空心石英玻璃纤维增强氰酸酯基低介电复合材料的制备及性能分析

研究了空心石英纤维增强新型改性氰酸酯树脂基复合材料的力学性能、热物理性能和介电性能,结果表明,空心石英纤维增强氰酸酯复合材料具有较好的力学性能和优异的介电性能。空心石英纤维增强新型改性氰酸酯树脂基复合材料的介电常数低且具有较好的频率稳定性,适合作为宽频高透波材料。     

高硅氧/有机硅透波材料性能研究

对低残炭率甲基硅树脂基透波复合材料进行了介电性能和力学性能研究,结果表明,采用低残炭率甲基硅树脂作为透波材料基体研制的透渡复合材料的介电性能优良,经低于1600℃高温处理后,在电磁波频率为9.30GHz时测试的介电常数小于3.5,透波率高达90%以上.采用甲基硅树脂研制的透波材料克服了传统树脂基透波材料耐热性差、强度低的缺点,是集防热、承载、透波和抗烧蚀等功能一体化的较理想的耐高温多功能透波复合材料.     

天线罩透波材料研究

主要进行了甲基硅树脂基透波材料介电性能研究,结果表明,采用甲基硅树脂做为透波材料基体研制的高性能透波复合材料介电性能优良,材料经800～1200℃高温处理后在电磁波频率为9.30GHz时测试的介电常数小于3.5、材料透波率高达90%以上,能够满足雷达天线罩在800～1200℃工作时对天线罩材料的电性能要求,是比较理想的耐高温高性能透波复合材料.     

石英纤维/KH308复合材料的介电性能

为研究石英纤维/聚酰亚胺（KH308）复合材料介电性能与纤维体积分数、频率、温度和吸水率之间的关系,通过热压成型法,制备了4种不同纤维体积含量的石英纤维/KH308复合材料,采用高Q谐腔法分别测试这4种复合材料在不同状态下的介电常数和介电损耗。结果表明：石英纤维/KH308复合材料的介电常数随着纤维体积分数增加而变大,介电损耗随纤维体积分数变化不大;7~18 GHz频率下,复合材料的介电常数和介电损耗基本不随频率变化;25~300℃下,复合材料的介电常数随温度增加变化比较平缓,而介电损耗随温度的增加而降低;复合材料吸水后,介电常数和介电损耗都会增加;复合材料介电常数ε<4,介电损耗tanδ<0.1,能满足导弹天线罩透波材料介电性能的要求。     

稀土烧结助剂对低介电多孔氮化硅陶瓷的性能影响

以CeO2,Y2O3和Yb2O3为烧结助剂,通过造粒、冷等静压成型和气氛压力烧结成功制备出介电常数ε低于3.0的氮化硅透波材料.伴随稀士氧化物烧结助剂量提高,材料介电性能不断下降,在7％时略有回升.含CeO2试样强度低于30MPa,而有Yb2O3的试样强度最高.通过XRD检测和SEM观察,发现其β相转化程度最高、长径比最大.     

石墨/碳化硅/铁氧体涂层复合材料性能研究

为了开发具备良好介电性能和力学性能的多功能吸波复合材料,以涤纶针织物为基布,以环氧树脂为基体,在基布上进行石墨/碳化硅/铁氧体三层复合涂层整理,制备1.5 mm涂层厚度的柔性纺织涂层复合材料.采用介电谱仪研究了吸波剂的含量对吸波涂层材料介电常数和损耗角正切的影响.鉴于该材料多用于工程领域,采用万能材料实验机测试了该复合材料的拉伸、弯曲、剪切等力学性能.结果表明,该复合材料在低频段具备良好的介电性能,且具备一定的力学性能.     

