Role of graphene in structural transformation of zirconium oxide

Fine powders of zirconium oxide (ZrO₂) were prepared using zirconium oxychloride by combustion method. The crystalline size of pure ZrO₂ was in range of 14–45 nm. Graphene was incorporated in ZrO₂ using graphene oxide as precursor and reducing it with hydrazine hydrate. X-Ray diffraction, Fourier transform infra-red spectroscopy, thermogravimetric analysis and Raman spectroscopy methods were used to characterize the samples. The role of graphene in structural transformation of ZrO₂ to monoclinic phase was clearly observed.     

The Synthesis,Characterization and DC Electrical Conductivity of Polypyrrole‐Zirconium Complex

Polypyrrole‐zirconium complex has been synthesized by reacting 2‐amino‐3,4‐dicyano‐5‐mercaptopyrrole with zirconium nitrate in absolute ethanol under reflux for 24 h. The product has been characterized by elemental analyses, FTIR spectroscopy, in addition to thermal analysis (TGA and DSC) and its solubility has been investigated. The DC electrical conductivity variation of polypyrrole‐zirconium complex has been studied in the temperature range 300–500 K after annealing for 24 h at 100°C and doping with I₂, FeCl₃ and CuCl₂ · H₂O for comparison. An attempt has been made to interpret the DC electrical conductivity behavior and thermal properties to chain length, dopant used, polymer structure and attached groups.     

Phase transformation and crystalline growth of 4 mol% yttria partially stabilized zirconia

The phase transformation and crystalline growth of 4 mol% yttria partially stabilized zirconia (4Y-PSZ) precursor powders have been investigated using the coprecipitation route, using zirconium oxide chloride octahydrate (ZrOCl₂·8H₂O) and yttrium nitrate (Y(NO₃)₃·6H₂O) as the initial materials. Differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED), and high resolution TEM (HRTEM) were utilized to characterize the behavior of phase transformation and crystalline growth of the 4Y-PSZ precursor powders after calcined. Tetragonal ZrO₂ crystallization occurred at about 718.2 K. The activation energy of tetragonal ZrO₂ crystallization was 227.0 ± 17.4 kJ/mol, obtained by a non-isothermal method. The growth morphology parameter (n) and growth mechanism index were close to 2.0, showing that tetragonal ZrO₂ had a plate-like morphology. The crystalline size of tetragonal ZrO₂ increased from 7.9 to 27.6 nm when the calcination temperature was increased from 973 to 1,273 K. The activation energies of tetragonal ZrO₂ growth were 14.97 ± 0.33 and 84.46 ± 6.65 kJ/mol when precursor powders after calcined from 723–973 and 973–1,273 K, respectively.     

Synthesis of submicrometer zirconium carbide formed from inorganic–organic hybrid precursor pyrolysis

Zirconium carbide (ZrC) was synthesized from inorganic–organic hybrid precursor’s pyrolysis by solution-based processing. Zirconium-containing complexes, which were obtained by chelation of oxide bidentate ligands to zirconium, were used to combine with phenolic resin to form precursors for ZrC. The precursors using specific ligands including acetylacetone, ethyleneglycol, and salicylic acid transformed into pure ZrC at a relatively low temperature (1,550 °C) in addition to that using lactic acid. As a comparison, synthesis of ZrC only using zirconium oxychloride octahydrate (ZrOCl₂·8H₂O) and phenolic resin was also conducted. The synthesized powders had a small average crystallite size (~300 nm), and a low oxygen content (~2.5 at.%). The conversions from as-synthesized preceramic precursors to ceramics were studied by means of FTIR, SEM, EDS, XRD, and XPS. The oxidation behavior of the synthesized ZrC in air was studied by DSC-TG analysis.     

