860 Matching Results

Search Results

Advanced search parameters have been applied.

Quartz and Silica: Part 1. - General Summary

Description: Report issued by the U.S. Bureau of Mines discussing quartz and silica minerals. As stated in the foreword, "the purpose of the present paper is to assemble brief summaries of the many widely differing industries engaged in the production and preparation of these minerals in their principal commercial forms" (p. 1). This report includes tables, and illustrations.
Date: August 1931
Creator: Santmyers, Reigart Meredith
Partner: UNT Libraries Government Documents Department

Technology and Uses of Silica and Sand

Description: Report issued by the Bureau of Mines over studies conducted on the production and uses of silica. Forms and different uses for silica are discussed. This report includes tables, illustrations, and photographs.
Date: 1927
Creator: Weigel, W. M.
Partner: UNT Libraries Government Documents Department

Investigations of silica alcogel aging using coherent light

Description: Light scattering methods have previously been used to monitor the formation of gels. In this report we present new light scattering techniques to study the properties of silica alcogels during the aging process. Monitoring one particular polarization transformation of scattered light with time reveals a clear increase in internal strain in standing alcogels with time. The stress birefringence coefficient of an acid-catalyzed SiO{sub 2} gel was found to be 3.4 x 10{sup 12} Brewsters. Additionally, the evolution of the stiffness of alcogels was investigated using laser speckle methods. Specifically, image analysis of specklegrams obtained during multi-frequency acoustic excitation of aging gels was used to non-destructively measure the hardening of alcogels. For an acid catalyzed gel with a theoretical density of {approx}0.05 g/cm{sup 3} SiO{sub 2}, the rate of hardening is found to be greatest between gelation and 2X the gel time, and drops considerably thereafter. The Young's modulus of the gel can be monitored over time with this method and was found to range from 6.2 x 10{sup 3} N/m{sup 2} after 6 hours to 2.2 x 10{sup 5} N/m{sup 2} after 24 hours for acid-catalyzed silica gels.
Date: June 1, 2001
Creator: Hunt, Arlon J. & Ayers, Michael R.
Partner: UNT Libraries Government Documents Department

Hydrophobic, fluorinated silica xerogel for low-k applications.

Description: A new hydrophobic hybrid silica film was synthesized by introducing one silicon precursor (as modifiers) into another precursor (network former). Hybrid films have improved properties. Hydrolysis and condensation of dimethyldiethoxysilane (DMDES) (solvent (EtOH) to DMDES molar ratio R = 4, water to DMDES molar ratio r = 4, 0.01 N HCl catalyst) was analyzed using high-resolution liquid 29Si NMR. It was found that after several hours, DMDES hydrolyzed and condensed into linear and cyclic species. Films from triethoxyfluorosilane (TEFS) have been shown to be promising interlayer dielectric materials for future integrated circuit applications due to their low dielectric constant and high mechanical properties (i.e., Young's modulus (E) and hardness (H)). Co-condensing with TEFS, linear structures from DMDES hydrolysis and condensation reactions rendered hybrid films hydrophobic, and cyclic structures induced the formation of pores. Hydrophobicity characterized by contact angle, thermal stability by thermogravimetric analysis (TGA), Fourier transform Infrared spectroscopy (FTIR), contact angle, and dynamic secondary ion mass spectroscopy (DSIMS), dielectric constant determined by impedance measurement, and mechanical properties (E and H) determined by nanoindentation of TEFS and TEFS + DMDES films were compared to study the effect of DMDES on the TEFS structure. Hybrid films were more hydrophobic and thermally stable. DMDES incorporation affected the dielectric constant, but showed little enhancement of mechanical properties.
Date: May 2004
Creator: Zhang, Zhengping
Partner: UNT Libraries

Measurements on the Thermal Expansion of Fused Silica

Description: Scientific paper issued by the Bureau of Standards over thermal expansion of fused silica. As stated in the abstract, "this paper gives the results of an investigation on the thermal expansion of transparent and nontransparent fused silica for various temperature ranges between -125 and +1,000 degrees Celsius. A detailed description of the apparatus and the methods used in this research and a summary of available data obtained by previous observers on the thermal expansion of fused silica are given" (p. 1). This paper includes tables, photographs, and illustrations.
Date: April 13, 1926
Creator: Souder, Wilmer H. & Hidnert, Peter
Partner: UNT Libraries Government Documents Department

