Dear Colleagues! Please help. How can carbonate inclusions (CaCO3) be neutralized in the ceramic mass for bricks? I develop engobe coatings for bricks. These carbonate inclusions destroy the brick even through a dense layer of engobe after firing.
During firing, CaCO3 decomposes to CaO and CO2. The later tries to find its way to the surrounding through the available paths or the newly created paths. Creations the new paths may causes damages in the brick when the released CO2 is much more than the capacity of the paths.
Reduction the size of the CaCO3 inclusions in the raw materials may help. This can be achieved by sieving and/or milling.
Imad Disher, Thank you. But this option is not suitable. I am tied to the factory ceramic mass, where the minimum size of stony particles is 1mm. Maybe there are some other ways? Not traditional ... 😊
dear O.s. Khomenko ; you have to treat the bricks below the temperature at which calcium oxide and calcium hydroxide forms( below 800C). as in the following reference;
Calcium Carbonate Inclusions In Pottery - UNL Digital Commons
https://digitalcommons.unl.edu/cgi/viewcontent.cgi?referer=https://www.google.com/&httpsredir=1&article=1432&context=tnas
Dear Khomenko... The decarboxylation of calcium carbonate is definite. Therefore, I suggest the replacement of calcium carbonate with calcium oxide (lime) to avoid any possible decomposition as unavoidable carbon dioxide penetration.... Good luck
surely I agree with prof Mahmood M. Barbooti regarding the replacement of calcium carbonate with calcium oxide to avoid decomposition
Dear Colleagues! Thank you for answering my question. However, the task is complicated as follows. 1. Below temperatures of 950 - 1100 degrees, it is impossible to burn a brick (it will not gain strength). 2. It is impossible to replace carbonate, since it is already in clay, and in large-tonnage production, clay is not enriched. Maybe there are some other versions?
Dear O.s. Khomenko ,
If we can NOT avoid using CaCO3, reduce its size, or reduce the temperature then generating enough paths in the materials seems to be an option. This can be done by:
1- Adding a pore-forming agent, like the sawdust, which is burned out, before the decomposition of the CaCO3, to form paths for CO2 escaping.
2- Increasing the volume percent of the CaCO3 in the mixture.
Belet françois Thank you. But here we are not talking about a blowing agent, but about carbonate impurities in clays - how to neutralize them.
if you have the ability to use other grain size of raw materials you could seperate the clay fraction (which maybe is enriched with clay minerals only)
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