The precipitation of calcium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

Calcium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate-excess hydroxide solutions at ambient temperature (at C_Al = 0.1 to 0.3 M and at XS OH/Al = 0 to above 8). The precipitations were monitored by potentiometric (pH) measurements. Precipitate morphologies were examined by optical microscopy and precipitate compositions were determine by chemical analysis, infra-red spectrophotometry and thermal analysis. Generally at OH/Al ratios of 4 to 4.5 (XS OH/Al = 1 to 1.5), the compound 2 CaO · · Al₂O₃ · 8 H₂O (C₂AH₈) was precipitated with some aluminium hydroxide; then at OH/Al ratios of 5 to above 11 (XS OH/Al = 2 to above 8), the compound 2 CaO · Al₂O₃ · 8 H₂O was precipitated with increasing amounts of the compound 4 CaO · Al₂O₃ · 13 H₂O (C₄AH₁₃).     

The precipitation of magnesium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

Magnesium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate-hydroxide solutions at ambient temperature, at C_Al = 0.1 M, OH/Al ratios = 4–9 and XS OH/Al ratios = 1–6. The precipitations were monitored by potentiometric (pH) measurements while the final precipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis. At solution OH/Al ratio = 4, the main precipitate phase at 20°C was Mg(H₂O)_n[Al(OH)₄]₂ admixed with some Al(OH)₃; at solution OH/Al ratio = 5, the main phase was Mg₂(H₂O)₄[Al₂(OH)₁₀]; at solution OH/Al ratio = 7, the main phase was Mg₄(H₂O)_n(OH)₄[Al₂(OH)₁₀] while at solution OH/Al ratio = 9, the main phase was Mg₆(H₂O)_n(OH)₈[Al₂(OH)₁₀] admixed with some Mg(OH)₂. These hydrates were dehydrated at 60–100°C probably to the compounds Mg₂[Al₂O₃(OH)₄], Mg₄(OH)₄[Al₂O₃(OH)₄] and Mg₆(OH)₈[Al₂O₃(OH)₄], respectively.     

The coprecipitation of calcium aluminium hydroxide (calcium hydroxoaluminate hydrate) powders from aqueous solution with sodium hydroxide: Precipitate compositions and percipitation mechanisms

Calcium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total C_M = 0.1 M and Ca/Al₂ ratios from 1 to 4 — with sodium hydroxide solution at ambient temperature. The coprecipitations were monitored by potentiometric (pH) titration and the final coprecipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis Generally, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then redissolved on further addition of sodium hydroxide to form hydroxoaluminate anion and polyanion and calcium aluminium hydroxide coprecipitates were formed continuously at pHs from about 9 to above 12. Their compositions were similar to the calcium hydroxoaluminate hydrates formed by direct precipitation from high pH sodium hydroxoaluminate solutions. At Ca/Al₂ ratio = 1, the main phase was probably Ca₂(H₂O)_h[Al₂(OH)₄]₂ with some Al(OH)₃; At Ca/Al₂ ratio = 2, the main phase was probably Ca₂(H₂O)_h[Al₂(OH)₁₀] dehydrating to Ca₂[Al₂O(OH)₈]; At Ca/Al₂ ratios = 3–4, the main phase was Ca₂(H₂O)_h[Al₂(OH)₁₀] with increasing amounts of Ca₄(H₂O)_h(OH)₄[Al₂(OH)₁₀] and 5–10 percent adsorbed or post-precipitated Ca(OH)₂.     

The coprecipitation of magnesium hydroxoaluminate hydrates from aqueous solution with ammonium hydroxide: Precipitate compositions and coprecipitation mechanisms

Magnesium hydroxoaluminate hydrates were coprecipitated from different mixed metal cation solutions at Mg/Al₂ ratios from 1 to 4 by ammonium hydroxide. The coprecipitations were monitored by potentiometric titration and the final precipitate compositions were examined by chemical analysis, X-ray diffraction, infra-red spectrophotometry and thermal analysis. The process of coprecipitation was similar to that for coprecipitation with sodium hydroxide but large excess of ammonium hydroxide was required for complete reaction at pHs from about 8 to 10.

