Silica Coating on Colloidal Maghemite Particles

Klotz, Michaela; Ayral, A.; Guizard, C.; Ménager, Christine; Cabuil, Valérie

doi:10.1006/jcis.1999.6517

Cited by 50 publications

(33 citation statements)

References 14 publications

(8 reference statements)

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“…This special interest arises from the fact that the silica grafting somehow stabilizes the particles in the ferromagnetic cFe 2 O 3 form, i.e., it decreases the transition efficiency to the antiferromagnetic a-Fe 2 O 3 form with an increase in temperature [12,15,16]. It also provides a transparent layer that can be used to stabilize the particles in suspension, providing a route to easily further graft it with organic molecules [9,10,12,18,19].…”

Section: Introductionmentioning

confidence: 98%

“…Another possible route to graft these particles, which has received special attention in recent years, involves the use of an inorganic material such as silica [9][10][11][12][13][14][15][16][17]. This special interest arises from the fact that the silica grafting somehow stabilizes the particles in the ferromagnetic cFe 2 O 3 form, i.e., it decreases the transition efficiency to the antiferromagnetic a-Fe 2 O 3 form with an increase in temperature [12,15,16].…”

Section: Introductionmentioning

confidence: 99%

“…Disperse the previously synthesized iron oxide particles in different sol-gel matrices. This is usually performed by coprecipitating the particles in aqueous solution, filtering and redispersing the precipitate in ethanol solution to perform the silica coating by silane hydrolysis and polymerization [9,10,11]. 2.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and characterization of silica-coated magnetic nanoparticles

Haddad¹,

Duarte²,

Baptista³

et al. 2004

Surface and Colloid Science

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The present work reports on the synthesis and properties of magnetic nanoparticles based on magnetite coated by a silica layer.A series of conditions was tested to allow the synthesis of the nanoparticles, usually performed in an aqueous medium, and could be efficiently coupled with the silica sol-gel process. The resulting particles were characterized by means of X-ray diffraction, transmission electron microscopy associated with electron energy loss spectra and electron spectroscopy imaging, Fourier transform IR, Mo¨ssbauer and magnetization measurements. Initially, magnetite particles with an average crystalline grain size of about 100 Å and a polydispersion of 30%, as revealed by X-ray diffraction and transmission electron microscopy analyses, respectively, were obtained with a mixture of FeCl 2 and FeCl 3 in aqueous and acid solution. The magnetization measurements, at room temperature, show that the particles are in the superparamagnetic regime. Magnetite was also synthesized in acid solutions in an alcoholic environment (25% methanol-to-base ratio), a medium that allows us to proceed with silicacoating by the sol-gel process in a one pot reaction. The resulting particles present size dispersion ranging from around 15 Å to about 200-300 Å as evidenced by electron micrographs. The superparamagnetic behavior is preserved, although its saturation magnetization value decreases from about 92 to about 50 emu g)1 , probably owing to the contribution of the smallest particles as well as to the surface spin disorder induced by addition of methanol to the synthesis medium. For higher values of the alcohol-to-base ratio, the resulting particles are amorphous, becoming crystalline under thermal treatment. When tetraethylorthosilicate is added to a solution containing 25% of methanol to base, iron oxides are SiO 2 -coated at room temperature, as evidenced by electron spectroscopy imaging and Fourier transform IR spectroscopy. The magnetization results are dependent on the Si-to-Fe volume ratio, in such a way that the values decrease as the SiO 2 amount increases, reflecting the nanoparticle coating.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Synthesis and characterization of silica-coated magnetic nanoparticles

Haddad¹,

Duarte²,

Baptista³

et al. 2004

Surface and Colloid Science

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“…Stable suspensions of magnetic nanoparticles in various polar solvents are needed in many technological fields such as hybrid material synthesis [1][2][3][4][5][6][7], medical application [8,9], and magnetic thin film fabrication [10,11]. In these research fields, the preparation of a stable and monodisperse suspension is the key issue in improving reproducibility, biocompatibility and film quality.…”

Section: Introductionmentioning

confidence: 99%

Surface modification of magnetic nanoparticles capped by oleic acids: Characterization and colloidal stability in polar solvents

Lee

Harris

2006

Journal of Colloid and Interface Science

133

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“…Ohmori and Matijević [11] coated a silica layer on spindle-type hematite particles by the sol-gel method and discussed the effects of the initial concentration of ammonia, water, and tetraethylorthosilicate (TEOS), as well as the reaction time on the silica layer thickness. Based on this paper, many kinds of core materials, such as alumina [12], zirconia [2], maghemite [13], magnetite [14], and barium sulfate [15], have been coated by the sol-gel method.…”

Section: Introductionmentioning

confidence: 99%