Browsing by Subject "glass"

Now showing 1 - 3 of 3
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    An Investigation Into Ground Glass-Based Alkali Activated Cement For Use In High-Temperature Applications
    (Spring 2024) Broemer, Garrett
    Glass-based alkali-activated cements (AACs) can withstand higher temperatures, up to 1100°C, compared to conventional portland cement (PC) failing above 200°C. AACs demonstrate beneficial vitrification, and expansive foam properties different from PC. AACs are manufactured using a reactive aluminosilicate powder mixed with concentrated alkali solution to dissolve and polymerize aluminosilicate precursors creating a binding matrix. Glass-based AAC mortar was exposed to 300, 600, 900, and 1100ºC, then air cooled and water quenched to determine the residual compressive strength of the samples as compared to PC and fly ash-based AAC. AACs retained higher flexural modulus at ambient temperatures and higher residual compressive strength properties compared to PC. Physical property characterization was completed on the glass-based AACs, retaining similar porosity, density, and leaching but better insulative properties compared to PC. Alkali-activated cements demonstrate beneficial insulative properties that could be effective in fire retardant coatings, passive heat protection, or other high temperature applications.
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    Investigation of Iron speciation in silicate glasses and its implications for magma oceans
    (2015-11) Zhang, Hongluo
    As the most abundant multi-valent element in silicate melt, iron plays an important role in many physical and chemical respects. The ratio of Fe3+ and total Fe concentration, Fe3+/ΣFe, not only reflects but also establishes the redox environment in many magmatic processes. The Fe3+/ΣFe ratio increases with oxygen fugacity, but also is affected by chemical composition, temperature and pressure. This thesis presents experimental investigations of the Fe3+/ΣFe ratio changing with pressure in silicate melts and its implications for the redox environments of early magma ocean. Mössbauer spectrum is one of the most common methods to determine Fe3+/ΣFe ratio in glasses. In Chapter 2, two andesitic glasses synthesized at 1 atm, 1400 °C and 3.5 GPa, 1600 °C, were examined with Mössbauer spectra collected from 47-293 K. The recoilless fractions (f) of Fe3+ and Fe2+, can be determined from those variable-temperature Mo ̈ssbauer spectra. The correction number, C, equals f(Fe3+), will be used to f (Fe2+ ) correct the Fe3+/ΣFe ratio of andesite glasses determined through Mössbauer spectra collected at room temperature in the following studies. For 1 atm andesitic glasses equilibrated over a range of oxygen fugacities (logfO2 from -8.63 to -0.68), were examined with Fe K-edge X- ray absorption near-edge structure (XANES) and Mo ̈ssbauer spectra in Chapter 3. XANES spectral features were calibrated as a function of Mössbauer derived Fe3+/ΣFe ratios. The coordination number (CN) of Fe3+ and Fe2+ ions in andesitic glass can be calculated from observations of pre-edge centroid energies and total intensities, combined with independent constraints on Fe3+/ΣFe ratio from spectra. The mean coordination of Fe2+ ions calculated this way is close to 5.5 for reduced and oxidized compositions, and this is consistent with in- ferences from hyperfine features of the Mössbauer spectra. The mean coordination number of Fe3+ inferred from XANES increases from ∼4.5 to ∼5 as andesitic glasses vary from reduced to oxidized; Mössbauer hyperfine parameters also suggest network-forming behavior of Fe3+, but with higher coordination for more reduced glasses. In Chapter 4, the Fe3+/ΣFe ratios in andesitic glasses synthesized from 1 atm to 7 GPa were examined with Mo ̈ssbauer spectra. The Fe3+/ΣFe ratios decrease as pressure increase, from 1 atm to 4 GPa, and become flatten af- terwards. Those glasses were also examined with XANES spectra. Both hyperfine parameters from Mössbauer spectra and mean coordination number calculated from XANES features show that the CNs of Fe3+ in glasses are ∼5 and vary little with pressure changing, while for Fe2+, the CN increases as pressure increasing. A new thermodynamic model is built to explore the relationship between oxygen fugacity and pressure and consequently, for a homogenous magma ocean, the oxidation states are more reduced at shallow part than at depth.
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    Waste Glass as a Primary Precursor and Secondary Aluminosilicate Source in Geopolymer Mortars
    (2018-10) Haapala, Kyrstyn
    Widespread use of concrete as a construction material has led to concerns with the level of CO2 emissions from the production of portland cement. This has led to the development of alternative cements; geopolymers are one of these binders and the focus of this research. Geopolymers are formed through the combination of an aluminosilicate source and an alkaline activator. One of the largest contributions to CO2 emissions associated with geopolymers comes from the production of sodium silicate, which is commonly used as an activator. One of the primary goals of this research was to reduce or eliminate the need for sodium silicate in geopolymers by investigating the use of waste glass as a primary precursor or a secondary aluminosilicate source. Two types of geopolymers were produced where waste glass was used both as the main aluminosilicate source (Phase I) and as a supplement to fly ash (Phase II). Three activators with varying ratios of sodium silicate to sodium hydroxide (SS/NaOH) were considered and mixed with various glass sources to determine the effect of glass composition on performance. Fresh properties and compressive strength were measured, and SEM imaging was completed. Curing time, curing temperature, and calcium content were also investigated. Overall, including sodium silicate as an activator reduced the strength of glass-based geopolymers. A SS/NaOH of 1:1 (SiO2/Na2O = 0.95) was found to be optimal to activate the fly ash sources. Waste glass could not fully replace sodium silicate in activating fly ash and had limited success as a partial replacement while reducing the amount of sodium silicate in the activator.