Analysis of the properties of chemically bound phosphate ceramics (CBPCs) produced from metakaolin with various acid phosphates

In this study, chemically bound phosphate ceramics (CBPCs), a type of geopolymer, were synthesized by reacting metakaolin (MK) with acidic solutions of phosphoric acid (PA), potassium dihydrogen phosphate (KDP), calcium dihydrogen phosphate (CDP), and aluminum dihydrogen phosphate (ADP). The obtained CBPCs were characterized using thermal analysis (DTA-TG), X-ray diffraction, dilatometry, and scanning electron microscopy and by their real density, porosity, water absorption, and compressive strength. The analyses revealed that the used acid phosphate type strongly influenced the properties of the resulting CBPCs. The best compressive strength results were found in CBPCs obtained using ADP, with an average value of 34.50 MPa and average porosity of 23.21%. For CBPCs obtained from PA, CDP, and KDP, the average compressive strength values were 14.18, 8.17, and 2.84 MPa, respectively; their average porosities were 18.79%, 36.23%, and 37.90%, respectively. The results demonstrate that CBPCs produced with MK can be cured at room temperature and that CBPCs obtained with ADP have higher compressive strength values than these of the other acids.