B2O3和Al2O3共同掺杂ZnO压敏陶瓷的性能

研究了B₂O₃(B)和Al₂O₃(Al)共掺杂对ZnO压敏陶瓷电学性能和微观结构的影响。结果表明,共掺杂B和Al的ZnO压敏陶瓷,具有低泄漏电流、高非线性和低剩余电压等优良电性能。B和Al的掺杂率为3.0%(摩尔分数)和0.015%(摩尔分数)的ZnO压敏陶瓷,其最佳样品的电参数为：击穿电压E_{1 mA}＝475 V/mm;泄漏电流J_L=0.16 μA/cm²;非线性系数α=106;剩余电压比K = 1.57。     

纳米Fe2O3对温压炸药中铝粉爆炸特性的影响

为提高温压炸药配方的威力,根据铝热反应的基本原理,在温压炸药固相组分中添加纳米Fe₂O₃,探究通过诱导铝热反应的方式来提高炸药威力的新途径。利用20 L柱形爆炸容器在10 kJ点火能量下研究了不同质量比的微米或纳米铝粉与纳米Fe₂O₃组成的混合体系的爆炸特性。研究发现,随着纳米Fe₂O₃含量的增大,Al/Fe₂O₃混合体系的最大爆炸压力和升压速率呈现先增大、后减小的趋势。当纳米Fe₂O₃质量分数为5.4%时,混合体系的最大爆炸压力最大。随后,在此配比下开展了混合体系粉尘浓度对爆炸特性的影响规律研究。结果表明,随着粉尘浓度的增加,最大爆炸压力先增加、后降低,在质量浓度为400 g/m³时达到峰值。结合理论分析认为,纳米Fe₂O₃的加入能够改善温压炸药固相体系的反应活性,且对铝粉的爆炸剧烈程度有促进和抑制的双面作用。     

CaxSr1-xBi2Nb2O9无铅压电陶瓷制备及其高温稳定性研究

采用传统固相法制备了Ca_xSr_1-xBi₂Nb₂O₉ (x=0、0.10、0.25、0.40)无铅压电陶瓷, 研究了Ca²⁺掺杂量对其微观结构、电学性能及其高温稳定性的影响。掺入Ca²⁺并未改变SrBi₂Nb₂O₉陶瓷的晶体结构; 随着Ca²⁺掺杂量的增加, 陶瓷晶粒由片状向长条状转变; 陶瓷的矫顽场(E_c)下降, 剩余极化强度(P_r)先增大后减小; 陶瓷的居里温度由450℃升高到672℃。当x=0.10时, 陶瓷具有较好的综合性能: 2P_r=14.8 μC/cm², d₃₃=22 pC/N, T_c=488℃; 当退火温度达到400℃时, 压电常数d₃₃仍达到20 pC/N, 说明该材料具有较好的温度稳定性, 可以在400℃的高温环境中应用。     

添加Bi2WO6对ZnO基压敏陶瓷电学性能的影响

用传统固相反应法研究了添加Bi₂WO₆(x=0%~9%,质量分数)对ZnO基压敏陶瓷的微观结构、压敏性能和介电性能的影响。结果表明：掺入适量的Bi₂WO₆能促进ZnO压敏陶瓷晶粒均匀生长、提高微观结构的均匀性、降低压敏场强和提高非线性系数;同时,Bi₂WO₆的添加可提高ZnO晶粒表面吸附氧的含量,从而提高界面态密度和势垒高度以及ZnO基压敏陶瓷的非线性特性。Bi₂WO₆的添加量为7%的ZnO基压敏陶瓷,其综合性能为：E_{1 mA}=263 V/mm,α=53,J_L=3.50 μA/cm²,φ_b=11.52 eV。     

Pebax/MIL-100(Cr)混合基质膜的制备及其在CH4/N2分离中的应用

以聚醚嵌段聚酰胺(Pebax)为聚合物基体，以铬基金属有机框架MIL-100(Cr)为填充粒子，采用溶剂挥发法制备了系列Pebax/MIL-100(Cr)混合基质膜，并用于CH₄/N₂分离研究。结果表明，固相法合成的MIL-100(Cr)的BET为1808m²/g,在0.1MPa下对CH₄的吸附量为0.5mmol/g,对N₂的吸附量为0.28mmol/g,说明MIL-100(Cr)对CH₄具有高亲和力。随着MIL-100(Cr)纳米粒子的加入，Pebax/MIL-100(Cr)混合基质膜的CH₄/N₂渗透选择性呈现先增大后减小的趋势，CH₄渗透率基本保持不变；当MIL-100(Cr)添加量为15%(wt,质量分数)时，混合基质膜的CH₄渗透性能保持在20Barrer, CH₄/N₂选择性能达到3.71。     

