Synthesis and characterization of nanocrystalline forsterite through citrate–nitrate route

Nanocrystalline forsterite, Mg₂SiO₄, powder was synthesized according to the citrate–nitrate technique using an aqueous solution of magnesium nitrate, colloidal silica, citric acid, and ammonia. The dried precursor and the powders calcined at different temperatures were characterized by X-ray diffraction (XRD), simultaneous thermal analysis (STA), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The initial crystallization temperature of forsterite was around 770 °C while fully crystallized forsterite was obtained at 860 °C with a crystallite size of about 30 nm.     

Growth temperature dependent properties of ZnO nanorod arrays on glass substrate prepared by wet chemical method

In this work, ZnO nanorod arrays were grown on glass substrate by the wet chemical method, and the effect of synthesis temperature on the properties was investigated. The grown nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman and Photoluminescence (PL) measurements. XRD pattern showed that nanorod prepared at 80 °C and 90 °C has high crystallinity with wurtzite structure and orientated along the c-axis. However, nanorods were not formed at 60 °C and 70 °C due to less energy supply for the growth of the ZnO. FE-SEM results showed that the morphology and the size of ZnO can be effectively controlled. In particular, as the temperature increased, diameter of the nanorod was increased while length decreased. Raman scattering spectra of ZnO nanorod arrays revealed the characteristic E₂^high mode that is related to the vibration of oxygen atoms in the wurtzite ZnO. Room-temperature PL spectra of the ZnO nanorods revealed a near-band-edge (NBE) emission peak. The NBE (UV light emission) band at ~383 nm might be attributed to the recombination of free exciton. The narrow full-width at half-maximum (FWHM) of the UV emission indicated that ZnO nanorods had high crystallinity.     

Development of metal oxide nanoparticles by soft chemical method

An extensive work for the study of SnO₂ samples doped with x-mol% of Sb (x = 0, 6, 10, 14 and 18) is reported. The materials were prepared by the polymeric precursor method (Pechini method), calcined for 4 h between 800 °C and 1200 °C. The Rietveld method with X-ray diffraction data (XRD) was used to analyze the unit cell dimensions, crystallite size and microstrain. It was observed the crystallite size increasing and decrease of the microstrain with the increase of the calcining temperature. The synthesis of tin oxide nanoparticles with high thermal stability against particle growth rate was achieved by doping SnO₂ particles with Sb₂O₃. All the phases tend to have the same dimension when the temperature increases, although its values varies with x and reaches the maximum value when fired at 1100 °C. These variations seem to be an indication that the oxidation state of the antimony changes with the amount of Sb added to the material.     

Pressureless sintered Al2O3–SiC nanocomposites

Al₂O₃ + 5 vol% SiC composite ceramics were prepared via a conventional powder processing route followed by pressureless sintering. Commercially available Al₂O₃ and SiC powders were milled together in an aqueous suspension. The slurry was freeze granulated, and green bodies were obtained by cold isostatic pressing of the granules. Pressureless sintering was carried out in a nitrogen atmosphere at 1750 and 1780 °C. Near full density (>99%) was achieved at 1780 °C. Densification at the lower sintering temperature was promoted by smaller additions of MgO. Vickers hardness and indentation fracture toughness varied around 18 GPa and 2.3 MPa m^1/2 after sintering at 1780 °C. Transmission electron microscopy revealed that the SiC particles were located predominantly to the interior of the matrix grains and well distributed throughout the composite microstructures. The intragranular particles had sizes in the range 50–200 nm while the intergranular particles were larger, typically 200–500 nm in diameter.     

Low temperature synthesis of nanocrystalline magnesium aluminate spinel by a soft chemical method

A new simple soft chemical method – synthesizing nanocrystalline MgAl₂O₄ spinel powder with oxalic acid as organic template and nitric acid as an oxidizing agent – is described. The method was developed with the objective of obtaining phase pure nanocrystalline MgAl₂O₄ spinel powder with uniform particle size and morphology at a much lower temperature than that used by conventional methods. The synthesized powders were characterized by X-ray diffractometry (XRD), thermogravimetry (TGA), Fourier transform infrared spectroscopy (FTIR), surface area analysis (BET) and field emission scanning electron microscopy (FE-SEM). The average crystallite size of the single phase material was 30 nm. Through this method, porous MgAl₂O₄ powder with a high surface area of 162.2 m²g⁻¹ and 141 m²g⁻¹ was obtained at 600 °C and 700 °C, respectively.     

