Nickel permanganate as a precursor in the synthesis of a NiMn2O4 spinel

The present study describes the preparation, characterization, and thermal decomposition of the compound Ni(MnO₄)₂·xH₂O, which was synthesized by a coprecipitation method at a low temperature. The role of this compound as a precursor in the synthesis of a Ni-Mn spinel was determined via X-ray, TG-DTA, electron diffraction, and EDAX measurements.     

The control of the diameter and length of α-MnO2 nanorods by regulation of reaction parameters and their thermogravimetric properties

α-MnO₂-type single-crystal nanorods were synthesized under hydrothermal conditions based on the redox reaction of KMnO₄ in an acidic environment. Several reaction parameters, like the reaction temperature, the reaction time and the concentration of KMnO₄ in the reaction mixture, were varied in order to determine their impact on the structure, the dimensions of the synthesized nanorods, and as well on their thermogravimetric properties. It was found that the reaction time has no significant influence on the diameter, although it has a strong influence on the length of the obtained nanorods. On the other hand, the concentration of KMnO₄ in the reaction mixture has a strong impact on both the diameter and the length. With an increasing concentration of KMnO₄ in the reaction mixture the average lengths and diameters of the isolated MnO₂ nanorods are reduced. The change in dimensions of the synthesized nanorods is reflected in their thermogravimetric properties.     

An oxygen nonstoichiometry study of barium polytitanates with hollandite structure

A series of barium titanium oxides with various Ba/Ti ratios having a hollandite structure were obtained by firing chemical synthesized oxide precursors under reducing atmosphere conditions (H₂/N₂ gas mixture flow) at temperatures of 1100°C and above. An oxygen nonstoichiometry was determined by a thermogravimetric analysis through oxidizing in air. It was shown that barium titanium hollandites may adopt both oxygen excess and oxygen-deficient stoichiometries within the structure. As a limiting case the barium titanium hollandites with only tetravalent titanium ions were obtained. The influence of oxygen nonstoichiometry on the hollandite monoclinic-tetragonal phase transition and a barium superstructure ordering was investigated and discussed. Distortion scaling rules are considered to compare this work with earlier investigations on hollandites.     

Sub-micrometer sized yttrium oxide fibers prepared through hydrothermal reaction

Yttrium oxide fibers have been synthesized via hydrothermal reaction and subsequent thermal treatment using yttrium chloride as precursor. The products before and after the thermal treatment were characterized by powder X-ray diffractions (XRD), scanning electron microscopy (SEM), ion-chromatograph analysis, and thermogravimetry and differential thermal analysis (TG-DTA). The fiber diameter ranged from 100 to 300 nm, while the length was up to tens of microns. It was found that the chemical composition and morphology of the products were closely related to the pH value of reaction solution, and fibrous products could be obtained at pH 9.5-10.25. These oxide fibers exhibited outstanding high-temperature stability, which maintained their morphology at temperature up to 1400 °C.     

Synthesis, thermal stability, and oxygen intake/release characteristics of YBa(Co1−xAlx)4O7+δ

The YBaCo₄O_7+d (Y-114) phase has recently attracted interests as a potential oxygen storage material due to its oxygen intake/release capability at 200-400 °C. Nevertheless, thermal instability of Y-114 has been an obstacle for future applications, since this compound immediately starts to decompose when the sample is heated at 700-800 °C in oxygen-rich atmosphere. Here we demonstrate that Al-for-Co substitution in Y-114 drastically enhances the thermal stability. Substituting only 10 at.% of aluminum for cobalt in Y-114 essentially suppresses the decomposition reaction seen at 700-800 °C, while well retaining its remarkable oxygen intake/release capability at 200-400 °C. It is also revealed that the addition of aluminum effectively reduces the particle size. The Al-substituted Y-114 products exhibit superior oxygen intake/release response to the Al-free products upon switching the atmosphere between O₂ and N₂.     

Decomposition of (Ti2xFe1−xSb1−x)O4 solid solutions below 1673 K

The pseudo-binary TiO₂-FeSbO₄ system was investigated by means of thermogravimetric analysis below 1673 K in O₂. Rutile-type solid solutions were synthesised at 1373 K in O₂ by means of a solid state reaction between the two pure end members TiO₂ (rutile) and FeSbO₄ mixed in stoichiometric amounts. Thermal stability of the (Ti_2xFe_1−xSb_1−x)O₄ solid solution increases with rutile content; equimolar (Ti_1.00Fe_0.50Sb_0.50)O₄ solid solutions decompose at about 1673 K forming a TiO₂-enriched solid solution and FeSbO₄, that subsequently decomposes into Fe₂O₃ (hematite) and a volatile Sb oxide, probably Sb₄O₆. For compositions characterised by higher Ti content the decomposition temperature is higher than 1673 K.     

