Synthesis and thermoelectric properties of Mg_2Si_(1-x)Sn_x solid solutions by microwave irradiation

In order to reduce the oxidizing and volatilizing caused by Mg element in the traditional methods for synthesizing Mg2Sil-xSnx （x=0.2, 0.4, 0.6, 0.8） solid solutions, microwave irradiation techniques were used in preparing them as thermoelectric materials. Structure and phase composition of the obtained materials were investigated by X-ray diffraction （XRD）. The electrical conductivity, Seebeck coefficient and thermal conductivity were measured as a function of temperature from 300 to 750 K. It is found that Mg2Si1-xSnx solid solutions are well formed with excessive content of 5% （molar fraction） Mg from the stoichiometric MgESil.xSnx under microwave irradiation. A maximum dimensionless figure of merit, ZT, of about 0.26 is obtained for Mg2Si1-xSnx solid solutions at about 500 K for x=0.6.

One-Step Synthesis of Nanocrytalline Perovskite LaMnO_3 Powders via Microwave-Induced Solution Combustion Route

Perovskite LaMnO3 powders with an average crystallite size of 12.5 nm were rapidly synthesized via a microwave-induced autocombustion reaction using glycine as a fuel and nitrate as an oxidant. After self-propagating combustion, the desired nanocrystalline perovskite LaMnO3 was obtained and no further calcination was carried out. The possible processes of combustion reaction were discussed according to the principle of propellant chemistry. The autocombustion and thermal decomposition of the precursor were investigated using the TG-DTA and FT-IR techniques. The influences of glycine-nitrate molar ratio and heat-treatment temperature on the perovskite phase formation and crystallite size of as-burnt powder were studied by XRD. The morphology and size of the as-burnt powder before and after milling were characterized and compared by TEM.

Microwave-induced synthesis and characterization of nanometer Ce_(0.5)Zr_(0.5)O_2 solid solution for the acidic catalytic reaction

Ce0.5Zr0.5O2 solid solution was successfully synthesized using cerium nitrate, zirconium nitrate, and urea as raw materials by the microwave irradiation method and characterized by X-ray diffraction, fluorescence spectrum, transmission electron microscopy, and infrared spectrum. Its acid catalytic activity was evaluated in the esterification reaction of acetic acid and n-butyl alcohol. The results show that Ce0.5Zr0.5O2 solid solution has cubic fluorite structure, and its particle diameter is in the nanometer scale. As a sort of solid acid, it possesses a higher acid catalytic activity and can be easily separated from reaction liquids. It can be used for several times, and basically, its activity keeps constant. The proton acid sites and Lewis acid sites exist in the structure of Ce0.5Zr0.5O2 solid solution.

An accurate automated technique for quasioptics measurement of the microwave diagnostics for fusion plasma

A new integrated technique for fast and accurate measurement of the quasi-optics, especially for the microwave/millimeter wave diagnostic systems of fusion plasma, has been developed. Using the LabVIEW-based comprehensive scanning system, we can realize not only automatic but also fast and accurate measurement, which will help to eliminate the effects of temperature drift and standing wave/multi-reflection. With the Matlab-based asymmetric two-dimensional Gaussian fitting method, all the desired parameters of the microwave beam can be obtained. This technique can be used in the design and testing of microwave diagnostic systems such as reflectometers and the electron cyclotron emission imaging diagnostic systems of the Experimental Advanced Superconducting Tokamak.

ON A NEW ALGORITHM OF CONSTRUCTING SOLITARY WAVE SOLUTIONS FOR SYSTEMS OF NONLINEAR EVOLU-TION EQUATIONS IN MATHEMATICAL PHYSICS

According to the improved sine-cosine method and Wu-elimination method, a new algorithm to construct solitary wave solutions for systems of nonlinear evolution equations is put forward. The algorithm has some conclusions which are better than what the hyperbolic function method known does and simpler in use. With the aid of MATHEMATICA, the algorithm can be carried out in computer.

