Mixture of fuels approach for the solution combustion synthesis of Al2O3-ZrO2 nanocomposite

A modified solution combustion approach was used for the first time in the preparation of nanosize zirconia toughened alumina (ZTA) composite. ZTA-1 with an average particle size of ∼37 nm was prepared using corresponding metal nitrates and urea. ZTA-2 with an average particle size of <10 nm was prepared by using mixture of fuels such as ammonium acetate, urea and glycine. The products formed were characterised by powder X-ray diffractometry, Transmission electron microscopy and BET surface area analysis. By using mixture of fuels, the energetics of the combustion reaction and eventually the properties of the combustion product have been changed. A series of combustion reactions were carried out to optimise the fuel ratio combinations required to obtain <10 nm ZTA particles. The microstructure of ZTA consisted of crystallites of Al₂O₃ and ZrO₂ both of which were nanocrystalline as evident from TEM.     

Synthesis and characterization of NiAl2O4 nanoparticles obtained through gelatin

Nanoparticles of NiAl₂O₄ were synthesized by heating (500-1000 °C) the dried resin resultant of a mixture in aqueous solution of gelatin, NiCl₂·6H₂O and AlCl₃·6H₂O. The particle size and microstrain were calculated from the line broadening of X-ray powder diffraction peaks through the Rietveld method refinement: these are 3.9-16 nm and − 0.743-0.139%, respectively. The NiAl₂O₄ nanoparticles were characterized by X-ray powder diffraction (XRPD), thermo gravimetric analysis (TG), BET and TEM techniques.     

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi₂O₃ and TiO₂. Only Bi₄Ti₃O₁₂ phase was formed after 3 h of milling time. The excess of 3 wt% Bi₂O₃ added in the initial mixture before milling does not improve significantly the formation of Bi₄Ti₃O₁₂ phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time. The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi₄Ti₃O₁₂ did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi₄Ti₃O₁₂ crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis.     

Combustion synthesis of Sr0.5Ba0.5Nb2O6 and effect of fuel on its microstructure and dielectric properties

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) powder has been synthesized, at very short reaction time, for the first time by a novel combustion method. Ba(NO₃)₂ and Sr(NO₃)₂ were used as source of Sr and Ba, respectively, while Nb-oxalate was used as the source of niobium. Urea, hexamethyltetramine (HMT) and glycine were used as fuel. The crystallite sizes in the powder ranged between 14-125 nm. X-ray diffraction analysis showed complete SBN50 phase formation at 700 °C, when urea/HMT was used as fuel, and at 800 °C when glycine was used as fuel. Ferroelectric-paraelectric phase transition temperature (T_c) close to 40 °C was observed when urea and HMT were used and the T_c was −49 °C when glycine was used. When urea was used as fuel highest dielectric constant was observed for the pellets sintered at 1250 °C for 4 h. Low dielectric loss was observed when HMT was used as fuel. Larger grain sizes in the sintered pellets were observed when glycine was used as fuel.     

Electrochemical properties of nano-sized LiNi1/3Co1/3Mn1/3O2 powders in the range from 56 to 101 nm prepared by flame spray pyrolysis

Nano-sized LiNi_1/3Co_1/3Mn_1/3O₂ powders in the range from 56 to 101 nm with hexagonal α-NaFeO₂ structures are prepared directly by flame spray pyrolysis. Post-treatment of the powders at 700 °C increases their crystallinity and mean particle sizes. The intensity ratios of the powders’ (0 0 3) and (1 0 4) peaks in the XRD patterns prepared from spray solutions with lithium excesses of 10, 15 and 20% of the stoichiometric amount are 0.83, 1.25 and 1.25, respectively. The powder prepared with 15% excess lithium results in the highest initial discharge capacity of 174 mAh g⁻¹ when post-treated at 700 °C. The discharge capacity of the powder post-treated at 800 °C decreases from 168 to 120 mAh g⁻¹ after 30 cycles.     

