Thermodynamics of solid and liquid aluminium

Based on thermodynamic calculations, it is shown that in the temperature range of 298–1273 K, heating and cooling of aluminum are thermodynamically equilibrium processes. When aluminum is heated, the molar volume energy of Gibbs decreases and the molar boundary energy of nanocrystals increases. When aluminum is cooled, the molar volume energy of Gibbs increases and the molar boundary energy of nanocrystals decreases. Liquid aluminum is a nanostructured system. Dendritic microcrystals are formed from nanocrystals. They play a large role in the processes of changing the structure of aluminum during its heating and cooling.

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Effects of Electric Pulse Modification with Different Technique Parameters on the Liquid Structure of Pure Aluminum

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.79-82.203 ◽

2009 ◽

Vol 79-82 ◽

pp. 203-206

Author(s):

Jin Gang Qi ◽

Jian Zhong Wang ◽

Bing Wang ◽

Li Jia He ◽

Hui Ling Du

Keyword(s):

Structure Factor ◽

Electric Pulse ◽

Pure Aluminum ◽

Liquid Aluminum ◽

Solidification Structure ◽

Strengthening Effect ◽

Atom Number ◽

Liquid Aluminium ◽

Principal Peak ◽

Structure Factor Curve

The modification of liquid metal by electric pulse (EP, EPM) is a novel method for grain refinement. In this study, based on the reported structural heredity of EP-modified liquid aluminium, the structure tests of EP-modified liquid aluminium with different technique parameters were conducted by using high temperature X-ray diffractometer. The results show that the quantitative structure changes of EP-modified liquid aluminium have a close relationship with the modifying time and modifying temperature. The decrease of modifying time could result in an obvious weaker principal peak in structure factor curve compared with the optimal EP technique parameters, but a slight increase of coordination number (Ns), correlation radius (rc) and average atom number per cluster (Nat) is still observed under this condition. These facts indicate that the EP-modified liquid aluminum could gain an increasing order degree, and thus have an advantage during the formation of a stable nucleus, eventually leading to a grain-refining solidification structure. On the other hand, the structure factor curve of EP-modified liquid aluminum at the high modifying temperature of 850°C tends to be overlapped with that of the unmodified during the principal peak range. In this case, the competition result between the EP strengthening effect and the destruction of superheating would determine the final structure of EP-modified liquid aluminum.

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Microstructural Characterization of the Reaction Product Region Formed Due to the High Temperature Interaction of ZnO[0001] Single Crystal with Liquid Aluminum

Archives of Metallurgy and Materials ◽

10.2478/v10172-012-0197-y ◽

2013 ◽

Vol 58 (2) ◽

pp. 351-355 ◽

Cited By ~ 2

Author(s):

J. Wojewoda-Budka ◽

N. Sobczak ◽

K. Stan ◽

R. Nowak

Keyword(s):

Single Crystal ◽

Sessile Drop ◽

Liquid Aluminum ◽

Microstructural Characterization ◽

Single Crystal Substrate ◽

Heating And Cooling ◽

Contact Heating ◽

Δ Phase ◽

Diffraction Patterns ◽

Temperature Interaction

The study was focused on the microstructure characterization at the micro- and nano scale of the reaction product region (RPR) formed due to the interaction between the liquid aluminum and ZnOSC[0001] single crystalline substrate at 1000ºC. The research was carried out on the Al/ZnO couple produced by the sessile drop method under vacuum within two different procedures: 1) classical contact heating and cooling; 2) pushing drop procedure allowing opening the Al/ZnO interface at the test temperature and, therefore, prevent influence of cooling with Al drop on interface structure. The microstructure observations of the sample after using classical contact heating procedure revealed the formation of the RPR of ∽50 μm in thickness extending into the ZnOSC single crystal substrate. It was composed of the ceramic α-Al2O3 and metallic Al(Zn) mutually interpenetrating lattices, typical for the C4 type structure. Additionally, at the ZnO/RPR interface, the presence of a thin (∽250 nm) layer of the metastable δ-Al2O3was detected. The obtained results were compared with experimental data found for the sample after pushing drop procedure resulting in the formation of two layers of ZnAl2O4 spinel and alumina, exhibiting strong epitaxial growth. The selected area diffraction patterns clearly evidenced that the crystal structure of formed Al2O3 corresponds to the tetragonal δ-phase.

