空心微珠铁氧体复合粉体的改性与吸波性能

研究了柠檬酸盐溶胶-凝胶方法制备空心微珠-钡、锶、钴镍钡铁氧体复合粉体的微观形貌, 采用化学添加剂改善铁氧体的包覆性能. SEM、EDS分析表明铁氧体在空心微珠表面的包覆状态与铁氧体种类无关; 在前驱体中加入乙二醇或聚乙二醇可以使铁氧体对空心微珠的包覆更加完整、牢固致密. 用网络分析仪测试了C波段5.0～6.5GHz、X波段8.2～12.4GHz、Ku波段12.5～18.0GHz内1.8mm厚铁氧体空心微珠复合粉体制备的吸波涂层的微波损耗. 试验表明：铁氧体空心微珠复合粉体具有良好的电磁吸波性能, 吸波涂层在5～18GHz内微波反射损失总体上大于单纯铁氧体涂层; 加入乙二醇或聚乙二醇有助于提高涂层的吸波效果.     

基于超材料设计的钡铁氧体吸波涂层研究

本工作设计了一种基于超材料结构的钡铁氧体吸波涂层,分析了超材料的结构设计对钡铁氧体涂层吸波性能的影响,并对涂层的吸波机理进行了研究和讨论。通过仿真发现,钡铁氧体涂层经超材料设计改进后,吸波性能得到大幅增强,改进后的钡铁氧体涂层存在最佳的匹配厚度2.5mm和电阻膜方块电阻值70Ω/,此时涂层的吸收带宽最大,并存在两个吸收峰,在8～18GHz频段内反射损耗都小于-10dB。钡铁氧体通过超材料设计改进后,吸波性能得到极大改善。     

溶胶-凝胶法制备空心微珠表面钡铁氧体包覆层的研究

铁氧体是微波吸收材料的主要成分之一,应用非常广泛,但由于铁氧体比重较大,制成吸波材料难以满足吸收频带宽、质量轻、厚度薄的要求,因此实际使用的铁氧体吸波涂层往往不是单一的铁氧体涂层,而是通过复合制备成复合铁氧体吸波涂层.以质量轻、化学性能稳定的热电厂粉煤灰空心微珠为基体,以硝酸铁、硝酸钡和柠檬酸为原料,用溶胶-凝胶法在空心微珠表面包覆钡铁氧体涂层,并用差热分析仪(DTA)、X射线衍射仪(XRD)、能谱仪(EDX)和扫描电镜(SEM)对其进行了分析表征,结果表明用溶胶-凝胶法在空心微珠表面能均匀地包覆一层薄的M-型钡铁氧体涂层.     

吸附钡铁氧体的多孔陶粒吸波材料制备及其性能

以硝酸铁、硝酸钡、柠檬酸为原料,采用溶胶-凝胶法合成钡铁氧体溶胶,将其吸附于多孔陶粒表面和微孔中,经焙烧制备得到电磁吸波功能陶粒;再将该功能陶粒用作集料制备新型水泥基复合吸波材料。研究了合成的钡铁氧体的物相、形貌、复介电常数和复磁导率;结果表明合成的钡铁氧体纯度高,合成温度对其结晶度和晶体形貌有影响,经1000℃煅烧制得的钡铁氧体具有良好的吸波能力;对制得的功能陶粒进行了测试,结果表明钡铁氧体能包覆至陶粒表面和孔壁上;采用弓形法测得的功能陶粒水泥基吸波材料在8~18GHz频率范围内的电磁波反射率明显优于采用碎石和普通陶粒制备的试样。     

空心微珠表面改性及其吸波特性

采用化学镀的方法对空心微珠表面金属化改性进行研究，并利用扫描电镜及能谱分析仪对表面镀镍后的形貌进行观察、测定，结果表明镍较均匀附着在微珠的表面。分别将改性前后的微珠制备成吸波材料，测试其吸波性能。测试结果表明，改性后的空心微珠具有较好的吸波性能，在8-18GHz扫频测试范围内，小于-10dB的频段范围在16.6-18GHz，最大吸收可达-13.57dB，对应的频率为17.2GHz。空工心微珠表面改性为其再利用找到有效的途径。     

自反应淬熄法制备Zn-Ti钡铁氧体空心陶瓷微珠及其超声化学镀Ni-Co合金后的吸波性能

通过自反应淬熄法制备Zn-Ti钡铁氧体空心陶瓷微珠吸波材料,再超声波化学镀Ni-Co合金,制成了具有核/壳/腔结构的吸波材料,以进一步提高陶瓷微珠的吸波性能;采用SEM、EDS和XRD法分析了其形貌及结构,并应用Aglient网络矢量仪和85055APC-7mm同轴空气线测试了其吸波性能。结果显示,空心陶瓷微珠具有中空的球形结构,主要物相Ba Zn Ti Fe10O19为一种M型钡铁氧体,表面化学镀Ni-Co合金层后吸波性能得到了提高,在2~18 GHz范围内,厚度为2.71 mm,吸波最低反射率达到了-21.38 d B,反射率小于-10 d B的带宽为3.51 GHz,带宽增宽。     

空心微珠表面改性及其吸波特性

通过CVD方法在空心微珠表面进行金属化改性,用扫描电镜对空心微珠表面镀铁的微观形貌和成分进行了观察、测定,结果表明铁较均匀附着在微珠的表面.分别将改性前后的空心微珠制备成吸波材料,测试其吸波性能.测试结果表明,改性后的空心微珠具有较好的吸波性能.在8～18GHz扫频测试范围内,小于-10dB的频段范围在17.2～18GHz,最大吸收可达-11.27dB,对应的频率为18GHz.空心微珠的表面改性为其再利用找到有效的途径.     

