Browsing by Subject "Quartz"

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Development and material characterization of quartz-reinforced UHTR/aerogel composites : morphology, thermal, and flammability properties
(2023-05-04) Kim, Steven Doyeon; Koo, Joseph H.; Li, Wei (Of University of Texas at Austin)
Aerogels are a class of highly porous solid materials with nano-sized open pores. It exhibits unique properties, such as extremely low density and thermal conductivity. The highly porous nature of silica aerogel combined with its high thermal stability also makes it an ideal candidate for thermal insulation under extreme environments. Quartz fibers are almost completely composed of silicon dioxide (SiO₂) and have commonly been used as reinforcement material due to its favorable mechanical and thermal properties. Traditionally, SiO₂ nanofillers have been used as reinforcement material; however, using quartz fiber may provide even greater improvements in mechanical properties than nanosilica powders. The solventless polysiloxane resin (UHTR) is a colorless semi-solid resin system that exhibits very high char yields and thermal stability. This grade of UHTR is formulated using proprietary polysiloxane chemistries to tailor it for flame shielding applications. In this study, the objectives are to develop processing methods to disperse aerogels and chopped quartz fibers thoroughly and homogenously into a polysiloxane resin and to investigate the processing conditions on morphology and thermal properties of a quartz fiber-reinforced aerogel composite material. The proposed composite exhibits high char yield, low density, and low thermal conductivity properties. The goal of this study is to create a quartz fiber-reinforced polysiloxane/aerogel composite that possesses low thermal conductivity and high char yield suitable for advanced aerospace and defense applications.
An evaluation of quartz-inclusion barometry by laser Raman microspectrometry : a case study from the Llano Uplift of central Texas
(2010-08) McDowell, Emily Allen 1985-; Carlson, William, 1952-
A new barometric technique measuring stored stress in quartz inclusions via laser Raman microspectrometry was employed in an attempt to elucidate the extent of highpressure (HP) metamorphism in the Llano Uplift of central Texas. Rare lithologies within the Llano Uplift contain mineralogical evidence of HP metamorphism (pressures from 1.4 to 2.4 GPa at temperatures from 650 to 775°C), but much of the uplift is composed of felsic gneisses lacking any HP signature; these felsic gneisses may never have transformed to HP assemblages, or they may have been thoroughly overprinted by later low-pressure events. Barometry via laser Raman microspectrometry computes entrapment pressure for a quartz inclusion in garnet from measurement of the displacements of its Raman peak positions from those of a quartz standard at atmospheric pressure. Quartz inclusions in garnets that grew in felsic gneisses under HP conditions should retain HP signatures, despite later overprinting. Application of the Raman microspectrometry technique should therefore allow barometry of previously uncharacterizable rocks. For two localities in the Llano Uplift, entrapment pressures from Raman barometry (0.6-0.7 GPa and 0.2-0.3 GPa) were substantially lower than pressures expected based on conventional barometers (1.4 GPa and 1.6-2.4 GPa). This absence of any HP signatures in the Llano rocks contrasts with more successful applications of the Raman technique by previous workers in high P/T blueschist-facies rocks. A key difference in the Llano rocks is that they reached peak temperatures at which intracrystalline diffusion in garnet, driven by compositional gradients produced during growth, had noticeable effects: complete homogenization of growth zoning had occurred in the locality that produced the greatest discrepancies between Raman and conventional pressures, and modest relaxation of zoning occurred in the locality with the smaller discrepancies. The failure of the Raman technique to recover pressures consistent with conventional barometry in the Llano Uplift is therefore attributed to relaxation of stress on the quartz inclusions as the result of intracrystalline diffusion within the garnet. This conclusion suggests that use of the Raman barometric technique must be restricted to rocks whose time-temperature histories produce only very limited intracrystalline diffusion in garnet, typically those rocks whose peak metamorphic temperatures fall at or below upper amphibolite-facies conditions.