Preparation and structure characterization of hairy nanoparticles consisting of hydrophobic core and thermosensitive hairs

Structural characterization of hairy nanoparticles consisting of poly(styrene-co-glycidyl methacrylate) (St/GMA) core and poly(NIPA-co-vinylimidazole) (NIPA/VIm) hair has been carried out by dynamic light scattering. The hairy molecules were introduced by surface graft-polymerization of a mixture of NIPA and VIm monomers to the St/GMA core particles with the hydrodynamic radius R_H of 135±10 nm. The R_H of St/GMA-core-NIPA/VIm-hair particles was R_H=360±20 nm at 20 °C, which gradually decreased to 285±10 nm by heating to 33.0 °C, and then underwent a sharp decrease to 175±10 nm by further heating to 33.8 °C. The final value went to 159±10 nm at 36 °C. This decrease in R_H is due to the shrinking transition of NIPA/VIm chain by hydrophobic association. The degree of shrinking of the hairy particles is compared with that of bulk NIPA gels from the viewpoint of geometrical constraints.     

Synthesis,characterization and magnetic properties of glass ceramics containing nanoparticles of both Ba-hexaferrite and Zn-ferrite

Differential thermal analysis, X-ray diffractometry and transmission electron microscopy were used to study the crystallization behavior of glass ribbons with a composition of 35% BaO, 35% Fe₂O₃, 20% B₂O₃ and 10% TiO₂ (mol.%). Replacement of different amounts of BaO by ZnO was studied. Heat treatment was applied at both 700 and 1000 °C for 1 h with heating rate 3 °C/min. Both Ba-hexaferrite and Zn-ferrite, with crystallite size 2–7 nm, were detected by XRD and TEM. The magnetic properties of ribbons prepared via cooling the melts between steel rollers were measured with a vibrating sample magnetometer. Magnetization saturation (Ms) was increased by increasing ZnO, while coercivity (Hci) increased by increasing BaO. Partial replacement of Ba by Zn revealed preparation of samples contains both Zn ferrite and Ba hexaferrite which give wide range for engineering application.     

Template assisted fabrication of TiO2 and WO3 nanotubes

Anodic aluminum oxide (AAO) templates with diameters of 200–500 nm were generated by anodizing a commercial aluminum (Al) substrate (99.7%) in 1 vol% phosphoric acid (H₃PO₄), with an applied voltage of 195 V. Titania and tungsten oxide nanotubes (NTs) were successfully grown on AAO template by the sol–gel process. Thermal gravimetric analyzer (TGA) curves showed that gel can be transfered to nanocrystalline particles after 19% weight loss of water molecule by evaporation. The results showed that the nanocrystalline TiO₂ NTs presented at 200 °C, and grains grew as temperature increased. At a temperature of 550 °C, the (101), (103), (004), (112), (200), (105), and (211) planes of anatase TiO₂ were detected clearly, whereas tungsten oxide NTs are amorphous after heat treatment at 200 °C or 300 °C. But the (110), (111), (002), (022), (222), and (004) planes of γ-WO₃ phase can be observed obviously after the heat treatment at 400 °C.     

Microstructure and optical properties of electrodeposited Al-doped ZnO nanosheets

This study grew A1-doped ZnO nanosheets on polycrystalline zinc foils using cathodic electrodeposition in an aqueous solution consisting of 0.02 M Zn(NO₃)₂ and 0.001 M Al(NO₃)₃ at 90 °C. The effects of the electrodepositing potential and thermal annealing on the physical properties of the Al-doped ZnO sheets were investigated. This study observed a high quality sheet-like structure of the electrodeposited Al-doped ZnO for the applied potential larger than −1.1 V, and the sheets were interconnected over the area of interest. The X-ray diffraction patterns showed that the intensity of the Bragg reflections of the electrodeposited Al-doped ZnO sheets increases with the electrodepositing potential because a larger applied potential results in the Al-doped ZnO sheets having a larger lateral dimension and thickness. However, the appearance of the Al-doped ZnO sheets becomes coarse and rough after thermal annealing at 400 °C in ambient air for 4 h. The intensity of the Bragg reflections of the Al-doped ZnO sheets was markedly increased through the thermal annealing due to the improvement of the crystalline quality of the annealed Al-doped ZnO sheets. Annealing caused a large decrease in structural defects of the Al-doped ZnO sheets electrodeposited at −1.3 V causing the sheets to exhibit a sharp photoluminescence peak at ∼380 nm.     

