Dear Sir,

Pls find herewith attached reference article.

Ceriodaphnia dubia as a Potential Bio-Indicator for Assessing Acute Aluminum Oxide Nanoparticle Toxicity in Fresh Water Environment (Sunandan Pakrashi et al., 2013), PLOSONE. Published: September 5, 2013 http://dx.doi.org/10.1371/journal.pone.0074003

Dear Murali,

Thanks for your suggestion, however, it doesn't have the % Al for the gamma alumina composition detected by ICP

               Gamma alumina is one of the cubic aluminas; that is, it is based on cubic close packing of oxygen anions with Al cations occupying interstitial sites within the ccp oxygen lattice. These structures may be described in terms of the structure of the closely related Mg-spinel . Mg-spinel has a crystallographers’ cubic unit cell of contents Mg_8Al_{16}O_{32}, and a primitive unit cell of contents Mg_2Al_4O_8. The Mg atoms occupy Td interstitial sites within the ccp oxygen lattice, and Al atoms occupy Oh interstitial sites. The space group is Fd3m. Alumina contains no Mg, and therefore all cations are Al. This necessitates the introduction of vacancies to maintain the balance of valance. In particular, one of every nine cation sites in the spinel structure must be vacant to produce the Al_2O_3 stoichiometry. The crystallographers’ cubic unit cell is V_{2.666}Al_{21.333}O_{32} and the primitive unit cell is V_2Al_{16}O_{24}.  (V = vacancy.) Referencing the spinel notation, we note that the primitive cell consists of (Td_6)(Oh_{12})O_{24}, showing that there are 6 Td sites and 12 Oh sites per primitive unit cell. Obviously, with 16 cations per primitive unit cell, neither the Td cation sublattice (which has 6 sites per primitive cell) nor the Oh cation sublattice (which has 12 sites per primitive unit cell) is sufficient to hold all of the Al atoms. The Al must therefore be distributed over both Td and Oh sites and will therefore fall within the range [25% ≤ XTd ≤ 37.5%], where XTd is the fraction of Al cations on Td sites. The extremes of this range are represented by XTd = 25% given by (V_2Al_4)(Al_{12})O_{32} and XTd = 37.5% given by (Al_6)(V_2Al_{10})O_{32}. Gamma alumina probably lies near the lower end of this range.

               A more complete understanding of the cubic aluminas is afforded when one recognizes that cubic aluminas are derived by dehydration of aluminum hydroxide minerals, and there exists the possibility of the presence of hydrogen within the bulk. This changes the allowed range of Al content slightly. Details may be found in these references:

Karl Sohlberg*, Stephen J. Pennycook, and Sokrates T. Pantelides, “Hydrogen and the structure of the transition aluminas,” J. Am. Chem. Soc., 121, 7493 (1999).

Karl Sohlberg*, Stephen J. Pennycook, and Sokrates T. Pantelides, “The bulk and surface structure of g-alumina,” Chem. Eng. Comm., 181, 107 (2000).

Karl Sohlberg* and Sergey N. Rashkeev, “Theoretical and Computational Atomic-Scale Studies of Complex Catalytic Materials,” Handbook of Theoretical and Computational Nanotechnology, 8, 615-645 (2006).

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