Natural fuel assisted synthesis of Mg–Cu ferrite nanoparticles: Evaluation of structural,dielectric, magnetic and humidity sensing properties

The effects of lemon juice and annealing treatment on phase composition, vibrational modes, microstructural and dielectric behavior of Mg doped copper ferrite nanoparticles have been synthesized and analyzed in detail in this present work. The various characterization techniques are used to examine the phase, microstructural, vibrational and dielectric nature of the samples at different annealing temperatures (600 °C and 900 °C). The phase and microstructure of Mg substituted CuFe₂O₄ nanoparticles have been analyzed by XRD, SEM and TEM. The secondary phase peaks free XRD spectra revealed that the as burst and the annealed Mg–CuFe₂O₄ nanoparticles have single phase cubic spinel structure. The average crystallite size of the as burnt, annealed 600 °C and annealed 900 °C of as prepared nanoparticles are calculated as 8.9 nm, 12.8 nm and 31.6 nm respectively. Another verification of the spherical shaped particle's size was confirmed by TEM analysis and it found as average size of 28.7 nm, this result is well matched with XRD analysis. The effect of size with impact of annealing treatment on magnetic and dielectric properties also analyzed. The size-dependent Mg–CuFe₂O₄ nanostructures exhibit promising sensing properties which ensure them as a potential candidate for humidity sensor applications. The as-burnt and annealed samples both show a humidity response over the humid range of 10–95 %RH. The sample annealed at 900 °C has the highest average sensor response (6.02 MΩ/%RH) among the as-burnt sample (6.38 MΩ/%RH) and annealed sample at 600 °C (7.11 MΩ/%RH).     

Sintering of Colloidal Ru/γ-Al2O3 Catalyst in Hydrogen

Colloidal 5.1 wt% Ru/γ-Al₂O₃ catalyst was prepared by a microwave assisted, solvothermal reduction of RuCl₃ in ethylene glycol in the presence of γ-Al₂O₃. The catalyst subjected to heat-treatment in hydrogen up to 700 °C, was characterized by BET, XRD, TEM and H₂ chemisorption. As-prepared catalyst contained Ru nanoparticles with mean size of 1.5 nm and narrow size distribution uniformly distributed over the support. The nanoparticles were stable on the alumina to 500 °C, but treatment at 600–700 °C caused some sintering of Ru due to migration and coalescence of a part of smallest ruthenium nanoparticles. However, even after H₂ treatment at 700 °C, large amount of Ru nanoparticles with sizes of 1–3 nm remained in the catalyst. H₂ chemisorption data revealed decrease of Ru dispersion from 0.28 to 0.19 by hydrogen treatment at 700 °C and were in good correspondence with TEM results. On the contrary, mean crystallite sizes obtained from XRD were strongly overestimated.     

Phase content,tetragonality, and crystallite size of nanoscaled barium titanate synthesized by the catecholate process: effect of calcination temperature

A modified catecholate process has been applied to synthesize high purity barium titanate powders in the submicron range. A barium titanium-catechol complex, Ba[Ti(C₆H₄O₂)₃] was prepared from TiCl₄, C₆H₄(OH)₂ and BaCO₃, freeze-dried, and calcined for 3 h at temperatures between 600 and 1300 °C. Phase transformation and crystallite size of the calcined powders were investigated as a function of the calcination temperature by X-ray diffraction methods, and particle morphology and size were studied by scanning electron microscopy. With increasing calcination temperature, BaTiO₃ transformed from the (pseudo)cubic to the ferroelectric tetragonal phase. The tetragonality (c/a-1) increases with increasing calcination temperature and increasing crystallite size, respectively. Higher temperatures clearly favoured particle growth and the formation of large and hard agglomerates. The crystallite size of the tetragonal phase increased from <60 nm at 600–800 °C to 1237±344 nm at 1300 °C.     

