共查询到20条相似文献,搜索用时 15 毫秒
1.
Wei Chen Steen Mørup Mikkel F. Hansen Tobias Banert Urs A. Peuker 《Journal of magnetism and magnetic materials》2008
We have prepared magnetic beads consisting of iron oxide nanoparticles in a polymethyl methacrylate (PMMA) and a polyvinyl butyral (PVB) matrix. High-field Mössbauer studies show that the particles have an almost perfect collinear spin structure and magnetization measurements show that they are superparamagnetic at room temperature at a time scale of seconds. We have followed the oxidation of the particles, which initially have a stoichiometry close to magnetite. The oxidation is fast during the first 2–3 weeks and then continues slowly such that even after 30 weeks the particles have not completely transformed to maghemite. The PVB beads are hydrophilic and biocompatible and are therefore well suited for applications in medicine and biology. 相似文献
2.
Role of N defects on thermally induced atomic-scale structural changes in transition-metal nitrides 总被引:1,自引:0,他引:1
Transition-metal nitrides (TMN) have exceptional stability, which underlies their use in various applications. Here, we study the role of N point defects on the stability of prototype TMNs using first-principles calculations. We find that distinct regimes for TMN changes relate to specific atomic-scale mechanisms, namely, diffusion of N interstitials (I(N)), of I(N) pairs, and of N vacancies. The activation of these processes occurs sequentially as the temperature is raised in a range of several hundreds of degrees, accounting for observed TMN changes under widely different conditions. 相似文献
3.
O. M. Golitsyna S. N. Drozhdin I. E. Zanin A. E. Gridnev 《Physics of the Solid State》2012,54(11):2296-2300
The X-ray diffraction investigations have been performed for nanocomposite materials based on porous aluminum oxide with inclusions of TGS and TGS, which is doped with L,α-alanine (ATGS). The presence of the TGS and ATGS textures in pores of Al2O3 films has been found. It has been established that, under conditions of confined geometry, the broadening of diffraction maxima of the reflection is caused by the size effect. The temperature dependences of the order parameter for porous aluminum oxide with TGS inclusions have been constructed. 相似文献
4.
The structural and optical properties of the novel porous iron oxide fabricated by wood template have been investigated. The obtained porous iron oxide was characterized to be α- Fe2O3 by Fourier transform infrared and Raman spectroscopy. X-ray absorption fine structure measurement revealed that the bond length of Fe-O1 of the porous iron oxide has good agreement with that reported for the α- Fe2O3 crystal structure while the bond lengths for Fe-O2 and Fe-Fe deviate slightly from those of the α- Fe2O3 crystal structure. Photoluminescence from the porous iron oxide exhibited broad emission bands around 760 and 890 nm, which are believed to be due to the unique nanoscale structure of the porous iron oxide. 相似文献
5.
We observe that light soaking for short durations and thermal quenching in nanocrystalline porous silicon (PS) produce metastable states. These metastable states show higher dark and photo currents, large photoluminescence and a weaker electron spin resonance (ESR) signal. However, long exposures to light produce the opposite effect. The metastable states are stable against sub-band gap light exposures. These metastable states can be removed by annealing at 150°C for 1 h. ESR shows the presence of a-Si phase (g ~ 2.0058, 6.4 G) in PS sample, but it is not sufficient to explain all the experimental results. Rather, our experiments suggest that light soaking causes more than one type of defects in porous silicon. The structural changes involving the movement of hydrogen present at the surface of PS or at the PS/a-Si interface may be responsible for these effects. 相似文献
6.
Hiroshi Matsunaga Makoto Kiguchi Philip D. Evans 《Journal of nanoparticle research》2009,11(5):1087-1098
Aqueous dispersions of copper-carbonate nanoparticles and microparticles have just begun to be exploited commercially for
the preservative treatment of wood. The success of the new systems will depend, in part, on the uniform distribution of the
preservative in wood and the ability of copper to penetrate cell walls. We examined the distribution of copper in wood treated
with a nano-Cu preservative. Copper particles are not uniformly distributed in treated wood, but they accumulate in voids
that act as the flow paths for liquids in wood. Particles are deposited on, but not within cell walls. Nevertheless, elemental
copper is present within cell walls, but at a lower level than that in wood treated with a conventional wood preservative.
These findings suggest that nano-Cu preservatives are able to deliver bioactive components into wood cell walls even though
the majority of copper particles are too large to penetrate the cell wall’s nanocapillary network. 相似文献
7.
