Browsing by Author "Barron, Andrew R."
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Item Advanced ceramic composites and coatings via alumoxane nanoparticles(1999) Callender, Rhonda Lynn; Barron, Andrew R.The objective of this research is the development of an environmentally-benign process for the synthesis and fabrication of alumina-based ceramic precursors and advanced ceramic materials. Carboxylate-alumoxanes, [Al(O)x(OH) y(O2CR)z]n, were synthesized by the reaction of boehmite, [Al(O)(OH)]n, with acetic acid (HO2 CCH3), methoxyacetic acid (HO2CCH2OCH 3), methoxyethoxyacetic acid (HO2CCH2OCH 2CH2OCH3) and methoxyethoxyethoxyacetic acid [HO 2CCH2(OCH2CH2)2OCH 3]. Carboxylate-alumoxanes can be considered inorganic-organic hybrid materials consisting of an aluminum-oxygen backbone with carboxylate substituents. These are infinitely stable at ambient conditions in solid and solution. In addition, they show no propensity to segregation or polymerization and are readily processed in aqueous or hydrocarbon medium. Upon thermolysis the carboxylate-alumoxanes are converted to alumina. The physical and spectroscopic properties of the carboxylate-alumoxanes have been determined. The potential environmental impact of the new alumoxane methodology will be discussed. Carboxylate-alumoxanes are reacted with metal acetylacetonate complexes, M(acac)n, to form metal-doped nanoparticles and aluminum acetylacetonate via a transmetalation reaction. This allows the facile formation of highly crystalline materials such as calcium hexaluminate (CaAl12O 19, hibonite) and lanthanum hexaluminate. The formation of highly phase pure materials is proposed to be due to the presence of atomic scale mixing within the metal doped alumina nanoparticle structure of the carboxylate-alumoxane. The potential of the carboxylate alumoxanes as interlayer coatings in ceramic matrix composites (CMCs) was investigated. Sapphire, SiC, carbon, and KevlarRTM fibers and carbon/KevlarRTM fabric have been dip-coated by aqueous and CHCl3 solutions of carboxylate-alumoxane nanoparticles and fired to 1400°C to form uniform alumina and aluminate coatings. Optimum solvent, dip/dry, and firing sequences were determined for the formation of crack-free coatings. Coatings produced were stable to thermal cycling under air at temperatures of 1400°C. The ability of the carboxylate-alumoxanes to provide crack infiltration and repair of damaged coatings is demonstrated.Item Aliphatic amine based nanocarbons for the absorption of carbon dioxide(2015-05-19) Barron, Andrew R.; Dillon, Eoghan; Rice University; United States Patent and Trademark OfficeA composition of matter, and method to make same, for a nano-based material including a nanocarbon support to which is attached an aliphatic amine. In particular, the composition of matter is an aliphatic amine-nanocarbon material that includes a nanocarbon (NC) support, such as C60, nano-graphite, graphene, nanocarbon ribbons, graphite intercalation compounds, graphite oxide, nano-coal, nanohorns, and combinations thereof, and further includes an aliphatic amine, such as polyethyleneimine (PEI).Item Aliphatic amine based nanocarbons for the absorption of carbon dioxide(2014-01-28) Barron, Andrew R.; Dillon, Eoghan; Rice University; United States Patent and Trademark OfficeA composition of matter, and method to make same, for a nano-based material including a nanocarbon support to which is attached an aliphatic amine. In particular, the composition of matter is an aliphatic amine-nanocarbon material that includes a nanocarbon (NC) support, such as C60, nano-graphite, graphene, nanocarbon ribbons, graphite intercalation compounds, graphite oxide, nano-coal, nanohorns, and combinations thereof, and further includes an aliphatic amine, such as polyethyleneimine (PEI).Item Aluminum and gallium chloride stabilized arene-mercury complexes(2001) Borovik, Alexander Sergeevich; Barron, Andrew R.Reaction of HgCl2 with two equivalents of MCl3 in an