多层介质单模光纤传输特性：一种简便有效的数值法

本文提供了多层介质光纤传输特性分析的快速有效的数值法,即对近似的标量边界条件建立矩阵型特征方程,为2×2矩阵运算,这样可节省大量的计算机内存加快运算速度。对弱导光纤计算结果的精度是能满足要求的可靠的。通过大量分析提出了保证低损耗小色散单模光纤优化设计的思路及方法。     

The effect of silane hydrolysis on aluminum oxide dispersion stability in ceramics processing

The controlled hydrolysis of organosilanes has been shown to greatly influence both the surface adsorption of silanes on alumina powder, and the resultant dispersion stability of alumina in organic solvent slurries. Plateau adsorption concentrations from settling experiments show that complete surface coverage for hydrolyzed forms of both n-octyltrimethoxysilane (NOS) and N-2-aminoethyl-3-aminopropyltrimethoxysilane (AAPS) is typically achieved at concentrations of approximately 6 μmol/m². Moreover, the settling densities of dispersions prepared with hydrolyzed silanes are consistently higher than densities achieved with monomeric silanes alone (as seen in case studies involving NOS in toluene, and AAPS in isopropyl alcohol). Similarly, ceramic slips prepared with polystyrene and alumina, or with poly(isobutyl methacrylate) and alumina also lead to ceramic green bodies with increased densities when the slips are prepared with hydrolyzed silanes. In addition, solid state NMR and dynamic mechanical analyses of resultant green bodies reveal that the molecular motional behavior of these polymers is strongly influenced by the presence of hydrolyzed silanes. These results collectively add to a growing body of evidence which supports the idea that not only is hydrolysis required for silanes to produce controllable and predictable effects in many industrial processes, but hydrolysis must be made to occur at the 'right time' within any sequence of steps that define an industrial process. In the case of ceramic slurries, the 'right time' is the period just prior to the mixing of the ceramic slip ingredients.     

Rheological behaviour of concentrated fused silica suspensions in presence of egg white

Abstract

Experiments with highly loaded fused silica slurries indicated a possible role of egg white in modifying interparticle interactions for egg white content in the range of 0·14–8·8 mg egg white/g of silica. Existence of an optimum amount of egg white that resulted in a minimum in slurry viscosity and thixotropy owing to weakened interparticle interaction was shown reproducibly. Turbidity measurements of supernatants from slurries prepared with different egg white amounts confirmed that addition of egg white resulted in enhanced dispersion of silica particles in suspensions. Potentiometric titrations showed that slurries with egg white addition had greater particle surface charge than the slurries without any egg white addition.     

The Oxidation Behavior of Oxide-Dispersed β-NiAl: I. Short-Term Performance at 1200°C

Oxide dispersions were added to -NiAlalloys using a powder-metallurgy technique. During 20,2-hr cycles at 1200°C, scale adhesion of theexternal alpha Al₃O₂ was improvedby the addition of Y₂O₃ and ZrO₂. Relative to an undoped, castNiAl alloy, no improvement was observed forTiO₂ and HfO₂ additions andnegative effects were observed forAl₂O₃ andLa₂O₃ additions. The variouscation additions also had differing effects on the scale morphologyand isothermal growth rates at 1200°C. The effect ofthe dopants added as oxide dispersions was compared tosimilar alloy additions of the dopants to -NiAl.     

Effect of process variables on dispersion and tape casting of nickel manganite based thermal sensors

Abstract

The present study deals with the tape casting of NiMn₂O₄ for the fabrication of chip thermistors. Dispersion behaviour of the negative temperature coefficient (NTC) powder in toluene–ethanol medium was studied by rheological characterisation. The influence of process parameters such as drying conditions, casting speed and blade gap on the properties and quality of green tapes were investigated. A critical cracking thickness was determined and the effect of the solvent rich atmosphere on drying behaviour was analysed by weight loss measurements.     

