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Quantum chemical approach toward the identification of
hydrolyzed chlorosilane oligomer
Takako Kudo
1)
, Yasuhiro Hanaue
2)
, and Norikazu Komada
3)
1) Division of Pure and Applied Science, Graduate School of Science and Technology,
Gunma University.
2) Process Technology Department, Yokkaichi Plant, Mitsubishi Materials
Corporation.
3) Electronic Materials and Components Company, Mitsubishi Materials Corporation.
Abstract
Seven candidates were proposed for the structural model of the unidentified explosive
molecule which caused the fatal accident at Yokkaichi Plant, Mitsubishi Materials
Corporation in 2014. Those models were optimized by means of ab initio molecular
orbital calculations including electron correlation effects at the level of MP2/6-31G*,
and compared with the available data in order to choose a model which is most
consistent with them for the further study. The chemical formula of the chosen model
(Model A) is Si
8
H
10
O
14
. Its structure is described as a partial hexahedron composed of
four Si-Si bonds, seven Si-O-Si bonds and one open ring. Three H atoms and seven
OH groups are attached to eight Si atoms. There is a hydrogen bond formed in the area
of the open ring.
Possible intramolecular reaction path was explored and one candidate path was found.
The reaction along the path is significantly exothermic and includes oxidation of a Si-
Si bond and formation of a H
2
molecule, which is qualitatively consistent with the
observation. The reaction products are a closed hexahedral Si
8
H
8
O
14
and a H
2
molecule.
The Si
8
H
8
O
14
molecule has three Si-Si and nine Si-O-Si bonds. The path consists of
three transition states and two metastable intermediates, each of which is interleaved
between the transition states, in serial sequence. H
2
molecule is formed in the path from
the 2
nd
transition state to the 2
nd
metastable intermediate counting from the reactant.
The reaction may be interpreted as the initial ignition stage of the explosion.
Background
There was an explosion and fire during opening/cleaning work of a heat exchanger in
Yokkaichi Plant on January 9, 2014. Five employees were killed and 13 employees
were injured by the accident. A committee was organized to investigate the cause of
the accident and to provide recommendations for preventive measures. The chemical
analysis, infrared absorption spectroscopy and several other measurements were
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