Development of mullite substrates and containers. silicon sheet growth development for the Large Area Silicon Sheet Task of the Low-Cost Silicon Solar Array Project. Quarterly report No. 2

Abstract

A study to develop, evaluate, and fabricate mullite for use in molten silicon containers and silicon sheet substrates for the Low-Cost Silicon Solar Array Project is described. Compositional variations in Mullite formulations have been found to lower the thermal expansion of Mullite. Increased glass phase has been found to lower thermal expansion of fired Mullite bodies. Attempts to lower the thermal expansion to that of Silicon are underway. Sessile drop experiments on a series of composition and firing variations of Mullite produced a drastic change in some of the materials after a 10 hour exposure time. At 5 and 20 minutes nothing unusual was noted. Mullite substrates 100 cm x 10 cm x 0.1 cm were fabricated and fired successfully. Slots and holes have been fabricated in smaller 3.75 x 5.0 cm substrates. Crucibles from the standard Mullite formulation have been fabricated both dense and porous. Cost projections have been made for large quantities of substrates.