Structure and microstructure of combustion synthesized MgO nanoparticles and nanocrystalline MgO thin films synthesized by solution growth route

In this work we describe the synthesis, micro structure (XRD, SEM, AFM) of magnesium oxide nanoparticles and magnesium oxide thin films synthesized by urea-based combustion method and solution growth route using magnesium nitrate as the source of Mg. We used fuel-to-oxidizer ratio (Ψ) as a control parameter to investigate how lattice parameter, particle size, and micro strain vary with Ψ = 0.25–2 in the steps of 0.25. Earlier we have studied NiO as a substitutional solute in MgO (Rao KV, Sunandana (2005) Solid State Phys 50:235). The average crystalline size of MgO was estimated from the full width half maximum (Gaussian and lorentzian fits) of the X-ray diffraction peaks using Sherrer’s formula and Williamson–Hall plot. The particle size varies from 15(±0.3) nm to 60(±1.2) nm as Ψ is varied systematically. Surface areas of the MgO powders measured using BET method were used to calculate the particle size, which is comparable with the crystalline size calculated from XRD. We also calculated porosity and microstrain in the MgO nanoparticles with varying Ψ. Thin films of MgO are well characterized from XRD and AFM. The size of the particles and RMS roughness of the thin films were calculated using AFM.     

Monoclinic zirconium oxide nanostructures synthesized by a hydrothermal route

Zirconium oxide (ZrO(2)) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of rice-grain-like and fiber-like ZrO(2) nanostructures at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO(2) product is of pure monoclinic phase (m-ZrO(2)). The clear and equally spaced lattice fringes in high-resolution transmission electron microscopy (HRTEM) images and discrete spot pattern of selected area electron diffraction (SAED) confirm the high quality of the synthesized product. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of m-ZrO(2).     

Mass synthesis of nanocrystalline spinel ferrites by a polymer-pyrolysis route

Nanocrystalline MeFe₂O₄ (Me = Mn, Ni and Zn) spinel ferrites have been synthesized by polymer-pyrolysis method. The pyrolysis behaviors of the polymeric precursors prepared via in situ polymerization of metal salts and acrylic acid are analyzed by use of simultaneous thermogravimetric and differential thermal analysis (TG-DTA). Then, the structural characteristics of the products are studied by powder X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscope (TEM) and electron diffraction (ED) pattern. The results revealed that the spinel ferrites have nano-sized morphology and good crystallinity even if calcined at moderate temperature like 500 °C for 3 h. The average sizes of nanocrystalline spinel ferrites range from 10 to 30 nm with narrow size distributions. Magnetic measurements at room temperature show that Mn, Ni and Zn ferrites with the small coercivity and remanence exhibit soft magnetic behaviors. The spinel ferrites (MnFe₂O₄ and NiFe₂O₄) obtained here show higher saturation magnetization than the corresponding spinel ferrites produced by other methods such as conventional ceramic and wet chemical route.     

Gas sensing performance of nanocrystalline ZnO prepared by a simple route

The nanocrystalline powders of pure and Al³⁺-doped ZnO with hexagonal structure were prepared by a simple hydrothermal decomposition route. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and the microstructure by transmission electron microscopy (TEM). All the compositions exhibited a single phase, suggesting a formation of solid solution between Al₂O₃ and ZnO. DC electrical properties of the prepared nanoparticles were studied by DC conductivity measurements. The indirect heating structure sensors based on pure and doped ZnO as sensitive materials were fabricated on an alumna tube with Au electrodes. Gas-sensing properties of the sensor elements were measured as a function of concentration of dopant, operating temperature and concentrations of the test gases. The pure ZnO exhibited high response to NH₃ gas at an operating temperature of 200 °C. Doping of ZnO with Al³⁺ increased its response towards NH₃ and the Al³⁺-doped ZnO (3.0 wt% Al₂O₃) showed the maximum response at 175 °C. The selectivity of the sensor elements for NH₃ against different reducing gases like LPG, H₂S and H₂ was studied. The results on response and recovery time were also discussed.     

Phase transformations in nanocrystalline alloys synthesized by mechanical alloying

The effect of nanometer grain size and extensive grain boundary regions in nanocrystalline alloy systems was investigated for the chemical order-disorder, structural, precipitation, and spinodal phase transformations. The kinetic paths for approach to the chemically ordered phase from the disordered phase in FeCo-Mo alloys were observed to be the same at different temperatures due to grain boundaries acting as short-circuited diffusion paths for atom movements. The structure of Fe₃Ge was bcc for small crystallite size and the equilibrium fcc phase developed only after a critical grain size was attained. This was understood as a manifestation of the Gibbs Thomson effect. The precipitation phase transformation in Fe-Mo alloys proceeded by a rapid movement and clustering of the Mo atoms to the grain boundaries that was correlated to the size of the nano grains, and subsequent formation of the Mo rich lambda phase directly in the grain boundary regions. The composition fluctuation domains for spinodal decomposition in nanophase Fe-Cr alloys were observed to be linearly correlated to the growth of grains.     

