Strengthening Large Thin Glass Shells by Overcoating with GDP

Large glass shells (≥ 1200 μm diameter) made by the traditional drop tower technique are usually thin walled (≤ 4 μm). Therefore, even the highest quality shells cannot hold more than ∼70 atmospheres (atm) of gas pressure. This report describes the strengthening of these shells by over-coating them with Glow Discharge Polymer (GDP). Glass shells overcoated with various thicknesses of GDP were 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 were made. The burst test survivors were tested against possible undetected microcracks 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 shell.