Effect Of Mechanical Activation Research Articles

Effect of mechanical activation of fly ash added to Moroccan Portland cement

Nowadays, the cement industry is the largest emitter of CO2. In 2015, cement production accounts for roughly 8% of global CO2 emissions. In order to reduce this impact, cement plants are working on alternative solutions, for instance, producing cement by adding additives like fly ash known for reducing the emissions of CO2 and minimizing production costs. The thermal power stations in Morocco produce more than 500 000 tons per year. For ecological and sustainable development reasons, it is desirable to recycle these quantities according to beneficial methods to their addition in the cement. This study aims to investigate the influence of grinding fly ash on the physico-chemical and mechanical properties of fly ash blended CPJ45 cement. The addition of the fly ash particles to the grinder leads respectively to the breakage of the particles and to reduce the agglomeration effect in the balls of cement grinder. Fly ash milling was found to improve particles fineness, and increase the silica and alumina content in the cement. Furthermore, milled fly ash blended cements show higher compressive strength compared to unmilled fly ash blended cements, due to improved fly ash reactivity through their mechanical activation.

Effects of mechanical activation on the fluxing properties of Gua Musang Feldspar

Effects of mechanical activation on the fluxing properties of Gua Musang Feldspar

Effect of mechanical activation on catalytic properties of Fe2O3-pillared bentonite for Fenton-like reaction

AbstractA layered composite of Fe2O3-pillared bentonite (Fe-P-Bet), used as a catalyst in a Fenton-like process, was prepared and then its mechanical activation was studied in detail. The optimum conditions for preparation of Fe-P-Bet and the effects of mechanical activation on the catalytic activity of Fe-P-Bet were investigated systematically. The impact of the mechanical activation on the catalytic activity was affected by the filling ratio of the grinding medium, by the combination of different sized milling balls, by the rotation speed of the planet carrier, by the milling time and by the powder-to-ball ratio. Compared with the removal ratio of orange II of 14.5%, catalysed by Fe-P-Bet, the removal ratio catalysed by activated Fe2O3-pillared bentonite (A-Fe-P-Bet) was as high as 93.6%, and A-Fe-P-Bet had the merit of good stability and only a small amount of Fe leaching during the Fenton-like process. The catalysts prepared were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and by the BET method; A-Fe-P-Bet has a small particle size and a rough surface. The lattice distortion and decrease in the crystal size of α-Fe2O3, as well as damage to the layer structure of smectite in the bentonite, were the main reasons for the increase in the catalytic activity of A-Fe-P-Bet. The results indicated that mechanical activation was an easy and effective method for improving the catalytic activity of this bentonite-based layered composite and that A-Fe-P-Bet was a safe, ‘green’, catalyst material for use in Fenton-like oxidation during treatment of wastewater.

Mechanical activation effect on structure, physicochemical, and biological properties of potassium/magnesium orotates

In the present paper, the possibility of the formation of the tautomeric structure of potassium orotate and magnesium orotate in the solid state is discussed. Using ball milling, we have received the orotate samples with the predominant content of hydroxy and dihydroxy forms. The crystalline and tautomeric structures have been analyzed by XRD, IR, NEXAFS and XPS spectroscopy. There is a slight difference in the water solubility of the orotate tautomers, but the physicochemical properties (viscosity and volumetric thermal expansion coefficients) of tautomers’ water solutions significantly differ. The above differences are related to variation of hydration area of orotate anions due to the composition of the functional groups being changed together with the structure of tautomers. The residual differences in the tautomeric structure of solid orotates formed during the milling process are observed in the orotate water solutions for 1.5-2.5 hours. The biological activity of the water solution of a hydroxy form relative to erythrocytes and epithelial cells is higher than that of oxo- and dihydroxy-form water solutions.

