Thermal Shock
Objective:To illustrate thermal shock and the effects of differing amounts of modifier on the properties of glass. Description: · Three different types of glass rods will be heated so that students can observe the amount of thermal shock that occurs. · Different formulas of glass affect the mechanical, electrical, chemical, optical, and thermal properties of the glasses that are produced. · The two most important properties that determine resistance to thermal shock in glass are thermal conductivity and coefficient of thermal expansion.
Thermal expansion is the tendency of matter to increase in length, area, or volume when heated. For liquids and solids, the amount of expansion will normally vary depending on the material’s coefficient of thermal expansion. When materials contract, tensile forces are created. When things expand, compressive forces are created. · Thermal shock is the name given to cracking as a result of rapid temperature change. Glass and ceramic objects are particularly vulnerable to this form of failure, due to their low toughness and low thermal conductivity, as well as their high melting point (which often leads to their use in high-temperature applications).