Mechanical alloying behavior of Ti6Al4V residual scraps with addition of Al2O3 to produce nanostructured powder

The present investigation has been based on production and subsequent comparison of different physical, mechanical and thermal properties of nanostructured Ti6Al4V and Ti6Al4V/Al₂O₃ powders by means of high energy ball milling. In this regard, the structural and morphological changes of powders were investigated by X-ray diffraction, scanning electron microscopy and microhardness measurements. The results revealed that ball milling process reduced the grain size of Ti6Al4V and Ti6Al4V + 10 wt% Al₂O₃ to approximately 20 and 15 nm, respectively. For both compositions also a remarkable change in morphology and particle size occurred during ball milling of powders with different compositions. Moreover, phase evolution during milling and heat treatment was taken into consideration. The as-milled Ti6Al4V + 10 wt% Al₂O₃ powder exhibited higher microhardness (∼900 Hv) comparing to as-milled Ti6Al4V (∼536 Hv) and as-received samples (∼400 Hv).     

Fabrication and photocatalytic activity of YMn2O5 nanoparticles

In this work, a polyacrylamide gel route is introduced to synthesize YMn₂O₅ nanoparticles. It is demonstrated that high-quality YMn₂O₅ nanoparticles with a uniform size and spherical shape can be prepared using different chelating agents. However, the average particle size of the products is found to have a dependence on the choice of the chelating agent. The sample prepared using citric acid as the chelating agent has an average particle size of ~ 45 nm, while the sample prepared by using the chelating agent EDTA has a particle size centered around 70 nm. The optical energy bandgap of the citric acid- and EDTA-resulted samples is obtained, from optical absorption measurements, to be 1.21 and 1.17 eV, respectively. The photocatalytic experiments reveal that the as-prepared YMn₂O₅ nanoparticles exhibit an interesting photocatalytic activity for oxidative decomposition of methyl red under ultraviolet and visible-light irradiation.     

Hydrothermal synthesis of alpha Fe2O3 nanoparticles capped by Tween-80

Surface modified α-Fe₂O₃ nanoparticles capped by Tween-80 were prepared by the hydrothermal treatment of Fe(NO₃)₂.9H₂O at 200 °C. The spherical nanoparticles possessed good crystallinity with an average crystallite size of 21 nm. The presence of Tween-80 on the surface of α-Fe₂O₃ was confirmed by FTIR and Mössbauer analysis. The surfactant was effective in controlling the particle shape and restricted the particle growth to a narrow range around 40-60 nm as observed by scanning electron microscopy. The α-Fe₂O₃ nanoparticles obtained without Tween-80 were irregular in shape with a wide size distribution in the range of 150-300 nm.     

Synthesis of nano-sized hydroxyapatite powders through solution combustion route under different reaction conditions

Calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (HAp) was synthesized by combustion in the aqueous system containing calcium nitrate-diammonium hydrogen orthophosphate with urea and glycine as fuels. These ceramics are important materials for biomedical applications. Thermo-gravimetric and differential thermal analysis were employed to understand the nature of synthesis process during combustion. Effects of different process parameters namely, nature of fuel (urea and glycine), fuel to oxidizer ratio (0.6-4.0) and initial furnace temperature (300-700 °C) on the combustion behavior as well as physical properties of as-formed powders were investigated. A series of combustion reactions were carried out to optimize the reaction parameters for synthesis of nano-sized HAp powders. The combustion temperature (T_f) for the oxidant and fuels were calculated to be 896 °C and 1035 °C for the stoichiometric system of urea and glycine respectively. The stoichiometric glycine-calcium nitrate produced higher flame temperature (both calculated and measured) and powder with lower specific surface area (8.75 m²/g) compared to the stoichiometric urea-calcium nitrate system (10.50 m²/g). Fuel excess combustion in both glycine and urea produced powders with higher surface area. Nanocrystalline HAp powder could be synthesized in situ with a large span of fuel to oxidizer ratio (φ) in case of urea system (0.8 < φ < 4) and (0.6 < φ < 1.5) for the glycine system. Calcium hydroxyapatite particles having diameters ranging between 20 nm and 120 nm could be successfully synthesized through optimized process variable.     

