Melting behavior of nanocrystalline aluminum powders

Eckert, J.; Holzer, J. C.; Ahn, Channing C.; Fu, Zheng; Johnson, W. L.

doi:10.1016/0965-9773(93)90183-c

Cited by 162 publications

(111 citation statements)

References 15 publications

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“…In the reflected pressure wave, the pressure profile for 1 Ͻ t Ͻ 1. 25 deviates from the lowest curve in some internal layer only. For t = 1.25 the velocity is zero everywhere and getting negative for t Ͼ 1.25 ͑not shown͒.…”

Section: ͑16͒mentioning

confidence: 99%

“…Data on the effect of the particle size and internal pressure on the melting temperature are compensatory and will not be taken into account in our model. For Al nanoparticles, the melting temperature reduces with the particle size, 25 however, it simultaneously increases with internal pressure by approximately 55 K / GPa. 24 Relationships f f ͑M͒ for several values of the ultimate strength u and several temperatures T 0 are shown in Fig.…”

Section: Parametric Study Of the Oxide Fracturementioning

confidence: 99%

See 1 more Smart Citation

Mechanochemical mechanism for fast reaction of metastable intermolecular composites based on dispersion of liquid metal

Levitas

Asay

Son

et al. 2007

Journal of Applied Physics

144

223

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An unexpected mechanism for fast reaction of Al nanoparticles covered by a thin oxide shell during fast heating is proposed and justified theoretically and experimentally. For nanoparticles, the melting of Al occurs before the oxide fracture. The volume change due to melting induces pressures of 1–2 GPa and causes dynamic spallation of the shell. The unbalanced pressure between the Al core and the exposed surface creates an unloading wave with high tensile pressures resulting in dispersion of atomic scale liquid Al clusters. These clusters fly at high velocity and their reaction is not limited by diffusion (this is the opposite of traditional mechanisms for micron particles and for nanoparticles at slow heating). Physical parameters controlling the melt dispersion mechanism are found by our analysis. In addition to an explanation of the extremely short reaction time, the following correspondence between our theory and experiments are obtained: (a) For the particle radius below some critical value, the flame propagation rate and the ignition time delay are independent of the radius; (b) damage of the oxide shell suppresses the melt dispersion mechanism and promotes the traditional diffusive oxidation mechanism; (c) nanoflakes react more like micron size (rather than nanosize) spherical particles. The reasons why the melt dispersion mechanism cannot operate for the micron particles or slow heating of nanoparticles are determined. Methods to promote the melt dispersion mechanism, to expand it to micron particles, and to improve efficiency of energetic metastable intermolecular composites are formulated. In particular, the following could promote the melt dispersion mechanism in micron particles: (a) Increasing the temperature at which the initial oxide shell is formed; (b) creating initial porosity in the Al; (c) mixing of the Al with a material with a low (even negative) thermal expansion coefficient or with a phase transformation accompanied by a volume reduction; (d) alloying the Al to decrease the cavitation pressure; (e) mixing nano- and micron particles; and (f) introducing gasifying or explosive inclusions in any fuel and oxidizer. A similar mechanism is expected for nitridation and fluorination of Al and may also be tailored for Ti and Mg fuel.

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Section: ͑16͒mentioning

confidence: 99%

Section: Parametric Study Of the Oxide Fracturementioning

confidence: 99%

Mechanochemical mechanism for fast reaction of metastable intermolecular composites based on dispersion of liquid metal

Levitas

Asay

Son

et al. 2007

Journal of Applied Physics

144

223

View full text Add to dashboard Cite

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“…With respect to previous investigations, 18) which revealed that for MgCuY powder mixtures the amorphization during mechanical alloying proceeds in a similar way as for binary systems 19) or other multicomponent glass-forming alloys 17) via interdiffusion in a mechanically formed arrangement of thin elemental layers, the influence of an initial addition of oxide particles on the amorphization process was studied. The XRD patterns in Fig.…”

Section: Microstructure Formationmentioning

confidence: 99%

“…Most likely, thin oxide layers covering the grain boundaries and the particle surfaces of the highly reactive powders are present, similar as in the case of mechanically attrited nanocrystalline aluminium. 19) This prevents complete alloying even after extended milling. Hence, the high reactivity of the elements prevents the formation of a homogeneous amorphous alloy and even the dispersoid-free sample has rather to be considered as a composite of amorphous matrix and nanoscale elemental particles and oxides.…”

Section: Microstructure Formationmentioning

confidence: 99%

High Strength Magnesium-based Glass Matrix Composites

2002

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Magnesium-based glass matrix composites containing oxide particles were produced by mechanical alloying of Mg 55 Cu 30 Y 15 elemental powder mixtures with the addition of MgO, CeO 2 , Cr 2 O 3 or Y 2 O 3 oxide particles. The formation of the glassy phase was characterized by X-ray-diffraction and transmission electron microscopy methods and was found to proceed almost unaffected by the presence of the oxides. Differential-scanning-calorimetry-analysis revealed, that the amorphous matrix features a wide supercooled liquid region with an extension of about 40-50 K. Differences in the thermal stability of the composites depending on the oxide addition are discussed. Viscosity measurements proved the existence of a characteristic minimum of viscosity in this temperature range which was used to consolidate the powders into bulk samples by uniaxial hot pressing. The deformation behaviour under compression at room temperature as well as at elevated temperature of 423 K yielded excellent properties compared to conventionally produced magnesium-based alloys.

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“…It has been reported that H 2 lowers the boiling point of the material and provides much better heat transfer properties to the plasma [41]. Hydrogen addition increases both the thermal conductivity and the enthalpy of the gas.…”

Section: Nap Prepared At Different H 2 Dilutionsmentioning

confidence: 99%

Preparation of Nano Aluminium Powder (NAP) using a Thermal Plasma: Process Development and Characterization

Pant¹,

Seth²,

Raut³

et al. 2016

Cent. Eur. J. Energ. Mater.

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A bottom up approach for the preparation of Nano Aluminium Powder (NAP) using a Transferred Arc Thermal Plasma Reactor (TAPR) is described. The aluminium block is subjected to evaporation by the application of a thermal plasma. The aluminium vapour produced is rapidly quenched to room temperature resulting in crystallization of the aluminium vapour in nano-particulate form. Various process parameters, such as the plasma torch power, reactor pressure and plasma gas composition were optimized. This paper also describes the characterization of NAP by analytical methods, for the estimation of the Active Aluminium Content (AAC), Total Aluminium Content (TAC), XRD, bulk density, BET surface area, HR-TEM etc. The results are compared with those for samples prepared in other thermal plasma reactors, such as the DC Arc Plasma Reactor (DCAPR) and the RF Induction Thermal Plasma Reactor (RFITPR), and for commercially available NAP samples (ALEX, prepared by the EEW technique).

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Melting behavior of nanocrystalline aluminum powders

Cited by 162 publications

References 15 publications

Mechanochemical mechanism for fast reaction of metastable intermolecular composites based on dispersion of liquid metal

Mechanochemical mechanism for fast reaction of metastable intermolecular composites based on dispersion of liquid metal

High Strength Magnesium-based Glass Matrix Composites

Preparation of Nano Aluminium Powder (NAP) using a Thermal Plasma: Process Development and Characterization

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