A New Elaboration Route by Sol-Gel Process for Cerium Doped SrHfO3 Films and Powders

We present for the first time the elaboration via sol gel route of cerium (1 mol%) doped SrHfO₃ powders and films. The sol is elaborated using hafnium and strontium ethoxides as precursors and cerium nitrate as dopant. The structure of powders and films are characterized by convergent methods: Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, Raman spectroscopy and optical measurements conducted by the prism coupling method. The powder crystallises from amorphous to pure SrHfO₃ orthorhombic perovskite phase after a 800°C heat treatment. Nevertheless HfO₂ monoclinic phase coexists with orthorhombic perovskite phase after a 1000°C heat treatment. The film is amorphous for annealing temperatures lower than 700°C and presents good waveguiding performances. The film heat-treated at 700°C exhibits a refractive index of 1.810 ± 0.001 (λ = 543.5 nm) for a thickness around 375 nm. The attenuation coefficient obtained on the 400°C heat-treated film is α = 4.0 ± 0.5 dB/cm (λ = 632.8 nm). The film starts to crystallize at 750°C into the SrHfO₃ orthorhombic phase but HfO₂ monoclinic phase is also detected after a heat treatment at 1000°C. The potentiality of sol gel Ce³⁺:SrHfO₃ powders and films for scintillation applications are investigated.     

Influence of the Conditions for Preparing LaPO<Subscript>4</Subscript>-Based Materials with Inclusions of the LaP<Subscript>3</Subscript>O<Subscript>9</Subscript> Phase on Their Thermal and Mechanical Properties

A material based on lanthanum orthophosphate LaPO₄ with inclusion of particles of lanthanum metaphosphate LaP³O₉ was synthesized. The influence of the process parameters of the synthesis on the structure and properties of the material was determined. Heat treatment of the coprecipitated lanthanum phosphates at 700°C leads to the formation of a nanopowder with the LaPO₄crystallite size of approximately 17 nm. Heat treatment of the nanopowder at temperatures from 1100 to 1500°C yields compact materials based on the LaPO₄–LaP₃O₉ system. The heat treatment of the nanopowder at 1100°C leads to a sharp decrease in the porosity of the material (to ~5%) at insignificant grain growth (200–400 nm); under these conditions, the thermal conductivity [λ(25°C) = 3.2 W m–1 K^–1], microhardness [Hv(25°C) = 4.6 ± 0.4 GPa], Young’s modulus [E(25°C) = 132 ± 9 GPa], and cracking resistance [K_1c(25°C) = 1.6 ± 0.1 MPa m^1/2] pass through maxima. The thermal expansion coefficient of the material depends on the heat treatment conditions only slightly and amounts to (8.2 ± 0.2) × 10^–6 K^–1.     

Thermal Decompositions of Pure and Mixed Manganese Carbonate and Ammonium Molybdate Tetrahydrate

The thermal decompositions of pure and mixed manganese carbonate and ammonium molybdate tetrahydrate in molar ratios of 3:1, 1:1 and1:3 were studied by DTA and TG techniques. The prepared mixed solid samples were calcined in air at 500, 750 or 1000°C and then investigated by means of an XRD technique. The results revealed that manganese carbonate decomposed in the range 300–1000°C, within termediate formation of MnO₂, Mn₂O₃ andMn₃O₄. Ammonium molybdate tetrahydrate first lost its water of crystallization on heating, and then decomposed, yielding water and ammonia. At 340°C,MoO₃ was the final product, which melts at 790°C. The thermal treatment of the mixed solids at 500, 750 or 1000°C led to solid-solid interactions between the produced oxides, with the formation of manganese molybdate. At 1000°C, Mn₂O₃ and MoO₃ were detected, due to the mutual stabilization effect of these oxides at this temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

A New Method for Producing a Nanosized γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Powder

A new method for producing a nanosized γ-Al₂O₃ powder was proposed, by which a saturated solution of aluminum oxychloride and sucrose was subjected to sequential heat treatment to 350°C to form a transient species and then to 800°C to form a nanosized γ-Al₂O₃ powder. The optimal treatment parameters were determined. Stages of the process were identified. The transient species and the nanosized γ-Al₂O₃ powder were studied.     

