Si3N4-MgO-CeO2陶瓷烧结过程中的致密化与相变

Silicon nitride ceramics show great potential for wide applications. It is difficult to densify silicon nitride due to its covalent nature of bonding. A new sintering aid with combination of MgO and CeO₂ was used in the present study. The effects of MgO-CeO₂ on densification and phase transformation during sintering of Si₃N₄ were discussed. For Si₃N₄-MgO-CeO₂ ceramics,a lot of liquid phase existed at 1450℃,and densification process took place rapidly from 1550℃ to 150℃;the phase transformation from α-Si₃N₄ to β-Si₃N₄ took place rapidly from 1550℃ to 1660℃,the phase transformation process lags behind the densification process. The nonpressure sintered Si₃N₄-MgO-CeO₂ ceramics achieved a bending strength of 948MPa. MgO-CeO₂ can be considered as an effective sintering aid for Si₃N₄.     

CoSi2薄膜电学性质研究

The resistivity of CoSi₂ films with thickness about 0.4 μm was studied.The resistivities of CoSi₂ films were measured in the temperature range from -200℃ to room temperature.At room temperature 9～20 μΩcm is obtained.The resistivity was approximately linear with temperature.     

NH3-TPD法表征RE2O3/HY的酸性

The acidity of RE₂O₃/HY was characterized by NH₃-TPD.The experimental results show that HY zeolite has a strong acidity. After RE₂O₃ mixed with HY zeolite in a special method, the interaction between RE₂O₃ and HY restrains strong acid sites. With the increase of amount of supported species, the acid site neutralizated increases. The neutralizating action isn，t end until the amount of supported species reach 30%.     

Phase-selection and metastable phase formation in highly undercooled eutectic Ni78.6Si21.4 alloys

A large undercooling (250 K) was achieved in eutectic Ni_78.6Si_21.4 melt by the combination of molten-glass denucleation and cyclic superheating. The metastable phase formation process in the bulk undercooled eutectic Ni_78.6Si_21.4 melts was investigated. With the increase of undercooling, different metastable phases form in eutectic Ni_78.6Si_21.4 melts and part of these metastable phases can be kept at room temperature through slow post-solidification. Under large undercooling, the metastable phases β₂-Ni₃Si, Ni₃₁Si₁₂ and Ni₃Si₂ were identified. Especially, the Ni₃Si₂ phase was obtained in eutectic Ni_78.6Si_21.4 alloy for the first time. Based on the principle of free energy minimum and transient nucleation theory, the solidification behavior of melts was analyzed with regard to the metastable phase formation when the melts were in highly undercooled state.     

Phase-selection and metastable phase formation in highly undercooled eutectic Ni78.6Si21.4 alloys

A large undercooling (250 K) was achieved in eutectic Ni_78.6Si_21.4 melt by the combination of molten-glass denucleation and cyclic superheating. The metastable phase formation process in the bulk undercooled eutectic Ni_78.6Si_21.4 melts was investigated. With the increase of undercooling, different metastable phases form in eutectic Ni_78.6Si_21.4 melts and part of these metastable phases can be kept at room temperature through slow post-solidification. Under large undercooling, the metastable phases β₂-Ni₃Si, Ni₃₁Si₁₂ and Ni₃Si₂ were identified. Especially, the Ni₃Si₂ phase was obtained in eutectic Ni_78.6Si_21.4 alloy for the first time. Based on the principle of free energy minimum and transient nucleation theory, the solidification behavior of melts was analyzed with regard to the metastable phase formation when the melts were in highly undercooled state.     

高温变形时Al67Mn8Ti25的动态回复和动态再结晶

The deformation microstructure of Ll₂-structure Al₆₇Mn₈Ti₂₅ compound after tension at high temperature was investigated by TEM. The results show that dynamic recovery occurs and there exist a high density of dislocations, dislocation walls and unstable networks within the grains after deformation at 1 173 K and a strain rate of 8.35×10^-5 s^-1. At 1 173 K and a strain rate of 3.34×10^-5s^-1, dynamic recrystallization took place and the deformation microstructures were fine recrystallized grains with stable sub-boundaries in the specimen. Owing to difficulties in the dislocation motion and the process concerned with atom diffusion, the dynamic recovery and dynamic recrystallization occur only at rather higher temperature and lower strain rates, and only under this condition can the appreciate tensile ductility be obtained for this compound.     

