Effect of powder dispersion on sintering behavior and mechanical properties of nanostructured 3YSZ ceramics

The aim of this work was to investigate the feasibility of producing dense nanostructured ceramics from commercial zirconia nanopowder by colloidal processing. Our study has demonstrated the adverse effect of the presence of aggregates in the production of nanostructured components. Two techniques were employed to remove aggregates – centrifugation and high energy milling. The finer powder thus produced by centrifugation and/or high energy milling, with an average size of particles around 60–70 nm was consolidated into a green body by a relatively simple low pressure filtration technique (300 kPa). It was possible to prepare green bodies of 47% density with relatively fine and uniform size pores from suspensions containing these powders. The green compacts obtained from finer powder could be sintered to fully dense nanostructured products at a significantly lower temperature (1200 °C) with a soaking period of 0.5 h only with an average grain size of 90 nm only in the sintered compact. In contrast the as received aggregated powder could not be sintered at all to full density even at as high temperature as 1600 °C. The bulk nanostructured 3 mol% yttria stabilized zirconia (3YSZ) compact with an average grain size of 110 nm exhibited Vickers hardness of 12.8 GPa, which is comparable to the available results in the literature.     

Self-assembly hydrothermal assisted synthesis of mesoporous anatase in the presence of ethylene glycol

Mesoporous nanocrystalline anatase was prepared hydrothermally employing P123 as structure-directing agent. Ethylene glycol was used as a key synthesis parameter to fine tune the morphology, crystal size and pore size of the resultant mesophases. The incorporation of EG in the synthesis gel resulted in the formation of 1–2 μm sphere-like shapes and led to an increase in the specific surface area from ∼95 to ∼170 m²/g, decrease in the average pore size from ∼11 to ∼4.8 nm, and decrease in the average crystallite size from ∼17 to ∼12 nm. These mesophases were used as photocatalysts for the UV degradation of methylene blue and methyl orange. The mesoporous anatase phases photodegraded MB ∼1.5–3× faster than commercially available P25 and showed limited photocatalytic behavior for methyl orange.     

Controllable synthesis of mesoporous alumina with large surface area for high and fast fluoride removal

Gamma phase of mesoporous alumina (MA) with large surface area was successfully synthesized by a facile hydrothermal method followed by thermal treatment for fluoride removal. The as-synthesized MA nanoparticles with average size of 20 nm–150 nm have ordered wormhole-like mesoporous structure. The pore size is 5 nm with a narrow distribution, and the specific surface area reaches 357 m² g⁻¹ while the bulk density is 0.45 cm³ g⁻¹. Glucose as a small-molecule template plays an important role on the morphology, surface area and pore diameter of the MA. As an ionic adsorbent for fluoride removal, the maximum adsorption capacity of MA is 8.25 mg g⁻¹, and the remove efficiency reaches 90% in several minutes at pH of 3. The Langmuir equilibrium model is found to be suitable for describing the fluoride sorption on MA and the adsorption behavior follows the pseudo-second-order equation well with a correlation coefficient larger than 0.99. The larger surface area and relatively narrow pore size of MA are believed to be responsible for improving the adsorption efficiency for fluoride in aqueous solution.     

Facile corrosion synthesis and sintering of disperse pure tetragonal zirconia nanoparticles

Disperse pure tetragonal zirconia (t-ZrO₂) nanoparticles smaller than 10 nm are essential for preparation of structural and functional zirconia materials, but syntheses of t-ZrO₂ nanoparticles using inorganic zirconium salts usually result in severe agglomeration. In this paper, we report a hydrothermal corrosion approach for improving the dispersity of t-ZrO₂ nanoparticles synthesized by precipitation using zirconium oxychloride without any surfactants. Disperse pure t-ZrO₂ nanoparticles with average sizes of 4.5 and 6 nm and size distributions of 2–11 and 3–12 nm were obtained by calcining precipitates at 400 °C for 2 h and 500 °C for 0.5 h followed by HCl corrosion at 120 °C for 75 h, respectively. Disperse t-ZrO₂ nanoparticles with an average size of 6 nm and a size distribution of 3–12 nm were pressed into green compacts at 500 MPa and sintered by two-step sintering (heating to 1150 °C without hold and decreasing to 1000 °C with a 10 h hold). The sintered bodies are dense pure monoclinic ZrO₂ nanocrystalline ceramic with a relative density of 99.9% and an average grain size of 110 nm.     

