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