Effect of Aluminum Incorporation on the Reaction Process and Reaction Products of Hydrated Magnesium Silicate

Abstract

In this study, we investigated the impact of aluminium ion (Al3+) incorporation on the microstructure and the phase transformation of the magnesium silicate hydrate system. The magnesium silicate hydrate system with aluminium was prepared by mixing magnesium oxide and silica fume with different aluminium ion contents (the Al/Si molar ratios of 0.01, 0.02, 0.05, 0.1, 0.2) at room temperature. The high degree of polymerization of the magnesium silicate hydrate phases resulted in the limited incorporation of aluminium in the structure of magnesium silicate hydrate. The silicon-oxygen tetrahedra sites of magnesium silicate hydrate layers, however, were unable to substitute for silicon sites through inverted silicon-oxygen linkages. The increase in aluminium ion content raised the degree of polymerization of the magnesium silicate hydrate phases from 0.84 to 0.92. A solid solution was formed from residual aluminum-amorphous phases such as hydroxyl-aluminum and magnesium silicate hydrate phases. X-ray diffraction (XRD), field emission scanning electron microscope (F-SEM), and 29Si and 27Al MAS NMR data showed that the addition of Al3+ promotes the hydration process of MgO and has an obvious effect on the appearance of M-S-H gel. The gel with low aluminum content is fluffy, while the gel with high aluminum content has irregular flakes. The amount of Al3+ that enters the M-S-H gel increased with the increase of Al3+ content, but there was a threshold: the highest Al/Si molar ratio of M-S-H gel can be maintained at about 0.006.

Evolution mechanism of the low-carbon MgO-based alkali-activated system under different heat-treatment conditions

“…When the MS-MR was 2.0, the main reaction product was forsterite. As the MS-MR increased, the magnesium silicate mineral changed from a chain structure to an island structure, which further showed that Mg atoms mainly played the role of bond breaking in the M-S-H gel, consistent with previous results [23][24][25].…”

Research progress on magnesium silicate hydrate phases and future opportunities

“…Hydrotalcite and zeolites were also observed in MgO and SiO 2 cements containing a high NaAlO 2 content [57], while at low amounts of NaAlO 2 and pH values below 10, no zeolites were observed, only hydrotalcite/Al(OH) 3 [50]. In any cases, the presence of extra Al-containing phases limited the Al incorporation in M-S-H. Also Jia et al [58] observed a limitation of Al/Si (< 0.05) in M-A-S-H in the presence of aluminium nitrate in the MgO-SiO 2 system. In most of the cases, the exact incorporation of Al in M-A-S-H is extremely difficult to quantify due to the nanocrystallinity of the Alcontaining phases, either Al-hydroxides, hydrotalcite-like phases, N-A-S-H gels or M-A-S-H.…”

Study on the Stability of Low-Carbon Magnesium Cementitious Materials in Sulfate Erosion Environments

“…In response to China's environmental policy, the development of new cementitious materials with complementary properties and environmental characteristics of traditional cement has become the research direction of the low-carbon cement industry, and, in this direction, magnesium oxide-based cementitious materials are of great importance. As a new type of green high-performance building material [1], magnesium oxide-based cementitious materials not only have good cementitious properties, but also have the characteristics of a low-pH alkali environment, high strength, and fast molding; besides, it is widely used in the curing of heavy metal ions and the comprehensive utilization of industrial solid wastes [2][3][4][5]. The development and research of magnesium oxide-based cementitious materials can aid in the rational utilization of abundant magnesium-based resources and idle industrial wastes, which are in line with China's national strategy for sustainable development, and have a wide range of potential applications.…”