Preparation and hierarchical porous structure of biomorphic woodceramics from sugarcane bagasse

Biomorphic woodceramics with controllable pore structure were prepared from sugarcane bagasse impregnated with epoxy resin followed by sintering at different temperatures. The phase composition, chemical composition, morphology and pore texture of the products were characterized by XRD, FTIR, SEM, mercury porosimetry and N₂ adsorption. The biomorphic woodceramics are typical non-graphitizable carbon and display a hierarchical porous structure from micrometer (0.6–21 μm) to nanometer scale (3.1–9.3 nm). The woodceramics retain the tubular structures of sugarcane bagasse before calcination at 1100 °C. Furthermore, an increase in the sintering temperature results in the decrease of BET surface area, average pore diameter and pore volume in the mesopore scale. This work provides a simple, economical, and environmentally friendly method for the production of hierarchical porous woodceramics. The final products have their potential applications as adsorbents, catalyst supports and filters.     

A study on the photoluminescence properties of electrospray deposited amorphous and crystalline nanostructured ZnO thin films

Transparent amorphous and crystalline nanostructured zinc oxide (ZnO) thin films were prepared by electrospray deposition technique on a glass substrate at 250 °C using zinc nitrate and ammonia as the precursors. The structural morphology and optical properties of the thin films were evaluated and also the effect of formation rate of basic generating species on the morphology of the thin films was discussed. Optical studies indicated that all of the thin films have a near band edge emission at 374 nm and a band gap of 3.32 eV. In addition, the films have an emission at 393 nm corresponding to ultra violet (UV) transmittance. However, the amorphous thin films have oxygen trap peak at 430 nm and two green transmittance peaks at 485 nm and 530 nm which are absent in the 0.1 molar nanostructured sample. The crystallite size of the thin films which calculated from XRD patterns via Debye–Scherrer's formula was around 30 nm.     

Particle size effect of starting SiC on processing,microstructures and mechanical properties of liquid phase-sintered SiC

Dense SiC (97.3–99.2% relative density) of 1.1–3.5 μm average grain size was prepared by the combination of colloidal processing of bimodal SiC particles with sintering additives (Al₂O₃ plus Y₂O₃, 2–4 vol%) and subsequent hot-pressing at 1900–1950 °C. The fracture toughness of SiC was sensitive to the grain boundary thickness which was controlled by grain size and amount of oxide additives. A maximum fracture toughness (6.2 MPa m^1/2) was measured at 20 nm of grain boundary thickness. The mixing of 30 nm SiC (25 vol%) with 800 nm SiC (75 vol%) was effective to reduce the flaw size of fracture origin, in addition to a high fracture toughness, leading to the increase of flexural strength. However, the processing of a mixture of 30 nm SiC (25 vol%)–330 nm SiC (75 vol%) provided too small grains (1.1 μm average grain size), resultant thin grain boundaries (12 nm), decreased fracture toughness, and relatively large defect of fracture origin, resulting in the decreased strength.     

The effect of TiO2 particle size on the characteristics of Au–Pd/TiO2 catalysts

The nanocrystalline TiO₂ materials with average crystallite sizes of 9 and 15 nm were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO₂ catalysts. The average size of Au–Pd alloy particles increased slightly from sub-nano (< 1 nm) to 2–3 nm with increasing TiO₂ crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H₂ 1 bar, 30 °C). The exertion of electronic modification of Pd by Au–Pd alloy formation depended on the TiO₂ crystallite size in which it was more pronounced for Au/Pd on the larger TiO₂ (15 nm) than on the smaller one (9 nm), resulting in higher hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.     

Effective Pd/C catalyst for chlorobenzene and hexachlorobenzene hydrodechlorination by direct pyrolysis of sawdust impregnated with palladium nitrate

Two Pd/C catalysts were prepared by pyrolysis of Pd(NO₃)₂ impregnated sawdust. At equal pyrolysis time slow ramping with shorter isothermal heating resulted in 0.9 wt.% Pd/C-S1 sample comprising carbon support with some oxygen-containing moieties and Pd⁰ with 2.6 nm average particle size (APS) partially decorated with carbon shell, whereas fast temperature ramping and long isothermal heating provided 0.6 wt.% Pd/C-S2 containing Pd⁰ with 3.7 nm APS, with larger fraction of carbon decorated particles. Pd/C-S1 is slightly more efficient than Pd/C-S2 in gas phase chlorobenzene hydrodechlorination to benzene at 100–250 °C. Only Pd/C-S1 provides hexachlorobenzene hydrodechlorination in liquid phase due to lower APS and probably smaller PdC_x content.     

Nucleation and growth of ZnO nanorods on the ZnO-coated seed surface by solution chemical method

ZnO nanorods on ZnO-coated seed surfaces were fabricated by solution chemical method using supersaturated (ZnNO₃)₂/NaOH at 70 °C. The seed surfaces were coated on glass substrates by sol–gel processing, and their texture was dominated by heating temperatures, cooling styles and layer thickness per dipping. The effects of the seed surface on the morphology of the resultant nanorods were primarily discussed. The orientation and morphology of both the seed surface and successive nanorods were analyzed by using XRD and SEM. It is proved that when the seed size increases from 15 to 50 nm with temperature increasing, the average diameter of the resultant nanorods increase from 25 to 50 nm, with a length of 800 nm after growing for 1.5 h. The seed surface prepared by heating at 300–400 °C, fast cooling or drawing at lower speed has better orientation and few surface defects, which leads to higher density of nuclei on the seed surface and thus to the optimal preferred crystal growth of ZnO rods standing perpendicular onto substrates.     

