宗翰文,杨海波,董镜镜,邱云,百晓宇,文博,林营

采用水热法制备了MoS2@CoFe2O4复合材料,探究了CoFe2O4添加量对复合材料吸波性能的影响,并通过矢量网络分析仪测试了该复合材料在2～18 GHz频率下的电磁参数,模拟分析了该复合材料的吸波性能。结果表明,当CoFe2O4添加量为0.4 g时,所制得的复合材料吸波性能最佳,最大吸收位于11 GHz,为-59.9 dB,相应的匹配厚度为2.7 mm,并且当匹配厚度为2 mm时,其有效吸收频带宽度(-10 dB以下)为4.63 GHz(12.58～17.21GHz)。表明MoS2@CoFe2O4复合材料在微波吸收方面具有潜在的应用价值。     

具有固定硅铝比的Al2O3-2SiO2纳米颗粒制备:过程优化与粉体转化（英文）

Attempts had been made to synthesize Al2O3-2SiO2 nanopowders by sol-gel method with tetraethoxysilane(TEOS) and aluminum nitrate(ANN) as the starting materials.DTS,TEM,SEM and BET were employed to study the effects of process parameters on the size,specific surface area and structure(morphology) of powders.The alkali-activation reactivity of the powders was tested for manufacturing geopolymers and their hydrothermal reactions were performed for fabricating zeolites.The results show that the optimum process parameters and drying method for preparing Al2O3-2SiO2 nanopowders are as follows:the molar ratio of water and ethanol to TEOS are 0:1 and 12:1 respectively at synthetic temperature of 50 ℃ and the drying method is azeotropic distillation with microwave drying.The average particle diameters of the powders were about 70 nm and the largest BET specific surface area was up to 669 m2·g·1.The compressive strength of the geopolymer and the calcium exchange capacity(by CaCO3) of NaA zeolite prepared with the powders reached to 29 MPa and 366 mg·g·1 respectively.     

Mechanical Properties and Electrical Conductivity of TiN-Al_2O_3 Composites

TIN-Al2O3 composite powders with different TiN contents (0,10 vol%,20 vol%,30 vol% and 40 vol%) were prepared with micrometer TiN and α-Al2O3 powder (their purities were 99%) as starting materials by wet ball milling for 5 h.TiN-Al2O3 com-posite were then prepared by pressing the above composite powders,drying at 200 ℃ for 12 h and firing at 1 800 ℃ for 3 h in nitrogen atmosphere in hot-pressing furnace.The influences of TiN content on mechanical properties and electrical conductivity of TiN-Al2O3 com-posites were studied.The results showed that the me-chanical properties of the composite increased with TiN content increasing,while the resistivity of composites de-creased.A composite with 40% TiN had 498 MPa ben-ding strength,4.285 MPa·m1/2 fracture toughness,1.34×10-3 Ω·cm resistivity.The SEM analysis showed that the fine TiN crystals distributed among the crystal boundary of Al2O3 matrix.They bonded together forming a net-like structure which played a role of re-straining Al2O3 grains from growing up,toughening and strengthening,so the mechanical properties of TIN -Al2O3 composite were enhanced.     

软模板水热法制备空心ZnFe2O4及吸波性能

以六水合氯化铁和氯化锌为原料,聚乙二醇4000为表面活性剂,采用软模板水热法一步合成了具有空心结构的ZnFe2O4纳米颗粒。采用XRD、XPS、FE-SEM和TEM对样品的物相和形貌进行了表征,通过振动样品磁强计（VSM）和矢量网络分析仪测试了样品的静磁性能和电磁参数,并模拟计算了样品的反射损耗,考察了其吸波性能。结果表明：所制备的ZnFe2O4粒径约为100 nm,分散均匀,具有明显的空心结构。吸波性能优异。当样品的匹配厚度为2.7 mm时,在12.41GHz处获得最小的反射损耗（-42.18dB）;而当匹配厚度为3.0mm时,样品的有效吸收带宽（反射损耗≤-10dB,即吸收率为90%）最宽,为2.60GHz（10.60~13.20GHz）。     