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VISCOSITY OF LIQUID ALUMINIUM MODIFIED BY ELECTRIC PULSE

International Journal of Modern Physics B ◽

10.1142/s0217979209060166 ◽

2009 ◽

Vol 23 (06n07) ◽

pp. 869-874 ◽

Cited By ~ 4

Author(s):

JINGANG QI ◽

JIANZHONG WANG ◽

BING WANG ◽

DAQIANG CANG

Keyword(s):

Electric Pulse ◽

Torsional Oscillation ◽

Liquid Aluminum ◽

Liquid Structure ◽

Scanning Calorimetry ◽

Liquid Aluminium ◽

Viscosity Change ◽

Electric Pulse Modification ◽

Order Degree ◽

Increasing Temperature

The modification of liquid metal by electric pulse (EP) is a novel method for grain refinement. In this work, based on the reported structural heredity of EP-modified liquid aluminum, we investigated its viscosity change by using torsional oscillation viscometer. The results validate the viscosity of EP-modified liquid aluminum also decreases with increasing temperature and meets approximately exponential correlation on the whole. Moreover, it is especially important that the EP-modified liquid aluminum has the higher viscosity and possesses the bigger viscous-flow cluster in a certain temperature range, which should be associated with the increase of the order degree of its liquid structure. Differential scanning calorimetry (DSC) measurement also confirms that viewpoint. These coupling results experimentally testify the proposed mechanism of electric pulse modification (EPM) modeled merely by postulation.

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Thermal Expansion and Excess Properties of Åkermanite-Gehlenite Synthetic Solid Solution Series

Materials Science Forum ◽

10.4028/www.scientific.net/msf.443-444.401 ◽

2004 ◽

Vol 443-444 ◽

pp. 401-406 ◽

Cited By ~ 1

Author(s):

Marco Proverbio ◽

Monica Dapiaggi ◽

Gilberto Artioli

Keyword(s):

Solid Solution ◽

Thermal Expansion ◽

High Temperature ◽

Molar Volume ◽

Excess Molar Volume ◽

Room Temperature ◽

Structural Features ◽

Excess Properties ◽

Heating And Cooling ◽

First Time

Thermal expansion of some members of the synthetic solid solution åkermanite-gehlenite was measured (in the range 25-1200°C) for the very first time, with the aim of clarifying the behaviour of this solid solution both with respect to composition and temperature. The results confirmed the non-ideal behaviour at room temperature (negative excess molar volume), and showed a different non-ideal response at high temperature. In fact, excess molar volume is different during the heating and cooling stages: for Xak<0.5 it becomes, from almost ideal, strongly positive at high temperature, while for Xak>0.5 it is always negative. It can then be inferred that (i) lattice dimensions are very sensitive to cation diffusion activated by temperature, (ii) intra-crystalline partition mechanisms, and their effects on the structural features, vary as a function of composition in the solid solution studied.

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Dissociated Σ=27 boundaries in silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105187 ◽

1988 ◽

Vol 46 ◽

pp. 624-625

Author(s):

A. Garg ◽

W.A.T. Clark ◽

J.P. Hirth

Keyword(s):

Electron Diffraction ◽

Local Minimum ◽

Boundary Energy ◽

Coincidence Site Lattice ◽

Boundary Plane ◽

Low Energy ◽

Theoretical Understanding ◽

Site Lattice ◽

Kikuchi Pattern ◽

Analysis Techniques

In the last twenty years, a significant amount of work has been done in the theoretical understanding of grain boundaries. The various proposed grain boundary models suggest the existence of coincidence site lattice (CSL) boundaries at specific misorientations where a periodic structure representing a local minimum of energy exists between the two crystals. In general, the boundary energy depends not only upon the density of CSL sites but also upon the boundary plane, so that different facets of the same boundary have different energy. Here we describe TEM observations of the dissociation of a Σ=27 boundary in silicon in order to reduce its surface energy and attain a low energy configuration.The boundary was identified as near CSL Σ=27 {255} having a misorientation of (38.7±0.2)°/[011] by standard Kikuchi pattern, electron diffraction and trace analysis techniques. Although the boundary appeared planar, in the TEM it was found to be dissociated in some regions into a Σ=3 {111} and a Σ=9 {122} boundary, as shown in Fig. 1.

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