Why does gypsum expand

Habboon Muhumed. Ashwini S at Not yet working. I am still studying. Show More. Views Total views. Actions Shares. No notes for slide. Gypsum products 1. Gypsum Products Dr. Mohammed Shammas 2. Discuss the differences between dental plaster, stone, and improved stone. Explain the meaning of initial and final setting times. Give examples of how to increase and decrease the setting times of gypsum products. Discuss wet and dry strength as it relates to gypsum products. Gypsum products are used mainly for positive reproductions or replicas of oral structures.

These replicas are called casts, models or dies, and they are obtained from negative reproductions impressions. A cast is more accurate than a study model. Gypsum rock is mined, ground into a fine powder, and then processed by heating to form a variety of products. Gypsum products are used in dentistry, medicine, homes, and industry. In homes, gypsum plaster is used to make walls; in industry, it is used to make molds.

Chemically, all three are calcium sulfate hemihydrate. This process is called calcination and is shown in the following equation: ADA Specification No. Heat is liberated. Setting Time It represents the available time for manipulating the product, and it indicates partial progress of the setting reaction.

The final setting time indicates the major completion of the setting reaction. Gillmore needles are commonly used for this measurement. In other words, each designated setting time is reached when its respective needle no longer makes an indentation in the gypsum specimen. Variation in Setting Times 1. A commonly used retarder is borax A commonly used accelerator is potassium sulfate If you continue browsing the site, you agree to the use of cookies on this website.

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Unnati Gupta. Abstract Abstract Gypsum products are used extensively in dentistry. Gypsum was found in mines around the city of Paris, so it is also called plaster of Paris. This is a misnomer as gypsum is found in most countries. The mineral gypsum CaSO4. Gypsum is also an industrial by-product. For centuries gypsum has been used for construction purposes and making statues.