Effect Of Mechanical Activation Research Articles

Synthesis of NiAl/TiC–Al2O3 composite by mechanically activated combustion synthesis

The NiAl/Al2O3–TiC composite was fabricated by the combustion synthesis of NiO/Al/Ti/C powder starting mixture. The effects of mechanical activation on phase formation and microstructure development were evaluated by X-ray diffraction, scanning electron microscopy using energy dispersive spectroscopy, and transmission electron microscopy. By the combustion synthesis of an as-mixed powder compact, a partial amount of NiO was reduced by molten aluminum with the formation of NiAl3 and Al2O3. Mechanical activation refined the particle size of the reactants and after combustion synthesis, Ni was reduced by the reaction of NiO/Al with molten Al giving rise to NiAl. NiAl formation is an exothermic reaction whose released energy starts the ignition resulting in the final NiAl/Al2O3–TiC composite.

Efficient separation of fluoride and graphite carbon in spent cathode carbon from aluminum electrolysis by mechanical activation assisted alkali fusion treatment

Spent cathode carbon (SCC) is the largest and most inevitable hazardous solid waste continuously discharged from the aluminum electrolysis industry. In this study, mechanical activation was used to assist alkali fusion treatment in dissociating toxic substances and recovering graphite carbon from SCC. The effect of mechanical activation (i.e., milling speed, ball-to-material mass ratio, and milling time) on the alkali fusion treatment was investigated. Its effect on the physicochemical properties of SCC–Na2CO3 mixtures was also analyzed through particle size distribution, Brunauer-Emmett-Teller surface area analysis, scanning electron microscopy, X–ray diffraction and thermogravimetric analysis–differential scanning calorimetry. Results showed that mechanical activation enhanced the alkali fusion treatment by improving the physical separation of fluoride, the mixing uniformity and reaction contact area of SCC and Na2CO3, and promoting the conversion of Na2CO3 to Na2O. The formation of agglomerates was the main reason that the carbon content of recovered graphite carbon and the fluoride ion leaching rate increased initially then decreased with the increment in mechanical activation conditions. Under optimal mechanical activation conditions, the carbon content of recovered graphite carbon and the fluoride ion leaching rate increased from 89.35% and 76.50% (non-activated sample) to 93.93% and 95.02%, respectively, indicating that mechanical activation assisted alkali fusion treatment effectively enhanced the separation efficiency of fluoride and graphite carbon. In addition, thermodynamic analysis of the alkali fusion treatment and characterization of recovered graphite carbon (under the optimal mechanical activation conditions) were performed. Results demonstrated that the simultaneous conversion of multiple fluorides (i.e., Na3AlF6 and CaF2) and oxidative decomposition of cyanide in SCC can be achieved via mechanical activation assisted alkali fusion treatment. These findings indicate that mechanical activation–assisted alkali fusion treatment is a promising method for the detoxification and utilization of SCC.

Молекулярные магнетики --- источники радиочастотного сверхизлучения при механической активации

The effect of mechanical activation of radio frequency superradiance in a composite based on a heterospin molecular magnet and a polystyrene matrix has been established. Mechanical activation was carried out for the first time in unloading mode of rheological explosion .

Structural evolution of arsenopyrite and dearsenification by mechanical activation

The effects of mechanical activation on the structural evolution and dearsenification of arsenopyrite were investigated herein by employing specific surface area, particle size, scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analyses. The results of leaching kinetic studies showed that mechanical activation can enhance the efficiency of dearsenification of arsenopyrite, causing the leaching activation energy to decrease from 54.3 kJ·mol−1 (non-activated) to 33.18 kJ·mol−1 (grinding speed of 300 r·min−1). Furthermore, the influence of temperature on leaching gradually declined with the enhancement of the activation effect. The improved dearsenification was associated with the evolution of the macro-structure and micro-structure of arsenopyrite under mechanical activation. Macroscopically, mechanical activation can reduce the particle size, and simultaneously increase the specific surface area of arsenopyrite, thereby providing the exceptional effect of dearsenification. Microscopically, the reduced lattice volume and grain size are beneficial for arsenic removal. Furthermore, the decreased crystallinity and increased lattice distortion rate can strongly enhance the arsenic removal rate. The leaching activity of activated arsenopyrite was related to increased microstrain along the a and b axes, but not the c axis. Moreover, the larger interplanar distance was conducive to leaching leading to dearsenification.

