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排序方式: 共有573条查询结果,搜索用时 15 毫秒
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The nanogranular nature of C-S-H 总被引:6,自引:0,他引:6
Despite its ubiquitous presence as binding phase in all cementitious materials, the mechanical behavior of calcium-silicate-hydrates (C-S-H) is still an enigma that has deceived many decoding attempts from experimental and theoretical sides. In this paper, we propose and validate a new technique and experimental protocol to rationally assess the nanomechanical behavior of C-S-H based on a statistical analysis of hundreds of nanoindentation tests. By means of this grid indentation technique we identify in situ two structurally distinct but compositionally similar C-S-H phases heretofore hypothesized to exist as low density (LD) C-S-H and high density (HD) C-S-H, or outer and inner products. The main finding of this paper is that both phases exhibit a unique nanogranular behavior which is driven by particle-to-particle contact forces rather than by mineral properties. We argue that this nanomechanical blueprint of material invariant behavior of C-S-H is a consequence of the hydration reactions during which precipitating C-S-H nanoparticles percolate generating contact surfaces. As hydration proceeds, these nanoparticles pack closer to center on-average around two characteristic limit packing densities, the random packing limit (η=64%) and the ordered face-centered cubic (fcc) or hexagonal close-packed (hcp) packing limit (η=74%), forming a characteristic LD C-S-H and HD C-S-H phase. 相似文献
4.
Paraskevas D. Tzanavaras Demetrius G. Themelis Anastasios Economou Georgios Theodoridis 《Mikrochimica acta》2003,142(1-2):55-62
Two new simple and rapid methods are reported for the accurate and precise spectrophotometric determination of captopril
(CPL) using flow (FI) and sequential injection (SI) analysis. The methods are based on the fast oxidation of CPL by Fe(III).
The produced Fe(II) reacts with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium to form a colored complex which
is monitored spectrophotometrically at 535 nm. Both methods allow the determination of the analyte up to 1000 mg L−1 at a sampling rate of 120 and 60 injections per hour for FI and SI, respectively. The methods are very precise [s
r=0.8 and 1.2% at 500 mg L−1 CPL (n=12) for FI and SI, respectively] and the 3σ detection limits (c
L=4.0 and 7.0 mg L1, respectively) are quite satisfactory. Their application to a variety of anti-hypertensive commercial pharmaceutical formulations
showed excellent results (relative errors, e
r, < ± 1.6% in all cases compared to an official HPLC method), while common pharmaceutical excipients were found not to interfere.
Recovery experiments further verified the accuracy of the developed methods, as the percent recoveries were in the range of
98.1–102.5%.
Author for correspondence. E-mail: themelis@chem.auth.gr
Received May 9, 2002; accepted January 8, 2003
Published online May 5, 2003 相似文献
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6.
Preparation of a molecularly imprinted polymer for the solid-phase extraction of scopolamine with hyoscyamine as a dummy template molecule 总被引:5,自引:0,他引:5
Theodoridis G Kantifes A Manesiotis P Raikos N Tsoukali-Papadopoulou H 《Journal of chromatography. A》2003,987(1-2):103-109
Molecularly imprinted polymers (MIPs) selective for scopolamine were produced using hyoscyamine (a close structural analogue) as template molecule. The produced polymers were used as media for solid-phase extraction, exhibiting selective binding properties for the analyte from biological samples. Human and calf urine and serum were processed on the MIP under various extraction protocols. The best performance was observed after loading the analyte in aqueous environment facilitating retention on the MIP by non-selective hydrophobic interactions. The MIPs were subsequently washed using an optimised solvent system to enable selective desorption of the analyte. Other related and non-related compounds were accessed to evaluate molecular recognition properties. Recoveries of up to 79% were achieved for the analyte of interest from biological samples. 相似文献
7.
Dimitrios P. CatsoulacosBarry R. Steele Georgios A. HeropoulosMaria Micha-Screttas Constantinos G. Screttas 《Tetrahedron letters》2003,44(24):4575-4578
DAB-dendr-(NH2)32 has been modified to produce two novel dendrimeric P,N-ligands, DAB-dendr-[1,2-(NCHC6H4PPh2)]32 and DAB-dendr-[1,2-(NHCH2C6H4PPh2)]32. These were both found to activate electron rich aryl bromides in the Heck reaction. The reactions seem to proceed better in a novel solvent system consisting of an equimolar mixture of a tertiary amine with acetic acid. A marked dependence of the conversion on the [equivalents of dendrimeric ligand]/[Pd] ratio has been observed with conversion decreasing as the ratio of dendrimer equivalents to Pd increases. This phenomenon is attributed to interactions of the arms bearing the metal with neighboring ones within the dendrimer. 相似文献
8.
A protic ionic liquid is designed and implemented for the first time as a solvent for a high energy density vanadium redox flow battery.Despite being less condu... 相似文献
9.
Theodosis Giousis Georgia Potsi Antonios Kouloumpis Konstantinos Spyrou Yiannis Georgantas Nikolaos Chalmpes Konstantinos Dimos Myrsini‐Kiriaki Antoniou Georgios Papavassiliou Athanasios B. Bourlinos Hae Jin Kim Vijay Kumar Shankarayya Wadi Saeed Alhassan Majid Ahmadi Bart J. Kooi Graeme Blake Daniel M. Balazs Maria A. Loi Dimitrios Gournis Petra Rudolf 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2021,133(1):364-369
Germanane (GeH), a germanium analogue of graphane, has recently attracted considerable interest because its remarkable combination of properties makes it an extremely suitable candidate to be used as 2D material for field effect devices, photovoltaics, and photocatalysis. Up to now, the synthesis of GeH has been conducted by substituting Ca by H in a β‐CaGe2 layered Zintl phase through topochemical deintercalation in aqueous HCl. This reaction is generally slow and takes place over 6 to 14 days. The new and facile protocol presented here allows to synthesize GeH at room temperature in a significantly shorter time (a few minutes), which renders this method highly attractive for technological applications. The GeH produced with this method is highly pure and has a band gap (Eg) close to 1.4 eV, a lower value than that reported for germanane synthesized using HCl, which is promising for incorporation of GeH in solar cells. 相似文献
10.
Recent theoretical and experimental studies have shown that polarizable anions, such as iodide and bromide, preferentially accumulate close to the surface of electrolyte solutions. This finding is in sharp contrast to the previously prevailing idea that salts are dielectrically excluded from the free water surface and opens up new avenues for research in specific salt effects. In this work, we have verified the ability of a recently introduced polarizable water model, SWM4-DP, to reproduce this behavior, by simulations of a NaI/water slab, corresponding to a 1.2 M solution. The water and ion polarizabilities are modeled by classical Drude oscillator particles. As revealed by the simulations, a double layer is formed close to the free water surface, with the iodide ions located closer to the interface and the sodium ions at a neighboring, interior layer. Near the surface, all solution species acquire an induced dipole moment, that is perpendicular to the surface and points toward the exterior. The double charge layer causes ordering of water at a subsurface region. Simulations with a simpler system of a single iodide ion in a water slab show that the surface position is stabilized by induced charge interactions; in contrast, the charge-dipole interactions between the iodide permanent charge and the water permanent dipole moment favor the bulk position. Thus, the polarizabilities of ion and water are essential for explaining the increased preference of iodide for the air-water interface, in accordance with other studies. 相似文献