二氧化硅陶瓷在微波场中的透波性能研究

为了研究厚度、温度以及频率对二氧化硅陶瓷耐火层透波性能的影响,以期设计出在整个微波加热过程中都具有良好透波性能的耐火层。根据传输线理论计算了0~0.1m厚度范围内的二氧化硅陶瓷在不同温度、频率下的功率透过系数;给出了二氧化硅陶瓷在不同温度下透波率大于90%的厚度区间。计算结果表明:随着耐火层厚度的增加,会依次出现多个透波峰,并且透波峰幅值逐渐减小;2.45GHz频率下,厚度为0.0375m、0.075m时,二氧化硅陶瓷展现出良好的透波性。     

微波加热用透波材料的研究进展

微波加热技术因其绿色环保、体积加热、选择性加热等优势,已被广泛应用于化工强化、金属冶炼、陶瓷烧结、食品加工等众多领域,但微波在反应器内普遍存在透波效果差、微波利用率低等问题。随着微波加热技术的不断发展,微波加热设备中透波材料的选用越来越受到大家的关注。本文主要针对透波材料在微波加热领域中的应用现状进行综述,对透波材料的种类进行简要介绍,分别从微波加热用容器和保温材料两方面进行论述。详细介绍了氧化物、氮化物、硅酸盐、磷酸盐等高温透波材料及聚四氟乙烯、玻纤增强树脂基、环氧树脂等中、低温透波材料的研究进展,并具体论述了目前微波加热常用纤维棉、纤维毯和纤维板等各种陶瓷纤维制品的介电特性和透波性能,最后指出了目前微波加热用透波材料普遍存在的问题,并对透波材料的应用和发展作出了展望。     

硅酸铝/氧化锆纤维板在微波加热中透波性研究

为了研究微波加热过程中温度、厚度对硅酸铝/氧化锆纤维板保温层透波性能的影响,以期设计出在整个微波加热过程中都具有良好透波性能的保温层,利用通过单层平板内电磁波传播的理论机制和计算模拟技术,分析了保温层厚度和温度变化对硅酸铝/氧化锆纤维板透波性能影响的规律。同时从透波性能的角度,提出了硅酸铝/氧化锆纤维板保温层在微波加热中厚度选择的基本原则。研究结果表明:20℃时,硅酸铝纤维板的功率透过系数随厚度增加呈波动状态变化,存在透波峰;随着温度的升高,这种波动状逐渐消失,近似呈线性递减,1 300℃时,0.1 m厚度的硅酸铝纤维透波率仅为0.62。氧化锆纤维板在20,200,500℃时,功率透过系数随着厚度的增加呈明显的波动变化,厚度为0.04,0.08 m时,功率透过系数曲线出现透波峰。该研究成果有助于微波高温加热设备的设计,微波加热工艺参数的优化以及微波能利用率的提高。     

透波复合材料研究进展

介绍透波材料的选用原则及其介电特性,探讨了树脂基、无机非金属基通用透波复合材料和人工介质材料、耐高温有机材料等特种透波复合材料的研究进展,简介湿度、树脂含量、孔隙率、吸水性、后处理温度及时间、纤维表面处理等因素对复合材料常温透波性能的影响及结构／微结构、成分／微成分、物态相变等材料的本征因素对复合材料高温透波性能的影响。     

二氧化硅体系透波材料的透波机理及研究现状

本文阐述了天线罩材料对二氧化硅体系透波材料的性能要求,分析了二氧化硅体系透波材料的透波机理,论述了二氧化硅体系透波材料的研究现状,并指出了其发展方向.     

