Mechanical Ball Milling Method Research Articles

Thermal conductivity and rheological properties of graphite/oil nanofluids

A series of colloidal graphite/oil nanofluids were prepared by mechanical ball milling method. Their thermal conductivity (TC) and rheological properties were detailedly investigated. The TC tests show that the TC enhancements of the nanofluids depend strongly on the volume fraction (vol.%) of graphite and increase nonlinearly with increasing loading but have a weak relationship with temperature, and promisingly, only adding 1.36vol.% of graphite into oil can result in a high TC enhancement of 36%. It is worth noting that the TC enhancement exhibits an abrupt variation, i.e., from 11% to 36%, when the amount of graphite increases from 0.68 to 1.36vol.%, which could be attributed to the formation of percolating aggregate structures. The rheological measurements were also conducted to demonstrate the microstructure and fluid behaviors of the colloidal graphite/oil nanofluids. Compared with the Newtonian fluid behaviors of base liquids and other nanofluids, the obvious shear thinning, significant viscosity increase, and slight viscoelasticity enhancement for a typical nanofluid sample containing 1.36vol.% graphite with dispersant can be created, offering the evidence for the formation of percolating aggregate structures. Our results may primarily provide a tremendous step on the way of finding abundant, low cost, commercially available, and high-performance nanomaterials for nanofluid production and secondarily determine if graphite-containing nanofluids toward practical applications are possible.

Synthesis and characterization of fine particles of La0.7Ca0.3MnO3 prepared by the mechanical ball milling method

A fine particle of La0.7Ca0.3MnO3 was synthesized by the mechanical synthesis. The average crystallite size of 1 micrometre was obtained by both scanning electron microscopy and X-ray diffraction. The X-ray diffraction based on the Rietveld method on a powder sample show that the obtained sample crystallizes in the orthorhombic structure with the Pnma space group. Magnetic measurements showed that the sample exhibits a paramagnetic-to-ferromagnetic phase transition with decreasing temperature and the obtained Curie temperature is Tc ≈ 120 K.

Structure, magnetic properties and Mössbauer spectra of La0.67Sr0.33FexMn1 − xO3 manganites oxide prepared by mechanical ball milling method

La0.67Sr0.33FexMn1-xO3, with x = 0.0, 0.1, 0.2 and 1 have been elaborated by mechanical system. X-ray diffraction, Scanning electron microscopy, Magnetic measurements and Mossbauer spectroscopy for the systems have been investigated. Rietveld analysis of the X-ray powder diffraction show that the samples crystallise in the orthorhombic perovskite system with Pnma space group. The average particle size of about 60 nanometre was obtained from scanning electron microscopy and X-ray diffraction. The investigated samples exhibit a ferromagnetic to paramagnetic transition with increasing temperature. The presence of manganese in the structure leads to an increase of the Curie temperature as well as to spontaneous magnetization. The magnetization versus applied magnetic field shows a small coercive field and an unsaturated magnetization which indicates that the nanoparticles of all samples are superparamagnetic at around room temperature. Room temperature Mossbauer spectra show that the samples with x = 0.1 and x = 1.0 contain minority α-Fe2O3 and other spinel ferrite species. Also, they indicate that Fe3 + ions are present in slightly distorted octahedral sites in the samples with x = 0.1 and 0.2, while mixed Fe valency was observed for the sample with x = 1.0.

Fabrication of Nanocrystalline Fe<sub>84</sub><sub>.</sub><sub>3</sub>Si<sub>4</sub>B<sub>8</sub>P<sub>3</sub>Cu<sub>0.</sub><sub>7</sub> Powders with High Magnetization

With the Aim of Preparing the Raw Powders Used for Soft Magnetic Compacts Production, Nanocrystalline Soft Magnetic Powders of Fe84.3Si4B8P3Cu0.7Were Successfully Fabricated Using Crystallization by Rapid Heat-Treatment and Mechanical Ball-Milling Methods. We Investigated the Relation of the Magnetic Properties, Crystallization Degree and Heat-Treatment Condition in Salt-Bath Process. In this Study, a Fine Nanocrystalline Structure with an Extremely Number of α-Fe Grains with the Similar Size of ~ 30 nm Was Obtained. This Led to Excellent Soft Magnetic Properties, i.e., 1.85 T (197.7 emu/g) and 10 A/m for Saturation Magnetization and Coercivity, Respectively. By Controlling the Milling Time, Different Particle Size of Powder Can Be Obtained.

