Creep of Lanthanum Gallate

2002 ◽  
Vol 17 (3) ◽  
pp. 532-541 ◽  
Author(s):  
William E. Luecke ◽  
Timothy R. Armstrong
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Apparent Activation Energy ◽  
Absolute Magnitude ◽  
Lanthanum Gallate ◽  
Stress Dependence ◽  
Creep Tests ◽  
Four Point Bending ◽  
Cation Impurity ◽  
A Site

Strontium- and magnesium-doped lanthanum gallate (LSGM) was deliberately prepared to give A-site deficient nonstoichiometry with compositions (La0.9Sr0.1)z(Ga0.8Mg0.2)O3-δ (z = 1.0, 0.98, and 0.95). Creep tests in four-point bending for 950 °C < T < 1350 °C and 15 MPa < σ < 75 MPa in air demonstrated that all three compositions shared a common stress dependence, n= 1.49 ± 0.10, and a common apparent activation energy, Q = 426 ± 9 kJ/mol. Despite this agreement, the creep rates of the different compositions depended on grain size in different ways: p = 3.1 ± 0.2 for z = 0.98, and p = 1.9 ± 0.1 for z = 0.95. The measured apparent activation energy, Q, for creep is similar, though statistically significantly smaller, than that measured in another LSGM. Both are nearly twice as large as reported activation energies for cation impurity diffusion. The absolute magnitude of the creep rates, after correction for grain size, were 30 to 100 times slower than in another LSGM of similar composition.

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 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.

Creep Behavior of Two Series Magnesium Alloys

2010 ◽  
Vol 638-642 ◽  
pp. 1596-1601 ◽  
Author(s):  
Yang Shan Sun ◽  
Jing Bai ◽  
Feng Xue
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Stress Exponent ◽  
Magnesium Alloys ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Grain Boundary Sliding ◽  
Creep Tests ◽  
Sharp Drop ◽  
Creep Properties

The creep behavior of two series of magnesium alloys, Mg-4Al based alloys with strontium addition and binary Mg-Nd alloys, has been studied. Results show that the high creep properties achieved by the Mg-Nd alloys are attributed to the precipitation of tiny dispersed β’ particles, which form and effectively restrict the dislocation slipping and climb during creep deformation. In terms of values of the stress exponent and apparent activation energy gained from systematic creep tests, the mechanism responsible for creep deformation of the Mg-Nd alloys is inferred as dislocation climb, which is supported by TEM observations performed on the Mg-2Nd alloy after creep test. For the Mg-4Al based alloys, however, microstructural observations reveal that the significant improvement on creep properties caused by Sr addition is accounted for the formation of an interphase network consisting of Al4Sr and a Mg-Al-Sr ternary compound distributing at grain boundaries. The breakage of the interphase network after extrusion results in a sharp drop of creep properties, indicating the creep deformation of the alloy is controlled mainly by grain boundary sliding, which is in contradiction to the mechanism for creep of the alloys inferred by the classical criterions based on the values of stress exponent and apparent activation energy.

scholarly journals Grain Growth Control of ZnO-V2O5-Cr2O3 Based Varistors by PrMnO3 Addition

2021 ◽  
Author(s):  
Chankun Cai ◽  
Yu Shi ◽  
Manyi Xie ◽  
Ke Xue ◽  
Maofeng Xu ◽  
...  
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Apparent Activation Energy ◽  
Size Distribution ◽  
Grain Growth ◽  
Growth Control ◽  
Growth Behaviour ◽  
Grain Sizes ◽  
Pinning Effect ◽  
Average Grain Size

Abstract In this work, the grain growth behaviour of ZnO+V2O5(1 mol%)+Cr2O3(0.35 mol%)-based ceramics with 0.25–0.75 mol% additions of PrMnO3 was systematically investigated during sintering from 850°C to 925°C with the aim to control the ZnO grain size for their application as varistors. It was found that with the increased addition of PrMnO3, not only did the average grain size decrease, but the grain size distribution also narrowed and eventually changed from a bimodal to unimodal distribution after a 0.75 mol% PrMnO3 addition. The grain growth control was achieved by a pinning effect of the secondary ZnCr2O4 and PrVO4 phases at the ZnO grain boundaries. The apparent activation energy of the ZnO grain growth in these ceramics was found to increase with increased additions of PrVO4; hence, the observed reduction in the ZnO grain sizes.

Surface Modification and its Influence on the Microstructure and Creep Resistance of Nickel Based Superalloy René 77 / Modyfikacja Powierzchniowa Oraz Jej Wpływ Na Mikrostrukture I Wytrzymałosc Na Pełzanie Odlewów Z Nadstopu Niklu Ren´E 77

2013 ◽  
Vol 58 (1) ◽  
pp. 95-98 ◽  
Author(s):  
M. Zielinska ◽  
J. Sieniawski
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Surface Modification ◽  
Turbine Blades ◽  
Processing Parameters ◽  
Grain Structure ◽  
Creep Tests ◽  
Cobalt Aluminate ◽  
Nickel Based Superalloy ◽  
Average Grain Size