碲镉汞吸收缘以上E1和E2峰的指认

The fundamental reflectivity spectrum of HgCdTe have been investigated.The feature of the spectra is the presence of E₁ and E₂ peaks in the fundamental absorption region.The lower energy peak can be split into a doublet (E₁ and E₁＋Δ₁）.A three-dimensional saddle point is used to fit the E₁ and E₁+Δ₁ critical point and some simulated calculation is done for E₂ at X point.The calculated results are compared with the measured results and prominent features of the dielectric spectra are identified with critical-point transitions at the Λ and X points in the Brillouin zone.     

固体超强酸SO2－4／ZrO2形成机理的研究

The formation of SO^2－₄／ZrO₂ solid superacid is studied with FT-IR、XRD and SEM techniques．Subtractive FT-IR measurement indicates the existence of chemical bonds between ZrO₂  and H₂SO₄,XRD determination reveals that the strength of SO^2－₄／ZrO₂ superacid strongly depends on temperature of calcination and reaches a maximum as the ZrO₂ transforms into tetragonal crystal phase.SEM analysis shows that the morphology of ZrO₂ surface is changed due to treatment of H₂SO₄.This catalyst shows higher esterification activity for synthesis of dibutyl moleate which is excellently related with the results of surface analysis.     

Microstructure and wear resistance of PTA clad Cr7C3/γ-Fe ceramal composite coating

A wear resistant Cr₇C₃/γ-Fe ceramal composite coating was fabricated on substrate of the hardening and tempering C degree steel by PTA (plasma transferred arc) cladding with (wt%) Fe-25Cr-7C elemental powder blends. Microstructure of the coating was characterized by OM, SEM, XRD and EDS. Wear resistance of the coating was tested under dry sliding wear condition at room temperature. The results indicate that the PTA clad ceramal composite coating has a rapidly solidified fine microstructure consisting of Cr₇C₃ primary particles uniformly distributed in the γ-Fe matrix and is metallurgically bonded to the C degree steel substrate. The PTA clad Cr₇C₃/γ-Fe ceramal composite coating has high hardness and excellent wear resistance under dry sliding wear test conditions. The excellent wear resistance of the Cr₇C₃/γ-Fe ceramal composite coating is attributed to the coating’s high hardness, strong covalent atomic bonding and refined microstructure.     

Microstructure and wear resistance of PTA clad Cr7C3/γ-Fe ceramal composite coating

A wear resistant Cr₇C₃/γ-Fe ceramal composite coating was fabricated on substrate of the hardening and tempering C degree steel by PTA (plasma transferred arc) cladding with (wt%) Fe-25Cr-7C elemental powder blends. Microstructure of the coating was characterized by OM, SEM, XRD and EDS. Wear resistance of the coating was tested under dry sliding wear condition at room temperature. The results indicate that the PTA clad ceramal composite coating has a rapidly solidified fine microstructure consisting of Cr₇C₃ primary particles uniformly distributed in the γ-Fe matrix and is metallurgically bonded to the C degree steel substrate. The PTA clad Cr₇C₃/γ-Fe ceramal composite coating has high hardness and excellent wear resistance under dry sliding wear test conditions. The excellent wear resistance of the Cr₇C₃/γ-Fe ceramal composite coating is attributed to the coating’s high hardness, strong covalent atomic bonding and refined microstructure.     

Density functional theory study of the reaction paths of reactions of CH3C(O)O2 radicals with HO2 in the gas phase

A DFT study on the reactions between CH₃C(O)O₂ and HO₂ radicals has been carried out. It is suggested that both the triplet and singlet potential surfaces involve a complex mechanism with the formation of loosely bound intermediate complexes of reactants and products. The reaction prefers to occur on the triplet surface to produce peracetic acid (CH₃C(O)O₂H) and triplet O₂ molecule. The CH₃C(O)O₂H can further convert into CH₃C(O)O and HO radicals.     

