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1.
为了探究甲烷CH4在富氧和非常压条件下的爆炸危险性,确保CH4气体在不同工况下的安全使用,借助5 L圆柱形爆炸装置,研究了初始压力p0和富氧系数E对CH4/O2/N2爆炸特性的影响。包括最大爆炸压力pmax、最大压力上升速率(dp/dtmax和最大压力到达时间tc等衡量CH4爆炸安全性的指标。结果表明:当E为 0.21、0.25和0.30时,pmaxp0的增加始终线性上升;而当E为 0.35和0.40时,pmaxp0的增加先缓慢线性上升、后快速线性上升;(dp/dtmaxp0的增加分为线性上升和一阶指数快速上升。在E为0.21和0.25时,tcp0的增加而线性增大,因为在燃烧初始阶段CH4活化自由基的销毁速率增加,降低了反应速率和燃速,引起预混气体tc的延长;但随着E的增加,氧气的促进作用与自由基销毁的抑制作用形成新的竞争效应,使得tc先增加、后下降。  相似文献   

2.
Adsorption of dihydrogen, carbon monoxide and methane, and co-adsorption of H2/CO, H2/CH4 and CO/CH4 on zinc oxide was studied by means of Fourier transform infrared spectroscopy. Besides the already known dissociation of dihydrogen and molecular adsorption of CO, methane was found to be adsorbed molecularly on coordinatively unsaturated Zn2+ ions. Adsorption lowers the CH4 symmetry from Td to C3v, which is reflected in activation of the v1 (symmetric stretching) mode and discrete frequency shifts of the v3 (antisymmetric stretching) and ν4 (bending) modes. Co-adsorption of the above gases on ZnO having pre-adsorbed hydrogen results, in all cases, in a bathochromic shift of the v(Zn–H) band and a hypsochromic shift of the v(O–H) band, which originally appear at 1710 and 3492 cm−1, respectively. The magnitude of these shifts depends upon the nature of the co-adsorbed gas.  相似文献   

3.
BaTiO3 thin films were prepared by using metal organic acid salts on MgO(100) substrates, which have large lattice-misfit with BaTiO3. Amorphous films prefired at 470°C were crystallized to BaTiO3 phase by heat treatment at higher temperature. Crystallinity and in-plane alignment of the prepared films were found to depend on the heat-treatment conditions. BaTiO3 films with high crystallinity but poor (100)-orientation were obtained in air at higher than 1200°C. Whereas, (100)-oriented epitaxial BaTiO3 film was fabricated by annealing at 900°C under low oxygen partial pressure (p(O2)). Low carbon dioxide partial pressure (p(CO2)) is also found to be essential for preparation of epitaxial BaTiO3 films on MgO substrates by using metal organic acid salts.  相似文献   

4.
Buckling analysis of functionally graded plates subjected to uniaxial loading   总被引:12,自引:0,他引:12  
Elastic bifurcational buckling of functionally graded plates under in-plane compressive loading is studied. It is supposed that the gradients of material properties throughout the structure are produced by a spatial distribution of the local reinforcement volume fraction vf = vf(x, y, z). To analyze the problem, a method based on a combination of micromechanical and structural approaches is employed. This establishes the effective constitutive behavior at every point of a nonhomogeneous composite plate and provides a buckling criterion. The derived criterion enables one to calculate the critical buckling load Rxcr for a given distribution v(x, y, z).

Furthermore, with the aim to improve the buckling resistance of the functionally graded plate, the functional Rxcr(vf) is maximized. This yields an optimal spatial distribution vf(x, y, z) of the reinforcement phase.

Results are presented for both short- and long-fiber SiC/Al plates in which the fibers are nonuniformly distributed in the x-, y-, or z-directions. The effects of length-to-width ratio of the plate, and of different types of boundary conditions are studied. Buckling load improvements of up to 100%, as compared to the corresponding uniformly reinforced structure, are shown.  相似文献   


5.
D. F. Diao  Y. Sawaki 《Thin solid films》1995,270(1-2):362-366
A typical buckling phenomenon of the coating on the wear groove caused by the residual compressed stress was analyzed by the interface fracture mechanics and the buckling theory. It has been found that there is a critical thickness of coating on the wear groove for the buckling. The critical thickness can be calculated by tb/cd = [12(1 − v2fR2Ef]1/2 (here tb is the coating thickness, cd the length of the interfacial crack, vf the Poisson's ratio of the coating, σR the residual compressed stress in the coating, and Ef the elastic modulus of the coating).  相似文献   