Numerical modeling dynamic process of multi-feed microwave heating of industrial solution media

The exothermic efficiency of microwave heating an electrolyte/water solution is remarkably high due to the dielectric heating by orientation polarization of water and resistance heating by the Joule process occurred simultaneously compared with pure water.A three-dimensional finite element numerical model of multi-feed microwave heating industrial liquids continuously flowing in a meter-scale circular tube is presented.The temperature field inside the applicator tube in the cavity is solved by COMSOL Multiphysics and professional programming to describe the momentum,energy and Maxwell's equations.The evaluations of the electromagnetic field,the temperature distribution and the velocity field are simulated for the fluids dynamically heated by singleand multi-feed microwave system,respectively.Both the pilot experimental investigations and numerical results of microwave with single-feed heating for fluids with different effective permittivity and flow rates show that the presented numerical modeling makes it possible to analyze dynamic process of multi-feed microwave heating the industrial liquid.The study aids in enhancing the understanding and optimizing of dynamic process in the use of multi-feed microwave heating industrial continuous flow for a variety of material properties and technical parameters.

The effect of substrate holder size on the electric field and discharge plasma on diamond-film formation at high deposition rates during MPCVD

The effect of the substrate holder feature dimensions on plasma density（ne）, power density（Qmw） and gas temperature（T） of a discharge marginal plasma（a plasma caused by marginal discharge） and homogeneous plasma were investigated for the microwave plasma chemical vapor deposition process. Our simulations show that decreasing the dimensions of the substrate holder in a radical direction and increasing its dimension in the direction of the axis helps to produce marginally inhomogeneous plasma. When the marginal discharge appears, the maximum plasma density and power density appear at the edge of the substrate. The gas temperature increases until a marginally inhomogeneous plasma develops. The marginally inhomogeneous plasma can be avoided using a movable substrate holder that can tune the plasma density, power density and gas temperature. It can also ensure that the power density and electron density are as high as possible with uniform distribution of plasma. Moreover, both inhomogeneous and homogeneous diamond films were prepared using a new substrate holder with a diameter of 30 mm. The observation of inhomogeneous diamond films indicates that the marginal discharge can limit the deposition rate in the central part of the diamond film. The successfully produced homogeneous diamond films show that by using a substrate holder it is possible to deposit diamond film at 7.2 μm h^（–1）at 2.5 kW microwave power.

Study of Microwave Absorbing Performances of Nanometer Fe-Al Solid solution

In this paper,Fe-Al solid solution was prepared by mechanical alloying technology,and Fe-Al powder was dispersed into unsaturated polyester (UP) with different contents as absorber to form mixture Fe-Al-UP.The results indicate that the alloying process is almost accomplished and most of the particles are nanometer.Meanwhile,the microwave absorbability of Fe-Al-UP samples in frequency from 0.3 MHz to 1.5 GHz was studied.The results indicate that the more the absorber,the better the absorbing property.The absorbing property of Fe-50Al-UP was slightly higher than Fe-28Al-UP.

Mechanism of Microwave Effects on Conductivity of Solution

The relation between microwave conductivity and normal conductivity of solution is compared in this thesis. By building mathematical model and theoretical analyses, it indicates that the relationship of in situ conductivity of solution in microwave field and temperature is similar to that in non-microwave field. It can be expressed by quadratic equation but the values of both conductivities are different. Microwave field has effect on the mean path δ or hot vibrational frequency ν of ions in solution. In microwave field, the mean energy barrier, which ions must surmount as they transit, is the function relation to temperature.

Interactions of Microwave with Plasmas

When plasma size scale is comparable with the wavelength of electromagnetic waves, W.K.B. solution isn't applicable. In this paper a new numerical solution technique to investigate interactions of microwave with plasmas is presented by using Runge-Kutta method. The results of numerical solution coincide with that of analytical solution while the model is linear electron density profile in calculated accuracy.

On Linear Algebra for Non Mathematics Majors

To find out what knowledge in linear algebra is essential to non-mathematics students, a reverse tracking method was used. Based on practical problems likely to encountered by students in subsequent engineering courses, the minimum contents required has been determined. Rules are proposed to meet the background of most freshman students. An application oriented, easy to understand, computer based text book “Applied Popular Linear Algebra with MATLAB” [1] was published.

