Structural properties of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 relaxor ferroelectric thin films on SrRuO3 conducting oxides

Coating of 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO₃ (SRO) metallic oxide electrodes on SrTiO₃ (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed.     

Organic‐acid‐catalyzed sol–gel route for preparing poly(methyl methacrylate)–silica hybrid materials

In this study, a series of organic–inorganic hybrid sol–gel materials consisting of a poly(methyl methacrylate) (PMMA) matrix and dispersed silica (SiO₂) particles were successfully prepared through an organic‐acid‐catalyzed sol–gel route with N‐methyl‐2‐pyrrolidone as the mixing solvent. The as‐synthesized PMMA–SiO₂ nanocomposites were subsequently characterized with Fourier transform infrared spectroscopy and transmission electron microscopy. The solid phase of organic camphor sulfonic acid was employed to catalyze the hydrolysis and condensation (i.e., sol–gel reactions) of tetraethyl orthosilicate in the PMMA matrix. The formation of the hybrid membranes was beneficial for the physical properties at low SiO₂ loadings, especially for enhanced mechanical strength and gas barrier properties, in comparison with the neat PMMA. The effects of material composition on the thermal stability, thermal conductivity, mechanical strength, molecular permeability, optical clarity, and surface morphology of the as‐prepared hybrid PMMA–SiO₂ nanocomposites in the form of membranes were investigated with thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, gas permeability analysis, ultraviolet–visible transmission spectroscopy, and atomic force microscopy, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Quantification of the layer dispersion degree in polymer layered silicate nanocomposites by transmission electron microscopy

As the performance of polymer layered silicate nanocomposites strongly depends on their interior layer dispersion, quantification of the layer dispersion degree is needed. In this work, a new methodology was developed to determine the dispersion parameter D_0.1, based on the measurement of the free-path spacing distance between the single clay sheets from the transmission electron microscopy (TEM) images. Several examples of exfoliated, intercalated, and immiscible composites were studied. It was found that the exfoliated composites had D_0.1 over 8%, while that of intercalated composites were between 4 and 8%. In the case of intercalation, a high frequency peak appeared at a short spacing distance in the histogram, which was a characteristic of the intercalation, distinct from the exfoliation. The main utility of this TEM methodology is for the quantification of exfoliated or intercalated samples with small number of layers with stacks. The dispersion parameter D_0.1 below 4% was suggested to classify as immiscible. A unique advantage of the TEM measurement is that the dispersion degree of different fillers can be counted individually.     

电话通信设备电磁干扰的测量分析

本文探讨了ＴＥＭ室测量电话通信设备辐射干扰的原理、方法，得出了在线电话终端０．１５～３０ＭＨｚ频段辐射干扰测量结果，并进行了分析。     

Models and observations of fcc/bcc interfaces

Whereas models of the structure and periodicity of CSL or near CSL high angle grain boundaries are relatively well developed and have been to some extent verified by experiment, the nature of more general (e.g. fcc/bcc) interfaces is very imperfectly understood. One of the major differences between homo- and heterophase boundaries is the occurrence, in the latter case, of reproducible orientation relationships due to the crystallographic requirements of phase transformation (e.g. a glissile interface for martensitic growth, low energy interfaces for classical nucleation). A review is given of the relationships commonly observed to obtain between fcc and bcc crystals (as well as ordered phases based upon these structures). Within a given relationship, it is possible to use models of the available interfaces to predict their dislocation content; the success of the various approaches is considered. It is shown that the dislocation arrays identified on fcc/bcc boundaries are consistent with the occurrence of a primary structural relaxation, but that the latter does not appear to be complete. Possible reasons for this are discussed, together with the extent to which secondary structural models may be applicable. Attempts to rationalize the observed orientation relationships and morphologies are discussed, and it is pointed out that these all rely on searches for situations of minimum primary misfit, but that the way in which the latter is quantified determines the results of the analyses. Nevertheless, the implication is that the primary misfit does appear to determine the actual behaviour, though no structural or mechanistic conclusions can safely be drawn from this observation.     