Preparation and microstructure of sol-gel derived silver-doped silica

Silver-doped silica was prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) in the presence of a silver nitrate (AgNO₃) solution by two different synthesis methods. In the first synthesis route, sol-gel mixtures were prepared using an acid catalyst. In the second synthesis route, silver-doped silica gels were formed by two-step acid/base catalysis. For the same concentration of silver dopant [AgNO₃]/[TEOS] = 0.015 acid-catalyzed sol-gel formed a microporous silica with an average pore size of <25 Å whereas the two-step catalyzed silica had an average pore size of 250 Å and exhibited a mesoporous structure when fully dried. The differences in the pore size affected the silver particle formation mechanism and post-calcination silver particle size. After calcination at 800 °C for 2 h the acid-catalyzed silica contained metallic silver particles size with an average particle size of 24 ± 2 nm whereas two-step catalyzed silica with the same concentration of [AgNO₃]/[TEOS] = 0.015 contained silver nanoparticles with an average size of approximately 32 ± 2 nm. Mechanisms for silver particle formation and for silica matrix crystallization with respect to the processing route and calcination temperature are discussed.     

Characterization and luminescence properties of Gd2O3 phosphor

Gd₂O₃ phosphor was synthesized by combustion synthesis using gadolinium nitrate hexahydrate as precursor and urea as fuel. Structural and surface morphology were studied by X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Chemical composition analysis of the phosphor was performed by Fourier-transform infrared spectroscopy, and tts optical properties were characterized by use of photoluminescence (PL) and thermoluminescence (TL) techniques. In PL spectra, feeble emission at 490 nm (blue) and intense emission at approximately 545 nm (green) are observed after excitation at 300 nm. TL measurement was performed on the Gd₂O₃ phosphor by irradiating it with γ-rays (1 kGy). A well resolved glow peak at 226.4 °C was observed. Kinetic data were estimated from the TL glow curve by use of Chen’s peak-shape method; the results are discussed in detail. The average particle size of the Gd₂O₃ phosphor was 41 nm; a monoclinic phase was formed at a firing temperature of 500 °C. This was in agreement with SEM and TEM results.     

Sonochemical synthesis and characterization of nano-sized zirconium(IV) complex: new precursor for the preparation of pure monoclinic and tetragonal zirconia nanoparticles

In this study, synthesis and characterization of two polymorphs of a new nano-sized zirconium(IV) complex, [ZrO(dmph)I₂] (1), {dmph = 2,9-dimethyl-1,10-phenanthroline (neocuproine)}, have been investigated in two different solvents. The reaction between zirconyl nitrate pentahydrate and potassium iodide with dmph as a ligand under ultrasonic irradiation in methanol and mono-ethylene glycol (MEG) leads to the formation of the nano-sized Zr(IV) complex. Characterization of the Zr(IV) complex has been performed using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and elemental analysis. The thermal stability of the compound 1 has been studied by thermal gravimetric and differential thermal analyses. Particle sizes of the compound 1 have been decreased after thermal treatments in an autoclave. Pure monoclinic (m) and tetragonal (t) zirconia (ZrO₂) nanoparticles were readily synthesized from thermal decomposition of the Zr(IV) complex as a new precursor in presence of methanol and MEG as solvents, respectively. Zirconium oxide was characterized by FT-IR, XRD, and SEM to depict the phase and morphology. The results showed that, pure zirconia was produced with particle size about 59 nm and crystal system was monoclinic when methanol was used as a solvent during complexation process. On the other hand, particle sizes of zirconia with tetragonal structure were significantly reduced to about 39 nm, when MEG was used as solvent.     

A zirconium Schiff base complex immobilized on starch-coated maghemite nanoparticles catalyzes heterogeneous condensation of 1,2-diamines with 1,2-dicarbonyl compounds

A magnetically separable zirconium Schiff base nanocatalyst was synthesized under ultrasonic agitation. TEM images revealed a uniform spherical particle shape with average size of 10–14 nm for the as-prepared catalyst. The catalytic performance of ZrOL₂@SMNP in the heterogeneous condensation of various 1,2-diamines and 1,2-dicarbonyls for the synthesis of heterocyclic compounds in ethanol has been explored.     

