A coprecipitation technique to prepare NaNbO3 and NaTaO3

A simple coprecipitation technique has been used successfully for the preparation of pure, ultrafine, single phases of NaNbO₃ (NN) and NaTaO₃ (NT). An alcoholic solution of ammonium carbonate and ammonium hydroxide was used to precipitate Na⁺ and Nb⁵⁺ (or Ta⁵⁺) cations under basic conditions as carbonate and hydroxide, respectively. On heating at 700°C, these precursors produce respective products. For comparison, both NN and NT powders were also prepared by the traditional solid state method. The phase purity and lattice parameters were studied by powder X-ray diffraction (XRD). The particle size and morphology were studied by scanning electron microscopy (SEM).     

A co-precipitation technique to prepare BiNbO4, MgTiO3 and Mg4Ta2O9 powders

A simple co-precipitation technique has been used successfully for the preparation of pure, ultrafine, single phase BiNbO₄ (BN), MgTiO₃ and Mg₄Ta₂O₉. An aqueous sodium hydroxide or ammonium hydroxide and ammonium carbonate solution was used to precipitate these cations as hydroxides and carbonates simultaneously under basic conditions. These precursors on heating at 750 °C, produce the respective powders. For comparison, these compounds were also prepared by the traditional solid state method. The phase purity and lattice parameters were studied by powder X-ray diffraction (XRD). Particle size and morphology was studied by transmission electron spectroscopy (TEM).     

A coprecipitation technique to prepare ZnNb2O6 powders

A simple coprecipitation technique was successfully applied for the preparation of pure ultrafine single phase, ZnNb₂O₆ (ZN). Ammonium hydroxide was used to precipitate Zn²⁺ and Nb⁵⁺ cations as hydroxides simultaneously. This precursor on heating at 750°, produced ZN powders. For comparison, ZN powders were also prepared by the traditional solid state method. The phase contents and lattice parameters were studied by the powder X-ray diffraction (XRD). Particle size and morphology were studied by transmission electron spectroscopy (TEM).     

A co-precipitation technique to prepare BiTaO4 powders

A simple co-precipitation technique has been successfully used for the preparation of pure ultrafine single phase BiTaO₄. A standard ammonium hydroxide solution was used to precipitate Bi³⁺ and Ta⁵⁺ cations as hydroxides simultaneously under basic conditions. This precursor, on heating at 600 °C, produced product phase. This is the lowest temperature for the formation of BiTaO₄ phase so far reported in the literature. For comparison BiTaO₄ powders were also prepared by the traditional solid state method. The phase contents and lattice parameters were studied by the powder X-ray diffraction (XRD).     

Co-precipitation method for the preparation of ferroelectric CaBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript>

A simple co-precipitation technique has been successfully applied for the preparation of pure single phase CaBi₄Ti₄O₁₅ (CBT) powders. Ammonium oxalate and ammonium hydroxide were used to precipitate Ca²⁺, Bi³⁺ and Ti⁴⁺ cations simultaneously. No pyrochlore phase was found while heating powder at 600 C and pure CBT phase was found to be formed by X-ray diffraction. Particle size and morphology was studied by transmission electron microscopy (TEM). The room temperature dielectric constant at 1 kHz is 400. The ferroelectric hysteresis loop parameters of these samples were also studied.     

Coprecipitation method for the preparation of nanocrystalline ferroelectric CaBi2Ta2O9

A simple coprecipitation technique had been successfully applied for the preparation of pure ultrafine single-phase CaBi₂Ta₂O₉ (CBT). Ammonium hydroxide and ammonium oxalate were used to precipitate Ca²⁺, Bi³⁺ and Ta⁵⁺ cations simultaneously. No pyrochlore phase was found while heating powder at 800 °C and pure CaBi₂Ta₂O₉ phase was found to be formed by XRD. Particle size and morphology was studied by transmission electron microscopy (TEM). The room temperature dielectric constant at 1 kHz is 100. The ferroelectric hysteresis loop parameters of these samples were also studied.     

Synthesis and luminescent characteristic of Eu-doped (Gd,Lu)2O3 nanopowders

Eu³⁺ doped (Gd,Lu)₂O₃ nanopowders with particle sizes ranging from 20 to 70 nm were synthesized by the co-precipitant method using mixed precipitants, namely the mixture of ammonium hydroxide (NH₃⋅H₂O) and ammonium hydrogen carbonate (NH₄HCO₃). The precipitate precursor prepared by this method was believed to possess a basic carbonate composition and its thermal decomposition of the (Gd,Lu)₂O₃:Eu³⁺ powders were investigated by Thermogravimetric analysis and differential thermal analysis (TG-DTA). This preparation was followed by a calcination process at 800-1100 °C and corresponding phosphor structure were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Photoluminescence measurement of the (Gd,Lu)₂O₃:Eu³⁺ particles show typical red emission at the 612 nm corresponding to the ⁵D₀ → ⁷F₂ transition. We found that the optimal Eu³⁺ molar doping concentration, calcined temperature and reaction time were 7 mol%, 1000 °C, and 2 h, respectively, which is helpful to obtain the final transparent ceramics with excellent properties.     

