Glass as a Material
- What is glass made of?
- How is glass made?
- Mechanical properties
- 2.Tensile strength
- 3.Compression resistance
- Thermal properties
- 1.Thermal resistance
- 2.Thermal expansion
- 3.Thermal conductivity
- Optical properties
- 1.Refractive index
- Chemical properties
- 1.Chemical resistance against water
- 2.Chemical resistance against acid
- Electrical properties
- Soda-lime glass
- Aluminosilicate glass
- Non-alkali glass
- Fused quartz glass
- Borosilicate glass
- Glass ceramics
01/What is glass?
Glass is a transparent amorphous solid material with various applications. Historically the origin of glass was very precious materials. Then the application expanded to household products as its chemical stability and transparency. In the industrial age, the glass used for lighting, architecture windows, automotive windshields etc. In the electronics age, it’s used to make windows or screens for electronic devices. While it’s a commonly used material, many people are unaware of where it comes from or how it is made.
What is glass made of?
Most types of glass are made from sand. The type of sand that’s used depends on the kind of glass that’s being made. However, the most commonly used sand consists of tiny silica crystals. These crystals are composed of silicon dioxide. During industrialization, we eliminate the impurity of the sand to get high quality glass products.
How is glass made?
Glass is made by heating raw materials at very high temperatures. Modern industries are using the same process in 2000 years ago. These temperatures are typically 1700°C (3090°F) or higher, and at this temperature. the raw materials melt into liquid state and mixed into new compositions. During the cooling process, the melted glass is frozen into solid with new “glass” compositions. The resulting structure has an amorphous solid (having no apparent crystalline atomic structure) .
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Glass has a wide range of applications. But it’s commonly used in architecture, automobiles, and electronics.
Architectural glass is used for building or construction purposes. Four main types of architectural glass are used:
- Insulating glass
- Laminated glass
- Wired glass
- Toughened glass
Each of these types have a specific purpose. For example, insulating glass helps a building to retain heat. In contrast, the other types prevent the glass from breaking or shattering, which improves its safety. However, wired glass also has flame-retardant properties.
Automotive glass is used for the windows of vehicles. Depending on the function, different types of glass are used for various purposes. For example, laminated or tempered glass is used to reduce shattering when the vehicle is in an accident. Other types of glass are tinted to provide privacy, and others have the vehicle’s antenna integrated into them.
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Glass for electronics is carefully designed the composition to meet the special requirement for electronic devices. It started to use for light bulbs, then it used for CRT TV tubes. In digital age, some glass types need to have a low thermal shrinkage to realize fine resolution electronics devices under high production temperature. And other types of glass are used to improve mechanical strength of the mobile devices.
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Glass has a unique range of properties, such as transparency, heat resistance, chemical resistance, and resistance to breakage and pressure. However, the composition of glass can be altered slightly to enhance some of its properties.
The mechanical properties of glass refer to its physical characteristics in response to an applied force. These include hardness, tensile strength, and compression resistance.
The hardness of glass refers to its resistance to scratching or abrasion when a force is applied. Under the Knoop hardness test, most types of glass have a hardness of 470 HK (Knoop hardness).
2. Tensile strength
The tensile strength of glass refers to its resistance to breaking or deforming when tension is applied. Tensile strength is also referred to as Young’s modulus or the elastic modulus. Therefore, when glass is under tension, it will deform at 70,000 MPa (megapascals).
3. Compression resistance
The compression resistance of glass refers to how well it can revert to its original shape after being compressed by force. Glass has a compression resistance of 800–100 MPa.
The thermal properties of glass are related to how it responds to heat—for example, its thermal resistance, expansion, and conductivity.
1. Thermal resistance
Thermal resistance relates to how well glass can resist the flow of heat. Therefore, this property determines how much heat a particular type of glass can withstand. Different types of glass have varying values for their thermal resistance depending on their applications. However, glass typically has a high thermal value, meaning it can withstand a relatively high temperature.
2. Thermal expansion
Thermal expansion relates to the tendency of glass to undergo a change in shape, volume, area, or density when it experiences a temperature change. The thermal expansion of glass is 9.10–6 K-1. Therefore, it doesn’t have a great tendency to change when the temperature is increased.
3. Thermal conductivity
Thermal conductivity refers to how well glass can conduct heat. The thermal conductivity of glass is 0.8 W/mK (Watts conducted per meter thickness) which means that glass is a poor conductor of heat.
Optical properties define how glass interacts with light. Some optical properties include refractive index, absorption, and reflection.
