共查询到20条相似文献，搜索用时 15 毫秒
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Benjamin Alexander Tyrone L. Daulton Guy M. Genin Justin Lipner Jill D. Pasteris Brigitte Wopenka Stavros Thomopoulos 《Journal of the Royal Society Interface》2012,9(73):1774-1786
The nanometre-scale structure of collagen and bioapatite within bone establishes bone''s physical properties, including strength and toughness. However, the nanostructural organization within bone is not well known and is debated. Widely accepted models hypothesize that apatite mineral (‘bioapatite’) is present predominantly inside collagen fibrils: in ‘gap channels’ between abutting collagen molecules, and in ‘intermolecular spaces’ between adjacent collagen molecules. However, recent studies report evidence of substantial extrafibrillar bioapatite, challenging this hypothesis. We studied the nanostructure of bioapatite and collagen in mouse bones by scanning transmission electron microscopy (STEM) using electron energy loss spectroscopy and high-angle annular dark-field imaging. Additionally, we developed a steric model to estimate the packing density of bioapatite within gap channels. Our steric model and STEM results constrain the fraction of total bioapatite in bone that is distributed within fibrils at less than or equal to 0.42 inside gap channels and less than or equal to 0.28 inside intermolecular overlap regions. Therefore, a significant fraction of bone''s bioapatite (greater than or equal to 0.3) must be external to the fibrils. Furthermore, we observe extrafibrillar bioapatite between non-mineralized collagen fibrils, suggesting that initial bioapatite nucleation and growth are not confined to the gap channels as hypothesized in some models. These results have important implications for the mechanics of partially mineralized and developing tissues. 相似文献
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球差校正扫描透射电子显微镜（STEM）因其原子级的空间分辨率和元素解析能力,在纳米功能材料的结构和成分分析中得到广泛使用。扫描透射电子显微镜高角环形暗场像技术（STEM-HAADF）凭借独特的原子序数衬度（Z衬度）和电子通道效应,在负载型纳米催化剂的结构研究中有着显著优势。通过STEM-HAADF成像,研究人员不仅可以直接观测到单个贵金属原子在较轻的载体上的实空间分布,还可以实现对载体表面上不同的负载贵金属物种的统计分析,这为近十年兴起的单原子催化剂研究提供了最重要的结构分析支持。相对于STEM-HAADF成像,基于STEM的X射线能谱（EDS）和电子能量损失谱（EELS）的谱学分析技术则能够在纳米尺度乃至原子尺度提供直接的化学成分或化学价态信息。成像和谱学的结合能够更准确地确定负载的金属原子在基底上的空间构型。进一步将原位电镜技术引入扫描透射电子显微镜内,则可以在时间尺度上探究催化剂在接近工作环境下的结构演化,从而更全面地揭示催化剂化学活性的结构起源与失效机制。本文结合近几年的部分代表性研究成果,简要介绍球差校正STEM技术在原子级分散负载催化剂研究中的应用,并对其在该研究领域的进一步发展进行了展望。 相似文献
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Zeynab Aalipour Abbas Zarei-Hanzaki Ali Moshiri Daudi Waryoba Anna Kisko L. Pentti Karjalainen Hamid Reza Abedi 《Advanced Engineering Materials》2023,25(17):2300297
Herein, dynamic and postdynamic recrystallization behaviors of GWZ magnesium are investigated. Toward this end, the single-hit and double-hit hot compression tests are conducted under strain rate of 0.001 s−1 at 400 °C. The prestrains of 0.1 and 0.5 are considered to investigate the effect of interpass time (5–300 s) on the compressive strength level. At the low strain level of 0.1, the contribution of Hall–Petch effect is considerable due to the occurrence of static recrystallization. In addition, the rare earth texture component is eliminated during interpass annealing. This causes increasing the strength of the material during second pass of hot compression. In contrast, at higher imposed strain, the strength level decreases with increasing the interpass time of annealing. The high amount of strain is completely consumed and the remaining stored energy is not high enough to trigger the occurrence of static recrystallization. The occurrence of metadynamic recrystallization and subsequent growth are characterized. In addition, the texture does not change in respect of the intensity or numbers/types of components. Accordingly, the observed decreasing trend of the strength is justified relying on the occurrence grain growth. 相似文献
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Al–Mg–Si aluminum wires for overhead power transmission have extensive applications in industry and daily life. Herein, superior strength and electrical conductivity combinations in the aged cold-drawn Al–Mg–Si–Ce–Cu wires fabricated by continuous casting and rolling are achieved. The cold-drawn wires exhibit high strength and electrical conductivity combinations of 383 ± 2 MPa, 51.16 ± 0.23% International Annealed Copper Standard (IACS); 373 ± 3 MPa, 51.98 ± 0.25%; and 357 ± 3 MPa, 53.16 ± 0.11% IACS, respectively, when aged at 160, 170, or 180 °C for 24 h. Subgrain boundaries are introduced into alloys by continuous casting and rolling and cold