金属氧化物在Si3N4陶瓷烧结中的使用现状

Si₃N₄陶瓷具有较高的热导率、良好的耐磨性和耐腐蚀性,高温强度高,且高温稳定性和抗热冲击性好,作为结构材料在机械工业,电子工业和化学工业中广泛应用。由于Si₃N₄陶瓷烧结温度过高,无法在工业生产中大量使用,为了降低其烧结温度、改善烧结致密度和强度等性能,在烧结过程中经常使用烧结助剂。综述了国内外金属氧化物作为烧结助剂在Si₃N₄陶瓷烧结中的研究现状,提出了其烧结过程中存在的问题。     

三价铁离子掺杂对钛酸锂结构和化学性能的影响

采用溶胶凝胶法制备Li4-x/3FexTi5-2x/3O12(x=0,0.03,0.06,0.09)粉体活性材料,并优化了最佳掺杂量为x=0.03。通过X射线衍射(XRD)、扫描电镜(SEM)、恒流充放电测试对材料进行结构、形貌及电化学性能表征。结果表明:掺杂适量的铁离子不会改变钛酸锂的尖晶石结构和形貌。1C时,Li3.99Fe0.03Ti4.98O12首次放电比容量为145.40 m A·h/g;纯相的首次放电比容量仅为116.95 m A·h/g。     

碱金属锂原子修饰硅原子链团簇的结构和储氢性能

采用密度泛函理论(DFT)方法研究Li2Sim(m=2,4,6)链状团簇结构及其储氢性能。研究结果表明,氢分子在碱金属Li原子修饰的三种硅链结构中均发生吸附,并且每个Li原子都可以吸附多个氢分子,其中两个Li原子修饰Si2链的结构能够吸附氢分子的储氢质量分数达18.6 wt%,氢分子的平均吸附能为1.850 kcal/moL。结果表明,碱金属Li原子修饰的硅链在室温条件下可作为氢气的存储媒介。     

Pu(H2O)53+和Pu(H2O)54+ 团簇的相对论密度泛函研究

用TPSSTPSS密度泛函方法, Pu离子和H₂O分子分别采用相对论有效原子实势(RECP)和6-31g基组, 研究了Pu(H₂O)₅³⁺和Pu(H₂O)₅⁴⁺ 团簇溶剂化和非溶剂化效应中的几何结构及紫外可见吸收光谱. 计算结果表明: 水溶剂环境对Pu(H₂O)₅³⁺及Pu(H₂O)₅⁴⁺ 团簇的几何结构影响都比较明显. NBO电荷分析表明水分子与钚离子之间没有直接的电荷转移. 所研究团簇的未配对电子都占据5f轨道. 在气相及水溶剂环境下, 所研究团簇的紫外可见吸收光谱存在较大差距. 主要的吸收峰大都源于f电子之间的跃迁.     

Spontaneous transformation of C60Br24 to C60 in solvents

It was found that C₆₀Br₂₄ transforms to C₆₀ spontaneously in some solvents. The intermediate, C₆₀Br₈, can be separated in some cases. When the bromine trap, phenol, was added,p-bromophenol and other brominated product were obtained and identified. The influences of time, the kind of solvent, etc were investigated. Possible mechanism was suggested. Supported by the National Natural Science Foundation of China Liu Ying: born in 1969, Ph. D     

The formation and stability of Si1-x C x alloys in Si implanted with carbon ions

Si_1-xC_x alloys of carbon (C) concentration between 0.6%—1.0% were grown in Si by ion implantation and high temperature annealing. The formation of Si_1-xC_x alloys under different ion doses and their stability during annealing were studied. If the implanted dose was less than that for amorphizing Si crystals, the implanted C atoms would like to combine with defects produced during implantation and it was difficult to form Si_1-xC_x alloys after being annealed at 850℃. With the increment of implanted C ion doses, the lattice damage increased and it was easier to form Si_1-xC_x alloys. But the lattice strain would become saturate and only part of implanted carbon atoms would occupy the substitutional positions to form Si_1-xC_x alloys as the implanted carbon dose increased to a certain degree. Once Si_1-xC_x alloys were formed, they were stable at 950℃, but part of their strain would release as the annealing temperature increased to 1 000℃. Stability of the alloys became worse with the increment of carbon concentration in the alloys.     

