Magnetic and microwave absorbing properties of M-type barium ferrite/graphene oxide composite microwave absorber

In order to improve the absorbing properties of M- type barium ferrite absorbing materials, M-type barium ferrite/graphene oxide composites with different graphene oxide contents were synthesized by the sol-gel autocombustion method. X-ray diffraction （XRD）, a scanning electronic microscopy （ SEM ）, a physical properties measurement system （PPMS-9）, and a vector network analyzer were used to analyze their structure, surface morphology, magnetic and absorbing properties, respectively. The results show that the absorbing band of the composite absorbing material is widened and the absorbing strength is increased compared with the pure M-type barium ferrite. The sample with the content of doped graphene oxide of 3% has the minimum reflectivity at 10 to 18 GHz frequencies. Hence, the doped graphene oxide effectively improves the absorbing properties of M-type barium ferrite.

HYBRID AND CHARACTERISTIC OF POLYANILINEBARIUM TITANATE NANOCOMPOSITE PARTICLES

Polyaniline-barium titanate (PAn-Ba-TiO3) ultrafine composite particles were prepared by the oxidative polymerization of aniline with H2O2 while barium titanate nanoparticles were synthesized with a sol-gel method. The infrared spectrogram shows that the polymerization of PAn in the hybrid process of PAn-BaTiO3 is similar with the polymeric process of pure aniline, and there is interaction of PAn and BaTiO3 in the PAn-Ba-TiO3. SEM and TEM results show that the average diameter of the composite particles is 1.50μm and the diameters of BaTiO3 nanoparticles are 5 - 15 nm in the composite particle. The electrical conductivity of the ultrafine com-posite particles is transformable from 10°to 10-11S/cm by equilibrium doping or dedoping method using various concentration of HCl or NaOH solutions.

Preparation and characterization of barium strontium titanate/silicon nanoporous pillar array composite thin films by a sol-gel method

Barium strontium titanate （Ba0.5Sr0.5TiO3, BST）/silicon nanoporous pillar array （Si-NPA） thin films were prepared by a spin-coating/annealing technique based on Si-NPA with micro/nano-structure. Both the isomer conversion of acetylacetone and the network structure combined by enol and Ti-alkoxide facilitate the formation of the BST sol and the subsequent crystallization. Before the perovskite BST begins to form, the intermediate phase （Ba, Sr）Ti2OsCO3 is found. The boundary between BST and Si-NPA is of clarity and little interface diffusion, disclosing that Si-NPA is an ideal template substrate in the preparation of multifunctional composite films.

Damping capacity of BaTiO_3/Al composites fabricated by hot extrusion

To develop new type of high damping metal matrix composites, large grain size barium titanate （BaTiO3） ceramic was sintered and added into Al powder to fabricate BaTiO3/Al composites through the powder metallurgy method and hot extrusion. The damping properties of BaTiO3 ceramic, Al matrix and BaTiO3/Al composites were examined by dynamic mechanical analysis in the temperature range from 273 K to 573 K. The results show that although BaTiO3 exhibits high damping （tan δ=0.12） below 400 K, the damping capacity of 10%BaTiO3/Al （mass fraction） composites below 400 K is not increased as compared to the Al matrix. On the other hand, the damping capacity above 450 K is greatly enhanced due to the motion of dislocations at the interfaces between ceramic particles and Al matrix. The failure of exerting the intrinsic damping of BaTiO3 particles in the composites is attributed to the poor interface bonding between the particles and the matrix. The tensile strength of the composite is 42% higher than that of the Al matrix, which indicates the possibility of obtaining high strength and high damping composites via interface improvement and the addition of high volume fraction of large grain BaTiO3 particles.

STUDY ON C-FIBER-REINFORCED CELSIAN-MATRIX COMPOSITES

Strong, tough, and almost fully dense C fiber reinforced celsian matrix composites have been fabricated by impregnation of the fiber tows with the matrix slurry, winding on a drum, drying, stacking the prepreg tapes in the desired orientation, and hot pressing. The monoclinic celsian phase in the matrix was produced in situ, during hot pressing, from amphosous BAS. The unidirectional composites having ≈20 vol% of fibers exhibited graceful failure with extensive fiber pullout in three point bend tests at room temperature. Values of ultimate flexural strength and fracture toughness were 379MPa and 8 3MPa·m 1/2 , respectively.

