scholarly journals Gas-Phase Nucleation of Diamond Clusters upon a Sharp Rise in Temperature under Conditions of CVD Synthesis

2021 ◽  
Vol 95 (12) ◽  
pp. 2444-2453
Author(s):  
N. I. Alekseev ◽  
V. S. Khadutin ◽  
I. K. Khmel’nitskii

Abstract It is shown that the predominant nucleation of diamond nuclei (instead of graphite ones) in plasma or hot-filament assisted CVD technology is due to a sharp increase in the temperature of the region of the initial gas mixture’s motion. The nucleation of diamond nuclei then occurs immediately in the gas phase. The reason for such predominant nucleation is high oversaturation by small hydrocarbon fragments in the gas mixture, due to a rapid change in temperature and substantial differences between the desorption of such fragments from the surfaces of nuclei and the oxidation of nuclei. A way is described of synthesizing massive diamonds without the use of high pressures and CVD technology in its traditional form.

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 965
Author(s):  
Zoé Perrin ◽  
Nathalie Carrasco ◽  
Audrey Chatain ◽  
Lora Jovanovic ◽  
Ludovic Vettier ◽  
...  

Titan’s haze is strongly suspected to be an HCN-derived polymer, but despite the first in situ measurements by the ESA-Huygens space probe, its chemical composition and formation process remain largely unknown. To investigate this question, we simulated the atmospheric haze formation process, experimentally. We synthesized analogues of Titan’s haze, named Titan tholins, in an irradiated N2–CH4 gas mixture, mimicking Titan’s upper atmosphere chemistry. HCN was monitored in situ in the gas phase simultaneously with the formation and evolution of the haze particles. We show that HCN is produced as long as the particles are absent, and is then progressively consumed when the particles appear and grow. This work highlights HCN as an effective precursor of Titan’s haze and confirms the HCN-derived polymer nature of the haze.


2021 ◽  
Vol 7 (3) ◽  
pp. eabd9954 ◽  
Author(s):  
Chenxi Li ◽  
Jan Krohn ◽  
Martina Lippe ◽  
Ruth Signorell

Gas phase nucleation is a ubiquitous phenomenon in planetary atmospheres and technical processes, yet our understanding of it is far from complete. In particular, the enhancement of nucleation by the addition of a more volatile, weakly interacting gaseous species to a nucleating vapor has escaped molecular-level experimental investigation. Here, we use a specially designed experiment to directly measure the chemical composition and the concentration of nucleating clusters in various binary CO2-containing vapors. Our analysis suggests that CO2 essentially catalyzes nucleation of the low vapor pressure component through the formation of transient, hetero-molecular clusters and thus provides alternative pathways for nucleation to proceed more efficiently. This work opens up new avenues for the quantitative assessment of nucleation mechanisms involving transient species in multicomponent vapors.


2016 ◽  
Vol 869 ◽  
pp. 721-726 ◽  
Author(s):  
Divani C. Barbosa ◽  
Ursula Andréia Mengui ◽  
Mauricio R. Baldan ◽  
Vladimir J. Trava-Airoldi ◽  
Evaldo José Corat

The effect of argon content upon the growth rate and the properties of diamond thin films grown with different grains sizes are explored. An argon-free and argon-rich gas mixture of methane and hydrogen is used in a hot filament chemical vapor deposition reactor. Characterization of the films is accomplished by scanning electron microscopy, Raman spectroscopy and high-resolution x-ray diffraction. An extensive comparison of the growth rate values and films morphologies obtained in this study with those found in the literature suggests that there are distinct common trends for microcrystalline and nanocrystalline diamond growth, despite a large variation in the gas mixture composition. Included is a discussion of the possible reasons for these observations.


1999 ◽  
Vol 61-62 ◽  
pp. 176-178 ◽  
Author(s):  
A.N Vorob’ev ◽  
A.E Komissarov ◽  
A.S Segal ◽  
Yu.N Makarov ◽  
S.Yu Karpov ◽  
...  

1994 ◽  
Vol 25 (1) ◽  
pp. 15-21 ◽  
Author(s):  
Frank Slootman ◽  
Jean-Claude Parent
Keyword(s):  

2009 ◽  
Vol 48 (11) ◽  
pp. 118003 ◽  
Author(s):  
Sawako Miyamoto ◽  
Toshihiro Shimada ◽  
Manabu Ohtomo ◽  
Akira Chikamatsu ◽  
Tetsuya Hasegawa

Isotherms of Kr and Xe in chabazite have been obtained for absolute sorption and for Gibbs excess sorption, in the temperature range 150 to 450 °C and at pressures up to 100 atm. Thermodynamic equilibrium constants for distribution of gas between the crystals and the gas phase, standard state concentrations and heats of sorption have been determined. At the highest pressures differences between absolute sorption and Gibbs excess sorption were large. The change of equilibrium fugacity with temperature for given absolute and Gibbs excess sorptions yielded two differential heats of sorption and two differential entropies of the sorbate. These heats, and the corresponding entropies, differed numerically and in their dependence upon amount sorbed. The thermodynamic relationship between the two heats has been derived and discussed.


1984 ◽  
Vol 57 (4) ◽  
pp. 1055-1068 ◽  
Author(s):  
J. V. Salzano ◽  
E. M. Camporesi ◽  
B. W. Stolp ◽  
R. E. Moon

Five male volunteers served as subjects for exercise studies during three dives to pressures of 47 and 66 ATA while breathing gases containing 0.5 ATA PO2 and varying amounts of N2 and He. The inspired gas density ranged from 1.1 g/l (BTPS) at the surface to 17.1 g/l at the highest pressure. Dyspnea at rest and during exercise was evident in all divers and was predominantly inspiratory in nature. Despite the dyspnea, divers were able to perform work requiring an O2 consumption larger than 2 l/min STPD at each depth. Compared with surface measurements, moderate work at depth was associated with alveolar hypoventilation, arterial hypercapnia, very large physiological dead space, and higher levels of arterial lactate and signs of simultaneous respiratory and metabolic acidosis. The increase of ventilation that accompanies the onset of acidemia at the surface was not present at depth. Acidemia at depth was more severe, and its onset occurred at lesser work rates than at 1 ATA. No large differences could be ascertained when a variety of responses obtained with inspired gas having a density of 7.9 g/l at 47 ATA were compared with those obtained with an inspired gas density of 17.1 g/l at 66 ATA. It appears that the major impact of the environment on the physiological responses to work was almost fully manifested at a pressure of 47 ATA with a He-O2 gas mixture. It is cautioned that maximum work tolerance may be an insufficient assessment of the physiological condition of a diver exposed to these high pressures.


2017 ◽  
Vol 743 ◽  
pp. 373-377
Author(s):  
Eugenii V. Nikolayev ◽  
Sergey N. Kharlamov ◽  
Laura Meucci

In this paper the features of separation processes modelling are analyzed in hydrocarbonic media within the limits of thermodynamics of equilibrium states. Approaches to calculation of phase equilibrium in multicomponent systems are discussed. Regularities and peculiarities of composition change of gas mixture depending on the temperature and pressure are studied. It has been established that there are specific conditions of non-monotonic change of composition with extremums for some separation regimes that significantly influences the physical properties and intensity of exchange processes at the heat-and mass transfer in multicomponent hydrocarbon media. In addition, the details of the behavior of gas phase with changing its thermal and physical properties have been discussed. Also, the calculated distributions of Prandtl, Schmidt and Lewis-Semenov numbers essentially influencing on the intensity of transport processes are considered.


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