Study on the thermal decomposition of chrysotile asbestos

This article reports the possibility of detoxification of chrysotile asbestos through a low temperature heating and grinding treatment. The effect of thermal treatment at different temperatures in the range from 500 to 725 °C for 3 h on raw natural asbestos was characterized by thermal analysis, X-ray diffraction, and scanning electron microscopy. It was found that an isothermal treatment at 650 °C caused the complete dehydroxylation of chrysotile Mg₃Si₂O₅(OH)₄. Transformation of the dehydroxylated phase to forsterite Mg₂SiO₄ was obtained by heat treatment in the range 650–725 °C. The study of microstructure changes of heated asbestos show the destruction of characteristic fibers of chrysotile and formation of strips of forsterite. It is easily milled to pulverulent-shape material by mechanical milling in vibratory mill.     

Synthesis of Pr<Superscript>3+</Superscript> doped or Tb<Superscript>3+</Superscript>–Mg codoped CaSnO<Subscript>3</Subscript> perovskite phosphor by the polymerized complex method

Pr³⁺ doped or Tb³⁺–Mg codoped CaSnO₃ phosphor powder with perovskite structure was synthesized by the polymerized complex method. Powder samples crystallized into the perovskite phase at approximately 600 °C, which is 400 °C lower than the crystallization temperature for the solid-state reaction method. Uniform-sized powders with average particle sizes of 1–2 μm were obtained after heat treatment at 1,400 °C. Although the samples heat-treated at 600 °C did not exhibit photoluminescence, white photoluminescence of Pr³⁺ doped CaSnO₃ or green photoluminescence of Tb³⁺–Mg codoped CaSnO₃ was observed from the sample heat-treated above 800 °C. The intensity of the photoluminescence increased with increase of the heat-treatment temperature and reached a maximum for heat treatment at 1,400 °C. The maximum photoluminescence intensity for the samples prepared by the polymerized complex method was larger than those prepared by solid-state reaction method, which is probably due to the homogeneous mixing of the doped rare earth ions.     

SrSnO<Subscript>3</Subscript>:Nd obtained by the polymeric precursor method

In this work, the synthesis of Nd-doped SrSnO₃ by the polymeric precursor method, with calcination between 250 and 700 °C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 °C for SrSnO₃ and SrSn_0.99Nd_0.01O₃. For Sr_0.99Nd_0.01SnO₃, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 °C, while a XRD patterns showed a crystalline material after calcination at 250 °C.     

Influence of mechanical activation time,annealing, and Fe/O ratio on Fe3O4/Fe composites formation from Fe2O3 and Fe powders mixture

Commercially, iron (α-Fe) and hematite (α-Fe₂O₃) powders were used for the synthesis of composite powders of Fe₂O₃/Fe type by mechanical milling. Several ratios of Fe₂O₃/Fe were chosen for the composite synthesis; the atomic percent of oxygen in the starting mixtures ranged from 21 to 46 %. The Fe₂O₃/Fe composite samples with various Fe/O ratios were milled for different milling times. The milled composite samples were subjected to the heat treatments in argon up to 900 °C. During the heat treatment at temperatures that do not exceed 550 °C, Fe₃O₄/Fe composite particles are formed by the reaction between the Fe₂O₃ and Fe. Further increase of the heat treatment up to 700 °C leads to the reaction of the Fe₃O₄/Fe composite component phases, resulting thus in the formation of FeO/Fe composite. The heat treatment up to 900 °C of the Fe₂O₃/Fe leads to the formation of a composite of FeO/Fe₃O₄/Fe independent of the milling time and Fe₂O₃/Fe ratios. The onset temperatures of the Fe₃O₄ and FeO formations decrease upon increasing the milling time. Another important aspect is that, in the case of the same milling time but with a large amount of iron into the composite powder the formations temperatures of Fe₃O₄ and FeO are also decreasing. The influence of the mechanical activation time, heat treatment temperature, and Fe/O ratio on the formation of the (Fe₃O₄, FeO)/Fe composite from Fe₂O₃+Fe precursor mixtures was studied by differential scanning calorimetry and X-ray diffraction techniques.     

