Experimental Evidence of Temperature Path Independence in the Polycrystalline Alloy Ni3AI

1995 ◽  
Vol 117 (4) ◽  
pp. 478-482 ◽  
Author(s):  
G. Webb ◽  
S. D. Antolovich
Keyword(s):  
Dislocation Substructure ◽  
Deformation Characteristic ◽  
Thermally Activated ◽  
Path Independence ◽  
History Independence ◽  
Polycrystalline Alloy ◽  
Different Temperatures ◽  
Deformation Processes ◽  
Thermal Reversibility ◽  
Temperature Path

The results from a series of elevated temperature prestrain experiments on a hypostoichiometric polycrstalline Ni3Al are presented. Experiments were conducted to examine the deformation characteristic of “thermal reversibility” or temperature path history independence (TPHI). Temperature path history independence was experimentally observed from prestraining experiments (also known as Cottrell-Stokes experiments) in which the specimen was deformed at different temperatures; the results were compared to those obtained from tests conducted at constant temperature. The purpose of such experiments was to macroscopically evaluate the effects of intrinsic dislocation mobility and dislocation substructure on deformation. These experiments provide a framework in which to evaluate fundamental characteristics of thermally activated deformation processes. The results for polycrystalline Ni3Al alloys indicate that the mechanisms responsible for thermal strengthening is independent of prior deformation history. This observation implies that the mechanism of anomalous strengthening in such alloys is fully reversible and independent of the development of a dislocation “substructure”.

scholarly journals Surface Modification of Fly Ash for Active Catalysis

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Deepti Jain ◽  
Renu Hada ◽  
Ashu Rani
Keyword(s):  
Fly Ash ◽  
Heterogeneous Catalysts ◽  
Chemical Activation ◽  
Alumina Content ◽  
Precipitation Method ◽  
Solid Base ◽  
Thermally Activated ◽  
Flame Atomic Absorption ◽  
Flame Atomic Absorption Spectrophotometer ◽  
Different Temperatures

Fly ash based effective solid base catalyst (KF/Al2O3/fly ash473, KF/Al2O3/fly ash673, and KF/Al2O3/fly ash873) was synthesized by loading KF over chemically and thermally activated fly ash. The chemical activation was done by treating fly ash with aluminum nitrate via precipitation method followed by thermal activation at 650°C to increase the alumina content in fly ash. The increased alumina content was confirmed by SEM-EDX analysis. The alumina enriched fly ash was then loaded with KF (10 wt%) and calcined at three different temperatures 473 K, 673 K and 873 K. The amount of loaded KF was monitored by XRD, FTIR spectroscopy, SEM-EDX, TEM and Flame Atomic Absorption Spectrophotometer. The catalytic activities of the catalysts were tested in the Claisen-Schmidt condensation of benzaldehyde and 4-methoxybenzaldehyde with 2′-hydroxyacetophenone to produce 2′-hydroxychalcone and 4-methoxy-2′-hydroxychalcone respectively. Higher conversion (83%) of benzaldehyde and (89%) of 4-methoxybenzaldehyde reveals that among these heterogeneous catalysts KF/Al2O3/fly ash673 is very active.

scholarly journals Long-term hydrophilization of polydimethylsiloxane (PDMS) for capillary filling microfluidic chips

2019 ◽  
Vol 24 (1) ◽  
Author(s):  
Farzin Jahangiri ◽  
Tuuli Hakala ◽  
Ville Jokinen
Keyword(s):  
Cold Storage ◽  
Storage Temperature ◽  
Microfluidic Channel ◽  
Vibration Band ◽  
Microfluidic Chips ◽  
Thermally Activated ◽  
Capillary Filling ◽  
Different Temperatures ◽  
Long Term Preservation

AbstractWe present a simple and facile method for long-term preservation of hydrophilicity of oxygen plasma-hydrophilized poly (dimethylsiloxane) (PDMS) by cold storage. We show that storage under temperature of − 80 °C can maintain superhydrophilicity of plasma-exposed PDMS for at least 100 days. Storage at − 15 °C and at 22 °C room temperature (RT) is shown to exhibit, respectively, about half and full recovery of the original hydrophobicity after 100 days in storage. Furthermore, we investigated the implications of the cold storage for microfluidic applications, the capillary filling rate and the ability of the flow to bypass geometrical obstacles in a microfluidic channel. It is shown that the preservation of capillary filling properties of microchannels is in close agreement with the contact angle (CA) measurements and that the colder the storage temperature, the better the capillary filling capability of the channels is preserved. We ascribe the significantly reduced recovery rate to reduced thermally activated relaxation phenomena such as diminished diffusion of low molecular weight species (LMW) in the polymer matrix at colder temperatures. This is supported by ATR-FTIR measurements of the OH vibration band over time for samples stored at different temperatures.

