Milling Intensity Research Articles

Selective mechanochemical alkaline leaching of zinc from zinc plant residue

A large amount of plant residue containing heavy and hazardous metals is generated in Iranian lead–zinc plant annually. The plant residue is known as hot filtercake (HFC) which contains 8–20% zinc, 6–16% manganese, 5–25% calcium and 0.5–3% cobalt. This paper is devoted to the mechanochemical alkaline leaching (MCAL) of zinc from HFC. The possibility of complete selective zinc leaching from HFC by the MCAL method was investigated through a 2×4×5 full factor design wherein effects of NaOH concentration, leaching time and milling speed were evaluated. In addition, the results were compared with the results of conventional leaching method.The results from the conventional alkaline leaching (CAL) indicated that just after a while from the beginning of the reaction, as confirmed by XRD investigations, an insoluble calcium manganese hydroxide layer forms on active surface of ZnO particles which prevents diffusion of leaching solution. Consequently, leaching process was halted and maximum recovery did not exceed 82.4%. Mechanochemical leaching results revealed that intensive milling in an attritor enhanced leaching performance, selectively. This is attributed to a wide structural change and abrasion of insoluble layer during MCAL. Subsequently, zinc recovery of 99.9% was obtained. The statistical analysis of the results showed that NaOH concentration, milling time and milling speed were statistically significant factors affecting the leaching process at 95% confidence level. In conclusion, approximately complete zinc recovery from HFC using the MCAL method can assist cobalt and manganese extraction process from the plant residue in the subsequent process.

Sub-100 nm drug particle suspensions prepared via wet milling with low bead contamination through novel process intensification

There is sustained interest in sub-100nm particles of poorly water-soluble drugs as such small particles offer improved permeation through various biological barriers and result in rapid onset of therapeutic action. An intensified wet stirred media milling process was developed here for fast production of sub-100nm drug particles with low bead contamination and reduced energy consumption. Griseofulvin and indomethacin, two model poorly water-soluble drugs, were wet-milled. Yttrium-stabilized zirconia beads with a nominal size ranging from 50µm to 800µm were used in the baseline process, which was subsequently intensified with the optimal bead size by increasing rotor tip speed, bead loading, and suspension flow rate stepwise, as guided by a microhydrodynamic model. Laser diffraction, dynamic light scattering, scanning electron microscopy, and XRD were used to characterize the milled suspensions. Results from the baseline process indicated that sub-100nm griseofulvin particles were only produced when 50 or 100µm beads were used in the 360min milling experiments. Interestingly, using 50µm beads led to the formation of sub-100nm griseofulvin particles within 240min with the lowest bead (zirconium) contamination and specific energy consumption. This could be explained though the microhydrodynamic model, revealing that 50µm beads led to the highest frequency of drug particle compressions yet generated the lowest bead contact pressure. The processing time was further reduced to as low as 64min producing griseofulvin particle size of 100nm through step-wise intensification of the milling process with the 50µm beads, as quantified by a milling intensity factor. Due to the enhancement of the breakage kinetics, the process intensification enabled shorter milling to attain 100nm particles, thus resulting in significant energy savings and low bead contamination despite an increase in power consumption. The general applicability of the process intensification method was confirmed through milling of indomethacin, which also led to sub-100nm particles faster with reduced energy consumption and low contamination.