多孔陶瓷透波材料研究现状及进展

综述了多孔陶瓷透波材料的选择、制备工艺、应用及研究现状。指出CVD/CVI工艺是目前制约我们国家在该领域发展的核心技术,CVD/CVI法在多孔陶瓷透波材料上开展致密化研究是研制高性能透波材料的关键。     

透波材料的优化设计

本文通过常规树脂基体、玻纤织物增强材料和蜂窝芯材等主要原材料之间的优化复合设计,开展单板、三夹层结构和五夹层结构各形式复合材料之间的制作、电性测试与分析,优化设计出了一种新型兼顾电性、力学性能的功能型五夹层复合结构透波材料,满足了高性能舰载雷达宽频带、高透波等电性指标要求,同时还满足了其高比强、刚度的力学指标要求,解决了传统型设计和材料通常无法满足其电性能、强刚度、低成本制作的矛盾。     

微波化学反应用聚四氟乙烯容器的透波性能

因聚四氟乙烯（PTFE）具有较低的复介电常数,其作为透波材料而被广泛用作微波化学反应用容器。透波材料的介电特性和透波性能对微波化学反应的速率和效果具有重要影响。本研究首先利用谐振腔微扰法测量了PTFE在23~250℃范围内的复介电常数,并分析了该材料介电属性的温度特性;其次,基于电磁波传输原理,计算了该材料受到不同因素影响下的功率透过系数（T²）,并对该材料的透波性能进行了分析。研究表明,随着温度的增加,PTFE的介电常数逐渐减小,损耗正切逐渐增大,但是二者变化幅度较小;在水平（TM）极化中存在一个布儒斯特角θ_B,当微波以该角度入射时会发生全透射现象;TM极化下的T²随着入射角的增大先增大后减小,垂直（TE）极化下的T²随着入射角的增加而减小,TM极化下的整体透波性能要优于TE极化;随着容器壁厚的增加,透波性能波动变化,存在极大值和极小值;在相同容器壁厚范围内（0~0.1m）,2450MHz频率下对应高透波性能的厚度值要多于915MHz。研究还表明,微波入射角度较小时,PTFE的T²始终保持在0.87~0.99之间,透波性能较好。最后给出了微波以不同频率入射时PTFE的优选壁厚以供实际应用过程中进行参考。     

可随机成型的透波性胶凝材料的微波加热特性

研究了硬化铝酸钙材料在不同煅烧温度（700,800,900,1000,1100,1200,1300,1400和1500℃）下的吸波能力、抗压强度、体积收缩率和质量损失率,采用XRF和XRD对不同煅烧温度（800,1000,1300和1500℃）下的试样进行表征,利用铝酸钙材料制备一种简易杯状容器并对其进行微波冲击特性测试。结果表明：硬化铝酸钙材料的吸波能力随煅烧温度的升高而降低,超过1000℃后,吸波能力趋于稳定;材料抗压强度随煅烧温度的升高先升高,在800℃左右达到最高,然后逐渐降低,并在1300℃达到最低,再经过小幅地升高后趋于稳定;同时,材料煅烧后体积收缩率和质量损失率都随着温度的升高而增加;微波冲击特性测试表明硬化铝酸钙材料在长时间微波辐照下强度基本不发生变化,微波-金属放电试验证明该胶凝材料硬化后的高温稳定性好,具有优异的抗高温冲击能力。综上所述,1000℃煅烧后的硬化铝酸钙材料具有透波性能好、力学性能优异、高温稳定性好的特点,非常适用于微波加热领域。     

透波复合材料树脂基体的研究进展

全面综述透波复合材料树脂基体的发展概况,介绍不饱和聚酯树脂、环氧树脂、改性酚醛树脂、氰酸酯树脂、有机硅树脂、双马来酰亚胺树脂、聚酰亚胺、聚四氟乙烯等树脂在透波复合材料中的应用,并指出了今后的发展方向,     

纳滤技术在矿冶领域的应用研究进展

纳滤具有传统处理方法不具备的低能耗、高截留率、较好选择性等优点,可望在国民经济各个领域得到广泛应用。介绍了纳滤技术在矿井水、矿山浸出液、矿山废水以及铅锌、钼、钨等冶炼废水处理中的情况。肯定了纳滤技术的应用效果,指出了现行纳滤技术在实际应用中可能存在的问题、不足与解决方法,同时展望了纳滤技术发展趋势。     

Microstructure,high-temperature mechanical and dielectric properties of novel Si3N4 f/SiNO wave-transparent composites

