窄谱带模型数值研究高温喷流动态红外特性

对高温超声速喷流流场的动态红外辐射特性进行研究.采用窄谱带模型结合光谱数据库及Mie散射理论建立求解非灰吸收、发射、散射性介质红外辐射传输计算模型.数值模拟了某高温喷流2～5μm光谱红外特性,获得了不同飞行高度时高温喷流的红外仿真热像、光谱、波段及总辐射强度仿真数据.比较结果表明:高温喷流在2～5μm光谱呈明显双峰特性;动态飞行时喷流红外光谱选择性是相类似的,光谱总辐射强度随高度增加先增大后减弱;低空时2～3μm波段辐射强度大于4～5μm波段辐射强度,而随着高度的增加,4～5μm波段辐射强度将大于2～3μm波段辐射强度。     

Regulation mechanism of EM parameters in natural ferrite and its application in microwave absorbing materials

1 Introduction Microwave absorbing materials (MAM) refer to a kind of materials that can be used to absorb the emitted electromagnetic (EM) energy and to minimize the wave reflected in the direction of an energy radar receiver. When the EM wave incidents into MAM, it is readily absorbed, attenuated, and changed into heat or other energy. MAM are functional materials that possess special performance for absorbing EM wave. Along with the advancement in radar and microwave technologies, MA…     

Microwave Absorption Properties of the Carbonyl Iron/EPDM Radar Absorbing Materials

Employing carbonyl iron powder and Ethylene-Propylene-Diene Monomer(EPDM)as the absorbent and matrix,rubber radar absorbing materials(RAM)were prepared.Effects of the carbonyl iron volume fraction and the thickness of the RAM on the microwave absorption properties in the frequency range of 2.6-18GHz were studied,and a mathematical analysis was made using the electromagnetic theory. The experimental results indicate that the minimum reflectivity of the radar absorbing materials continuously decreases with the increase of the carbonyl iron volume fraction,and the absorption peak also moves towards the low frequency for the same thickness of the RAM.The minimum reflectivity of the 3.0 mm RAM is -21.7dB at 3.5 GHz when the volume fraction of carbonyl iron is 45%.The reflectivity of the RAM is not in direct proportional to the thickness of the RAM,when the RAM has the same volume fraction of the carbonyl iron.The reflectivity of the RAM presents a regular trend at a given carbonyl iron volume fraction in the frequency range of 2.6-18 GHz.With the increase of the thickness,the maximum absorption peak moves towards low frequency band,the minimum reflectivity firstly decreases and then increases,and the absorption bandwidth for reflectivity<-10 dB firstly increases and then decreases.The microwave absorption properties of the RAM are determined by the thickness and the composition of the radar absorbing materials. Theoretical analysis indicates that the reflectivity of the RAM is determined by the matching degree of the air’s characteristic impedance and the input impedance.     

Biocompatibility of implantable electrodes coated with PVA films in the brain of rats: a histological evaluation

The biocompatibility of silicone rubber (SR) based electrodes coating with poly (vinyl alcohol) (PVA) films after implanted in the brain of rats was investigated. Twenty-two Wistar rats were used and implanted with SR electrodes and PVA/PAA films coated electrodes in left and right cerebral cortex respectively. After 4 and 8 weeks, the expression of glial fibrillary acidic protein (GFAP, a specific marker of astrocytes) and cluster of differentiation 68 (CD68, a specific marker of macrophages) were evaluated by immunohistochemistry. After 8 weeks, GFAP and CD68 expressions around PVA electrodes were significantly lower than those around SR electrodes in every stratified area (0–50 μm, 50–100 μm, 100 μm from further up to the electrode-tissue interface). The results show that PVA coating can reduce the expressions of GFAP and CD68, suggesting the PVA coating can improve the biocompatibility of the SR while it is implanted in brain. Funded by the “863” Program of China (No.2006AA02Z4E6) and the National Nature Science Foundation of China (No.30570516)     

Fabrication of Porous Scaffolds Using NaHCO3 Particulates as the Porogen Material

A new method of fabricating porous polymer scaffolds was developed, using sodium hydrogen carbonate particulates as the porogen to foam. The pore structure of polymer scaffolds can easily be manipulated by controlling the size and weight fraction of sodium hydrogen carbonate particulates. The scaffolds are highly porous with a porosity greater than 90% and with a larger pore size ranging from 100-400μm, and are well distributed with the interconnected and open pore wall structure which is necessary for tissue engineering. We investigated the effect of the porosity of scaffolds, the pore size of scaffolds and material of polymer on the mechanical properties of scaffolds. The scaffolds fabricated by the method have more big pores than those by the convenient method of salt leaching.     