烧结直接淬火对WC－TiC－Co合金WC相微观结构及力学性能的影响

本文以ＴＥＭ和ＸＲＤ为主要手段，研究ＷＣ－ＴｉＣ－Ｃｏ硬质合金（ＹＴ１４）在直接淬火后ＷＣ相的微观结构和微观应力，比较了常规烧结态与淬火态试样ＷＣ相之间的差异，探讨了直接淬火对合金力学性能的影响。结果表明，在保持合金其他性能不降低的同时，直接淬火的抗弯强度比常规烧结提高２８％左右。并首次发现，经直接淬火热处理的ＹＴＩ４合会中与Ｃｏ相相邻的ＷＣ晶粒边界出现滑移台阶，这是淬火过程中热应力使ＷＣ晶粒内位错在｛０００１｝密排面聚集，并可能沿｛０００１｝＜１１２０＞易滑移系统强滑移的结果。直接淬火试样的微观应力比重新加热淬火的低。     

Microstructural evolution and interfacial reactions between Ti and ZrO2/CaTiO3 composites

Various proportions of ZrO₂/CaTiO₃ powders were mixed and hot pressed at 1500°C/30 min for Ti casting. The hot-pressed ZrO₂/CaTiO₃ composites were reacted with pure Ti at 1700°C/10 min in Ar. The interfacial reaction between Ti and ZrO₂/CaTiO₃ composites was investigated through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The ZrO₂/CaTiO₃ composites with less than 10 vol.%, CaTiO₃, and a minor amount of residual TiO₂ were found. When the content of ZrO₂ was increased to larger than 10 vol.%, two Ca₂Zr₅Ti₂O₁₆ and CaZrTi₂O₇ phases appeared in the composites. The amount of CaTiO₃ and CaZrTi₂O₇ in the composites gradually decreased as the amount of ZrO₂ increased. When Ti came in contact with ZrO₂/CaTiO₃ composites with less than 10 vol.% ZrO₂, the resulting eutectic reaction produced a liquid phase and induced melting. When ZrO₂ was increased to more than 30 vol.% in the composites, Ca₂Zr₅Ti₂O₁₆ and CaZrTi₂O₇ changed completely to CaZrO₃, Ti₂O, CaO, and ZrO₂. With more than 30 vol.% ZrO₂, no other reaction phases occurred in the Ti side after contact with the ZrO₂/CaTiO₃ composites, which is conducive for producing ceramic composites for Ti casting applications.     

Enhanced oxidation of the 9%Cr steel P91 in water vapour containing environments

The short term (∼100 h) oxidation behaviour of the 9%Cr steel P91 was studied at 650 °C in N₂-O₂-H₂O gas mixtures containing a relatively low oxygen level of 1%. The oxidation kinetics were measured thermogravimetrically and the oxide scale growth mechanisms were studied using H₂¹⁸O-tracer with subsequent analyses of oxide scale composition and tracer distribution by MCs⁺-SIMS depth profiling. The corrosion products were additionally characterised by light optical microscopy, SEM-EDX and XRD. It was found that the transition from protective, Cr-rich oxide formation into non-protective mixed oxide scales is governed by the ratio H₂O^(g)/O₂ ratio rather than the absolute level of H₂O^(g). The results of the tracer studies in combination with the data obtained from experiments involving in situ gas changes clearly illustrated that under the prevailing conditions the penetration of water vapour molecules triggers the enhanced oxidation and sustains the high growth rates of the poorly protective Fe-rich oxide scale formed in atmospheres with high H₂O^(g)/O₂ ratios. The experimental observations can be explained if one assumes the scale growth to be governed by a competitive adsorption of oxygen and water vapour molecules on external and internal surfaces of the oxide scales in combination with the formation of a volatile Fe-hydroxide during transient oxidation. The formation of the non-protective Fe-rich oxide scales is suppressed in atmospheres with low H₂O^(g)/O₂ -ratios, and the healing of any such scale is promoted.     

回火温度对65Mn钢应力松弛性能的影响

测定了65Mn盘条经830℃淬火、380℃中温回火和540℃高温回火处理后的应力松弛曲线,并推导出应力松弛方程,利用透射电镜对松弛前后的形貌进行了分析,探讨了回火温度对应力松弛性能的影响.     

Quantitative analysis of complex carbo-nitride precipitates in steels

Two new types of extraction replicas for precipitate analysis in steels have been developed. These replicas, based on alumina, allow accurate quantification of the carbon to nitrogen ratios in carbo-nitride precipitates using parallel electron energy loss spectroscopy in the TEM. Experiments on microalloyed steels show the importance of the nitrogen content in promoting precipitation even at low temperatures.