Growth and characterization of Ba(Cd1/3Ta2/3)O3 thin films

We have synthesized stoichiometric Ba(Cd_1/3Ta_2/3)O₃ [BCT] (100) dielectric thin films on MgO (100) substrates using Pulsed Laser Deposition. Over 99% of the BCT film was found to be epitaxial [BCT (100) || MgO (100) and BCT (010) || MgO (010)] when grown with an elevated substrate temperature of 635 °C, an enhanced oxygen pressure of 53 Pa and a Cd-enriched BCT target with a 1 mol BCT: 1.5 mol CdO composition. A dielectric constant of 32 was inferred from low-frequency capacitance measurements of a planar interdigital metal pattern. Analysis of ultra violet optical absorption results indicates that BCT has a bandgap of 4.9 eV; while the interference pattern in the visible range is consistent with a refractive index of 2.1. Temperature-dependent electrical measurements indicate that the BCT films have a room temperature conductivity of 3 × 10^− 12 Ω^− 1 cm^− 1 with a thermal activation energy of 0.7 eV. A mean particle size of ~ 100 nm and a root mean square surface roughness of 5 to 6 nm were measured using Atomic Force Microscopy.     

Preparation and characterization of porous ultrafine Fe2O3 particles

Porous ultrafine Fe₂O₃ particles were prepared by homogeneous precipitation method. Fe³⁺ and urea were chosen as starting materials and anionic surfactant as the template. It is shown that the reaction results in the precipitation of a gelatinous hydrous iron oxide/surfactant mixture, which gives ultrafine Fe₂O₃ particles after drying and calcinations. The products were characterized by XRD, TEM, TG/DTA and BET. Conventional XRD patterns show that the products are mixture of γ-Fe₂O₃ and α-Fe₂O₃ phase after being sintered at 350 °C, and γ-Fe₂O₃ transforms entirely to α-Fe₂O₃ when sintered at 650 °C. The low-angle XRD patterns indicate that the mesostructure can only exist between 350 and 400 °C. TEM results show that the Fe₂O₃ particles have diameters of about 30 nm and lengths ranging from 100 to 120 nm; in each particle, there are several vermiculate-like mesopores with diameter of about 20-25 nm. The BET surface areas in excess of 50 m²/g are obtained after calcinations at 350 °C. The BJH desorption average pore width is around 22 nm, which is in agreement with the TEM results. The results show that anionic surfactant and sintering temperature are important to obtain this special morphology.     

Fabrication of transparent La2Hf2O7 ceramics from combustion synthesized powders

Transparent La₂Hf₂O₇ (LHO) ceramics were, for the first time, successfully fabricated from combustion-synthesized powders. Nanosized La₂Hf₂O₇ powders were obtained through combustion reaction, using glycine or EDTA as a fuel. The as-made powders were isostatically pressed at 180 MPa and then sintered at 1850 °C for 6 h in hydrogen atmosphere. The resulting ceramics have high optical transmittance.     

Physicochemical characterization of Fe3O4/SiO2/Au multilayer nanostructure

The purpose of this research was to synthesize and characterize gold-coated Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetite nanoparticles (NPs) were prepared using co-precipitation method. Smaller particles were synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g⁻¹. For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of 80–100 emu g⁻¹ and coercivity of 80–120 Oe for particles between 35 and 96 nm, respectively. The magnetic NPs were modified with a thin layer of silica using Stober method. Small gold colloids (1–3 nm) were synthesized using Duff method and covered the amino functionalized particle surface. Magnetic and optical properties of gold nanoshells were assessed using Brunauer–Emmett–Teller (BET), vibrating sample magnetometer (VSM), UV–Vis spectrophotometer, atomic and magnetic force microscope (AFM, MFM), and transmission electron microscope (TEM). Based on the X-ray diffraction (XRD) results, three main peaks of Au (1 1 1), (2 0 0) and (2 2 0) were identified. The formation of each layer of a nanoshell is also demonstrated by Fourier transform infrared (FTIR) results. The Fe₃O₄/SiO₂/Au nanostructures, with 85 nm as particle size, exhibited an absorption peak at ∼550 nm with a magnetization value of 1.3 emu g⁻¹ with a specific surface area of 71 m² g⁻¹.     

