Physical properties and microstructures of poly(phospho-siloxo) and poly(sialate-siloxo) networks from two metakaolins

The aim of this investigation is to compare the properties of poly(phospho-siloxo) and poly(sialate-siloxo) networks. Commercial sodium waterglass and sodium waterglass from rice husk ash were used as alkaline reagents and phosphoric acid with molarities 8 and 10 M was used as acid reagents. Local metakaolin and commercial ones containing 0.99 and 0.0% of Fe2O3, respectively, were used as aluminosilicate sources. The physical properties of the prepared poly(phospho-siloxo) and poly(sialate-siloxo) networks were monitored by measuring the apparent and absolute density. The microstructures were assessed by scanning electron microscopy and mercury intrusion porosimetry. The engineering property was checked by the determination of their compressive strengths. The results indicated that the apparent densities of poly(phospho-siloxo) and poly(sialate-siloxo) networks are in the ranges 1.918–2.177 and 1.814–1.959 g/cm3, respectively, while their absolute densities are not significantly different. Their compressive strengths are ranging from 14.21 to 30.03 and 50.22 to 75.77 MPa, respectively. The average pore diameters of the specimens from acid reagents are between 30.0 and 83.9 nm whereas those from alkaline reagents are between 8.3 and 14.8 nm. The log differential intrusion versus pore size diameters showed that the obtained products using acid and alkaline solutions are ranging from 6000 to 110,000 nm and 5.59 to 13.84 nm, respectively. This indicates that poly(phospho-siloxo) and poly(sialate-siloxo) networks are macroporous and mesoporous materials, respectively. It was found that the chemical and mineralogical compositions and the degree of the purity of the aluminosilicate source could significantly affect the physical properties and microstructures of poly(phospho-siloxo) network.