The concentration quenching characteristics of 5D3-7FJ and 5D4-7FJ (J=0―6) transitions of Tb3+ in YBO3:Tb3+ phosphor

The photoluminescence quenching behaviors of ^5D3-^7Fj and ^5D4-^7Fj （J = 0—6） transitions of Tb^3＋ in YBO3：Tb under 130—290 nm excitation were systematically investigated. The results revealed that the quenching concentrations of both ^5D3-^7Fj and ^5D4-^7Fj transitions of Tb^3＋ in YBO3：Tb were mainly dependent on excitation wavelength. Particularly, the quenching concentrations of ^5D4-^7Fj transitions of Tb^3＋ under 130—290 nm excitation were correlated with excitation bands of YBO3：Tb. The quenching concentrations of ^5D3-^7Fj transitions remained at low concentration （2%） under 186—290 nm excitation and then increased gradually with energy of incoming excitation photon when excited at 130—186 nm. This dependence should be involved in their excitation mechanisms and quenching pathway in particular excitation region.[第一段]     

Preparation and luminescence characteristics of Sr3SiO5：Eu^2＋ phosphor for white LED

The Sr3SiO5：Eu^2＋ phosphor was synthesized by high temperature solid-state reaction. The emission spectrum of Sr3SiO5：Eu^2＋ shows two bands centered at 487 and 575 nm, which well agree with the theoretic values of emission spectrum. The excitation spectrum for 575 nm emission center has several excitation bands at 365, 418, 458 and 473 nm. And the results show that the emission spectrum of Sr3SiO5：Eu^2＋ is influenced by the Eu^2＋ concentration. The relative emission spectra of the white-emitting InGaN-based YAG：Ce^3＋ LED and Sr3SiO5：Eu^2＋ LED were investigated. The results show that the color development of InGaN-based Sr3SiO5：Eu^2＋ is better than that of InGaN-based YAG：Ce^3＋, and the CIE chromaticity of InGaN-based Sr3SiO5：Eu^2＋ is （x=0.348, y=0.326）.     

Harmonic mixing of Bi2Sr2CaCu2O8+x intrinsic junction at millimeter waveband

Using intrinsic Josephson junctions in Ba₂Sr₂CaCu₂O_8+x single crystal, harmonic frequency mixing at 8 and 3 mm wavebands was successfully demonstrated at liquid nitrogen temperatures with harmonic numbers up to 68 and 50 respectively. The dependences of intermediate frequency output on the local oscillator power and dc bias were carefully studied.     

Ferroelectricity of nanocrystalline BaTiO<Subscript>3</Subscript> ceramics by first principle calculation

The vibrational modes of BaTiO₃ in different crystalline phases have been investigated by means of density functional theory pseudo potential method. The evidence of tetragonal to orthorhombic and orthorhombic to rhombohedral phase transitions present for 8 nm BaTiO₃ ceramics further demonstrates that the similar successive transitions in 8 nm BaTiO₃ ceramics from rhombohedral to orthorhombic, tetragonal and cubic transitions are as those in coarse BaTiO₃ ceramics.     

Subsolidus phase relations in the system MgO-ZnO-SiO2 at high pressure

The subsolidus phase relations were determined experimentally in the system MgO-ZnO-SiO2 at 1.0 GPa and 1 200℃, by use of the high-pressure apparatus "piston-cylinder". The results showed characteristics of the phases assemblage different from that in similar ternary systems. It is impossible to form complete Mg2SiO4-Zn2SiO4 olivine and Mg2Si2O6-Zn2Si2O6 pyroxene solid solution. This is controlled by the properties of Zn2+ with an outer layer of electron (Ar)3d10, different from others transition metal ions, like Fe2+ , Ni2+ , Co2+ .     

Pr3+∶Y2SiO5 晶体中电磁感应光透明及群速度减慢

利用光与物质相互作用的密度矩阵方程及其数值解研究Λ型Pr³⁺∶Y₂SiO₅晶体的电磁感应光透明（EIT）和光群速度减慢（SGV）, 分析非均匀加宽及相干驱动场强度对EIT和SGV的影响, 理论与实验结果相符.      

