Chemical composition of a mirror? Explain in details different chemical properties of mirror.
A traditional mirror does not have an inherent chemical composition. However, the chemical properties of the materials used in mirrors can still be discussed. Let’s examine the different chemical properties associated with the materials commonly used in mirrors:
- Glass: The primary component of most mirrors is glass. Glass is primarily composed of silica (SiO2), which is a chemical compound with unique properties. Silica is chemically stable, meaning it is resistant to most chemical reactions. It is not easily affected by acids or bases, which makes it suitable for mirror manufacturing. However, prolonged exposure to strong alkalis or hydrofluoric acid can etch or damage the glass surface.
- Metal Coatings: Mirrors often have a thin layer of metal deposited on the glass surface to create a reflective coating. The choice of metal affects the mirror’s chemical properties, including its reactivity and reflectivity:a. Aluminum: Aluminum is commonly used as a reflective coating in mirrors. It is a lightweight metal with excellent reflectivity to visible light. Aluminum is chemically reactive with strong acids and alkalis, leading to corrosion and the loss of reflective properties. Therefore, a protective coating, such as a clear coat or dielectric layer, is often applied to prevent direct contact between aluminum and corrosive substances.b. Silver: Silver is another metal used in mirrors, particularly in high-quality mirrors. It has superior reflectivity across a broad spectrum of light, including visible and infrared regions. Silver is relatively chemically inert, meaning it does not readily react with most substances. However, silver can tarnish over time when exposed to air or certain gases, resulting in a decrease in reflectivity. To prevent tarnishing, protective coatings are applied to silver-coated mirrors.
- Protective Coatings: To enhance the durability and longevity of mirrors, protective coatings are often applied to the metal layer. These coatings provide a barrier that protects the metal from chemical reactions and physical damage. Some common protective coatings include:a. Clear Coat: A transparent protective layer, such as a lacquer or varnish, is applied over the metal coating to prevent corrosion and oxidation. This clear coat acts as a barrier between the metal and the environment, ensuring the reflective properties of the mirror are maintained.b. Dielectric Coating: Dielectric coatings consist of multiple layers of thin films made of materials like silicon dioxide (SiO2) or titanium dioxide (TiO2). These coatings enhance the mirror’s reflectivity by reducing surface reflections and minimizing light absorption. They also provide protection against environmental factors and chemical reactions.
In summary, while a mirror itself does not have a distinct chemical composition, the materials used in mirrors, such as glass and metal coatings, exhibit chemical properties that influence the mirror’s reflectivity, durability, and resistance to corrosion.