108 posts
Re: catalysis or sintering
Dear Davo,
What changes are brought about by " Fusion" and "Sintering" in materials' crystal structures?
I have heard that fusion entails new crystal crystal while sintering entails mixed crystal
structure. And mixed crystal structures are basically glass, is this means that sintering
gives glassy materials?
Moreover what is a basic difference between a mineraliser and flux?
Regards,
Gulam Dastgir
Know the answer to this question? Join the community and register for a free guest account to post a reply.
44 posts
Re: catalysis or sintering
Dear Gulam
In portland cement kilns takes place burning process. Sintering of material with 20-30% of flux. Flux downs the temperiture of C3S synthesis, because, as you've already known, without a flux it's very difficult to form clniker with necessary mineral composition. For example
in the system CaO-SiO2-Al2O3 flux starts to form at 1455 deg.
CaO-SiO2-Al2O3-Fe2O3 flux starts to form at 1338 deg.
It's known very well that ammount of flux depennds on quantity of Fe2O3, R2O3, MgO
The amount of flux at 1450 deg = 3xAl2O3 + 2,25xFe2O3 + R2O + MgO
So flux reduces melting point of a material, and mineralizer increase reactivity in a solid phase.
Regards. Davit Babayan
138 posts
Re: catalysis or sintering
Dastgir:
What would have been the temp. of this reaction if not substantiated by melt formation.
Mr Dastgir,
You can read everything that is known about the CaO-SiO2 system in the phase diagram.
You can find the phase diagram for example in Cement chemistry by H.F.W. Taylor , on page 30.
Reading the diagram, the c3s and c2s phase are stable above 1250°C.
However, thousands years might be needed before this equilibrium would be reached.
On the same diagram, you will see that liquid phase can appear above 2050°C if the composition is about 50/50 c3s/c2s .
For pure c2s, the liquid would appear only at 2130°C.
For increasing c3s (about 75%), the liquidus temperature could increase up to 2150°C.
For still higher c3s, the liquidus temperature would increase still further, but free lime would appear in the liquid instead of c3s. The c3s would be formed then only during the cooling. Since the cooling never follows perfectly the thermodynamic equilibrium, it is likely that more free lime would be left in the clinker.
Lal