Annealing impact on the structural and optical properties of electrospun SnO2 nanofibers for TCOs

Tin oxide (SnO₂) nanofibers were fabricated by electrospinning technique and subsequent annealed at different temperatures. The structure, morphology and optical properties of the annealed samples were characterized by X-ray diffraction (XRD), Raman, scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR),and optical absorption techniques. The phase of SnO₂ of all samples is rutile (tetragonal), and at higher annealing temperatures, good crystallinity and lower absorption were obtained. Annealing of the samples at 600 °C caused the lower absorption and higher optical band gap, and the decrease of the absorption was probably because the fiber structure changed from solid to hollow structure. From PL spectra, it was observed that the SnO₂ hollow nanofibers annealed at 600 °C revealed green emission at 530 nm.     

The effect of pre-annealing and post-annealing on the transparency of MgAl2O4, prepared by slip casting and spark plasma sintering (SPS)

The aim of this paper is to investigate the effect of slip casting process and the annealing before and after sintering to achieve a transparent MgAl₂O₄. To remove contaminants such as carbon from the structure of shaped spinel bodies, at first, the samples were annealed at temperature of 800?°C, 900?°C and 1000?°C for 2?h and then sintered at 1400?°C. By annealing the sample before sintering at 900?°C, the transmission increased (15% at IR region and 10% at visible region). Although by annealing the samples, the amount of carbon contamination reduced. Annealing the samples after sintering also had some desirable results. The samples annealed at temperature of 1200?°C for a time of 3, 5 and 10?h. The darkness of samples reduced due to the removal of carbon impurities and the sample was annealed at 1200?°C for 5?h had the most transparency in the visible and infrared regions.     

Size Controlling of L1<Subscript>0</Subscript>-FePt Nanoparticles During High Temperature Annealing on the Surface of Carbon Nanotubes

Mono-size FePt nanoparticles with particles size about 2.5 nm have been prepared by polyol method on the surface of carbon nanotubes (CNTs). The CNTs functinalization time and the mass ratio of nanoparticles to CNTs affects on the CNTs surface coating. The as-synthesis nanocomposites have a superparamagnetic behavior with chemically disordered fcc structure at room temperature and they can be transformed into chemically ordered fct structure after thermal annealing above 600 °C. Their magnetic behavior changes from the superparamagnetic to the ferromagnetic with a large coercivity up to 0.83 T for the nanocomposites which annealed at 800 °C. The CNTs surfaces as a substrate prevent the agglomeration of nanoparticles during high temperature annealing and the FePt nanoparticles after annealing at 800 °C have finite size with an average about 10 nm. The structure, composition and magnetic properties of nanocomposite were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometer.     

Luminescent and structural properties of manganese-doped zinc aluminate spinel nanocrystals

Manganese-doped zinc aluminate spinel (ZnAl₂O₄:Mn; Mn=0–6.0 mol%) phosphor nanoparticles were prepared by the sol–gel process. The effects of thermal annealing and dopant concentration on the structure, microstructure and luminescence of the powder phosphors were investigated. The X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) results confirmed that a single-phase spinel started to crystallize at around 600 °C for the investigated powders. On heating at 600–1200 °C, the powders had the average crystallite sizes of around 12–33 nm. The crystallite size and lattice constant increased as the doping level of Mn increased. FT-IR spectra exhibited only absorption bands of the AlO₆ octahedral groups, which suggested that the powder phosphors mainly crystallized in a normal spinel structure. Scanning electron microscopy (SEM) investigations showed the primary particle sizes were around 20–25 nm for the powders annealed at 1000 °C, and less than ca. 50 nm for those annealed at 1200 °C. Photoluminescence (PL) spectra under UV or visible light excitation exhibited a strong green emission band centered at 510 nm, corresponding to the typical ⁴T₁(⁴G)—⁶A₁(⁶S) transition of tetrahedral Mn²⁺ ions. The most intense PL emission was obtained by exciting at 458 nm. The PL intensity was significantly enhanced by the improved crystallinity and diminished OH^? groups. Optimum brightness occurred at a doping of 3.0 mol% Mn.     