drawing, causing significant lattice distortion within the grains and providing sites for the nucleation of precipitates. Moreover, high-angle-annular dark-field scanning transmission electron microscopy and density functional theory results show that Ce atoms could enter the lattice of β” and replace the Si3 sites, which is energetically preferred. The underlying mechanisms for achieving superior strength–electrical conductivity combination are to introduce subgrain boundaries via continuous casting and rolling and cold drawing for promoting the transformation of solid solution atoms to finely dispersed precipitates, which significantly reduces the scattering of electrons and hence improves the electrical conductivity. This work provides a new strategy for designing high-strength and high-conductivity aluminum alloy wire conductors. 相似文献
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Martina Cihova Patrik Schmutz Robin Schublin Jrg F. Lffler 《Advanced materials (Deerfield Beach, Fla.)》2019,31(42)
Biodegradable magnesium alloys generally contain intermetallic phases on the micro‐ or nanoscale, which can initiate and control local corrosion processes via microgalvanic coupling. However, the experimental difficulties in characterizing active degradation on the nanoscale have so far limited the understanding of how these materials degrade in complex physiological environments. Here a quasi‐in situ experiment based on transmission electron microscopy (TEM) is designed, which enables the initial corrosion attack at nanometric particles to be accessed within the first seconds of immersion. Combined with high‐resolution ex situ cross‐sectional TEM analysis of a well‐developed corrosion‐product layer, mechanistic insights into Mg‐alloys' degradation on the nanoscale are provided over a large range of immersion times. Applying this methodology to lean Mg–Zn?Ca alloys and following in detail the dissolution of their nanometric Zn‐ and Ca‐rich particles the in statu nascendi observation of intermetallic‐particle dealloying is documented for magnesium alloys, where electrochemically active Ca and Mg preferentially dissolve and electropositive Zn enriches, inducing the particles' gradual ennoblement. Based on electrochemical theory, here, the concept of cathodic‐polarization‐induced dealloying, which controls the dynamic microstructural changes, is presented. The general prerequisites for this new dealloying mechanism to occur in multicomponent alloys and its distinction to other dealloying modes are also discussed. 相似文献
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Background: This study was designed for investigating the effect of soybean (SS) extract and chitosan (CTN) in facilitating the permeation of carvedilol (CDL) across rat epidermis. Method: Transdermal flux of carvedilol through heat-separated rat epidermis was investigated in vitro using vertical Keshary–Chien diffusion cells. Biophysical and microscopic manifestations of epidermis treated with SS-extract, CTN, and SS extract–CTN mixture were investigated by using DSC, TEWL, SEM, and TEM. Biochemical estimations of cholesterol, sphingosine, and triglycerides were carried out for treated excised as well as viable rat epidermis. The antihypertensive activity of the patches in comparison to that after oral administration of carvedilol was studied in deoxycorticosterone acetate-induced hypertensive rats. Results: The solubility of CDL was found to be maximum in the presence of 1% (w/v) SS extract. The KIPM/PB of CDL decreased with increase in concentration of SS extract. The in vitro permeation of CDL across rat epidermis increased and was maximum with combination of SS extract and chitosan (CTN). Biochemical and microscopic studies revealed the initiation of reversal of barrier integrity after 12 hours. Furthermore, the application of patches containing SS extract–CTN mixture resulted in sustained release of carvedilol, which was able to control the hypertension in deoxycorticosterone acetate (DOCA) induced hypertensive rats through 24 hours. CTN was found to potentiate the permeation enhancing activity of SS extract. Conclusion: The developed transdermal patches of CDL containing SS extract–CTN mixture exhibited better performance as compared to oral administration in controlling hypertension in rats. 相似文献
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Xuan Hu Zahra Hemmat Leily Majidi John Cavin Rohan Mishra Amin Salehi‐Khojin Serdar Ogut Robert F. Klie 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(3)