Electrochemical Characteristics of Carbon-coated Si/Cu/graphite Composite Anode

The carbon-coated Si/Cu powder has been prepared by mechanical ball milling and hydrocarbon gas decomposition methods. The phase of Si/Cu powder was analyzed using X-ray diffraction (XRD), dispersive Raman spectroscopy, electron probe microanalysis (EPMA) and transmission electron microscope (TEM). The carbon-coated Si/Cu powders were used as anode active material for lithium-ion batteries. Their electrochemical properties were investigated by charge/discharge test using commercial LiCoO2 cathode and lithium foil electrode, respectively. The surface phase of Si/Cu powders consisted of carbon phase like the carbon nanotubes (CNTs) with a spacing layer of 0.35 nm. The carbon-coated Si/Cu/graphite composite anode exhibited a higher capacity than commercial graphite anode. However, the cyclic efficiency and the capacity retention of the composite anode were lower compared with graphite anode as cycling proceeds. This effect may be attributed to some mass limitations in LiCoO2 cathode materials during the cycling.

리튬이차전지용 Si/Cu/Graphite 복합체 음극의 전기화학적 거동

탄소 피복된 Si/Cu 분말을 기계적인 볼-밀링(ball-milling) 방법과 고온에서 탄화수소가스 분해 방법에 의해 제조하여 리튬이차전지용 음극으로 사용하였고 이에 대한 전기화학적 거동을 조사하였다. 천연흑연(natural graphite)을 이용하여 탄소 피복된 Si/Cu/graphite 복합체 음극소재를 제조하였으며 천연흑연 음극소재와 전기화학적 특성을 비교하였다. 탄소 피복된 Si/Cu 음극의 가역적 비용량은 초기 10 싸이클까지 지속적인 증가를 나타냈다. 탄소 피복된 Si/Cu/graphite 복합체 음극의 가역적 비용량은 <TEX>$0.25mA/cm^2$</TEX> 전류밀도에서 450mAh/g이고 초기 싸이클 효율은 81.3%로 나타났다. 복합체 음극의 싸이클 성능은 가역적인 비용량값을 제외하고 천연흑연 음극과 유사하게 나타났다. The carbon-coated Si/Cu powders were synthesized by mechanical ball-milling and hydrocarbon gas decomposition methods at high temperature. The carbon-coated Si/Cu powder was used as anode for lithium secondary battery and its electrochemical behavior was investigated. In addition, the carbon-coated Si/Cu/graphite composite anode material was prepared using natural graphite powder and their electrochemical characteristics were compared with natural graphite anode. The specific capacity of carbon-coated Si/Cu anode increased to the initial 10 cycles. The carbon-coated Si/Cu/graphite composite anode exhibited the reversible specific capacity of 450mAh/g and the first cycle efficiency of 81.3% at <TEX>$0.25mA/cm^2$</TEX>. The cycling performance of the composite anode was similar to that of pure graphite anode except the reversible specific capacity value.

Hydrogen storage properties of the Mg–Ti–H system prepared by high-energy–high-pressure reactive milling

Magnesium-based alloys are among the promising materials for hydrogen storage and fuel cell applications due to their high hydrogen content. In the present work, we investigated the hydrogen release/uptake properties of the Mg–Ti–H system. Samples were prepared from the mixtures of MgH 2 and TiH 2 in molar ratios of 7:1 and 4:1 using a high-energy-high-pressure (HEHP) mechanical ball-milling method under 13.8 MPa hydrogen pressure. Thermogravimetric analysis (TGA) showed that a relatively large amount of hydrogen (5.91 and 4.82 wt.%, respectively, for the above two samples) was released between 126 and 313 °C while temperature was increased at a heating rate of 5 °C min −1 under an argon flow. The onset dehydrogenation temperature of these mixtures, which is 126 °C, is much lower than that of MgH 2 alone, which is 381 °C. The activation energy of dehydrogenation was 71 kJ mol −1, which is much smaller than that of as-received MgH 2 (153 kJ mol −1) or as-milled MgH 2 (96 kJ mol −1). Furthermore, the hydrogen capacity and the dehydrogenation temperature remained largely unchanged over five dehydrogenation and rehydrogenation cycles.

