Effect Of High-energy Milling Research Articles

The Structure and Magnetic Properties of (Sm,Er)-Fe-N Powders Prepared by Ball Milling

Nitrides of ‘2:17’ - type based on rare earth metals and iron are of interest as promising magnetic materials for the development of high-energy permanent magnets. The magnetic properties and phase composition of the starting compound Sm1.8Er0.2Fe17, nitride Sm1.8Er0.2Fe17N2.1 and its crushed powders have been investigated. The magnetic measurements of the samples were studied in magnetic fields up to 70 kOe at room temperature. It was found that the introduction of nitrogen atoms into the crystal lattice of the substituted composition (Sm,Er)2Fe17 in combination with the effect of high-energy milling of nitride leads to an increase in the saturation magnetization (σS) and coercive force (HC).

Effect of High-Energy Milling on the Dissolution of Anti-HIV Drug Efavirenz in Different Solvents

The anti-HIV drug efavirenz (EFV) displays low and variable bioavailability because of its poor aqueous solubility. Ball milling is a simple and cost-effective alternative to traditional micronization to improve the solubility and dissolution rate of EFV. A multibody dynamics model was employed to optimize the milling process parameters, while the motion of the balls in the mill jar was monitored in operando. This led to a better understanding of the milling dynamics for efficient comminution and enhancement of EFV dissolution. The variability of results for different EFV batches was also considered. Depending on the EFV batch, there were intrinsic differences in how the milling affected the dissolution behavior and inhibition of HIV-1 infection. High-energy grinding is more effective on EFV materials containing an amorphous fraction; it helps to remove agglomeration and enhances dissolution. Polyvinylpyrrolidone (PVP) addition improves the dissolution by forming a hydrophilic layer on the EFV surface, thereby increasing the drug wettability. Polymorphism also affects the quality, dosage, and effectiveness of the drug. The mechanical stress effect and PVP addition on the EFV polymorphic transformation were monitored by X-ray powder diffraction, while the residual of ground EFV was collected after dissolution, analyzed by scanning electron microscopy, and provided insights into the morphological changes.

Effect of High-Energy Milling and Sintering Temperature on the Properties of Al2O3-WC-Co Composites

Al2O3-WC-Co composites have specific properties, such as low density, high oxidation resistance and high melting point. In this work, Al2O3-WC-Co composites obtained by high-energy milling (HEM) were thermally and microstructurally assessed by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and dilatometry. Powder mixtures containing 80 wt.% Al2O3—18 wt.% WC—2 wt.% Co were processed by HEM using milling times in the range of 2 h to 50 h. The milled powders were compacted at 200 MPa and further sintered in a dilatometer (using argon atmosphere) at 1300 °C and 1550 °C. The raw materials were characterized by SEM, dynamic light scattering (DLS) and energy-dispersive X-ray spectroscopy (EDS). The XRD results showed a decrease in crystallite sizes, accompanied by an increase in the lattice micro-strain. The dilatometric curves showed that samples sintered at 1550 oC are denser than those prepared at 1300 oC. Moreover, higher grain growth was observed with increasing the sintering temperature. The green density values of the samples varied from 56 to 58%. The sintered samples obtained relative densities between 60 and 80%. The improved sample densification, achieving a relative density of 80% after sintering at 1550 °C is ascribed to a liquid-phase-assisted sintering mechanism.

The effect of high energy milling and high thermal treatment on the structure and thermal decomposition of minerals from natural CaO-SiO2-P2O5 ceramic system

The major issue studied in this paper is a natural mineral aggregate of quartz, calcite, and fluorapatite (the raw material originated from Bulgaria) before and after high energy milling and thermal treatment, in the order to investigate the properties of natural CaO-SiO2-P2O5 ceramic system. The activation effects are monitored by chemical analysis, X-ray powder diffraction, Fourier transformed infrared spectroscopy, and Thermal analysis (TG/DTG).The activation effect study shows: (i) change of chemical bond strength; (ii) deformation of structural polyhedrons with the formation of new isomorphic phases; (iii) the prolonged time of HEM activation leads to lower raw mineral stability and to the formation of new phases; iv) increased SiO2 reactivity resulting in solid-phase crystallization.The obtained results can be used in the study of ceramic and cement materials (ancient and modern), soil conditioners, etc.