Deposition of silver nanoparticles into porous system of sol–gel silica monoliths and properties of silver/porous silica composites

Porous monolithic gels based on silica with pore size from 16 nm to 3–5 μm have been synthesized using sol–gel technology. Parameters of porous structure are determined by the components molar ratio in the reaction mixture. The reduction processes of silver ions by formamide in the synthesized porous gel were studied. It has been shown that at the initial stage of the reaction, silver particles with size up to 10 nm are formed in the absence of any stabilizers. The composites Ag/SiO₂ were synthesized by means of the threefold impregnation of porous monoliths using the solution of silver nitrate in the mixture of methanol and formamide. Their catalytic activity in the CO oxidation was studied. It was discovered that after activation in oxygen and hydrogen the samples display a low temperature activity, which depends on the number of Si–O-nonbridging oxygen groups on the surface of silica porous monoliths.     

Light scattering studies to determine molecular weight of freshly prepared Zr(IV) hydrous polymer

In the present work, Zr(IV) has been taken as a homologue for Pu(IV) in order to study the behaviour of Pu in aqueous systems. The direct detection of polymerization of tetravalent zirconium and determination of molecular weight of freshly prepared Zr(IV) polymer was performed by using dynamic light scattering device. Experiments were conducted at 4 different concentrations of zirconium prepared in 1 M nitric acid at 298 K. Particle diameter d ₅₀ was estimated as 255 nm. Differential refractive index increment was also measured. The molecular weight of freshly prepared Zr(IV) polymer was determined as 1,610 Da and second virial coefficient A ₂ = ?0.0106 ml g^?1 Da by using Debye plot showing that Zr(IV) can undergo hydrolysis even under strongly acidic conditions leading to the formation of high molecular weight hydrated polymers.     

Thermal and structural studies of zinc zirconate nanoscale composite derived from sol–gel process

In the present investigation, a novel synthetic zinc zirconate nanocomposites were prepared by a sol–gel technique using a very stable sol containing zirconium acetylacetonate, zinc acetate, monoethanolamine, and 1,3-propanediol as chelating agent. Thermal analysis results indicated that the decomposition of zinc zirconate precursors occurred at 225 and 234 °C. The influence of thermal annealing (temperatures and duration) on their structural properties has been studied by means of X-ray diffraction and Fourier transform-infrared spectroscopy techniques. The results indicated that a higher percent of zinc zirconate is formed at 800 °C and reached maximum at 1,000 °C in 120 min. The morphology, composition, and bandgap properties of zinc zirconate nanoparticles were characterized by transmission electron microscope, scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy, and ultraviolet diffiuse reflectance. The SEM observation showed that average grain size of zinc zirconate nanopowders was 58 nm. The optical results revealed maximum absorbances at 394, 413, and 438 nm for ZnZrO₃ sample annealed at 400, 800, and 900 °C for 30 min, respectively. This is an indication that the nanopowder can absorb lights in the higher wavelength.     

Synthesis of zirconium diboride nano-powders by novel complex sol–gel technology at low temperature

Zirconium diboride nano-powders were synthesized by novel complex sol–gel technology at low temperature. Zirconium oxychloride as source of zirconium was complexed via adding propylene oxide that could form the stable zirconium sol by protonation and ring-opening reactions and boric acid as source of boron was dissolved effectively using glycerol that acted as complexing agent to create the boron network through forming stable coordination compound. Additionally, glycerol could be carbonized as source of carbon, which could replace the conventional carbon source additives. Then the mixed sols were gelated, dried, and exposed to 1,450 °C for 2 h with flowing argon in the furnace. High purity of ZrB₂ nano-powders with spherical shape of ca. 200 nm were synthesized via carbothermal reduction. The mechanism of two complexing agents were discussed combining with the infrared spectroscopy analysis results, and the powder characteristics were performed by using X-ray diffraction and transmission electron microscopy.     

