Impact Of Mechanical Activation Research Articles

Impact of mechanical activation and mechanochemical activation on microstructural changes, leaching rate and leachability of natural chalcopyrite

The influence of mechanical activation (MA) and mechanochemical activation (MCA) with Fe and Fe2O3 on the microstructural changes, leachability and leaching rate of natural chalcopyrite was investigated and compared. MCA pretreatments were carried out by chalcopyrite co-milling with Fe and Fe2O3 for 20 and 50 min. The XRD analysis indicated that even after 50 min MA and MCA, constituent phases of chalcopyrite, Fe and Fe2O3 could be detectable beside the newly formed bornite. Regarding the peak broadening and peak intensity reduction, MCA generally intensified the microstructural changes of chalcopyrite in comparison with MA. The microstructural study performed by the Rietveld method also proved that all microstructural parameters changed in favor of reactivity, such that the amorphization degree and microstrain were increased to 96 % and 0.164 (%), respectively, while crystallite size was reduced to 14.6 nm after 50 min MCA of chalcopyrite with Fe2O3. It could be concluded from the leaching tests that MCA along with Fe and Fe2O3 addition could promote the leachability and leaching rate of chalcopyrite, as compared to MA and nonactivated chalcopyrite. Although both the MCA of chalcopyrite with Fe and Fe2O3 could enhance copper extractions in the 1 M sulfuric acid leaching tests at 80 °C, Fe addition was slightly more effective than Fe2O3. The results obtained from the kinetic study also revealed that the leaching mechanism of nonactivated chalcopyrite, mechanically activated chalcopyrite and mechanochemically activated chalcopyrite with Fe2O3 changed from diffusion control to chemical control due to MCA with Fe. Finally, the combination of kinetic and microstructural studies proved that all microstructural parameters, except for the microstrain parameters of chalcopyrite MCA with Fe2O3, could be effective in chalcopyrite reactivity promotion.

Concrete Modification for Hot Weather Using Crushed Dolomite Stone

Crushed dolomite stone can be used as a part of concrete for hot weather. Fine dolomite as a filler is not commonly included in Portland cement. In this paper, the properties of a blended binder based on Portland cement and dolomite filler are presented. Dolomite filler was obtained from dust grains by mechanical activation in a laboratory ball mill to increase the specific surface area and its chemical activity. It is shown that the impact of mechanical activation allows to obtain dolomite filler with a median particle size of 1.4 μm and a specific surface area of 639.9 m2/kg. The content of dolomite filler in Portland cement was 10, 30 and 50%. The main properties of blended cements, i.e., the standard consistency, setting time, compressive strength, average density, and drying shrinkage, were determined on pastes. The mineralogical composition of the hydrated pastes was determined by XRD at 28 days. The presence of dolomite filler at levels higher than 10% decreases the compressive strength of blended cements. The dolomite filler decreases the water demand, shortens the setting time, and mitigates the development of drying shrinkage in the blended binder. To prevent concrete cracking, the application of dolomite filler in blended cement is relevant in hot weather due to its reduced drying shrinkage.

Impact of mechanical activation on the crystal structure and dielectric properties of ceramics based on bismuth ferrite

The solid solutions of the (1-x)BiFeO3 – x/2PbFe1/2Nb1/2O3 -x/2PbFe2/3W1/3O3 system (x = 0.05, x = 0.50) were produced by conventional solid state technology using mechanical activation (MA). It is discovered that particle destruction occurs along planar defects (crystallographic shear planes, CSP) during MA. The MA has a different impact on the microstructure formation of the solid solutions (1-x)BiFeO3 – x/2PbFe1/2Nb1/2O3 – x/2PbFe2/3W1/3O3 system, depending on their localization on the phase diagram. It is shown that MA leads to an increase in the temperature stability of the dielectric properties in the solid solutions of the studied system.

