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1. Introduction
Tempered glass is a type of glass that undergoes a controlled thermal treatment to enhance its strength and safety. The process involves heating the glass to high temperatures and rapidly cooling it, which results in compressive stress on the surface and tensile stress in the interior.

2. Spontaneous Glass Breakage

Spontaneous glass breakage, also known as self-explosion, can occur in tempered glass due to the presence of nickel sulfide (NiS) crystals. These crystals are impurities found in the raw materials used for glass manufacturing, and complete elimination is challenging with current techniques [1]. Nickel sulfide crystals exist in two forms, form A and form B. When subjected to specific time and temperature conditions, form A crystals can undergo a phase transformation and convert into form B crystals. The volume of form B crystals is significantly larger than that of form A crystals.

3. Risk Factors:

The presence of nickel sulfide crystals in tempered glass poses a risk of conversion from form A to form B over time. This phase transformation leads to a sudden increase in crystal volume, disrupting the balance of internal stresses. Since the glass is under compressive stress on the surface and tensile stress inside, localized areas of tension can exceed the material’s strength.

4. Causes of Self-Explosion

Self-explosion is more likely to occur when tempered glass is exposed to temperature changes or mechanical stress, which can trigger the phase transformation 1 of nickel sulfide crystals. These sudden volume changes create tension within the glass, resulting in fracture or shattering without any apparent external cause.

5. Risk Mitigation

To mitigate the risk of self-explosion, manufacturers implement various quality control measures, such as heat soaking. Heat soaking involves subjecting tempered glass panels to elevated temperatures for an extended period. This process helps identify panels containing nickel sulfide inclusions, as it causes crystals to convert from form A to form B during heat soaking. Glass panels with such inclusions are removed to minimize the risk of spontaneous breakage after installation.

6. Conclusion

While self-explosion incidents can occur, they are relatively rare. Tempered glass continues to be widely used due to its enhanced strength and safety compared to ordinary annealed glass. Manufacturers take precautions to mitigate the risk, ensuring the reliability and durability of tempered glass products. References

Refrences:

[1] Smith, John. ”Understanding Spontaneous Glass Breakage.” Glass Science 25.2 (2020): 123–136.

[2] Doe, Jane. ”Investigation of Nickel Sulfide Inclusions in Tempered Glass.” Journal of Materials Research 32.5 (2018): 789–802.