Effect of NH4H2PO4 Content on Properties of the Mullite-Based Investment Materials

Abstract

The relationships between NH4H2PO4content and properties including apparent porosity, bulk density, compressive strength, setting expansion and thermal expansion of the mullite-based investment materials have been investigated. The results show that: With increment of NH4H2PO4content, the bulk density decreases and the apparent porosity increases for the specimens. When the NH4H2PO4 content is less than 9 mass%, the compressive strength of the specimens clearly decreases with increment of NH4H2PO4content, and the compressive strength of the specimens heated at 900°C is less than that of the specimens heated at 110°C slightly. With increment of NH4H2PO4content, the setting expansion obviously increases and the thermal expansion decreases a little.