Synthesis and surface characterization of alumina-silica-zirconia nanocomposite ceramic fibres on aluminium at room temperature

Alumina-silica-zirconia nanocomposite (ASZNC) ceramic fibres were synthesized by conventional anodization route. Scanning Electron Microscopy (SEM), Atomic Force microscopy (AFM), X-Ray Diffraction (XRD) and Energy Dispersive X-Ray spectroscopy (EDAX) were used to characterize the morphology and crystalloid structure of ASZNC fibres. Current density (DC) is one of the important parameters to get the alumina-silica-zirconia nanocomposite (ASZNC) ceramic fibres by this route. Annealing of the films exhibited a drastic change in the properties due to improved crystallinity. The root mean square roughness of the sample observed from atomic force microscopic analysis is about 71.5 nm which is comparable to the average grain size of the coatings which is about 72 nm obtained from X-Ray diffraction. The results indicate that, the ASZNC fibres are arranged well in the nanostructure. The thickness of the coating increased with the anodizing time, but the coatings turned rougher and more porous. At the initial stage the growth of ceramic coating increases inwards to the metal substrate and outwards to the coating surface simultaneously. Subsequently, it mainly grows towards the metal substrate and the density of the ceramic coating increases gradually, which results in the decrease of the total thickness as anodizing time increases. This new approach of preparing ASZNC ceramic fibres may be important in applications ranging from gas sensors to various engineering materials.     

Indentation studies of alkali halides at elevated temperatures

The hardness of NaCl and KCl crystals has been estimated from the lengths of dislocation rosette formed around indentation at various temperatures up to 400°C. The hardness decreases with increasing temperature. This is due to the softening of the crystals at elevated temperatures which results in the easy movement of dislocations. The results are discussed using a few available relations which connect hardness to temperature. Arms of indentation dislocation rosette are well defined up to 300°C but around 400°C the rosette pattern is spread over a circular region. A possible mechanism is discussed.     

Ultrasonic characterization of a fluid layer using a broadband transducer

A measurement method is proposed for the ultrasonic characterization of a fluid layer, corresponding to the resin transfer molding (RTM) manufacturing process. The ultrasonic velocity and attenuation of the silicone oil are measured in three samples having different viscosities. The measurement method is established on the basis of the attenuation of ultrasonic waves in fluids. A correction of the beam diffraction is implemented to improve measurement precision. A single element transducer with central frequency of 15 MHz is used. The tested fluids simulate the industrial resin used to manufacture composite materials. When injecting this resin, its viscosity increases until it reaches a critical state of polymerization. In this paper we focus on ultrasonic characterization of three fluids representing three intermediate cases of fluid resin during its injection before reaching the polymerization state.     

激光超声的原理及其在固体中的应用

激光超声是指脉冲激光所产生的脉冲超声。激光超声是较新的产生超声的方法。它的主要特色是，可以遥发遥收，这样就有可能在高温、有危险辐射等恶劣环境下以及在样品运动的生产线上进行超声检测。皮秒级和飞秒级的激光所激发的超声近来又用来研究固体中电子和声子的相互作用。文章介绍了固体中激光超声的声学性能及两种产生机理：热弹机理和电子机理。     

Electroless coating of copper on ceramic in an ultrasonic field

The effect of ultrasonic irradiation on electroless copper coating on ceramic in a copper sulphate-potassium sodium tartrate-formaldehyde system was studied in terms of temperature, coating solution composition, acoustic power, frequency and irradiation time with an orthogonal design method in mathematical statistics. Sonication can produce a more uniform and well bonded coating with a faster coating rate compared with a control process. The mechanism of the coating rate increase under sonication is discussed.     

Static and cyclic mechanical behaviours and fracture mechanisms of Zr-based metallic glass at elevated temperatures

To comprehensively understand the quantitative mechanical–thermal properties and fracture mechanisms of Zr-based bulk metallic glass (BMG), by using self-made miniature tensile/compressive device and motor-piezoelectric coupling driven fatigue device, a series of static and dynamic mechanical tests at elevated temperatures of bulk Zr₅₅Cu₃₀Al₁₀Ni₅ BMG with glass transition temperature T_g of 411°C were carried out. Uniaxial tensile and compressive behaviours at temperatures with range from RT to 400°C were experimentally obtained by means of digital speckle correlation analysis, the estimation of Young’s modulus and fracture strengths as a function of the applied temperatures were investigated. The static and cyclic fracture morphologies at various temperatures were obtained to describe the mechanical–thermal fracture mechanisms in detail. The coupling effect of loading types, stress-induced temperature rise and applied temperature on the evolution of cleavage features, dimples, vein patterns and shear softening behaviours were investigated.     