The Meyer–Neldel Rule in Conduction Mechanism of the Electrospun ZnO Nanofibers

NANO ◽  
2016 ◽  
Vol 11 (03) ◽  
pp. 1650025 ◽  
Author(s):  
Andrzej Stafiniak ◽  
Marek Tłaczała
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Conduction Mechanism ◽  
Deep Level ◽  
Electrical Measurements ◽  
Thermally Activated ◽  
Theoretical Assumptions ◽  
Different Temperatures ◽  
Zno Nanofibers ◽  
Improved Model

An analytical model describing the conductivity of ZnO nanofibers depending on the grains size is proposed. The research is based on the thermal dc electrical measurements of a single electrospun ZnO nanofiber calcined at different temperatures. In the our previous research, we showed that electrical conduction of ZnO nanofibers is mainly thermally activated. The activation energy of conductivity was strongly dependent on the grain size, which in turn depended on the calcination temperature. This could be due to migration of a point defect in the grain of ZnO and could change the carrier concentration. Our recent studies have shown that ZnO nanofibers behavior is consistent with the Meyer–Neldel rule. This indicates an exponential energy distribution of deep level traps in the material. Based on the theoretical assumptions and experimental data, the improved model of conductivity in a single ZnO nanofiber calcined at different temperatures was proposed.

scholarly journals Effect of Different Surface-charged Lamellar Materials on Swelling Properties of Nanocomposite Hydrogels

2021 ◽  
Author(s):  
Marcela Pfeifer ◽  
Flávio A. C. Andrade ◽  
Ricardo Bortoletto-Santos ◽  
Fauze A. Aouada ◽  
Caue Ribeiro
Keyword(s):  
Water Absorption ◽  
Anomalous Behavior ◽  
Absorption Capacity ◽  
Water Absorption Capacity ◽  
Swelling Properties ◽  
Ph Variation ◽  
Nanocomposite Hydrogels ◽  
Thermally Activated ◽  
Different Temperatures ◽  
Lamellar Materials

Abstract This study investigated the effect of different surface-charged lamellar materials on the swelling and diffusion properties of synthesized polyacrylamide-methylcellulose hydrogels (HG). Montmorillonite and hydrotalcite thermally activated at two different temperatures (300 and 550 ºC) were incorporated in the preparation of nanocomposite (NC) hydrogels. A series of NC hydrogels were prepared by varying the lamellar material content (1:1, 2:1 and 4:1). The results showed that the HG with hydrotalcite (550 ºC) was strongly dependent on the ionic intensity, and that the swelling degree increased by 50%, 65% and 78% with reducing the hydrotalcite content at (1:1), (2:1) and (4:1), respectively. The water absorption capacity of HG containing montmorillonite or hydrotalcite (300 ºC) was slightly affected when the pH decreased from 7 to 3. However, the pH variation from 7 to 10 increased the water absorption capacity of most HG, except those containing hydrotalcite (550 ºC) at (2:1) and (4:1). The presence of lamellar nanoparticles in hydrogels made the polymer matrix more rigid, and less likely to absorb water. In contrast, HG with hydrotalcite (550 ºC) at (2:1) and (4:1) showed anomalous behavior with an increase in their water absorption capacity. The results support that the developed NC-HG can be suitable candidates for applications as controlled released materials.

Assessment of pozzolanic activity of thermally activated clay and its impact on strength development in cement mortar

RSC Advances ◽  
2015 ◽  
Vol 5 (8) ◽  
pp. 6079-6084 ◽  
Author(s):  
Noor-ul- Amin ◽  
Sultan Alam ◽  
Saeed gul
Keyword(s):  
Cement Mortar ◽  
Pozzolanic Activity ◽  
Strength Development ◽  
Thermally Activated ◽  
Different Temperatures ◽  
Kaolinitic Clay

Natural kaolinitic clay from Khyber Pakhtoonkhwa, Pakistan was thermally activated at different temperatures and its pozzolanic behavior was studied.

Severe Plastic Deformation of Amorphous Alloys

2008 ◽  
Vol 584-586 ◽  
pp. 227-230 ◽  
Author(s):  
Alex M. Glezer ◽  
Sergey V. Dobatkin ◽  
Margarita R. Plotnikova ◽  
Anna V. Shalimova
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Amorphous Alloy ◽  
Severe Plastic Deformation ◽  
Physical Properties ◽  
Plastic Flow ◽  
Low Temperatures ◽  
Amorphous Alloys ◽  
Thermally Activated ◽  
Different Temperatures

The structure and mechanical properties of amorphous alloy Ni44Fe29Co15Si2B10 after severe plastic deformation (SPD) in Bridgman chamber at the different temperatures (77 and 298 K) have been studied. It is shown that the early stages of the SPD of amorphous alloy cause a noticeable decrease in microhardness HV and significant changes in the physical properties. With increasing the value of SPD the transition from inhomogeneous to homogeneous (or to qualitatively different) mode of plastic flow is observed, which is accompanied by the effects of homogeneous nanocrystallization. The nanoparticle size does not exceed 10 nm. It is established that the thermally activated nanocrystallization processes can occur at very low temperatures (77 K).

