The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Michael Moseler - One of the best experts on this subject based on the ideXlab platform.
-
Mechano-Chemical Decomposition of organic friction modifiers with multiple reactive centres induces superlubricity of ta-C
Nature Communications, 2019Co-Authors: Takuya Kuwahara, Stefan Makowski, Gianpietro Moras, Volker Weihnacht, Pedro A. Romero, Michael MoselerAbstract:Superlubricity of tetrahedral amorphous carbon (ta-C) coatings under boundary lubrication with organic friction modifiers is important for industrial applications, but the underlying mechanisms remain elusive. Here, combined experiments and simulations unveil a universal triboChemical mechanism leading to superlubricity of ta-C/ta-C tribopairs. Pin-on-disc sliding experiments show that ultra- and superlow friction with negligible wear can be achieved by lubrication with unsaturated fatty acids or glycerol, but not with saturated fatty acids and hydrocarbons. Atomistic simulations reveal that, due to the simultaneous presence of two reactive centers (carboxylic group and C=C double bond), unsaturated fatty acids can concurrently chemisorb on both ta-C surfaces and bridge the tribogap. Sliding-induced mechanical strain triggers a cascade of molecular fragmentation reactions releasing passivating hydroxyl, keto, epoxy, hydrogen and olefinic groups. Similarly, glycerol’s three hydroxyl groups react simultaneously with both ta-C surfaces, causing the molecule’s complete mechano-Chemical fragmentation and formation of aromatic passivation layers with superlow friction. The mechanism underlying the superlubricity of tetrahedral amorphous carbon coatings lubricated with organic friction modifiers is still under debate. Here the authors combine experiments and simulations to reveal that superlubricious layers form due the mechano-Chemical Decomposition of friction modifiers.
-
Mechano-Chemical Decomposition of organic friction modifiers with multiple reactive centres induces superlubricity of ta-C
Nature Publishing Group, 2019Co-Authors: Takuya Kuwahara, Stefan Makowski, Gianpietro Moras, Volker Weihnacht, Pedro A. Romero, Michael MoselerAbstract:The mechanism underlying the superlubricity of tetrahedral amorphous carbon coatings lubricated with organic friction modifiers is still under debate. Here the authors combine experiments and simulations to reveal that superlubricious layers form due the mechano-Chemical Decomposition of friction modifiers
Jing Chang - One of the best experts on this subject based on the ideXlab platform.
-
thermal Decomposition of the solid phase of nitromethane ab initio molecular dynamics simulations
Physical Review Letters, 2010Co-Authors: Jing Chang, Peng Lian, Dongqing Wei, Xiangrong Chen, Qingming Zhang, Zizheng GongAbstract:The Car-Parrinello molecular dynamics simulations were employed to investigate thermal Decomposition of the solid nitromethane. It is found that it undergoes Chemical Decomposition at about 2200 K under ambient pressure. The initiation of reactions involves both proton transfer and commonly known C-N bond cleavage. About 75 species and 100 elementary reactions were observed with the final products being H2O, CO2, N2, and CNCNC. It represents the first complete simulation of solid-phase explosive reactions reported to date, which is of far-reaching implication for design and development of new energetic materials.
Mu Pan - One of the best experts on this subject based on the ideXlab platform.
-
ex situ investigation of the proton exchange membrane Chemical Decomposition
International Journal of Hydrogen Energy, 2008Co-Authors: Fang Wang, Haolin Tang, Mu PanAbstract:Abstract The durability of Nafion ® polymer electrolyte membranes (PEMs) with potential application in PEM fuel cells has been investigated using accelerated durability tests to understand their degradation mechanism. After the attack by Fenton radicals, the Nafion ® 111 membranes and the solution produced were collected for analysis. The existence of F ions in the solution indicated the Chemical Decomposition of the Nafion ® membranes during radical attacks. The F - emission rate (FER) was about 0.15 mg h - 1 , corresponding to 0.024 wt% of F released from the membrane per hour. The NMR and FTIR spectrums demonstrated the polymer fragments mostly existed as whole side chains of the Nafion ® membrane. This result revealed that the degradation was originated from the Decomposition of polymer main chain. Furthermore, the reflectance-FTIR revealed that the degradation of the PEMs was from the Decomposition of the repeating units in the polymer main chains. With the increased loss of repeating units, small bubbles with the diameter of several microns started to form in Nafion ® membrane. These bubbles made the membrane vulnerable to hazards of gas crossover, which further led a catastrophic failure of the proton exchange membrane.