Effect of high-energy milling on the structure, some physicochemical and photocatalytic properties of clinoptilolite

The Natural and H-form of clinoptilolite were subjected to mechanochemical treatment in water and in air. Initial and milled samples were studied using a combination of XRD, FTIR, XPS/UV–vis spectroscopies, SEM and low-temperature nitrogen ad-/desorption. Dry milling leads to the destruction of the crystalline structure, whilst milling in water partially maintains the crystalline structure with a meso- macroporous structure formed in both cases. Surface was enriched with impurity iron, whose oxygen-containing species served as photocatalytic centres. The milled samples exhibit an improved photocatalytic activity in the process of rhodamine B degradation under visible light.

Effect of high energy milling on microstructure and mechanical properties of Al2O3-10 wt% Co composites consolidated by spark plasma sintering (SPS)

Al2O3-10 wt% Co composites were prepared by high energy milling in the presence of ethyl alcohol and with subsequent spark plasma sintering (SPS). The powders milled for 5 and 30 h were sintered by SPS at 1350 °C for 5 min. The effect of milling time on the sinterability and mechanical properties was studied. The morphology and structure of milled powders were investigated by scanning electron microscopy, dynamic light scattering and X-ray diffraction. The Co phase forms plate-like particles of different sizes, while finely fragmented Al2O3 particles are incorporated in the Co phase, forming composite particles. The average size of the composite particles decreases with increasing milling time, achieving 1.33 μm after 30 h. Crystallite size and micro-strain are inversely proportional. Overall, all the samples display homogeneous microstructures, high density (85.29–91.60%) and microhardness in the range 11.41–14.37 GPa.

Influence of high energy milling on powder morphology and photoluminescence behavior of Eu-doped YBO3 material

The effect of high energy milling on the powder morphology and photoluminescence of Eu (5mol %)-doped YBO3 phosphor materials was studied. The Eu-doped YBO3 materials were prepared via conventional solid-state mixing method followed by milling for 30 min and 1 h. The crystallite and particle size of the phase pure Eu-doped YBO3 powders were found decrease with milling time, as confirmed from Scherrer's formula and electron micrographs, respectively. Rupture of the phosphor powders led to formation of smaller particles, which were also found deposited on the surface of bigger particles during milling. The emission spectra of un-milled and milled samples were excited at 238 nm, 254 nm and 394 nm, and several peaks were observed in the emission spectra in the region from 580 nm to 700 nm, which correspond to the transition of europium ions from 5D0→7FJ (J = 0, 1, 2, 3, 4) levels. The emission intensity ratio between red and orange (R/O) is greater than unity for all samples when excited at 238 nm, 254 nm and 394 nm, which indicates that the samples are red in color purity. Further, the CIE co-ordinates suggest that all of the samples fall in the reddish region and using 254 nm as an excitation wavelength gives better CIE co-ordinates for all samples.

Effects of high mechanical treatment and long-term annealing on crystal structure and thermal stability of Ti2O3 nanocrystals.

The effect of high-energy milling and long-term annealing on the stability of Ti2O3 nanocrystals was studied using a magnetic susceptibility method. In situ temperature dependences revealed that the crystal size greatly affects the magnetic susceptibility value. According to XRD, SEM and TEM data, Magnéli phases Ti9O10, Ti4O7, Ti7O19 and Ti3O5 are formed.

Improved Mg–Al–Zn Magnesium Alloys Produced by High Energy Milling and Hot Sintering

Powders of commercially pure magnesium (c.p. Mg), AZ91 magnesium alloy and zinc were milled using a high-energy mill. The effect of high energy milling (HEM) on powders morphology, chemical composition, crystallite size and compaction of different powders mixtures were studied. After compaction, samples were thermally treated at 450 °C and both density and hardness were evaluated. It was found that as milling speed and time increases, the AZ91 alloy and c.p. Mg particles were deformed and fractured up to sizes below 10 μm. X-ray diffraction patterns for both the c.p. Mg and the AZ91 powders revealed that the milling process induced changes in both the α-Mg and the β-Mg17Al12 phases. By increasing the milling speed, the crystallite size decreases by up to 70% for AZ91 powders and by 80% for magnesium powders. The relative densities of the compacted AZ samples were greater than 85% and this parameter increased for all samples after thermal treatment at 450 °C, obtaining densities higher than 88%. Hardness measurements disclosed values as high as 84.3 HR15T. Theoretical calculations of mechanical strength were obtained for all samples based on the hardness values measured, finding very encouraging results for the three Mg alloys.

