Abstract

Refractories are essential for all highly industrialized processes which are performed at elevated temperatures. When in use, the temperatures at which these processes are run tend to change more often and more rapidly, as large scale industrial processes become more flexible to the availability of raw materials and the demand for products. Repeatedly cooling down and heating up the refractory linings (thermal shock) can cause severe damages to them and their service life and thus the uninterrupted operation time of the equipment are considerably reduced. Consequently, it is necessary to develop new refractory lining materials which have a good resistance to thermal shock, which in addition to long service life also leads to improved corrosion resistance at high temperatures.

To support the development of new refractory products with a higher thermal shock resistance, a new advanced testing device was developed based on the disc irradiation method. It is able to determine the critical thermal shock induced stress of refractory materials under ascending thermal shock conditions. The disc-shaped test pieces are irradiated centrally on both sides using focused halogen lamps. Within a few seconds, a circular temperature field is generated in the test piece. The heating-up regime causes a higher thermal expansion at the heated centre of the test piece compared to its edge, inducing a stress gradient. When the maximal tensile stress is reached at the edge of the test piece, fracture occurs and propagates towards to the centre.

With an appropriate in situ damaging detection using microphones, the disc irradiation method can be used to investigate the fracture process taking place within refractory test pieces during thermal shock. Using in situ detection of the acoustic emission during cracking, fracture pattern in the stressed test pieces were identified (through the matrix, the grains, the interface) by evaluation of the complex noises of the fracture during the thermal shock procedure. This fracture analysis can contribute to the development of new generations of refractory linings with a higher thermal shock resistance.