO ceramic sintered at 1100 °C for 60 min showed the highest in-line transmittance, of 80% at 1030 nm, a value close to that of MgO single crystals. Yb dopant improved the transmittance, degree of densification and control of grain growth. Herein, the influence of Yb doping on the crystalline phase and microstructure was explored, and the photoluminescence properties of Yb in transparent MgO ceramics were investigated.