Tb掺杂双钙钛矿氧化物Pr2CoMnO6的磁热效应

采用高温固相反应法制备双钙钛矿氧化物Pr_(2-x)Tb_xCoMnO₆(x=0,0.05,0.1,0.15)系列陶瓷样品,研究了Tb的掺杂量对Pr₂CoMnO₆样品的居里温度、磁熵变以及磁相变的影响。结果表明:系列样品Pr_(2-x)Tb_xCoMnO₆(x=0,0.05,0.1,0.15)的空间点群为单斜晶系P2₁/n,具有良好的单相性;该组样品均有两个磁转变点(T_C1和T_C2);随着Tb掺杂量的增加T_C1和T_C2均降低下降;在测量温区内,随着温度的降低4个样品均先后经历顺磁态、顺磁-铁磁共存态;该组样品在7 T外加磁场中的最大磁熵变值ΔS_M分别为-1.862、-1.779、-1.768和-1.766 J/(kg·K)。掺杂Tb元素使最大磁熵变值变小,但是拓宽了半高宽温区。结合RCP值可以判断,Pr_1.9Tb_0.1CoMnO₆比其他三个样品更具有作为高温区磁制冷材料的潜能;根据对Arrott曲线、重标定曲线以及Loop曲线的分析,该组样品在此阶段经历了一级相变。     

CO2/O2环境下L320钢在不同流速下的腐蚀行为研究

为了确定L320钢在CO₂/O₂环境中不同流速下的腐蚀行为,通过多相流瞬态模拟仿真软件,模拟目标管道的流动状态,确定室内模拟试验的流速范围,选择L320钢进行CO₂/O₂共存体系下不同流速的高温高压动态反应釜试验,采用扫描电镜、X射线衍射仪对腐蚀产物进行微观形貌表征和成分分析。结果表明:温度和压力随着里程的增加呈现下降的趋势;管道气体流速和壁面剪切力随着里程的增加呈现逐渐上升的趋势。基于Pearson相关系数法,确定了流速是影响腐蚀速率的主控因素。随着流速的增加,L320在CO₂/O₂共存条件下的均匀腐蚀速率逐渐增大。CO₂/O₂共存体系的腐蚀产物为Fe 2 O₃、FeOOH、Fe(OH)3、Fe 3 O 4、FeCO₃等。研究结论可为不同流速下的L320钢在CO₂/O₂共存环境中的防护提供借鉴。     

爆炸复合Cu-Al-Ni-Mn-Ti 与Qbe2 合金减振弹性复合板材料

利用Cu-Al-Ni-Mn-Ti 与QBe₂ 合金爆炸复合研制出一种新型的减振弹性复合板材料, 用多功能内耗仪测试了该复合板材料的阻尼性能。结果表明: 其内耗值比QBe₂ 增加了近一个数量级, 而且具有明显的振幅效应。复合板材料的电阻率介于Cu-Al-Ni-Mn-Ti 与QBe₂ 合金之间, 复合界面对电阻率的影响较小。爆炸复合的界面多呈波浪型, 在界面附近有融化区, 780 ℃等温处理, 界面随保温时间延长而展宽。      

Er2O3掺杂Gd2(Zr0.8Ti0.2)2O7陶瓷的物理性能

用固相反应法制备(Gd_1-xEr_x)₂(Zr_0.8Ti_0.2)₂O₇(摩尔分数x=0,0.2,0.4)陶瓷并测试其晶体结构、显微形貌和物理性能,研究了Er₂O₃掺杂的影响。结果表明,(Gd_1-xEr_x)₂(Zr_0.8Ti_0.2)₂O₇陶瓷具有立方烧绿石结构,显微结构致密,在室温至1200℃高温相的稳定性良好;Er³⁺掺杂降低了陶瓷材料的热导率和平均热膨胀系数,当x=0.2时,其1000℃的热导率最低(为1.26 W·m^-1·k^-1)。同时,Er³⁺掺杂还提高了这种材料的硬度和断裂韧性。     

Er3+ 掺杂对Bi3Ti1.5W0.5O9-Bi4Ti3O12 共生无铅压电陶瓷性能的影响

用传统固相法制备了Bi_7-x Er _x Ti_4.5W_0.5O₂₁(BTW-BIT-xEr³⁺,x=0.05、0.10、0.15、0.25、0.35)共生铋层结构无铅压电陶瓷,用BTW-BIT-xEr³⁺的XRD和SEM表征其相结构和形貌,研究了Er³⁺掺杂对其上转换发光性能和电学性能的影响。结果表明：在这种陶瓷中生成了铋层状结构的单一晶相。在980 nm光波激发下所有组分的上转换荧光谱中都能清晰地观察到两个绿光和一个红光发射峰,峰的中心分别位于532 nm、548 nm和660 nm处。改变掺杂Er³⁺离子浓度可调节其强度比。根据BTW-BIT-0.15Er³⁺样品在532 nm和548 nm绿光的光强比拟合了290~440 K的温度灵敏度,结果表明440 K处的灵敏度最大为0.0023 K^-1。Er³⁺离子替代BTW-BIT-xEr³⁺伪钙钛矿层的Bi³⁺使氧空位浓度的降低,降低了高温介电损耗,提高了激活能和压电常数。BTW-BIT-0.15Er³⁺陶瓷的综合电学性能最优,分别为d₃₃=14 pC/N、T_c=697℃,tanδ=0.53%、Q_m=2055。这种陶瓷材料具有最优的发光性能和良好的热稳定性。     