Moisture Transport in Silica Gel Particle Beds: I. Theoretical Study

Description: Diffusion mechanisms of moisture within silica gel particles are investigated. It is found that for microporous silica gel surface diffusion is the dominant mechanism of moisture transport, while for macroporous silica gel both Knudsen and surface diffusion are important.
Date: August 1, 1986
Creator: Pesaran, A. A. & Mills, A. F.
Partner: UNT Libraries Government Documents Department

Growth of laser damage in fused silica: diameter to depth ratio

Description: Growth of laser initiated damage plays a major role in determining optics lifetime in high power laser systems. Previous measurements have established that the lateral diameter grows exponentially. Knowledge of the growth of the site in the propagation direction is also important, especially so when considering techniques designed to mitigate damage growth, where it is required to reach all the subsurface damage. In this work, we present data on both the diameter and the depth of a growing exit surface damage sites in fused silica. Measured growth rates with both 351 nm illumination and with combined 351 nm and 1054 nm illumination are discussed.
Date: October 29, 2007
Creator: Norton, M A; Adams, J J; Carr, C W; Donohue, E E; Feit, M D; Hackel, R P et al.
Partner: UNT Libraries Government Documents Department

Growth of Laser Damage in SiO2 under Multiple Wavelength Irradiation

Description: In laser systems using frequency conversion, multiple wavelengths will be present on optical components. We have investigated the growth of laser initiated damage in fused silica in the presence of multiple wavelengths. In particular, we measured growth at 351 nm in the presence of 1053 nm near the threshold of growth for 351 nm alone. The data shows that the sum fluence determines the onset of growth as well as the growth rate. The measured growth coefficient is consistent with all the energy being delivered at 351 nm. Additionally, we measured growth at 527 nm in the presence of 1053 nm near the threshold of growth at 527 nm alone. In this case, the sum fluence also determines the growth coefficient but the rate is consistent with all the energy being delivered at 1053 nm. We present the measurements and discuss possible reasons for the behavior.
Date: October 28, 2005
Creator: Norton, M A; Donohue, E E; Feit, M D; Hackel, R P; Hollingsworth, W G; Rubenchik, A M et al.
Partner: UNT Libraries Government Documents Department

Wettability of Silicon, Silicon Dioxide, and Organosilicate Glass

Description: Wetting of a substance has been widely investigated since it has many applications to many different fields. Wetting principles can be applied to better select cleans for front end of line (FEOL) and back end of line (BEOL) cleaning processes. These principles can also be used to help determine processes that best repel water from a semiconductor device. It is known that the value of the dielectric constant in an insulator increases when water is absorbed. These contact angle experiments will determine which processes can eliminate water absorption. Wetting is measured by the contact angle between a solid and a liquid. It is known that roughness plays a crucial role on the wetting of a substance. Different surface groups also affect the wetting of a surface. In this work, it was investigated how wetting was affected by different solid surfaces with different chemistries and different roughness. Four different materials were used: silicon; thermally grown silicon dioxide on silicon; chemically vapor deposited (CVD) silicon dioxide on silicon made from tetraethyl orthosilicate (TEOS); and organosilicate glass (OSG) on silicon. The contact angle of each of the samples was measured using a goniometer. The roughness of the samples was measured by atomic force microscopy (AFM). The chemistry of each of the samples were characterized by using X-ray photoelectron spectroscopy (XPS) and grazing angle total attenuated total reflection Fourier transform infrared spectroscopy (FTIR/GATR). Also, the contact angle was measured at the micro scale by using an environmental scanning electron microscope (ESEM).
Date: December 2009
Creator: Martinez, Nelson
Partner: UNT Libraries

Geochemical Methods for the Identification of ASR Gel

Description: This paper presents a geochemical method for staining various products of the alkali-silica reaction. The method is based on both the composition of ASR gel and one of its properties (the ability to exchange cations with a fluid). The stained concrete can be observed in normal light and serves as both a rapid field screening method and a useful aid for detailed petrographic examinations.
Date: July 1, 1998
Creator: Guthrie, G.D. & Carey, J.W.
Partner: UNT Libraries Government Documents Department

Structural Formation Studies of UV-Catalyzed Gels and Aerogels byLight Scattering

