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

Barium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate solutions at 20 °C; C_Al varied from 0.1 to 0.5 M and initial Ba/Al₂ ratios ( = excess OH/Al ratios) varied from 1 to 7. Precipitate compositions were determined by chemical analysis, infra-red spectrophotometry and thermal analysis. The compound BaO · Al₂O₃ · 7 H₂O was precipitated at initial Ba/Al₂ ratios of one to well above two while the compound 2 BaO · Al₂O₃ · 5 H₂O was only precipitated over a narrow range of concentrations. The compound Ba(OH)₂ · 8 H₂O was precipitated from solutions of high hydroxide and barium ion concentrations. The ionic equilibria and precipitation mechanisms in different solutions are 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.     

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 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.

     

The precipitation of aluminium hydroxocarbonates powders from aqueous solution: Precipitate compositions and precipitation mechanisms

A series of aluminium hydroxocarbonate hydrates were prepared by precipitation from aluminium nitrate solution, with five sodium hydrogen carbonate-sodium carbonate solutions of different pH, at ambient temperature. The course of precipitation was monitored by pH measurement and the final precipitate compositions were determined by chemical analysis, infra-red spectrophotometry, X-ray diffraction and thermal analysis. Precipitation generally occurred through three stages, primary precipitation of materials with low carbonate content at low pH with evolution of carbon dioxide, their dissolution to form hydroxcarbonato anions and then secondary reprecipitation of the final products at higher pH. These materials were mixtures of polyhydroxoaluminium carbonate hydrates of general composition Al_n(OH)_3n-2CO₃ · hH₂O (where n = 2, 4, 6 and h = 6–8); their CO₃ content increased with increasing pH and carbonate anion content of the precipitant solution.     

Crystal Growth,Thermal and Linear Optical Properties of the Non‐Centrosymmetric Hydrated Tetraborates Na2[B4O5(OH)4] . 3H2O (Tincalconite) and K2[B4O5(OH)4] . 2H2O

Large single crystals of the non‐centrosymmetric hydrated tetraborates Na₂[B₄O₅(OH)₄] . 3H₂O (Tincalconite) (point group 32) and K₂[B₄O₅(OH)₄] . 2H₂O(point group 222) were grown from aqueous solutions and the linear optical properties (refractive indices between 365 nm and 1530 nm and unpolarized absorption spectra) as a basis for nonlinear optical investigations were determined. The uniaxial positive sodium salt is not phase matchable; in the orthorhombic potassium compound type I phase matching is possible in the near infrared region. Thermal investigations indicate a phase transition at ≈285 K for Na₂[B₄O₅(OH)₄] . 3H₂O.     

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.     

The crystal structure of an iron-rich variety of zanazziite belonging to heteropolyhedral framework roscherite-group beryllophosphates

The iron-rich variety of zanazziite Ca₂[Mg_0.65Fe_0.35□_1.0][Mg_1.90Fe_1.25Al_0.5Mn_0.35]_Σ4Be₄(PO₄)₆(OH)₄(H₂O,OH)₂ · 4H₂O, which is a heteropolyhedral framework roscherite-group beryllophos-phate from the Sapucaia pegmatite (Minas Gerais, Brazil), was studied by X-ray diffraction. The refinement was carried out in the triclinic and monoclinic systems. It was found that the cation distribution on octahedral sites in the crystal structure is in better agreement with the monoclinic symmetry (a = 15.876 Å, b = 11.860 Å, c = 6.607 Å, β = 95.49°, sp. gr. C2/c). In the sample under study, no ordering of Mg or Fe atoms in octahedral sites is observed in sp. gr. P \(\bar 1\), unlike the more iron-rich member of the roscherite group (atencioite).     

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.     

Crystal structure of sakhaite from the Solongo deposit in connection with the crystallochemical interpretation of the sakhaite-harkerite mineral series

The crystal structure of mineral sakhaite Ca₄₈[Mg_13.2(Fe, Mn)_2.8](CO₃)₁₆{ Al[SiO_3.75(OH)_0.25]₄}(BO₃)₂₈[(H₂O)_3.3(HCl)_3.3] from the Solongo deposit, Zabaykalye, is established (R 0.047) by X-ray diffraction analysis (Bruker Smart CCD diffractometer, 2θ: θ scan, λMoK_α radiation, graphite monochromator): a = 14.679(2) Å, sp. gr. Fd3m, Z = 1, ρ_calcd = 2.99 g/cm³. It is shown that some part of BO₃ triangles in the structure of sakhaite from Solongo is replaced with five-member complexes {Al[SiO₃(O,OH)]₄}, established previously in the harkerite structure. Three schemes of isomorphism, which are characteristic of the sakhaite-harkerite mineral series, are selected and the general formula is proposed: Ca₄₈(Mg,Fe,Mn)₁₆(CO₃)₁₆{Al[SiO₃(O, OH)]₄}_y(B₃)_32?y · n(H₂O,HCl) (Z = 1), y_max = 8, n_max = 16 ? y. The structural relationship of sakhaite-harkerite minerals with borate-sulfates of the tychite family Na₆(Mg,Fe,Mn)₂(BO₃)₄(SO₄) is revealed. The correlation between the number of harkerite fragments forming the mineral structure, the structural symmetry, and the degree of imperfection is ascertained.     

