Dielectric and Thermal Investigations on PbNb2O6 in Pure Piezoelectric Phase and Pure Non-Piezoelectric Phase

A high piezoelectric transition temperature is indicated for present orthorhombic samples of lead meta-niobate (PbNb₂O₆) by the high value of the temperature (T_m) at which the real part (?′) of electrical permittivity peaks. It is 573 to 580°C. The imaginary component (?″) increases sharply at these temperatures. Cooling run after heating to 700°C gives changed values of ?′ and ?″ and T_m. Present work reports impedance spectroscopy (up to 700°C over 20 Hz to 5.5 MHz) and Differential Scanning Calorimetry or DSC on the pure orthorhombic phase, and, for the first time, on the pure rhombohedral phase. DSC shows an endothermic dip across T_m during heating and an exothermic peak during cooling for the orthorhombic sample only.     

A control system for thermal zones of electric resistance furnaces

A functional diagram of a temperature controller of electric resistance furnaces with temperature difference compensation in thermal zones by means of automatic correction of power arriving to the thermal zone is given. The additional power required for compensation of the temperature difference in thermal zones of the furnace is determined. The power depends on the temperature difference between thermal zones during heating, heating temperature, and given permissible temperature difference between thermal zones. Dependences of the relative additional power upon the temperature difference between thermal zones at heating temperatures in a range of 700–1600°C and permissible temperature differences between thermal zones 5, 15, 30, and 50°C are determined. Recommendations on the control system adjustment are given. The adaptive control system for thermal zones of electric resistance furnaces is developed.     

High Temperature Characterization of Electrical Barriers in ZnO Varistors*

Two main models have been proposed to describe the potential barriers in ZnO varistors: the surface oxidation and the surface states. It has been difficult to decide which of them better corresponds to the experimental observations. High temperature electrical characterization of these materials is an important tool to understand the formation of the electrical barriers. In this work, using literature data describing ZnO varistor characteristics at high temperature, up to 1153°C, we calculate the energy position of the equilibrium Fermi level at the grain boundary interface, and found that this parameter decreases with the increase of temperature, and for temperatures higher than ～700°C it stays close to the ZnO band gap without crossing it. This behavior shows that the interface never presents a p-type character, a starting point to develop the surface states model. On the other hand, 700°C is a temperature too low for the surface oxidation mechanism to be operative. It is then proposed that, during cooling down to ～700°C, the interface Fermi level stays close to the middle of the band gap due to the adsorption and subsequent reaction of oxygen with ZnO surfaces/grain boundaries. For lower temperatures, when the interface Fermi level separates from the middle of the band gap, it is proposed that it follows the variation of the bulk Fermi level, which in turn is caused by shallow donors in ZnO. A calculation assuming a reduced electroneutrality condition, gave a donor density of ～ 3 × 10¹⁷ cm^-3, which corresponds approximately to the density of carriers in the material for temperatures down to room temperature. This value is in a good agreement with those available in the literature. Knowing both the bulk and the interface Fermi levels, it is then possible to calculate the barrier height at any temperature, and it is observed that it is almost constant from room temperature up to ～400°C, with a value of 0.8 eV, and than decreases monotonously up to 1153°C. Taking these values, it is possible to calculate the variation of the low voltage conductivity with temperature, and it is found that, apart from the variation between room temperature and 400°C, with no special significance, the decrease of the barrier height from 400°–1153°C induces an extra change of the conductivity from which a fictitious activation energy of 1.5 eV is obtained. Therefore, these two energies are not related to shallow and deep donors in ZnO grains.     

TLM representation of the hyperbolic heat conduction equation

Many heat transfer situations are adequately described by the parabolic thermal diffusion equation. However, in situations in which very rapid heating occurs or in slower heating regimes for particular materials, the hyperbolic heat conduction equation is a better representation. Here, a parameterized nodal structure for transmission line modelling (TLM) representation of hyperbolic heat conduction processes is devised. A TLM model based on the nodal structure is implemented and temperature field predicted by the model are compared with analytical results for the same physical situation. Copyright © 2002 John Wiley & Sons, Ltd.     

