基于LSCM/3YSZ致密扩散障型极限电流氧传感器的研究

采用固相法制备了LSCM(La0.75Sr0.25Cr0.5Mn0.5O3)粉体。按不同质量比将其与3%-mol氧化钇稳定氧化锆粉体(3YSZ)混合,制备得到系列混合导体。根据热膨张系数、微观形貌等物理特性,选取合适比例的混合导体。采用Pt浆粘合法将其与8YSZ固体电解质叠层制作成致密扩散障型极限电流氧传感器。经测试,使用LSCM质量比分别为60%和70%的混合导体作为致密扩散障时,对应的氧传感器在973 K氧浓度分别为6 000×10-6～2.28%和1.22%～8.01%范围内具有良好的测氧特性,并且极限电流与氧浓度之间存在良好的线性关系;其在不同氧浓度下的响应时间曲线显示传感器重复性好,响应时间约数十秒。     

CeO_2基极限电流氧传感器的研究

采用Gd掺杂的CeO2(Ce0.8Gd0.2O1.9,CGO)粉体,干压成型后于空气气氛下1450℃烧结4 h。通过物理特性分析,发现在该烧结制度下烧结成型的样品基本满足氧传感器对敏感材料的要求。制备了一种新型结构的致密扩散障型极限电流氧传感器。经测试,发现该传感器在较高氧体积分数范围内有较好的极限电流特性,并为此建立了相关的理论模型,较好地解释了此类传感器极限电流和氧体积分数的关系。     

丝网印刷法制备极限电流氧传感器扩散孔的研究

为了研究采用丝网印刷法制备的小孔扩散障对极限电流氧传感器的影响,采用流延法制备8%molY_2O_3稳定ZrO_2(8YSZ)膜片;通过丝网印制法制备了敏感电极和扩散障,最后通过共烧获得小孔扩散障型极限电流氧传感器。利用扫描电镜(SEM)等手段对氧传感器进行物理结构的表征,发现通过丝网印刷获得的传感器扩散障结构良好,多层对位效果良好。通过计算验证了8YSZ电导率能产生足够大的泵氧电流。进一步对传感器的气敏特性进行测试,发现传感器具有一定的饱和平台,工作温度对极限电流具有一定的影响,同时发现极限电流与氧气浓度存在正常扩散模型的线性关系。     

流延共烧结制备极限电流式氧传感器的研究

以流延成型工艺制备钇稳氧化锆(YSZ)基片,采用丝网印刷、等静压叠层工艺,经1450℃共烧结制备极限电流式氧传感器。采用XRD,SEM对其物理性能进行表征,并在650℃、氧体积分数为0%～90%范围内对该陶瓷器件的伏—安特性、响应时间等输出特性进行研究,实验结果表明:该传感器在其体积分数范围内具有良好的极限电流平台,响应时间小于9 s(氧体积分数从20%～75%),准确度达到0.5%。     

通用氧弹量热数据处理系统的开发与应用

基于氧弹燃烧法原理,利用Matlab可视化编程技术,开发了通用氧弹量热数据处理系统。系统不仅适用于有机物燃烧热数据处理,还可广泛用于化合物分解焓以及诸如煤、焦炭、污泥、生活垃圾、建筑材料、饲料、水泥黑生料等复杂样品的发热量测定数据分析。通过对测定数据选取优化数学模型,采用最小二乘法进行曲线拟合,能比较精确地计算出反应过程中的温度变化和测试结果,并且在屏幕上直观地显示出雷诺校正曲线图。在文中也列出了氧弹量热数据处理Matlab实用程序。系统对进一步开拓氧弹量热技术的应用领域,解决热力学数据应用的实际问题具有参考价值。     

复合障碍层限流型氧传感器的研究

本文采用一种新的制备工艺-共压共烧法,以8mol%Y2O3稳定的ZrO2(YSZ)为固体电解质,混合导体材料La0.8Sr0.2MnO3和YSZ的混合物作复合障碍扩散层,成功制备出了限流型氧传感器.借助动态电位扫描分别研究了电流与施加电压的关系,极限电流与氧浓度的关系.结果表明,在T=998K,氧浓度为0～3.375 ppm时该传感器给出了较好的电流平台,极限电流与氧浓度存在很好的线性关系,相关系数达到0.99以上.该传感器对微量的氧有很好的敏感性,与以往的极限电流氧传感器相比具有结构简单,成本低廉等优点.     

