CHARACTERIZATION OF ZIRCONIA POWDER SYNTHESIZED VIA REVERSE MICROEMULSION PRECIPITATION

A two-reverse-microemulsion precipitation technique was applied to synthesize nanocrystalline tetragonal zirconia using H₂O solution/CTAB/hexanol as the microemulsion system. Two solutions of reverse microemulsion, one containing Zr⁴⁺ aqueous droplets and the other aqueous ammonia droplets with the same water/surfactant ratio, were prepared separately and mixed together to form a slurry of nanosized ZrO₂ precursors, which filled the matrix of the surfactant, CTAB. The precursors were recovered, calcined to form nanocrystalline zirconia powder, and then characterized by using a transmission electron microscope to determine the particle size, a scanning electron microscope to examine the microstructure of the zirconia powder, and an X-ray diffractometer to determine the crystal phase and crystallite size. It is concluded that the primary particle size of the precursor determines the transformation temperature of the precursor and the crystal structure of the calcined zirconia.     

Aqueous Co-precipitated spherical shape PbZrO3 nanopowders: Perovskite phase formation

The perovskite phase formation of nanocrystalline powder of lead zirconate (PbZrO₃, PZ) was investigated. The structure, phase formation and morphology of PZ powders were characterized using the X-ray diffraction technique (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscope (TEM) and differential scanning calorimetry (DSC). Tetragonal zirconia (t-ZrO₂) phase was found as an intermediate phase during the calcinations process, followed by the crystallization of the orthorhombic PZ phase. The change in relative amount of the residual t-ZrO₂ phase as a function of calcination temperature was estimated from the relative intensities of selected Raman peaks. From a TEM photograph, the PbZrO₃ powder was found to be spherical in shape with uniform nanosized features. The average particle size for the calcined powders was about 10.44±1.21 nm.     

Non-isothermal decomposition kinetics of nano-scale CaCO3 as a function of particle size variation

We report the synthesis of nanocrystalline calcium carbonate with varying particle sizes by precipitation techniques from an aqueous solution of calcium nitrate and sodium carbonate at controlled pH. The particle size of the carbonate powder was precisely controlled by changing the precursor concentration. The synthesized carbonate powders were characterized by using scanning electron microscopy, X-ray diffraction technique, and transmission electron microscopy. The particle size, along with the crystallite size of as-synthesized carbonate powder, decreases with increasing precursor concentration. The non-isothermal decomposition kinetics of the carbonate powder was also evaluated by using near to the modified Arrhenius equation's exact solution. The experimental results were best fitted at n = 0.5, and the one-dimensional diffusion-controlled transport process mechanism (D₁) and one-dimensional phase boundary movement mechanism (R₁) was found to be very close fit of the corresponding evaluated g(α) value. The apparent activation energy of the nano calcium carbonate decomposition was found in the range of 120–175 kJ/mol, which is also inherently functioning with the average particle size. The apparent activation energy of decomposition of CaCO₃ found to be decreased with decreasing average particle size of nanocrystalline calcium carbonate.     

Effect of calcination temperature on morphology of mesoporous YSZ

A nano-structured mesoporous yttria-stabilized zirconia (YSZ) powders were prepared for the first time using cetyltrimethylammonium bromide (CTAB) as the surfactant and urea as the hydrolyzing agent and using ZrO(NO₃)·6H₂O and Y(NO₃)₃·6H₂O as inorganic precursors. The Brunauer–Emmett–Teller (BET) surface area, Barrett–Joyner–Halender (BJH) pore size distribution and crystallite/particle size of mesoporous YSZ varied with calcine temperatures were studied. Characterizations revealed that the mesoporous YSZ powder calcined at 600 °C was weakly agglomerated and had a high surface area of 137 m²/g with an average grain size of ∼5.8 nm. It was demonstrated that the mesoporous structure remained up to 900 °C. The low-densified YSZ sample with porosity as high as 33% was prepared from mesoporous YSZ powder sintered at 1500 °C for 6 h.     

