Importance of optical homogeneity for high-quality transparent ceramics

Two types of transparent Y₂O₃ ceramics without including large scattering sources such as residual pores, one with very high optical homogeneity (type A) and another one with slightly insufficient optical homogeneity (type B), are purposely prepared, and their optical properties are investigated and compared qualitatively and quantitatively. Type A ceramic exhibits transmittance characteristics with very low internal loss in the visible to infrared wavelength region, while type B ceramic is inferior in various optical performances especially in the short (visible) wavelength region. In type B ceramic, birefringence occurs due to optical inhomogeneity in the visible region, resulting in a decrease in the extinction ratio. Non-uniform refractive index distribution is also observed in the Schlieren image of type B ceramic, hence the laser beam quality through that material is degraded. This study proved the importance of optical homogeneity of transparent ceramics and clarified the problems in actual applications.     

Compliance-based testing method for fatigue crack propagation rates of mixed-mode I–II cracks

Science China Technological Sciences - Mixed-mode I-II crack-based fatigue crack propagation (FCPI-II) usually occurs in engineering structures; however, no theoretical formula or effective...     

Ultrathin graphitic carbon nitride nanosheets and graphene composite material as high-performance PtRu catalyst support for methanol electro-oxidation

Graphitic carbon nitride (g-C₃N₄) has been demonstrated as an advanced support material for Pt nanoparticles (NPs) due to its excellent stability and abundant Lewis acid for anchoring metal NPs. However, its non-conductive nature and low surface areas still impede its application in electrochemical fields. Herein, a π–π stacking method is presented to prepare graphene/ultrathin g-C₃N₄ nanosheets composite support for PtRu catalyst. The weaknesses of g-C₃N₄ are greatly overcome by establishing a 2D layered structure. The significantly enhanced performance for this novel PtRu catalyst is ascribed to reasons as follows: the homogeneous dispersion of PtRu NPs on g-C₃N₄ nanosheets due to its abundant Lewis acid sites for anchoring PtRu NPs; the excellent mechanical resistance and stability of g-C₃N₄ nanosheets in acidic and oxidative environments; the increased electron conductivity of support by forming a layered structure and the strong metal-support interaction (SMSI) between metal NPs and g-C₃N₄ NS.     

Effect of color,gloss, and surface texture perception on scratch and mar visibility in polymers

Scratch and mar can critically impact the aesthetics of polymeric surfaces. Their quantification poses considerable challenges, especially for subtle mar damages. Here, we report a new standardized approach that utilizes a modified ASTM/ISO scratch test standard and a psychophysical tool to quantify scratch and mar visibility. The new methodology was then used to study the influence of color, gloss, and texture perception on scratch and mar visibility resistance. These factors have limited influence on scratch visibility onset. However, faint mar damage is more sensitive to surface perceptual properties. It has been found that overall visibility throughout the entire damage path is a better indicator for ranking mar damage. Results show that contrast slope variation parameter can consistently quantify mar visibility and simulate human perception. Green, glossy, and smooth surfaces tend to have less mar visibility resistance. The effect of a fatty amide slip agent was also investigated. These modifiers improved both scratch and mar visibility resistance. This unique approach paves the way for a straightforward universal standard that can be utilized to reliably quantify scratch and mar visibility in polymers, thereby opening up a new avenue for the design of polymeric materials with better scratch and mar visibility resistance.     

Conversion kinetics of container glass batch melting

Understanding the batch-to-glass conversion process is fundamental to optimizing the performance of glass-melting furnaces and ensuring that furnace modeling can correctly predict the observed outcome when batch materials or furnace conditions change. To investigate the kinetics of silica dissolution, gas evolution, and primary foam formation and collapse, we performed X-ray diffraction, thermal gravimetry, feed expansion tests, and evolved gas analysis of batch samples heated at several constant heating rates. We found that gas evolving reactions, foaming, and silica dissolution depend on the thermal history of the batch in a similar manner: the kinetic parameters of each process were linear functions of the square root of the heating rate. This kinetic similarity reflects the stronger-than-expected interdependence of these processes. On the basis of our results, we suggest that changes in furnace operating conditions, such as firing or boosting, influence the melting rate less than what one would expect without consideration of batch conversion kinetics.     

