Attrition Milling Research Articles

High temperature tensile behavior and microstructure of Al-SiC nanocomposite fabricated by mechanical milling and hot extrusion technique

This paper investigates the high-temperature tensile behavior of Al-SiC nanocomposite reinforced with 0, 1.5, and 3 vol% SiC nano particles. To fabricate the samples, SiC nano reinforcements and aluminum (Al) powders were milled using an attritor milling and then were cold pressed and hot extruded at 500 °C. Afterward, mechanical and microstructural characteristics were studied in different temperatures. To this end, tensile and compressive tests, micro-hardness test, microscopic examinations, and XRD analysis were performed. The results showed significant improvement of mechanical properties of Al-SiC nanocomposite in room temperature including 40% of ultimate tensile strength (UTS), 36% of ultimate compressive strength (UCS), and 44% of micro-hardness. Moreover, performing tensile tests at elevated temperatures (up to 270 °C) decreased the tensile strength by about 53%, 46%, and 45% for Al-0 vol% SiC, Al-1.5 vol% SiC, and Al-3 vol% SiC, respectively. This temperature rise also enhanced the elongation by about 11% and 133% for non-reinforced Al and Al-3 vol% SiC, respectively.

Enhanced Dispersion of Yttria Stabilized Zirconia by Mixed Dispersants Containing Carboxyl Group in Aqueous System

Stable slurries of YSZ in aqueous suspension with added polymer dispersants, namely, poly-methacrylic acid ammonium salt (PMMA), poly-acrylic acid (PAA) and poly-acrylic-co-maleic acid (PAMA), were mixed with the monomolecular dispersants citric acid and oxalic acid. The dispersion properties of the suspension were investigated using PSA, viscosity, sedimentation, and FT-IR. The polymer dispersants and monomolecular dispersants were attached to the YSZ surface by the carboxylic group, as shown by the FTIR results. A stabilized aqueous suspension was obtained when the polymer dispersant and citric acid were mixed and compared to the use of citric acid alone as a dispersant agent. When the polymer dispersant and citric acid were mixed and milled through attrition milling, there was a smaller particle size compared to when the polymer dispersant alone was used as a dispersant agent. This study determined that the particle size of the mixed dispersant was affected by the properties of the monomolecular dispersant and that the stability of the suspension was affected by the polymer dispersant. However, when slurries of YSZ were mixed with oxalic acid, the particle bridging behavior was the result of the high degree of viscosity and the small sedimentation height.

Cryogenic Milling of Titanium Powder

Ti Grade 2 was prepared by cryogenic attritor milling in liquid nitrogen and liquid argon. Two types of milling balls were used—stainless steel balls and heavy tungsten carbide balls. The effect of processing parameters on particle size and morphology, contamination of powder and its microhardness was investigated. Milling in liquid nitrogen was not feasible due to excessive contamination by nitrogen. Minor reduction of particle size and significant alterations in particle morphology depended on type of milling balls and application of stearic acid as processing control agent. Heavily deformed ultra-fine grained (UFG) internal microstructure of powder particles was observed by the method of “transmission Kikuchi diffraction”.

Examination of milled h-BN addition on sintered Si3N4/h-BN ceramic composites

Silicon nitride (Si3N4) ceramics containing 1 and 5 wt.% of hexagonal boron nitride (h-BN) were prepared by attrition milling and hot-isostatic pressing. Thorough morphological characterizations have been carried out to reveal the influence of the milling parameters on the size of the h-BN additives. The results confirmed significant decrease in h-BN particle size by increasing milling time. The transmission electron microscopy observations revealed that the h-BN particles were incorporated into the ceramic matrix. The results showed that the increase of the h-BN content decreased significantly the hardness of materials. Moreover, the hardness values were higher when the size of h-BN was larger. The same tendency was observed in the case of Young?s modulus.