Synthesis of mesoporous nanocrystalline MgAl2O4 spinel via surfactant assisted precipitation route

In this research, mesoporous nanocrystalline MgAl₂O₄ spinel powders were synthesized with a facile synthesis method by co-precipitation route using CTAB as surfactant. The prepared samples were characterized by X-ray diffraction, N₂ adsorption, thermal gravimetric and differential thermal analyses, Fourier transform infrared spectroscopy and transmission electron microscope. The effects of surfactant to metal molar ratio on the structural properties of the samples were investigated. The obtained results showed that the sample prepared without addition of surfactant presented a lower specific surface area and bigger crystallite size compared with those obtained for the samples prepared by CTAB/metal molar ratio of 0.3. The results showed that the sample prepared by CTAB/metal molar ratio of 0.3 has the highest specific surface area and the smallest crystallite size. Moreover, the CTAB/metal molar ratio higher than 0.3 led to a decrease in the specific surface area, due to destruction of the pore walls.     

Coating organic pigment particles with hydrous alumina through direct precipitation

A novel coating process of hydrous alumina on organic pigment particles through direct precipitation in aqueous solution was developed in this work. The aqueous suspensions of organic pigment particles were prepared using cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzene sulfonate (SDBS) as additives before the coating. The organic pigment particles were then coated with hydrous alumina using Al₂(SO₄)₃ as precursor. The morphology and surface states of as-coated organic pigment particles were analyzed by high-resolution transmission electron microscopy (HRTEM) and zeta-potential. TEM images showed that a uniform hydrous alumina film could be formed on the organic pigment particle surface with anion surfactant SDBS. However, with cation surfactant CTAB, no alumina coating film was generated on the organic pigment particle surface.     

Sulfur Nanoparticles Synthesis and Characterization from H2S Gas, Using Novel Biodegradable Iron Chelates in W/O Microemulsion

Sulfur nanoparticles were synthesized from hazardous H₂S gas using novel biodegradable iron chelates in w/o microemulsion system. Fe³⁺–malic acid chelate (0.05 M aqueous solution) was studied in w/o microemulsion containing cyclohexane, Triton X-100 and n-hexanol as oil phase, surfactant, co-surfactant, respectively, for catalytic oxidation of H₂S gas at ambient conditions of temperature, pressure, and neutral pH. The structural features of sulfur nanoparticles have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), diffused reflectance infra-red Fourier transform technique, and BET surface area measurements. XRD analysis indicates the presence of α-sulfur. TEM analysis shows that the morphology of sulfur nanoparticles synthesized in w/o microemulsion system is nearly uniform in size (average particle size 10 nm) and narrow particle size distribution (in range of 5–15 nm) as compared to that in aqueous surfactant systems. The EDS analysis indicated high purity of sulfur (>99%). Moreover, sulfur nanoparticles synthesized in w/o microemulsion system exhibit higher antimicrobial activity (against bacteria, yeast, and fungi) than that of colloidal sulfur.     

Preparation of spherical nanoparticles of LaAlO3 via the reverse microemulsion process

Spherical LaAlO₃ nanoparticles in a reverse microemulsion consisting of solution (water phase), Tween-80 and Span-80 (surfactant), n-butanol (cosurfactant, and cyclohexane (oil phase) were prepared. Precursor powders and calcined powders were characterized by differential thermal analysis (DTA), thermogravimetry analysis (TG), X-ray diffraction (XRD) and transmission electron microscopy (TEM). A pure perovskite LaAlO₃ formed when the precursor hydroxides calcined at 800 °C for 2 h. The particle size was about 50 nm and the shape of the monodisperse particles is spherical. The reverse microemulsion process can dramatically lower the crystallization temperature of LaAlO₃ about 700 °C than the classical solid-state reaction method.     