Effect of mechanical activation on thermal energy storage properties of Co3O4/CoO system

The heat produced by a solar receiver during on-sun operation can be employed to drive the endothermic reduction reaction of Co3O4 to CoO; then the consumed thermal energy can be recovered completely by the exothermic reverse oxidation reaction of CoO to Co3O4 which can take place during off-sun operation. In this research, the effect of mechanical activation duration (1, 2, 4, 8, and 16 h) on thermal energy storage by Co3O4/CoO redox pair was investigated. It was found that increasing the mechanical activation duration increases the sintering and particle size of the cobalt oxide powder after one cycle redox, and subsequently the thermal energy storage properties are declined. The weight loss was about 4–5 wt.% for samples heated by 1, 3, and 5 °C/min, while it was about 2 wt.% for 10 °C/min heating rate and less than 1 wt.% for 15 °C/min heating rate. The comparison of cycleability of as-received and 1 h mechanical activated cobalt oxide showed that mechanical activation weakens the cycleability of redox reactions of cobalt oxide. The as-received cobalt oxide cycleability continued up to three cycles, although the reduction and oxidation capacities gradually declined. The cycleability of 1 h mechanical activated sample entirely diminished after two cycles.

Non-isothermal carbothermic reduction kinetics of mechanically activated ilmenite containing self-reducing mixtures

Effect of mechanical activation on carbothermic reduction kinetics and mechanism of ilmenite concentrate containing self-reducing mixture has been investigated using a combination of thermogravimetry and X-ray diffraction. Thermogravimetric comparative study of mechanically activated and non-activated ilmenite concentrate containing self-reducing mixtures with C/O molar ratio of 1.5 was conducted non-isothermally. The samples were heated up to 1573 K at three different heating rates (10, 15, and 20 K min−1) under controlled atmosphere. The reduction mechanism of mechanically activated mixture was followed by X-ray diffraction analysis of arrested samples at different reduction extents. In addition, reaction kinetics was further investigated and corresponding kinetic parameters were estimated using isoconversional (model-free) and model-fitting (Coats–Redfern) methods.

The effect of mechanical activation on the structure and sorption activity of chitin

A mechanical activation of chitin suspended in water has been employed under conditions of a combined impact of cavitation and high shear stresses realized in a rotor-pulse device. For chitin samples that underwent preliminary activation for 5–20 s, the value of sorption capacity toward copper ions increased twoto fourfold in dependence on the treatment duration as compared to the initial sample. The experimental data corroborating that the main factors of mechanical activation are the increase of the specific surface area, porosity, and particle-chitin amorphization are presented. It has been established that the increase of the duration of mechanical treatment over the experimentally determined optimal value yields a decrease of the activation effect, which is related to the processes of restructuring and recrystallization. It has been shown that the Langmuir model allows rather adequate description of the sorption process with the correlation coefficient of 0.98–0.99.

Research of the chemical activity of microgrinding coals of various metamorphism degree

In this paper, we investigate the effect of mechanically activating grinding of coals of various degrees of metamorphism by two different methods - determination of the flash time in a vertical tubular furnace and thermogravimetric analysis. In the experiments, the coals that had been processed on a vibrating centrifugal mill and a disintegrator, aged for some time, were compared. The experiments showed a decrease in the ignition temperature of mechanically activated coals - deactivation of fuel, as well as the effect of mechanical activation on the further process of thermal-oxidative degradation.

Malahit Cevherinin Amonyum Nitrat ile Liç Edilmesine Mekanik Aktivasyonun Ektisinin İncelenmesi

Malahit Cevherinin Amonyum Nitrat ile Liç Edilmesine Mekanik Aktivasyonun Ektisinin İncelenmesi

Effect of mechanical activation on solid-state synthesis process of neodymium disilicate ceramic pigment

The effect of mechanical activation of precursors ground in a high-energy density stirred bead mill on the synthesis of Nd2Si2O7 powders was investigated. The reaction of precursors after the mechanical treatment at different milling time was analyzed by laser particles size analysis, thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that the precursors without grinding and fired at 1200 °C cannot form the Nd2Si2O7 phase. Nd2Si2O7 can be formed at 986.9 °C when the precursors are ground for 3.0 h. To further clarify the effect of mechanical activation, two raw materials (i.e., SiO2 and Nd2O3) were pre-treated by different methods. The raw materials mixed and subsequently ground is conducive to decreasing the temperature of forming pure Nd2Si2O7 phase. The results indicate that the mechanical activation favors the promotion of the crystal growth of Nd2Si2O7. In addition, the color properties of the synthesized Nd2Si2O7 powders were also evaluated by reflection differential colorimetry. It is indicated that Nd2Si2O7 powders that possess a high-temperature stability can be used as a ceramic pigment.

