Thermal Shock Lesson

Thermal Shock at a glance

Background

Have you ever wondered why some glass dishes can go from the oven to the fridge without breaking, while others might crack? The answer lies in how different materials handle temperature changes—a concept known as thermal shock.

In this lesson, students will learn about thermal expansion, which is the tendency of materials to expand when heated and contract when cooled. They’ll explore how this expansion can create forces within an object that might cause it to crack if the temperature changes too quickly. This cracking is what we call thermal shock.

Students will compare different types of glass used in homes and labs, such as borosilicate (used in Pyrex cookware) and soda lime (common in everyday glassware), to see why some are better at resisting thermal shock. They’ll discover that borosilicate glass, with its lower thermal expansion and greater strength, is designed to withstand these temperature changes much better than soda lime glass.

By the end of this lesson, students will understand how materials engineers have developed special types of glass and ceramics that are highly resistant to thermal shock, making them safer and more durable for everyday use.

Lesson Objective

Students will explore thermal shock by heating different types of glass rods to observe how they respond to rapid temperature changes. They will learn how variations in glass composition affect its resistance to thermal shock and its ability to handle sudden temperature shifts.

Experiment Description

In this experiment, students will heat soda-lime, borosilicate, and fused silica glass rods and then quickly cool them in ice water to observe the effects of thermal shock. They will compare the amount of cracking and deformation among the different types of glass to understand how modifiers and composition influence thermal shock resistance.

Materials List

3 soda-lime (flint) glass rods
3 borosilicate glass rods
3 fused silica (quartz) glass rods
Glass beaker
Torch head
Propane
Ice water
Strike lighter or matches

Safety Precautions

Wear safety glasses to protect against potential flying glass shards and use caution when handling hot glass and equipment.
Ensure students keep a safe distance from the demo area to avoid injury from broken glass and hot surfaces.

The Experiment

1. To set up the demonstration, each station should be equipped with Bunsen burners or propane torches and a beaker of ice water for quenching the heated glass rods. Safety glasses are required for all students. First, students will observe the green tint of soda-lime glass, caused by iron oxide impurities, and then heat one end of the rod in the flame, noting the "sodium flare" that appears as the glass heats.

2. When the glass is quenched in ice water, thermal shock will cause visible cracks. Next, students will examine borosilicate glass, which is light gray in color. Upon heating, it will exhibit less sodium flare and will be more resistant to softening. Quenching the borosilicate glass will result in fewer cracks, showing its improved resistance to thermal shock.

3. Finally, students will work with fused silica glass, which is clear or white and shows no sodium flare or softening when heated. When quenched, the fused silica glass will not crack, demonstrating its high resistance to thermal shock. Throughout the demonstration, students should record their observations, focusing on how each type of glass responds to heating and quenching, to help them understand the relationship between the physical properties of glass and its behavior under thermal stress.