Milling Medium Research Articles

Mechanochemical treatment of Serbian kaolin clay to obtain high reactive pozzolana

Mechanochemical treatment of Serbian kaolin clay was carried out in a planetary ball mill using two different milling media, hardened steel or zirconia vials and balls. The samples obtained with various milling times were characterized by the particle size laser diffraction (PSLD), X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DTA/TGA) and Fourier-transform infrared (FTIR) analyses. Mechanochemical treatment induced amorphization of the kaolinite phase accompanied by dehydroxylation. It was found that for the given milling parameters, amorphization mainly took place in the milling period up to 15 min, and was completed after about 30 min of milling for both milling media used. The pozzolanic activities were determined by the Chapelle method. Milling in the hardened steel milling medium had no significant influence on pozzolanic activity, even though there was accumulated iron contamination. For both milling media, pozzolanic activity of 0.79 was obtained for the samples milled for 15 min and it remained almost unchanged with prolonged milling. The determined pozzolanic activity values are close to these of commercial metakaolinite or metakaolinite obtained by the calcination of the same clay, therefore, indicating possibility for obtaining high reactive pozzolana by mechanochemical treatment of Serbian kaoline clay.

Studies on Low-Field and Room-Temperature Magnetoresistance in La2/3(Ca1−x Sr x )1/3MnO3 Perovskites

The polycrystalline perovskites La2/3(Ca1−x Sr x )1/3MnO3 (x=0,0.2,0.4,0.6,0.8,1) were successfully prepared by a modified method of solid-state reactions, in which the ingredient mixture with ethanol as a liquid milling medium to form suspension was milled by high-energy ball milling for 10 h and sintered in air at 1400 °C for 10 h. The microstructure, electrical transport, and low-field magnetoresistance (LFMR) of the perovskites were investigated to study the room-temperature magnetoresistance (RTMR) behavior. The results reveal that the metal-to-insulator transition temperature (T MI) increased with increasing doping level x, and the peak values of the magnetoresistance (MR) near T MI dropped with the more Ca2+ substituted. A single-phase La2/3Ca1/3MnO3 showed T MI at 263 K and the peak MR of 23 % in the applied field of 3 kOe near T MI. The LFMR effect at room temperature could be obtained by controlling the doping Sr2+-substituted Ca2+ level. When x=0.29, transition temperature (T MI) was 305.30 K, and the MR effect was recorded up to 12.9 % at 298.55 K and 3 kOe. Finally, the possible mechanism is discussed.

Mechanochemical Synthesis of Hydroxyapatite Bioceramics through Two Different Milling Media

This work presents the wet mechanochemical synthesis of hydroxyapatite (HA) powder through two different milling mediums. The effect of milling mediums on powder properties was investigated. Two types of medium: water and ethanol were chosen with 370 rpm milling speed for 15 hours time. Characterization of synthesized powders was accomplished by X-ray diffraction (XRD) analysis. The green compacts were prepared and sintered in atmosphere condition at various temperatures ranging from 900oC - 1300oC. The mechanical and physical properties were evaluated under Vickers microhardness test and density measurement. Both of synthesis mediums yielded HA phases in the synthesized powders as detected by the peaks obtained in XRD analysis. Compacts synthesized in water medium (M1) showed a maximum density, 99% sintered at 1000oC and 1300oC. However, the hardness in water medium is closely similar to the ethanol medium as a function of sintering temperature where the maximum hardness was found in compacts synthesized in ethanol medium (M2) sintered at 1300oC (5.8GPa). The microstructure observed from SEM analysis was in line with the density obtained as the surface of sintered compacts synthesized in water medium (M1) contained less pores with large grain growth.