6.
ZnSe films and fully developed p-on-n laser structures, including CdZnSe-active and ZnSSe-guiding layers were grown by molecular beam epitaxy (MBE) on lattice matched p-GaAs, p-AlGaAs and p-GaInP buffer layers. The structural characteristics of these layers were studied by combined cross-section and planar view transmission electron microscopy (TEM). The defect density of the ZnSxSe1−x epilayers was shown to be very low, <105 cm−2. However, on their interfaces with the GaAs substrate, a high density of small dislocation loops and clusters of the order of 3×1010 cm−2 was observed. In situ TEM experiments revealed that dislocations and stacking faults (SFs) were generated under the electron beam influence. From them, the perfect dislocations were confined at the ZnSe/GaAs interface, while the SFs propagated to the ZnSe overgrowth or the GaAs substrate, having one of their partial dislocations at the interface. The generation of dislocations under the electron beam was not related to radiation damage but to thermal strain, which was developed by the heating effect due to differential thermal dilatation. Defects around the active zone of fully developed p-on-n laser structures were also studied. The nature of such defects was defined by Burgers vector determination experiments. The critical role of growth variations, such as compositional changes resulting in strain, in the MBE process of IIVI materials was demonstrated. The destructive role of the defected guiding layers in the laser structure was shown.  相似文献   

7.
The secondary electron emission (SEE) yield δ of ZnO films was investigated. The films were deposited in an r.f. sputtering system using the r.f. power W, the argon pressure p, the O2 partial pressure pO2 and the substrate temperature Ts as parameters. Complementary measurements of the electrical resistivity and the optical absorption were performed. The ratio x of oxygen to zinc is an essential factor which determines the values of δ, and for the ZnO films.

Auger analyses showed that excess (overstoichiometric, x =1) oxygen is present in ZnO films obtained at room temperature. For x =1 the values of , the maximum SEE yield δm and the energy band gap Eg (determined from ) were found to be higher than those for stoichiometric ZnO (obtained at Ts200 °C). The highest values of (104 Ω m), δm (4.4) and Eg (3.44 eV) were obtained for films with x = 1.7.  相似文献   


8.
Stress corrosion crack growth rates are measured at sveral stress intensity levels for low-tempered 4340 steel in 0.1N H2SO4 solution. The characteristics of the growth rates are divided into three regions of stress intensity factors: Region I near K1SCC; Region III near unstable fracture toughness, K1SC; and Region II, which lies between the two. K1SCC is the value of K at which no crack growth can be detected after 240 hr.

In order to explain these experimental results, the crack initiation analysis reported in a previous paper is extended to the growth rates. A detached crack initiates and grows at the tip of an already existing crack. When the detached crack reaches the tip of the main crack, the process repeats as a new existing crack.

A relationship between crack growth rate, v, and stress intensity factor, K, is obtained as a function of b/a and a = b + d, where b is the distance from the tip of the main crack to the detached crack, and d is the ydrogen atom saturated domain.

The experimental data are in good agreement with the theoretical values in Region II when a = 0.02 mm, b/a = 0.8, c1/c0 = 2.8 for 200°C tempered specimens and a = 0.015 mm, b/a = 0.7, c1/c0 = 3.0, ρb = 0.055 mm for 400°C tempered specimens, where ρb is a fictitious notch radius. The plateau part in Region II for 400°C tempered specimens is also successfully explained by the present theory. For Region III, the value of b/a will be almost equal to 1 because v → ∞ for b/a → 1. On the other hand, for Region I, b/a will be zero, since the value of v becomes negligibly small and no crack growth is observable.  相似文献   


9.
C60O is studied by means of the AM1 quantum-chemical method. Full geometry optimization of its Cs and C2v structures, and harmonic vibrational analysis, are employed in the evaluation of the temperature dependence of their relative stabilities. The C2v structure remains a minor component of the equilibrium gas-phase mixture even at high temperatures.  相似文献   

10.
通过超声辅助和低温热处理在二维Ti3C2Tx 纳米片层间原位生长SnO2纳米颗粒,制备出纳米结构的SnO2@Ti3C2Tx 复合材料。使用X射线衍射、X射线光电子能谱和高分辨透射电子显微镜等手段对其表征,研究了这种材料的结构和性能。结果表明,SnO2纳米粒子密集分布在Ti3C2Tx 片层表面与片层之间,Ti3C2Tx 纳米薄片突出的限制效应和良好的类石墨层状结构抑制了SnO2纳米粒子的体积膨胀和团聚,加速了锂离子和电子的跃迁。同时,嵌入在片层之间的SnO2纳米粒子防止纳米片层在锂插入/脱出过程中重新堆积,使Ti3C2Tx 基体的纵向结构稳定性提高。SnO2@Ti3C2Tx 复合材料两组分之间的协同效应,使其具有良好的倍率性能与长循环性能。  相似文献   

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