Milling Period Research Articles

New Coating Technique for Al–B4C Composite Coatings by Mechanical Milling and Composite Coating

Mechanical milling (MM) process as a novel technique for producing Al–B4C composite coatings on the surface of low carbon steel was investigated. The coating thickness, morphology, and cross-section microstructure of the composite coatings were analyzed with scanning electron microscopy (SEM). Also, Vickers microhardness and surface roughness of the coating layer were measured. It was found that a dense Al–B4C composite coating could deposit on the surface, particularly, if longer milling periods. The microstructure of Al–B4C composite coatings revealed that the distribution of B4C particles in the Al matrix was homogenous. Increasing milling time from 6 to 30 h resulted in increase of the microhardness values from 220 to 280 HV for the pre-interface layer (5 μm).

Defect generation and analysis in mechanically alloyed stoichiometric Fe–Ni alloys

FeNi, with the chemically-ordered L10 tetragonal structure, is a promising material for next-generation rare-earth-free permanent magnets. Due to the extremely low atomic Fe and Ni mobility below the critical chemical order/disorder temperature of 320°C, no conventional metallurgical methods are able to induce its formation. Diffusion rates could be enhanced with the creation of excessive vacancies. High-energy mechanical alloying was employed to produce a nanocrystalline Fe–50at.%Ni alloy. The high energy mechanical milling is expected to change the defect characteristics that would be used to study the effect that mechanical alloying has on the defect concentrations. X-ray diffraction revealed that over the entirety of the milling period, the Fe and Ni powders formed an fcc solid solution. The Williamson–Hall equation and Scherrer equation revealed that reductions in grain sizes were caused during alloying. The initial increase in internal strain, and by extension dislocations, was followed by a decrease in strain with further alloying, which was due to the combination effect of creation of dislocation from mechanical deformation and annihilation of dislocations at increasing grain boundaries. Doppler broadening positron annihilation spectroscopy (DB-PAS) showed that the overall number of open-volume defects decreased with increased milling time. Finally, changes of relative permeability, for the mechanically alloyed FeNi phase, were explained by the pinning effect of dislocations.

Room temperature ferromagnetism in finite sized ZnO nanoparticles

We report systematic investigations on the evolution of nanostructured ZnO, room temperature ferromagnetism, and tunable optical properties of ZnO nanoparticles prepared by a mechanical alloying process. It was observed that both un-milled and as-milled powders exhibited a wurtzite structure, but average crystallite size decreased and the effective strain increased for the initial periods of milling. Paramagnetic nature observed in un-milled ZnO gradually unveils room temperature ferromagnetic ordering with modest moment and coercivity. A maximum moment of 0.013µB/f.u. at 12kOe applied field and a coercivity of 172Oe were obtained for 40h milled ZnO powder. Thermo-magnetization data reveal a clear magnetic phase transition from ferromagnetic to paramagnetic state around 500°C, which shifts slightly towards higher temperature with an increasing milling period up to 20h. Annealing of as-milled ZnO powder and UV–vis studies display a drastic reduction in room temperature magnetic moment and blue-shifting of excitonic absorption peak. The observed ferromagnetic properties are intrinsic and discussed on the basis of finite size effect, defect density due to oxygen vacancy. These nanoparticles with tunable magnetic and optical properties are promising to find applications in multifunctional spintronic and photonic devices.

Scalable route to mesoporous iron oxides and their Cr(VI) ions uptake capacity study

Here we demonstrate a simple and scalable synthetic route for preparing porous iron oxides with tunable porosity characteristics by using the high-energy mechanical ball milling technique. Nanocomposites composed of networked hematite encapsulated in silica were produced. Silica was utilized as scaffolds to form nanocomposites and then was etched off hydrothermally in a NaOH solution. The formation mechanism of porous iron oxides, effects of volume ratio of silica to magnetite, milling period, calcination temperature and concentration of NaOH solution were studied systematically. The formation process was monitored by applying a variety of techniques, such as scanning and transition electron microscopes (SEM and TEM), and X-Ray diffractometer (XRD). SEM and TEM studies revealed that a jelly-like solid-state nanocomposite of silica and iron oxide was produced after milling process, and networked iron oxide structures encapsulated in silica displayed a high mass contrast and their grain size decreased with elongating milling period. Barrett–Joyner–Halender (BJH) method analysis indicated that the pore width and Brunauer–Emmett–Teller (BET) specific surface area of iron oxide decreased with the increase of milling period and volume ratio of silica to iron oxide, and porosity increased with increasing volume ratio of silica to iron oxide. Magnetic measurement revealed the superparamagnetic nature of the mesoporous materials at room temperature. Further, absorption capacity of Cr (VI) ions onto mesoporous magnetite was checked to evaluate its toxic ions uptake ability.