Effect of Mechanical Activation on the In Situ Formation of TiB2 Particulates in the Powder Mixture of TiH2 and FeB

AbstractThe in situ formation of TiB2particulates via an interface reaction between Ti and FeB powders was studied. The effects of mechanical activation by high-energy milling on the decomposition of TiH2and the interface reactions between Ti and FeB powders to form TiB2were investigated. Powder mixtures were fabricated using planetary ball-milling under various milling conditions. The specific ball-milling energy was calculated from the measured electrical power consumption during milling process. High specific milling energy (152.6 kJ/g) resulted in a size reduction and homogeneous dispersion of constituent powders. This resulted in a decrease in the decomposition temperature of TiH2and an increase in the formation reaction of TiB2particulates in the Fe matrix, resulting in a homogeneous microstructure of nanoscale TiB2evenly distributed within the Fe matrix. In contrast, the powder mixture milled with low specific milling energy (36.5 kJ/g) showed an inhomogeneous microstructure composed of relatively large Fe-Fe2B particles surrounded by a thin layer of Fe-TiB2within a finely dispersed Fe-TiB2matrix region.

Effects of mechanical activation on physicochemical properties and alkaline leaching of boron concentrate

Boron concentrate is one of the major products created during the magnetic separation and gravity treatment of ludwigite. Nevertheless, achieving high B2O3 leaching efficiency in alkaline solution is difficult owing to its low B2O3 grade. This study proposes a mechanical activation (MA) method for the pretreatment of boron concentrate and describes the changes in B2O3 leaching rate of boron concentrate as a function of different ball-milling conditions. This work examines the changes in the physicochemical properties change of samples arising as a result of the MA process, in particular by PSD, BET, SEM, XRD, FTIR and TG-DSC analyses. The experimental results show that particle size, specific surface area, crystal structure, stability of chemical bonds, energy accumulation and the B2O3 leaching rate of boron concentrate are all significantly affected by the milling process. The B2O3 leaching rate exhibits an initial increase as the rotation speed and milling time are increased, and the optimum MA conditions are established as 500rpm and 60min. Under these conditions, the B2O3 leaching rate increases from 67.52% (unmilled sample) to 89.47%. The decrease in particle size from 13.2μm to 6.2μm and the increase in the BET specific surface area from 15.6m2/g to 27.7m2/g in samples milled for 60min produces an increase in the contact area between the sample and the alkaline solution. Additionally, the increased extent of crystal structure amorphization and the weakening of chemical bonds increase the active points on the surface of sample particles or within their lattice structure, thereby facilitating the reaction with the alkaline medium. Finally, the increase in energy and dehydroxylation caused by the milling process increase the OH− absorption during the leaching process.

Effect of mechanical activation on the hydrogen reduction kinetics of magnetite concentrate

The effect of mechanical activation on the reduction kinetics of magnetite concentrate by hydrogen was studied. The magnetite concentrate was milled for 8 h in a planetary ball mill. After 8 h of milling, the average particle size was reduced from 14 to 4.4 µm, resulting in a lattice microstrain of 0.3. Isothermal reduction experiments were conducted by thermogravimetry to focus on the chemical reaction as the rate-controlling factor by eliminating external mass transfer effects and using a thin layer of particles to remove interstitial diffusion resistance. Thus, about 2 mg of magnetite powder was reduced at different temperatures under a sufficient flow of hydrogen. The magnetite concentrate and reduction products were analyzed by SEM and XRD. It was found that the onset reduction temperature decreased from 587 to 500 K (314–227 °C) due to the mechanical activation. The activation energy for hydrogen reduction of the activated concentrate decreased about 10% compared with the as-received concentrate. In view of the results, a reaction rate expression was established based on the nucleation and growth model with an Avrami parameter n = 2.5.

