Low Milling Times Research Articles

The Catalytic Effect of Vanadium on Sorption Properties of MgH2-Based Nanocomposites Obtained Using Low Milling Time.

The effects of catalysis using vanadium as an additive (2 and 5 wt.%) in a high-energy ball mill on composite desorption properties were examined. The influence of microstructure on the dehydration temperature and hydrogen desorption kinetics was monitored. Morphological and microstructural studies of the synthesized sample were performed by X-ray diffraction (XRD), laser particle size distribution (PSD), and scanning electron microscopy (SEM) methods, while differential scanning calorimetry (DSC) determined thermal properties. To further access amorph species in the milling blend, the absorption spectra were obtained by FTIR-ATR analysis (Fourier transform infrared spectroscopy attenuated total reflection). The results show lower apparent activation energy (Eapp) and H2 desorption temperature are obtained for milling bland with 5 wt.% added vanadium. The best explanation of hydrogen desorption reaction shows the Avrami-Erofeev model for parameter n = 4. Since the obtained value of apparent activation energy is close to the Mg-H bond-breaking energy, one can conclude that breaking this bond would be the rate-limiting step of the process.

Influence of nano hexagonal boron nitride on the wear properties of aluminium alloy

ABSTRACT Spark plasma sintered, AA7050 reinforced with nano hexagonal boron nitride (n-h-BN) particles followed by characterisation research was carried out to determine the impact of h-BN in the aluminium matrix. With the aid of field-emission scanning electron microscopy , the uniform dispersion of hexagonal boron nitride was examined, and the impact of altering h-BN concentration on the mechanical and tribological properties was studied. In order to achieve individual dispersion of h-BN particles at low milling time without causing any structural damage, pre-mixing of powders prior to high-energy ball milling proved beneficial. Using the X-ray diffraction method, structural and phase analysis was performed on the powders as well as sintered samples. Pin-on disc apparatus is used for testing the weight loss of the composites. SEM was used to examine the worn surfaces of the substrate. According to the wear analysis, adding reinforcement with 0.5 wt% h-BN resulted in a 65% reduction in wear rate and a 33% increase in hardness. It has been found that h-BN tends to aggregate in composite powder above 0.5 wt%, reducing its physical and mechanical qualities.

Investigating the Size and Microstrain Influence in the Magnetic Order/Disorder State of GdCu2 Nanoparticles.

A series of GdCu nanoparticles with controlled sizes ranging from 7 nm to 40 nm has been produced via high-energy inert-gas ball milling. Rietveld refinements on the X-ray diffraction measurements ensure that the bulk crystalline structure is retained within the nanoparticles, thanks to the employed low milling times ranging from t = 0.5 to t = 5 h. The analysis of the magnetic measurements shows a crossover from Superantiferromagnetism (SAF) to a Super Spin Glass state as the size decreases at NP size of 18 nm. The microstrain contribution, which is always kept below 1%, together with the increasing surface-to-core ratio of the magnetic moments, trigger the magnetic disorder. Additionally, an extra contribution to the magnetic disorder is revealed within the SAF state, as the oscillating RKKY indirect exchange achieves to couple with the aforementioned contribution that emerges from the size reduction. The combination of both sources of disorder leads to a maximised frustration for 25 nm sized NPs.

In situ fabrication of Al-Al2O3-TiB2 hybrid nanocomposite; evaluating the effect of TiO2 and B2O3 mechanical milling time on properties of composite created through vortex casting

In this study, the fabrication of Al-Al2O3-TiB2 hybrid composite using TiO2, B2O3, and Al5083 powders through aluminothermy method has been studied. TiO2, B2O3, and Al5083 powders were attrition milled (20:1 bullet to powder ratio, under argon atmosphere, the speed of 650 rpm for 2, 4, 6 and 20 h). After the completion of the milling process, the milled powder was added to the aluminum molten at 900 °C and finally, the Al5083-Al2O3-TiB2 composite was produced in situ. After the hot extrusion process, specimens were characterized by SEM and XRD analyses and the strength of the composite was investigated. The results of the microstructure analysis and the strength of the specimens indicate the efficiency of low milling times and the absence of TiB2 in milling. The observations from microstructure show presence of TiB2 ceramic particles less than 300 nm in size. The strength tests done on 2, 4, 6 and 20-h specimens represent values of 294, 336, 295 and 276 MPa, respectively.

