Microwave Calcination Research Articles

Evaluation of superparamagnetic and biocompatible properties of mesoporous silica coated cobalt ferrite nanoparticles synthesized via microwave modified Pechini method

Cobalt ferrite nano particles were synthesized by Pechini sol-gel method and calcined at 700°C in electrical and microwave furnace. The microwave calcined sample was coated with mesoporous silica by hydrothermal method. Characterization was performed by XRD, FESEM, TEM, VSM, BET and FTIR analysis. The cytotoxicity was evaluated by MTT assay with 3T3 fibroblast cells. The XRD and FTIR results confirmed spinal formation in both cases and verified the formation of silica coating on the nanoparticles. For microwave calcination, The XRD and SEM results demonstrated smaller and flat adhesion forms of nanoparticles with the average size of 15nm. The VSM results demonstrated nearly superparamagnetic nanoparticles with significant saturation magnetization equal to 64emu/g. By coating, saturation magnetization was decreased to 36emu/g. Moreover, the BET results confirmed the formation of mesoporous coating with the average pore diameters of 2.8nm and average pore volume of 0.82cm3g−1. Microwave calcined nanoparticles had the best structural and magnetic properties.

Photocatalytic property of perovskite LaFeO3 synthesized by sol-gel process and vacuum microwave calcination

Perovskite LaFeO3 nanoparticles with an orthorhombic structure were synthesized by a sol-gel route and subsequent vacuum microwave calcination. The effects of vacuum microwave calcination temperature and duration on the formation of LaFeO3 single phase were investigated. The use of vacuum microwave calcination can effectively reduce the crystallization time of LaFeO3 nanoparticles. The synthesized LaFeO3 nanoparticles have a perfect crystal structure, a single phase composition without any impurity, uniform particle size, and a suitable energy band of ∼1.86eV. According to the PL spectrum of LaFeO3 nanoparticles, the recombination rate of photo-generated electrons and holes can be reduced due to the use of vacuum microwave calcination. Furthermore, LaFeO3 nanoparticles calcined by vacuum microwave calcination have a superior visible photo-catalytic efficiency on organic dye methyl orange and methyl blue, and a higher photodegradation efficiency rate, compared to those calcined by conventional calcination. LaFeO3 nanoparticles obtained by vacuum microwave calcination at 700°C for 30min (sample MW-700-30) exhibits superior photocatalytic efficiency, and the MB and MO dye solution in the presence of LaFeO3 nanoparticle becomes colorless during 240min under visible light irradiation. The photodegradation process of MB on the as-synthesized LaFeO3 follows a pseudo-first-order kinetic process.

Optical Characterization of Eu3+ Doped and Undoped Sr2CeO4 Phosphors

Optical Characterization of Eu 3+ Doped and Undoped Sr 2 CeO 4 Phosphors The typical blue phosphor Sr 2 CeO 4 material was prepared by different routes and also synthesized by different techniquies such as Pechini’s method, high temperature solid–state reaction, citrate–gel/sol-gel method, microwave calcination method, combustion method, and microwave–accelerated hydrothermal method. The luminescent compound materials doped with Europium (Eu) have various luminescence features in different lattice parameters, which are important in fields of displays (FEDs), plasma display panel devices, lamps and cathode ray tubes (CRTs) etc. In this study, a rare earth material Eu doped Sr 2 CeO 4 phosphors and undoped Sr 2 CeO 4 were synthesized by the conventional solid–state reaction method and characterized by X–ray diffraction (XRD), scanning electron microscopy images (SEM) and radioluminescence (RL) measurements. The Undoped Sr 2 CeO 4 has a broad band with a peak position around 500nm due to the charge transfer (CT) mechanism. The Eu is an excellent host lattice activator yielding a strong emission in comparison to the luminescence from the well–known Sr 2 CeO 4 . Strong red emission coming from the hypersensitive 5 D 0 ® 7 F 2 transition of Eu 3+ ion suggested the presence of the dopant ion in a structurally disordered environment. From the XRD data, the average crystallite sizes of undoped and Eu doped Sr 2 CeO 4 , calculated using the Scherer’s Formula are found to be 72nm and 73nm respectively.