Investigation of the impact of mechanical activation on synthesis of the MgO-TiO2 system

In this study, a mixture of magnesium oxide and titanium dioxide was mechanically activated in order to investigate the possibility of mechanochemical synthesis of magnesium titanate. Mechanical activation was performed for 1000 min in a high-energy vibro mill (type MH954/3, KHD Humboldt Wedag AG, Germany). The mill is equipped with housing having a horizontally placed shutter. The cylindrical stainless steel working vessel, with inner dimensions of 40 mm in height and 170 mm in diameter, has working elements consisting of two free concentric stainless steel rings with a total weight of 3 kg. The engine power is 0.8 kW. Respecting the optimal amount of powder to be activated of 50-150 g and the stoichiometric ratio of the reactants in the equation presenting the chemical reaction of magnesium titanate synthesis, the starting amounts were 20.2 g (0.5 mol) of MgO and 39.9 g (0.5 mol) TiO2. During the experiments, X-ray diffraction analysis of the samples taken from the reaction system after 60, 180, 330, and 1000 min of mechanical activation was performed. Atomic absorption spectrophotometry was used for chemical composition analysis of samples taken at different activation times. Based on the X-ray diffraction analysis results, it can be concluded that the greatest changes in the system took place at the very beginning of the mechanical activation due to the disturbance of the crystal structure of the initial components. X-ray diffraction analysis of the sample after 1000 min of activation showed complete amorphization of the mixture, but diffraction maxima characteristic for magnesium titanate were not identified. Therefore, the mechanical activation experiments were stopped. Evidently, the energy input was not sufficient to overcome the energy barrier to form a new chemical compound - magnesium titanate. The failure to synthesize magnesium titanate is explained by the low negative Gibbs energy value of -25.8 kJ/mol (despite the theoretical possibility that the reaction will happen), as well as by the amount of mechanical energy entered into the system during activation which was insufficient to obtain the reaction product. Although the synthesis of MgTiO3 was not achieved, significant results were obtained which identify models for further investigations of the possibility of mechanochemical reactions of alkaline earth metals and titanium dioxide.

Carbonation, Regeneration, and Cycle Stability of the Mechanically Activated Ca(OH)2 Sorbents for CO2 Capture: An In Situ X-ray Diffraction Study

The impact of mechanical activation on calcium hydroxide-based sorbent was investigated. Carbonation/decarbonation kinetics and sorbent cycle stability were characterized by in situ X-ray diffracti...

Impact of mechanical activation on bioleaching of pyrite: A DFT study

The impact of mechanical activation on the bioleaching of pyrite was studied, and the mechanisms were elucidated by DFT (density functional theory). The characterization result of the pyrite that were mechanically activated showed that the average diameter of the pyrite particles decreased sharply when the activation time was up to 80 min and remained constant from 80 min to 120 min due to the sample agglomeration effect. The change in the specific surface area exhibited the opposite trend, and the contact angles of the pyrite particles decreased gradually as the grinding time increased from 0 to 120 min, which implied that the hydrophilic property of the pyrite increased. The pyrite lattices increased after mechanical activation, indicating the presence of S defect sites on the pyrite surface. Notably, all these changes favored the increase in the bioleaching rate of pyrite. The result showed that the leaching rate of pyrite increased noticeably after mechanical activation by Sulfobacillus thermosulfidooxidans (S.t), and the cell exhibited enhanced adsorption on the activated pyrite surface. The DFT result proved that the activated pyrite could be easily adsorbed by H2O and cells, with relatively large adsorption energies, strong bonds, and an increased number of electron transfers.

Development of a new controlled low strength filling material from the activation of copper slag: Influencing factors and mechanism analysis

During copper ore smelting process, large amount of copper slag is created, which has excellent use in variance ways. In the common case, copper slag were deposited on the surface without treatment, which inevitably caused serious environmental problems. To deal with the pollution created and better utilize copper slag, a new controlled low strength filling material (CLSFM) was proposed for the copper slag from a mine in Africa.The filling cost of using CLSFM is equivalent to that of cement, as well as the method is more ecological and conforms to the local government environment policy. In order to study the influencing factors of this material, orthogonal test method and data visualization were used in the experiment, which make it possible to observe the effect of multifactor composite action on copper slag and the optimum ratio. The experimental results show that mechanical activation and alkali excitation can effectively activate the copper slag. Microscopic analysis shows that the main hydration product of CLSFM, C–S–H, makes the copper slag cementitious, and improves its structural strength. • The impact of Mechanical activation and Chemical activation on the copper slag was investigated. • Orthogonal test, regression analysis and data visualization were used to optimize the ratio. • The microstructure and hydration products of copper slag after mechanical and chemical excitation were analyzed.