Crystallization behaviour and microstructural development in ZrSiO4 and V-ZrSiO4 solid solutions from colloidal gels

Zircon and vanadium-doped zircon blue pigments were prepared by heat treatment of gel precursors. Gels with nominal compositions V_x-ZrSiO₄ with x=0.0, 0.002, 0.004, 0.02 and 0.2 were prepared by formation of a silica coating on zirconia colloidal particles previously obtained. The crystallization behavior and microstructural evolution were studied using X-ray powder diffraction (XRD), energy dispersive X-rays microanalysis (EDX), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results indicated that the vanadia loading in the precursor gels speeds up the crystallization of the vanadium-containing tetragonal zirconia solid solutions and their transformation to the monoclinic form. The overall conversion rate of gel precursors to pigmenting powders increased when the vanadia content was higher. Microstructural data revealed that the used procedure for the preparation of vanadium-zircon pigments allowed high-purity and non-agglomerated powders with controlled particle size to be obtained.     

Synthesis of spherical zirconia by precipitation between two water/Oil emulsions

Microparticles of ZrO₂ are produced by using precipitation method between two emulsion solutions. First, two solutions of stable reverse emulsion (water-in-oil) are prepared and mixed to form gelled precipitates, using normal heptane as the continuous oil phase and aqueous solutions of zirconium oxyacetate and aqueous ammonia as the suspending droplets. Through a series of operations, including distillation, filtration and washing, the dried precursors are obtained. After calcining the precursors at 750°C, ZrO₂ powder with a tetragonal structure is obtained. Principle factors that influence the emulsion stability, which subsequently affects the morphology and particle size of ZrO₂ powder, are investigated, including the type and concentration of surfactant, volume ratio of water/oil, concentration of solute in water phases, and mixing intensity and time for emulsion formation. Four kinds of anionic surfactants are put to test for emulsion stability; among them Span 40 and Span 80 are considered as suitable surfactants for producing spherical microparticles of ZrO₂, which has a size range from several hundred nanometers to micrometers depending on the synthesis conditions. ©     

Facile and highly efficient wet synthesis of nanocrystalline BiFeO3particles by reverse co-precipitation method

In this study a nanocrystalline bismuth ferrite BiFeO₃ (BFO) powder was synthesized using a novel, facile and highly efficient reverse co-precipitation method. Proposed method is also highly cost-efficient and environmentally friendly. It was demonstrated that the optimal calcination temperature for the preparation of phase-pure BFO is 400 °C, while at higher temperatures formation of undesirable crystal phases occur. X-Ray diffraction studies were employed for the investigation of crystal structure and phase composition of obtained powders. Scanning electron microscopy (SEM) was used to evaluate the morphology of synthesized powders. For piezoelectric studies, precursors powders were pressed into 12.5 mm diameter pellets and calcined at the same temperatures. Obtained materials show very good piezoelectric properties, as a result of high defects homogeneity and very low crystallite size. Determined piezoelectric coefficient is comparable with praseodymium, samarium or europium doped BiFeO₃ ceramic.     

Controllable synthesis of pure monodispersed zirconia nanopowders with tetragonal phase

Nanopowders of pure zirconia have been synthesized using citric acid (CA)-assisted lamellar liquid crystal template method. The microstructure of the zirconia powder prepared at the different mole ratios of CA to zirconium oxynitrate (ZN) was characterized by FT-IR, X-ray diffraction (XRD), laser particle size analyzer, Raman spectroscopy, and scanning electron microscope (SEM) methods. The phase structure of the sodium dodecyl sulfate (SDS)/C₁₀H₂₁OH/H₂O system before and after adding mixing solution CA and ZN was determined by POM (Polarizing Optical Microscope). The results show that lamellar structure of the SDS/C₁₀H₂₁OH/H₂O system after adding mixing solution CA and ZN is stable. The presence of CA inhibits agglomeration and growth of zirconia particle. The crystallite size of zirconia powders decreases and agglomerates lowly with addition of CA. Fourier transform infrared spectrometry (FI-IR) analyses reveal that the structure of chelating organic complex is maintained in zirconia structure at high-temperature calcination to cause oxygen vacancies which stabilizes the tetragonal phase of zirconia. The zirconia powders remained the single metastable tetragonal phase at the molar ratios of CA to ZN ranging from 1:3 to 5:1. The crystallite size of zirconia with spherical morphology varied from 32.2 to 20.1 nm with the increase of the molar ratio of CA to ZN in the range of 1:3 to 5:1.     