沿轴向飞行粘弹性夹层梁热弹耦合振动响应分析

研究了沿轴向飞行粘弹性夹层梁的热弹耦合振动响应.考虑材料变形与传热的相互影响,建立了轴向运动粘弹性夹层梁的热弹耦合振动控制方程;将方程中激励项(温度函数与外激力)拟合为时间的函数,采用伽辽金法得到方程的位移解,并在每一个微小的时间段内采用迭代收敛的数值方法对热传导方程进行求解得到温度场.使用数值方法讨论了轴向飞行运动速度和热载荷持续时间对其振动响应的影响.研究表明:稳定振动时飞行速度对位移影响较大,对温度影响较小;热冲击对振动位移响应有较大影响,并改变振动特性.     

氧等离子体处理ZnO纳米纤维材料的制备及其对丙酮气敏性能的研究

采用静电纺丝法制备了ZnO纳米纤维材料并使用氧等离子体对其进行表面处理.通过X射线衍射(XRD),扫描电子显微镜(SEM),BET比表面积测试以及X射线光电子能谱分析(XPS)等手段对样品的结构与形貌进行了表征分析.将氧等离子体处理前后的ZnO纳米纤维分别制成气体传感器,对浓度为1×10-6~100×10-6(体积分数)丙酮气体的敏感特性进行了测试分析.测试结果表明,氧等离子体处理后的ZnO纳米纤维响应值较未处理的ZnO纳米纤维有大幅度的提升,最佳工作温度也有所降低,且对甲醛、苯、甲苯、二甲苯等几种干扰气体表现出更好的选择性.从晶粒间势垒和耗尽层厚度等角度初步分析了氧等离子体处理改善ZnO气敏特性的机理.     

气压变化对极限电流型氧传感器输出特性的影响

对气压变化对极限电流型氧传感器扩散机理的影响进行了研究。实验中将扩散孔径为30μm的极限电流型氧传感器先后放置在不同气压环境中进行了电学性能测试。实验结果显示:在常压下该氧传感器的极限电流IL与氧浓度的对数表达式ln(1-XO2)具有很好的线性关系,呈现正常扩散模型的特征。但在低气压环境下,该传感器的极限电流IL受气压P的影响,并呈现Knudsen模型的某些特征。     

纺锤状氧化锌的制备及气敏性能研究

以硝酸锌和氢氧化钾为原料,采用传统的溶剂热法于150℃时合成了纺锤状氧化锌粉体,通过X射线衍射仪(XRD)和扫描电镜(SEM)及红外光谱仪(IR)对产物的物相、微观形貌及化学键进行了分析,结果表明,产物属于六方晶系纤锌矿结构的ZnO,结晶良好,呈规则的纺锤状,尺寸比较均一,长约20μm,利用该粉体制成厚膜型气敏原件,并用静态配气法测试其气敏性能,测试结果表明,纺锤状氧化锌在加热温度为220℃时对乙醇和丙酮气体具有很好的气敏性能,且具有很低的检测极限和极短的响应时间。     

Simulation of the transient response of limiting current oxygen sensor

The transient response of the limiting current oxygen sensors following step changes in gas composition has been simulated by assuming a Knudsen diffusion of the gases in the diffusion barrier. The simulation results showed that the expression of the stable state current had the same form as that deduced from stable state model. The response time values in the simulation results were independent of the oxygen molar fractions (X₁, X₂), the operation pressure (P) and the effective cross section area of the diffusion barrier (S × θ), but decreased with the pore radius (r) in the diffusion barrier and the operation temperature (T), and increased with the effective diffusion barrier length (L × τ). The simulation results were compared with some experimental measurements on our designed amperometric sensors.     

State‐limiting PID controller for a class of nonlinear systems with constant uncertainties

Proportional Integral Derivative (PID) controllers still represent the core control method for achieving output regulation of either linear or nonlinear systems in the majority of industrial applications. However, conventional PID control cannot guarantee specific state constraint requirements for the plant, when the system introduces uncertainties. In this paper, a novel nonlinear PID control that achieves output regulation and guarantees a desired state limitation below a given value for a wide class of nonlinear systems with constant uncertainties is proposed. Using nonlinear ultimate boundedness theory, it is shown that the proposed state‐limiting PID (sl‐PID) control maintains a given bound for the desired system states at all times, ie, even during transients, whereas an analytic method for selecting the controller gains is also presented to ensure closed‐loop system stability and convergence at the desired equilibrium. Two nonlinear engineering examples that include an electric motor and a dc/dc converter are investigated using the conventional PID and the proposed sl‐PID to validate the superiority of the proposed controller in achieving the desired output regulation with a given bounded state requirement.     

