School of Chemistry, Faculty of Science, University of Witwatersrand, Johannesburg, South
Africa
Johannesburg, 2016 / The synthesis of pure layered clay minerals has to be evaluated at low temperatures,
pressures and short reaction times to scale up to commercial processes. However, it has been
discovered that under such reaction conditions, reactions experience considerable difficulties.
Such difficulties include low yields of products that occur with associated other minerals, and
long reaction times. Thus, the synthesis of synthetic clay minerals is commonly approached
by the hydrothermal technique, which involves the crystallization of substances at high
vapour pressures and temperatures. However, the employment of the hydrothermal technique
is time- and water consuming, thus, the need for an energy-saving and reaction accelerating
process method. In the work presented here particular interest is paid to the synthetic layered
clay mineral pyrophyllite, which is used as a pressure transmitting medium in the making of
synthetic diamond. As opposed to the hydrothermal technique, this work adopts the synthetic
method resin gel for the synthesis of these layered materials. Preliminary results by Loren
Purcell have shown that the resin-gel synthesis method has been able to make apparently
layered materials that appear to have a thermal gravimetric profile that indicates a gradual
mass loss of both surface and structural water. The work presented here reproduces these
results and further explores other Si\Al ratio’s, silica and alumina precursors for the synthesis
of pyrophyllite-like materials and the different heating methods of the gels. Transmission
electron microscopy (TEM) shows that irrespective of the synthesis conditions sheet-like or
platy crystals are formed. Scanning electron microscopy (SEM) confirms on the TEM
observations and shows that the surface texture of the crystals has a compact appearance.
Thermal gravimetric analysis (TGA) of the materials confirms on previous observations from
preliminary results, materials indicate both adsorbed surface and interlayer water. Powder Xray
diffraction (PXRD) is inconclusive of the determination of phase pure pyrophyllite.
Furthermore, Brunauer-Emmett-Teller (BET) reveals that the materials are mesoporous solids
and the materials were also characterised by DSC, Raman and HRTEM. / MT2016
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21072 |
| Date | January 2016 |
| Creators | Tsieane, Sebabatso |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xv, 99 leaves), application/pdf |
Page generated in 0.0021 seconds