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1999 (1)
1996 (1)
1Author    Carla Cannas, Giorgio Concas, Anna Musinu, Giorgio Piccaluga, Giorgio SpanoRequires cookie*
 Title    Mössbauer Spectroscopic Study of Fe 2 0 3 Nanoparticles Dispersed over a Silica Matrix  
 Abstract    A series of Fe 2 0 3 -Si02 nanocomposites (9 -33 wt% of Fe 2 0 3) has been prepared by a sol-gel method and submitted to thermal treatments at 300 -900 °C. The samples were characterized by X-ray diffraction and Mössbauer Spectroscopy measurements. Superparamagnetic behavior is exhibited by all the samples, indicating that the size of iron oxide grains is in the nanometer range (4-6 nm). Increase of iron content and temperature treatment give rise to a small particle growth, while the spread of sizes around the average value increases with the iron concentration. The Mössbauer spectra, at all the explored compositions, show a very steep increase of the peak width by treatment temperature at 900 °C, indicating the formation of the ferrimagnetic 7-Fe 2 0 3 phase from the antiferromagnetic amorphous Fe 2 0 3 phase, which dominates in the samples treated at lower temperatures. The samples at 28.5% and 33.2%, treated at 900 °C, also show a component of 7-Fe 2 0 3 in the blocked state at room temperature. Moreover, the growth of the particles favours the formation of other oxide phases (a and £ phase) along with the 7 phase. 
  Reference    Z. Naturforsch. 54a, 513—518 (1999); received June 28 1999 
  Published    1999 
  Keywords    Nanocomposite, Ferric Oxide, Mössbauer Spectroscopy, X-ray Diffraction 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0513.pdf 
 Identifier    ZNA-1999-54a-0513 
 Volume    54 
2Author    Giorgio Concas, Francesco Congiu, Anna Corrias, Carlo Muntoni, Giorgio Paschina, Daniela ZeddaRequires cookie*
 Title    Investigation of the Reaction between Fe 2 0 3 and Si Activated by Ball Milling  
 Abstract    The path of the reaction between Fe 2 0 3 and Si, activated by high energy ball milling, has been investigated by X-ray diffraction and Mössbauer spectroscopy. Hematite reduction involves oxygen transfer from Fe to Si with the formation of intermediate phases containing Fe(II), which are then reduced to Fe(0). A steady state is reached in the milling process where the reduction of stoichiomet-ric amounts of Fe 2 0 3 and Si is not complete and an amount of Fe(II) in an amorphous matrix still remains. The same intermediate compounds are also observed in the milling process of mixtures with higher Fe 2 0 3 /Si molar ratio. 
  Reference    Z. Naturforsch. 51a, 915—922 (1996); received April 1 1996 
  Published    1996 
  Keywords    Mechanosynthesis, Nanocomposite, Reduction reaction, Mössbauer spectroscopy, X-ray diffraction 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0915.pdf 
 Identifier    ZNA-1996-51a-0915 
 Volume    51