Preparation and characterization of nanocrystalline and mesoporous strontium titanate thin films at room temperature

The low temperature perovskite-type strontium titanate (SrTiO₃) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol–gel route. The prepared sol had a narrow particle size distribution with hydrodynamic diameter of about 17 nm. X-ray diffraction (XRD) revealed that the synthesized powders had a perovskite-SrTiO₃ structure with preferable orientation growth along the (1 0 0) direction. TEM images showed that the average crystallite size of the powders annealed in the range 300–800°C was around 8 nm. FE-SEM analysis and AFM images revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 25 nm at 600°C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 92–75 m²/g at 400–600°C. One of the smallest crystallite sizes and one of the highest surface areas reported in the literature were obtained, which can be used in many applications, such as photocatalysts.     

Samarium doped hafnium oxide cubic and monoclinic nanometric powders synthesized by hydrothermal route

Hafnium oxide nanoparticles doped with trivalent samarium (HfO₂:Sm³⁺) were synthesized by hydrothermal route from chloride reagents. Different samarium doping concentrations (0, 0.5, 1, 3, 5 and 10?at% with respect to Hf) and different post-annealing temperatures (200, 400, 600, 800 and 1000?°C) were evaluated. The resulting nanoparticles showed an oval morphology with average sizes below 30?nm. A sensitive relationship between the samarium concentration and the resulting crystal structure of the material was observed by X-Ray diffraction and further evidenced by the cathodoluminescence and photoluminescence spectra. Low concentrations of samarium (0, 0.5 and 1?at%) generated a monoclinic phase, whereas higher concentrations of samarium (5 and 10?at%) generated a metastable cubic phase. The average crystallite sizes calculated by the Scherrer's equation were close to 8?nm and 12?nm for cubic and monoclinic phases, respectively. The luminescent emission corresponded to the characteristic 4f-4f transitions of the samarium ion with a principal peak centered at 610?nm. The best luminescent properties were obtained with the sample doped with samarium at 0.5?at%, annealed at 600?°C.     

Structural and magnetic properties of CoFe2O4 nanopowders,prepared using a modified Pechini method

Cobalt ferrite nanopowders were synthesized by means of the sol-gel method, using citric acid as a chelating agent, and various alcohols as gelling agent: ethanol (ET), ethylene glycol (EG), polyvinyl alcohol (PVA), 1,3 propanediol (PD) and a mixture of PVA and EG. The simultaneous TG/DTA analysis revealed different thermal behaviours of the synthesized gels, depending on the gelling agent. The powders obtained at 500 °C and annealed at 700 °C and 1000 °C contain a single CoFe₂O₄ phase. Scanning electron microscopy (SEM) revealed the influence of the gelling agent on the morphology of cobalt ferrite particles. The coercivity and the saturation magnetization of the powders obtained at 500 °C showed a strong dependence on the crystallite size, determined by the nature of the gelling agent.     

Effects of annealing temperature on the phase formation,optical, photoluminescence and magnetic properties of sol-gel YFeO3 films

YFeO₃ (YFO) thin films were deposited onto quartz substrates via sol-gel spin-coating technique and annealed at different temperature ranged between 650 and 900 °C. The impact of annealing temperature on the phase formation, microstructural, optical, photoluminescence (PL) and magnetic properties of the films were systematically investigated. X-ray diffraction analysis revealed an amorphous structure in film annealed at 650 °C and formation of hexagonal-YFO (h-YFO) phase in films annealed at 750–800 °C. The films annealed at 850–900 °C exhibited an orthorhombic-YFO (o-YFO) structure. Atomic force microscopy images of h-YFO films showed homogeneous surface with uniform particles size and shape. The particle size increased and had irregular shape in o-YFO films. The average particle size was 44 and 117 nm, while the root square roughness was 1.38 and 2.55 nm for h- and o-YFO films annealed at 750 and 850 °C, respectively. The optical band gap (E_g) was 2.53 and 2.86 eV for h- and o-YFO films annealed at 750 and 850 °C, respectively. The PL spectra of h-YFO films were red-shifted compared with that of o-YFO films. The PL emission related to near band edge was observed at 459.0 and 441.9 nm for h- and o-YFO films annealed at 750 and 850 °C, respectively. The magnetization was enhanced with the increasing of annealing temperature and has the value of 4.8 and 12.5 emu/cm³ at 5000 Oe for h- and o-YFO films annealed at 750 and 850 °C, respectively.     