Optimization and dissolution performance of spray-dried naproxen nano-crystals

The purpose of this study was to investigate the in vitro dissolution performance of the different sized spray-dried nano-crystalline powders of naproxen. A DoE approach was used to formulate and optimize nano-crystalline suspensions. The critical wet milling operation parameters were i.e., drug concentration, drug-to-stabilizer ratio, stabilizer type (HPMC E15 or Tween 80) and milling intensity. The nano-crystalline suspensions were optimized for size and physical stability and then spray-dried to obtain nano-crystalline powders. Trehalose and lactose were investigated as spray-drying auxiliary excipients to achieve non-aggregating powders. Particle size, DSC and PXRD were utilized for characterization of powder formulations. A modified USP apparatus II was utilized to determine the in vitro release/dissolution of powder formulations. The size of the nano-crystalline suspensions was dependent on drug concentration and milling intensity. HPMC E15 containing formulations were better in terms of the spray-dried powder yield compared to Tween 80 containing formulations. Trehalose was selected to formulate non-aggregating nano-crystalline powders. No polymorphic changes were observed following the wet milling and spray-drying processes. Size dependent in vitro dissolution profiles, utilizing a dialysis sac method were obtained for the crystalline powders.

Crystalline structure, energy calculation and dehydriding thermodynamics of magnesium hydride from reactive milling

Magnesium hydride was prepared by reactive milling under hydrogen atmosphere using carbon from anthracite coal as milling aid, and then its crystal structure and thermal stability were investigated. The phase transition of β-MgH2 to γ-MgH2 during intensive milling is confirmed by electron diffraction, high resolution electron microscope observation and X-ray diffraction. According to first-principles calculation, the supercell based on γ-MgH2 (1 1 0) plane is the most unstable with surface energy of 1.23 J/m2 and dehydriding enthalpy change of 44.66 kJ/mol, while that of β-MgH2 (1 1 0) plane is the most stable with surface energy of 0.19 J/m2 and enthalpy change of 78.16 kJ/mol. The differential scanning calorimetric analysis shows that γ-MgH2 presents much lower hydrogen desorption temperature and heat absorption than β-MgH2. The enthalpy change determined by experimental isotherms also indicates that the material with more γ-MgH2 from longer time of milling is lower.

Jet Milling Effect on Functionality, Quality and In Vitro Digestibility of Whole Wheat Flour and Bread

Jet milling is an ultragrinding process in order to produce superfine powders with increased functionalities. The effect of milling pressure, feed rate, vibration rate of feeder, and feedback of jet milling on whole wheat flour functionality and the potential of those flours for breadmaking with the goal of improving bread quality and digestibility were investigated. Increasing milling pressure (from 4 to 8 bar), decreasing feed rate (from 0.67 to 5.18 kg/h), and/or using recirculation augmented the severity of the process and reduced flour particle size from 84.15 to 17.02 μm. Breakage of aleurone particle layer and the reduction of particle size in jet milled flours were detected using scanning electron microscopy (SEM). Ash and protein content did not change after jet milling. However, total fiber content and digestible starch increased from 13.01 to 14.72 % and from 33.80 to 43.23 mg/100 mg, respectively, when subjected to jet milling at 8-bar air pressure. Mixolab® data indicated that water absorption increased from 64.1 to 68.0 %, while pasting temperature decreased from 63.4 to 66.1 °C owing to the milling intensity. Referring to bread, jet milled flour addition reduced the specific volume from 2.50 to 1.90 cm3/g, luminosity from 60.48 to 55.87, and moisture content from 35.78 to 33.49 %, and increased crumb hardness from 707 to 1808 g. Jet milled breads presented a slight decrease in estimated glycemic index (eGI) (from 86 to 81), suggesting that jet milling treatment could also have nutritional benefits.

Study of Al composites prepared by high-energy ball milling; Effect of processing conditions

The present work deals with the synthesis of some Al-based composites prepared by mechanical milling and processing by powder metallurgy followed by the evaluation of process conditions as: type of additive, their concentration and milling intensity studying its effect on the characteristics of the powder composite and mechanical performance of the composite. Powder samples were microstructural characterized by electronic microscopy (SEM–TEM) and the mechanical response was followed by hardness and compressive tests. A pronounced effect on the mechanical response of the specimens was evident after the addition of reinforced particles and milling intensity. Microscopy studies showed a uniform dispersion of the reinforcing particles in the metallic matrix at nanometric scale and an important grain refinement of the Al matrix was confirmed. After processing, a 66% increase on the mechanical response was reached with 1% of additive complemented with short milling intensities.