Jerzy ChomaKatarzyna Jedynak Michal MarszewskiMietek Jaroniec 《Applied Surface Science》2012,258(8):3763-3770
Mesoporous carbon composites, containing nickel and nickel oxide nanoparticles, were obtained by soft-templating method. Samples were synthesized under acidic conditions using resorcinol and formaldehyde as carbon precursors, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock co-polymer Lutrol F127 as a soft template and nickel and nickel oxide nanoparticles, and nickel nitrate as metal precursors. In addition, a one set of samples was obtained by impregnation of mesoporous carbons with a nickel nitrate solution followed by further annealing at 400 °C. Wide angle X-ray powder diffraction along with thermogravimetric analysis proved the presence of nickel nanoparticles in the final composites obtained using nickel and nickel oxide nanoparticles, and Ni(NO3)2 solution. Whereas, the impregnation of carbons with a nickel nitrate solution followed by annealing at 400 °C resulted in needle-like nickel oxide nanoparticles present inside the composites’ pores. Low-temperature (−196 °C) nitrogen physisorption, X-ray powder diffraction, and thermogravimetric analysis confirmed good adsorption and structural properties of the synthesized nickel-carbon composites, in particular, the samples possessed high surface areas (>600 m2/g), large total pore volumes (>0.50 cm3/g), and maxima of pore size distribution functions at circa 7 nm. It was found that the composites were partially graphitized during carbonization process at 850 °C. The samples are stable in an air environment below temperature of 500 °C. All these features make the synthesized nickel-carbon composites attractive materials for adsorption, catalysis, energy storage, and environmental applications. 相似文献
8.
D. Mutter P. Nielaba 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(1):109-113
The reverse martensitic (“austenitic”) transformation upon heating of equiatomic
nickel-titanium nanoparticles with diameters between 4 and 17 nm is analyzed by means of
molecular-dynamics simulations with a semi-empirical model potential. After constructing
an appropriate order parameter to distinguish locally between the monoclinic
B19′ at low and the cubic B2 structure at high temperatures, the process of
the phase transition is visualized. This shows a heterogeneous nucleation of austenite at
the surface of the particles, which propagates to the interior by plane sliding,
explaining a difference in austenite start and end temperatures. Their absolute values and
dependence on particle diameter are obtained and related to calculations of the surface
induced size dependence of the difference in free energy between austenite and martensite. 相似文献
9.
Ruusunen Jarno Ihalainen Mika Koponen Tarmo Torvela Tiina Tenho Mikko Salonen Jarno Sippula Olli Joutsensaari Jorma Jokiniemi Jorma Lähde Anna 《Journal of nanoparticle research》2014,16(2):1-11
Enteric-coated formulations can delay the release of drugs until they have passed through the stomach. However, high concentration of drugs caused by rapidly released in the small intestine leads to the intestinal damage, and frequent administration would increase the probability of missing medication and reduce the patient compliance. To solve the above-mentioned problems, aspirin-loaded enteric-coated sustained-release nanoparticles with core–shell structure were prepared via one-step method using coaxial electrospray in this study. Eudragit L100-55 as pH-sensitive polymer and Eudragit RS as sustained-release polymer were used for the outer coating and inner core of the nanoparticles, respectively. The maximum loading capacity of nanoparticles was 23.66 % by changing the flow rate ratio of outer/inner solutions, and the entrapment efficiency was nearly 100 %. Nanoparticles with core–shell structure were observed via fluorescence microscope and transmission electron microscope. And pH-sensitive and sustained drug release profiles were observed in the media with different pH values (1.2 and 6.8). In addition, mild cytotoxicity in vitro was detected, and the nanoparticles could be taken up by Caco-2 cells within 1.0 h in cellular uptake study. These results indicate that prepared enteric-coated sustained-release nanoparticles would be a more safety and effective carrier for oral drug delivery. 相似文献
10.