Xuerui Cheng - One of the best experts on this subject based on the ideXlab platform.
-
ab initio molecular dynamics study on Chemical Decomposition reaction of α hmx
Chemical Physics Letters, 2020Co-Authors: Shiquan Feng, Feng Guo, Chaosheng Yuan, Xuerui ChengAbstract:Abstract In this work, the ab-initio molecular dynamics simulations were performed to investigate thermal Decomposition reaction of α-HMX. It is found that the initiation of reactions main involves unlooping of C-N rings and NO2 groups detachment from C-N rings for α-HMX molecules at 1800 K. More than 20 species were observed with the main products H2O, CO2, NO, C-H, N-H, C-N groups. Using the atomic tracking method, we discussed the main reaction path of thermal Decomposition process for α-HMX. This work has an important significant for revealing the reaction mechanism of α-HMX.
Blaine W. Asay - One of the best experts on this subject based on the ideXlab platform.
-
the evolution of solid density within a thermal explosion i proton radiography of pre ignition expansion material motion and Chemical Decomposition
Journal of Applied Physics, 2012Co-Authors: Laura Smilowitz, B F Henson, F E Merrill, G Grim, K. Kwiatkowski, A Saunders, C. L. Morris, Blaine W. Asay, J J Romero, F G MariamAbstract:We report proton transmission images obtained during direct heating of a sample of PBX 9501 (a plastic bonded formulation of the explosive nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)) prior to the ignition of a thermal explosion. We describe the application of proton radiography using the 800 MeV proton accelerator at Los Alamos National Laboratory to obtain transmission images in these thermal explosion experiments. We have obtained images at two spatial magnifications and viewing both the radial and the transverse axes of a solid cylindrical sample encased in aluminum. During heating we observe the slow evolution of proton transmission through the samples, with particular detail during material flow associated with the HMX β-δ phase transition. We also directly observe the loss of solid density to Decomposition associated with elevated temperatures in the volume defining the ignition location in these experiments. We measure a diameter associated with this volume of 1–2 mm, in agree...
-
coupled phase transformation Chemical Decomposition and deformation in plastic bonded explosive models
Journal of Applied Physics, 2007Co-Authors: Valery I Levitas, Laura Smilowitz, B F Henson, David K Zerkle, Blaine W. AsayAbstract:A continuum thermomechanoChemical model of the behavior of a plastic-bonded explosive (PBX) 9501 formulation consisting of the energetic crystal octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) embedded in a polymeric binder is developed. Our main focus is on the study of the β↔δ phase transformations (PTs) in crystalline HMX under a complex pressure-temperature path. To reproduce the pressure-temperature path, in particular during heating of PBX inside of a rigid cylinder, the β↔δ PTs in HMX are coupled to Chemical Decomposition of the HMX and binder leading to gas formation, gas leaking from the cylinder, elastic, thermal, and transformational straining as well as straining due to mass loss. A fully physically based thermodynamic and kinetic model of the β↔δ PT in HMX crystal is developed. It is based on a suggested nucleation mechanism via melt mediated nanocluster transformation and the recently revealed growth mechanism via internal stress-induced virtual melting. During the nucleation, nanosiz...
-
ignition chemistry in hmx from thermal explosion to detonation
Shock Compression of Condensed Matter - 2001: 12th APS Topical Conference, 2002Co-Authors: B F Henson, Laura Smilowitz, Blaine W. Asay, Peter DicksonAbstract:We present a global Chemical Decomposition model for HMX based materials. The model contains three component processes, the initial beta to delta phase transition, solid to gas Decomposition and gas phase ignition, for which all kinetic and thermodynamic parameters are fixed by independent measurement. We present an isothermal ignition calculation over the range of temperatures from thermal explosion to detonation. The calculation is performed for a sphere of material and the critical diameter and time for ignition are determined. The sample diameter, and thus the balance of heat generation and dissipation, is the only degree of freedom in the calculation. The results of the calculation are in good agreement with data with respect to both the ignition times and length scales over the full temperature range of energetic response in HMX.