High Temperature Internal Friction Behavior of Unidirectionally Solidified Al2O3/YAG Eutectic

2010 ◽  
Vol 638-642 ◽  
pp. 2482-2486
Author(s):  
Shunkichi Ueno ◽  
Satoshi Takata ◽  
Yasuhiro Tanabe ◽  
Takashi Akatsu ◽  
Eiichi Yasuda ◽  
...  
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
Internal Friction ◽  
Single Crystal ◽  
Apparent Activation Energy ◽  
Elevated Temperatures ◽  
Torsional Loading ◽  
Friction Behavior

In this paper, the internal friction behaviors of unidirectionally solidified Al2O3/YAG eutectic that are examined by the authors in passed several years are reviewed. The internal friction of this eutectic increased with increasing temperatures above 1200oC. The apparent activation energy of the eutectic sample in the range from 1100 to 1400oC was same to that of Al2O3 single crystal. Above 1200oC, the internal friction of this material drastically increased with increasing temperatures. The magnitude of the internal friction strongly depended on the elevated temperatures and the cycle numbers of the torsional loading. For the 1400oC test, the internal friction gradually increased with the loading cycles and then saturated by 103 times of the loading cycles.

The activation energy U(T,B) in high temperature superconductor

2020 ◽  
Vol 92 (2) ◽  
pp. 20601
Author(s):  
Abdelaziz Labrag ◽  
Mustapha Bghour ◽  
Ahmed Abou El Hassan ◽  
Habiba El Hamidi ◽  
Ahmed Taoufik ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Activation Energy ◽  
Phase Diagram ◽  
High Temperature ◽  
Apparent Activation Energy ◽  
High Temperature Superconductor ◽  
Flux Flow ◽  
Resistivity Measurements ◽  
Vortex Phase ◽  
The Magnetic Field

It is reported in this paper on the thermally assisted flux flow in epitaxial YBa2Cu3O7-δ deposited by Laser ablation method on the SrTiO3 substrate. The resistivity measurements ρ (T, B) of the sample under various values of the magnetic field up to 14T in directions B∥ab-plane and B∥c-axis with a dc weak transport current density were investigated in order to determine the activation energy and then understand the vortex dynamic phenomena and therefore deduce the vortex phase diagram of this material. The apparent activation energy U0 (B) calculated using an Arrhenius relation. The measured results of the resistivity were then adjusted to the modified thermally assisted flux flow model in order to account for the temperature-field dependence of the activation energy U (T, B). The obtained values from the thermally assisted activation energy, exhibit a behavior similar to the one showed with the Arrhenius model, albeit larger than the apparent activation energy with ∼1.5 order on magnitude for both cases of the magnetic field directions. The vortex glass model was also used to obtain the vortex-glass transition temperature from the linear fitting of [d ln ρ/dT ] −1 plots. In the course of this work thanks to the resistivity measurements the upper critical magnetic field Hc2 (T), the irreversibility line Hirr (T) and the crossover field HCrossOver (T) were located. These three parameters allowed us to establish a phase diagram of the studied material where limits of each vortex phase are sketched in order to optimize its applicability as a practical high temperature superconductor used for diverse purposes.

scholarly journals A Constitutive Model for the Mechanical Behavior of Single Crystal Silicon at Elevated Temperature

2001 ◽  
Vol 687 ◽  
Author(s):  
H.-S. Moon ◽  
L. Anand ◽  
S. M. Spearing
Keyword(s):  
High Temperature ◽  
Constitutive Model ◽  
Single Crystal ◽  
Mechanical Behavior ◽  
Elevated Temperatures ◽  
Single Crystal Silicon ◽  
Operational Environment ◽  
Localized Deformation ◽  
Creep Tests ◽  
Crystal Silicon

