Gypsum Morphology

At pH 5.0 Cerium tends to be precipitated with higher concentration than other rare earths. Figure (8) shows the SEM separated at pH 5.0. It was found that the gypsum morphology diminished as the pH increased and at dilute sulfate leach liquor the needle shape... 

Impression Plasters. Impression plasters are prepared by mixing with water. Types I and II plasters are weaker than dental stone (types III and IV) because of particle morphology and void content. There are two factors that contribute to the weakness of plaster compared to that of dental stone. First, the porosity of the particles makes it necessary to use more water for a mix, and second, the irregular shapes of the particles prevent them from fitting together tightly. Thus, for equally pourable consistencies, less gypsum per unit volume is present in plaster than in dental stone, and the plaster is considerably weaker. 

Dominant gangue minerals in Kuroko deposits are quartz, barite, anhydrite, gypsum, chlorite, sericite, and sericite/smectite. Morphology of quartz changes from euhedral in the centre to the irregular in the margin of the deposits (Urabe, 1978). No amorphous silica and cristobalite have been found. 

There is some retardation of cement hydration but at 28 days the products of C3S hydration are essentially the same as in an unsuperplasticized cement system. The C3A/gypsum reaction products may be changed morphologically to a cubic rather than a hexagonal form. 

Cody, R.D. Cody, A.M. (1988) Gypsum nucleation and crystal morphology in analog saline terrestrial environments. Journal of Sedimentary Petrobgy 58, 247-255. 

There are five major clues to help us identify a particle. They are morphology, refractive index, birefringence, angle of extinction, and dispersion staining. These clues will help us identify impurities in gypsum, mainly, limestone, silica, and natural anhydrite. They will also help distinguish the different phases of gypsum dihydrate, hemihydrate, alpha and beta, and anhydrite. 

In considering other factors that may influence water demand, many intrinsic stucco properties must be taken into account such as purity, particle size and morphology of the gypsum, calcination methods, and stucco surface properties. In addition, the water demand of stucco is dependent on its history such as aging time and conditions, aridization, and presence of surface active agents. 

Some reported examples of the use of PBC analysis to predict crystal morphology include hexamethylenetetramine (Hartman and Perdok, 1955), calcium sulphate (gypsum) (van Rosmalen, Marchee and Bennema, 1976), anthracene (Hartman, 1980), magnesium hydrogenphosphate (newberyite) (Boistelle and Abbona, 1981), sodium sulphite and potassium sulphate (Follner and Schwarz, 1982), succinic acid (Davey, Mullin and Whiting, 1982), sucrose (Aquilano et al, 1983). 

In the case of sulphur present as lead sulphate, the treatment with lime (about the cheapest material suitable for this purpose) forming gypsum is preferred, which subsequently is removed by filtration. TR has developed techniques whereby pure gypsum can be produced in any of its three morphologies (hydrated, hemi-hydrated and anhydrous) to suit market demands. Therefore, the obtained gypsum residue could be converted to commercial gypsum products, if commercially feasible. The real benefit in this is not having to pay for its disposal. 

Figure 3 (left) - Detailed morphology of the commercial jarofix product after >3 months of curing (polished section). 1- Ca-Al-Fe oxide, 2- Ca-Fe oxide, 3- cement reaction product, 4-gypsum, 5- Fc203, 6- reacted Na-jarosite, 7- ZnFe204. 

Figure 16 (right) - Detailed morphology of the laboratory jarofix product after >4 years of storage (polished section). 1- CaCOa, 2- (Mg,Ca)C03, 3- gypsum, 4- reacted Na-jarosite, 5-reacted cement compound, 6- ZnFc204,7- Fe203. 

In concrete mixes the microstracture of the interfacial zone differs markedly from that of the plain bulk paste (Lu et al., 19%). Here, ettringite is the main hydrate present, but its morphology varies, depending on the amormt of gypsum in the original cement and the conditions of hydration. Three-dimensional restraint of the hydrating mix may improve the interfacial microstracture the thickness of the interfacial zone decreases and the size of the formed crystalline hydration prodncts becomes smaller. 

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