我国高强度玻璃纤维的研制与应用

玻璃纤维具有耐高温、抗腐蚀、强度高、吸湿性低及伸长率小等一系列优异特性,是国民经济中不可或缺的高新技术材料。自20世纪30年代末期玻璃纤维问世以来,世界各国均致力于开发具有更高性能的特种功能玻璃纤维。科研人员通过改变玻璃的化学组分与性能关系、改变玻璃纤维的截面形状、采用新的纤维成型工艺和表面处理技术等,成功研制了各种性能优异的玻璃纤维,如高强玻璃纤维、低介电常数玻璃纤维、耐高温的高硅氧玻璃纤维、异形截面玻璃纤维、轻质透波空心玻璃纤维、镀金属玻璃纤维、耐辐射和中子混合辐射的耐辐照玻璃纤维等。这些     

尼龙6/粘土聚合物纳米复合材料的性能表征——(I)电性能研究

使用Haake-90型双螺杆挤出机制备一系列粘土含量不同的尼龙6/粘土纳米聚合物复合材料,测试其介电常数、介电损耗、介电稳定性能以及电击穿强度,并讨论了粘土含量对纳米复合体系电性能的影响。研究发现,加入纳米粘土后材料的介电常数、介电损耗明显减小,同时介电稳定性能有了大幅度提高,但电击穿强度无明显变化。     

尼龙6/粘土聚合物纳米复合材料的性能表征--(Ⅰ)电性能研究

使用Haake-90型双螺杆挤出机制备一系列粘土含量不同的尼龙6／粘土纳米聚合物复合材料，测试其介电常数、介电损耗、介电稳定性能以及电击穿强度，并讨论了粘土含量对纳米复合体系电性能的影响。研究发现，加入纳米粘土后材料的介电常数、介电损耗明显减小，同时介电稳定性能有了大幅度提高．但电击穿强度无明显变化。     

连续氮化硅陶瓷纤维的组成结构与性能研究

连续氮化硅陶瓷纤维是透波/承载一体化陶瓷基复合材料的关键原材料,也是制约复合材料耐高温性能与力学性能的关键因素。系统研究了国防科技大学研制的连续氮化硅纤维的组成结构及其力学性能和介电性能,分析了纤维在氮气中高温处理后组成结构与单丝强度变化规律。结果表明,氮化硅纤维主要以Si_3N_4结构存在,组成上接近化学计量比,介电常数为68,介电损耗为0.01~0.08,室温单丝强度约1.5GPa,弹性模量140GPa,在1 350℃以下纤维强度保留率超过90%,在1 400和1 450℃氮气中处理1h仍保持了非晶结构,强度保留率分别为75%和30%,综合性能满足了高温透波复合材料的基本要求。     

低损耗ZrTi2O6填充PTFE复合基板性能

采用热压成型工艺,制备了一种低损耗ZrTi₂O₆陶瓷填充聚四氟乙烯（PTFE）的新型微波复合基板材料。采用介质谐振器法研究了ZrTi₂O₆/PTFE复合材料的微波介电性能（8~12 GHz）。结果表明,ZrTi₂O₆/PTFE复合材料的相对介电常数（ε _r）和介电损耗（tanδ）随着ZrTi₂O₆陶瓷体积分数（0~46%）的增加而增大,介电常数实验值与Lichtenecker模型预测值最吻合。ZrTi₂O₆/PTFE复合材料的热膨胀系数和介电常数温度系数随着ZrTi₂O₆陶瓷体积分数的增加而减小。46%的ZrTi₂O₆为较优填料比例,ZrTi₂O₆/PTFE的相对介电常数为7.42,介电损耗为0.0022（10 GHz）。     

碳化硅/石墨涂层复合材料的介电性探讨

研究了碳化硅和石墨含量对碳化硅/石墨双层复合材料介电常数实部、虚部、损耗角正切的影响。鉴于该材料多用于工程领域,测试了该复合材料的弯曲、剪切、拉伸等力学性能。结果表明:在低频段,该材料介电性能良好,碳化硅含量、石墨含量均对涂层复合材料的实部、虚部和损耗角正切影响较大;当碳化硅含量为24%,石墨含量为60%时,涂层复合材料的介电常数实部、虚部最大,其极化和损耗能力最强。另外,该复合材料具备良好的力学性能,最大弯曲强力为48.3N,最大剪切强力为57.5N,最大拉伸强力为618N。     

