Summary
Boehmite powders were prepared by controlled hydrolysis of aluminium isopropoxide solution and recrystallisation in hot water; these were cylinders (fibres) of lengths (I 0) = 0.06 to 0.10μm. The dissolution of dilute suspensions of these powders in well-stirred sodium hydroxide solutions was studied at 35 ° to 65 °C. Reaction solid and solution were analysed after different times by chemical and physical methods.
Reaction occurred by three-directional dissolution of the cylinders: the reactions of the first (non-aggregated) thirty percent material were four-third order w. r. t. powder weight (and second order w. r. t. powder surface area). The initial rate constantsk wi (g−″ hr−1) for reactions with sodium hydroxide of unit mean ionic activity at 20 °C varied from 0.012 to 0.040. Rate constants increased linearly with the mean ionic activity of the hydroxide solution and exponentially with reciprocal temperature, five-six times for 15 °C temperature rise. Energies of activation varied from 115–125 kJ mole−1.
Zusammenfassung
Boehmit-Pulver wurden durch kontrollierte Hydrolyse von Aluminiumisopropoxid-Lösungen hergestellt und in heißem Wasser rekristallisiert. Die Kristalle bildeten Zylinder (Fasern) mit einer Länge von 0,06–0,10μm. Die Auflösung dieser Präparate in verdünnten Suspensionen in Natriumhydroxidlösungen wurde bei 35–65 °C untersucht. Festkörper und Lösung wurden nach vorgegebenen Zeiten analysiert.
Die Lösung erfolgt in einer 3dimensionalen Reaktion der Zylinder. Die Anfangsgeschwindigkeitskonstanten für Reaktionen mit Natriumhydroxidlösungen bei 20 °C variierte von 0,012 bis 0,040 (g−″ h−1). Die Geschwindigkeitskonstanten steigen linear mit der Ionenaktivität der Hydroxidlösungen und exponentiell mit der reziproken Temperatur. Aktivierungsenergien liegen zwischen 115 und 125 kJ mol−1.
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References
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Packter, A. Studies on recrystallised aluminium mono-hydroxide precipitates. Kinetics of dissolution by sodium hydroxide solutions. Colloid & Polymer Sci 254, 1024–1029 (1976). https://doi.org/10.1007/BF01516921
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DOI: https://doi.org/10.1007/BF01516921