Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ACTIVATION ENERGY”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Activation Energies for Oxide- and Interface-Trap Charge Generation Due to Negative-Bias Temperature Stress of Si-Capped SiGe-pMOSFETs

We investigate negative-bias temperature instabilities in SiGe pMOSFETs with SiO 2 /HfO 2 gate dielectrics. The measured activation energies for interface-trap charge buildup during negative-bias temperature stress are lower for SiGe channel pMOSFETs with SiO 2 /HfO 2 gate dielectrics and Si capping layers than for conventional Si channel pMOSFETs with SiO 2 gate dielectrics. Electron energy loss spectroscopy and scanning transmission electron microscopy images demonstrate that Ge atoms can diffuse from the SiGe layer into the Si capping layer, which is adjacent to the SiO 2 /HfO 2 gate dielectric. Density functional calculations show that these Ge atoms reduce the strength of nearby Si-H bonds and that Ge-H bond energies are still lower, thereby reducing the activation energy for interface-trap generation for the SiGe devices. Activation energies for oxide-trap charge buildup during negative-bias temperature stress are similarly small for SiGe pMOSFETs with SiO 2 /HfO 2 gate dielectrics and Si pMOSFETs with SiO 2 gate dielectrics, suggesting that, in both cases, the oxide-trap charge buildup likely is rate-limited by hole tunneling into the near-interfacial SiO 2 .

activation energy↗
DOE OSTI2016

Removing the barrier to the calculation of activation energies

Approaches for directly calculating the activation energy for a chemical reaction from a simulation at a single temperature are explored with applications to both classical and quantum systems. The activation energy is obtained from a time correlation function that can be evaluated from the same molecular dynamics trajectories or quantum dynamics used to evaluate the rate constant itself and thus requires essentially no extra computational work.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Activation Energies of Harvested Boston Insulated Wire and Okonite Cable Materials

As part of the Cable Aging Task within the Material Aging and Degradation (MAaD) pathway of the DOE Light Water Reactor Sustainability (LWRS) program, ORNL is collaborating with Pacific Northwest National Laboratory (PNNL), the Electric Power Research Institute (EPRI), and the US Nuclear Regulatory Commission (NCR) to study cable aging mechanisms. Understanding cable aging mechanisms in cable nuclear power plants (NPPs) with needed information as they seek plant life extensions to 80 years of operations. This report summarizes activities in the characterization of harvested electrical I&C cables related to activation energy and their role in determining the remaining margin of time cable insulation in NPPs can be used. Activation energy is the amount of energy that is required to break chemical bonds in a polymer through an endothermic reaction. For I&C cables that are utilized in NPPs, activation energy is used with a time and temperature dependent cable property like elongation at break (EAB) and/or an electrical property like voltage withstand to determine whether a cable insulation material meets the performance requirements for the environmental conditions such as temperature, radiation, and humidity for a given plant location. Considering differences in activation energies that were observed in harvested cable jackets when compared to previous measurements, an assessment of the cable insulation activation energy in harvested I&C cables was performed given that the insulation performance ultimately determines that lifetime performance for a cable. This assessment consisted of the mechanical and chemical characterization of harvested Boston Insulated Wire (BIW) and Okonite cable insulations from Zion NPP from a series of thermal accelerated aging exposures between 140°C and 160°C. Cables were obtained as part of the LWRS Zion Harvesting Project in cooperation with Energy Solutions and the NRC. Activation energies of 1.10 eV and 0.61 eV were obtained for BIW and Okonite manufactured ethylene propylene rubber (EPR) insulation with individual chlorosulfonated polyethylene (CSPE) jackets respectively. When compared to previous measurements, the activation energy of BIW agreed well, while there was a sizeable gap for previous Okonite activation energies near 0.91 eV. The lack of agreement could be attributed to differences in raw materials used in a given insulation and/or jacket, differences in the thicknesses of the EPR insulation and CSPE individual jacket or the environmental conditions that the insulation from previous measurements experienced prior to characterization especially if cables were not stored at manufacturer recommended conditions. Comparison of harvested insulation compositions from multiple NPP sites and locations in a given NPP with respect to activation energy could provide some guidance on property sensitivity and insulation variations. To address the issue of material thickness, an initial assessment of the influence of the CPSE individual jacket was also done. This was motivated by the different combinations of EPR insulation and CSPE individual jacket thicknesses that were found in harvested cables and previous measurements. Accelerated thermal aging of BIW-manufactured EPR insulation with individual CSPE jackets removed did show that the CSPE layer affected insulation degradation, further comparison of the compositional make-up of the CSPE and EPR for both BIW and Okonite insulation, along with a limited amount of additional accelerated aging, is needed to increase the level of confidence regarding the influence of the CSPE.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Apparent Activation Energies in Complex Reaction Mechanisms: A Simple Relationship via Degrees of Rate Control

