Trends of Parallel Microstructure and Magnetic Properties Evolution in Co0.5Zn0.5Fe2O4

The present paper reports on an effort to expose and scientifically explain the microstructure–magnetic properties relationship as they evolve with increasing sintering temperature. Mechanical alloying was used to prepare cobalt–zinc ferrite nanoparticles with sintering temperature from 800 to 1,350 °C with 50 °C increment. The microstructure of the samples was observed using a field emission scanning electron microscope, and the magnetic parameters, such as the real permeability and loss factor, were measured at room temperature in the frequency range from 10 MHz to 1.0 GHz using an Agilent 4291B impedance/material analyzer. The B–H hysteresis of the samples was investigated using a MATS-2010SD Static Hysteresisgraph. From the results, the real permeability and loss factor were observed to increase up to 1,250 °C. These increases corresponded to increases in grain size and are mainly due to easier domain wall movement. However, due to zinc loss, \(\mu ^{\prime }\) and \(\mu ^{\prime \prime }\) as well as the saturation induction decreased from 1,300 to 1,350 °C. The coercivity increased up to 850 °C and decreased with increasing temperature. This increasing-to-decreasing coercivity trend corresponded well with the single- to multi-domain grain size transition marked by critical grain size at about 0.13 μm.     

Carbosilisiothermic Reduction of Rutile to Produce Nano-Sized Particles of TiC and Its Composite with SiO2

Ceramic nanoparticles of TiC were successfully synthesized in a matrix of SiO₂ by high-energy ball milling with subsequent heat treatment. The milling procedure includes milling of a mixture of TiO₂, Si, and graphite powders at ambient temperature in an inert gas (Ar) atmosphere. The structural evaluation of powder particles has been accomplished by XRD, TEM, SEM, EDX, and DSC. XRD results suggest that the TiC-SiO₂ nonocomposite was produced after 10 hours of mechanical activation with subsequent heat treatment at 1473 K (1200 °C) for 7 minutes. TEM images reveal that the TiC and SiO₂ crystallites are <14 and 12 nm in size, respectively. The fracture toughness, and Vickers hardness values of the TiC-SiO₂ nanocomposite are measured to be 3.82 MPa m^1/2 and 19.9 GPa, respectively. Dimethylsulfoxide is used to eliminate SiO₂ from the final products.     

Rapid Hydrogen Generation from the Reaction of Aluminum Powders and Water Using Synthesized Aluminum Hydroxide Catalysts

A synthesized and nano-sized Al(OH)₃ powder that promotes the generation of hydrogen from a Al/water reaction is demonstrated. In this study, aluminum hydroxides are synthesized using sodium aluminate NaAlO₂, distilled water and ethanol. The mole ratio of ethanol/water and the concentration of sodium aluminate in solution affect the crystal structure, morphology and sizes of the Al(OH)₃ powders significantly. These Al(OH)₃ powders contain both gibbsite and bayerite phases and exhibit excellent catalytic power on the hydrogen generation of Al/water system. It is proposed that two major characteristics of Al(OH)₃ powders dominate the catalytic power. That is, the surface area and the high-energy sites of Al(OH)₃. When mole ratio of ethanol/water is between 0.3–0.6 and the concentration of NaAlO₂ is higher than 0.0167 g/ml, the synthesized Al(OH)₃ powders are in a more gibbsite-oriented and plate-like structure. Other than above conditions result in a more bayerite-oriented and particulate-like structure. The plate-like structure exhibits strong catalytic power due to the existence of high-energy sites on the edge of plates even its surface area is not so high. The particulate-like structure may also have strong catalytic power when it has a high surface area. By taking advantage of the exothermic reaction, ~?100% yield of hydrogen can be produced from 1 g Al/10 g water system within 30 s using 3 g synthesized Al(OH)₃. A aluminum waste scrap can also react with water using these effective catalysts and generate?~?95% yield of hydrogen within 8 min.     

Electrodeposition of aluminum on needle cathode using AlCl3/urea molten salts at low-temperature and its application to hydrogen generation

The electrodeposition of aluminum(Al) was studied using two electrolyte solutions, such as anhydrous AlCl_3-urea and hydrated AlCl_3·6 H_2 O-urea. A systematic examination using cell voltages 1.0–2.0 V was carried out at temperatures((50–100) ± 2) °C. A needle-shaped cathode was employed for the deposition of aluminum. A dendrite and particulate microstructure of Al were observed on the needle-shaped cathode. An improved condition for the manufacturing of small sizes and high purity of aluminum deposits was obtained. Pure Al with a current efficiency(yield) of 84%–99% was obtained from those of non-aqueous electrolytes and only of 8.6%–9.3% from those of hydrated electrolytes. The electrical conductivities of electrolytes remained considerable at((50–100)± 2) °C. The improved aluminum powders were used for the reaction with water. The aluminum reacts with water at room temperature, producing pure H_2 with 100% yield. The electrodeposited aluminum metal can be used as an excellent energy carrier.     

