ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The Partial Charge Model has been applied to analyse quantitatively experimental data on the process of hydrolysis and condensation, leading to gelation of Al3+ and Zr4+ cations in acidic concentrated inorganic sols. Both Al3+ and Zr4+ can condense to high polymeric species, but Zr4+ requires a higher ratio of hydrolysis than aluminium to initiate polymerization. Oxolation may occur in both aluminium and zirconium precursors. The role of anions in the polymerization process may also be calculated by this model and is assessed. In mixed Al-Zr gel systems, 27Al nuclear magnetic resonance shows that Al3+ does not participate in the initial polymerization, but instead decomposes to low polymer species upon mixing. Ageing has little effect on the polymerization of Al3+. Calorimetry shows that the polymerization of Zr4+, initiated by aluminium, accelerates at the beginning and gradually slows down after passing through a rate maximum. For mixtures of aluminium and zirconium precursors, temperature, composition (Al/Zr ratio) and concentration can significantly affect the rate of polymerization, as estimated from the rate of heat evolution.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00400902
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