Role of intensive milling in the processing of barium ferrite/magnetite/iron hybrid magnetic nano-composites via partial reduction of barium ferrite

In this research a mixture of barium ferrite and graphite was milled for different periods of time and then heat treated at different temperatures. The effects of milling time and heat treatment temperature on the phase composition, thermal behavior, morphology and magnetic properties of the samples have been investigated using X-ray diffraction, differential thermal analysis, high resolution transmission electron microscopy and vibrating sample magnetometer techniques, respectively. X-ray diffraction results revealed that BaFe12O19/Fe3O4 nanocomposites form after a 20h milling due to the partial reduction of BaFe12O19. High resolution transmission electron microscope images of a 40h milled sample showed agglomerated structure consisting of nanoparticles with a mean particle size of 30nm. Thermal analysis of the samples via differential thermal analysis indicated that for un-milled samples, heat treatment up to 900°C did not result in α-Fe formation, while for a 20h milled sample heat treatment at 700°C resulted in reduction process progress to the formation of α-Fe. Wustite was disappeared in an X-ray diffraction pattern of a heat treated sample at 850°C, by increasing the milling time from 20 to 40h. By increasing the milling time, the structure of heat treated samples becomes magnetically softer due to an increase in saturation magnetization and a decrease in coercivity. Saturation magnetization and coercivity of a sample milled for 20h and heat treated at 850°C were 126.3emu/g and 149.5Oe which by increasing the milling time to 40h, alter to 169.1emu/g and 24.3Oe, respectively. High coercivity values of milled and heat treated samples were attributed to the nano-scale formed iron particles.

Synthesizing of Nanostructured Fe-Mn Alloys by Mechanical Alloying Process

In the present study, nanostructured Fe-30wt.% Mn alloys produced by mechanical alloying of Fe and Mn powders mixture. The phase composition and morphology of nanostructured powder were analyzed by X-ray diffraction and scanning electron microscopy. It was found that by milling time up to 10h, crystallite size was decreased to 6nm, on the contrary lattice strain was increased. Solid solubility levels were determined from changes in the lattice parameter values. The lattice parameter increases slightly from 0.28167 to 0.35776nm. Increasing milling intensity by higher ball to powder mass ratio resulted in Fe-Mn alloy formation with smaller crystallite size. The SEM results showed that, plate like particles were formed in initial milling time and particles morphology was changed to equiaxed form in final stage of milling process.

Mechanosynthesis of Nanodispersed Titanium Diboride

Structural and morphological changes of titanium during intensive milling of titanium and boron powder mixtures in an AIR-015M planetary-ball mill are investigated. It is shown that the structural transformations in titanium lead to the formation of cluster precipitates (like Guinier–Preston zones) of titanium and boron atoms that are regularly oriented with respect to the titanium lattice and coherently associated with it. Cluster precipitates are very effective nuclei for the further reaction and provide an explosive transition to the almost single-phase titanium diboride. It was found that, in the investigated mechanosynthesis conditions, nanostructured titanium diboride forms in the form of flat and spatial polycrystalline particles, composed of oriented nanograins no larger than 20 nm.

A green and efficient technology for the degradation of cellulosic materials: Structure changes and enhanced enzymatic hydrolysis of natural cellulose pretreated by synergistic interaction of mechanical activation and metal salt

A new technology for the pretreatment of natural cellulose was developed, which combined mechanical activation (MA) and metal salt treatments in a stirring ball mill. Different valent metal nitrates were used to investigate the changes in degree of polymerization (DP) and crystallinity index (CrI) of cellulose after MA+metal salt (MAMS) pretreatment, and Al(NO3)3 showed better pretreatment effect than NaNO3 and Zn(NO3)2. The destruction of morphological structure of cellulose was mainly resulted from intense ball milling, and the comparative studies on the changes of DP and crystal structure of MA and MA+Al(NO3)3 pretreated cellulose samples showed a synergistic interaction of MA and Al(NO3)3 treatments with more effective changes of structural characteristics of MA+Al(NO3)3 pretreated cellulose and substantial increase of reducing sugar yield in enzymatic hydrolysis of cellulose. In addition, the results indicated that the presence of Al(NO3)3 had significant enhancement for the enzymatic hydrolysis of cellulose.

