Assertion (A): In CO2 casting process, the mould or core attains maximum strength.
Reason (R): The optimum gassing time of CO2 through the mould or core forms Silica Gel which imparts sufficient strength to the mould or core.
Option (A)
Both A & R are true & R is the correct explanation of A
Option (B)
Both. A and R are true but R is NOT the correct explanation of A
A is true but R is false
A is false but R is true
Correct Option:
Question Solution:
CO2 gas used for mould hardening. It consists of thorough mixing of silica sand with 3.5 to 5% by weight of sodium silicate liquid base binder in a Muller. After packing CO2 is forced into the mould at a pressure of about 1.4 kg/cm2. The sodium silicate present in the mould react with CO2 and gives hard substance called the silica gel.
Na2Sio2. xH2o + CO2 ® Na2CO3 + (Sio2 x H2o)