Are you wondering why the quality of products from your previous silicone supplier has suddenly changed? Do you know the impact that silicon metals, which are integral to the silicone manufacturing process, have on the quality of silicone products? Today’s article will take you inside the silicon metal and silicone manufacturing process to help you better select the right silicone manufacturer.
What Is Silicon Metal?
Although silicon metal is called a “metal”, it is actually a nonmetal or semi-metal. It is called “silicon metal” because it also has a metal-like luster and can conduct heat and electricity. Because most silicon metal is used in industry, it is called industrial silicon in standards such as ISO.
It consists almost entirely of silicon (Si) and is a fairly pure substance. The purity of silicon metal used in silicone production and other industrial production ranges from 98% to 99.5%. Silicon metal is necessarily involved in the production of silicone and is the source of the silicone industry.
Silicon Metal and The Silicone Manufacturing Process
Silicon metal is the raw material for silicone production and is involved in the preparation of silica, the most important filler of silicone.
Step 1: Synthesis of Silanes
The first step in the production of silicones is reacting high-purity silicon metal with chloromethane to produce the silanes used to synthesize silicones, including the important dimethyldichlorosilane. This process requires heat and the addition of a copper catalyst, followed by repeated distillation.
The purity of the silicon metal will undoubtedly have a great impact on the purity of the silane. You can also easily imagine that if the silane contains too many impurities, even after many distillations, the impurities in the mixture will be difficult to remove cleanly and become a major hazard in the subsequent production process.
Impurities in the silicon metal can also interfere with the catalyst functioning, resulting in a lower percentage of dimethyldichlorosilane used to make silicone. This will cost the manufacturer more time and effort to purify, ultimately making the silicone you buy more expensive.
Step 2: Hydrolysis and Condensation
Once the silane is obtained, it is then hydrolyzed to form the dimethyl cyclosiloxane mixture (DMC). These chemicals lay down the silicone skeleton of the silicone, which you can probably understand as being like a section of a fish bone that has not yet been put together to form the complete skeleton.
The next step in the condensation process allows these chemicals to join with each other to form the complete skeleton, which is polysiloxane. It is the main ingredient in silicone rubber gum.
Silicones at this point are not what you would normally see in a silicone product. They lack mechanical strength and can’t be directly made into silicone products. Only when fillers, additives, and vulcanizing agents are added in the next step does the silicone elastomer actually become usable.
Step 3: Mixing and Molding
By adding different vulcanizing agents, fillers, as well as other ingredients to the silicone rubber and then mixing and processing, you can get silicone to meet different needs. Silica is usually added to silicone rubber, although the specific molding methods and chemicals added vary depending on the type of silicone.
The silica used as a filler is not quartz sand or the sand you see on the beach, but fine fumed silica or precipitated silica. Silicon metal is also very important in order to manufacture fumed silica with very small particle sizes added to high-quality silicone rubber.
One of the raw materials for fumed silica is silicon metal powder. At high temperatures, it reacts with hydrogen chloride to form silicon trichloride, which is then hydrolyzed and transformed into nano-sized silicon dioxide. As long as there is a lack of silicon metal, the entire production process of fumed silica and silicone can’t be carried out.
In short, silicon metal is a very important part of the silicone manufacturing process.
If you are interested in the specific ingredients added to silicone, you can read What Is Silicone Made Of? How Compositions Affect Safety and Performance.
How Is Silicon Metal Produced?
Silicon metal hardly exists naturally in nature. The silicon metal used to make silicones and fumed silica is artificially refined. You may have seen the phrase “quartz sand is the raw material for silicones”, but that actually means that quartz sand is the raw material for the silicon metal used to produce silicones.
To obtain pure silicon metal, quartz sand, coke, and other reducing agents are added to an electric arc furnace. The silicon is separated by reacting at temperatures up to 2000°C inside it. The general course of the reaction is that the carbon in the coke forcibly snatches the oxygen out of the silica, leaving the remaining silicon in place.
The exact reaction process is complex and may produce silicon oxide, carbon monoxide, and many other chemicals, but in the end, you get silicon in liquid form. These liquids are collected and further processed, such as removing impurities, to become silicon metal for industrial manufacturing.
The Effect of Silicon Metal Purity on Silicone Quality
Purity and Safety
The purity of the silicon metal directly affects the purity of the silicone product. Impurities in the silicon metal extracted from the quartz sand will remain present throughout the silicone manufacturing process. The most significant impurities in silicon metal are the elements iron(Fe), aluminum(Al), and calcium(Ca).
The difference between different grades of silicon metal is mainly in the amount of these impurities, and a large part of the quality of the silicone material also depends on the impurities present within.
For food and medical-grade silicones, these impurities can be an unsettling factor, making them less safe and may also cause silicone products to have an odor. All of this finally leads to them being of substandard quality and failing to pass safety standards and regulations, such as the FDA.
Recommended reading: Is Silicone Toxic: Silicone Safety Guide.
Transparency
The presence of impurities in the silicon metal affects the transparency of the final silicone rubber product obtained in two directions. When iron in raw silicone rubber and fumed silica oxidizes, it will make the silicone rubber more yellow, so the silicone rubber’s transparency will be reduced.
In addition, impurities mixed into the silicone may form other chemicals during the manufacturing process, and these additional chemicals may change the transparency of the silicone. The poor quality silicone rubber that you come into contact with that is whitish may contain these chemicals.