Kinetic analysis of the second stage of the solid-phase synthesis of Li4Ti5O12 from a mechanically activated mixture of rutile and lithium carbonate

The effect of mechanical activation of a mixture of micron-sized rutile and lithium carbonate in a Pulverisette-5 ball mill on the kinetics of the second stage of Li4Ti5O12 synthesis was investigated. The values of the energy of activation of the second stage of lithium pentatitanate synthesis from starting mixtures that were mechanically activated for 1 and 60 min were determined to be 463 ± 23 kJ·mol−1 and 393 ± 20 kJ·mol−1, respectively. It was shown that mechanical activation of the starting mixture leads to the destruction of lithium carbonate with the release of CO2 and an increase in the reactivity of TiO2, which strongly influences the synthesis of lithium pentatitanate. The results of our study demonstrate that mechanical activation promotes a reduction in the temperature of the first stage of lithium pentatitanate synthesis, that is, the formation of Li2TiO3, by approximately 230°С and a reduction in the temperature of the second stage, i.e., the the formation of Li4Ti5O12, by 50 °C. We show that single-phase Li4Ti5O12 with a particle size of ca. 200 nm can be successfully synthesized from a mechanically activated starting mixture at 750 °C with a 3 h holding time or at 800 °C with a 0.5 h holding time.

Effect of alumina added by mechanical mixing and co-doping on the densification mechanisms of zirconia nanoparticles at the initial stage of sintering

The comparative analysis of the mechanical activation and Al2O3 doping effect on the densification behavior of tetragonal 3Y-TZP nanopowders has been carried out. Two types of zirconia nanopowders doped by alumina have been studied. Namely, nanopowders obtained by the mechanical mixing and co-precipitation methods. The behavior of nanopowders at initial stage of sintering was examined by the constant rate of heating technique.It was found that the volume diffusion mechanism, which is realized by sintering the 3Y-TZP nanopowders undoped and doped with a small amount of Al2O3 nanopowders obtained by co-precipitation, ceases to function when the Al2O3 content increases to 2 wt% and the Al2O3 inclusions block the diffusion flux of Zr4+ cations from the volume of ZrO2 particles to the necks. Annealing of the structure defects caused by milling of the 3Y-TZP and Tosoh TZ-3Y powders during preliminary heating leads to the realization of the volume diffusion mechanism instead of the grain boundary diffusion mechanism at the initial sintering stage in milled nanopowders. Therefore, the GBD mechanism in the milled zirconia powders caused by the stressed and defective state of zirconia nanoparticles, and not by size effects.It was shown that the Al2O3 particles added to zirconia nanopowders by mechanical mixing did not change the volume diffusion mechanism at the initial stage of sintering of 3Y-TZP NPs until the Al2O3 concentration did not blocked the diffusion of cation to the necks.It was proposed to separate the effects of mechanical activation of nanopowders from the influence of doping on the diffusion mechanism at the initial stage of sintering of doped zirconia nanopowders. The simultaneous influence of both impacts (mechanical energy and chemical composition) can complicate and confuse reasoning.

Investigation into the effect of mechanical activation on the leaching of chalcopyrite in a glycine medium

The effect of mechanical activation on the leaching and electrochemistry of chalcopyrite was investigated in a glycine medium. Leaching experiments were conducted to evaluate the effect of particle size (with re-ground sample in ball mill) and mechanical activation (with re-ground sample in planetary mill for 4 h) on chalcopyrite dissolution in a stirred tank reactor. Results show that a maximum copper extraction (95.1%) was obtained for mechanically activated chalcopyrite after 12 h leaching in a 0.4 M glycine solution at 60 °C, 2% (w/v) pulp density and an initial solution pH of 10.5. Under these same leaching conditions, a decrease in particle size for conventionally ground chalcopyrite from 106 to 125 μm to <20 μm, led to a substantial increase in the level of copper extraction - from 0.6% to 33.8%. Analysis of solid residue by XRD showed that iron could be precipitated as maghemite and a part of dissolved copper could be removed from the solution as copper glycinate crystals and covellite. Result of the electrochemical analysis showed that the anodic current of the chalcopyrite‑carbon paste electrode was significantly increased for the mechanically activated sample. Nevertheless, anodic current densities were observed to reduce during subsequent voltammetry cycles as a consequence of passivating the surface of chalcopyrite electrode by reaction products and decreasing electroactive cites the electrode surface. A new 2-stage leaching flowsheet was proposed to extract copper from chalcopyrite concentrates in glycine media. Glycine leaching with mechanical activated pretreatment could be a promising method for treating low-grade chalcopyrite concentrates.

