Thermal expansion
Referenzprobe aus Korund-Einkristall
Reference sample of corundum single crystal

Generally ceramic components extend while heating up. While constructing assemblies or refractory linings with fire-resistant material this thermal expansion has to be taken into account. The determination of the thermal expansion is carried out by a dilatometer which operated at temperatures up to 1500°C. A reference materials used in the dilatometer (e.g., platinum or sapphire) depend on the temperature range of intrest. The typical length of the samples is up to 50mm and the usual diameter is around 7,5mm.

Prozentuale thermische Längenänderung unterschiedlicher keramischer Werkstoffe
Percentage thermal change in length of different ceramic materials
Thermischer Längenausdehnungskoeffizient α unterschiedlicher keramischer Werkstoffe
Linear thermal expansion coefficient a of different ceramic materials
RCS-Messung an ZrO2- Grünling
RCS measurement at ZrO2 green shape

In addition, the dilatometer makes it possible to record the shrinkage behavior of green parts during the sintering process. Therefore so called RCS measurements are carried out.

Refractoriness / pressure flow
Schematischer Versuchsaufbau für Druckerweichen bzw. Druckfließen
Schematic experimental setup for Refractoriness or pressure flow

The dilatometer testing apparatus is also used to investigate softening and yield of samples under pressure. The measurement set-up differs from standard dilatometer measurements only in the measurement parameters. The samples have a diameter and height of 50 mm and have a central drill-hole.

Beispiel einer ausgewerteten DE-Kurve
Example of an evaluated DE Curve

For pressure softening – according to DIN EN 993-8 – the deformation or softening is measured for increasing temperatures under constant load. The behavior of the sample is then described by illustrating pre-defined temperatures.

Beispiel einer ausgewerteten DFL-Kurve
Example of an evaluated DFL Curve

For pressure yield – according to DIN EN 993-9 – the deformation is investigated under constant load and temperature but with proceeding time. Here a measurement time of 25 h is usually considered.

Hot bending strength
Probe nach der Prüfung der Heißbiegefestigkeit bei 1500°C
Sample after the hot bending strength test at 1500°C

We at WZR are able determine the bending strength of ceramic specimen at temperatures up to 1500°C. The Test for refractory materials is determined by the DIN standard EN 993-7. A special construction makes it possible to measure the deflection of the sample, while the load increases. Out of this data the E module and the V module for the measured samples can

Hot abrasion

The determination of the abrasion resistance of ceramic materials at ambient temperature is described in the C ASTM 704-88. At the WZR it is possible to determine the abrasion at temperatures up to 1500°C in following this norm. Therefore the sample is irradiated with SiC particles. The irradiation is divided into cycles to prevent the sample from cooling down. The impact angle can be varied between 0 ° and 90 °. The relation between reduction of weight and raw density is seen as indicator for the abrasion.

Thermal shock resistance
TWB Prüfung einer Beschichtung mittels Flamme: a) Aufheizen, b) Abschrecken c) Schicht ohne Schädigung, d) Rissbildung, e) Abplatzung
TWB testing of a coating by flame: a) heating, b) quenching, c) layer without damage, d) cracking, e) flaking

If components are influenced by sudden thermal shocks during their use, the thermal shock resistance (TSR) is an important characteristic to be considered. The changes in temperature lead to internal stresses which cause cracks in the material. The determination of the TSR is carried out by defined heating and splat cooling of the samples. For the heating process the samples are placed in a furnace or heated with a gas flame. Heating the sample in the furnace leads to a homogeneous heating while heating with a gas flame causes a warming of the surface. According to DIN 51068-1 and DIN EN 993-11 the splat cooling can be operated by using water or compressed air. The norm signifies that the number of heating and cooling cycles has to be repeated until the specimen cracks. After reaching this point it is possible to investigate the residual strength of the samples. This can either be carried out in dependency of the number of repetitions or the applied temperature difference.

Temperaturempfindlichkeit dichter und poröser Keramik.
Temperature sensitivity of dense and porous ceramics
Biegefestigkeit und dyn. E-Modul in Abhängigkeit der Thermoschocks
Flexural strength and dyn. e-module as a dependence of thermal shock