Hello, I'm Dr. Emily Carter, a materials scientist specializing in glass properties. I've spent years studying the fascinating world of glass, from its structure to its behavior under various conditions. Let's discuss your question about glass breaking temperatures.

The question of "what temperature does glass break at" doesn't have a simple, singular answer. It's not like a specific melting point where glass suddenly transitions from solid to liquid. Instead, glass transitions through various states as temperature changes, and its behavior depends significantly on factors like:

* Type of Glass: Different glass compositions have different thermal properties. For instance, soda-lime glass, the most common type used for windows and bottles, has different characteristics than borosilicate glass used in cookware or lead crystal used for decorative purposes.
* Heating Rate: Heating glass rapidly can lead to thermal shock, which can cause it to crack or shatter. Slower heating allows for more uniform expansion.
* Shape & Thickness: Thin glass can withstand higher temperatures than thick glass, especially in rapid heating scenarios.
* Internal Stress: Manufacturing processes can leave internal stresses within the glass. These stresses can be exacerbated by temperature changes, potentially leading to fracture.

Now, let's explore some key temperature points for glass behavior:

1. Glass Transition Temperature (Tg): This is a crucial temperature where glass transitions from a rigid, solid-like state to a more viscous, rubbery state. It's not a sharp melting point but rather a range where the glass becomes increasingly deformable. The Tg varies widely depending on the glass composition. For soda-lime glass, the Tg is around 550°C (1022°F), while borosilicate glass has a much higher Tg of about 820°C (1508°F).

2. Softening Point: This temperature is where the glass becomes sufficiently soft to deform under its own weight. It's significantly higher than Tg, and again, varies depending on the glass composition.
Soda-lime glass softens around 700°C (1292°F), while borosilicate glass has a higher softening point of around 900°C (1652°F).

3. Strain Point: This temperature is where the glass becomes rigid enough to withstand stress without significant deformation. It's lower than the softening point and signifies a point where the glass can be safely handled without significant shape change. The strain point for soda-lime glass is around 500°C (932°F), while borosilicate glass has a strain point around 700°C (1292°F).

4. Annealing Point: This temperature is crucial for stress relief in glass. Heating glass above its annealing point and then slowly cooling it allows for internal stresses to dissipate, making the glass more resistant to cracking. The annealing point for soda-lime glass is around 550°C (1022°F), while for borosilicate glass, it's around 800°C (1472°F).

Breaking Point: Ultimately, the temperature at which glass breaks depends on the specific situation. As discussed, factors like heating rate, shape, thickness, and internal stresses play a crucial role. It's not a single point, but rather a range where glass may experience cracking or shattering under specific conditions.

For example, soda-lime glass can withstand a quick dip in boiling water (around 100°C (212°F)) without breaking, but if subjected to sudden extreme temperature changes, such as being heated over an open flame or plunged into very cold water, it can shatter. In contrast, borosilicate glass can withstand much more drastic temperature changes due to its higher Tg and softening point, making it suitable for cookware.

**In summary, there's no single temperature that universally dictates when glass breaks. It's a complex interplay of various factors that determines its behavior under different conditions. Understanding these factors and the specific properties of different glass types is essential for working with and manipulating glass safely.**
read more >>

Here, an important distinction needs to be made. When a window pane of ordinary float glass is first heated, it tends to crack when the glass reaches a temperature of about 150 - 200oC. The first crack initiates from one of the edges.read more >>