The Effects of Ammonium Polyacrylate and Diammonium Citrate as Base and Acid Dispersion Agents on Yttria‐Stabilized Zirconia (3Y‐TZP) Dispersion Properties

Stable slurries in dispersions of 3Y‐TZP in aqueous suspension with the addition of different concentrations of dispersants such as ammonium polyacrylate (APA) and diammonium citrate (DAC) were investigated. The dispersion properties were investigated by measuring the particle size, zeta potential, sedimentation, and viscosity as a function of the wt.% of the dispersant. Both dispersant agents were attached to the 3Y‐TZP surface by the carboxylic group, as shown by the FTIR results. The addition of dispersants was found to produce more dispersed and stabilized aqueous suspension. As shown the viscosity result, that there is no being viscosity peak has been occurring and viscosity going decrease as the shear rates increasing which mean that the suspension has shear thinning behavior and there is no agglomeration as the shear rate is increased. It was determined that 3.5 wt.% of DAC and APA produced the best and most stable slurry; when 3.5 wt.% of DAC and APA was added, the zeta potential showed the largest value in the monodisperse condition. The low pH value of DAC has obtained the higher zeta potential value than APA, which was assumed due to low pH of DAC suspension. At low pH, the adsorption of the adsorbate will occur in a flat adsorbed, while at higher pH the polyelectrolyte will dangle into solution, thus reducing electrostatic repulsion as it is found in the case of APA addition. In this condition, the particle size was decreased to the lower value and the slurry’s stability was obtained with the lowest sedimentation height after the sedimentation test for 30 days. The sample was milled in an attrition mill at 1,000 rpm for four hours.

Naturally cured foamed concrete with improved thermal insulation properties

The paper is dedicated to investigation on improvement of thermal insulation properties of non-autoclaved concrete by increasing aggregate stability of foamed concrete mixture. The study demonstrates influence of mineral admixtures on the foam stability index in the mortar mixture and on decrease of foamed concrete density and thermal conductivity. The effect of mineral admixtures on thermal conductivity properties of non-autoclaved concrete was assessed through different ways of their addition: to the foam and to the mortar mixture. The admixtures were milled up to the specific surface area of 300 and 600 m2/kg using an AГO-9 centrifugal attrition mill with continuous operation mode (Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk). Laboratory turbulent foam concrete mixer was used to prepare foamed concrete. Thermal conductivity coefficient was defined by a quick method using “ИTП-MГ 4 “Zond” thermal conductivity meter in accordance with the regulatory documents. The impact of modifiers on the foam structure stability was defined using the foam stability index for the mortar mixture. The research demonstrated the increase in stability of porous structure of non-autoclaved concrete when adding wollastonite and diopside. Improvement of thermal and physical properties was demonstrated, the decrease of thermal conductivity coefficient reaches 0.069 W/(m×°C)

Functionally graded nanocrystalline silicon powders by mechanical alloying

Functionally graded nanocrystalline silicon powder, having varied bandgap. has been prepared using mechanical alloying technique. The solar grade (99.999% pure) nanocrystalline silicon (nc-Si) powder was ball milled in argon atmosphere in an attrition mill for 4 h to 20 h (4 h, 12 h and 20 h) to reduce crystallite size in it. The milled powder samples were then degassed, to remove entrapped gases, in a vacuum of 10−2 torr at 200 °C for 1 h. Transmission electron microscopy and X-ray diffraction studies show the crystallite size of all the powders are in the nanometer range and decrease in crystallite size was seen with increasing milling time. Raman spectroscopy shows nanocrystalline phases in the milled powder particles with 100% crystalline volume fraction. UV–Vis-IR spectroscopy was used to determine bandgap of the powder samples using Tauc formula. The bandgap and crystallite size in silicon powder is found to be the function of milling duration, without addition of any alloying element. The nc-Si powder with different bandgaps may find potential applications in the field of functionally graded solar cells.

Preparation of dense La0.9Sr0.1Ga0.8Mg0.2O3-δ with high ionic conductivity by solid-state synthesis

The results of a systematic investigation on the effects of processing steps, via solid-state reactions, on structural phase characteristics and ionic conductivity of La0.9Sr0.1Ga0.8Mg0.2O3-δ solid electrolyte are reported. The main purpose of this work is to establish an optimized route for obtaining good densification and high ionic conductivity of this solid electrolyte. Processing routes with three successive calcinations at 1250 °C followed by attrition milling (R1), and with two sequences of calcination at 1350 °C with intermediary attrition milling (R2) give rise to near full density at 1450 °C sintering temperature. The rate of grain growth is fast when the relative density reaches 95%. Elemental mapping reveals uniform distribution of the constituents in the matrix along with La4Ga2O9, LaSrGa3O7 and sub-micrometer MgO grains at grain boundaries. The ionic conductivity of grains remains unchanged with the processing route and sintering profile. The blocking effect of charge carriers at grain boundaries decreases with increasing the dwell temperature.

