Gallium -oxide

Gallium Oxides. The preparation conditions of gallium oxides and hydroxides are Hsted iu Table 6. 

Gainum (HI) Ga203 is the single gallium oxide that is stable under normal conditions. Like alumina, it exists iu several crystalline forms. The... 

Figure 7.13 Chart illustrating transformation relationships among the forms of gallium oxide and its hydrates.

Kisailus, D., Choi, J.H., Weaver, J.C., Yang, W. and Morse, D.E. (2005) Enzymatic synthesis and nanostructural control of gallium oxide at low temperature. Advanced-Materials, 17, 314—318. 

Shimizu, K Takamatsu, M Nishi, K Yoshida, H Satsuma, A Tanaka, T Yoshida, S Hattori, T. Alumina-supported gallium oxide catalysts for NO selective reduction Influence of the local structure of surface gallium oxide species on the catalytic activity, J. Phys. Chem., B, 1999, Volume 103, Issue 9, 1542-1549. 

Another study examined the acidity and basicity of bulk Ga203 by NH3 and SO2 adsorptions microcalorimetry performed at 150°C. As alumina, Ga203 is amphoteric, with heats higher than 100 kJ/mol for both NH3 and SO2 adsorption, respectively [186]. The amphoteric character of bulk gallium oxides and strong heterogeneity of the surface acidic and basic sites were proved also by Petre et al. [179] using microcalorimetry of pyridine adsorption at 150°C and CO2 adsorption at 30°C. 

Gallium sesquioxide is precipitated in hydrated form upon neutralization of acidic or basic solution of gallium salt. Also, it is prepared by thermal decomposition of gallium salts. Gallium oxide hydroxide, GaOOH [20665-52-5] on calcinations at high temperatures yields beta- Ga203. 

The finding of the low-temperature activation of propane on zeolite Ga/HZSM-5 indicates a bifunctional reaction mechanism 179,181. The highly dispersed gallium oxide species in close vicinity to the Bronsted acid sites promote the initial activation of propane. Derouane et al. 179,181 further showed that hydrogen inhibits the activation of propane. This effect was explained by a competitive adsorption of hydrogen on the gallium species or even by a reduction of Ga to Ga species. 

Galliuni (III). Ga C is the single gallium oxide that is stable under normal conditions. Like alumina, it exists in several crystalline forms. The most stable form is the beta oxide, mp ca 1725°C, density 5.88 g/cm3. The density of (X-Ga C is 5.18 g/cm3. 

The base dissolves the amphoteric gallium oxide and the acidic arsenic oxides. The selenide-diselenide solution dissolves residual arsenic, when present, by the reaction... 

---