Alumina-yttrium aluminum garnet

The possibilities offered by the sol-gel method for obtaining nanosized powders were reviewed. The influence of nanosized oxide powders obtained by different types of sol-gel methods on their sintering behavior was evaluated. 

The mostly used sol-gel processes for the sol-gel oxide preparation were the formation of dispersed powders in the solution, the formation of solid 

The advantage of the sol-gel method is that besides the homogeneity of the precursors at the molecular level, in the case of multicomponent systems chemical bond formation among the reagents takes place in a solution, enhancing the homogeneity and reactivity of the obtained gels/powders. 

The sintering of pressed oxides to form dense ceramics occurs at much lower temperature than that in the case of oxides obtained by conventional methods, due to their small particle size and uniform distribution. At the same time, using nanosized oxide powders the ultrafine grain size is retained after sintering close to theoretical density, conveying superior properties to the obtained ceramics. 

Powders derived from sol-gel processing have superior properties and enhanced sintering behavior leading to dense ceramics with advanced applications. They are recommended especially for systems that present low sintering ability and/or sintering difficulties (evaporation of some components, lower density of the obtained compounds compared with the initial oxides, etc.). 

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Fig. 7 Creep-resistance of the eutectic fiber consisting of interpenetrating phases of alpha-alumina and yttrium-aluminum-garnet (YAG) up to very high temperatures compared with other types of oxide fibers... 

M.K. Cinibulk, K.A. Keller, and T.I. Mah, Effect of yttrium aluminum garnet additions on alumina-fiber-reinforced porous-alumina-matrix composites. J. Am. Ceram. Soc. 87(5), 881-887 (2004). 

All currently available commercial oxide fibers are based on aluminum oxides. Examples are alumina (AI2O3) yttrium aluminum garnet (YAG) and mullite (3Al203-2Si02). 

Flow chart of the mixed precipitation method is shown in Fig. 3.42. Briefly, alumina precursor powder was first synthesized by adding aluminum nitrate solution (0.15 M) dropwisely into the ammonium bicarbonate solution (1.5 M) under vigorous stirring. The as-prepared alumina precursor powder was then dispersed in yttrium nitrate solution to form uniform suspension. After that, ammonium bicarbonate solution (0.5 M) was added dropwisely into the suspension, so that yttrium precipitate was coated on the alumina precursor powder. The mixed precursor was aged, washed, dried, and then calcined to form yttrium aluminum garnet, with a phase formation temperature about 300 °C lower than that required by the traditional solid-state reaction process. Alternatively, it is also worth trying to coat yttria with alumina. 

Zhang QW, Saito F (2003) Mechanochemical sohd reaction of yttrium oxide alumina leading to the synthesis of yttrium aluminum garnet Powder Technol 129 86-91... 

In ruby lasers, which are well known, a single crystal of alumina is doped with a small quantity of Cr + ions and laser light with a wavelength of 0.694 xm is emitted. Yttrium aluminum garnet (YAG) doped with Nd ions emits laser light at a wavelength of 1.06 pm. Since YAG ceramic lasers were discussed in the section on synthesis, here we will describe consisting of yttria ceramics. 

Regarding ceramic-containment materials," sihca, SiO, and alumina, Al O, are strongly attacked and hence readily dissolve in liquid lithium. By contrast, alkaline-earth oxides such as beryllia (BeO), magnesia (MgO), and calcia (CaO) and rare-earth oxides such as ceria (CeOJ, yttria (YfiJ, chromite spinel (FeCr OJ, and yttrium aluminum garnet (Y AljOj ) seem to be noncorroded below 500 C, while aluminum, titanium, and zirconium nitrides or... 

The diffusion of rare-earth elements was studied in yttrium aluminum garnet. The source of the diffiisant was a mixture of alumina and the rare-earth element oxide. The diffusion profiles were measured using Rutherford back-scattering spectrometry. The Arrhenius relationship was ... 

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