Direct conversion of electrodeposited nanocrystalline ε-MnO2 into LiMn2O4 by microwave calcination

Firstly, e-MnO2 films with good adhesion and high surface area were electrolytically deposited on platinum plates. After being soaked for 48 h in a 0.1 mol L−1 LiOH aqueous solution, these oxide films were directly converted to the LiMn2O4 spinel by microwave calcination using very short irradiation times (t ir) of 3, 4, or 5 min. As inferred from XRD data, clearly the crystalline LiMn2O4 spinel in a single phase can be obtained even at t ir = 3 min. The voltammetric profiles for all obtained Pt/LiMn2O4 electrodes presented the characteristic peaks for the lithium-ion insertion-extraction processes in the spinel structure. For the LiMn2O4 spinel obtained using t ir = 3 min, the diffusion coefficient associated to those processes was estimated as equal to 1.1 × 10−11 cm s−1. From the charge-discharge tests, the specific capacity for this material was about 80 mA h g−1 at C/10. Therefore, the proposed methodology made possible to directly produce Pt/LiMn2O4 electrodes, without the need of using conductivity enhancers or binders for the attachment of the oxide film to the current collector.

Optimization of preparation of CO3O4 by microwave calcination from basic cobalt carbonate

ABSTRACTThe parameters to prepare of Co3O4 by microwave calcination from basic cobalt carbonate were optimized based on the thermal gravity analysis–differential thermal gravity (TG–DTG) using with central composite concept of response surface methodology. A quadratic equation model for decomposition rate was built and rising behaviour of basic cobalt carbonate in fields of microwave and effects of main factors and their corresponding relationships on response were obtained. The results showed that a sample 20% addition of Co3O4 with the basic cobalt carbonate has ability to strongly absorb microwave energy, and the calcination temperature and calcination time significantly affect on the decomposition rate of basic cobalt carbonate in this range studied. The decomposition rate of basic cobalt carbonate was 99.56% under optimum calcination temperature 642.65 K, and calcination time 8.89 min and 4.34 g, respectively. The validity of the model was confirmed experimentally and the results were satisfactory. Furthermore, the Co3O4 was analysed using X-ray powder diffraction. It was feasible to prepare of Co3O4 by microwave calcination from the basic cobalt carbonate though addition of small amounts cobalt oxide.

Preparation of Mg/Al bimetallic oxides as sorbents: microwave calcination, characterization, and adsorption of Cr(VI)

In the study, Mg/Al bimetallic oxides as sorbents have been successfully prepared via a novel and facile approach (Microwave Calcination). The characterizations of Mg/Al bimetallic oxides were performed using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption, and pHPZC analyses. The results showed that microwave calcination resulted in enhanced crystallinity, pHPZC, and specific surface area of the Mg/Al bimetallic oxides, compared to conventional calcination. Comparison of the performance of Cr(VI) adsorption between Mg/Al bimetallic oxides prepared by conventional (CHTC) and microwave (CHTM) calcination was made and discussed. The results demonstrated that the adsorption experiment data from the CHTC and CHTM were both fitted well to Langmuir–Freundlich isotherm model and pseudo-second-order kinetic model, and the adsorption process was chemisorption and controlled by diffusion. Microwave calcination did not change the adsorption properties for Cr(VI), but the Cr(VI) adsorption capacities of Mg/Al bimetallic oxides obtained by microwave calcination were improved.

