Ignacio Medina Fernández @Ignacio-Medina-Fernandez

Hi,

I've been trying to prepare bredigite (Ca7Mg(SiO4)4) using a sol-gel process. The procedure basically consists of the following steps:

- TEOS hydrolisis with water and HNO3 (mol ratio: TEOS/H20/HNO3 -> 1/4/0.08)

- Addition of magnesium nitrate hexahydrate and calcium nitrate tetrahydrate (mol ratio: TEOS/Mg(NO3)2.6H2O/Ca(NO3)2.4H2O=4/1/7)

- Stirring at RT for 5 hours and aging at 60ºC for 1 day

- Drying for 2 days in fume hood at 120ºC

- Grinding with pestle and mortar and calcination at 1150ºC for 3 hours

The problem is that after this procedure (described here by Wu and Chang: Article Synthesis and In vitro Bioactivity of Bredigite Powders

), I don't obtain pure phase bredigite according to XRD analysis, with many peaks indicating the presence of larnite (Ca2SiO4) in considerable amounts. X'Pert Highscore Plus software was used to analyse the data. Does anyone know why this is happening and how could I solve it? I have checked my calculations for the sol-gel process several times and they appear to be correct.