12182-58-0Relevant articles and documents
A tale of two metals: New cerium iron borocarbide intermetallics grown from rare-earth/transition metal eutectic fluxes
Tucker, Patricia C.,Nyffeler, Jason,Chen, Banghao,Ozarowski, Andrew,Stillwell, Ryan,Latturner, Susan E.
, p. 12138 - 12148 (2012)
R33Fe14-xAlx+yB25-yC 34 (R = La or Ce; x ≥ 0.9; y ≥ 0.2) and R33Fe 13-xAlxB18C34 (R = Ce or Pr; x a = 14.617(1) A, Z = 2, R1 = 0.0155 for Ce33Fe13.1Al1.1B24.8C34, and a = 14.246(8) A, Z = 2, R1 = 0.0142 for Ce 33Fe13B18C34). Their structures can be described as body-centered cubic arrays of large Fe13 or Fe 14 clusters which are capped by borocarbide chains and surrounded by rare earth cations. The magnetic behavior of the cerium-containing analogs is complicated by the possibility of two valence states for cerium and possible presence of magnetic moments on the iron sites. Temperature-dependent magnetic susceptibility measurements and Moessbauer data show that the boron-centered Fe14 clusters in Ce33Fe14-xAl x+yB25-yC34 are not magnetic. X-ray photoelectron spectroscopy data indicate that the cerium is trivalent at room temperature, but the temperature dependence of the resistivity and the magnetic susceptibility data suggest Ce3+/4+ valence fluctuation beginning at 120 K. Bond length analysis and XPS studies of Ce33Fe 13B18C34 indicate the cerium in this phase is tetravalent, and the observed magnetic ordering at TC = 180 K is due to magnetic moments on the Fe13 clusters.
Genesis of iron carbides and their role in the synthesis of hydrocarbons from synthesis gas
Herranz, Tirma,Rojas, Sergio,Perez-Alonso, Francisco J.,Ojeda, Manuel,Terreros, Pilar,Fierro, Jose Luis G.
, p. 199 - 211 (2006)
A series of iron-based Fischer-Tropsch catalysts, either pure or promoted with Ce or Mn, were subjected to different activation treatments with H2, CO, or H2/CO. The surface species formed after different treatments were characterized by temperature-programmed surface reaction with hydrogen (TPSR-H2) and temperature-programmed surface desorption with argon (TPD-Ar). After activation and temperature-programmed treatments, the samples were passivated and characterized by X-ray diffraction and Raman spectroscopy. After each activation treatment, the catalysts were tested in the Fischer-Tropsch synthesis, and selected postreaction samples were characterized by Moessbauer spectroscopy. After CO and syngas treatment, cementite (θ-Fe3C) and Haegg (χ-Fe2.5C) carbides were formed, respectively. Different surface carbonaceous species were stabilized over these carbides. Cementite species are less active in the Fischer-Tropsch synthesis; however, under the Fischer-Tropsch reaction environment, they can evolve into the Haegg carbide, over which the more active carbonaceous intermediate species are formed. Modification of the catalyst composition by Mn and Ce is effective only when the samples are activated under CO, accelerating the stabilization of active carbonaceous intermediates.
Large spontaneous volume magnetostriction and pressure effects on the magnetic properties of amorphous Ce-Fe alloys
Fukamichi,Aoki,Masumoto,Goto,Murayama,Mori
, p. [d]18-26 (1997)
The thermal expansion anomaly, the effects of pressure and hydrogenation on the magnetization and the Curie temperature have been investigated in order to discuss the magnetovolume effects in the amorphous CexFe100-x alloys prepared by high-rate DC sputtering. These amorphous alloys have a large spontaneous volume magnetostriction which increases with decreasing x. The pressure effects on the magnetization, the spin freezing temperature and the Curie temperature are significant. The magnetization M varies linearly with the square of temperature T2 in the ferromagnetic state. The hydrogenation increases markedly both the Curie temperature and the magnetization of the amorphous CeFe2 alloy. However, no huge coercive force related to the random magnetic anisotropy has been confirmed at 4.2 K against the expectation based on a valence change of the Ce ion. For the amorphous CeFe2 alloy, the compressibility estimated from the increases in the Curie temperature and the Fe-Fe interatomic distance by hydrogenation, does not coincide with the experimental value obtained by Brillouin scattering. Therefore, the expansion due to hydrogenation is not regarded to be caused by a so-called negative hydrostatic pressure effect.