Microwave assisted synthesis of Sn-modified MgAlO as support for platinum catalyst in cyclohexane dehydrogenation to cyclohexene

This paper described an investigation on catalytic properties of Pt nanoparticles supported on hydrotalcite-like oxide (MgAl(Sn)O) calcinated by microwave for cyclohexane dehydrogenation to cyclohexene. The PtSn catalysts were investigated with several state-of-art characterizations such as BET, XRD, NH3-TPD, H2-TPR, H2-TPD and XPS. Particular emphasis was focused on the changes in the Sn-support interaction and in the character of Pt active sites. H2-TPR showed that the microwave calcination strengthened the interaction between Sn and support. The strengthened interaction could maintain more amounts of Sn in oxidized. H2-TPD revealed that microwave calcination facilitated Sn in changing the interfacial character between Pt and support. This was beneficial for the migration of carbonaceous materials to the support. These effects resulted in higher activity and stability in cyclohexane dehydrogenation to cyclohexene.

Effect of microwave calcination on catalytic properties of Pt/MgAl(Sn)Ox catalyst in cyclohexane dehydrogenation to cyclohexene

This paper describes an investigation on catalytic properties of Pt nanoparticles supported on MgAl(Sn)Ox mixed oxide for cyclohexane dehydrogenation to cyclohexene. The MgAl(Sn)Ox supports were synthesized by microwave calcined hydrotalcite-derived precursors, and Pt/MgAl(Sn)Ox catalysts were prepared by an incipient wetness impregnation method. The catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), hydrogen temperature-programmed desorption (H2-TPD), X-Ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that the microwave calcination changed the interfacial character between Pt and support, and strengthened the interaction between tin and support, and facilitated the high dispersion of Pt nanoparticles presented on the support. These effects resulted in higher activity, stability and cyclohexene selectivity in cyclohexane dehydrogenation to cyclohexene.

Influence of Compound Additive CeO2-MxOy on Catalytic Performace of Pd/γ-Al2O3 Catalyst for One-step Synthesis of Dimethylether

A series of Pd/γ-Al2O3 catalysts with different types of compound additives were prepared by impregnation under microwave calcination; the physicochemical properties and catalytic performance of catalysts for one-step synthesis of dimethylether from sulfur-containing syngas were investigated. The results show that the catalysts added CeO2-ZrO2 showed much better catalytic performance and sulfur tolerance than those added CeO2-ZnO or CeO2-CaO in terms of CO conversion, methanol, and dimethylether selectivities and time space yield of dimethylether, which are closely related to higher pore volume and Pd dispersity, moderate CO adsorption, and moderate surface acidity of the catalyst. The optimum compound additive content was determined to be 2%CeO2-1%ZrO2. Under such optimum conditions, CO conversion, dimethylether selectivity, and time space yield of dimethylether are 63.2%, 68.5%, and 30.92 mmol·(ml·h)−1, respectively.

Microwave-Assisted Synthesis of High Dielectric Constant CaCu3Ti4O12 from Sol–Gel Precursor

CaCu3Ti4O12 (CCTO) powders derived from sol–gel precursors were calcined and sintered via microwave radiation. The obtained CCTO powders were compared with that obtained via a conventional heating method. For microwave heating, 89.1 wt.% CCTO was achieved from the sol–gel precursor, after only 17 min at 950°C. In contrast, the conventional calcination method required 3 h to generate 87.6 wt.% CCTO content at 1100°C. In addition, the CCTO powders prepared through 17 min of microwave calcination exhibited a small particle size distribution of D50 = 3.826 μm. It was found that a lengthy hold time of 1 h by microwave sintering is required to obtain a high dielectric constant (3.14 × 103 at 102 Hz) and a reasonably low dielectric loss (0.161) in the sintered CCTO ceramic. Based upon the distinct microstructures, the dielectric responses of the CCTO samples sintered by different methods are attributed to space charge polarization and internal barrier layer capacitor mechanism.

