氧的低温吸附模型与计算

受化学氧碘激光器(COIL)高效率小型化及新型压力恢复技术发展的推动,考虑COIL中气体氧的低温吸附问题。从质量守恒观点出发考察了气体流过沸石多孔床的压力与速度的关系,建立了吸附剂吸收的物质与气流中物质关系的吸附平衡方程。由吸附物较少的特点,得出在确定的压力梯度下速度为常数的近似。由吸附平衡方程与吸附速率方程,构成低温吸附模型方程,其中,亨利等温线方程作为辅助关系。对低温吸附模型方程作数值求解,得到了气流中氧质量浓度及吸收的氧质量浓度随时间变化的规律,以及这些质量浓度分布的长时间渐近特征。     

一种气体/液滴混合流动模型与数值计算

研究均匀液滴单态氧发生器(TUDOG)的工作机理,为Cl₂/He混合气体横向流过垂直下落的BHP(按重量25%KOH,25%H₂O₂,及50%H₂O)液滴场的化学反应流动建立模型,并对模型方程做数值求解.模型方程中考虑液滴与气体间的质量、动量交换.混合流动的二维模型方程用SIMPLEC方法求解.模拟结果与相关文献提供的实测结果对比较好.结果发现:氯气利用率、单态氧产率随入流气体速度增大而减小,随液滴速度增大而增大;在含液滴区域的上游氯气的吸收利用较显著,对TUDOG的工程设计有参考价值.     

氯气/BHP液滴化学反应流动一维数值模拟

为研究横向均匀液滴发生器的机理,对Cl₂/He气体横向流过BHP液滴场的物理化学行为建立一维化学反应流动模型.其中气流场按不可压缩假设近似为一维均匀流动;发生于液滴内的化学反应由四种物质的反应扩散方程描述;气相中各种物质浓度由对流扩散方程描述.液滴是这些物质的源或汇,两个模型方程通过此源项相联系.对模型方程作数值求解.结果显示,氯气利用率、单态氧产率及效率与文献所提供的实验结果较为接近,反映了所建模型具备模拟混合气体与BHP液滴反应的基本能力.     

气体临界温度以上吸附平衡的预测研究

采用容积法测定了CH4和N2 在微孔活性炭K0 2上的吸附平衡数据 ,温度为 2 73～ 333K ,压力为 0～12MPa .提出了一个可以从单一气体吸附等温线预测其它条件下吸附平衡的理论模型 .该模型考虑了临界温度以上吸附相密度和饱和吸附量与温度的关系 ,并采用孔径分布来表征吸附剂表面吸附势场的不均一性 ,局部方程使用Langmuir描述 .利用此模型预测了CH4和N2 在K0 2活性炭上的吸附平衡 ,在所研究的温度、压力范围内的整体预测偏差不超过 3% .另外 ,对文献中不同实验条件下气体临界温度以上的吸附平衡进行了研究 ,在较宽的范围内也取得了很好的预测结果     

沸石～湿空气系统共吸附平衡曲线的实验测定

1前言干沸石对水蒸汽分子具有强烈的吸附能力，早在七十年代就有人提出利用沸石的吸附～脱附循环实现制冷、供热及对太阳能的低温储存，这是能源领域中的前沿课题。沸石的吸附平衡曲线是定量分析沸石吸附～脱附循环的基础。吸附平衡方程描写吸附剂（沸石）与吸附质（湿空气）处于吸附平衡状态时，吸附量随系统的温度、压力（或浓度）的变化规律。吸附平衡方程目前尚无法由理论导出，完全依赖于实验测取吸附平衡数据，经拟合得到其经验表达式。传统的平衡吸附量测定法分静态吸附法和动态吸附法[1]。文献[2-3]报导的几种沸石的吸附量测定均属…     

轴对称谐振势阱中玻色凝聚气体基态和单涡旋态解

对囚禁在轴对称谐振势阱中的玻色凝聚气体，提出一种新的试探波函数，运用Gross-Pitaevskii(G-P)平均场能量泛函和变分的方法，得到玻色凝聚气体基态和单涡旋态波函数的解析表达式，并计算出凝聚原子的平均能量、原子云轴向和径向尺度比，以及产生单涡旋态的临界角速度等重要物理量与凝聚原子数N之间的关系.其结果与Dalfovo等人直接数值求解G-P方程所得到的结果相一致. 关键词： 玻色凝聚气体 G-P泛函 波函数 谐振势阱     

