Graphitization of diamond at zero pressure and at a high pressure

1972 ◽  
Vol 328 (1574) ◽  
pp. 413-427 ◽  
Keyword(s):  
High Pressure ◽  
Activation Volume ◽  
Activation Energies ◽  
Single Atom ◽  
Diamond Surface ◽  
Temperature Range ◽  
Natural Diamonds ◽  
Rate Controlling Step

Natural diamonds have been heated in the temperature range of 1850 to 2000 °C at zero pressure and the rates at which diamond transforms to graphite measured. For {111} and {110} surfaces activation energies of 253+18 and 174+12 kcal mol -1 (1159 + 75 and 728 + 50 kJ/mol) respectively have been obtained. Diamonds have also been heated in the temperature range of 1950 to 2200 °C under a pressure of 48 + 3 kbar (4.8 + 0.3 GPa) and an activation volume of about 10 cm 3 mol -1 obtained for both {111} and {110} surfaces. It is proposed that the rate controlling process in the graphitization of diamond is the detachment of a single atom from the diamond surface. This is contrary to previous proposals in which the detachment of groups of atoms have been considered to be the rate-controlling process. In the present work, it is suggested that the rate-controlling step for graphitization is the detachment of a triply bonded atom from a {111} surface and of a doubly bonded atom from a {110} surface.

scholarly journals Incipient stages of transformation of round natural diamonds under dissolution in Fe-S melt at high pressure

LITOSFERA ◽  
2020 ◽  
Vol 19 (6) ◽  
pp. 945-952
Author(s):  
V. M. Sonin ◽  
E. I. Zhimulev ◽  
A. A. Chepurov ◽  
B. S. Pomazanskiy ◽  
V. P. Afanasiev ◽  
...  
Keyword(s):  
High Pressure ◽  
Solid Phase ◽  
Natural Diamond ◽  
Sulphur Content ◽  
Diamond Surface ◽  
Minor Role ◽  
Cylindrical Shape ◽  
Natural Diamonds ◽  
Diamond Crystals ◽  
Kimberlite Magma

Research subject. The article presents the results of a microscopic and photogoniometric study of natural rounded diamonds of tetraghexahedral habit from the kimberlite pipe “Internationalnaya” (Yakutia). The diamonds was partially dissolved in a sulphur-containing iron melt (sulphur content of 15–30 wt %) at 4.5 GPa and 1450ºС.Methods. The experiments were carried out on a multi-puncheon apparatus of a “split-sphere” type in high-pressure solid-phase cells made of refractory oxides ZrO2, CaO, MgO using a cylindrical shape graphite heater. The crystals were studied using an MBS-10 optical microscope with a photo camera, and a Jeol JSM-6510LV scanning electron microscope. A goniometric study of diamond crystals was carried out by a photo method in a cylindrical chamber. It was found that when a sulphur content was 15 wt %, diamond crystals of tetrahexahedral habit were transformed into a curved shaped octahedroids with morphological features similar to natural diamonds found in kimberlites. When the sulphur content was 23–30 wt %, the rate of dissolution of diamonds in the Fe-S melt sharply reduced, while the diamond surface at the micro level became covered with numerous etching hillocks, whose sidewalls have surfaces similar to flat-faced {111} form. Dissolution of the rounded diamonds in the Fe-S melt at high pressure occurred by a “normal” mechanism, that is perpendicular to the surface of the dissolving crystal through trigonal dissolution layers, while a tangential-layered mechanism played a minor role.Conclusion. The natural diamond crystals could underwent dissolution in the mantle before they were captured by kimberlite magma. Two fundamentally different types of homomorphic and typomorphic features of the dissolution forms observed on natural diamonds can be determined, namely: on one side, those associated with storage in mantle before the crystals were captured by the kimberlite magma, and on the other side, with the kimberlite process itself. The presence of octahedral diamonds with parallel (trigonal) striation in kimberlite deposits may indicate on a high degree of diamond preservation due to relatively insignificant effect of the kimberlite magma. This, undoubtedly, should help to decipher the diamond genesis and, possibly, improve the mineralogical criteria used in diamond exploration. 

scholarly journals High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 581
Author(s):  
Abdulhakim A. Almajid
Keyword(s):  
Activation Energy ◽  
Aluminum Alloy ◽  
High Temperature ◽  
Threshold Stress ◽  
Activation Energies ◽  
Temperature Deformation ◽  
High Temperature Range ◽  
Temperature Range ◽  
True Activation Energy ◽  
Two Temperatures