Anisotropic Nd$_{2}$Fe$_{14}$B Submicron Flakes by Non-Surfactant-Assisted High Energy Ball Milling

This paper reports on the formation mechanism, structure, crystallographic anisotropy, magnetic properties and postannealing of single-crystal and [001] textured poly-nanocrystalline Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B flakes with a micron, submicron or nanosize thickness prepared by a non-surfactant-assisted high energy ball milling (HEBM) technique. Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15.5</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">78.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ingot micro-powders were the precursor while ethanol was the only milling medium. Similar to the structural evolution process in the surfactant-assisted HEBM, single-crystal flakes with a micron then submicron thickness were first formed. With further milling, [001] textured poly-nanocrystalline flakes with a submicron then nanosize thickness were formed. The formation of anisotropic flakes was mainly related to the polar nature of ethanol which would form a thin coating layer on the flakes through carboxylate bonds to prevent cold welding and agglomeration during the HEBM. The Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B flakes prepared by the HEBM in ethanol for 5 h have a [001]-in-plane texture, a thickness in the range of 100-450 nm and a width in the range of 0.7-18 μ m, a coercivity <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of 2.3 kOe, and a I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">006</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">105</sub> value of Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B phase of 5.3. Postannealing at 400-550 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C for 0.5 h had little effect on the flake dimensions while resulting in a reduced [001] texture and reduced remanence values besides coarser grain sizes. With increasing annealing temperature, <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> first increased, reached its maximum value of 2.8 kOe at 450 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, then decreased. An anisotropic magnetic behavior was found in all of the as-milled and annealed flakes.

Phase Transformation and Magnetic Property of Ni-Mn-Ga Powders Prepared by Dry Ball Milling

This study investigated the phase transformations and magnetic properties of Ni-Mn-Ga alloy powders prepared by dry ball milling in argon atmosphere. The Fe and Cr elements were found to be introduced in the alloy after ball milling, which should result from the severe collision and friction among the particles, balls, and vial. The x-ray diffraction result indicated that the Fe and Cr elements should have alloyed with the Ni-Mn-Ga matrix. The martensitic transformation temperature and Curie temperature of the 800 °C annealed powders decreased by ~33 °C and increased by ~28 °C, respectively, as compared to that of the bulk alloy. The comprehensive effect of the changing of valence electron concentration of the alloy due to the introduction of Fe and Cr and the grain refinement of the alloy caused by ball milling should be responsible for the reduction of martensitic transformation temperature. The saturation magnetization of the 800 °C annealed powders became larger (~5 emu/g) than that of the bulk alloy. The enhancement of magnetic properties, such as the increase of Curie temperature and enhancement of saturation magnetization of the annealed Ni-Mn-Ga powders, should be attributed to the increase of magnetic exchange caused by introduction of Fe in the alloy. The contaminations of Fe and Cr elements emerging from the dry ball milling process changed the phase transformation and magnetic properties of the Ni-Mn-Ga alloy. Therefore, the dry ball milling process is difficult to control the contamination from the milling medium and not suitable to prepare Ni-Mn-Ga powders. On the contrary, the wet ball milling method under liquid medium should be a better method to prevent the contamination and fabricate pure Ni-Mn-Ga ferromagnetic shape memory alloy powders.

Correlations between milling conditions and iron contamination, microstructure and hardness of mechanically alloyed cubic BN particle reinforced NiCrAl matrix composite powders

Contamination from milling vials and grinding balls is one of the major problems for mechanically alloyed materials especially when brittle hard components are included. In this study, 40vol.% cubic BN/NiCrAl alloy composite, a typical example in ductile–brittle materials system, was prepared by mechanical alloying (MA) process. To minimize iron contamination arising from the stainless steel milling medium, two types of precautions, including coating NiCrAl alloy on milling medium surface by mechanical milling and a novel ‘step-fashion’ MA method, were employed. Without any approaches, a high iron content of 10.9wt.% was yielded. After coating a ∼20μm thick NiCrAl layer on milling medium surface, the iron contamination was decreased to 7.3wt.% because the coated NiCrAl layer played an important role in preventing the milled powders from directly tearing and wearing the milling medium. By the ‘step-fashion’ MA method, the iron contamination was reduced to 4.4wt.%. Combining these two pretreatments, a low iron content of 2.2wt.% was achieved. After 40h of milling, crystals of NiCrAl matrix for powders prepared under all of the conditions were refined to be sizes of 30–40nm. Furthermore, by the ‘step-fashion’ milling method, NiCrAl powders exhibited an enhanced ability to incorporate more cBN ceramic dispersoids. As many as 40vol.% of cBN was embedded into NiCrAl matrix for composite powders prepared by the ‘step-fashion’ method and thus resulted in a high hardness of ∼1150HV. However, powders prepared by conventional method incorporated only 20vol.% of cBN and exhibited a relative low hardness of 800HV. To make clear the mechanisms that how milling conditions actually influence the iron contamination level, the interactions between milled powders and milling medium during MA were also investigated.