The formation mechanism and control methods of high temperature infrared radiant coating defects

Using high aluminum refractory material as substrate at 1400℃, we studied the connections between several oxides such as Fe203, MnOv CuO, and the formation of defects such as coating crack, exfoliation, blistering, erosion, and fading away appeared in the application of high temperature infrared radiation coating. Analyses showed that thermal stress formed during the heating process due to the thermal expansion coefficient differential between the coating and the substrate, and volume effect caused by the crystal transferred when the temperature changed, which resulted in the coating crack and exfoliation. The gas produced by the reactions between components and binder or the components themselves during the heating process caused the coating blistering. The EMPA and XRD analyses show that oxides with low melting point in the penetrating area of the substrate may form eutectic with low melting point and produced thermal defects, which leads to the erosion by penetrating to the substrate. The valent changes of Fe2O3 and MnO2 during the heating process cause the volatilization of the oxides or the pulverization of the coatings, resulting in the coating fades away easily at high temperature for a long time.     

Cerium chemical conversion coating on a novel Mg-Li alloy

A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investigated. The influential factors of cerium conversion coating were discussed through orthogonal experiments, and the optimum processing parameters were confirmed. XPS spectra displayed that the conversion coating consisted of cerium compounds, and the major component of the protective layer was a mixture of Ce (IV) oxide and Ce (IV) hydroxide. In addition, XRD pattern illustrated that there was crystalline CeO₂ in the conversion coating. Analysis by SEM showed that the cerium conversion coating was uniform with a fiber-like morphology. The thickness of the conversion coating was 12 μm. The results of electrochemical potentiodynamic polarization and hydrogen evolution measurement indicated that the cerium conversion coating provided effective protection to the novel Mg-Li alloy.     

Research on the preparation of amorphous diamond nanorod arrays and their excellent field emitting properties

During recent years, with the rapid development of IT and micro-electrics, the ultra- thin, ultra-large display screen with low power consumption, has attracted more and more attention. As the core of devices, cathode materials are made much more demands in the vacuum microelectronic technology. So the materials with low power consumption, outstanding field emission properties and extreme stability are very important. To resolve the problem, many researchers have been making efforts. Diamonds…     

Microwave Permeability Change of FeCo Nanocrystalline During High Energy Ball Milling

The microwave magnetic properties of the ball milled FeCo panicles were investigated as functions of ball milling time （ t ） using microwave electromagnetic parameters analysis techniques. The results show that the imaginary part of intrinsic dynamic permeability （ ui ） of the ball- milled panicles is much bigger than that of raw powders. ui strongly depends on t and exhibits several slightly damped ferromagnetic resonances. These phenomena are in qualitative agreement with the formation of the corresponding microstructure or the Aharoni ＇ s model of non-uniform exchange resonance modes. The present microwave permeabilhy behavior indicates that nanocrystalline materials with the same grain size may exhibit different properties that depend upon the microstructure, which provides a possibility for manufacturing high performance microwave absorber.     

Improved visible transparency of SIO<Subscript>2</Subscript>/ZNO:AL /CEO<Subscript>2</Subscript>-TIO<Subscript>2</Subscript>/SIO<Subscript>2</Subscript> multilayer films with high UV absorption and infrared reflection rate

New visible transparent, UV absorption, and high infrared reflection properties have been realized by depositing multilayer SiO₂/ZnO: Al/CeO₂-TiO₂/SiO₂ films onto glass substrates at low temperature by radio frequency magnetron sputtering. Optimum thickness of SiO₂, ZnO: Al (ZAO) and CeO₂-TiO₂ (CTO) films were designed with the aid of thin film design software. The degree of antireflection can be controlled by adjusting the thickness and refractive index. The outer SiO₂ film can diminish the interference coloring and increase the transparency; the inner SiO₂ film improves the adhesion of the coating on the glass substrate and prevents Ca²⁺, Na⁺ in the glass substrate from entering the ZAO film. The average transmittance in the visible light range increases by nearly 18%-20%, as compared to double layer ZAO/CTO films. And the films display high infrared reflection rate of above 75% in the wavelength range of 10-25 μm and good UV absorption (> 98%) properties. These systems are easy to produce on a large scale at low cost and exhibit high mechanical and chemical durability. The triple functional films with high UV absorption, antireflective and high infrared reflection rate will adapt to application in flat panel display and architectural coating glass, automotive glass, with diminishing light pollution as well as decreasing eye fatigue and increasing comfort.     