Effect of High-Energy Milling on Magnesiothermic Self-Propagating High-Temperature Synthesis in a Mixture of SiO2, C, and Mg Reactant Powders

A mixture of SiO2, C, and Mg powders is mechanically milled in a planetary ball mill during different milling times of 60, 90, 120, and 150 min. The milled powders are then used in a self-propagating high-temperature synthesis (SHS) reaction to produce the Si–SiC composite. The thermal properties of the milled powders are determined by using differential scanning calorimetry and thermogravimetry. The chemical composition and microstructure of both as-synthesized products and as-leached powders are characterized by the x-ray diffraction analysis and scanning electron microscopy, respectively. The results show that an increase in the milling times of the mixture of the reactant powders has a significant effect on the thermal properties, diffusion processes, and SHS reaction mechanisms, as well as on the phase conversion and the final yield of the products.

Mechanochemically driven amorphization of nanostructurized arsenicals, the case of \u03b2-As4S4

The amorphization is studied in mechanically activated β-As4S4 using high-energy ball milling in a dry mode with 100–600 min−1 rotational speeds, employing complementary methods of X-ray powder diffraction (XRPD) related to the first sharp diffraction peak, positron annihilation lifetime (PAL) spectroscopy, and ab initio quantum-chemical simulation within cation-interlinking network cluster approach (CINCA). The amorphous substance appeared under milling in addition to nanostructurized β-As4S4 shows character XRPD halos parameterized as extrapolation of the FSDPs, proper to near-stoichiometric amorphous As–S alloys. The structural network of amorphized arsenicals is assumed as built of randomly packed multifold cycle-type entities proper to As4S4 network. The depressing and time-enhancing tendency in the PAL spectrum peak is direct indicative of milling-driven amorphization, associated with free-volume evolution of interrelated positron- and Ps-trapping sites. At lower speeds (200–500 min−1), these changes include Ps-to-positron trapping conversion, but they attain an opposite direction at higher speed (600 min−1) due to consolidation of β-As4S4 crystallites. In respect of CINCA modeling, the effect of high-energy milling is identified as destruction–polymerization action on monomer cage-type As4S4 molecules and existing amorphous phase, transforming them to amorphous network of triple-broken As4S4 derivatives. These findings testify in a favor of “shell” kinetic model of solid-state amorphization, the amorphous phase continuously generated under speed-increased milling being identified as compositionally authentic to arsenic monosulfide, different in medium range ordering from stoichiometric As2S3.

High energy milled Ba<inf>0.06</inf>Na<inf>0.47</inf>Bi<inf>0.47</inf>TiO<inf>3</inf> ceramic: Structural and electrical properties

The present work reports on the effect of high energy milling on the structural, microstructural, electrical and electrostriction properties of Ba 0.06 Na 0.47 Bi 0.47 TiO 3 (BNBT) ceramics prepared using standard solid-state reaction technique. X-ray diffraction studies showed that the unit cell structure of un-milled and milled samples is rhombohedral (space group: R3c). FTIR spectra also indicated the formation of BNBT without any new phase. The 10 h milled BNBT (spherical nanoparticles of 25–50 nm) ceramic showed the formation of small grain sizes (∼ 1.2 μm) which is advantageous for dielectric applications in high density integrated circuits. Milling could suppress the resonance effect which is beneficial for extending the upper limit if frequency for the use of a capacitor. The correlated barrier hopping model successfully demonstrated the mechanism of charge transport in present ceramic system and ac conductivity data obeyed Jonscher's universal power law. A marked enhancement in the remnant polarization and lowering of the value of coercive field of milled BNBT sample was observed. The electric field dependent polarization and strain studies carried out at room temperature indicated that BNBT nanoceramic might be a propitious lead-free electrostriction material for industrial applications.