AbstractSilicon in single crystal form has been the material of choice for the first demonstration of the MIT microengine project. However, because it has a relatively low melting temperature, silicon is not an ideal material for the intended operational environment of high temperature and stress. In addition, preliminary work indicates that single crystal silicon has a tendency to undergo localized deformation by slip band formation. Thus it is critical to obtain a better understanding of the mechanical behavior of this material at elevated temperatures in order to properly exploit its capabilities as a structural material. Creep tests in simple compression with n-type single crystal silicon, with low initial dislocation density, were conducted over a temperature range of 900 K to 1200 K and a stress range of 10 MPa to 120 MPa. The compression specimens were machined such that the multi-slip <100> or <111> orientations were coincident with the compression axis. The creep tests reveal that response can be delineated into two broad regimes: (a) in the first regime rapid dislocation multiplication is responsible for accelerating creep rates, and (b) in the second regime an increasing resistance to dislocation motion is responsible for the decelerating creep rates, as is typically observed for creep in metals. An isotropic elasto-viscoplastic constitutive model that accounts for these two mechanisms has been developed in support of the design of the high temperature turbine structure of the MIT microengine.

Effect of high temperature on the apparent activation energy of respiration of fresh produce

2005 ◽  
Vol 37 (3) ◽  
pp. 277-285 ◽  
Author(s):  
Daisuke Nei ◽  
Toshitaka Uchino ◽  
Natsumi Sakai ◽  
Shun-ichirou Tanaka
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
Apparent Activation Energy ◽  
Fresh Produce

Internal friction behavior of an unidirectionally solidified Al2O3/YAG eutectic at high temperature

2007 ◽  
Vol 33 (8) ◽  
pp. 1569-1571 ◽  
Author(s):  
Satoshi Takata ◽  
Shunkichi Ueno ◽  
Yasuhiro Tanabe ◽  
Takashi Akatsu ◽  
Eiichi Yasuda ◽  
...  
Keyword(s):  
High Temperature ◽  
Internal Friction ◽  
Friction Behavior

scholarly journals High Temperature Hardness of Bulk Single Crystal GaN

2000 ◽  
Vol 5 (S1) ◽  
pp. 343-348
Author(s):  
I. Yonenaga ◽  
T. Hoshi ◽  
A. Usui
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Room Temperature ◽  
Applied Load ◽  
Elevated Temperatures ◽  
Mechanical Stability ◽  
Bulk Single Crystal ◽  
Indentation Method ◽  
First Time ◽  
High Mechanical Stability

The hardness of single crystal GaN (gallium nitride) at elevated temperature is measured for the first time and compared with other materials. A Vickers indentation method was used to determine the hardness of crack-free GaN samples under an applied load of 0.5N in the temperature range 20 - 1200°C. The hardness is 10.8 GPa at room temperature, which is comparable to that of Si. At elevated temperatures GaN shows higher hardness than Si and GaAs. A high mechanical stability for GaN at high temperature is deduced.

Incommensurately modulated ordering of tetrahedral chains in Ca2Fe2O5 at elevated temperatures

2005 ◽  
Vol 61 (6) ◽  
pp. 656-662 ◽  
Author(s):  
Hannes Krüger ◽  
Volker Kahlenberg
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Elevated Temperatures ◽  
Three Dimensional ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Modulated Structure ◽  
X Ray ◽  
Left Handed ◽  
Lattice Periodicity

The basic building units of brownmillerite-type A 2 B 2O5 structures are perovskite-like layers of corner-sharing BO6 octahedra and zweier single chains of BO4 tetrahedra. A three-dimensional framework is formed by alternate stacking of octahedral layers and sheets of tetrahedral chains. The compound Ca2Fe2O5 is known to have Pnma symmetry at ambient conditions. The space group Imma was reported to be evident above 963 K. New high-temperature single-crystal X-ray diffraction experiments at 1100 K revealed that Ca2Fe2O5 forms an incommensurately modulated structure adopting the superspace group Imma(00γ)s00, with γ = 0.588 (2). The modulation affects the sequence of the enantiomorphic (right- and left-handed) oriented tetrahedral chains within the layer, breaking the lattice periodicity along c. This ordering can be modelled with crenel occupation modulation functions for the tetrahedrally coordinated Fe, as well as for the O atom interconnecting the tetrahedra.