Application of the theory of linear elastic materials with voids to NDT of interfaces of bilaminates

Non-destructive testing (NDT) of interfaces in composite structural elements is mandatory in several industries. This calls for modeling of composite interfaces incorporating real world conditions of imperfect bonding. Theories of materials that modern continuum mechanics offer can be profitably employed to develop these models. For instance, distributed voids are often present in the adhesive zone of a structural element and these voids may lead to a failure of the element due to the imperfect bond. As the theory of linear elastic materials with voids (LEMV) provides a model for solids with properties akin to viscoelastic materials, it is employed in the present work to represent the thin adhesive viscoelastic layer with its minutes pores spread over the interface region of a symmetric bilaminate. The bilaminate is assumed to be insonified in water and the governing leaky Lamb wave (LLW) frequency equation is derived. The dispersion and attenuation of LLWs in an Al/adhesive/Al bilaminate are graphically-presented for various porosity-coupling parameter values and are compared with those in perfectly-bonded Al plates. The results presented in this paper showing the influence of pore-infested adhesive layer on the early leaky Lamb modes promises to be useful in identifying interfacial porosity.     

Dispersion,rheology and aqueous tape casting of alumina–zirconia composites

Abstract

Alumina and zirconia were dispersed individually in aqueous media using Darvan C as the dispersant and at optimised pH condition. Based on sedimentation, rheology, yield stress, electrodeposition and zeta potential measurements, 2 wt-% of the dispersant and a pH of 10·5 were found to be the optimum condition for the codispersion of alumina and zirconia. Aqueous tape casting slurries with a solid loading of 32 wt-% were prepared under the optimised conditions of dispersion. Alumina–zirconia (50 : 50) composite tapes of 40 μm thickness and 56% green density were obtained.     

Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging Part 1 – Processing parameters,mechanical properties and microstructure

Abstract

A study simulating thin slab continuous casting followed by direct charging into an equalisation furnace has been undertaken based on six low carbon (0·06 wt-%) vanadium microalloyed steels. Mechanical and impact test data showed that properties were similar or better than those obtained from similar microalloyed conventional thick cast as rolled slabs. The dispersion plus dislocation strengthening was estimated to be in the range 80–250 MPa. A detailed TEM/EELS analysis of the dispersion sized sub 15 nm particles showed that in all the steels, they were essentially nitrides with little crystalline carbon detected. In the steels V–Nb, V–Ti and V–Nb–Ti, mixed transition metal nitrides were present. Modelling of equilibrium precipitates in these steels, based on a modified version of ChemSage, predicted that only vanadium rich nitrides would precipitate in austenite but that the C/N ratio would increase through the two phase field and in ferrite. The experimental analytical data clearly point to the thin slab direct charging process, which has substantially higher cooling rates than conventional casting, nucleating non-equilibrium particles in ferrite which are close to stoichiometric nitrides. These did not coarsen during the final stages of processing, but retained their highly stable average size of, ～7 nm resulting in substantial dispersion strengthening. The results are considered in conjunction with pertinent published literature.     

Preparation and water resistance of crosslinked waterborne polyurethaneurea

Abstract

Two series of cross-linked polyurethaneurea (PUU) aqueous dispersions with polyoxypropylene glycerol and pentaerythritol as internal cross-linking agents were prepared and characterised. The results revealed that in comparison with the uncross-linked one, the cross-linked PUU films exhibited excellent waterproof performance and mechanical properties. The amount of water absorption was as low as 2?5 wt-%, the contact angle of water on the surface of this kind of film was as high as 96°, and the tensile strength was as high as 42?8 MPa. The cross-linked PUU films with polyoxypropylene glycerol and pentaerythritol as cross-linked agents showed different properties at the same cross-linking agent content. The prepared triol-cross-linked or tetra-cross-linked PUUs had great potential application in meeting the highly diversified demands in modern technologies such as coatings, leather finishing, adhesives, sealants, plastic coatings and wood finishes, where high water resistance and durability were required.