Density functional theory study of the reaction paths of reactions of CH3C(O)O2 radicals with HO2 in the gas phase

A DFT study on the reactions between CH₃C(O)O₂ and HO₂ radicals has been carried out. It is suggested that both the triplet and singlet potential surfaces involve a complex mechanism with the formation of loosely bound intermediate complexes of reactants and products. The reaction prefers to occur on the triplet surface to produce peracetic acid (CH₃C(O)O₂H) and triplet O₂ molecule. The CH₃C(O)O₂H can further convert into CH₃C(O)O and HO radicals.     

Comparative analysis of temperature and CO2 fluxes for winter wheat in Tibetan Plain and North China Plain using the EMD method

Comparative study of spectral properties of temperature and CO₂ fluxes measured by eddy covariance method at Yucheng (36°57′N, 116°36′E, 28 m a.s.l., in the North China Plain) and at Lhasa (29°41′N, 91°20′E, 3688 m a.s.l., on the Tibetan Plateau) is described using the empirical mode decomposition (EMD) method. The main results are: (1) The intrinsic oscillation modes or intrinsic mode functions (IMFs) were extracted from data of temperature (T) and CO₂ fluxes (F) measured at Yucheng (T₁ and F₁) and Lhasa (T₂ and F₂). (2) Hilbert transform was applied to these IMF components, then the Hilbert-Huang spectra and the marginal spectra of these data were obtained. (3) Comparison of temperature and CO₂ fluxes in North China Plain and on Tibetan Plain illustrated that the characteristic frequencies corresponding to T₁, F₁, T₂ and F₂ are 0.05 Hz, 0.03 Hz, 0.014 Hz and 0.005 Hz, respectively.     

Comparative analysis of temperature and CO2 fluxes for winter wheat in Tibetan Plain and North China Plain using the EMD method

Comparative study of spectral properties of temperature and CO₂ fluxes measured by eddy covariance method at Yucheng (36°57′N, 116°36′E, 28 m a.s.l., in the North China Plain) and at Lhasa (29°41′N, 91°20′E, 3688 m a.s.l., on the Tibetan Plateau) is described using the empirical mode decomposition (EMD) method. The main results are: (1) The intrinsic oscillation modes or intrinsic mode functions (IMFs) were extracted from data of temperature (T) and CO₂ fluxes (F) measured at Yucheng (T₁ and F₁) and Lhasa (T₂ and F₂). (2) Hilbert transform was applied to these IMF components, then the Hilbert-Huang spectra and the marginal spectra of these data were obtained. (3) Comparison of temperature and CO₂ fluxes in North China Plain and on Tibetan Plain illustrated that the characteristic frequencies corresponding to T₁, F₁, T₂ and F₂ are 0.05 Hz, 0.03 Hz, 0.014 Hz and 0.005 Hz, respectively.     

Acidic catalysis of microporous polyoxometalate H3PW12O40/Sio2 in acetal reaction between benzaldehyde and ethylene glycol

Microporous Keggin-type polyoxometalate material was synthesised by supporting H3PW12O40 into a silica matrix via a sol-gel technique. The silica-supported 12-tungstophosphoric acid ( H₃PW₁₂O₄₀/Sio₂ ) obtained is insoluble and readily separable porous materials with uniform micropores (0. 57 nm) and a high specific surface area (350. 5 m2/g) in oxygen-containing polar solvents. H3PW12 O4o/Si02 was characterized by infrared spectrophotometer (IR). ultraviolet-visible spectrophotometer (UV-vis). inductively coupled plasma (ICP)> thermogravimetric analysis (TGA) and Brunner-Emmett-Teller method (BET) measurements. H3PWi204o/Si02 obtained catalyzed the acetal reaction between benzaldehyde and ethylene glycol to produce 2-phenyl-l > 3-dioxolane more efficiently than the typical solid acids such as SO4 /ZrO2' Nafion-H and H-ZSM-5. Conversion was 93. 8% for benzaldehyde during the reaction period of 2 h. H₃PW₁₂O₄₀/Sio₂ kept its initial activity during three times of reuse. The initial acetal reaction follows a second-order kinetics model at 298 K.     