Characterization of structural changes of mechanically activated natural pyrite using XRD line profile analysis

In the present study, the X-ray diffraction line profile analysis was used for the characterization of structural changes in mechanically activated pyrite by a planetary ball mill. Applying the Williamson-Hall integral breadth and Warren-Averbach methods, comprehensive investigations were carried out on the XRD patterns in order to separate the crystallite size and microstrain contributions in XRD broadened patterns. The analysis of XRD patterns of mechanically activated pyrite indicated that no phase transformation occurred during milling operation. The results revealed that crystallite size and microstrain decreased and increased, respectively, during mechanical activation process. Volume weighted crystallite size (Dv), surface weighted crystallite size (Ds), strain (ε) and root mean square strain (RMSS) changed from 316nm, 103.6nm, 0.05% and 0.04% in initial pyrite to 57.73nm, 25.1nm, 0.224% and 0.117%, respectively, in mechanically activated pyrite for 100min. In addition, the lattice parameter of mechanically activated pyrite increased as a function of milling time, implying that pyrite lattice volumes were expanded probably due to vacancy formation. Regarding to shape parameter study, the crystallite size broadening portion is more than the strain broadening portion on the broadened peaks in the XRD patterns of mechanically activated pyrite. This may be related to the fracture toughness of pyrite lattice, implying that pyrite structure is refined mainly by decreasing crystallite size rather than lattice strain. From surface area and particle size analysis, it can be confirmed that the agglomeration begins after 50min mechanical activation. The X-ray amorphization degree increases to about 70% after 100min intensive milling, reflecting the refractory nature of pyrite.

What Is Unique About Mechanochemical Reactions?

Mechanochemical reactions can provide compounds, phases, and microstructures that are essentially di erent from the products of ordinary reactions. In this paper, the origin of this uniqueness is discussed in light of the recent advances of the eld. It is claimed that the local availability of large batches of energy, well above kT , is the key feature of mechanochemical reactions. As a consequence, reactions that cannot occur thermally become possible, similarly to the reactions induced by the energy of photons in photochemistry. However, the situation is more complex, as macroscopic deformation a ects many defect sites simultaneously. The direction of the mechanical load relative to the orientation of a molecule or the crystallographic axes of a solid can be important. Many mechanochemical reactions of organic compounds take place at low milling energy that is not su cient to break primary bonds, but the gentle mechanical grinding can in uence the relative position of macromolecules, leading to the formation of unique cocrystals and compounds. In inorganic systems, unusual products form due to forced mixing and the high defect density generated by intense milling.

Characteristics of tiger nut milk: effects of milling

SummaryA standard method for the extraction of tiger nut milk has been introduced. It has been shown that, although milling duration improves the yield of tiger nut milk solids and its nutrient composition, there is a quantifiable loss of nutrient in the pressing residue during milk extraction. Milling duration improved the colloidal stability of the milk against creaming during 16 h of storage. A higher milling intensity resulted in the aggregation of biological polymers which resulted in colloidal destabilisation. Milling improved the lightness and stability and reduced browning rate of the tiger nut milk during storage. This report is important for the production of tiger nut milk of consistent and comparable characteristics. Milling has been introduced as a processing method for the qualitative and quantitative modulation of the properties of tiger nut milk. It is recommended to develop further strategies to improve the colloidal stability of tiger nut milk as a beverage.

