Phosphate-Bonded Investment
A high-strength refractory casting investment material, bonded by magnesium ammonium phosphate, used for fabricating metal-ceramic and high-gold alloy restorations requiring elevated burnout temperatures.
Full Definition
Phosphate-bonded investments consist of a refractory filler (typically cristobalite and quartz) bound by a magnesium oxide and ammonium dihydrogen phosphate reaction product. They are formulated to withstand the high burnout temperatures (up to 1000 °C) required for base-metal and some noble-metal alloy casting. Editors working on dental laboratory or prosthetic manuscripts should distinguish this material clearly from gypsum-bonded investments, which are limited to lower casting temperatures. The term is always hyphenated. Setting expansion and thermal expansion are the key dimensional properties reported. Phosphate-bonded investments are also used as refractory dies in the fabrication of pressed ceramics.
Usage
Usage note: Hyphenation is mandatory: 'phosphate-bonded investment', not 'phosphate bonded investment'. Distinguish from 'gypsum-bonded investment' in all prosthetic and laboratory contexts.
In Context
- "Base-metal alloys require a phosphate-bonded investment capable of withstanding burnout temperatures exceeding 900 °C." — Dental laboratory technology textbook
- "The manuscript incorrectly described the investment as gypsum-bonded; given the alloy's liquidus temperature, a phosphate-bonded investment would have been mandatory." — Peer-review comment