流延共烧法极限电流氧传感器研究

采用固相法合成La0.8 Sr0.2MnO3 (LSM)粉体,利用干压法制备自合成LSM粉体和商业化8钇稳定氧化锆(8YSZ)粉体的条样;利用流延法以及多层高温共烧工艺制备以LSM致密层为扩散障的8YSZ基极限电流氧传感器;利用四端子测电阻法对LSM和8YSZ条样在干燥空气和氦气中进行电导率的剥离测试,结果发现:在700℃时,LSM和8YSZ电子电导率分别占总电导率的99.7％和0.03％.进一步对传感器进行测试,发现传感器均具有一定的饱和平台,且随着致密扩散障厚度的增加极限电流减小.     

CO气体对极限电流型氧传感器特性的影响

研究了CO气体对极限电流型氧传感器特性的影响,将小孔型极限电流型氧传感器放置在不同CO体积分数的环境中进行了电学性能测试。实验结果表明:在CO-O2-N2环境中,O2体积分数分别为7.5%,10%,CO体积分数在0.75%～4.25%变化时,传感器的电压—电流特性曲线均有良好的极限电流平台,且极限电流IL随着CO体积分数的增大而减小。理论分析在CO-O2-N2环境中IL与-ln(1-(XO-47XCO))有良好的线性关系,且该传感器对CO的上升响应时间与下降响应时间分别在10 s和15 s以内。     

A model of the behavior of the limiting current oxygen sensors

A physical model describing the I(V) characteristics of planar limiting current oxygen sensors based in an ion-conducting electrolyte is presented. The model focuses on the minimization of the electrochemical potential and the diffusion across a porous layer covering the measuring electrode. The proposed model describes three key phenomena in the response of the sensors: the influence of the polarization resistance on the slope of I(V), the linearity between the limiting current and the diffusivity of the porous layer and a low non-zero current at zero polarization.     

Investigation into gas dynamics in an oxyfuel coal fired boiler during master fuel trip and blackout

In an oxygen fired power plant, a large amount of flue gas is recirculated, leading to an unavoidable interaction between the involved fans. The presented paper investigates the dynamics of the gas side at different safety related scenarios. A dynamic simulation model is therefore developed to study the flue gas behaviour in an oxyfuel pulverized coal fired boiler during a master fuel trip and a blackout of the plant. The generated numerical model contains the water/steam side of the boiler, starting from economiser inlet and ending at the hot reheat outlet, and the gas side, including all relevant fans, convective heat exchangers, gas–gas heat exchangers and flue gas cleaning devices. Furthermore, a set of additional models for coast down behaviour of axial fans has been implemented. For the master fuel trip case, different relevant parameters of process control measures regarding the gas dynamics have been analyzed and an optimized master fuel trip scenario is proposed. The blackout of an oxyfuel coal fired boiler at nominal load is detailed demonstrated. The numerical results show that the blackout scenario will not have any negative impact on investigated gas part of the boiler system since the observed lowest negative furnace pressure of −36 mbar can be handled with current state of the art technology.     

Modification of the oxygen diffusivity in limiting current oxygen sensors

Effect of sacrificial carbon on microstructure of protective layer and sensing properties of limiting current oxygen sensors were studied. Graphite and carbon nanofiber with different concentrations were examined as sacrificial layer. Therefore, several YSZ-based electrochemical gas sensors were fabricated with dissimilarity in the diffusivity of the layer covering their measuring electrodes.Gas sensors were tested as potentiometric and amperometric devices under O₂-N₂ mixtures, and synthetic gases similar to the exhaust gas mixtures from combustion engines. Sensors with low diffusivity (low concentration of sacrificial material) exhibit more abrupt and O₂-sensitive potentiometric responses. Indeed, less O₂-linear amperometric responses and higher response times are their characteristics. Sensors with high diffusion in their layers (high concentration of sacrificial material) show a less abrupt step-drop potentiometric response but a more linear O₂ dependence for the amperometric response and, in general, lower response times.Results suggest that the configuration of the diffusive layer shall be controlled in terms of the expected performance of the sensor, as an amperometric or potentiometric device. The controlling parameters are discussed and given in this study.