Mierostrueture and Properties of Coating from Cemented Carbide on Surface of H13 Steel

The microstructures and properties of coating from cemented carbide on the substrate of H 13 by vacuum powder sintering were studied. The effect of sintering temperature on the microstructures of coating was discussed. The interface characteristics between coating and H 13 steel substrate, microhardness distribution and wear resistance in the coating were analyzed. The coating from cemented carbide with thickness of 1-3 mm by vacuum powder sintering at temperature ranging from 1280℃to 1300 ℃ was obtained. The experimental results indicated that the coating with microhardness of HV 1600 favorable to wear resistance is strongly bonded with the H 13 steel substrate by mutual diffusion and penetration of Fe,Cr, Mo,V in substrate towards the coating and W, Co,Ni in coating towards the substrate.     

<Emphasis Type="Italic">In-situ</Emphasis> synthesis and characteristics of TiC−Fe cermet graded composite coating on a steel substrate

By means of an inherent elevated-temperature of poured liquid steel, a Ti-C-30 wt% Fe preform, which was pre-placed in a mould cavity, was directly ignited and a combustion synthesis reaction took place. As a result, a TiC−Fe cermet coating with a thickness of about 10 mm was simutaneously synthesized on the solidified steel matrix. The synthesized coating exhibits a feature of graded composite structure, in which both the amount and size of TiC particles decrease gradually with an increasing distance from the furface of the coating. Moreover, by a proper casting technique, the pores formed during the combustion synthesis of the preform could be centrally distributed in 2–3 mm in outer layer of the coating. When this outer porous layer was worn off, the rest coating with a thickness of about 8 mm possesses a dense structure and a high abrasive wear resistance. YAN You-wei Born in 1965 Financially supported by the National Natural Science Foundation of China (No. 50276023)     

纳米ZnO的光吸收特性研究

用沉淀法制备了纳米ZnO,通过反应条件和工艺参数的控制得到了几种不同粒径分布范围的纳米级ZnO粉体,用AFM和XRD方法对纳米ZnO样品进行了表征,并着重研究了这些不同粒径分布的粉体在红外、紫外-可见光波段的吸收性能,且与普通ZnO进行了对比.结果表明:纳米ZnO在紫外有强的宽带吸收,对紫外光的吸收能力远远强于普通ZnO,且随着波长的减小,吸收峰不断增大,随着纳米ZnO粒径的减小,其吸收带边向短波方向移动产生蓝移现象;在可见光区,纳米ZnO比普通ZnO对可见光的吸收较弱,有很好的透过率;红外吸收能力随着纳米ZnO粒径的减少而增强,同时红外吸收出现红移和宽化现象.     

Analyses of Microarc Oxidation Coating Formed on AZ91D Alloy in Phosphate Electrolytes

This paper studied the appearance transition of microdischarges, the phase composition and the morphology evolution of the oxide film formed by microarc oxidation on AZ91D magnesium alloy. The appearance of microdischarges population experienced apparent changes in size, spatial density and color, which was related with the changes of the type and quantity of the disintegrated gas bubbles generated at the interface between the electrolyte and substrate. Correspondingly, the diameter of micropores together with net-like fine microcracks increased when a higher voltage was employed. The coating was composed of MgO, MgAl2O4 and there existed a fluoride-enriched zone of about 3-5μm at the film/substrate interface.     

Thermodynamic analysis of the preparation process of EB-PVD SiC coating

The process of preparing SiC coating by electron beam-physical vapor deposition (EB-PVD) was discussed from viewpoint of thermodynamis. Results show that within the temperature range of 2 700–3 300 K, the ratio of SiC in the SiC coating doesn’t change much and keeps around 0.7. Purity of the as-deposited SiC coating is not high. To improve the purity of the SiC coating, the SiC ingot is required to not be, necessary in full density but be fine-grained.     