Structure, Magnetic and Microwave Properties of Granular Fe&lt;sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;&lt;/sub&gt;(SiO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;1-x&lt;/sub&gt; Alloys Obtained by Mechanochemical Synthesis

The structural-phase composition, magnetic and microwave properties of Fex(SiO2)1-x (x=30, 70, 90, 95) nanocomposites have been studied. The composites are produced by high-energy ball milling with either Ar or acetone as a milling medium and milling time of 1 to 64 h. The microwave magnetic properties of the composite in the frequency range of 0.1 to 6 GHz are shown to depend slightly on the phase composition and be governed mainly by the particle size. Reduction of the particle size to about 1 μm results in elimination of magnetic loss at frequencies below 1 GHz, which is attributed to the domain walls motion.

Effect of Ball Milling on Powder Preparation by Mechanical Methods

In the milling process, the particles experience mechanical stresses at their contact points due to compression, impact, or shear with the mill medium or with other particles. The rate of grinding depends on a number of factors, including the mill parameters, the properties of the grinding media, and the properties of the particles to be ground. SEM photomicrographs show that the mean sizes of final refined powders are about 200–400 nm, and are quite uniformly distributed by wet ball milling, so the quasi-nano powders are very suitable for sintering.

Synthesis of pure nano-sized Li4Ti5O12 powder via solid-state reaction using very fine grinding media

Li4Ti5O12 was synthesized by a solid-state reaction using Li2CO3 and anatase TiO2 at 800°C for 3h for anode application in Li-ion batteries. In order to examine the effects of milling conditions on the properties of Li4Ti5O12, 3 different ZrO2 media of sizes 0.45, 0.10 and 0.05mm were subjected to 5h of high energy milling, while 5mm balls were subjected to 24h of ball milling for comparison. High energy milling was found to be much more effective in decreasing both the reaction temperature and the final Li4Ti5O12 particle size than ball milling through the efficient size reduction and mechanochemical activation of the starting materials. The use of 0.10 and 0.05mm beads resulted in the synthesis of pure nanosized Li4Ti5O12, depressing the formation of unwanted rutile TiO2 in the final products, whereby the finer milling media showed more desirable particle properties. Consequently, pure Li4Ti5O12 of 145nm size, which is comparable to the particle sizes from expensive wet chemical methods, could be synthesized by an economic solid-state reaction.

Crystallographic alignment evolution and magnetic properties of Nd-Fe-B nanoflakes prepared by surfactant-assisted ball milling

The microstructure, crystal structure, and magnetic properties were studied for Nd-Fe-B nanoflakes prepared by surfactant-assisted high-energy ball milling (HEBM) with heptane and oleic acid as the milling medium. The microstructure, crystal structure, and magnetic properties of the nanoflakes were examined with scanning electronic microscopy, x ray diffraction, and vibrating sample magnetometer, respectively. Effect of ball-milling time on the c-axis crystallographic alignment and coercivity of Nd-Fe-B nanoflakes were systematically investigated. Microstructure observation shows that the Nd-Fe-B nanoflakes have an average thickness of tens of nanometers, an average diameter in the range of 500 ∼ 1000 nm, and an aspect ratio as high as 100. As the ball-milling time increases from 2 h to 12 h, the intensity ratio between (006) and (105) reflection peaks, which indicates the degree of c-axis crystal texture of the Nd2Fe14B phase, drops gradually, indicating that the long time-milling process undermines the c-axis crystal texture of Nd2Fe14B phase in the nanoflakes. On the other hand, the coercivity of the nanoflakes firstly increases, peaks at 3.8 kOe for 8 h, and then decreases again along with the ball milling.