Isothermal Redox Kinetics of Co3O4-Fe2O3 Nano-Composite as a Thermochemical Heat Storage Material

Isothermal redox kinetics of as-received Co3O4 (AC), 1 h ball milled Co3O4 (BC), and 1 h ball milled Co3O4-15wt.% Fe2O3 (BCF) was investigated at various temperatures (1130, 1100, 1070, and 1040 °C for reduction and 830, 860, and 890°C for re-oxidation) by thermogravimetric method. It was found that mechanical activation with and without Fe2O3 addition decreases the rate of reduction in all isothermal reduction temperatures, while it improves the rate of re-oxidation in lower re-oxidation temperatures. Mechanical activation with and without Fe2O3 addition preserves and decreases the rate of re-oxidation at higher re-oxidation temperatures, respectively. In addition, according to the results, the re-oxidation kinetics was slower than reduction kinetics. A model-free method was used to calculate the redox activation energies. It was found that mechanical activation individually increases the reduction activation energy, while mechanical activation along with Fe2O3 addition decreases the reduction activation energy in comparison with as-received Co3O4. The results showed that reduction activation energies of AC, BC, and BCF samples varies depending on the reacted fraction (α) and are in the range of 140.6 – 166.6 kJ/mol, 175.5 – 213.7 kJ/mol and 111.5 – 121.3 kJ/mol, respectively. The results also showed that although both mechanical activations with and without Fe2O3 addition decreases the re-oxidation activation energy in comparison with as-received cobalt oxide, but the impact of mechanical activation without Fe2O3 addition on activation energy decline, is higher. Moreover, it was found that activation energies for the re-oxidation of AC, BC, and BCF samples are negative, variations depending on the reacted fraction (α), and are in the range of -76.8 to -133.5 kJ/mol, -440.2 to -471.9 kJ/mol, and -190.8 to -196.05 kJ/mol, respectively.

Impact of mechanical activation on sintering kinetics and mechanical properties of ultrafine-grained 95W-Ni-Fe tungsten heavy alloys

This paper is a study of sintering mechanisms, structure, and mechanical properties of ultrafine-grained 95W-Ni-Fe tungsten heavy alloys. Powder particle sizes were controlled by mechanical activation (MA) of original coarse-grained components and by addition of ultrafine particles. W-Ni-Fe alloys were obtained by sintering in hydrogen and Spark Plasma Sintering (SPS) in a vacuum. The dependence of ultrafine-grained (UFG) alloy density on sintering temperatures has been found to be non-monotonic with a maximum corresponding to the optimal sintering temperature. It has been demonstrated that the sintering activation energy of UFG alloys is significantly lower than that of coarse-grained alloys. It has been shown that the optimal SPS temperature for mechanically activated nanopowders goes down by 350–400 °C in comparison with the optimal sintering temperature in hydrogen for coarse-grained 95W-Ni-Fe powder composition. The reason for a lower optimal sintering temperature lies in a decreased activation energy of grain-boundary diffusion and formation of a non-equilibrium solid solution of nickel and iron in the surface layer of tungsten α-W particles during high-energy MA. High-energy MA and SPS were used to obtain samples of UFG tungsten alloys with high mechanical properties: macro-elastic limit – up to 2250 MPa, yield stress – up to 2500 MPa.

The influence of mechanical activation on the dielectric and dynamic properties and structural parameters of the solid solution of Pb(Zr0.56Ti0.44)O3

The impact of mechanical activation on the dielectric properties, structural parameters, and lattice dynamics of the Pb(Zr0.56Ti0.44)O3 solid solution was investigated. The solution features coexisting metastable tetragonal (T) and rhombohedric (R) phases, whose ratio can be altered by applying the uniaxial compression load up to 320 MPa under torsion in Bridgman anvils. The strain-induced changes of the unit cell parameters, dielectric permittivity, Debye characteristic temperatures, temperature-dependent Debye-Waller factors, and mean square displacements were critically analyzed.

