Topologically Invariant Reaction Coordinates for Simulating Multistate Chemical Reactions

2012 ◽  
Vol 116 (51) ◽  
pp. 14876-14885 ◽  
Author(s):  
Letif Mones ◽  
Gábor Csányi
Keyword(s):  
Chemical Reactions ◽  
Invariant Reaction ◽  
Reaction Coordinates

scholarly journals CHEMICAL REACTIONS IN PROCESSES OF CARBON GASIFICATION

2019 ◽  
Vol 62 (9) ◽  
pp. 705-712
Author(s):  
V. I. Berdnikov ◽  
Yu. A. Gudim
Keyword(s):  
Chemical Reactions ◽  
Chemical Process ◽  
Quantitative Description ◽  
Absolute Error ◽  
Chemical Components ◽  
Reaction Products ◽  
Carbon Gasification ◽  
Reaction Coordinates ◽  
Gasification Process ◽  
Single Chemical

Thermodynamic analysis of carbon gasification process in the presence of moisture was carried out. The chemical process was displayed by the system C – O – H with the ratios of elements in it: 1:1:2 and 1:2: 2. To work out the methods of research and verification of the results, we used a well-studied subsystem C – O. The initial array of processed data was presented by the contents of chemical components C, CO, CO2 , CH4 , H2 and H2O calculated by TERRA program. There is no single chemical reaction in the C – O – H system, so the full operating temperature range of 298 – 1400 K was divided into three characteristic areas, and each of them was analyzed separately. By comparing the numerical values of the components contents at the regions’ boundaries, we determined changes in their values during the transition from one region to another. These values were multiples of stoichiometric coefficients of the expected chemical reactions. Thus, the problem with establishment of the chemical reactions’ type was solved. But two areas of three identified reactions were complex containing more than four components. Therefore, their decomposition was performed on the basis of three more simple and characteristic reactions for these areas. As a result, the total number of reaction varieties was reduced to four – two main reactions of carbon gasification (C + 2Н2О = CO2 + 2Н2, C + CO2 = 2СО) and two reactions of formation and decomposition of methane (2C + 2Н2О = CH4 + CO2 , CH4 = C + 2Н2 ). At the same time, the proportion of each reaction in the total chemical process was determined by the balance coefficients β.The type of chemical reactions provides the necessary information about content of the system components only at the regions’ boundaries. A quantitative assessment of the chemical process within the regions can be obtained by determining the temperature dependence of the reaction coordinates on Gibbs energy of the reactions and the pressure – ξ(Т) = f [ΔrG°(Т), Р]. The coordinates of reactions ξ in combination with the balance coefficients of reactions β allow us to calculate not only the content of reagents and reaction products at any moment of reactions, but also the conditional temperatures of the beginning and end of the reactions themselves. No coefficients and parameters of the fitting character were used in the calculations. The average absolute error of the quantitative description of the results of machine simulation of the system C – O – Н – is less than 0.02 mole (per 1 mole of carbon), and for the subsystem C – O it is almost zero. 

Surface reactions observed by photoemission electron microscopy (PEEM)

1992 ◽  
Vol 50 (1) ◽  
pp. 286-287
Author(s):  
H.H. Rotermund
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Work Function ◽  
Chemical Reactions ◽  
Reaction Diffusion ◽  
Dynamic Processes ◽  
Clean Surface ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Photoemission Electron

Chemical reactions at a surface will in most cases show a measurable influence on the work function of the clean surface. This change of the work function δφ can be used to image the local distributions of the investigated reaction,.if one of the reacting partners is adsorbed at the surface in form of islands of sufficient size (Δ>0.2μm). These can than be visualized via a photoemission electron microscope (PEEM). Changes of φ as low as 2 meV give already a change in the total intensity of a PEEM picture. To achieve reasonable contrast for an image several 10 meV of δφ are needed. Dynamic processes as surface diffusion of CO or O on single crystal surfaces as well as reaction / diffusion fronts have been observed in real time and space.

Microwaves: Application in Electron Microscopy

1990 ◽  
Vol 48 (3) ◽  
pp. 140-141
Author(s):  
Anthony S-Y Leong ◽  
David W Gove
Keyword(s):  
Electron Microscopy ◽  
Light Microscopy ◽  
Chemical Reactions ◽  
Electromagnetic Waves ◽  
Tissue Fixation ◽  
Primary Method ◽  
Dipolar Molecules ◽  
Wide Range ◽  
Time Required ◽  
Cryostat Sections

Microwaves (MW) are electromagnetic waves which are commonly generated at a frequency of 2.45 GHz. When dipolar molecules such as water, the polar side chains of proteins and other molecules with an uneven distribution of electrical charge are exposed to such non-ionizing radiation, they oscillate through 180° at a rate of 2,450 million cycles/s. This rapid kinetic movement results in accelerated chemical reactions and produces instantaneous heat. MWs have recently been applied to a wide range of procedures for light microscopy. MWs generated by domestic ovens have been used as a primary method of tissue fixation, it has been applied to the various stages of tissue processing as well as to a wide variety of staining procedures. This use of MWs has not only resulted in drastic reductions in the time required for tissue fixation, processing and staining, but have also produced better cytologic images in cryostat sections, and more importantly, have resulted in better preservation of cellular antigens.

Fine structure and properties of defects in naturally occurring silicates and oxides

1990 ◽  
Vol 48 (4) ◽  
pp. 460-461
Author(s):  
David R. Veblen
Keyword(s):  
Chemical Reactions ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Single Chain ◽  
Naturally Occurring ◽  
Resolution Electron ◽  
Fine Structures ◽  
Image Simulations ◽  
Similar Crystal Structure

Extended defects and interfaces control many processes in rock-forming minerals, from chemical reactions to rock deformation. In many cases, it is not the average structure of a defect or interface that is most important, but rather the structure of defect terminations or offsets in an interface. One of the major thrusts of high-resolution electron microscopy in the earth sciences has been to identify the role of defect fine structures in reactions and to determine the structures of such features. This paper will review studies using HREM and image simulations to determine the structures of defects in silicate and oxide minerals and present several examples of the role of defects in mineral chemical reactions. In some cases, the geological occurrence can be used to constrain the diffusional properties of defects.The simplest reactions in minerals involve exsolution (precipitation) of one mineral from another with a similar crystal structure, and pyroxenes (single-chain silicates) provide a good example. Although conventional TEM studies have led to a basic understanding of this sort of phase separation in pyroxenes via spinodal decomposition or nucleation and growth, HREM has provided a much more detailed appreciation of the processes involved.

Gum Arabic in Chemical Reactions

1883 ◽  
Vol 15 (366supp) ◽  
pp. 5844-5844
Author(s):  
MM. Jules Lefort ◽  
P. Thibault
Keyword(s):  
Chemical Reactions ◽  
Gum Arabic
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