Description: The skeletal structure of aerogel is determined before, during, and after the gel is formed. Supercritical drying of aerogel largely preserves the pore structure that is determined near the time of gelation. To better understand these gel formation mechanisms we carried out measurements of the time evolution of light scattering in a series of gels prepared without conventional acid or base catalysis. Instead, ultraviolet light was used to catalyze the formation of silica gels made from the hydrolysis of tetraethylorthosilicate and partly prehydrolyzed tetraethylorthosilicate in ethanol. Time evolution of light scattering provides information regarding the rate and geometrical nature of the assembly of the primary silica particles formed in the sol. UV-catalyzed gels show volumetric growth typical of acid-catalyzed gels, except when UV exposure is discontinued at the gel point, where gels then show linear chain formation typical of base-catalyzed gels. Long term UV exposure leads to coarsening of the pore network, a decrease in the clarity of the aerogel, and an increase in the surface area of the aerogel. Additionally, UV exposure up to the gel point leads to increased crystallinity in the final aerogel.
Date: April 1, 1998
Creator: Hunt, Arlon J. & Ayers, Michael R.
Partner: UNT Libraries Government Documents Department

The Aqueous Thermodynamics and Complexation Reactions of Anionic Silica and Uranium Species to High Concentration

Description: During this contract period, a number of papers were published. The papers prior to this report have been reported in earlier annual reports. This final report covers the 2005 & 2006 publications which have been published as well as the last few which have been submitted, but are still under review for acceptance for publication. The titles and Abstract of the papers are presented in Section A, and the full published papers in Section B.
Date: November 28, 2006
Creator: Choppin, Gregory R.
Partner: UNT Libraries Government Documents Department

Reactions and Interfacial Behaviors of the Water–Amorphous Silica System from Classical and Ab Initio Molecular Dynamics Simulations

Description: Due to the wide application of silica based systems ranging from microelectronics to nuclear waste disposal, detailed knowledge of water-silica interactions plays an important role in understanding fundamental processes, such as glass corrosion and the long term reliability of devices. In this dissertation, atomistic computer simulation methods have been used to explore and identify the mechanisms of water-silica reactions and the detailed processes that control the properties of the water-silica interfaces due to their ability to provide atomic level details of the structure and reaction pathways. The main challenges of the amorphous nature of the silica based systems and nano-porosity of the structures were overcome by a combination of simulation methodologies based on classical molecular dynamics (MD) simulations with Reactive Force Field (ReaxFF) and density functional theory (DFT) based ab initio MD simulations. Through the development of nanoporous amorphous silica structure models, the interactions between water and the complex unhydroxylated internal surfaces identified the unusual stability of strained siloxane bonds in high energy ring structure defects, as well as the hydroxylation reaction kinetics, which suggests the difficulty in using DFT methods to simulate Si-O bond breakage with reasonable efficiency. Another important problem addressed is the development of silica gel structures and their interfaces, which is considered to control the long term residual dissolution rate in borosilicate glasses. Through application of the ReaxFF classical MD potential, silica gel structures which mimic the development of interfacial layers during silica dissolution were created A structural model, consisting of dense silica, silica gel, and bulk water, and the related interfaces was generated, to represent the dissolution gel structure. High temperature evolution of the silica-gel-water (SGW) structure was performed through classical MD simulation of the system, and growth of the gel into the water region occurred, as well as the formation of intermediate range structural ...
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: May 2016
Creator: Rimsza, Jessica M
Partner: UNT Libraries

A Well-Defined, Silica-Supported Tungsten Imido Alkylidene OlefinMetathesis Catalyst

Description: The reaction of [W(=NAr)(=CHtBu)(CH2tBu)2](1; Ar =2,6-iPrC6H3) with a silica partially dehydroxylated at 700oC, SiO2-(700),gives syn-[(_SiO)W(=NAr)(=CHtBu)(CH2tBu)](2) as a major surface species,which was fully characterized by mass balance analysis, IR, NMR, EXAFS,and DFT periodic calculations. Similarly, complex 1 reacts with[(c-C5H9)7Si7O12SiOH]to give [(SiO)W(=NAr)(=CHtBu)(CH2tBu)](2m), whichshows similar spectroscopic properties. Surface complex 2 is a highlyactive propene metathesis catalyst, which can achieve a TON of 16000within 100 h, with only a slow deactivation.
Date: June 13, 2006
Creator: Rhers, Bochra; Salameh, Alain; Baudouin, Anne; Quadrelli, ElsjeA.; Taoufik, Mostafa; Coperet, Christophe et al.
Partner: UNT Libraries Government Documents Department

Morphological, rheological and electrochemical studies ofpoly(ethylene oxide) electrolytes containing fumed silicananoparticles