Measurement of the bulk acoustic properties of fibrous materials at high temperatures

It is common for fibrous porous materials to be used in high temperature applications such as automotive and gas turbine exhaust silencers. Understanding the effect of temperature on the acoustic properties of these materials is crucial when attempting to predict silencer performance. This requires knowledge of the bulk acoustic properties of the porous materials and so this article aims to quantify the effect of temperature on the bulk acoustic properties of three fibrous materials: rock wool, basalt wool and an E-glass fibre. Measurements are undertaken here using a standard impedance tube that has been modified to accommodate temperatures of up to 500 °C. It is shown that measured data for the bulk acoustic properties may be collapsed using a standard Delany and Bazley curve fitting methodology provided one modifies the properties of the material flow resistivity and air to account for a change in temperature. Moreover, by using a previously proposed power law describing the dependence of the flow resistivity with temperature, one may successfully collapse data measured at every temperature and obtain the Delany and Bazley coefficients in the usual way. Accordingly, to predict the bulk acoustic properties of a fibrous material at elevated temperatures it is necessary only to measure these properties at room temperature, and then to apply the appropriate temperature corrections to the properties of the material flow resistivity and air when using the Delany and Bazley formulae.     

不同温度条件下单层石墨烯纳米带弛豫性能的分子动力学研究

分别采用Tersoff-Brenner势和AIREBO势,对三种长宽比的单层石墨烯纳米带在不同热力学温度(0.01—4000 K)下的弛豫性能进行了分子动力学模拟.对基于两种势函数模拟的石墨烯纳米带弛豫的能量曲线和表面形貌进行了分析对比,研究了石墨烯纳米带在弛豫过程中的动态平衡过程.模拟结果表明:单层石墨烯纳米带并非完美的平面结构,边缘处和内部都会呈现一定程度的起伏和皱褶,这与已有的实验结果相符合;石墨烯纳米带的表面起伏程度随长宽比的减小而减小,并且在不同温度条件下,系统动能对石墨烯纳米带的弛豫变形的影响很大,即系统温度越高,石墨烯纳米带的弛豫变形幅度愈大;高长宽比纳米带在一定温度条件下甚至会出现卷曲现象.最后,对采用Tersoff-Brenner势和AIREBO势进行石墨烯的分子动力学模拟进行了深入分析.     

Development and application of ferrite materials for low temperature co-fired ceramic technology

Development and application of ferrite materials for low temperature co-fired ceramic(LTCC)technology are discussed,specifically addressing several typical ferrite materials such as M-type barium ferrite,NiCuZn ferrite,YIG ferrite,and lithium ferrite.In order to permit co-firing with a silver internal electrode in LTCC process,the sintering temperature of ferrite materials should be less than 950°C.These ferrite materials are research focuses and are applied in many ways in electronics.     

Infrared-optical characteristics of ceramics at elevated temperatures

In this work the infrared-optical properties of ceramic samples at ambient and elevated temperatures are presented. The aim of this work is the determination and interpretation of the spectral transmittance, reflectance and emittance of three oxide ceramic samples (MgO, Al₂O₃/ZrO₂, TiO₂/Y₂O₃) and one carbide ceramic sample (SiC) as a function of the temperature from 300 K up to 1100 K. The semi-transparency of the ceramics in the near infrared region has to be considered when performing the measurements and evaluating the data.The experimentally derived spectra are compared with the values derived from theoretical calculations. The complex dielectric function of a ceramic can be deduced from the Lorentz oscillator model. The complex refractive index is correlated with the complex dielectric function by the Maxwell relation. Scattering effects can be described by radiative transfer models. Finally the infrared-optical properties transmittance, reflectance and emittance depend on the complex refractive index and the morphology of the ceramic sample.Of special interest is the Christiansen wavelength as well as the location of the free running frequencies of the longitudinal and transversal optical oscillations. Usually the ceramic is highly reflecting between the free running frequencies of the longitudinal and transversal optical oscillations whereas at the Christiansen wavelength the reflectance vanishes which leads to an emittance of one for an optically thick sample at the Christiansen wavelength. Due to the known emittance it is possible to use the Christiansen wavelength for determining the temperature of the investigated sample.Finally the obtained infrared-optical spectra are presented and their temperature dependencies are discussed which are mainly due to phonon excitations. Additionally it has been shown that for example the location of the Christiansen wavelength can be influenced by varying the composition of the ceramic.     

