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Waterproofing Measures for High-Purity Magnesium
Waterproofing Measures for High-Purity Magnesium
High-purity magnesium is an important raw material for the preparation of magnesia castables, but currently High-purity magnesium The waterproofing measures are not yet fully developed and remain under investigation. Given its similarity to magnesia-calcia castable, the waterproofing strategies employed for magnesia-calcia castable can serve as a useful reference.
Compared with the waterproofing measures for magnesia–calcia bricks, one approach involves using high-density, large-crystal magnesia sand and incorporating organic coatings to encapsulate the magnesia particles. Although this method can enhance the hydration resistance of magnesium oxide, its practical application is constrained by product availability as well as factors such as cost and technology, making it difficult to implement in real-world operations.
An important approach to enhancing the hydration resistance of high-purity magnesium is the addition of additives. Boron oxide is a water-repellent additive. In small amounts, boron oxide can be uniformly distributed within periclase particles in conjunction with calcium oxide and silicon dioxide, thereby encapsulating the periclase crystals and improving hydration resistance. However, the addition of boron oxide has a critical drawback: it forms low-melting-point compounds that degrade the performance of magnesium oxide. Therefore, the incorporation of boron oxide is not a reliable method for improving High-purity magnesium Methods for enhancing hydration resistance. In addition, nickel oxide is also a water-resistant additive. Unlike boron oxide, which is dissolved in the intergranular spaces of periclase particles, nickel oxide can dissolve directly into the periclase crystals. Performance tests on magnesia prepared with added nickel oxide demonstrate that the addition of nickel oxide effectively improves the hydration resistance of magnesia.
Ultrafine SiO2 powder is currently a commonly used additive in magnesia-based castables. In such castables, upon contact with water at room temperature, hydroxyl groups—i.e., Si–OH bonds—are formed on the surface of the ultrafine SiO2 particles. Following natural curing and drying, dehydration leads to the formation of a siloxane network structure. Meanwhile, because the surfaces of MgO particles are rich in unbound O²⁻ and O₂²⁻ ions, these ions readily adsorb onto the Mg²⁺ ions on the particle surfaces, thereby forming MgO–silicon chains and reducing the number of bound OH groups. Compared with the formation of H–O–Mg–O–H linkages and hydroxyl–silicon chains via interactions with Mg²⁺, the consumption of water molecules is reduced. Specifically, for each MgO–Si chain that forms, one water molecule is effectively “reduced.” Consequently, as the amount of water released decreases, High-purity magnesium The likelihood of cracking during the baking process is reduced. Meanwhile, the interconnection of MgO particles via high-purity magnesium-silicon chains enhances the product’s strength.
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