Suitability of 'Hathi –Ki- Dhani' Bentonite as a binder for use in Foundries

Bentonite, belonging to the Montmorillonite group is used for bonding synthetic sand mixture for use in foundries. Montmorillonite is a di-silicate mineral having a three-layered structure, consisting of a gibbsite layer Al(OH)3 between two di-silicate layers (Si2O5)-2. When Al3 ions in the gibbsite layer are replaced by Mg2 and Fe2, the mineral montmorillonite (bentonite) is formed. It is known that the bonding within each of the three layer of one unit and the oxygen layer starting the adjacent unit is lacking. As a result, a plane of weakness exists at this point and the crystal is easily deformed into thin plates by cleavage along this inter-oxygen plane. Water molecules can also be adsorbed between these oxygen layers, forcing them apart and resulting in the swelling observed in bentonite. This property of swelling mainly helps in bonding synthetic silica sand mixtures.