掺杂稀土元素镧的钡铁氧体超微粉末的微波吸收特性研究

采用溶胶-凝胶法制备了掺杂稀土元素镧的钡铁氧体超微粉末,就镧元素的掺杂含量对钡铁氧体吸波性能的影响进行了对比研究.实验表明,用聚乙二醇凝胶法制备的BaLaxFe12-xO19超微粉末,当x为0.03时,对微波吸收效果最佳.在涂层厚度1.0mm,测试频段为7.5～11.9GHz内,吸收量均在25dB以上,在11.6GHz处,吸收峰值达41.4dB.     

钡铁氧体、炭黑填充聚氨酯软质泡沫基吸波材料性能的研究

通过陶瓷法制备了M型钡铁氧体，并对其进行了X射线衍射（XRD）分析和扫描电镜（SEM）的表征，结果表明在1300℃下煅烧3h空冷后经研磨得到均匀的铁氧体粉末，经XRD分析为较纯单相钡铁氧体，从SEM可以看出钡铁氧体的形貌主要呈六角形分布。用聚氨酯软质泡沫为基材，分别充填铁氧体、碳粉以及他们的混合体，制备了平板，通过弓形反射法测量聚氨酯软质泡沫复合材料的微波吸收性能，测试频段为4～8GHz。实验表明，充填5g铁氧体和15g炭黑的平板具有良好的吸波效果，反射系数约为-7dB。     

天然尖晶石型铁氧体(铁砂)基复合吸波涂料特性研究

天然尖晶石型铁氧体（铁砂）与聚氨脂粘结剂制成的吸波涂料在7～12GHz频段有两个吸收峰，涂层厚度1．25mm时，吸收量5．2～8．5dB，在基础吸波材料(铁砂)中添加尖晶石型铁氧体、顺磁性稀土材料和六角铁氧体制成复合吸波涂料，使其吸收量达18～25aB，匹配厚度1．1～1．2mm，两吸收峰间距＞4．4GHz，它加工简单，价格低廉。     

A离子缺陷型钙钛矿La0.66TiO2.993的水热合成和表征

本文利用水热晶化法首次合成出正交钙钛矿结构的Ｌａ０．６６ＴｉＯ２２．９９３产物约３００ｎｍ粒径的多晶粉末，且有一定团聚现象，水热条件对合成的影响研究表明，最佳合成条件为：ＫＯＨ／Ｔｉ＝８０，Ｌａ／Ｔｉ＝０．７，（Ｔｉ）＝０．１ｍｏｌ．Ｌ＾－１，２６０℃下晶化７天。     

EDTA络合溶胶-凝胶法制备Y2O3:Eu纳米晶

以金属硝酸盐和EDTA为原料，用EDTA络合溶胶-凝胶法制备出Y2O3:Eu纳米晶，并对合成条件进行了优化。分别用TG-DTA、FTIR、XRD、SEM、荧光分光光度计等手段对凝胶的热分解机理、Y2O3:Eu的形成过程以及纳米晶的性质进行了研究。结果表明：硝酸根离子可以加速EDTA凝胶的热分解，仅600℃焙烧即可得到颗粒细小、组分均匀、纯立方相的Y2O3:Eu纳米晶，颗粒基本呈球形，粒径随温度升高逐渐长大，600℃时，约为20nm,1000℃时，约为70nm。     

Intrinsic defects and metastability effects in Cu2O

Cu₂O based junctions (both Schottky and ZnO/Cu₂O heterojunctions) exhibit a metastable capacitance increase after illumination or reverse bias application. We show that this effect is related to the persistent photoconductivity in Cu₂O substrates. To obtain a quantitative evaluation of defect properties we have measured conductivity vs T, Capacitance-Voltage, persistent photoconductivity decay and capacitance transient at different temperatures.We show that it is impossible to explain these data using an electronic mechanism only. A new model which includes the formation-dissociation of intrinsic defect complexes (V_Cu-V_O) can give instead a better agreement with the experimental data.     

A citrate complex process to prepare nanocrystalline PbBi2Nb2O9 at a low temperature

PbBi₂Nb₂O₉ nanocrystals with a perovskite-type structure were successfully synthesized at a relative low temperature via a citrate complex method. Metal ions were dispersed by citric acid in ethanol and ethylene glycol solvent, and then reacted with NH₄H₂[NbO(C₂O₄)₃·3H₂O] to form the gel. XRD results showed that pure PbBi₂Nb₂O₉ nanocrystals could be obtained after calcined treatment of xerogel at 800 °C. The average particles size was 57 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the sintering process led to the agglomeration of the nanoparticles. The photocatalytic test showed that the sample prepared by the citrate complex method exhibited a higher photocatalytic activity than that of the sample prepared by the solid-state reaction.     

