Morphology of silica aerogels obtained from the process catalyzed by NH4F and NH4OH

Julita Mrowiec-Białoń; Lucjan Paja̧k; Andrzej B. Jarzȩbski; Andrzej I. Lachowski; Janusz J. Malinowski

doi:10.1021/la9703454

Morphology of silica aerogels obtained from the process catalyzed by NH₄F and NH₄OH

Julita Mrowiec-Białoń
, Lucjan Paja̧k
, Andrzej B. Jarzȩbski
, Andrzej I. Lachowski
, Janusz J. Malinowski

Department of Chemical Engineering and Process Design (RCH/RCH3)

44-100 Baltycka 5
University of Silesia in Katowice

Research output: Contribution to journal › Article › peer-review

33 Citations (Scopus)

Abstract

Twelve samples of silica aerogels were synthesized using different concentrations of catalysts (NU₄F, NH₄OH), and their morphology was investigated by means of small-angle X-ray scattering (SAXS), N₂ adsorption, and transmission electron microscopy. Both SAXS and the nitrogen adsorption method consistently show a different influence of the catalysts; fluoride anions promote formation of a tenuous branched-polymeric structure, with mass fractal dimension D_m @#2242; 2.3-2.5, while addition of hydroxyl ions results in a sparser structure (D_m @#2242; 2.1-2.2) self-similar over a narrower range. The morphology of aerogels obtained from the process catalyzed by fluoride hydroxide resembles that of aerogels produced by the two-step method. This may suggest similar mechanisms of gel formation in both processes, and, consequently, a dramatic acceleration of the hydrolysis reaction caused by NH₄F.

Original language	English
Pages (from-to)	6310-6314
Number of pages	5
Journal	Langmuir
Volume	13
Issue number	23
DOIs	https://doi.org/10.1021/la9703454
Publication status	Published - 12 Nov 1997

ASJC Scopus subject areas

General Materials Science
Condensed Matter Physics
Surfaces and Interfaces
Spectroscopy
Electrochemistry

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title = "Morphology of silica aerogels obtained from the process catalyzed by NH4F and NH4OH",

abstract = "Twelve samples of silica aerogels were synthesized using different concentrations of catalysts (NU4F, NH4OH), and their morphology was investigated by means of small-angle X-ray scattering (SAXS), N2 adsorption, and transmission electron microscopy. Both SAXS and the nitrogen adsorption method consistently show a different influence of the catalysts; fluoride anions promote formation of a tenuous branched-polymeric structure, with mass fractal dimension Dm @\#2242; 2.3-2.5, while addition of hydroxyl ions results in a sparser structure (Dm @\#2242; 2.1-2.2) self-similar over a narrower range. The morphology of aerogels obtained from the process catalyzed by fluoride hydroxide resembles that of aerogels produced by the two-step method. This may suggest similar mechanisms of gel formation in both processes, and, consequently, a dramatic acceleration of the hydrolysis reaction caused by NH4F.",

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doi = "10.1021/la9703454",

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T1 - Morphology of silica aerogels obtained from the process catalyzed by NH4F and NH4OH

AU - Mrowiec-Białoń, Julita

AU - Paja̧k, Lucjan

AU - Jarzȩbski, Andrzej B.

AU - Lachowski, Andrzej I.

AU - Malinowski, Janusz J.

PY - 1997/11/12

Y1 - 1997/11/12

N2 - Twelve samples of silica aerogels were synthesized using different concentrations of catalysts (NU4F, NH4OH), and their morphology was investigated by means of small-angle X-ray scattering (SAXS), N2 adsorption, and transmission electron microscopy. Both SAXS and the nitrogen adsorption method consistently show a different influence of the catalysts; fluoride anions promote formation of a tenuous branched-polymeric structure, with mass fractal dimension Dm @#2242; 2.3-2.5, while addition of hydroxyl ions results in a sparser structure (Dm @#2242; 2.1-2.2) self-similar over a narrower range. The morphology of aerogels obtained from the process catalyzed by fluoride hydroxide resembles that of aerogels produced by the two-step method. This may suggest similar mechanisms of gel formation in both processes, and, consequently, a dramatic acceleration of the hydrolysis reaction caused by NH4F.

AB - Twelve samples of silica aerogels were synthesized using different concentrations of catalysts (NU4F, NH4OH), and their morphology was investigated by means of small-angle X-ray scattering (SAXS), N2 adsorption, and transmission electron microscopy. Both SAXS and the nitrogen adsorption method consistently show a different influence of the catalysts; fluoride anions promote formation of a tenuous branched-polymeric structure, with mass fractal dimension Dm @#2242; 2.3-2.5, while addition of hydroxyl ions results in a sparser structure (Dm @#2242; 2.1-2.2) self-similar over a narrower range. The morphology of aerogels obtained from the process catalyzed by fluoride hydroxide resembles that of aerogels produced by the two-step method. This may suggest similar mechanisms of gel formation in both processes, and, consequently, a dramatic acceleration of the hydrolysis reaction caused by NH4F.

UR - https://www.scopus.com/pages/publications/0031268590

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DO - 10.1021/la9703454

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JO - Langmuir

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IS - 23

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Morphology of silica aerogels obtained from the process catalyzed by NH₄F and NH₄OH

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