• At Mg/Al₂ = 1, the main phase was probably Mg(H₂O)_h [Al(OH)₄]₂;
• at Mg/Al₂ = 2, the main phase was probably Mg₂(H₂O)_h [Al₂(OH)₁₀];
• at Mg/Al₂ = 4, the main phase was probably (MgOH₄) (H₂O)^h [Al₂(OH)₁₀].

     

The Coprecipitation of Zinc Aluminium Hydroxide Powders from Aqueous Solution with Sodium Hydroxide: Precipitate Compositions and Coprecipitation Mechanisms

Zine aluminium hydroxides were coprecipitated from different mixed metal cation solutions, at C_{M tot} = 0.1 M and at Zn/Al₂ ratios from 1 to 4, with sodium hydroxide solution. The coprecipitations were monitored by potentiometrie (pH) titration and the final coprecipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis. Generally, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then partially redissolved on further addition of sodium hydroxide (to form hydroxoaluminate anion) and zinc aluminium hydroxide coprecipitates were formed continuously at pHs from 5.5–6 to above 9. Their compositions were similar to the magnesium hydroxoaluminate coprecipitated from magnesium aluminium solutions. At Zn/Al₂ ratio = 1, the main phase was probably Zn(H₂O)_n [Al(OH)₄]₂; at Zn/Al₂ ratio = 2, the main phase was probably Zn₂(H₂O)_n [Al₂(OH)₁₀], whereas at Zn/Al₂ ratio = 4, the main phase was probably Zn(H₂O)_n(OH)₄[Al₂(OH)₁₀].     

The precipitation of alkaline-earth metal polymetaphosphate hydrate powders from aqueous solution. Nucleation and crystal growth processes,final precipitate compositions and crystal sizes

The precipitation of barium, strontium, calcium and magnesium polymetaphosphate hydrates was studied from aqueous solutions of initial metal salt concentrations from 0.001 to 3 M at 20 °C; equivalent sodium polymetaphosphate solutions were added to the alkaline-earth metal chloride solutions. Precipitate compositions were determined by chemical analysis, paper chromatography, potentiometric analysis, thermogravimetric and differential thermal analysis and infra-red spectrophotometry; final crystallite morphologies and sizes were studied by scanning electron microscopy and X-ray powder diffraction. Nucleation rates and nucleus numbers (at the end of the induction periods) were very high; crystal numbers varied from 10¹⁴ to 10¹⁵ at the critical concentrations to above 10¹⁷ per 1. solution. Crystal growth rates were also very high and varied as the fourth power of the initial metal salt concentration. High molecular-weight metal polymetaphosphate hydrates were precipitated from the more dilute solutions (0.001 to 0.025 M) while increasing amounts of the more soluble intermediate and low molecular-weight products were precipitated from the more concentrated solutions. Washing with cold water removed the tri- and tetralinear and cyclic phosphate products. The magnesium salts were not precipitated even from 3 M aqueous solutions. The precipitates from aqueous (NaPO₃(I))_n (n = 12) solutions had the compositions (BaP₂O₆ · 2.5 H₂O)₆, (SrP₂O₆ · 3 H₂O)_n and (CaP₂O₆ · 4 H₂O)_n while the magnesium salt precipitate from 20 percent aqueous acetone solution had the composition (MgP₂O₆ · 4 H₂O)_n, the precipitate n values varied from 19 to 13. The precipitates from aqueous (NaPO₃(II))_n (n = 20) solutions contained 0.5n to n additional adsorbed water molecules; these precipitate n values varied in turn from 40 to 26. The final precipitate powders consisted of ‘spherules’ of highly microcrystalline or amorphous polymer glass; the spherule diameters were about 0.2 μm at the critical concentrations and decreased to below 0.05 μm with increasing solution concentrations.     

