Calorimetry and other methods in the studies of reactive magnesia–hydratable alumina–microsilica hydrating mixtures

Abstract

The reactivities of the binary and ternary mixtures of reactive magnesia (MgO:M), hydratable alumina (Al 2 O 3 :A) and microsilica (SiO 2 :S) micropowders were investigated by calorimetric method and other analytical techniques (X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential thermal/thermogravimetric (DTA-TG) analysis and scanning electron microscope (SEM) observations). Effect of water/solid mass ratio and temperature on the hydration behavior of the M-A, M-A-S, M-S, A-M-S and A-S hydratable binders were established. The methodological considerations on both in situ and ex situ mixing techniques have also been taken. The initial mixing peak was due to wetting of the binder particles and initial dissolution reactions. A second, extensive heat peak was associated with the formation of crystalline and noncrystalline hydration products, i.e., brucite Mg(OH) 2 , magnesium aluminate hydrate (MAH; H:H 2 O)-like phase, magnesium silicate hydrate (MSH)-like phase and magnesium aluminum silicate hydrate gels (MASH). Negligible heat was evolved during the hydration reaction of A-S mixture, and the second reaction peak was not observed. Nevertheless, the presence of Al 2 O 3 and SiO 2 in other combinations contributes to the consumption of Mg(OH) 2 which was formed during the initial stages of hydration and leads to the formation of cementitious products, like M-A-H, M-S-H and M-A-S-H.

Influence of hydrothermal conditions on the phase composition of materials from the system MgO-Al2O3-SiO2-H2O

“…The micrographs presented in Figs. 4,5,6,7,8 show the results of SEM-EDS analysis of the studied samples. The Fig.…”

“…In the Al 2 O 3 -MgO-SiO 2 system, we can obtain different binding materials depending on its chemical composition. Those materials, based on several hydraulic phases like M-S-H phase, M-A-S-H phase (M = MgO, A = Al 2 O 3 , S=SiO 2 , H=H 2 O), brucite, double magnesium aluminum hydroxide, and gibbsite, can be successfully utilized in many kinds of castables [3][4][5]. These phases can play a meaningful role in synthesis of spinel and forsterite on early stage of firing process and facilitate formation of ceramic bond [6].…”

An experimental investigation of hydration mechanism of the binary cementitious pastes containing MgO and Al2O3 micro-powders

“…An in situ mixing procedure using admix ampoule was applied for this purpose [16]. In all cases, two grams specimen of dry homogenized mixture was poured into a glass vial.…”

“…Processing of simple metal-oxides, i.e., fine nano-and micro-powders of both MgO and Al 2 O 3 in unshaped refractory materials (castables) technology, is now up-to-date trend of corundumspinel castables, mainly cement-bonded refractory castable and no-cement-content (NCC) castables [10,[12][13][14][15]. Some literature reports concern a combination of MgO-Al 2 O 3 oxide system as a promising stateof-the-art binding system based on M-A-H (A:Al 2 O 3 ) phase designed for the calcia-free refractory castables [10,15,16]. In our recent paper [15], it has been shown that the powder fineness and particle size distribution result in a size-dependent hydration mechanism and kinetics for MgO and Al 2 O 3 , and also determine cementitious (hydraulic) activities.…”

“…In situ reactions based on the formation of hydrotalcite-like phases inside the refractory MgO-bonded alumina castables were recently evaluated by Santos Jr. et al [12] and Ye et al [10]. Hydrotalcite, a natural mineral of chemical formula Mg 6 Al 2 (OH) 16 (CO 3 )Á4H 2 O, is a close mineral belonging to the layered double hydroxide family of anionic clays [17][18][19][20][21]. It was proved that the hydrotalcite-like phases might enhance the explosion resistance of Al 2 O 3 -MgO refractory castables, since these compounds exhibit crystalline lamellas separated by water molecules [12].…”