微波辐照对小米印度谷螟卵灭除效果及品质影响的研究

[目的]印度谷螟(Plodia interpunctella)在小米中繁殖能力很强,对小米的破坏性很大,主要使用的化学药剂熏蒸防治方法易引起环境污染、药剂残留、印度谷螟的抗药性增强等一系列的问题。微波技术可用于防治粮食虫害且绿色环保。本研究旨在获得微波辐照对小米印度谷螟卵灭除效果及品质影响的研究。[方法]采用微波160、320、480、640和800 W的功率和5、10、15、20、25和30 s的时间辐照小米,通过测量小米0、3、5、8、10 cm深度的印度谷螟卵的存活率和小米温度,观测微波辐照在小米不同深度的灭卵效果和微波在小米中的传播规律。同时测量微波辐照后小米的黏滞特性、色度和含水率,观测微波辐照对小米品质的影响。[结果]相同功率和时间的微波辐照小米,深度越小处印度谷螟卵存活率越低,灭卵效果越好。160W30s和320W15s低强度微波直接辐照印度谷螟卵,卵的外部形态基本保持不变,无法灭卵;采用800W15s、640W20s、480W25s微波辐照能有效消灭小米0 cm(平铺)处卵;800W20s、640W25s、480W30s辐照能有效消灭小米3 cm深度处卵;800W30s高强度微波辐照后,小米5 cm深度卵的存活率为25%,8、10 cm深处卵的存活率仍相对较高,灭卵效果不佳。相同功率和时间的微波辐照小米,深度越大处小米内部温度越小,且小米内部温度随深度以指数规律衰减。640W30s微波辐照后小米峰值粘度和衰减值升高,480W25s、800W25s和800W30s微波辐照后小米的糊化温度升高;除800W30s高强度处理外,微波辐照对小米色度无明显影响;微波辐照后小米含水率降低,为小米储藏创造了更好的条件。640W30s微波辐照提升了小米的食用品质,而800W25s和800W30s高强度辐照降低小米品质。[结论]小米深度是影响微波辐照灭卵效果的重要因素,微波辐照灭卵小米深度不宜超过3 cm。采用640W30s微波辐照厚度3 cm内的小米,既能有效灭卵又能提升小米的品质。本研究为微波技术防治小米储藏虫害,减少经济损失提供科学依据。

饲料微波消解液组成与配比对消解效果的影响研究

针对饲料中铅含量检测,采用微波消解法对饲料进行前处理,重点研究了消解液不同组成与配比对消解结果的影响,以探寻对各种饲料普遍通用的消解液,推动将微波消解法列为国标饲料中铅含量检测的前处理方法之一。实验结果表明,对于所研究的10种饲料和饲料添加剂,消解液组成分别为8 mL硝酸溶液+2 mL氢氟酸和8 mL硝酸溶液+2 mL氢氟酸+12 mL硼酸溶液对其中8种饲料和饲料添加剂均呈现非常理想或比较理想的消解效果,可将沉淀(或絮状物)去除或只有极少量沉淀物(或絮状物)残留。经综合考虑最终选定消解液含8 mL硝酸溶液+2 mL氢氟酸为普适性最广的消解液,可保证消解完全、彻底。

最小二乘解与高斯消元法的注记

若在对超定线性方程组求最小二乘解的过程中使用高斯消元法(即对增广的系数矩阵作初等行变换),有时会得到正确的最小二乘解,但大多数情况下是错误的.探讨了高斯消元法和最小二乘解的一些关系.建议授课时提醒学生注意最小二乘法和求解一般的线性方程组的区别.

基于LBS+微波暗室的GNSS接收机检定方法的研究

随着市场对全球导航卫星系统(GNSS)接收机检定需求的增加及室外检定环境的影响,提高GNSS接收机的检定效率和降低工作成本成为现阶段面临的一个难题。为此,本文提出应用信号接收器+微波暗室组合的方式对GNSS接收机进行室内静态模拟检定。该组合方式通过基于位置服务(LBS)+微波暗室法对GNSS接收机的静态基线误差等进行试验,可确保GNSS接收机检定符合相关规程要求,且所获检测结果与传统室外检定法的测量结果基本一致,有效提高了检定效率,为GNSS接收机检定提供了新思路。

Microwave synthesis of duplexα/β-SiAlON ceramic cutting inserts:Modifying m,n,z values,synthesis temperature,and excess Y_(2)O_(3) synthesis additive

Duplexα/β-SiAlON ceramic cutting inserts(30α:70β)were synthesized by microwave sintering.The effects of solid solution parameters(m,n,z),synthesis temperature,and amount of excess Y_(2)O_(3) synthesis additive on phase assemblage,microstructure,mechanical properties,and cutting performance were systematically investigated.It was found that increasing m value could improve the formation ofαphase while high z value over 1.0 resulted in the dissolution ofαphase intoβphase and intergranular phase.Increasing the amount of excess Y_(2)O_(3) could promote densification and elongatedβgrain growth;however,the excess Y_(2)O_(3) amount above 4 wt%resulted in substantial crystallization of M'SS phase,thus declining the mechanical properties and wear resistance.The microwave-synthesizedα/β-SiAlON cutting insert with modified parameters(m=1.7,n=1.0,z=0.7,and 3 wt%excess Y_(2)O_(3))was obtained with optimal comprehensive properties,whose tool life was found to increase by approximately 75%in high-speed milling of Inconel 718 superalloy compared to the commercialα/β-SiAlON cutting insert.