Microwave effects on the structure of CeO2-doped zinc oxide sorbents for H2S removal

Cerium oxide-doped ZnO sorbents were prepared by microwave calcination and conventional heating, respectively. The results show that microwave heating results in much better performance of the sorbents due to microwave effects on the structure of sorbents. XRD, XPS, N2 adsorption and SEM were used to characterize the structure of sorbents calcinated in two ways. The data indicate that microwave irradiation leads to better pore structure and smaller crystallite size of ZnO, which favors the dispersion of active components and the increase of contact area between ZnO and H2S. Microwave heating also results in greater outer layer electron density of surface atoms (Zn and O) and higher content of surface elements including Zn and O, which is favorable for the adsorption of acidic H2S and the reaction of H2S with ZnO on the surface of sorbents.

Combined method for obtaining ultradispersed powders of vanadium oxides and carbide

New opportunity to synthesize nano- and ultradispersed powdered materials by combining of two procedures, classical liquid-phase precipitation and low-temperature microwave calcination, at a rather simple instrumentation is described. It was found in precipitation of precursors that, depending on the synthesis conditions (solution pH, amount of carbon, synthesis on the vessel surface or in the solution bulk), particles of hydrated vanadium oxide have different morphologies. It was also found that precursor powders have an insignificant microporosity, which is preserved in the final products in trace amounts upon thermal treatment of samples. Intermediate and final vanadium products were synthesized in an electromagnetic field in a flow of argon, their phase composition and structure were examined in the stages of thermolysis, reduction, and carbidization, and their lattice constants were calculated. The morphology, size, and particle size distribution in the samples under study were determined.

Study on the calcination experiments of rare earth carbonates using microwave heating

AbstractThe heating behavior and effect of experimental parameters like holding time, calcination temperature and microwave power on the weight loss of the mixed rare earth carbonate using microwave heating have been studied, also characterized by X-ray diffraction, thermogravimetry-differential scanning calorimetry, scanning electron microscopy (SEM), particle analysis and Fourier transform infrared (FT-IR). The results show the following: rare earth oxides are obtained at 850°C for holding 1 h; FT-IR analysis indicates that the vibration absorption peak of carbonate disappears after calcination using microwave, confirming the feasibility of microwave calcination for the rare earth carbonates; SEM shows that the rare earth oxides have the characteristics of better and finer particles, have better dispersion and have surface that is more loose and porous than that of products using conventional calcination; particle analysis indicates that average size (D

Enhanced Coercivity of CaLaCo‐Doped SrM Hexaferrites by Microwave‐Calcination Technique

The effects of microwave calcination (MC) and conventional muffle furnace calcination (CC) on the microstructure and magnetic properties of M‐type hexagonal ferrite Ca0.15La0.39Sr0.46Fe11.7Co0.3O19 were investigated. The phase composition, microstructure, and magnetic properties of calcined materials were examined using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry. Experiments indicated that the MC method can achieve both pure phase, and fine and uniform grains for both calcined and sintered M‐type hexaferrites. MC treatments resulted in a magnetization at 15 kOe of 67 emu/g and an increase in coercivity by 12% over the CC technique. The improved magnetic properties resulting from microwave‐assisted calcination were attributed to the formation of a fine‐grained morphology, which yielded a narrow grain size distribution. The microwave calcinating technique was shown here to possess unique potential for fabrication of high‐performance ferrites and possibly other ceramics.

Microstructure and magnetic properties of M-type Sr0.61−La0.39Ca Fe11.7Co0.3O19 hexaferrite prepared by microwave calcination

Abstract M-type Sr 0.61− x La 0.39 Ca x Fe 11.7 Co 0.3 O 19 ferrites with various calcium concentrations ( x = 0, 0.1, 0.2, 0.3) were prepared through microwave calcining. The microstructure, morphology and magnetic properties of the samples were evaluated by X-ray diffraction, scanning electron microstructure and vibrating sample magnetometry, respectively. Results showed that more Fe 3+ ions were substituted by Co 2+ with the increase of calcium substitution, which suppressed the formation of the impurity phases to improve the magnetic properties. The coercivity and saturation magnetization of the samples with the composition of Sr 0.61− x La 0.39 Ca x Fe 11.7 Co 0.3 O 19 can be remarkably improved when x = 0.2.