Extremely high surface area of ordered mesoporous MCM-41 by atrane route

Silatrane synthesized from inexpensive oxide precursor, silica and TEA was used as the precursor for MCM-41 synthesis at low temperature because of its stability in aqueous solutions. Using cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB) as a template, the resulting meso-structure mimics the liquid crystal phase. Varying the surfactant concentration, ion concentration and temperature of the system, changes the structure of the liquid crystal phase, resulting in different pore structures and surface area. After heat treatment, very high surface area mesoporous silica was obtained and characterized using XRD, BET and TEM. XRD and TEM results show a clear picture of hexagonal structure. The surface area is extraordinarily high, up to more than 2400 m² g⁻¹ at a pore volume of 1.29 cm³ g⁻¹. However, the pore volume is up to 1.72 cm³ g⁻¹ when the surface area is greater than 2100 m² g⁻¹.     

Mesoporous indium oxide synthesized via a nanocasting route

The synthesis of crystalline mesoporous indium oxide by using a mesoporous carbon (CMK-3) as hard template is described. Transmission electron microscopy (TEM) exhibits the presence of mesoporous structure in our sample and the corresponding wide-angle X-ray diffraction (XRD) pattern confirmed the crystalline wall of sample. N₂ adsorption measurement exhibits the synthesized crystalline mesoporous indium oxide possesses a specific surface area of 39 m²/g and the total pore volume of 0.17 cm³/g, and the corresponding pore size distribution curve reveals the presence of a mesopore of 7.0 nm in maximum. Our work demonstrates that the maintenance of the ordered structure of carbon template is very significant for obtaining high quality replicas via the nanocasting route.     

Synthesis of nanocrystalline forsterite fiber via a chemical route

Forsterite gel fibers were drawn from acetic acid-modified viscous solutions prepared by alkoxide sol-gel processing. The crystallization behavior and microstructural evolution of the gel fibers were investigated. Besides enhancing spinnability, an appropriate amount of acetic acid also increased the intimate mixing of the condensed species, significantly reducing the crystallization temperature of forsterite, although X-ray diffraction revealed some inhomogeneity. Thermal analysis and X-ray diffraction revealed that gel fibers began crystallizing into forsterite at 550°C. Furthermore, the infrared spectra on heating gel fibers indicated that further condensation might occur between the silanol groups and the decomposition of the acetate ligand groups. On heating to 800°C, forsterite ceramic fibers exhibited nanocrystals of approximately 20-30 nm in size, and the nanocrystalline structures remained up to 1100°C; further heating to 1300°C caused grain size growth to 0.3-0.5 μm, with a dielectric constant of around 7.2±0.6, at 1 MHz.     

Characterization of Mo-Al-N nanocrystalline films synthesized by reactive magnetron sputtering

Mo-Al-N films were deposited by a dc reactive magnetron sputtering technique. The effects of N₂ partial pressure, substrate temperature, and aluminum content on the phase composition, microstructure, hardness and oxidation resistance of the films were studied. The MoAlN films as prepared are fcc Mo₂N structure where partial Mo sites were substituted by Al, and the grain size of the crystallites increased from 8 to 30 nm when the Al concentration was increased from 6% to 33%. In the Mo_0.94Al_0.06N film, the hardness can reach 29 GPa, which is much higher than that in binary Mo-N systems. The oxidation resistance temperature of Mo-Al-N film with an Al content of 6% was higher than that of Mo-N films, and with further addition of Al content, the oxidation resistance temperature increased slightly.     

Synthesis of nanocrystalline SnO2 powder by amorphous citrate route

Nanocrystalline SnO₂ has been synthesized by liquid mix technique using citric acid as the complexing agent. The tin oxide powder obtained at different calcination temperatures (773–1223 K) is characterized using powder X-ray diffraction (XRD), SEM, TEM, TG-DTG and UV spectroscopic techniques. The material obtained is nanocrystalline, having particle size in the range of 10–14 nm. The technique is cost-effective and yields the desired product at temperatures as low as 773 K.     

Deep oxidation of pollutants using gold deposited on a high surface area cobalt oxide prepared by a nanocasting route

