Insulation capacity +1! What kind of material is the silicone rubber used in the "Little Red Riding Hood" of electricity?

Recently, Chaoyang Power Supply Company of State Grid Corporation of China has used silicone rubber as an insulating shield on overhead power lines, which has effectively improved the insulation level and safety of power transmission lines. It is affectionately called "Little Red Riding Hood" by everyone. In fact, silicone rubber is a kind of silicone material. Silicone materials have shown great power in many fields. Let us get to know them today!

Figure 1 The insulator protective cover, affectionately called "Little Red Riding Hood", is made of silicone rubber (Source: Webpage screenshot)

01 What is silicone material?

Organic silicon materials, also known as organic silicon compounds, refer to compounds containing silicon-carbon bonds (Si-C) and at least one organic group directly connected to the silicon atom. Compounds in which organic groups are connected to silicon atoms through oxygen, sulfur, nitrogen , etc. are also usually considered organic silicon compounds.

Organosilicon compounds have not been found in nature. Chemists combined the silicon in quartz sand with organic macromolecules to create a new "hybrid" material, which people call "organosilicon". There are many types of organosilicon compounds, including polysiloxanes, polysilanes, polycarbosilanes, polynitrosilanes, etc. Organopolysiloxanes are the most important type, accounting for more than 90% of the total amount of organosilicon materials. Today, China's polysiloxane production capacity accounts for 67% of the global production, making it the world's largest producer, consumer and net exporter of organosilicon raw materials [1].

At present, there are more than 2,000 kinds of silicone products, and the commonly used ones include silicone oil, silicone rubber, silicone resin, etc. There are more than 1,000 kinds. The following is a detailed introduction to the three most commonly used organopolysiloxane products:

1. Silicone oil: A linear polysiloxane product that remains liquid at room temperature. It is generally divided into two categories: methyl silicone oil and modified silicone oil.

♦The insulating properties of silicone oil make it an important material in the electrical industry , used to make insulating oil, cable oil, transformer oil , etc.

♦It can be used as a processing aid for rubber and plastics to improve their processing performance and product quality.

♦As an important ingredient of cosmetics , it has good lubricity and skin penetration.

♦Due to the excellent thermal stability of silicone oil, the laboratory selects dimethyl silicone oil as the oil for the oil bath.

2. Silicone rubber: A synthetic elastomer produced by mixing linear polysiloxane with reinforcing fillers and vulcanizing under heating and pressure. Silicone rubber itself is transparent, and silicone rubber products of different colors can be obtained by surface coloring and mixing coloring.

♦Automobile industry: automobile ignition wires, spark plug protection covers, heating and radiator hoses and battery connectors, etc.

♦ Electronic and electrical industries: high-voltage protective covers, cable equipment, and insulators made of silicone rubber, etc. [2]

♦Aerospace: Aircraft sealing switches and oxygen masks, etc. Burn-resistant silicone rubber can also be used to make rocket fuel valves and power source cables, etc.

♦Medical field: noise-isolating earplugs, contact lenses, artificial blood vessels and organs, etc. [3]

Figure 2 China's first fully magnetically suspended "artificial heart" independently developed (Source: CCTV News video screenshot)

3. Silicone resin: A thermosetting plastic containing a highly cross-linked network of polysiloxanes.

♦It can be used to prepare coatings with anti-corrosion, high temperature resistance and hydrophobic properties, such as in electronic packaging, exterior wall coatings and other fields.

♦Due to its insulating properties, it can be used in wires, motors, transformers and other fields.

♦Used in the preparation of organic silicon plastics, semiconductor packaging plastics and foam plastics. Commonly used in packaging, pipes and other fields.

Figure 3 The outer layer of a large ship is coated with an anti-corrosion silicone resin coating (Source: Xinhua News Agency)

02 The birth and development of silicone materials

As early as the 18th century, French scientists prepared tetraethylsilane (SiEt4), an organosilicon material, for the first time. Later, Kipping, a scientist at the University of Nottingham in the UK, conducted a systematic study on organosilicon materials. He not only used the Grignard reaction to synthesize organochlorosilanes, but also established naming rules for organosilicon compounds, laying the foundation for future scientists to study organosilicon materials [4].

During World War II, scholars such as Hyde and Patnode developed silicone insulating grease, which was moisture-resistant and heat-resistant and could be used in electrical equipment and aircraft ignition systems that operated at high temperatures and high speeds. Since then, a variety of early silicone materials have been introduced, such as the dimethyl silicone oil and silicone coatings mentioned above.

In 1940, scholar Rochow invented a method for synthesizing hydrocarbyl chlorosilanes by directly reacting silicon with chlorocarbons at high temperatures , which greatly improved the shortcomings of the previous Grignard reaction . The direct synthesis of hydrocarbyl chlorosilanes is considered to be one of the epoch-making achievements in the history of organosilicon chemistry. Subsequently, based on this invention, the first fluidized bed for synthesizing methylchlorosilane in history was developed, laying the foundation for the industrial production of organosilicon.

