catalysis or sintering

Dears All,

What is the actual role of C3A and C4AF in clincker formation?

Is it work as catalyst for the formation of C3S and C2S or simply help sintering between them by bringing them close effectively by virtue of its liquidity?

In my opinion if first case is true then, if they are not present then we may have to 

increase temp. of the process to bring about the required process.

 But if the second case is true, then both C3S and C2S will be formed and will be in powder form if not aided by C3A and C4AF.

Is this true or i am mistaken. Pl help.

Kind Regards

Gulam Dastgir

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Re: catalysis or sintering

CaO and C2S are solids at the temperatures in the cement kiln, as is the C3S which is formed by their combination. If only these minerals were present then the combination temperature in the cement kiln would have to be very high. However the presence of the C4AF and C3A liquid phases lowers the combination temperature as the solid reactants (C2S and CaO) and the solid product (C3S) dissolve in and are precipitated from the liquid. This is why the combination process is called a "sintering" process. The partial liquid formation promotes the combination and formation of nthe solid phases.

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Re: catalysis or sintering

Dear Clarck,

What would have been the temp. of this reaction if not substantiated by melt formation.

Kind regards

Gulam Dastgir

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Re: catalysis or sintering

Dear Dastgir

After calculation raw mix composition,  the synthesis of C3S and C2S in lab furnace with only CaO and SiO2 (without A2O3 and Fe2O3) mentioned bellow:

Times of sintering:                                4-6  

Material retention time in max temp.:     1st time: 3-4 hour, other times: 5-7 hour  

Max. sinterig temp.                               1500 - 1550 deg

The synthesis of C2S:

Times of sintering:                                   2

Material retention time in max temp.:        3 hours

Max. sintering temp.                                1450 - 1500 deg

At first time clinker  will be cooled rapidly. In second time of sintering boron anhydrate must be added for stabilizing betta form of C2S.

Synthesis of ordinary raw mix for portland cement clinker (for comparison): 

Times of sintering:                                   1

Material retention time:

in  900 deg.:                                           30 min

in max. temp.:                                        30 - 40 min 

Max. sintering temp.:                              1450 deg.

You can see how hard to sinter Calcium Silicates without Al2O3 and Fe2O3

Regards: Davit Babayan

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