The precipitation of sparingly-soluble alkaline-earth metal phosphates in gelatine gels by diffusion of anion (i). the precipitation of calcium hydrogen phosphate dihydrate and basic calcium phosphates

The precipitation of different calcium phosphates in gelatine gels was studied by diffusion of disodium hydrogen phosphate solutions into ten percent gels containing calcium cation at liquid gel pHs from 6 to 11. At pHs 6.0 to 7.5, calcium hydrogen phosphate dihydrate (CaHPO₄ · 2 H₂O) was deposited as a continuous precipitate and then as rings of precipitate (the Liesegang phenomenon): their spacing coefficients varied with the reciprocal initial anion concentrations according to the Packter-Matalon relation. At liquid gel pHs 8.0, 8.5, tretacalcium phosphate (Ca₄H(PO₄)₃) was deposited as a continuous precipitate. At liquid gel pHs from 8.5 to 11, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, Ca/P ratios = 1.50 to 1.67) was deposited as a continuous precipitate. The mechanisms of precipitation of the different calcium phosphates (in gelatine gels) is briefly discussed.     

The coprecipitation of zinc aluminium hydroxides (refractory-, absorbent-, and catalyst precursors) from aqueous solution with ammonium hydroxide: Precipitate compositions and coprecipitation mechanisms

Zinc aluminium hydroxide hydrates were coprecipitated from different mixed cation solutions at Zn/Al₂ ratios from 1/2 to 4/1. The coprecipitations were monitored by potentiometric titrations and the final coprecipitate compositions were examined by chemical analysis and atomic absorption spectrophotometry, X-ray diffraction and preliminary thermal analysis. The product from Zn/Al₂ = 1/2 solution was amorphous: at Zn/Al₂ = 1/1.5, the main phase (after drying at 95 °C) was a zinc hydroxoaluminate Zn[Al(OH)₄]₂ together with some gibbsite: at Zn/Al₂ = 1, the main phase was probably a solid solution (of Zn[Al(OH)₄]₂ with Zn₂[Al₂(OH)₁₀]) together with Zn₂[Al₂(OH)₁₀]: at Zn/Al₂ = 2, the main phase was a mixture of Zn₂[Al₂(OH)₁₀] with (ZnOH)₄ [Al₂(OH)₁₀] and some gibbsite: at Zn/Al₂ = 4, the main phase was (ZnOH)₄ [Al₂(OH)₁₀] with some zinc hydroxide.     

Growth of single crystals of NaH2PO4 (NaDP), NaH2PO4 · H2O (NaDP · H2O), and NaH2PO4 · 2H2O (NaDP · 2H2O) sodium dihydrogenphosphate based on the analysis of the Na2O-P2O5-H2O phase diagram

The crystallization conditions for the NaH₂PO₄, NaH₂PO₄ · H₂O, and NaH₂PO₄ · 2H₂O solid phases have been established from the analysis of the phase diagram of solubility of the ternary Na₂O-P₂O₅-H₂O system in the temperature range from 0 to 100°C. Based on these data, the methods for growing sodium dihydrogenphosphate single crystals of the above compositions are developed. The initial components for preparing mother solutions were H₃PO₄ and NaOH solutions taken in certain weight ratios. For the first time, NaDP, NaDP · H₂O, and NaDP · 2H₂O single crystals were grown on a seed by the method of temperature decrease. The habits of the NaDP and NaDP · H₂O single crystals are determined. __________ Translated from Kristallografiya, Vol. 47, No. 5, 2002, pp. 937–944. Original Russian Text Copyright ? 2002 by Soboleva, Voloshin.     

Structures and properties of layered barium borates Ba0.975[B6O9(OH)(O0.975Br0.025) · B2O(OH)3], Ba2[B5O8(OH)2](OH), Na2Ba2[B20O34(OH)4], and Ba5[B20O33(OH)4]H2O

A new hexaborate, Ba_0.975[B₆O₉(OH)(O_0.975Br_0.025) · B₂O(OH)₃], was synthesized under hydrothermal conditions. This compound is structurally similar to tunnelite and the synthetic borates Pb[B₆O₁₀(OH) · B₂O(OH)₃], Pr[B₆O₁₀(OH) · B₂O(OH)₄], and Nd[B₆O₁₀ · B₃O₃(OH)₄] · H₂O studied earlier. In the new hexaborate and the refined pentaborate Ba₂[B₅O₈(OH)₂]OH, in which the polyanions adopt an orientation in layers unusual for pentaborates, thermal vibrations of the terminal groups were revealed. This fact reflects the real crystal structure. The nonlinear optical properties of the crystals of the polar pentaborate Na₄Ba₄[B₂₀O₃₄(OH)₄] were determined. The crystal structure of the related pentaborate Ba₅[B₂₀O₃₃(OH)₄]H₂O was considered. The factors most likely responsible for the difference in the second-harmonic generation signal for this pair were revealed.     

