| 1. |
- Gustafsson, Håkan, et al.
(författare)
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Magnetic and Electron Spin Relaxation Properties of (GdxY1-x)(2)O-3 (0 <= x <= 1) Nanoparticles Synthesized by the Combustion Method. Increased Electron Spin Relaxation Times with Increasing Yttrium Content
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:13, s. 5469-5477
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a magnetic resonance imaging contrast agent (CA) depends on several factors, including the relaxation times of the unpaired electrons in the CA. The electron spin relaxation time may be a key factor for the performance of new CAs, such as nanosized Gd2O3 particles. The aim of this work is, therefore, to study changes in the magnetic susceptibility and the electron spin relaxation time of paramagnetic Gd2O3 nanoparticles diluted with increasing amounts of diamagnetic Y2O3. Nanoparticles of (GdxY1-x)(2)O-3 (0 <= x <= 1) were prepared by the combustion method and thoroughly characterized (by X-ray diffraction, transmission electron microscopy, thermogravimetry coupled with mass spectroscopy, photoelectron spectroscopy, Fourier transform infrared spectroscopy, and magnetic susceptibility measurements). Changes in the electron spin relaxation time were estimated by observations of the signal line width in electron paramagnetic resonance spectroscopy, and it was found that the line width was dependent on the concentration of yttrium, indicating that diamagnetic Y2O3 may increase the electron spin relaxation time of Gd2O3 nanoparticles.
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| 2. |
- Gustafsson, Håkan, 1976-, et al.
(författare)
-
Magnetic and Electron Spin Relaxation Properties of (GdxY1-x)2O3 (0 ≤ x ≤ 1) Nanoparticles Synthesized by the Combustion Method. Increased Electron Spin Relaxation Times with Increasing Yttrium Content
- 2011
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Ingår i: The Journal of Physical Chemistry C. - United States : American Chemical Society. - 1932-7447 .- 1932-7455. ; 115:13, s. 5469-5477
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a magnetic resonance imaging contrast agent (CA) depends on several factors, including the relaxation times of the unpaired electrons in the CA. The electron spin relaxation time may be a key factor for the performance of new CAs, such as nanosized Gd2O3 particles. The aim of this work is, therefore, to study changes in the magnetic susceptibility and the electron spin relaxation time of paramagnetic Gd2O3 nanoparticles diluted with increasing amounts of diamagnetic Y2O3. Nanoparticles of (GdxY1-x)2O3 (0 e x e 1) were prepared by the combustion method and thoroughly characterized (by X-ray di.raction, transmission electron microscopy, thermogravimetry coupled with mass spectroscopy, photoelectron spectroscopy, Fourier transform infrared spectroscopy, and magnetic susceptibility measurements). Changes in the electron spin relaxation time were estimated by observations of the signal line width in electron paramagnetic resonance spectroscopy, and it was found that the line width was dependent on the concentration of yttrium, indicating that diamagnetic Y2O3 may increase the electron spin relaxation time of Gd2O3 nanoparticles.
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| 3. |
- Ballem, Mohamed Ali, et al.
(författare)
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Growth of Gd2O3 nanoparticles inside mesoporous silica frameworks
- 2013
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 168, s. 221-224
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Tidskriftsartikel (refereegranskat)abstract
- Gadolinium oxide (Gd2O3) nanoparticles with very small size and narrow size distribution were synthesized by infiltration of Gd(NO3)(3)center dot 6H(2)O as an oxide precursor into the pores of SBA-15 mesoporous silica using a wet-impregnation technique. High resolution transmission electron microscopy and X-ray diffraction show that during the hydrothermal treatment of the precursor at 550 degrees C, gadolinium oxide nanoparticles inside the silica pores are formed. Subsequent dissolution of the silica framework in aqueous NaOH resulted in well dispersed nanoparticles with an average diameter of 3.6 +/- 0.9 nm. If GdCl3 center dot 6H(2)O is used as precursor, GdOCl is formed instead of Gd2O3. The Gd2O3 nanoparticles showed a weak antiferromagnetic behavior, as expected.
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| 4. |
- Ekström, Thommy, et al.