A series of Er~(3+)-activated SrLaGa_3O_7 single crystal fibers for mid-infrared laser application

A multidisciplinary approach for the production and characterization of a series of high concentration Er~(3+)activated SrLaGa_3 O_7(abbreviated as Er:SLGO) crystal fibers is shown to have a great promise for implementation in mid-infrared laser applications.The current approach includes the design and formation of unique layered tetrahedral network structures with several kinds of rare earth(RE) ions including Er ions distributing statistically between layers,such as Er:SLGO,Er,Nd:SLGO,Er,Yb,Ho:SLGO,Er,Eu:SLGO and Er,Ho:SLGO.Five kinds of Er:SLGO crystal fibers were designed to grow via a micropulling down method.Spectroscopic analyses show that Er,Yb,Ho:SLGO and Nd,Er:SLGO crystal fibers were superiorly endowed with inhomogeneous broadening absorption and strong emission.The unique structural components design enables the generation of improved absorption and emission recombination,and the inhibition of self-termination as well.Generally,the use of structural components design may warrant high-efficiency emissions in RE-doped crystal fibers.     

Dry versus hydrated collagen scaffolds: are dry states representative of hydrated states?

Collagen composite scaffolds have been used for a number of studies in tissue engineering. The hydration of such highly porous and hydrophilic structures may influence mechanical behaviour and porosity due to swelling. The differences in physical properties following hydration would represent a significant limiting factor for the seeding, growth and differentiation of cells in vitro and the overall applicability of such hydrophilic materials in vivo. Scaffolds based on collagen matrix, poly(DL-lactide) nanofibers, calcium phosphate particles and sodium hyaluronate with 8 different material compositions were characterised in the dry and hydrated states using X-ray microcomputed tomography, compression tests, hydraulic permeability measurement, degradation tests and infrared spectrometry. Hydration, simulating the conditions of cell seeding and cultivation up to 48?h and 576?h, was found to exert a minor effect on the morphological parameters and permeability. Conversely, hydration had a major statistically significant effect on the mechanical behaviour of all the tested scaffolds. The elastic modulus and compressive strength of all the scaffolds decreased by ~95%. The quantitative results provided confirm the importance of analysing scaffolds in the hydrated rather than the dry state since the former more precisely simulates the real environment for which such materials are designed.

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基于Lagrange法的金属切削加工过程数值模拟

利用Lagrange法在SuperForm软件中对金属切削加工过程及加工过程中的切削热、切削力耦合问题进行了数值仿真。模拟结果与实验结果非常接近，可以为实际加工过程的控制提供参考和依据。     

Out-of-plane behavior of brick wall of historical masonry structures

针对历史建筑砌体结构在地震作用下容易发生砖墙平面外破坏与倒塌的问题，设计并制作了4片足尺带正交横墙的砖墙，采用气囊加载施加均布荷载进行了砖墙平面外静力试验，研究历史建筑砖墙平面外破坏模式和受力性能。在此基础上，通过理论分析研究了竖向荷载、墙厚、墙宽、楼(屋)盖形式和砂浆强度等因素的影响，提出了砖墙平面外承载力计算方法。研究结果表明：峰值荷载后砖墙平面外位移急剧增大，但开裂后仍能保持较大的平面外位移而不倒塌；与无楼板砖墙相比，木楼板和混凝土楼板砖墙的初始刚度分别提高了69.9%和68.8%，平面外承载力分别提高了44.5%和54.0%；竖向荷载、墙宽和墙厚对砖墙平面外承载力影响显著，楼板形式有一定的影响，而砂浆强度的影响较小；砖墙平面外承载力的理论结果与试验结果吻合较好。     

Deformability enhancement in ultra-fine grained, Ar-contained W compacts by TiC additions up to 1.1%

Nano-sized Ar bubbles give negative influence on the fracture resistance and occurrence of superplasticity in ultra-fine grained (UFG) W–TiC compacts. In order to enhance deformability in UFG, Ar-contained W–TiC compacts, effects of TiC addition on the high-temperature deformation behavior were examined. W–TiC compacts with TiC additions of 0, 0.25, 0.5, 0.8 and 1.1 wt% were fabricated by mechanical alloying in a purified Ar atmosphere and hot isostatic pressing. Tensile tests were conducted at 1673–1973 K (0.45–0.54 T_m, T_m: melting point of W) at initial strain rates from 5 × 10⁻⁵ to 5 × 10⁻³ s⁻¹. It is found that as TiC addition increases, the elongation to fracture significantly increases, e.g., from 3 to 7% for W–0 and 0.25TiC/Ar to above 160% for W–1.1TiC/Ar when tested at 1873 and 1973 K at 5 × 10⁻⁴ s⁻¹. The flow stress takes a peak at 0.25%TiC and decreases to a nearly constant level at 0.5–1.1%TiC. The ranges of the strain rate sensitivity of flow stress, m, and the activation energy for deformation, Q, with TiC additions are 0.17–0.30 and 310–600 kJ/mol, respectively. The observed effects of the TiC additions on the tensile properties are discussed.