Shaped silicon nitride bead aggregates

Silicon nitride-containing spheroidal beads 3–4 mm in diameter were made by an alginate route from Si3N4 powder in such a way that their surface contained calcium alginate. Wet beads were rendered tacky upon treatment with an ethylenediaminetetraacetic acid diammonium salt chelating solution. These tacky beads were transferred to containers of desired shape, microwave-dried, calcined, and sintered in nitrogen. The result was shaped Si3N4 bead aggregates with enough cohesive strength to permit their use as insulation board in high-temperature furnaces.