关键词： Microphase   Organic polymers   Insulators   Differential scanning calorimetry   Phase transitions  

摘要： To molecularly investigate the role of the microstructure in controlling the dynamics of segmented polyurethanes (PUs), a series of them were systematically designed, synthesized, and experimentally scrutinized. Broadband dielectric spectroscopy and rheometry along with small-angle X-ray scattering and differential scanning calorimetry were applied to provide insights into molecular origins, particularly the role of transitional friction coefficients (zeta), affecting dynamics and rheology of the various microstructures of PUs. In this way, first, the effective zeta s of model PUs were extracted from their rheological data using the Bueche-Ferry procedure. Second, the experienced zeta by the hard and soft segments (SS and HS) in pure components and resultant PUs were calculated using BDS data and were applied in a Rouse model based methodology to estimate the effective zeta. Finally, the obtained effective zeta from rheometry (zeta(eff)) and BDS (zeta(Rouse)(eff)) were compared at the same temperatures. For highly microphase-mixed system with liquid-like terminal behavior, zeta(Rouse)(eff) was consistent with zeta(eff). For microphase-separated PUs with their nonterminal behavior, however, a fairly large difference between zeta(eff) and zeta(Rouse)(eff) was found. A universal curve was also prepared to illustrate the relationship between the dynamics and microstructural features of model PUs. According to these results and the SAXS data analyses, the frictional forces acting at the interfaces between SS-rich and HS-rich phases were suggested as a main origin for the deviation from terminal Rouse-like dynamics in the microphase-separated PUs, while bare friction coefficients in their pure components play an insignificant role in the dynamics of these systems.

关键词： 钙钛矿太阳能电池   TiO2纳米阵列   SnCl4修饰   SnO2纳米晶粒   光电性能  

摘要： TiO2一维纳米阵列具有直接的电子传输通道,在钙钛矿太阳能电池的电子传导方面具有明显优势。采用SnCl4溶液水浴在水热制备的TiO2纳米阵列表面引入SnO2纳米晶粒,详细研究不同浓度SnCl4处理对TiO2纳米阵列微结构和钙钛矿太阳能电池光电性能的影响。研究发现,TiO2纳米阵列表面引入SnO2纳米晶粒,不仅获得了TiO2具有的高电子传导,而且SnO2颗粒的引入增强了钙钛矿中光生电子向电子传导层的注入;同时SnO2纳米晶颗粒的引入有助于填补纳米阵列支架中的缝隙,抑制器件中的载流子复合。TiO2纳米阵列经0.02 mol/L SnCl4溶液处理,基于SnO2纳米晶粒修饰的TiO2纳米阵列组装钙钛矿太阳能电池获得了最佳的光电性能,其光电转换效率达到17.13%。

关键词： Fast Fourier transform   Design   Reconstruction   Optimization   Composites  

摘要： An efficient micromechanical methodology is developed for tailoring elastic and thermal properties of random heterogeneous materials. The methodology involves three steps: (i) statistical reconstruction based on the two-point correlation function (TPCF), (ii) thermomechanical homogenization, and (iii) optimization. The method relies on the tailoring the state of anisotropy of the microstructure to achieve desired directional effective properties. This capability is demonstrated by designing heterogeneous microstructures with optimal elastic modulus and thermal conductivity in perpendicular directions. The study aims at presenting optimal computational algorithms for the reconstruction, homogenization and optimization steps. Several studies study are presented to demonstrate the feasibility of obtaining desired thermomechanical properties with a minimal set of design variables. These case studies highlight the advantages and limitations of the method, along with its computational cost. Graphic abstract

关键词： Tricalcium phosphate   Diopside   Scaffolds   Mechanical properties   Freeze casting  

