Preparation of PbTiO_3 Conductive Powders and Coatings

La2O3 and Ce2O3 were penetrated into PbTiO3 to obtain conductive powders, and then they were mixed with polyurethane and butyl acetate to prepare conductive coatings. The results showed that the electric property of modified PbTiO3 powders was improved by penetration of La2O3 and Ce2O3. XRD patterns showed that some new compounds such as La2Ti6O15, CeTi21O38 and Pb0.634La0.209Ti0.948O2.284 were formed, which led to the rapid increase of conductivity. The resistivity of modified PbTiO3 powders decreased to 3.88 Ω·m. The coatings using modified PbTiO3 powders as fillings also had a good conductivity. When the PbTiO3 powders were 10% and antisettle agent (bentonite) content was 0.50%, and mass ratio between polyurethane and butyl acetate was 1.05, the surface resistivity of the coatings fell down to 1.3×108 Ω·m. This kind of conductive coatings could be used in electromagnetic shielding.

Effects of Shielding Coatings on the Anode Shaping Process during Counter-rotating Electrochemical Machining

Electrochemical machining （ECM） has been widely used in the aerospace, automotive, defense and medical industries for its many advantages over traditional machining methods. However, the machining accuracy in ECM is to a great extent limited by the stray corrosion of the unwanted material removal. Many attempts have been made to improve the ECM accuracy, such as the use of a pulse power, passivating electrolytes and auxiliary electrodes. However, they are sometimes insufficient for the reduction of the stray removal and have their limitations in many cases. To solve the stray corrosion problem in CRECM, insulating and conductive coatings are respectively used. The different implement processes of the two kinds of coatings are introduced. The effects of the two kinds of shielding coatings on the anode shaping process are investigated. Numerical simulations and experiments are conducted for the comparison of the two coatings. The simulation and experimental results show that both the two kinds of coatings are valid for the reduction of stray corrosion on the top surface of the convex structure. However, for insulating coating, the convex sidewall becomes concave when the height of the convex structure is over 1.26 ram. In addition, it is easy to peel off by the high-speed electrolyte. In contrast, the conductive coating has a strong adhesion, and can be well reserved during the whole machining process. The convex structure fabricated by using a conductive iron coating layer presents a favorable sidewall profile. It is concluded that the conductive coating is more effective for the improvement of the machining quality in CRECM. The proposed shielding coatings can also be employed to reduce the stray corrosion in other schemes of ECM.

A UTD SOLUTION FOR THE RADIATED FIELD FROM MONOPOLE ON A CONDUCTING CYLINDER SURFACE WITH A DIELECTRIC COATING

A can0nical problem is investigated for high frequency electromagnetic radiation from amonopo1e on a conducting cylinder with c0ating-At first, the exact solution of this problem is given interms of Dyadic Green's function method. Then, using Watson transformation and high frequency asymptotic approximate technique to the exact soluton, a UTD soultion is obtained. The radiation field excitedby a monopole is expressed in terms of the compound Fock' S functions (CFF), which reduce to the geomertrical optics result in the deep lit region and the creeping waves in the shadow region.

Microstructure and Thermal Properties of SiCp/Cu Composites with Mo Coating on SiC Particles

SiCp/Cu composites with a compact microstructure were successfully fabricated by vacuum hot-pressing method. In order to suppress the detrimental interfacial reactions and ameliorate the interfacial bonding between copper and silicon carbide, molybdenum coating was deposited on the surface of silicon carbide by magnetron sputtering method and crystallized heat-treatment. The effects of the interfacial design on the thermo-physical properties of Si Cp/Cu composites were studied in detail. Thermal conductivity and expansion test results showed that silicon carbide particles coated with uniform and compact molybdenum coating have improved the comprehensive thermal properties of the Si Cp/Cu composites. Furthermore, the adhesion of the interface between silicon carbide and copper was significantly strengthened after molybdenum coating. Si Cp/Cu composites with a maximum thermal conductivity of 274.056 W/（m·K） and a coefficient of thermal expansion of 9 ppm/K were successfully prepared when the volume of silicon carbide was about 50%, and these Si Cp/Cu composites have potential applications for the electronic packageing of the high integration electronic devices.