Influence of Catalyst Pretreatments on Propane Oxidation Over Ru/γ-Al2O3

The influence of different treatments (in H₂ or in O₂ at 250 or 600 °C) of alumina supported Ru catalysts on the total oxidation of propane was investigated. Ruthenium catalysts were prepared using RuCl₃ as metal precursor and characterized by H₂ chemisorption, O₂ uptake, BET, XRD and TEM. The presence of chloride on the catalyst surface was found to exert an inhibiting effect on the activity of Ru. The reduced Ru/γ-Al₂O₃ catalysts after partial removing chlorine ions were more active than the same samples oxidized at 250 °C. The higher activity of the reduced Ru/γ-Al₂O₃ catalysts was attributed to the presence of a large amount of active sites on small Ru _x O _y clusters without well defined stoichiometry or on a poorly ordered layer of a ruthenium oxide on the larger Ru particles. The formation of highly dispersed, but in some extent crystallized RuO₂ phase in catalysts oxidized at 250 °C, leads to slightly lower activity of the Ru phase. Strong decline of the activity was found for catalysts oxidized at 600 °C. At this temperature, the Ru particles were completely oxidized to well-crystallized RuO₂ oxide, and the mean crystallite size of the Ru oxide phase was much higher (9–25 nm) than that of after oxidation at 250 °C (~4 nm). The effect of the regeneration treatment in H₂ on the activity of the Ru/γ-Al₂O₃ catalysts was also studied. The active ruthenium species for propane oxidation were discussed based on the catalytic and characterization data both before and after activity tests.     

Temperature Stability and Photocatalytic Activity of Nanocrystalline Cristobalite Powders with Cu Dopant

The SiO₂ nanoparticles doped by 10 % mol Cu were prepared via a sol-gel method under process control. The effects of doping and calcination temperature on the structural and photo-catalytic properties of SiO₂ nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis absorption spectroscopy. Cristobalite and tridymite crystalline phases were found at a calcinations temperature range of 900～1200 °C and amorphous phase was formed at a temperature of 800 °C for doped SiO₂. The photocatalyst activity was evaluated by photocatalytic degradation kinetics of aqueous methyl orange (MO) under visible radiation. The results show that the photocatalytic activity of the 10 % mol Cu doped SiO₂ nanopowders have a larger degradation efficiency than pure SiO₂ under visible light at 900 °C temperature.     

Silica-coated nanocrystalline TiO2 with improved thermal stability

Deposition of a SiO₂ coating on anatase TiO₂ nanocrystals is shown to improve their thermal stability. As low as 0.5% Si was shown to preserve the small anatase crystallite size after calcination at 600?°C. Such treatment led to considerable sintering of TiO₂ nanocrystals without the silica with the average particle size growth from 9 to 50?nm, surface area decrease from 135 to 22?m²/g and partial anatase conversion to rutile. The phase composition, crystallite size, and surface area of 5%Si-TiO₂ samples were largely preserved till the temperatures as high as 800?°C whereas the anatase phase was mostly stably even after calcination at 1000?°C. The phase transformation from anatase to rutile in xerogel TiO₂ and TiO₂@SiO₂ samples apparently did not occur until the crystallites grew larger than the critical size about 50?nm. Electron-acceptor sites capable of ionizing perylene to its radical cations were observed on all samples with anatase crystalline structure. So, the silica shell deposition improves the TiO₂ thermal stability without limiting access to the surface active sites.     

