Molecular orbital study of an environmentally enhanced crack growth process in silica

Journal Article · Mon Aug 01 04:00:00 EDT 1994 · Journal of the American Ceramic Society; (United States)

DOI:https://doi.org/10.1111/j.1151-2916.1994.tb07115.x· OSTI ID:6988502

Lindsay, C G; White, G S; Freiman, S W; Wong-Ng, W ^[1]

---

1. National Inst. of Standards and Technology, Gaithersburg, MD (United States). Ceramics Div.

The authors have used molecular orbital calculations to investigate effects of environmental substances and strain on fracture of the Si-O bond in an H[sub 6]Si[sub 2]O[sub 7] molecule. They believe that the tendencies observed simulate crack growth in silica in the vicinity of a crack tip. This study is focused on the initial stage of environmental enhancement, in which a molecule of a substance from the environment approaches a reaction site in silica. Five environmental substances--ammonia, water, formamide, nitrogen and argon--were considered. The total energy of each H[sub 6]Si[sub 2]O[sub 7]-environmental molecule system was calculated with H[sub 6]Si[sub 2]O[sub 7] in each of two strain conditions and with the environmental molecule at two different distances from the bridging O in H[sub 6]Si[sub 2]O[sub 7]. This provides estimates of the average force required to move an environmental molecule toward the reaction site in silica. The energy difference due to environmental molecule position is relatively small for ammonia and water, and is relatively large for nitrogen and argon. Experimentally, ammonia and water have shown the greatest tendency to enhance crack growth in silica, whereas nitrogen has shown virtually no such tendency. The tendency for a substance to enhance crack growth therefore appears to be at least partly an inverse function of the energy required to move a molecule of that substance toward the reaction site on the silica surface.

• OSTI ID: 6988502
• Journal Information: Journal of the American Ceramic Society; (United States), Journal Name: Journal of the American Ceramic Society; (United States) Vol. 77:8; ISSN 0002-7820; ISSN JACTAW
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360203* -- Ceramics
Cermets
& Refractories-- Mechanical Properties
360205 -- Ceramics
Cermets
& Refractories-- Corrosion & Erosion
AMIDES
AMMONIA
ARGON
CHALCOGENIDES
CHEMICAL REACTIONS
CORROSION
CORROSIVE EFFECTS
CRACK PROPAGATION
ELEMENTS
FLUIDS
FORMAMIDE
GASES
HYDRIDES
HYDROGEN COMPOUNDS
NITROGEN
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
RARE GASES
SILICON COMPOUNDS
SILICON OXIDES
STRESS INTENSITY FACTORS
WATER