Silicon nitride formation by the carbothermal reduction and ammonolysis of silica

Technical Report · Fri Aug 01 04:00:00 EDT 1986

OSTI ID:5284871

Durham, B G

The production rates of silicon nitride are greater at 1350 and 1400/sup 0/C in the SiO/sub 2/-C-NH/sub 3/ system than in the SiO/sub 2/-C-N/sub 2/ system. When NH/sub 3/ is used as the nitriding gas, silicon nitride appears to be produced through the following overall reactions: 3SiO/sub 2/ + 6C + 4NH/sub 3/ ..-->.. Si/sub 3/N/sub 4/ + 6CO + 6H/sub 2/ and 3SiO/sub 2/ + 4NH/sub 3/ ..-->.. Si/sub 3/N/sub 4/ + 6H/sub 2/O. The following reactions appear to be taking place in the SiO/sub 2/-C-NH/sub 3/ system: SiO/sub 2/ + C ..-->.. SiO + CO; SiO/sub 2/ + CO ..-->.. SiO + CO/sub 2/; SiO/sub 2/ + H/sub 2/ ..-->.. SiO + H/sub 2/O; CO/sub 2/ + C ..-->.. 2CO; 3SiO + 3C + 4NH/sub 3/ ..-->.. Si/sub 3/N/sub 4/ + 3CO + 6H/sub 2/; 3SiO + 3CO + 4NH/sub 3/ ..-->.. Si/sub 3/N/sub 4/ + 3CO/sub 2/ + 6H/sub 2/; 3SiO/sub 2/ + 4NH/sub 3/ ..-->.. Si/sub 3/N/sub 4/ + 6H/sub 2/O. Increased reactant surface area results in a higher production of silicon nitride for a given time of reaction. Therefore, the first four reactions are the rate-limiting steps in the formation of silicon nitride in the SiO/sub 2/-C-NH/sub 3/ system. The use of NH/sub 3/ appears to result in a higher production of SiO available for reaction to silicon nitride due to the increased reducing capabilities of hydrogen in the gas stream. The best silicon nitride powder produced from the SiO/sub 2/-C-NH/sub 3/ system is high in alpha content, low in carbon and oxygen levels, and exhibits a uniform particle shape and size on the order of two microns.

• Research Organization: Ames Lab., IA (USA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 5284871
• Report Number(s): IS-T-1274; ON: DE86015771
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201* -- Ceramics
Cermets
& Refractories-- Preparation & Fabrication
AMMONIA
CARBON
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
ELEMENTS
HYDRIDES
HYDROGEN COMPOUNDS
KINETICS
MINERALS
NITRIDATION
NITRIDES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
POWDERS
REACTION KINETICS
REDUCTION
SILICA
SILICON COMPOUNDS
SILICON NITRIDES
SILICON OXIDES
SYNTHESIS