3M offers low cost micro milling media

3M offers low cost micro milling media

Effects of mechanical alloying process on thermoelectric properties of Bi2S3 Bulk

Bismuth sulfide (Bi2S3) polycrystalline bulks are fabricated by spark plasma sintering (SPS) combined with a mechanical alloying (MA) process. The electrical transport properties are investigated with a special emphasis on dry-milling speed, wet-milling time and mediums in MA process. The phase structure, the microstructure, and the electrical/thermal transport properties for the bulk samples are measured. The results suggest that the second Bi2O3 phase is formed because of the micro-oxidation when the wet medium is fixed to absolute ethyl alcohol, which refines the grain sizes and affects electrical transport properties of the bulk samples. Prolonging the wet-milling time in absolute ethyl alcohol causes the increase of resistivity and the decrease of the power factor. The electrical transport properties degrade due to the porous microstructure in bulk samples even without oxidization as the acetone is used as a milling medium. The largest ZT value 0.25 is obtained at 573 K for the samples dry-milled under 425 r/min for 15 h without wet-milling, which is the highest value in the reported values so far.

A discrete elements simulation and analysis of a high energy stirred milling process

Stirred bead mills used in industry allow to split up particules in suspension by agitating a milling medium. The multiple impacts may damage beads and thus reduce the stirred milling process efficiency. A discrete numerical approach including simple fluid effects is proposed and carried out in this paper to model and study finely the damage phenomenon. The simulation data allow to identify internal variables of the milling medium and to localize high energy zones. The order of magnitude of contact forces including fluid contribution will enhance the bead wear law.

SYNTHESIS OF BARIUM HEXAFERRITE/IRON OXIDES MAGNETIC NANO-COMPOSITES VIA HIGH ENERGY BALL MILLING AND SUBSEQUENT HEAT TREATMENT

Barium hexaferrite ( BaFe 12 O 19) is a hard magnetic ceramic with superior magnetic properties and in powder form has potential for application in high density recording media. In this research a mechano-chemical approach was applied in order to achieve a nano-structured magnetic composite. Graphite was used to reduce barium hexaferrite in mechanical milling medium under argon atmosphere. Milling was carried out with a ball to powder mass ratio of 35 and rotation speed of 300 rpm. Effects of milling time on phase composition and morphology of the samples were evaluated by XRD and SEM techniques, respectively. XRD results revealed that after 20 hours of milling, nano-composite of BaFe 12 O 19/ Fe 3 O 4/ Fe 2 O 3 was obtained. By extending the milling time to 40 hours, FeO was detected as the dominant crystalline phase with crystallite size of 22 nm. Composite of Fe / FeO / Fe 3 O 4 was synthesized by controlled heat treatment of the 40 hours milled sample. SEM results revealed that particle size in the aforementioned heat treated composite sample reached to about 89 nm and the morphology of the samples changed slightly.

Mechanical alloying of carbon nanotube and Al6061 powder for metal matrix composites

Abstract Mechanical alloying has been widely utilized to break down the clustered CNTs for incorporation in the metal matrix composites. However, the breakage of CNTs during the ball milling process degrades their effectiveness. Due to the challenges in collecting the CNTs for measurement, quantitative study of CNT breakage has been difficult. In this study, the CNTs with Al6061 powder were mechanically alloyed with high energy milling equipment. The CNTs from the surface of mechanically alloyed particles were collected and measured. Due to the difficulty in obtaining the CNTs embedded inside the particles, a mathematical model has been developed to predict the overall CNT length distribution in the composite. Significant CNT breakage occurred during the initial phase of the mechanical alloying due to the crushing of the clusters. The model predicted that no further change occurred in the overall CNT length during time greater than 1 h of mechanical alloying because most of the CNTs had already become embedded within the particles and were thus protected from further milling media impacts. A faster dispersion of CNTs and lower particle fracturing rate may help preserve the original CNTs.

