SiO2-B2O3 xerogels: The problem of boron leaching

Borosilicate materials are of interest for many technological applications. Whereas sol-gel techniques are well suited for the preparation of these materials, the nominal concentration of boron is often not maintained, and a considerable amount of boron is lost during the preparation procedure. In this work we deal with the synthesis of borosilicate systems in order to analyse the problem of the boron loss. Different sol-gel precursors of B2O3 were explored and organically modified silicon alcoxide were tested, in addition P2O5 co-doping was proposed. IR spectroscopy, differential Scanning Calorimetry, Thermogravimetry and ICP-OES analyses were performed. Sol-gel synthesis of SiO2-B2O3 xerogels with a high boron content (> 18 wt.%) was successfully obtained by employing trimethoxyboroxine and 3-aminopropyltriethoxysilane.

► Sol–gel borosilicates are difficult to prepare without significative loss of boron.
► Many sol–gel recipes are tried and studied in order to face the above problem.
► SiO2-B2O3 xerogels with no loss of boron was obtained by an aminosilane precursor.
► A possible explanation of that result has been proposed.