The apparent activation energy of chemical reactions previously played a central role in the field of chemical kinetics and has served as an important tool for analyzing and understanding reaction rates, mechanistic details of complex reaction mechanisms, elementary-step energetics, catalytic activity and reaction selectivity. In this work, we derive a general expression which shows that the apparent activation energy equals a weighted average of the standard-state enthalpies (relative to reactants) of all the species (intermediates, transition states and products) in the reaction mechanism, each weighted by its generalized degree of rate control (DRC). Since the DRC is zero for most of these species, even in very complex mechanisms, the weighted average includes only a few terms. This simplicity provides deep insight into the connection between the reaction energy diagram and the apparent activation energy. We prove both this and the quantitative validity of this equation by analysis of numerous reaction mechanisms. We also show the failures or weaknesses of previous equations for the apparent activation energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Activation Energy Determination for Photovoltaic Encapsulant Discoloration by Indoor Accelerated UV Testing

A novel methodology for determining the activation energy of photovoltaic encapsulant discoloration using an indoor accelerated ultraviolet (UV) stress test while simultaneously maintaining multiple module temperatures in a single weathering chamber is presented. The testing was performed on some fresh mini-modules with a glass/EVA/cell/EVA/backsheet construction. The short-circuit current degradation from individual cells was used to quantify transmittance losses due to discoloration. Activation energy determined using indoor accelerated UV test data and Modified Arrhenius model ranges from 26 to 44 kJ/mol (0.27 to 0.46 eV). Activation energy was also determined from the outdoor field degradation data by employing different physical models that consider the individual or combined effects of key environmental factors. The approach here is instrumental to evaluating the reliability studies on encapsulant degradation mechanisms using relatively less time and resources.

14 SOLAR ENERGY↗
DOE OSTI2020

DFT-Based Calculation of Dissolution Activation Energy and Kinetics of Ni–Cr Alloys

A density functional theory investigation of the process of dissolution of Ni and Cr adatoms from model Ni–Cr(111) alloy surfaces is presented, both in vacuum and with explicit water molecules. The goal is to understand how the electronic structures solved using DFT can provide insights as to changes in valence, energy and coordination of the adatoms in the process of dissolving from the alloy surface. It is found that nearby Cr solute atoms increase the dissolution activation energy of Ni. Cr adatoms have a similar dissolution activation energy as Ni adatoms, except for one particular surface configuration that has a much smaller dissolution activation energy, which might promote selective dissolution of Cr in Ni–Cr alloys. To interpret the first-principles modeling results for the potential energy trajectory along the dissolution reaction coordinate, we provide a thermodynamic breakdown of the various terms that contribute to the dissolution activation and total reaction energy. The role of addition of Cr is explored on the dissolution kinetics of a Ni–Cr alloys of varying composition by constructing a model for the corrosion current density with DFT-based activation energies. Lastly, dissolution resistance index is proposed as a quantifiable descriptor of the dissolution resistance of corrosion resistant alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Polymer etching by atmospheric-pressure plasma jet and surface micro-discharge sources: Activation energy analysis and etching directionality

