| Thermal Decomposition and Phase Evolution
Behaviour of Precursors for Y 3AI50 12
Prepared by Homogeneous Precipitation |
S. RAMANATHAN, S. K. RoY AND P. V. RAVINDRAN
Pages : 12-15
DOI : 10.1080/0371750X.2000.10799892 |
| Abstract |
| Formation of precursors for yttrium aluminium garnet
(Y_1Al50 12-YAG) composition by homogeneous precipitation
method was studied. Two reactions occurring in the aqueous
system- aluminium nitrate-yttrium nitrate-urea and aluminium
sulphate-yttrium nitrate-urea, at 100°C were studied. The former
reaction yielded a gelatinous precipitate while a granular
precipitate was obtained by the second reaction. The gelatinous
precipitate after washing and drying in air oven at 90°C formed
a strongly agglomerated mass. However, final washing of the
gel with acetone was found to yield an easily friable mass. The
granular precipitate formed by the latter reaction, after washing
with water and drying in an oven, was found to be quite
friable. Both precursors were amorphous and contained
carbonates. A detailed thermogravimety-differential thermal
analysis and X-ray difTraction studies revealed that the former
precursor exhibited a continuous loss of weight up to 980°C and
formed an amorphous oxide compound of aluminium and
yttrium which crystallized into yttrium aluminium garnet at
1040°C. No loss of weight occurred at this stage. The latter
precursor lost weight in stages (endotherms at 860° and 1140°C),
formed crystalline intermediates (mixture of phases Y 20 3,
Y4Al20 9 and Y_1Al50 12) above 1140°C and finally formed a single
phase Y AG after calcining at 1400°C. This difference in the
behaviour of formation of phases from the precursors has been
attributed to the difference in the degree of compositional
homogeneities in the re!ipective precursor powders. The particle
size distributions of the as-formed precursors were in the range
of 5-10 pm while by grinding it could be reduced to the range
of 0.5-1 pm. The particle size distributions of the oxides obtained
hy calcining the ground precursors at 1200°C remained the same
as those of the precursors. |
| Full text : Subscribe to Download Full Text |
| [Go Back] |
|