Superalloy René 77 is very wide used for turbine blades, turbine disks of aircraft engines which work up to 1050°C. These elements are generally produced by the investment casting method. Turbine blades produced by conventional precision casting methods have coarse and inhomogeneous grain structure. Such a material often does not fulfil basic requirements, which concern mechanical properties for the stuff used in aeronautical engineering. The incorporation of controlled grain size improved mechanical properties. This control of grain size in the casting operation was accomplished by the control of processing parameters such as casting temperature, mould preheating temperature, and the use of grain nucleates in the face of the mould. For nickel and cobalt based superalloys, it was found that cobalt aluminate (CoAl2O4) has the best nucleating effect. The objective of this work was to determine the influence of the inoculant’s content (cobalt aluminate) in the surface layer of the ceramic mould on the microstructure and mechanical properties at high temperature of nickel based superalloy René 77. For this purpose, the ceramic moulds were made with different concentration of cobalt aluminate in the primary slurry was from 0 to 10% mass. in zirconium flour. Stepped and cylindrical samples were casted for microstructure and mechanical examinations. The average grain size of the matrix ( phase), was determined on the stepped samples. The influence of surface modification on the grain size of up to section thickness was considered. The microstructure investigations with the use of light microscopy and scanning electron microscopy (SEM) enable to examine the influence of the surface modification on the morphology of ’ phase and carbides precipitations. Verification of the influence of CoAl2O4 on the mechanical properties of castings were investigated on the basis of results obtained form creep tests.

scholarly journals The Hydrothermal Stability and the Properties of Non- and Strongly-Interacting Rh Species over Rh/γ, θ-Al2O3 Catalysts

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 99
Author(s):  
Guanghao Cheng ◽  
Gurong Shen ◽  
Jun Wang ◽  
Yunhao Wang ◽  
Weibo Zhang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Aging Time ◽  
Reaction Path ◽  
Aging Treatment ◽  
Hydrothermal Stability ◽  
Hydrothermal Aging ◽  
Strongly Interacting

The present work reports the effects of γ-, θ-phase of alumina on the hydrothermal stability and the properties of non- and strongly-interacting Rh species of the Rh/Al2O3 catalysts. Comparing to γ-Al2O3, θ-Al2O3 can not only reduce the amount of occluded Rh but also better stabilize Rh during hydrothermal aging treatment. When the aging time was prolonged to 70 h, all the non-interacting Rh was transformed into strongly-interacting Rh and occluded Rh. The XPS results indicated that non- and strongly-interacting Rh might exist in the form of Rh/Rh3+ and Rh4+, respectively. CO-NO reaction was chosen as a probe reaction to research more information about non- and strongly-interacting Rh. The two Rh species had similar apparent activation energy (Eapp) of 170 kJ/mol, which indicated that non- and strongly-interacting Rh follow the same reaction path. The non-interacting Rh was removed from aged samples by the acid-treated method, and obtained results showed that only 2.5% and 4.0% non-interacting Rh was maintained in aged Rh/γ-Al2O3 and Rh/θ-Al2O3.

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 Effect of CaO on catalytic combustion of semi-coke

2021 ◽  
Vol 10 (1) ◽  
pp. 011-020
Author(s):  
Luyao Kou ◽  
Junjing Tang ◽  
Tu Hu ◽  
Baocheng Zhou ◽  
Li Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Combustion Rate ◽  
Activation Energies ◽  
Combustion Reaction ◽  
Tg Analysis ◽  
Conversion Rates ◽  
Apparent Activation Energies ◽  
Ozawa Integral Method ◽  
Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

Effect of orienting coatings on the apparent activation energy of boundary film destruction

2007 ◽  
Vol 28 (1) ◽  
pp. 12-18 ◽  
Author(s):  
I. A. Buyanovskii ◽  
Yu. N. Drozdov ◽  
Z. V. Ignatieva ◽  
T. M. Savinova ◽  
V. A. Levchenko ◽  
...  
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Boundary Film

Quantitative Modelling of Nucleation Kinetics in Experiments for Poly-Si Growth on Sio2 by Hot-Wire Chemical Vapor Deposition

2001 ◽  
Vol 664 ◽  
Author(s):  
Maribeth Swiatek ◽  
Jason K. Holt ◽  
Harry A. Atwater
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Nucleation Density ◽  
Hot Wire ◽  
Nucleation Kinetics ◽  
Temperature Dependent ◽  
Cluster Density

ABSTRACTWe apply a rate-equation pair binding model of nucleation kinetics [1] to the nucleation of Si islands grown by hot-wire chemical vapor deposition on SiO2 substrates. Previously, we had demonstrated an increase in grain size of polycrystalline Si films with H2 dilution from 40 nm using 100 mTorr of 1% SiH4 in He to 85 nm with the addition of 20 mTorr H2. [2] This increase in grain size is attributed to atomic H etching of Si monomers rather than stable Si clusters during the early stages of nucleation, decreasing the nucleation density. Atomic force microscopy (AFM) measurements show that the nucleation density increases sublinearly with time at low coverage, implying a fast nucleation rate until a critical density is reached, after which grain growth begins. The nucleation density decreases with increasing H2 dilution (H2:SiH4), which is an effect of the etching mechanism, and with increasing temperature, due to enhanced Si monomer diffusivity on SiO2. From temperature-dependent measurements, we estimate the activation energy for surface diffusion of Si monomers on SiO2 to be 0.47 ± 0.09 eV. Simulations of the temperature-dependent supercritical cluster density lead to an estimated activation energy of 0.42 eV ± 0.01 eV and a surface diffusion coefficient prefactor of 0.1 ± 0.03 cm2/s. H2-dilution-dependent simulations of the supercritical cluster density show an approximately linear relationship between the H2 dilution and the etch rate of clusters.

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