Formation of Perovskite and Pyrochlore Phases during Mechanochemical Synthesis of Lead Ferroniobate

We have studied the effect of mechanical activation in lead ferroniobate synthesis on the formation of perovskite and pyrochlore phases during both mechanochemical synthesis and subsequent firing. It has been shown that, during mechanical activation, the first to form is the perovskite structure. During subsequent sintering of the material, the pyrochlore structure begins to form as well. As the firing temperature is raised to 650–750°C, the perovskite structure is again formed. We provide explanation for this process.

Effect of Mechanical Activation on Leachability of Fayalite in Sulfuric Acid Solution

Background: Being by-products of non-ferrous metallurgy, slags contain fayalite (Fe2SiO4) as the major component. Since hydrometallurgical methods are considered as the most promising for processing such material to obtain valuable metals, increasing the leachability of fayalite in sulfuric acid as a widely used leaching agent is an important task. Objective : The present work was devoted to increasing the reactivity of fayalite by using mechanical activation. Methods: Fayalite, synthesized with the use of powders of metallic Fe, Fe2O3, and SiO2, was subjected to mechanical activation in the planetary ball mill at 400 rpm with a ball/powder ratio of 5 for 45 minutes. Then, activated and non-activated fayalite samples were subjected to sulfuric acid leaching. Before leaching, solid samples were characterized by XRD and Dynamic Light Scattering (DLS). Quantitative analysis of Fe and Si in the leachate was determined by Inductively Coupled Plasma-Atomic Emission Spectroscopy. Results: Mechanical activation led to partial amorphization of the initial fayalite sample. It was found that the leaching rate constants of the treated samples in sulfuric acid solution (50-80 g×L-1) at 298, 338, and 368 K increased and the activation energy of the leaching process decreased, i.e. mechanical activation enhances the reactivity of fayalite in H2SO4 solution. Conclusion: Mechanical activation can be applied to improve fayalite leachability in sulfuric acid solution. The results obtained can be used in the development of methods for leaching slag of non-ferrous metallurgy, in particular, copper smelter slags, the major component of which is fayalite.

Structure and properties of the CoCuTiZrHf coating obtained by the HVOF method

The article is devoted to the comprehensive studies of high-entropy CoCuTiZrHf coating obtained by high-velocity oxygen-fuel (HVOF) in a protective atmosphere. The authors examined the metallophysical properties of the coating (using electron microscopy and X-ray diffraction analysis) in order to obtain new information about its structure, mechanical properties and phase composition. Functional properties were also determined. The authors studied the effect of mechanical activation of highly entropic material powder on the structural phase state and coating quality. The optimal technological parameters of HVOF in a protective atmosphere were determined for the formation of a highly entropic CoCuTiZrHf coating, which provides the highest adhesion and a low porosity. The authors have developed statistical process models with parameter optimisation. On the basis of complex metallophysical studies, the structure formation in highly entropic coatings was researched after HVOF in a protective atmosphere and subsequent heat treatment. Calorimetric tests of the CoCuTiZrHf alloy were performed to identify the exo-effect corresponding to the manifestation of phase transformation. The authors determined what the mechanical properties of coated steel are.

Application of X-Ray Methods for Determining the Dimensions of Nanoparticles in the Nanosized Anatase–Poly(N-vinylcaprolactam) System

Nanocomposites prepared by mechanical mixing with grinding and mechanical activation of a mixture of Hombifine N with nanosized anatase (NA) and poly(N-vinylcaprolactam) (PVCL) polymer (PVCL25 and PVCL40 polymers were obtained by drying a PVC aqueous solution at 25 and 40°C, respectively) in different weight ratios have been studied by wide-angle X-ray scattering (WAXS) and (for the first time) small-angle X-ray scattering (SAXS). Amorphization of anatase (decrease in the average size of the coherent-scattering region), selection of X-ray amorphous hydrated titanium dioxide from the amorphous shell of anatase nanoparticles, destruction of PVCL, and disordering of its heterocycles in NA/PVCL (NA : PVCL = 1 : 1) nanocomposites upon mechanical activation have been revealed. The interaction (with water molecule exchange) between anatase, anatase, and PVCL nanoparticles during formation of NA/PVCL25 (NA : PVCL = 1 : 2) upon mechanical mixing with grinding is found to lead to segregation of anatase nanoparticles into two groups: particles with reduced and enhanced (formation of texture) degree of crystallinity (average sizes of coherent-scattering regions) in comparison with the initial anatase. SAXS made it possible to reveal structural inhomogeneities of different sizes in PVCL25 and PVCL40, which change differently upon mechanical activation, retaining the tendency to smaller sizes in PVCL25 (a coil) in comparison with PVCL40 (a globule). It is shown that the effects of mechanical activation and mechanical mixing with grinding on the components of NA–PVCL system differ, and that anatase nanoparticles play a decisive role in NA/PVCL nanocomposites, facilitating averaging of the inhomogeneity sizes upon mechanical activation. The results of studying the photocatalytic activity in the reaction of methyl orange decomposition (UV irradiation) in the presence of NA–PVCL samples indicate that it depends on the average sizes of coherent-scattering regions and is independent of the inhomogeneity sizes.

