Milling Intensity Research Articles

The evolution of structure induced by intensive milling in the system 2Bi2O3 · 3TiO2

Concurrent mechanochemical treatment of either a stoichiometric 2Bi2O3·3TiO2 powder mixture or (pulverized) Bi4Ti3O12 compound was performed in a planetary ball mill. Relevant structural parameters: crystallite size, amount of amorphous phase and the transformed fraction (as a result of chemical reaction between Bi2O3 and TiO2) of the powders milled for various milling times and intensities were derived from X-ray powder diffraction data. The obtained structural parameters were used to follow the kinetics of the reduction of crystallite size, amorphous phase formation and chemical reaction. In the powder mixture, during the early stage of mechanochemical treatment the Bi2(CO3)O2 phase was found as an intermediate product which transformed into the highly amorphized Bi4Ti3O12 phase as the milling progressed. On the other hand, mechanochemical treatment of Bi4Ti3O12 powder induced a gradual deformation of the crystal lattice and destruction of the perovskite-type structure. However, in both cases, after a certain milling time, a very disordered, amorphous/nanocrystalline structure was obtained. It was demonstrated that in the steady state, the amorphous/nanocrystalline phase ratio depends on the milling conditions. Higher milling intensities induce ‘nanocrystallization’ of the amorphous phase, i.e., precipitation of crystallites with an average size below 20nm. A kinetic model involving a nanocrystalline↔amorphous reaction, in which the forward and reverse reaction were first-order was postulated and used to analyze the formation of an amorphous phase.

Electroluminescent efficiency of alternating current thick film devices using ZnS:Cu,Cl phosphor

ZnS:Cu,Cl phosphor is prepared with the help of low intensity milling of the precursor material in two step firing process. The synthesized phosphor is used for the preparation of alternating current thick film electroluminescent (ACTFEL) devices with screen-printing method. The commission international de l’Eclairge (CIE) color co-ordinates of the ACTFEL devices prepared by these phosphor layers shows a shift from bluish-green to green region with the change in the amount of Cu in the phosphor. The various parameters to improve the efficiency and luminance of the devices have also been investigated. The brightness of the ac thick film EL device depends on the particle size of the phosphor, crystallinity, amount of binding material and applied voltage. The EL device fabricated with phosphor having average particle size of 25 μm shows maximum luminescence, when 60% phosphor concentration is used with respect to binding material. EL intensity is also linearly dependent on frequency. It is due the increase of excitation chances of the host matrix or dopant ions with increasing frequency.

Formation and Magnetic Properties of Nanocrystalline Fe<SUB>60</SUB>Co<SUB>40</SUB> Alloys Produced by Mechanical Alloying

The Fe60Co40 alloys were prepared by mechanical alloying of the Fe and Co powders using a high-energy ball mill. They were studied with respect to phase formation and magnetic properties using x-ray diffraction, scanning electron microscopy, and measurements of coercivity and remanence (Br). The evaluation of Fe lattice parameters during milling showed that formation of a body-centered cubic solid solution occurred by mechanical alloying after 12 h of milling. Intensive milling of Fe-Co powders results in a nonequilibrium microstructure characterized by grain refinement to a minimum of 10–13 nm and the introduction of internal strain up to 0.5%.

Temperature of the milling balls in shaker and planetary mills

The temperature increase of the milling balls in two laboratory mills, frequently used for mechanical alloying and mechanochemical experiments, was studied using direct calorimetric measurements. The ball temper- ature remains below 100 � C in a SPEX 8000 shaker mill and it is cooler when flat-ended rather than round-ended vial is used, although the milling intensity, as measured by the mechanical dose rate, follows the opposite trend. Temperatures over 200 � C are typical in planetary mills operating at similar milling intensities. It is suggested that the higher ball temperatures result from more oblique collisions and friction, while the lower temperature but higher intensity of the shaker mill with flat-ended vial is due to the larger proportion of frontal impacts.