Effect of Raw Bauxite Addition on Thermal Behaviour of Ultra-low Cement Al_2O_3-SiO_2 Castables

This work investigated the thermo-gravimetric(TG) change and explosion resistance of ultra-low cement Al2O3-SiO2 castables added with 0,5%,10%,15% and 20% of ≤74 μm raw bauxite powders containing 72.8% Al2O3,respectively.The castables were prepared using white fused alumina as aggregate,powders of white fused alumina,fused mullite,α-Al2O3 ultrafines,3% CA cement and 5% microsilica as the matrix portion.TG change of the castables was investigated by a thermo-gravimetric analyzer for large size specimen.When ...     

钢纤维复合水泥砂浆的吸波性能研究

为了研究钢纤维在水泥砂浆中的吸收电磁波性能,将长度为15 mm和30 mm的波浪型钢纤维以2％、4％、6％的质量比掺入水泥砂浆中,制成长宽为180 mm×180 mm,厚度分别为10 mm、15 mm、20 mm、25 mm、30 mm的试样;养护3个月以后,采用弓形反射法进行不同厚度试样的反射率测试.结果显示:波浪型钢纤维对水泥砂浆的吸波性能具有明显的改善作用;30 mm长钢纤维掺量为4％时吸波性能最好,在厚度为10～20 mm时,具有多个吸收峰;大于6 dB吸收峰累计带宽都超过10 GHz,最大吸收率为8.5 ～16.5 dB;厚度为30 mm的试样,15 mm长钢纤维掺量为4％时,大于6 dB吸收峰累计带宽超过12 GHz.     

Effect of Zircon Addition on Properties of Low Carbon Al2O3-C Refractories

Using tabular alumina as aggregate,tabular alumina fines, reactive alumina ultra-fines, aluminum powders,silicon powders,carbon black,flake graphite,B4C and zircon fines as matrix,low carbon Al2O3- C refractories were prepared. Influences of zircon powders additions( 0,3%,5% and 7%,in mass,the same hereinafter) on properties,phase composition and microstructure were investigated. The results show that the ZrO2- nitride can be in-situ formed through carbothermal reduction and nitridation in Al2O3- C refractories.With the increase of zircon powder,the oxidation resistance of the Al2O3- C refractories improves obviously,the oxidized layer thickness decreases from 7. 94 mm without zircon to 2. 71 mm with 5% zircon. HMOR at 1 400 ℃of the Al2O3- C refractories reaches the maximum 14. 9MPa when zircon addition is 5%. With the increase of zircon powder,the apparent porosity and bulk density change a little,CMOR and CCS increase.     

Influences of Al and Si Powders on Microstructure and Hot Mechanical Properties of Al2O3-C Slide Plates

The basic formulation of Al2O3- C slide plates was65%( in mass,the same hereinafter) white fused corundum particles,25% white fused corundum fines,6% active α-Al2O3 micropowder,4% carbon black and flake graphite, and additional 4% phenolic resin.Based on this formulation,3% Al powder,3% Si powder,and 3% Al + 3% Si powder were used to substitute equivalent white corundum fines to improve the hot mechanical properties of Al2O3- C slide plates. The specimens with dimensions of 140 mm × 25 mm × 25 mm were pressed at 150 MPa,dried at 200 ℃ for 24 h,and hot treated at 1 400 ℃ for 3 h in carbon embedded condition. Then hot modulus of rupture and thermal shock resistance of the specimens were tested and the phase compositions and microstructure were analyzed. The results show that specimen with 3% Al powder has the higher hot modulus of rupture but lower residual modulus of rupture after thermal shock than the specimen with3% Si powder; the specimen with 3% Al + 3% Si powders exhibits the highest hot modulus of rupture and the best thermal shock resistance; the change of mechanical property is closely related with the in-situ formed nonoxides: AlN in the form of bars is formed in specimens with Al powder; fibrous SiC whiskers are formed in specimens with Si powder; in the specimens with both Al and Sipowders,besides AlN and SiC whiskers,hexagonal tabular SiAlON is in-situ synthesized,which interlocks with each other.     