Co-precipitation preparation and burning performance test of delay composition containing barium chromate

In order to optimize the performance of delay composition containing barium chromate,the preparation conditions of barium chromate were optimized,and S/BaCrO 4/KClO 4 delay composition was prepared by co-precipitation using barium chromate as precipitant.Then,the ignition temperature,delay time and other burning performance were tested.The results show that the ignition temperature of S/BaCrO 4/KClO 4 delay composition prepared by co-precipitation method is higher than that by traditional mechanical mixing method;the burning rate is faster and the burning time precision is higher because co-precipitation method can make the components mix more evenly.This co-precipitation method with barium chromate can be extended to the preparation of other mixed explosive agents containing barium chromate.

Dependence of dielectric properties on BT particle size in EP/BT composites

The polymer-ceramic composites of epoxy resin (EP) and barium titanate (BT) were prepared. BT powders of different BT particle sizes from 100 nm to 1 μm were used in the preparation. The dielectric properties, such as dielectric constant, dielectric loss and electrical breakdown strength, of the EP/BT composites were studied. The morphology of the composites was characterized by the means of scanning electron microscopy (SEM). The results show that the dielectric constant of the composites is much higher than the epoxy matrix at frequency range from 1 kHz to 10 MHz, and it is also obviously dependent on the size of BT particles. The electrical breakdown strength of the composites decreases with the increase of the BT content. The dependence of electrical breakdown strength on BT particle sizes was also discussed.

New method for measuring high field electrostrictive response of barium titanate/polyurethane elastomer

A new method for measuring the characteristic of electrostriction by a digital speckle correlation method （DSCM） is presented. The in-plane displacement is obtained by using the DSCM, and the out-plane displacement is obtained by the geometrical relation of the triangle theory. In this application, high field electrostrictive strains of barium titanate/polyurethane elastomer composite materials are measured. The electrostrictive strain is evaluated when the application of an electric field is repeated, and then the electrostrictive coefficient of the sample is obtained. To improve the measuring accuracy, the bilinear interpolation of gray value is used to obtain the sub-pixel gray value. The results are compared with those obtained from the surface fitting algorithm. The experimental results demonstrate that the electrostrictive response of polyurethane increases with the introduction of barium titanate into polyurethane. And by using the DSCM, the measurement of the characteristic of electrostriction can be done quickly and accurately. The DSCM provides an effective tool for the evaluation of electrostrictive response.

Factors Controlling Precipitation of Barite and Witherite and Genesis of the Ankang-Xunyang Barium Deposits,Shaanxi,China

The barium deposits in Ankang and Xunyang counties,Shaanxi Province,China,occur in the northernmost part of the world-class barium metallogenic belt in south Qinling.The deposits are hosted by the Lower Silurian carbonaceous siliceous rocks,with a unique combination of barite and witherite.The homogenization temperatures of fluid inclusions in the barite are mainly concentrated between 135 and 155 ℃,whereas those from the witherite have two peaks of 165-175 ℃,and 215-225℃,respectively.Laser Raman analysis of fluid inclusions indicates that the vapor phase of fluid inclusions in barite is dominated by H_2O,although some contains N_2,H_2S,and CH_4.The compositions of the vapor and liquid phases of fluid inclusions in witherite can be divided into two end-members,one dominated by H_2O without other volatiles,and the other containing CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6 in addition to H_2O.CO_2,H_2S,and some CH_4 are interpreted as products of chemical reactions during mineralization.Organic gases（CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6） in the fluids were critical in the formation of barium sulfate versus carbonate.The δ^（34）S values of barite range from 38.26‰ to54.23‰（CDT）,the δ^（34）S values of sulfides coexisting with barium minerals vary from 22.44‰ to25.11‰（CDT）,and those in the wall rock from 11.60‰ to 19.06‰（CDT）.We propose that the SO_4^（2-）generally experienced bacterial sulfate reduction in seawater before mineralization,and some SO_4^（2-）also experienced thermochemical sulfate reduction in hydrothermal system during mineralization.The δ^（13）C values of witherite range from-27.30‰ to-11.80‰（PDB）,suggesting that carbon was sourced from organic substances（like CH_4,C_2H_4,and C_2H_6）.The formation of witherite was possibly associated with thermochemical sulfate reduction,which caused the consumption of the organic gases and SO_4^（2-） in the hydrothermal solutions,consequently inhibiting barite formation.The important conditions for forming witherite include high fluid temperatures,high Ba^（2＋） concentrations,CO_2 in the fluids,low HS^- concentrations,and the subsequent rapid diffusion of H_2S during thermochemical sulfate reduction of the fluids.

