Fluidized bed deposition and evaluation of silicon carbide coatings on microspheres

Technical Report · Sat Jan 01 04:00:00 EST 1977

DOI:https://doi.org/10.2172/7331487· OSTI ID:7331487

Federer, J. I.

The fuel element for the HTGR is an array of closely packed fuel microspheres in a carbonaceous matrix. A coating of dense silicon carbide (SiC), along with pyrocarbon layers, is deposited on the fueled microspheres to serve as a barrier against diffusion of fission products. The microspheres are coated with silicon carbide in a fluidized bed by reaction of methyltrichlorosilane (CH/sub 3/SiCl/sub 3/ or MTS) and hydrogen at elevated temperatures. The principal variables of coating temperature and reactant gas composition (H/sub 2//MTS ratio) have been correlated with coating rate, morphology, stoichiometry, microstructure, and density. The optimum temperature for depositing highly dense coatings is in the range 1475 to 1675/sup 0/C. Lower temperatures result in silicon-rich deposits, while higher temperatures may cause unacceptable porosity. The optimum H/sub 2//MTS ratio for highly dense coatings is 20 or more (approximately 5% MTS or less). The amount of grown-in porosity increases as the H/sub 2//MTS ratio decreases below 20. The requirement that the H/sub 2//MTS ratio be about 20 or more imposes a practical restraint on coating rate, since increasing the total flow rate would eventually expel microspheres from the coating tube. Evaluation of stoichiometry, morphology, and microstructure support the above mentioned optimum conditions of temperature and reactant gas composition. 18 figures, 3 tables.

• Research Organization: Oak Ridge National Lab., Tenn. (USA)
• DOE Contract Number: W-7405-ENG-26
• OSTI ID: 7331487
• Report Number(s): ORNL/TM-5152
• Country of Publication: United States
• Language: English

Related Subjects

050700* -- Nuclear Fuels-- Fuels Production & Properties
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
210300 -- Power Reactors
Nonbreeding
Graphite Moderated
36 MATERIALS SCIENCE
360201 -- Ceramics
Cermets
& Refractories-- Preparation & Fabrication
CARBIDES
CARBON COMPOUNDS
CHEMICAL COATING
CHEMICAL VAPOR DEPOSITION
COATED FUEL PARTICLES
COATINGS
CRYOGENIC FLUIDS
CRYSTAL STRUCTURE
DEPOSITION
ELEMENTS
FABRICATION
FLUIDIZED BED
FLUIDS
FUEL PARTICLES
GAS COOLED REACTORS
GRAPHITE MODERATED REACTORS
HTGR TYPE REACTORS
HYDRIDES
HYDROGEN
HYDROGEN COMPOUNDS
MICROSPHERES
MICROSTRUCTURE
NONMETALS
OPTIMIZATION
POROSITY
REACTORS
SILANES
SILICON CARBIDES
SILICON COMPOUNDS
STOICHIOMETRY
SURFACE COATING
TEMPERATURE DEPENDENCE