Hydrothermally synthesized aluminium phosphate cements
1993; Volume: 5; Issue: 17 Linguagem: Inglês
10.1680/adcr.1993.5.17.31
ISSN1751-7605
Autores Tópico(s)Concrete and Cement Materials Research
ResumoThe phase compOSitIOn, exothermal reaction energy, hydrothermal-induced phase transition and development of microstructure in aluminium phosphate cements (APCs), formed by the hydrothermal-catalyzed acid-base reaction between alumina as the base reactant and NH 2 H 2 PO 4 -based fertilizer (Poly-N) as the acid reactant, were investigated. Although the phase compositions of APC depended mainly on the species of alumina and the hydrothermal temperature, the acid-base reaction at 100°C led to the formation of amorphous ammonium aluminium orthophosphate (AmAOP) salt complexes as the major reaction product. The phase transition of AmAOP → crystalline (NH 4 ) 3 Al 2 (PO 4 ) 3 and NH 4 Al(PO 4 ) 2 · OH · 2 · 5H 2 O occurred at 200°C. Increasing the temperature to 300°C promoted the phase transformations (NH 4 ) 3 Al 2 (PO 4 ) 3 → Al 2 PO 4 (OH) 3 , and NH 4 Al(PO 4 ) 2 · OH · 2 · 5H 2 O → AlPO 4 : conversion of non-reactive alumina reactant into γ-AlOOH also occurred. A moderate combination of amorphous and crystalline phases in the cement bodies was responsible for the development of strength. An excessive amorphous → crystal phase transition resulted in a loss in strength, because of the in situ growth of crystalline compounds formed in the amorphous salt matrices, which bind the non-reactive alumina particles into a coherent mass.
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