Wurtzite ZnSe quantum dots: synthesis, characterization and PL properties

A facile method for synthesis of monodispersed, starch-capped ZnSe nanoparticles at room temperature is being reported. The nanoparticles exhibited strong quantum confinement effect with respect to the bulk ZnSe. The transmission electron microscopy image indicated that the particles were well dispersed and spherical in shape. The X-ray diffraction analysis showed that the ZnSe nanoparticles were of the wurtzite structure, with average particle diameter of about 3.6 nm. The Fourier transform infrared spectrum confirmed the presence of starch as passivating agent.     

Magnetic Phase-Transition Dependence on Nano-to-Micron Grain-Size Microstructural Changes of Mechanically Alloyed and Sintered Ni0.6Zn0.4Fe2 O 4

The microstructure evolution in several polycrystalline Ni_0.6Zn_0.4Fe₂O₄ samples as a result of a sintering scheme was studied in detail, in parallel with the changes in their magnetic properties. The Ni_0.6Zn_0.4Fe₂O₄ toroidal sample was prepared via mechanical alloying and subsequent molding; the sample with nanometer-sized compacted powder was repeatedly sintered from 600 to 1200 °C with an increment of 25 °C. An integrated analysis of phase, microstructural and hysteresis data pointed to existence of three distinct shape-differentiated groups of B–H hysteresis loops which belong to samples with weak, moderate and strong magnetism (Idza in Mater. Res. Bull. 47:1345–1352, 2012), respectively. The real permeability, μ′, and loss factor, μ″, increased with grain size which increased due to increase in sintering temperature and these two magnetic properties also seem to belong to three value-differentiated groups corresponding to the same temperature ranges found for the B–H groupings. These groupings are tentatively explained using Snoek’s Law.     

Magnetic properties of Ni–Co doped barium strontium hexaferrite

A series of Ni–Co substituted barium strontium hexaferrite materials, Ba_0.5Sr_0.5Ni _x Co _x Fe_12–2x O₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8 mol%) was synthesized by the sol–gel method. X-ray diffraction analysis has shown that the Ni–Co substitutions maintain in a single hexagonal magnetoplumbite phase. The room temperature magnetic properties and the cation site preferences of Ni–Co substituted ferrite were investigated by VSM. Substitutions led to decrease in coercivity while saturation magnetization remains the almost same. It indicates that the saturation magnetization (52.81–59.8 Am²/kg) and coercivity (69.83–804.97 Oe) of barium strontium hexaferrite samples can be varied over a very wide range by an appropriate amount of Ni–Co doping contents.     

Synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powder via PVA assisted sol–gel process

CoFe₂O₄ ferrites were synthesized by sol–gel method, having metal nitrates as precursors and PVA as surfactant, followed by a heat treatment at 960 °C for 2 h. The ultrafine ferrite powders obtained have been characterized by X-ray diffraction, thermal gravimetry, differential scanning calorimetry and room temperature magnetic measurement studies. The morphology of the powder was identified by high resolution-scanning electron microscopy. X-ray diffraction results indicate that the resultant CoFe₂O₄ crystallites consist of spinel phase. Significant differences in magnetic properties of CoFe₂O₄ samples synthesized with various concentrations of PVA were observed. The magnetisation measurements show that when the PVA concentration increased, coercivity initially decreased and then increased where as retentivity and magnetisation decreased. The optimum concentration of PVA for the synthesis of CoFe₂O₄ ferrites is obtained from this investigation. Obviously this material can be used as an efficient candidate for practical recording purpose.     

Synthesis and magnetic properties of conventional and microwave calcined barium hexaferrite powder

Single phase nanoparticles of barium hexaferrite (BaFe₁₂O₁₉–BaF) were synthesized by sol–gel method using metal nitrates as source and d-Fructose as a fuel. The prepared precursors were calcined by two different calcination techniques, using conventional furnace and microwave furnace. The samples are characterized using powder X-ray diffraction, theromogravimetric analysis and vibration sample magnetometer. Thermal analysis studies showed exothermic and endothermic reaction peaks from room temperature to 1,200 °C. X-ray diffraction studies established the formation temperature of single phase BaFe₁₂O₁₉. HR-SEM results showed the dispersed particles of hexagonal structure in platelet form. The broad hysteresis loop showed that the barium hexaferrite powder was in good crystalline nature.     

Phase formation and high dielectric constant of calcium copper titanate using sol–gel route

Nano-sized calcium copper titanate (CCTO) powder was synthesized from a quick and innovative sol–gel process. Calcium nitrate, copper nitrate and titanium isopropoxide were used as the raw materials to synthesize the precursor product. The dried precursor powder was then milled and calcined at 450, 550, 650, 800, 850 and 950 °C for 3 h. The XRD results of the powder calcined at 800 °C indicates the formation of CCTO single phase. AFM studies shows that the average particle size of CCTO powder ranges around 80 nm. From the FTIR spectra the modes observed at 606, 525 and 463 cm⁻¹ was assigned to vibration modes of Ca–O, Cu–O and Ti–O–Ti, respectively. The samples sintered at 1,040 °C shows high density (96%) as compared to the theoretical value. The grain sizes of sintered pellets were determined by FE-SEM and the dielectric properties were studied by LCR meter.