Finite Size Effects in Magnetic and Optical Properties of Antiferromagnetic NiO Nanoparticles

We report systematic investigations on structural, magnetic and optical properties of NiO nanoparticles prepared by mechanical alloying. As-milled powders exhibit face centred cubic structure, but average particle size decreases and effective strain increases for the initial periods of milling. Lattice volume increases monotonically with a reduction in particle size. Antiferromagnetic NiO particles exhibit significant room temperature (RT) ferromagnetism with modest moment and coercivity. A maximum moment of 0.0147 μB/f.u at 12 kOe applied field and a coercivity of 160 Oe were obtained for 30 h milled NiO powder. Exchange bias decreases linearly with a decrease in NiO particle size. Thermo-magnetization data reveal the presence of mixed magnetic phases in milled powders and shifts magnetic phase transition towards high temperature with increasing milling. Annealing of milled NiO powder and photoluminescence studies show a large reduction in RT magnetic moment and blue-shifting of band edge emission peak. The observed properties are discussed on the basis of finite size effect, defect density, oxidation/reduction of Ni, increase in number of sublattices, uncompensated spins from surface to particle core, and interaction between uncompensated surfaces and particle core with lattice expansion.

Sol Gel Characterization of Nano Kaolin

Nano kaolin is product from kaolin also known as white clay. Kaolin was established as supplementary cementitious materials in concrete. The inclusion of kaolin in concrete enhances strength and durability properties and prolongs concrete life span. In this research, nanokaolin will be develop by using sol gel technique by that involves high energy milling. The process of milling been influenced by time of milling, ball and jar type. Ceramic type Zirconia (Zi) is been used as jar and ball type in this process. Time of milling was set from four (4) hours and one (1) days. Sample will be analyse by using particle size analyser to see the particle size and surface area of kaolin. From the result shows the optimum milling period for nanokaolin is one day base on particle size compare to 4 hours. Furthermore, one day milling produces a massive increment of surface area compare to others. In conclusion, one day can be considered as the optimum cycle time in the production of nano kaolin.

Preparation and electrochemical characterization of (100 − x)(0.7Li2S·0.3P2S5)·xLiBr glass–ceramic electrolytes

Glass and glass–ceramic electrolytes of (100 − x)(0.7Li2S·0.3P2S5)·xLiBr (x = 0, 5, 10, 12.5, 15 and 20) (mol %) were synthesized by mechanical milling and subsequent heat treatment. Glass powders with no crystal phase were obtained by mechanical milling. The conductivities of the glasses increased concomitantly with increasing LiBr content. The conductivity at x = 20 was 3.1 × 10−4 S cm−1 at room temperature. The Li7P3S11 crystal with high Li ion conductivity was precipitated in the glass–ceramics obtained by heat treatment. LiBr crystal was also precipitated in the glass–ceramics containing LiBr as a starting material. The glass–ceramic at x = 10 showed conductivity of 6.4 × 10−3 S cm−1. It increased to 8.4 × 10−3 S cm−1 by control of the milling period to prepare the precursor glass. 90(0.7Li2S·0.3P2S5)·10LiBr glass–ceramic with high Li ion conductivity had a wide electrochemical window of 10 V. An all-solid-state lithium secondary battery using 90(0.7Li2S·0.3P2S5)·10LiBr glass–ceramic as an electrolyte was charged and discharged successfully.