Effects of milling parameters on the microstructure and Charpy impact properties of MA/ODS ferritic steels

ODS ferritic steels were produced by mechanical alloying (MA) in either attritor or planetary ball mills under argon atmosphere and hot extrusion. Milling in argon with controlling excess oxygen (Ex.O) and nitrogen was effective to reduce the particle size of MA powders. Coarse Al2O3 particles and fine AlN precipitates were found to be formed in an Al added steel when the Ex.O and nitrogen concentrations are increased. Lowering the Ex.O and nitrogen concentrations in ODS ferritic steels acted as a key parameter for enhancing their impact properties.

Effect of Si3N4 addition on the morphological and structural properties of the 316L stainless steel for nuclear applications

The effect of the submicrometer-sized Si3N4 addition on the morphological and structural properties of the ceramic dispersion strengthened (CDS) 316L stainless steels prepared by powder technology has been studied. Two composites were prepared: 316L/0.33 wt. % Si3N4 and 316L/1 wt. % Si3N4. In order to assure a good dispersion of the ceramic particles in the stainless steel powders and a grain size reduction at the same time, the high efficient attrition milling has been used. Spark plasma sintering (SPS) was used for fast compacting of milled composites. Structural and morphological changes were studied after milling and sintering process. It was found that the amount of Si3N4 addition influenced the efficiency of milling process resulting in powder mixtures with different 316L stainless steel grain size and shapes. In the case of 0.33 wt. % Si3N4 addition, the flat 316L stainless steel grains with submicrometer size in thickness have been resulted after milling compared to 1 wt. % Si3N4 added powder mixt...

Microstructure and mechanical characterization of Al6061-CNT nanocomposites fabricated by spark plasma sintering

In this research the effect of spark plasma sintering at different temperature on the microstructure and mechanical properties of the milled Al6061 alloy and Al6061-CNTs metal matrix composites was studied. Horizontal attritor mill were used as milling technique and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the morphology of products. The results indicate that the tensile stress of the Al alloy decrease from 325 to 290MPa with increasing sintering temperature from 450 to 550°C, due to rapid grain growth of aluminum nanocrystals. On the contrary, the tensile strength of the nanocrystalline aluminum-CNT increased from 375 to 430MPa with an increase in sintering temperature. TEM images show the existence of aluminum carbide at higher sintering temperature which has positive effect on the metal-CNT bonding. Another reason of improved properties of Al6061/CNT nanocomposite is the homogenous distribution of CNT as reinforcement and its effect on the grain size stability even at higher sintering temperature. Studies on densification behavior revealed that Al6061 with CNT addition densified in ~100°C lower temperature when compared with unreinforced Al6061. In presence of CNT, the activated carbon can act as reducing agent for powder surface oxide film which finally improves metal/metal bonding. The elongation of Al6061/CNT composite sintered at 550°C is also enhanced 20% comparing with that sintered at 450°C, mainly due to aluminum infiltration into the small CNT clusters and improved bonding conditions between CNT and matrix.

Mechanical properties and microstructure characterization of well-dispersed carbon nanotubes reinforced copper matrix composites

Copper (Cu) matrix composites reinforced with 0.3, 0.5, 1.0, and 2.0 vol% multi-wall carbon nanotubes (MWCNTs) were processed by ultrasonication and high-energy attritor milling of pure copper powder with carbon nanotubes (CNTs), followed by spark plasma sintering and annealing. Microstructural characterization shows that the CNTs are well-dispersed in Cu-0.5 vol% CNTs composite, and the aggregation of CNTs increases with the increase in the volume fraction of carbon nanotubes. Raman spectroscopy results indicate that there is an increase in the number of defects in the nanotube after milling and sintering of the composite. Mechanical property and strengthening mechanism analysis indicates that the grain size effect, hindering effect of dislocations interacting with the grain boundary, and load transfer effect are the main mechanisms affecting the mechanical properties of composites, and the experimental strength of the composite can be close to 81% of the theoretical strength.