Composition, structure, and dielectric properties of SiC-AlN ceramic materials

We have studied the structure, relative dielectric permittivity (?), and dielectric loss tangent (tan??) of SiC-AlN ceramic materials. The results demonstrate that both ? and tan?? are anomalously high in the composition range 30?C50 wt % AlN at low frequencies (0.1 kHz). We show that the increase in ? may be due to a barrier effect on silicon carbide and aluminum nitride grain boundaries and to migration polarization.     

聚吡咯/聚酯纤维复合材料吸波性能的探讨

聚吡咯是含有π电子共扼体系的高聚物,经掺杂反应电导率发生变化,当其电导率处于半导体状态时,具有良好的吸波性能.本文采用原位聚合法以聚酯纤维为基布,以吡咯为单体,制备具有良好吸波性能的柔性聚吡咯/聚酯纤维复合材料.首先探讨了吡咯浓度,温度,时间对复合材料吸波性能和表面电阻的影响;其次研究了其外观形貌和强力.结果表明:制备的聚吡咯复合材料具有良好的吸波性能;在0~106Hz频率内,吡咯浓度0.8 mol/L实验组,介电常数的实部、虚部均最大;1.0 mol/L实验组的损耗角正切最大;吡咯浓度0.8 mol/L实验组表面电阻最小;室温实验组的介电常数实部、虚部、损耗角正切最大,且明显优于其他组.反应时间150 min实验组的各项介电性能都明显优于其他组,且其电阻最小,导电率最好.     

The dielectric properties and dielectric mechanism of perovskite ceramic CLST/PTFE composites

Polytetrafluorethylene (PTFE) composites filled with perovskite (Ca,Li,Sm)TiO₃ (CLST) dielectric ceramic of various volume fractions filler up to 60% were prepared. The effects of volume fraction of ceramic filler on the microstructure and dielectric properties of the composites have been investigated. A comparative study of dielectric properties of experiment and modeling analysis has been carried out at high frequencies for the CLST/PTFE composites. The results indicate that both the dielectric constant and the dielectric loss increase with the filler. The CLST/PTFE composite with 40% ceramic has exhibited good dielectric properties: ε _r?=?7.92 (~10 GHz), tan δ?=?1.2?×?10^?3 (~10 GHz), and τ _f?=??45 ppm/°C. The dielectric properties are obviously better than most composites reported previously at high frequencies in the aspects of dielectric loss and thermal stability. The dielectric constant and dielectric loss of composites predicted by the Rother–Lichtenecker equation and the general mixing model are in good agreement with the experiment data when the volume fraction of ceramic is less than 40%. When the volume fraction of the ceramic is more than 40%, the deviation occurs. By introducing the correction factor, the theoretical values of the dielectric constant agrees well with the experimental values.     

氮化硅晶须对反应烧结氮化硅多孔陶瓷介电性能的影响

以硅粉和氮化硅晶须为原料,通过添加30%(质量分数)成孔剂球形颗粒,以聚乙烯醇作粘结剂,采用干压成型工艺,反应烧结制备了多孔氮化硅陶瓷,分析对比了氮化硅晶须对反应烧结氮化硅多孔陶瓷介电性能的影响.实验结果表明,随着氮化硅晶须加入量的升高,氮化硅多孔陶瓷的介电常数和介电损耗都升高,介电性能恶化.     

