Al 2 O 3 -Doped TiO 2 Ceramic Waste Forms Produced by Melting Method
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The starting materials were commercially supplied A120 3, ZrO 2, CeO 2 , Nd 2 0 3, SrO, TiN (from Nacalai Tesque) and TiO 2 (from Kanto Kagaku), all in powder form and of purity exceeding 99.9%. The starting mixture mixed in an agate mortar was put in a ZrO2 crucible and heated by a Nagano-Keiki carbon heater furnace. The temperature of samples was raised to 1673 K in 5 hours, maintained at the temperature for 1 hour and then cooled to room temperature in 5 hours in flowing argon. The reaction products were identified by X-ray diffraction. The X-ray diffraction was performed with Cu-K 01 radiation on a Rigaku RINT-2000 diffractometer equipped with a curved graphite monochrometer. The distribution of elements in the reaction products was studied by Electron probe micro analysis (EPMA) using Topkon MINI-SEM 100 and Horiba EMAX-8000 units.
443 Mat. Res. Soc. Symp. Proc. Vol. 608 ©2000 Materials Research Society
The melting temperature induced on a 10mg sample by heating at a rate 25K/min in flowing argon was monitored by differential scanning calorimetry (DSC), using MAC Science DSC-3000 system. Condensed sample after cooling was cut using a diamond impregnated saw and polished with emery papers and a diamond paste had a geometric surface area of 540-600 mm2 . Chemical durability was estimated by the Soxhlet leach test(MCC-5) method [1] followed by the analysis of the leachate by Inductively Coupled Plasma Spectrometry ( ICP-ES) method by Shimazu ICP - 7500. The leaching test was performed in distilled water at 337 K for 7 days, in accordance with the procedure of MCC-5. After 7 days, the sample and the leachate were separated. The sample was washed with deionized water, and was dried to constant mass in a 383 K oven and weighed. Density (d) was measured by the method of Archimedes using Wardon Pycnometer supplied by Shibata Scientific Tec. ltd. The Vickers hardness measurement was carried out using MHT- I micro Vickers hardness tester supplied by Matsuzawa Seiki co. ltd. RESULTS AND DISCUSSION As it is not clear that aluminum atom dissolves in RE site or Ti site runs Nos. 1-7 shown in Table I were performed. The identified phases, matching of the identification, occurrence of melting and melting temperature measured DSC are also summarized in Table 1. In run No. 1, only perovskite type Nd 2TiO 3 was obtained, but this compound did not melt at 1673K. In runs Nos. 2-4, the atomic ratio, (AI+Nd)/Ti of the starting mixture was fixed the products melted, but were not perovskite phases. Although the broadening of the X-ray diffraction peaks suggested the low crystallinity but the products might be the mixture of orthorhombic Nd 2TiO 5 and monoclinic Nd2Ti 2O 7 both of which containing Al. The reactions of the staring mixtures which contained the fixed atomic ratio, Nd/(Ti+A1) (runs No. 5-7) produced the perovskite Nd 2(Ti,AI) 30 9. However these products did not melt at 1673K. Since the atomic ratio, Nd/(Ti+AI)=2/3 caused the formation of the perovskite type Nd 2(Ti,AI) 30 9 it is suggested that the replacement of a Ti
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