Behavior of Graphite and Graphene under Mechanochemical Activation with Hematite and Magnetite Nanoparticles

ABSTRACTEquimolar mixtures of graphene and iron oxide nanoparticles were subjected to mechanochemical activation. The phase sequence was investigated using Mӧssbauer spectroscopy as function of ball milling time. For low milling times (2-4 hours) the series with hematite (Fe2O3) nanoparticles was fitted with 2 sextets, corresponding to hematite with carbon introduced in the lattice. At high milling times (8-12 hours) the same series exhibited an additional sextet with hyperfine parameters characteristic to iron carbides and a quadrupole-split doublet, which could be assigned to carbon clusters with small amounts of iron in them. The series with magnetite nanoparticles (Fe3O4) at low milling times was analyzed considering 2 sextets, corresponding to the tetrahedral and octahedral sites of magnetite. At high milling times, the magnetite series also exhibited a broad sextet representing iron carbides and the doublet associated with iron-containing carbon clusters. Supporting information was obtained by determinations of the recoilless fraction. The results were compared with those obtained by ball milling graphite with hematite and magnetite nanoparticles.

Characterisation of the Fe-10 wt% Si nanocrystalline powder obtained by mechanical alloying and annealing

Nanocrystalline Fe-10wt% Si powders has been obtained by mechanical alloying. The synthesis conditions as well as their influence on the structural and magnetic properties of this soft magnetic alloy have been investigated in the light of several experimental techniques (X-ray diffraction, neutron diffraction, DSC, magnetic measurement, SEM). By X-ray diffraction (XRD) investigations have been highlighted that Fe-Si alloy is formed after 4h of mechanical milling and the mean crystallite size is down to 14nm (8h milled sample). The heat treatment leads to the formation of the Fe3Si compound with DO3-type superstructure for low milling times. The saturation magnetisation of the as-milled powders decreases in the first 4h of milling due to the formation of the Fe-Si alloy. The behaviour of the saturation magnetisation versus milling time and annealing was explained by the different magnetic moment of iron atoms in Fe3Si structure. The Curie temperature decreases from 770°C (the Curie temperature for pure iron) to about 650°C after 8h of milling.

Characterization of HoCo3 nanoflakes synthesized via high energy ball – milling

The microstructure and magnetic properties of bulk crystalline and ball – milled binary HoCo3 intermetallic compounds were studied. The presence of PuNi3 type of crystal phase was confirmed in all investigated specimens. The emergence of a partly amorphous phase was demonstrated at the end of grinding process. The influence of the applied high energy ball – milling parameters on the microstructure was investigated. The influence of the increased milling time on the final size of particles and crystallites was characterized by a variety of complementary measurement methods. The fabrication of nanoflakes and agglomerates for long pulverization times was demonstrated. Furthermore, the non-linear dependence of the saturation magnetization, coercivity and remanence driven by high energy ball – milling was evidenced. The enhancement of the coercivity for a low milling time was shown. A quantitative analysis of the XPS spectra over ion etching indicates the formation of Co oxides on the nanoflakes surface.

Influence of preparation pathway on the glass forming ability

The glass forming ability (GFA), i.e. the ease of amorphization of drugs, is mostly investigated using the critical cooling rate upon melt quenching to generate an amorphous product via the thermodynamic pathway. However, amorphous materials can also be prepared via the kinetic pathway by milling. In this case, the time required to generate an amorphous product is called the minimal milling time. This study investigates the correlation of the GFA between these two pathways. Eighteen compounds were chosen and their GFA was investigated by determining the critical cooling rate and the minimal milling time. It was observed that drugs, which turned amorphous upon cooling from the melt at slow cooling rates also had a low minimal milling time and vice versa. It was found that the GFA of the studied set of drugs was inherent and independent of the preparation method. It can be concluded that a drug with low critical cooling rate will also have a low minimal milling time and is thus a good glass former.

Magnetocaloric effect and evidence of superparamagnetism inGdAl2nanocrystallites: A magnetic-structural correlation

The correlation between structural and magnetic properties of $\mathrm{GdA}{\mathrm{l}}_{2}$, focusing on the role played by the disorder in magnetic ordering and how it influences the magnetocaloric effect (MCE) are discussed. Micrometric-sized particles, consisting of nanocrystallites embedded in an amorphous matrix, were prepared by a mechanical milling technique and characterized by means of x-ray diffraction, scanning and high-resolution transmission electron microscopy as well as magnetic measurements as a function of an applied external magnetic field and temperature. The results show that the average particle size is just slightly diminished (\ensuremath{\approx}7%) with the milling time (between 3 and 13 h), whereas the average crystallite size undergoes an expressive reduction (\ensuremath{\approx}43%). For long milling times, structural disorders mostly associated with crystallite size singularly affect the magnetic properties, leading to a large tablelike MCE in the temperature range between 30 and 165 K. Below 30 K, nanocrystallites with dimensions below a given critical size cause an enhancement in the magnetic entropy change related to superparamagnetic behavior. In contrast, for low milling times, relative cooling power values are improved. These striking features along with the small magnetic hysteresis observed make the milled $\mathrm{GdA}{\mathrm{l}}_{2}$ a promising material for application in the magnetic refrigeration technology. Finally, a discussion in an attempt to elucidate the origin of the spin-glass states previously reported in the literature for mechanically milled $\mathrm{GdA}{\mathrm{l}}_{2}$ samples for very long times (400 and 1000 h) is presented.

