High temperature oxidation protection for composites

A method for forming an oxidation protection system on a carbon-carbon composite structure, comprising:

• applying a first slurry onto a surface of the composite structure, wherein the first slurry is a sol gel comprising a metal organic salt comprising aluminum tri-sec butoxide, a first carrier fluid, ethanol, acetic acid, methanol, and a ceramic material;
• heating the composite structure to a first sol gel temperature sufficient to form a sol gel-derived base layer on the composite structure;
• forming a second slurry by combining a pre-slurry composition with a second carrier fluid, wherein the pre-slurry composition comprises a phosphate glass composition,
• wherein the phosphate glass composition comprises at least one of phosphate glass or borophosphate glass;
• applying the second slurry to the sol gel-derived base layer;
• and
• heating the composite structure to a sealing temperature sufficient to form a sealing layer on the sol gel-derived base layer.