Chemical strengthened glass speaks to what is chemical strengthened glass and why use chemical strengthened glass.
It is produced by an ion exchange program process that takes place when annealed glass is immersed in a molten salt bath.
As smaller sodium ions in the glass are replaced with larger potassium ions from the salt solution, The faces of the glass are put into compression relative to the core and the glass is prestressed in a manner similar to the one that occurs with heat treating.
However because the temperatures involved in strengthening are lower, strengthened glass does not experience the optical distortions or warping that are common with heat treated glass. Dependant on the particulars of the treatment process, the strength and toughness of this strengthened glass can exceed that of tempered glass..
Unlike tempered glass, the strengthened can be cut after the process, although its strength is diminished along the cut edges. When this glass breaks it produces large, hazardous shards. So like the glass which is heat treated, it cannot be used where safety glazing is required unless laminated.
This type of strengthening is used for pieces of glass that are not easily heat treated, such as those that are small, thin or oddly shaped. It is also used in some fire rated glass products and in laminated form for security glass, blast resistant glass and wind borne debris resistant glass.
This is a type of glass that has increased strength as a result of a post-production chemical strengthened glass process. When broken, it still shatters in long pointed splinters similar to float glass. For this reason, it is not considered a safety glass and must be laminated if a safety glass is required. However, chemically strengthened glass is typically six to eight times the strength of float glass.
The glass is chemically strengthened by a surface finishing process. Glass is submersed in a bath containing a potassium salt (typically potassium nitrate) at 300°C. This causes sodium ions in the glass surface to be replaced by potassium ions from the bath solution.
These potassium ions are larger than the sodium ions and therefore wedge into the gaps left by the smaller sodium ions when they migrate to the potassium nitrate solution. This replacement of ions causes the surface of the glass to be in a state of compression and the core in compensating tension. The surface compression of chemically strengthened glass may reach up to 690 MPa.
There also exists a more advanced two-stage process for making chemically strengthened glass, in which the glass article is first immersed in a sodium nitrate bath at 450 °C, which enriches the surface with sodium ions. This leaves more sodium ions on the glass for the immersion in potassium nitrate to replace with potassium ions. In this way, the use of a sodium nitrate bath increases the potential for surface compression in the finished article.
Chemical strengthening results in a strengthening similar to toughed glass. However, the process does not use extreme variations of temperature and therefore chemically strengthened glass has little or no bow or warp, optical distortion or strain pattern. This differs from toughened glass, in which slender pieces can be significantly bowed.
Also unlike toughened glass, chemically strengthened glass may be cut after strengthening, but loses its added strength within the region of approximately 20 mm of the cut. Similarly, when the surface of chemically strengthened glass is deeply scratched, this area loses its additional strength.
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