Treatments of polymer films using either a MHz atmospheric pressure plasma jet (APPJ) or an atmospheric pressure surface micro-discharge (SMD) plasma are investigated. While the typical approach to determine relevant reactive species is to correlate surface effects with gas phase species measurement, this does not capture potential synergistic or other complex effects that may be occurring. Activation energy and directionality of the etching process can characterize what is occurring at the surface for these processes in more detail. The APPJ source shows an apparent activation energy of ~0.18 eV at 8 mm distance and up to ~0.34 eV at 16mmdistance for a temperature range of 20–80 °C tested with thin polymer films. The APPJ source shows directional etching at 8 mm distance with less anisotropy the more distance is increased. The SMD source has an apparent activation energy of ~0.8–0.9 eV at a distance of 3 mm. The SMD also only shows isotropic etching behavior. However the SMD surface chemistry changes significantly to less oxidation with increased temperature while the APPJ source induced modifications remain very similar with temperature change. The lower apparent activation energy of the APPJ induced etching reactions as compared with low pressure work (0.5 eV) and observation of line-of-sight contribution to etching suggests the involvement of a directional species at closer distances facilitating the etching which falls off with increasing distance. The high activation energy of the SMD suggests that species with less capability for etching is responsible compared to the APPJ and low pressure plasma. In conclusion, the high surface oxidation from low temperature SMD treatments shows that the surface is being oxidized but not sufficiently to reach the desorption step of the etching process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Activation energy of metastable amorphous Ge 2 Sb 2 Te 5 from room temperature to melt

Resistivity of metastable amorphous Ge 2 Sb 2 Te 5 (GST) measured at device level show an exponential decline with temperature matching with the steady-state thin-film resistivity measured at 858 K (melting temperature). This suggests that the free carrier activation mechanisms form a continuum in a large temperature scale (300 K – 858 K) and the metastable amorphous phase can be treated as a super-cooled liquid. The effective activation energy calculated using the resistivity versus temperature data follow a parabolic behavior, with a room temperature value of 333 meV, peaking to ~377 meV at ~465 K and reaching zero at ~930 K, using a reference activation energy of 111 meV (3kBT/2) at melt. Amorphous GST is expected to behave as a p-type semiconductor at T melt ~ 858 K and transitions from the semiconducting-liquid phase to the metallic-liquid phase at ~930 K at equilibrium. The simultaneous Seebeck (S) and resistivity versus temperature measurements of amorphous-fcc mixed-phase GST thin-films show linear S-T trends that meet S = 0 at 0 K, consistent with degenerate semiconductors, and the dS/dT and room temperature activation energy show a linear correlation. The single-crystal fcc is calculated to have dS/dT = 0.153 μ V/K 2 for an activation energy of zero and a Fermi level 0.16 eV below the valance band edge.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Effect of Using Different Y{sub 2}O{sub 3} Layers on the Activation Energy and Irreversibility Line of MPMG YBCO Bulk at 1050 °C Growth Temperature

In this study, three kinds of YBCO samples which are named Y1, Y2 and Y3 were fabricated by a melt–powder–melt–growth (MPMG) method. The Y1 sample was placed into a platinum (Pt) crucible without Y{sub 2}O{sub 3}, the Y2 sample was located on a Al{sub 2}O{sub 3} crucible with a freely poured Y{sub 2}O{sub 3} powder and the Y3 sample was located on a Al{sub 2}O{sub 3} crucible with a 1-mm-thick buffer layer of Y{sub 2}O{sub 3}. YBCO samples were investigated by magnetoresistivity (ρ–T) measurements in dc magnetic fields (parallel to the c-axis) up to 5 T. The effect of the Y{sub 2}O{sub 3} layer on the activation energy and irreversible flux of the samples was studied. The activation energies (U) were determined using the Arrhenius activation energy law from ρ–T. The power law relationship for U with H{sup −α} was investigated. α was calculated to find out which defects were dominant in the samples. Irreversibility fields (H{sub irr}) and upper critical fields (H{sub c2}) were obtained using 10 and 90% criteria of the normal-state resistivity value from ρ–T curves. Irreversibility lines (ILs) were estimated from the equation H{sub irr} ∼ (1 − T{sub irr}(H)/T{sub irr}(0)){sup n}. The fitting results to giant flux creep and vortex glass models were discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Phase Change-Driven Negative Activation Energies in Pd/Carbon-Based/Organic Getter Hydrogenation Reactions