芳纶纳米纤维/钛酸钡纳米纤维复合电介质薄膜制备与介电性能研究

选用芳纶纳米纤维(ANF)作为耐高温基体,并填充钛酸钡纳米纤维(BTNF)制备ANF/BTNF纸基复合薄膜,研究不同BTNF填充量对复合薄膜介电性能的影响。结果表明:ANF/BTNF复合薄膜的厚度约为10μm。当BTNF质量分数为0~20%时,随着BTNF填充量的增加,复合薄膜的介电常数和电气强度均提升。当BTNF的质量分数增大到40%时,复合薄膜的介电常数显著提升,但是在高频区快速降低,介质损耗因数显著增大,同时复合薄膜的电气强度略微下降。因此,BTNF质量分数为20%的ANF/20BTNF复合薄膜综合介电性能最佳,在1 kHz时介电常数达到4.78,电气强度为8.90 kV/mm。

Size effects of polydopamine-coated BaTiO_(3) nanoparticles on the piezoelectric performance of P(VDF-TrFE)/BaTiO_(3) composite

The size effect of the polydopamine(PDA)-coated BaTiO_(3)(BTO)(BTO@PDA)nanoparticles(NPs)on the interfacial compatibility between BTO NPs and the polymer matrix and the resultant piezoelectric performance of the composite films remain elusive.In this study,BTO and BTO@PDA NPs of various sizes were incorporated into a P(VDF-TrFE)matrix to prepare two series of P(VDF-TrFE)/BTO and P(VDF-TrFE)/BTO@PDA composites.Subsequently,the effects of the NP size on the dielectric,ferroelectric,and piezoelectric properties of the composite films were comprehensively studied.As the size of the BTO@PDA NPs increased,residual hole defects were clearly observed in the cross section of the composite film.The deteriorated interfacial compatibility due to the large size of the BTO@PDA NPs was also confirmed by the increased dielectric permittivity of the composite film,which was induced by the intensified interfacial polarisation.The P(VDF-TrFE)/BTO@PDA composite with NPs of the smallest size(100 nm)exhibited superior piezoelectric performance owing to the excellent interfacial compatibility between the fillers and the matrix.The piezoelectric performance was significantly enhanced by the reduced leakage current during electrical poling and reduced trap charges.Finally,the pulse waveform originating from the radial artery was precisely measured using the optimised P(VDF-TrFE)/BTO@PDA composite film.

模板法构筑三维钛酸钡/聚乙烯醇-氮化硼柔性电介质材料的介电储能特性

为研究三维钛酸钡(3DBT)网络结构和BN含量对复合体系介电储能特性的影响规律,以无尘纸为模板,溶胶凝胶法制备3DBT陶瓷网络;然后将含有不同比例氮化硼(BN)纳米片/聚乙烯醇溶液(PVA-BN)反向引入到3DBT网络中,制得了3DBT/PVA-BN复合电介质材料。研究表明,反向引入PVA溶液能够实现其对3DBT的有效包埋,赋予3DBT良好的柔韧性。当PVA达到饱和时,3DBT网络的质量分数约为27%(体积分数6.9%)。其中,3DBT/PVA-0.50%BN复合电介质材料表现出综合的介电储能特性,其介电常数和储能密度为18.1(1kHz)和1.24J/cm~3(90k V/mm下),分别是传统方法制备27%nano-BT/PVA复合材料的1.74和3.54倍。此外,获得的3DBT/PVA-BN介电材料具有更好的热稳定性,表现出良好的应用前景。

