Resumen

MORENO, Lisbeth; MILLAN, Arnaldo  y  CAMACHO, Nelson. Additives s efects upon the alpha- hemihydrate plaster crystalline structure during the production. Rev. Fac. Ing. UCV [online]. 2015, vol.30, n.1, pp.137-146. ISSN 0798-4065.

The α- Hemihydrate Plaster is a hydraulic binder which has a variety of applications, this material is almost exclusively used for the production of dental models for either prosthetic or orthodontic rehabilitation, and the analysis of temporomandibular joint. The setting time and the mix workability (plaster/water) are the useful properties in this kind of applications, which depends directly and largely on the crystal structure, since the order will interfere in the final product properties. In this regard, it has been demonstrated that the crystal structure of hemihydrate may vary or change depending on the type of additive used in the production process. Consequently, this paper proposes to evaluate the effect of different additives, capable of modifying the crystal structure, the shape, appearance and size of the crystals. To accomplish these characteristics, it was necessary to perform different mixtures and assemblies in presence of a saturated atmosphere under thermal treatments and controlled pressures, using different diameters of raw material (≤90 μm and 4 mm) in presence of organic or inorganic additives. The samples obtained were evaluated by XRD, SEM, OM and measure real densities. The α- Hemihydrate better crystallized with a marked hexagonal tendency and compact crystalline structure without the presence of other phases were obtained from CaCl2 and/or C6H8O7 and increased residence time between 82 and 88 ºC, produced using mixture “M5”, made of CaCl2 in contact with gypsum (Φ= 4 mm) under the thermal treatment R3 with five heating stages based on the reference thermal treatment.

Palabras clave : Plaster; Models; Odontology; Additives; Temperature; Structure; Crystals.

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