Synthesis of TiCr2 intermetallic compound from mechanically activated starting powders via calcio-thermic co-reduction

Effect of mechanical activation of TiO2 and Cr2O3 oxides as starting materials was investigated for direct synthesis of TiCr2. Differential thermal analysis (DTA) indicated that increasing the ball milling time resulted in lower exothermic reaction temperatures between molten Ca–Cr2O3 and molten Ca–TiO2. A model-free Kissinger type method was applied to DTA data to evaluate the reaction kinetics. The results reveal that the activation energy of the exothermic reactions decreased with increasing the milling time. The structure, oxygen content, and average particle sizes of the obtained TiCr2 product were affected by the ball milling time of the starting materials. Increasing the milling time from 10 to 40 h decreased the average particle size and oxygen content of the obtained TiCr2 from 10 to 2 μm and from 1690 to 1290 ppm, respectively. The X-ray diffraction (XRD) results showed that TiCr2 compounds with metastable bcc phase can be produced using nano-sized starting materials, while only a slight amount of bcc phase can be obtained in the TiCr2 compounds, using micron-sized starting materials. The TiCr2 obtained by this method had a hydrogen absorption capability of 0.63 wt % and the kinetics of the hydrogen absorption increased for the 40 h milled sample.

Solid-state synthesis of nanocrystalline BaZrO3 using mechanical activation

Nanocrystalline BaZrO3 has been prepared by solid-state reaction, using preliminary mechanical activation of a stoichiometric mixture of BaCO3 and ZrO2. The mechanical activation was performed in an AGO-2 centrifugal planetary mill for 10 min at a centrifugal factor of 40g. The effect of mechanical activation of the reactant mixture on the processes that take place during subsequent heating of the mixture has been studied using a combination of thermoanalytical techniques. The synthesized barium zirconate, with an average crystallite size from 50 to 100 nm, has been characterized by X-ray diffraction and scanning and transmission electron microscopy.

The role of mechanical activation on atmospheric leaching of a lateritic nickel ore

The effect of mechanical activation on the atmospheric pressure leaching of a lateritic nickel ore was investigated to develop a superior alternative. Under the influence of mechanical activation, certain physico-chemical changes were observed. Accelerated leaching kinetics and less sulfuric acid consumption were found as the most beneficial effects of mechanical activation. 80.6% Ni and 84.5% Co in leach were obtained with the mechanically activated sample after 2h of leaching in 30% H2SO4 at 85°C and 1/2.5 solid/liquid ratio (w/w). When non-activated sample was leached under the same conditions, similar metal extractions could be obtained after 8h of leaching. Finally, a process flow sheet was developed including mechanical activation of the laterite, agitation leaching, iron precipitation step, and nickel-cobalt solvent extraction.

Effects of mechanical activation on the kinetics of terbium leaching from waste phosphors using hydrochloric acid

The effect of mechanical activation (MA) on the kinetics of terbium (Tb) leaching from waste phosphors using hydrochloric acid was investigated. Leaching kinetics, such as apparent reaction rate, activation energy and reaction order, were determined using the shrinking-core model and the Arrhenius equation. Results obtained from experiments with different concentrations of HCl and under different leaching temperatures were used for the determinations. The impacts of factors such as rotational speed, HCl concentration and leaching temperature on the leaching rate of Tb were also discussed. The results showed that MA could dramatically increase the leaching rate of Tb from waste phosphors, and the apparent reaction rate (kap) of leaching was accelerated as well. For inactivated waste phosphors, the apparent activation energy (Eap) was 52.82±3.95 kJ/mol, indicating that the rate-controlling step of the leaching process was the chemical reaction. The Eap dropped to 25.96 ±3.90 kJ/mol and 10.96±2.79 kJ/mol when the waste phosphors were mechanically activated at rotational speeds of 400 and 600 r/min, respectively; the leaching process transformed to a hybrid (chemical-reaction and diffusion) control process, and even a reagent-diffusion (through the product layer) control process. The apparent reaction order for Tb leaching from 400 r/min-activated waste phosphors was 2.49±0.11, and it decreased to 1.16±0.17 when the rotational speed of 600 r/min was used. Kinetics results indicated that MA could make Tb leaching occur spontaneously, and the activation intensity of waste phosphors was strengthened with higher rotational speed.