Mechanochemical solid state synthesis and optical properties of Cd0.5Zn0.5Se nanocrystals

High-quality Cd0.5Zn0.5Se nanoparticles with diameters ranging from 2.6 to 4.3 nm were synthesized via intensive mechanical milling for up to 20 h. The full width at half maximum (FWHM) and broadening of the diffraction peaks increased with increasing ball milling process and later decreased. XRD pattern confirmed a dominant zinc blende phase at (x = 0.5) composition. The optical spectra of the nanoparticles exhibited an onset absorption peak at 349 nm, with maximum absorption at 290 nm. The luminescence properties of the nanoparticles at room temperature were analyzed via photoluminescence spectroscopy, revealing band-edge emission at 354 nm. Photoluminescence (PL) spectra exhibit broad emission band at the range of (380–508) nm photon energy. The PL spectrum has two distinctive shoulders at 403 and 450 nm. Band emissions of 1.74, 1.54 and 1.4 eV at longer wavelengths that were associated with the surface state were also observed. High-transmission electron microscopy (HRTEM) revealed the successful annihilation of such defects with continuous milling.

Processing of Mn–Al nanostructured magnets by spark plasma sintering and subsequent rapid thermal annealing

Abstract The potential of spark plasma sintering (SPS) in combination with rapid thermal annealing (RTA) for the processing of Mn–Al nanostructured magnets is explored in this study. Ferromagnetic α-Mn alloy powders were processed by high-energy ball milling using Mn (56 at%) and Al (44 at%) as constituent metal elements. The alloying action between Mn and Al due to intensive milling was studied by X-ray diffraction and field-emission scanning electron microscope; while the phase transformation kinetics was investigated using differential scanning calorimetry. The evolution of ferromagnetic properties in the as-milled powders was studied by superconducting quantum interference device (SQUID). Among the Mn–Al alloy powders collected at various milling intervals, the 25 h milled Mn–Al powders showed a good combination of coercivity, Hc (11.3 kA/m) and saturation magnetization, Ms (5.0 A/m2/kg); accordingly, these powders were chosen for SPS. The SPS experiments were conducted at different temperatures: 773, 873 and 973 K and its effect on the density, phase composition and magnetic properties of the Mn–Al bulk samples were investigated. Upon increasing the SPS temperature from 773 to 973 K, the bulk density was found to increase from 3.6 to 4.0 g/cm3. The occurrence of equilibrium β-phase with significant amount of γ2-phase was obvious at all the SPS temperatures; however, crystallization of some amount of τ-phase was evident at 973 K. Irrespective of the SPS temperatures, all the samples demonstrated soft magnetic behavior with Hc and Ms values similar to those obtained for the 25 h milled powders. The magnetic properties of the SPSed samples were significantly improved upon subjecting them to RTA at 1100 K. Through the RTA process, Hc values of 75, 174 and 194 kA/m and Ms values of 19, 21 and 28 A/m2/kg were achieved for the samples SPSed at 773, 873 and 973 K, respectively. The possible reasons for the observed improvement in the magnetic properties of the SPSed samples due to RTA in correlation with their phase composition and microstructure were analyzed and discussed.

A green and efficient method for preparing acetylated cassava stillage residue and the production of all-plant fibre composites

Cassava stillage residue (CSR), a kind of agro-industrial plant fibres , was directly acetylated and converted into thermoplastic material by mechanical activation-assisted solid phase reaction (MASPR) in a stirring ball mill without the use of organic solvent and additives. As combining mechanical activation and chemical modification in the same equipment, the destruction of hydrogen bonds and crystalline structure of CSR induced by intense milling improved the reactivity of CSR, leading to the effective acetylation of CSR. After acetylation by MASPR, the modified CSRs possessed thermoplasticity, ascribing to the introduction of acetyl groups and the destruction of high crystallinity structure of cellulose. The self-reinforced all-plant fibre composites (APFC) were successfully produced with the modified CSRs as both matrix and reinforcement by hot pressing technology. The direct acetylation of CSR and successful production of APFC suggested that MASPR was a simple, efficient and environmentally friendly method for chemical modification of agro-industrial lignocellulose biomass.

