In your own words, briefly describe what happens as a glass piece is thermally tempered.

Thermal tempering is a process used to improve the strength and durability of glass. During this process, the glass is heated to a high temperature and then rapidly cooled by forced air. This controlled process increases the overall strength of the glass and makes it more resistant to breakage and impact.

1. Preheating: The glass piece is first cleaned and then heated to a uniform temperature, typically ranging from 620℃ to 650℃. This is usually done in a furnace. 2. Transition phase: At this high temperature, the glass undergoes a phase transition and becomes a softer, more pliable material. This temporary change allows the glass to be more readily shaped and strengthens it when the process is finished. 3. Quick cooling: In this step, the glass is rapidly cooled by blowing forced air on its surface. This process locks in the improved molecular structure of the tempered glass, causing the outer surfaces to contract while the core remains hot. 4. Gradual cooling: The glass is slowly cooled to room temperature, allowing the core to cool and the glass pieces to stabilize. This slow cooling phase is necessary for properly aligning the structure of the glass, enhancing its overall strength, and preventing defects.

As the glass is tempered, there are a few significant changes that occur: 1. Improved strength: Thermal tempering increases the mechanical strength of glass, making it more resistant to breakage and impact. This is mainly due to the compressed surface layers and greater degree of cross-linking achieved during the tempering process. 2. Enhanced safety: When the tempered glass is broken, it shatters into small granular pieces, which are much less likely to cause injury compared to the dangerous shards formed when untreated glass breaks. 3. Increased thermal resistance: Tempered glass has a higher tolerance to temperature changes, making it more suitable for applications exposed to extreme temperatures or rapid temperature fluctuations. In summary, thermal tempering improves the strength, safety, and thermal resistance of the glass, making it more durable and suitable for various applications.