A reexamination of the chemisorption of trimethylaluminum on silica
- Sandia National Lab., Albuquerque, NM (United States)
Fourier transform infrared spectroscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy have been used to study the chemisorption and decomposition of trimethylaluminum (TMA) on silica under high vacuum. By annealing a series of silica substrates from 425 to 1,573 K prior to TMA exposures at 300 K, the authors have examined the distributions of chemisorption products as a function of the relative concentrations of isolated hydroxyls (OH{sub i}), hydrogen-bonded hydroxyls (OH{sub H}), and siloxane bridges. The observed variation in the Si-methyl to Al-methyl population ratios supports a new chemisorption model in which a monomethylaluminum surface complex and methyl groups bonded to silicon are proposed as the majority species on the surface at 300 K. Although the initial reactive sticking probability for TMA on the silica substrates is < 0.01 at 300 K, TMA chemisorption affects OH{sub i}, OH{sub H}, and siloxane bridges on the surface with equivalent probability. The common reaction probability (equivalent rate constants) implies that similar requirements may be involved in the reactive adsorption that consumes each site. Decomposition of the monomethylaluminum adsorbate begins above 373 K and increases the population of methyl groups bonded to silicon on the surface. The methyl groups react to form methane{sub g} and ethane{sub g} and adsorbed hydrocarbon fragments. In addition, the methyl groups also react further with the surface to form tetramethylsilane{sub g}. At coverages of one-third saturation and greater, the monomethylaluminum surface complex can also react with methyl groups to yield TMA{sub g} above 500 K.
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 6014258
- Journal Information:
- Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 95:11; ISSN 0022-3654; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALUMINIUM COMPOUNDS
ANNEALING
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
DATA
DECOMPOSITION
DESORPTION
ELECTROMAGNETIC RADIATION
ELECTRON SPECTROSCOPY
EXPERIMENTAL DATA
FOURIER TRANSFORM SPECTROMETERS
HEAT TREATMENTS
HIGH VACUUM
INFORMATION
INFRARED RADIATION
INFRARED SPECTRA
KINETICS
MEASURING INSTRUMENTS
MINERALS
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
PYROLYSIS
QUANTITATIVE CHEMICAL ANALYSIS
RADIATIONS
REACTION KINETICS
SEPARATION PROCESSES
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
SORPTIVE PROPERTIES
SPECTRA
SPECTROMETERS
SPECTROSCOPY
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THERMOCHEMICAL PROCESSES
X-RAY SPECTROSCOPY