Bulk crystallisation in mixed alkali disilicate glasses doped with a nucleating agent

Kinetics of crystallisation in mixed alkali disilicate (Li 2 O.2SiO 2 -Na 2 O.2SiO 2 ) glasses doped with platinum as a nucleating agent was studied by DTA, XRD and microscopic techniques. The addition of Pt induced bulk crystallisation in the wider range of the glass system, xLi 2 O.(1-x)Na 2 O.2SiO 2 . Bulk crystallisation was observed in the range of x>0·6 without additives but x>0·4 with the addition of 50 ppm Pt. A number of crystal particles were precipitated in the interior of the glasses with Pt addition (x=0·4 to 0·6) after two stage heat treatments. The crystal particle is of needle like shape. The crystalline phase is identified as lithium metasilicate by XRD, which is a metastable phase. The Li 2 O.SiO 2 crystals grow linearly with heating time. The rate of the crystal growth of Li 2 O.SiO 2 increases steadily with increasing lithia content. The activation energy for crystal growth is also estimated. The addition of large amounts of the nucleating agent gives rise to the increase in nucleation site of Li 2 O.SiO 2 , while the growth rate is unchanged.