A new nonlinear optical borate, Na0.5Pb2[B5O9](OH)1.5 · 0.5H2O, from the orthorhombic hilgardite family

A new polar representative of the hilgardite structural family, Na_0.5Pb₂[B₅O₉](OH)_1.5 · 0.5H₂O (space group Pnn2), is synthesized under hydrothermal conditions. The crystal structure of the compound synthesized is similar to the structure of the previously studied polar compound Na_0.5Pb₂[B₅O₉]Cl(OH)_0.5 and is intermediate between the latter compound and the centrosymmetric hydrate Pb₂[B₅O₉](OH) · 0.5H₂O. The additional peak revealed in the electron density in the vicinity of the Pb(1) atom is attributed to the stereochemically active lone electron pair of this atom. The lone electron pair is oriented toward the two most distant oxygen atoms involved in the Pb(1) coordination environment, namely, O(7) and O(2), which are located in a boron-oxygen framework layer in the ac plane, not toward the (00_z) channel occupied by water molecules. The nonequivalence in the stereochemical activity of two lead atoms [Pb(1) > Pb(2)] is similar to that observed in the nonlinear optical borate Pb₂[B₄O₅(OH)₄](OH)₂ · H₂O related to BiB₃O₆.     

The coprecipitation of magnesium hydroxide aluminium hydroxide powders from aqueous solution with sodium hydroxide: Precipitate compositions and coprecipitation mechanisms

Magnesium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total C_M = 0.1 M and Mg/Al₂ ratios from 1 to 6 — with sodium hydroxide solution at ambient temperature, with different pre-ageing conditions for the aluminium hydroxide pre-precipitate. The coprecipitations were monitored by potentiometric (pH) titration and the final precipitate compositions were examined by chemical analysis, infrared spectrophotometry and thermal analysis. Magnesium hydroxide was coprecipitated onto completely recrystallised aluminium hydroxide as a simple mixture. Generally, with no to three days pre-ageing, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then partially redissolved on further addition of sodium hydroxide (to form hydroxoaluminate anion) and magnesium aluminium hydroxide coprecipitates were formed continuously at pHs from 8.0–8.7 to 12.0–12.5. Their compositions were similar to the magnesium hydroxoaluminate hydrates formed by direct precipitation from high pH sodium hydroxoaluminate solutions.      

Application of D‐optimal experimental design in nano‐sized ZSM‐5 synthesis for obtaining higher crystallinity

D‐optimal experimental design with three levels of SiO₂/Al₂O₃, template/SiO₂, H₂O/SiO₂, SiO₂/Na₂O and TPABr/TPAOH ratio parameters was used to optimize the experimental parameters by the analysis of variance (ANOVA). The effects of above mentioned ratios in the initial synthetic mixture on the crystallinity of the ZSM‐5 zeolite were studied. The synthesized samples were characterized by XRD, FE‐SEM, and TEM analysis. Fischer test results showed that SiO₂/Al₂O₃ and H₂O/SiO₂ molar ratios are the most and least effective parameters, respectively, in the range studied. The most important two‐way interaction variable was that of template/SiO₂ and Na₂O/SiO₂ molar ratios. The optimum composition of the gel compound to achieve relative maximum crystallinity is SiO₂/Al₂O₃ = 99.96, template/SiO₂ = 0.16, H₂O/SiO₂ = 34.68, Na₂O/SiO₂ = 0.02 and TPABr/TPAOH = 1.44.     

