Decomposition Kinetics of Tetraethoxysilane on SiO2

1992 ◽  
Vol 282 ◽  
Author(s):  
Bradley G. Todd ◽  
John B. Hudson ◽  
Peter K-C. Wu
Keyword(s):  
Time Of Flight ◽  
Initial Step ◽  
Sample Surface ◽  
Molecular Beam Scattering ◽  
Surface Time ◽  
Beam Scattering ◽  
Product Species ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Flight Measurements

ABSTRACTThe decomposition of tetraethoxysilane (TEOS) on a thermally grown SiO2 surface has been studied using molecular beam scattering, with mass spectrometric detection and time of flight techniques. Decomposition was characterized over a range of temperatures from ambient to 1100 K using a mass spectrometer having a line of sight to the sample surface. Time of flight measurements were used to characterize parent and product species and to determine surface residence time. The initial step in the decomposition process at low temperatures is the loss of one ethoxy ligand to produce triethoxysilane, ethylene and possibly water as gas phase products. At temperatures above 850 K there is a change in the rate limiting process and an abrupt increase in the decomposition probability. Observed kinetics are explained in terms or an adsorbed molecular precursor mechanism.

High field 1H NMR Studies of Sol-Gel Kinetics

1986 ◽  
Vol 73 ◽  
Author(s):  
Bruce D. Kay ◽  
Roger A. Assink
Keyword(s):  
Equilibrium Distribution ◽  
Sol Gel ◽  
Nmr Studies ◽  
H Nmr ◽  
Rate Limiting Step ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Product Species ◽  
Rate Limiting ◽  
Kinetics Of

ABSTRACTHigh resolution 1H NMR spectroscopy at high magnetic fields is employed to study the reaction kinetics of the Si(OCH3)4:CH3OH:H2O sol-gel system. Both the overall extent of reaction as a function of time and the equilibrium distribution of species are measured. In acid catalyzed solution, condensation is the rate limiting step while in base catalyzed solution, hydrolysis becomes rate limiting. A kinetic model in which the rate of hydrolysis is assumed to be independent of the adjacent functional groups is presented. This model correctly predicts the distribution of product species during the initial stages of the sol-gel reaction.

Effect of degradation kinetics on the microstructure of anaerobic biogranules

1995 ◽  
Vol 32 (8) ◽  
pp. 165-172 ◽  
Author(s):  
Herbert H. P. Fang ◽  
Chui Ho-Kwong ◽  
Li Yu-You
Keyword(s):  
Degradation Kinetics ◽  
Monosodium Glutamate ◽  
Initial Step ◽  
Upflow Anaerobic Sludge Blanket ◽  
Anaerobic Sludge ◽  
Electron Microscopies ◽  
Subsequent Degradation ◽  
Anaerobic Sludge Blanket ◽  
Rate Limiting ◽  
Kinetics Of

The microstructure of anaerobic biogranules treating a wide variety of wastewaters was investigated using light and scanning electron microscopies. Biogranules were sampled from upflow anaerobic sludge blanket (UASB) reactors treating wastewater individually containing formate, acetate, propionate, butyrate, peptone, sucrose, starch, benzoate, brewery and monosodium glutamate. Results indicated that the microstructure of the biogranules was strongly dependent on the degradation kinetics of substrates. Anaerobic degradation is a multi-step process, involving fermentation/acidogenesis, acetogenesis and methanogenesis. For substrates, such as carbohydrates, of which the initial step of degradation was considerably faster than the subsequent degradation of intermediates, biogranules developed a layered microstructure. On the other hand, for substrates, such as proteins, of which the initial step of degradation was rate-limiting, a uniform microstructure would be developed. These findings are of significance for the development of kinetic models for biogranule and biofilm.

Gaas Etching by C12 and HCI: Ga- vs. As- Limited Etching

1993 ◽  
Vol 334 ◽  
Author(s):  
Chaochin Su ◽  
Zi-Guo Dai ◽  
Hui-Qi Hou ◽  
Ming Xi ◽  
Matthew F. Vernon ◽  
...  
Keyword(s):  
Surface Analysis ◽  
Room Temperature ◽  
Molecular Beam ◽  
Molecular Beam Scattering ◽  
Analysis Techniques ◽  
Surface Analysis Techniques ◽  
Beam Scattering ◽  
Two Systems ◽  
Measurable Rate ◽  
Kinetics Of

AbstractResults in the literature indicate that C12 etches GaAs at room temperature but HCl etches GaAs at a measurable rate only at temperatures above ∼670 K. In this work, molecular beam scattering and surface analysis techniques have been applied to address the fundamental kinetic differences between these two systems. The results indicate that the onset of GaAs etching by C12 is determined by the kinetics of Ga-removal as GaC13 while etching by HCl is limited by As evaporation as As2. The results also suggest that HCl selectively etches gallium from GaAs at temperatures between 600 and 650 K.

Angle Resolved Time-of-Flight Measurements of the Excimer Laser Induced Etching of Silicon in a Chlorine Environment

1988 ◽  
Vol 129 ◽  
Author(s):  
T.S. Baller ◽  
J. van Zwol ◽  
S.T. de Zwart ◽  
G.N.A. van Veen ◽  
H. Fell ◽  
...  
Keyword(s):  
Gas Phase ◽  
Excimer Laser ◽  
Time Of Flight ◽  
Laser Pulses ◽  
Angular Distributions ◽  
Desorption Process ◽  
Surface Time ◽  
The Mean ◽  
Laser Induced Etching ◽  
Flight Measurements

ABSTRACTSi (100) samples have been irradiated with excimer laser pulses (λ = 308nm, pulsewidth =28ns) in a low pressure chlorine environment, at a fluence just enough to melt the surface. Time-of-flight spectra of the particles desorbed due to the laser irradiation have been measured as a function of effective chlorine pressure and desorption angle. Maxwell- Boltzmann distributions have been used to fit the measurements. The mean kinetic energy per particle increases with increasing chlorine pressure. Angular distributions of the desorbed particles are found to be cosine like at a chlorine coverage much less than a monolayer and sharply peaked along the surface normal at coverages on the order of a monolayer. Monte-Carlo simulations of the desorption process show that due to collisions between the desorbed particles the change in angular distribution can be explained. The increase in mean energy with increasing chlorine coverage however cannot be explained by gas phase collisions. A possible desorption process is suggested.

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Kinetics and mechanism of cyclization of N-(2-methoxycarbonylphenyl)-N’-methylsulphonamide to 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide

1991 ◽  
Vol 56 (8) ◽  
pp. 1701-1710 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Potassium Hydroxide ◽  
Acid Catalysis ◽  
Potassium Hydroxide Solution ◽  
Hydroxide Solution ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Cyclization Kinetics ◽  
Rate Limiting ◽  
Kinetics Of

The cyclization kinetics of N-(2-methylcarbonylphenyl)-N’-methylsulfonamide (IIb) into 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (Ib) has been studied in ethanolamine, morpholine, and butylamine buffers and in potassium hydroxide solution. The cyclization is subject to general base and general acid catalysis. The value of the Bronsted coefficient β is about 0.1, which indicates that splitting off of the proton from negatively charged tetrahedral intermediate represents the rate-limiting and thermodynamically favourable step. In the solutions of potassium hydroxide the cyclization of dianion of the starting ester IIb probably becomes the rate-limiting step.

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