Sol–gel synthesis,optical and structural characterization of ZrOS nanopowder

In this paper, we report the synthesis of tetragonal zirconium oxysulfide t-ZrOS nanopowder by the sol–gel method using water solution of a precursor containing thiourea [CS(NH₂)₂] and zirconium in the form of an anionic oxalate complex [Zr(C₂O₄)]^4?. The tetragonal t-ZrOS structure with space group P4/nmm revealed by X-ray patterns showed preferred orientation along (101) plane. For surface morphology, compositional and optical absorption studies, scanning electron microscopy, energy dispersive X-ray and ultraviolet–visible spectroscopy were employed for characterization of the powder respectively. A nearly constant value of the refractive index at higher wavelength λ ≥ 1,100 nm was found to be 2.19. High indirect and direct optical band gap of ~2.0 and 2.50 eV with absorbance <40 % were obtained for the powder.     

Sol–gel combustion synthesis and characterization of nanostructure copper chromite spinel

Nanocomposite copper chromite spinel was fabricated by sol–gel process using copper nitrate trihydrate, chromium nitrate nonahydrate, ethylene glycol, diethyl ether, and citric acid. The thermoanalytical measurements (TG–DTG), X-ray powder diffractometry (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray analysis were used to characterize the structural and the chemical features of the nanocomposites. TG–DTG results showed that the major mass loss for copper(II) nitrate, chromium(III) nitrate as precursors occur at 258 and 140 °C, respectively. The major mass loss for dried gel of copper chromite occurs at 310 °C. XRD data revealed the formation of pure copper chromite after thermal decomposition at 1,000 °C for 2 h. The observation of XRD patterns reveals the presence of single-phase tetragonal spinel CuCr₂O₄. FESEM analysis of calcined composite was found to be in the range of 20–30 nm.     

Carbothermal synthesis of ultra-fine zirconium carbide powders using inorganic precursors via sol–gel method

Ultra-fine zirconium carbide (ZrC) powders have been synthesized by carbothermal reduction reactions using inorganic precursors zirconium oxychloride (ZrOCl₂ · 8H₂O) as sources of zirconium and phenolic resin as the carbon source. The reactions were substantially completed at relatively lower temperatures (∼1400 °C/1 h) and the synthesized powders had a small average crystallite size (<200 nm) and a large specific area (54 m²/g). The oxygen content of the powder synthesized at 1400 °C/1 h was less than 1.0 wt%. The thermodynamic change process in the ZrO₂–C system and the synthesis mechanism were studied.     

Synthesis of La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> by thermal treatment of mechanically activated salt mixture

A lanthanum zirconate La₂Zr₂O₇ was synthesized by soft mechanochemical method using zirconium oxynitrate ZrO(NO₃)₂·6H₂O and lanthanum carbonate La₂(CO₃)₃·8H₂O as reagents. Mechanical activation of the reagents was carried out in a centrifugal planetary ball mill. The processes occurring during calcination of the jointly and the separately mechanically activated salt mixture were studied using DSC, TG coupled with mass spectrometry, XRD analysis, and FTIR spectroscopy. It was shown that in the course of joint mechanical activation in the mill alongside with intimate mixing of the reagents and their amorphization exchange reaction occurred, producing lanthanum nitrate, basic lanthanum nitrate, basic zirconium carbonate, and hydrated zirconium oxide. The DSC curve of the jointly mechanically activated salt mixture showed a strong exothermic peak at 878 °C which was not associated with mass loss. This peak was attributed to La₂Zr₂O₇ crystallization in agreement with XRD data. Nanocrystalline lanthanum zirconate synthesized by annealing of the jointly mechanically activated salt mixture was characterized using XRD analysis, scanning, and transmission electron microscopy.     