Effect of milling on the electrical properties of Ba(Fe1/2Ta1/2)O3 ceramic

In this work effect of high energy milling on the structural and electrical properties of Ba(Fe1/2Ta1/2)O3 (BFT) ceramic synthesized using standard solid-state reaction method were investigated. X-ray diffraction studies indicated that the unit cell structure for all the samples to be hexagonal (space group: P3m1). FTIR spectra also confirmed the formation of BFT without any new phase. The milled (10 h) BFT ceramic showed the formation of small grain sizes (<2 µm) which is beneficial for dielectric applications in high density integrated devices. Besides, the milled (10 h) BFT ceramic sample exhibited superior dielectric properties (enhancement in e´-value and reduction in tgδ - value) compared to un-milled one. Impedance analysis indicated the negative temperature coefficient of resistance (NTCR) character. The correlated barrier hopping model (jump relaxation type) is found to successfully explain the mechanism of charge transport in present ceramic samples.

Effect of high-energy ball milling on the electrical properties of NaTaO3 ceramic

In this work, the effect of high energy milling time on the structural and electrical properties of NaTaO3 (NT) ceramics synthesized using standard solid-state reaction method was investigated. X-ray diffraction studies indicated that the unit cell structure for all samples is orthorhombic (space group: Pnma). FTIR spectra also confirmed the formation of NT without any new phase. The NT ceramics prepared with 10 h milled powder showed the formation of small grain sizes (?1.2 ?m) which is beneficial for dielectric applications in high density integrated devices. The NT ceramics prepared with the 10 h milled powder exhibited superior dielectric properties, i.e. enhancement in ?? value (from 290 to 1270) and reduction in tg ? (from 0.59 to 0.23) at 1 kHz compared to the ceramics prepared with the unmilled powder. Impedance analysis indicated the negative temperature coefficient of resistance (NTCR) character with non-Debye type of dielectric relaxation. The correlated barrier hopping model successfully explains the mechanism of charge transport in the present ceramic samples. The values of remnant polarization and coercive field of the poled samples prepared with the unmilled and 10 h milled powders were found to be 0.71 ?C/cm2 and 2.03 kV/cm and 8.74 ?C/cm2 and 4.14 kV/cm, respectively. The field dependent polarization studies at room temperature indicated that NT is a promising lead-free electrostrictive material for industrial applications.

Effect of high energy milling and compaction pressure on density of a sintered Nb–20%Cu composite powder

This work reports the influence of the use of composite particles of composition Nb–20wt.%Cu and the compaction pressure on density and structure of sintered pieces. High energy milling is used to produce the composite powders. Milling times of 2, 20, 50 and 100h were used. The powders were pressed under 200, 300, 400 and 500MPa and sintered at 1100°C for 60min. After sintering, density was measured and cross sections of the structures were observed under SEM. The electric conductivity was also measured. Density and electric conductivity behave similarly with respect to compaction pressure and milling time. Cracks are created during pressing and ejection of the green pieces from the die. The cracks are mainly present in samples prepared with powders milled longer and are not closed by sintering. On the other hand, sintering can close most of the pores formed by the composite particles.

Effect of high-energy milling and thermal treatment on the solid-phase reactions in apatite–ammonium sulphate system

The phosphorous fertilizers are a product of natural sedimentary phosphorite ores. Using this raw material to produce phosphoric acid and classic phosphorous fertilizers has generated well-known ecological problems. A new and perspective way to use the same materials is creating a new type of time-delayed fertilizers applying high-energy milling (HEM) activation method. The impact of the mechanical forces over the solids is mostly revealed through the changes of the quantities being related to the energetic stability and reactivity of the solid phase. The aim of this work is to report the results from the investigation on the chemical and thermal reactions in composites of natural apatite , which are HEM activated for different times and thermally treated, (from Tunisia) and ammonium sulphate. The Tunisian phosphorite belongs to the ‘basic’ apatites having a Ca/P ratio of 1.70–1.77 and is characterized by a complex mineral composition with major component carbonate-fluorapatite. The used ammonium sulphate—(NH4)2SO4 is obtained as a by-product from cleaning industrial waste gases, using e-beam technology. The composites of Tunisian phosphorite ores and ammonium sulphate, mixed in a mass ratio 1:1, were HEM activated during 10 min to 50 h with 20 mm Fe-milling bodies and temperature treated up to 1,100 °C. As a result, the chemical properties of the treated composites changed. Proofs were found for (i) formation of new phases during HEM activation such as NH4Ca(PO3)3 (NH4)2CaH4(P2O7)2, (NH4)2Ca3(P2O7)2.6H2O, CaH2P2O7 and α-Ca2P2O7; and (ii) decreasing of temperature intervals of phase changes in comparison to untreated composite.