Atomic Scale Characterization and Magneto-Transport Properties of Mechanically Milled Cu–Co Type Alloys

We have prepared Cu80Co20 powders by high-energy ball milling under ambient atmosphere. The evolutions of both the microstructure and the magnetic properties have been investigated as a function of milling time. 3D-focused ion beam was used for microstructural characterization for low milling time (1.5 h). For higher milling time (20 h) atom probe tomography was used to investigate at the atomic scale the elemental distribution of chemical species. In the first steps of milling, the powder presents a ferromagnetic signal due to the presence of micrometric cobalt particles. After 20 h of milling, the powder is composed of CoO particles with diameter around 10–50 nm surrounded by a copper rich matrix (Cu-84 ± 2%, Co-16 ± 2%) and a few cobalt-rich nanoclusters. For this milling time, a typical giant magnetoresistive effect is observed. A positive magnetoresistive effect is also observed at 5 K under low magnetic fields, which is related to the presence of Co oxides clusters. After a heat treatment at 450 °C ...

Microstructural, thermal and magnetic properties of amorphous/nanocrystalline FeCrMnN alloys prepared by mechanical alloying and subsequent heat treatment

Amorphous FeCrMnN alloys were synthesized by mechanical alloying (MA) of the elemental powder mixtures under a nitrogen gas atmosphere. The phase identification and structural properties, morphological evolution, thermal behavior and magnetic properties of the mechanically alloyed powders were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively. According to the results, at the low milling times the structure consists of the nanocrystalline ferrite and austenite phases. By progression of the MA process, the quantity and homogeneity of the amorphous phase increase. At sufficiently high milling times (>120 h), the XRD pattern becomes halo, indicating complete amorphization. The results also show that the amorphous powders exhibit a wide supercooled liquid region. The crystallization of the amorphous phase occurs during the heating cycle in the DSC equipment and the amorphous phase is transformed into the crystalline compounds containing ferrite, CrN and Cr 2N. The magnetic studies reveal that the magnetic coercivity increases and then decreases. Also, the saturation magnetization decreases with the milling time and after the completion of the amorphization process (>120 h), the material shows a paramagnetic behavior. Although the magnetic behavior does not considerably change by heating the amorphous powders up to the crystallization temperature via DSC equipment, the material depicts a considerable saturation magnetization after the transformation of the amorphous phase to the nanocrystalline compounds.

Nanocrystalline Mg 2Ni-based powders produced by high-energy ball milling and subsequent annealing

High-energy milling technique using a planetary ball mill and subsequent annealing have been employed for producing nanocrystalline powders based on Mg 2Ni intermetallic compound. Characterization of the crystal structure of the milled product using X-ray diffractometry revealed that formation of Mg 2Ni-based nanocrystallites occurred at ball to powder weight ratios of 10:1 and 20:1 after 30 and 12.5 milling hours, respectively. However, its kinetic and volume fraction were found to be greater at the higher ball to powder weight ratio. The calculated average Mg 2Ni crystallite size was 10 nm at ball to powder weight ratio of 20:1 after 60 h of milling and showed decreasing with increasing ball to powder weight ratio. Subsequent annealing of the milled product at low milling time of 5 h resulted in the formation of the dominant Mg 2Ni intermetallic compound with average crystallite size similar to the long period milled product.

Characterization by X ray diffraction of mechanically alloyed tripotassium sodium sulfate

Nanocrystalline powder of tripotassium sodium sulfate (K3Na(SO4)2 - KNS) was successfully obtained by mechanical alloying a mixture of potassium sulfate (K2SO4) and sodium sulfate (Na2SO4) with a proportion of 3:1 in a planetary mill. X ray powder diffraction (XRPD) was used to characterize this material. Powders produced with high milling times: 15, 30, 45 and 60 hours, have shown a single phase. For 60 hours of milling time, the powder was formed with very small grains (60 nm in average). We also prepared several samples with low milling times: 30, 60, 120, 150 and 180 minutes. The results for this series show that 120 minutes of milling is enough to produce a single crystalline phase of KNS. Therefore, we showed that a nanocrystalline powder of tripotassium sodium sulfate is easily obtained by mechanical alloying and that the grain size can be controlled by the amount of milling time.

