Abstract:Chlormagaluminite is the only Cl-dominated hydrotalcite-supergroup mineral species with M2+:M3+ = 2:1. The holotype sample of chlormagaluminite from the Kapaevskaya volcanic pipe (Irkutsk Oblast, Siberia, Russia) has been chemically and structurally characterized. The average chemical composition of the mineral is (electron microprobe, OH content is calculated by stoichiometry and H2O from the crystal-structure data, wt. %): MgO 33.85, FeO 1.09, Al2O3 22.07, Cl 14.72, H2Otot 30.96, Cl=O −3.39, total 99.30. The… Show more
“…In-plane distribution of water molecules and interlayer species for: (a) carbonate and (b) chloride members, in accord with an earlier study [31,32,37,38], and the connection of water molecules and interlayer species along the stacking axis for (c) carbonate and (d) chloride members.…”
Section: Figuresupporting
confidence: 89%
“…For better understanding of the reason carbonate LDH members transform to high-temperature "collapsed" modifications [26][27][28][29], whereas chloride members do not, it is necessary to consider aspects of the crystal structure. Recently natural LDH members with carbonate: quintinite [31], hydrotalcite [32] and with chloride: chlormagaluminite [37] and dritsite [38] have been subjected to single-crystal X-ray diffraction study that allowed determination of fine structural detail (a summary is given in Figure 7). For easier interpretation of the crystal structure, it is convenient to consider the 3D atom arrangement as consisting of trigonal prisms, comprising the H atoms of an upper and lower metal-hydroxide layer (in accord with the approach of Bookin and Drits [39]).…”
Section: The Influence Of Interlayer Species On High-temperature Behaviormentioning
confidence: 99%
“…However, owing to the cation avoidance rule, the Al cations in the natural quintinite sample of Mg:Al = 2, must all be in an identical, ordered coordination state with 2 Mg atoms and no Al-O-Al moieties. The ordering of M 2+ and M 3+ cations has been demonstrated (apart from NMR) by single-crystal and powder X-ray diffraction study by appearance of superstructure reflection [31,37,38] that result in the fact that unit cell parameter a = √ 3a', where a' is the distance between two cations within octahedral layer. This poses a challenge to the previous assertion that the two, separate, endothermic events indicate two different Mg or Al rich domains as, were the Al cations perfectly ordered, there should only be one type of Mg 2 Al(OH) 6 environment and, thus, only one thermally driven dehydroxylation event, not two.…”
Section: Insight From Natural Quintinite Into Ldh Structure and Thermal Decomposition Eventsmentioning
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.
“…In-plane distribution of water molecules and interlayer species for: (a) carbonate and (b) chloride members, in accord with an earlier study [31,32,37,38], and the connection of water molecules and interlayer species along the stacking axis for (c) carbonate and (d) chloride members.…”
Section: Figuresupporting
confidence: 89%
“…For better understanding of the reason carbonate LDH members transform to high-temperature "collapsed" modifications [26][27][28][29], whereas chloride members do not, it is necessary to consider aspects of the crystal structure. Recently natural LDH members with carbonate: quintinite [31], hydrotalcite [32] and with chloride: chlormagaluminite [37] and dritsite [38] have been subjected to single-crystal X-ray diffraction study that allowed determination of fine structural detail (a summary is given in Figure 7). For easier interpretation of the crystal structure, it is convenient to consider the 3D atom arrangement as consisting of trigonal prisms, comprising the H atoms of an upper and lower metal-hydroxide layer (in accord with the approach of Bookin and Drits [39]).…”
Section: The Influence Of Interlayer Species On High-temperature Behaviormentioning
confidence: 99%
“…However, owing to the cation avoidance rule, the Al cations in the natural quintinite sample of Mg:Al = 2, must all be in an identical, ordered coordination state with 2 Mg atoms and no Al-O-Al moieties. The ordering of M 2+ and M 3+ cations has been demonstrated (apart from NMR) by single-crystal and powder X-ray diffraction study by appearance of superstructure reflection [31,37,38] that result in the fact that unit cell parameter a = √ 3a', where a' is the distance between two cations within octahedral layer. This poses a challenge to the previous assertion that the two, separate, endothermic events indicate two different Mg or Al rich domains as, were the Al cations perfectly ordered, there should only be one type of Mg 2 Al(OH) 6 environment and, thus, only one thermally driven dehydroxylation event, not two.…”
Section: Insight From Natural Quintinite Into Ldh Structure and Thermal Decomposition Eventsmentioning
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.
“…Among them, layered double hydroxides (LDHs) recently attracted considerable research interest owing to their intriguing electrocatalytic activities, earth abundance, ultrastability, and low-toxic properties [11][12][13][14]. LDHs can be represented by a general formula as M 1−x 2+ M x 3+ (OH) 2 (A n− ) x/n •yH 2 O [15][16][17][18][19][20][21]. As depicted in Fig.…”
• Synthesis strategies of layered double hydroxides (LDHs) were summarized with classifications of traditional coprecipitation, homogeneous precipitation, and newly developed topochemical oxidation. • Diverse approaches of structural modulation and hybridization to enhance the electrocatalytic activity of LDHs were systematically reviewed.
“…8). The same is observed for recently described dritsite (Zhitova et al ., 2019a) and chlormagaluminite (Zhitova et al ., 2019c) that are isotypic taking into account Mg 2 Al → Al 2 Li substitution and differ from akopovaite and quintinite by the dominance of Cl – in the interlayer instead of (CO 3 ) 2– . Fig.…”
Akopovaite, ideally Li2Al4(OH)12(CO3)(H2O)3, is a new hydrotalcite-supergroup mineral from the Karasu–Karavshinskoye Sn deposit, Turkestan Range, Kyrgyzstan. It occurs as white or pale yellowish rosette-like aggregates that are composed of tiny curved plates up to 20–30 μm. Akopovaite is associated with gibbsite, quartz, albite, microcline, muscovite, montebrasite, siderite, schorl and birnessite-like Fe–Mn oxides. Akopovaite has a perfect cleavage along {001}, the mineral is transparent and very soft (VHN = 24 that corresponds to Mohs hardness of ca. 1). Dmeas = 2.12(2) g/cm3 and Dcalc = 2.106 g/cm3. The Raman spectra contain bands of carbonate groups and bands of O–H stretching vibrations. The chemical composition (wt.%, electron microprobe for Al and Fe; ICP-OES for Li; CHN method for CO2 and H2O) is Li2O 6.43, Al2O3 45.79, Fe2O3 0.27, CO2 10.09, H2O 36.1, total 98.68. The empirical formula based on (Li + Al + Fe) = 6 apfu is Li1.94(Al4.05Fe0.02)Σ4.07(OH)12(CO3)1.03(H2O)3.03. The crystal structure was refined by the Rietveld method with RB = 0.006 and Rwp = 0.014. Akopovaite is monoclinic, C2/m, a = 5.0953(6), b = 8.877(1), c = 7.806(1) Å, β = 102.572(6)°, V = 344.61(8) Å3 and Z = 1. The polytype should be denoted as 1M. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.66(100)(001), 4.397(27)(020), 3.821(45)(002,021), 2.4881(27)(200), 2.2273(16)(201) and 1.9027(18)(202). Akopovaite is the first naturally occurring hydrotalcite-supergroup carbonate species of Al and Li; its synthetic analogue is known.
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