How does magnesium hydroxide improve the fire resistance limit of cables by forming a ｃｈａｒ layer
In the context of frequent fires, improving the fire resistance limit of cables has become one of the key links to ensure public safety. Magnesium hydroxide, as an efficient halogen-free flame retardant, plays an important role in enhancing the fire resistance of cables, especially by forming a protective carbon layer, effectively improving the fire resistance limit of cables.
Basic characteristics and mechanism of action of magnesium hydroxide
Magnesium hydroxide (Mg (OH) ₂) is a white powdery substance with good thermal stability and chemical inertness. When the temperature rises to a certain value, magnesium hydroxide will decompose into magnesium oxide (MgO) and water vapor (H ₂ O). This process is a strong endothermic reaction that can significantly reduce the surface temperature of the material, and the released water helps dilute the surrounding oxygen concentration and suppress combustion.
In addition to the direct physical cooling effect mentioned above, magnesium hydroxide can also promote the formation of a ｃｈａｒ layer, which is crucial for improving the fire resistance limit of cables.
Principle of Charcoal Formation
Under high temperature or flame conditions, cable materials containing magnesium hydroxide undergo a series of complex chemical reactions. One important phenomenon is that as magnesium hydroxide decomposes, a dense and continuous layer of carbon is formed on the surface of the material. This layer of carbon is not just a simple accumulation of carbides, but a composite structure formed by the combined action of multiple components.
Firstly, the carbon layer itself has high thermal stability, which can maintain structural integrity at high temperatures and prevent heat conduction to the internal materials. Secondly, the carbon layer can effectively block the contact between external oxygen and flammable substances inside the cable, reducing the possibility of further combustion. In addition, due to the presence of the charcoal layer, the speed of flame spread will be greatly slowed down, which will buy valuable time for personnel evacuation and firefighting rescue.
Mechanism of Magnesium Hydroxide Promoting the Formation of Charcoal Layer
The reason why magnesium hydroxide can promote the formation of a ｃｈａｒ layer is mainly attributed to the following aspects:
Dehydration reaction provides water: During the decomposition process of magnesium hydroxide, a large amount of water is released, which participates in the initial stage of carbon layer formation and helps certain components in the polymer matrix undergo dehydration condensation reactions, thereby promoting the formation of the carbon layer.
Catalytic carbonization in alkaline environment: Magnesium oxide produced by the decomposition of magnesium hydroxide is weakly alkaline, which is conducive to the dehydration and carbonization reactions of certain oxygen-containing organic compounds, promoting the deposition of more carbonaceous substances on the surface of the material.
Physical barrier effect: The decomposition product magnesium oxide particles are dispersed in the carbon layer, enhancing the mechanical strength and thermal stability of the carbon layer, making it more difficult to be destroyed by flames, thus better exerting its protective effect.
Challenges and Solutions in Practical Applications
Although magnesium hydroxide has excellent carbonization ability, it still faces some technical challenges in practical application in cable manufacturing:
Uniform dispersion problem: In order to ensure that magnesium hydroxide can be evenly distributed and fully utilized in cable materials, it is necessary to solve the problem of powder agglomeration. The commonly used methods include surface modification and nanotechnology treatment to improve its dispersibility in polymer matrices.
Balance between filling amount and mechanical properties: Although increasing the filling amount of magnesium hydroxide can improve the flame retardant effect, it may lead to a decrease in the flexibility and mechanical strength of the cable material. Therefore, finding the appropriate filling ratio is crucial.
Synergistic effect with other additives: Sometimes using magnesium hydroxide alone may not achieve the best flame retardant effect. In this case, it is possible to consider adding other types of flame retardants or additives, such as zinc borate, phosphorus compounds, etc., to optimize overall performance through synergistic effects.
With the advancement of science and technology and the increasing emphasis on fire safety in society, the application prospects of magnesium hydroxide as an efficient and environmentally friendly flame retardant are very broad. On the one hand, researchers will continue to explore how to improve production processes to enhance the performance of magnesium hydroxide in cable materials; On the other hand, developing new composite flame retardant systems that combine the advantages of magnesium hydroxide with the characteristics of other high-performance flame retardants will be one of the future development trends.