Towards 3D photonic crystals

Synthesis of artificial opals with the structural and optical properties of three-dimensional (3D) photonic crystals has been carried out. We describe the stages of the uniform silica globules preparation by the multistage build-up method, their packing in the 3D lattice by centrifugation, and their sintering. The correlation between technological parameters used and structural and optical properties of the fabricated opals with the photonic band gap maximum range from 475 to 650 nm is discussed.     

Optical properties of bare,sintered and coated opal-based photonic crystals

The transmission properties of close-packed opal-based photonic crystals with a SiO₂ (n=1.5) matrix have been examined using the transfer matrix method. The response for bare, sintered and coated opals at the X- and L-points has been studied, which corresponds to plane waves normally incident onto the (1 0 0) and (1 1 1) crystal planes. The incomplete gap at the L-point fully inhibits the transmission of waves propagating in the [1 1 1] direction for opal sample thickness of around 20 layers. This property shows that bare opals could be good candidates for complete inhibition of transmission in the near-infrared and visible frequency range for specific orientation.     

Microstructural study of CdS/opal composites

CdS/opal photonic materials have been characterised by transmission electron microscopy. The photonic properties of opals formed by SiO₂ nanospheres 380 nm in diameter, face-centred cubic ordered and with different CdS filling factors were studied by means of specular reflectance or transmission spectroscopy. It is shown that CdS semiconductor grows homogeneously in the opal interstices, in a cubic phase, with 24 nm being the microcrystal particle size. We show here that chemical bath deposition (CBD) is a useful method to fill the opal interstices, a crucial step for producing photonic band gap materials.     

光致变色染料螺(口恶)嗪对光子晶体能带结构的调节

利用垂直沉积法获得了聚苯乙烯(Polystyrene,PS)蛋白石模板,采用垂直提拉法将SiO2溶胶填充到PS蛋白石模板,制备出SiO2反蛋白石模板,并利用扫描电镜对蛋白石及反蛋白石的微观形貌进行表征.制备了一种光致变色染料渗透入光子晶体结构空隙的复合材料,该结构表现出截然不同于未填充染料时的蛋白石结构的光学性质.通过利用分子聚集体中的协同激励效应带来的折射率的剧变来实现光子晶体能带结构的控制.     

Morphology and optical properties of bare and polydiacetylenes-infiltrated opals

Polystyrene artificial opals have been grown by slow gravity sedimentation from aqueous suspension of monodisperse nano-spheres of different diameters. These opals have been infiltrated with diacetylenic monomers, which have been subsequently polymerized. The morphology of the surface has been characterized by atomic force and scanning electron microscopies. In addition, a careful micro-optical characterization of these samples has been performed. The photonic band structure of the opals was derived from variable-angle micro-reflectance measurements and favorably compared with that theoretically calculated.     

Dispersion and negative refraction in photonic crystals without negative index

It is reported that certain photonic crystals posses negative refraction without relying on negative index. The findings show that both the intrinsic permittivity ?(f) and μ(f) must be strongly dispersive and having negative values over a limited frequency range. To meet that requirement, the band structure of the photonic crystal is performed. The photonic crystal consists of dielectric cylinders with metallic cores of ?(f) and μ(f) and a varying radius. The outer cylinders coated with a dielectric of radius 0.45a. The expanded plane wave method is developed and used to determine the band structure.     

燃料类型及喷涂参数对HVOF喷涂WC10Co4Cr涂层的组织及力学性能的影响

超音速火焰喷涂（HVOF）制备的WC基金属陶瓷涂层广泛应用于金属构件的磨损、腐蚀及空蚀防护。分别采用氢气燃料及煤油液体燃料HVOF喷涂设备分别在9种不同的工艺条件下制备了WC10Co4Cr涂层,研究了燃料类型对涂层的组织、残余应力及力学性能的影响规律。在两种燃料HVOF工艺各自优化的喷涂参数条件下,通过对基体曲率的原位监测对比测试了涂层中的平均残余应力;利用显微维氏硬度、压痕法（断裂韧性）和球盘摩擦磨损对比研究了涂层的力学性能。结果表明：液体燃料（LF）HVOF焰流中粒子的温度更低,速度更高。LF-HVOF喷涂的WC10Co4Cr涂层内的残余压应力更高且涂层致密度更高,而气体燃料（GF）HVOF喷涂的WC10Co4Cr涂层内为残余拉应力。LF-HVOF涂层（1280 HV_0.3, 7.3 MPa·m^0.5）比GF-HVOF涂层（1032 HV_0.3, 4.5 MPa·m^0.5）具有更高的硬度和断裂韧性,LF-HVOF涂层的耐磨性约为GF-HVOF涂层的1.7倍。     

