Thermal Evolution of Natural Layered Double Hydroxides: Insight from Quintinite, Hydrotalcite, Stichtite, and Iowaite as Reference Samples for CO3- and Cl-Members of the Hydrotalcite Supergroup

Abstract

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.

Preparation of Magnesium-Aluminum Hydrotalcite by Mechanochemical Method and Its Application as Heat Stabilizer in poly(vinyl chloride)

“…The second stage (~28%) is between 235 °C and 450 °C, mainly due to the decompose of hydroxyl in the layer and carbonate ion between the layers [ 29 ]. It can be expressed by the Equation (2).…”

“…The second and third peaks at 334 • C and 399 • C corresponds to the dehydroxylation of aluminum hydroxide and magnesium hydroxide, respectively [22]. The second stage (28%) is between 235°C and 450°C, mainly due to the decompose of hydroxyl in the layer and carbonate ion between the layers [29]. It can be expressed by the Equation (2).…”

ELUCIDACIÓN DE LA FÓRMULA ESTEQUIOMÉTRICA DE NANOHIDROTALCITAS DE Mg Y Ni SINTETIZADAS POR EL MÉTODO DE COPRECIPITACIÓN

“…Los LDH poseen una composición química general [M 2+ 1-x •M 3+ x •(OH) 2 ] (A n-) x/n .y•H 2 O, la cual se obtiene cuando parte del metal divalente, M 2+ , en el M(OH) 2 se reemplaza parcialmente con un trivalente, M 3+ , de radio iónico similar, donde "x" generalmente varía de 0,20 < x < 0,33 (Zhitova et al, 2020;Mishra et al, 2018). Se han descrito otras formulaciones, como las fases ricas en aluminio (Britto, & Kamath, 2014;Hawthorne & Cooper, 2013), donde los sitios octaédricos vacíos en el Al(OH) 3 (gibbsita, bayerita) están ocupados por cationes de Li + u otros cationes metálicos divalentes.…”

Synthesis and Thermal Degradation of MAl4(OH)12SO4·3H2O with M = Co2+, Ni2+, Cu2+, and Zn2+

“…200 °C followed by dehydroxylation of the hydroxide layer and removal of interlayer anions between 200 and 500 °C. 1,12,30,34,40 This yields an amorphous phase, 1,12,30,34,40 often embedded with crystalline metal oxide (MO) particles as observed for MgAl−CO 3 -and ZnAl−CO 3 -LDH. 12,30,34 Moreover, the amorphous phase contains both tetrahedral and octahedral Al based on solid-state 27 Al nuclear magnetic resonance (NMR) spectroscopy.…”

“…Many studies have investigated the thermal degradation of hydrotalcite-type LDH, 1,10−15,28−40 especially MgAl−CO 3 -a n d Z n A l − C O 3 -L D H w i t h v a r i o u s M / A l r atios. 10,12,[28][29][30][31][32]37,38,40 Generally, hydrotalcite M 1−x Al x -LDH degradation proceeds by the loss of surface and interlayer water at ca. 200 °C followed by dehydroxylation of the hydroxide layer and removal of interlayer anions between 200 and 500 °C.…”