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.      

The Coprecipitation of Magnesium Iron (III) Hydroxide Powders from Aqueous Solution: Precipitate Compositions and Coprecipitation and Ageing Mechanisms

Series of magnesium iron(111) hydroxides were coprecipitated at ambient temperature from different mixed metal cation solutions, at C_{M tot} = 0.1 M and Mg/Fe₂ ratios from 4 to 1/4, with sodium hydroxide solution. The relevant single precipitations and the coprecipitations were monitored by potentiometric (pH) titration and the final coprecipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis. The coprecipitates onto aged α-FeOOH were simple mixtures of α-FeOOH and Mg(OH)₂. The main coprecipitates were either «molecular inclusion mixtures» of microcrystalline α-FeOOH with excess Mg(OH)₂ or similar mixtures of Mg(OH)₂ with excess α-FeOOH and some ten-twenty percent (relative to the Mg content) of magnesium hydroxo-ferrate(III) hydrate Mg[Fe(OH)₄]₂ · h H₂O. The coprecipitates aged in alkaline magnesium hydroxide suspension at 20 °C and 40 °C were mixtures of Mg(OH)₂, α-FeOOH and forty to ninety percent (relative to the Mg content) of Mg[Fe(OH)₄]₂ · h H₂O. The related α-FeOOH NaOH and α-FeOOH Mg(OH)₂ equilibria and the different coprecipitation mechanisms are discussed.     

The coprecipitation of Magnesium Nickel Oxalate Dihydrate Powders (solid solutions) from aqueous solution: Precipitate compositions and Cporecipitate Mechanisms

The coprecipitation of magnesium nickel oxalate dihydrates from mixed metal cation solutions was monitored by conductivity measurements. A series of coprecipitates was then prepared from 0.2 M solutions with Mg contents varying from 0.2 to 0.9 total metal cation and their compositions and structures studied by chemical analysis, infra-red spectrophotometry, thermogravimetric analysis and detailed differential calorimetry. The coprecipitates with upto 20 percent Mg content were solid solutions with structures similar to nickel oxalate dihydrate, the coprecipitates with 20 to 80 percent Mg content were probably mixed solid solutions while the coprecipitates with over 80 percent Mg content were solid solutions with structures similar to magnesium oxalate dihydrate. The ionic equilibria in supersaturated magnesium nickel oxalate solutions were analysed and mechanisms are proposed for coprecipitations from solutions of different Mg/(Mg + Ni) ratios.     

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 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 iron (II) and nickel oxalates with alkaline-earth metal oxalates: Induction periods,nucleation rates and mechanisms

The coprecipitations of magnesium (and barium) iron(II) and nickel oxalate dihydrates were studied from excess magnesium and barium oxalate solutions. Nucleation rates were estimated from the induction periods for the coprecipitations. The nucleation rates in excess magnesium oxalate solutions first decreased with increasing excess oxalate anion concentration to minimum values and then increased with increasing magnesium cation concentration. At low to intermediate Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were FeOx (and NiOx); at intermediate Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were probably MgOx FeOx (and MgOx NiOx) mixtures and/or solid solutions of compositions Mg_αFe_{1 α}Ox (and Mg_αNi_{1 α}Ox); at high Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were MgOx. The nucleation rates in excess barium oxalate solutions were similar to those for the precipitation of barium oxalate from supersaturated equivalent solutions. The main nuclei in most systems were BaOx.     

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 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 precipitation of alkaline-earth metal-nickel,aluminium (chromium (III) and iron (III)), silicyl(titanyl and zirconyl) hydroxide,carbonate and oxalate precipitate precursors for alkaline-earth metal oxyanion salt ceramics and allied materials – a review of small scale laboratory studies and industrial patents

The alkaline-earth metal – nickel, aluminium, chromium III, iron III, silicyl, titanyl and zirconyl hydroxide, carbonate and oxalate coprecipitates are the precursors for the preparation of the corresponding alkaline-earth metal oxyanion salt refractories, magnetics, dielectric and optical ceramics, cements and allied materials. The small-scale laboratory studies on the coprecipitations of these precursor materials, their compositions and the coprecipitation mechanisms are reviewed and the relevant industrial patents are described (140 references).     

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 coprecipitation of magnesium nickel hydroxide solid solutions from aqueous solution: Precipitate compositions and precipitation mechanisms

Magnesium nickel hydroxides (solid solutions) were coprecipitated from different mixed metal cation solutions (overall concentration 0.1 M) and from hydroxide solution (0.1 M). The course of different coprecipitations was monitored by potentiometric (pH) titrations. Final Coprecipitate compositions were determined by chemical analysis, infra-red spectrophotometry and thermal analysis. The ionic equilibria involved in different coprecipitations and the precipitation mechanisms are discussed.     

