Thermal expansion properties and hygroscopicity of Y2?xSmxW3O12 (x = 0.0–0.4) compounds

A novel class of solid solutions of Y_2−x Sm _x W₃O₁₂ (x = 0.0−0.4) were synthesized and studied by means of powder X-ray diffraction. All samples crystallize in an orthorhombic space group Pnca. The lattice parameters a, b and c of Y_2−x Sm _x W₃O₁₂ increase with increasing Sm content. Since the compounds of this series hydrate at room temperature, thermogravimetric (TG) analysis was carried out. The result shows that the compound stores less water with increasing Sm content. The thermal expansion properties of Y_2−x Sm _x W₃O₁₂ (x = 0.1, 0.3 and 0.4) were investigated with high temperature X-ray diffraction. Negative thermal expansion coefficient α _I becomes less negative from −6.644×10⁻⁶ to −6.211×10⁻⁶°C⁻¹ when x changes from 0.1 to 0.4.     

Study on the thermal stability and electrical properties of the high-k dielectrics (ZrO2)x(SiO2)1?x

(ZrO₂) _x (SiO₂)_1−x (Zr-Si-O) films with different compositions were deposited on p-Si(100) substrates by using pulsed laser deposition technique. X-ray photoelectron spectra (XPS) showed that these films remained amorphous after annealing at 800°C with RTA process in N₂ for 60 s. The XPS spectra indicated that Zr-Si-O films with x=0.5 suffered no obvious phase separation after annealing at 800°C, and no interface layer was formed between Zr-Si-O film and Si substrate. While Zr-Si-O films with x >0.5 suffered phase separation to precipitate ZrO₂ after annealing under the same condition, and SiO₂ was formed at the interface. To get a good interface between Zr-Si-O films and Si substrate, Zr-Si-O films with bi-layer structure (ZrO₂)_0.7(SiO₂)_0.3/(ZrO₂)_0.5(SiO₂)_0.5/Si was deposited. The electrical properties showed that the bi-layer Zr-Si-O film is of the lowest equivalent oxide thickness and good interface with Si substrate. Supported by the National Nature Science Foundation of China (Grant No. 60636010) and the National Basic Research Program of China (“973” Program) (Grant No. 2004CB619004)     

Synthesis and photoluminescence property of red phosphors LiEu1?xYx(WO4)0.5(MoO4)1.5 for white LED

A series of novel red phosphors LiEu_1−x Y _x (WO₄)_0.5(MoO₄)_1.5 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8) were synthesized by conventional solid state reaction method with the starting materials: WO₃, MoO₃, Eu₂O₃, Li₂CO₃ and Y₂O₃. The spectrum and the crystal structure of the phosphors were characterized by F-4500 and XRD respectively. Meanwhile the effects of flux and Y³⁺ concentration on the crystal structure and luminescent properties of the phosphors were investigated. The results showed that the optimal content of flux () was 1 wt% and the optimal doping concentration of Y³⁺ was 0.5 mol. The emission spectrum showed the most intense peak was located at 615 nm, which corresponds to the ⁵ D ₀→⁷ F ₂ transition of Eu³⁺ and that Eu³⁺ occupied the lattice site of noncentrosymmetric environment in the scheelite phases. The excitation spectrum displayed that these phosphors could be effectively excited by ultraviolet (UV) (396 nm) and blue (466 nm) light, nicely in correspondence with the widely applied output wavelengths of ultraviolet or blue LED chips. The influence of flux on the luminescent properties of LiEu_0.5Y_0.5(WO₄)_0.5(MoO₄)_1.5 phosphor was analyzed. The XRD spectra indicated that the flux could help to crystallize the phosphor, and no other phases were formed except the tetragonal. When adding flux, the relative intensity of LiEu_0.5Y_0.5(WO₄)_0.5(MoO₄)_1.5 became much stronger and the average particle size of the phosphor decreased. Supported by the Key Programs for Science and Technology Development of Hubei Province (Grant No. 2005AA105A05)     

Effect of Dy on structure and magnetic properties of DyxFe60.5?xPt39.5 Alloys

Effects of the content of Dy on structure and magnetic properties of Dy _x Fe_60.5−x Pt_39.5 alloys(x=0, 0.5, 1.0, 1.5) were investigated. The results of XRD analysis proved that the phase-transitional temperature of Dy _x Fe_60.5−x Pt_39.5 alloys from disordered face-centered-cubic structure to ordered face-centered-tetragonal cubic structure decreases with the increase of the content of Dy(x). Suitable content of Dy can improve the exchange coupling between soft magnetic phase and hard magnetic phase by refining grain size, while the remanence ratio and coercivity of the Fe_60.5Pt_39.5 alloy can be significantly improved by a small replacement of Fe by Dy, good magnetic properties were obtained in Dy_0.5Fe_60.0Pt_39.5 alloys.     

