Have you ever wondered why wine glasses break to pieces on impact? Or was there a moment of fear that the glass walls of the building would break and fall? The structure of glass is very complicated. It's hard and strong, but at the same time it's fragile. For something so common, the science behind broken glass is also complex.
Why does glass break?
In fact, the reason why glass is so easy to break is because of its molecular structure. Glass is made of silica. Silica forms a rigid, random molecular network. Unlike most solids, the silicon and oxygen atoms in glass are connected at random angles in an irregular pattern.
This disordered arrangement gives the glass transparency and is easy to shape into different shapes when heated. However, this also means that there are no weak spots. As a result, when external pressure is applied, the glass will break in a jagged, uncontrolled manner. Any small surface defect or scratch can also become a stress concentrator. Once a crack is triggered, it quickly spreads throughout the material.
When cracks start to spread, they are hard to stop. Even though the bond between the silicon and oxygen atoms is strong. But it is difficult for the crack to change direction or stop at the edge of the defect. Due to the irregular geometry of the silico-oxygen bonds, they will simply continue to pass through the random network. Glass lacks an orderly structure, so it's hard to predict when it breaks.
The only way to improve the impact resistance of glass is to introduce a more ordered molecular arrangement. Just like the safety of tempered glass is high, it is because its molecular arrangement is ordered. By rapidly heating and then rapidly cooling, compressive stress can be created inside the glass. These stresses help to counteract the spread of the crack. So tempered glass can withstand a higher load. But that doesn't mean it can't break. It just breaks in a safer form. That is, it breaks into small particles, rather than the sharp pieces of ordinary glass.
Why does heat break glass?
Glass will break except when impacted by external forces. It also breaks when subjected to thermal stress. In high temperature environments, the imbalance of temperature causes the glass to expand unevenly, which puts pressure on its structure. When an area of glass becomes hot, expansion occurs. But cooler regions don't expand at the same rate.
So you can imagine that one part of the glass is expanding rapidly, while the other part is expanding slowly. In this case, stress will be created inside the glass. So it pulls on the glass and causes it to deform. If these stresses become too severe, the glass will break. In fact, the glass is broken only to reduce its own stress. But in our opinion, the glass is too fragile.
Thermal stress levels also depend on three factors
Temperature difference
The greater the temperature difference between the hot part and the cold part of the glass, the greater the stress.
The speed of temperature change
Generally speaking, when the temperature rises or cools rapidly, the speed of glass expansion or contraction is faster. Which increases the stress.
The thickness and shape of the glass
Thinner, more irregular glass is more likely to break. Because it can't withstand temperature fluctuations.
To minimize thermal stress, avoid exposing the glass to extreme or rapid temperature changes. For example, do not pour boiling water over cold glass and do not expose the glass to freezing temperatures. This rapid temperature change makes the glass more likely to break. Protecting glass from thermal stress is the key to preventing glass breakage. Therefore, we should pay attention to the temperature environment of the glass in our life.