In this study, the hydrogenation of 1,4-diphenylbutadiyne (DPB) blended with carbon-supported Pd (DPB–Pd/C) in the form of pellets was investigated by isothermal–isobaric experiments at 1333 Pa of H 2 and in the temperature range of 291–315 K. The extracted kinetics were then used in conjunction with a complementary constant rate of H 2 input experimentation to model the performance of a DPB-catalysis/support system as a function of temperature and H 2 partial pressure. First-principles density functional theory (DFT) calculations were also performed to shed light on the molecular level energetics of DPB and its intermediate states. A seemingly puzzling formation of alternate positive activation energy barrier (higher reaction rate with higher temperature) and negative activation energy barrier (higher reaction rate with lower temperature) zones during the hydrogenation process was discovered. However, this observed phenomenon can be logically explained in terms of the associated phase changes and H 2 transport in the material. This work provides a good illustration of a rarely encountered chemical process with a negative activation energy barrier.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Composition-dependent apparent activation-energy and sluggish grain-growth in high entropy alloys

Experimental results reveal that the apparent activation-energy for grain-growth in an fcc-based Al x CoCrFeNi high entropy alloy (HEA) system increases from 179 to 486 kJ/mol when the Al content increases from x = 0.1 to 0.3. These unexpectedly high apparent activation-energy values can be potentially attributed to solute clustering within the fcc solid-solution phase that develops with increasing Al content in this HEA. Detailed microstructural analysis using atom-probe tomography and density functional theory (DFT) calculations strongly indicate the presence of such nanoscale clusters. This phenomenon can change grain-growth from a classical solute-drag regime to a much more sluggish cluster-drag based mechanism in these HEAs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Activation Energy for End-of-Life Solder Bond Degradation: Thermal Cycling of Field-Aged PV Modules

The longevity of solar photovoltaic modules depends on the durability and reliability of their components, one of which is the solder bonds in interconnect ribbons. The solder joints experience stresses from thermal cycling and constant elevated temperatures (40 °C-70 °C) in regular field operation leading to thermo-mechanical fatigue and intermetallic compound formation. To study the end-of-life wear-out mechanisms and to obtain activation energy of solder bond degradation, here two field-aged modules from Arizona-a 21-year-old Solarex MSX60 module (with Sn62Pb36Ag2 at the solder joints) and an 18-year-old Siemens M55 module (with Sn60Pb40 at the solder joints)-underwent 800 and 400 modified thermal cycles, respectively. Using three heating blankets, each module had three temperature zones maintained at 85, 95, and 105 °C during the 15-min hot dwell time of the thermal cycle. Cell-level series resistance data obtained from three temperature zones enabled the calculation of activation energy for solder bond degradation for the MSX60 and the M55 modules to be 0.12 eV and 0.35 eV, respectively. From each temperature zone in both modules, busbar-solder samples were obtained, imaged through SEM, and analyzed with energy-dispersive X-ray spectroscopy. In the MSX60 module with traces of Ag in the solder material, phase segregation and growth were primarily observed at high temperatures. For M55 modules without Ag in the solder material, major phase segregation was observed in all temperature zones. The IMC thickness for both modules increased with increasing module temperature. The beneficial effect of Ag in solder material on mitigating solder bond degradation is presented.

14 SOLAR ENERGY↗
DOE OSTI2021

Heavily Tungsten–Doped Sodium Thioantimonate Solid–State Electrolytes with Exceptionally Low Activation Energy for Ionic Diffusion

A strategy for modifying the structure of solid-state electrolytes (SSEs) to reduce the cation diffusion activation energy is presented. Two heavily W-doped sodium thioantimonate SSEs, Na 2.895 W 0.3 Sb 0.7 S 4 and Na 2.7 W 0.3 Sb 0.7 S 4 are designed, both exhibiting exceptionally low activation energy and enhanced room temperature (RT) ionic conductivity; 0.09 eV, 24.2 mS/cm and 0.12 eV, 14.5 mS/cm. At –15 °C the Na 2.895 W 0.3 Sb 0.7 S 4 displays a total ionic conductivity of 5.5 mS/cm. Here, the 30 % W content goes far beyond the 10–12 % reported in the prior studies, and results in novel pseudo-cubic or orthorhombic structures. Calculations reveal that these properties result from a combination of multiple diffusion mechanisms, including vacancy defects, strongly correlated modes and excessive Na-ions. An all-solid-state battery (ASSB) using Na 2.895 W 0.3 Sb 0.7 S 4 as the primary SSE and a sodium sulfide (Na 2 S) cathode achieves a reversible capacity of 400 mAh g –1 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Heavily Tungsten-Doped Sodium Thioantimonate Solid-State Electrolytes with Exceptionally Low Activation Energy for Ionic Diffusion