Difference of optical properties between porous alumina and sapphire using two-substrate method at elevated temperature

We report on simultaneous measurements of the emittance, transmittance and reflectance of a porous alumina under same environment at 573 K, which has not been obtained. It is demonstrated that the correction of substrate radiation and multiple reflections is important for the accurate measurement of infrared (IR) optical properties of porous materials in a two-substrate method. We deduced the extinction, absorption and scattering coefficients of the alumina from the measured three quantities, based on the classical geometry model. The coefficients explain the difference of the IR optical properties between the alumina and the sapphire. The increasing reflectance of the alumina with thickness, unlike the sapphire, is attributed to the relatively high scattering coefficient at short wavelengths.     

Fluorescence spectroscopy of anisole at elevated temperatures and pressures

Laser-induced fluorescence of anisole as tracer of isooctane at an excitation wavelength of 266 nm was investigated for conditions relevant to rapid compression machine studies and for more general application of internal combustion engines regarding temperature, pressure, and ambient gas composition. An optically accessible high pressure and high temperature chamber was operated by using different ambient gases (Ar, N₂, CO₂, air, and gas mixtures). Fluorescence experiments were investigated at a large range of pressure and temperature (0.2–4 MPa and 473–823 K). Anisole fluorescence quantum yield decreases strongly with temperature for every considered ambient gas, due to efficient radiative mechanisms of intersystem crossing. Concerning the pressure effect, the fluorescence signal decreases with increasing pressure, because increasing the collisional rate leads to more important non-radiative collisional relaxation. The quenching effect is strongly efficient in oxygen, with a fluorescence evolution described by Stern–Volmer relation. The dependence of anisole fluorescence versus thermodynamic parameters suggests the use of this tracer for temperature imaging in specific conditions detailed in this paper. The calibration procedure for temperature measurements is established for the single-excitation wavelength and two-color detection technique.     

Autoignition of surrogate fuels at elevated temperatures and pressures

Autoignition of Jet-A and mixtures of benzene, hexane, and decane in air has been studied using a heated shock tube at mean post-shock pressures of 8.5 ± 1 atm within the temperature range of 1000–1700 K with the objective of identifying surrogate fuels for aviation kerosene. The influence of each component on ignition delay time and on critical conditions required for strong ignition of the mixture has been deduced from experimental observations. Correlation equation for Jet-A ignition times has been derived from the measurements. It is found that within the scatter of experimental data dilution of n-decane with benzene and n-hexane leads to slight increase in ignition times at low temperatures and does not change critical temperatures required for direct initiation of detonations in comparison with pure n-decane/air mixtures. Ignition times in 20% hexane/80% decane (HD), 20% benzene/80% decane (BD) and 18.2% benzene/9.1% hexane/72.7% decane (BHD) mixtures at temperature range of T  1450–1750 K correlate well with induction time of Jet-A fuel suggesting that these mixtures could serve as surrogates for aviation kerosene. At the same time, HD, BD and BHD surrogate fuels demonstrate a stronger autoignition and peak velocities of reflected shock front in comparison with Jet-A and n-decane/air mixtures.     

Ultrasonic spectrum characterization of pig''''s pathological liver tissues

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Fibre-matrix interphases and interfaces in ceramic matrix composites processed by CVI

The fibre-matrix (FM) interfacial zone plays a key role in the mechanical behaviour of Si-C(O)/SiC inverse composites fabricated by chemical vapour infiltration (CVI) from ex-polycarbosilane Si-C(O) fibres precoated with pyrocarbon or boron nitride. It consists not only of the C (or BN) main interphase, but also of very thin secondary interphases (i.e. carbon and silica) resulting from the decomposition of the metastable Si-C(O) fibres thought to occur during the fabrication of the fibres and/or the composites. The FM interfacial zone may play two complementary roles: (i) it provides low-energy microcrack propagation paths parallel to the fibre axis, and (ii) it may act as a compliant buffer for the relaxation of the residual thermal compression stresses on the interface. The FM bond strength is low or moderate when a quasi-continuous thin layer of anisotropic carbon is present between the fibre and the main interphase and when the fibre surface remains smooth. The mechanical behaviour in tension is non-brittle with a wide non-linear stress-strain domain when the FM bonding is low or moderate, and tends to become brittle when the bonding is too strong. Finally, the thickness (and presumably the microtexture) of the carbon main interphase plays an important role in the oxidation resistance of the material, a self-healing behaviour being observed at high temperatures with a thin interphase. Replacing carbon by BN and adding an external coating of SiC (or Si₃N₄) to the composite improves its oxidation resistance.     

