Dear Sir. Concerning your issue about the difference between anodized alumina and gamma alumina from chemical property aspects. Natural crystalline aluminum oxide or alumina (Al203) is named corundum; the monocrystals are colorless and transparent. If they contain, intimately mixed, microcrystals of magnetite (Fe304) or hematite (Fe2 03), they are called emery. If the corundum monocrystals contain some elements in isomorphic substitutiton for Al3+ in their structure, gemstones and semi-precious gemstones are formed, also receiving specific names for their colors: (a) sapphire - blue (Fe, Ti); (b) ruby - red (Cr); oriental topaz - yellow (Fe3+, Fe2+); amethyst - purple (Fe, Mn, Ti); oriental emerald - green (Fe2+). Since, by definition, a mineral is formed in Nature, the expression “synthetic mineral” may be criticized. However, it is used for synthetic rubies and sapphires that are industrially produced today by the Verneuil (oxi - hydrogen flame) or by hydrothermal processes2. It is a common practice in X-Ray Crystallography to take the crystalline structures of some minerals (and also of some chemical compounds) as standards, these structures receiving the name of the mineral. The crystal structure of corundum is called corundum structure, but also is called a-Al203 or alpha-alumina structure . The aluminas, heated at temperatures under 1100 °C, were considered in the early days of X-ray powder diffraction method as amorphous or non-crystalline materials, in spite of the fact that they have important adsorptive and catalytic properties; in other words, they were considered very ill defined and complex materials, that above 1100 °C changed into crystalline a-alumina; sometimes, they were loosely called “gamma-alumina” by Ulrich.Later, it was recognized the existence of five crystalline aluminum hydroxides: gibbsite; bayerite; nordstrandite; diaspore; and boehmite; they have crystals varying from micro to milimetric size; their dehydroxilation occurs by heating between 300 °C and 600 °C and aluminas are formed, all as micrometer sized powders; these fine grained powders change their structure at 1100 °C, but remain as powders; increasing the temperatures from 1100 °C up to near the melting point of a-Al2 03 (2050 °C), the powder particles start to coalesce, sinter and recrystallize as microplatelets of hexagonal profile or even hexagonal prisms with a-Al203 structure; they are called “tabular crystals” of aluminas and must not be confused with the commercial product patented under the name “tabular alumina”. The formation of the hexagonal crystals of a-Al2 03 may be accelerated by the addition of 0.1% AlF3. Stumpf et al. (from ALCOA’S Research Laboratories, now Technical Center, Pittsburgh, USA), showed that, between the temperatures of dehydroxilation of the aluminum hydroxides and the alpha-alumina first crystallization, a number of well characterized and reproducible intermediate crystalline alumina structures are formed; each one has a stable different crystalline structure at a given temperature range, with just one exception which is “amorphous”. The type or structure of each alumina and its temperature range of existence are determined by the structure of the starting or precursor hydroxide; they are different for gibbsite, bayerite, nordstrandite, boehmite or diaspore .Extensive literature exists on the dehydroxilation of the crystalline hydroxides, in special on gibbsite, because it is the phase formed in the industrial Bayer Process. These seven aluminas are called “Transition Aluminas” and received Greek letters to identify them: gamma; delta; theta; kappa; chi; eta and rho. The electron microscope examination of the six standard Transition Alumina powders allowed the following specific conclusions to be drawn on their morphology and about the precursors of their microcrystals:

(a). chi-Al203 crystals are pseudomorphs from pseudohexagonal plates of gibbsite (tabular gibbsite).

(b). kappa-Al203 crystals are platy irregular crystals formed from chi-Al203 and from gibbsite, as former precursors, probably being pseudomorphs after them.

(c). gamma-Al203 crystals are pseudomorphs from rhombs or lozange platy crystals of boehmite as former precursors.

(d). delta-Al203 crystals are pseudomorphs from rhombs of gamma-Al203 and from boehmite as former precursors.

(e). theta-Al203 crystals are agglomerates of round particles that are not pseudomorphs from delta-Al203 rhombs.

(f). eta-Al203 are agglomerates of small round particles, probably from C02-precipitated bayerite crystals (not somatoids).

(g). All the six Transition Aluminas microcrystals present internal porous textures which are different among the several forms, depending from the precursor and the temperatures of formation.

(h). alpha-Al203 crystals at 1100 °C are pseudomorphs from the Alumina precursor; at 1200 °C, pseudomorphs and round shaped sintered crystals of alpha-Al203 may coexist; at 1500 °C only the sintered crystals exist as coalesced round plates, some with 120° angles, because perfect hexagonal platelets are only formed by addition of small percentages of AlF3. I think the following below links may help you in your analysis:

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392000000400003

https://www.ncbi.nlm.nih.gov/pubmed/16706463

http://pubs.acs.org/doi/abs/10.1021/cm034917j

Thanks