Description: In this paper, the rheology and crystallization of composite Poly(Ethylene Oxide) (PEO) electrolytes were studied by dynamic mechanical analysis, DSC and polarized light microscopy. The effects of fumed silica nanoparticles on the conductivities of the polymer electrolytes at temperatures above and below their melting point were measured and related to their rheology and crystallization behavior, respectively. The electrolyte/electrode interfacial properties and cycling performances of the composite polymer electrolytes in Li/Li cells are also discussed. The measured electrochemical properties were found to depend heavily on the operational environments and sample processing history.
Date: June 1, 2003
Creator: Xie, Jiangbing; Kerr, John B.; Duan, Robert G. & Han, Yongbong
Partner: UNT Libraries Government Documents Department

Molecular modeling in support of CO2 sequestration and enhanced oil recovery.

Description: Classical molecular dynamics simulations were used to investigate the formation of water droplets on two kaolinite surfaces: the gibbsite-like surface which is hydrophilic and the silica surface which is hydrophobic. Two methods for calculating contact angles were investigated in detail. The method of Giovambattista et al. was successful in calculating contact angles on both surfaces that compare well to the experimental data available. This is the first time that contact angles have been calculated for kaolinite surfaces from molecular simulations. This preliminary study provides the groundwork for investigating contact angles for more complex systems involving multiple fluids (water, CO{sub 2}, oil) in contact with different minerals in the subsurface environment.
Date: January 1, 2011
Creator: Criscenti, Louise Jacqueline & Bracco, Jacquelyn (Georgia Institute of Technology, Atlanta, GA)
Partner: UNT Libraries Government Documents Department

The effect of CO2(aq), Al(aq) and temperature on feldspar dissolution

Description: The authors measured labradorite (Ca{sub 0.6}Na{sub 0.4}Al{sub 1.6}Si{sub 2.4}O{sub 8}) dissolution rates using a mixed flow reactor from 30 to 130 C as a function of CO{sub 2} (3 x 10{sup -3} and 0.6 M), and aluminum (10{sup -6} to 10{sup -3}M) at pH 3.2. Over these conditions, labradorite dissolution can be described with a single rate expression that accounts for observed increases in dissolution rate with temperature and decreases in dissolution rate with dissolved aluminum: Rate{sub Si} (mol Labradorite cm{sup -2} s{sup -1}) = k{double_prime} x 10{sup -Ea/2.303RT} [(a{sub H{sup +}}{sup 3n}/a{sub Al{sup 3+}}{sup n})K{sub T}/(1+K{sub T} (a{sub H{sup +}}{sup 3n}/a{sub Al{sup 3+}}{sup n}))] where the apparent dissolution rate constant, k{double_prime} = 10{sup -5.69} (mol Labradorite cm{sup -2}s{sup -1}); the net activation energy, E{sub a} = 10.06 (kcal mol{sup -1}); H{sup +}-Al{sup 3+} exchange coefficient, n = 0.31; and silica rich surface complex formation constant K{sub T} = 4.5 to 5.6 from 30 to 130 C. The effect of CO{sub 2}(aq) on mineral dissolution is accounted for by changes in solution pH. At temperatures below 60 C, labradorite dissolves incongruently with preferential dissolution of Na, Ca and Al over Si.
Date: October 14, 2003
Creator: Carroll, S & Knauss, K
Partner: UNT Libraries Government Documents Department

Measurement and Prediction of H2O Outgassing Kinetics from Silica-Filled Polydimethylsiloxane TR55 and S5370

Description: The isoconversional technique was employed for the measurement and prediction of H2O outgassing kinetics from silica-filled polydimethylsiloxane TR55 and S5370 in a vacuum or dry environment. Isoconversional analysis indicates that the energy barrier for H2O release from TR55 and S5370 is an increasing function of the fractional H2O release. This can be interpreted as the release of H2O from physisorbed water and then chemisorbed water with decreasing OH density from the surfaces of the embedded silica particles. Model independent predictions of H2O outgassing based on the measured kinetics follow the trend of actual isothermal outgassing at elevated temperatures, and suggest gradual outgassing in dry storage over many decades at low temperatures for both TR55 and S5370.
Date: August 28, 2006
Creator: Dinh, L N; Burnham, A K; Schildbach, M A; Smith, R A; Maxwell, R S; Balazs, B et al.
Partner: UNT Libraries Government Documents Department