Investigation on possibility of mechanochemical synthesis of CaTiO 3 from different precursors

Recently, mechanochemical synthesis was widely used in preparation of perovskite type of materials, such as BaTiO 3, PbTiO 3, PZT, etc. In this work, the possibility of mechanochemical synthesis of CaTiO 3 from different precursors, such as CaCO 3 or CaO and TiO 2 was investigated. Intensive milling of mixture of CaO and TiO 2, under optimal milling conditions, resulted in synthesis of single phase CaTiO 3. It was also found that intensive milling of powder mixture containing CaCO 3 and TiO 2 only activate the powders for the sintering process; hence the CaTiO 3 could be obtained at lower temperatures of sintering. To complete reaction of CaTiO 3 formation during milling it is necessary to reduce CO 2 partial pressure, i.e. it is necessary to change the atmosphere inside the vials during milling. In this work, an explanation for difference in milling behavior of different precursors was proposed and discussed.

Microstructure characterization of mechanically activated hematite using XRD line broadening

The effect of dry milling in a vibratory mill on the structural changes and microstructural characteristics of hematite using different methods was investigated. We have described the line profile analysis (LPA) to extract the size of coherently diffracting domains and the lattice strain of activated hematite in a vibratory mill. The Warren–Averbach and Williamson–Hall methods were used as the main tools for characterization. The changes in the particle size, surface area and new phase formation of hematite concentrate were also investigated. It was concluded that the breakage and agglomeration of particles take place mainly at lower and higher levels of specific energy input, respectively. The pores in agglomerates remain accessible for the nitrogen gas. Milling of hematite increased specific surface area up to 18.4 m 2/g. The hematite milled under various levels of specific energy input did not undergo a significant reaction or phase transformation during milling. The Williamson–Hall method confirms its merit for a rapid overview of the line broadening effects and possible understanding of the main causes. The anisotropic character of line broadening for deformed hematite as a function of specific energy input was revealed. Higher level of specific energy input favors the generation of small crystallite size, higher microstrain, BET surface area, amorphization and line breadth. The Warren–Averbach method suggested that the nanocrystalline hematite with grain sizes of 73.5–12.2 nm was formed by mechanical treatment using different milling intensities in the vibratory mill. The root mean square strain (RMSS) at L = 10 nm varies between 1.7 × 10 − 3 and 4.0 × 10 − 3 depending on the level of energy input. Limits in the applicability of Williamson–Hall method and reliability of the results are discussed in detail.

Mechanical Alloying of Al<sub>2</sub>O<sub>3</sub>-Co Powders Mixture

Nanocomposite Al2O3-Co was prepared by high-energy ball milling technique. Nanoscaled alumina particles (γ-Al2O3) of 5wt% with nominal size 39 nm were dispersed in cobalt matrix. The phase transformation of the element occurs in the powders mixture during the process was monitored by X-ray diffractometry (XRD). The results showed that cobalt exhibits phase transformation when subjected to ball milling. The phase formation of cobalt was found to depend on the milling intensity. As the milling time increased, the amount of the hexagonal close-packed (hcp) phase decreased.

Synthesis of Al<sub>2</sub>O<sub>3</sub>-Ni<sub>3</sub>Al Cermets by Room-Temperature Ball Milling of Al, Ni and Al<sub>2</sub>O<sub>3</sub> Mixtures

The synthesis of Al2O3-Ni3Al cermets with interpenetrating networks has been performed via a pressureless reactive sintering process. The synthesis has been induced by means of a solidstate reaction of Al + Ni + Al2O3 powders under intensive ball milling. The mixtures have been heat treated in an inert atmosphere (N2) in order to control the exothermic reaction between Ni and Al, with special care at temperatures near the melting point of Al. Dense and homogeneous microstructures have been obtained, composed by a matrix of Al2O3 reinforced with a Ni3Al intermetallic. Thermodynamic calculations indicate that such a cermet can be fabricated by in situ reaction synthesis. This suggests that a pressureless reaction sintering process may be a general route to synthesizing cermets with the prospect for the production of cermets with interpenetrating networks.