等离子原位合成Cr-Al2 O3金属陶瓷涂层的组织与性能

利用等离子激发原位反应在碳钢表面合成了Cr-Al2O3金属陶瓷涂层。借助扫描电镜、电子探针、X射线衍射仪和显微硬度计对涂层的组织、结构和性能进行了测试。结果表明,涂层的主要组成相为Cr和Al2O3;涂层的微观组织形貌是以树枝状Al2O3陶瓷为骨架,金属晶粒Cr分散在Al2O3陶瓷相的周围;涂层的硬度高于基体,硬度可达1630HV;在其它工艺参数不变的条件下,电流越大,涂层越厚;利用等离子原位合成技术处理的抽油泵管,其使用寿命分别高于未处理、激光淬火及电镀处理的管道。     

Effect of Fe–Mo–Cr pre-alloyed powder on the microstructure and mechanical properties of TiC–high-Mn-steel cermet

In the study, a TiC–high-Mn-steel cermet is fabricated using FeMo and Fe–Mo–Cr pre-alloyed powders as metallic binders by powder metallurgy techniques. The effect of Cr on the microstructure and mechanical properties of the cermet is studied and the cermet preparation process is optimized. The microstructure and fracture morphology of the cermets are observed with scanning electron microscopy, while phase identification and analysis are performed by X-ray diffractometry. The results show that the particles of Cr-free cermet are angular and polygonal, while those of cermet with added Cr are rounded and ellipsoidal. The grains of Cr-free cermet are larger than those of the Cr-added cermet, which is unlike similar conventional cermets. The grain size of the Cr-added cermet increases slightly with increased Cr content. In addition, the relative density of the cermet decreases slightly with increased Cr content. The hardness of cermet is maximized at HRC 64.8 with the Cr content of 1.0 wt%; with further increases in Cr, the hardness decreases gradually. The transverse rupture strength and impact toughness first increase and then decrease with increasing Cr content, reaching the maxima of 2355 MPa and 13.42 J/cm², respectively, at the Cr content of 1.5 wt%. The strength and toughness of the cermet are improved greatly compared to those of conventional similar TiC–high-Mn-steel cermets.     

NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-based cermet inert anodes for aluminum electrolysis

Recent developments in the preparation, sintering process, mechanical properties, and thermal shock resistance of cermet inert anodes for aluminum electrolysis are reviewed in this paper. To obtain the desired technologies of low-temperature activated sintering of cermet inert anodes, the effects of material composition, sintering atmosphere, sintering temperature, and sintering aids on the densifi cation and microstructure of NiFe₂O₄-10NiO- based ceramics and cermets were studied. To obtain the toughening and strengthening technology of the cermet, the effects of material composition including ceramic and metallic phases are discussed. The cermet inert anodes with high density and mechanical properties were prepared through adjustment of material composition and sintering technology and selection of feasible sintering aids.     

Thermal analysis of functionally graded coating AlSi alloy and steel pistons

Functionally graded coatings are coating systems used to increase performances of high temperature components in diesel engines. These coatings consist of a transition from the metallic bond layer to cermet and from cermet to the ceramic layer. In this study, thermal behavior of functional graded coatings on AlSi and steel piston materials was investigated by means of using a commercial code, namely ANSYS. Thermal analyses were employed to deposit metallic, cermet and ceramic powders such as NiCrAl, NiCrAl + MgZrO₃ and MgZrO₃ on the substrate. The numerical results of AlSi and steel pistons are compared with each other. It was shown that the maximum surface temperature of the functional graded coating AlSi alloy and steel pistons was increased by 28% and 17%, respectively.     

