Alkali activated materials are a promising generation of binders, which can be significantly recognized by having lower carbon footprint, being waste originated, and having unique chemistry and thermodynamics. It appears that alkali activated materials can be engineered to exhibit high-tech and intelligent performances with less effort compared to Portland cement-based binders, if appropriately formulated. In addition, alkali activated materials have several inherent properties such as adjustable microstructure and strength, and heat and chemical resistances.
Based on these explanations, the focus of this doctoral thesis was on the fabrication and characterization of multifunctional and smart alkali activated nanocomposites. The investigated alkali activated system was composed of fly ash, ground granulated blast-furnace slag (GGBS), and sodium-based silicate and hydroxide. Carbon nanotubes (CNTs) were incorporated into the alkali activated matrix to constitute a functional complex nano system. Multi-walled carbon nanotubes (MWCNTs) were utilized for colloidal, mechanical and microstructural studies and single-walled carbon nanotubes (SWCNTs) applied for electrical, thermoelectric and sensing assessments.
The colloidal and mechanical performances and microstructural characteristics have been assessed for the alkali activated nanocomposites, which were fabricated by a dispersion of MWCNTs (0.05 wt.%) into sodium-based silicate and hydroxide solutions and their combination. The highest MWCNTs’ dispersibility and in-solution stability and smallest dimension of agglomerations were observed in the sodium silicate dispersion media. Accordingly, the highest compressive and flexural strengths were accomplished for mentioned nanocomposites, ≈60 MPa & ≈10 MPa, respectively. The reason for the mechanical improvement was the effective reinforcement of MWCNTs when dispersed in sodium silicate. The MWCNTs were more functional in pore refinement and crack propagation control of the nanocomposites’ microstructure.
Thermoelectric properties and thermoelectric power generation performances have been studied for the alkali activated nanocomposites and the resultant generator device. SWCNTs were used for the alkali activated thermoelectric generator fabrications. A single piece of nanocomposite with SWCNT content of 1 wt.% could achieve a Seebeck coefficient of ≈16 μV·K-1 and power factor of 0.4 μW·m-1·K-2. The thermoelectric generator device consisted of 10 serially interconnected alkali activated thermoelements (p-type elements). The highest generated thermoelectric voltage and power with inclusion of 1 wt.% of SWCNTs in the nanocomposites were ≈7 mV and ≈0.7 µW, respectively at ΔΤ of 60 K.
In the last phase of this doctoral research the idea of ion discrimination and the potential of being a sensor have been conceptualized and demonstrated for SWCNT alkali activated nanocomposites. The alkali activated sensors were produced by incorporation of 0.1 wt.% of SWCNTs based on the results of conducted percolation study. The sensors displayed an ion discrimination potential by transmitting signals with a detectable difference in geometry and magnitude in exposure to the introduced analytes. The discrimination criteria were analytes’ type, concentration, and volumetric quantity. The SWCNT alkali activated sensors showed a higher magnitude of relative resistance in exposure to the sulphuric acid compared to the magnesium sulphate. In addition, the obtained signals in sulphuric acid exposure had a curvature shape but the signals of magnesium sulphate were rectangular. The introduced sensors were applicable for the sulphuric acid concentration detection in a range of 0.001 to 0.1 M. The sensors did not have any upper threshold limit, however the lower threshold limit for sulphuric acid concentration detection was 0.001 M. There was a direct relation between the exposed quantity of sulphuric acid and relative resistance of the alkali activated sensors.
