Hydrogen release during the thermal decomposition of magnesium hydroxide to magnesium oxide

Martens, R.; Gentsch, H.; Freund, Friedemann

doi:10.1016/0021-9517(76)90413-9

Cited by 99 publications

(16 citation statements)

References 10 publications

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“…Although not explored by the DFT calculations, such a reaction scenario would not change the fact that different recombinations are possible between hydrogen atoms, all with different probability of occurrence and activation energy. Already Martens et al (1976) have successfully demonstrated the release of hydrogen and atomic oxygen during the dehydroxylation of brucite under controlled vacuum conditions. Therefore, similar reactions could also occur in complex phyllosilicates.…”

Section: Discussionmentioning

confidence: 99%

Dehydroxylation kinetics of lizardite

Trittschack¹,

Grobéty²

2012

ejm

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Abstract:The thermally induced dehydroxylation of lizardite and its phase transformation to forsterite were studied by hightemperature X-ray diffraction (HT-XRD), thermogravimetry (TGA) and Fourier-transformed infrared spectroscopy (FTIR). Primary sample characteristics like chemical composition and crystallographical structure were determined by combined (HR)TEM-EDX, electron-microprobe analyses (EMPA) as well as conventional X-ray diffraction (XRD). Isothermal HT-XRD and non-isothermal TGA data were treated with the classical Avrami-Erofe'ev method and more advanced isoconversional methods in order to obtain kinetic data of a multi-step decomposition reaction. A highly precise activation energy E a versus reaction progress (a) dependency based on non-isothermal TGA data of lizardite is provided and associated mechanisms are discussed. Here, the main focus is on recently published ab initio calculations from the phase transformation of other phyllosilicates. Moreover, the calculated overall apparent activation energy is compared with discrepant data from the literature and discussed. Especially, the usability of overall activation energies of multi-step decomposition reactions is critically discussed. The presented and discussed reaction steps of water formation from different hydroxyl species in lizardite can be used to improve ab initio calculations, especially the pre-selection of reacting hydroxyl species in hydrous sheet like minerals.

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Section: Discussionmentioning

confidence: 99%

Dehydroxylation kinetics of lizardite

Trittschack¹,

Grobéty²

2012

ejm

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“…The low intensity of the 3560 cm À1 band relative to the 3300 cm À1 band in Figure 9b and the pervasive evolution of H 2 measured by mass spectrometry (Martens et al 1976) suggest that the equilibrium of this redox reaction lies far to the right. We rewrite equation (A1) as…”

Section: A2 Solid Solutions With H 2 Omentioning

confidence: 95%

Solid Solution Model for Interstellar Dust Grains and Their Organics

Freund

2006

ApJ

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We present a dust grain model based on the fundamental principle of solid solutions. The model is applicable to the mineral (silicate) component of the dust in the interstellar medium (ISM ). We show that nanometer-sized mineral grains, which condense in the gas-rich outflow of late-stage stars or expanding gas shells of supernova explosions, do not consist of just high melting point oxides or silicates. Instead they form solid solutions with gas-phase components H 2 O, CO, and CO 2 that are omnipresent in environments where the grains condense. Through a series of thermodynamically well-understood solid-state processes, these solid solutions become ''parents'' of organic matter that precipitates inside the grains. Thus, the mineral dust grains and their organics become part of the same thermodynamically defined solid phase and, hence, physically inseparable. This model can account for many astronomical observations, which no prior model can adequately address, specifically: (1) Organics in the diffuse ISM are identified by a 3.4 m IR band, characteristic of aliphatic hydrocarbons composed of ÀCH 2 À and of ÀCH 3 groups. (2) The methylene-to-methyl ratio is nearly constant, implying a CH 2 :CH 3 ratio of $5:2. (3) The intensity ratio between the 9.7 and the 3.4 m band is nearly constant, implying a silicate-to-organics ratio of $10:1. (4) In dense clouds the complex 3.4 m band is replaced by a weak, featureless 3.47 m band. (5) Whereas silicate grains identified by their 9.7 m band tend to align in magnetic fields, grains with a strong 3.4 m organic signature do not tend to align.

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“…Because a peroxy anion represents an excess O atom, this effectively describes a ''water splitting'' reaction, H 2 O ϭ H 2 ϩ O. Although well documented (30,31), this redox conversion has so far not been considered in the geosciences as an entry to better understand the interactions between H 2 O and minerals.…”

Section: Discussionmentioning

confidence: 99%

Organic protomolecule assembly in igneous minerals

Freund

Staple

Scoville

2001

Proc. Natl. Acad. Sci. U.S.A.

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COH stretching bands, CH, in the infrared spectrum of single crystals of nominally high purity, of laboratory-grown MgO, and of natural upper mantle olivine, provide an ''organic'' signature that closely resembles the symmetrical and asymmetrical COH stretching modes of aliphatic OCH 2 units. The CH bands indicate that H2O and CO2, dissolved in the matrix of these minerals, converted to form H 2 and chemically reduced C, which in turn formed COH entities, probably through segregation into defects such as dislocations. Heating causes the COH bonds to pyrolyze and the CH bands to disappear, but annealing at 70°C causes them to reappear within a few days or weeks. Modeling dislocations in MgO suggests that the segregation of C can lead to C x chains, x ‫؍‬ 4, with the terminal C atoms anchored to the MgO matrix by bonding to two O ؊ . Allowing H2 to react with such Cx chains leads to [O2C(CH2)2CO2] or similar precipitates. It is suggested that such C xOHyOOz entities represent protomolecules from which derive the short-chain carboxylic and dicarboxylic and the medium-chain fatty acids that have been solvent-extracted from crushed MgO and olivine single crystals, respectively. Thus, it appears that the hard, dense matrix of igneous minerals represents a medium in which protomolecular units can be assembled. During weathering of rocks, the protomolecular units turn into complex organic molecules. These processes may have provided stereochemically constrained organics to the early Earth that were crucial to the emergence of life.

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Hydrogen release during the thermal decomposition of magnesium hydroxide to magnesium oxide

Cited by 99 publications

References 10 publications

Dehydroxylation kinetics of lizardite

Dehydroxylation kinetics of lizardite

Solid Solution Model for Interstellar Dust Grains and Their Organics

Organic protomolecule assembly in igneous minerals

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