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NiS and spontaneous breakage
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In various situations fully-tempered glass may break for no reason. Many factors might cause such spontaneous breakages, but the most common are nickel sulphide inclusions.
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 Nickel sulphide inclusion, also known as NiS, occurs during the manufacturing process for float glass. In the glass batch, nickel-rich contaminants such as stainless steel might be present, and then combine with sulphur form nickel sulphide inclusions. Glass manufacturers take extraordinary steps to minimize the potential for nickel sulphide inclusions. Considering that a large furnace may produce up to 600 tons of glass per day, total elimination of contaminants is extremely difficult. When glass is heat-treated during successive stages, in order to obtain fully-tempered glass, nickel sulphide inclusions change in size from what is known as a low-temperature (LT) structure to a high-temperature (HT), crystalline structure. When cooled quickly the NiS particle is unable to change back to its original form(LT). Over a certain period of time NiS will slowly convert to the original form (LT) phase with an increase in volume of about 2 - 4%. Such increase of NiS will cause glass breakage. Additional information available on the selected links.
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Photos: Web
Last review: November, 2012 |
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Glassresource
Find out more about nickel sulphide inclusions.
Heat Soak
Learn more about spontaneous breakage.
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Spontaneous tempered glass breakage on greenhouse.
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