Magnesium hydroxide decomposition product, magnesium oxide: a natural barrier for cable refractory layers
In modern buildings and industrial power systems, cables serve as the core carrier of electrical energy transmission, and their safety performance directly affects the stability and reliability of the entire system. Especially in extreme environments such as fires, how to improve the flame retardancy and fire resistance of cables has become an important issue in engineering design and material research and development.
So, why can magnesium hydroxide be transformed into such a crucial 'guardian' at high temperatures? Why can magnesium oxide build a natural barrier in a fire? We will explore from three aspects: material properties, application principles, and actual effects.
1、 The decomposition mechanism of magnesium hydroxide and its flame retardant advantages
Magnesium hydroxide is a white powdery substance with the chemical formula Mg (OH) ₂, belonging to the typical metal hydroxide flame retardant class. Under heating conditions, magnesium hydroxide will begin to dehydrate and decompose at around 340 ℃, producing magnesium oxide and releasing water vapor
Mg(OH)₂ → MgO + H₂O↑
This reaction is not only an endothermic process that can effectively reduce the temperature of the combustion zone, but also the released water vapor can dilute combustible gases and suppress flame spread. In addition, magnesium hydroxide does not contain halogen elements and does not produce toxic gases or corrosive smoke during combustion, which is in line with the current development trend of balancing environmental protection and safety.
Therefore, magnesium hydroxide is widely used in insulation and sheathing materials for wires and cables, especially in densely populated areas such as high-rise buildings, subways, tunnels, ships, and places with extremely high safety requirements.
2、 Physical and chemical properties and refractory performance of magnesium oxide
Magnesium oxide produced by the thermal decomposition of magnesium hydroxide is an alkaline oxide with a high melting point (2852 ℃) and high thermal stability. It is in a white solid state at room temperature, chemically stable, and not easily reactive with other substances.
In cable structures, when the external environment is exposed to high temperatures or flames, magnesium hydroxide rapidly decomposes to form a dense magnesium oxide layer. This layer of magnesium oxide not only has good insulation performance, but also forms a hard ceramic shell on the surface of the cable, which serves to isolate oxygen and prevent heat conduction. This "self-protection" mechanism allows cables to maintain normal operation for a certain period of time in a fire, buying valuable time for personnel evacuation and emergency response.
In addition, magnesium oxide also has excellent electrical insulation properties. Even at high temperatures, its resistivity remains at a high level, which helps prevent cable short circuits or leakage accidents and further enhances the overall safety of the system.
3、 The practical application of magnesium oxide in the refractory layer of online cables
In practical engineering applications, magnesium oxide is usually embedded in cable structures in the form of mineral insulation materials, with the most typical application being mineral insulated cables (MI cables). This type of cable consists of copper conductors, magnesium oxide insulation layer, and copper sheath, and has various excellent properties such as high temperature resistance, fire resistance, explosion resistance, waterproofing, and radiation resistance.
The working principle of MI cable is to use magnesium oxide as the intermediate insulation medium, and its fire resistance limit is much higher than that of traditional plastic insulation materials. Even if burned continuously for several hours in flames exceeding 1000 ℃, the cable can still maintain circuit integrity and functional continuity. Therefore, MI cables are widely used in fire protection systems, emergency lighting, elevator control systems, data centers, and other applications that require extremely high power continuity.
In addition to MI cables, in recent years, some new composite fire-resistant cables have also begun to try to combine magnesium hydroxide with other inorganic fillers. By optimizing the formula and process, the cables can meet the requirements of flame retardancy while also balancing flexibility and mechanical strength. For example, adding an appropriate amount of magnesium hydroxide to cross-linked polyethylene (XLPE) or low smoke halogen-free materials can not only increase the oxygen index of the material, but also generate magnesium oxide residue with thermal insulation during combustion, thereby enhancing the overall fire resistance of the cable.
4、 The development trend driven by both environmental protection and economy
In the context of promoting sustainable development globally, traditional halogenated flame retardant materials are gradually being phased out due to the toxic gases and secondary pollution generated during their combustion. Magnesium hydroxide, as a green and environmentally friendly alternative, is becoming a research and development focus for the new generation of cable materials due to its excellent flame retardant properties and harmless decomposition products.
From an economic perspective, although the cost of magnesium hydroxide is slightly higher than that of some organic flame retardants, its long-term safety benefits and reduced maintenance costs make it more cost-effective throughout its entire lifecycle. Especially in large public facilities, rail transit, new energy and other fields, the use of high-performance cables containing magnesium hydroxide has become the mainstream trend.
At the same time, with the advancement of nanotechnology and materials science, key technologies such as particle size control and surface modification of magnesium hydroxide are constantly breaking through, further improving its dispersibility and compatibility in polymer substrates, laying the foundation for wider applications in the future.
Magnesium hydroxide, as an efficient and environmentally friendly halogen-free flame retardant, has broad application prospects in the cable industry. The magnesium oxide generated after thermal decomposition not only has excellent high temperature resistance, thermal insulation and insulation properties, but also provides a strong natural barrier for cables. Whether it is emergency protection in case of fire or safety protection in daily operation, magnesium oxide has demonstrated irreplaceable advantages.
With the continuous improvement of social awareness of fire safety and the increasingly strict national standards, it is believed that in the next few years, fire-resistant cables containing magnesium hydroxide/magnesium oxide systems will increasingly appear in our lives and work, becoming an important force in ensuring the safety of urban infrastructure.