Fabrication of barium-strontium aluminosilicate coatings on C/SiC composites via laser cladding

Barium-strontium aluminosilicate （BSAS） and Si/BSAS coatings were fabricated on the surface of C/SiC composites via a two-step laser cladding process. The microstructure, mechanical properties, and the water vapor corrosion behavior of the samples were investigated. The BSAS coating was found to be tightly bonded to the substrate and only a few pores and microcracks were observed. The introduction of a silicon middle layer was revealed to reduce thermal stress and promote the healing of defects formed during the laser cladding process. To evaluate the corrosion resistance, the BSAS and Si/BSAS-coated C/SiC com- posites were exposed to an atmosphere of 50% H2O and 50% O2 at 1250 ℃. The resulting weight change and flexural strength were measured as a function of the corrosion time. The addition of the silicon middle layer below the BSAS top layer resulted in a better resistance to water vapor corrosion. Furthermore, the Si/BSAS-coated samples showed a lower weight loss and a smaller reduction in flexural strength than the BSAS-coated and the uncoated samples during water vapor corrosion. Thus, laser cladding is dem- onstrated to be an effective and feasible method to fabricate high-quality ceramic coatings on C/SiC composites. The introduction of a silicon middle layer can inhibit defect formation during the laser clad- ding process and protect the composite from water vapor corrosion.

高居里温度BaTiO_(3)基无铅热敏陶瓷的研究进展

钛酸钡(BaTiO_(3))基正温度系数电阻(PTCR)陶瓷材料由于具有独特的电阻-温度特性,被广泛用于制作各种热敏电阻器件。随着电子材料及元器件无铅化的要求日益迫切,高居里温度BaTiO_(3)基PTCR陶瓷的无铅化是必然发展趋势。介绍了PTCR效应的物理机制、BaTiO_(3)基PTCR陶瓷材料的性能指标及其影响因素,综述了高居里温度无铅BaTiO_(3)基PTCR陶瓷材料的研究进展,讨论了提高无铅BaTiO_(3)基PTCR陶瓷材料性能的策略与途径,以促进这一领域的进一步发展。

钡铁氧体粉体的制备及其涂层织物的吸波性能研究

采用微波水热法合成钡铁氧体(BaFe_(12)O_(19))磁性粉体,采用机械混合法将BaFe_(12)O_(19)和聚偏氟乙烯(PVDF)粉体混合,以水性聚氨酯作为黏结剂,通过流延法制备BaFe_(12)O_(19)/PVDF复合吸波剂,将复合吸波剂涂覆在锦纶织物上制备吸波织物;研究了BaFe_(12)O_(19)粉体的晶体结构、化学结构、磁性能,以及吸波织物的力学性能、疏水性能、吸波性能。结果表明:合成的BaFe_(12)O_(19)粉体的相组成和晶体结构与已知的标准BaFe_(12)O_(19)相一致,具有较高的纯度,且具有良好的磁性能;随着涂层厚度的增加,吸波织物的断裂强力和断裂伸长率均呈现上升趋势,涂层厚度为3.5 mm时吸波织物的力学性能最好,断裂强力为1734.32 N,断裂伸长率为57.36%;随着PVDF加入量的增加,吸波织物的水接触角有所增大,但均小于90°;PVDF的加入有效提高了吸波织物的吸波性能,在BaFe_(12)O_(19)/PVDF质量比为1.00.6、涂层厚度为2.5 mm时,吸波织物的有效吸收带宽最宽,达2.48 GHz,吸波性能最好。