A new acrylic anion exchanger with both tertiary and quaternary ammonium as well as ketone groups in the structural unit has been prepared by the nucleophilic substitution reaction of aminolyzed vinylacetate:acrylonitrile:divinylbenzene copolymer of porosity structure in the swelling state with 2-chloroacetone as a halogenated compound. The new compound exhibits better qualities of strong base exchange capacity than the weak base anion exchangers. The obtained acrylic anion exchanger was used to remove Cr(VI) from the aqueous solution. Batch adsorption studies have been carried out to determine the effect of contact time, concentration of hexavalent chromium in the solution and pH on the sorption capacity. The kinetic parameters were determined on the basis of the static results. The thermodynamic parameters of Cr(VI) sorption process on the anion exchanger were calculated based on the Langmuir and Freundlich isotherms. Sorption was studied in the pH range of 1.5-7 and it was found that it depends on the solution acidity. At the pH values of 3.5 and 7 the anion exchanger exhibited large values of chromium sorption capacity. The speciation of chromium was investigated in the studied pH range by the Diffuse Reflectance Spectroscopy (DRS) method. Reduction of chromium(VI) to chromium(III) under acidic conditions was observed. The performed acrylic strong base anion exchanger is superior compared to the conventional one based on the styrene:divinylbenzene matrix due to its ability for reposition of the long spacer arm for providing exchange sites, hydrophilic character of matrix, and possible hydrogen bonds provided by carbonyl functional groups.     

Structural and microstructural characterizations of nanocrystalline hydroxyapatite synthesized by mechanical alloying

Single phase nanocrystalline hydroxyapatite (HAp) powder has been synthesized by mechanical alloying the stoichiometric mixture of CaCO₃ and CaHPO₄ powders in open air at room temperature, for the first time, within 2 h of milling. Nanocrystalline hexagonal single crystals are obtained by sintering of 2 h milled sample at 500 °C. Structural and microstructural properties of as-milled and sintered powders are revealed from both the X-ray line profile analysis and transmission electron microscopy. Shape and lattice strain of nanocrystalline HAp particles are found to be anisotropic in nature. Particle size of HAp powder remains almost invariant up to 10 h of milling and there is no significant growth of nanocrystalline HAp particles after sintering at 500 °C for 3 h. Changes in lattice volume and some primary bond lengths of as-milled and sintered are critically measured, which indicate that lattice imperfections introduced into the HAp lattice during ball milling have been reduced partially after sintering the powder at elevated temperatures. We could achieve ~ 96.7% of theoretical density of HAp within 3 h by sintering the pellet of nanocrystalline powder at a lower temperature of 1000 °C. Vickers microhardness (VHN) of the uni-axially pressed (6.86 MPa) pellet of nanocrystalline HAp is 4.5 GPa at 100 gm load which is close to the VHN of bulk HAp sintered at higher temperature. The strain-hardening index (n) of the sintered pellet is found to be > 2, indicating a further increase in microhardness value at higher load.     

Photoluminescence of nanocrystalline SrMgF4 prepared by a solution chemical route

SrMgF₄ was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF₄ was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis.     

Self-assembled polyaniline nanorods synthesized by facile route of dispersion polymerization

We report the preparation of ordered polyaniline nanorod arrays by a simple method without the use of any template. The synthesis method is by a chemical route, viz. dispersion polymerization of aniline in polyvinyl alcohol. The nanorods obtained have a diameter of 100-500 nm and a length of a few micrometers. Films containing the nanorod assembly have been characterized by SEM, XRD and FTIR spectroscopy. We have also measured I-V characteristics and the temperature dependence of the conductivity of the films. We discuss the formation mechanism of the self-assembled nanostructures, the morphology of the films, and the crystallinity and the transport mechanism.     

CuS:Ni flowerlike morphologies synthesized by the solvothermal route

CuS:Ni flowerlike morphologies composed of nanosheets were fabricated by the solvothermal route with polyvinyl pyrrolidon as surfactant and ethylene glycol as solvent. The as-prepared CuS:Ni morphologies were characterized by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The size of CuS:Ni flowerlike morphologies was about 2 and 5 μm corresponding to the Ni doping concentration of 3.7 and 7.1 at.%, respectively. The thickness of the nanosheets changes with changing Ni doping. The magnetic properties of the CuS:Ni products have been investigated in detail.     

Synthesis of nanocrystalline CeAlO3 by solution-combustion route

CeAlO₃ was synthesised by a modified solution-combustion route using a mixture of urea and glycine as fuel. A trivalent oxidation state of cerium was stabilised and high-quality single phase polycrystalline CeAlO₃ was obtained by optimising the ratio of fuels. The transmission electron micrography and powder X-ray diffraction investigations showed that the particles were nanocrystalline in nature. Rietveld refinement confirmed the space group of the structure to be I4/mcm$I4/mcm$ with lattice parameters a=5.3278(1)$a=5.3278(1)$ Å, c=7.5717(3)$c=7.5717(3)$ Å. Magnetisation measurements indicated that the sample was paramagnetic up to 2 K. The susceptibility data fitted the Curie–Weiss model in the temperature range 100–300 K with _θp=−40${\theta }_p=-40$ K. The value of _μeff=2.2_μB${\mu }_{\text{eff}}=2.2{\mu }_B$ was close to that expected for a Ce³⁺ ion. The magnetic properties were comparable to that reported for single crystals indicating the high quality of CeAlO₃ prepared in the present work. The semiconducting band gap as estimated from UV–visible spectroscopy was 3.26 eV.