Kinetics of Reactions Between Silica and Carbon and the Formation of Silicon Carbide

1995 ◽  
Vol 410 ◽  
Author(s):  
Kjell Wiik ◽  
Ketil Motzfeldt
Keyword(s):  
Silicon Carbide ◽  
Reaction Mechanism ◽  
Partial Pressure ◽  
Diffusion Path ◽  
Reaction Rates ◽  
Coarse Grained ◽  
Continuous Formation ◽  
Thermogravimetric Investigation ◽  
Kinetics Of

ABSTRACTThe reactions taking place between coarse grained mixtures of silica (cristobalite) and carbon (graphite) at 1558°C in pure CO as well as mixtures of CO and Ar, have been subjected to a thermogravimetric investigation. A model is developed in the regime where the formation of SiC does not take place. The primary steps are assumed to be: Reaction betweefn SiO2 and CO to give SiO(g) and CO2 followed by the reaction between CO2 and C to give CO. The model predicts the prevailing partial pressure of SiO throughout the charge, and the correlation between observations and model strongly supports the above given reaction mechanism.Enhanced and accelerating reaction rates were observed when the formation of β-SiC took place. It is suggested that this is due to the continuous formation of stable SiC-nucleus on the Csurface and the subsequent shortening of the diffusion path for SiO.

KINETICS OF THE CUPRIC ACETATE CATALYZED HYDROGENATION OF DICHROMATE IN AQUEOUS SOLUTION

1955 ◽  
Vol 33 (2) ◽  
pp. 356-364 ◽  
Author(s):  
E. Peters ◽  
J. Halpern
Keyword(s):  
Activation Energy ◽  
Aqueous Solution ◽  
Partial Pressure ◽  
Kinetic Study ◽  
Reaction Rates ◽  
Homogeneous Catalyst ◽  
Cupric Acetate ◽  
Partial Pressures ◽  
Kinetics Of

In aqueous solution, cupric acetate was found to act as a homogeneous catalyst for the reduction of dichromate by hydrogen, i.e.[Formula: see text] The paper describes a kinetic study of this reaction. Rates were determined at temperatures between 80° and 140 °C. and hydrogen partial pressures up to 27 atmospheres. The rate is independent of the dichromate concentration but varies directly with the partial pressure of hydrogen and is nearly proportional to the concentration of cupric acetate. The activation energy is 24,600 calories per mole. Cupric acetate, apparently acting as a true catalyst, activates the hydrogen through formation of a complex with it. An extension of the mechanism proposed earlier for the reaction of cupric acetate itself with hydrogen also accounts for the kinetics of the dichromate reaction.

Reactions of ethyl 2-alkyl-3-oxobutanoate with thiourea and methylthiourea

1983 ◽  
Vol 48 (7) ◽  
pp. 1872-1877 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Vojeslav Štěrba
Keyword(s):  
Reaction Mechanism ◽  
Dissociation Constants ◽  
Reaction Rates ◽  
Medium Effects ◽  
Alkyl Derivatives ◽  
Alkyl Groups ◽  
Independent Synthesis ◽  
Kinetics Of ◽  
Derivatives Of

The reaction of ethyl 3-oxobutanoate with N-methylthiourea in alkoxide medium gives a mixture (1 : 20) of 1,6-dimethyl-2-thiouracil and 3,6-dimethyl-2-thiouracil: the latter isomer has been isolated from the mixture and the former isomer has been prepared by independent synthesis. Dissociation constants of ethyl 2-alkyl-3-oxobutanoates (alkyl = methyl, butyl, or isopropyl) have been measured in methanol. Reaction of these esters with thiourea and N-methylthiourea gives the corresponding alkyl derivatives of 6-methyl-2-thiouracil. Kinetics of these reactions have been measured in methoxide medium. Effects of the alkyl groups on the reaction rates have been investigated, and a reaction mechanism is suggested.

scholarly journals Kinetics and mechanism of As2S2 oxidation

2005 ◽  
Vol 70 (6) ◽  
pp. 869-877 ◽  
Author(s):  
Ivan Mihajlovic ◽  
Nada Strbac ◽  
Zivan Zivkovic ◽  
Ilija Ilic
Keyword(s):  
Activation Energy ◽  
Thermal Analysis ◽  
Reaction Mechanism ◽  
Kinetic Equation ◽  
Chemical Transformation ◽  
Chemical Reaction ◽  
Reaction Rates ◽  
Fast Reaction ◽  
Isothermal Conditions ◽  
Kinetics Of

The kinetics of realgar (As2S2) oxidation was studied under isothermal and non-isothermal conditions. The obtained values of the activation energy indicate that the process occurs in the kinetic domainwith the realgar particles being converted to As2O3 and As4O6 (g). The very fast reaction rates were limited by the chemical reaction. The kinetic equation was found to be: ?ln (1??) = 4.56 x 103 x e(?8780/T) x t. The proposed reaction mechanism and chemical transformation investigated by ICP?AES, EDXRF and thermal analysis are discussed.

