Reactions in pyrite framboids induced by electron beam heating in a HVEM
Pyrite is a common mineral constituent in most bituminous coals. In addition to being a source of sulfur pollution, pyrite is also thought to act as an internal catalyst in coal liquefaction processes. Since much of the pyrite in coal is in the form of submicron to micron size crystals, their location and identity may be obtained by means of electron microscopy in conjunction with electron microprobe analysis (EMA). Transmission and scanning electron microscopy (TEM and SEM) are generally nondestructive techniques; however, in recent studies reactions have been observed to occur in several pyrite framboids on exposure to the focussed electron beam of a high voltage electron microscope (HVEM). The reaction resulted in the formation of a rim surrounding the reactive pyrite crystals as well as conversion of some pyrite to pyrrhotite (Fe/sub 1-x/S). On further examination of these specimens it was found that only some framboids were reactive whereas others remained inert. Detailed TEM, SEM, and EMA studies of the coal revealed the presence of iron sulfate hydrate minerals, especially szomolnokite (FeSO/sub 4/.H/sub 2/O) associated with some pyrite framboids. In addition to the iron sulfates, the electron diffraction patterns contained ring patterns that could be indexed as magnetite, Fe/sub 3/O/sub 4/. These data suggest that at least one possible cause for the reactivity of pyrite framboids is the oxidation of the iron disulfide phase. Other possibilities are related to the effect of specimen configuration on local heating in the electron beam and the specific iron disulfide mineral that is present in the framboid (pyrite or marcasite).
- Research Organization:
- Oak Ridge National Lab., TN
- DOE Contract Number:
- W-7405-ENG-26
- OSTI ID:
- 6040393
- Journal Information:
- Scanning Electron Microsc.; (United States), Vol. 1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
15 GEOTHERMAL ENERGY
COAL
SCANNING ELECTRON MICROSCOPY
TRANSMISSION ELECTRON MICROSCOPY
PYRITE
CHEMICAL REACTIONS
HEATING
CATALYSIS
COAL LIQUEFACTION
ELECTRON BEAMS
IRON SULFATES
BEAMS
CARBONACEOUS MATERIALS
CHALCOGENIDES
ELECTRON MICROSCOPY
ENERGY SOURCES
FOSSIL FUELS
FUELS
IRON COMPOUNDS
IRON SULFIDES
LEPTON BEAMS
LIQUEFACTION
MATERIALS
MICROSCOPY
MINERALS
OXYGEN COMPOUNDS
PARTICLE BEAMS
SULFATES
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
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