Thermal expansion of glass–ceramics in the system BaO/Al2O3/B2O3

Glasses in the system BaO/Al₂O₃/B₂O₃ with and without the addition of platinum were melted. In one sample series, the BaO-concentration was varied while the ratio [Al₂O₃]/[B₂O₃] was kept constant. In another sample series, the [BaO]/[Al₂O₃]-ratio (= 0.9) was kept constant and the B₂O₃ concentration was varied. The samples were thermally treated at 720 °C for 24 h and subsequently at 780 °C for 4 h. In most thermally treated samples, the crystalline phase BaO · Al₂O₃ · B₂O₃ occurred. At some compositions, the platinum-doped samples showed larger concentrations of the crystalline phases. The most remarkable property of the obtained glass–ceramics is their zero or negative thermal expansion coefficient. Here, notable differences were observed: samples with fine grained microstructures showed thermal expansion coefficients approximately zero up to temperatures of around 80 °C. By contrast, samples with coarser microstructures and large spheroidal crystals exhibit negative expansion coefficients up to temperatures of around 280–375 °C. The thermal expansions of these samples were close to those of the mean thermal expansion of the unit cell of the BaO · Al₂O₃ · B₂O₃ phase. The thermal expansion of the fine grained samples was approximately equal to that of the crystallographic a-axis of the BaO · Al₂O₃ · B₂O₃ phase.     

Crystallization of Calcium and Magnesium Phosphates from Solutions of Medium and Low Concentrations

Calcium phosphates are precipitated at 25 °C from solutions of medium (Ca = P = 50 mM) and low (Ca = P = 10 mM) concentrations in the presence of magnesium. Experiments are also performed with solutions in which Ca + Mg = P = 50 mM and Ca + Mg = P = 10 mM. An amorphous calcium phosphate, Ca₃ (PO₄)₂ · nH₂O, and brushite, CaHPO₄ · 2 H₂O, are the phases first nucleated. The phases occurring one year later are brushite in the more concentrated solutions, hydroxyapatite (Ca₅OH(PO₄)₃) and whitlockite (Ca₉MgH(PO₄)₇) in the others. Octacalciumphosphate, Ca₈H₂ (PO₄)₆ · 5H₂O, occurs as transitory phase. The effects of concentration, pH, supersaturation and magnesium on the precipitation and evolution of calcium phosphates, and the conditions for phase stability are discussed.     

Water-soluble amorphous alumina-based ceramic precursors and alumosols: Structural and chemical characterization

We examined the solid-state water-soluble amorphous precursors that are formed by partial thermal decomposition of Al(NO₃)₃·9H₂O (aluminum nitrate nonahydrate: ANN) using Raman and FTIR and solid-state magic-angle spinning NMR spectroscopy. We also studied the species formed in the aqueous alumosols formed by dissolution of the pre-ceramic precursors using ²⁷Al NMR spectroscopy. Species identified in the alumosols included the Al³⁺(H₂O)₆ monomer, the [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺(Al₁₃) Keggin ion, and the Al₃₀ polycation, [Al₃₀O₈(OH)₅₆(H₂O)₂₄]¹⁸⁺, as well as various other oligomers or nanoparticles containing IV-, V- and VI-coordinated Al³⁺ ions.     

Crystallization of 2(Ca,Sr,Ba)O-TiO2-2SiO2 composition glasses

Crystallization was examined for glasses having chemical composition of 2(Ca,Sr,Ba)O-TiO₂-2SiO₂ in which the CaO/SrO/BaO molar ratio varied. Powdered glass samples were pelleted into disks and sintered at 950 °C for 2 h. The major phase precipitated in the sintered samples was (Ca,Sr,Ba)₂TiSi₂O₈ and minor phase of perovskite such as CaTiO₃ or SrTiO₃ increased with CaO content in the samples containing more than 40 mol% of CaO in total CaO+SrO+BaO. Three regions having different slopes were found in linear relationships between SrO mol% and exothermal peak temperature on DSC curves or d[0 0 2] values determined by powder XRD method. These facts suggested that the major phase precipitated in each region was a solid solution containing a different amount of CaO, SrO, BaO and that these compositions varied depending on SrO content in the sample. The micro-crystalline structure, which could be useful in fabricating a dielectric dense body, was observed for samples containing 30-70 mol% of SrO.     