中、小雷诺数下围绕渗透出可燃气体的圆柱强迫对流时火焰结构的数值分析

一、前言 气流中的扩散火焰结构的数学分析在理论和实践上都具有一定意义.前人曾提出“折算薄膜”,“边界层燃烧”,“厚交换层”等数学模型来分析中、小雷诺数下强迫对流中单燃料滴的燃烧,并与实验结果进行了对比.本文对围绕渗透出可燃气体的圆柱在强迫对流的空气气流中求解流场,并与扩散方程和能量方程联立,用松弛迭代求解浓度场和温度     

ITO负载单原子钇吸附NO和CO的第一性原理研究

基于密度泛函理论,对氧化铟锡(Indium Tin Oxide,ITO)表面负载单原子Y模型的表面性能进行了第一性原理计算.根据表面能计算结果可知,单原子Y最稳定负载位置为空位(H),即确定了ITO负载单原子钇(Single-atom Y supported on ITO,Y/ITO)稳定模型.对ITO和Y/ITO表面吸附气体分子(NO和CO)模型的吸附性能进行了第一性原理计算.根据对比ITO和Y/ITO表面的吸附能和态密度计算结果可知,单原子钇负载提高了ITO表面的稳定性和吸附性能.根据对比Y/ITO表面吸附NO和CO气体分子的吸附能和态密度计算结果可知,NO和CO气体分子吸附均为自发行为,过程放热.且NO气体分子更容易吸附在Y/ITO表面,即Y/ITO对NO气体分子更敏感.     

YK-1活性炭平衡储氢特性分析

文中基于氢在椰壳活性炭YK-1上的平衡吸附数据,以探寻氢在碳基材料上适宜存储条件为目的,研究吸附氢分子间相互作用能随储存系统温度、压力、表面遮盖率的变化规律。首先,依据容积法的原理,在温度区间113K—293K、压力范围0—13MPa测试氢在YK-1椰壳活性炭上的吸附等温线。其次,应用格子理论推导通用吸附等温方程,通过等温方程的线性标绘确定氢分子在吸附表面的最大浓度,并由氢分子在活性炭典型吸附空间内受到的壁面作用势函数迭代求解氢分子受到的壁面作用势,进而获得与各吸附平衡态对应的氢分子间相互作用能。最后,根据氢分子间作用能随温度、表面遮盖率等的变化关系,分析氢分子在此活性炭上吸附的特点。     

O2中α型射频放电的理论研究

根据射频放电中电流连续性方程、稳态时电子数密度的连续性方程以及电子的能量平衡方程,建立了气体放电氧碘激光器中α型射频放电等离子体的理论模型,通过数值求解得到了射频放电等离子体中电场、电子数密度的空间分布,分析了放电参数对放电特性的影响.结果表明采用频率高的射频放电会使放电空间电场降低,电子数密度增加,从而有利于单重氧的生成,为提高气体放电中单重氧的产率提供了理论依据.     

Electron stimulated desorption of O2 from gadolinia-doped ceria surfaces

The interactions of gas phase oxygen with gadolinia-doped ceria (GDC) surfaces are investigated by electron stimulated desorption (ESD). The primary desorbed cationic species related to molecular oxygen adsorption is O₂⁺. The threshold energy for ESD of O₂⁺ is 13–14 eV, indicating electron impact ionization of molecular oxygen bound at oxygen vacancies. Dependence of O₂⁺ velocities upon incident electron energy and substrate temperature reveals the dominant influence of the effective charge of the adsorption complex. The O₂⁺ velocity distribution is bimodal, and the onset of the faster components at room temperature is related to the balance between fluxes of incident electrons and secondary electron emission, causing effective hole production and neutralization of trapped electrons at surface states.     