Formation of phase composition of aluminum matrix composites during mechanical activation and self-propagating high-temperature synthesis

The authors investigated the effect of mechanical activation and self-propagating high-temperature synthesis (SHS) on the phase composition of composite materials of Al-TiO2-B system. It has been shown that with increasing the duration of mechanical activation of initial powders the amount of crystalline boron-containing phases in the mixture increases. X-ray diffraction analysis of powder mixtures after SHS allows making conclusion about necessity of activation for at least 45 min to obtain a target compounds. Experimental results allow reasonably choosing the modes of mechanical activation for production of aluminium matrix composites with specified composition and controllable properties.

Effect of Mechanical Activation on the Reactivity of Composites for Flameless Heaters

The work is devoted to the activation of metal powder mixtures suitable for use in flameless food heaters. Four activated powders have been manufactured starting from the reference material using a standard technique. Activated powders exhibited a significant increment of the reactivity for the reference mixture. Experimental tests were carried out to characterize the resulting composites in terms of the combustion rate. The oxidation reaction at a low heating rate was monitored using a SEIKO EXTAR II thermal analysis machine and its tests were carried out at open air in temperature range starting from room temperature up to 1150 °C at the heating rate of 10 °C/min. Powders activated by mechanical activations and the initial mixture of materials were characterized in terms of apparent density, absorbed surfactant with the mass of sizing, i.e. granulometry, oxidation properties at a low heating rate. With increase the grinding time, the color of the powder switches to dark tones. Powder granulometry was performed on a MALVERN laser granulometer MASTERSIZER 2000 using dry block SCIROCCO. Three measurements for each sample were performed and the results were averaged. The tests were recorded and processed by digital technology to make the combustion rate of the powders, also the experimental setup used for investigations was presented. The sample AlS-AlF_MnO2_SiO-150 is characterized by the lowest metal content, and by the most regular combustion propagation. The powder AlS-AlF_MnO2_SiO-50 features the highest metal content, but the less regular combustion propagation. The use of mechanical activation allows increasing the number of nanoscale materials, which contributes to the synthesis of highly effective flameless food heaters.

Effect of mechanical activation on enhancement of carbothermal reduction of nickel slag

The effects of mechanical activation on particle size distribution, crystalline phase, morphology, and mechanical energy storage of nickel slag were studied. Then, the direct reduction experiments of mechanically activated nickel slag mixed with reducing agent graphite powder were performed under conditions of 873–1273 K and reduction for 30–70 min. The results show that after 12 h of activation, 90% of the nickel slag has a particle diameter less than 1.05 μm, and the total energy storage is 1790.4 kJ mol−1. With the extension of the mechanical activation duration, the intensity of the diffraction peaks of the main crystalline phases Fe2SiO4 and Mg2SiO4 in the nickel slag decreases. Mechanical activation is also an effective means to enhance the reduction of nickel slag. With the extension of the activation time, the reduction effect of the nickel slag and metallization degree increase. After 12 h of mechanical activation, the nickel slag was reduced at 1273 K for 70 min, and the metallization degree of the reduced product could reach 83.12%.

Investigation of the Effect of Mechanical Activation of Powder Components on the Properties of Polyimide Composites

This study presents the results of an analysis of the influence of joint mechanical activation of a polyimide matrix and tungsten (IV) oxide (WO2) on the mechanical properties of their composites. Mechanical activation of the powder components of the matrix and the filler is performed in a vortex jet mill. The ultimate tensile strength, tensile modulus and relative elongation at break of the composites are all investigated. When using mechanical activation, an increase in tensile strength of 9% is observed with a content of 30 wt.% WO2 filler and of 12% with a content of 70 wt.% WO2 filler compared to composites in which the joint mechanical activation of components is not used. Using scanning electron microscopy, it is shown that the use of mechanical activation by dispersing in a jet-vortex mill made it possible to achieve a uniform distribution of highly dispersed filler based on tungsten dioxide in a polyimide matrix.

