Grain boundary structures and O tracer diffusivities (table 15) were studied in transparent ceramics whose compositions varied from a 2% excess of Y2O3 to an 0.5% excess of Al2O3. In the former case, a second phase (yttrium aluminum perovskite) which contained Si was found in the grain boundaries. In the case of an Al2O3 excess, both Al-rich particles (alumina) and a Si-rich segregated layer were found in the grain boundaries. It was found that volume diffusion of the O tracer was little affected by the excesses. On the other hand, the grain boundary diffusion of O (table 16) was suppressed in Y2O3-excess specimens, as compared with Al2O3-excess specimens. These differences were attributed to the effect of chemical reactions between second phases and intergranular liquid during sintering.

I.Sakaguchi, H.Haneda, J.Tanaka, T.Yanagitani: Journal of the American Ceramic Society, 1996, 79[6], 1627-32

 

 

 

Table 15

Arrhenius Parameters for Bulk O Diffusion in Al5Y3O12

 

Condition

Addition

Do (m2/s)

Q (kJ/mol)

non-annealed

2%Y2O3

5.8 x 10-10

259.6

non-annealed

1%Y2O3

7.7 x 10-11

223.9

non-annealed

stoichiometric

4.3 x 10-8

304.1

non-annealed

0.5%Al2O3

3.9

519.4

annealed

2%Y2O3

2.1 x 10-7

348.2

annealed

1%Y2O3

2.2 x 10-9

286.1

annealed

stoichiometric

2.6 x 10-10

265.8

annealed

0.5%Al2O3

2.3 x 10-5

408.5

 

 

 

 

Table 16

Arrhenius Parameters for Grain Boundary O Diffusion in Al5Y3O12

 

Condition

Addition

Do (m2/s)

E (kJ/mol)

non-annealed

stoichiometric

2.1 x 10-10

393.8

non-annealed

0.5%Al2O3

124

688.8

annealed

stoichiometric

1.1 x 10-8

463.9

annealed

0.5%Al2O3

5.6 x 10-9

459.2