Mechanical activation-induced structural changes in a 5Ti + 3Si mixture

A 5Ti + 3Si powder mixture has been studied by X-ray diffraction in order to assess the effect of mechanical activation (MA) time on its structural state. MA for 11 min or a shorter time leads to the degradation of the crystal structure and partial amorphization of titanium and silicon. MA has been shown to produce different structural changes in silicon and titanium. MA reduces the crystallite size of silicon to 300 nm and increases microstress to 700 MPa, whereas the only consequence of the MA of Ti is an increase in microstress to 550 MPa. MA for more than 11 min initiates a solid-state reaction which results in the mechanochemical synthesis of Ti5Si3.

Effects of mechanical activation on the co-liquefaction of Xigou sub-bituminous coal from Xinjiang and Karamay petroleum vacuum residues

The effects of mechanical activation on the co-liquefaction of Xigou sub-bituminous coal (XSBC) and a mixture solvent of creosote oil and Karamay petroleum vacuum residues were investigated. The structure of the mechanically activated coal was more porous than the structure of XSBC according to the characterization results. Compared to XSBC, the average pore size of the activated coal increased by 106.7%, whereas the specific surface area decreased by 74.7%. The absorption peaks of OH at 3300cm−1 and CO at 1720–1650cm−1 decreased. The ratio of the fractions of aromatic carbon and sp2-hybridized carbon decreased by 13%. The mass loss from 100°C to 300°C increased by 237% and the apparent activation energy in the liquefaction temperature range of 300–400°C decreased by 21.6%. The yields of total oil, asphaltene and preasphaltene (A+PA), gas and residue of mechanical activated coal slurry were 82.67, 10.80, 4.12 and 2.40%, respectively. Compared to raw coal slurry, the total oil yield and the gas yield of activated coal slurry increased by 8.2 and 63.5%, respectively, whereas the A+PA yield and the residue yield decreased by 29.9 and 57.5%, respectively. The H2 consumption decreased by 19.9%. Moreover, the yield of heavy oil and distillate in the liquefied product decreased by 51.1 and 31.3%, respectively, whereas the yields of gasoline and diesel increased by 65.5 and 10.7%, respectively.

Improvement in rare earth element recovery from waste trichromatic phosphors by mechanical activation

This research introduced a pretreatment process -mechanical activation- for extracting rare earth elements (REE) from waste trichromatic phosphors separated from e-waste. The effects of mechanical activation on the physicochemical properties of waste trichromatic phosphors were investigated using multiple methods by scanning electron microscopy (SEM), Brunauer-Emmett-Teller measurement (BET), particle size analysis, and X-ray diffraction (XRD). The results show that mechanical activation has noticeable effects on the microstructure of waste trichromatic phosphors. Increasing the rotational speed could cause the changes of SA, structural defects, and breakage of the crystalline network, which could significantly improve in REE extraction rates. Specifically, changes in the crystalline degree of disorder caused by mechanical activation played a crucial role in enhancing the REE leachability from waste trichromatic phosphors. In addition, the sulfuric acid leaching behaviors of the activated waste trichromatic phosphors were studied by varying several parameters, including leaching time, liquid-to-solid ratio, acid concentration, heating temperature, and various activation conditions: Y, Eu, and Ce recovery rates reached approximately 96.3%, 91.1%, and 77.3%, respectively, from waste trichromatic phosphors activated for 60 min at the rotational speed of 550 rpm (by ball mill) compared with 46.7%, 42.3%, and 31.2%, respectively, from the raw sample. The method is promising to be put into practice to promote the recycling REE from various waste electric and electronic products.