Microwave-activated formation of lattice defects in alumina polycrystals consolidated by spark plasma sintering

A wet-chemical synthesis and microwave calcination approach was found to be efficient for synthesizing α-alumina powders and polycrystals with high levels of lattice defects. The defects of the as-produced powders were determined from the optical transmittance of spark-plasma-sintered compacts with an identical microstructure using a conventional calcination method. The existence of a high lattice defect concentration was verified by positron annihilation lifetime analysis and X-ray diffraction. The microwave-activated lattice defect phenomenon has potential applications in the production of semiconductor materials or films with high chemical activity or crystal doping.

Support Vector Linearly Inseparable Algorithm and its Optimizing Microwave Calcining Technology of Ammonium Uranyl Carbonate

Support vector machines (SVMs) are a promising type of learning machine based on structural risk minimization and statistical learning theory, which can be divided into two categories: support vector classification (SVC) machines and support vector regression machines (SVR). The basic elements and algorithms of SVC machines are discussed. As modeling and prediction methods are introduced into the experiment of microwave calcining AUC, the better prediction accuracy and the better fitting results are compare with back propagation (BP) neural network method. This is conducted to elucidate the good generalization performance of SVMs, especially good for dealing with the data of some nonlinearity.

Microwave-assisted synthesis and sintering of potassium sodium niobate lead-free piezoelectric ceramics

Abstract Synthesis and sintering of (K,Na)NbO3 lead-free piezoelectric ceramics (KNN) were carried out using conventional and microwave heating processes. Microwave calcination resulted in the formation of single-phase orthorhombic perovskite structure by heating up to 950 °C. Characterization of synthesized powders with FTIR, XRD and DSC techniques revealed that without soaking time and in spite of the very short heating time in microwave, the powder calcined at 950 °C has all physical properties similar to powder synthesized in conventional furnace at the same temperature with a step by step heating regime. The bulk density of 93.8 %, piezoelectric charge coefficient (d33) of 85 pC/N and remnant polarization (Pr) of 18 µC/cm2 were achieved for sample sintered in microwave furnace at 1115 °C. These values are satisfactorily comparable with corresponding values of conventional sintering. Results showed that the microwave heating is a promising method in calcination, synthesis and sintering of potassium sodium niobate lead-free piezoelectric ceramics.

Investigation on Preparation of Micro-Sized Hematite Powder from Hydrous Ferrous Sulfate Using Microwave and Conventional Heating

AbstractMicrowave and conventional heating were employed to synthesize micro-sized hematite powder from hydrous ferrous sulfate, a by-product in the process of titanium pigment manufacture. The TG/DTG analysis was used to study thermal behavior of the industrial ferrous sulfate. Therefore the temperature which was significant to product was defined. The calcination experiments were carried out to assess the effect of calcination temperature covering three different temperatures (650°C, 750°C and 850°C, respectively). X-ray powder diffraction (XRD) was used to characterize the structure of the product, while the scanning electron microscopy (SEM) was utilized to characterize the morphology of the product. Microwave calcination process resulted in a mixture of hematite and minor magnetite while a considerable amount of magnesium sulfate was detected with the conventional calcination process. The transformation from periclase to magnesium was discussed during the calcinations as well. The conventional heating resulted in porous product while the microwave heating resulted in smaller particle size.

Influence of Microwave Calcination on Microstructure and Magnetic Properties of Sr-Hexagonal Ferrite

The improvement of the microstructure of Sr-hexagonal ferrite and their magnetic properties by microwave calcined method was studied, the aim of the study was to obtain a fine grained microstructure in calcined stage. There was tendency to induce a large anisotropic during grain growth, microwave calcination method can succeed in obtaining homogeneous grain growth ,and help to reduce the calcination temperature and shorten the calcination time. The ferrites with saturation magnetization, remanent magnetization and intrinsic coercivity of 70.322emu/g, 36.182emu/g, 3343.1Oe, respectively, obtained in samples calcined at 1140°C for 30 min.