Influence Of High-energy Ball Milling Research Articles

Influence of high energy ball milling on structural, microstructural and optical properties of TiO2 nanoparticles

The influence of high-energy ball milling on structural, microstructural, and optical properties of TiO 2 by modifying the nanoparticle size was studied. Five samples were extracted at different milling times (0, 2, 4, 8, and 13 h). The average particle sizes estimated by dynamic light scattering (DLS) were 205, 155.8, 116.8, 82.9, and 82.7 nm at 0, 2, 4, 8, and 13 h, respectively. X-ray diffraction analysis confirmed progressive broadening of the peaks as the milling time elapsed. Besides, a correlation was found between d spacing and the average crystal size. The UV–Vis diffuse reflectance spectra of TiO 2 revealed a decrease in reflectance due to particle size reduction. Similarly, an alteration of the bandgap transition energy was presented, whose values gradually decreased from 2.966 eV to 2.861 eV for the sample without and with the maximum duration milling performed (13 h), respectively. Likewise, the SEM analysis showed a distribution in nanoparticle size that became more homogeneous and smaller average grain size as the milling duration was longer.

Corrosion behavior of age hardening aluminum alloys produced by high-energy ball milling

The influence of high energy-ball milling (HEBM) on corrosion and hardness of age hardening aluminum alloys was investigated. Nanocrystalline age hardening (AA2024, AA6061 and AA7075) alloys were produced by HEBM of pre-alloyed powder and subsequent cold compaction under uniaxial pressure of 3 GPa. Cyclic potentiodynamic polarization and immersion tests were conducted in 0.6 M NaCl solution which revealed significantly increased pitting and protection potentials in the HEBM alloys compared to wrought alloys of same composition. X-ray diffraction analysis and transmission electron microscopy indicated grain refinement below 100 nm in the ball milled alloys which was the major strengthening mechanism in the age hardening HEBM alloys. The superior corrosion resistance and hardness of the age hardening ball milled alloys were attributed to nanocrystalline structure, extended solid solubility and homogenous microstructure- free from coarse intermetallic phases.

The influence of high-energy ball milling and nanoadditives on the kinetics of heterogeneous reaction in Ni-Al system

Kinetic studies were performed utilizing high-speed temperature scanner in the Ni-Al system including those with and without mechanical activation (MA) of different duration in a planetary ball mill, with and without using carbon nanoadditives (NA). The temperature profiles were taken and treated at different heating rates from 100 up to 2600 °C/min considering the influence of activation duration and the role of nanoadditive on the characteristic points of thermograms. Kissinger method allowed to evaluate activation energy (Ea) for non-activated, activated (1, 2, 3, 5 min), nanoadditive (1 wt.%) containing and nanoadditive (1 wt.%) containing mechanoactivated (1, 3, 5 min) mixtures. The beneficial influence of NA on the interaction between Ni and Al in the non-activated and moderately mechanoactivated mixtures was demonstrated. The influence of MA and NA on the microstructure features and phase formation sequence at various heating rates were revealed. For all the mixtures under study, T* characteristic temperatures (the temperature, where the maximum exothermic effect was observed) were found to increase with increasing heating rates. It was unravelled that mechanical treatment leads to significant changes in the reaction kinetics and phase formation laws. Particularly, in an activated mixture, the formation of Ni3Al is followed by NiAl intermetallic, in contrast to non-activated mixture, where the reaction proceeds only with the NiAl formation. The both MA in 1 min and addition of 1 wt.% NA decreased the activation energy of the Ni-Al reaction, exhibiting commensurate impact on the effective activation energy value of the Ni-Al system. However, > 3 min MA in the presence of 1 wt.% NA have prohibitive effect on the reaction in the Ni-Al system.

Influence of high-energy ball milling on the optical transmittance and some mechanical and tribological properties of a bone china

Bone china samples were produced using two different milling methods: low-energy ball milling (LEBM) for 3 and 24h, and high-energy ball milling (HEBM) for 5min. After pressing, the samples were sintered at temperatures ranging from 1100°C to 1250°C. HEBM 5min yields a raw materials’ specific surface area (BET) almost 50% higher than LEBM 24h. The highest density was obtained for samples prepared by HEBM 5min (2.65g/cm3), sintered at 1200°C, which is 4.4% higher than that obtained for the sample made by LEBM 24h. Samples prepared by HEBM 5min and LEBM 24h exhibit similar Vickers hardness, indentation fracture toughness and, wear coefficient. Overall, these samples exhibit better mechanical properties than those of the samples prepared by LEBM 3h. The milling method influences the translucency of bone china up to a firing temperature of about 1150°C. Above this temperature, the formation of the liquid phase reduces porosity and, consequently, light scattering, regardless of the milling method used to produce bone china. Even so, HEBM still has a beneficial role in making bone china more homogeneous as compared to those produced by LEBM.

