Effects Of High-energy Milling Research Articles

Study of Soft/Hard Bimagnetic CoFe²/CoFe²O⁴ Nanocomposite.

We report an experimental study of the bimagnetic nanocomposites CoFe₂/CoFe₂O₄. The precursor material, CoFe₂O₄ was prepared using the conventional stoichiometric combustion method. The nano-structured material CoFe₂/CoFe₂O₄ was obtained by total oxygen reduction of CoFe₂O₄ using a thermal treatment at 350 °C in H₂ atmospheres following the partial oxidation in O₂ atmospheres at 380 °C during 120; 30; 15, 10, and 5 min. The X-ray diffraction, Mössbauer spectroscopy and transmission electronic microscopy images confirmed the formation of the material CoFe₂/CoFe₂O₄. The magnetic hysteresis for the nanocomposite with different saturation magnetization (from 87 to 108 emu/g) also confirms the formation of the CoFe₂/CoFe₂O₄ with different content of CoFe₂O₄. Furthermore, the magnetic hysteresis curves for all samples presented a single magnetic behavior, suggesting the magnetic coupling between the phases of the nanocomposite. The effects of high energy milling on the magnetic properties of the precursor material and nanocomposites samples were evaluated.

Effect of high energy ball milling and low temperature densification of plate-like alumina powder

The effects of high energy milling on the shape, size and low temperature sinterability of plate-like alumina powder was studied. The milling effects were studied under three different processing conditions, designed by varying the charge ratio and the milling medium. 10:1 and 20:1 ball to powder charge ratios were considered in wet and dry milling media, with powder samples collected after 4, 8, 16 and 32 h of milling. Analysis demonstrates that 20:1 wet milled powders underwent greatest size reduction with a final average particle size of 0.29 um and crystallite size of 10.13 nm. 20:1 wet milled powders were subsequently sintered at 1300 °C for 10 and 20 h. Results indicate that densification and hardness increased as a function of milling time, reaching to a maximum for 16 h milled samples with the least amount of porosity.

Effects of Zr on the amorphization of Cu-Ni-Zr alloys prepared by mechanical alloying

This work presents the effects of high energy milling with different Ni and Zr ratios on the amorphization of ternary Cu-Ni-Zr alloys (initially, Cu-43Ni-7Zr, Cu-12Ni-31Zr, Cu-33Ni-7Zr, and Cu-12Ni-23Zr; and later, Cu-23Ni-15Zr and Cu-11Ni-7Zr). Microstructure was determined using X-Ray diffraction and electron microscopy. Results were compared to thermodynamic models. In the ternary alloys under study, the lattice parameter of the Cu-Ni solid solution was generally correlated to the amounts of nickel incorporated into the Cu lattice. However, longer milling times reduced that lattice parameter and facilitated Zr insertion into the solid solution. For example, after 5 h of milling time, microstructural analysis showed the formation of a solid solution with cubic structure in Cu-43Ni-7Zr. This pattern is consistent with the presence of a lattice parameter between that of Cu and Ni (α−phase); in contrast, the Cu-33Ni-7Zr alloy showed an α-phase and another similar to Zr. Results suggest that, as the amount of nickel increases, the ability to form an amorphous phase decreases. Additionally, experimental and thermodynamic data showed a solid-solution formation stage, followed by an amorphous phase formation stage that occurred as milling time and Zr content increased.

TiC whisker reinforced ultra-fine TiC-based cermets: Microstructure and mechanical properties

TiC whisker reinforced ultra-fine TiC-based cermets were fabricated and their microstructures as well as mechanical properties were characterized and compared with microsized and ultra-fine cermets. The effects of high energy milling and subsequent annealing on the composition and microstructure of microsized TiC powders were studied. It was shown that the particle size distribution of TiC powders played a critical role in determining cermets׳ microstructure and properties. Inverse grain (White core with grey rim) only exists in ultra-fine cermet with a narrow size distribution of annealed TiC powders. Large discrepancy of larger TiC powders (microsized particles or whiskers) and ultra-fine particles in size resulted in a bimodal grain size feature. Additionally, mechanical property testing was conducted and was related to the microstructural features. The whisker reinforced cermets own much higher toughness of 12.43Mpam1/2 than the microsized and ultra-fine cermets, with a hardness (Hv30, 1620) between them.

Effects of High Energy Milling on the Carboncoated Lithium Iron Phosphate Precursor Nature

LiFePO 4 precursor is produced in planetary milling with LiOH·H 2O , H 3 PO 4 , Fe 2 O 3 and sucrose, which is characterized by X-ray diffraction, scanning electron microscope(SEM), laser particle size analyzer (LPSA). The results showed that the particle size was submicron level, the LPSA data showed that there was double peak of the sample, which the big one appeared around 0.66 μm and the small one appeared around 1.71 μm and the positions did not change with the change of parameters. The mixture was conductive to obtain narrow-size-range LiFePO 4 .

Effects of high-energy milling on the solid-state synthesis of pure nano-sized Li4Ti5O12 for high power lithium battery applications

Li4Ti5O12 was synthesized from Li2CO3 and anatase TiO2 using different degree of milling to test the hypothesis that finer starting materials can result in a smaller Li4Ti5O12 particle size and better high-rate discharging capacities. The degree of milling was controlled using three different ZrO2 media sizes for 3 hours of high-energy milling, whereas 5 mm balls were used for 24 hours ball milling. High-energy milling produced significantly finer starting materials and Li4Ti5O12 particles compared to those produced by ball milling. Among the three different balls used in high-energy milling, the 0.10 mm media showed the most favorable results. Pure Li4Ti5O12 with a mean particle size of 146 and 175 nm were synthesized by an economic solid-state reaction combined with high-energy milling using 0.05 and 0.10 mm beads, respectively. These pure nano-sized Li4Ti5O12 exhibited a much higher specific capacity and superior rate capability than those of coarse rutile TiO2-contained Li4Ti5O12 particles.