Preparation and properties of borosilicate glass-coated Cu powder for internal electrode of multilayer ceramic device

In this study, a process was proposed which allows a base metal electrode to be burnt-out in an oxidative atmosphere for fabrication of multilayer ceramic device. To protect Cu in an oxidative atmosphere, the Cu powder was coated with borosilicate glass via a sol-gel process. The oxidation resistance and shrinkage of the glass-coated Cu were investigated. When a 10% glass-coated Cu was heated up to 500°C under an oxidative atmosphere, the Cu could survive without formation of copper oxide. The oxidation of the Cu was observed when heating at temperatures above 700°C. This might be due to exposure of Cu to oxidative atmosphere related to softening behavior of glass. The glass-coated Cu exhibited a shrinkage behavior which follows the shrinkage behavior of glass in the low temperature range and the shrinkage of pure Cu in the high temperature range. To measure the electrical conductivity of the glass-coated Cu electrode, the Cu pastes were prepared and printed onto alumina substrate. The binder-burn-out process of the glass-coated Cu was carried out at 550°C under an air atmosphere, and was then sintered at 1000°C under a nitrogen atmosphere. The electrical conductivity of the Cu electrode measured was above 10⁴ /Ωcm which means that it can be used as the internal electrode of a multilayer device.     

Fabrication and evaluation of LaCrO3 thin film heaters

Lanthanum chromium oxide (LaCrO₃) has excellent high‐temperature properties. LaCrO₃ doped with alkaline earth metals also has high electric conductivity. The purpose of this study is to fabricate thin film heaters using LaCrO₃ doped with Ca by RF magnetron sputtering method. The crystal structure of thin films was evaluated and the surface form was studied. The results show that the thin film deposited on Si(100) single crystal and quartz glass substrates in Ar gas had a strong orientation and that its surface form was comparatively smooth. The crystal structure of the thin films deposited on Si(100) and quartz glass substrate at temperatures of 700 and 800 °C by sputtering in a mixture of Ar and O₂ gases was the same as the crystal structure of LaCrO₃. The heating characteristics of a thin film heater on Si(100) substrate with Pt electrodes were evaluated by measurement of the equilibrium temperature‐current (T–I) and resistance‐equilibrium temperature (R–T) characteristics. The maximum equilibrium heating temperature was about 1100 °C. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 18–25, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1156     

TLM for diffusion: consistent first time step. Two‐dimensional case

In initializing a transmission line matrix (TLM) diffusion model it is necessary to consider both initial concentration (temperature) and initial flow. As usual, only one of them is given; an auxiliary formula is necessary to calculate the distribution for the first time step. It has been shown that the standard formula may introduce additional numerical errors (International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1993; 6 :135; International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 1993; 6 :161) and that these errors can persist over many time steps. In this paper, we show how an initial modification to the normal TLM algorithm can remove such errors, and we demonstrate the method by applying it to a two‐dimensional TLM heat diffusion model for a copper plate. Copyright © 2002 John Wiley & Sons, Ltd.     

基于多尺度特征融合的皮肤烧伤创面分级算法

为实现遭受重大火灾等灾害后,对伤员皮肤烧伤自动化分级,加快诊断效率,提出提出一种用于皮肤烧伤分类的轻量化模型BI-YOLOv5算法。替换Swish激活函数,提高模型收敛能力及检测效率;使用K-means++算法对anchors聚类分析,增强对不同尺度目标的适应能力;修改特征提取网络,提取多个尺度的特征信息,建立多尺度特征融合网络,提高模型对深层特征信息的利用率,提高小面积烧伤的识别精度。实验结果表明,BI-YOLOv5算法在检测并区分不同烧伤类别及环境干扰下烧伤检测有较高的精度和效率,mAP达到97.6,对比YOLOv5提升8.4个百分点。     

Formation and properties of nitrogen‐rich phases in austenitic stainless steel by plasma‐based ion implantation

Surface modification of austenitic stainless steel by plasma‐based ion implantation at elevated temperatures below 450°C has been studied experimentally. The nitrogen depth profile at room temperature was similar to that obtained by TRIM code simulation, but the depth of nitrogen penetration increases with target temperature and reaches a few micrometers at a treatment condition of 450°C and an implantation time of 2 h. High‐dose nitrogen implantation exceeding 10¹⁸ cm^?2 at temperatures above 350°C results in the formation of expanded austenite phase (supersaturated f.c.c. phase) with little CrN precipitation, leading to remarkable enhancement of surface hardness without loss of corrosion resistance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(4): 9–16, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10340     

LED灯光辐射对人皮肤的影响

目的:产生评价演播室中使用的一种LED光源对人皮肤颜色和皮肤屏障功能的影响。方法:选择了30名健康女性志愿者,以照度为2800lxLED光源照射上臂屈侧的皮肤,照射时间15分钟,每天照射一次,连续照射30天。比较照射前后反应皮肤颜色的L*a*b*值、M和E值以及角质层含水量和经皮水分丢失。结果:照射前后L*a*b*值、M和E值以及角质层含水量和经皮水分丢失均无统计学差异。结论:演播室中使用的此种LED光源短期照射对人体肤色和皮肤含水量无影响。     

Spatially weighted numerical models for the two-dimensional wave equation: FD algorithm and synthesis of the equivalent TLM model

