dear raj 

many thanks

regards

raju verma

Hello Raju,

At lower concentrations <1% P2O5 causes a partial decomposition of C3S into a stabilised form of C2S containing phosphorus, which coats the surface of the C3S.

A higher concentrations P2O5 acts similarly to SO3 in that it forms solid solutions with the silicate minerals... in particular C2S, which it stabilises, inhibiting further reaction with CaO.

Both of these reactions result in an increased amount of free lime in the clinker. Also a smaller amount of C3S is produced which reduces cement strengths.  The effect on C3S content caused by P2O5 in concetrations above 1% is quite severe. C3S concentration drops by about 10% for every additional percent of P2O5 above 1%. (C2S increases by roughly the same amount.) 

However, it has been found that this effect can be controlled by increasing the Silica Ratio of  raw mixes containing up to as much as 3 or 4% P2O5.  Values of SR = 2.7 - 2.8  make the raw mix harder to burn causing the clinkerisation temperature to be increased which allows the formation and preservation of C3S in a non-equilibrium state.

Also adding a flux such as fluoride to high P2O5 raw mixes has beed shown to permit normal concentrations of C3S to form in the clinker. Fluoride is preferentially dissolved into the silicate minerals, thus preventing the effects of the phosphorus.

More information is given in these papers;-

 http://www.ceramics-silikaty.cz/2012/pdf/2012_01_76.pdf

http://hal.archives-ouvertes.fr/docs/00/42/15/77/PDF/de_Noirfontaine_et_al._JACS_2009.pdf

Regards,

Ted.

dear ted

many thanks

Dear Ted thanks for the explaination

but it's all about the clinker phase but  I really want to know impact P2O5 in cement ( strength and setting) . Because some of the plant also use the phospho gypsum which content high % of P2O5?

your comments most welcome

kind regards

raju verma