新しいエネルギー集中型媒体ミルによるＺｎＯ‐ＴｉＯ２系化合物粉末のメカノケミカル合成

Mechano-chemical (MC) synthesis of photocatalyst compound powders in ZnO-TiO2 system was carried out by a new high energy ball mill with functions of the powder layer formation onto inner wall of revolving vessel and the intensive impact of medium ball on the layer. Crystal grown of compound zinc titanate in MC treatment, shown in XRD patterns, was different with inner diameter of revolving vessel and inclined angle of "guide vane". Higher diffraction peaks and narrower half width of compound ZnTiO3 powders synthesized in MC treatment were obtained over 20 h of treatment time, compared to that by a planetary ball mill. Furthermore, the high intensive mill is capable to obtain higher yield of MC treated powders.

エネルギー集中型高速・高純度ミルの基本性能

The milling and mechanical alloying (MA) performances of a new high energy ball mill with functions of the powder layer formation onto inner wall of revolving vessel and the intensive impact of medium ball on the layer were studied. The high intensive mill is capable to decrease of powder size under 5 μm at 1.8 ks of treatment time for glass, bottom ash and tourmaline, and at 7.2 ks for Japanese cedar powder. In Ni-Al system, crystallite size of Ni (111) was dramatically decreased under 18 nm within 14.4 ks of milling, and further milling led to the formation of Ni3Al at 180 ks of treatment time. In this study, we develop the performance of this high intensive mill for milling, mechanical alloying and mechanochemical synthesis, which permit us to obtain higher rate of collection and lower impurity concentration of treated powders.

Effect of milling and sieving on functionality of dry powder inhalation products

α-Lactose monohydrate is the standard excipient used as diluent or carrier in dry powder inhaler (DPI) formulations. Earlier studies have already revealed that raw materials for the production of inhalation grade lactose have to be carefully selected in order to avoid batch-to-batch variability. In the present study, the effect of milling and milling intensity on the flow properties and the physico-chemical characteristics of lactose crystals has been determined. The milled lactoses were then further processed by sieving to give lactose qualities with identical size distribution data, but different batch history (non-milled and milled at different conditions). These were then used to manufacture low concentration (0.25%) drug blends with the model drugs salbutamol sulphate (SBS) and beclometasonedipropionate (BDP); the blends were analysed with a Multistage Liquid Impinger (MLI) after delivery from an Easyhaler ® and an Aerolizer ® device. It could be shown that gentle milling already results in surface defects on the lactose crystal which are further enhanced by using a higher milling intensity. Produced fine lactose particles during the milling process strongly adhere to the lactose surface and cannot be removed by compressed air which is used for the particle sizing. By trend, a higher milling intensity resulted in higher fine particle fractions (FPF) with both devices. Also, SBS was found to generally give higher fine particle fractions than BDP, independent from the device used. In conclusion, lactose pre-treatment by gentle or strong milling affects the carrier surface and thereby the aerosolization properties of drug/lactose blends produced.

Hydriding kinetics and process parameters in reactive milling

We focus on the hydriding kinetics of Mg 2Ni/Ni nanocrystalline and Zr 55Cu 30Al 10Ni 5 amorphous powders under reactive milling conditions. A methodological approach, based on mechanochemical parameters, is presented to quantify the different behaviour shown by the two systems. A decelerating course characterized the H 2 absorption rate in the Mg based powders. Although they were able to absorb H 2 under static conditions, a speeding up of the kinetics was observed under milling. The mechanochemical gain, g m , that is the rate increase at the milling outset, was found to depend on the specific milling intensity I M . By contrast an incubation period preceded the absorption in the case of the Zr based amorphous powders. Furthermore, S-shaped trends described the reactive behaviour in this case even if the kinetics was still dependent on I M . Irrespective of the milling intensity it was found that the same mechanical work, that is the energy dose, was required to reach the maximum hydriding rate.

Hydrogen sorption properties of Mg–1 wt.% Ni–0.2 wt.% Pd prepared by reactive milling

Despite the large differences in melting points and the high vapour pressure of Mg, we succeeded in the preparation of induction-melted Mg–1 wt.% Ni–0.2 wt.% Pd alloy. The alloy was then reactively ball milled in 10 bar hydrogen. The structural changes during milling were characterised by XRD and high resolution scanning electron microscopy. The hydrogen sorption properties have been systematically studied by gravimetric analysis in a wide temperature and pressure range for absorption (1–10 bar, 50–300 ° C) and desorption (250–350 ° C, 50 mbar–1 bar). The combined effects of Pd and Ni additions prove particularly useful in providing superior kinetics at very modest absorption conditions and excellent cyclic stability. These data are compared with those of nanocrystalline MgH 2 powders, obtained by intensive milling in argon atmosphere.