Dissociation process of CH4/H2 gas mixture during EACVD

The dissociation process of CH₄/H₂ gas mixture during EACVD has been investigated using Monte Carlo simulation for the first time. The electron velocity distribution and H₂ dissociation were obtained over a wide range: 100<E/N<2000 Td. The variation of CH₄ dissociation with CH₄ concentration in the filling gas has been simulated. The electron velocity profile is asymmetric for the component parallel to the field. Most electrons possess non-zero velocity parallel to the substrate. The number of atomic H is a function of E/N. There are two peaks at E/N=177 Td and 460 Td. The appropriate E/N is suggested to be 500–800 Td for low temperature deposition. The main diamond growth precursor is proposed to be CH₃ and CH₃⁺.     

Determination of the E1 and E1+Δ1 energy bands by photoreflectance in AlxGa1−xAs in the region 0<x<0.55

The E₁ and E₁+Δ₁ energy bands of metal–organic chemical vapor deposition grown Al_xGa_1−xAs, with x in the range 0–0.55, have been determined using photoreflectance technique. The aluminum composition for each sample was determined using the energy of the room-temperature photoluminescence compensated peak value and a suitable fundamental band gap formula. The positions of the E₁ and E₁+Δ₁ peaks were determined from curve-fitting an appropriate theoretical model to our experimental data by a modified downhill simplex method. Using the results, we propose new E₁ and E₁+Δ₁ cubic expressions as functions of the aluminum composition, x, and compare them with the available reported expressions.     

Ferroelectric, dielectric and piezoelectric properties of potassium lanthanum bismuth titanate K0.5La0.5Bi4Ti4O15 ceramics

The Aurivillius type bismuth layer-structured compound potassium lanthanum bismuth titanate (K_0.5La_0.5Bi₄Ti₄O₁₅) is synthesized using conventional solid-state processing. The phase analysis is performed by X-ray diffraction (XRD) and the microstructural morphology is conducted by scanning electron microscopy (SEM). The ferroelectric, dielectric and piezoelectric properties of K_0.5La_0.5Bi₄Ti₄O₁₅ (KLBT) ceramics are investigated in detail. The remnant polarization (P_r) and coercive field (E_c) are found to be 8.6 μC cm⁻² and 60 kV cm⁻¹, respectively. The Curie temperature T_c and piezoelectric coefficient d₃₃ are 413 °C and 18 pC N⁻¹, respectively.     

First principles calculations of thermal equations of state and thermodynamical properties of MgH2 at finite temperatures

We present the first principles calculations of the thermodynamical properties of magnesium hydride (MgH₂) over a temperature range of 0–1000 K. The phonon dispersions are determined within the density functional framework and are used to calculate the free energy of MgH₂ within the quasiharmonic approximation (QHA) at each cell volume and temperature T. Using the free energies the thermal equation of state (EOS) is derived at several temperatures. From the thermal EOS structural parameters such as the equilibrium cell volume (V₀) and elastic properties, namely, bulk modulus (K₀) and its pressure derivative are computed. The free energies are also used to calculate various thermodynamical properties within QHA. These include internal energy E, entropy S, specific heat capacity at constant pressure C_P, thermal pressure P_thermal(V, T) and volume thermal expansion ΔV/V (%). The good agreement of calculated values of S and C_P with experimental data exhibits that QHA can be used as a tool for calculating the thermodynamical properties of MgH₂ over a wide temperature range. P_thermal(V,T) increases strongly with T at all the volumes but it is a slowly varying function of volume for T = 298–500 K. According to Karki [B.B. Karki, Am. Miner. 85 (2000) 1447] such volume based variations can be neglected and so it is possible to estimate the thermal EOS only with the knowledge of the measured P_thermal(V, T) versus temperature at ambient pressure and isothermal compression data at ambient temperature. Temperature dependence of ΔV/V(%) shows that V₀ increased with increase in temperature. However, the percentage decrease in K₀ superseded this percentage increase in V₀ even at temperatures moderately higher than 298 K. Therefore, we suggest application of temperature (T > 298 K) as an approach to enhance the hydrogen storage capacity of MgH₂ because of its better compressibility at these temperatures.     