This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are existed in the alloy at the testing temperatures. The threshold stress decreases in an exponential manner as temperature increases. The true activation energy was computed by incorporating the threshold stress in the power-law relation between the stress and the strain. The magnitude of the true activation energy, Qt dropped to 234 and 102 kJ/mol at the low and high-temperature range, respectively. These values are close to that of diffusion of Zinc in Aluminum and diffusion of Magnesium in Aluminum, respectively. The Zener–Hollomon parameter for the alloy was developed as a function of effective stress. The data in each region (low and high-temperature region) coalescence in a segment line in each region.

scholarly journals Effect of Nitrogen on the Growth of (100)-, (110)-, and (111)-Oriented Diamond Films

2020 ◽  
Vol 11 (1) ◽  
pp. 126
Author(s):  
Jen-Chuan Tung ◽  
Tsung-Che Li ◽  
Yen-Jui Teseng ◽  
Po-Liang Liu
Keyword(s):  
Growth Mechanism ◽  
Density Functional ◽  
Film Growth ◽  
Hydrogen Abstraction ◽  
Diamond Films ◽  
Activation Energies ◽  
Diamond Surface ◽  
Nitrogen Doped ◽  
Nitrogen Substitution ◽  
Diamond Film Growth

The aim of this research is the study of hydrogen abstraction reactions and methyl adsorption reactions on the surfaces of (100), (110), and (111) oriented nitrogen-doped diamond through first-principles density-functional calculations. The three steps of the growth mechanism for diamond thin films are hydrogen abstraction from the diamond surface, methyl adsorption on the diamond surface, and hydrogen abstraction from the methylated diamond surface. The activation energies for hydrogen abstraction from the surface of nitrogen-undoped and nitrogen-doped diamond (111) films were −0.64 and −2.95 eV, respectively. The results revealed that nitrogen substitution was beneficial for hydrogen abstraction and the subsequent adsorption of methyl molecules on the diamond (111) surface. The adsorption energy for methyl molecules on the diamond surface was generated during the growth of (100)-, (110)-, and (111)-oriented diamond films. Compared with nitrogen-doped diamond (100) films, adsorption energies for methyl molecule adsorption were by 0.14 and 0.69 eV higher for diamond (111) and (110) films, respectively. Moreover, compared with methylated diamond (100), the activation energies for hydrogen abstraction were by 0.36 and 1.25 eV higher from the surfaces of diamond (111) and (110), respectively. Growth mechanism simulations confirmed that nitrogen-doped diamond (100) films were preferred, which was in agreement with the experimental and theoretical observations of diamond film growth.

Wide-Temperature-Range Dielectric Permittivity Measurement under High Pressure

2017 ◽  
Vol 34 (4) ◽  
pp. 040701
Author(s):  
Zhen Yuan ◽  
Jin-Long Zhu ◽  
Shao-Min Feng ◽  
Chang-Chun Wang ◽  
Li-Juan Wang ◽  
...  
Keyword(s):  
High Pressure ◽  
Dielectric Permittivity ◽  
Wide Temperature Range ◽  
Temperature Range ◽  
Permittivity Measurement

scholarly journals High-Pressure Inactivation of Hepatitis A Virus within Oysters

2005 ◽  
Vol 71 (1) ◽  
pp. 339-343 ◽  
Author(s):  
Kevin R. Calci ◽  
Gloria K. Meade ◽  
Robert C. Tezloff ◽  
David H. Kingsley
Keyword(s):  
High Pressure ◽  
Hydrostatic Pressure ◽  
High Hydrostatic Pressure ◽  
Hepatitis A ◽  
Hepatitis A Virus ◽  
Natural Conditions ◽  
Direct Evaluation ◽  
Temperature Range

ABSTRACT Previous results demonstrated that hepatitis A virus (HAV) could be inactivated by high hydrostatic pressure (HHP) (D. H. Kingsley, D. Hoover, E. Papafragkou, and G. P. Richards, J. Food Prot. 65:1605-1609, 2002); however, direct evaluation of HAV inactivation within contaminated oysters was not performed. In this study, we report confirmation that HAV within contaminated shellfish is inactivated by HHP. Shellfish were initially contaminated with HAV by using a flowthrough system. PFU reductions of >1, >2, and >3 log10 were observed for 1-min treatments at 350, 375, and 400 megapascals, respectively, within a temperature range of 8.7 to 10.3�C. Bioconcentration of nearly 6 log10 PFU of HAV per oyster was achieved under simulated natural conditions. These results suggest that HHP treatment of raw shellfish will be a viable strategy for the reduction of infectious HAV.