Development of high temperature creep resistance in Fe-Al alloys

2004 ◽  
Vol 842 ◽  
Author(s):  
D. G. Morris ◽  
M. A. Muñoz-Morris ◽  
C. Baudin
Keyword(s):  
High Temperature ◽  
High Temperatures ◽  
Creep Resistance ◽  
Good Strength ◽  
Thermally Activated ◽  
Intermediate Temperature Range ◽  
Deformation Processes ◽  
Good Creep Resistance ◽  
Oxidation And Corrosion ◽  
Very High

ABSTRACTMost of the studies aimed at the development of creep-resisting Fe-Al intermetallics have been oriented at application temperatures of the order of 500–650°C, where these materials may compete with conventional stainless steels. The Fe-Al intermetallics are, however, particularly excellent in their oxidation and corrosion resistances at temperatures of the order of 1000°C, where Chromium-Nickel steels are no longer able to withstand the aggressive environments. This presentation is part of a study aimed at the development of good creep resistance at such high temperatures.Studies of a variety of cast Fe3Al-base alloys, strengthened by solution or precipitate/dispersoid-forming alloying additions, are reported. The alloys show good strength from room temperature to about 500°C, but thereafter strength falls rapidly as thermally-activated deformation processes become operative. Solution additions are capable of producing good low temperature strength, but do not contribute significantly to creep strength at very high temperatures (above 700°C). Precipitation hardening has been examined in Nb-containing alloys, where Fe2Nb Laves precipitates form at intermediate temperatures. These materials show good strength up to about 700°C, but at higher temperatures the fine precipitates coarsen excessively. Strengthening in the intermediate temperature range varies depending on whether the solute is precipitated prior to high temperature testing or concurrent with this.

Mössbauer effect study on the mixed valence state of iron in tourmaline

1988 ◽  
Vol 52 (365) ◽  
pp. 221-228 ◽  
Author(s):  
E. A. Ferrow ◽  
H. Annersten ◽  
R. P. Gunawardane
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Valence State ◽  
Mixed Valence ◽  
Effect Study ◽  
High Activation ◽  
Charge Delocalization ◽  
Thermally Activated ◽  
Different Temperatures ◽  
Iron Bearing

AbstractMössbauer spectra of iron-bearing tourmaline, obtained at different temperatures, show the existence of thermally-activated charge delocalization among clusters of iron atoms situated in the Y and Z octahedra of the tourmaline structure. The temperature dependence indicates an unusually high activation energy for the delocalization process which suggests that the process takes place between crystallographically non-equivalent sites. Annealing of the tourmaline in hydrogen is observed to inhibit the delocalization process, thus localizing the electron into the Z-site.

scholarly journals Ultrasonic relaxation of some CdO boro-tellurate glasses

2016 ◽  
Vol 94 (10) ◽  
pp. 1008-1016 ◽  
Author(s):  
M.S. Gaafar ◽  
I.S. Mahmoud
Keyword(s):  
Activation Energy ◽  
Relaxation Process ◽  
Ultrasonic Attenuation ◽  
Operating Frequency ◽  
Thermally Activated ◽  
Different Temperatures ◽  
Standard Linear Solid ◽  
Standard Linear ◽  
Double Well Potential ◽  
Solid Type

50B2O3–(50-x)TeO2–xCdO glass system, with x = 0, 10, 20, 30, 40, and 50 mol% have been prepared, to measure the longitudinal ultrasonic attenuation at frequencies of 2, 4, 6, and 14 MHz in the temperature range from 120 to 300 K. Well-defined broad peaks of the absorption curves were observed at different temperatures depending on the glass composition and the operating frequency. The maximum peaks shifted to higher temperatures with the increase of the operating frequency implying the presence of some kind of relaxation process. This process is suggested as due to the thermally activated relaxation process. The variation of the average activation energy of the process mainly depends on the CdO mol% content. Such dependence was analyzed in terms of the loss of standard linear solid type, with low dispersion and a broad distribution of Arrhenius type relaxation with temperature independent relaxation strength. The obtained acoustic activation energy values were quantitatively interpreted in terms of the number of loss centers (number of oxygen atoms that vibrate in the double well potential).

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