Ceramics-Silikáty 45, (4) 143 - 149 (2001)

Mechanism of nitric acid attack on hardened paste of geopolymeric cements, in addition to the leaching process discussed in part I [1], consists of an electrophilic attack by acid protons on polymeric Si-O-Al bonds resulting in the ejection of tetrahedral aluminium from the aluminosilicate framework. The framework vacancies are mostly re-occupied by silicon atoms resulting in the formation of an imperfect highly siliceous framework that is relatively hard but brittle. The ejected aluminium converted to octahedrally coordinated aluminium mostly accumulates in the intraframework space.