Evolution of Phase Composition and Microstructure of Al_2O_3-Si-Al Composite at High Temperatures in Reducing Atmosphere

Al2 O3-Si-Al composite specimens with the size of 25 mm × 25 mm × 125 mm were prepared using fused alumina （as aggregates and fines）,ultra-fine α-Al2O3,Si and Al powders as starting materials,liquid phenol formaldehyde resin as the binder,pressing and heating at 800-1 500 ℃ for 3 h under carbon embedded condition.Evolution of phase composition and microstructure of Al2 O3-Si-Al composite during heating from 800 to 1 500 ℃ under carbon embedded condition were studied.The results show that：（1） Al4 C3,AlN and SiC are initially formed at 800-900 ℃ due to reactions of Al and Si with C or CO and N2 ; （2） at 1 000-1 300 ℃,the amounts of Al4C3,AlN and SiC increase with temperature rising and their crystals grow; （3） at 1 400-1 500 ℃,Al4 C3 and AlN disappear,and minor SiAlON crystals are observed; the nonoxide crystals develop well and they are interlaced in the corundum skeleton structure,which creates strengthening and toughening     

软模板水热法制备空心ZnFe2O4及其吸波性能

以六水合氯化铁和氯化锌为原料,聚乙二醇4000为表面活性剂,采用软模板水热法一步合成了具有空心结构的ZnFe2O4纳米颗粒。采用XRD、XPS、FE-SEM和TEM对样品的物相和形貌进行了表征,通过振动样品磁强计(VSM)和矢量网络分析仪测试了样品的静磁性能和电磁参数,并模拟计算了样品的反射损耗,考察了其吸波性能。结果表明,所制备的ZnFe_2O_4粒径约为100 nm,分散均匀,具有明显的空心结构,吸波性能优异。当样品的匹配厚度为2.7 mm时,在12.41 GHz处获得最小的反射损耗(–42.18 dB);而当匹配厚度为3.0 mm时,样品的有效吸收带宽(反射损耗≤–10 dB,即吸收率为90%)最宽,为2.60 GHz(10.60～13.20 GHz)。     

化学镀钴活性炭的微波吸收性能研究

采用化学镀的方法对活性炭进行表面镀钴,透射电镜（TEM）观察证实了活性炭的表面上已经镀覆上了钴层。采用HP8722ES矢量网络分析仪测量了样品在2—18GHz频率范围内的复介电常数（εT=ε＇-jε＇＇）和复磁导率（μT=μ＇-μ＇＇）。用吸收屏理论公式计算其反射损耗（R．L．）、匹配厚度（dm）及匹配频率（fm）。结果表明,随着匹配厚度的增大,吸收峰没有发生移动,但吸收峰值有所下降。在匹配厚度dm=0．2mm时,样品最大反射损耗达-5．23dB,对应的匹配频率fm=10．59GHz,而且在整个电磁波频率测试范围内,反射损耗值均小于-4．8dB。     

Dielectric and microwave absorption properties of CB doped SiO2f/PI double-layer composites

Carbon black (CB) with contents of 5.5?wt% and 15?wt% filled quartz glass fiber reinforced polyimide (SiO_2f/PI) composite were designed and prepared. A double-layer absorbing material was designed using the two composites materials as a matching layer and an absorption layer, respectively. The microwave absorption property of single-layer and double-layer composites is calculated according to transmission line theory. The results show that the microwave absorbing property of double-layer composite is better than that of single-layer at the same thickness. When the 5.5?wt%CB doped SiO_2f/PI composite is used as the matching layer with a thickness of 0.7?mm and 15?wt%CB doped SiO_2f/PI composite is used as the absorption layer with a thickness of 0.9?mm, the RL (reflection loss) of the composite reaches a minimum value of ?46.18?dB at 16.07?GHz. Meanwhile, the bandwidth of RL?≤??5?dB is 5.87?GHz and the bandwidth of RL?≤??10?dB is 3.95?GHz.     