Effects of doping with CeO2 and calcination temperature on physicochemical properties of the NiO/Al2O3 system

The effects of doping with CeO₂ and calcination temperature on the physicochemical properties of the NiO/Al₂O₃ system have been investigated using DTA, XRD, nitrogen adsorption measurements at −196°C and decomposition of H₂O₂ at 30–50°C. The pure and variously doped solids were subjected to heat treatment at 300, 400, 700, 900 and 1000°C. The results revealed that the specific surface areas increased with increasing calcination temperature from 300 to 400°C and with doping of the system with CeO₂. The pure and variously doped solids calcined at 300 and 400°C consisted of poorly crystalline NiO dispersed on γ-Al₂O₃. Heating at 700°C resulted in formation of well crystalline NiO and γ-Al₂O₃ phases beside CeO₂ for the doped solids. Crystalline NiAl₂O₄ phase was formed starting from 900°C. The degree of crystallinity of NiAl₂O₄ increased with increasing the calcination temperature from 900 to 1000°C. An opposite effect was observed upon doping with CeO₂. The NiO/Al₂O₃ system calcined at 300 and 400°C has catalytic activity higher than individual NiO obtained at the same calcination temperatures. The catalytic activity of NiO/Al₂O₃ system increased, progressively, with increasing the amount of CeO₂ dopant and decreased with increasing the calcination temperature.     

AgNbO<Subscript>3</Subscript> ceramics synthesized by aqueous solution-gel method

AgNbO₃ powders and ceramics were prepared by aqueous solution-gel method. The phase evolution of the powders was investigated by TG/DSC and XRD. The results showed that the pure AgNbO₃ phase was obtained at 600 °C without special treatment. The sintering behavior and dielectric properties of the AgNbO₃ ceramics were also investigated. It showed the dense ceramics were obtained as lower as 925 °C, which had the excellent dielectric properties with the permittivity of 291 and dielectric loss of about 1.7% at 1 MHz. The coarse grains were observed for the sample sintered over 975 °C, and then they decreased with the sintering temperature further increasing to 1,050 °C.     

Stability constants determination of successive metal complexes by hyphenated CE‐ICPMS

The study of radionuclides speciation requires accurate evaluation of stability constants, which can be achieved by CE‐ICPMS. We have previously described a method for 1:1 metal complexes stability constants determination. In this paper, we present its extension to the case of successive complexations and its application to uranyl‐oxalate and lanthanum‐oxalate systems. Several significant steps are discussed: analytical conditions choice, mathematical treatment by non‐linear regression, ligand concentration and ionic strength corrections. The following values were obtained: at infinite dilution, log(β₁°(UO₂Oxa))=6.93±0.05, log(β₂°(UO₂(Oxa)₂^2?))=11.92±0.43 and log(β₃°(UO₂(Oxa)₃^4?))=15.11±0.12; log(β₁°(LaOxa⁺))=5.90±0.07, log(β₂°(La(Oxa)₂^?))=9.18±0.19 and log(β₃°(La(Oxa)₃^3?))=9.81±0.33. These values are in good agreement with the literature data, even though we suggest the existence of a new lanthanum‐oxalate complex: La(Oxa)₃^3?. This study confirms the suitability of CE‐ICPMS for complexation studies.     

Etude par rayons X à haute temperature des transformations polymorphiques des pérovskites LnAlO3 (Ln = élément lanthanidique)

The temperatures of phase transitions of the rare earth aluminates have been determined by high temperature X-ray diffractometry. All of the transitions are reversible and occur respectively for Rh ? C at 500°C (LaAlO₃), 1330°C (PrAlO₃), 1550°C (NdAlO₃), and 1950°C (SmAlO₃) and for O ? Rh at 770°C (SmAlO₃), 1330°C (EuAlO₃), and 1700°C (GdAlO₃). LnAlO₃ perovskites from TbAlO₃ up to LuAlO₃ are orthorhombic without any phase transition.     

