Graphite immobilisation in glass composite materials
Irradiated graphite is a problematic nuclear waste stream and currently raises significant concern worldwide in identifying its long-term disposal route. This thesis describes the use of glass materials for the immobilisation of irradiated graphite prepared by microwave, conventional and spark...
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| Format: | Thesis |
| Language: | English |
| Published: |
2015
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| Subjects: | |
| Online Access: | http://eprints.uthm.edu.my/1738/1/24p%20MOHD%20ZUL%20HILMI%20MAYZAN.pdf |
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| Summary: | Irradiated graphite is a problematic nuclear waste stream and currently raises significant concern
worldwide in identifying its long-term disposal route. This thesis describes the use of glass
materials for the immobilisation of irradiated graphite prepared by microwave, conventional and
sparks plasma sintering methods. Several potential glass compositions namely iron phosphate,
aluminoborosilicate, calcium aluminosilicate, alkali borosilicate and obsidian were considered
for the immobilisation of various loadings of graphite simulating irradiated graphite. The
properties of the samples produced using different processing methods are compared selectively.
An investigation of microwave processing using an iron phosphate glass composition revealed
that full reaction of the raw materials and formation of a glass melt occurs with consequent
removal of porosity at 8 minutes microwave processing. When graphite is present, iron
phosphate crystalline phases are formed with much higher levels of residual porosity of up to 43
% than in the samples prepared using conventional sintering under argon. It is found that
graphite reacts with the microwave field when in powder form but this reaction is minimised
when the graphite is incorporated into a pellet, and that the graphite also impedes sintering of the
glass. Mössbauer spectroscopy indicates that reduction of iron occurs with concomitant graphite
oxidation. The production of graphite-glass samples using various powdered glass compositions
by conventional sintering method still resulted in high porosity with an average of 6-17 % for
graphite loadings of 20-25 wt%. Due to the use of pre-made glasses and controlled sintering
parameters, the loss of graphite from the total mass is reduced compared to the microwaved
samples; the average mass loss is < 0.8 %. The complication of iron oxidation and reduction is
present in all the iron containing base glasses considered and this increases the total porosity of
the graphite-glass samples. It is concluded that the presence of iron in the raw materials or base
glasses as an encapsulation media for the immobilisation of the irradiated graphite waste is not
advisable. The production of glass and graphite-glass samples based calcium aluminosilicate
composition by spark plasma sintering method is found highly suitable for the immobilisation of
irradiated graphite wastes. The advantages of the method includes short processing time i.e. < 40
minutes, improved sintering transport mechanisms, limited graphite oxidation, low porosity (1-4
%) and acceptable tensile strength (2-7 MPa). The most promising samples prepared using spark
plasma sintering method were loaded with 30-50 wt% graphite. |
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