Nickel Sulfide (NiS) inclusions in glass

Nickel sulfide (NiS) inclusions in glass, particularly toughened glass, can pose a significant safety risk. These inclusions are tiny, naturally occurring crystalline particles of nickel and sulfur that can be found in raw materials used for glass manufacturing. When present in toughened glass, they can lead to spontaneous glass breakage, which can have serious consequences. To address this issue, various strategies have been developed, one of which is the use of non-toughened laminated glass.

Nickel sulfide inclusions occur during the formation of glass when the raw materials contain trace amounts of nickel and sulfur. These impurities can combine to form NiS crystals within the glass structure. The problem arises when the glass is heat-treated or toughened. During the toughening process, the glass is rapidly heated and then cooled, which can cause the NiS crystals to expand. When these crystals expand, they can exert internal stress on the glass, eventually leading to spontaneous breakage. This breakage can occur days, months, or even years after installation, posing a safety hazard in architectural and automotive applications.

Non-toughened laminated glass is an alternative solution to mitigate the risk of nickel sulfide inclusion-induced spontaneous breakage. Laminated glass consists of two or more layers of glass bonded together with an interlayer of polyvinyl butyral (PVB) or ionoplast. The primary advantage of laminated glass is that, even if one of the glass layers breaks, the interlayer holds the broken glass pieces together, preventing them from shattering and causing harm.

Laminated glass reduces the risk of nickel sulfide inclusions in the following ways:

1. Retains NiS Inclusions: When nickel sulfide inclusions are present in one of the glass layers, laminated glass retains the particles within that layer. This is because the interlayer effectively traps the inclusions and prevents them from expanding and causing the glass to break.

2. Enhances Safety: In the event that a toughened glass layer containing NiS inclusions breaks, the laminated interlayer ensures that the glass remains intact and in place. This significantly reduces the safety risk associated with spontaneous breakage, making it a preferred choice for applications where safety is paramount, such as balustrades, facades, and automotive windshields.

3. Reduces Risk of Spalling: Toughened glass breakage can lead to spalling, where tiny glass fragments can be expelled with force. Laminated glass, due to its structural integrity, mitigates the risk of spalling, further enhancing safety.

It is important to note that the use of non-toughened laminated glass does not eliminate the presence of nickel sulfide inclusions but rather provides a safer way to deal with them in applications where the risk of spontaneous breakage is a concern.

To further minimize the risk of nickel sulfide inclusion-related breakage, it is essential to follow industry standards and guidelines. For instance, the Centre for Window and Cladding Technology (CWCT) standards may provide specific recommendations and requirements for glass selection and installation to ensure the safety and reliability of glass systems in various building applications.

In conclusion, nickel sulfide inclusions in toughened glass can lead to spontaneous breakage, posing a safety hazard. Non-toughened laminated glass, with its ability to retain inclusions and enhance safety, is a viable solution to mitigate this risk. While it does not eliminate the presence of inclusions, it significantly reduces the potential consequences of their expansion. Adherence to industry standards, such as those provided by CWCT, is essential to ensure the proper selection and installation of glass in various architectural applications, safeguarding both people and property.