A strategy for modifying the structure of solid-state electrolytes (SSEs) to reduce the cation diffusion activation energy is presented. Two heavily W-doped sodium thioantimonate SSEs, Na 2.895 W 0.3 Sb 0.7 S 4 and Na 2.7 W 0.3 Sb 0.7 S 4 are designed, both exhibiting exceptionally low activation energy and enhanced room temperature (RT) ionic conductivity; 0.09 eV, 24.2 mS/cm and 0.12 eV, 14.5 mS/cm. At –15 °C the Na 2.895 W 0.3 Sb 0.7 S 4 displays a total ionic conductivity of 5.5 mS/cm. The 30 % W content goes far beyond the 10–12 % reported in the prior studies, and results in novel pseudo-cubic or orthorhombic structures. Here, calculations reveal that these properties result from a combination of multiple diffusion mechanisms, including vacancy defects, strongly correlated modes and excessive Na-ions. An all-solid-state battery (ASSB) using Na 2.895 W 0.3 Sb 0.7 S 4 as the primary SSE and a sodium sulfide (Na 2 S) cathode achieves a reversible capacity of 400 mAh g –1 .

sodium metal battery (SMB)↗
DOE OSTI2017

Apparent activation energy for hydrogen permeation and its relation to the composition of homogeneous PdAu alloy thin-film membranes

PdAu alloy composite membranes are often fabricated by sequential electroless plating of Pd and Au, but this forms a layered structure that must be annealed to form a homogenous alloy. Using ex situ analysis techniques such as X-ray diffraction (XRD) or energy dispersive X-ray spectroscopy (EDS) to judge the extent of homogenization can be time-consuming as the composite membranes must be cooled to ambient temperatures prior to analysis. However, an in situ alternative is to use the apparent activation energy for H 2 permeation (E act ). Here in this work, 27 – 41 wt% Au films were fabricated to expand upon a range of 0 – 21 wt% that has been previously reported. Homogenization (confirmed by XRD and EDS) was achieved by heat treatment in 3 MPa H 2 at 550 °C for up to 120 h. The apparent E act was found to initially decrease with increasing Au composition from 12.2 kJ mol -1 (pure Pd) to 7.5 kJ mol -1 (21 wt% Au) after which it slowly increased to 9.0 kJ mol -1 (41 wt% Au). The two distinct regimes can be explained using the relation E act = ΔH H + E D , wherein E act is the sum of the partial enthalpy of solution of H into the PdAu alloy (ΔH H ) and the activation energy for diffusion of H in the alloy (E D ). Essentially, the two components of E act have opposite signs that counteract each other and cause a non-linear trend with increasing Au compositions.

42 ENGINEERING↗
DOE OSTI2015

Effect of the Electric Double Layer on the Activation Energy of Ion Transport in Conical Nanopores

Measured apparent activation energies, $E_A$, of ion transport (K + and Cl – ) in conical glass nanopores are reported as a function of applied voltage (-0.5 to 0.5 V), pore size (20–2000 nm), and electrolyte concentration (0.1–50 mM). $E_A$ values for transport within an electrically charged conical glass nanopore differ from the bulk values due to the voltage and temperature-dependent distribution of the ions within the double layer. Remarkably, nanopores that display ion current rectification also display a large decrease in $E_A$ under accumulation mode conditions (at applied negative voltages versus an external ground) and a large increase in $E_A$ under depletion mode conditions (at positive voltages). Finite element simulations based on the Poisson–Nernst–Planck model semiquantitatively predict the measured temperature-dependent conductivity and dependence of $E_A$ on applied voltage. The results highlight the relationships between the distribution of ions with the nanopore, ionic current, and $E_A$ and their dependencies on pore size, temperature, ion concentration, and applied voltage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