Thermal explosion of a reactive mixture under conditions of oscillating ambient temperature

The problem of the thermal explosion of a finite volume of a reactive material in a medium with harmonically oscillating temperature is solved in the classical formulation. A kind of resonance is shown to arise when the oscillation period is commensurate with the adiabatic induction period of thermal explosion at the mean ambient temperature. At both high and very low oscillation frequencies, the critical condition parameter and induction period are only slightly affected by ambient temperature oscillations. By contrast, at moderately low frequencies, even small-amplitude oscillations of ambient temperature can strongly influence the critical condition and, especially, induction period of thermal explosion.     

Thermal explosion in a stirred medium

The critical conditions of a thermal explosion in a cylindrical chemical reactor with several symmetrically positioned agitators for creating a forced convection of the reaction mixture are examined. The analysis is carried out for an arbitrary Peclet number on the assumption that the flow of the fluid is laminar. The critical value of the thermal explosion parameter (Frank-Kamenetskii parameter) is determined as a function of the number of agitators, Peclet number, and the distances between the axes of the agitators and the reactor axis. In contrast to the previous studies, the dependence of the thermal explosion parameter on the rate of stirring of the medium is considered. Calculations show that, as the number of agitators and mixing rate increases, the thermal explosion probability decreases, so that the critical value of the thermal explosion parameter can be several times greater than its classical value. It is demonstrated that, depending on the values of the parameters, the problem can have four stationary solutions, two of which are stable.     

The kinetics of D2 desorption from Ni(110) (2 × 1)C in the presence of reactive intermediates

A kinetic study of D₂ formation from HCOOD decomposition on Ni(110) (2 × 1)C was performed using the flash desorption technique. The surface structure and surface composition were monitored by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Flash curves were obtained using initial coverage and heating rate variations. D₂ formation exhibited a single second-order rate-determining step. Three different techniques were employed in obtaining the activation energy, two of which did not require the assumption of reaction order. Using an average value of 12.6 kcal/mole for the activation energy the pre-exponential factor was calculated to be 2.7 × 10^?4 cm² molecules^?1 sec^?1. Good agreement was achieved with the theoretically generated second-order flash curves only up to the peak temperature. The discrepancy on the high temperature side was explained using the model proposed by Clavenna and Schmidt utilizing a coverage dependent pre-exponential factor.     

On the Thermal Explosion Theory of a Heterogeneous Liquid–Liquid System

In this paper, the regularities of a thermal explosion of a heterogeneous system consisting of two immiscible liquids have been studied. Each phase is a solution of A and B reagents. Reagent B is extracted into a solution of reagent A, where the bimolecular exothermic reaction A + B → Products takes place. It has been shown that an exothermic reaction (combustion regime) continues to proceed in the system at high mass-exchange rates between phases after a thermal explosion. As a result, the maximal temperature may significantly exceed the temperature of the thermal explosion. The critical value of the Semenov parameter decreases with an increase in the mass-exchange rate between phases. In the limited range of values of the distribution coefficient of reagent B between phases, the increase of this coefficient is also accompanied by a decrease in the critical value of the Semenov parameter. The concentration of reagent B in the initial phase decreases monotonically due to its extraction into another phase. However, the equilibrium of the extraction of reagent B can shift, due to the temperature dependence of the distribution coefficient during the reaction. Thus, the time dependence of the concentration of reagent B on may be more complex and can pass through a minimum.     

Simulation of Quasi-One-Dimensional Wigner Solid Melting in a Parabolic Confinement

A computer simulation of a quasi-one-dimensional Coulomb crystal in a parabolic confinement has been carried out using molecular dynamics. The melting transition has been investigated and critical temperatures have been determined from the behavior of the modified Lindemann parameter, translational correlation function, and structure factor. The values obtained for the critical temperature are in good agreement with the earlier experiment.

     

Effects of Lorentz Breaking on the Accretion onto a Schwarzschild-like Black Hole

We formulate and solve the problem of spherically symmetric, steady state, adiabatic accretion onto a Schwarzschild-like black hole obtained recently. We derive the general analytic expressions for the critical points, the critical velocity, the critical speed of sound, and subsequently the mass accretion rate. The case for polytropic gas is discussed in detail. We find the parameter characterizing the breaking of Lorentz symmetry will slow down the mass accretion rate, while has no effect on the gas compression and the temperature profile below the critical radius and at the event horizon.     