Since then, silicone production plants of all sizes have emerged around the world. By the beginning of the 21st century, several large-scale multinational corporations had been formed, and the number of varieties of silicone products developed has reached thousands.

Figure 4 Important nodes in the overseas development history of silicone materials (Source: author’s own)

03 Coming from behind! The development of silicone in my country

In the early days of the founding of New China, organosilicon materials were still an emerging industry in the world. A large number of Chinese scientists relied on their own strength and self-reliance to embark on the road of research and development of organosilicon materials. They first started with the preparation of literature and materials. The Beijing Chemical Experimental Institute of the Ministry of Heavy Industry established an organosilicon research group headed by engineer Yang Dahai, who collected and sorted out a large amount of foreign literature, carried out research on the world's cutting-edge organosilicon disciplines, and then invested in the tasks assigned by the organization.

The research team decided to first try to synthesize ethylchlorosilane using ethyl chloride, which has a higher boiling point. After hard work, ethylchlorosilane was successfully synthesized in 1954, and the organic silicon exploration experiment was successful. At the same time, one of the team members at that time, Comrade Chen Yanhan, compiled and published the earliest Chinese translation of organic silicon in my country, "Silicon Organic Compounds" [5]. (Silicon is the old name of the chemical element silicon)

Figure 5: Book image of Silicon-Organic Compounds (Source: Screenshot from the Internet)

In 1955, under the leadership of Comrade Yang Donglin, Shenyang Chemical Comprehensive Experimental Institute (relocated and integrated from the Beijing Chemical Experimental Institute mentioned above) developed my country's first silicone product - a coating that can withstand high temperatures of 500°C. Immediately afterwards, the country established the first silicone production workshop - Workshop 208, which produced 500°C high-temperature coatings and supplied them in large quantities to aircraft manufacturers.

After analyzing the demand for silicone materials in the domestic electrical, military, aviation and other fields, the development of synthetic silicone monomers became the top priority. Chief Engineer Yang Dahai led a group of capable people to select methylchlorosilane as the basic monomer for synthetic silicone oil and silicone rubber, and established a methylchlorosilane synthesis section in Workshop 208.

In 1958, aviation lubricants and greases that can be used on aircraft were developed (the raw material is very high-purity dimethyldichlorosilane). In 1997, the domestic production of methylchlorosilane exceeded the 10,000-ton mark. Since the beginning of the 21st century, the production of methylchlorosilane has continued to rise, and today the production of organic silicon ranks first in the world[6].

After several generations of hard work and struggle, we have broken the situation in which the Chinese silicone market was dominated by multinational corporations and the barriers formed, achieved independent innovation and intellectual property rights, and mastered core technologies, fully proving that the Chinese people, unwilling to lag behind, have the ability and determination to build China's silicone industry.

Figure 6 Development of silicone materials in China (Source: author’s own)

04Frontier research and future application prospects of new silicone materials

In 1987, my country founded the current Chinese journal "Organic Silicone Materials", which mainly reports on new technologies, new processes, new products and new applications of silicone products at home and abroad, and provides information on the silicone material market, conferences and information at home and abroad. Today's silicone industry is booming. Under the background of carbon neutrality and carbon peak, the substantial increase in demand for new energy vehicles will directly drive the growth of silicone demand. Relevant departments have also introduced corresponding policies to encourage and support the development of silicone materials [7]. Silicone materials have broad application prospects, especially in the fields of electronic devices, biomedicine, optoelectronic materials and 3D printing. With in-depth research and exploration, silicone materials will play a more outstanding role in the fields of materials science and engineering.

References:

[1] Hu Juan, Xiao Nan, Tan Yike, et al. Progress of domestic silicone in 2022[J]. Organic Silicon Materials, 2023, 37(03): 68-89.

[2] Li Xiuzhi. Application of silicone rubber materials in external insulation of power equipment[J]. Electrical Technology and Economy, 2023(06):159-161+166.

[3] Zhang Chengyan. Application of silicone rubber in biomedical field[J]. Organic Silicon Materials, 2002(06):14-17.

[4] Thomas, NR Frederic Stanley Kipping—Pioneer in Silicon Chemistry: His Life & Legacy. Silicon 2, 187–193 (2010). https://doi.org/10.1007/s12633-010-9051-x

[5] Fu Jilai. Organic silicon industry and its development in China[M]. Beijing: Chemical Industry Press, 2006.

[6] Xie Man, Gan Yong, Wang Hui. Research on the new material power strategy towards 2035[J]. Chinese Journal of Engineering Science, 2020, 22(05): 1-9.

[7] People’s Daily Online. Anhui Province issues the “14th Five-Year Plan” new materials industry development plan [EB/OL] (2022-04-13) [2024-07-09]. http://ah.people.com.cn/n2/2022/0413/c358428-35219807.html

Author: Gao Huang, PhD student in Materials Science, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences

Reviewer: Yao Qiaohong, Senior Engineer, PhD, School of Chemistry and Molecular Engineering, Peking University

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.