Interparticle and collective states of interactions in mechanically milled Fe/CoO nanocomposites

The effect of high-energy milling on magnetic properties of Fe/CoO nanocomposites has been studied. Formation of pure phase polycrystalline sample having size in the range 15–20 nm is confirmed from micro-structural analysis. Mossbauer spectroscopy indicates the formation of a broad distribution of particle sizes in the samples milled for higher duration. Enhancement in coercivity as well as exchange field is confirmed from magnetic hysteresis measurements. High-field bifurcation in temperature dependent magnetization measurement points toward the formation of spin-glass like state. Wait time dependent magnetization relaxation confirmed this possibility and is supported by the field cooled memory effect. Complexity arises when the absence of memory effect is observed in time dependent magnetic relaxation measurement. Polydispersity and defects are argued to be possible causes for observed spin-glass behavior.

Effect of high energy milling on the synthesis temperature, magnetic and electrical properties of barium hexagonal ferrite

Nanoparticles of barium hexagonal ferrite (BaFe12O19) have been synthesized by initial high energy milling of the precursors and sintering subsequently. X-ray Diffraction pattern reveals the hexagonal phase with a crystallite size of 42nm. Scanning Electron Micrograph (SEM) shows the size of nanoparticles to lie in the range of single domain particles. X-ray Photoelectron Spectroscopy (XPS) indicates Fe in +3 state and an associated surface peak indicates its presence at different environments. Vibrating Sample Magnetometer measurements (VSM) illustrate ferrimagnetism with high coercivity and non-saturation of hysteresis behavior up to 8500Oe. The initial high energy milling confines the particle size to the nanoscale which leads to high coercivity. Temperature dependent magnetization shows a sharp peak before transition which is the characteristic of the single domain magnetic behavior. Resistivity plot shows a decreasing trend with temperature. Two thermal activation energy values of 0.81eV and 0.29eV indicate the existence of two different conduction processes. The frequency dependent dielectric constant plot shows a semiconducting behavior. The dielectric loss plot shows a drastic change at high temperature due to the anion vacancies in addition to four types of polarization.

Effects of grinding on the preg-robbing potential of quartz in an acidic chloride medium

The effect of high-energy milling on the surface properties of quartz is examined with regard to its preg-robbing behavior towards gold. A standard ring mill is used to process dry quartz samples, and the changes in the morphology of the particles, structural deformations and surface chemistry are investigated to explain the increased preg-robbing ability of quartz in acidic chloride solutions. The transition from fine grinding to mechanochemical activation of quartz can be observed from changes in the morphology of the particles, as well as the types of structural deformations. The transition occurs between 1 and 5min of grinding in the mill used, corresponding to particle sizes around 0.55μm. Structural studies differentiate two stages of fine grinding: particle breakage with limited structural disruption, and structural disturbance by mechanochemical alteration, which occurs after particles reach their grinding limits. Quartz keeps its structural order to some degree even after 30min of aggressive grinding. The surface chemistry of ground quartz demonstrates generation of point defects including low valence silicon and non-bridging oxygen centers. These defect sites play an important role in the surface reactivity of the quartz, and influence the extent of gold loss during preg-robbing.

Efeito da Moagem de Alta Intensidade e da Irradiação Gama Sobre a Liberação de Potássio da Moscovita

eFFect oF the high energY milling AnD gAmmA irrADiAtion on the releAse oF potAssium From muscovite Brazil has a large and growing dependence on imports of potassium for use in agriculture. The development of potassium alternative sources has strategic importance. The grinding of rocks rich in structural potassium occurring in various regions of the country should be considered as a possibility, because the finer particles has shown accelerate the release of potassium. The objective of this paper was to investigate the effect of high energy milling and gamma irradiation on the rate of release of potassium from muscovite. It was observed that it is possible to obtain a particle size ranging from 10 to 11 µm by grinding with a planetary mill of high energy at 800 revolutions per minute for 6 hours. The ground samples in these conditions showed a rate of potassium release two times higher than a sample pulverized by conventional grinding with a particle size of 92µm. No effect of gamma irradiation until 600 kGy dose