Preparation and characterization of a ZnO powder with the hexagonal plate particles

Zinc oxide precursors were obtained by the reaction of excess urea with 0.05-0.30 M ZnSO₄ in boiling aqueous solution. The precursors precipitated were dried at 100 °C for 2 h to yield powdery products and these products were calcined at 1000 °C for 2 h to yield zinc oxide powders. Differential thermal analysis (DTA) and thermal gravimetric analysis (TGA) curves of the air-dried precursor precipitates show that the suitable temperatures for dehydration of crystal water, of ligand water and of dehydroxylation are 76, 290, and 866 °C, respectively. From the scanning electron microscopy (SEM) photographs and particle size distribution (PSD) curves, the average sizes of the hexagonal plate particles in precursor and ZnO powders are found to be 55 and 35 μm, respectively. X-ray diffraction (XRD) data were evaluated by Scherrer equation for the estimation of the average crystal size of the precursor (11 nm) and ZnO (45 nm). The specific surface area and specific micro-mesopore volume of the ZnO powders are so small as to fall into the experimental error limits. It was concluded that all the measured quantities are not affected considerably by the Zn²⁺ concentration.     

Calcia Stabilized Ceria Doped Zirconia Nanocrystalline Ceramic

Calcia-stabilized cerium doped cubic zirconia nanocrystalline ceramic was synthesized using poly (vinyl alcohol) as a polymeric precursor. Obtained ceramic was pressed into a cylindrical pellet and sintered at 850 °C. The calcined and sintered ceramics were characterized by XRF, XRD, BET and SEM. The XRD pattern of the calcined ceramic shows that the ceramic has a face centered cubic crystal structure. The SEM results show that the grain size of the ceramic was increased after sintering. The BET surface areas were determined as 13.236 and 4.397 m² g^?1 for the calcined and sintered ceramics, respectively.     

Reverse Micelle-Mediated Synthesis and Characterization of Tricalcium Phosphate Nanopowder for Bone Graft Applications

Nanocrystalline β-tricalcium phosphate (β-TCP) powder was synthesized using reverse micelle as a template system. Cyclohexane was used as the oil phase, aqueous solutions of calcium nitrate and phosphoric acid as the aqueous phase, and poly(oxyethylene)₅ nonylphenol ether (NP-5) and/or poly(oxyethylene)₁₂ nonylphenol ether (NP-12) as the surfactants. The powder were synthesized at a fixed Ca/P molar ratio of 1.5 at a pH of 10. The synthesized powder were calcined at 800°C to obtain monophasic β-TCP. Particle size, morphology, and surface area of the synthesized powder were dependent on the chemistry of the surfactant and composition of the microemulsion. The powder were characterized using a BET surface area analyzer, powder X-ray diffraction, dynamic light scattering technique, and transmission electron microscopy. TCP nanoparticles had a particle size between 32 and 135 nm, and a BET-specific average surface area between 57 and 103 m²/g with controlled morphology. The powder were consolidated and sintered at 1250°C in a 3 kW microwave furnace in the form of a compact disk. Human osteoprecursor cells (osteoblastic precursor cell line 1 [OPC1]) were used to assess the biocompatibility of TCP disks after 1, 5, and 11 days in culture using scanning electron microscopy, MTT assay, and alkaline phosphatase expressions. Disk samples were biocompatible and showed excellent OPC1 cell adhesion, growth, and proliferation. Biocompatible β-TCP nanopowder were synthesized with controlled particle size, morphology, and surface area using a reverse micelle-mediated template system.     

