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1.
Magnesium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total CM = 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.   相似文献   

2.
Series of magnesium iron(111) hydroxides were coprecipitated at ambient temperature from different mixed metal cation solutions, at CM 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.  相似文献   

3.
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.  相似文献   

4.
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].
  相似文献   

5.
Calcium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total CM = 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.  相似文献   

6.
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 MgαFe1 αOx (and MgαNi1 αOx); 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.  相似文献   

7.
Zine aluminium hydroxides were coprecipitated from different mixed metal cation solutions, at CM 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].  相似文献   

8.
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.  相似文献   

9.
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).  相似文献   

10.
Magnesium aluminium hydroxocarbonate hydrates were coprecipitated from mixed metal nitrate solutions, at total CM = 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.
  相似文献   

11.
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.  相似文献   

12.
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)  相似文献   

13.
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, lt = 2 kg tα = Rg1 tα, 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.  相似文献   

14.
Calcium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate-excess hydroxide solutions at ambient temperature (at CAl = 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).  相似文献   

15.
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.  相似文献   

16.
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)  相似文献   

17.
Magnesium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate-hydroxide solutions at ambient temperature, at CAl = 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.  相似文献   

18.
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.  相似文献   

19.
Single‐crystals of the polar compound magnesium hydrogen vanadate(V), Mg13.4(OH)6(HVO4)2(H0.2VO4)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 Mg13.4(OH)6(HVO4)2(H0.2VO4)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)  相似文献   

20.
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.  相似文献   

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