Anomalous grain refinement trends during mechanical milling of Bi2Te3

The structural evolution of nanocrystalline bismuth telluride (Bi2Te3) during mechanical milling is investigated under different milling energies and temperatures. After prolonged milling, the compound evolves toward a steady-state nanostructure that is found to be unusually strongly dependent on the processing conditions. In contrast to most literature on mechanical milling, in Bi2Te3 we find that the smallest steady-state grain sizes are attained under the lowest energy milling conditions. An analysis based on the balance between refinement and recovery in the steady state shows that two regimes of behavior are expected based on the thermo-physical properties of the milled powder. Bi2Te3 lies in a relatively unusual regime where greater impact energy promotes adiabatic heating and recovery more than it does defect accumulation; hence more intense milling leads to larger steady-state grain sizes. Implications for other materials are discussed with reference to a “milling intensity map” that delineates the set of material properties for which this behavior will be observed.

Mechanical Response and Microstructure of Al-SiO<sub>2</sub> Composites Prepared by Means of a Solid-State Route

This study deals with the production of some Al-SiO2composites and the evaluation of milling intensity over the distribution of silica particles into the Al matrix. Samples for mechanical characterization were prepared from powders by compaction and sintering using a solid-state route complemented with mechanical milling. The mechanical response was modified as a direct function of the milling intensity, but an adverse effect was observed with prolonged milling times. Electron microscopy studies reveal a homogeneous dispersion of insoluble particles into the Al matrix, which is associated with the high grain refinement in the synthetized composites giving an important improvement on the composites strength. Also, the silica spheroidal structure is not altered nor destroyed (mechanically and/or chemically) during the composite synthesis.

Reduction of Surface Roughness and Rounding of Limestone Particles in a Stirred Media Mill

AbstractThe process and end‐use behavior of ground material not only depends on the particle size or specific surface but is also influenced by the particle shape. Particle shaping can be done in a stirred media mill if the stress intensity is not enough to break the particle, so mainly abrasion and chipping are carried out. Low‐stress intensity milling is presented in a dry stirred media mill to reveal the particle base rounding and surface roughness reduction. The main parameters of the product‐related stress model are connected to the descriptive parameters of particle shaping. Batch grinding of limestone particles with narrow size distribution was carried out with different milling parameters. The product‐related stress model can be used for the description of particle shaping.

Wet milling induced physical and chemical instabilities of naproxen nano-crystalline suspensions

Wet-milling is the most common approach to formulate nano-crystalline suspensions. The effect of high intensity wet-milling on the physical and chemical stability of a poorly soluble drug was investigated. Naproxen (1%, w/v) was suspended in two different stabilizers (i.e. HPMC E15 and Tween 80) and stabilizer concentrations (0.2% or 0.6%, w/v) in distilled water. Wet-milling was performed at two different speeds (i.e. 3,400 rpm and 2,000 rpm) for four continuous hours. The milled samples were analyzed for physical and chemical instabilities. Wet-milling of naproxen-HPMC E15 at high milling intensity caused both physical and chemical instabilities as observed by particle size measurement and chemical analysis, respectively. The naproxen-Tween 80 formulations were stable regardless of milling intensity. Naproxen-HPMC E15 wet-milled samples, showed an IR peak shift suggesting strong bond formation or molecular interaction (i.e. amorphous phase). In addition, naproxen has a strong interaction with HPMC E15 as determined by MTDSC (i.e. melting point depression). The generation of amorphous phase at the naproxen-HPMC E15 crystal surface may be responsible for both aggregation and degradation during wet milling. Decarboxylated naproxen was identified as a degradation product. Milling intensity and/or selection of stabilizer/s are crucial for the stability of nano-crystalline suspensions.