Influence Of High-energy Milling Research Articles

The Influence of High-Energy Milling on the Phase Formation, Structural, and Photoluminescent Properties of CaWO4 Nanoparticles.

CaWO4 nanoparticles were obtained by facile mechanochemical synthesis at room temperature, applying two different milling speeds. Additionally, a solid-state reaction was employed to assess the phase composition, structural, and optical characteristics of CaWO4. The samples were analyzed by X-ray diffraction (XRD), transition electron microscopy (TEM), and Raman, infrared (IR), ultraviolet-visible (UV-Vis) reflectance, and photoluminescence (PL) spectroscopies. The phase formation of CaWO4 was achieved after 1 and 5 h of applied milling speeds of 850 and 500 rpm, respectively. CaWO4 was also obtained after heat treatment at 900 °C for 12 h. TEM and X-ray analyses were used to calculate the average crystallite and grain size. The Raman and infrared spectroscopies revealed the main vibrations of the WO4 groups and indicated that more distorted structural units were formed when the compound was synthesized by the solid-state method. The calculated value of the optical band gap of CaWO4 significantly increased from 2.67 eV to 4.53 eV at lower and higher milling speeds, respectively. The determined optical band gap of CaWO4, prepared by a solid-state reaction, was 5.36 eV. Blue emission at 425 (422) nm was observed for all samples under an excitation wavelength of 230 nm. CaWO4 synthesized by the solid-state method had the highest emission intensity. It was established that the intensity of the PL peak depended on two factors: the morphology of the particles and the crystallite sizes. The calculated color coordinates of the CaWO4 samples were located in the blue region of the CIE diagram. This work demonstrates that materials with optical properties can be obtained simply and affordably using the mechanochemical method.

Influence of high energy milling on powder morphology and photoluminescence behavior of Eu-doped YBO3 material

The effect of high energy milling on the powder morphology and photoluminescence of Eu (5mol %)-doped YBO3 phosphor materials was studied. The Eu-doped YBO3 materials were prepared via conventional solid-state mixing method followed by milling for 30 min and 1 h. The crystallite and particle size of the phase pure Eu-doped YBO3 powders were found decrease with milling time, as confirmed from Scherrer's formula and electron micrographs, respectively. Rupture of the phosphor powders led to formation of smaller particles, which were also found deposited on the surface of bigger particles during milling. The emission spectra of un-milled and milled samples were excited at 238 nm, 254 nm and 394 nm, and several peaks were observed in the emission spectra in the region from 580 nm to 700 nm, which correspond to the transition of europium ions from 5D0→7FJ (J = 0, 1, 2, 3, 4) levels. The emission intensity ratio between red and orange (R/O) is greater than unity for all samples when excited at 238 nm, 254 nm and 394 nm, which indicates that the samples are red in color purity. Further, the CIE co-ordinates suggest that all of the samples fall in the reddish region and using 254 nm as an excitation wavelength gives better CIE co-ordinates for all samples.

The influence of high energy milling to the adsorption of Cd(II) and Zn(II) ions on activated zeolite

Natural zeolite is believed to be able to effectively reduce heavy metal levels in water. However, due to the weakness of natural zeolites which have a low surface area and impurity so that the adsorption ability of heavy metals becomes less optimal. Increasing the surface area by using high energy milling is expected to optimize the ability of adsorption. In this study, the particle size of natural zeolite was reduced by using high energy milling then activated with HCl and NH4Cl. The adsorption process was carried out by mixing activated zeolite and activated zeolite milling(activated zeolite fine powder) in a solution of metal ions Zn(II) and Cd(II). SEM-EDX analysis showed a change in surface morphology size on activated zeolite milling and GSA indicated an increase in surface area from 69.48 m2/g to 97.9 m2/g. Activated zeolite tends to having a little bigger in ability of adsorption to Cd(II) ions and Zn (II) ions than activated zeolite milling in highest variation of concentration, 800 ppm. In optimum contact time of adsorption, activated zeolite could adsorp Cd(II) ions shorter nevertheless longer to Zn(II) ions than activated zeolite milling. Both of the zeolites have ability to adsorp Zn(II) ions more than Cd(II) ions.