Synthesis of nanocrystalline magnesium aluminate (MgAl2O4) spinel powder by the urea-formaldehyde polymer gel combustion route

Nanocrystalline MgAl₂O₄ spinel powder was synthesized by the urea-formaldehyde (UF) polymer gel combustion route. A transparent gel formed from magnesium nitrate, aluminium nitrate and UF after drying underwet self-sustained combustion when initiated with a burning splinter. The combustion product on calcinations at 850 °C formed MgAl₂O₄ spinel. Calcination of the combustion product resulted in particle coarsening. The powder obtained by planetary ball milling of the spinel had a median particle size of 1.58 μm. The spinel particles are agglomerates of nanocrystallites of size in the range 10-30 nm. The compacts prepared by uni-axial pressing of the spinel powder sintered to >99% TD at 1600 °C.     

Low temperature combustion synthesis of CoxMg1−xAl2O4 nano pigments using oxalyldihydrazide as a fuel

Oxalyldihydrazide as a fuel was used to prepare new nano size blue refractory ceramic pigments MgAl₂O₄: xCo²⁺ (0.00 ≤ x ≤ 0.10) using low temperature combustion synthesis (LCS) method. The synthesized and calcined powders were characterized by Fourier transform infra red (FTIR) spectrometry, electronic spectra, thermogravimetry, differential thermogravimetry, differential thermal analysis, X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). Also, the color measurements of nano pigments are studied by diffuse reflectance spectroscopy (DRS) using CIE-L*a*b* parameter method. The FTIR spectra show frequency bands in range the 422–700 cm⁻¹ correspond to metal oxygen bonds through vibrations for the spinel structure compound. The average particle size of prepared samples as determined from XRD and TEM was 30 nm at 1100 °C. Also, the results revealed the varying bulk density, particle size, shape and color with different calcination times and temperatures.     

Nanocrystalline pirochromite spinel through solution combustion synthesis

The production of magnesium–chromium oxides by solution combustion synthesis was investigated using glycine and urea for the first time. Ammonium dichromate, urea/glycine and ammonium nitrate aqueous solutions were used as the precursors of the oxides. The effect of different reaction parameters, such as fuel richness, stoichiometry and fuel leanness was evaluated; such parameters were modified by changing the reagents and the fuel/oxidant ratio. The results suggest that glycine is an interesting complexing/combustible agent for ammonium dichromate to produce chromite spinel. Addition of extra ammonium nitrate to stoichiometric compositions improved the specific surface area and reduced the crystallite size. The highest specific surface area (153.40 m²/g) was obtained for the stoichiometric fuel/oxidant mixtures containing glycine as combustible in combination with ammonium nitrate; however, the smallest crystallite size (approximately 9 nm) of Pirochromite (MgCr₂O₄) was synthesized using urea as combustible.     

A yellow-emitting Ca3Si2O7: Eu phosphor for white LEDs

A series of yellow-emitting phosphors based on a silicate host matrix, Ca_3 − xSi₂O₇: xEu²⁺, was prepared by solid-state reaction method. The structure and photoluminescent properties of the phosphors were investigated. The XRD results show that the Eu²⁺ substitution of Ca²⁺ does not change the structure of Ca₃Si₂O₇ host and there is no impurity phase for x < 0.12. The SEM images display that phosphors aggregate obviously and the shape of the phosphor particle is irregular. The EDX results reveal that the phosphors consist of Ca, Si, O, Eu and the concentration of these elements is close to the stoichiometric composition. The Ca_3 − xSi₂O₇: xEu²⁺ phosphors can be excited at a wavelength of 300-490 nm, which is suitable for the emission band of near ultraviolet or blue light-emitting-diode (LED) chips. The phosphors exhibit a broad emission region from 520 to 650 nm and the emission peak centered at 568 nm. In addition, the shape and the position of the emission peak are not influenced by the Eu²⁺ concentration and excitation wavelength. The phosphor for x = 0.045 has the strongest excitation and emission intensity, and the Ca_3 − xSi₂O₇: xEu²⁺ phosphors can be used as candidates for the white LEDs.     