The finding of this doctoral research can be utilized for development of alkali activated nanocomposites with industrial implementations. That may include nano reinforced structural elements, thermoelectric generators for green energy production and sensors for structural health monitoring of concrete infrastructures.:Chapter 1. Motivation and innovation 1
1.1. Introduction 1
1.2. Alkali activated materials and geopolymers 1
1.3. Mechanical properties 2
1.3.1. Challenge 2
1.3.2. Novelty 4
1.4. Thermoelectricity 5
1.4.1. Challenge 6
1.4.2. Novelty 6
1.5. Sensing concept 7
1.5.1. Challenge 8
1.5.2. Innovation 10
1.6. Aim 10
1.7. Strength and shortcoming 11
1.8. Structure 11
Chapter 2. Methodology 17
2.1. Materials 17
2.1.1. Carbon nanotubes 17
2.1.2. Surfactants 18
2.1.3. Precursors 19
2.1.4. Activators 20
2.1.5. Analytes 20
2.2. Methods 21
2.2.1. Two-part activation technology 21
2.2.1.1. MWCNTs and naphthalene sulphonate concentrations 21
2.2.1.2. Fabrication methodologies of nanofluids and nanocomposites 21
2.2.1.2.1. Na2Si3.5O9 based nanofluids and nanocomposites (strategy I) 22
2.2.1.2.2. NaOH based nanofluids and nanocomposites (strategy II) 22
2.2.1.2.3. Combined (Na2Si3.5O9+NaOH) nanofluids and nanocomposites (strategy III) 23
2.2.1.3. Dispersion of nanofluids 23
2.2.1.4. Mixing of nanocomposites 24
2.2.2. One-part activation technology 24
2.2.2.1. SWCNTs and SDBS concentrations 25
2.2.2.2. Fabrication methodology of nanofluids 25
2.2.2.2.1. Thermoelectricity 25
2.2.2.2.2. Sulphate sensing 25
2.2.2.2.3. Sulphuric acid sensing 25
2.2.2.3. Fabrication methodology of nanocomposites 26
2.2.2.3.1. Thermoelectricity 26
2.2.2.3.2. Sulphate sensing 26
2.2.2.3.3. Sulphuric acid sensing 26
2.3. Characterizations 27
2.3.1. Optical microscopy 27
2.3.2. Integral light transmission (ILT) 27
2.3.3. Scanning electron microscopy (SEM) 27
2.3.4. Transmission electron microscopy (TEM) 28
2.3.5. Fourier-transform infrared spectroscopy (FTIR) 28
2.3.5.1. Alkaline nanofluids 28
2.3.5.2. Chemiresistor nanocomposites 29
2.3.6. Mercury intrusion porosimetry (MIP) 29
2.3.7. Roughness measurements 29
2.3.8. pH measurements 29
2.3.9. Mechanical properties 29
2.3.10. Thermoelectric acquisitions 30
2.3.11. Thermoelectric generator acquisitions 31
2.3.12. Sensing and discriminating acquisitions 31
Chapter 3. Dispersion of CNTs 33
3.1. Introduction 33
3.2. MWCNTs dispersibility 33
3.3. MWCNTs dispersion stability 36
3.4. MWCNTs and naphthalene sulphonate interactions 38
3.5. Potential physisorption 42
3.6. Conclusion 44
3.7. Perspective 44
Chapter 4. Microstructure refinement 45
4.1. Introduction 45
4.2. Mechanical reinforcement 45
4.3. Reinforcement mechanism 49
4.3.1. Morphology 49
4.3.2. Porosity 55
4.4. Conclusion 60
4.5. Perspective 61
Chapter 5. Thermoelectricity 63
5.1. Introduction 63
5.2. Thermoelectric properties 63
5.3. Thermoelectric generator 65
5.3.1. Power output 65
5.3.2. Stability performance 69
5.4. Mechanical properties 70
5.5. Multifunctional behaviour 71
5.6. Conclusion 73
5.7. Perspective 74
Chapter 6. Sulphate discrimination 77
6.1. Introduction 77
6.2. Percolation threshold 77
6.3. Sulphate discrimination 80
6.4. Concentration differentiation 84
6.5. Quantity differentiation 86
6.6. Conclusion 88
6.7. Perspective 89
Chapter 7. Sulphuric acid sensing 91
7.1. Introduction 91
7.2. Electrical properties 91
7.3. Morphology of the SWCNTs’ conductive network 92
7.4. Sensing properties 96
7.4.1. Exposure to ultrapure water 96
7.4.2. Exposure to sulphuric acid 97
7.4.2.1. pH influence 100
7.4.2.2. Surface composition change 103
7.4.3. Sensor sensitivity 106
7.5. Microstructure dependency 109
7.5.1. SWCNTs and matrix interactions 109
7.5.2. Matrix porosity 113
7.5.3. Matrix roughness 115
7.6. Conclusion 118
7.7. Perspective 119
Summary 121
References 123
Publications from this doctoral research 151
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:84014 |
| Date | 08 March 2023 |
| Creators | Davoodabadi, Maliheh |
| Contributors | Mechtcherine, Viktor, Cuniberti, Gianaurelio, Provis, John L., Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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