Post-synthetic treatments on NixMnxCo1 − 2x(OH)2 for the preparation of lithium metal oxides

A series of hydroxides Ni_xMn_xCo_(1−2x)(OH)₂ for x = 0.00–0.50 were prepared. These hydroxides were used as the precursors in the synthesis of electrochemical active lithiated mixed metal oxides, LiNi_xMn_xCo_{(1 − 2x)}O₂. The traditional co-precipitation method was used to synthesize the hydroxides and the effect of different post-synthetic treatments were tested. The solutions after co-precipitation of the hydroxides were heated under hydrothermal or microwave assisted hydrothermal conditions at 180 °C. All samples were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. We observed that the hydroxides undergo oxidation to an oxyhydroxide phase as the stoichiometry varies during their synthesis and with post-synthetic treatments. As the concentration of Ni and Mn increases in the sample, a mixture of both hydroxide and oxyhydroxide phases is obtained. SEM images demonstrate a sintering effect on the hydroxide particles after post-synthetic treatment, while XRD measurements on these samples show an increase in crystallinity and reduced turbostratic disorder. The oxides synthesized from these precursors demonstrate similar electrochemical performance with one another.     

Preparation of porous lanthanum phosphate with templates

Malonic acid, propionic acid, glycine, n-butylamine, and urea were added to the preparation of lanthanum phosphate from lanthanum nitrate and phosphoric acid solutions. All additives were taken into lanthanum phosphate particles. The additives that have a basic site were easy to contain in precipitates. The addition of templates improved the specific surface area of lanthanum phosphate. The amount of pore, with radius smaller than 4 nm, increased with the addition of templates. The remained additives had influence on the acidic properties of lanthanum phosphate.     

Deposition of nickel nanoparticles onto aluminum powders using a modified polyol process

Aluminum is commonly used as fuel additive for propellants. The main limitation to its use lies in comparatively slow ignition and oxidation/combustion kinetics. Combustion performance of aluminized propellants can be improved through the use of Ni-coated Al particles. Nanoparticles, with its increased reactivity, also improve combustion performance. Hence, in this work, nano-sized Ni particles coated onto commercially available micron-sized Al powders using a modified polyol process were synthesized and evaluated. Ni-coated Al powders of various compositions produced by this method showed significant improvement in the oxidation kinetics as compared to untreated Al powders. The onset oxidation temperatures for the Ni-coated Al powders were found to be significantly reduced as compared to pure untreated Al. Other than the oxides, the intermetallic compound, Al₃Ni was also detected in the 10 wt% Ni-Al powders that were heated to temperature above 1050 °C.     

Characterization of zinc carbonate hydroxides synthesized by precipitation from zinc acetate and potassium carbonate solutions

Addition of potassium carbonate solution to zinc acetate solution at room temperature causes the precipitation of a white solid, whose composition and structure depend on the initial concentrations of the reagents. Hydrozincite, Zn₅(CO₃)₂(OH)₆, forms when the K₂CO₃ concentration is low and a new K-containing zinc carbonate hydroxide phase forms when the K₂CO₃ concentration is high. The chemical formula of the new phase has been determined to be Zn(CO₃)_0.61(OH)_0.780.233K₂CO₃ by TGA, CHNO and AA analysis. The new phase is insoluble in water and extensive water washing of the new phase does not change its composition or structure, suggesting the new phase is a single phase compound salt. Exposure of the new phase to a stream of humidified CO₂ causes disproportionation to separate phases of ZnCO₃ and K₂CO₃. Pure ZnCO₃ was synthesized for comparison by a new procedure under atmospheric conditions instead of the more common hydrothermal synthesis of ZnCO₃.     

Influence of spectator ions on the reactivity of divalent metal salts in molten alkali metal nitrates: Morphology of the resulting metal oxides

This work focuses on the investigation of the reaction of alkali metal nitrates (LiNO₃, NaNO₃ and KNO₃) with divalent metal salts (Cu²⁺, Ni²⁺ and Zn²⁺). Thermogravimetric analysis (TGA) was employed to study the kinetics and mechanisms of the above reactions, which led to the formation of the corresponding metal oxides. The reaction temperature was found to depend not only on the alkali metal but also on the metal salt (MCl₂ or M(NO₃)₂) involved in the reaction.SEM observations show that the spectator ions present in the reacting medium have varying degrees of influence on the morphology of the powder; the growth directions, sizes and the homogeneity of their distribution, are modified. KNO₃ generates the most significant differences compared to LiNO₃ and NaNO₃.     