高剂量离子辐照效应对CdZnTe:In晶体光电性能的影响

研究了离子辐照效应对CdZnTe（CZT）晶体光电性能的影响。采用Ar离子对改进的垂直布里奇曼法生长的CZT晶体进行辐照，剂量范围为10¹⁴~10¹⁵ cm^-2。红外透过光谱测试结果表明，辐照前晶体样品的高直型光谱转变为辐照后的上升性光谱。辐照诱导产生的高浓度自由载流子引起的光吸收在红外透过光谱的中红外范围内占主导地位。由于离子辐照发生在单侧照射面的近表面区域，辐照后晶体样品的I-V特性曲线变得极不对称。在负偏压的条件下，电流随着电压的增大而急剧增大。霍尔效应测试结果表明，辐照前晶体样品的净载流子浓度约为10⁶ cm^-3，而辐照后的净载流子浓度大幅增加，约为10¹⁶ cm^-3。CZT晶体的导电类型在离子辐照前后并没有发生变化，施主缺陷能级在辐照诱导缺陷中占主导地位。     

金属碳化物涂层的反应熔覆研究进展

反应熔覆制备金属碳化物涂层是在熔覆过程中原位生成碳化物颗粒相,来增强基体表面的耐磨耐蚀性能。综述了反应熔覆制备金属碳化物涂层的材料构成、工艺方法、组织、力学性能及发展方向。     

WC-based composite coatings prepared by the pulsed gas dynamic spraying process: Effect of the feedstock powders

WC-based cermet coatings are typically produced using the HVOF process, due to high particle velocity and the lower heating characteristic of this technique. Despite the effort of optimisation of the coating process, degradation of the feedstock materials such as decarburisation of WC and amorphization of the metallic phase still occurs. It is known that the coating properties do not depend only on the spray process and its parameters, but also on the feedstock powder characteristics such as its chemistry, carbide size, particle morphology and production method. The work presented here is part of a research program aimed at exploring the possible advantages of the Pulsed Gas Dynamic Spray (PGDS) process, as an alternative technique for the preparation WC-based cermet coatings. In this paper, WC-based coatings have been prepared using six different types of cermets powders. In order to study the effects of the feedstock powder on the coatings microstructures and hardness, the selected starting powders differed not only in microstructural features such as size and morphology but also in the chemistry and phases. Using different analysis technique (OM, SEM, XRD, and HV), a detailed comparison of powders and coatings microstructures, phase compositions, and hardness are presented and discussed in detail. It was found that the PGDS process preserves the microstructure of the starting cermet powders in such a way that no significant degradation of the phase composition, even those that show the pre-existence of complex carbides, has been observed. Furthermore, although the same spray parameters were used, the thickness, deposition efficiency, porosity, and micro-cracks within the coatings are different from one type of cermet to another, suggesting that PGDS optimum process parameters are material dependant.     

Influence of Bond Coat on HVOF-Sprayed Gradient Cermet Coating on Copper Alloy

Coatings are required on mold copper plates to prolong their service life through enhanced hardness, wear resistance, and oxidation resistance. In the present study, NiCr-30 wt.%Cr₃C₂ ceramic–metallic (cermet) layers were deposited by high velocity oxy-fuel (HVOF) spraying on different designed bond layers, including electroplated Ni, HVOF-sprayed NiCr, and double-decker Ni-NiCr. Annealing was also conducted on the gradient coating (GC) with NiCr bond layer to improve the wear resistance and adhesion strength. Coating microstructure was investigated by scanning electron microscopy and x-ray diffraction analysis. Mechanical properties including microhardness, wear resistance, and adhesion strength of the different coatings were evaluated systematically. The results show that the types of metallic bond layer and annealing process had a significant impact on the mechanical properties of the GCs. The GCs with electroplated Ni bond layer exhibited the highest adhesion strength (about 70 MPa). However, the GC with HVOF-sprayed NiCr bond layer exhibited better wear resistance. The wear resistance and adhesion strength of the coating with NiCr metallic bond layer were enhanced after annealing.     

Microstructure and Properties of Porous Ni50Cr50-Al2O3 Cermet Support for Solid Oxide Fuel Cells

The microstructure of the cermet support significantly influences the performance of solid oxide fuel cells (SOFCs). The properties required for the support include high electrical conductivity, necessary permeability, good match of thermal expansion with other layers, and high strength. In this study, a flame-sprayed porous Ni50Cr50-Al₂O₃ cermet was designed as the support of SOFCs. The effect of cermet microstructure on its gas permeability, electrical conductivity, thermal expansion coefficient (TEC), and bending strength was investigated. Results show that the gas leakage rate of the cermet increased with the increase of polyester content in the starting powder. The cermet exhibited a thermal expansion coefficient of 11.39 × 10^?6 K^?1 from 25 to 1000 °C. Moreover, the electrical conductivity of the cermet increased significantly and reached 1015 S/cm after sintering at 1000 °C for 15 h. The bending strength of the cermet reached 171 MPa. The cermet stability at high temperatures and SOFCs’ performance are discussed.     

