TY - JOUR

T1 - Thermal evolution of natural layered double hydroxides

T2 - Insight from quintinite, hydrotalcite, stichtite, and iowaite as reference samples for co3-and cl-members of the hydrotalcite supergroup

AU - Zhitova, Elena S.

AU - Chris Greenwell, H.

AU - Krzhizhanovskaya, Mariya G.

AU - Apperley, David C.

AU - Pekov, Igor V.

AU - Yakovenchuk, Victor N.

N1 - Funding Information: The reported study was funded by Russian Fund for Basic Research and the Royal Society according to the research project ? 19-55-10005. The research has been carried out using facilities of XRD Research Center of Saint Petersburg State University and the Solid-State NMR service at the Department of Chemistry, Durham University. We thank the reviewers for their comments and the editor for the manuscript handling. Publisher Copyright: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/10/28

Y1 - 2020/10/28

N2 - In situ high-temperature powder X-ray diffraction experiments were undertaken for the coarse crystalline natural layered double hydroxides (LDHs) quintinite, hydrotalcite, stichtite, and iowaite in the temperature range 25–1000◦C, with thermal analyses of these minerals and their annealed forms carried out in parallel. In the temperature range from 25◦C to 170–210◦C quintinite, hydrotalcite, and stichtite (carbonate members of the LDH family) demonstrated contraction of the basal d00n-value of 0.1–0.3 Å, followed by a sharp contraction of 1.0–1.1 Å at T > 170–210◦C. The high-temperature modified states were stable up to 380–420◦C, before decomposing to an amorphous phase. Iowaite (chloride member of the family) was stable up to 320◦C and transformed to an amorphous phase at higher temperature. Iowaite experiences continuous contraction of the d00n-value of up to 0.5 Å in the temperature range 25–200◦C, reaching a plateau at a temperature range of 200–320◦C. Assessing the reversibility of thermal transformation shows complete reconstruction of the crystal structure of the hydrotalcite and iowaite heated to 300◦C. Solid-state nuclear magnetic resonance analysis shows that some Al changes coordination from 6-to 4-fold, synchronously with quintinite transformation to the amorphous phase. All phases transform to periclase and a spinel-type compound upon further heating. Thermal analysis of samples annealed at 125◦C shows that carbonate members do not have a tendency to form dehydrated phases, whereas for iowaite, a dehydrated phase having 0.9 apfu lesser water content as in the initial sample has been obtained. Thermal evolution of LDHs is found to depend on the nature of the interaction of interlayer species and water molecules to H atoms of the metal-hydroxide layer.

AB - In situ high-temperature powder X-ray diffraction experiments were undertaken for the coarse crystalline natural layered double hydroxides (LDHs) quintinite, hydrotalcite, stichtite, and iowaite in the temperature range 25–1000◦C, with thermal analyses of these minerals and their annealed forms carried out in parallel. In the temperature range from 25◦C to 170–210◦C quintinite, hydrotalcite, and stichtite (carbonate members of the LDH family) demonstrated contraction of the basal d00n-value of 0.1–0.3 Å, followed by a sharp contraction of 1.0–1.1 Å at T > 170–210◦C. The high-temperature modified states were stable up to 380–420◦C, before decomposing to an amorphous phase. Iowaite (chloride member of the family) was stable up to 320◦C and transformed to an amorphous phase at higher temperature. Iowaite experiences continuous contraction of the d00n-value of up to 0.5 Å in the temperature range 25–200◦C, reaching a plateau at a temperature range of 200–320◦C. Assessing the reversibility of thermal transformation shows complete reconstruction of the crystal structure of the hydrotalcite and iowaite heated to 300◦C. Solid-state nuclear magnetic resonance analysis shows that some Al changes coordination from 6-to 4-fold, synchronously with quintinite transformation to the amorphous phase. All phases transform to periclase and a spinel-type compound upon further heating. Thermal analysis of samples annealed at 125◦C shows that carbonate members do not have a tendency to form dehydrated phases, whereas for iowaite, a dehydrated phase having 0.9 apfu lesser water content as in the initial sample has been obtained. Thermal evolution of LDHs is found to depend on the nature of the interaction of interlayer species and water molecules to H atoms of the metal-hydroxide layer.

KW - High-temperature behavior

KW - High-temperature crystal chemistry

KW - Hydrotalcite supergroup

KW - Iowaite

KW - Layered double hydroxides

KW - LDH

KW - Powder X-ray diffraction

KW - Quintinite

KW - Stichtite

KW - Thermal decomposition

KW - Thermal degradation

KW - Thermal evolution

KW - Thermogravimetric analysis

UR - http://www.scopus.com/inward/record.url?scp=85094598601&partnerID=8YFLogxK

U2 - 10.3390/min10110961

DO - 10.3390/min10110961

M3 - Article

AN - SCOPUS:85094598601

VL - 10

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 11

M1 - 961

ER -