变热流条件下XPS板辐射引燃特性试验研究

为研究XPS保温板在变化热流作用下的引燃特性,对10组变热流条件下2.2,4.5cm厚XPS保温板辐射引燃特性进行了试验.测量了XPS保温板表面接受到的热辐射强度、引燃时间、表面温度以及质量损失速率.结果表明：0.0194kW/（m2·s）热流变化率不足以引燃XPS保温板试样;当热流变化率大于0.0373kW/（m2·s）时,在热流的作用下XPS保温板表面温度逐渐升高;当温度达到临界着火点时,XPS保温板瞬间燃烧,发出耀眼火焰和黑色浓烟,同时温度闪升至970.5℃左右;当有焰燃烧结束时,表面温度突降,燃烧过程结束;在有焰燃烧阶段,XPS板质量呈线性递减;临界着火点温度为336.0~387.0℃,且XPS保温板引燃时间与热流变化率具有乘幂关系,幂指数约为-0.765.     

棉纤维在NMMO溶液中的溶胀与溶解

用不同质量分数的N-甲基吗啉-N-氧化物(NMMO)溶液,在不同的温度和时间条件下,探究棉纤维的溶胀和溶解情况,并利用X射线衍射和红外光谱对纤维素溶胀前后的结构变化进行表征。结果表明:NMMO质量分数低于80%时,棉纤维只溶胀不溶解;在质量分数分别为83%、85%、87%的NMMO溶液中,棉纤维出现溶解现象;随着NMMO质量分数的增大、温度的升高、时间的延长,棉纤维的溶胀程度不断增加。在质量分数为83%的NMMO溶液中,棉纤维先溶胀后溶解;在质量分数为87%的NMMO溶液中,棉纤维不溶胀直接溶解;在质量分数为85%的NMMO溶液中,棉纤维的溶解存在先溶胀后溶解和直接溶解两种形式。质量分数为80%以下的NMMO水溶液处理后的棉纤维,结晶结构和化学结构均没有变化。     

Synchrotron X-ray tomographic characterization of CVI engineered 2D-woven and 3D-braided SiCf/SiC composites

The properties of ceramic matrix composites strongly depend upon their complex internal structures. To better understand and improve the properties of the silicon carbide fiber-reinforced silicon carbide matrix composites (SiC_f/SiC), we explored the microstructural properties of composites reinforced with either two-dimensional (2D) woven or three-dimensional (3D) braided preforms using synchrotron X-ray computed microtomography. Transects and volumetric images of the composites were reconstructed from objection images and the microstructures were investigated in three spatial directions. The network of void space in a composites was visualized in 3D and quantitative analysis of the porosity was performed to characterize the fiber-tissue structures. 2D-woven SiC_f/SiC composite exhibited important fluctuations of porosity in different directions and the stacking of plies had a significant effect on the porosity distribution. In contrast, 3D-braided SiC_f/SiC composites showed much less variation of porosity. We found the degree of densification of the composite also influenced the porosity distribution.     

富马酰基桥联双冠醚的晶体结构及其对金属离子的选择键合

通过母体冠醚环(苯并氮杂-15-冠-5)与富马酰氯反应,合成了一种新型的富马酰基桥连的双冠醚,其单晶结构经X-射线单晶衍射仪测定;继而采用溶剂萃取法考察了其对金属离子(Li~+、Na~+、K~+、Rb~+、Cs~+、Ag~+、Tl~+)的识别能力。结果显示,该双冠醚对Li~+具有较高的萃取率和选择性。     

Natural convection heat and moisture transfer with thermal radiation in a cavity partially filled with hygroscopic porous medium

This article deals with natural convection heat and moisture transfer with thermal radiation in a cavity partially filled with hygroscopic porous medium. The governing equations for the momentum and heat transfer in both free fluid and hygroscopic porous medium and moisture content transfer in hygroscopic porous medium were solved by the finite element method. The radiative heat transfer is calculated by making use of the radiosity of the surfaces that are assumed to be grey. Comparisons with experimental and numerical results in the literature have been carried out. Effects of thermal radiation and Rayleigh number on natural convection and heat transfer in both free fluid and porous medium and moisture content transfer in porous medium were analyzed. It was found that surface thermal radiation can significantly change the temperature and moisture content fields in the regions of free flow and porous medium. The mean temperature at the interface decreases, the temperature and moisture content gradients are created on the upper two corners of the porous medium region, and the moisture content in the porous medium decreases in the porous medium as Ra increases.     