热爆炸临界参数的数值解法

本文提出的热爆炸临界参数的数值解法是一种变分方法.这种方法依据的是文献[1]给出的热爆炸临界参数的一个变分原理。数值计算的结果表明,这种方法是一种简便、经济而又精确度较高的方法。     

非晶调制多层膜Nb/Si中的互扩散研究

利用原位Ｘ射线衍射技术得到非晶调制多层膜Ｎｂ／Ｓｉ中的互扩散系数与退火温度的关系，调制周期Ｌ＝３.２ｎｍ的非晶调制多层膜是用粒子溅射方法制备的．温度范围为４２３—５２３Ｋ的有效互扩散系数通过原位测量多层膜的一级调制峰强度与退火温度之间的关系而得到．利用缺陷陷阱延迟扩散机制解释了所得到的扩散系数与退火温度的关系．建立了可以解释较小前置系数的模型 关键词：     

A model of laser ablation with temperature-dependent material properties,vaporization, phase explosion and plasma shielding

Laser ablation of metals using nanosecond pulses occurs mainly due to vaporization. However, at high fluences, when the target is heated close to its critical temperature, phase explosion also occurs due to homogeneous nucleation. Due to a wide variation in target temperature, the material properties also show a considerable variation. In this paper, a model of laser ablation is presented that considers vaporization and phase explosion as mechanisms of material removal and also accounts for the variation in material properties up to critical temperature using some general and empirical theories. In addition, plasma shielding due to inverse bremsstrahlung and photo-ionization is considered. The model predicts accurately (within 5 %) the phase explosion threshold fluence of Al. The predictions of ablation depth by the model are in reasonable agreement with experimental measurements at low fluences. Whereas, the degree of error marginally increases at high laser fluences.     

Structural Characterization and Thermal Properties of 1-Amino-1-ethylamino-2,2-dinitroethylene

1,1-二氨基-2,2-二硝基乙烯(FOX-7)和乙胺水溶液在92 oC下反应合成出了一种新型含能材料1-氨基-1-乙氨基-2,2-二硝基乙烯(AEFOX-7). 利用理论计算方法研究了AEFOX-7的分子结构、红外吸收和核磁共振化学位移. 用DSC和TG/DTG研究了AEFOX-7的热行为. 其热行为可分为一个熔化过程和一个紧接的剧烈放热分解过程. 热分解反应的放热焓、表观活化能和指前因子分别为：374.88,169.7 kJ/mol和1019.24 s^-1, 热爆炸的临界温度 是145.2 oC. 采用微量热法和理论计算方法研究了AEFOX-7的比热容,298.15 K时为214.50 J/(mol K).     

Thermal explosion in a batch reactor charged with a liquid–solid heterogeneous system

The characteristics of a thermal explosion in an ideal mixing batch reactor charged with a liquid–solid heterogeneous system are studied. The reactor initially contains both phases. The solid reagent dissolves and reacts in the liquid phase. A strong dependence of the critical value of the Semenov parameter on the dimensionless time of complete dissolution of the solid reagent is established. It is shown that, at short times of complete dissolution, the critical value of the Semenov parameter is practically independent on this time, and the thermal explosion occurs as in a homogeneous system, according to Semenov theory. The heterogeneous properties of the reaction system manifest themselves only at long times of complete dissolution.     

硝酸胺晶体中硝酸根的u_1全对称振动模的临界拉曼强度行为及其热力学解释

硝酸胺晶体中硝酸根的ｕ＿１全对称振动模的临界拉曼强度行为及其热力学解释丁贤德，吴国初（中科院化学所北京１０００８０）ＴｈｅＣｒｉｔｉｃａｌＲａｍａｎＩｎｔｅｎｓｉｔｙＢｅｈａｖｉｏｒｏｆｔｈｅＮｉｔｒａｔｅｕ＿１ＭｏｄｅａｎｄＩ０ｓＴｈｅｒｍｏｄｙｎ...     

The Finite-Size Scaling Relation for the Order-Parameter Probability Distribution of the Six-Dimensional Ising Model

The six dimensional Ising model with nearest-neighbor pair interactions has been simulated and verified numerically on the Creutz Cellular Automaton by using five bit demons near the infinite-lattice critical temperature with the linear dimensions L=4,6,8,10. The order parameter probability distribution for six dimensional Ising model has been calculated at the critical temperature. The constants of the analytical function have been estimated by fitting to probability function obtained numerically at the finite size critical point.     

