Crystallization-hydrothermal method: efficient preparation of hexagonal magnesium hydroxide

The crystallization-hydrothermal method is an efficient synthesis method that can prepare magnesium hydroxide crystals with specific morphology and size. The properties of these crystals have a significant impact on the performance of materials and are widely used in many fields.

Preparation steps

1. Mixing: Mix magnesium hydroxide precursor and alkaline solution (such as NaOH) to form a uniform slurry. Other alkali metal hydroxides (such as LiOH or KOH) are sometimes added to promote the growth of specific crystal planes.

2. Hydrothermal reaction: Place the slurry in a high-pressure reactor, seal and heat to 140°C~200°C for several hours. The hydrothermal conditions of high temperature and high pressure promote the dissolution and recrystallization of magnesium hydroxide crystals, which is beneficial to the directional growth of crystals.

3. Cooling and washing: After the reaction is completed, cool the reaction kettle naturally or quickly, filter the product, and wash it multiple times with deionized or distilled water to remove impurities and residues.

4. Drying and processing: The washed magnesium hydroxide crystals need to be dried, usually using air drying or low-temperature oven drying to remove moisture. Finally, grinding or crushing may be required to obtain the desired particle size.

Growth mechanism Under hydrothermal conditions, the growth of magnesium hydroxide crystals is affected by factors such as ion concentration, temperature, pH value and pressure in the solution. The formation process of hexagonal flake magnesium hydroxide includes:

· Initial nucleation: The magnesium hydroxide precursor dissolves in an alkaline environment to generate Mg2+ and OH- ions.

· Crystal nucleation formation: When the ion concentration is supersaturated, Mg2+ and OH- recombine to form crystal nuclei.

· Directional growth: Under specific hydrothermal conditions, the crystal nuclei grow along the (001) crystal plane to form hexagonal lamellar crystals.

Hexagonal flake magnesium hydroxide is widely used in flame retardants, catalyst carriers, adsorbents and other fields due to its unique morphology and high dispersion. In composite materials, as a flame retardant additive, it can effectively improve the flame retardant properties of the material and improve the mechanical properties at the same time.

Optimization and adjustment The preparation method can be adjusted according to specific needs, such as changing the reaction temperature, time, type and concentration of alkali, etc., to optimize the morphology and performance of the product.

Hexagonal plate-shaped magnesium hydroxide prepared by crystallization-hydrothermal method not only has important application value in the field of materials science, but also provides new possibilities for related industrial applications.