Characterization and Thermal Behaviour of Garnets from Almandine–Pyrope Series at 1200°C

Zbořil, Radek; Mashlan, M.; Machala, Lubomír; Walla, Jan; Barčová, Karla; Martinec, Petr

doi:10.1023/b:hype.0000043260.24239.48

Cited by 6 publications

(4 citation statements)

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“…2a) shows sharp endothermic peaks indicating the decomposition process of the garnet. With exception of pyrope (Prp 80 Alm 20 ), all garnets showed one endothermic peak at temperatures greater than 1000 °C but less than 1200 °C, which is similar to the decomposition temperatures found in experiments under oxidative atmosphere [13,17,18]. From these peaks, it was possible to calculate the onset temperature of thermal decomposition for each garnet (see Table 2).…”

Section: Variation Of Onset Temperature With Respect To the Fe Contensupporting

confidence: 59%

“…Garnets of pyrope-almandine solid solution heated up to 1200 °C in air decompose into spinel (Mg(Al,Fe 3+ ) 2 O 4 ), anorthite, and enstatite when they have composition close to pyrope, while cordierite, anorthite, and spinel or maghemite were detected after the decomposition of garnet of almandine-pyrope intermediate composition [17]. Thermal decomposition of ideal end-member pyrope, in air, gives corundum and enstatite as decomposition products [13], and when pyrope contains Fe 2+ in the dodecahedral sites, the decomposition products are enstatite, Fe-spinel, cristobalite, and hematite; hematite is a product of subsequent oxidation of enstatite at high temperature [18].…”

Section: Introductionmentioning

confidence: 99%

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The influence of the iron content on the reductive decomposition of A3−xFexAl2Si3O12 garnets (A = Mg, Mn; 0.47 ≤ x ≤ 2.85)

Aparicio¹,

Filip²,

Mashlan³

et al. 2014

AIP Conference Proceedings

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Abstract. Thermally-induced reductive decomposition of natural iron-bearing garnets of the almandine-pyrope and almandine-spessartine series were studied at temperatures up to 1200 °C (heating rate of 10 °C/min) under atmosphere of forming gas (10% of H 2 in N 2 ). Crystallochemical formula of the studied garnet was calculated as VIII (A 3-x Fe 2+x ) VI (Al, Fe 3+ ) 2 Si 3 O 12 , where the amount of Fe 3+ in the octahedral sites is negligible with the exception of pyrope, A = Mg, Mn, and 0.47 x 2.85. The observed decomposition temperature, determined from differential scanning calorimetry and thermogravimetry, is greater than 1000 °C in all cases and showed almost linear dependence on the iron content in the dodecahedral sites of the studied garnets, with the exception of garnet with a near-pyrope composition (Prp 80 Alm 20 ). The initial garnet samples and decomposition products were characterized in details by means of X-ray powder diffraction and 57 Fe Mössbauer spectroscopy. We found that all studied garnets have common decomposition products such as metallic iron (in general, rounded particles below 4 μm) and Fe-spinel; the other identified decomposition products depend on starting chemical composition of the garnet: Fe-cordierite, olivine (fayalite or tephroite), cristobalite, pyroxene (enstatite or pigeonite), and anorthite. Anorthite and pigeonite were only present in garnets with Ca in the dodecahedral site. All the identified phases were usually well crystallized.

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Section: Variation Of Onset Temperature With Respect To the Fe Contensupporting

confidence: 59%

Section: Introductionmentioning

confidence: 99%

The influence of the iron content on the reductive decomposition of A3−xFexAl2Si3O12 garnets (A = Mg, Mn; 0.47 ≤ x ≤ 2.85)

Aparicio¹,

Filip²,

Mashlan³

et al. 2014

AIP Conference Proceedings

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“…Thermal analysis of some members of garnets from almandine-pyrope series at 1200°C have been reported by Zboril et al 2 The magnetic properties of some natural pyrope-almandine garnets were investigated by Oliveira et al 6 Raman and infrared spectroscopic analysis of synthetic garnets have been reported by various authors. 3,[7][8][9] The influence of cationic substitution in the dodecahedral site of almandine-pyrope solid solution in the IR and Raman spectrum was studied by Tarte et al, 10 Ferrari et al 11 and Hofmeister et al 7 Mossbauer spectroscopic studies of garnets with Fe have been reported by a number of authors.…”

Section: Introductionmentioning

confidence: 98%

“…3,[7][8][9] The influence of cationic substitution in the dodecahedral site of almandine-pyrope solid solution in the IR and Raman spectrum was studied by Tarte et al, 10 Ferrari et al 11 and Hofmeister et al 7 Mossbauer spectroscopic studies of garnets with Fe have been reported by a number of authors. 2,6 Although, the geological peculiarities of garnets found in India have been extensively reported, investigations on structural and physical properties of garnets in almandine-pyrope series are limited.…”

Section: Introductionmentioning

confidence: 99%

Structural and Microstructural Correlations of Physical Properties in Natural Almandine-Pyrope Solid Solution: Al70Py29

Sibi

Subodh

2017

Journal of Elec Materi

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Thermal behavior of almandine at temperatures up to 1,200°C in hydrogen

et al. 2012

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The thermally induced reductive decomposition of a natural near end-member almandine [ VIII (Fe 2.85 Mg 0.11 Ca 0.05 Mn 0.02 ) VI (Al 1.99 ) IV (Si 2.99 )O 12 ] and possible hydrogen diffusion into its structure have been carried out at temperatures up to 1,200°C, monitored by simultaneous thermogravimetric analysis and differential scanning calorimetry (DSC), infrared and 57 Fe Mössbauer spectroscopy and X-ray powder diffraction. Below 1,000°C, evidence for hydrogen diffusion into almandine structure was not observed. At temperatures above 1,000°C, reductive decomposition sets in, as displayed by a sharp endothermic peak at 1,055°C on the DSC curve accompanied by a total mass loss of 3.51%. We observe the following decomposition mechanism: almandine ? hydrogen ? a-Fe ? cristobalite ? hercynite ? water. At higher temperatures, fayalite and sekaninaite are formed by consecutive reaction of a-Fe with cristobalite and water, and cristobalite with hercynite, respectively. The metallic a-Fe phase forms spherical and isolated particles (*1 lm).

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Characterization and Thermal Behaviour of Garnets from Almandine–Pyrope Series at 1200°C

Cited by 6 publications

References 0 publications

The influence of the iron content on the reductive decomposition of A3−xFexAl2Si3O12 garnets (A = Mg, Mn; 0.47 ≤ x ≤ 2.85)

The influence of the iron content on the reductive decomposition of A3−xFexAl2Si3O12 garnets (A = Mg, Mn; 0.47 ≤ x ≤ 2.85)

Structural and Microstructural Correlations of Physical Properties in Natural Almandine-Pyrope Solid Solution: Al70Py29

Thermal behavior of almandine at temperatures up to 1,200°C in hydrogen

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