Assessment of Methods to Consolidate Iodine-Loaded Silver-Functionalized Silica Aerogel

Description: The U.S. Department of Energy is currently investigating alternative sorbents for the removal and immobilization of radioiodine from the gas streams in a nuclear fuel reprocessing plant. One of these new sorbents, Ag0-functionalized silica aerogels, shows great promise as a potential replacement for Ag-bearing mordenites because of its high selectivity and sorption capacity for iodine. Moreover, a feasible consolidation of iodine-loaded Ag0-functionalized silica aerogels to a durable SiO2-based waste form makes this aerogel an attractive choice for sequestering radioiodine. This report provides a preliminary assessment of the methods that can be used to consolidate iodine-loaded Ag0-functionalized silica aerogels into a final waste form. In particular, it focuses on experimental investigation of densification of as prepared Ag0-functionalized silica aerogels powders, with or without organic moiety and with or without sintering additive (colloidal silica), with three commercially available techniques: 1) hot uniaxial pressing (HUP), 2) hot isostatic pressing (HIP), and 3) spark plasma sintering (SPS). The densified products were evaluated with helium gas pycnometer for apparent density, with the Archimedes method for apparent density and open porosity, and with high-resolution scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) for the extent of densification and distribution of individual elements. The preliminary investigation of HUP, HIP, and SPS showed that these sintering methods can effectively consolidate powders of Ag0-functionalized silica aerogel into products of near-theoretical density. Also, removal of organic moiety and adding 5.6 mass% of colloidal silica to Ag0-functionalized silica aerogel powders before processing provided denser products. Furthermore, the ram travel data for SPS indicated that rapid consolidation of powders can be performed at temperatures below 950°C.
Date: September 1, 2013
Creator: Matyas, Josef & Engler, Robert K.
Partner: UNT Libraries Government Documents Department

Supported Molecular Catalysts: Synthesis, In-Situ Characterization and Performance

Description: The objectives of our work are: (i) to create solid catalysts with active sites that can function in a cooperative manner to enhance reactivity and selectivity, and (ii) to prepare solid catalysts that can perform multiple reactions in a network that in some cases would not be possible in solution due to the incompatibilities of the various catalytic entities (for example an acid and a base). We carried out extensive reactions to test the nature of the cooperative effect caused by thiol/sulfonic acid interactions. The acid/thiol combination provided an example where the two organic groups should be positioned as close to one another as possible. We also studied a system where this is not possible (acid-base). We investigated simultaneously incorporating acid and base groups into the same material. For the case of acid and bases, there is an optimal separation distance (too close allows for neutralization while too far eliminates any cooperative behavior).
Date: March 13, 2009
Creator: Davis, Mark E.
Partner: UNT Libraries Government Documents Department

The minimum pore size obtainable in a silica gel during drying

Description: The pore size r{sub p} in a gel is determined by the extent of shrinkage of the gel network during drying. Shrinkage is driven by the collapse of the gel network in response to the capillary pressure P{sub c} exerted by the pore fluid. The extent of shrinkage depends on the balance between the capillary pressure P{sub c} in the pore fluid and the bulk modulus K{sub p} of the gel. The hydraulic pore radius, r{sub H} = 2V{sub p}/S{sub a}, where V{sub p} is the pore volume and S{sub a} is the apparent N{sub 2} BET surface area, is often used to characterize the pore size of a gel. A series of acid catalyzed silica gels dried in pore fluids with different {gamma}{sub lv}, showed that there is a limit to the minimum apparent r{sub H} obtainable in a gel, and when the volume fraction of porosity {phi} {le} 0.37, r{sub H} becomes constant and {approximately}0.8 nm. In contrast, experimental data show that the true pore size r{sub p} of gels continues to decrease when {phi} {le} 0.37. Analysis of their adsorption isotherms show that while r{sub H} apparently stays constant: (a) the BET C constant continues to increase, (b) the width and average of their pore size distributions continue to decrease, and (c) as shrinkage continues the gels eventually become non-porous to N{sub 2} at 77K but are still porous to CO{sub 2} at 273K. This paper reviews these results and addresses micropore formation in silica gels with the goal of determining how P{sub c} influences the final r{sub p}, and why r{sub p} and r{sub H} diverge when {phi} {le} 0.37.
Date: December 1994
Creator: Wallace, S.; Brinker, C. J. & Smith, D. M.
Partner: UNT Libraries Government Documents Department