aromatic solvent yields Hg(arene)2(MCl4) 2 where arene = C6H5Me, C6H5Et, o-C6H4Me2, C6H3 -1,2,3-Me3, M = Al, Ga. Reaction of HgCl2 with MCl3 in benzene, m-xylene, and p-xylene results in the formation of liquid clathrates whose spectroscopic characterization is reported. In the solid state, all compounds, with the exception of o-xylene complexes, exist as neutral complexes in which two arenes are bound to the mercury and the MCl3 groups are bound through bridging chlorides to the mercury. o-xylene complex exists as a cation anion pair [Hg(o-C6H4Me 2)2(AlCl4)][AlCl4]. However, in solution all mercury-arene compounds exist as neutral complexes. The structures of Hg(arene)2(AlCl4)2 and [Hg(arene)2(AlCl 4)]+ have been optimized by DFT calculations to facilitate the assignment of the 13C CPMAS NMR spectra, and are in good agreement with the X-ray diffraction structures. Dissolution of Hg(arene)2(MCl4)2 in C6D6 results in a rapid H/D exchange and the formation of the appropriate dn-arene and C6D5H. H/D exchange between excess arene and C6D6 is also found to be catalyzed by Hg(arene)2(MCl4)2 including those with a different arene ligand. Based on DTF calculations the inter- and intra-molecular mechanism of the exchange is proposed. Mercury-arene complexes are found to be very active catalysts for the alkylation of arenes by olefins. Ethylene, propylene, and cyclohexene reacts with benzene or toluene to form mono- and polyalkylated products, the distribution being dependent on the nature of olefin. Based on the deuterium labeling experiments two different mechanisms of arene alkylation are discussed. Reaction of K[CpFe(CO)2] with a large excess of GaCl 3 yields [{CpFe(CO)2}Ga(Cl·GaCl3)(mu-Cl)] 2, while reactions with 1 and 0.5 equivalents yields [{CpFe(CO) 2}GaCl2]n, and [{CpFe(CO)2}2Ga(mu-Cl)] infinity, respectively. [{CpFe(CO)2}GaCl2] n reacts with MeCN to yield [CpFe(CO)2]GaCl2(MeCN). Reduction of [{CpFe(CO)2}2Ga(mu-Cl)]infinity with potassium in Et2O yields the previously reported [CpFe(CO) 2]3Ga and gallium metal. Reaction of K[CpFe(CO)2] with GaI3 yields [CpFe(CO)2]GaI2, which upon hydrolysis gives the unusual galloxane, [CpFe(CO)2]6Ga 6(mu3-O)4(mu-OH)2I2. Reaction of K[CpFe(CO)2] with InCl in toluene results in the formation of previously reported [CpFe(CO)2]3In and indium metal. Reaction of CpMo(CO)3H with Ga(tBu)3 yields [CpMo(CO)3]Ga(tBu)2 which forms a Lewis acid-base complex with MeCN: [CpMo(CO)3]Ga(tBu) 2(MeCN). The structure of [CpMo(CO)3]Ga(tBu) 2 shows evidence of unusual intra- and inter-molecular carbonyl &cdots; gallium interactions.Item Alumoxane/ferroxane nanoparticles for the removal of viral pathogens: the importance of surface functionality to nanoparticle activity(The Royal Society of Chemistry, 2012) Maguire-Boyle, Samuel J.; Liga, Michael V.; Li, Qilin; Barron, Andrew R.; Richard E. Smalley Institute for Nanoscale Science and TechnologyA bi-functional nano-composite coating has been created on a porous Nomex fabric support as a trap for aspirated virus contaminated water. Nomex fabric was successively dip-coated in solutions containing cysteic acid functionalized alumina (alumoxane) nanoparticles and cysteic acid functionalized iron oxide (ferroxane) nanoparticles to form a nanoparticle coated Nomex (NPN) fabric. From SEM and EDX the nanoparticle coating of the Nomex fibers is uniform, continuous, and conformal. The NPN was used as a filter for aspirated bacteriophage MS2 viruses using end-on filtration. All measurements were repeated to give statistical reliability. The NPN fabrics show a large decrease as compared to Nomex alone or alumoxane coated Nomex . An increase in the ferroxane content results in an equivalent increase in virus retention. This suggests that it is the ferroxane that has an active role in deactivating and/or binding the virus. Heating the NPN to 160 C results in the loss of cysteic acid functional groups (without loss of the iron nanoparticleﾒs core structure) and the resulting fabric behaves