Preparation and properties of novel epoxy/graphene oxide nanosheets (GON) composites functionalized with flame retardant containing phosphorus and silicon

2-(Diphenylphosphino)ethyltriethoxy silane (DPPES) was grafted onto the surface of graphene oxide nanosheets (GON) via a condensation reaction. X-ray photoelectron spectroscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and Raman spectroscopy verify that DPPES did not only covalently bond to GON as a functionalization moiety, but partly restored its conjugated structure as a reducing agent. DPPES on graphene sheets oxide was observed by transmission electron microscopy, and contributed to the favorable dispersion of DPPES-GON in nonpolar toluene. Additionally, the flame retardancy and thermal stability of epoxy/DPPES-GON nanocomposites that contain various weight fractions of DPPES-GON were studied using the limiting oxygen index test, UL-94 test and by thermogravimetric analysis in nitrogen. The composites containing 10 wt% DPPES-GON can pass V-0 rating in UL-94 test. Adding 10 wt% DPPES-GON in epoxy greatly increased the char yield and LOI by 42% and 80%, respectively. Epoxy/DPPES-GON nanocomposites with phosphorus, silicon and graphene layer structures were found to exhibit much greater flame retardancy than neat epoxy. The synergistic effects among silicon, phosphorus and GON can improve the flame retardancy of epoxy resin.     

Oxygen vacancy ordering in strontium doped rare earth cobaltate perovskites Ln1−xSrxCoO3−δ (Ln = La, Pr and Nd; x > 0.60)

A family of Sr-doped perovskite compounds Ln_1−xSr_xCoO_3−δ (Ln = La³⁺, Pr³⁺ and Nd³⁺; x > 0.60), were prepared by sol-gel chemistry and reaction at 1100 °C under 1 atm of oxygen. This structural family has been shown to be present only for rare earth ions larger than Sm³⁺ and an upper limit of Sr²⁺ solubility in these phases was found to exist between x = 0.90 and 0.95. X-ray diffraction shows oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction reveals that oxygen vacancy ordering occurs, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln³⁺/Sr²⁺ cation ordering was observed.     

Synthesis and properties of poly(methyl methacrylate-2-acrylamido-2-methylpropane sulfonic acid)/PbS hybrid composite

The synthesis of a new hybrid composite based on PbS nanoparticles and poly(methyl methacrylate-2-acrylamido-2-methylpropane sulfonic acid) [P(MMA-AMPSA)] copolymer is reported. The chemical synthesis consists in two steps: (i) a surfactant-free emulsion copolymerization between methyl methacrylate and 2-acrylamido-2-methylpropane sulfonic acid and (ii) the generation of PbS particles in the presence of the P(MMA-AMPSA) latex, from the reaction between lead nitrate and thiourea. The composite was studied by scanning electron microscopy (SEM), X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The microstructure observed using SEM proves that the PbS nanoparticles are well dispersed in the copolymer matrix. The X-ray diffraction measurements demonstrate that the PbS nanoparticles have a cubic rock salt structure. It was also found that the inorganic semiconductor nanoparticles improve the thermal stability of the copolymer matrix.     

Synthesis and characterization of nickel ferrite magnetic nanoparticles

Nickel ferrite (NiFe₂O₄) nanoparticles are prepared by a polyvinyl alcohol (PVA) assisted sol-gel auto-combustion method. The structure, composition, morphology and magnetic properties of the gel precursor are characterized by powder XRD, FT-IR, TGA, HR-SEM, TEM, HR-TEM and VSM. XRD confirms the formation of single-phase nickel ferrite with space group of Fd3m and inverse spinel structure. The vibration properties of nanoparticles are analysed by FT-IR spectrum. The thermal decomposition of the gel precursors is investigated by TGA. HR-SEM and TEM images show that the particles have spherical shape with particle size in the range of ∼30 nm and consistent with XRD result. The magnetic properties of these nanoparticles are studied for confirming the ferromagnetic behaviour at room temperature.     

New solid acids in the triple-layer Dion-Jacobson layered perovskite family

Dion-Jacobson type layered perovskites such as A′Ca₂Nb₃O₁₀ (A′ = K, Rb, H) have continued to be of great interest due to their compositional variability, rich interlayer chemistry, and wide range of physical properties. In this study, we investigated the range and effects of substitutional doping of Ta⁵⁺ for Nb⁵⁺ and of Sr²⁺ for Ca²⁺ in A′Ca₂Nb₃O₁₀. We have prepared and characterized three new solid solutions: KCa₂Nb_3−xTa_xO₁₀, RbCa₂Nb_3−xTa_xO₁₀, and RbCa_2−xSr_xNb₃O₁₀. These materials all readily undergo proton exchange to form two new series of hydrated solid acid phases, which in most cases can be dehydrated to form stable HCa₂Nb_3−xTa_xO₁₀ and HCa_2−xSr_xNb₃O₁₀ compounds. Intercalation studies with n-hexylamine and pyridine were carried out to gauge the relative Brønsted acidities across the HCa₂Nb_3−xTa_xO₁₀ series, and we determined that materials with the highest tantalum contents are weaker acids than the parent compound HCa₂Nb₃O₁₀. Preliminary intercalation studies with pyridine for the HCa_2−xSr_xNb₃O₁₀·yH₂O solid acids, however, showed no significant difference in acidity with varying strontium content.     