Irradiation behavior of pyrolytic silicon carbide

1983 ◽  
Vol 41 ◽  
pp. 72-73
Author(s):  
R. J. Lauf
Keyword(s):  
Silicon Carbide ◽  
Fission Products ◽  
Thermodynamics And Kinetics ◽  
Neutron Fluences ◽  
Fuel Particles ◽  
Sic Coatings ◽  
Irradiation Behavior ◽  
Kinetics Of ◽  
Htgr Fuel

Fuel particles for the High-Temperature Gas-Cooled Reactor (HTGR) contain a layer of pyrolytic silicon carbide to act as a miniature pressure vessel and primary fission product barrier. Optimization of the SiC with respect to fuel performance involves four areas of study: (a) characterization of as-deposited SiC coatings; (b) thermodynamics and kinetics of chemical reactions between SiC and fission products; (c) irradiation behavior of SiC in the absence of fission products; and (d) combined effects of irradiation and fission products. This paper reports the behavior of SiC deposited on inert microspheres and irradiated to fast neutron fluences typical of HTGR fuel at end-of-life.

Effect of H2O Partial Pressure on Reduction Kinetics of Iron-Based Fischer-Tropsch Catalyst

2010 ◽  
Vol 31 (2) ◽  
pp. 205-212
Author(s):  
Hong WANG ◽  
Yong YANG ◽  
Baoshan WU ◽  
Jian XU ◽  
Hulin WANG ◽  
...  
Keyword(s):  
Partial Pressure ◽  
Reduction Kinetics ◽  
Fischer Tropsch ◽  
Iron Based ◽  
Kinetics Of

Kinetics of esterification of monoisopropylphenols with phosphoryl trichloride

1989 ◽  
Vol 54 (5) ◽  
pp. 1311-1317
Author(s):  
Miroslav Magura ◽  
Ján Vojtko ◽  
Ján Ilavský
Keyword(s):  
Liquid Phase ◽  
Rate Constants ◽  
Reaction Rates ◽  
Activation Energies ◽  
The Individual ◽  
Kinetics Of

The kinetics of liquid-phase isothermal esterification of POCl3 with 2-isopropylphenol and 4-isopropylphenol have been studied within the temperature intervals of 110 to 130 and 90 to 110 °C, respectively. The rate constants and activation energies of the individual steps of this three-step reaction have been calculated from the values measured. The reaction rates of the two isomers markedly differ: at 110 °C 4-isopropylphenol reacts faster by the factors of about 7 and 20 for k1 and k3, respectively. This finding can be utilized in preparation of mixed triaryl phosphates, since the alkylation mixture after reaction of phenol with propene contains an excess of 2-isopropylphenol over 4-isopropylphenol.

Reordering and Crystallization of Silicon Carbide Amorphized by Neutron Irradiation

2000 ◽  
Vol 650 ◽  
Author(s):  
Lance L. Snead ◽  
Martin Balden
Keyword(s):  
Thin Film ◽  
Silicon Carbide ◽  
Crystallization Kinetics ◽  
Neutron Irradiation ◽  
Onset Temperature ◽  
Kinetics Of Crystallization ◽  
Crystallization Onset Temperature ◽  
Crystallization Onset ◽  
Kinetics Of

ABSTRACTDensification and crystallization kinetics of bulk SiC amorphized by neutron irradiation is studied. The temperature of crystallization onset of this highly pure, fully amorphous bulk SiC was found to be between 875-885°C and crystallization is nearly complete by 950°C. In-situ TEM imaging confirms the onset of crystallization, though thin-film effects apparently alter the kinetics of crystallization above this temperature. It requires >1125°C for complete crystallization of the TEM foil. Annealing at temperatures between the irradiation and crystallization onset temperature is seen to cause significant densification attributed to a relaxation, or reordering, of the as-amorphized structure.

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