The study on electrical behavior of Gd2O3-WO3 complex ceramics at high temperature

Gd₂O₃-WO₃ complex ceramics are fabricated by the conventional solid-state reaction process. The electrical characteristics and dielectric properties of the samples were measured at various ambient temperatures in a low electric field (E < 150 V/mm). As the temperature increases, the dielectric constant and the loss tangent show an obvious change at about 50 °C and 330 °C. When the temperature is above 200 °C, the samples display stable nonlinear electrical properties characterized by semiconductivity, and the nonlinearity increases along with increasing temperature. XRD analysis reveals that Gd₂W₂O₉ is the main phase and Gd₂O₃ is the secondary phase. Based on the phase transition of tungsten trioxide, these electrical properties of Gd₂O₃-WO₃ complex ceramics can be simply explained.     

复合沉淀法制备(Y,Gd)2O3:Eu纳米粉体及其发光性能

报道了一种采用氨水和碳酸氢铵的混合溶液作为复合沉淀剂来制备(Y，Gd)203：Eu发光粉体的新工艺，采用热分析(TG-DTA)、红外光谱(FT-IR)、X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等手段对粉体制备过程中的物理化学变化进行了研究．通过X射线激发的发射光谱研究了Eu掺杂浓度和煅烧温度对(Y，Gd)2O3：Eu粉体发光性能的影响．结果表明采用复合沉淀法制备工艺，经过850℃烧2h，可以得到晶粒尺寸为50nm左右，且基本无团聚的(Y，Gd)2O3：Eu粉体，比表面积为23m^2／g，其X射线激发的发光强度较草酸盐沉淀法所得到的相同组分的粉体大大增强．     

CuO+ZnO/CeO2/Al2O3水煤气变换活性及其表面形貌网络特征分析

以φ3mm Al₂O₃作为主载体,采用浸渍与焙烧工艺,制备水煤气低温变换催化剂：CuO+ZnO/CeO₂/Al₂O₃.利用X射线衍射（XRD）、扫描电子显微镜（SEM）、Raman散射光谱分别对催化剂的化学组成、表面形貌以及表面元素键合状态进行表征;对催化剂的水煤气变换反应(WGSR)活性进行测试.在对催化剂表面形貌进行数据挖掘的基础上,利用复杂网络方法对催化剂的表面形貌进行网络建模,并对其网络拓扑参数和同步性进行了计算.计算结果表明,CuO+ZnO/CeO₂/Al₂O₃表面形貌网络度分布具有幂律分布特征;在催化WGSR以后,催化剂表面形貌网络同步性有所增强.     

A polymeric complex method to nanocrystalline BiCu2VO6 with visible light photocatalytic activity

Nanocrystalline BiCu₂VO₆ was successfully synthesized by a facile polymeric citrate complex method. The samples were characterized by X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectra (DRS), thermogravimetric analyses (TG) and differential thermal analyses (DTA). BiCu₂VO₆ showed photocatalytic activity for the degradation of RhB under visible light irradiations with the coexistence of H₂O₂. As compared to BiCu₂VO₆ prepared via a solid state reaction, BiCu₂VO₆ prepared via a polymeric citrate complex method showed higher photocatalytic activity. The visible light photocatalytic activity of BiCu₂VO₆ was also proposed.     

Magnetic coupling in La0.67Ca0.33MnO3/La0.67Sr0.33CoO3/La0.67Ca0.33MnO3 sandwiches

La_0.67Ca_0.33MnO₃ (LCMO)/La_0.67Sr_0.33CoO₃ (LSCO)/LCMO trilayer films are fabricated on single-crystal substrates NdGaO₃ (110) and the interlayer coupling are investigated. Compared with LCMO single layer, sandwiches showed the enhanced metal-insulator transition temperature of LCMO layers. The magnetoresistance is dependent on spacer thickness and the peak value dramatically decreases when LSCO layer is thick enough because of shorting by the LSCO layer. The magnetic coercivity H_C shows a nonmonotonic behavior with changing spacer layer thickness and the waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom LCMO layers across the spacer layer.     

Varistor properties of ZnO-Pr6O11-CoO-Cr2O3-Y2O3-In2O3 ceramics

The varistor properties of the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃-In₂O₃ ceramics were investigated for different concentrations of In₂O₃. The increase of In₂O₃ concentration slightly increased the sintered density (5.60-5.63 g/cm³) and slightly decreased the average grain size (3.4-2.9 μm). The breakdown field increased from 6023 to 14822 V/cm with increasing concentration of In₂O₃. The nonlinear coefficient increased from 17.6 to 44.6 for up to 0.005 mol%, whereas the further doping caused it to decrease to 36.8. In₂O₃ acted as an acceptor due to the donor concentration, which decreases in the range of 1.02 × 10¹⁷ to 0.24 × 10¹⁷/cm³ with increasing concentration of In₂O₃.