From morphology of attrited copper/MWCNT hybrid fillers to thermal and mechanical characteristics of their respective polymer‐matrix composites: An analytical and experimental study

ABSTRACTSynergistic effect of copper and multiwalled carbon nanotube on thermal and mechanical properties of high‐density polyethylene (HDPE)‐matrix composite was evaluated. Attrition mill was employed to prepare the hybrid powder. Reinforcing the polymer‐matrix was carried out using different contents of simultaneously (Sim) and separately (Sep) milled powders as hybrid fillers. X‐ray diffraction and microscopy results show different trends of particle size for Sep and Sim affected by both milling time and volume fraction ratio. Thermal characterization indicates that conductivity was enhanced by 90% and thermal expansion was reduced to 53% of neat HDPE. Young's modulus and tensile strength were improved by 7.8 and 1.22 times of neat HDPE, respectively. Also, characteristics of Sim‐reinforced composites exhibited better correlated relation with milling time compared with erratic behavior of Sep. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45397.

Modeling and Analysis of High-Energy Ball Milling Through Attritors

The effects of major processing parameters of attritor mills on ball milling efficiency (i.e., minimum energy consumption with maximum milling progress) are investigated using discrete element modeling (DEM). The major processing parameters investigated include the size of balls, ball volume fraction inside the canister, ball milling velocity, and design of the impeller shaft of the attritor mill. Their effects are studied through examination of the output parameters including the average speed of balls, maximum speed of balls, and torque applied on the impeller shaft. The torque on the impeller shaft represents the energy consumption during ball milling, while the difference between the maximum and average speeds of balls scales with the compressive pressure during “mini-forging” of powder particles trapped between the colliding balls and thus scales with milling progress (particle deformation and size reduction). The simulation reveals that the ball milling velocity, ball volume fraction inside the canister, ball size, and impeller shaft design are all important parameters for energy-efficient ball milling. In particular, high ball milling velocities can lead to larger particle deformation and faster size reduction with minimum energy consumption. Further, ball sizes smaller than the gap that will not be hit by impellers directly are good for high-energy-efficient ball milling. Otherwise, energy consumption increases substantially.

Doping of nano-crystalline silicon powders by mechanical alloying: the process and characterization

Silicon is the most used semiconductor material in photovoltaic applications. Doping of silicon with III and V group elements to synthesize p and n-type Si requires high temperature (~1000 °C). In the present studies, doping was accomplished in nanocrystalline Si powder at room temperature using mechanical alloying (MA) technique. Aqueous solution of boric acid or phosphoric acid in requisite amount for 50 ppm doping was added to the pristine Si powder and dried. Mechanical alloying of the dried Si powder was performed in the attrition mill in argon atmosphere. MA Si powders were then degassed to remove entrapped argon and other volatiles in a vacuum of 10−2 torr at 200 °C. Scanning electron microscopy and energy dispersive X-ray analysis were performed to study the morphology and composition of ball milled powder. XRD analysis was done to ascertain phases present and crystallite size in the ball milled powders. Micro-Raman results showed an asymmetric peak in terms of Fano type interference and due to phonon scattering, confirming the doping. Degree of crystallinity was studied by deconvoluting Raman peaks. Synchrotron XRF of phosphorus doped Si powder confirms phosphorus doping, in coherence with the results of Raman spectra. XPS spectrum confirms the presence of bounded boron in doped Si powder with binding energy of 186 eV. Charge carrier concentrations and hall mobilities were determined at room temperature. The carrier concentration was found to be matched with the dopants concentration added initially.

Preparation of high performance Bi2Sr2Co1.8Ox thermoelectric materials from nanosized precursors

ABSTRACTBi2Sr2Co1.8Ox thermoelectric (TE) materials were prepared by three different synthesis methods producing nanosized precursors: coprecipitation (with ammonium carbonate or oxalic acid) and attrition milling, which were compared with those obtained by the classical solid state method. Microstructure has shown that precursors produced by coprecipitation and attrition milling methods produced nanometric precursors much smaller than the typical sizes produced by the solid state route. The TE properties are in agreement with the microstructural features, leading to lower resistivity in all the samples, compared with the solid state ones, while Seebeck coefficient is practically unchanged in all cases. As a consequence, maximum power factor values of around four times higher than those obtained in the classical solid state method have been determined. Moreover, the highest power factor value at 650°C is higher than the best results obtained in as-grown textured materials produced by the laser floating zone technique.

