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Understand the physical properties of glass
Different types of glass have different qualities depending on their chemical composition and production method. Choosing the right type of glass for a particular application also means understanding the different physical properties of each different type of glass.
There are 5 main properties of glass to consider:
Thermal properties
Optical properties
Chemical properties
Electrical Properties
Mechanical properties
Thermal properties:
Glass is measured based on a variety of factors that will greatly influence your choice of glass. The coefficient of thermal expansion (CTE) is the measurement of the expansion of glass as the temperature rises. This is an important factor to consider when placing glass in a frame, as glass expands much less than most metals and plastics and can break as it cools. Thermal conductivity is the ability to conduct heat through the glass or away from the heat / light source. This is important when viewing glass as a viewing window subject to high temperatures or for high infrared applications. Each type of glass has a maximum operating temperature and a maximum thermal shock rating. These determine the choice of glass based on the amount of heat the glass can withstand and how it cools after the glass has been exposed to a rapid change in temperature. Glass can be reinforced to change these thermal properties through heat reinforcement, heat treatment, or chemical reinforcement. Click here to learn more about glass reinforcement.
Optical properties:
There are several important measurements in determining the amount of light that passes through glass. The refractive index determines how much a light wave is “bent” when it enters or leaves the glass surface. This is important in the manufacture of certain optical devices or effects, such as e.g. B. Lenses. Dispersion measures the separation of light into its component colors, such as B. a prism that distributes white light in a ribbon, or a rainbow effect. Transmission measures the amount of light passing through the glass material and its opposite reflectivity, which measures the return of light from the surface. The absorption property is the amount of light energy that is converted inside the glass into heat that is neither transmitted nor reflected. Tinted materials absorb more light than clear materials.
Chemical properties:
All soda lime glasses and some borosilicate glasses contain sodium or alkali metal ions. Prolonged contact with liquids or vapors such as water causes the sodium / alkali ions to migrate to the surface of the glass, which is known as sodium or alkali leaching. This can lead to cloudiness or cloudiness on the glass surface. Porous coatings can also cause this phenomenon and cause a break in the connection between the coating and the glass surface. For applications with high humidity or critical surfaces, this must be taken into account when specifying the material. Applying a “barrier” coating such as silicon dioxide to the glass limits the amount of reaction. Acid resistance and alkali resistance measure the time it takes to remove a layer of the specified thickness for each test.
Electrical Properties:
There are several properties to consider when choosing a glass for electrical or electronic applications. Volume resistivity is the resistance in ohms between opposing surfaces of a centimeter cube of the tested glass. This is important when using glass as an electrical insulator. The dielectric constant of a glass is the ratio of the energy stored in a capacitor to the glass as the dielectric compared to the energy stored in the same capacitor with air as the dielectric. This measures the ability of a glass to store electrical energy and varies with the frequency of the voltage applied to the capacitor. This is important when the glass is used as a substrate for electrical or electronic equipment. The surface resistance is the ratio of the potential gradient parallel to the current along its surface to the current per unit width of the surface.