Synthesis of BaTi4O9 ceramics by reaction-sintering process

Synthesis of BaTi₄O₉ ceramics by a reaction-sintering process was investigated. The mixture of raw materials for stoichiometric BaTi₄O₉ were pressed and sintered into ceramics without any calcination stage involved. Pure BaTi₄O₉ phases were obtained at 1150-1280 °C. High-sintered density, 98.2-99.5% of theoretical value (4.533 g/cm³), can be obtained for pellets sintered at 1200-1280 °C for 2-6 h. Some rod-shaped grains 3-7 μm in the longitudinal axis appear in pellets sintered at 1230 °C. Both the size and the amount of these rod-shaped grains increase at higher sintering temperature.     

Hydrothermal fabrication of various morphological α-Fe2O3 nanoparticles modified by surfactants

Two kinds of various morphological α-Fe₂O₃ nanoparticles modified by anionic surfactant (sodium dodecylsulfonate, SDS) and cationic surfactant (hexadecyipyridinium chloride, HPC), respectively, have been synthesized via hydrothermal method, using simple inorganic salt (NH₄)₃Fe(C₂O₄)₃ and alkali NaOH as starting precursors. Meanwhile, α-Fe₂O₃ nanoparticles without surfactant are also fabricated under the same conditions for comparison. The resultant products were characterized by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron micrograph (TEM) combined with electron diffraction (ED) and magnetization measurements. It is interesting that the obtained α-Fe₂O₃ nanoparticles without surfactant are polyhedral with average particle size of 90 ± 35 nm; while the obtained α-Fe₂O₃ nanoparticles modified by SDS are ellipsoidal with mean particle size of major axis: ca. 420 nm; minor axis: ca. 205 nm and those modified by HPC are spherical with mean particle size of ca. 185 nm observed from TEM. In addition, magnetic hysteresis measurements reveal that the α-Fe₂O₃ nanoparticles modified by two surfactants show enhancement in coercivity (H_c) and the remanent magnetization (M_r) compared with those of the obtained α-Fe₂O₃ nanoparticles without surfactant at room temperature. The experimental results suggest that the surfactants not only significantly influence the size and shape of the particles, but also their magnetic properties.     

Synthesis of submicron-sized spherical Y2O3 powder for transparent YAG ceramics

Spherical monodispersed, submicron-sized Y₂O₃ powder was prepared via a homogeneous precipitation method using nitrate and urea as raw materials. The structure, phase evolution and morphology of Y₂O₃ precursor and the calcined powder were studied by FTIR, TG/DTA, XRD and SEM methods. The sphere size of the precursor was about 250 nm and that of Y₂O₃ powder calcined at 800 °C for 2 h was about 200-210 nm. With the spherical Y₂O₃ powder and a commercial Al₂O₃ ultrafine powder, high transparent YAG ceramics was fabricated by vacuum sintering at 1780 °C for 6 h through a solid-state reaction method. The in-line transmittances of the as-fabricated YAG ceramics at the wavelength of 1064 nm and 400 nm were 82.8% and 79.5%, respectively, which were much higher than that of the YAG ceramics with a commercial Y₂O₃ powder and a commercial Al₂O₃ ultrafine powder directly. The superior properties are attributed to the good morphology, dispersibility and uniform grain size of the as-prepared spherical Y₂O₃ powder, which matches that of the commercial Al₂O₃ powder.