Phase transition , structure and shape memory effect of Ni47Ti43Hf10 alloy

A Ni₄₇Ti₄₃Hf₁₀ high temperature shape memory alloy is fabricated. The martensitic transformation temperature (TT) is obtained by differential scanning calorimetry and four-probe electrical resistivity measurements. The effect of thermal cycling is investigated and it is found that the TT tends to be stable quickly, which is of benefit to practical applications. The martensite structure is determined to be B19' monoclinic by X-ray diffraction and transmission electron microscopy. One-way and two-way (which is seldom reported before) shape memory properties are studied by tensile and bending tests. The cycling number of two-way shape memory effect is tested for more than 20000 times.     

The fluid inclusions in jadeitite from Pharkant area, Myanmar

A lot of liquid-gas and liquid-gas-solid inclusions were found in Pharkant jadeitites, northwestern Myanmar and their characteristics, geological setting and porphyroclastic jadeites with inclusions in them were described in detail. The results analyzed by Raman spectrometer showed that the component of liquid-gas phase and solid phase (daughter minerals) in fluid inclusions is H₂O + CH₄ and jadeite separately. The results indicated that Pharkant jadeitites were crystallized from H₂O + CH₄ bearing jadeitic melt which may originate from mantle. The P-T conditions in which the jadeitites were crystallized were speculated to be T ＞650℃, P ＞1.5 GPa.     

Application of backflush and micro-flow techniques to the analysis of C5—C13 hydrocarbons in crude oils and its geochemical significance

An Agilent 6890N GC equipped with both FID and Agilent 5975 MSD analyzer has been employed to analyze C₅—C₁₃ hydrocarbon fractions of crude oils. A technical combination of program temperature volatilizer injection, backflush and micro-flow controller afforded a fine separation of C₅—C₁₃ compounds on a PONA column with the heavy part of crude oils being cut off before entering the analytical column. Both GC-FID chromatogram and GC-MS mass chromatograms (MID and full scan) could be obtained at the same time. The retension time differences of nC₆—nC₁₃ alkanes between GC and TIC were in the range of 0.02—0.58 minutes. Totally 286 peaks have been assigned group compositions. Results on 8 typical oil samples from CNPC Key Laboratory Crude Oil Library showed that the characteristics of C₆—C₁₃ hydrocarbon group composition could be used in oil-oil correlation studies.     

Application of backflush and micro-flow techniques to the analysis of C5—C13 hydrocarbons in crude oils and its geochemical significance

An Agilent 6890N GC equipped with both FID and Agilent 5975 MSD analyzer has been employed to analyze C₅—C₁₃ hydrocarbon fractions of crude oils. A technical combination of program temperature volatilizer injection, backflush and micro-flow controller afforded a fine separation of C₅—C₁₃ compounds on a PONA column with the heavy part of crude oils being cut off before entering the analytical column. Both GC-FID chromatogram and GC-MS mass chromatograms (MID and full scan) could be obtained at the same time. The retension time differences of nC₆—nC₁₃ alkanes between GC and TIC were in the range of 0.02—0.58 minutes. Totally 286 peaks have been assigned group compositions. Results on 8 typical oil samples from CNPC Key Laboratory Crude Oil Library showed that the characteristics of C₆—C₁₃ hydrocarbon group composition could be used in oil-oil correlation studies.     

Al2O3/WO3/ZrO2催化剂的制备及在酯交换反应中的研究

以松木为模板,采用模板法将不同含量的Al₂O₃添加到WO₃/ZrO₂复合氧化物中,采用X射线衍射、BET比表面积分析、拉曼光谱和NH₃等温吸附测试等手段对其进行表征,以评估其改进结果。将Al₂O₃/WO₃/ZrO₂催化剂应用到甲醇与乌桕油（非食用油）的酯交换反应中,在其他反应条件相同,Al₂O₃质量分数为3%时,生物柴油最高产率达到83.1%。结果表明：添加Al₂O₃稳定了ZrO₂的四方相结构,使得催化剂比表面积更大、孔数量增加;模板法制备的催化剂孔径分布均匀,WO₃呈高度分散无定型状态;引入Al₂O₃增加了WO₃/ZrO₂催化剂的中强酸性,对弱酸性和强酸性无明显改变。