Macroporous zirconia particles prepared by subcritical water in batch and flow processes

Porous zirconia particles were synthesized through a low-temperature hydrothermal synthesis process. Under hydrothermal conditions, water can control the direction of crystal growth, morphology, particle size, and size distribution because thermodynamics and transport properties can be controlled by pressure and temperature. In a batch process, the hydrothermal synthesis was conducted at 200–300 °C and 30 MPa with an SUS-304 tube as the reactor. At the same reaction pressure, experiments were also performed for a flow process with temperatures of 180–200 °C. The synthesized products were calcined and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results showed that the macroporous zirconia particles that were formed had pore diameters around 419 nm. The XRD pattern indicated that the products were composed of zirconium oxide particles with monoclinic, tetragonal, and cubic structures.     

Size-Controlled Synthesis of Palladium Nanoparticles

Palladium nanoparticles protected by PVP were obtained first by reducing PdCl₂ with NaBH₄ solution. Then different size palladium nanoparticles with a large size range (1.49 nm ～ 23.26 nm) were prepared by the multi-step reduction of PdCl₂ by hydrogen adsorbed on the surface of palladium nanoparticles. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to characterize the nanoparticles. The increasing value of average diameter from the first to the eighth reduction reaction is about 0.58 nm, from the ninth to the fifteenth reduction reaction the value is about 2.44 nm.     

Use of ultra-filtration in organic-rich groundwater for the physical separation of thorium

During this work, size fractionation technique “ultra filtration” is used in physical speciation of thorium in organic rich groundwater. Laboratory simulated experiments were carried out to study the physical speciation of thorium in aquatic environment having elevated level of dissolved humus material classified as dissolved organic carbon (DOC). Samples were collected from organic rich environment having DOC in the range of 50–60 µg mL^?1. Th(IV) ions are extremely particle reactive having K _d value of the order of 10^5–6, hence to avoid adsorption on suspended particulate matter, spiking of the solution with Th(NO₃)₄ was carried out in ground water samples after filtering through 450 nm pore size using suction filtration. Particles in dissolved state (colloids) ranging between <450 and >220 nm were separated using suction filtration assembly having a membrane with a pore diameter of 220 nm. Thereafter, solution was sequentially passed through the ultra-filtration membranes having pore diameters of 14 nm [300 k NMWL (nominal molecular weight limit)], 3.1 nm (50 k NMWL), 2.2 nm (30 k NMWL), 1.6 nm (10 k NMWL) and 1.1 nm (0.5 k NMWL) by using “Stirred Ultra-filtration Cells”, operating in concentration mode. Thorium has only one stable oxidation state i.e. IV, under all redox conditions in natural waters and therefore, its speciation is dominated by its interaction with various fractions of DOC. Experimental results show 50–60 % of the spiked Th is in association with fraction enriched with particles of 10 k NMWL (1.6 nm) followed by fraction enriched with particle of 0.5 k NMWL and <220 nm.     

Characterization of metal oxide-doped lutetium orthoferrite powders from the pigmentary point of view

This thesis deals with the preparation and characterization of inorganic pigments based on perovskite structure of metal oxide-doped LuFeO₃. Powder samples were prepared by the conventional ceramic method, i.e., solid-state reaction. Heating temperature was chosen according to results of TG/DTA. Prepared pigments were incorporated into an organic binder system, and their color properties were evaluated by measuring the reflectance in the visible region of light. The most interesting color properties were obtained by preparation of sample Lu_0.98Ca_0.02FeO_3?δ with mineralizer LiF at the temperature 900 °C. Mean size of its particles is 4 μm. X-ray diffraction analysis confirmed a single-phase orthorhombic structure with lattice parameters a = 0.521310 nm, b = 0.55535 nm, and c = 0.75626 nm. Thermal stability of the sample is limited by the temperature of 1,150 °C. Further, the effectiveness of other metal oxide (CoO-, ZnO-, Bi₂O₃-, and Sb₂O₃)-doped Lu_0.98Ca_0.02FeO_3?δ system was evaluated with respect to their phase composition, thermal stability, particle size distribution, and color properties. The conclusions of the research showed that a sample containing antimony oxide is the mixture with the best pigmentary-application properties. The powder has a clear orange color, high thermal stability up to 1,340 °C, and mean particle size 4 μm.