Strengthening large thin glass shells by overcoating with GDP

Large glass shells (greater than or equal to 1200 mu m diameter) made by th e traditional drop tower technique are usually thin walled (less than or eq ual to 4 mu m). Therefore, even the highest quality shells cannot hold more than similar to 70 atmospheres (atm) of gas pressure. This report describe s the strengthening of these shells by over-coating them with Glow Discharg e Polymer (GDP). Glass shells overcoated with various thicknesses of GDP we re permeation-filled and burst tested. It was found that tens of microns of GDP overcoating significantly increased the strength of the original glass shells. In particular, composite shells able to hold 200 atm of helium wer e made. The burst test survivors were tested against possible undetected mi crocracks by confirming that the half-life for the release of the gas from filled shells was consistent with the expected half-life for an intact shel l.