PROCESSING AND MICROSTRUCTURAL CHARACTERIZATION OF SINTERED LANTHANUM ALUMINATE OBTAINED BY TWO DIFFERENT ROUTES

摘要

Lanthanum aluminate (LaAlO_3, LAO) belongs to the sintering resistant oxides and thus is interesting for high temperature applications.LAOpowder were obtained by two processing routes: 1) Reverse precipitation of La(OH)_3 on colloidal pseudoboehmite (prepared from Al_2(SO_4)_3) and 2) reverseco-precipitation of nitrates of La and Al, followed by subsequent agglomeration-homogenization by spray drying. Measurements of particle size of spherical agglomerates were doneafterspray drying and calcination.Sintering wasdriven by pressing either crushed dried powder obtained from the first route or calcined agglomerates from the second route at temperatures of 1500 and 1600°C, respectively. Characterization was carried out by XRD, RAMANand SEM.Transformation temperature to LAO phase was found at 1300°C with remaining of lanthanum oxide phase and in the range 800°C-900°C with a mixture rhombohedral and cubic phases for the first and second route, respectively. The maximum theoretical density achieved was close to 95% and 90% for the first and second route, respectively. On both routes the sintered samples show rhombohedral phase. A small proportion of a hexagonal phase corresponding to La_(0.827)Al_(11.9)O_( 19.09) was detected in samples from route 2. Low densification, particularly in samples from route 2 is associated to the growth morphology of La_(0.827)Al_(11.9)O_(19.09) grains and the poor packing conditions from calcined powder.