(författare)
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Dense single-phase β-sialon ceramics by glass-encapsulated hot isostatic pressing
- 1989
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Ingår i: Journal of Materials Science. - 0022-2461. ; 24:5, s. 1853-1861
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Tidskriftsartikel (refereegranskat)abstract
- Single phase-sialon ceramics, Si6–z Al z O z N8–z , have been prepared from carefully balanced powder mixtures, also taking account of any excess oxygen in the starting materials. Sintering powder compacts in a nitrogen atmosphere (0.1 MPa) at 1800° C or higher transforms the starting mixture into a-sialon solid solution atz-values up to about 4.3, but the sintered material has an open porosity. Addition of 1 wt% Y2O3 to the starting mix improved the sintering behaviour somewhat and the density of the sintered compacts reached 95% of the theoretical value. By glass-encapsulated hot isostatic pressing at 1825° C, however, sintered materials of virtually theoretical density could be obtained, with or without the 1 wt% Y2O3 addition. These latter samples have been studied by X-ray diffraction and electron microscopy, and their hardness and indentation fracture toughness have been measured. It was found that the maximum extension of the-sialon phase composition at 1825° C and 200 MPa pressure is slightly below 4,z 3.85 and about 4.1 at atmospheric pressure, and that the hexagonal unit cell parameters are linear functions of thez-value. The single-phase-sialon ceramics had no residual glassy grain-boundary phase. The grain shape was equi-axed and the grain size increased from about 1m at lowz-values to 5m at highz-values. At lowz-values the hardness at a 98 N load was 1700 and the fracture toughness 3, whereas an increase inz above 1 caused both the hardness and fracture toughness to decrease significantly. Addition of 1 wt % Y2O3 to the starting mix prior to the HIP-sintering gave rise to a small amount of amorphous intergranular phase, changes in grain size and shape, a clear increase in fracture toughness and a moderate decrease in hardness.
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| 5. |
- Ekström, Thommy, et al.
(författare)
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Mixed α- and β-(Si-Al-O-N) Materials with Yttria and Neodymia Additions
- 1988
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 105/106, s. 161-168
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Tidskriftsartikel (refereegranskat)abstract
- A number of ceramic materials have been fabricated on a semipilot plant scale at different overall compositions in the (Y, Nd)---Al---O---N system at 177°C. Constant molar amounts of oxide mixtures of Y2O3: Nd2O3 in the ratios 100:0, 75:25, 50:50, 25:75 or 0:100 have been added. Dense materials were obtained for all compositions except those corresponding to mixed α- and β-(Si---Al---O---N) with higher α-(Si---Al---O---N) contents and high Nd2O3 contents. At the preparation temperature used in this study, the formation of an α-(Nd---Si---Al---O---N) seems prohibited and, thus, with increasing Nd2O3 content the amount of α-(Si---Al---O---N) decreased. The Nd2O3 added mainly formed crystalline intergranular phases such as the N-melilite phase, which increased in amount with increasing Nd2O3 in the starting mix. Hardness and indentation fracture toughness measurements were made and are discussed in relation to the phase composition and the microstructure. Some of the high Nd2O3 content Si---Al---O---N materials have as high fracture toughness values as the pure Y2O3 Si---Al---O---N materials do.
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| 6. |
- Käll, Per-Olov, et al.
(författare)
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Preparation and Crystal Structure of of U-Phase Ln3(Si3-xAl3+x)O12+xN2-x (x≈0.5, Ln=La,Nd)
- 1991
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 1:2, s. 239-244
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Tidskriftsartikel (refereegranskat)abstract
- U-phase Ln3(Si3 –xAl3 +x)O12 +xN2 –x(Ln = La, Nd) occurs as a crystalline phase in rare-earth sialon ceramics formed by devitrification of grain-boundary glasses at 1000–1400 °C. The crystal structure of Nd U-phase has been determined from Cu-Kα X-ray powder diffractometer data and refined by the Rietveld full-profile technique to RF= 0.028. The space group is P321 and the cell dimensions are a= 7.974(1)Å, c= 4.873(1)Å and V= 268.29 Å3. The structure is isomorphic with the La3Ga5GeO14 structure, and exhibits corner-shared layers of (Si,Al)(O,N)4 tetrahedra interconnected by AlO6 octahedra. The rare-earth cations occupy sites between the tetrahedral layers. Transmission electron microscopy and lattice imaging studies support the X-ray structural findings. The structural relationship of the U-phase to other nitrogen-containing ceramic phases is discussed.
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| 7. |
- Lenz, Annika, et al.