Adsorption Regularity and Characteristics of sp~3-Hybridized Gas Molecules on Anatase TiO_2(101) Surface

We report the anatase titanium dioxide(101) surface adsorption of sp~3-hybridized gas molecules,including NH_3,H_2O and CH_4,using first-principles plane-wave ultrasoft pseudopotential based on the density functional theory.The results show that it is much easier for a surface with oxygen vacancies to adsorb gas molecules than it is for a surface without oxygen vacancies.The main factor affecting adsorption stability and energy is the polarizability of molecules,and adsorption is induced by surface oxygen vacancies of the negatively charged center.The analyses of state densities and charge population show that charge transfer occurs at the molecule surface upon adsorption and that the number of transferred charge reduces in the order of N,O and C.Moreover,the adsorption method is chemical adsorption,and adsorption stability decreases in the order of NH_3,H_2O and CH_4.Analyses of absorption and reflectance spectra reveal that after absorbed CH_4 and H_2O,compared with the surface with oxygen vacancy,the optical properties of materials surface,including its absorption coefficients and reflectivity index,have slight changes,however,absorption coefficient and reflectivity would greatly increase after NH_3 adsorption.These findings illustrate that anatase titanium dioxide(101) surface is extremely sensitive to NH_3.     

Influence of oxygen adsorption on the surface potential of a metal oxide semiconductor

Analytical expressions describing dependences of the surface density of adsorbed oxygen ions and energy band bending in the subsurface region of a metal oxide semiconductor on the oxygen concentration that consider not only the process of neutral gas particle adsorption, but also their charge transfer at the expense of electron capture from the conduction band are presented. It is demonstrated that the heat of oxygen ion absorption is equal to the sum of the heat of neutral particle adsorption and the energy gap between the Fermi level and the level of the oxygen ion on the semiconductor surface. When the adsorption equilibrium is established, an analytical expression describing the time dependence of the energy band bending can be obtained only for small change of the oxygen concentration in the gas mixture.     

Is hydrogen storage possible in metal-doped graphite 2D systems in conditions found on Earth?

Density functional theory (DFT) calculations are performed for the adsorption energy of hydrogen and oxygen on graphene decorated with a wide set of metals (Li, Na, K, Al, Ti, V, Ni, Cu, Pd, Pt). It is found that oxygen interferes with hydrogen adsorption by either blocking the adsorption site or by the irreversible oxidation of the metal decoration. The most promising decorations are Ni, Pd, and Pt due to a reasonable relationship of adsorption energies which minimize the oxygen interference. The DFT results are used to parametrize a statistical mechanical model which allows evaluation of the effect of partial pressures in the gas phase during storage. According to this model, even in the most promising case, it is necessary to reduce the oxygen partial pressure close to ultrahigh vacuum conditions to allow hydrogen storage.     

Thermal desorption study of Oxygen adsorption on Pt, Ag & Au films deposited on YSZ

The Thermal Desorption or Temperature Programmed Desorption (TPD) technique has been used for the study of oxygen adsorption on Pt, Ag and Au catalyst films deposited on YSZ. The catalyst film was deposited on the one side of the YSZ specimen while on the other side gold counter and reference electrodes were deposited, constructing a three-electrode electrochemical cell similar to those used in Electrochemical Promotion studies. Oxygen adsorption has been carried out either by exposing the samples to gaseous oxygen (gas phase adsorption) or by the application of a constant current between the catalyst/working electrode and the counter electrode (electrochemical adsorption) or by mixed gas phase and electrochemical adsorption. Oxygen adsorption was carried out at temperatures between 200 and 480 °C. After exposure to gaseous oxygen, normal adsorbed atomic oxygen species have been observed on Pt and Ag surfaces while there was no detectable amount of adsorbed oxygen on Au. Electrochemical O²⁻ pumping to Pt, Ag and Au catalyst films creates strongly bonded “backspillover” anionic oxygen, along with the more weakly bonded atomic oxygen. Electrochemical O²⁻ pumping to Pt, Ag and Au catalyst films in presence of preadsorbed oxygen creates strongly bonded “backspillover” anionic oxygen, with a concomitant pronounced lowering of the T_p of the more weakly bound preadsorbed atomic oxygen. The two oxygen species co-exist on the surface. The activation energy for oxygen desorption or, equivalently, the binding strength of adsorbed oxygen was found to decrease linearly with increasing catalyst potential, for all three metal electrodes. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland Sept. 13–19, 1997     