Razvan Stefan Petru Pascuta Adriana Popa Oana Raita Emil Indrea Eugen Culea 《Journal of Physics and Chemistry of Solids》2012,73(2):221-226
Glasses in the system xFe2O3·(100?x) [45ZnO·55B2O3] (0≤x≤10 mol%) have been prepared by melting at 1200 °C and rapidly cooling at room temperature. The obtained samples were submitted to an additional thermal treatment at 570 °C for 12 h in order to relax the glass structure as well as to improve the local order. The as cast and heat treated samples were investigated using X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) measurements. The XRD patterns of all the studied samples show their vitreous nature. Structural modifications occurring in the heat treated samples compared to the untreated ones have been pointed out. EPR spectra of untreated and heat treated samples revealed resonance absorptions centered at g≈2.0, g≈4.3 and g≈6.4. The compositional variation of the line intensity and linewidth of the absorptions from g≈4.3 and g≈2.0 have been interpreted in terms of the variation in the concentration of the Fe3+ ions and the interaction between the iron ions. The EPR spectra of the untreated samples containing 5 mol% Fe2O3 have been studied at different temperatures (110–290 K). The line intensity of the resonance signals decreases with increase in temperature whereas the linewidth is found to be independent of temperature. It was also found that the temperature variation of reciprocal line intensity obeys the Boltzmann law. 相似文献
11.
Optical nonlinearities of Au nanoparticles embedded in zinc oxide (ZnO) matrix have been investigated by the Z-scan method at the wavelength of 532 nm using nanosecond Nd3+:YAG laser radiation. The nonlinear refractive index has been measured and the real part of the third-order nonlinear susceptibility is deduced. The results of the investigation of nonlinear refraction using the off-axis Z-scan configuration are presented and the mechanisms responsible for the nonlinear response are discussed. The nonlinear refraction is found to be negative (self-defocusing) in the vicinity of the surface plasmon resonance. Moreover, its strength is shown to be larger for materials having higher gold concentration. Finally, the prevailing influence of the electronic Kerr effect over the possible thermo-optical contribution is demonstrated. 相似文献
12.
Galina Goloverda 《Journal of magnetism and magnetic materials》2009,321(10):1372-1376
Colloidal nanoparticles of Fe3O4 (4 nm) were synthesized by high-temperature hydrolysis of chelated iron (II) and (III) diethylene glycol alkoxide complexes in a solution of the parent alcohol (H2DEG) without using capping ligands or surfactants: [Fe(DEG)Cl2]2−+2[Fe(DEG)Cl3]2−+2H2O+2OH−→Fe3O4+3H2DEG+8Cl− The obtained particles were reacted with different small-molecule polydentate ligands, and the resulting adducts were tested for aqueous colloid formation. Both the carboxyl and α-hydroxyl groups of the hydroxyacids are involved in coordination to the nanoparticles’ surface. This coordination provides the major contribution to the stability of the ligand-coated nanoparticles against hydrolysis. 相似文献
13.
R. F. C. Marques A. F. R. Rodriguez J. A. H. Coaquira J. G. Santos V. K. Garg M. Jafelicci Jr. S. J. L. Ribeiro M. Verelst J. Dexpert-Ghys P. C. Morais 《Hyperfine Interactions》2009,189(1-3):159-166
Mössbauer spectroscopy was used in this study to investigate magnetite nanoparticles, obtained by spray pyrolysis and thermal treatment under H2 reduction atmosphere. Room temperature XRD data indicate the formation of magnetite phase and a second phase (metallic iron) which amount increases as the time of reduction under H2 is increased. While room temperature Mössbauer data confirm the formation of the cubic phase of magnetite and the occurrence of metallic iron phase, the more complex features of 77 K-Mössbauer spectra suggest the occurrence of electronic localization favored by the different crystalline phase of magnetite at low temperatures which transition to the lower symmetry structure should occur at T ~120 K (Verwey transition). 相似文献
14.
B. Coasne S. K. Jain K. E. Gubbins 《The European physical journal. Special topics》2007,141(1):121-125
Molecular simulations are used to investigate the
adsorption and dynamics of argon in ordered and disordered models of porous
carbons. The pore shape and pore connectivity are found to affect
significantly the properties of the confined fluid. 相似文献
15.
Zhanhu Guo Koo Shin Amar B. Karki David P. Young Richard B. Kaner H. Thomas Hahn 《Journal of nanoparticle research》2009,11(6):1441-1452
The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated.
In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network
structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy
exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring
over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis
(TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide
nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of
the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping
conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic
stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A
tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles
during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication. 相似文献
16.