Micronization of ketoprofen by the rapid expansion of supercritical solution process

The particle size of the pharmaceutical substances is important for their bioavailability (the percentage of the drug absorbed compared to its initial dosage). The absorption rate can be increased by reducing particle size of the drug particles. This study was conducted to investigate the effects of the extraction pressure (140–220 bar), extraction temperature (308–338 K), nozzle length (2–15 mm), effective nozzle diameter (450–1700 μm), and collection distance (1–10 cm) on the size and morphology of the precipitated ketoprofen particles. The characterization (size and morphology) of the particles was investigated using scanning electron microscopy (SEM). The average particle size of the original material was 115.42 μm, while the average particle size of the micronized particles is between 0.35 and 7.03 μm near to quisi-spherical, needle and irregular shape depending upon the experimental conditions.     

Synthesis and physicochemical characterizations of nanostructured Pd/carbon-clinoptilolite-CeO2 catalyst for abatement of xylene from waste gas streams at low temperature

Xylene removal from waste gas streams was carried out via catalytic oxidation over Pd/carbon-clinoptilolite-CeO₂. The synthesized samples were characterized by XRD, FESEM, BET, FTIR and TG techniques. The XRD patterns confirmed the formation of nano ceria with an average crystallite size of 11.6 nm. FESEM results indicated a good morphology for prepared carbon with deep pores, confirmed structure modification of zeolite, and showed that nanocatalyst has nanometric particles with an average size of 60.85 nm. Reaction data illustrated 98% abatement of xylene at 250 °C. The stability test of catalyst demonstrated that the removal efficiency has remained constant for 1200 min.     

Effect of atomization methods on the size and morphology of Gd0.1Ce0.9O2−δ powder synthesized by aerosol flame synthesis

Nano-sized gadolinium doped ceria (GDC) powders were successfully synthesized by aerosol flame deposition (AFD) with two different atomization methods; ultrasonic and electrostatic atomization. The effect of the atomization method on the size and morphology of GDC particles were investigated. It was observed that the diameter range of the GDC small primary particles synthesized by the ultrasonic atomization method was 10–50 nm while with the electrostatic method was 5–25 nm. In addition, the size of primary large particle found to be decreased from 200 nm to 50 nm with increasing electric field up to 15 kV. The GDC powder synthesized by the electrostatic atomization exhibited reduced crystallite size, particle size, and similar electrical conductivity compared to GDC powder synthesized by ultrasonic atomization. This work demonstrated the benefits of the electrostatic atomization for producing smaller-sized GDC nanopowders for the application in intermediate temperature solid oxide fuel cells.     

Grain size effect on electromechanical properties and non-linear response of dense nano and microstructured PIN–PT ceramics

Nanopowders of 0.63Pb(In_1/2Nb_1/2)O₃–0.37PbTiO₃ were synthesized by solid state reaction using the continuous attrition milling followed by high-energy ball milling techniques in air at room temperature. After milling for 8 h nanopowders of 20–30 nm grain size are obtained. Sintering by hot pressing of PIN–37PT green pellets leads to dense ceramics with average grain size varying from 100 nm to 1 μm. The dielectric and piezoelectric properties of PIN–37PT nanostructured ceramics with grain size bigger than about 160 nm remain roughly unchanged and comparable to those of microstructured ceramics. In addition, the stability of the permittivity and dielectric losses under high ac electric field grows when the grain size decreases. The material becomes less non-linear with decreasing grain size. This result is attractive for acoustic transducer applications.     

Spectrophotometric studies of photo-induced degradation of Tertrodirect Light Blue (TLB) using a nanostructure zinc zirconate composite

Zinc zirconate nanopowder (ZZN) photocatalyst was prepared by sol–gel method using zinc acetate and zirconium acetylacetonate as precursors. The optimal calcination temperature was 800 °C and ZnZrO₃ phase was formed. The structural and morphology properties of the nanocomposite were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and ultraviolet visible diffuse reflectance (UV-DRS). The SEM observation for ZZN showed the average grain size of 26 nm. UV–vis diffuse reflectance spectra (DRS) of the nanocomposite showed an absorption edge at 355 nm. The catalytic activity of ZZN was investigated by degradation of Tertrodirect Light Blue (TLB) dye in water using UV–vis spectroscopy (UV–vis) with an initial concentration of 20 mg/L dye. The influence of the catalyst concentration, time of irradiation and pH on photodegradation of dye was investigated. The results showed that degradation of TLB dye can be conducted in the photocatalytic process. Accordingly, a degradation of more than 97% of dye was achieved by applying the optimal operational parameters with 30 mg/L of catalyst, pH 9 at 1 h irradiation.     