Lignin-based carbon fibers: Oxidative thermostabilization of kraft lignin

The thermostabilization of lignin fibers used as precursors for carbon fibers was studied at temperatures up to 340 °C at various heating rates in the presence of air. The glass transition temperature (T_g) of the thermally treated lignin varied inversely with hydrogen content and was found to be independent of heating rate or oxidation temperature. A continuous heating transformation (CHT) diagram was constructed from kinetic data and used to predict the optimum heating rate for thermostabilization; a heating rate of 0.06 °C/min or lower was required in order to maintain T_g > T during thermostabilization. Elemental and mass analyses show that carbon and hydrogen content decrease during air oxidation at constant heating rates. The hydrogen loss is sigmoidal, which is consistent with autocatalytic processes. A net increase in oxygen occurs up to 200-250 °C; at higher temperatures, oxygen is lost. Spectroscopic analyses revealed the oxidation of susceptible groups within the lignin macromolecule to ketones, phenols and possibly carboxylic acids in the early stage of the reaction; the later stage involving the loss of CO₂ and water and the formation of anhydrides and possibly esters. Slower heating rates favored oxygen gain and, consequently, higher glass transition temperatures (T_g) as opposed to faster heating rates.     

Chemical reduction of nanocrystalline CeO2

The reduction of commercial and mechanochemically processed CeO₂ powders was studied. Nanostructured CeO₂, with the crystallite size of 21 nm and the lattice distortion of 0.37%, was obtained during 60 min of milling in a high-energetic vibratory mill. X-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller method were applied to characterize the milled powders. During the thermal treatment at 1200 and 1400 °C in an argon atmosphere the nonstoichiometric CeO_2−x oxides with the defect fluorite structure were formed. Compositions of CeO_2−x oxides were determined according to its lattice parameter. The results showed that the release of oxygen, as well as the rate of reduction, was more effective in nanocrystalline then in the microcrystalline CeO₂, producing at 1200 °C CeO_1.80 and CeO_1.85 oxides, while at 1400 °C were obtained similarly, CeO_1.77 and CeO_1.78, compositions.     

Effect of ZnO–WO3 additives on sintering behavior and microwave dielectric properties of 0.95MgTiO3–0.05CaTiO3 ceramics

The effect of WO₃ addition on the phase formation, the microstructures and the microwave dielectric properties of 1 wt% ZnO doped 0.95MgTiO₃–0.05CaTiO₃ ceramics system were investigated. Formation of second phase MgTi₂O₅ could be effectively restrained through the addition of WO₃, but should be in right amount. WO₃ as additives could not only effectively lower the sintering temperature of the ceramics to 1310 °C, but also promote the densification. A dielectric constant ε_r of 20.02, a Q×f value of 62,000 (at 7 GHz), and a τ_f value of −5.1 ppm/°C were obtained for 1 wt% ZnO doped 0.95MgTiO₃–0.05CaTiO₃ ceramics with 0.5 wt% WO₃ addition sintered at 1310 °C.     