One-step hydrothermal synthesis and enhanced microwave absorption properties of Ni0.5Co0.5Fe2O4/graphene composites in low frequency band

Ni_0.5Co_0.5Fe₂O₄/graphene composites were synthesized successfully via one-step hydrothermal method. The crystal structure, morphology and corresponding elemental distribution, electromagnetic parameters and microwave absorption performances of the as-prepared composites were measured by XRD, SEM, TEM and VNA, respectively. The results indicated that the microwave absorbing performance can be obviously enhanced through the addition of graphene in a suitable range, the magnetic loss plays a dominant contribution for the microwave absorption of composites. The maximum reflection loss of ?30.92?dB at 0.84?GHz with a ?10?dB bandwidth over the frequency range of 0.58–1.19?GHz is obtained when the composite contains 12?wt% graphene and the thickness of sample is 4?mm. This investigation presents a simple method to prepare Ni_0.5Co_0.5Fe₂O₄/graphene composites with excellent microwave absorption performance in the low frequency band of 0.1–3?GHz.     

Dielectric and microwave absorption properties of FeSiAl/Al2O3 composites containing FeSiAl particles of different sizes

Here in, the effects of FeSiAl particle size on the dielectric and microwave absorption properties of FeSiAl/Al₂O₃ composites were studied. FeSiAl/Al₂O₃ composites containing 18–25 μm, 25–48 μm, and 48–75 μm FeSiAl particles were prepared by hot-pressed sintering based on uniformly mixed FeSiAl and Al₂O₃ powders. Results show that the real permittivity and the imaginary permittivity are significantly promoted with increasing FeSiAl particle size, which is ascribed to the enhanced interfacial polarization and conductance loss. In addition, the favorable matching impedance and suitable attenuation coefficient enabled the composite containing 25–48 μm FeSiAl powder to show a minimum reflection loss of ?34.4 dB at 11.7 GHz and an effective absorption bandwidth (<-10 dB) of 1.4 GHz in 11.0–12.4 GHz, when the thickness is 1.1 mm. By adjusting the thickness to 1.4 mm, the effective absorption bandwidth of the composite reaches a maximum value of 2.0 GHz in the 8.3–10.3 GHz range, indicating tunable, strong, and highly efficient microwave absorption performance.     

Microwave absorbing properties of carbon black/silicone rubber blend

In the frequency range of 2–18 GHz, the microwave absorbing properties of a carbon black/silicone rubber blend were investigated by changing the carbon black content and the thickness. The real part (ε′) and the imaginary part (ε″) of permittivity of the blends were calculated from the S‐parameters measured by a network analyzer. The reflection loss was simulated by using ε′ and ε″. The reflection loss less than ?10 dB could be obtained in the frequency range of 9.6ε13.5 GHz from the sample with 10 wt% of carbon black at 1.9 mm of thickness.     

壳核结构SiC/C纤维的制备与吸波性能的研究

采用活性碳纤维转换法制备了壳核结构SiC/C纤维,采用拉曼光谱、SEM、XRD以及热重分析等测试方法对比研究了生成SiC的厚度对壳核结构SiC/C纤维样品的热重及吸波性能的影响。结果表明:包裹SiC壳层后样品吸波性能得到提高,样品厚度为3.0 mm时,保温4 h样品的最小反射损耗在8.24 GHz处达到-17.22 dB,低于-10 dB(90%的电磁波被吸收)的频宽在2.0 mm处达到4.8 GHz(11.12~15.92 GHz);保温3 h样品的最小反射损耗在8.23 GHz处达到-14.45 dB,低于-10 dB(90%的电磁波被吸收)的频宽在2.0 mm处达到4.56 GHz(10.88~15.44 GHz);且随着SiC含量的升高,试样微波吸收性能有所增强;制备的壳核结构SiC/C纤维样品起始氧化温度提高了150 ℃以上,并且最终残余质量在50%左右,即包裹SiC纤维后样品的抗氧化能力大大提高。     