Grazing-incidence small-angle X-ray scattering study on ultrananocrystalline diamond films

In this work, an ultrananocrystalline diamond film was studied with grazing-incidence small-angle X-ray scattering (GISAXS) to determine the diamond grain size and average distance of the grains with a non-destructive method and with excellent sampling statistics. The measured 2D GISAXS patterns were modelled with the assumption of monodisperse spheres. The best fits were obtained with the "buried layer" model where the spheres are correlated within the film plane. This correlation was approximated with a two-dimensional Percus–Yevick structure factor. The average diamond grain size of D = 8.0–8.5 nm and a centre-to-centre distance of the grains with 10.4–11.9 nm agrees well with transmission electron microscopy results of comparable samples.     

Characterization and X-ray peak broadening analysis in PZT nanoparticles prepared by modified sol–gel method

Lead zirconate titanate nanoparticles (PZT-NPs) were synthesized by a modified sol–gel method and were calcinated at temperatures of 600, 650 and 700 °C. Fourier transform infrared (FTIR), powder X-ray diffraction (XRD) and thermal analysis (TGA/DTA), indicate that single-phase perovskite PZT-NPs are obtained after heat treatment at a temperature of 650 °C. The TEM results obtained from the PZT-NPs confirm that the morphology of the PZT nanoparticles is spherical, with an average diameter size of 17 nm. We also investigated the crystallite development in the nanostructured PZT by X-ray peak broadening analysis. The individual contribution of many small crystallite sizes and lattice strains to the peak broadening in the PZT nanoparticles prepared at different temperatures were studied using Williamson–Hall (W–H) analysis in the range of 2θ = 15–80°.     

Onion-like carbon-encapsulated Co,Ni, and Fe magnetic nanoparticles with low cytotoxicity synthesized by a pulsed plasma in a liquid

We synthesized onion-like carbon-encapsulated Co, Ni, and Fe (Co–C, Ni–C, and Fe–C) magnetic nanoparticles with low cytotoxicity using pulsed plasma in a liquid. The pulsed plasma is induced by a low-voltage spark discharge submerged in a dielectric liquid. The face-centered cubic Co and Ni, and body-centered cubic Fe core nanoparticles showed good crystalline structures with an average size between 20 and 30 nm were encapsulated in onion-like carbon coatings with a thickness of 2–10 nm. Vibrating-sample magnetometer measurements revealed the ferromagnetic properties of as-synthesized samples at room temperature (Co–C = 360 Oe, Fe–C = 380 Oe, and Ni–C = 211 Oe). Raman-spectroscopy analysis found onion-like carbon shells composed of well-organized graphitic structures. Thermal gravimetric analysis showed a high stability of the as-synthesized samples under thermal treatment and oxidation. Cytotoxicity measurements showed higher cancer cell viability than samples synthesized by different methods.     

Photoluminescent carbon nanoparticles produced by confined combustion of aromatic compounds

We report new photoluminescent carbon nanoparticles having an average particle size of 50 nm. When dispersed in chloroform and excited with 325 nm wavelength, the solution showed strong photoluminescence at 475 nm with 12–13% quantum yield. A well dispersed photoluminescent solution can also be prepared with ethanol, xylene or hexane using the nanoparticles. The nanoparticles were prepared by a simple confined combustion of an aromatic compound such as benzene, toluene, xylene or a mixture thereof in air.     

Preparation of nanocrystalline SrTiO3 powder by sol–gel combustion method

In this research a sol–gel combustion route has been presented to synthesize strontium titanate (SrTiO₃:ST) nanocrystalline, using citric acid as fuel. The synthesis procedure was optimized by systematically varying the molar ratios of total metal nitrate to citric acid (MN:CA) from 1:1 to 1:3. The effect was investigated through XRD, SEM and TEM analysis. Analysis of XRD spectrum shows the complete of SrTiO₃ nanocrystalline, however, a minor phase of SrCO₃ impurity was found. Hence, an acid treatment process, with 1 mol/l HNO₃ solution and deionized water, was applied to remove the impurity. The results show that the appropriate condition to prepare the single phase nanocrystalline SrTiO₃ powders is MN:CA molar ratio of 1:3, coupled with an acid treatment process and at the lower calcination temperature of 500 °C. The particle size of powders was in nanometer ranges. The average crystallite size calculated from FWHM was about 23 nm. Morphology of powders was identified by SEM analysis. However, TEM estimated the average particle size about 7.5 nm after applying an acid treatment technique at 600 °C.