Influence of solvents on the hydrothermal formation of one‐dimensional magnesium hydroxide

The influence of solvents on the hydrothermal formation of one‐dimensional (1D) magnesium hydroxide (Mg(OH)₂) was investigated in this paper. Uniform 1D Mg(OH)₂ with a length of 10‐20 μm, a width of 100‐200 nm and a preferential growth along [110] direction have been synthesized by treating magnesium oxysulfate (5Mg(OH)₂·MgSO₄·3H₂O, abbreviated as 513MOS) nanowires in NaOH ethanol solution at 180 °C for 2.0 h. The experimental results indicated that the solvent of ethanol and NaOH concentration were essential for the conversion of 513MOS nanowires to 1D Mg(OH)₂. The slow release of MgSO₄ from 513MOS and the heterogenous precipitation of Mg(OH)₂ at the defects left by MgSO₄ dissolution promoted the formation of 1D Mg(OH)₂. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The crystallisation of chromite-magnesiochromite spinels from a calcium magnesium aluminosilicate glass: Nucleation,crystal growth and final crystal sizes

The crystallisation of chromite-magnesiochromite spinels was studied from a calcium magnesium aluminosilicate glass (a simulated slag) containing 3 to 12 percent total iron oxides and 0.3 to 1.5 percent chromium(III) oxide, at temperatures from 1400° to 700 °C. – Spinel crystallisation occurred in glasses with 3–7 percent FeO and 0.7–1.1 percent Cr₂O₃. At temperatures 1100 °C and above, the nucleation was rapid and crystal numbers very high, at FeO contents above 3 percent and Cr₂O₃ contents above 0.7 percent; at 1056° and 1000 °C however, the crystal numbers reached some optimum values but then decreased as clinopyroxene crystals grew onto and enveloped the spinel microcrystals. In these glasses, the crystal lengths varied with growth time according to the relation, l_t = 2 k_g t^α = R_g1 t^α, where α = 0.7–1.0: this time dependence was a compromise between a relation for dendritic growth and one for facetted growth. The growth rates generally increased about five to seven times for 160 °C temperature rise: the energy of activation for the spinel crystal growth was then estimated as 180 ± 60 kJ mole⁻¹. – No spinel crystals were observed in glasses with more than 7 percent FeO content, only clinopyroxene crystals. Probably, these latter had nucleated rapidly and grown onto spinel microcrystals, while the spinel microcrystals were still of < 0.1 μm size.     

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).     

Luminescence of SnO2: Eu; dependence on the oxidation state of the precursor

Preparation conditions and phase composition of polycrystalline SnO₂: Eu luminophores are investigated. The results show that the luminescence intensity of SnO₂: Eu obtained from Sn(II)-containing precursors, (hydroxide or oxide), is considerably higher than that from Sn(IV) oxide hydrate. It is considered that the creation of luminescence centers in SnO₂: Eu is connected to the formation of intermediate Sn(II)—Sn(IV) oxides during the oxidation.     

Recharging processes of Cr ions in Mg2SiO4 and Y3Al5O12 crystals under influence of annealing and γ ‐ irradiation

Recharging processes of chromium ions were investigated for Mg₂SiO₄:Mg, Cr single crystals using annealing in O₂ and in air and γ‐irradiation, as compare to YAG :Ca, Cr single crystals. The formation of tetravalent Cr ions in the Mg₂SiO₄ :Mg, Cr is related not only to the initial Cr content in the melt, oxygen partial pressure and O₂‐ vacancy existing in the crystal, but also to the external field such as γ‐irradiation. The additional absorption after γ‐irradiation shows the decrease in intensity of the absorption of Cr³⁺ and Cr⁴⁺ ions in some part of the spectrum and increase in the other giving evidence on recharging effects between Cr³⁺ and Cr⁴⁺. There arises also color centers observed between 380 nm and 570 nm that may participate in energy transfer of any excitation to Cr⁴⁺ giving rise to Cr⁴⁺ emission. Opposite to forsterite crystal, absorption spectrum of YAG:Ca, Cr crystal after γ‐irradiation reveals only increase in the absorption of the Cr bands. The observed behavior of the absorption spectrum of YAG:Ca, Cr crystal under influence of γ‐irradiation suggests that γ‐irradiation ionizes only Cr ions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

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.     

Structural and spectroscopic study of Mg13.4(OH)6(HVO4)2(H0.2VO4)6

Single‐crystals of the polar compound magnesium hydrogen vanadate(V), Mg_13.4(OH)₆(HVO₄)₂(H_0.2VO₄)₆, were synthesized hydrothermally. It represents the first hydrogen vanadate(V) among inorganic compounds. Its structure was determined by single‐crystal X‐ray diffraction [space group P 6₃mc, a = 12.9096(2), c = 5.0755(1) Å, V = 732.55(2) ų, Z = 1]. The crystal structure of Mg_13.4(OH)₆(HVO₄)₂(H_0.2VO₄)₆ consists of well separated, vacancy‐interrupted chains of face sharing Mg2O₆ octahedra, with short Mg2—Mg2 distances of 2.537(1) Å, embedded in a porous magnesium vanadate 3D framework having the topology of the zeolite cancrinite. All three hydrogen positions in the structure were confirmed by FTIR spectroscopy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

LEED-AES-Untersuchungen der Oxydation von austenitischen Cr-Ni-Stählen an der (100)-Ebene

Oxidation of austenitic stainless steel has been studied on the (100)-face. Temperature region examinated reaches from room temperature to 1000°C. Oxidation begins with formation of chromium oxide (Cr₂O₃). After this iron oxide (Fe₃O₄) covering the chromium oxide arises gradually. At 500°C Fe₃O₄ is destroyed, and a layer of chromium oxide increases. At 700°C the LEED-pattern was observed to represante Cr₂O₃(111), and at 750°C you can prove FeO(111) on that. At 1000°C the oxide layer is destroyed. All the oxides grow in form of islands.