Temperature factor in interaction of nanotubular magnesium hydrosilicate,Mg3Si2O5(OH)4, with titanium tetrachloride and water vapors

The conditions were found for modification of Mg₃Si₂O₅(OH)₄ nanotubes without altering their inherent chrysolite structure by calcination at 400°C, followed by treatment with TiCl₄ vapor at 150–400°C and vapor-phase hydrolysis at 400°C. The procedure for modification of Mg₃Si₂O₅(OH)₄ nanotubes can be used for the development of high-performance filtration systems, nanocontainers for storage and transportation of substances, supports for heterogeneous catalysts, and modified sorbents.     

Estimation of the conformation of 2-hydroxy-4,6-dimethylbenzophenone and 2,4,6-trimethoxybenzophenone from electronic absorption spectra and PPP LCI ca

The twisting effect of benzene rings on the electronic spectra of derivatives of benzophenone (BPh), 2-hydroxy-4,6-dimethylbenzophenone (2-OH-4,6-diCH₃BPh) and 2,4,6-trimethoxybenzophenone (2,4,6-triOCH₃BPh) has been interpreted by the PPP method. The effect of structure, protonation, ionization and interaction with proton-acceptor solvent on the twisting of aromatic rings is discussed. The following twist angles of substituted ring (θ_I) and unsubstituted ring (θ_II) in 2-OH-4,6-diCH₃BPh were found: neutral form in cyclohexane θ_I = 39°–48°, θ_II = ?30°–(?45°); neutral form in ethanol θ_I = 66°–72°, θ_II = ?30°–0°; protonized form θ_I = 64°–6°, θ_II = ?30°–0°; ionized form θ_I = 66°–74°, θ_II = ?30°–0°. In the neutral form of 2,4,6-triOCH₃PBh the substituted ring is twisted by angle θ_I ~ 70° while in the protonated form the unsubstituted ring is twisted by angle θ_II ~ 60° and the substituted one is coplanar with the CO group.     

The obtaining of NiCr2O4 nanoparticles by unconventional synthesis methods

This paper presents a study regarding the obtaining of NiCr₂O₄ by two new unconventional synthesis methods: (i) the first method is based on the formation of Cr(III) and Ni(II) carboxylate-type precursors in the redox reaction between the nitrate ion and 1,3-propanediol. The thermal decomposition of these complex combinations, at ~300 °C, leads to an oxide mixture of Cr₂O_3+x and NiO, with advanced homogeneity, small particles and high reactivity. On heating this mixture at 500 °C, Cr₂O₃ reacts with NiO to form NiCr₂O₄, which was evidenced by FT-IR and X-ray diffractometry (XRD) analysis; (ii) the second method starts from a mechanical mixture of (NH₄)₂Cr₂O₇ and Ni(NO₃)₂·6H₂O. On heating this mixture, a violent decomposition at 240 °C with formation of an oxides mixture (Cr₂O₃ + CrO₃) and NiO takes place. On thermal treatment up to 500 °C, an intermediary phase NiCrO₄ is formed, which by decomposition at ~700 °C leads to NiCr₂O₄, evidenced by FT-IR and XRD analysis. NiCr₂O₄ is formed, in both cases, starting with a temperature higher than 400 °C, when the non-stoichiometric chromium oxide (Cr₂O_3+x ) loses the oxygen excess and turns to stoichiometric chromium oxide (Cr₂O₃), which further reacts with NiO.     

Effect of alkaline earth metal dopants on the thermal decomposition of the CaCO3-SiO2 system: Part II. Formation of dicalcium silicate

Mixtures of calcium oxide (taken as carbonate) and silica in 2:1 molar ratio containing varying amounts of MgO, SrCO₃ and BaCO₃ as dopants were subjected to thermal treatment up to 1450°C. The exothermic peaks at 1200°C and above (beyond the decomposition temperature of calcium carbonate) have been examined to elucidate the phases formed. The exothermic peak at 1210°C without dopant was found to conform to the β-dicalcium silicate phase with a significant amount of free lime and cristobalite along with small amounts of the γ-C₂S phase. MgO at 0.1–1% leads to the formation of β- and γ-dicalcium silicate phases at 1420–1430°C, while 5% MgO results in the formation of the β-C₂ S phase at 1360°C. SrCO₃, in the concentration range studied, leads to the stabilization of β-C₂S, but does not lower its temperature of formation. BaCO₃ at 0.1–1% assists in the formation of the β-dicalcium silicate phase, but 5% BaO forms a mixture of β- and α'_H-C₂S phases at a lower temperature.     