Structure evolution of Y2O3 nanoparticle/Fe composite during mechanical milling and annealing

Fe-25wt% Y2O3 composite powders have been fabricated by mechanical milling (MM) Fe powders of 100μm in diameter and Y2O3 nanoparticles in an argon atmosphere for the milling periods of 4, 8, 12, 24, 36, and 48h, respectively. The features of these powders were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and transmission electron microscopy (TEM). The experimental results showed that the mean particle size and crystalline size of MM powders decreased with the milling time increasing. All the elements distributed homogenously inside the powders after 48h of MM. The lattice constant of the matrix α-Fe kept constant with the milling time, and no solid solution took place during MM process. After 8h of MM, the α-Fe in each powder became nanocrystalline. After 48h of MM, Y2O3 changes from nanostructure into amorphous structure, and the crystalline size of α-Fe further decreased to 10nm. The Y2O3 in the powders mechanically milled for 48h kept the amorphous structure after being annealed at 400°C, and starts to crystallize when the powders are annealed at 600°C. The amorphous Y2O3 contains a small amount of Fe, and crystalline FeYO3 appears at 800°C.

Highly productive synthesis process of well dispersed Cu2O and Cu/Cu2O nanoparticles and its thermal characterization

The article reports a simple, economical and highly productive synthesis process of cuprous oxide (Cu2O) and copper/cuprous oxide (Cu/Cu2O) nanoparticles with an average size of below 30 nm. A hydrolysis of copper (Cu) particles (200 nm or even microsize) employing low energy ball milling in aqueous circumstance results a controlled synthesis of Cu2O and cermets of Cu/Cu2O nanoparticles. Ground particles are found both in nanobar and spherical shape with cluster nano-clouds into aqueous solution. X-ray diffraction patterns of the sample powder confirm Cu2O nanoparticles and Cu/Cu2O cermets synthesized by complete and incomplete oxidation of Cu particles, respectively. The process is accomplished at room temperature in presence of de-ionized (DI) water and controlled by changing milling period and ball sizes. Enhanced thermal conductivity of Cu2O–water and Cu/Cu2O–water nanofluids are recorded and compared with non-ground Cu–water nanofluids.

Magnetic and charge derived properties of ball milled dilute magnetic semiconductor Si0.98Mn0.02

The dilute magnetic semiconductor (DMS) material Si0.98Mn0.02 was prepared by a ball milling technique at two different milling periods. The samples have been analyzed for electron density distribution and local structure using powder X-ray diffraction (XRD) data sets. The results were compared with those of pure silicon. Structural changes and their implications on the bond-length distributions were analyzed and compared. Electron density distributions of the defect structure were plotted on 2D planes and along the bonding direction in the unit cell for each case using the maximum entropy method (MEM). The incorporation of transition metal ion (Mn) at substitutional sites of the host lattice (Si) is verified for Si0.98Mn0.02 from XRD and magnetic hysteresis measurements were taken using vibrating sample magnetometer (VSM). Room temperature ferromagnetism due to Mn substitution was observed in the prepared samples.

Development and Study of Tantalum and Niobium Carbides as Electrocatalyst Supports for the Oxygen Electrode for PEM Water Electrolysis at Elevated Temperatures

Polymer electrolyte membrane (PEM) water electrolysis is a prospective method of producing hydrogen. We focused on one of its issues - the lack of a suitable support material for the anode electrocatalyst. TaC and NbC were studied as possible electrocatalyst supports for the PEM water electrolysis. Resistance to oxidation of the TaC and NbC was investigated by exposing them to air at 84 and 150 ºC. Subsequently, their electrical conductivity was measured as the indicator of oxidation. Change in specific surface area and conductivity was measured after different periods of ball milling. We found that the TaC was significantly more resistant to oxidation than the NbC. Eventually, both materials retained relatively high electrical conductivity even with the oxidized surface. TaC can thus be recommended as an electrocatalyst support for the oxygen evolution reaction and both materials are proposed to be tested as alternative electrocatalyst supports for the hydrogen evolution reaction.