型壳中央散热对一种单晶高温合金凝固组织与持久性能的影响

单晶凝固过程中温度场均匀性控制对单晶制备过程特别重要。本文以国内广泛应用的第二代单晶高温合金DD6为研究对象,研究型壳中央散热对其凝固组织与持久性能的影响。结果表明,与合金中柱型壳相比,石墨中柱型壳能有效地改善单晶凝固过程中温度场的均匀性,提高温度梯度,有利于保持单晶凝固过程中热流方向的平直。因此,石墨中柱型壳有利于降低一次枝晶间距,细化γ-γ’共晶相,减少单晶生长方向与[001]方向的角度差,使单晶高温合金获得较高的持久寿命。     

Comparison of EBSD patterns simulated by two multislice methods

The extraction of crystallography information from electron backscatter diffraction (EBSD) patterns can be facilitated by diffraction simulations based on the dynamical electron diffraction theory. In this work, the EBSD patterns are successfully simulated by two multislice methods, that is, the real space (RS) method and the revised real space (RRS) method. The calculation results by the two multislice methods are compared and analyzed in detail with respect to different accelerating voltages, Debye–Waller factors and aperture radii. It is found that the RRS method provides a larger view field of the EBSD patterns than that by the RS method under the same calculation conditions. Moreover, the Kikuchi bands of the EBSD patterns obtained by the RRS method have a better match with the experimental patterns than those by the RS method. Especially, the lattice parameters obtained by the RRS method are more accurate than those by the RS method. These results demonstrate that the RRS method is more accurate for simulating the EBSD patterns than the RS method within the accepted computation time.     

Titanium diffusion in shinbone of rats with osseointegrated implants

Dental implants are composed of commercially pure Ti (which is actually an alloy of titanium, and minor or trace components such as aluminium and vanadium). When the implant is inserted, its surface undergoes a number of chemical and mechanical processes, releasing particles of titanium to the medium. The metabolism of free ions of titanium is uncertain; the uptaking processes in the body are not well known, nor their toxic dose. In addition, physical properties of newly formed bone, such as diffusivity and activation energy, are scarce and rarely studied. In this study, we analysed the diffusion of titanium in the titanium‐implanted shinbones of six adult male Wistar rats by spatially resolved micro x‐ray fluorescence. The measurements were carried out at the microfluorescence station of the x‐ray fluorescence (XRF) beamline of the Brazilian synchrotron facility LNLS (from Portuguese ‘Laboratorio Nacional de Luz Sincrotron’). For each sample, XRF spectra were taken by linear scanning in area near the new bone formed around the Ti implant. The scanning line shows a clear effect of titanium diffusion whereas calcium intensity presents a different behaviour. Moreover, a clear correlation among the different structures of bones is observed in the Ti and Ca intensities. The results obtained in these measurements may allow determining quantitatively the parameters of diffusion rates and other physical properties of new bone like diffusion coefficients.     

Measurement accuracy in X-ray computed tomography metrology: Toward a systematic analysis of interference effects in tomographic imaging

In this paper an investigation of interference effects leading to limitations of metrological performance of X-ray computed tomography (CT) used as a coordinate measuring technique is presented. Using reconstruction data, image quality metrics, and calculations of artifact formation, a deeper understanding and explanation of the physical and technical limitations of CT used in dimensional metrology is given. This is demonstrated in a case study using a simple hollow cylinder made of steel as a test object and calibration measurements from a tactile coordinate measuring machine (CMM). Two different threshold determination strategies for surface computation are applied. Within the study it is also shown that CT image properties, threshold determination strategies, and systematic and random measurement errors must have a definite correlation. As a conclusion it is recommended to focus more strongly on the correlation of local CT image quality and data evaluation operations in order to reduce systematic errors in surface computation and to increase repeatability of dimensional CT measurements.     

Effect on crystalline structure of AISI M2 steel using tungsten–thorium electrode through MRR,EWR, and surface finish

To investigate on the crystalline structure of AISI M2 steel by using tungsten–thorium electrode in electrical discharge machining (EDM) process was studied. Furthermore, the investigation were carried out for finding the value of material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) of tool steel material depending upon three variable input process parameters. On the basis of weight loss, the value of MRR and EWR were calculated at optimized process parameter. Subsequently, surface topography of the processed material were examined through different characterization techniques like scanning electron microscopy (SEM), Optical surface profiler (OSP) and Atomic force microscopy (AFM), respectively. In XRD study, broadening of the peak was observed which confirmed the change in material properties due to the homogeneous dispersion of the particles inside the matrix. Lowest surface roughness and MRR of 0.001208 mg/min was obtained. Minimum surface roughness was obtained 1.12 μm and 2.18427 nm by OSP and AFM study, respectively. Also, minimum EWR was found as 0.013986 mg/min.