Crystal structures of K-and Cs-exchanged forms of zorite

The crystal structures of K-and Cs-exchanged forms of zorite were studied by X-ray diffraction and IR spectroscopy: K_4.75Na_1.82[Ti(Ti_0.79Nb_0.20)₄Si₁₂O₃₄(O,OH)_5.2] × 10.62 H₂O (sp. gr. Cmmm, R= 0.0481 for 516 independent reflections) and Cs_4.34Na_1.90[Ti(Ti_0.80Nb_0.18)₄Si₁₂O₃₄(O,OH)₅] × 5.37 H₂O (sp. gr. Cmmm, R = 0.0285 for 621 independent reflections). Both structures retain the mixed polyhedral framework of zorite: Na₆Ti(Ti,Nb)₄(Si₆O₁₇)₂(O,OH)₅ × nH₂O, where n ～ 11. It is shown that the positions of the atoms located in the cavities of the frameworks of these compounds differ from those in the structures of zorite and its synthetic analogs.     

A novel representative {[Rb1.94(H2O,OH)3.84](H2O)0.1}{Al4(OH)4[PO4]3} in the pharmacosiderite structure type

The crystal structure of a new synthetic aluminophosphate {[Rb_1.94(H₂O,OH)_3.84](H₂O)_0.1}{Al₄(OH)₄[PO₄]₃} synthesized under mild hydrothermal conditions (T = 280°C, P = 100 atm) in the Rb₂O-Al₂O₃-P₂O₅-H₂O system is determined using X-ray diffraction (Stoe IPDS diffractometer, λMoK _α, graphite monochromator, 2θ_max = 64.33°, R = 0.032 for 312 reflections). The main crystal data are as follows: a = 7.4931(6) ?, space group P 3m, Z = 1, and ρ_calcd = 2.76 g/cm³. It is shown that the synthesized compound belongs to the pharmacosiderite structure type with a characteristic mixed open microporous framework composed of octahedra and tetrahedra. A comparative crystal chemical analysis of related phases is performed, and the chemical compositions of promising absorbents, i.e., hypothetical compounds potentially possible in the structure type under consideration, are proposed. It is established that pharmacosiderite and rhodizite are homeotypic to each other. Original Russian Text ? O.V. Yakubovich, W. Massa, O.V. Dimitrova, 2008, published in Kristallografiya, 2008, Vol. 53, No. 3, pp. 442–449.     

Room,low, and high temperature dehydration and phase transitions of kernite in vacuum and in air

Kernite Na₂B₄O₆(OH)₂·3H₂O dehydration in air at high temperature and in vacuum at room temperature has been studied. It was found that kernite easily dehydrates forming a new phase‐I both on heating and in vacuum. The chemical formula Na₂B₄O₆(OH)₂·1.5H₂O of the new phase‐I has been estimated on the basis of thermogravity analysis. It is triclinic with the unit cell parameters a = 7.047(8), b = 8.76(1), c = 13.08(2) Å, α = 93.40(9), β = 95.32(9), γ = 90.28(9)° changing slightly on pressure reduction. Due to the relatively low temperature (353 K) and reversibility of the kernite ⟷ phase‐I transition an anion of the new phase‐I likely consists of the same chains [B₄O₆(OH)₂]^2– like in kernite structure. The high anisotropy of kernite thermal expansion was explained by approaching of NaO chains due to the initial removing of water molecules from kernite crystal structure. The behaviour of the new phase‐I at low temperatures in vacuum was also investigated. A formation of an additional new phase II has been detected at the temperature of 93 K. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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 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.      

Iron-Chloranilate Intercalation Compounds: Synthesis,Crystal Structures,and Thermal Properties

Abstract

Hydrogen bond supported new iron-chloranilate assemblies, {(Hpy)[Fe(CA)₂(H₂O)₂](H₂O)}_n (py = pyridine, H₂CA = chloranilic acid, C₆H₂O₄Cl₂) (1), and [(phz)₂[Fe(CA)₂(H₂O)₂](H₂O)₂]_n (phz = phenazine, C₁₂H₈N₂) (2) have been synthesized and characterized. Compound 2 crystallizes in the monoclinic, space group C2/m (#12), with a= 29.135(6) Å, b= 16.886(6) Å, c = 15.017(5) Å, ß = 165.907(1)°, V= 1798(2) ų, Z = 2. In both the compounds two chloranilate dianions and two water molecules are coordinated to the iron ion making anionic monomers [Fe(CA)₂(H₂O)₂]^?, which are the building blocks of the compounds. The coordination environment around the iron ion in the building block is a distorted octahedron, where two water molecules sit on the trans position to each other. [Fe(CA)₂(H₂O)₂]^? anions form common layer structures, supported by hydrogen bonds. Hpy⁺ are intercalated in between the layers of 1 by electrostatic and hydrogen bonding interactions and phz are intercalated in that of 2 by electrostatic interactions. DSC traces of 1 show anomaly at 174 K, indicating phase transition in the compound.     

Hydrothermal crystallization and X-ray structure determination of a new decavanadate with mixed cations [Mn(H2O)6]2[N(CH3)4]2[V10O28]·2H2O

A new decavanadate with mixed cations, [Mn(H₂O)₆]₂[N(CH₃)₄]₂[V₁₀O₂₈]·2H₂O (1), was crystallized from a hydrothermal reaction between MnCO₃ and V₂O₅ in the presence of N(CH₃)₄Br at 100°C. The structure of 1, as determined by x-ray single crystal analysis, consists of cations and anions of hexa-aqua manganese [Mn(H₂O)₆]²⁺, tetramethyl ammonium [N(CH₃)₄]⁺ and decavanadate [V₁₀O₂₈]^6–. The extended H-bonding between the [Mn(H₂O)₆]²⁺ and [V₁₀O₂₈]^6– ions gives rise to a pseudo- two-dimensional network in the crystal lattice x-ray crystallographic data for 1: monoclinic P2₁/n, a = 9.1499(5), b = 12.8725(7), c = 18.625(1) Å, = 92.252(1)°, V = 2192.0(2) ų, MZ = 2, and D _calcd = 2.22 g cm^–3.