热处理对原位烧结合成Mo_2FeB_2陶瓷组织与性能的影响

用X射线衍射仪、扫描电镜、万能材料试验机研究了真空液相烧结制备的Mo2FeB2金属陶瓷热处理后的组织与性能。结果表明,真空液相烧结Mo2FeB2金属陶瓷主要由Mo2FeB2、MoB2、Fe2B相和铁基粘结相组成,经700～1000℃热处理后,MoB2、Fe2B相逐渐转化为Mo2FeB2相,并且Mo2FeB2晶粒细化,呈规则块状均匀分布在铁基粘结相中。Mo2FeB2金属陶瓷在700～1000℃范围内随热处理温度的升高,弯曲强度、断裂韧性与维氏硬度均增加,当热处理温度为1000℃时,其值分别达到1182.42MPa、13.59MPa·m1/2、9.114GPa,与未处理试样相比,分别增加了5.4%、6.0%、7.0%。     

Early high-temperature oxidation behavior of Ti(C,N)-based cermets with multi-component AlCoCrFeNi high-entropy alloy binder

The early high-temperature oxidation behavior of Ti(C,N)-based cermets with equiatomic AlCoCrFeNi high-entropy alloy binder has been studied, as well as the cermet with Ni/Co binder as a reference. Experiments were performed at the temperature range of 800–1100 °C in static laboratory air. The micro-structural evolution of the multi-layered oxide scales on the cermets was investigated and the effect of binder phase constituent on the oxidation characteristics of Ti(C,N)-based cermets was evaluated. The results demonstrated that the cermet with AlCoCrFeNi multi-element alloy binder possesses superior oxidation resistance, which is greatly better than that of the cermet with Ni/Co metallic binder under the same condition. We suggest that the formation of a continuous and dense external oxide scale can effectively impede the outward diffusion of volatile tungsten oxides and inward oxygen transport, leading to a remarkable improvement of oxidation resistance. In addition, the enhanced oxidation resistance was related to the high Cr and Al concentration in AlCoCrFeNi binder phase that urges the formation of oxide layers with more efficient passivation effect against oxidation.     

Advances in 2D semiconductor photonic crystals

Two-dimensional photonic crystals (PCs) in thin-slab or waveguide structures open new possibilities in optoelectronic devices. We present experiments on a variety of structures and devices, as well as modelling tools, which show that 2D-PCs etched through waveguides supported by substrates are a viable route to high-performance PC-based photonic integrated circuits (PICs).     

铝电解用NiFe2O4-Cu金属陶瓷惰性阳极的制备

以高温固相合成法合成的NiFe2O4陶瓷粉体和金属Cu粉为原料, 采用冷压-烧结法制备了Cu含量在5%～20%之间的NiFe2O4-Cu金属陶瓷惰性阳极, 研究了烧结气氛和烧结温度对其物相组成、微观形貌和基本物理性能的影响. 结果表明 通过控制烧结气氛中氧分压在NiO和Cu2O的离解反应平衡氧分压之间, 可以制备出具有目标物相组成的NiFe2O4-Cu金属陶瓷; 烧结温度和保温时间对所得NiFe2O4-Cu金属陶瓷的相对密度有较大影响; NiFe2O4和Cu之间的不润湿性限制了NiFe2O4-Cu金属陶瓷烧结温度的提高和保温时间的延长, 在保证金属相分布均匀且不溢出的前提下, 所制备的NiFe2O4-Cu金属陶瓷的相对密度较小; 金属相Cu含量越高, NiFe2O4-Cu金属陶瓷最高烧结温度越低、最长保温时间越短, 从而相对密度越低、孔隙率越高; 除了尽量降低金属相含量外, 还可向NiFe2O4-Cu金属陶瓷中添加其他金属如Ni和Co等, 以改善陶瓷相与金属相之间的润湿性, 以提高烧结温度, 进而提高其相对密度和耐腐蚀性能.