(författare)
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ZnO Nanoparticles Functionalized with Organic Acids: An Experimental and Quantum-Chemical Study
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:40, s. 17332-17341
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical synthesis and physical characterization of ZnO nanoparticles functionalized with four different organic acids, three aromatic (benzoic, nicotinic, and trans-cinnamic acid) and one nonaromatic (formic acid), are reported. The functionalized nanoparticles have been characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV−vis, and photoluminescence spectroscopy. The adsorption of the organic acids at ZnO nanoparticles was further analyzed and interpreted using quantum-chemical density-functional theory computations. Successful functionalization of the nanoparticles was confirmed experimentally by the measured splitting of the carboxylic group stretching vibrations as well as by the N(1s) and C(1s) peaks from XPS. From a comparison between computed and experimental IR spectra, a bridging mode adsorption geometry was inferred. PL spectra exhibited a remarkably stronger near band edge emission for nanoparticles functionalized with formic acid as compared to the larger aromatic acids. From the quantum-chemical computations, this was interpreted to be due to the absence of aromatic adsorbate or surface states in the band gap of ZnO, caused by the formation of a complete monolayer of HCOOH. In the UV−vis spectra, strong charge-transfer transitions were observed.
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| 8. |
- Nordberg, Lars-Olov, et al.
(författare)
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Stability and oxidation properties of RE–α-Sialon ceramics (RE = Y, Nd, Sm, Yb)
- 1998
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 81:6, s. 1461-1470
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation studies of hot-pressed RE–α-sialons, REx-Si12−4.5xAl4.5xO1.5xN16−1.5x (with x = 0.40 for RE = Nd, Sm,Yb; and x = 0.48 for RE = Y) were carried out in oxygen in a TG apparatus for ca. 20 h. Very good oxidation resistance was found for the Yb-doped samples, with parabolic rateconstants Kp ≈ 0.09 × 10−6–3 × 10−6 mg2 cm−4 s−1 in the temperature range 1250–1350°C. The promising performance of this material was corroborated by long-term oxidation experiments (5 days) in air at 1350°C. Although the oxidation kinetics can be described by simple equations related to the parabolic rate law (e.g., the arctan equation, ΔW/Ao = α·arctan(bt)½+ct½), the oxidation process in these materials is likely to be complex. The significantly lower oxidation resistance of the RE = Nd, Sm doped α-sialons, especially at higher temperatures, is related to the formation of melilite, RE2Si3−yAlyO3+yN4−y (y ≈ 1), in these systems. The melilite phase is also responsible for the thermal instability of the Nd– and Sm–α-sialons.
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| 9. |
- Söderlind, Fredrik, et al.
(författare)
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Sol-gel synthesis and characterization of polycrystalline GdFeO3 and Gd3Fe5O12 thin films
- 2009
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Ingår i: Journal of Sol-Gel Science and Technology. - : Springer Science and Business Media LLC. - 0928-0707 .- 1573-4846. ; 49:2, s. 253-259
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of the perovskite and garnet structured gadolinium ferrites GdFeO3 and Gd3Fe5O12 have been synthesized by a sol-gel method, based on stoichiometric mixtures of acetyl acetone chelated Gd3+ and Fe3+ dissolved in 2-methoxy ethanol. After spin coating onto Si wafers, and heating in air at 700 degrees C for 20 h, neatly grown essentially single phase films were obtained. From X-ray photoelectron spectroscopy an iron deficiency is observed in the uppermost layer of both films, implying that the crystallites preferably end in planes rich in Gd and O but not in Fe. The films were also characterized by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, and magnetic measurements.
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| 10. |
- Ahrén, Maria, et al.
(författare)
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A simple polyol-free synthesis route to Gd 2O 3 nanoparticles for MRI applications : An experimental and theoretical study
- 2012
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Ingår i: Journal of nanoparticle research. - : Springer. - 1388-0764 .- 1572-896X. ; 14:8
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Tidskriftsartikel (refereegranskat)abstract
- Chelated gadolinium ions, e.g., Gd-DTPA, are today used clinically as contrast agents for magnetic resonance imaging (MRI). An attractive alternative contrast agent is composed of gadolinium oxide nanoparticles as they have shown to provide enhanced contrast and, in principle, more straightforward molecular capping possibilities. In this study, we report a new, simple, and polyol-free way of synthesizing 4-5-nm-sized Gd 2O 3 nanoparticles at room temperature, with high stability and water solubility. The nanoparticles induce high-proton relaxivity compared to Gd-DTPA showing r 1 and r 2 values almost as high as those for free Gd 3+ ions in water. The Gd 2O 3 nanoparticles are capped with acetate and carbonate groups, as shown with infrared spectroscopy, near-edge X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and combined thermogravimetric and mass spectroscopy analysis. Interpretation of infrared spectroscopy data is corroborated by extensive quantum chemical calculations. This nanomaterial is easily prepared and has promising properties to function as a core in a future contrast agent for MRI.
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