Role of milling parameters on the mechano-chemically synthesized mesoporous nanosilicon properties for Li-ion batteries anode

The current study aims to investigate the influence of high energy milling of nano-silica and magnesium on the products of reduction reaction induced by such mechano-chemical route. Collision energy driven by ball-milling was calculated to enable the surveying of the level of energy on the obtained nano-silicon at the room temperature and in the argon atmosphere. The phase composition analysis was conducted by the Rietveld method. Silicon products of above 97% purity were obtained in a mechanochemically-synthesized system. Morphologically, this route results in a mesoporous silicon nanoparticle with surface area 134.01 m2/g and also a mean pore diameter of 20.12 nm for the Si sample obtained via the highest energy applied, respectively. The carbonized final product is evidenced by Raman spectroscopy. Electrochemical characterizations revealed that the Si/C product exhibit the reversible specific capacity of 3113 mAh.g−1 at a current density of 0.4 A g−1 and electrical resistivity of 1.823 Ω cm2.

Influence of High-Energy Milling in Hydrogen on the Structural-Phase State of Alloys Based on the Laves Phases

The influence of high-energy milling in a planetary mill in the atmosphere of hydrogen on the structure and phase composition of alloys based on the Laves phases is analyzed. We study ZrMn2 and ZrCrNi alloys containing an MgZn2 -type hexagonal Laves phase in the initial state. The changes in the phase-and-structural states of these alloys after milling in hydrogen and thermal treatment in a vacuum are studied with the help of scanning electron microscopy, electron-probe microanalysis, and X-ray phase-diffraction analysis. It is shown that, under the conditions of milling in hydrogen, the main phases of the ZrMn2 and ZrCrNi alloys decompose into zirconium hydride and manganese and into zirconium hydride and chromium, respectively. As the duration of milling increases, the iron content of the samples becomes higher as a result of wear of the milling balls. Depending on the duration of milling, the phases with MgZn2- or Th6Mn23 -type structures are formed in the ZrMn2 alloy after heat treatment in a vacuum. At the same time, the Mg Cu2 - and Th6Mn23 -type phases are formed in the ZrCrNi alloy.

Influence of high-energy milling and heat treatment on the thermal and mechanical properties of a ZrMgMo3O12p/2024Al composite

In this study, ZrMgMo 3 O 12particle (p) /2024Al composites were fabricated with 10 vol% of a near-zero expansion material, ZrMgMo 3 O 12 , as a reinforcement via high-energy milling followed by vacuum hot pressing (VHP). The influences of the milling conditions and the heat treatment on the hardness, thermal expansion properties and dimensional stabilities of the composites were studied. The results show that high-energy (HE) ball milling refined the ZrMgMo 3 O 12 particles and the grains of the α-Al matrix, increased the hardness and decreased the coefficients of thermal expansion (CTEs) of the ZrMgMo 3 O 12p /2024Al composites. Compared with those of the ZrMgMo 3 O 12p /2024Al composites prepared via low-energy (LE) milling, the hardness value increased to 183 HV from 91.8 HV and the CTE decreased to 16 × 10 −6 /°C (RT - 400 °C) from 22 × 10 −6 /°C (RT - 300 °C). Heat treatment of the solution for 24 h followed by ageing at 190 °C for 5 h (i.e., P2 process) further increased the hardness value to 277 HV and decreased the CTE to 13.4 × 10 −6 /°C (RT - 400 °C), which represent an increase of 83% and decrease of 39%, respectively, compared with those of the heat-treated LE ZrMgMo 3 O 12p /2024Al composites. High-energy ball milling and heat treatment could improve the dimensional stabilities of the composites as well. In particular, the HE ZrMgMo 3 O 12p /2024Al composites heat treated with the P2 process showed no variation in their hysteretic strain or CTEs during thermal cycling from RT to 400 °C. Therefore, the P2 HE ZrMgMo 3 O 12p /2024Al composites are in a thermostable state and have the best dimensional stabilities of the tested samples.