Composites Derived from Zirconia Nanopowders Stabilized with Yttria and Containing Alumina Particles Incorporated Physically or Chemically

Two methods of incorporating Al2O3 inclusions into a polycrystalline matrix of tetragonal zirconia stabilized with yttria (3Y-TZP) were used, and their influence on the microstructure and properties of TZP/Al2O3 composites has been studied. The first method consisted in the physical mixing of the component powders by means of intensive milling. The second method utilized the possibilities of the coprecipitation method of chemically homogeneous deposits followed by their calcination. An aqueous solution of zirconium, yttrium, and aluminum salts was used. Green compacts were shaped by cold isostatic pressing under a pressure of 300 MPa, and then they were sintered under no pressure for 2 h at 1500–1650°C in air. The powders were also consolidated using hot pressing under 25 MPa in argon and under the same heating cycle as in the case of pressureless sintering. The composites studied contained from 0 to 20 vol % of alumina inclusions, whose sizes depended on the powder preparation method. The morphology and phase composition of the powders and the microstructure of the green compacts and sintered materials were characterized. Bending strength, fracture toughness, and wear were measured. The coprecipitation method enabled us to produce composites that contained nanosize alumina inclusions. The inclusions derived from this method were much smaller than those derived from the physical mixing method (d 50 = 0.21 ± 0.01 and 0.32 ± 0.2 µm, respectively). The reduction in the alumina inclusion size nearly to the nanometer level did not increase the fracture strength and fracture toughness of the composites. The density of the composites and the size of microstructural flaws were the critical factors controlling the fracture strength. The highest strength value, namely, 1.7 ± 0.2 GPa, was measured for the TZP containing 5 vol % of alumina particles incorporated by means of the physical mixing process. The 20 vol % content of alumina particles increased the wear resistance of the 3Y-TZP materials by 51 and 41% for the physical and chemical methods of inclusion incorporation, respectively.

Cu 5Si–Si/C composites for lithium-ion battery anodes

Cu 5Si–Si/C composites with precursor atomic ratio of Si:Cu = 1, 2 and 4.5 have been produced by high-energy ball-milling of a mixture of copper–silicon alloy and graphite powder for anode materials of lithium-ion battery. X-ray diffraction and scanning electron microscope measurements show that Cu 5Si alloy is formed after the intensive ball milling and alloy particles along with low-crystallite Si are interspersed in graphite uniformly. Cu 5Si–Si/C composite electrodes deliver a larger reversible capacity than commercialized graphite and better cyclability than silicon. The increase of copper amount in the composites decreases reversible capacity but improves cycling performance. Cu 5Si–Si/C composite with Si:Cu = 1 demonstrates an initial reversible capacity of 612 mAh g −1 at 0.2 mA cm −2 in the voltage range from 0.02 to 1.5 V. The capacity retention is respectively 74.5 and 70.0% at the 40th cycle at the current density of 0.2 and 1 mA cm −2.

Kinetics of structural evolution in immiscible Ag–Cu and Co–Cu systems under mechanical processing conditions

The effects of mechanical processing by ball milling on powder mixtures consisting of immiscible elements were studied. Equiatomic Ag–Cu and Co–Cu mixtures were subjected to mechanical treatment at different values of milling intensity. The kinetics of structural evolution were characterized by means of X-ray diffraction analyses taking advantage of the Rietveld method. The evolution processes followed sigmoidal trends, the rate of evolution being proportional to the milling intensity and thereby connected with the impact energy. A threshold impact energy was determined below which no structural evolution is observed.