Selective microwave absorption in Nd3+ substituted barium ferrite composites

Microwave(MW)frequency based wireless communications and electronic devices became prospective due to several ramifications.To meet this need,a series of neodymium ions(Nd3+)substituted barium ferrite composites with composition(20)BaO:(80-x)Fe2 O3:(x)Nd2 O3(0≤x≤3 mol%)was prepared at1100℃using solid-state reaction method.We evaluated the effect of various Nd3+ions contents on the surface morphology,structure,and magnetic properties of the as-synthesized barium ferrite composites.Meanwhile,microwave reflection loss,complex permittivity and permeability were determined using the transmission/reflection line method in the X-band(8-12 GHz).SEM image of the composites shows that the surface morphology consists of rough and porous microstructures.XRD patterns of the un-doped composites reveal the existence of BaFe12O19(hexagonal)and Fe21.333O32(tetragonal)crystalline phases.Furthermore,a new hexagonal crystalline phase of Ba6 Nd2 Fe4 O15 with the crystallite sizes between 15 and 67 nm is observed due to Nd3+ions substitution in the composite.The saturation magnetization of the composite containing 2 mol%of Nd3+does not exhibit any significant alteration compared to the one devoid of Nd3+.The complex relative permitivity and permeability of the achieved composites enriched in Ba6 Nd2 Fe4 O15 and BaFe2 O4 phases disclose significant MW frequency dependence.The composites also display selective MW absorption in the X-band which could be useful for diverse applications.

Dielectric property of polyimide/barium titanate composites and its influence factors (Ⅱ)

Using poly(amic acid)(PAA)as a precursor followed by thermal imidization,the polyimide/barium titanate composite films were successfully prepared by a direct mixing method and in situ process.The influence of processing factors,such as particle size,distribution mode and polymerization method on dielectric prop-erties was studied.Results revealed that the dielectric constant(ε)of the composite film increased by using bigger fillers or employing in situ polymerization and bimodal distribution.When the composite film contain-ing 50 Vol-%of BaTiO3 with size in 100 nm was pre-pared via in situ process,its dielectric constant reached 45 at 10 kHz.

Fabrication of Z-type barium ferrite/silica composites with enhanced microwave absorption

The Z-type barium ferrite/silica composites(Z-BCF/SiO2)were fabricated by in situ chemical synthesis method.The composition,structure,morphology and magnetic behavior of the composites were characterized by chemical analysis,IR,XRD,SEM,TEM and VSM.The results indicated that there were some interactions between two components in the Z-BCF/SiO2 composites due to the coating of SiO2 on the Z-BCF particles.The magnetic properties of the Z-BCF/SiO2 composites were evidently less than that of the Z-BCF,owing to the small volume fraction of magnetic components in the samples.Due to the good transmission and loss properties on electromagnetic waves,the composites were better at microwave absorption than the parent component.Therefore,this research laid a foundation for the fabrication of highly efficient microwave absorbing material with enhanced wave impedance matching.

Surface-modified barium titanate by MEEAA for high-energy storage application of polymer composites

In this study,2-[2-(2-methoxyethoxy)ethoxy]acetic acid(MEEAA)was used to modify the surface of barium titanate nanoparticles(BT NPs)to enhance the compatibility and dispersion of the BT ceramic fillers in polymer matrix.A uniform coating layer with a thickness about 2 nm was formed on the surface of BT after modification.The poly(vinylidene fluoride)-hexafluoropropene[P(VDF-HFP)]composites filled with MEEAA-modified BT NPs achieved higher permittivity(∼13 at 3.0 vol%filler)and discharged energy density than that of the untreated BT filled composite.The maximum discharge energy density of 7.8 J/cm^(3)was obtained in the nanocomposites with 3 vol%MEEAA-modified BT NPs at electric field of 425 kV/mm,which is 77%higher than that of 4.4 J/cm^(3)of pure P(VDF-HFP)film at electric field of 420 kV/mm.

钡酚醛树脂体系化学流变特性研究

在粘度实验和 DSC热分析实验的基础上 ,对用于 RTM工艺的钡酚醛树脂体系的化学流变特性进行研究 ,并根据双阿累尼乌斯方程建立树脂体系的流变模型。模型与实验结果具有良好的一致性。模型可揭示树脂体系在不同工艺条件下的粘度变化规律 ,定量预报 RTM工艺树脂的低粘度平台工艺窗口 ,为合理制定 RTM工艺参数。