Influence of high-energy milling on structure and microstructure of asbestos-cement materials

Asbestos-Containing Waste (ACW) in the form of a fragment from an asbestos-cement board was subjected to high-energy milling in a planetary mill at a constant rotational speed of 650 rpm and for variable milling times: 1, 2, and 3 h. The initial and the milled materials were subjected to infrared spectroscopic examination to identify the asbestos variety and to evaluate changes in the structure caused by high-energy milling. FT-IR (Fourier Transform Infrared Spectroscopy) examinations followed optical microscopy and SEM (Scanning Electron Microscopy) studies as well as X-ray analysis of the phase composition. It was found that the asbestos fibres present in the asbestos-cement board were respirable fibres with pathogenic properties. Identifying asbestos using the spectroscopic method showed that chrysotile asbestos was present in the as-received ACW while no characteristics of absorption bands from crocidolite or amosite were found. The results of the spectroscopic examinations were confirmed by the X-ray phase analysis. During SEM investigations of the milled ACW, complete loss of the fibrous structure of chrysotile was observed. The FT-IR examinations of the milled material showed that with an increased milling time, the characteristic absorption bands characteristic for chrysotile diminished and already after 2 h of milling their almost complete decay was observed. Thereby, it was confirmed that high-energy milling results in destruction of the crystalline structure of the asbestos phase. The conducted studies have shown that the treatment of asbestos-cement materials using high-energy milling is an effective method for asbestos disposal, capable of competing with other technologies and solutions. Moreover, FT-IR spectroscopy was found to be useful to identify asbestos phases and to assess changes caused by high-energy milling.

Synthesis and Photocatalytic Evaluation of Nanocrystalline ZnO Obtained by High Energy Milling

Photocatalytic processes have been applied to treatment of organic effluents through the mineralization of these pollutants on a semiconductor surface. Obtaining nanosemiconductors is desirable for the increasing of particle surface area and improvement in photocatalytic efficiency. In this paper, it was evaluated the influence of High Energy Milling (HEM) as a technique to produce nanocrystalline zinc oxide. The photocatalytic activity of the milled powders to degrade Rhodamine-B dye when exposed to ultraviolet and visible radiation also was investigated. The powders were milled during 4 and 10 hours by dry media milling and 10 hours by wet media milling. The results indicated that there were no detectable powder contamination during the millings and the reduction of crystallite size was function of time and media of milling. All of the assessed samples demonstrate high degradation of the dye, which corroborates with the potentiality of this technique to photocatalysts production. The material milled during 10 hours by dry media milling showed the best results under the experimental conditions.

Influence of High Energy Milling on the Airflow Sensorproperty of the NBCa Ceramic

Some materials have been applied in many surrounding conditions as sensors, electronic devices and other applications. Inexpensive and reliable temperature and flow measurement are important in many applications including, for example, environmental monitoring and control, indoor air conditioning, weather forecasting, automotive and aerospace systems. Special ceramics are an example of such materials. Neodymium-Barium-Copper is a special ceramic that has high electrical conductivity and airflow sensor characteristics. This property is influenced by high energy milling of the powder, when it is not sintered. To evaluate the influence of this type of milling it was carried out an analysis of particle size as a function of milling time. SEM images and granulometric analysis showed significant reduction of particle size with the increase of milling time. For longer times of milling the mixture of precursor powders is favored, resulting in better homogeneity of the ceramic. This is reflected in the properties of airflow sensor.

Influence of high energy milling on the kinetics of the polymorphic transition from the monoclinic form to the orthorhombic form of (±)5-methyl-5-(4’-methylphenyl)hydantoin

5-methyl-5-(4’-methylphenyl) hydantoin is a chiral compound whose racemic mixture crystallizes as a conglomerate. This molecule has two polymorphs: an orthorhombic form (stable form) and a monoclinic form of monotropic character. These forms share extensive structural analogies (identical 2D periodic fragment) and consistently their lattice energies are quite close. The analyses of the crystal structures lead to propose an irreversible polymorphic transition based on a destructive/reconstructive mechanism.

Influence of High-Energy Milling and Sintering Cycle on Obtaining TiAl from Elemental Ti and Al Powders

The present work studies the influence of high-energy milling (HEM) and sintering cycle of Ti and Al powders on the obtainment of TiAl. This study shows that HEM modifies the diffusion processes during the sintering stage. The ignition temperature of the exothermic reaction (SHS) that occurs between Ti and Al, was considered as the key parameter of the sintering process, leading to the study of sintering cycles that avoid uncontrolled processes caused by the SHS reaction. The samples were obtained by cold uniaxial and isostatic pressing, pre-sintered at different temperatures, and then heated up to the sintering temperature. This study also shows the effect of powder additions processed by HEM on the sintering behavior of blended elemental Ti and Al powder compacts.