The invariant laws of the amorphization processes by mechanical alloying

Delogu, Fiorenzo; Schiffini, L.; Cocco, G.

doi:10.1080/01418610108216644

Cited by 26 publications

(74 citation statements)

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“…The occurrence of collisions inside the reactor was monitored using piezoelectric transducers attached to the external reactor surface, according to the experimental methodology described in detail elsewhere [22,[37][38][39]. Here, it is simply worth remembering that the piezoelectric sensor generates an electric signal every time a ball collides with either the lateral wall of the cylindrical reactor, or the bases.…”

Section: Discussionmentioning

confidence: 99%

Mechanically activated metathesis reaction in NaNH2–MgH2 powder mixtures

et al. 2017

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The present work addresses the kinetics of chemical transformations activated by the mechanical processing of powder by ball milling. In particular, attention focuses on the reaction between NaNH 2 and MgH 2 , specific case studies suitably chosen to throw light on the kinetic features emerging in connection with the exchange of anionic ligands induced by mechanical activation. Experimental findings indicate that the mechanical treatment of NaNH 2 -MgH 2 powder mixtures induces a simple metathetic reaction with formation of NaH and Mg(NH 2 ) 2 phases. Chemical conversion data obtained by X-ray diffraction analysis have been interpreted using a kinetic model incorporating the statistical character of the mechanical processing by ball milling. The apparent rate constant measuring the reaction rate is related to the volume of powder effectively processed during individual collisions, and tentatively connected with the transfer of mechanical energy across the network formed by the points of contact between the powder particles trapped during collisions.

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Section: Discussionmentioning

confidence: 99%

Mechanically activated metathesis reaction in NaNH2–MgH2 powder mixtures

et al. 2017

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“…Total energy dissipation is calculated by estimating the vial heat capacity to be 419 J/K. This is then normalized per unit mass of milling media, to allow comparison between this study (approximately 50 g of balls) to the results of velocity measurements made on a single 12 g ball [42]. Good agreement is found between the two techniques, which suggests that collisions under many ball conditions are mainly inelastic.…”

Section: ) Conclusionmentioning

confidence: 99%

“…The term E represents the impact energy of a collision, and in general is dependent on the milling vial geometry, dynamics of the milling balls, thermomechanical properties of the materials involved and hence is not known a priori [41]. However for a given experimental configuration the impact energy can be empirically measured [42]. We performed such a measurement using the calorimetric method [40] under different milling frequencies, the details of which are given in Appendix A.…”

Section: Mechanical Millingmentioning

confidence: 99%

“…Where mb is the ball mass, and vr is the media velocity and can be obtained experimentally using the time lag method [42] or through the amount of heat released using the calorimetric method [40] under the assumption that most plastic work is dissipated as heat [73]. N is the number of hits per second, t is the milling time, mp is the mass of the powder, and CR is the charge ratio, i.e., ratio of total powder mass to total ball mass.…”

Section: Appendix A: Terminology and Impact Energy Evaluationmentioning

confidence: 99%

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Anomalous grain refinement trends during mechanical milling of Bi2Te3

Humphry-Baker

Schuh

2014

Acta Materialia

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Abstract:The structural evolution of nanocrystalline Bismuth Telluride (Bi2Te3) during mechanical milling is investigated under different milling energies and temperatures.After prolonged milling, the compound evolves toward a steady-state nanostructure that is found to be unusually strongly dependent on the processing conditions. In contrast to most literature on mechanical milling, in Bi2Te3 we find that the smallest steady-state grain sizes are attained under the lowest energy milling conditions. An analysis based on the balance between refinement and recovery in the steady state shows that two regimes of behavior are expected based on the thermo-physical properties of the milled powder. Bi2Te3 lies in a relatively unusual regime where greater impact energy promotes adiabatic heating and recovery more than it does defect accumulation; hence more intense milling leads to larger steady-state grain sizes. Implications for other materials are discussed with reference to a "milling intensity map" that delineates the set of material properties for which this behavior will be observed.

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“…10 Such impact velocity roughly reproduces the average impact velocity in ball mills. [6][7][8]34 In some cases a tangential force F t was also applied along the x Cartesian direction to simulate a shear stress 10 and obtain a couple of sliding. Correspondingly, opposite center-ofmass velocities of about 5 m s −1 were given to the Ni and Zr systems.…”

Section: B Interactions and Simulation Methodsmentioning

confidence: 99%

Numerical simulations of atomic-scale disordering processes at impact between two rough crystalline surfaces

Delogu

Cocco

2006

Phys. Rev. B

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Numerical calculations have been used to throw light on the mechanical deformation and the atomic mixing processes taking place when two different metallic systems collide at low temperature. To this end, two semicrystals terminating with a free surface were pushed each against the other at a given relative velocity. Surfaces of different roughness were considered under different impact conditions. Simple mechanical loads on plane surfaces did not induce any significant mixing of atomic species at the interface, observed instead in collisions involving either rough surfaces or plane surfaces undergoing a relative sliding. In the case of rough surfaces, the local contact between the semicrystals is initially sustained by surface asperities. The atoms there located experience thus sudden mechanical loads and an unusual localization of kinetic energy, which enhance their mobility and favor the mixing process. A diffuse interfacial region with a disordered structure correspondingly appears. Its structural features were not significantly modified by the thermal relaxation processes occurring after the compressive load removal.

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The invariant laws of the amorphization processes by mechanical alloying

Cited by 26 publications

References 0 publications

Mechanically activated metathesis reaction in NaNH2–MgH2 powder mixtures

Mechanically activated metathesis reaction in NaNH2–MgH2 powder mixtures

Anomalous grain refinement trends during mechanical milling of Bi2Te3

Numerical simulations of atomic-scale disordering processes at impact between two rough crystalline surfaces

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