Effect of CH4 and H2 on CVD of SiC and TiC for possible fabrication of SiC/TiC/C FGM

SiC and TiC coatings were deposited by CVD on graphite substrates and the effect of the variation of the methane (CH₄) and hydrogen (H₂) ratio on deposition was investigated. SiCl₄, TiCl₄ and CH₄ were used as sources of Si, Ti and C. In case of the SiC coatings, stoichiometric SiC was obtained when the ratios of CH₄/(SiCl₄ + CH₄)andH₂/(SiCl₄ + CH₄) are 0.4 and 10, respectively. Stoichiometric TiC was also obtained under similar conditions. In order to obtain non-stoichiometric materials for possible fabrication of functionally gradient materials (FGM), a change of microstructure and composition was observed with changes of the CH₄ and H₂ ratio. As a result, SiC, TiC and C contents were more easily controlled by a change of the H₂ ratio compared to the CH₄ ratio for SiC and TiC deposition. It has been verified that the change of the H₂ ratio is more desirable for possible manufacturing of SiC/TiC/C FGM.     

Effect of Ca2PbO4 on the formation of the (2223) phase in the Bi---Pb---Sr---Ca---Cu---O system

The effect of excess Ca₂PbO₄ on the superconducting properties of Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O_yB_x (B ≡ Ca₂PbO₄) is investigated through X-ray diffraction, resistivity and a.c. magnetic susceptibility measurements. The Xpray diffraction results show that the volume friction of the low T_c (221s) phase decreases and that of (2223) phase increases with the addition of Ca₂PbO₄. For x = 0.6 and 1.5, only the (2223) phase exists. At higher Ca₂PbO₄ concentrations, i.e. for x = 3.0, the low T_c phase again appears along with the high T_c phase. Diffraction peaks appear at d = 2.02, 2.814 and 2.85, which are characteristic peaks of Ca₂PbO₄, and their intensities increase with increasing x, indicating that Ca₂PbO₄ exists in the lattice in the same form. However, the T_c(0) values decreased gradually from 107 to 98 K with increasing Ca₂PbO₄ concentration. Compared with the undoped sample, the width of the transition δT_c is broad for impurity-added samples and reaches a maximum value for x = 3.0. Pure and Ca₂PbO₄-doped samples showed two peaks in ξ″ vs. T curves and two steps in ξ′ vs. T curves. The first peak is close to the transition temperature and corresponds to the midpoint of the first step in the ξ′ curve. The second peak appears below 98 K and this peak maximum corresponds to the midpoint of the second step. The position of both sets of peaks remained almost the same up to x = 1.5 and shifted towards lower temperatures thereafter. The role of Ca₂PbO₄ in the growth of the (2223) phase and the mechanism of energy loss are discussed.     

Evaluation of neutron thermalization parameters and benchmark reactor calculations using a synthetic scattering function for molecular gases

Using a synthetic incoherent scattering function which describes the interaction of neutrons with molecular gases we provide analytical expressions for zero- and first-order scattering kernels, σ₀(E₀ → E), σ₁(E₀ → E), and total cross section σ₀(E₀). Based on these quantities, we have performed calculations of thermalization parameters and transport coefficients for H₂O, D₂O, C₆H₆ and (CH₂)_n at room temperature. Comparison of such values with available experimental data and other calculations is satisfactory. We also generated nuclear data libraries for H₂O with 47 thermal groups at 300 K and performed some benchmark calculations (²³⁵U, ²³⁹Pu, PWR cell and typical APWR cell); the resulting reactivities are compared with experimental data and ENDF/B-IV calculations.     

Molecular dynamics simulations of ionized cluster beam deposition: case of study of aluminum

In order to understand interactions between energetic Al clusters and Al(1 0 0) surfaces, we investigated the cluster-size dependence of the maximum substrate temperature T_max and of the time t_max within which this temperature is reached. We considered two cases: (1) clusters with the same total energy E_T and (2) clusters with the same energy per atom. The temperature T_max changed linearly with both the energy per atom and the total energy of the cluster. When E_T was constant and the cluster size increased, the time t_max approached a constant value because energy was rapidly transferred to the substrate by correlated collisions. As the size and energy of clusters increase, such correlated collisions play a progressively important role in their interactions with surfaces.     

Determination of the fracture toughness of fabric reinforced composites by the J-integral approach

The fracture behaviour of a glass-fabric-reinforced epoxy composite has been investigated experimentally. Load-displacement curves for single-edge-notched specimens were obtained on an MTS system and the J-integral evaluated through its energy rate interpretation. J_c, the critical value of the J-integral, obtained directly for a₀/w > 0·4 and that obtained through an extrapolation procedure for a₀/w < 0·4 compare quite well. J_c appears to be independent of crack length for specimen widths between 15 and 45 mm. J_c for ±45° specimens is less than half that for 0/90 specimens.