Continuous Si₃N₄ fiber reinforced SiNO matrix composites (Si₃N_4 f/SiNO composites) were innovatively prepared for long-time high-temperature resistant wave-transparent materials of hypersonic aircraft. The microstructure, high-temperature mechanical and dielectric properties of Si₃N_4 f/SiNO composites were investigated in detail. The as-fabricated Si₃N_4 f/SiNO composites have homogeneous SiNO matrix distribution for the special winding process, which is beneficial for the mechanical strength and wave-transparent properties. The average tensile strength and flexural strength at room temperature is 87.8 MPa and 171.2 MPa respectively, which suggests Si₃N_4 f/SiNO composites have excellent mechanical strength. The tensile strength value decreases to 54.6 MPa after heat-treated at 1000 ℃ for the surface reactions between the SiNO matrix and Si₃N₄ fibers. After heat-treated at 1550 ℃, the composites have the tensile strength value of 24.2 MPa for the high strength retention rate of Si₃N₄ fibers at this temperature. Si₃N_4 f/SiNO composites have excellent room temperature dielectric properties and excellent dielectric stability in different frequency bands (7–18 GHz). The dielectric constant values vary from 3.69 to 3.75 while the dielectric loss attains the order of 10^?3. The dielectric constants and dielectric loss of Si₃N_4 f/SiNO composites are relatively stable from RT to 800 ℃. The as-fabricated Si₃N_4 f/SiNO composites that have excellent high temperature resistance and dielectric properties are the ideal high temperature wave-transparent composites.     

微波合成纳米氧化锌及其应用研究进展

介绍了近年来微波技术在制备特殊形态和性能的纳米氧化锌中的方法应用及纳米氧化锌的晶体生长机理,阐述了利用微波技术制备的纳米氧化锌在应用于催化合成有机物和光催化降解有机污染物过程中所表现出的优异性能,并对微波技术在制备纳米氧化锌领域的应用前景进行了展望。     

Microstructure and properties of BN/Si3N4 composites with addition of microwave synthesized Y2O3-MgO nanopowders

Y₂O₃-MgO nanocomposite powder was synthesized by a microwave technique and doped into gas-pressure sintered BN/Si₃N₄ composites to acquire a highly wave-transparent material that could be utilized in spacecrafts. The XRD and SEM analyses indicated that the main phases were rod-like β-Si₃N₄ particles and MgSiO₃. In this case, a BN/Si₃N₄ ceramic with 8?wt% Y₂O₃-MgO nanopowder displayed a density of 2.5?g/cm³. The permittivity and transmission efficiency were approximately 4.6% and 71.4%, respectively, at frequencies of 8.2–12.4?GHz, which achieved the best overall wave-transparent performance. The porosity of the material in combination with the inclusion of the boron nitride component creates a synergistic effect that appears to contribute to wave-transparent efficiency.     

Targeted design and analysis of microwave absorbing properties in iron-doped SiCN/Si3N4 composite ceramics

The SiCN(Fe)/Si₃N₄ composite ceramics containing C, β-SiC and α-Fe were designed by impregnating polysilazane followed by pyrolysis at 1–5 times with porous silicon nitride matrix. After the heat treatment, these new phases gradually formed and filled in the pores of the matrix to form a large whole. They bond together to facilitate the formation of conductive networks, which can improve the storage and transport capacity of the charge, thus improving the dielectric properties of the material. In this way, the highest dielectric and magnetic loss tangent values were achieved as 0.49 and 0.29 after third and fourth cycles, respectively. The electromagnetic wave can be absorbed ~80–90% in the range of 8–18 GHz with the thickness of 2 mm. The minimum reflectivity was ?12.5 dB at 16 GHz with the thickness of 5 mm, showing >90% electromagnetic wave absorption at this frequency.     

