29Si and 27Al NMR study of amorphous and paracrystalline opals from Australia

Brown, L.D.; Ray, Avik; Thomas, Paul

doi:10.1016/j.jnoncrysol.2003.09.027

Cited by 39 publications

(45 citation statements)

References 18 publications

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“…Infrared studies at ambient conditions indicate that water is present in various forms: free water between spheres, surface water, and silanol (Si-OH) groups on the surface of the silica spherules (Day & Jones, 2008;Bobon et al, 2011). The presence of silanol groups in silica has been firmly established by nuclear magnetic resonance spectroscopy (Brown et al, 2003). However, surface water, hydrogenbonded to the layer of silanol groups covering the silica surface, represents only a small amount of the detected water.…”

Section: Introductionmentioning

confidence: 99%

Ordering of water in opals with different microstructures

Eckert¹,

Gourdon²,

Jacob³

et al. 2015

ejm

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Opal has long fascinated scientists. It is one of the few minerals with an amorphous structure, and yet, compared to silica glass, it is highly organized on the mesoscale. By means of inelastic neutron scattering (INS), we could document that in four samples of opal at low temperature an ice-like structure of water is present, with details depending on microstructural characteristics. While FTIR spectra for all samples are nearly identical and thus not very informative, INS shows clear differences, highlighting the significance of microstructures. Neutron diffraction at 100 K on one of the opal samples provides evidence for crystalline cubic ice.

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Section: Introductionmentioning

confidence: 99%

Ordering of water in opals with different microstructures

Eckert¹,

Gourdon²,

Jacob³

et al. 2015

ejm

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“…A second possibility is the Al is occluded within the amorphous silica. The 27 Al spectra for the Al [4] phases are broadly similar to those collected for Al incorporated as defects in opal (Brown et al, 2003;Paris et al, 2007). This particular substitution could be locally charged balanced through the co-location of silanol groups on neighboring silicate tetrahedra.…”

Section: Structure Of the Solid Precipitatesmentioning

confidence: 60%

“…Allophane-like phases have also been implicated in controlling the bioavailability of Al (Doucet et al, 2001;Exley et al, 2002). Al [4] containing aluminosilicate phases have been identified as the dominant phases in hydrothermal scales (Gallup, 1997;Nishida et al, 2009) siliceous hot spring deposits (Yokoyama et al, 2004), biogenic silica (Gehlen et al, 2002), and inorganic opals (Brown et al, 2003;Paris et al, 2007). Houston et al (2008) indicated that metastable Al [4] dominant aluminosilicate phases form during uptake experiments performed at pH >5 and higher dissolved silica concentrations despite thermodynamic forces driving the formation of kaolinite.…”

Section: Introductionmentioning

confidence: 99%

“…/j.gca.2011 Solid-state nuclear magnetic resonance spectroscopy has been applied in numerous studies to provide basic characterization of the phases formed during reactions between Al and silica. Basic differences in the Al and Si coordination environments in allophane, imogolite, and other hydrous aluminosilicates can all be identified from solid-state 27 Al and 29 Si NMR techniques (Barron et al, 1982;Idlefonse et al, 1994;Gallup, 1997;Exley et al, 2002;Yokoyama et al, 2002Yokoyama et al, , 2004Brown et al, 2003;Paris et al, 2007;Nishida et al, 2009). Advanced techniques which exploit the couplings between neighboring elements can provide more detailed structural determination of these Al containing phases.…”

Section: Introductionmentioning

confidence: 99%

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The formation of metastable aluminosilicates in the Al–Si–H2O system: Results from solution chemistry and solid-state NMR spectroscopy

Mason

Maxwell

Carroll

2011

Geochimica et Cosmochimica Acta

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We present the results of a series of experiments designed to probe the interactions between Al and the amorphous silica surface as a function of thermodynamic driving forces. The results from 27 Al single pulse magic angle spinning (SP/MAS) and 27 Al{ 1 H} rotational echo double resonance (REDOR) allow us to identify the reaction products and constrain their structure. In all cases, despite low Al and Si concentrations we observe the formation of metastable aluminosilicates. Results from low temperature experiments indicate that despite thermodynamic driving forces for the formation of gibbsite we observe the precipitation of separate octahedrally coordinated Al (Al [6] ) and tetrahedrally coordinated Al (Al [4] ) silicate phases. At higher temperatures the Al [4] silicate phase dominates the speciation. Structural models derived from the NMR data are also proposed, and the results are discussed as they relate to previous work on Al/Si cycling. Published by Elsevier Ltd.

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“…13 where no correlation is observed ( Table 2). The water in opal is known to be predominantly molecular in character although a proportion of the water, 10-25 % is bound as silanol water [6,11,18,19]. The bulk of the water is lost in the range to 500°C and the hydrogen signal corresponds to this water loss.…”

Section: Resultsmentioning

confidence: 99%

Water and hydrogen release from perlites and opal

Thomas

Heide

Földvári

2014

J Therm Anal Calorim

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The dehydration of two specimens of perlite from Pálháza (Hungary) and from Borovitza (Bulgaria) along with a specimen of Australian precious opal has been investigated by temperature controlled high-vacuum degassing experiments (DEGAS). Dehydration results in the loss of water over a wide range of temperatures due to the presence of both molecular and bound (silanol, Si-OH) water. A surprising observation is that hydrogen (H 2 ) is also released. The hydrogen is observed to be released from both perlites and opal and both by diffusional processes and through the sudden explosive, bursting of inclusions which produce sharp spikes in the MS data. The origin of the hydrogen cannot be explained by a simple statistical distribution of the silanol species in the vitreous matrix; rather, it is more likely to be associated with an inversemicellar decomposition of silanol species. Alternate sources of hydrogen such as meteoric waters or specific genetic origins based on the perlite or opal location and formation are discounted as the hydrogen release is found to be independent of CO 2 and SO 2 evolution.

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29Si and 27Al NMR study of amorphous and paracrystalline opals from Australia

Cited by 39 publications

References 18 publications

Ordering of water in opals with different microstructures

Ordering of water in opals with different microstructures

The formation of metastable aluminosilicates in the Al–Si–H2O system: Results from solution chemistry and solid-state NMR spectroscopy

Water and hydrogen release from perlites and opal

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