Grinding characteristics, physical, and flow specific properties of roasted maize and soybean flour

Grinding characteristics (one and two stage grinding) of roasted maize (RM) and soybean (RS) were conducted in attrition mill to find the effect of feed rate and peripheral speed on average particle size (APS), specific energy consumption (SEC), size reduction ratio (SRR), and grinding constants. Carr Index (CI), Housner ratio (HR), density, water, and oil absorption capacity of flour were also studied as a function of particle size. The higher SRR, APS, and grinding recovery were recorded in the first stage grinding as compared with second one. SEC was decreasing significantly (p < .05) from 0.0039 ± 0.0011 to 0.0013 ± 0.0019 kwh/kg as, feed rate increased from 9 to 15 kg/hr. The grinding constants were significantly increased in the second stage grinding. The flowability of flour such as CI and HR was poor at lower particle size. SEC and APS analysis revealed that a two-stage segregated grinding would be suitable for RM and RS grinding. Practical applications Roasted maize and soybean flour are highly nutritive food and prepared by roasting, grinding and sieving. Flour particle sizes and flow specific properties play an important role in addressing malnutrition and ready-to-eat food formulations. The digestibility and release of bioactive components also depend upon particle size and granular morphology of the food. Though, the present study is also acquainted with energy consumption during processing operation and product quality and which are key parameters for scaling-up and designing the grinding equipment. The information generated regarding the energy consumption and health benefits may be useful for food processors and consumers as well.

Processing, characterization, room temperature mechanical properties and fracture behavior of hot extruded multi-scale B4C reinforced 5083 aluminum alloy based composites

Microstructural characteristics and mechanical behavior of hot extruded Al5083/B4C nanocomposites were studied. Al5083 and Al5083/B4C powders were milled for 50 h under argon atmosphere in attrition mill with rotational speed of 400 r/min. For increasing the elongation, milled powders were mixed with 30% and 50% unmilled aluminum powder (mass fraction) with mean particle size of >100 μm and <100 μm and then consolidated by hot pressing and hot extrusion with 9:1 extrusion ratio. Hot extruded samples were studied by optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), tensile and hardness tests. The results showed that mechanical milling process and presence of B4C particles increase the yield strength of Al5083 alloy from 130 to 566 MPa but strongly decrease elongation (from 11.3% to 0.49%). Adding <100 μm unmilled particles enhanced the ductility and reduced tensile strength and hardness, but using the >100 μm unmilled particles reduced the tensile strength and ductility at the same time. By increasing the content of unmilled particles failure mechanism changed from brittle to ductile.

Effect of precursors on the microstructure and electrical properties of Bi2Ba2Co2O x

Bi2Ba2Co2O x thermoelectric materials have been prepared through three different synthesis methods. The corresponding precursors were obtained from a coprecipitation method using oxalic acid, attrition milling, and classical solid state method (used as reference). Microstructural studies of precursors have shown that the ones produced by coprecipitation and attrition milling led to smaller grain sizes than the ones obtained through ball milling. Infrared spectroscopy has demonstrated that a thermal treatment at 450 °C totally decomposes the metallic oxalates, producing a mixture of Bi and Co oxides, and Ba carbonate, the same average composition of the other precursors. After sintering procedure, it has been determined that the small grain size precursors produce high-density samples, reflected in a decrease of electrical resistivity without significant modification of the Seebeck coefficient. As a consequence, power factor values are more than two times higher than the measured in samples prepared by the classical solid state method. Moreover, the highest power factor values are in the order of the best reported in textured materials, demonstrating the critical role of precursors in the final properties of these materials.

A comparative study on different aqueous-phase graphite exfoliation methods for few-layer graphene production and its application in alumina matrix composites

Four different methods (attrition milling, shear mixing, low-power bath sonication and tip sonication) used for the aqueous-phase, surfactant-assisted exfoliation of graphite were compared. Few-layer graphene (FLG) concentration, yield and production rate were measured for each method at different production times and the quality of the as produced FLG was determined using Raman spectroscopy and X-ray diffraction. It was inferred from the results that a combined method comprising tip sonication and shear exfoliation would offer the best balance between quality and quantity of FLG for relatively short processing times (<6h). FLG dispersions produced with this method were used to fabricate 1wt.% FLG/Al2O3 nanocomposites by ball milling and extrusion, followed by pressure-less sintering. The influence of the FLG addition on the microstructure and mechanical properties was studied, with observed increases of 26.4% and 67.6% in flexural strength and fracture toughness,respectively, and a 25.3% decrease in average grain size.