Die Oxidfluoride des Niobs und Tantals

Oxidefluorides of Niobium and Tantalum The reaction of NbF₅ with SiO₂ (silica glass ampules) at 310°C or with SiO₂ (Aerosil) at 180°C always leads to NbO₂F. To the contrary the reaction with laboratory glass (Jenaer Geräteglas) at 130°C leads to NbOF₃. TaF₅ reacts in silica glass ampules at 400°C by formation of TaO₂F, however at 300°C or 260°C by formation of TaOF₃. Silica glass did not react with NbF₅ at 130°C, however Nb₂O₅ and NbF₅ gave at 130°C in silica glass ampoules NbOF₃. Similarly, TaF₅ and Ta₂O₅ or TaO₂F formed at 260°C in nickel ampoules TaOF₃. The chemical and the thermochemical behaviour of oxidefluorides have been investigated. The compounds NbOF₃ and TaOF₃ are isomorphic. Lattice constants are mentioned.     

Structural characterization of Fe/Ti oxide photocatalysts by X-ray,ESR, and Mössbauer methods

The polycrystalline solids TiO₂Fe₂O₃, with iron contents in the range 0–10 at.%, prepared by coprecipitation and by impregnation, and treated in air at temperatures in the range 500–1000°C, have been studied by X-ray, ESR, and Mössbauer methods. The TiO₂ in the samples treated at 800 and 1000°C always forms the rutile phase and the Fe³⁺ has a rather low solubility in it (～0.1 at.%). The Fe³⁺ in excess forms the antiferromagnetic pseudobrookite phase (Fe₂TiO₅). The samples treated at 500 and 650°C show a dependence on the preparation method. Those prepared by coprecipitation give at 500°C the pure anatase phase in which the Fe³⁺ has a higher solubility (≥ 1%); those prepared by impregnation give the anatase phase accompanied by a variable amount of rutile. The treatment at 650°C provokes the partial transformation of anatase to rutile and the complete development of the Fe₂TiO₅ phase. The relevance of these results to the photocatalytic properties shown by these solids for the photoreduction of dinitrogen to ammonia is discussed.     

A method for increasing the surface area of perovskite-type oxides

A method based on hydrothermal treatments is described for increasing the surface area of sintered ABO₃-type perovskite oxides. Influence of hydrothermal treatments, such as water treatment at 125–300°C under autogeneous pressure and steam treatment at 350–800°C, to low surface area (or sintered) LaCoO₃ and LaMnO₃ perovskite oxides on their surface properties (viz. surface area, crystal size and morphology and surface La/(Co or Mn) ratio) and also catalytic activity in complete combustion of methane at different temperatures (450–600°C) has been thoroughly investigated. The hydrothermal treatments result in the activation of the perovskite oxides by increasing their surface area very markedly.     

Preparation, structure, morphology, and dc and ac conductivity of the 88SiO2-6Li2O-6Nb2O5 (% mole) sol-gel derived glass-ceramics

The glass composition 88SiO₂-6Li₂O-6Nb₂O₅ (mole %) was successfully prepared by the sol-gel technique. The dried and translucent gel was heat-treated at temperatures between 500°C and 800°C. Lithium niobate crystallites, an important ferroelectric material, were detected in the gel derived glass-ceramics treated above 650°C. In the samples treated at 700 and 800°C the Li₂Si₂O₅ crystalline phase is present. The 800°C treated sample also presents the Li₃NbO₄ phase. The structure and morphology of the samples were studied by X-ray powder diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The SEM revealed that all the samples, heat-treated above 650°C, present crystallites embedded in the glass matrix. The particles detected in the 600°C treated sample are essentially amorphous, or with an incipient structure. The temperature dependence of the dc electrical conductivity (σ _dc ) shows two regions with different activation energies. The conductivity behaviour of the sample is mainly due to the mobile ion number. The ac conductivity (σ _ac ), measured at 1 kHz decreases with the rise of the treatment temperature due to the increase of the LiNbO₃ crystallites amount. The electrical behavior of the glass and glass-ceramics reflects the important role carried out by the treatment temperature in the gel-glass structure.