Novel insights into MgO hydroxylation: Effects of testing temperature, samples׳ volume and solid load

A systemic investigation on the hydroxylation behavior of caustic magnesia and magnesia sinter

“…CM and MS have been the focus of many investigations for over half a century and an aspect that has drawn plenty of attention is their hydroxylation (or hydration) behavior [17][18][19][20][21][22][23][24][25][26]. Depending on the application aimed at, MgO hydroxylation can be either valuable or undesired and, in both cases, the knowledge of how this process occurs can be highly useful.…”

“…The characteristics of the reacting medium (temperature and solid load) and the MgO source (single crystal or polycrystalline grains) affect the rates of steps 4-6 differently [14,16,18,22,25,26]. When the dissolution steps (expressions (4) and (5)) occur gradually (for instance, in very diluted suspensions of monocrystalline particles at temperatures below 20 1C), the precipitation (expression (6)) necessarily slows down and Mg(OH) 2 is formed orderly as a dense thin layer on the surface of the MgO particles [16,22,25,26,37,42].…”

“…When the dissolution steps (expressions (4) and (5)) occur gradually (for instance, in very diluted suspensions of monocrystalline particles at temperatures below 20 1C), the precipitation (expression (6)) necessarily slows down and Mg(OH) 2 is formed orderly as a dense thin layer on the surface of the MgO particles [16,22,25,26,37,42]. This layer behaves as protective coating preventing further MgO dissolution and halting the process.…”

“…The exposure of unreacted surfaces and the heat released restart and speed up the hydroxylation process up to the total consumption of MgO after few hours of reaction [16,30]. The mechanisms described above enable the MgO conversion to Mg(OH) 2 to be maximized by (i) the replacement of particles of monocrystalline magnesia by polycrystalline ones [14,15] and (ii) use of thermally isolated reactors (autoclaves, for instance) for keeping the heat released during the reaction and using it to accelerate the process [16,25,26]. Alternatively, to prevent hydroxylation, several studies have proposed antihydroxylation (or anti-hydration) additives particularly useful to refractory castables.…”

Kinetic study of photocatalytic degradation of Ifos famide in a microchannel and simulation

“…Thus, the precipitation continues in a slower rate, until the diffusion of water into the MgO particle is blocked, leading to the end of magnesium hydroxide formation [43]. It is important to highlight that magnesium hydroxide precipitation into the pores the water diffusivity in the solid matrix.…”