In this paper a new TLM model for the two-dimensional wave equation is introduced. It is synthesized directly from a FD algorithm. The FD algorithm is second-order-accurate in both space and time, and is explicitly time-stepped. The spatial derivatives in the FD algorithm are approximated by the weighted combination of two standard central difference stencils, one oriented as usual, the other rotated by 45° with its arms extended by a factor of (2)^1/2. The TLM model is realized as the weighted connection of two original models (with the same geometrical configuration as the FD algorithm). The weighting in the TLM model is accomplished by using a variable intrinsic impedance for specific elemental transmission lines. The FD and TLM methods possess identical dispersion relations if the former is operated at its upper limit of stability. Therefore, under these conditions both represent identical models for the simulation of wave propagation. The propagation characteristics of the new model are investigated and the conditions for approximate numerical isotropy are provided. The numerical implementation (scattering matrix and transfer event) is described. To validate the new model, the calculation of cutoff frequencies of various modes in rectangular waveguide is performed. Comparison with analytical results (for an unfilled waveguide) and other numerical results (for a waveguide partially filled with a dielectric) validate the implementation of the model.     

Forming gas annealing effects on the microstructure and ferroelectricity of SrBi2Ta2O9 thin films prepared by metalorganic decomposition

Abstract

Ferroelectric SrBi₂Ta₂O₉(SBT) thin films prepared by metalorganic decomposition (MOD) method were annealed in forming gas (5% hydrogen + 95% nitrogen) at different temperatures for 60 min. SEM analysis results showed that an amount of columnar structures appeared on SBT surface when the annealing temperature was up to 450°C. When the annealing temperature raised up to 500°C, these columnar structures grew along one dimension and changed into wire structures. The EDX micro-area mapping analysis result showed that Bi was concentrated in the columnar or wire structures on SBT surface. The ferroelectric property analysis results showed that the hysteresis loops still existed after 5 min forming gas processing (350°C or 400°C), but when the annealing time was longer than 10 min, the resistance of the SBT samples became too low to measure the hysteresis loops.     

Low temperature metal-organic chemical vapor deposition of Ru thin films as electrode for high dielectric capacitors

Abstract

Low temperature metal-organic chemical vapor deposition (MOCVD) process of Ru films for use as electrode material was studied using a noble dome type reactor, liquid delivery technique and a new precursor. The films were grown at temperatures ranging from 275°C to 480°C in which film growth was controlled by a surface chemical reaction with a small activation energy of 0.21 eV. The root-mean-squared surface roughness was as low as 23 Å for a film grown at 290°C on a SiO₂ surface.     

Electrical Breakdown and Space Charge Formation at High‐Temperature Region in Long‐Time Heating Treatment PVC

Polyvinyl chloride (PVC) is widely used as an insulating material in various electrical products. It is reported that an exothermic reaction reaching temperatures above 150 °C can be caused by overload currents or inferior electrical wire connections before the ignition of electrical products. The exothermic phenomenon may cause deterioration of insulating properties in PVC due to its chemical decomposition. It is necessary to clarify the degradation of insulating properties in PVC under thermal stress exceeding 150 °C for the safe use of electric products. In this investigation the space charge distribution and conduction current in the heat‐treated PVC sheet were measured in the range from room temperature to 200 °C in the presence of a dc electric field, using a high‐temperature PEA system. Positive charge injection and increasing conduction currents were observed before breakdown above 100 °C in 100 °C 300‐h heat‐treated samples and in non–heat‐treated samples. The results indicate the thermal breakdown process from the analysis of conduction currents and electric fields. In samples exposed to higher temperatures (150 °C 100 h), the breakdown strength deteriorated strongly in the range from room temperature to 90 °C. Increases in conduction current were observed in the entire temperature range before breakdown of the 150 °C 100‐h heat‐treated PVC. This indicates that heat treatment above 150 °C degrades the breakdown properties in the range from room temperature to 90 °C due to thermal decomposition accompanied by dehydrochlorination in PVC. The electric field is intensified near the cathode due to positive charge accumulation, and the breakdown strength begins to deteriorate only above 90 °C. This shows that thermal stress exceeding 150 °C causes deterioration of insulating properties and that the breakdown process is affected by space charge formation in PVC.     

Spherical shape Ba-based glass powders prepared by spray pyrolysis for MLCCs

Spherical shape BaO–B₂O₃–SiO₂ glass powders were directly prepared by high temperature spray pyrolysis at >1000 °C. The thermal and morphological characteristics of the prepared glass powders were investigated. The glass powders prepared at temperature of 1000 °C had spherical shape and hollow inner structure. On the other hand, the powders prepared at high temperature of 1300 °C had complete spherical shape and dense inner structure by complete melting. The mean size of the glass powders was 0.9 μm. The glass transition temperatures (T _g) of the glass powders obtained by spray pyrolysis at preparation temperatures between 1000 and 1300 °C were 601.1 °C regardless of the preparation temperatures. The specimen of the glass powders obtained by spray pyrolysis at the preparation temperature of 1300 °C had small number of voids even at low sintering temperature of 700 °C. In addition, the specimen sintered at temperature of 800 °C had dense microstructure without voids.     