摘要： Dense tricalcium phosphate, Ca-3(PO4)(2)(TCP) - diopside, CaMg(SiO3)(2), composites present better mechanical properties than single phase TCP. In this work, it is investigated whether the mechanical behaviour improvement by diopside is maintained in porous scaffolds. The processing parameters to obtain cylinders with approximate to 50% of aligned pores of elliptical cross sections with major axis up to 100 mu m by freeze casting and sintering were established. Pore channels were introduced in the green specimens by laser ablation. After sintering, the diameter of the cross sections of the channels was approximate to 700 mu m. The ceramic composite microstructure was constituted by a substructure of small diopside particles (2 - 7 mu m) and dense beta-TCP zones of larger dimensions (up to 40 mu m). Strength values, determined by diametral compression (DCDT) (approximate to 2.5-4 MPa) are in the range of strength of cancellous bone. Diopside presents transgranular fracture, hindering crack propagation from the beta-TCP areas and the pores, as occurred in the dense materials.

关键词： Uncertainty analysis  

摘要： This study quantified the microstructure of polyurethane foams and elucidated its relationship to fluid-acoustic parameters. The complex morphology derived from the three-dimensional images obtained by micro-computed tomography was analyzed using digital image processing and represented by a pore network model (PNM) and a distance map model. The PNM describes the fluid phase of a porous medium with equivalent spherical pores and circular throats, whereas the distance map model describes the solid phase with the average frame thickness. The porous materials were then modeled by six representative microstructural parameters that describe the geometry and topology of the fluid and solid phases. These parameters were pore radius, throat radius, distance between adjacent pores, coordination number, pore inclination angle, and frame thickness. Semi-phenomenological and empirical approaches were proposed to relate the microstructural properties to the fluid-acoustic parameters. These models effectively described the acoustic parameters and sound absorption performance of six different polyurethane foams. Since the representative microstructural parameters were obtained from small sample volumes of a heterogeneous material, notable variations were observed across different regions of the sample. Hence, this study quantified the effect of the uncertainty in each microstructural parameter on the resulting acoustic parameters using global sensitivity analysis.

关键词： SZ/TiO2 nanocomposites   Photocatalytic   Microstructure   Photo-luminescence   Optical properties  

摘要： In this work, we are mainly interested in the development of active photocatalysts based on TiO2 modified by coupling to ZnO:Mn/SiO2 (Zn-Si). Structural characterization by XRD and microstructural study by TEM performed on samples of TiO2 nanoparticles and Zn-Si/TiO2 (Ti-SZ) nanocomposites revealed the formation of anatase nanoparticles and Zn-Si phase. However, analysis of optical properties of these samples has shown a significant improvement in absorption over the visible range. The study of the optical properties of TiO2 modified by the SZ shows a displacement of the absorption front towards the visible range that is in between 420 and 550 nm, reflecting a significant enlarge in the energy gap band of the TiO2 at 3.30 eV. The emission PL around 535 nm is attributed to the recombination of photo-generated electrons with oxygen defects at the surface. This photo-activity was compared with that of the commercial catalyst TiO2-P25. The obtained photocatalytic results show that the activity of TiO2 modified by SZ remains close to that of the reference TiO2-P25.

关键词： Delafossite   Thin film   RF-Sputtering   Seebeck coefficient   Thin film thermal conductivity   Temperature sensors  

摘要： Delafossite type Mg doped CuFeO2 thin films have been deposited on fused silica by radio-frequency magnetron sputtering. As-deposited 300 nm thick films have been obtained and post-annealed between 350 and 750 degrees C under primary vacuum. The delafossite structure appears for the samples annealed above 550 degrees C. The microstructural analysis showed the presence of cracks and an inhomogeneous distribution of the dopant in the thickness. Only the sample annealed at 700 degrees C showed CuFeO2 stable phases, lower impurities amount, a high and constant Seebeck coefficient (+416 +/- 3 mu V K-1) and good electrical conductivity (1.08 S cm(-1) at 25 degrees C). High accuracy temperature sensors based on the Seebeck effect not only need high Seebeck coefficient without any drift with the temperature, but also a sufficient electrical conductivity and high phase stability. Thanks to its properties and also its low thermal conductivity (4.8 +/- 0.6 W m(-1)K(-1) at 25 degrees C) due to the thin film configuration and the polaronic transport, the Mg doped CuFeO2 thin film annealed at 700 degrees C was found to be a very good p-type material for high accuracy miniaturized temperature measurement sensors based on the Seebeck effect in the medium temperature range. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Semi-flexible pavement material   Grouting influence   Equivalent phase modulus   Micromechanics   Nano-techniques  