Disorder in ball-milled graphite revealed by Raman spectroscopy

High-energy ball milling has been used to produce nanocrystalline and amorphous structures in nature graphite, but Raman spectroscopy analysis shows that the structure of the amorphous phase produced by ball milling is less disordered than the amorphous structures in ion-beam bombarded graphite and sputtered amorphous carbon. The band intensity ratio (ID/IG) increases first and then drops to 1.1 after 40h of milling treatment, and remains constant during extended milling up to 100h. Electron microscopy observation and surface area measurement show that the formation of some nanosized clusters during the extended milling period might be responsible for the less disordered structure in the milled graphite.

Synthesis of Nano-WC by High-Energy Ball Milling

Nanosized tungsten carbide (nanoWC) has been widely studied and applied in many industries as hard materials since it has good combination of high hardness and strength. Thermal mechanical alloying method consisting of high-energy ball milling and subsequent carbonization is a common synthetic approach to prepare nanoWC. In this paper, a special milling process has been reviewed, in which the dielectric barrier discharge plasma (DBDP) is introduced, for the preparation of nanoWC. The DBDP milling renders the W+C powders with specific flake-like structure possible owing to the cooperative effect of DBDP and mechanical milling. The obtained W+C powders are activated significantly within shortened milling period. Furthermore, pure nanoWC powders can be synthesized after subsequent carbonization at a significantly lowered temperature. DBDP milling is demonstrated to be an efficient way to synthesize nanoWC.

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.

Preparation and Characterization of Silica Nanoparticles by Wet Mechanical Attrition of White and Yellow Sand

Mechanical alloying is a simple and useful processing technique that is now being employed in the production of nanocrystals and/or nanoparticles from all material classes. In the present work, preparation of silica nanoparticles (SiO2 NPs) by wet mechanical attrition of white and yellow sand using a lab scaled ball mill was investigated. The different experimental parameters affecting the milling process were thoroughly studied such as the milling period, water volume and the initial size of sand particles. Analysis of the results obtained revealed that SiO2 NPs with particle size 22-33 nm and 38-48 nm could successfully be prepared from original white and yellow sand, respectively. The optimum experimental parameters to obtain these SiO2 NPs are 25 g original sand particle, 50 ml water, 113 g media weight and 8 hr milling period at 400 rpm mill speed. The SiO2 NPs obtained were characterized by SEM, XRD, EDS and FTIR. The results obtained showed high homogeneity of the produced spherical SiO2 NPs. These SiO2 NPs have good potentials for use in industry such as their use as additive materials in ultrahigh performance concrete for the next development. Based on economic value, the produced SiO2 NPs have excellent potential to be developed.

Study on Milling Periods on the Iron Mill Scale Particle Size and Properties

The relations between the milling periods with the iron mill scale particle size have been studied. Iron mill scale has been chosen for this research due to the nature of itself, as a by-product. From this research, the average optimum size for the final iron mill scale particle size intended to produce is at 300 μm. Raw iron mill scale received from the industries was in the form of chip with the average size of 10 mm across and 1.5 mm thickness. Three different samples from three different steel mill companies have been used for this study. Rolling ball mill has been used to mill the iron mill scale with two different milling periods, which were two hours and six hours. After the milling process, the iron mill scale was sieved using sieving machine to a few specified grating sizes. Weight of each sample collected from each grating size was calculated in order to get the percentage of the particle size distribution of the iron mill scale after the milling process. Sample collected from Steel Mill 1 (SM1) and Steel Mill 3 (SM3) showing finer particle size produced after the milling period of six hours as compared to two hours. However sample from Steel Mill 2 (SM2) showing different trend of particle size collected as compared to SM1 and SM3. Coarser particle size was collected after the milling periods of six hours as compared to two hours. Characterization process have been conducted to all mill scale samples from each steel mill company in order to determine the relationship between the mill scale properties and the result gathered after the milling process.