Growth mechanism of octahedron-like BaMoO_4 microcrystals processed in microwave-hydrothermal:Experimental observations and computational modeling

Octahedron-like BaMoO4 microcrystals were synthesized by the co-precipitation method at room temperature and processed in microwave-hydrothermal at 413 K for different times （from 30 min to 5 h）. These microcrystals were analyzed by X-ray diffraction （XRD）, field-emission gun scanning electron microscopy （FEG-SEM） and transmission electron microscopy （TEM）. XRD patterns showed that this material presents a tetragonal structure without the presence of deleterious phases. FEG-SEM and TEM micrographs revealed that the BaMoO4 microcrystals present an octahedron-like morphology with agglomerate nature and polydisperse particle size distribution. These micrographs also indicated that the microcrystals grow along the [0 01 ] direction. The observed crystallographic planes in these structures were modeled computationally and a crystal growth model was proposed in order to explain the morphological changes as a function of processing time.

求解传输线方程定解的一般边界条件

求解传输线上电压/电流分布是分析其工作状态的基础,“微波技术与天线”教材给出了三种边界条件(源端条件、终端条件、电源和阻抗条件)来求解传输线方程通解中的待定系数,从而确定传输线上电压/电流分布。给出传输线方程定解的一般边界条件,即假定已知传输线上任意某点的电压/电流,确定传输线上的电压/电流分布,并将教材中的三种边界条件归纳为一般边界条件的特例。

微波消解火焰原子吸收光谱法测定土壤中六价铬

目前用于土壤中六价铬检测的提取方法较为单一,一般是使用HJ 1082—2019《土壤和沉积物六价铬的测定碱溶液提取-火焰原子吸收分光光度法》中提到的碱溶液提取法.但该方法在进行大批量土壤检测时存在耗时长、试剂用量大、温度不易控制等问题.因此,建立高效、准确的土壤中六价铬测试方法,对开展土壤中六价铬污染风险评价及修复工作具有十分重要的意义.本研究提出了微波消解火焰原子吸收光谱法,用于快速、准确测试土壤中六价铬.通过开展提取剂组成与用量、微波消解方式、消解液过滤及pH调整等参数优化研究,确定了土壤中六价铬提取与测试的优化条件:消解液组成为碱性提取液20 mL、氯化镁100 mg、磷酸氢二钾-磷酸二氢钾缓冲溶液0.2 mL,3次微波消解,消解液用中速定量滤纸过滤,待测液pH调节至7.0~8.0.在优化条件下,土壤六价铬的有证标准样品的测量结果均在标准值范围内,土壤基体加标回收率为85.5%~88.7%,相对标准偏差为7.6%~8.0%.与HJ 1082—2019相比,本文建立的微波消解火焰原子吸收光谱法更适用于大批量土壤样品的六价铬检测分析,所采用的微波消解技术,操作相对简单、提取效率较高,易于在不同种类实验室中普及和推广,可为土壤中六价铬的快速准确检测提供技术支持和方法补充.

A surfactant-free route to synthesize Ba_xSr_(1-x)TiO_3 nanoparticles at room temperature, their dielectric and microwave absorption properties

Perovskite materials, such as Ba_xSr_(1-x)Ti_O3(BST), have been continuously receiving attentions due to their unique ferroelectric, pyroelectric, dielectric, piezoelectric and electric-optic properties. Here, we report a facile route for the synthesis of BST nanocrystalline materials by fast mixing of MCl_2(M = Ba, Sr) aqueous solution and titanium isopropoxide ethanol solution at room temperature without using any surfactants or structure-directing templates.The molar ratio of Ba/Sr was controlled by adjusting the original molar ratio of BaCl_2·2H_2O and SrCl_2·6H_2O. The dielectric properties and microwave absorption capability of the BST nanocrystalline were studied. The results indicate that the BST nanocrystalline material has the best dielectric and microwave absorption properties in the case of Ba_(0.7)Sr_(0.3)TiO_3. The present strategy is facile, low cost and high yield, which may provide a new route for the synthesis of other perovskite materials.