Microstructure evolution during reactive sintering of Y3Al5O12:Nd3+ transparent ceramics: Influence of green body annealing

The effect of green bodies’ mesostructure on the porosity, optical properties and laser performance of reactive sintered Y₃Al₅O₁₂:Nd³⁺ transparent ceramics was studied. Only minor changes in microstructure were revealed for green bodies without annealing and those annealed at 600, 800, 1000 °C, while average pore size increases to 140 nm for sample annealed at 1200 °C. Y₃Al₅O₁₂:Nd³⁺ ceramics sintered at 1750 °C for 10 hours possess significant differences in the final porosity, optical and laser characteristics. Despite all green bodies exhibit a similar phase evolution and sintering behavior on heating, the differences appear in the final stage, when the latest percentage of porosity is removed. The green bodies annealed at 600 °C have an optimal mesostructure from the standpoint of uniform densification. Y₃Al₅O₁₂:Nd³⁺ ceramics prepared using these green bodies exhibit porosity ≤0.001 vol% and yield efficient laser emission at 1.06 μm with slope efficiency as high as 67% in quasi-continuous pumping at 807 nm.     

Synthesis and characterization of tetragonal / monoclinic mixed phases nanozirconia powders

Mixed phases nanozirconia was synthesized using the sol-gel process in different basic pH. Calcination was performed at 700 °C for 1 and 2 h. The synthesis process and characterization of the nanoparticles were studied by TGA, DTA, FTIR, XRD, FE-SEM and UV–visible. The presence of stable monoclinic and meta-stable tetragonal phases was confirmed by X-ray diffraction patterns for synthesized powders. As pH increased, the amount of tetragonal phase and crystallite size is increased and decreased, respectively. Also, due to the increase of calcination time, the amount of tetragonal phase and crystallite size increased. Micrographs confirmed that the particle shape is semi-spherical after calcination. Moreover, the size of zirconia nanoparticles decreased to 29.8 and 32.9%, as pH increased from 8 to 10 for samples with 1 and 2 h calcination time, respectively. The lowest particle size, 19.3 nm, is related to the sample that was synthesized at pH 10 and calcined at 700 °C for 1 h. UV analysis showed that by increasing the amount of pH, the amount of absorption and the band gap decreased and increased, respectively.     

Effect of surfactant in a modified sol on the physicochemical properties and photocatalytic activity of crystalline TiO<Subscript>2</Subscript> nanoparticles

This study describes the effect of amphiphilic organic molecules (surfactants) in a sol on the physicochemical properties and photocatalytic activity of crystalline TiO₂ nanoparticles prepared via a simple sol–gel route at high temperatures from 400 to 800 °C. Addition of polyoxyethylenesorbitan surfactant and polyethylene oxide and polypropylene oxide triblock copolymer as particle size inhibitors and pore directing agents into a stable titania sol affected the physicochemical properties of TiO₂ nanoparticles such as their crystallographic structure, morphology, and defect structure. With the addition of the surfactants, the ratio of anatase and rutile crystal phases of TiO₂ was controlled and an active anatase crystal phase was maintained during heat treatment up to 800 °C. Decrease in the sintering rate and inhibition in crystal growth were also observed, which resulted in higher surface area and inhibition of crystallite aggregation. Bulk defects in TiO₂ were reduced while surface defects were increased as a result of the addition of surfactants. These physicochemical properties of TiO₂ nanoparticles were correlated with photocatalytic degradation of 4-chlorophenol in water. The results revealed that high crystallinity, anatase crystal phase, high specific surface area, surface defects, and segregated morphology of TiO₂ nanoparticles, which were induced by the addition of surfactants, were more advantageous for enhancing photocatalytic destruction of the model organic compound tested in the study.     

