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Precipitation of aluminum hydroxide from sodium aluminate, by treatment with formalin, and preparation of aluminum oxide

Hayrapetyan S. S., Mangasaryan L. G., Tovmasyan M. R., Khachatryan H. G.

Acta Chromatographica

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2006

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No. 16

192-203

EN

Aluminum oxide has been prepared by thermal dissociation of aluminum hydroxide obtained by precipitation, with formalin, from sodium aluminate with Na2O/Al2O3 molar ratio, M, between 1.5 and 2.0. The effect of aluminate molar ratio on the pore volume and specific surface area of the aluminum oxide was investigated. It was found that pore volume and specific surface area increased with decreasing Na2O/Al2O3 molar ratio. Aluminum oxide of pore volume 0.60–0.63 cm3 g-1 and specific sur-face area 300–320 m2 g-1 was obtained from sodium aluminate with M = 1.5. It was found that the concentration of the sodium aluminate mother liquor affects the yield of aluminum oxide and the pore volume but does not significantly affect the specific surface area.

2

Wide-porosity silicas for high-performance liquid chromatography

Hayrapetyan S. S., Khachatryan H. G.

Acta Chromatographica

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2005

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No. 15

162-172

EN

The possibility of using wide-porosity micro-spherical silica gels (MS), obtained by hydrothermal modification, as packing materials for high-performance liquid chromatography (HPLC), has been studied. The systems obtained were applied in both normal-phase and reversed-phase HPLC. In the first, linear dependence of retention factor (k) on specific sur-face area was observed. In the second, this dependence is too far from li-nearity and can be explained by inaccessibility of part of the MS surface to molecules of modifier.

3

Problems with the gelling of emulsified colloidal silica

Hayrapetyan S. S., Khachatryan H. G.

Acta Chromatographica

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2004

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No. 14

49-59

EN

Important aspects of the rapid gelling of the stabilized silica sols used to produce silica gel have been studied. Rapid gelling is necessary when producing micro-spherical silica gels from stabilized silica sols, because silica sol emulsions are not stable for long periods of time. The effect on rapid gel formation of potassium silicate, added to the silica sol before emulsification, has been studied and the possibility of efficient control of these processes has been investigated. It has been shown that it is possible to control the gelling of silica sol by adding potassium silicate, which not only secures rapid gelling of emulsified silica sols but also ensures introduction of active silica to the silica hydrogel, which reinfor-ces the structure of the gel obtained. The effect of exchange of intermicellar water in micro-spherical silica hydrogels, by acetic acid, acetone, and ethanol, on the sorption volu-me of micro-spherical silica gels obtained from stabilized silica sols has been investigated. The use of stabilized silica sols as initial raw material ensures constancy of specific surface area and pore volume, because these primarily depend on the properties of the colloidal particles and their size distribution. Data characterizing the pore structure of the silica gels reveal that exchange of intermicellar water by other liquids of lower surface tension affects the pore volume only.