过/再热器受热面壁温与氧化皮厚度在线监测研究

提出了一种锅炉过/再热器受热面金属壁温与氧化皮(垢层)厚度定量在线监测的方法,利用两个神经网络分别预测监测段受热面烟气温度、速度分布及无氧化皮时的热阻。在此基础上,根据传热数学模型,得到了过/再热面受热面壁温的分布。具有简单快速、可连续进行和定期自动学习的优点,可用于在实际煤粉锅炉运行中进行受热面壁温、氧化皮厚度的定量监测,为锅炉通过优化调整控制热偏差防止爆管及为受热面寿命管理提供定量依据。     

Transmission‐line matrix models for solving transient problems of diffusion with recombination

Starting from the general telegrapher's equation, we investigate two nodal network constructions for modelling diffusion with recombination by means of the transmission‐line matrix (TLM) method. The diffusion effect is modelled by the series and shunt capacitance in one approach, and by the series inductance and shunt resistance in the other. Both approaches use the series and shunt resistances to model the recombination effect. The constraint of using both TLM networks for solving transient problems of diffusion with recombination is found to be identical in terms of the physics behind the numerical routines. A practical way of determining the spatial resolution and iteration time step for accurate TLM numerical computations is suggested based on a simple frequency analysis. Copyright © 2003 John Wiley & Sons, Ltd.     

On the dispersion of a non‐orthogonal TLM cell

The numerical dispersion of a non‐orthogonal transmission line matrix (TLM) algorithm is for the first time investigated. First of all, the dispersion relation is derived in the most general possible case. Then, the validation is carried out in the analysis of a simple one‐dimensional example. Results show that the theory is in excellent agreement with the numerical simulation. Numerical results concerning various cell shape dispersion characteristics are presented and show some relatively weak numerical dispersion even for rather highly distorted cells. Finally, some indications concerning cell shape selection to minimize the non‐orthogonal TLM cell are proposed. Copyright © 2007 John Wiley & Sons, Ltd.     

基于HHT的双馈异步发电机电刷滑环烧伤故障诊断

在实际工程应用中,双馈异步发电机电刷滑环故障发生较为频繁,对电机励磁稳定性影响也较大,严重时还会导致发电机组的解列。因此提出一种基于HHT的双馈异步发电机电刷滑环烧伤故障诊断方法。首先通过PSCAD/EMTDC电力系统仿真软件模拟滑环烧伤故障,得到故障前后流经电刷滑环的励磁电流。然后基于希尔伯特-黄变换理论提取故障特征量,并将仿真结果与实测励磁电流信号所得Hilbert谱图进行对比分析,验证了故障特征量诊断法的可行性。最后提出能量商的诊断特征值概念,计算不同故障等级下特征量的能量商值,并与红外测温探头测量滑环表面的温度值进行对比。分析二者变化趋势,发现高于100 Hz的周期性高频分量不但可以作为故障特征量,而且其能量商在诊断滑环发生轻微烧伤故障时具有更高的精度和灵敏度。该方法为实际工程研究提供了一定的指导意义。     

Ferroelectric phase transition and electrical properties of Ba(Bi0.5Ta0.5)O3

A lead free polycrystalline material Ba(Bi_0.5Ta_0.5)O₃ was prepared by a standard high-temperature solid-state technique (calcination temperature?=?1180 °C and sintering temperature?=?1200 °C) using high-purity ingredients. The room temperature X-rays diffraction analysis of the material has confirmed its formation in the monoclinic crystal system. The study of microstructure using scanning electron microscopy (SEM) shows that the compound has well-defined grains uniformly distributed throughout the surface of the sample. Detailed studies of dielectric and impedance properties of the material were carried out in a wide frequency range (1 kHz ?1 MHz) at different temperatures (30 °C to 490 °C). Dielectric study shows that the material has ferroelectric properties with diffuse-phase transition around 315 °C. Complex impedance spectroscopic analysis establishes some correlation between the microstructure and electrical properties of the material. The frequency dependence of ac conductivity follows the Jonscher’s power law. The dc conductivity, calculated from the ac conductivity spectrum, shows the negative temperature coefficient of resistance behavior similar to that of a semiconductor. The temperature dependent pre-exponential factor shows peak, and frequency exponent possesses a minimum at transition temperature.