Tetraethoxysilane (TEOS) is used as a precursor in the industrial production of silica nanoparticles using thermal decomposition methods such as flame spray pyrolysis (FSP). Despite the industrial importance of this process, the current kinetic model of high-temperature decomposition of TEOS to produce intermediate silicon species and eventually form amorphous silica (R-SiO2) nanoparticles remains inadequate. This is partly due to the fact only a small proportion of the possible species is considered. This work presents the thermochemistry of practically all of the species that can exist in the early stages of the reaction mechanism. In order to ensure that all possible species are considered, the process is automated by considering all species that can be formed from the reactions that are deemed reasonable in the standard ethanol combustion model in the literature. Thermochemical data for 180 species (over 160 of which have not appeared in the literature before) are calculated using density functional theory with two different hybrid functionals, B3LYP and B97-1. The standard enthalpy of formation (DeltafH(298.15K) degrees) values for these species are calculated using isodesmic reactions. It is observed that internal rotation may be important because the barriers to rotation are reasonably low. Comparisons are then made between the rigid rotor harmonic oscillator approximation (RRHO) and the RRHO with some of the vibrational modes treated as hindered rotors. It is found that full treatment of the hindered rotors makes a significant difference to the thermochemistry and thus has an impact on equilibrium concentrations and kinetics in this system. For this reason, all of the species are treated using the hindered rotor approximation where appropriate. Finally, equilibrium calculations are performed to identify the intermediates that are likely to be most prevalent in the high-temperature industrial process. Particularly, Si(OH)4, SiH(OH)3, SiH2(OH)2, SiH3(OH), Si(OH)3(OCH3), Si(OH)2(OCH3)2, the silicon dimers (CH3)3-SiOSi(CH3)3 and SiH3OSiH3, and the smaller hydrocarbon species CH4, CO2, C2H4, and C2H6 are highlighted as the important species.
This paper introduces a subdomain chemistry format for storing computational chemistry data called CompChem. It has been developed based on the design, concepts and methodologies of Chemical Markup Language (CML) by adding computational chemistry semantics on top of the CML Schema. The format allows a wide range of ab initio quantum chemistry calculations of individual molecules to be stored. These calculations include, for example, single point energy calculation, molecular geometry optimization, and vibrational frequency analysis. The paper also describes the supporting infrastructure, such as processing software, dictionaries, validation tools and database repositories. In addition, some of the challenges and difficulties in developing common computational chemistry dictionaries are discussed. The uses of CompChem are illustrated by two practical applications.
The semantic architecture of CML consists of conventions, dictionaries and units. The conventions conform to a top-level specification and each convention can constrain compliant documents through machine-processing (validation). Dictionaries conform to a dictionary specification which also imposes machine validation on the dictionaries. Each dictionary can also be used to validate data in a CML document, and provide human-readable descriptions. An additional set of conventions and dictionaries are used to support scientific units. All conventions, dictionaries and dictionary elements are identifiable and addressable through unique URIs.
This work presents thermochemical data for possible gas phase intermediate species in an industrial rutile chlorinator. An algorithm developed for previous work is employed to ensure that all possible species are considered, reducing the number of important species neglected. Thermochemical data and enthalpies of formation are calculated for 22 new species using density functional theory, post Hartree-Fock coupled cluster calculations, and statistical mechanics. Equilibrium calculations are performed to identify whether any Ti/C intermediates are likely to be important to the high temperature industrial process. These new species are not present at high concentration in the exit stream. It is therefore likely that the two chemical processes do not interact. Rather, the Cl₂ rapidly reacts with the solid TiO₂ to form TiCl₄ and O₂. The latter then reacts with the solid C to form CO and CO₂ and provide the heat. Data for all the new species is provided as Supporting Information. Finally, a new methodology for data collaboration is investigated in which the data is made openly accessible using the resource description framework. Example scripts are provided to demonstrate how to query and retrieve the data automatically.
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