PROS 8120 Study Guide - Final Guide: Calcination, Edentulism, Gypsum
3 Jan 2020
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Changing the water/powder ratio or mixing time will affect the properties of the gel. Using warm water = increase the setting rate (set faster) Mixing time is 45 seconds to 1 minute. Set time is usually 2-3 minutes in the mouth. Impression plasters, model stones, die materials, binder for silica. Heating process performed by manufacturer to create hemihydrate powder form of product. Once treated, we have 5 classes for types of gypsum. Physical properties depend on how water is driven off in the calcination reaction. Rough rocks, rough, irregular, mixes easily, sets quickly. More crystals, increased density, smaller crystals that are more uniform. Dehydration under pressure in presence of water vapor to control rate of water loss. For the type of stone we are using**** Milling of final product for very uniform sized particle. Type 5: increased expansion by lower concentration of salts. Chemically, all gypsum products set by the same reaction:
