Effects of hydrothermal process parameters on the physical,magnetic and thermal properties of Zn0.3Fe2.7O4 nanoparticles for magnetic hyperthermia applications

Effects of hydrothermal temperature and time on physical, magnetic and thermal properties of Zn-substituted magnetite nanoparticles (Zn_0.3Fe_2.7O₄) were assessed. The magnetic nanoparticles were synthesized via citric acid-assisted hydrothermal reduction route at temperatures of 150, 175 and 200 °C for duration of 10, 15 and 20 h. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and specific loss power (SLP) measurements. The results showed that temperature and time of the hydrothermal process both had significant effects on nanoparticles composition and properties. It was observed that at 150 °C, heat generation was insufficient to produce activation energy required for nucleation of Zn_0.3Fe_2.7O₄ spinel nanoparticles, even after a long time. At 175 °C, although temperature was low, but the suitable condition for nucleation of nanoparticles was made and spinel nanoparticles with the size of about 13 nm were formed after 15 h. Nonetheless, since crystallinity and SLP of the nanoparticles was low, they showed weak performance for magnetic hyperthermia. At 200 °C, the required activation energy was provided for nanoparticles nucleation; however, the spinel was oxidized to hematite, resulting in a decrease in thermal and magnetic properties. In overall, the nanoparticles synthesized at 200 °C for 15 h possessed the best characteristics of reasonable purity, saturation magnetization of about 35.9 emu/g and SLP of 18.7 W/g.     

Characteristics of samaria-doped ceria nanoparticles prepared by spray pyrolysis

Samaria-doped ceria (SDC) nanoparticles were prepared by spray pyrolysis. The means sizes of the samaria-doped ceria nanoparticles were controlled from 21 to 150 nm by changing the calcination temperatures between 700 and 1200 °C. The pellets formed from the SDC particles calcined at temperatures between 700 and 1000 °C had similar grain sizes between 0.75 and 0.82 μm. However, pellet formed from the SDC particles calcined at a temperature of 1200 °C had large grain size of 1.22 μm. The pellet formed from the SDC particles calcined at a temperature of 1000 °C had slightly smaller resistance of grain-boundary than those of the pellets formed from the SDC particles calcined at temperatures between 700 and 900 °C. However, the pellet formed from the SDC particles calcined at a temperature of 1200 °C had low resistance of grain-boundary. The pellet formed from the SDC particles calcined at a temperature of 1200 °C had conductivity of 44.65 × 10^?3 S cm^?1 at a measuring temperature of 700 °C that more twice than those of the pellets formed from the SDC calcined below 1000 °C.     

Effect of synthesis parameters on the size of cobalt ferrite crystallite

Nanoparticles of cobalt ferrite (CoFe₂O₄) were synthesized by the EDTA/Citrate complexing method and hydrothermal method without addition of surfactant. The influence of the pH of the reaction medium (8, 9 or 10), the temperature of the thermal treatment (600 °C, 800 °C or 1000 °C for the EDTA/Citrate method, and 120 °C, 140 °C or 160 °C for the hydrothermal method), and the duration of the thermal treatment (2, 4 or 6 h for the EDTA/Citrate complexing method, and 6, 15 or 24 h for the hydrothermal method) on the average crystallite size was studied by means of an experimental design based on the results obtained by XRD. Statistical analysis led to quantification of the influence of the synthesis parameters on the crystallite size of the powders. Results showed that the pH of the reaction medium is the parameter that shows the greatest influence on the growth of the crystallites of the powders obtained by the hydrothermal method, while calcination temperature is the most significant one for the powders produced by the EDTA/Citrate complexing method.     

Continuous synthesis of lithium iron phosphate (LiFePO4) nanoparticles in supercritical water: Effect of mixing tee

Continuous supercritical hydrothermal synthesis of olivine (LiFePO₄) nanoparticles was carried out using mixing tees of three different geometries; a 90° tee (a conventional Swagelok^® T-union), a 50° tee, and a swirling tee. The effects of mixing tee geometry and flow rates on the properties of the synthesized LiFePO₄, including particle size, surface area, crystalline structure, morphology, and electrochemical performance, were examined. It was found that, when the flow rate increased, the particle size decreased; however, the discharge capacity of the particles synthesized at the high flow rate was lower due to the enhanced formation of Fe³⁺ impurities. The use of a swirling tee led to smaller-sized LiFePO₄ particles with fewer impurities. As a result, a higher discharge capacity was observed with particles synthesized with a swirling tee when compared with discharge capacities of those synthesized using the 90° and 50° tees. After carbon coating, the order of initial discharge capacity of LiFePO₄ at a current density of 17 mA/g (0.1C) and at 25 °C was swirling tee (149 mAh/g) > 50° tee (141 mAh/g) > 90° tee (135 mAh/g). The carbon-coated LiFePO₄ synthesized using the swirling tee delivered 85 mAh/g at 20C-rate and at 55 °C.     

Hydrothermal synthesis of 3D TiO2 nanostructures using nitric acid: Characterization and evolution mechanism

Various morphologies of TiO₂ nanostructures were synthesized by HNO₃ assisted hydrothermal treatment with respect to the acid molarity (1 M, 3 M, and 8 M), temperature (110, 140, and 180 °C), and time (1, 3, and 6 h). An additional sample was synthesized inside the protonated titanate nanoribbon coated vessel with the acid molarity of 8M at 140 °C for 3 h. The crystal structure and morphology of the nanostructures synthesized were investigated using X-Ray diffractometer, scanning electron microscope, and transmission electron microscope. The results revealed that lower acid concentrations, longer synthesis durations and higher temperatures favored anatase phase formation. Meanwhile, a phase pure 3D lotus structure rutile TiO₂ could be obtained by hydrothermal synthesis at 8M HNO₃ concentration at 140 °C for 3 h using protonated H-titanate nanoribbons. A probable mechanism for the evolution of 3D rutile lotus structure was highlighted.     

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.     

Ball milling assisted hydrothermal synthesis of ZrO2 nanopowders

The formation of ZrO₂ nanopowders under various hydrothermal conditions such as temperature, time, autoclave rotation speed, heating rate and particularly assistance of ball milling during reaction was investigated. Full ZrO₂ formation (with monoclinic phase) from zirconium solution was completed at shorter times with increasing temperature such as after 4 h at 150 °C, 2 h at 175 °C and less than 2 h at 200 °C. Crystallite size increased from 2.9 to 4 nm with increasing reaction temperature from 125 °C to 200 °C, respectively. Ball milling assisted hydrothermal runs were performed to understand the effect of mechanical force on phase formation, crystallinity and particle size distribution. Monoclinic ZrO₂ was formed in both milled and non-milled runs when zirconium solution was used. Mean particle size for the 2 M solution was measured to be 94 nm for the milled and 117 nm for the non-milled powders. However, when amorphous aqueous zirconia gels (precipitated at pH 5.8) were used, tetragonal phase was also formed in addition to monoclinic phase. Mean particle size was measured to be 0.7 μm (d₉₀≅1.3 μm) for the milled and 7.9 μm (d₉₀≅13 μm) for the non-milled powders. Ball milling during hydrothermal reactions of both zirconium solution and aqueous zirconium gel resulted in smaller crystallite size and mean particle size and, at the same time, effectively controlled particle size distribution (or agglomeration) of nanopowders.     

Formation of RuO2 nanoparticles by thermal decomposition of Ru(NO)(NO3)3

A simple one-pot synthesis of RuO₂ nanoparticles by the thermal decomposition of ruthenium nitrosyl nitrate [Ru(NO)(NO₃)₃] up to 800 °C was investigated. The RuO₂ phase was characterized by XRD, SAXS, FE SEM/EDS, Raman, DTA/TGA and FT-IR techniques. Broadening of prominent diffraction lines (110), (101) and (211) was used to estimate nanocrystallite sizes in RuO₂ particles. FE SEM showed the formation of RuO₂ plates at 400 °C which consisted of RuO₂ nanoparticles of about 15–25 nm in size. At 800 °C RuO₂ nanoparticles showed the sintering effect and some of them increased in size to about 200 nm. Raman and FT-IR spectra consolidated the findings. Moreover, DTA curves showed the decomposition and release of NO and NO₃⁻ groups to be a stepwise process.     

Characterization of surface-modified ceria oxide nanoparticles synthesized continuously in supercritical methanol

Surface-modified ceria oxide (CeO₂) nanoparticles were synthesized continuously in supercritical methanol at 400 °C, 30 MPa and a residence time of ∼40 s using a flow type reactor system. Oleic acid and decanoic acid were used as the surface modifiers. Transmission electron microscopy (TEM) showed that the surface modifiers changed drastically the shape and size of the nanoparticles. When 0.3 M of the surface modifiers were used, primary particles with diameter of 2–3 nm loosely aggregated and formed secondary particles with size of 30–50 nm. Wide angle X-ray diffraction (WAXD) analysis revealed that the surface-modified nanoparticles retained CeO₂ crystalline structure. The surface-modified CeO₂ nanoparticles had a very high surface area (140–193 m²/g) compared to the unmodified CeO₂ particles synthesized in supercritical water (8.5 m²/g). Fourier transform infrared (FT-IR) and thermogravimetric analysis (TGA) indicated that aliphatic, carboxylate and hydroxyl groups were chemically bounded on the surface of CeO₂ nanoparticles. Dispersability test using ultraviolet transmittance showed that most of the surface-modified CeO₂ nanoparticles were dispersed in ethylene glycol for 30 days while the unmodified CeO₂ particles synthesized in supercritical water or in supercritical methanol were precipitated after 7–15 days.     

A novel CO and C3H8 sensor made of CuSb2O6 nanoparticles

Trirutile-type CuSb₂O₆ nanoparticles were synthesized by a simple and economical route, starting from copper nitrate, antimony chloride, ethylenediamine, and ethyl alcohol as solvent. The latter was evaporated by microwave radiation at 140 W. The precursor material was calcined at 200, 300, 400, 500, and 600 °C, and analyzed by powder XRD. The oxide phase was obtained at the last calcination step (600 °C), whose powders were analyzed by field-emission scanning electron (FE-SEM) and transmission electron (TEM) microscopies. Microrods, hexagonal microplates, and nanoparticles with an average size of ~ 51.2 nm were observed. A forbidden bandwidth of 3.41 eV was detected for the direct transition with UV–vis. Tests were carried out on pellets made of the powders in carbon monoxide (CO) and propane (C₃H₈) atmospheres at different concentrations and operating temperatures, obtaining high response at 300 ppm of CO and 500 ppm of C₃H₈, both at 300 °C.     

From nanometric zirconia powder to transparent polycrystal

Coprecipitated zirconia-yttria (8 mol%) gel subjected to hydrothermal treatment at 240 °C resulted in the solid solution powder of 8 nm particle sizes and specific surface area 132.7 m²/g. Uniaxial compaction followed by cold isostatic pressing under 300 MPa resulted in samples of the extremely small and narrow pore size distribution. Such samples start to shrink at about 200 °C which is related to the desorption of water layers surrounding particles. The state of closed porosity is achieved at 1150 °C. Pore closing was performed in air or oxygen atmosphere. Hot isostatic pressing at 1150 °C for 2 h under 250 MPa argon pressure led to transparent materials. Some pores remained in the material whose preliminary pore closure was performed in air. The samples initially sintered in oxygen atmosphere show no porosity and higher light transmittance than the former ones.     

Low-temperature densification of Mg-doped hydroxyapatite fine powders under hydrothermal hot processing conditions

Densification of calcium hydroxyapatite fine powders doped with different concentrations of Mg (2, 4 and 6 mol% Mg, MgHA) was successfully achieved for the first time in a nearly fully dense state using the hydrothermal hot pressing (HHP) technique at low temperatures. Consolidation of MgHA powders was studied under different temperatures (150–240 °C), reaction times (1–6 h), and powder particle size (20 nm–1.5 µm). X-Ray diffraction analyses indicated that the particle densification under HHP conditions proceeded without any variation in the crystalline structure and regardless of the Mg content. The results from this work showed that an increase in temperature accelerates the reaction between MgHA particles and water (solvent) mixed during the hydrothermal treatment. Particle packing associated with bulk densification was achieved through a massive dissolution-recrystallisation mechanism, which induced the formation of small particles that rapidly crystallised on the surface of the partially dissolved original MgHA particles. The optimum conditions to obtain pellets with a high apparent density of 3.0758 ± 0.001 g/cm³ and tensile strength value of 12.6 ± 0.6 MPa were 10 wt% of water at a temperature of 240 °C with a 6 h reaction time and 6 mol% of Mg (MgHA3). The use of the HHP technique coupled with the fine particle size and reactivity of the MgHA precursor powders with water allowed us to produce disks that were compacted to a nearly full dense state with a low content of open porosity of 2.0%.     

Preparation,characterization and performance of Pd/SiO2 catalyst for benzene catalytic hydrogenation

Palladium nanoparticles supported on silica were prepared by hydrazine reduction in aqueous medium at room temperature. They were characterized by XRD, TEM, EDX, H₂-adsorption, and H₂-TPD. The catalytic properties were evaluated in the gas-phase hydrogenation of benzene in the temperature range of 75–250 °C. Metal particles with a size range of 4.0–25.8 nm were obtained. The metal surface area and hydrogen storage increase with decreasing metal particle size. The H₂-TPD profiles exhibited a main peak appeared at 540 °C with two shoulders at lower (445 °C) and higher (605 °C) temperatures. These peaks were ascribed to strongly adsorbed hydrogen on the surface catalyst. The catalytic activity of the catalysts strongly depends on the metal loading. It increases with decreasing Pd loading. This is ascribed to metal surface area, which increases with decreasing Pd content.     

Synthesis and characterization of titanium oxide nanotubes and its performance in epoxy nanocomposite coating

Titanium oxide nanotubes (TiO₂ nanotube, TNT) were prepared from hydrothermal treatment of TiO₂ particles in NaOH at 140 °C, followed by neutralization with HCl. The structure of the nanotubes was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). TNT synthesized under the optimal conditions with approximately 10–20 nm wide, and several (100–200) of nanometers long. TNT is used as white pigment for two component epoxy-based coating. Ultrasonication followed by mechanical stirring has been applied for dispersion of TNT powder in an epoxy matrix. The resulting perfect dispersion of TNT particles in epoxy coating revealed by scanning electron microscopy (SEM) ensured white particles embedded in the epoxy matrix. The effects of TNT particle concentrations on thermal, mechanical and corrosion resistance of epoxy coatings composite were studied and compared to that of submicron particles. It was found that the TNT significantly enhances the heat resistance, the thermal stability and the glass transition temperature of epoxy resin. Epoxy/TNT nanocomposite with 5.0 wt.% TNT shows the highest thermal stability, the temperature of 50% weight loss increased from 365 to 378 °C, the amount of char yields or residues at 600 °C increased from 7.13 to 13.50 wt.%, respectively to 1.0 and 5.0 wt.% TNT. The glass transition temperature (Tg) increased from 182 to 220 °C too. The mechanical properties and corrosion resistance of epoxy resin greatly improved by using reinforcing TNT and this improvement increases with increase TNT wt.%.     

Synthesis of nanosized zirconium carbide by a sol–gel route

Nanosized zirconium carbide was synthesized by a new simple sol–gel method using zirconium n-propoxide, acetic acid as chemical modifier, and saccharose as carbon source. When heat-treated at 900 °C under flowing argon, gels transformed into intimately mixed amorphous carbon and nanosized tetragonal ZrO₂. Further heat treatments above 1200 °C led to the formation of zirconium carbide with some dissolved oxygen in the lattice. Oxygen content could be reduced by increasing the heat treatment temperature from 1400 to 1600 °C, which unfortunately also induced a mean crystallites size increase from 90 to 150 nm. Short heat treatments above 1600 °C were carried out to further purify the samples and to limit the particles growth. A compromise between purity and average crystallite's size could then be found. Powders were assessed using X-ray diffraction, thermal analysis and scanning electron microscopy.     

Creating new materials with melamine resins

Acid catalyzed condensation of hexa-methoxy methyl melamine (HMMM) in aqueous phase leads to new functional particles and up to now unknown lamellar mesoscopic gels. The investigation with transmission electron microscopy (TEM) shows that the polymer formation starts with nonspherical nanoparticles. Dynamic light scattering experiments reveal a particle size of about 60–100 nm. Atomic force microscopy (AFM) measurements disclose nonuniform flat particles with an aspect ratio of about 0.3. These nanoparticle dispersions form thermoreversible gels. Molecular modeling investigations indicate energy minimized layer-by-layer condensation of the melamine resin molecules. The next step in growth is the nucleation of the nanoparticles via the narrow sides. This forms nonperfect lamellar layers. This time, we get a thermoreversible gel which is fluid at 80 °C and gets fixed at 20 °C. Out of these platelet structures as precursors, a mesoporous, nonthermoreversible gel with essentially lamellar sides and pore sizes about 10 μm is formed. Scanning electron microscopy (SEM) studies show very uniform wall and plate sizes with a directed three-dimensional structure.     