AgNi Alloy Used as Anodic Catalyst for Direct Borohydride Fuel Cells

AgNi alloy power was prepared as anodic catalyst for direct borohydride fuel cells by mechanical ball-milling method. The XRD and SEM evidences revealed that the alloy powder was composed of nanosized crystallites aggregated into micrometer particles. It was found from electrochemical experiments that the AgNi catalyst could not only catalyze the direct electrochemical oxidation of borohydride ions, but also depress the chemical hydrolysis of borohydride ions, so as to produce a discharge capacity of KBH4 over 3500 mAh·g-1, which corresponded to a 90% utilization of the BH-4 ions as anodic fuel.

Catalytic effect of niobium oxide on hydrogen storage properties of mechanically ball milled MgH 2

We examined a catalytic effect of niobium oxide (Nb 2O 5) on the hydrogen storage properties of MgH 2 prepared by mechanical ball milling method. The MgH 2 composite doped with 1 mol% Nb 2O 5 by ball milling for 20 h desorbed hydrogen up to ∼6 mass% in the temperature range from 200 to 250 °C at the heating rate of 5 °C/min under a purified helium flow. After dehydrogenation at 200 °C, the product showed remarkable hydrogen absorption kinetics. A large amount of gaseous hydrogen up to ∼4.5 mass% was absorbed even at room temperature under 1 MPa hydrogen pressure within 15 s and finally its capacity reached up to 5 mass%. Furthermore, the valence state of Nb 2O 5 doped in MgH 2 was examined by X-ray absorption near edge structure (XANES) measurement. The results indicated that additive Nb 2O 5 was reduced by MgH 2 during mechanical milling. This suggests that the Nb compound, in which the valence state of Nb atom is less than 5+, acts as a catalyst for the hydrogen absorbing/desorbing kinetics.

Catalytic Effect of Nanoparticle 3d-Transition Metals on Hydrogen Storage Properties in Magnesium Hydride MgH2 Prepared by Mechanical Milling

We examined the catalytic effect of nanoparticle 3d-transition metals on hydrogen desorption (HD) properties of MgH(2) prepared by mechanical ball milling method. All the MgH(2) composites prepared by adding a small amount of nanoparticle Fe(nano), Co(nano), Ni(nano), and Cu(nano) metals and by ball milling for 2 h showed much better HD properties than the pure ball-milled MgH(2) itself. In particular, the 2 mol % Ni(nano)-doped MgH(2) composite prepared by soft milling for a short milling time of 15 min under a slow milling revolution speed of 200 rpm shows the most superior hydrogen storage properties: A large amount of hydrogen ( approximately 6.5 wt %) is desorbed in the temperature range from 150 to 250 degrees C at a heating rate of 5 degrees C/min under He gas flow with no partial pressure of hydrogen. The EDX micrographs corresponding to Mg and Ni elemental profiles indicated that nanoparticle Ni metals as catalyst homogeneously dispersed on the surface of MgH(2). In addition, it was confirmed that the product revealed good reversible hydriding/dehydriding cycles even at 150 degrees C. The hydrogen desorption kinetics of catalyzed and noncatalyzed MgH(2) could be understood by a modified first-order reaction model, in which the surface condition was taken into account.

The evaluation of powder processing on microstructure and mechanical properties of hydroxyapatite (HA)/yttria stabilized zirconia (YSZ) composite coatings

In clinical applications, the mechanical failure of HA-coated titanium alloy implants suffered at the interface of the HA coating and titanium alloy substrate will be a potential weakness in prosthesis. Yttria stabilized zirconia (YSZ) reinforced HA coatings have been proven to enhance the mechanical properties of the HA coating significantly and reduce the formation of calcium oxide (CaO). In this paper, HA/YSZ (30 wt.% YSZ) composite coatings were sprayed by the plasma technique. The effects of the powder processing–mechanical ball milling method and spheroidization method on the microstructure and mechanical properties of the HA/YSZ composite coatings were evaluated. The experimental results showed that the spheroidized powders melted better than the ball milled powders during plasma spraying and formed higher mechanical property coatings (1.6326±0.08 MPa m −0.5 of fracture toughness, 58.59±2.91 GPa of elastic modulus and 43.42±2.53 MPa of tensile bond strength). HA/YSZ solid solution formed during deposition on the substrate, which played a very important role in the mechanical properties of the HA/YSZ composite coatings. Tensile bond strength tests showed that the fracture mode was cohesive and that failure occurred at the interface of HA and unmelted YSZ particles. The molten state of YSZ had a great influence on the properties of the HA/YSZ composite coatings.