Initial stages of oxidation of GaAs(111)2 × 2-Ga surfaces

The initial interaction of oxygen at room temperature with GaAs(111)2 × 2-Ga surfaces has been studied by quantitative Auger analysis and low-energy electron diffraction, under different electron irradiation and gas ionization conditions. Oxygen fills first the non-vacancy overlayer sites with a preferential bond to the Ga atoms. This adsorption phase is characterized by the absence of chemical shifts in the Ga Auger peaks that involve core levels. The oxidation stage begins with the occupation of the underlayer sites below the first Ga-As bilayer. For coverages lower than 2 monolayers oxygen adsorption and incorporation takes place without any loss of Ga or As atoms of the surface layers. Electron irradiation and gas ionization of the oxygen-covered surface increase the kinetics up to two orders of magnitude, but no changes in the adsorption sites and/or occupation sequence have been detected.     

A New Approach for Modeling of Industrial Adsorption Column

A theoretical analysis of the effect of velocity radial nonuniformity on nonstationary gas-solid adsorption processes in the column apparatuses is presented. The average concentration model, where the radial velocity component in the gas phase is equal to zero (in cases of a constant velocity radial nonuniformity along the column height), is used in the cases of an axial modification of the radial nonuniformity of the axial velocity components in the gas phase. The use of experimental data, for average concentrations in the gas phase at the column end, for a concrete process (physical or chemical adsorption), permits obtaining the gas phase model parameters related with the radial nonuniformity of the velocity. These parameter values allow using the average concentration model for modeling different adsorption processes.     

锐钛矿型氧化物XO2（X=Ti,Sn,Zr,Ir）表面氧化性对NH3气体光学气敏传感特性的影响

摘要 金属氧化物气敏传感材料一直是当今的热门研究课题,锐钛矿相金属氧化物XO2（X=Ti,Sn,Zr,Ir）是具有传感特性的常见材料。光学气敏效应是指气体分子吸附在气敏传感材料上,与表面氧空位发生氧化还原反应,由于光学性质发生改变而检测出气体的成分和浓度,因此,氧化还原反应的强弱是反应传感性能的核心原因。本文采用密度泛函理论(DFT)体系下广义梯度近似(GGA)第一性原理平面波超软赝势方法,分析和计算了含氧空位的锐钛矿相XO2（X=Ti,Sn,Zr,Ir）表面特性。通过以NH3为目标分子,研究分子表面吸附引起的氧化还原反应的机理,分析不相同的氧化物表面的几何结构、吸附能、态密度、差分电荷密度、电荷布居、电荷转移、光学性质等。研究发现：目标分子稳定吸附在氧化物表面后改变材料光学性质。SnO2表面对分子的吸附能最大,IrO2表面与分子的吸附距离最小。NH3分子与表面间存在电荷转移,其转移电子数目大小为:IrO2＞TiO2＞ZrO2＞SnO2,氧化物表面氧化性的大小为:IrO2氧空位＞TiO2氧空位＞ZrO2氧空位＞SnO2氧空位;比较吸收谱和反射谱发生变化最为明显的是TiO2表面。结论,在可见光范围内,波长在400~530nm时,SnO2表面光学气敏传感效应更好。而在530~760nm范围TiO2表面光学气敏传感效应更好。     

氢气在炭狭缝微孔内吸附的预测

通过边界的平均场近似,推导二平板狭缝孔格子理论Ono-Kondo吸附等温方程。利用格子模型特性和微观物理学理论,计算氢分子在石墨平面的最大吸附容量。比较由氢分子在石墨平面二典型聚集状态标定的Ono-Kondo方程,并用预测精度较高的方程计算了与文献相同条件下的吸附等温线。在比较了计算结果、试验结果和GCMC分子模拟结果后,对Ono-Kondo吸附等温方程的特点、理论基础作了分析,指出了方程的适用范围。