How Property Of Thermal Shock Resistance Effect The Ceramic Material
Traditionally, the most important ceramic materials were bricks, tiles, cements, pottery, and glass. These materials show extraordinary mechanical strength and physical properties. However, today with technological improvement, ceramics are found in a broad range of applications. Some important fields of ceramic applications are as insulator material, biomedical implants, and coatings of jet engine, in ballistic protection, turbine blades, ceramic disk brake and many more.
The Thermal shock behavior of ceramic materials plays a significant role in their industrial use. Rapid heating and cooling of ceramics result in thermal stresses that can lead to damage or catastrophic failure.
Thermal shock occurs when different parts of an object to expand due to thermal gradient. This differential expansion can be understood in terms of stress or of strain. When stress exceeds the strength of the material it causes a crack in its formation and ultimately objects's structure failure.
When ceramics are subjected to severe thermal shock they suffer strength degradation. It is also known that the thermal shock strength behavior is size-dependent. Damage and strength deficit are determined based on fracture and damage mechanics. Higher fracture energy can enhance the residual strength of thermally shocked ceramics.
How to prevent the Failure due to thermal shock:
Reducing the thermal gradient of the object.
Changing the temperature of the material.
Reducing the coefficient of thermal expansion.
Establishing compressive stress, e.g. tempered glass
Lowering the value of Young's modulus
Increasing its toughness or crack deflection.
Method of thermal shock testing in Ceramics:
Thermal shock testing is the method in which a material is exposed to continuous alternating temperatures. This accelerates the material failures caused by thermal shocks. The transition temperature in general is greater than 15 °C per minute.
Equipment which has multiple chambers to transfer the material is used for thermal shock testing. In case of single chamber equipment, the chamber air temperature is rapidly cooled and heated. The products remain in the same chamber. There are some equipment available that separate hot and cold chambers. These equipments have an elevator mechanism to transports the products.
Glass containers are not used for testing the property of Thermal Shock Resistance Materials. This is because these materials are very sensitive to sudden temperature changes. Another essential method of testing thermal shock resistance involves rapid transfer of ceramics from cold to hot water baths.
Quenching technique is another method to determine thermal shock resistance in ceramics. This is an important laboratory experimental method to investigate the thermal shock behavior of ceramics. In this method, the samples are quenched with air, water or oil, after heating the furnace. Afterward the residual mechanical properties are measured. This is the general method to characterize the thermal resistance of ceramics and other high-density materials. However, the quenching parameters and experimental results do not agree well with the real application conditions and theory.
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