Synthesis of Pr6O11 and Y2O3 Doped Zinc Varistors by High Energy Milling

High voltage zinc varistors were synthesized by high-energy milling with Pr6O11 and Y2O3 doped ZnO-Bi2O3 system as raw materials. The effects of high-energy milling on the microstructures, electrical properties and densities of samples were investigated in detail. The results show that high-energy milling make the as-prepared varistors have refined and homogeneous microstructures, which result in improving their electrical properties. The optimal prepared samples were obtained by milling for 7.5 hours and sintering at 1100°C, which exhibited varistor voltage (V1mA ) of about 533 V/mm, non linear coefficient (α) reaching 36 and leakage current (IL ) of 2.96 μA.

Synthesis of Ti 3AlC 2/Al 2O 3 nanopowders by mechano-chemical reaction

Ti 3AlC 2/Al 2O 3 nanopowders were synthesized by the combination of mechanically-induce self-propagating reaction (MSR) of Ti, C, Al and TiO 2 powder mixtures and subsequently heat treatment. Effects of high energy milling and heat treatment temperatures on the phase transformation were investigated in detail. X-ray diffraction (XRD) was used to characterize the powders of milled and annealed, respectively. The morphology and microstructure of as fabricated products were also studied by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). Results show that TiC, Ti x Al y and Al 2O 3 transitional phases were formed when the initial powder mixtures were milled for 24 h. The desired Ti 3AlC 2/Al 2O 3 nanopowders with high purity were obtained when annealed the as-milled powders at 1100 °C. SEM image confirmed that the as fabricated Ti 3AlC 2/Al 2O 3 particles has nanocrystalline layered structural matrix of Ti 3AlC 2, and the second phase of nanosized Al 2O 3 disperses uniformly in the Ti 3AlC 2 matrix.

Electrochemical Properties of LiFePO<sub>4</sub>/C Composite Improved by High Energy Milling

The electrochemical properties of LiFePO4 as a cathode of lithium ion batteries considerably depend on a particle size of LiFePO4 and a condition of carbon coating. In this study, LiFePO4 powders were prepared using ultrasonic spray pyrolysis method, and then LiFePO4/C composites were made by infiltrating sucrose solution into LiFePO4 powders, drying, high-energy milling and annealing. The effects of high-energy milling were analyzed by comparing with electrochemical properties of powders synthesized without high-energy milling. It was found that the milling process drastically reduced the particle size of synthesized powders and electrical conductivity, and improved discharge capacity, cycle stability and rate performance.

Mechanical Milling of Prealloyed Cu-Cr Powders Prepared by Gas Atomization

In this study, we investigate the effects of high energy milling under Ar atmosphere on the morphology, size and microstructure of Cu-Cr alloy powders prepared by gas atomization. The attrition milling using stainless steel balls is performed up to 60 hrs. The observation by SEM and TEM shows apparent sequential changes of morphology and size of powders similar to those that are typical for mechanically alloyed elemental powders. Prolonged milling in the steady state regime produces a nano-crystalline structure, consisting of extremely small grains of 20 to 50 nm in size and finely dispersed Cr particles. It is also shown that the uptake of Fe from the stainless steel balls and vessel is appreciable. The microhardness of milled powder increases with the milling time, reaches its peak and then slightly decreases.

Effects of high energy milling on densification behaviour of Mo–Si powder mixtures during pressureless sintering

The present paper reports on basic investigations of the controlled reaction sintering of MoSi 2-based materials, including particle reinforced composites. It is shown, that certain amounts of pre-formed silicide phase in the powder mixtures are useful to achieve high densities by pressureless sintering of green compacts. This partial phase formation of αMoSi 2 can already take place during the mechanical treatment of the elemental powder mixtures by milling. In this context the role of volume changes linked with the phase formations is discussed.

The effects of high-energy milling on GdFe 2

With the aim of better understanding, the effects of severe milling on the magnetic and structural properties of crystalline compounds, samples of the intermetallic compound GdFe 2 were milled up to 276h under inert atmosphere and characterized by X-ray diffractometry (XRD) and Mössbauer spectroscopy (MS). On milling GdFe 2 a strong segregation of the elements Gd and Fe initially occurred, and the characteristic peaks of the initial compound GdFe 2 in the XRD pattern are absent after 1 h of milling. MS and XRD results also show that the milled samples contain a mixture of three main components: the segregated elements, the initial compound and an amorphous alloy, with relative proportions that vary with milling time. At the longer milling times the process induces a solid-state reaction between these components leading to the formation of an amorphous solid solution of Gd and Fe. In these cases the Mössbauer spectra taken at 300, 84 and 4.2 K were fitted with a combination of a set of peaks typical of metallic α-Fe and a continuous distribution of hyperfine magnetic fields that are ascribed to the amorphous Gd-Fe phase.

The effects of high-energy milling on the structural and hyperfine properties of YFe 2

Mössbauer spectroscopy, X-ray diffraction and nuclear magnetic resonance have been used to study the effects of severe milling on the atomic and magnetic properties of the ferromagnetic intermetallic Laves phase compound YFe 2. The Mössbauer effect and nuclear magnetic resonance were carried out on the Fe site and on the Y site, respectively. Consistently, after 30 h of milling, the results indicate that the milling process induces structure and atomic disorder. The X-ray diffraction pattern shows no crystalline reflection planes, indicating that the structure is amorphous within the experimental resolution. The Curie temperature reduces from 542 K to less than 100 K after 50 h milling, although at 4.2 K the average 57Fe magnetic hyperfine field value remains near the same as in the original crystalline compound.