煤的热天平燃烧反应动力学特性的研究

采用热天平获得同一种煤在不同升温速率下的TG、DTG曲线,可求出燃烧速率、燃烧温度随燃烬度的变化曲线,根据两个不同升温速率下的数据,可计算出化学动力学参数活化能和指前因子随燃烬度的变化曲线。根据实验数据计算得到四个煤种的反应动力学参数随燃烬度变化的曲线,并预测其中一种煤在第三个升温速率下的燃烧速率随燃烬度的变化曲线,计算结果与实验结果符合较好。用此模型预测了在不同的恒定温度下试验煤种的煤粉燃烧速率随燃烬度的变化趋势。     

A new model for spectral sensitization of photoconduction in zinc oxide powder

Seven organic dyes were adsorbed on photoconductive zinc oxide powder and their sensitizing efficiencies were examined. The adsorption of dye induced a change in the dark conductivity, the magnitude of which appeared to represent the sensitizing power of the dye. The initial slope of sensitized photocurrent was found to be an exponential function of σ₀, the pre-exponential factor in the conductivity equation. A model is proposed, which is consistent with all the observations. In this model, the sensitized photoinjection of electrons is assumed to occur from surface states to the bulk, depending upon the population of the surface states. A critical surface level for the spectral sensitization is introduced to account for the observed temperature effect. Surface states located below the critical energy are assumed not to contribute for the sensitization.     

Influence of disordering on the critical temperature of superconductors with a short coherence length

The influence of disordering on the critical temperature of s-wave superconductors with a short coherence length is studied by numerical simulation using the two-dimensional Hubbard model with attraction. The calculations are carried out within the Bogolyubov-De Gennes approach, which allows one to include the spatial inhomogeneity of the order parameter. The influence of the spatial inhomogeneity of physical quantities on the results obtained is studied. Disordering is shown to be able to cause a significant increase in the critical temperature.     

Asymptotic approach to the description of nonclassical transport processes. Fermat’s principle

A method has been proposed to calculate the concentration distribution at asymptotically long distances from a source of impurity in a medium including long-scale heterogeneities. It has been found that the exponent Γ ? 1 in an expression for the concentration satisfies a nonlinear equation with first-order partial derivatives. This has allowed using the variational principle to calculate the function Γ. The pre-exponential factor in the expression for the concentration has been determined in the leading approximation in the small parameter Γ^?1. An analogy with geometrical optics and semiclassical approximation in quantum mechanics has been demonstrated.     

室温下用脉冲激光沉积E-BN薄膜

 在利用等离子体增强脉冲激光沉积系统沉积立方氮化硼（cBN）薄膜时，发现了氮化硼（BN）材料的E-BN相，并利用扫描电镜和红外吸收光谱及X射线衍射技术对薄膜样品进行了分析，得到了制备较高质量E-BN薄膜的一些热力学参数及时间参数，验证了现有的E-BN结构的形成理论。     

Numerical study of three-dimensional detonation wave dynamics in a circular tube

The three-dimensional structures of a detonation wave propagating in a circular tube were investigated using a one-step irreversible Arrhenius kinetics model. A series of parametric studies were carried out to investigate the different modes of cell structure formation by changing the pre-exponential factor. Maximum pressure trace was recorded along the tube wall to investigate the detonation cell structures. The unsteady results obtained in three dimensions revealed the generation mechanism of the wave front structures of two-, three- and four-cell mode detonations. A six-cell mode detonation could be obtained using a finer grid. With the increase in pre-exponential factor, it was found that the number of detonation cells is increased while the cell size is reduced accordingly. In all the multi-cell modes, the detonation wave structures and smoked-foil records on the wall are formed by the propagation of transverse waves along the wall in clockwise and counter-clockwise directions, while the slapping wave moves in the radial direction. The presence of the slapping wave further strengthens the wave interactions in three-dimensional simulation. Comparison with two-dimensional simulation confirms the effect of the slapping wave in the radial direction. As a result, the detonation wave front structures changes from the polygonal shape to the multi-bladed fan shape, periodically.     

Modeling of reactive kinetics in the metal surface contaminant cleaning using atmospheric pressure plasma arc

Atmospheric pressure plasma arc (APPA) cleaning is a newly developed method of metal surface cleaning. In this paper, a mathematical model of reactive kinetics in the metal surface contaminant cleaning using APPA has been developed. Based on the analysis of APPA cleaning mechanism and the feature of cleaning interface, a governing equation was established with heat transfer equation and energy conservation on the moving interface. Using fourth-order Rounge-Kutta method, above equation was solved and removal percentages of the cleaning contaminant at different time were obtained. In virtue of reactive kinetics theory, a reactive kinetics model of metal surface cleaning using APPA was established on the base of above calculation results. Afterwards, reactive kinetics parameters such as activation energy and pre-exponential factor were calculated. Cleaning lubricant was taken as an example, the results indicated that predictive values of lubricant removal percentages gotten from this established reactive kinetics model show good consistent with experimental data at the same time. Furthermore, the ambient temperature on the cleaning lubricant surface affects the removal rate strongly. The removal rate increases with the increase of the ambient temperature. To avoid the damage of metal substrate surface because of higher temperature and ensure the removal rate of the lubricant, the appropriate temperature which lies between the lubricant decomposition temperature and damage temperature of metal substrate under given calculation conditions should be determined.