Formation and crystallization behavior of gels in the Na2O-SiO2-TiO2-ZrO2 system

SiO2-TiO2-ZrO2 and 5Na(2)O . 95(SiO2 + TiO2 + ZrO2) gels were synthesized a nd role of Na2O in gel formation and crystallization behavior of gels were studied. From Si(OC2H5)(4), Ti(iso-OC3H7)(4), Zr(n-OC3H7)(4) and NaOCH3 sol utions in EtOH without H2O, transparent and opaque gels were obtained. Opaq ue bulk gels, rich in TiO2 or ZrO2 composition in Na2O containing SiO2-TiO2 -ZrO2 system, contain agglomerated spherical particles of diameter small < 10 mum, in contrast with opaque gels having large particles < 30 mum in alk ali-free SiO2-TiO2-ZrO2 system. Crystallization temperature (Tc) was measur ed by DTA on dried gels. Compared with the alkali-free SiO2-TiO2-ZrO2 gels, 5 mol% Na2O containing gels gave lower Tc in SiO2 rich compositions and hi gher in TiO2 rich or ZrO2 rich compositions.