Ball Milling of WC-Co Powder as Injection Molding Feedstock

In this paper, an attempt has been made to mill constituent of WC and Co powder towards achieving volumetric percentage of WC (91%) and Co (9%). The ball milling technique was conducted under dry and wet condition using various milling parameters, rotation speed, time and ethanol as milling medium. Electron dispersive spectrometer (EDS) detected the elemental distribution, whilst SEM and particle size analysis was done to study the effect of changes in particle morphology and reduction of particle size. As a conclusion, powder milled by parameter of wet milling by ethanol, speed of rotation at 250 rpm and 90 minutes of milling time exhibits best results in term of volumetric percentage of 91%WC and 9%Co and particle size reduction.

Artificial Intelligence Model of Surface Roughness for End Milling Operation of Steel and its Verification by Genetic Algorithm

Surface roughness is important for evaluating the machined surface quality. In this work, an Artificial Neural Network (ANN) surface roughness prediction model was developed by coupling it with Response Surface Methodology (RSM). For this interpretation, advantages of statistical experimental design techniques, experimental measurements, and artificial neural network were exploited in an integrated manner. Cutting experiments were designed based on small centre composite design technique to develop a RSM model. The input cutting parameters were: cutting speed, feed, and axial depth of cut, and the output parameter was surface roughness. The predictive model was created using a feed-forward back-propagation neural network exploiting the experimental data. The network was trained with pairs of inputs/outputs datasets generated by end milling medium carbon steel with TiN coated carbide inserts. The model can be used for the analysis and prediction of the complex relationships between cutting conditions and surface roughness, in metal-cutting operations, with the ultimate goal of efficient production. The ANN model was verified with the optimized parameters predicted by a coupled genetic algorithm (GA) and RSM technique also developed by the authors.

An 11 Electron Redox Couple for Anodic Charge Storage: VB2

Nanochemical improvements of vanadium diboride are probed to facilitate anodic charge transfer, and an extractable casette chemical recharge concept for this anode is introduced. VB2 releases 11 electrons per molecule, via electrochemical oxidation, at a favorable, electrochemical potential. The discharge voltage is highly level throughout a deep discharge. This unusual multi-electron redox couple provides a charge capacity of 4060 mAh/g, which is greater than other anodes, including more than lithium. Coupled with an air cathode, the VB2 anode has energy capacity among the highest of any electrochemical storage battery or fuel cell. Nanoparticle formation is accomplished with a planetary ball mill media (tungsten carbide) with hardness comparable to that of VB2 (8-9 Mohs2). Mechanochemical synthesized, VB2 nanorods, exhibit higher voltage, sustain higher rate, and depth of discharge than macroscopic VB2.

Spark plasma sintering of B 4C ceramics: The effects of milling medium and TiB 2 addition

Boron carbide (B 4C) ceramics, with a relative density up to 98.4% and limited grain growth, were prepared at 1600–1800 °C by spark plasma sintering (SPS) technique. The effects of powder milling medium (water and 2-propanol) on the powders' surface characteristics and TiB 2 addition on the sintering densification were investigated. The ball milling processing of B 4C powders in water can promote the sintering of B 4C ceramics. A B 2O 3 layer on B 4C particle surface is concluded to promote the densification of the B 4C ceramics at an early sintering stage. This B 2O 3 layer, which normally inhibits the densification process at the final stage of the sintering, can be reduced through reaction with TiB 2 particles, resulting in further densification of the B 4C ceramics.

Proceso de molturación mecánica en medio seco, húmedo y criogénico de polvo de hierro dúctil nanoestructurado

The main objective of this study, is to obtain an effective particle and grain size reduction of a nanostructured iron powder by mechanical milling under different milling media. One of the main challenges in this study is to work with this material of great ductility.The variables of the study to be optimized have been the following: speed of rotation, powder to ball ratio (PBR) and the percentage of control agent to induce an effective powder fracturing in front of cold welding. The powder has been characterized by a Laser Diffraction Particle Size Analyser, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and, X-ray diffraction.Through the comparative study, it is found that operating under dry milling conditions: there is a more effective particle size reduction of 43 % and grain size reduction of 62 %. In wet conditions has been reduced the amount of oxide, as well as to obtain a more homogenous distribution of the resulting powder. The results under cryogenic media is presented as promising.