摘要： Semi-flexible pavement (SFP) has been promoted to apply in pavement engineering mainly for its excellent performance in rutting resistance. However, due to the material characteristics of three-phase heterogeneous phase and the structural characteristics of dense skeleton interlocking structure, the microstructure of semi-flexible pavement material is complicated, greatly influencing the mechanical properties of the material. This research aims to identify the two characteristics of SFP employing micromechanical models as well as nano-techniques, including nanoindentation (NI), Scanning Electron Microscope (SEM) and energy dispersive spectrum analysis (EDS). Two interlocking factors were introduced in the three-phase micromechanical model to characterize the interlocking effect. Identification of the asphalt mastic phase in SFP was implemented as the basis of stiffening correction in the micromechanical model. Because four different layers were found in the asphalt phase of SFP that was difficult to simulate, a general stiffening correction was used in the improved micromechanical model. The final model considering the interlocking and asphalt stiffening effects can characterize the property of SFP well. It was found that grouting cement has an enhancement function on the viscoelastic interlocking effect while does little on the elastic interlocking effect. Meanwhile, more grouting cement will lead to more asphalt-cement stiffening effect. An equivalent dynamic modulus of the asphalt phase-phase from the micromechanical model was proposed in the end, which has been proven corresponding to the experimental results of NI test. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Deformation and fracture   Grain refinement   Transformation induced plasticity   Third-generation steels   X-ray techniques  

摘要： We have investigated the capabilities of first and third-generation high strength steels for sustainable accommodation of microstructural damage before fracture occurs. Steels have been subjected to tensile tests followed by X-ray computed tomography to record the evolution of microstructural damage during deformation. Damage growth is correlated with the Rice-Tracey model. Results show that both grain refinement and transformation induced plasticity of retained austenite to martensite lead to enhanced damage tolerance, leading to the suppression of fracture and improved ductility. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Metakaolin   Hydraulic lime   Hydration heat   Early age   Microstructure  

摘要： Hydraulic lime is an ancient building repair material, and its good early performance is necessary to ensure a successful application. In this study, hydraulic lime (metakaolin (MK)-air lime (AL), MK-AL) were prepared by the amount of MK was used for different mixtures in AL, which provided the materials with both hydraulicity and the ability to air harden. The early-age (before 28 days) properties of natural hydraulic lime (NHL5), AL and MK-AL (MK20-AL and MK40-AL) pastes were studied through an examination of their physical and mechanical properties, hydration heat, thermal properties and microstructure. The strength growth trend of the MK-AL paste was similar to that of the NHL5 paste, and the compressive strength of the MK40-AL paste reached 21.06 MPa at 28 days. There was only a carbonation reaction in the AL paste, C-S-H formed mainly by the hydration reaction of C2S in the NHL5 paste, the pozzolanic reaction and carbonation reaction occurred in the MK-AL pastes, and the carbonation reaction in the MK-AL pastes was at a low level before 28 days. The MK-AL pastes had a longer hydration stage than the NHL5 paste, and there were two exothermic hydration peaks during the pozzolanic reaction for the MK-AL pastes. Laminar Ca(OH)\(2) and amorphous C-S-H gel comprised the skeleton in the NHL5 paste, and the large laminar Ca(OH)(2) structures that formed the skeleton were converted into an interweaved structure of the pozzolanic reaction products and carbonated products in the MK-AL pastes. There were many large pores (>200 nm) in the AL, NHL and MK20-AL pastes, while the pore size of the MK40AL paste was relatively small (<100 nm). The porosity of all lime pastes had the following trend: NHL (38.96%) < MK40-AL (42.89%) < MK20-AL (45.47%) < AL (51.22%).