Influence of Fe component from milling yield on characteristics of perlite based geopolymers

Abstract

The mineral and chemical composition of aluminosilicates used in geopolymer systems is critical for optimal structure formation and the overall performance of the geopolymer products. The composition of alumosilicates can be altered during the technological processing, especially, at the stage of fine milling. This study investigated the effect of aluminosilicate contamination with Fe from milling yield, the characteristics of the aluminosilicates with a metal lining, structure formation, and hardened properties of geopolymers based on different natural and technogenic persilicic aluminosilicates. The formation of Fe-phases due to milling yield was detected by the XRF analysis and the XRD investigation revealed the formation of nanosized ferrous hydroxide or bernalite Fe(OH)3(H2O)0.25. The volume of an elemental cell of the nanosized bernalite per Fe atom is 4.5 times larger than that of the metallic iron. This results in the disintegration of the matrix, which was observed by SEM and then confirmed by reduced strength performance of geopolymer composites. Based on this study, the negative effect of Fe-phases from milling and nanosized ferrous hydroxide on structural characteristics and service performance of geopolymer composites based on natural and technogenic raw materials was concluded.

The Correlation of Temperature-Mineral Phase Transformation as a Controlling Factor of Thermal and Mechanical Performance of Fly Ash-Based Alkali-Activated Binders

“…The results of XRF analysis demonstrated an elevated concentration of carbon, wherein the case of FA1 and FA2 ash products, those concentrations exceeded the limits regulated by ASTM C618. In previous research studies, the authors of [ 36 , 37 ] reported on the negative impact of unburned carbon as an inert component in a fly ash system, which resulted in poor alkali-activated binder structure formation, and therefore a reduction in strength performance.…”

“…Earlier studies [ 36 , 37 ] have shown that the use of milling equipment with metallic lining for dispersion fly ash powders resulted in milling yield in the form of Fe component. When Fe reacts with water during the alkali activation process, it turns into iron hydroxide Fe(OH) 2 with the volume 3–4.5 times larger than that of Fe.…”

Effect of Mixing Procedure and Chemical Composition on Physical and Mechanical Performance of Geopolymers

“…-Aluminosilicate composition of solid phase component with SiO2/ Al2O3 in range of 1.5-2.5; -Concentration of alkaline-earth elements (CaO, MgO) is 10 %, no more; -Vitreous phase content in aluminosilicate component is 50-60 % at least; -Presence of iron, calcium, and inert particles in fly ash [11].…”

“…-preparation of an aqueous alkali solution and its subsequent introduction into the aluminosilicate mixture [28] -preliminary exposure of aqueous alkali solution after preparation for 24 hours, followed by adding into the aluminosilicate mixture [29] -activation of alkaline components that presents in aluminosilicate raw materials (exp., perlite) by grinding [11].…”