Investigation of Particle Size Effects on the Magnetic Properties and Corrosion Behaviour of Mechanically Alloyed Nd-Fe-B Powder

Elemental powders of Nd, Fe and B were mechanically alloyed using a planetary ball mill. The change of structure and particle size was examined. XRD pattern revealed that with prolong milling, the mixture of the powders was transformed to nearly amorphous state. Smaller particle size was observed with prolong milling. Magnetization of the mixture of powders was studied using AGM. The saturation magnetization of the mixture was observed to increase initially and then decrease with increasing milling time. The reduction of the magnetic properties was suspected to be due to surface damage which was incurred by extensive milling. The corrosion rate was observed to be higher for larger particle size (low milling time). This indicated higher mass gain percentage of larger particle size compared to lower particle size. The magnetic properties however, did not should any significant improvement after corrosion effect.

Development of Fe based materials obtained by mechanical alloying

Fe rich alloys with ZrNi or Nb and with non metallic B were developed by means of mechanical alloying. The material is nanocrystalline with a minoritary amorphous phase (about 12%). The reduction of the crystallite size is favoured by the addition of Zr, Nb or B. The mechanical alloying parameters were optimised to obtain a nanocrystalline state at low milling time. Furthermore, the apparent activation energy of the crystallisation processes was obtained by thermal treatment, controlled by differential scanning calorimetry. Typical values between 280 and 410 kJ mol - 1 are associated to crystalline growth. The control of the crystal size is related to the kinetic study of the non-equilibrium transformations where the incipient phase as different composition that the initial phase.

Magnetic properties of Mg-ferrite after milling process

Abstract An analysis of magnetic properties of powder of Mg-ferrite processed with a centrifugal mill was carried out. The starting ferrite powder was prepared by solid-state reaction at 1400 °C for 48 h. The powder:balls mass ratio was 1:14, and the container and balls were made of agate. The crystalline size and internal strain were evaluated by XRD patterns using Williamson–Hall and Scherrer methods. The powders get a nanometric scale for low milling time. The X-ray study showed that after 17 h of milling peaks corresponding to α-Fe2O3 appear. The TC were also evaluated by thermogravimetric analysis and correlate to crystalline size. Hysteresis curves are typical of soft magnetic materials with higher values of saturation magnetisation and lower coercivity. The starting sample has a saturation magnetisation of 39.2 emu/g and 0.4 Oe. At longer milling times, saturation magnetisation keeps nearly constant indicating the lack of inversion degree, while that coercivity increase up 576.7 Oe as a consequence of high density of internal stresses due to the mechanical grinding.

Magnetic and Structural Properties of Fe–Mn–Al Alloys Produced by Mechanical Alloying

The effects of concentration and preparation conditions on the magnetic and structural properties of samples of the Fe-Mn-Al system prepared by mechanical alloying were studied by Mossbauer spectroscopy, X-ray diffraction and susceptibility techniques. X-ray diffraction showed that samples with high Al content (40 at.%) and prepared with low milling times (lest than 12 hours) present the peaks of Mn, Fe-Al alloy and broad peaks which correspond to the ternary bcc alloy. For 12 hours the Mn peak disappears and for 24 h or more the bcc ternary phase is totally formed. For t≥24 h Mossbauer spectroscopy studies proved that: samples rich in Fe are ferromagnetic (F) at room temperature (RT) and present a reentrant spin-glass (RSG) behavior for low T; samples with intermediate Fe values are paramagnetic (P) at RT and SG for low T; and those with low Fe content are P at RT, antiferromagnetic (AF) at low T and RSG at very low T. By ac magnetic susceptibility it was possible to detect an additional magnetic phase in the F and P regions which was attributed to a superparamagnetic (SP)-like behavior. XRD and Mossbauer spectroscopy of samples with low Al content (7.5 at.%) showed that they present a fcc AF phase and a Fe-Al F phase for low milling times (≤10 h). For bigger times the only detected phase is the fcc, which is AF for low Fe contents and P for high Fe contents. The effect of using small balls is to enhance the alloyed process.

Influence of grinding on magnetic properties of FeV and Fe powders

Powders of iron-vanadium, in equiatomic proportions, and pure iron were ground down by high-energy milling for different times. The evolution of the magnetic properties was investigated by the flux measurement technique. On increasing the milling time we observed the effects of particle size change and interatomic intermixing which were checked by Mössbauer spectroscopy and X-ray diffraction. After 48 h of milling, the structure and magnetic results agree in proving that an amorphous phase develops in the FeV system. Moreover, at low milling times (< 5 h) the saturayion magnetization and the coercive field reveal an interesting behaviour which is related to the change in mass density induced by grinding.