High performance lithium-sulfur batteries by facilely coating a conductive carbon nanotube or graphene layer

Lithium sulfur(Li-S) batteries are regarded as promising candidates for next-generation rechargeable batteries. However, the insulation characteristic of sulfur and severe polysulfide dissolution hindered their development. We presented a facile approach to fabricate Li-S batteries by coating commercial carbon nanotube or graphene slurries on normal sulfur cathode electrode to construct a dual-layer cathode electrode. The conductive CNT or graphene layer could not only improve the conductivity of sulfur cathode, but also suppress the polysulfide diffusion. The CNT@S cathode delivered a high reversible capacity of 740 mAh/g over 300 cycles at 1 C and 870 mAh/g over 100 cycles at 0.2 C. Furthermore, this strategy could be realized on the commercial product line of lithium-ion batteries, which made it possible to large-scale produce Li-S batteries.

A novel lightweight metamaterial with ultra broadband electromagnetic wave absorption induced by three-dimensional CNTs conductive-coated arrays

Lightweight metamaterials for broadband electromagnetic wave absorption have become a significant requirement for electromagnetic interference and stealth technologies.In this study,a novel lightweight metamaterial absorber with three-dimensional(3D)carbon nanotubes(CNTs)conductive-coated arrays is designed and fabricated through 3D printing and dipping process,which realized less than-10 dB reflection loss in the frequency range of 7.0–40 GHz.The effect of the sheet resistance of CNTs conductive coatings and geometric parameters of meta-structure on the frequency-dependent absorption properties is investigated,and the improved absorbing efficiency is discussed based on the synergy effect of multiscale structures of 3D conductive-coated arrays.Moreover,the volume of the proposed ultra broadband absorber is reduced by approximately 60.5%compared with that of the dense plate structure,indicating a significant lightening with efficient absorbing capacities.Additionally,the absorption bandwidth and intensity of the proposed absorber have insensitive changes with the variation of incident angle.Therefore,an ultra broadband electromagnetic absorption is designed and realized,indicating a promising lightweight ultra broadband electromagnetic absorbing candidate for lightweight metamaterial absorbers.

Thermal properties of diamond/Al composites by pressure infiltration:comparison between methods of coating Ti onto diamond surfaces and adding Si into Al matrix

This study was pertained to the effects of Ti coating on diamond surfaces and Si addition into Al matrix on the thermal conductivity（TC） and the coefficient of thermal expansion（CTE） of diamond/Al composites by pressure infiltration.The fracture surfaces,interface microstructures by metal electro-etching and interfacial thermal conductance of the composites prepared by two methods were compared.The results reveal that Ti coating on diamond surfaces and only12.2 wt% Si addition into Al matrix could both improve the interfacial bonding and increase the TCs of the composites.But the Ti coating layer introduces more interfacial thermal barrier at the diamond/Al interface compared to adding 12.2 wt% Si into Al matrix.The diamond/Al composite with 12.2 wt% Si addition exhibits maximum TC of 534 W·m^-1·K^-1and a very low CTE of 8.9×10^-6K^-1,while the coating Ti-diamond/Al composite has a TC of 514 W·m^-1·K^-1 and a CTE of 11.0×10^-6K^-1.

Synthesis kinetics and thermophysical properties of La_2(Zr_(0.7)Ce_(0.3))_2O_7 ceramic for thermal barrier coatings

La2（Zr0.7Ce0.3）2O7 （LZ7C3） ceramic was synthesized by solid state reaction with La2O3, ZrO2 and CeO2 as starting materials. The synthesis kinetics, phase structure, mass loss and microstructure were studied by thermo gravimetric-different thermal analyzer （TG-DTA）, X-ray difference （XRD） and scanning electron microscopy （SEM）. The thermal conductivity and thermal expansion coefficient were measured by laser-flash method and pushing-rod method, respectively. XRD results showed that LZ7C3 was a mixture of La2Zr2O7 （LZ, pyro- chlore） and La2Ce2O7 （LC, fluorite）. The lowest synthesis temperature and time of LZ7C3 were 1400 oC and 5 h. There were no peaks of La2O3 when the powder granularity was about 0.82 μm in the synthesis process. The atom ratio La：Zr：Ce of prepared LZ7C3 powder was very close to 10：7：3 which was the theory value of LZ7C3. The thermal conductivity of LZ7C3 decreased gradually with the temperature increased up to 1200 oC, and was located within 0.79 to 1.02 W/（m·K）, which was almost 50% lower than that of LZ, whereas its thermal expansion coefficient was larger and the value was 11.6×10-6 K-1.