Dortech was recently commissioned by Morgan Sindall to high level glass replacement services at Teeside University which had broken as a result of a nickel sulphide impurity.
Glass may contain nickel sulphide impurities, in the form of small crystals. As glass is heated during the toughening process these impurities change state. The high temperature a-state of the impurities may be frozen when the glass is quenched, and recovery to the low temperature b-state may then take several years.
Spontaneous breakage of the glass may follow, as the low temperature b-state of the nickel sulphide impurities occupies a slightly greater volume and so generates a local stress concentration. However, only the largest impurities will cause failure, and only then if they are in the core tensile zone of the glass.
The broken glass was situated on the 5th Floor at the university, so Dortechs team had to employ a large 35 meter truck mounted mahine with glass mounts to carry out the work.