Oxygen quenching of toluene fluorescence at elevated temperatures

Gas-phase oxygen quenching of toluene laser-induced fluorescence (LIF) is studied between 300 and 650 K in a nitrogen/oxygen bath gas of 1-bar total pressure with oxygen partial pressures up to 400 mbar. With increasing vibrational excitation of the laser-excited toluene, intramolecular decay becomes faster, resulting in a decreasing relative strength of collisional quenching by oxygen. Additionally, Stern–Volmer plots are found to be non-linear for temperatures above 500 K in the case of 266-nm excitation and at all temperatures for 248-nm excitation. This is attributed to the onset of internal conversion from specific vibrational levels. A photophysical model is developed that describes the experimental data and predicts toluene LIF signal strengths for higher oxygen partial pressures. One important result for practical application is that oxygen quenching is not the dominant de-excitation process for engine-related temperature and pressure conditions, and thus application of the popular fuel–air ratio LIF (FARLIF) concept leads to erroneous signal interpretation.This revised version was published online in August 2005 with a corrected cover date.     

流体-镀层基底界面波的传播特性

理论分析了脉冲激光激发的流体-分层固体结构声场,在此基础上数值计算了流体-慢层快底固体和流体-快层慢底固体结构液-固界面Scholte波的频散特性与瞬态响应.数值结果显示,对于流体-慢层快底结构,Scholte界面波呈现出正常频散特性;而对于流体-快层慢底结构,Scholte波在较小的频厚积范围呈反常频散特性.理论瞬态信号也显示了同样的特性.采用脉冲激光激励,用水听器接收的方式进行了Scholte界面波的实验测量.实验测量和分析结果与理论结果有很好的一致性.此工作可为水浸检测条件下镀层与薄膜材料参数的超声无损表征、海底沉积物参数反演等应用提供理论基础.     

Ultrasonic velocity of binary systems at elevated pressures

Various empirical theories of ultrasonic velocity have been applied to three binary liquid mixtures, under pressures up to 200 MPa and their validity have been tested. A pressure dependent study of ultrasonic velocities has been made at 303.15 K. The agreement between theory and experiment is found to be quite satisfactory.     

X-ray characterization and phase transformation kinetics of ball-mill prepared nanocrystalline Mg–Zn-ferrite at elevated temperatures

Nanocrystalline Mg–Zn-ferrite is prepared by ball milling the stoichiometric powder mixture of MgO, ZnO and α-Fe₂O₃. A non-stoichiometric ferrite phase is noticed to form after 3 h of milling when particles of starting materials became nano-sized. After 25 h of milling, stoichiometric ferrite phase is formed with 9 nm particle size. Post annealing study of ball-milled sample reveals that the nanocrystalline ferrite phase is stable up to 873 K and then starts to decompose into individual starting phases. However, heat treatment of unmilled stoichiometric powder mixture even at 1473 K for 1 h duration does not result in formation of stoichiometric Mg–Zn-ferrite phase.     

Detection of necking deformation along polypropylene fibres axis at low draw ratios using multiple-beam microinterferometry

A modified drawing device attached with an automated system for producing multiple-beam Fizeau fringes in transmission is used to study the mechanical deformation along polypropylene (PP) fibres at low draw ratios. Two drawing processes are used for drawing PP fibres. In the first process (fast drawing), the necking deformations are formed at draw ratios from 1.2 to 1.9 along the fibre axis. While in the other process (slow/step drawing), these deformations disappeared. The refractive indices calculated at different positions along the fibre axis during the fast- and slow-drawing processes. To overcome the formation of necking deformation along the PP fibres during fast-drawing process, the slow-drawing technique is recommended. Microinterferograms are given for illustration.