View source for K9 glass

{{Short description|Type of borosilicate crown glass}}
'''K9 glass''', sometimes referred to as '''K9 crystal''', is a variety of optical [[borosilicate]] [[Crown glass (optics)|crown glass]].  The letter "K" is a reference to the German word for "crown" (''Krone'') and the number 9 refers to the lead oxide content of the glass (9%).  K9 glass has high optical clarity, and is used in many contexts requiring this characteristic.  It has been regarded as a difficult-to-cut material because of its superior mechanical properties.<ref>{{cite journal|journal=Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture|volume= 228|issue=4|page=504|date=2014|author=Zhang, Chenglong|author2=Cong, Weilong|author3=Feng, Pingfa|author4=Pei, Zhijian J.|title=Rotary ultrasonic machining of optical K9 glass using compressed air as coolant: a feasibility study|doi= 10.1177/0954405413506195|hdl= 2097/17898|s2cid= 53380862|url=https://krex.k-state.edu/dspace/handle/2097/17898 |hdl-access=free}}</ref>  It has an [[elastic modulus]] per [[pascal (unit)|pascal]] of 8x10<sup>10</sup>, a [[Poisson's ratio]] of 0.21, and a density of 2510 kilograms per cubic meter (less dense than most other leaded glass).<ref name="Tan2010">{{cite book|author=Hong Hua Tan|title=Applied Mechanics And Mechanical Engineering|url=https://books.google.com/books?id=w_63DwAAQBAJ&pg=PA49|date=13 August 2010|publisher=Trans Tech Publications Ltd.|isbn=978-3-03813-388-9|page=49}}</ref>  Its [[refractive index]] is 1.517 at 590 nm wavelength<ref name=yin>{{cite web | title=K9(BK7) Yinxing Optical | access-date=May 29, 2023 | url=http://www.ygofg.com/products/Colorless_Filter_Glass/119.htm}}</ref> (compared to 1.523 for crown glass (soda-lime)  and 1.618 for 45% leaded glass)<ref>{{cite web | title=Refraction (The Physics Hypertextbook) | access-date=May 29, 2023 | url=https://physics.info/refraction/}}</ref> Its clarity (90% transmission at 590 nm<ref name=yin/>), combined with low cost have made it desirable for chandeliers, lasers, telescopes, etc.
K9 is produced in large quantities by China, which sells it at a price far below higher-quality well-known glass manufacturers such as [[Swarovski]].  A similar product to K9 (but without lead) is [[BK7]].<ref>{{cite web|title=What Is K9 Crystal? |url=https://www.reference.com/science/k9-crystal-871bd3cefb4a597c|work=Reference.com|date=4 August 2015 }}</ref>
==References==
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[[Category:Glass types]]
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