SHS of Titanium Silicide: 1. Impact of Mechanical Activation and Ti Granulometry

SHS of Titanium Silicide: 1. Impact of Mechanical Activation and Ti Granulometry

Studies into the impact of mechanical activation on optimal sintering temperature of UFG heavy tungsten alloys

The paper dwells on the research conducted into sintering mechanisms, the structure and mechanical properties of ultrafine-grained heavy tungsten W-Ni-Fe alloys. The dependence of alloy density on temperature of sintering (Tsint) is found to be nonmonotonic with a maximum equivalent to the optimal sintering temperature. Studies also encompassed the impact that the size of tungsten particles may have on the optimal Tsint. An increase in time of mechanical activation (MA) and acceleration of grinding bodies accompanied by a decrease in alloy particle size and formation of non-equilibrium solid solutions is shown to reduce the optimal Tsint of alloys. High-energy MA and Spark Plasma Sintering methods were applied to obtain samples of tungsten alloys with high mechanical properties: macroelasticity limit of up to 2,250 MPa, yield strength of up to 2,500 MPa.

139-06: Impact of mechanical activation and right-to-left ventricular interlead electrical delay on response to cardiac resynchronization therapy

Purpose: Prior studies suggest that a LV lead position in the latest mechanically activated segment (mechanically concordant) and a long right-to-left interlead sensed electrical delay (RL-IED) improves cardiac resynchronization therapy (CRT) outcome. We compared the effect of a mechanically concordant LV lead and a long RL-IED on clinical and echocardiographic outcome in patients receiving a CRT device. Methods: We prospectively included 161 patients in NYHA class II-IV and an ECG with a left bundle branch block (age 70 ± 9 years, 39 (24%) female, QRS width 173 ± 21 ms, LV EF 25 ± 6 %, end-systolic (ESV) volume 197 ± 71 ml). The LV lead position was verified by postimplant cardiac CT. The segment with the latest mechanical activation segment was determined by preimplant speckle tracking radial strain echocardiography. The RL-IED was measured during CRT implant and expressed as a percentage of preimplant QRS width. Follow-up was performed after six months. Results: The LV lead was positioned mechanically concordant in 75 (47%) patients, while 82 (51%) and 4 (2%) had the lead in an adjacent or remote segment, respectively. The median RL_IED was 63 (range 1–84) %. The proportion of patients improving in NYHA class, the increase in LV EF, and reduction in ESV was similar in patients with or without a mechanically concordant LV lead (51 vs. 68 %, P = 0.12; 13 ± 9 vs. 11 ± 9 %, P = 0.11; 74 ± 56 vs. 66 ± 53 ml, P = 0.39, respectively). Separated by the median RL-IED, 69 % with a long RL-IED improved in NYHA class compared to 46 % with a short RL-IED (P < 0.01). Patients with a long RL-EID had a larger increase in LVEF and reduction in ESV (13 ± 10 vs. 11 ± 7 %, P = 0.04; 86 ± 54 vs. 54 ± 50 ml, P < 0.001, respectively). Conclusion: A long RL-IED, but not a mechanically concordant LV lead position, is associated with improved clinical and echocardiographic CRT outcome in patients with a high degree of mechanically optimal LV lead positions concordant or adjacent to the segment with latest mechanical activation.

Impact of mechanical activation on the burning rate of pressed and bulk-density samples from a Ni + Al mixture

This paper describes a study on the burning of pressed and bulk-density samples from a Ni + Al mixture subjected to mechanical activation. It is shown that mechanical activation and dispersion have a different impact on the burning rate of the samples under study. The gas flow hardly changes the burning rate of the bulk-density mixtures. The linear burning rate of the dispersed bulk-density mixture is 1.7 times greater than that of the pressed mixture, and the mass burning rates are equal to each other. The calculations showed that the conductive heat transfer mechanism in the combustion wave of the dispersed bulk density mixture is the principal mechanism.