Effect of microwave sintering on the microstructure and mechanical properties of AA7075/B4C/ZrC hybrid nano composite fabricated by powder metallurgy techniques

AA7075 + 6%B4C+3%ZrC nano hybrid composite was successfully fabricated, with nano reinforcements composition in AA7075 alloy selected based on previous investigation, to achieve better mechanical performance. Two different sintering techniques, namely conventional and microwave, were implemented to determine the effect on microstructural and mechanical properties. Microstructural investigation was performed with the help of W-SEM. Tensile, compression, and hardness were measured with the help of UTM and Vickers microhardness machine. Porosity was calculated by using Archimedes principle. It was observed that the added nano ZrC particles formed agglomerates and the B₄C particles were distributed homogenously. Composites processed by microwave sintering showed excellent mechanical properties compared to the conventionally sintered composites. No intermetallic compounds were detected in microwave sintered composites through XRD analysis, indicating strong and clean interface bonds between matrix and reinforcement particles. High strain to fracture value of 12.24% was noted in microwave sintered nano hybrid composite, while it was 6.12% for conventional sintered one. Fractography revealed no peeling action of reinforcements from the matrix material, and the mode of failure was brittle. It was concluded that, while fabricating nano range hybrid composites, the implementation of advanced sintering technique (microwave sintering) with low sintering temperatures and low sintering times with internal heat generations, helps in eliminating defects that may develop because of high surface energies of nano range reinforcements.     

Effects of Ni2+, Zr4+, or Ti4+ doping on the electromagnetic and microwave absorption properties of CaMnO3 particles

Although CaMnO₃ has been widely studied and used for its thermoelectric properties and giant magnetoresistance effect, little information exists about its application for microwave absorption. In this study, we synthesized CaMnO₃, CaNi_0.05Mn_0.95O₃ CaTi_0.05Mn_0.95O₃ and CaZr_0.05Mn_0.95O₃ with an orthorhombic system using a simple high-temperature solid-phase method. The minimum reflection loss value and effective absorption bandwidth could be efficiently improved due to the enhanced match complex permittivity produced after the Ni, Ti or Zr ions were substituted for Mn ions in CaMnO₃. The minimum reflection loss value increases to ?39.7 dB from ?14.1 dB and the effective absorption bandwidth increases to 4.9 GHz from 2.7 GHz. The magnetic loss results only in a negligible influence on the microwave absorption. The enhancement of microwave absorption properties was primarily due to the stronger polarization effect. When Ni²⁺, Ti⁴⁺, or Zr⁴⁺ is introduced in the CaMnO₃ lattice, the charge balance is broken, and the crystal lattice distortion increases because of the substitutive ions, interstitial ions, oxygen vacancy and exchange effect of Mn³⁺~Mn⁴⁺. The results indicate that CaMnO₃ with reasonable doping at the Mn-site could achieve excellent microwave properties of wide bandwidth, high-efficiency absorption, and adjustable response frequency.     

废活性炭微波加热法再生研究进展

论述了微波加热技术的特点,初步探讨了微波加热再生废活性炭的原理,综述了国内外微波再生废活性炭的研究进展。与传统加热技术相比较,微波加热再生废活性炭具有耗时短、产品质量好、能耗低、污染少等优点,并且微波加热再生废活性炭产品有更发达的孔隙结构,吸附性能较好。影响微波再生废活性炭的因素依次是微波功率、加热时间、活性炭吸附量。展望了微波加热再生废活性炭的发展方向。     

羟肟酸类化合物的合成与应用研究进展

羟肟酸类化合物具有配位活性良好的羟肟基,可以与多种金属离子形成稳定的螯合环,是一类高活性螯合剂,具有广泛的应用价值。本文介绍了羟肟酸类化合物的结构特征与化学性质;综述了羟肟酸及羟肟酸高分子的合成方法,介绍了羟胺法合成技术的国内外研究进展;同时详述了羟肟酸类化合物在医药、金属矿物浮选、冶金领域中的应用新进展,认为应深入研究羟肟酸类化合物与矿物的作用机理,以拓宽其在矿物浮选中的应用范围。最后指出羟肟酸类化合物存在新型产品少、生产成本高和具有低毒性等问题,在未来的研究中应向设计合成新型、高效、绿色的羟肟酸类化合物方向发展。