Dielectric and pyroelectric characteristics of the infrared sensitive (Pb1?xSrx)TiO3 ceramics

PST ferroelectric ceramics were fabricated successfully by a two-step method, i e first, PbTiO₃ and SrTiO₃ were sintered respectively, then mixed and sintered together. The process and characteristics of PST ferroelectric ceramics were introduced and researched. Their dielectric and pyroelectric characteristics are as follows dielectric constant 10⁴ order, low dielectric loss (lower than 3.0% in the working frequency range of 1–1 000 kHz), saturation polarization intensity 10⁻¹ C/m² order, and pyroelectric coefficient 10⁻³ C/m²·K order.     

Synthesis and luminescence properties of Pr3+ doped CaxBa1?xTiO3 (0.3?x<1) fine particles

Ca _x Ba_1−x TiO₃ (CBT) fine particles doped with red luminescence center of Pr³⁺ ions (Pr: CBT) were successfully synthesized by salt assisted spray pyrolysis (SASP) process. Scanning electronic microscope (SEM) and laser scattering analysis demonstrate that salt can be removed from the surface of particles by washing with Milli-Q water and the particles can be further separated by ball-milling to get well-dispersed Pr³⁺ ions doped CBT fine particles. The luminescence properties, such as photoluminescence (PL) and mechanoluminescence (ML), of as-synthesized Pr: CBT particles were investigated. For Pr: CBT fine particles with different Ca molar ratios, all the samples show one emission at 612 nm, with increasing Ca molar ratio, PL intensity of Pr: CBT fine particles become stronger and stronger. When pressure was loaded on the Pr: CBT pellet, mechanoluminescence(ML) emission was measured. The results show that the ML intensity is proportional to the applied pressure.     

Adsorption of NO and NH3 over CuO/γ-Al2O3 catalyst

The selective catalytic reduction reaction belongs to the gas-solid multiphase reaction, and the adsorption of NH₃ and NO on CuO/γ-Al₂O₃ catalysts plays an important role in the reaction. Performance of the CuO/γ-Al₂O₃ catalysts was explored in a fixed bed adsorption system. The catalysts maintain nearly 100% NO conversion efficiency at 350 °C. Comprehensive tests were carried out to study the adsorption behavior of NH₃ and NO over the catalysts. The desorption experiments prove that NH₃ and NO are adsorbed on CuO/γ-Al₂O₃ catalysts. The adsorption behaviors of NH₃ and NO were also studied with the in-situ diffusion reflectance infrared Fourier transform spectroscopy methods. The results show that NH₃ could be strongly adsorbed on the catalysts, resulting in coordinated NH₃ and NH₄⁺ NO adsorption leads to the formation of bridging bidentate nitrate, chelating bidentate nitrate, and chelating nitro. The interaction of NH₃ and NO molecules with the Cu²⁺ present on the CuAl₂O₄ (100) surface was investigated by using a periodic density functional theory. The results show that the adsorption of all the molecules on the Cu²⁺ site is energetically favorable, whereas NO bound is stronger than that of NH₃ with the adsorption site, and key information about the structural and energetic properties was also addressed.     

Heat treatment behavior of can-forged titanium aluminide alloy in ( α + γ ) region

The effect of initial microstructures on the heat treatment behavior of can-forged titanium aluminide alloy has been studied. Optical microscopy and EDX analyses results show that different initial microstructures, including difference in dislocation density, phase distribution and morphology, have inherent effects on the final heat treatment microstructure although at the same heat treatment temperature. An almost full lamellar (NFL) microstructure with an average α ₂/γ colony size of 20 μm was obtained through adjusting initial microstructure. Project supported by the “863” High Tech Program and the National Natural Science Foundation of China Synopsis of the first author Liu Yong, Doctoral student, born in April 1973. Specializing in powder metallurgy of ceramics, intermetallics and metal: 1) Ca/P based bioceramics; 2) TiAl based intermetallics; 3) Fe, Cu materials.     