Preparation of Fe3O4@Au nano-composites by self-assembly technique for immobilization of glucose oxidase

Superparamagnetism amination nanocrystals Fe₃O₄ with 3-aminopropyltriethyloxy silane (APTES) were prepared by modified co-precipitation method. Next, 4-5 nm gold nanoparticles, prepared by classical Frens procedure, were coated on the surface of the amination Fe₃O₄ by self-assembly technology. The prepared Fe₃O₄@Au nanocomposite particles were investigated by transmission electron microscopy (TEM), UV-vis, infrared spectrum (FT-IR), and vibrating sample magnetometer (VSM) in order to elucidate the morphology, optics and magnetic properties of the nanocomposites. Their uniform distribution of particle size, which is about 15 nm, and good magnetic responsiveness were observed. In view of the fact that Fe₃O₄ owns superparamagnetism and that nano-gold can readily combine with biological molecules, glucose oxidase (GO _x ) was chosen as a model to penetrate the condition of immobilizing enzyme, and enzymatic properties of resultant immobilized enzyme were studied as well. By systematic optimization, we established that at 28°C, and pH (5.5) and when mole ratio of Fe₃O₄:HAuCl₄ was 0.5:1, the immobilization provided the best results. Finally, we are glad to find that the immobilized enzyme exhibits excellent thermostability in addition to its better stability than free enzyme. Thus, herein described immobilized enzyme could be used repeatedly with the assistance of an external magnetic field. Supported by the Science Foundation of Sichuan Province, China (Grant No. 2005A033) and Science Foundation of Sichuan Agricultural University for Distinguished Young Teachers (Grant No. 007202)     

中温SOFC阴极材料La0.7Sr0.3Co1-xCuxO3-δ的制备及性能

采用固相反应法制备了La_0.7Sr_0.3Co_1-xCu_xO_3-δ系列中温固体氧化物燃料电池（SOFC）阴极材料粉体.对其进行晶体结构表征,高温电导率和热膨胀曲线测试,并选取其中性能较好的样品进行了单电池实验.结果表明,Cu的掺杂降低了（La,Sr）CoO La₃体系阴极材料的热膨胀系数,在x=0.05时电导率略高于未掺Cu的样品.以La_0.7Sr_0.3Co_0.95Cu _0.05O _3-δ为阴极、Ce_0.8Sm_0.2O_1.9为电解质组成的SOFC单电池,在850℃最大短路电流密度达511mA/cm²,最大输出功率密度约为0.106W/cm².     

Ca5Zn3相稳定性和物理性质的第一性原理研究

利用基于密度泛函理论的第一性原理方法对Ca_5Zn_3化合物的晶格常数、形成焓、弹性常数、以及电子态密度等进行计算研究。为了获得Ca_5Zn_3化合物的结构稳定性,考虑了Cr_5B_3、W_5Si_3以及Mn_5Si_3 3种结构类型,计算得到的形成焓表明:具有Cr5B3结构类型的Ca_5Zn_3最稳定,其次为Mn_5Si_3型,最后是W_5Si_3型。对该化合物的弹性常数、电子态密度和电荷密度差进行了计算。最后利用德拜模型,对Ca_5Zn_3的热物理性能进行了计算,获得体积、体积模量、热膨胀系数以及等容热容随温度和压强变化的规律,为该化合物在热电方面的应用提供了理论依据。     

Improvement of oxidation resistance of Nb–Ti–Si based alloys with additions of Al,Cr and B at different temperatures

