Nuclear power safety cables: research and development progress of boron doped magnesium hydroxide
In nuclear power engineering, safety has always been the core consideration in design and operation. With the continuous improvement of performance requirements for nuclear power cable materials, traditional flame retardant fillers such as aluminum hydroxide (ATH) and ordinary magnesium hydroxide (MDH) are no longer able to fully meet the demand for high-performance insulation and sheath materials in the new generation of nuclear power plants. In this context, boron doped magnesium hydroxide, as a new type of functional flame retardant material, is receiving increasing attention from research institutions and enterprises.
1、 Special requirements for materials of nuclear power cables
The operating environment of nuclear power plants is complex and ever-changing, and cables not only have to withstand harsh conditions such as long-term radiation, high temperature, and humidity, but also need to maintain functional integrity for a certain period of time in case of sudden accidents. Therefore, its material needs to have the following key properties:
Excellent flame retardancy: Even in fire or high temperature environments, it cannot promote the spread of fire.
Low smoke and halogen-free characteristics: The amount of smoke released during combustion should be minimized, and no toxic or corrosive gases should be released.
Good thermal stability: able to maintain structural integrity and electrical performance under high temperature conditions.
Anti radiation aging ability: It is not easily degraded or degraded in long-term radiation environments.
These stringent requirements have driven the development of new flame retardants, and boron doped magnesium hydroxide has emerged in this context.
2、 The flame retardant mechanism and limitations of magnesium hydroxide
Magnesium hydroxide is a common environmentally friendly inorganic flame retardant, and its flame retardant effect is mainly reflected in the following aspects:
During the heating process, it decomposes into water vapor, which plays a role in absorbing heat and cooling down;
The decomposition product magnesium oxide has a good coverage effect and can form a dense carbon layer on the surface of the material, isolating oxygen;
Does not contain halogen elements, does not produce harmful gases during combustion, and conforms to the concept of green environmental protection.
However, pure magnesium hydroxide also has certain limitations, such as a low initial decomposition temperature (about 300 ℃), which makes it prone to premature decomposition during processing and affects material formation; In addition, its flame retardant efficiency is limited and often requires a higher amount of additives to achieve the desired effect, which in turn reduces the mechanical properties of the material.
To address these issues, researchers attempted to modify it through element doping, with the introduction of boron showing significant advantages.
3、 Technological breakthrough of boron doped magnesium hydroxide
Boron doped magnesium hydroxide introduces boron element into the crystal structure of magnesium hydroxide, thereby changing its physical and chemical properties. The main advantages of this modification method include:
1. Improve thermal stability
The addition of boron element can effectively increase the starting temperature of thermal decomposition of magnesium hydroxide, making it more suitable for high-temperature processing technology. Experiments have shown that after reasonable doping, its decomposition temperature can be increased to over 400 ℃, greatly reducing heat loss during extrusion, vulcanization and other processing.
2. Enhance flame retardant efficiency
Boron doping can improve the dispersibility of magnesium hydroxide and promote its interfacial bonding with the polymer matrix. At the same time, boron compounds themselves have good carbonization properties, which help to form a denser and more stable carbon layer during combustion, further enhancing the flame retardant effect.
3. Improve mechanical performance
Due to the smaller size and more uniform distribution of magnesium hydroxide particles after doping, the effect on the mechanical properties of polymer substrates is relatively small at the same addition amount, which helps to prepare composite materials with good flame retardancy and mechanical strength.
4、 Application prospects in nuclear power cables
Boron doped magnesium hydroxide has shown extensive potential in the field of flame retardant materials for nuclear power cables due to its excellent comprehensive performance. At present, some companies have applied it to cable sheaths and insulation materials such as cross-linked polyolefins, ethylene vinyl acetate copolymers (EVA), thermoplastic elastomers, etc.
The actual test results show that the cable prepared with this material not only performs well in vertical combustion tests and smoke density tests, but also maintains good electrical performance and structural integrity in high-temperature and high-pressure environments under simulated nuclear power plant accident conditions.
In addition, boron doped magnesium hydroxide also has a certain neutron absorption ability, which allows it to also serve as a shielding function for nuclear reactors in certain specific scenarios, expanding its application boundaries in the field of nuclear power.
Today, as nuclear power safety is increasingly valued, the development of high-performance and environmentally friendly flame retardant materials has become an inevitable trend in the industry. Boron doped magnesium hydroxide is becoming an important candidate for the new generation of nuclear power cable materials due to its excellent thermal stability, flame retardancy, and environmentally friendly properties.