Untersuchungen zur Reaktion der Alkoholdehydrogenase mit Tritium-markierten Substraten

1966 ◽  
Vol 21 (6) ◽  
pp. 540-546 ◽  
Author(s):  
Dieter Palm
Keyword(s):  
Alcohol Dehydrogenase ◽  
Temperature Dependence ◽  
Isotope Effect ◽  
Substrate Binding ◽  
Isotope Effects ◽  
Direct Interaction ◽  
Enzyme Complex ◽  
Temperature Range ◽  
Yeast Alcohol Dehydrogenase ◽  
Rate Controlling Step

Unexpectedly, the isotope effect of ethanol-1-Τ as a substrate of yeast alcohol dehydrogenase, increases with rising temperature from kH/kT = 3.2 at 5 —15°C to 3.8—4.7 at 20 —35 °C. This suggests a change of the rate controlling step as proposed by MÜLLER-HILL and WALLENFELS, who investigated the temperature dependence of the activation energies in this temperature range. A comparison of the affinities of propanol and butanol with the isotope effects of the corresponding tritium labelled compounds (propanol-1-Τ 6.7 at 25 °C, butanol-1-Τ 6.8 at 25 °C) supports the proposal, that during substrate binding, there must be a direct interaction between the enzyme complex and hydrogen which is removed in the reaction. These influences are less pronounced for the ethanol homologues which are bound less tightly to the enzyme. Therefore the H transfering step proper gives a greater contribution to the overall experimental isotope effect.

Free Activation Energies and Activation Volumes for the Amide Rotation in Some Peptides Studied by High Pressure 1H-High Resolution NMR

1982 ◽  
Vol 37 (1-2) ◽  
pp. 51-56 ◽  
Author(s):  
H. Hauer ◽  
H.-D. Lüdemann ◽  
R. Jaenicke
Keyword(s):  
High Pressure ◽  
High Resolution ◽  
Pressure Dependence ◽  
Nmr Spectra ◽  
Conformational Transition ◽  
Activation Energies ◽  
High Resolution Nmr ◽  
Maximum Contribution ◽  
The Given ◽  
Amide Rotation

From the pressure dependence of 1H high resolution NMR spectra of two dipeptides (glycylsarcosine and N-acetyl-ʟ-proline-NH-methylamide in the range 0.1 MPa ≤p ≤ 150 MPa the activation volumes ⊿V≠ for the amide rotation are derived. This conformational transition is characterized for glycylsarcosine by ⊿V≠ = 4 ± 1 cm3 · mol-1 and for. the proline derivative by ⊿V≠ = 7.5±1 cm3 · mol-1. From the given results the maximum contribution of proline cis ⇌ trans isomerisation to the pressure dependence of the rate of reactivation of proteins can be estimated to ~ - 30% per MPa and proline present.

Reactions of trifluoromethyl radicals. V. Hydrogen abstraction from methyl acetate and methyl (2H3)Acetate

1980 ◽  
Vol 33 (7) ◽  
pp. 1437
Author(s):  
NL Arthur ◽  
PJ Newitt
Keyword(s):  
Isotope Effect ◽  
Rate Constants ◽  
Methoxy Group ◽  
Methyl Acetate ◽  
Kinetic Isotope Effect ◽  
Hydrogen Abstraction ◽  
Activation Energies ◽  
Temperature Range ◽  
Kinetic Isotope ◽  
Acetyl Group

Hydrogen abstraction by CF3 radicals from CH3COOCH3 and CD3COOCH3 has been studied in the temperature range 78-242°, and data have been obtained for the reactions: CF3 + CH3COOCH3 → CF3H+[C3H5O2] �������������(3) CF3 + CH3COOCH3 → CF3H+CH2COOCH3������������ (4) CF3 + CD3COOCH3 → CF3D+CD2COOCH3������������ (6) CF3 + CD3COOCH3 → CF3H+CD3COOCH2������������ (7) The corresponding rate constants, based on the value of 1013.36 cm3 mol-1 S-1 for the recombination of CF3 radicals, are given by (k in cm3 mol-1 s-1 and E in J mol-1): logk3 = (11.52�0.05)-(35430�380)/19.145T ���� (3)logk4 = (11.19�0.07)-(34680�550)/19.145T ���� (4)logk6 = (11.34�0.06)-(46490�490)/19.145T ���� (6)logk7 = (11.26�0.05)-(36440�400)/19.145T ���� (7)At 400 K, 59% of abstraction occurs from the acetyl group, and 41 % from the methoxy group. The kinetic isotope effect at 400 K for attack on the acetyl group is 25, due mainly to a difference in activation energies.

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