Influence of high-energy ball milling on Mg-PSZ-reinforced TRIP steel-matrix composites synthesized by FAST / SPS

A composite with a high-alloy steel matrix was reinforced with varying amounts of Mg-PSZ and synthesized using Spark Plasma Sintering (SPS) technology. To prepare the powders for sintering, they were mixed in a planetary ball mill at two different rates of 100 rpm and 250 rpm. The influence of the rotation speed on the microstructures and compressive strengths of the sintered composites was investigated. Due to the high degree of deformation of the steel powder particles during milling at 250 rpm, the steel phase underwent grain refinement during SPS. Furthermore, the Mg-PSZ was more homogeneously distributed within the steel matrix and mechanically interlocked with the steel matrix. Thus, the compressive strength of the composite increased with increasing Mg-PSZ content and increasing rotation speed during milling of the powder due to grain refinement and the improved strength of the steel/ceramic interface. Furthermore, a larger amount of Mg-PSZ underwent stress-induced transformation under compressive loading.

Influence of high-energy ball milling and additives on the formation of sphere-like α-Al2O3 powder by high-temperature calcination

Abstract In comparison with the typically worm-like α-Al2O3 powders formed from an unground Al(OH)3 precursor calcined at 1450°C, spherical α-Al2O3 powders with ~1 μm in size were prepared by the calcination of a ground Al(OH)3 precursor with 5 wt.% [NH4]+BF4 − under the same calcination conditions. The influence of a high-energy ball milling pretreatment as well as of the additives on the morphological evolution of α-Al2O3 powders was studied using the commercial precursor Al(OH)3 as raw material. The results indicate that the morphology of α-Al2O3 powders is closely related to the morphology of the Al(OH)3 precursor and to the introduction of different additives. The refinement of the Al(OH)3 precursor in aggregate size and of the primary crystal size by high-energy ball milling has effectively suppressed the neck growth of α-Al2O3 grains. In contrast to the findings made previously with the introduction of 5 wt.% [NH4]+Cl−, the morphology of the α-Al2O3 particles could be significantly improved from a ground Al(OH)3 precursor with the addition of 5 wt.% [NH4]+BF4 −, which resulted in the formation of spherical α-Al2O3 powders with 1 μm size at 1450°C.

The influence of high-energy ball milling on the heterogeneous reaction kinetics in the Ti-Si system

The high-temperature (1300–1600 K) kinetics for the Ti-Si reactive system were investigated using electro-thermal analysis. The influence of short-term (1–3 min) high-energy ball milling (HEBM) of Ti+0.6Si heterogeneous powder mixtures on the kinetic parameters was also studied. It was shown that HEBM leads to a significant decrease of the apparent activation energy (Ea) of the solid-state reaction between silicon and titanium. For the non-milled mixture, Ea is 339 ± 63 kJ/mol, while after 3 min of HEBM it drops more than twice to 148 ± 12 kJ/mol. The reaction initiation temperature also decreases with an increase of HEBM time: from 1467 ± 62 K for the pristine mixture to 1110 ± 42 K after 3 min of mechanical treatment. The conclusion was made that a decrease of crystalline size and an increase of the crystal lattice defect concentration, which in combination enhance the grain boundary diffusion, can be responsible for the high reactivity of the mechanically activated mixtures.

Influence of high-energy ball milling on electrical resistance of Cu and Cu/Cr nanocomposite materials produced by Spark Plasma Sintering

A combination of High Energy Ball Milling in the planetary mills (HEBM) with Spark Plasma Sintering (SPS) allows production of dense (>97%) nano-composites of immiscible metals, Cu and Cr, so-called pseudo-alloys. New results on electrical resistance of the pseudo-alloys have been obtained from cryogenic to elevated temperatures, in comparison with the Cu-Cr micro-composites and pure Cu. The results show that duration of HEBM influences hardness and electric resistivity of the materials in a wide temperature range, including cryogenic residual resistivity. This influence remains after SPS. Increasing of the electrical resistivity and hardness with increasing of the mechanical impact is explained by significant increase of specific surface of grain boundaries due to grains refinement. At the same time, some regimes of HEBM results in increasing of the electrical conductivity (decreasing resistance) due to mechanical boundaries purification. These findings allow optimization of the process for preparation of the alloys with desired electrical conductivity and mechanical properties, specifically for application as electrode materials.

Influence of high-energy ball milling on reaction kinetics in the Ni-Al system: An electrothermorgaphic study

A new electrothermographic method, viz. high-speed temperature scanning, was applied to kinetic studies of reactions taking place in the Ni-Al system, including those after mechanical activation in a planetary ball mill. Treatment of the temperature profiles taken at different heating rates in terms of the Kissinger-Akahira-Sunose (KAS) approximation gave activation energy E for non-activated mixtures: E = 155 kJ/mol (for temperature range 650–850°C). But for mechanically activated mixtures, the characteristic points (reaction onset temperature, temperature of maximum reaction rate) were found to decrease with increasing heating rate, which makes the KAS method inapplicable to these compositions. It has been concluded that mechanical treatment leads to significant changes in the reaction kinetics, possibly due to splitting the reaction route into two stages the first of which has very low activation energy.