Dielectric,thermal and mechanical properties of Sr<Subscript>2</Subscript>ZnSi<Subscript>2</Subscript>O<Subscript>7</Subscript> based polymer/ceramic composites

Polymer/Sr₂ZnSi₂O₇ (SZS) ceramic composites suitable for substrate applications have been developed using the polymers polystyrene (PS), high density polyethylene (HDPE) and Di-Glycidyl Ether of Bisphenol A (DGEBA). The dielectric, thermal and mechanical properties of the composites are investigated as a function of various concentrations of the ceramic filler. The obtained values of relative permittivity, dielectric loss tangent, thermal conductivity and coefficient of thermal expansion of the composites are compared with the corresponding theoretical predictions. The relative permittivity of the polymer/ceramic composites increases with filler loading. The dielectric loss tangent also shows the same trend except for DGEBA/SZS composites. The major advantages of the ceramic loading are improvement in thermal conductivity and a decrease in the coefficient of thermal expansion. The tensile strength of the composites decreases with increase in filler content, whereas an improvement is observed in microhardness. The variation of relative permittivity (at 1 MHz) of the composites is also studied as a function of temperature.     

低介电常数多孔氮化硅陶瓷的制备

采用凝胶注模成型工艺,以SiO2含量大于等于95%的空芯玻璃微珠作造孔剂,通过控制造孔剂的加入量和调节造孔剂的孔径成功制备出低介电常数、高强度的多孔Si3N4陶瓷。结果表明,随着造孔剂含量的增加,试样气孔率增大,弯曲强度降低,ε和tanδ都相应降低,ε最低为1.77;在造孔剂加入量为10%时,随着造孔剂的孔径尺寸变大,试样的孔径变大,弯曲强度降低,试样的ε和tanδ也相应降低。当造孔剂含量为10%、孔径尺寸为80μm时制备的多孔氮化硅陶瓷ε为2.13,弯曲强度达到38MPa,适合作为宽频带天线罩的夹层材料。     

A comparative study of the effect of γ-radiation on electrical parameters of oxide dielectrics

The effect of ionizing radiation on electrical properties of oxide dielectrics is studied. A comparative analysis of the temperature dependence of electrical conduction is performed for non-irradiated and irradiated samples of three types of oxide dielectrics—aluminum oxide, silicon dioxide, and alumina ceramics—in the temperature range between 200 and 700 K. The data obtained are correlated with special features of thermoradiation modification of dielectric parameters of oxides. The behavior of the dielectric loss tangent and permittivity is determined in a wide range of temperatures and γ-radiation doses. The peak conductivity parameters of ceramic samples are calculated. An assumption is made on the nature of the observed features of temperature and dose dependences of electrical properties of oxide dielectrics as well as on a possible admittance mechanism in these materials.     

Modeling of high-k dielectric nanocomposites

In this paper, based on recent research on BaTiO₃ (BT) nanoparticles, BT/P(VDF-HFP) nanocomposites, frequency-dependent dielectric properties of such a material system with high energy density have been investigated as functions of the volume fraction of the nanoparticles at room temperature by several theoretical models. For single domain and single crystals of BT, a Debye type of dissipation and soft mode theory have been adopted to obtain a more precise frequency-dependent dielectric spectrum of BT. For nanodielectric composites, among the others, Wiener Rule, Lichtenecker model, Maxwell–Wagner model, Yamada, and modified Kerner model were applied to evaluate the frequency-dependent dielectric spectrum of nanocomposites. A simple rule of mixture for the dielectric loss tangent was obtained using Lichtenecker logarithmic rule. The results from theoretical calculations are compared with the experimental data. For the dielectric constant, Lichtenecker model, Maxwell–Wagner model, and Yamada model show reasonable agreements with the experimental data up to 50 % volume fraction of the nanoparticles. At the higher volume fraction of the nanoparticles, the experimental data show a decreasing trend of the dielectric constant of the composites due to an increase in porosity of the system. In this case, a three-phase model (nanoparticles/pores/matrix) was developed to predict dielectric properties of the system at higher volume fraction of the nanoparticles (up to 80 %). The results showed reasonable agreements for a wide range of frequency. This theoretical study provides an essential information on dielectric properties of polymer-based BT nanocomposites with a wide frequency range instead of the trial-and-error strategy of experiments and can be used for designing high energy density dielectric materials in the future.