Setting reaction alginate impression PDF

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explanation on setting reaction of alginate impression and its equation...

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Describe the setting reaction of alginate impression materials.

Setting reaction of alginate impression materials occur by a chemical reaction, crosslinking a carbohydrate polymer. Mixing of the powder and water will form a sol which later set by a chemical reaction forming a gel. The gel formed is insoluble calcium alginate which is produced form the reaction of soluble sodium alginate and calcium sulphate. +¿ 2+¿+2 Na3 PO 4 →Ca3 (PO 4 )2+6 Na¿ ¿ 3Ca However, there is insufficient working time as the reaction occurs too fast hence a retarder such as sodium phosphate is added to delay the reaction thus provide adequate working time and setting time. The retarder works by reacting with calcium sulphate preventing reaction with sodium alginate to form gel by producing calcium phosphate. After sodium phosphate has been used up, the remaining calcium sulphate reacts with sodium alginate and gelation occurs forming insoluble calcium alginate and then sets as a gel with water....