Role of interface on electrical conductivity of carbon nanotube/alumina nanocomposite

Interface of multiwalled carbon nanotube (MWCNT)/alumina (Al₂O₃) nanocomposites have been studied using TEM. At low sintering temperature (T_sin=1500 °C), a 3–5 nm thick amorphous interface region was noticed. Nanocomposite sintered at 1700 °C possessed a well-defined graphene layer coating on matrix grains as the interface between CNT and Al₂O₃. A mechanism of such layered interface formation has been proposed. No traceable chemical reaction product was observed at the interface even after sintering at 1700 °C. It was noticed that while DC electrical conductivity (σ_DC) of 1500 °C sintered 2.4 vol% MWCNT/Al₂O₃ nanocomposite was only~0.02 S/m, it raised to ~21 S/m when sintering was done at 1700 °C. Such 10³ times increase in σ_DC of present nanocomposite at a constant CNT loading was not only resulted from the exceptionally high electron mobility of CNT but the well-crystallized graphene interface on insulating type Al₂O₃ grains also significantly contributed in the overall increase of electrical performance of the nanocomposite, especially, when sintering was done at 1700 °C.     

Lyothermal synthesis of nanocrystalline BaSnO3 powders

The synthesis of BaSnO₃ powders has been investigated at lyothermal conditions (temperature of 250 °C; t = 6 h), starting from SnO₂·xH₂O and Ba(OH)₂ and methanol, ethanol, isopropanol and acetone as solvents. Among them isopropanol was found to be the most suitable medium for preparing BaSnO₃. By addition of the modifier Genapol X-080 during the processing, the BET specific surface area of the end-powder was increased by a factor of 10. The as-prepared powder consisted of BaSn(OH)₆. The thermal behavior, the crystallization behavior and the structure evolution of the powder during heating treatment have been studied with the TG–DTA–MS, XRD and FTIR. The weight loss of the as-prepared powder of about 12 wt% heated up to 1200 °C is mainly attributed to the dehydration around 260 °C which leads to the structure rearrangement and the building of the [SnO₆] octahedra. At this temperature BaSn(OH)₆ converts to an amorphous phase, from which BaSnO₃ nucleates and grows with increasing temperature. The obtained BaSnO₃ powders had a BET specific surface area of 16.56 m²/g and a primary crystallite size of 49 nm.     

Preparation of microporous sorbents from cedar nutshells and hydrolytic lignin

Carbon nutshells and hydrolytic lignin were used as starting materials for the preparation of microporous active carbons. Optimum parameters for cedar nutshell carbonization have been selected (temperature of carbonization 700-800 °C, rate of heating less than 3 °C/min) for the preparation of microporous carbons (average pore width 0.56 nm). The textural characteristics of microporous carbons made from nutshell are similar to those of a ‘Coconut’ carbon molecular sieve, but the latter has both a higher CO₂ adsorption capacity and a higher coefficient of N₂/O₂ separation. The influence of carbonization and steam-activation parameters on the microtexture and molecular-sieve properties of granular carbons made from hydrolytic lignin was also investigated. A low rate of heating (less 3 °C/min) promotes the formation of micropores with average sizes around 0.56-0.58 nm at carbonization temperature 700 °C. At the same carbonization temperature the average sizes of micropores were 0.7-0.78 nm at rates of heating more than 3 °C/min. The activation of lignin-char with steam at 800 °C resulted in the formation of active carbons with more developed micropore volume (0.3-0.35 cm³ g⁻¹) and with micropores of widths around 0.6-0.66 nm which are able to separate He from a He-CH₄ mixture. The size of the micropores was varied as a function of burn off value.     

Dependence of optical properties on doping metal, crystallite size and defect concentration of M-doped ZnO nanopowders (M = Al, Mg, Ti)

ZnO, Al-, Mg- and Ti-doped ZnO nanopowders were synthesized from CTAB-assisted oxalate intermediate by thermal decomposition method at 600 °C in air. All samples presented a hexagonal wurtzite structure. The spherical nanoparticles assembled in a porous octahedron-like shape for all samples. The size of Al-doped ZnO nanopowders increased as a function of Al ion concentration whereas the size of Mg- and Ti-doped ZnO nanopowders decreased when Mg and Ti ion concentrations were increased. The increment and reduction of their sizes can be explained by the Zener pinning effect. The E_g value of Al-doped ZnO nanopowders slightly decreased when Al ions were increased due to the crystallite size and defect concentration increased. In contrast, the E_g value of Mg- and Ti-doped ZnO nanopowders increased as a function of Mg and Ti ion concentration which can be explained by the Moss-Burstein effect.     