Effect on the Vulcanization Process
Silicone rubber is vulcanized in three main ways: peroxide vulcanization, platinum vulcanization, and condensation vulcanization. The catalyst used in platinum vulcanization is sensitive to impurities. Impurities mixed into the silicon metal may cause the silicone rubber to vulcanize unevenly, particulate or even render the catalyst completely ineffective.
Performance
Impurities present in the silicon metal can cause impurities to be present in the silicone as well, which in turn can cause certain properties to deteriorate and fail to meet expectations.
Those silicone rubber products that use less pure silicon metals are more likely to crack when subjected to force and have a shorter service life at high temperatures than higher quality products.
Silicone products can be used as an insulating seal in the automotive and electronics industries, but silicone products with excessive impurities, especially metal content, have increased electrical conductivity. This difference in conductivity may lead to economic loss or even safety accidents.
If you notice a change in the quality of the product from the silicone manufacturer you were working with, but they haven’t actually made any changes to the silicone production process, then the cause of the change is likely to be a different supplier or quality of silicon metal as a source.
Silicon Metal Supply Challenges
Silicon metal is so important to the production of silicones that its quality affects the quality of the silicone product, but the supply of silicon metal is actually being challenged right now.
Multiple Industrial Applications of Silicon Metal
In fact, silicon metal is not only used in the manufacture of silicones, but it is also a raw material for the production of semiconductors, polycrystalline silicon cells, and aluminum alloys, and the demand for silicon metal in these industries is growing. This makes it necessary for the silicone industry to compete with these industries for high-quality silicon metal.
High Energy Consumption in Silicon Metal Production
Because separating the silicon from the quartz sand needs to be done at very high temperatures, making silicon metal is actually very energy and water-intensive and produces large amounts of carbon dioxide.
This is a challenge for suppliers of silicon metal and manufacturers of high-volume silicone products. Governments have very strict controls on the production of energy-intensive silicon metal. In some areas of France and China, policy changes and changes in energy prices have affected silicon metal production and even shut down some plants.
Lack of High-quality Raw Materials
Not all quartz sand can be used to produce silicon metal. Quartz sand used for silicon metal production must not be too high in impurities, and fewer mines are able to produce such a high-quality quartz sand resource. Quartz sand needs to be screened and further processed after it has been mined, which makes high-quality quartz sand more expensive.
FAQ
Is Silicon a Metal, Nonmetal, or Metalloid?
Silicon metal is a kind of metal or semi-metal. Outwardly, it does resemble a metal like iron, with that special shiny luster. But it also has certain non-metallic properties, being brittle while still being hard.
Silicon vs. Silicone vs. Silica
Silicon metal: high-purity silicon, is used in the production of silicone, fumed silica, and other industrial materials.
Silicone: a class of polymers with a skeleton composed of silicon and oxygen. Silicone rubber, silicone oil, and silicone resin are forms of it.
Silica: the main component of sand, also known as silicon dioxide. The common source of silica in industry is quartz sand. The fumed silica filler added to silicone rubber is a filler with higher purity and finer particles.
Why Have Silicone Prices Changed a Lot in Recent Years?
The supply of silicon metal affects the price of silicone to some extent. Because of policy restrictions and energy price increases, the price of silicon metal has moved and even sometimes caused interruptions in its supply, which in turn has led to higher silicone prices. Competition from other industries for silicon metal has also made it more difficult for silicone manufacturers to buy high-quality silicon metal feedstock.
Are There Different Grades of Silicon Metal Used in Silicone Manufacturing Processes?
Silicon metals are differentiated by grade. Silicon metals used in the production of silicones are generally graded according to their impurity content. The most commonly used in the silicone manufacturing process is Silicon CG 0.4/0.2/0.1. This standard means that it contains ≤0.4% iron, ≤0.2% aluminum, and ≤0.1% calcium.
Will the Purity of Silicon Metal Influence Silicone Lifespan?
The purity of the silicon metal can have an impact on the lifespan of the silicone product. Impurities present in the silicon metal can affect the purity of the silicone, and impurities present in the silicone product may make it more susceptible to deterioration. These impurities also affect the production process of the silicone, which may result in uneven texture and altered electrical insulation, so silicone may require more frequent replacement.
Why Use Silicon Metal to Manufacture Silicone, Instead of Other Silicon-containing Chemicals?
Silicon-containing substances used in the manufacture of silicones are subject to very high requirements, and silicon metal is the most cost-effective of the chemicals that fulfill these requirements.
First of all, the silicon in the silicone-containing substances used as raw materials must not be firmly attached to other atoms. Silicon in quartz sand, silicon carbide, and other substances don’t meet this requirement, so silicon metal is produced by destroying the molecular structure of the quartz sand so that the silicon atoms can be set free.
The price of other silicon-containing substances that meet the standard is too high, which can greatly limit the mass production of silicone. Moreover, after reaching a certain purity, the purity continues to increase, and the improvement of silicone performance becomes very small and uneconomical.
For these reasons, we now choose silicon metal as the raw material for silicone manufacturing.
Final Thoughts
Because the quality of silicon metal is so important to silicone production, selecting a silicone manufacturer with a consistent, high-quality silicon metal supplier for your product or project is important.
Legensilico has more than 20 years of experience in silicone product manufacturing, and our 8 advanced production lines and stabilization of feedstock supply have the ability to provide you with a stable supply of high-quality silicone products, as well as customized silicone product services. Start your inquiry for your high-quality silicone products!