Mg70(A0.25Ni0.75)30合金结构及储氢性能

为研究稀土元素Ce、Y对非晶储氢合金催化及其性能的影响,采用快淬法制备Mg70(A0.25Ni0.75)30(A=Ce,Y)合金,使用Sievert’s气体吸附技术和差示热扫描技术研究其储氢性能和热力学稳定性。XRD衍射分析显示,快淬制备的合金为非晶合金,但在573K、2MPa的氢压下,氢化后的Mg70(Y0.25Ni0.75)30会产生MgH2、Mg2NiH4和2相,Mg70(Ce0.25Ni0.75)30会产生Mg2NiH4、CeNi5和MgH2相。不同温度的动力学测试结果表明,快淬法制备的Mg70-(Ce0.25Ni0.75)30和Mg70(Y0.25Ni0.75)30合金分别获得的最大吸氢量为质量分数4.42%和3.09%,Mg70(Ce0.25Ni0.75)30和Mg70(Y0.25Ni0.75)30合金前100s吸氢量分别达到各自最大吸氢量的97%和87%。通过对DSC曲线的分析发现,Mg70(A0.25Ni0.75)30的脱氢活化能较低,分别为111.025±2.790kJ/mol(A=Ce)、84.843±2.057kJ/mol(A=Y)和152.207±6.764kJ/mol(A=Y)。实验结果表明,Y元素对Mg70(A0.25Ni0.75)30合金催化及储氢性能的改善要优于Ce元素。     

Non-fragile delay-dependent H ∞ control of linear time-delay system with uncertainties in state and control input

The problem of designing a non-fragile delay-dependent H∞ state-feedback controller was investigated for a linear time-delay system with uncertainties in state and control input. First, a recently derived integral inequality method and Lyapunov-Krasovskii stability theory were used to derive new delay-dependent bounded real lemmas for a non-fragile state-feedback controller containing additive or multiplicative uncertainties. They ensure that the closed-loop system is internally stable and has a given H∞ disturbance attenuation level. Then, methods of designing a non-fragile H∞ state feedback controller were presented. No parameters need to be tuned and can be easily determined by solving linear matrix inequalities. Finally, the validity of the proposed methods was demonstrated by a numerical example with the asymptotically stable curves of system state and controller output under the initial condition of x（0）=[1 0 -1]^T and h=0.8 time-delay boundary.     

Bi2O3和Fe2O3掺杂对BaTiO3陶瓷显微结构的影响

利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和X射线能量色散谱(EDAX)等结构分析技术,研究了施主(Bi     

Delay-independent decentralized H ∞ control for multi-channel discrete-time systems with uncertainties

A robust decentralized H∞ control problem was considered for uncertain multi-channel discrete-time systems with time-delay. The uncertainties were assumed to be time-invariant, norm-bounded, and exist in the system, the time-delay and the output matrices. Dynamic output feedback was focused on. A sufficient condition for the multi-channel uncertain discrete time-delay system to be robustly stabilizable with a specified disturbance attenuation level was derived based on the theorem of Lyapunov stability theory. By setting the Lyapunov matrix as block diagonal appropriately according to the desired order of the controller, the problem was reduced to a linear matrix inequality （LMI） which is sufficient to existence condition but much more tractable. An example was given to show the efficiency of this method.     

La2(Ce0.3Zr0.7)2O7-NiCr2O4材料高温红外发射率研究

固相法合成了La₂(Ce_0.3Zr_0.7)₂O₇-nNiCr₂O₄(n=0%,5%,10%,15%)陶瓷材料,利用X射线衍射仪、扫描电镜以及傅里叶变换红外光谱仪对其物相结构、显微形貌、高温红外发射率以及红外吸收光谱进行表征.结果表明：合成的La₂(Ce_0.3Zr_0.7)₂O₇-nNiCr₂O₄陶瓷材料均为以烧绿石晶体为主相的立方结构,显微结构致密,晶粒尺寸均匀且随NiCr₂O₄含量的增加而增大.随NiCr₂O₄(n=0%,5%,10%,15%)质量分数的增加,陶瓷材料1 100℃红外发射率(3～5μm)不断升高,n=15%时,高温红外发射率最高可达0.76.红外吸收光谱分析结果显示,NiCr     

2BaTiO3/1SrTiO3/1CaTiO3超晶格的纵向挠曲电系数计算

采用基于密度泛函理论的第一性原理方法,研究了由²BaTiO₃/¹SrTiO₃/¹CaTiO₃所构成的超晶格材料的纵向挠曲电系数。构建了三种超晶胞构型,钛酸钡、钛酸锶和钛酸钙的层数比都为2：1：1,并且保持超晶胞的总层数为16层。对三种超晶胞构型,分别施加余弦应变,分析超晶格中各原子的位移和应变,以及每种构型的纵向挠曲电系数。结果表明,构型Ⅱ的纵向挠曲电系数可达5.63 nC/m,比单晶BaTiO₃、单晶SrTiO₃材料分别提升了16倍和6倍。本文的研究结果对遴选纵向挠曲电系数的材料具有较好的指导意义。     