A fluid inclusion and cathodoluminescence approach to reconstruct fracture growth in the Triassic-Jurassic La Boca Formation, Northeastern Mexico
(2011-12) Kaylor, Autumn Leigh; Laubach, Stephen E. (Stephen Ernest), 1955-; Eichhubl, Peter; Catlos, Elizabeth; Ketcham, Richard
Opening-mode fracture shapes are typically the result of brittle deformation and proportional growth in fracture height, length, and width. Based on the typical fracture shape, it is assumed that fracture tips are free to propagate in all directions. Some natural rock fractures have been shown to form as a result of slow non-elastic deformation processes. Such fractures may propagate to a finite length or height and accommodate further growth by aperture widening only. To determine the growth conditions of a fracture in the Triassic-Jurassic La Boca Formation of northeastern Mexico and to test fracture growth models, I combined fluid inclusion microthermometry and SEM-based cathodoluminescence cement texture analysis to determine the relative timing of fracture cement precipitation and related fracture opening for five samples collected along its trace. Fracture growth initiated at a minimum age of 70 Ma as two separate fractures with branching fracture tips that coalesced to a single continuous fracture under prograde burial conditions at a minimum age of 54 Ma. At this stage, fracture growth was accommodated by both propagation (i.e. increase in trace length) and by an increase in aperture during maximum burial and early exhumation. Samples collected at the fracture tips recorded temperatures reflecting fracture opening starting with maximum burial at a minimum age of 48 Ma at one tip and of 38 Ma at the other tip. Synkinematic fluid inclusions in crack-seal cement track continued fracture opening close to the fracture tips without a concurrent increase in trace length after 38 Ma until about 21 Ma. I attribute the observed change in fracture growth mechanism to a change in material response. The stage in aperture increase without propagation corresponds to an increase in elastic compliance or in non-elastic flow properties. Non-elastic flow can be attributed to solution-precipitation creep of the host rock. Dissolution of host quartz grains and subsequent quartz precipitation is consistent with the abundance of quartz fracture cement formed during exhumation. Cement textures from fractures in the La Boca Formation mimic those found in subsurface core, which allows application of the results to a variety of geologic environments.
The genetic association between brittle deformation and quartz cementation: examples from burial compaction and cataclasis
(2004) Makowitz, Astrid; McBride, Earle F.; Milliken, Kitty L.
Brittle deformation of quartz grains accompanied by quartz cementation is a porosity-reducing mechanism in sandstones. Brittle deformation has historically been overlooked as a mechanism of compaction because it has been poorly understood and techniques for observing it are not commonly used. I have used scanned cathodoluminescence (CL) to quantify brittle deformation of quartz grains, in sandstones undergoing burial and cataclasis. Sandstone samples of different ages and compositions, taken from two basins with contrasting burial histories, are used to examine the interaction viii between brittle deformation and quartz cementation in burial compaction. Trends of increasing deformation by microfracturing with maximum burial depth are observed in both the lithic-rich Frio Formation from the Gulf of Mexico basin and in the quartz-rich Mount Simon Formation of the Illinois basin. Combining information on the degree of brittle deformation and the amount of quartz cement localized within microfractures allows for the calculation of the amount that brittle deformation influences compaction (i.e. porosity loss). For the Frio, 0.12 to 8.37% of initial porosity is lost due to cementation related to brittle deformation, whereas the values for the Mount Simon lie between 0.25 and 2.16%. Diagenetic forward models are constructed for each formation using petrographic modal analysis and burial history information to determine the depth of quartz cement commencement as an influential factor affecting brittle grain deformation. Most fracturing probably occurred prior to the precipitation of > 2% quartz cement. Commencement of quartz cementation at shallow depths combined with slower burial rates resulted in less brittle deformation in the Mount Simon compared with the Frio, where sandstones underwent rapid burial and quartz cementation began at greater depths. Cataclastic sandstones within the Pine Mountain Overthrust, eastern Kentucky, show more extreme porosity reduction by fracturing and cementation than normally compacted sandstones. In contrast to normal burial compaction, cataclasis and cementation within the cataclasites occurred over several discrete episodes as evidenced by cross-cutting relationships of fractures and cement. Quantitative data on the distribution of inter- and intragranular quartz cement within cataclasized sandstones combined with CL observations show that the timing of deformation is in agreement with published dates of fault movement.
Magma mingling
(2009-04) Barker, Daniel S.
Sills and laccoliths
(2009-04) Barker, Daniel S.
Vesicles and pumice
(2009-03) Barker, Daniel S.