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INTRODUCTION: THE EVOLUTION OF THIS RESEARCH PROJECT
Fly ash is an industrial waste resulting from burning coal in the production of electricity. Sphere-Fill, which sources fly ash from the Lethabo Power Station in the Northern Free State, aims to extend the market of this by-product. Cosmetic changes, for example changing the trade name to Plasfill, size separation and packaging was, however, not enough. The grey colour (Figure 0-1), familiar from the cinders of a barbeque, was detrimental to the marketing of fly ash as a filler for plastics. Fillers were used to make up volume, thereby using less of the expensive polymer, to impart strength and/or colour to the plastics, performing a functional role. The inherent grey colour of fly ash was strong enough to mask the effects of pigments in plastics. Changing the colour of fly ash to make it more marketable was, therefore, the original aim of the project in 1999 (Figure 0-2). The spherical form of fly ash formed the basis of its marketability (Figure 0-3).
The amorphous aluminosilicate nature of fly ash made it difficult to characterise, but versatile. Solid-state chemistry could theoretically be used to change the colour of fly ash in order to make fly ash a valuable marketable product. This process, however, needed to be supported by scientific method. Vibrational spectroscopy was chosen to monitor the process and add scientific value to the syntheses. The search for answers regarding fly ash and its reactions resulted in extending the technique ofvibrational spectroscopy to an even more useful tool.
During the first part of the research it was clear that wet chemistry was not adequate to realise the original goals. Therefore, solid-state chemistry was chosen as research methodology. Treating fly ash at 1 000 °C led to a cream colour (Figure 0-1). Transition metals seemed most likely to solve the colour problem. Unfortunately the transition metals did not deliver, except cobalt and vanadium. Cobalt reacted at 1 000 ºC to yield a blue pigment, at an unfortunate high loading. Vanadium, on the Aspects of solid-state chemistry of fly ash and ultramarine pigments other hand yielded interesting results. Ammonium metavanadate was expected to decompose to V2O5, a brown crystalline powder. A yellow colour was, however, observed in the presence of fly ash. The interaction between vanadium species and fly ash was not reported in this thesis, but left for later publication, after the refinement of the ideas.
The other interesting and valuable element turned out to be sulphur. Sulphur together with an aluminosilicate starting reagent led to the commercial artificial pigments, Ultramarine Blue, Green and Red. Theoretical studies into proposed structures for the chromophores proved beneficial (Figure 0-4 and Figure 0-5). The kinetics of the reactions involved posed research opportunities (Chapter 3). Spectroscopic models for the characterisation of aluminosilicates were initiated (Figure 0-4 and Figure 0-5).
INTRODUCTION: THE EVOLUTION OF THIS RESEARCH PROJECT
0.1. The Original Objectives
0.2. Limitations of Current Techniques and the Development of New Techniques
0.3. Synthetic Methods
0.4. Aims of this Research
0.5. Format of the Thesis
1. LITERATURE REVIEW OF FLY ASH
1.1. Introduction
1.2. Need for Research into Fly Ash
1.3. Characteristics of Fly Ash
1.4. Past Applications of Fly Ash
1.5. Potential Uses of Fly Ash
1.6. Conclusion
2. EXPERIMENTAL METHODS
2.1. Chemicals
2.2. Infrared Spectroscopy
2.3. Raman Spectroscopy
2.4. X-Ray Diffraction
2.5. X-Ray Fluorescence
2.6. Scanning Electron Microscopy
2.7. pH Measurement
2.9. Molecular Modelling
2.9.1. Semi-empirical ZINDO/1 Modelling Scheme
2.9.2. Ab Initio – 6-311G** Modelling Scheme
2.9.3. Vibrational Analyses
2.9.4. Configuration Interaction and Electronic Transitions
3. SYNTHESIS OF ULTRAMARINE BLE FROM FLY ASH
3.1. Introduction
3.2. Experimental
3.2.1. Synthesis
3.2.2. Kinetic Experiment
3.3. Results and Discussion
3.4. Conclusions
4. THE ROLE SULPHUR PLAYS IN THE FORMATION OF ULTRAMARINE BLUE
4.1. Introduction
4.2. Synthesis
4.3. Results
4.4. Discussion
4.5. Conclusion
5. MODELLING SULPHUR CLUSTERS IN ULTRAMARINE
5.1. Introduction
5.2. Experimental Data
5.3. Molecular Modelling
5.4. Results
5.5. Discussion
5.6. Conclusion
6. AN AB INITIO STUDY OF THE RED CHROMOPHORE IN ULTRAMARINE
6.1. Introduction
6.2. Experimental Data
6.3. Molecular Modelling
6.4. Results
6.4.1. Modelling the Cavities in the Ultramarine Structure
6.5. Discussion
6.6. Conclusion
7. SUGGESTIONS FOR FURTHER INVESTIGATION
7.1. The Spectroscopy of Silicates
7.2. Ultramarine Blue
7.2.1. Industrial Process for the Synthesis of Ultramarine Blue
7.2.2. Kinetics
7.2.3. The Crystal Structure of Ultramarine Pigments
7.3. Treating Fly Ash with Surfactants
7.3.1. Anionic Surfactants
7.3.2. Cationic Surfactant
7.4. Adding Colour to Fly Ash
7.4.1. Alkali Metals
7.4.2. Alkaline-earth Metals
7.4.3. Main Group Elements
7.4.4. Transition Metals
7.5. Artificial Neural Networks
7.6. Molecular Mechanics
7.7. Density Functional Theory
APPENDIX
A. Programs
B. Raw Data
C. Raw Data for the Calculation of the Truncated Octahedron Volume
in Sodalite Crystals
D. Posters
E. Beneficiaries
F. Published Articles