Synthesis, magnetic and optical properties of core/shell Co1-xZnxFe2O4/SiO2 nanoparticles

The optical properties of multi-functionalized cobalt ferrite (CoFe₂O₄), cobalt zinc ferrite (Co_0.5Zn_0.5Fe₂O₄), and zinc ferrite (ZnFe₂O₄) nanoparticles have been enhanced by coating them with silica shell using a modified Stöber method. The ferrites nanoparticles were prepared by a modified citrate gel technique. These core/shell ferrites nanoparticles have been fired at temperatures: 400°C, 600°C and 800°C, respectively, for 2 h. The composition, phase, and morphology of the prepared core/shell ferrites nanoparticles were determined by X-ray diffraction and transmission electron microscopy, respectively. The diffuse reflectance and magnetic properties of the core/shell ferrites nanoparticles at room temperature were investigated using UV/VIS double-beam spectrophotometer and vibrating sample magnetometer, respectively. It was found that, by increasing the firing temperature from 400°C to 800°C, the average crystallite size of the core/shell ferrites nanoparticles increases. The cobalt ferrite nanoparticles fired at temperature 800°C; show the highest saturation magnetization while the zinc ferrite nanoparticles coated with silica shell shows the highest diffuse reflectance. On the other hand, core/shell zinc ferrite/silica nanoparticles fired at 400°C show a ferromagnetic behavior and high diffuse reflectance when compared with all the uncoated or coated ferrites nanoparticles. These characteristics of core/shell zinc ferrite/silica nanostructures make them promising candidates for magneto-optical nanodevice applications.     

Effects of crystallization and dopant concentration on the emission behavior of TiO2:Eu nanophosphors

Uniform, spherical-shaped TiO₂:Eu nanoparticles with different doping concentrations have been synthesized through controlled hydrolysis of titanium tetrabutoxide under appropriate pH and temperature in the presence of EuCl₃·6H₂O. Through air annealing at 500°C for 2 h, the amorphous, as-grown nanoparticles could be converted to a pure anatase phase. The morphology, structural, and optical properties of the annealed nanostructures were studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy [EDS], and UV-Visible diffuse reflectance spectroscopy techniques. Optoelectronic behaviors of the nanostructures were studied using micro-Raman and photoluminescence [PL] spectroscopies at room temperature. EDS results confirmed a systematic increase of Eu content in the as-prepared samples with the increase of nominal europium content in the reaction solution. With the increasing dopant concentration, crystallinity and crystallite size of the titania particles decreased gradually. Incorporation of europium in the titania particles induced a structural deformation and a blueshift of their absorption edge. While the room-temperature PL emission of the as-grown samples is dominated by the ⁵D₀ - ⁷F _j transition of Eu⁺³ ions, the emission intensity reduced drastically after thermal annealing due to outwards segregation of dopant ions.     

Influence of annealing temperature on microstructure evolution of TiAlSiN coating and its tribological behavior against Ti6Al4V alloys

TiAlSiN multicomponent coating, owing to its high hardness and excellent high temperature resistance, was widely used in the cutting field of difficult-to-cut materials such as titanium alloys. For machining titanium alloys, high temperature is easy to gather on the tool chips and deteriorate the cutting tools. Moreover, high temperature will also promote the microstructure evolution and make the wear mechanism more complex. In this paper, TiAlSiN coatings were deposited on cemented carbides and annealed at 400 °C, 600 °C and 800 °C respectively for 60 min in air, followed by reciprocating friction tests against Ti6Al4V counterparts. AFM, SEM, EDS and XPS were applied to investigate the microstructure evolution and tribological behavior of TiAlSiN coating after high temperature annealing. The results demonstrated that the oxidation resistance of TiN phase in TiAlSiN coating was worse than Si₃N₄ and AlN phases. These nitrides can be oxidized to TiO₂, SiO_x and AlO_x under 600 °C, and the depth of oxide layer was increased with the rising annealing temperature, resulting in the coarsened microstructure. The wear mechanisms of as-deposited TiAlSiN coating were oxidation wear and adhesion wear. With the rising annealing temperature, abrasive wear was gradually enhanced. For the TiAlSiN coating annealed at 800 °C, abrasive wear became the dominant wear mechanism.