Mössbauer Study of the Mechanical Activation Effect on the Magnetic Properties of PbFe0.5Ta0.5O3

The Mossbauer spectra of PbFe0.5Ta0.5O3 samples prepared by mechanical activation of a mixture of PbO, Fe2O3, and Ta2O5 with subsequent annealing at different temperatures Ta have been investigated. The Mossbauer study showed that Fe3+ ions in these samples can be either in the octahedral coordination or in the state with a coordination number equal to 5, which indicates the presence of oxygen vacancies in the samples. The magnetic-phase transition temperatures TM are found for all samples. The dependence of TM on Ta is peaking in the vicinity of Ta ≈ 700°C. The factors affecting the TM values of the mechanically activated PbFe0.5Ta0.5O3 samples are discussed.

The Mechanism of Forming Coagulated Particles in Selective Laser Melting of Cobalt-Chromium-Molybdenum Powder

Selective laser melting (SLM) is thought to be a prospective manufacturing technology of complex metal components. Formation of coagulated particles when melting is reported to be an important factor for target mechanical properties of the end product. This paper discusses the effect of SLM parameters, including laser output power, laser movement velocity, preheating temperature of the powder, laser beam diameter on the mechanism of forming coagulated particles in melting cobalt-chromium-molybdenum powdered material. The study shows that a rise of power to 60 W at a scanning velocity 6 mm/s causes coagulated particles to expand to 350 μm; that is far bigger than a size of powder in as delivered state (90 μm). The work investigates the effect of mechanical activation of cobalt-chromium-molybdenum powder on dimensions of coagulated particles. The research data can be applied to the improvement of up-to-date optimization approaches to manufacturing process parameters in SLM technology.

Changes in the Crystallinity Degree of Starch Having Different Types of Crystal Structure after Mechanical Pretreatment.

This paper examines the effect of mechanical activation on the amorphization of starch having different types of crystalline structure (A-type corn starch; B-type potato starch; and C-type tapioca starch). Structural properties of the starches were studied by X-ray diffraction analysis. Mechanical activation in a planetary ball mill reduces the degree of crystallinity in proportion to pretreatment duration. C-type tapioca starch was found to have the highest degree of crystallinity. Energy consumed to achieve complete amorphization of the starches having different types of crystalline structure was measured. The kinetic parameters of the process (the effective rate constants) were determined. The rate constant and the strongest decline in the crystallinity degree after mechanical activation change in the following series: C-type starch, A-type starch, and B-type starch.

Energy-saving technology and equipment for the production of composite binder using local raw materials

The article presents the technology and energy-saving equipment for producing a composite binder with a reduction in the energy cost reduction of the process up to 50%, due to the synergistic effect of mechanical activation of the raw material mixture with the replacement of the clinker component with a mineral hydroactive additive. The energy efficiency of the line is achieved by the joint work of the press-roll unit, and the rotor-vortex mill of superfine, which allow the grinding of raw materials to a dispersion with a specific surface area of 4000…4500 cm2/g. The resulting equation for calculating the effort of grinding materials, which is implemented between the conical rollers in the press-roll unit (PRU). It has been established that the power spent on grinding the material and overcoming the friction in the axles of the pivots rolls and proposed the equation for calculating its variable.

Mechanical activation effect on the biostability of modified cement compositions

The creation of materials with high strength, durability, and biostability is a relevant development area for modern building materials science. This paper studies a number of modified cement compositions obtained by the mechanical activation of the vortex layer device binder. A superplasticizer and carbon nanotubes of various structure and functionality were used as modifiers. The cement composition was determined in a laboratory kinetic unit designed by the authors. It is found that the biostability coefficient values of the cement composition samples obtained by the mechanical activation of the binder and with the introduction of the superplasticizer are 13% higher than the same control composition value. It is indicated that the additional introduction of single and multilayer carbon nanotubes increases the cement composition biostability by 50%. It is found that the highest biostability values are observed in cement compositions obtained by the mechanical activation of the binder with the combined introduction of the superplasticizer and multilayer (MWCNT) «Graphistrength» carboxyl-functionalized (–COOH) nanotubes. The x-ray phase analysis method found that during the exposure of the cement composition samples under study in a model citric acid medium, the portlandite is carbonized with calcite formed which causes a decrease in the compression and bending strength of the cement composition samples.