Bhavani Palagiri Rajababu Chintaparty Venkata subbha Reddy Imma Reddy 《Phase Transitions》2017,90(6):578-589
The iron oxide nanoparticles were synthesized by a simple hydrothermal method at different heating temperatures and pH conditions. The synthesized materials were characterized by X-ray diffractometer, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV–visible spectrometer and vibrating sample magnetometer. With increment in pH of the synthesized materials were resulted in orthorhombic (goethite) and cubic (magnetite) structures at pH 6 and 12, respectively. The banding nature of synthesized materials was analyzed by infrared spectra. The synthesized powders at 130?°C showed higher percent of nanorods (length = 90–120 nm) in addition to lower percentage of nanoparticles. The material at pH 12 consisted of maximum nanoparticles with size = 10–60 nm with small agglomerations. Band gap energy of synthesized materials was 2.2–2.8 eV. Herein, the reaction conditions tuned the saturation magnetization (MS). The maximum MS (59.38 emu/g) was obtained at pH 12 and lower MS (0.65 emu/g) was observed at pH 6 due to intrinsic property of goethite phase. 相似文献
17.
T. Gleitsmann T.M. Bernhardt L. Wöste 《Applied Physics A: Materials Science & Processing》2006,82(1):125-130
Strong visible luminescence is observed from silver clusters generated by femtosecond-laser-induced reduction of silver oxide nanoparticles embedded in a polymeric gelatin matrix. Light emission from the femtosecond-laser-activated matrix areas considerably exceeds the luminescence intensity of similarly activated bare silver oxide nanoparticle films. Optical spectroscopy of the activated polymer films supports the assignment of the emissive properties to the formation of small silver clusters under focused femtosecond-laser irradiation. The size of the photogenerated clusters is found to sensitively depend on the laser exposure time, eventually leading to the formation of areas of metallic silver in the biopolymer matrix. In this case, luminescence can still be observed in the periphery of the metallic silver structures, emphasizing the importance of the organic matrix for the stabilization of the luminescent nanocluster structures at the metal–matrix interface. PACS 78.66.Qn; 78.20.-e; 78.40.-q; 78.67.Bf; 78.68.+m 相似文献
18.
Arham S. Ahmed Ameer Azam M. Chaman S. Tabassum 《Journal of Physics and Chemistry of Solids》2012,73(7):943-947
Nanocrystalline tin oxide (SnO2) powders were synthesized through wet chemical route using tin metal as precursor. The morphology and optical properties, as well as the effect of sintering on the structural attributes of SnO2 particles were analyzed using Transmission electron microscopy (TEM), UV–visible spectrophotometry (UV–vis) and X-ray diffraction (XRD), respectively. The data revealed that the lattice strain plays a significant role in determining the structural properties of sintered nanoparticles. The particle size was found to be 5.8 nm, 19.1 nm and 21.7 nm for samples sintered at 300 °C, 500 °C, and 700 °C, respectively. Also, the band gaps were substantially reduced from 4.1 eV to 3.8 eV with increasing sintering temperatures. The results elucidated that the structural and optical properties of the SnO2 nanoparticles can be easily modulated by altering sintering temperature during de novo synthesis. 相似文献
19.
Harishchandra Singh A.K. Sinha M.N. Singh P. Tiwari D.M. Phase S.K. Deb 《Journal of Physics and Chemistry of Solids》2014
X-ray absorption near edge structure (XANES) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Synchrotron X-ray diffraction (SXRD) techniques are used to study as synthesized and isochronally annealed samples of cobalt oxide nanoparticles (NPs) grown using the wet chemical route. Quantitative phase composition determined using Linear Combination Fitting (LCF) on XANES data is found to be in reasonably good agreement with that obtained from Rietveld refinement on SXRD data. XPS data qualitatively indicate that Co3O4 concentration increases with increase in the annealing temperature, in confirmation with SXRD and XANES data. Larger shifts in the satellite peaks from the main peaks compared to these in bulk suggest larger crystal field splitting in nanoparticles as compared to the bulk. 相似文献
20.
Small-angle neutron scattering study on the stability of oxide nanoparticles in long-term thermally aged 9Cr-oxide dispersion strengthened steel 下载免费PDF全文
Peng-Lin Gao 《中国物理 B》2022,31(5):56102-056102
A 9Cr-oxide dispersion strengthened (ODS) steel was thermally aged at 873 K for up to 5000 h. The size distribution and chemical composition of the dispersed oxide nanoparticles were analyzed by small-angle neutron scattering under a magnetic field. Combined with transmission electron microscopy, Vickers micro-hardness tests and electron backscattered diffraction measurements, all the results showed that the thermal treatment had little or no effect on the size distributions and volume fractions of the oxide nanoparticles in the ferromagnetic matrix, which suggested excellent thermal stability of the 9Cr-ODS steel. 相似文献