Hydrothermal formation of dispersive Mg(OH)2
particles in NaOH solution①
particles in NaOH solution①
(Department of Chemical Engineering, Tsinghua University, Beijing 100084, China)
Abstract: The hydrothermal modification of Mg(OH)2 crystals in NaOH solution was investigated. The aggregated Mg(OH)2 particles with irregular shape are converted to regular Mg(OH)2 hexagonal plates after hydrothermal treatment.The prolongation of reaction time from 1 4 h or the increase of temperature from 140℃to 200℃can promote the formation of Mg(OH)2 plates with big particle size but small cluster size. The dispersion characteristics of the hydrothermal products are improved owing to the improvement of Mg(OH)2crystalline degree and the increase ofI(001)/I(101)ratio. The proper hydrothermal modification condition is as follows: solid content 0.075 g/mL, NaOH concentration 5.0 mol/L, temperature 200℃and time 4 h. Thermodynamic analysis indicates that the increase of MgOH+concentration at elevated temperature or the increase of OH-concentration in concentrated NaOH solution is favorable for the hydrothermal formation of Mg(OH)2 particles.
Key words: magnesium hydroxide; hydrothermal treatment; sodium hydroxide; structure; dispersion