Magnesia–phosphate bond for cold-setting cordierite-based refractories

Effect of early hydration temperature on hydration product and strength development of magnesium phosphate cement (MPC)

“…The dead-burned magnesia (MgO) powder with a specific gravity of 3.25 g/cm 3 and specific surface of 230 m 2 /kg, calcined at 1700°C for 6 h, was used and its chemical composition is listed in 4 and borate with a certain proportion in laboratory, and then MPC pastes were obtained by mixing rapidly in a planetary orbital mixer for 3 min after adding water into MPCs. Four MPC pastes were prepared with the same mass ratios of MgO powder to NH 4 H 2 PO 4 (4:1) and water to MPC powder (0.12), but four different borate contents of 3%, 6%, 9% and 12% by the weight of MgO powder, respectively.…”

“…The results indicate that the borate only acts as a retarder without affecting the hydration degree of MPC. The retardation mechanism of borate is associated with the absorption of B(OH) 4 − dissolved form Fig. 4 shows the XRD patterns of MPC samples at different peak hydration temperatures ( Table 2).…”

“…Previous studies showed that the hydration products of MPC include NH 4 [8,[10][11][12][13][14][15]. For MgO-KH 2 PO 4 system, MgKPO 4 ·6H 2 O (struvite-K) is the main hydration product, and its composition and structure are analogous to those of NH 4 MgPO 4 ·6H 2 O (struvite) [6,[16][17][18][19].…”

“…Magnesium phosphate cement (MPC) is a potential cementitious material used for quick repair and reinforcement of structure, solidification of nuclear waste, and biomedical application due to a lot of significant advantages such as ultra-fast setting, ultra-early strength, high bond strength and good volume stability [1][2][3][4][5][6][7][8][9]. However, the performance of MPC may be affected by many factors, especially by temperature.…”

“…Abdelrazig et al [21] concluded that NH 4 MgPO 4 ·6H 2 O will start losing 5 water molecules to form NH 4 MgPO 4 ·H 2 O at about 65°C in TGA test. However, Sarkar [26] concluded that NH 4 MgPO 4 ·6H 2 O will start lose all water molecules and NH 3 at about 55°C, and the remaining is MgHPO 4 instead of NH 4 Due to the decomposition of the hydration products at a certain temperature, the types of hydration products probably depend on the peak hydration temperature.…”