1. Refractive index
The refractive index (n) is the measure of bending that a light ray undergoes when it passes from one medium to another. For example, how much the light bends when passing from air to glass. The refractive index of glass is 1.52, which means that the speed of light slows down when passing through the glass. Understanding how refraction affects glass is important for lenses and prisms.
Absorption refers to how much light is absorbed by a certain material, such as glass. Since glass is a clear, transparent material, it doesn’t absorb much light in the visible wavelength because most of the light passes through it. Therefore, most types of glass typically absorb between 2% and 4% of light.
Reflection is the light ray that bounces off a surface from an incident ray. Reflection occurs when the incoming light hits the surface at a particular angle. At certain angles, you can see light being reflected from glass. However, glass only reflects about 4% of light; the rest is absorbed or passes through.
The chemical properties of glass relate to how well it can withstand damage from particular substances such as water or acid.
1. Chemical resistance against water
Glass has a high chemical resistance to water, which means it can withstand water corrosion. Therefore, it’s not prone to water damage, making it an ideal material to contain or protect against water.
2. Chemical resistance against acid
Glass is resistant to most types of acids. However, it isn’t resistant to acids such as hydrofluoric acid or phosphoric acid. Therefore, glass has limited resistance against acids compared to its resistance against water but can still be used to contain or protect against some acids.
Electrical properties relate to the ability of glass to conduct or store an electrical current. Examples of these include conductivity and permittivity.
Conductivity is the degree to which a material can conduct electricity. Materials that typically have a high degree of conductivity are metals. However, glass has an extremely low electrical conductivity in contrast to metals. Since glass is often used for electronic devices or light bulbs, this property is favorable because it can help by insulating the electricity being used.
Permittivity refers to the amount of potential electrical energy that can be stored under the influence of an electric field. The ability of a material to store electrical potential energy is called capacitance. Glass is known to decrease capacitance; therefore, it has a low permittivity and doesn’t hold electrical energy well.
04/Types of glass
Soda-lime glass is the most commonly used glass. It’s used for various items, such as window panes, bottles, jars, containers, and bakeware. This type of glass is sustainable because this glass can be remelted several times and is easy to manufacture. Therefore, it’s among the best glasses for recycling and it’s inexpensive to use.
Soda-lime glass is typically composed of 70% silicon dioxide, 15% soda (sodium oxide), and 9% lime (calcium oxide). A variety of other compounds may make up the rest of its composition.
Aluminosilicate glass is more heat resistant than generic types of glass. It can resist temperatures of up to 800°C (1472°F). Because of this, it’s often used for lamps, high-temperature thermometers, or anything that needs to resist high temperatures.
Aluminosilicate glass typically is composed of 57% silicon dioxide, 20.5% alumina, 12% magnesia, 5.5% lime (calcium oxide), 4% boric oxide, and 1% soda (sodium oxide).
Non-alkali or alkali-free glass is used for FPD like LCD or OLED (Organic Light-Emitting Diode) displays. Therefore, it enhances the resolution like smartphones. Non-alkali glass can also be very thin while having minimal deformation. As a result, this type of glass, though very thin, is considerably resistant to damage.
Non-alkali glass contains a range of compounds, mainly silicon dioxide, aluminum oxide, and boron trioxide. Depending on how it’s made, it may also contain small amounts of magnesium oxide, lime (calcium oxide), barium oxide, strontium oxide, or zinc oxide.
Fused quartz glass
Fused quartz glass is considerably different from commercial types of glass. That’s because it contains pure silica and doesn’t contain other compounds like commercial glass does. Because of this, it’s sometimes referred to as pure glass. Therefore, fused quartz glass has some unique properties. For example, it has a higher chemical and thermal resistance and increased transparency when compared to commercial glass.
Fused quartz glass has a range of applications. Due to its high transparency, it’s primarily used for transmitting ultraviolet light. However, this glass can also be used for laser technology, electronics, and high-temperature operations.
Borosilicate glass is made from silicon dioxide and boron trioxide. It’s widely used for laboratory glassware because it has good thermal and chemical resistance. Therefore, it’s ideal for scientific experiments that require heat or the use of harsh chemicals.
Glass ceramics combine the properties of glass with ceramics. Therefore, this material is a cross between glass and ceramics. The resulting material is highly crystalline. Depending on how it’s made, glass ceramics can be transparent or opaque. Other properties include lower thermal expansion, increased hardness, and higher resistance to thermal shock compared to commercial glass.
Glass ceramics are commonly used for cooking purposes, such as cooktops, cooking appliances, grills, and barbeques. Most types contain lithium, aluminum, and silicon oxides. They may also include smaller quantities of sodium oxide, potassium oxide, magnesium oxide, or lime (calcium oxide).