Effect of MgO calcination temperature on the reaction products and kinetics of MgO–SiO₂–H₂O system

Abstract

MgO‐based binders have been widely studied for decades. Recently, the MgO–SiO2–H2O system was developed as a novel construction material, however, its reaction mechanism remains unclear. This paper investigated the reaction products and kinetics of MgO/silica fume (SF) pastes with MgO calcinated at different temperatures. The results indicate that MgO presented larger grain size after calcination at higher temperature. Mg(OH)2 and magnesium silicate hydrate (M–S–H) gel were formed when using MgO calcined at 850, 950, and 1050°C. However, only M–S–H gel was formed when using MgO calcined at 1450°C. The reaction kinetics of MgO could be described using α = 1 − e−k*t. The reaction rate of MgO increased with decreasing calcination temperature, increasing SF dosage, and the addition of sodium hexametaphosphate. Only M–S–H gel was formed when the reaction rate of MgO was below the demarcation line (about 0.250 × 10−6 s−1), and the corresponding demarcation area was around 14 days.

Characterization of Magnesium Silicate Hydrate (MSH) Gel Formed by Reacting MgO and Silica Fume

“…As the hydration process progresses, SF dissolves gradually as the silicon hydroxyl content increases. Figure 8 shows that the band at 1200 cm −1 shifts toward 1010 cm −1 /1065 cm −1 (anti-symmetric stretching vibration of Si–O–Mg) and the 800 cm −1 band almost disappears [ 39 , 41 , 47 ]. This suggests that the framework silica atoms change into layer-structured magnesium silicate hydrate.…”

“…A series of new bands appear from 550 to 650 cm −1 which can be attributed to the symmetric stretching vibration of Si–O–Mg of layer-structured magnesium silicate hydrate [ 33 , 34 ]. The band at 3690 cm −1 comes from the –OH stretching band of Mg(OH) 2 and the weak band at 895 cm −1 comes from the stretching vibration of silanol groups (Si–OH) [ 41 ].…”

“…The formation rate of MSH gel is determined by the hydration rate of MgO and the dissolution rate of SF. Li et al investigate the performance of MgO-SiO 2 -H 2 O system based on the dissolution rate of MgO [ 41 ]. Figure 11 illustrates the consumption of MgO and SF and suggests MgO reaction rate is faster than SF dissolution rate, leading to the formation of magnesium hydroxide.…”

“…The crystalline phases in hydrated solid residue samples were determined using XRD, (D8 Advance, Bruker, Karlsruhe, Germany, Max 2400 V diffractometer with Cu Kα radiation at a scan rate of 0.5° 2 θ min −1 ). The residual MgO content in MgO/SF pastes was determined by quantitative X-ray diffraction (Q-XRD, Bruker, Karlsruhe, Germany, Cu Kα, 40 kV and 40 mA) using the K-value method, with TiO 2 used as an internal standard material [ 41 , 42 ]. The ground MgO and internal standard material (TiO 2 ) were uniformly mixed at a mass ratio of 1:1 in a mortar with ethanol.…”

Effect of the MgO/Silica Fume Ratio on the Reaction Process of the MgO–SiO2–H2O System

“…The MgO–SiO 2 –H 2 O system was developed as a novel cementitious material [1,2,3,4,5]. Numerous applications have been realized, including usage in thermal insulation material [6], waste sealing material [7], refractory material [8], and soil stabilization [9].…”