Oxidation treatments for SiC particles and its compatibility with glass

Different thermal treatments were performed to produce a protective coating on the surface of SiC particles in order to allow their incorporation in a glass matrix. These oxidation treatments were carried out in air at different temperatures ranging from 800 °C to 1500 °C and different times at 1200 °C (10 min–48 h). The oxidation kinetics followed the Deal–Grove model and the thickness of the protective coating increased with temperature and SiC particle size. Protected SiC particles with different particle sizes were incorporated in a borosilicate glass. With small particles sizes foam glasses were obtained, whereas particles with higher grain size, i.e., higher coating thickness, were stable in the glass matrix and a smooth glass was obtained.     

Boehmite derived surface functionalized carbon nanotube-reinforced macroporous alumina ceramics

Carbon nanotube (CNT)-reinforced macroporous alumina ceramics with tailored porosity were fabricated using hydrothermally synthesized (200 °C for 2 h) boehmite–CNT starting composite powders. Multi-wall CNTs were first mixed with a mixture of chemicals suitable to synthesize stoichiometric boehmite powders and then put in an autoclave. During hydrothermal synthesis, the formation of fine particles of boehmite was accompanied by the functionalization of CNTs. Subsequently, CNT–boehmite powders were used to produce bulk ceramics and sintering took place in a vacuum furnace at 1450 °C for 3 h for the formation of CNT-reinforced alumina ceramics. The pore network in various dimensions occurred as a consequence of the reconstructive transformation and dehydration of boehmite during the transformation to alumina. FEG-SEM and TEM analysis were used to determine the CNT distribution in the matrix, the morphology and size of particles, as well as the visual properties of the pores. The final macroporous alumina ceramics can be considered to be ideal for the separation and filtration of contaminants in liquid or air environment.     

Synthesis and characterization of NiO and Ni nanoparticles using nanocrystalline cellulose (NCC) as a template

In this study, nanosized nickel oxide (NiO) and nickel (Ni) powders were synthesised via glycine-nitrate (GN) combustion process, assisted by nanocrystalline cellulose (NCC) as a template. Despite the unique morphology of NCC, it has yet to be applied as a sacrificial bio-template for GN combustion process. In addition, NiO and Ni nanoparticles were obtained at relatively low temperatures in this study, whereby the calcination temperatures were varied from 400 °C to 600 °C, with calcination durations of 2, 4, and 6 h. The morphological analysis of the resulting products were conducted using FESEM, which showed uniformly dispersed NiO and Ni particles with average crystallite size of 25 nm and 27 nm, respectively. These results were confirmed using X-ray diffraction (XRD) technique. The Raman and Fourier transform infrared (FTIR) spectra revealed that the molecular fingerprints of the samples were in agreement with each other. Further analyses revealed that samples calcined at 600 °C for 4 h showed the lowest particle size for pure NiO, whereas the lowest particle size for pure Ni was obtained at 400 °C for 4 h. The TGA results were also consistent with the XRD analysis, whereby pure Ni was initially formed and upon heating, had gradually converted into NiO.     

Preparation of calcium doped LaCrO3 fine powders by hydrothermal method and its sintering

The synthesis of fine powders of LaCrO₃ and its solid solutions doped with calcium under hydrothermal conditions and the sintering of these powders were investigated. Precursor alkaline coprecipitated lanthanum chromite gels with three different compositions: LaCrO₃, La_0.9Ca_0.1CrO₃ and La_0.8Ca_0.2CrO₃, were processed under hydrothermal conditions at low temperatures (350–425 °C), for a reaction time between 30 and 120 min. Powders of a single phase with orthorhombic structure of LaCrO₃, La_0.9Ca_0.1CrO₃ and La_0.8Ca_0.2CrO₃ were obtained at a temperature as low as 350, 400 and 425 °C, respectively, for a short reaction interval of 1 h. SEM and TEM micrographs showed that particles with an irregular morphology and an average particle size of 300 nm, were mainly obtained under hydrothermal conditions. The powders were pressed by cold isostatic pressing at 200 MPa, and then sintered in air at a temperature range of 1200–1500 °C for various intervals (1 to 5 h). A maximum apparent density of 97.7% was achieved on specimens with high calcium content, La_0.8Ca_0.2CrO₃, at 1400 °C for 5 h. The average grain size measured on the sintered specimens was 6 μm.