CONSINTEC: Contributions to CO2 reduction in ceramic production

Rauschert has one of the broadest material portfolios in the ceramics industry. The range covers almost all areas of oxide, non-oxide and silicate ceramics [2]. The company offers both series products and customer-specific solutions - from material development, toolmaking and shaping through to precision machining [3].
In the CONSINTEC [1] funding project, Rauschert is working closely with the University of Bayreuth to characterize the debinding behaviour of ceramic components, among other things. The Chair of Ceramic Materials has high-precision measuring equipment for recording the debinding kinetics with simultaneous in-depth analysis to determine the gases released during debinding. The core of this analysis is the combination of a simultaneous thermal analyzer (STA 449 F3 Jupiter, Netzsch Gerätebau, Selb) with a coupled infrared spectrometer (Alpha II, Bruker Optics, Ettlingen) and at the same time a combination of a gas chromatograph (GC; 7890B, Agilent Technologies, USA) and mass spectrometer (MS; Q1500-GC, JEOL, Japan). This allows the debinding of various ceramic bodies to be investigated under changing gas atmospheres and heating rates, while at the same time reliably analyzing the gases released down to the trace level (ppb, parts per billion). From this, meaningful conclusions can then be drawn about the organics used, their quantity and their decomposition kinetics over the entire debinding firing, resolved in terms of time and temperature.

As an example, the following measurement curve (Figure 1) shows the debinding of a zirconium oxide molding compound and the sum signal from the GC/MS analysis for a gas sample in the main decomposition stage.

The measurement curve impressively shows the multi-stage decrease in mass of the ceramic material examined, which can be attributed to the decomposition of the various organic additives. The emission gases during debinding are highly complex due to the large number of additives added, their decomposition and interaction with each other and therefore require in-depth analysis using GC/MS. The total ion flow chromatogram for the emission gases in the main decomposition phase at around 373 °C is shown as an example. Using database analysis, a total of more than 200 individual substances could be detected in the gas, allowing conclusions to be drawn about the organic additives used.
Real debinding firings are generally characterized by slow heating rates and very long process times in order to avoid any deformation or cracking in the ceramic green bodies during the transition to brown bodies. However, standard small crucibles and small sample weights in the range of a few 10 to a few 100 milligrams are unsuitable for such measurements due to the - in absolute terms low - mass loss over a very long period of time. However, the high weighing range of current thermobalances makes it possible to obtain reproducible, reliable data even for these very long debinding fires using large sample weights and thus to demonstrate the influence of the debinding heating rate on the start and uniformity of the decomposition of the organics under realistic conditions. The debinding of a zirconia mass at different heating rates is shown below as an example.

The figure clearly shows the high influence of the debinding heating rate. Typical heating rates in thermal analysis (300 - 600 K/h) show a strongly deviating decomposition behavior of the ceramic mass compared to realistic heating rates of 60 K/h and less. A shift in the onset of decomposition up to 59 °C from 252 °C at 600 K/h to 193 °C at a heating rate of 20-50 K/h is recognizable. This corresponds to a shift of several hours in the real process. By analyzing the debinding rate (mass release rate DTG), the stability and uniformity of the debinding can be analyzed. In addition, the scaling effects can be used to map real processes in the furnace.

By moving the windows, i.e. changing the arrangement of the same individual fires, the total load of organic components for the TNV can now be optimized so that a maximum amount of organic decomposition products emitted is not exceeded at any given time. The example in Figure 5 (b) shows such a variation, whereby with the exception of one firing (marked in red), all other firings were positioned in the same furnace as in example (a), but at a different time. The start times for the program were also partially adjusted - but always within the available production window (i.e. on the same calendar days), and also ensuring that there was sufficient time for cooling as well as for loading and unloading processes.

Greater efficiency in exhaust gas aftertreatment not only contributes to a significant reduction in CO₂ emissions and other pollutants, but also offers economic benefits through lower energy consumption, reduced operating costs and an extended service life of the system components.
The prerequisite for this is forward-looking production planning that takes into account the logistical challenges - from optimum furnace utilization to coordinated control of thermal post-combustion - while meeting the highest demands on product quality and delivery reliability.
The protection of our environment and the efficient use of resources are not only a social responsibility towards present and future generations, but increasingly also a decisive competitive factor for the industry. Companies that combine technological innovation with sustainable business practices secure their own resilience and that of their customers in the long term [7].