Ethanol-induced formation of precursor for 8 mol% Yttria-stabilized zirconia: Towards the production of well-dispersed,easily sintering,and high-conductivity nano-powders

This study aims to prepare novel precursor powders for 8 mol% yttria-stabilized zirconia nano-powders. Precursor powders were extracted from the ethanol-water solution, which utilizes the changing solvation energy for different ions impacted by ethanol. An aqueous solution containing zirconium sulfate tetrahydrate and yttrium sulfate octahydrate was mixed with different volumes of ethanol to prepare precursor powders, then calcinating to obtain 8 mol% yttria-stabilized zirconia nano-powders. The scanning electron microscope and particle size measurements for precursor powders suggested that the ideal volume ratio between ethanol and the aqueous solution was 2.5, corresponding to the complete precipitation and well-dispersion. The X-ray diffraction measurements, crystallization kinetics calculations, and scanning electron microscope after calcinating precursor powders indicated the successful formation of 8 mol% yttria-stabilized zirconia powders and the particle growth through a one-dimensional growth mechanism in the 60–120 nm size range. The densification experiments and electrochemical performance measurements after sintering 8YSZ nano-powders showed high density and high ionic conductivity compared with commercial powders. An efficient process, successfully designed to achieve the commercial requirement, was used to prepare 8YSZ nano-powders.     

Synthesis of Lithium-Cobalt Oxide Nanoparticles by Flame Spray Pyrolysis

Crystalline LiCoO2nanoparticles were synthesized from an aqueous solution of acetate compounds of lithium and cobalt by a flame spray pyrolysis, and characterized by TEM, XRD, and BET method. We investigated the evolution of LiCoO2nanoparticles from liquid droplets sprayed along the flame and observed disintegration of aqueous precursor droplets about 10μm into smaller fragments around 50 nm in the high temperature flame, as well as decomposition/oxidation of the precursor and coalescence/coagulation. We also examined effects of process variables such as molar concentrations of the precursors and flow rates of combustible gases on the particle size and crystal structure. The average particle diameter increased with an increase in the molar concentration of the precursor. Raising the maximum flame temperature by controlling the gas flow rates also led to an increase in the average diameter of the particles. The crystalline nanoparticles synthesized were nearly spherical, and their average primary particle diameters ranged from 11 to 35 nm.     

Structure of reverse microemulsion-templated metal hexacyanoferrate nanoparticles

The droplet phase of a reverse microemulsion formed by the surfactant cetyltrimethylammonium ferrocyanide was used as a matrix to synthesize nanoparticles of nickel hexacyanoferrate by adding just a solution of NiCl₂ to the microemulsion media. Dynamic light scattering and small-angle neutron scattering measurements show that the reverse microemulsion droplets employed have a globular structure, with sizes that depend on water content. Transmission electron microscopy and electron diffraction are used to obtain information about the structure of the synthesized nanoparticles. The results show that the size and shape of the coordination compound nanoparticles correspond with the size and shape of the droplets, suggesting that the presented system constitutes an alternative method of the synthesis of metal hexacyanoferrate nanoparticles.     

Study of the process parameters in the synthesis of TiO2 nanospheres through reactive microemulsion precipitation

Spherical particles constituted by nanocrystals of titanium oxide TiO₂ have been prepared through reactive microemulsion precipitation. A water-in-oil microemulsion, added with a suitable emulsifier, has been used. The effect of the process parameters (water to oil ratio, type and amount of surfactant, concentration of precursor solution, mixing velocity) on the final characteristics has been investigated, in terms of structural phase and particle size. The titania nanopowders were characterized by means of X-ray diffraction, thermogravimetric and differential thermal analyses and scanning electron microscopy. The results obtained by different process conditions showed the development of both titania rutile and anatase spherical particles, with particle size ranging from tens to hundreds of nanometers.     

LaMgAl11O19 synthesis using non-hydrolytic sol-gel methods

Polycrystalline LaMgAl₁₁O₁₉ (LMA) was prepared by four different non-hydrolytic sol-gel methods. From stable solutions, four powder precursors containing an amorphous and nanocrystalline phase with specific reactivity were obtained. The particle size, morphology, thermal behaviour, and phase composition of the powder precursors were studied using DLS, TEM, DSC/TG and XRD. Bulk ceramic samples containing LMA were prepared at 1200?°C for 16?h and examined in terms of phase purity and microstructure using XRD, SEM, and TEM. Raman spectroscopy of pure LMA was used to study the structure in detail. A mechanism of LMA formation and a relation between powder precursor properties and final phase composition is proposed. These findings may be useful for designing modern technologies for fabrication of LMA for optical or protective coating applications.