铜铁尾矿制酸烧渣制备纳米Fe/SiO2核壳复合粒子的微波吸收性能

以铜铁尾矿制酸烧渣为原料,经熟化、酸浸、还原和净化等步骤制备亚铁离子;在乙醇-水液相体系中,以NaBH₄作为还原剂,反应生成纳米Fe粒子;最后通过正硅酸四已酯（TEOS）水解包覆制得纳米Fe/SiO₂核壳复合粒子。产物分别采用XRD、TEM、IR等手段进行表征。进一步地,使用矢量网络分析仪在2.0 ~ 18.0 GHz波段内来研究样品的吸波性能。结果表明,IR光谱上在1389 cm^-1和878 cm^-1分别出现对应于四配位Si—O键和Si—O—Fe键的特征吸收峰,说明在Fe粒子表面包覆有SiO₂。通过测试计算得知,当吸波样品厚度为4.5 mm时,其微波吸收性能在17.2 GHz处达到最小值-39.0 dB。由此可见,以铜铁尾矿制酸烧渣为原料,可制得吸波性能优良的纳米Fe/SiO₂核壳复合粒子微波吸收材料。     

Ti3C2Tx/Ni/TiO2复合粉体的制备及吸波性能研究

采用热处理的方法制备出二维层状Ti3C2Tx/Ni/TiO2复合粉体,并利用TG-DSC、SEM、XRD和XPS对样品进行表征分析,通过矢量网络分析仪测试样品的电磁参数并模拟计算不同涂层厚度下样品的反射损耗值(RL).结果表明:随着热处理温度的升高,样品中TiO2质量含量增加;当热处理温度为300℃时,在频率f=17....     

3D printed SiC nanowire reinforced composites for broadband electromagnetic absorption

SiC nanowire/acrylic resin (SiC_nw/ACR) composites with broadband electromagnetic (EM) absorption capabilities were fabricated by a novel procedure using 3D stereolithography (3D-SL) printing technology. The EM absorption abilities of the composites can be adjusted by tuning the SiC_nw content and the thickness of the printing layer. When the SiC_nw content is 3?wt% and the thickness of the printing layer is 25?μm–50?μm, the SiC_nw/ACR composite has an optimally broad effective absorption bandwidth (EAB) and a high efficiency for EM absorption, whether assessing the C, X or Ku band, because of the high dielectric loss and proper impedance matching between the materials and free space. In the C band (4–8?GHz), the EAB reaches 2.9?GHz, and the reflection loss (RL) reaches ?34.1?dB; in the X band (8–12?GHz), the EAB reaches 4?GHz, which covers the entire X band, and the RL reaches ?34.5?dB; in the Ku band (12–18?GHz), the EAB exceeds 6?GHz, which covers the whole Ku band, and the RL reaches ?34.7?dB. This research is of great importance to the rapid preparation of parts, shells or devices with arbitrarily complex shapes and high efficiency broadband EM absorption abilities.     

Synthesis of PPy/Ni/RGO and enhancement on its electromagnetic wave absorption performance

The ternary composites of hollow tubular polypyrrole (PPy) and Ni particles based on reduced graphene oxide (RGO) were synthesized by a low-energy method. PPy and Ni particles were uniformly distributed on the surface of RGO. Specifically, multilayer interfaces existed in the hybrid, residual defects and folded structures of RGO and the hollow tubular structures of PPy made a significant contribution to electromagnetic (EM) wave attenuation. The final results showed that the strongest reflection loss (RL) value of PNR-2 sample could achieve ??47.32?dB at 5.76?GHz. The PNR-3 sample's RL value was ??18.21?dB at 15.92?GHz with the thickness of only 1.5?mm, and its corresponding effective absorption bandwidth reached 4.32?GHz (13.68–18?GHz). Hence, with the changes of PPy mass ratio, the impedance matching and attenuation were regulated to realize remarkable EM wave absorption performance including lightweight, thin thickness, wide bandwidth and strong absorption.