Basic Properties of Glass
Edit date:2018-11-27 10:10
Basic Properties of Glass
(1) Apparent density: The apparent density of glass is related to its chemical composition, so it varies greatly. And it decreases with the increase of temperature. The apparent density of ordinary silicate glass is about 2500 kg/m3 at room temperature.
(2) Mechanical properties: The mechanical properties of glass depend on chemical composition, product shape, surface properties and processing methods. All products containing unmelted impurities, stones, nodules or micro-cracks will result in stress concentration, which will sharply reduce their mechanical strength. Glass is often subjected to bending, tension, impact and vibration in buildings, and rarely to compression. Therefore, the main indicators of mechanical properties of glass are tensile strength and brittleness. The actual tensile strength of glass is 30-60 MPa. The brittleness index of ordinary glass (E/R ratio of elastic modulus to tensile strength) is 1300-1500 (rubber 0.4-0.6). The bigger the brittleness index is, the bigger the brittleness is.
(3) Thermophysical properties: (1) The thermal conductivity of glass is very poor. At room temperature, the thermal conductivity of glass is only 1/400 of that of copper, but it will increase with the increase of temperature. In addition, it is also affected by the color and chemical composition of glass. (2) The thermal expansion of glass depends on its chemical composition and purity, and the higher the purity, the smaller the thermal expansion coefficient. (3) The thermal stability of glass depends on its ability to resist cracking when the temperature changes dramatically. The smaller the thermal expansion coefficient of glass is, the higher its thermal stability is. The thicker the glass products, the larger the volume, the worse the thermal stability. Therefore, heat treatment should be used to improve the thermal stability of products.
(4) Chemical stability: Glass has high chemical stability, but long-term corrosion by corrosive media can also lead to deterioration and destruction.
(5) Optical properties of glass: Glass can not only pass through light, but also reflect and absorb light, so thick glass and multi-layer overlapping glass are often not transparent: the ratio of reflected light energy to projected light energy of glass is called reflection coefficient. The magnitude of the reflection coefficient depends on the smoothness of the reflector, the refractive index, the incident angle of the projected light, whether the glass surface is coated or not, and the type of the film.
The solar radiation energy through 3mm thick standard transparent glass is taken as 1.0. The relative value of solar radiation energy through other glass under the same conditions is called the shielding coefficient. The more the shelter coefficient, the less the solar radiation energy entering the room through glass, the better the cold room effect and the softer the light.
(1) Apparent density: The apparent density of glass is related to its chemical composition, so it varies greatly. And it decreases with the increase of temperature. The apparent density of ordinary silicate glass is about 2500 kg/m3 at room temperature.
(2) Mechanical properties: The mechanical properties of glass depend on chemical composition, product shape, surface properties and processing methods. All products containing unmelted impurities, stones, nodules or micro-cracks will result in stress concentration, which will sharply reduce their mechanical strength. Glass is often subjected to bending, tension, impact and vibration in buildings, and rarely to compression. Therefore, the main indicators of mechanical properties of glass are tensile strength and brittleness. The actual tensile strength of glass is 30-60 MPa. The brittleness index of ordinary glass (E/R ratio of elastic modulus to tensile strength) is 1300-1500 (rubber 0.4-0.6). The bigger the brittleness index is, the bigger the brittleness is.
(3) Thermophysical properties: (1) The thermal conductivity of glass is very poor. At room temperature, the thermal conductivity of glass is only 1/400 of that of copper, but it will increase with the increase of temperature. In addition, it is also affected by the color and chemical composition of glass. (2) The thermal expansion of glass depends on its chemical composition and purity, and the higher the purity, the smaller the thermal expansion coefficient. (3) The thermal stability of glass depends on its ability to resist cracking when the temperature changes dramatically. The smaller the thermal expansion coefficient of glass is, the higher its thermal stability is. The thicker the glass products, the larger the volume, the worse the thermal stability. Therefore, heat treatment should be used to improve the thermal stability of products.
(4) Chemical stability: Glass has high chemical stability, but long-term corrosion by corrosive media can also lead to deterioration and destruction.
(5) Optical properties of glass: Glass can not only pass through light, but also reflect and absorb light, so thick glass and multi-layer overlapping glass are often not transparent: the ratio of reflected light energy to projected light energy of glass is called reflection coefficient. The magnitude of the reflection coefficient depends on the smoothness of the reflector, the refractive index, the incident angle of the projected light, whether the glass surface is coated or not, and the type of the film.
The solar radiation energy through 3mm thick standard transparent glass is taken as 1.0. The relative value of solar radiation energy through other glass under the same conditions is called the shielding coefficient. The more the shelter coefficient, the less the solar radiation energy entering the room through glass, the better the cold room effect and the softer the light.