A coprecipitation technique to prepare NiNb2O6

A mixture of ammonium carbonate and ammonium hydroxide was used to coprecipitate nickel and niobium ions as nickel carbonate and niobium hydroxide under basic conditions. This precursor yielded NiNb₂O₆ (NN) ceramics on calcining at 700 °C (at a temperature lower than 800 °C which is necessary for the formation of NiNb₂O₆ when prepared by the traditional solid state method). The average particle size and morphology of these powders were investigated by transmission electron microscope (TEM).     

Hydrous oxides of titanium: cation exchange properties and kinetics of exchange

The ion exchange properties of hydrous titania gels of different particle sizes, precipitated from titanous chloride through the agency of ammonium carbonate and hydroxide have been studied. Such studies were carried out under acidic and alkaline conditions with respect to Cu²⁺, Ni²⁺, Co²⁺ and Cr³⁺ ions.In the case of gels precipitated by ammonium carbonate, oxygen gas was used as the oxidizing agent whereas with ammonium hydroxide as precipitant, oxidation was performed with hydrogen peroxide.Ion exchange capacities were determined by visible spectrophotometry. Increasing the pH of preparation lead to an increase in exchange capacities of the hydroxide precipitated gels that are characterized to be mesoporous. Such an increase is not observed in the case of carbonate precipitated microporous gels. It is shown that in the latter case the NH ₄ ⁺ ions generated by the initial interaction of (NH₄)₂CO₃ with the acidic titanous chloride lead to the formation of titania exchangers that are predominantly in the ammonium form. The textural characteristics of the exchanger resulting from different conditions of preparation is a significant contributing parameter to the resulting data.Ageing of the microporous titania samples markedly reduces the exchanger capacity of the smaller Ni²⁺ ions but increases that of the bulkier Cr³⁺ as a result of the presence of some wide pores that appear upon agglomeration. The presence of Cr³⁺ ions in the hydroxo form in solution seems to inhibit its exchange with the appropriate surface species.Studies on the kinetics of exchange with respect to the Ni²⁺ ions seem to indicate that a particle diffusion mechanism is partly or completely responsible for the rate of exchange.     

Co-precipitation technique for the preparation of nanocrystalline ferroelectric SrBi2Ta2O9

A simple co-precipitation technique had been successfully applied for the preparation of pure ultrafine single phase SrBi₂Ta₂O₉. Ammonium hydroxide was used to precipitate Sr²⁺, Bi³⁺ and Ta⁵⁺ cations simultaneously. No pyrochlore phase was found while heating powder at 800 °C and pure SrBi₂Ta₂O₉ phase was found to be formed by X-ray diffraction. Particle size and morphology was studied by scanning electron spectroscopy. Ferroelectric hysteresis loop parameters of these samples were also studied.     

The effects of different precipitant agents on the formation of alumina-magnesia composite powders as the magnesium aluminate spinel precursor

Al₂O₃/MgO composite powders were synthesized via a partially wet chemical method. The effects of precipitant agent on the morphology, size and chemical composition of the resultant powders were investigated. The structures of rod-like with polygonal prism surface, platelet-like and uniform spherical Mg-compound particles were successfully prepared by using ammonium hydrogen carbonate, sodium hydroxide and ammonia water as precipitant agents, respectively. Analysis results proved that using ammonium hydrogen carbonate as precipitant agent produced nesquehonite (MgCO₃·3H₂O) Mg-compounds but in the case of other two precipitant agents, Mg-compound particles with magnesium hydroxide (Mg(OH)₂) chemical composition were obtained. The morphological features of MgO particles in Al₂O₃/MgO composite powders were the same as individual Mg-compound particles. Furthermore, conversion of the Al₂O₃/Mg-compound precursor synthesized with ammonia water to pure magnesium aluminate spinel particles was studied. The precursor converted to pure magnesium aluminate spinel phase with 220?nm particle size at 1200?°C.     