绿色太阳光谱反射涂层的性能研究

研究了具有重要实用价值的绿色太阳光谱反射涂层的近红外反射率,探讨了影响涂层反射性能的因素．通过采用新型颜料体系,优化配方组成,并对有关填料进行了特殊处理,提高了有效反射成分在体系中的含量,研制出了近红外反射率达78．7％的军用绿色太阳光谱反射涂层,并对其性能进行了研究．结果表明,其近红外反射,陛能比目前国内外同类型材料有较大幅度上升,拓展了其应用领域。     

Multi-channel micro neural probe fabricated with SOI

Silicon-on-insulator(SOI) substrate is widely used in micro-electro-mechanical systems(MEMS).With the buried oxide layer of SOI acting as an etching stop,silicon based micro neural probe can be fabri-cated with improved uniformity and manufacturability.A seven-record-site neural probe was formed by inductive-coupled plasma(ICP) dry etching of an SOI substrate.The thickness of the probe is 15 μm.The shaft of the probe has dimensions of 3 mm×100 μm×15 μm with typical area of the record site of 78.5 μm2.The im...     

Characteristics of radiation and convection heat transfer in indirect near-infrared-ray heating chamber

Numerical study was performed to evaluate the characteristics of combined heat transfer of radiation,conduction and convection in indirect near infrared ray (NIR) heating chamber.The effects of important design parameters such as the shape of heat absorbing cylinder and heat releasing fin on the pressure drop and heat transfer coefficient were analyzed with different Reynolds numbers.The Reynolds numbers were varied from 103 to 3×106,which was defined based on the hydraulic diameter of the heat absorbing cy...     

Structure and Infrared Radiation Properties of Substituted Cordierites

Zn^2＋ - or Ti^4＋ -substituted cordierites with the nominal compositions of Mg1 .6 Zn0.4 Al4 Si5 O18 and Mg1.8 Ti0.2 Al4.4 Si4.6 O18 respectively, were prepared by a conventional solid state reaction method. The structure of the substituted eordierites was characterized by X- ray diffraction （ XRD ）, infrared （ 1R ） spectroscopy and 29 Si magic angle spinning （ MAS ） nuclear magnetic resonance （ NMR ）. The infoared radiation properties were investigated in the bands within 2.5-25μm. Compared with the na-substituted cordierite composition （ Mg2 Al4 Si5 O18 ）, Zn^2＋ - or Ti^4＋ -substituted cordierites show superior infrared properties. XRD and IR results confirm the formation of hexagonal a-eordierite as the main eo＇stal phase for the substituted cordierites. 29 Si MAS NMR result indicates that Zn^2＋ or Ti^4＋ Substitutions for partial Mg^2＋ of a-eordierite promoted the ordering of the distribution oral and Si atoms in T1 （ tetrahedra connecting six-raembered rings together with [ MgO6] octahedra ） and T2 （ tetraheda forming six-reentered rings） tetrahedral sites. This resulted in a lattice deformation and increased the anharmonicity of polarization vibration, which is responsible for the improvement of infrared radiation properties of the substituted eordierites.     

Synthesis and Performance of Transparent Casting Polyurethane Resin

A series of transparent casting polyurethane resins (TCPU) were synthesized from cycloaliphatic diisocyaruae ( 1PDI or H12 MDI) , polyol, chain extender, crosslinking agents, catalyst and special aids (T),which were characterized by FTIR. The thermal stabilities of the obtained TCPU were examined by DSC and TGA , the glass transition temperature ( Tg ) was in the range of 95- 110 ℃ , the initial decomposition temperature (5% weight loss) was 250-265 ℃, and 10% weight loss at the temperature was in the range of 260-286℃ in nitrogen atmosphere. The morphologies of the fractured surfaces of TCPU were revealed by a scanning electron microscope (SEM). The crystalline-amorphous characters of TCPU were studied by WAXD, the result shows that TCPU possesses amorphous glassy characters. The optical properties of TCPU were studied by a UV7500 visible light absorbance measurement. All the samples exhibited excellent optical properties and possessed light transmittarwe in the range of 91%-93% .