The effects of Cr, Al and B addition on the microstructure and high-temperature oxidation behaviors (at 1200, 1250 and 1300 ?°C) of Nb–Ti–Si based alloys were investigated. The results showed that the addition of Cr stabilized α-Nb₅Si₃, while Al promoted the formation of β-Nb₅Si₃ and adding B promoted the formation of γ-Nb₅Si₃. Among the three elements, Al and Cr were beneficial to oxidation resistance at 1200 ?°C, and B was favorable to the oxidation resistance at 1300 ?°C. At 1250 ?°C, Al and B had the same effects on the improvement of oxidation resistance. The ratio of these alloying elements might play an important role in enhancing oxidation resistance. The oxidation resistance of the three kinds of silicides was compared, and the sequence was: γ-Nb₅Si₃> β-Nb₅Si₃> α-Nb₅Si₃. To predict the effects of the investigated alloying elements on the oxidation resistance of Nb–Ti–Si based alloys in a wider range of concentration, an artificial neural network (ANN) model was established, showing excellent accuracy and generalization ability. With the instructions of the ANN model, the oxidation resistance can be optimized with less additions of alloying elements.     

Hydrothermal synthesis, characterization and nonlinear optical effect of orthorhombic phase Ca2B6O11 · H2O

Hydrothermal treatment of calcium oxide and boric acid mixtures at temperatures between 234 °C and 300 °C has produced a colorless, transparent, orthorhombic compound Ca₂B₆O₁₁ · H₂O. Of the seven known members of the series of hydrated dicalcium hexaborate containing boron-oxygen six-membered ring anionic group (B₃O₈)^-7, only the title compound has been found to have the nonlinear optical effect. The second harmanic generation (SHG) effect of its crystal is larger than that of KH₂PO₄ (KDP). The reflection spectrum has shown that this compound has no absorption in the experimental wavelength range (800–240 nm). Its crystal structure is favorable for generating the nonlinear optical effect.     

Y_2O_3/GeO_2/环氧树脂基辐射防护材料的制备及性能研究

用表面处理稀土氧化物Y_2O_3,GeO_2的方法制备了Y_2O_3/GeO_2/环氧树脂辐射防护材料.采用X射线衍射仪(XRD)研究了材料的微观结构;用多道γ谱仪测试并分析了材料的辐射防护能力.结果表明,制得的材料中的Y_2O_3和GeO_2粒子并未与环氧树脂发生键和反应,Y_2O_3与GeO_2粉末的加入明显提升了材料防护射线的效果.     

Microstructure and mechanical properties of Nb–Si alloys fabricated by spark plasma sintering

This paper deals with microstructural evolutions and mechanical properties of Nb-Si binaries containing dual-phase Nb/Nb5Si3 with Nb to Nb5Si3 fraction ratios of 90:10,80:20,70:30 and 50:50,prepared by spark plasma sintering(SPS).Dense Nb/Nb5Si3 samples with a relative density larger than 99.5% were obtained by SPS processing.The SPS samples consist of the Nb and Nb5Si3 phases with less than 3% fraction of NbO oxide.Hv at room temperature,and compressive strength at 1150℃ and 1250 1C of the bulk SPS alloys increase monolithically by enhancing fraction of the stiffening Nb5Si3 phase.For example,0.2% yield strength,σ0.2,increases from 175 MPa to 420 MPa at 1150℃ and from 110 MPa to 280 MPa at 1250℃,when the Nb5Si3 fraction increases from 10% to 50%.It is interesting that the fracture toughness,KQ,of the bulk SPS samples seems not to be sensitive to phase fraction.Heat treatment,however,plays a key role on the KQ as compared with that of the as-sintered state,at the corresponding Nb5Si3 fraction and considerably improves the KQ by about 100% for samples with the Nb5Si3 fractions of 10%-30%,and by about 50% for the sample with 50% Nb5Si3 fraction.     

不同形貌LaBO_3型钙钛矿的制备及其催化H_2O_2分解反应性能

采用柠檬酸络合法制备了La BO3(B=Fe,Co,Ni)钙钛矿催化剂,通过X-射线粉末衍射(XRD)、傅立叶-红外光谱(FT-IR)、透射电镜(TEM)、X-射线光电子能谱(XPS)等对催化剂进行了表征,在室温下测定了其对H2O2的催化分解能力.结果表明:催化分解能力依次为La Ni O3>La Co O3>La Fe O3,说明Ni较Co和Fe能更好地分解H2O2.通过改变La Fe O3催化剂的形貌也能提高催化剂性能,如多孔状La Fe O3较负载在SBA-15上的La Fe O3具有更好的催化分解活性.