Doped nanocrystalline calcium carbonate phosphates

The formation of nanocrystalline calcium carbonate phosphates doped with Fe²⁺, Mg², Zn²⁺, K⁺, Si⁴⁺, and Mn²⁺ has been studied by X-ray diffraction, IR spectroscopy, differential thermal analysis, and energy dispersive X-ray fluorescence analysis. The results indicate that the synthesis involves the formation of hydroxy carbonate complexes from the three calcium carbonate polymorphs (calcite, vaterite, and aragonite) in a solution of ammonium chloride and ammonium carbonate, followed by reaction with orthophosphoric acid. This ensures the preparation of a bioactive material based on chlorophosphates, octacalcium hydrogen phosphate, and calcium chloride hydroxide phosphates containing cation vacancies. Particle-size analysis data show that the materials contain nanoparticles down to 10 nm in size. Heat treatment of the doped calcium carbonate phosphates produces calcium hydroxyapatite containing cation vacancies, which can be used as a bioactive ceramic.     

A coprecipitation technique to prepare Sro.5Bao.5Nb206

An aqueous mixture of ammonium oxalate and ammonium hydroxide was used to coprecipitate barium and strontium ions as oxalates and niobium ions as hydroxide under basic conditions. This precursor on calcining at 750°C yielded Sr_0.5Ba_0.5Nb₂O₆ phase. This is a much lower temperature than that prepared by traditional solid state method (1000°C) as reported for the formation of Sr_0.5Ba_0.5Nb₂0₆ (SBN). Transmission electron microscopic (TEM) investigations revealed that the average particle size was 80 nm for the calcined powders. The room temperature dielectric constant at 1 kHz was found to be 1100. The ferroelectric hysteresis loop parameters of these samples were also studied.     

A coprecipitation technique to prepare CoTa2O6 and CoNb2O6

An aqueous solution of sodium hydroxide was used to coprecipitate cobalt and tantalum (or niobium) ions from their precursors as hydroxides under basic conditions. This precipitate yielded CoTa₂O₆ (CT) or CoNb₂O₆ (CN) ceramics on calcining at 700 °C, i.e. at a temperature much lower than 900 °C, reported for the formation of these powders prepared by the traditional solid state method. The X-ray diffraction (XRD) studies were employed to investigate phase contents and lattice parameters. The morphology of the synthesized powders was investigated by transmission electron microscopy (TEM).     

Synthesis of yttria-doped strontium-zirconium oxide powders via ammonium glycolate combustion methods as precursors for dense ceramic membranes

Ammonium glycolate combustion was used to synthesize SrZr_0.95Y_0.05O_{3 – x} powders. Soluble metal-glycolate complexes, detected by infrared spectroscopy, were formed with Y⁺³ and Zr⁺⁴, which maintain atomic level mixing of metal cations with glycolic acid. Sr⁺²/glycolic acid mixtures did not form glycolate complexes. Temperature-programmed reaction studies showed that only precursor solutions with metal-glycolate complexes combust, indicating that the combustion is initiated by metal-glycolate complexes. Varying the ammonium hydroxide content and glycolic acid levels above that required to form glycolate complexes did not affect surface area and crystallinity. Decreasing the glycolic acid/nitrate ratio increases the temperatures reached during combustion. Thick disks prepared from co-precipitated and ammonium glycolate powders demonstrated that combustion synthesized powders reach higher densities. Surface area and SEM indicated that the ammonium glycolate powders have smaller particle sizes, which favor densification, than co-precipitated powders.     

A novel approach for synthesis of M-type hexaferrites nanopowders via the co-precipitation method

M-type hexaferrites; barium hexaferrite BaFe₁₂O₁₉ and strontium hexaferrite SrFe₁₂O₁₉ powders have been successfully prepared via the co-precipitation method using 5 M sodium carbonate solution as alkali. Effects of the molar ratio and the annealing temperature on the crystal structure, crystallite size, microstructure and the magnetic properties of the produced powders were systematically studied. The results indicated that a single phase of barium hexaferrite was obtained at Fe³⁺/Ba²⁺ molar ratio 12 annealed at 800–1,200 °C for 2 h whereas the orthorhombic barium iron oxide BaFe₂O₄ phase was formed as a impurity phase with barium M-type ferrite at Fe³⁺/Ba²⁺ molar ratio 8. On the other hand, a single phase of strontium hexaferrite was produced with the Fe³⁺/Sr²⁺ molar ratio to 12 at the different annealing temperatures from 800 to 1,200 °C for 2 h whereas the orthorhombic strontium iron oxide Sr₄Fe₆O₁₃ phase was formed as a secondary phase with SrFe₁₂O₁₉ phase at Fe³⁺/Sr²⁺ molar ratio of 9.23. The crystallite sizes of the produced nanopowders were increased with increasing the annealing temperature and the molar ratios. The microstructure of the produced single phase M-type ferrites powders displayed as a hexagonal-platelet like structure. A saturation magnetization (53.8 emu/g) was achieved for the pure barium hexaferrite phase formed at low temperature 800 °C for 2 h. On the other hand, a higher saturation magnetization value (M _s = 85.4 emu/g) was obtained for the strontium hexaferrite powders from the precipitated precursors synthesized at Fe³⁺/Sr²⁺ molar ratio 12 and thermally treated at 1,000 °C for 2 h.     

