Spinel preparation

Mandemack KW, Bazylinski DA, Shanks III WC, Bullen TD (1999) Oxygen and iron isotope studies of magnetite produced by magnetotactic bacteria. Science 285 1892-189 Mann S, Sparks NHC, Couling SB, Larcombe MC, Franke RB (1989) Crystallochemical characterization of magnetite spinels prepared from aqueous solution. J Chem Soc Far Trans 85 3033-3044 Matthews A, Zhu XK, O Nions K (2001) Kinetic iron stable isotope fractionation between iron (-II) and (-III) complexes in solution. Earth Planet Sci Lett 192 81-92... 

Mann, S. Sparks, N.H.C. Couling, S.B. Lar-combe, M.C. Frankel, R.B. (1989) Crystallo-chemical characterization of magnetic spinels prepared from aqueous solution. J. Chem. Soc. Faraday Trans. I. 85 3033-3044 Mann, S. Sparks, N.H.C. Frankel, R.B. Bazy-linski, D.A. Jannasch, H.W. (1990) Biomineralization of ferrimagnetic greigite (FejS4) and iron pyrite (FeS2) in a magnetotactic bacterium. Nature 343 258—261... 

Cerium Impregnation. All of the above spinels were impregnated(1) by cerium nitrate hexahydrate. A portion (87.7 g) of the spinel prepared by any of the above methods was impregnated with a solution containing 42.9 g of 70% Ce(N03)3.6H20 (Ce02 content 28.7%) and 40 g water. This material was dried at 120°C for 3 h and calcined at 700°C for 1 h. 

Table I. Physical and Chemical Properties of Spinels Prepared by Different Methods...

The physical properties of the spinels prepared by this method (Table I) are very different from those prepared by the co-condensation method. The spinels prepared by this method have a very high surface area (-150 m2/g). 

According to Fig. 6.26, spinels, prepared by mechanical activation followed by heat treatment, are characterized by very low lattice parameter a, which increases as temperature rises. It is well known that the radius of Mu ions is lower than that of Mn . Mn ions are more stable at lower temperatures. Thus, low values of a parameter for the samples with molar ratio Li/Mn=l/2 point to the increased amount of Mn ions comparing with that of stoichiometric spinel [93]. One can see that in the samples prepared from Li2C0 by mechanical activation and heating at 450°C, the value of a and the amount of Mn ions are higher than in the case of LiOH samples because of reducing character of CO2, eliminating in the course of interaction [98]. 

T ) ion in presece of Mn ( J - T ) ion on the structure of spinel lattice. The compounds with x = 0, 0.2, 0.4, 0.6 and 0.8 showed cubic structure while spinel with x = 1 showed tetragonal spinel phase. Electrical resistivity as well as thermoelectric measurements showed above spinels to be p-type semiconductors. The catalytic behaviour of spinels prepared was investigted for decomposition of hydrogen peroxide. 

Evidence of spinel structure was determined in the reaction bed by x-ray powder diffraction. The mineral spinel, magnesium aluminate, possessed unusual catalytic activity. Artificial spinels, prepared from other elements but still having the basic spinel structure, also were found to be active catalysts. 

Amdouni N, Zaghib K, Gendron F, Mauger A, Julien CM (2006) Structure and insertion properties of disordered and ordered LiNio.5Mn1.5O4 spinels prepared by wet chemistry. Ionics 12 117-126... 

Xu HY, Xie S, Ding N, Liu BL, Shang Y, Chen CH (2006) Improvement of electrochemical properties of LiNio.sMni 5O4 spinel prepared by radiated polymer gel method. Electrochem... 

Wu, S.Fl., Chen, Fl.L. 2003. The effects of heat-treatment temperature on the retention capacities of spinels prepared by the Pechini process, 119-121 134-138. 

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