Sol-gel synthesis of phosphate ceramic composites I

Monolithic gels of phosphate ceramics were synthesized using PO(OH)_3−x(OR)_x and alkoxides of silicon and titanium. The PO(OH)_3−x(OR)_x species were synthesized from the reaction of P₂O₅ and ethanol or n-butanol, and the products consisted of approximately equal molar amounts of mono- and dialkyl phosphate. The phosphate gels containing titanium lost less phosphorus than from the gels of silicon/phosphorus upon firing of gels in air. At phosphorus contents above 60 mole %, the gels were completely crystallized upon firing at temperatures above 700 °C, while the gels containing zinc and alkali metals remained amorphous after firing at 850 °C. Solid state nuclear magnetic resonance spectroscopy showed that all of the silicon is hexacoordinated in the phosphate gels containing silicon and titanium upon firing at temperatures above 520 °C