Impact of Mechanical Activation on the Burning Rate of Pressed and Bulk-Density Samples from a Ni + Al Mixture

Impact of Mechanical Activation on the Burning Rate of Pressed and Bulk-Density Samples from a Ni + Al Mixture

Impact of mechanical activation and mechanochemical activation on natural pyrite dissolution

In this paper, a new pretreatment method was employed for the enhancement of pyrite mineral dissolution by using mechanochemical activation. The mechanochemical activation was carried out by co-milling of pyrite and iron powder for 20 and 50min. The XRD analysis indicated that a fraction of pyrite and iron phase remained and troilite (FeS) was formed as a new phase after 50min milling. In addition, the microstructural changes of mechanochemically and mechanically activated pyrite were investigated by Rietveld method. The results revealed that amorphization degree increased from 53% in mechanically activated pyrite for 50min to 83% in mechanochemically activated pyrite for 50min. The mechanochemical activation intensified crystallite size reduction of pyrite in comparison with mechanical activation. In spite of mechanical activation, the microstrain measures slightly reduced during mechanochemical activation due to mechanochemical reaction. Although, both the mechanochemical and mechanical activations of pyrite can enhance the dissolution of pyrite, total iron extractions in the 1M sulfuric acid leaching tests at ambient temperature increase from 1.12% for the initial pyrite to 21.22% for 50min mechanically activated pyrite leaching and then abruptly climb to 87.2% for 50min mechanochemically activated pyrite leaching.

Impact of Mechanical Activation, Scar, and Electrical Timing on Cardiac Resynchronization Therapy Response and Clinical Outcomes

Using cardiac magnetic resonance (CMR), we sought to evaluate the relative influences of mechanical, electrical, and scar properties at the left ventricular lead position (LVLP) on cardiac resynchronization therapy (CRT) response and clinical events. CMR cine displacement encoding with stimulated echoes (DENSE) provides high-quality strain for overall dyssynchrony (circumferential uniformity ratio estimate [CURE] 0 to 1) and timing of onset of circumferential contraction at the LVLP. CMR DENSE, late gadolinium enhancement, and electrical timing together could improve upon other imaging modalities for evaluating the optimal LVLP. Patients had complete CMR studies and echocardiography before CRT. CRT response was defined as a 15% reduction in left ventricular end-systolic volume. Electrical activation was assessed as the time from QRS onset to LVLP electrogram (QLV). Patients were then followed for clinical events. In 75 patients, multivariable logistic modeling accurately identified the 40 patients (53%) with CRT response (area under the curve: 0.95 [p < 0.0001]) based on CURE (odds ratio [OR]: 2.59/0.1 decrease), delayed circumferential contraction onset at LVLP (OR: 6.55), absent LVLP scar (OR: 14.9), and QLV (OR: 1.31/10 ms increase). The 33% of patients with CURE <0.70, absence of LVLP scar, and delayed LVLP contraction onset had a 100% response rate, whereas those with CURE ≥0.70 had a 0% CRT response rate and a 12-fold increased risk of death; the remaining patients had a mixed response profile. Mechanical, electrical, and scar properties at the LVLP together with CMR mechanical dyssynchrony are strongly associated with echocardiographic CRT response and clinical events after CRT. Modeling these findings holds promise for improving CRT outcomes.

Impact of mechanical activation on physical and chemical properties of phosphorite concentrates

The mineralogical and chemical composition of phosphorite concentrates from Tunisia, Estonia (from the Kabala and Toolse deposits), Uzbekistan (Dzheroi-Sardara) and Kazakhstan (Dzhanatas) as well as their apatite structures were studied before and after mechanical activation in a planetary mill for 5 to 240 min. The specific surface area of these concentrates increased during the first 10–30 min and thereafter decreased. The solubility of phosphorus increased proportionally with the size of the apatite crystallites. The changes in the physical and chemical properties following mechanical activation depend mainly on the mineralogical composition of phosphorite concentrates and on the structural characteristics of the apatite. Mechanical treatment in a planetary mill is more efficient in the case of sedimentary phosphorites, particularly Estonian phosphorites, and is less effective in the case of igneous phosphorites.