Synthesis and characterization of Al2O3 nanopowders by a simple chitosan-polymer complex solution route

Al₂O₃ nanopowders were synthesized by a simple chitosan-polymer complex solution route. The precursors were calcined at 800–1200 °C for 2 h in air. The prepared samples were characterized by XRD, FTIR and TEM. The results showed that for the precursors prepared with pH 3–9 γ-Al₂O₃ and δ-Al₂O₃ are the two main phases formed after calcination at 800–1000 °C. Interestingly, when the precursor prepared with pH 2 was used, α-Al₂O₃ was formed after calcination at 1000 °C, and pure α-Al₂O₃ was obtained after calcination at 1200 °C. The crystallite sizes of the prepared powders were found to be in the range of 4–49 nm, as evaluated by the XRD line broadening method. TEM investigation revealed that the Al₂O₃ nanopowders consisted of rod-like shaped particles and nanospheres with particle sizes in the range of 10–300 nm. The corresponding selected-area electron diffraction (SAED) analysis confirmed the formation of γ- and α-Al₂O₃ phases in the samples.     

Preparation and characterization of nanocrystalline La-doped ZnO powders through a mechanical milling and their optical properties

Structural and optical properties of mechanically milled La-doped ZnO powders are presented in this paper. The Zn_1−xLa_xO phase formed when x varied in a range of 0.02-0.06 and milled at 400 rpm for 20 h. The secondary La₂O₃ phase occurred with an increase of La content. The crystallite and particle size decreased as a function of La content as x = 0-0.14 due to the effect of Zener pinning and solute drag. The absorption edge shifted to a lower wavelength when La content was increased to x = 0.14 because of the size effect. The energy band gap of Zn_1−xLa_xO powders varied in a range of 2.96-3.12 eV depending on the crystallite size. The broad emission bands in a visible region centered at about 640 nm are attributed to oxygen deficiency.     

Synthesis and characterization of chlorapatite–ZnO composite nanopowders

The influence of zinc oxide content on the formation of chlorapatite-based composite nanopowders in the mechanically alloyed CaO–CaCl₂–P₂O₅–ZnO system was studied. To mechanosynthesize composite nanopowders, different amounts of hydrothermally synthesized zinc oxide nanoparticles (0–10 wt%) were mixed with ingredients and then were mechanically activated for 5 h. Results showed that in the absence of zinc oxide, high crystalline chlorapatite nanopowder was obtained after 5 h of milling. In the presence of 4 and 7 wt% zinc oxide, the main product of milling for 5 h was chlorapatite–zinc oxide composite nanopowder. On increasing the zinc oxide content to 10 wt%, composite nanopowder was not formed due to improper stoichiometric ratio of the reactants. The crystallite size, lattice strain, volume fraction of grain boundary, and crystallinity degree of the samples fluctuated significantly during the milling process. In the presence of 7 wt% zinc oxide, the crystallite size and crystallinity degree reached 51±2 nm and 79±2%, respectively. During annealing at 900 °C for 1 h, the crystallization of composite nanopowder occurred and as a result the crystallinity degree rose sharply to 96±3%. In addition, the crystallite size increased to 77±2 nm after annealing at 900 °C. According to SEM and TEM images, the composite nanopowder was composed of both ellipse-like and polygonal particles with a mean size of about 98 nm.     

Synthesis, characterization and optical properties of Zn1−xTixO nanoparticles prepared via a high-energy ball milling technique

Zn_1−xTi_xO (x = 0, 0.01, 0.03 and 0.05) nanoparticles were prepared by high-energy ball milling at 400 rpm. The milled powders were characterized by X-ray diffractometer (XRD) and the results exhibited that Ti-doped ZnO nanoparticles consisted of single phase with hexagonal structure when the mixtures of ZnO and TiO₂ powders were milled for 20 h. The crystallite size reduced as a function of the doping content and milling time from 1 to 10 h then increased after milling for 20 h and when the annealing temperature increased. The strain changed inversely to the crystallite size. A wider band-gap was obtained by increasing the doping content and annealing temperature because of a reduction in defect concentration. Both ZnO- and Ti-doped ZnO nanoparticles caused damage to S. aureus, E. coli, P. mirabilis, S. typhi and P. aeruginosa.