TiO<sub>2</sub> Nanoparticles-Coated Polypropylene Copolymer as Photocatalyst on Methylene Blue Photodegradation under Solar Exposure

Problem statement: Pollutions of water bodies by dye wastes from text ile industries and other sources have become critical consideration. A photocatalytic technique using semiconductor materials such as Titanium Dioxide (TiO 2) activated by lights has been considered as one ec onomical method to solve this problem. Approach: We attached titanium dioxide on the surface of pol ymer grains as photocatalyc agents using a cylinder mill ing method. Photodegradation processes were observed in decomposition of Methylene Blue (MB) solutions, as waste model, under solar illumination. Several parameters were optimized suc h as the milling temperature, the milling period, number of coated grain layers on the surface of the waste. The repeatability of using the coated grain s was also sipected. Results: Two layers of TiO 2 coated grains resulted the optimum decomposition r ate of the MB solution. The milling temperature of 100° C and the milling period of 90 min produced the optimal decomposition rate. After five times repeti tion, the TiO 2 coated grains still function well by decomposition up to 97% MB compound. Conclusion: These materials have the potential in large scale wastewater treatment in the tropical regions and nearly do not require a complicated late handli ng in the process of separating the catalyst for treat ed water as well as requires very small energy, exp ect the sunlight energy.

Defects induced ferromagnetism in Mn doped ZnO

Single phase Mn doped (2 at%) ZnO samples have been synthesized by the solid-state reaction technique. Before the final sintering at 500 °C, the mixed powders have been milled for different milling periods (6, 24, 48 and 96 h). The grain sizes of the samples are very close to each other (∼32±4 nm). However, the defective state of the samples is different from each other as manifested from the variation of magnetic properties and electrical resistivity with milling time. All the samples have been found to be ferromagnetic with clear hysteresis loops at room temperature. The maximum value for saturation magnetization (0.11 μ B/Mn atom) was achieved for 96 h milled sample. Electrical resistivity has been found to increase with increase in milling time. The most resistive sample bears the largest saturation magnetization. Variation of average positron lifetime with milling time bears a close similarity with that of the saturation magnetization. This indicates the key role played by open volume vacancy defects, presumably zinc vacancies near grain surfaces, in inducing ferromagnetic order in Mn doped ZnO. To attain optimum defect configuration favorable for ferromagnetism in this kind of samples proper choice of milling period and annealing conditions is required.

Mechanical alloying of Fe–Si and milling of α- and β-FeSi 2 bulk phases

Iron disilicide synthesis by mechanical alloying was performed. ɛ-FeSi, α-Fe 1− x Si 2, amorphous FeSi 2 were formed with relative intensities depending on the milling period. β-FeSi 2 phase was formed after annealing the gridded powder at the temperature where this phase is stable. Mössbauer spectroscopy and X-ray diffraction methods were applied to determine the different phases formed. The morphology of the resulting particles was observed by high resolution scanning electron microscopy. The effect of the milling on bulk iron–silicide samples was and studied chemical effects of the ball milling on Fe–Si 2 systems have been studied.

Effect of addition of planetary milled Gd-211 on the microstructures and superconducting properties of air-processed single grain Gd–Ba–Cu–O/Ag bulk superconductors

Planetary milling technique has been a very promising way to obtain bulk superconductors with very high critical current density, Jc, albeit a detail characterisation of milled secondary phase precursor powders in particular has not been reported to date. Hence we report systematic studies of the effect of addition of planetary milled Gd2BaCuO5 (Gd-211) on the final microstructures and superconducting properties of air-processed Gd–Ba–Cu–O/Ag bulk samples. Average size of Gd-211 precursor particles, which were planetary milled with 1.0mm ZrO2 beads, has been observed to decrease significantly from 1.03μm to 0.52μm with increasing milling duration. Besides the size distribution of milled Gd-211 was narrow compared to that of the reference powder. A small amount of Zr was detected, however, in the milled Gd-211 powder by the inductively coupled plasma-optical emission spectroscopy (ICP-OES) and its content was increased with increasing milling period, which led to an inhomogeneous bulk microstructure. Significantly, the average size of Gd-211 particles milled for 45min has been observed to decrease from 0.73μm to 0.48μm without severe contamination of Zr when the diameter of the beads were reduced from 1.0mm to 0.3mm. Trapped magnetic field of single grain Gd–Ba–Cu–O/Ag bulk sample with 32mm in diameter prepared from almost Zr free Gd-211 fine particles recorded over 1.5T at 77K, which was almost 1.3 times greater than that of the reference sample. Nevertheless the repulsive force of both bulk samples showed around 57N at a gap of zero between the sample surface and SmCo5 permanent magnet.