Improved chemical route for quantitative precipitation of lead zirconyl oxalate (PZO) leading to lead zirconate (PZ) powders

An improved chemical route is described to precipitate quantitatively a molecular precursor lead zirconyl oxalate tetrahydrate, PbZrO(C₂O₄)₂·4H₂O (PZO) at room temperature. In this route, soluble ammonium zirconyl oxalate, (NH₄)₂ZrO(C₂O₄)₂ (AZO), is initially prepared by chemical reaction of 0.1-M solution of zirconyl nitrate with 0.2-M solution of ammonium oxalate. The anionic species ZrO(C₂O₄)₂⁻² thus obtained is exchanged by adding equimolar solution of lead acetate to precipitate single-phase PZO with higher yield. The improvement in the presently described route is to drive exchange reaction to its completion by suitably manoeuvring the choice of precursor, pH and reaction conditions, in such a way that single-phase PZO is precipitated without any destabilization of anionic species ZrO(C₂O₄)₂⁻². The pyrolysis of PZO produced stoichiometric, monophasic, orthorhombic PbZrO₃ (PZ) powders at temperature T=700°C. Various physico-chemical techniques were used to characterize both molecular precursor PZO as well as PZ powders obtained by its pyrolysis. All our experimental results related to the synthesis and characterization of these powders are presented in this paper.     

Effects of CeO2 coating uniformity on high temperature cycle life performance of LiMn2O4

CeO₂ is coated using different precipitants on the surface of LiMn₂O₄ in order to investigate the effect of CeO₂ coating uniformity on the cycle life performance at high temperature. CeO₂ is prepared by a precipitation method without the use of a surfactant. Ammonium carbonate or ammonium hydroxide is respectively used as a precipitant in order to control the morphology and particle size of CeO₂. More uniform coating layer composed of well dispersed CeO₂ nanoparticles is obtained with ammonium hydroxide while aggregation lead to non-uniform coating layer when ammonium carbonate is used. The CeO₂-coated LiMn₂O₄ shows better cyclability both at room temperature and 60 °C than the pristine sample but much higher capacity retention rate can be achieved by using ammonium hydroxide. The smaller particle size and uniform coating layer obtained using ammonium hydroxide appear to contribute to the better cycling performance.     

Synthesis of porous,high surface area MgO microspheres

Porous MgO microspheres with nanocrystallites have been prepared by a wet precipitation process using ammonium hydrogen carbonate and ammonium hydroxide as precipitants. The as-precipitated powders are composed of crystalline Mg₅(OH)₂(CO₃)₄.4H₂O microspheres with porous and hollow microstructure and are decomposed and transformed to nanocrystalline cubic MgO after being calcined at 500 °C. The average crystallite size of MgO microspheres increases from 10 nm to 31.6 nm with increasing temperature from 500 °C to 1100 °C. The surface area of the MgO powder decreases from 90.7 m²/g to 31.5 m²/g with increasing temperature from 500 °C to 1100 °C.     

Al2O3:Cr3+ microfibers by hydrothermal route: Luminescence properties

Uniform Al₂O₃:Cr³⁺ microfibers were synthesized by using a hydrothermal route and thermal decomposition of a precursor of Cr³⁺ doped ammonium aluminum hydroxide carbonate (denoted as AAHC), and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curves. XRD indicated that Cr³⁺ doped samples calcined at 1473 K were the most of α-Al₂O₃ phase. SEM showed that the length and diameter of these Cr³⁺ doped alumina microfibers were about 3–9 μm and 300 nm, respectively. PL spectra showed that the Al₂O₃:Cr³⁺ microfibers presented a broad R band at 696 nm. It is shown that the 0.07 mol% of doping concentration of Cr³⁺ ions in α-Al₂O₃:Cr³⁺ was optimum. According to Dexter's theory, the critical distance between Cr³⁺ ions for energy transfer was determined to be 38 Å. It is found that the curve followed the single-exponential decay.