Key Engineering Materials Vols. 368-372

Abstract: In this work, nickel-zinc ferrite nanocrystalline powder has been prepared by a sol-gel autocombustion technique using nitrate-citrate gel obtained from metal nitrates and citric acid solution. Characterization of the nitrate-citrate gel, as-burnt powder and calcined powder at different calcination conditions were investigated by using XRD, FTIR and SEM techniques. The results revealed that the nitrate-citrate gel exhibits a self-propagating behavior after ignition and showed that the different calcination conditions affect the crystallite size of the synthesized powder as well as its phase constitution.

Abstract: Dense NiCuZn ferrites consisting of fine grains were prepared by spark plasma sintering (SPS) at 750°C for 3 min under a uniaxial pressure of 15 MPa. The powders were densified to >95% of theoretical density by the SPS process, and the average grain size of the prepared NiCuZn ferrite was < 1 /m. The saturation magnetization of prepared specimens (without further annealing treatment) was approximate 50.54 emu/g, which was slightly smaller than that of 52.21 emu/g for specimens prepared by conventional sintering at 980°C for 4 h. Phase identifications indicated that prepared NiCuZn ferrite existed impurity phase (Cu2O), and Cu2O would gradually transform to CuO when annealing temperature increased.

Abstract: Copper ferrite powders were successfully synthesized by sonochemical method. The resultant powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR, differential thermal analysis-thermal gravimetric (DTA-TG), differential scanning calorimetry (DSC) and VSM. The particle saturation magnetization (Ms) is 66 emu/g and an intrinsic coercive force (iHc) is 2100 Oe when the precursor calcined at 950 °C for 15 h.

Abstract: Nanosized barium ferrite spinel particles were prepared with the aid of ultrasound radiation by a precursor approach. A precursor was got by sonicating an aqueous solution of BaCl2, Fe (NO3)3·9H2O and urea firstly. Nanosized BaFe2O4 particles with a size of ca.40nm were prepared after the precursor was heated at 950 °C for 15 h. The nanosized barium ferrite particles and the precursor were characterized by powder X-ray diffraction, scanning electron microscopy, FT-IR and differential scanning calorimetry.

Abstract: Nano-crystalline barium hexaferrite powders have been prepared by mechanical alloying of nFe2O3+Ba(CH3COO)2 with Fe/Ba molar ratios of 10-12 and subsequent heat treatment. Thermal behavior, phase composition, morphology and magnetic properties of samples were studied using DTA/TGA, XRD, SEM and VSM, respectively. Nano-crystalline Ba-hexaferrite with a mean crystallite size of 46 nm and magnetic properties as high as Ms = 73.9 A.m2/kg and Hci = 334.2 kA/m was formed for mixture of 5.5Fe2O3+Ba(CH3COO)2 which was milled for 48 h and then annealed at 1100 °C.

Abstract: Hydrogen treatment and re-calcination (HTR) and nitrogen treatment and re-calcination (NTR) processes have marked effects on enhancement of the magnetic properties , particularly coercivity, of the strontium hexaferrite powder synthesized conventionally. This improvement is mainly attributed to finer structure obtaining after gas treatment. In this work, the effects of different combinations of these processes on the powder and bulk magnetic properties have been studied by using VSM and Permeameter. XRD and SEM techniques have also been used for characterization of the processes.

Abstract: Iron oxide nanometer powders were prepared by using sol-gel method and the supercritical fluid drying technology (SCFD) from inorganic salts. The characteristics of the iron oxide nanometer powders were characterized systematically. The results showed that the drying and crystallization of the production could be achieved in one step by SCFD method; furthermore, a highly dispersed, size uniformed and with better crystallization magnetite (Fe3O4) nanoparticles can be obtained. Phase transformation of the as-synthesized powders occurs at about 80°C, and only hematite (α-Fe2O3) can be obtained when being heated at temperatures higher than 400°C. The production synthesized by SCFD exhibits significant magnetic properties. As the heat-treated temperature increase, the magnetic properties of the sample decrease gradually.

Abstract: Zn1-xCoxO diluted magnetic semiconductor was prepared by hydrothermal method at 200 °C and 240 °C for 24h with the Co2+ doping content of 5~15 mol%. NaOH was used as the mineralizer. X-ray diffraction analysis indicated that the as-prepared Co-doped ZnO had the pure ZnO wurtzite structure. UV–Visible spectroscopy had shown that the Co ions are substituted to Zn ions in ZnO matrix. Room temperature VSM revealed a paramagnetic behavior of the Co-doped ZnO samples. FE-SEM analyses showed that nanocrystalline powders of pure Zn095Co0.05O and Zn09Co0.1O could be prepared by the hydrothermal method.

Abstract: Polycrystalline BiFeO3 multiferroic films were fabricated on Ti substrates by hydrothermal method from an aqueous Bi (NO3)3•5H2O, FeCl3•6H2O and NaOH solution. The films grow in alkaline solution at low temperatures of 120°C-240°C for 18 hours. XRD analysis showed that well-developed crystallines with single perovskite crystal phase were obtained. It was also found that the increase of reaction temperature and concentration of NaOH were favorable for crystal growth and crystallographic regularization. The microstructure, thickness and cross-section of the films were characterized by FE SEM and EDS. Results indicated that dense and homogeneous BiFeO3 thin films could be obtained in an appropriate hydrothermal condition.

Abstract: The paper aims at synthesizing La substituted BaM hexaferrites (BaLa0.5Fe11.5O19) in the presence of SiO2 nano-particles by sol-gel method. Effects of SiO2 nano-particles on the structure and particle size of hexaferrites are investigated by XRD and SEM. Magnetic properties of BaFe12O19, BaLa0.5Fe11.5O19 and BaLa0.5Fe11.5xO19/SiO2 are compared by vibrating sample magnetometer (VSM). The XRD patterns of BaLa0.5Fe11.5O19/SiO2 calcined at 1000°C manifest that all the species have hexagonal crystal structure and no diffraction peaks of SiO2 are found. Compared with BaLa0.5Fe11.5O19 powders, those synthesized in the presence of SiO2 nanoparticles present in smaller powder size, as proved by SEM. The results of VSM reveal that BaLa0.5Fe11.5O19 possesses much higher saturation magnetization than BaFe12O19. BaLa0.5Fe11.5xO19/SiO2 also shows higher saturation magnetization than BaFe12O19, but lower than BaLa0.5Fe11.5O19 because of addition of nano-SiO2.