Hydrogen production via hydrolysis reaction from ball-milled Mg-based materials

Hydrogen generation by hydrolysis of Mg and MgH 2 has been investigated in pure water and 1 M KCl. It has been found that hydrolysis reaction of Mg and Mg–Ni composite, both obtained by high-energy ball milling, is faster and extensive when they are immersed in 1 M KCl. In contrast, milled Mg and Mg–Ni composite in pure water, MgH 2 and MgH 2 –Ni composites in pure water and in 1 M KCl show low yield and reactivity. Hydrolysis kinetics and yield are maximum with Mg–10 at% Ni composite milled for 30 min, so reaction is fully completed within an hour in the presence of chloride ions. It is related to the creation of micro-galvanic cells between Mg and dispersed Ni elements, accentuating greatly Mg corrosion in highly conductive aqueous media. A significant increase of the H 2 production is also observed with 30 min milled Mg sample, likely because of the accentuation in the pitting corrosion resulting from the creation of numerous defects and fresh surfaces through the milling process. On the other hand, intensive ball milling of pure magnesium has no effect on the Mg reactivity in pure water. Ball milling effect is likely masked by the significant Mg passivation in pure water. A correlation is established between the conversion yield of ball-milled MgH 2 powder in pure water and its effective surface area, which is increased by the milling process. Ni addition has no effect on the hydrolysis reaction in nonconductive media (i.e. pure water) and with nonconductive material (i.e. MgH 2 ).

Abnormal growth of TiB2 crystals during sintering of TiB2-Ni3(Al,Ti) cemented borides

TiB2-Ni3(Al,Ti) cermets present both normal and abnormal growth of faceted titanium diboride (TiB2) grains during liquid-phase sintering. Abnormal grain growth (AGG) is preferentially found at high sintering temperatures in specimens processed from powder mixtures with a wide particle size distribution. The WC additions to the initial powder mixtures have proved efficient in reducing the number and size of these large TiB2 grains. However, the sinterability of these materials is dramatically reduced, which suggests that TiB2 AGG control is obtained by decreasing TiB2 dissolution kinetics in the liquid phase. On the other hand, an alternative method based on intensive powder milling not only reduces TiB2 AGG but also the porosity levels obtained by previous powder processing routes. TiB2 cermets produced by aggressive milling present a higher amount of alumina particles in the matrix after sintering, which, in addition, appear more homogeneously dispersed in the microstructure. The distortion produced by these particles on the facets of TiB2 growing grains suggests a possible dragging effect responsible for the AGG reduction found in these cermets. Moreover, aggressive milling removes large TiB2 particles from the powder mixtures, which could act as seeds for TiB2 uncontrolled growth. TiB2-Ni3(Al,Ti) cermets obtained by intensive milling combine hardness over 20 GPa with K IC of about 10 MPa √m, data clearly out of the range covered so far by other TiB2-based materials.

Structural Refinement in Al-MoO3 Nanocomposites Prepared by Arrested Reactive Milling

AbstractAl-MoO3 nanocomposites were synthesized based on arrested reactive milling. Altering the milling parameters leads to different scales of refinement in the structure of the reactive nanocomposites. The objective of this work is to determine the range in which the degree of structural refinement can be changed in a controlled manner. The milling intensity was controlled by using different milling media along with varying amounts of process control agent (PCA). XRD, SEM, DSC and wire-ignition tests were performed to analyze the Al-MoO3 nanocomposites. Results indicate that there is a decrease in the crystallite size with increase in the milling intensity. However increase in milling intensity also stimulates the undesired reaction between Al and MoO3. Milling conditions resulting in the highest structural refinement and lowest ignition temperatures were identified.

Corrosion behavior of Nd–Fe–B/α–Fe nanocomposite magnets

For the fundamental evaluation of corrosion properties of nanocrystalline Nd–Fe–B-based magnets, different phase mixtures with compositions varying from single phase Nd 2Fe 14B to Nd 2Fe 14B+10 wt% Fe, Nd 2Fe 14B+25 wt% Fe and Nd 2Fe 14B+35 wt% Fe were prepared via intensive ball milling and subsequent hot-pressing. Before and after corrosion measurements, the samples were investigated by means of high-resolution scanning electron microscopy. Potentiodynamic polarisation measurements were performed in 0.5 M phthalate buffer ( pH = 5 ). With increasing α–Fe fraction, a decrease of the corrosion rate is observed as well as improved passivation.