Effect of high-energy ball milling in the structural and textural properties of kaolinite

Through the process of high-energy ball milling it is possible to obtain solid materials with higher surface area and different particle sizes. These characteristics are very important for some application such as adsorption. Besides, applications of some clays depend on the functionalization which, for kaolinite, takes place in the aluminol groups. Modification in the structural and textural properties of kaolinite by high-energy milling can improve functionalization of kaolinite due to the exposure of aluminol groups. In this work studies were done on the influence of high-energy ball milling on the morphological properties of kaolinite, taking into account parameters such as filling of the miller, number of balls and amount of mass to be milled. Moreover, studies involving milling kinetics of purified kaolinite were carried out to verify modification in the morphology of kaolinite with milling time.

The Influence of High-Energy Ball Milling and Sintering Process on the Microstructure and Mechanical Properties of Al-Ni-Y-Co-La Alloy

Al86Ni7Y4.5Co1La1.5 (at.%) alloy powder was produced by argon gas atomization process. After high-energy ball milling, the powder was consolidated and extruded by using vacuum hot press sintering under different process conditions, sintering temperature, extrusion pressure, sintering time, etc.. The microstructure and morphology of the powder and consolidated bulk alloy were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The phase transformation of the powder was investigated by differential scanning calorimetry (DSC). Mechanical properties of the consolidated bulk alloy were examined. The results showed that as the milling time increase, the volume fraction of amorphous materials and the hardness and yield strength of the bulk alloy were obvious improved.

Direct Combustion Synthesis of Silicon Carbide Nanopowder from the Elements

Direct synthesis of silicon carbide (SiC) nanopowders (size 50–200 nm, BET ~20 m2/g) in Si–C system is conducted in an inert atmosphere (argon) using a self‐propagating high‐temperature synthesis (SHS) approach. A preliminary short‐term (e.g., minutes) high‐energy ball milling (HEBM) of the initial mixture, which involves pure Si and C powders, is used to enhance system reactivity. Two conditions of HEBM with different force fields (17G and 90G) are applied and the results are compared. The influence of HEBM's conditions on the microstructure of mechanically treated mixtures and combustion products is also investigated and discussed. Obtained results suggest that by changing the intensity of mechanical treatment one may prepare a completely amorphous reactive mixture containing carbon and silicon, or gradually change the ratio of (Si/C)–SiC phases and finally produce pure silicon carbide powder during the milling process. The influence of HEBM on the combustibility of the Si/C mixture possesses a critical character: the self‐sustained reaction becomes feasible only after a critical time of ball milling (i.e., 10 min for 90G; 30 min for 17G). Comparison of the microstructures for as‐milled and as‐synthesized powders reveals that for all investigated conditions the morphologies of the as‐milled reactive Si/C media are essentially the same as that for SiC combustion products. The mechanism for direct synthesis of SiC by combustion reaction is also proposed.

Influence of high-energy ball milling of precursor on the morphology and electrochemical performance of Li 4Ti 5O 12–ball-milling time

High-energy ball milling (HEBM) was applied for the synthesis of spinel Li 4Ti 5O 12 and the influence of milling time was investigated systematically. With the increase of ball-milling time, the average particle size of the as-synthesized Li 4Ti 5O 12 powder decreased from ~ 900 nm to ~ 150 nm, while the particle morphology changed little. At the same time, the main particle size distribution peak split up into two parts, which were narrowed and moved to a smaller range. Electrochemical testing results showed that the Li 4Ti 5O 12 with precursor milled for 60 min at 500 rpm rotational speed showed a favorable discharge capacity of ~ 146.9 mAh/g with corresponding coulombic efficiency of 99.9% at 1 C rate. The rate performance was improved with the increase of milling time because of the smaller particle size of the resulted Li 4Ti 5O 12. The voltage change between oxidation peak and reduction peak of Li 4Ti 5O 12 also became wider with milling time increasing.

Synthesis of SrFeO2.5 from mechanically activated reactants

The influence of high-energy ball milling of reactants on a heat activated synthesis of SrFeO2.5 from hematite and strontium carbonate was investigated by X-ray diffraction and thermogravimetric analysis. According to our study the temperature and time required for the reaction can be significantly lowered by ball milling of reactants. A wet mechanical processing of the mixture is the fastest way to reduce the size of reactants' grains and therefore bring the temperature down. Apart from this, milling causes partial transformation of hematite to magnetite, which results in a smaller mass loss of the samples during calcination. However, SrFeO2.5 is synthesized together with some transient phases that finally vanish. This equilibration process is much faster in ball milled samples than in specimens prepared by the traditional ceramic method as a result of the higher homogeneity of the milled ones.

Influence of high-energy ball milling on the physico-chemical and catalytic properties of titanium silicalite TS-1

The present work aims at examining the structural stability as well as the changes in the state of titanium silicalite upon high-energy ball milling. Various techniques including XRD, BET, UV -visible, FTIR and XPS were used to monitor the physico-chemical properties of TS-1 as a function of milling time. The changes in catalytic activity of TS-1 in n-hexane oxyfunctionalization and 1-hexene epoxidation by H 2O 2 with grinding time were also correlated with the corresponding variations in micropore volume, external surface area and BET surface area. The clear differences observed in the catalytic results for the two reactions allow definite conclusions with respect to the nature of the Ti-sites responsible for n-hcxane and 1-hexene reactions.