Which substance is added to prolong the thickening of gypsum?

Prepare for the Orthodontics 5th Year SC Exam with comprehensive flashcards and multiple-choice questions. Each question offers detailed hints and explanations to ensure you're ready for test day!

Multiple Choice

Which substance is added to prolong the thickening of gypsum?

Explanation:
Prolonging thickening in gypsum is about slowing the setting reaction to keep the mix workable longer. Sodium citrate acts as a chemical retarder: it binds calcium ions released during the hydration of calcium sulfate hemihydrate, which slows the growth of the calcium sulfate dihydrate crystals. That interference delays gelation and extends the thickening (working) time of the mix. The other substances listed are not used for this purpose and can either have no reliable retarding effect or may even speed up the setting, so they don’t achieve the same extension of thickening.

Prolonging thickening in gypsum is about slowing the setting reaction to keep the mix workable longer. Sodium citrate acts as a chemical retarder: it binds calcium ions released during the hydration of calcium sulfate hemihydrate, which slows the growth of the calcium sulfate dihydrate crystals. That interference delays gelation and extends the thickening (working) time of the mix. The other substances listed are not used for this purpose and can either have no reliable retarding effect or may even speed up the setting, so they don’t achieve the same extension of thickening.

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