A new modification of Ba[B5O8(OH)] · H2O, the refined structure of Ba2[B5O9]Cl · 0.5H2O, and the role of the pentaborate structural units in the formation of the quadratic optical nonlinearity

The structure of a new modification of the barium pentaborate β-Ba[B₅O₈(OH)] · H₂O synthesized under hydrothermal conditions is investigated. This structure differs from the previously studied structure of the α-Ba[B₅O₈(OH)] · H₂O compound by a shorter interlayer spacing and a higher degree of filling of the intersheet space with water molecules and barium atoms (the space group P is retained). The structure of the Ba₂[B₅O₉] Cl · 0.5H₂O pentaborate from the family of orthorhombic hilgardites (space group Pnn2) is refined, and the property of this crystal to generate the second optical harmonic is revealed. It is found that the previously studied pentaborate Ba₅[B₂₀O₃₃(OH)₄]H₂O exhibits a nonlinear optical activity. The relationship between the structure and properties of hydrous and anhydrous pentaborates is discussed. Original Russian Text ? E.L. Belokoneva, S.Yu. Stefanovich, M.A. Erilov, O.V. Dimitrova, N.N. Mochenova, 2008, published in Kristallografiya, 2008, Vol. 53, No. 2, pp. 255–263.     

The Precipitation of Alkaline-Earth Metal Polyacrylate Hydrate Powders from Aqueous Solution: Ionic Equilibria,Precipitate Compositions and Morphologies

The precipitation of barium, strontium, calcium and magnexium polyacryate hydrates was studied from equivalent aqueous solutions of initial concentrations 0.03 M to 0.30 M at ambient temperature: sodium polyacrylate (m. wt = 30,000 to 300,000) was added to metal chloride solution. The final yields of precipitate increased with decreasing solubility and/or peptisation (Ba > Sr > Ca > Mg) and increasing molecular weight of the polyacrylate; the precipitates had the compositions [BaA(COO)₂ · 1–2H₂O]_n, [SrA(COO)₂ · 1–2 H₂O]_n, [CaA(COO)₂ · 2 H₂O]_n and [MgA(COO)₂ · 2 H₂O]_n. The final yields of the precipitates from sodium polyacrylate solutions were far lower and these had the compositions [Na_2αM_1-αCA(COO)₂ · 2 H₂O]_n; A =  CH CH₂ CH . The metal polyacrylate hydrate powders consisted of microcrystalline ‘spherules’; their average diameters were from 0.03–0.05 μm (for lower m. wt products) to 0.01 to 0.02 μ,m (for higher m. wt products).     

The coprecipitation of magnesium aluminium hydroxocarbonate powders from aqueous solution: Precipitate compositions and coprecipitation mechanisms

Magnesium aluminium hydroxocarbonate hydrates were coprecipitated from mixed metal nitrate solutions, at total C_M = 0.2 M and Mg/Al₂ = 1 ratio, with four sodium hydrogen carbonate-sodium carbonate solutions (of pH 8.1 to 11.5) at ambient temperature. The course of precipitation was monitored by potentiometric (pH) titration, and the compositions of the primary and final precipitates were determined by chemical analysis, infrared spectrophotometry and X-ray diffraction. Precipitation generally occurred through three stages, primary precipitation (of low CO₃ aluminium hydroxocarbonates) at low pH with evolution of carbon dioxide, their dissolution by complexing to form hydroxocarbonatoaluminate anions and then secondary precipitation of the final coprecipitate at higher pHs. The final product from coprecipitation by sodium hydrogen carbonate solution (pH 8.1) was mainly the magnesium hydroxocarbonatoaluminate ‘MAHC I’; the final products from coprecipitation by sodium hydrogen carbonate-sodium carbonate solutions (pH 9.4 and 10.3) were ‘MAHC I’/‘MAHC II’ mixture and ‘MAHC II’/‘MAHC I’ mixture whereas the final product from coprecipitation by sodium carbonate solution (pH 11.5) was a complex mixture if ‘MAHC II’ with ‘MAHC I’ and ‘MAHC III’;

• ‘MAHC I’ was probably Mg₂[Al₄(OH)₁₀(CO₃)₃] · hH₂O,
• ‘MAHC II’ was probably Mg[Al₂(OH)₄(CO₃)₂] · h H₂O whereas
• ‘MAHC III’ was probably Mg[Al₂(OH)₆CO₃] · h H₂O.