煤对N2/CH4/CO2混合气体竞争吸附特征与机理研究

为研究煤对N₂,CH₄及CO₂混合气体的竞争吸附特征及其机理,通过混合气体吸附/解吸装置,结合穿透曲线法,对大柳塔(DLT)、硫磺沟(LHG)、瑞能(RN)、山阳(SY)和屯宝(TB)5种煤样,开展了温度为20℃、注气压力为0.25 MPa条件下N₂,CH₄和CO₂等比例混合气体的竞争吸附试验,得到了不同煤样对混合气体竞争吸附的规律;通过低温氮气吸附法,分析了5种煤样的孔隙结构,研究了孔隙对混合气体竞争吸附的影响.结果表明：DLT,LHG和RN煤样中N₂和CH₄先达到吸附平衡,一段时间后这2种气体在装置出口端的体积分数均超过其初始体积分数,而SY和TB煤样中只有N₂的出口端体积分数超过了其初始体积分数.试验结果与Yoon-Nelson模型拟合结果较好,线性相关系数R²基本可达0.9以上;各煤样传质速率常数均有k(N₂)>k(CH_4<...     

Preparation and Characterization of Alumina-coated Hollow Quartz Fiber Reinforced Al2O3–SiO2 Aerogel Composite

Al₂O₃-SiO₂ sols were synthesized by using aluminum chloride hex hydrate and tetraethoxysilane (TEOS) as precursors,deionized water and ethanol mixture as the solvent,and propylene oxide as the coagulant aids.Alumina coatings were prepared on the surfaces of hollow quartz filament fiber,then a new lightweight and thermal insulating material were successfully prepared by impregnating Al₂O₃-SiO₂ sol into a needle fabric made by coate...     

Mixed H2/H∞ State Feedback Attitude Control of Microsatellite Based on Extended LMI Method

For the appearance of the additive perturbation of controller gain when the controller parameter has minute adjustment at the initial running stage of system,to avoid the adverse effects,this paper investigates the mixed H_2/H_∞ state feedback attitude control problem of microsatellite based on extended LMI method.Firstly,the microsatellite attitude control system is established and transformed into corresponding state space form.Then,without the equivalence restriction of the two Lyapunov variables of H_2 and H∞performance,this paper introduces additional variables to design the mixed H_2/H_∞ control method based on LMI which can also reduce the conservatives.Finally,numerical simulations are analyzed to show that the proposed method can make the satellite stable within 20 s whether there is additive perturbation of the controller gain or not.The comparative analysis of the simulation results between extended LMI method and traditional LMI method also demonstrates the effectiveness and feasibility of the proposed method in this paper.     

Fe2(SO4)3对活性污泥微生物活性的影响

为了解Fe₂(SO₄)₃作为絮凝剂对活性污泥中微生物活性的影响,向活性污泥系统中投加质量浓度为20、40、60、80,100 mg·L-1的Fe₂(SO₄)₃,反应4 h后测定活性污泥的脱氢酶活性、比耗氧速率(R_SOU)、胞外聚合物(EPS)及各组分含量,同时测定系统出水的COD等各项指标．结果表明:Fe₂(SO₄)₃质量浓度在20～60 mg·L-1时对活性污泥的脱氢酶活性、R_SOUEPS及各组分含量影响均不大,此时污水中COD、TP、UV₂₅₄等污染物随Fe₂(SO₄)₃质量浓度增加而有较大幅度去除．Fe₂(SO₄)₃质量浓度为80 mg·L-1时,污泥的脱氢酶活性、R_SOU、总EPS含量均明显下降．当Fe₂(SO₄)₃质量浓度增加到100 mg·L-1时,污泥的脱氢酶活性、R_SOU进一步受到抑制,而总EPS含量则大幅度提升．此时污水中COD、TP、UV₂₅₄等污染物去除率增加幅度变缓,SCOD及NH₃-N去除作用有所下降．     

N2与CH4对CO2非混相驱油效果的影响

在矿场应用中,注入CO2中混有的杂质气体会影响其驱油效果.为制定更加合理有效的开发方案,有必要研究杂质气体对CO2驱的影响.利用油藏数值模拟方法,在纯CO2气体注入参数优化的基础上,研究了N2与CH4两种杂质气体对CO2非混相驱体积波及系数、驱油效率、油井见气时间和采收率的影响;以尽量提高原油采收率为目标,确定了注入气中杂质气体的临界含量.结果表明,杂质气体的存在会导致CO2非混相驱体积波及系数增大,驱油效率降低,油井见气时间缩短;注入的CO2中N2的摩尔分数最高不应超过5%,CH4的摩尔分数最高不应超过14%.