scholarly journals Effect of Temperature on the Creep of Ice

1969 ◽  
Vol 8 (52) ◽  
pp. 131-145 ◽  
Author(s):  
Malcolm Mellor ◽  
Richard Testa
Keyword(s):  
Activation Energy ◽  
Creep Rate ◽  
Single Crystal ◽  
Apparent Activation Energy ◽  
Creep Curve ◽  
Effect Of Temperature ◽  
Temperature Dependent ◽  
Creep Tests ◽  
Polycrystalline Ice ◽  
Rate Relation

Creep tests on homogeneous, isotropic polycrystalline ice gave an apparent activation energy for creep of 16.4 kcal/mol (68.8 kJ/mol) over the temperature range −10° to −60° C. Above −10° C the Arrhenius relation for temperature dependence is invalid, and creep rate becomes progressively more temperature dependent as the melting point is approached. Between −20° and −50° C the apparent activation energy for creep of a single crystal of ice was found to be 16.5 kcal/mol (69.1 kJ/mol). A complete creep curve for a single crystal loaded in uniaxial compression parallel to the basal plane was qualitatively similar to the classical creep curve; creep rate at all stages was very much faster than for polycrystalline ice under the same conditions. Creep tests on polycrystalline ice at 0° C gave a stress/strain-rate relation for that temperature, but its precise meaning is unclear, since recrystallization complicated the results.

scholarly journals Kinetics of Smelting Chromia–Bearing Vanadiferous Titanomagnetite Ore via High–Temperature CO2–Containing Gas Injection

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1008
Author(s):  
Hanlin Song ◽  
Gongjin Cheng ◽  
Jianxing Liu ◽  
Jinpeng Zhang ◽  
Xiangxin Xue
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
Apparent Activation Energy ◽  
Gas Injection ◽  
Reduction Rate ◽  
Co2 Concentration ◽  
Thermodynamic Calculations ◽  
Isothermal Kinetics ◽  
Smelting Process ◽  
Fuel Gas

Through thermodynamic smelting experiments, nonisothermal and isothermal kinetics experiments, the effects of CO2–containing gas injection on the smelting of chromia–bearing vanadiferous titanomagnetite ore were investigated. The experiments at 900 °C, 1000 °C, 1100 °C, 1200 °C, and 1300 °C, and CO2 concentration of 0, 10 vol.%, 20 vol.%, and 30 vol.% were studied. The samples after the kinetics experiments were analyzed through thermodynamic calculations and characterized by XRD, XRF, XPS, and SEM. The results of thermodynamic experiments show that the injection of CO2–containing gas significantly improves the softening–melting–dripping behavior during the smelting process. As the concentration of injected CO2 increased from 0 vol.% to 30 vol.%, the range of softening temperature [T40–T4] decreased from 109 °C to 97 °C, and the range of droplet temperature [Td–Ts] decreased rapidly from 196 °C to 162 °C. Moreover, when CO2 concentration was 20 vol.%, the minimum apparent activation energy of nonisothermal kinetics reached 75.58 kJ·mol−1. Combining the lowest permeability index and the fastest nonisothermal reduction rate, the optimal CO2 concentration in the fuel gas was considered to be 20 vol.%. The isothermal parameters were fitted according to 1 − (1 − α)1/3 − t (CG3 model), and the apparent activation energy was 121.93 kJ·mol−1 (less than 150 kJ·mol−1), which means that the restrictive step of the polymetallic reaction is mainly determined by diffusion. Finally, thermodynamic calculations and characterizations show that CO2–containing gas injection helps titanium stabilize in a higher valence state, which is conducive to improve the high–temperature characteristics of titanium–containing slag.

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