Mao, Jishen (2012)
M.Res. thesis, University of Birmingham.
Plasma arc technology is a novel method that widely applied in industry for the hazardous waste vitrification. After the plasma arc process, the wastes are transformed into inert and glassy materials ready for storage or other applications.
The aim of this project is to characterise a plasma arc processed waste product. Two types of samples were characterised in this study, Sample A is sodium-free and Sample B is sodium-contained. The microstructure of the samples was characterised using XRD, SEM and TEM; mechanical properties of the samples were measured including Vickers hardness and compressive strength; dissolution of the samples in alkaline solution was measured to test the chemical stability. XRD results show that both of the samples are amorphous, which is confirmed by the TEM electron diffraction study. The sodium-free sample contains areas in green color and areas in white color, while the sodium-contained sample is all in green. SEM results show that the green area in sodium-free sample has homogenous structure and the white area has a dendrite-like structure. The bright part in the dendrite-like structure contains more Al, Si, Ce but less Mg than the dark part. A black fiber-like structure can be found in the sodium-contained sample. The fiber-like structure contains more O, Mg, Al but less Si than the rest of the sample. A detail study of electron diffraction in TEM was performed by transforming the electron diffraction patterns into reduced density function G(r) (RDF). The results show that the nearest-neighbor distance in sodium-contained sample is larger than the sodium-free sample.
Mechanical property measurements show that the sodium-free sample has higher Vickers hardness and compressive strength values than the sodium-contained sample. The sodium-free sample also has a higher dissolution rate than the sodium-contained sample as indicated in the chemical stability study.
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