2D materials, such as transition metal dichalcogenides (TMDs), graphene, and boron nitride, are seen as promising materials for future high power/high frequency electronics. However, the large difference in the thermal expansion coefficient (TEC) between many of these 2D materials could impose a serious challenge for the design of monolayer‐material‐based nanodevices. To address this challenge, alloy engineering of TMDs is used to tailor their TECs. Here, in situ heating experiments in a scanning transmission electron microscope are combined with electron energy‐loss spectroscopy and first‐principles modeling of monolayer Mo1?xWxS2 with different alloying concentrations to determine the TEC. Significant changes in the TEC are seen as a function of chemical composition in Mo1?xWxS2, with the smallest TEC being reported for a configuration with the highest entropy. This study provides key insights into understanding the nanoscale phenomena that control TEC values of 2D materials. 相似文献
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奥氏体合金广泛应用于核电领域。应力腐蚀开裂是核电材料主要的失效形式之一,奥氏体合金的应力腐蚀开裂关系到核电站的安全运行。综述了评估应力腐蚀开裂的试样方法以及运用现代电子显微分析技术表征应力腐蚀开裂的方法。对这些电子显微分析技术的优点进行了总结,并指出未来电子显微分析技术在应力腐蚀开裂研究中的发展方向。 相似文献
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本文涉及两个和电子显微技术有关的问题：豆．透射电子显微镜试样薄片表面沉淀相颗粒存在状况的实验观察．２．扫描电子显微镜背反射电子象用作定量金相测定的建议。 相似文献
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环境扫描电子显微镜的特性及应用概况 总被引：1，自引：0，他引：1
简要叙述了环境扫描电子显微镜的原理,着重介绍了它的特性和在国内外应用的概况。与普通的扫描电子显微镜相比,它具有能直接检测不导电样品和含油含水样品的独特性能,为扫描电子显微镜的应用开拓了新的领域。 相似文献
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G. P. Dimitrakopulos C. Bazioti E. Papadomanolaki K. Filintoglou M. Katsikini J. Arvanitidis 《Materials Science & Technology》2018,34(13):1565-1574
ABSTRACTThe structural properties of InxGa1?xN epilayers, deposited on (0001) AlN templates by plasma-assisted molecular beam epitaxy, were studied by transmission electron microscopy and Raman spectroscopy, as a function of growth temperature. Single phase films with high indium content and well-ordered heteroepitaxial interfaces were attained at lower temperatures. Delayed plastic relaxation resulted in the structural stratification of high-temperature films due to the compositional pulling. Such films relaxed by a stacking fault mechanism, contrary to low temperature ones that exhibited relaxation by misfit dislocations. Despite the higher defect content of the former, their phonon mean free path was also higher, showing that alloying-induced fluctuations of the periodic potential constitute a more critical parameter. Cubic interfacial zones were suppressed at lower growth temperatures.This is part of a thematic issue on Nanoscale Materials Characterisation and Modeling by Advances Microscopy Methods - EUROMAT. 相似文献
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《Journal of Experimental Nanoscience》2013,8(7-8):971-992
This study aimed to evaluate the crystalline and amorphous carvedilol along with their lipidic mixtures using various instrumental techniques and to use response surface methodology in conjunction with factorial design to establish the functional relationships between operating variables (capmul GMS 50?K and cremophor RH 40). The response variables selected are spectroscopic absorbance (Y 1), mean particle size in distilled water (Y 2) and in phosphate buffer pH 6.8 (Y 3), polydispersibility index (PDI) (Y 4) and zeta potential (Y 5). The optimal formulations of crystalline and amorphous carvedilol-loaded nanoemulsions were composed of fixed levels, ?0.41 and ?0.42, of capmul GMS 50?K and cremophor RH 40, respectively. The predicted and observed values of Y 1–Y 5 for blank nanoemulsions showed the percentage bias error of ?12.12%, ?10.25%, ?18.47%, +14.81 and ?2.89, respectively. The bias percent ranged between ?2.70% and ?29.41% for the responses Y 1–Y 4 for both crystalline and amorphous carvedilol-loaded nanoemulsions, indicating high degree of prognosis. However, the bias percent values for the response variable Y 5 were 294.2% and 262.6%, for the crystalline and amorphous carvedilol-loaded nanoemulsions, respectively, possibly due to cationisation of emulsion droplets. The transmission electron microscopy of selected optimal nanoemulsions showed the spherical shape of globules with no signs of coalescence and precipitation of drug. This study demonstrates the use of factorial design for the preparation of nanoemulsions of crystalline and amorphous carvedilol. The desirable goals can be obtained by systematic formulation approach in the shortest possible time. 相似文献
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