Thermal expansion of ceramic
Thermal expansion - Testing of ceramics at high temperatures
At WZR ceramic solutions we test the thermal expansion of your ceramic in a dilatometer up to 1500°C. Here we respond to your questions and carry out the tests according to standards and task related.
We are happy to assist you with our knowledge and many years of experience in finding solutions to prevent possible temperature-related stresses.
What is thermal expansion?
Thermal strain describes the change in length of a material caused by a change in temperature. It is given as a relative change in length in percent. Furthermore, this specific material property can be defined by the thermal expansion coefficient α in K-1, which represents the ratio of the relative change in length to the change in temperature.
How does thermal length change occur?
The most common cause of length change at rising temperatures is phase transformations in components of the ceramic. This changes the arrangement of the atoms in the structural components and produces denser or less dense minerals.
A distinction is made between two forms: reversible and irreversible length changes. With reversible length changes, the initial length of the sample is reached again after cooling. In the case of irreversible length changes, the length of the sample after cooling deviates from the initial length. Reasons for this can be irreversible phase changes and the re-sintering of ceramics.
Why is it important to determine the thermal expansion of a ceramic using dilatometry?
Ceramic materials can be used at temperatures > 1,000°C – when plastics and metals already fail. However, like all materials, they react to changing temperatures. Here, expansion or shrinkage of the material can lead to damage to the component and the surrounding areas. In order to make the right choice of material and to design the component or a refractory lining according to requirements, the characteristic value of thermal expansion must therefore be known. However, since ceramics are often component mixtures, their behavior at high temperatures cannot be predicted. For this reason, the thermal strain must be determined in advance by dilatometry.
How is the thermal expansion of a ceramic determined?
We measure the thermal expansion in a dilatometer up to 1500°C. For this purpose, a sample of maximum 50 mm length and 6.5 mm width is sufficient. As reference material we use a corundum single crystal.
For the measurement, the prepared ceramic sample is placed in the dilatometer and heated up. The heating rate is determined by us in advance in accordance with the task and the standards. After reaching the maximum temperature, the system is cooled down evenly to room temperature, just like during heating. Meanwhile, the instrument records the change in length of the clamped sample during the entire measuring period. Based on the relationship between the change in length and temperature, the thermal expansion coefficient and thus the thermal expansion of the material can be determined.
It is also possible to examine the shrinkage behaviour of green parts on the dilatometer before the production of a component. The heating rate of the measurement can be selected according to the planned sintering curve, which allows the shrinkage behavior of the green body to be documented.
What are the limits of thermal expansion testing?
Since the foundation of WZR ceramic solutions, we have built on close contact with our customers. When testing thermal expansion, the exchange with you is particularly important in order to optimally adjust the test temperature to your material. Please note that we test the thermal expansion of materials up to a maximum temperature of 1500°C.
By means of standards we ensure a validation of the measurement results. For this reason, the specimen to be tested must have a comparable specimen length or allow preparation for a suitable specimen geometry. We would be pleased to contact you to discuss the testing of the thermal expansion of your ceramic.