Cr(VI) adsorption on functionalized amorphous and mesoporous silica from aqueous and non-aqueous media

A mesoporous silica (SBA-15) and amorphous silica (SG) have been chemically modified with 2-mercaptopyridine using the homogeneous route. This synthetic route involved the reaction of 2-mercaptopyridine with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry and elemental analysis. The solid was employed as a Cr(VI) adsorbent from aqueous and non-aqueous solutions at room temperature. The effect of several variables (stirring time, pH, metal concentration and solvent polarity) has been studied using the batch technique. The results indicate that under the optimum conditions, the maximum adsorption value for Cr(VI) was 1.83 ± 0.03 mmol/g for MP-SBA-15, whereas the adsorption capacity of the MP-SG was 0.86 ± 0.02 mmol/g. On the basis of these results, it can be concluded that it is possible to modify chemically SBA-15 and SG with 2-mercaptopyridine and to use the resulting modified silicas as effective adsorbents for Cr(VI).     

Chemical preparation, crystallographic characterization, thermal behavior and IR studies of a new cyclotriphosphate SrTlP3O9·3H2O

Chemical preparation, crystallographic characterization, thermal behavior and IR studies are given for two new cyclotriphosphates SrTlP₃O₉·3H₂O and SrTlP₃O₉. SrTlP₃O₉·3H₂O is orthorhombic, space group Pnma, with the following unit-cell dimensions: a=9.147(7) Å, b=8.180(7) Å, c=15.458(2) Å and Z=4. The total dehydration of SrTlP₃O₉·3H₂O leads between 300 and 650°C to its anhydrous form SrTlP₃O₉. SrTlP₃O₉ is monoclinic, space group P2₁/m or P2₁, with the following unit-cell dimensions: a=14.544(2) Å, b=8.639(1) Å, c=7.727(1) Å, β=102.05(1)° and Z=4. The thermal behavior has been investigated and interpreted in agreement with IR absorption spectrometry and X-ray diffraction experiments. We calculated the 30 normal frequencies of the P₃O₉ ring with Cs symmetry and proposed the interpretation of the vibrational spectrum of SrTlP₃O₉·3H₂O. The vibrations were assigned and precised to each frequency for different atoms of the ring on the basis of the results of the theoretical isotopic substitutions and in the light of the crystalline structure of the isotypic compounds, SrM^IP₃O₉·3H₂O (M^I=Rb⁺, K⁺ and NH₄⁺), of SrTlP₃O₉·3H₂O.     

Low temperature synthesis of nanocrystalline Li4Mn5O12 by a hydrothermal method

A mild hydrothermal method using Li-birnessite (Li_xMnO₂·nH₂O) ultrafine fiber as the precursor has been adopted to prepare Li₄Mn₅O₁₂, which is of interest as an electrode material for 3 V rechargeable lithium ion batteries. X-ray diffraction data reveal that the obtained powders have a pure spinel structure with a lattice constant of 8.135 Å. The scanning electron microscopy image of the obtained powders shows the particles are cubic-shaped whose average size is about 40-50 nm. The results from inductively coupled plasma-atomic emission spectroscope and wet chemical analysis indicate that a Li/Mn ratio of 0.796, and an average valence of 3.96 of Mn ion have been achieved in the as-prepared products. The thermogravimetric and differential thermal analysis data also agree with the previous reports on Li₄Mn₅O₁₂, suggesting that near stoichiometry of Li₄Mn₅O₁₂ has been synthesized by this procedure at the rather low temperature 110°C.     

Formation and structure of zinc-substituted calcium hydroxyapatite

Zn-substituted Ca hydroxyapatites were synthesized by precipitation method under the specific conditions (pH 8, 90 °C) and their structural properties were investigated. The substituting limit of Zn was estimated at about 15 mol%. The lattice parameter a decreased up to 5 mol% Zn, and started to increase over 5 mol% Zn. The lattice parameter c monotonously decreased with increase in Zn fraction. The increase in lattice parameter a for higher Zn fraction was ascribed to increasing amount of lattice H₂O which substituted for OH sites in the apatite structure. The lattice H₂O in the Zn-substituted apatites was lost by the heat treatment at 400 °C. As a result, both the lattice parameters a and c of the heat-treated apatites decreased with increasing Zn fraction. Only the difference in ionic radius between Zn²⁺ (0.074 nm) and Ca²⁺ (0.099 nm) was decisive to the change in both lattice parameters after the heat treatment at 400 °C.