similar to that of untreated Nomex , showing that the surface functionalization of the nanoparticles is vital for the surface collapse of aspirated water droplets and the absorption and immobilization of the MS2 viruses. Thus, for virus immobilization, it is not sufficient to have iron oxide nanoparticles per se, but the surface functionality of a nanoparticle is vitally important in ensuring efficacy.Item Amplification of carbon nanotubes via seeded-growth methods(2013-10-22) Smalley, Richard E.; Hauge, Robert H.; Barron, Andrew R.; Tour, James M.; Schmidt, Howard K.; Billups, Edward W.; Dyke, Christopher A.; Moore, Valerie C.; Whitsitt, Elizabeth Anne; Anderson, Robin E.; Colorado Jr., Ramon; Stewart, Michael P.; Ogrin, Douglas C.; Rice University; United States Patent and Trademark OfficeThe present invention is directed towards methods (processes) of providing large quantities of carbon nanotubes (CNTs) of defined diameter and chirality (i.e., precise populations). In such processes, CNT seeds of a pre-selected diameter and chirality are grown to many (e.g., hundreds) times their original length. This is optionally followed by cycling some of the newly grown material back as seed material for regrowth. Thus, the present invention provides for the large-scale production of precise populations of CNTs, the precise composition of such populations capable of being optimized for a particular application (e.g., hydrogen storage). The present invention is also directed to complexes of CNTs and transition metal catalyst precurors, such complexes typically being formed en route to forming CNT seeds.Item Analyzing the transport of plasmonic particles through mineral formations(2013-11-05) Barron, Andrew R.; Maguire-Boyle, Samuel J.; Orbaek, Alvin White; Rice University; United States Patent and Trademark OfficeA transport of plasmonic particles through a mineral formation is analyzed by flowing a plasmonic particles solution through an immobile phase (e.g., a mineral formation), determining an absorbance of the plasmonic particles solution subsequent to flowing the plasmonic particles solution through the immobile phase, comparing the determined absorbance of the plasmonic particles solution with an absorbance of the plasmonic particles solution determined previous to flowing the plasmonic particles solution through the immobile phase, and determining an absorbance of the plasmonic particles to the immobile phase as a function of the comparison. The plasmonic particles solution may be produced by dissolving or suspending plasmonic particles in a mobile phase. Flowing the plasmonic particles solution through the immobile phase may include injecting the plasmonic particles solution into the immobile phase, and then flushing the plasmonic particles solution through the immobile phase.Item Apparatus for Scalable Functionalization of Single-Walled Carbon Nanotubes via the Billups-Birch Reduction(MDPI, 2017) Pham, David; Zhang, Kevin S.; Lawal, Olawale; Ghosh, Saunab; Gangoli, Varun Shenoy; Ainscough, Thomas J.; Kellogg, Bernie; Hauge, Robert H.; Adams, W. Wade; Barron, Andrew R.A prototype design of a reactor for scalable functionalization of SWCNTs by the reaction of alkyl halides with Billups-Birch reduced SWCNTs is described. The Hauge apparatus is designed to allow for the safe handling of all the reagents and products under an inert atmosphere at controlled temperatures. The extent of reaction of Li/NH3 solution with the SWCNTs is measured in-situ by solution conduction, while homogenous mixing is ensured by the use of a homogenizer, and thermocouple are placed at different heights within the reactor flask. Addition of an alkyl halide yield alkyl-functionalized SWCNTs, which may be isolated by solvent extraction leaving a solid sample that is readily purified by hydrocarbon extraction. As an example, reaction of SWCNT/Li/NH3 with 1-iododecane yields dodecane-functionalized SWCNTs (C12-SWCNTs), which have been characterized by TG/DTA, XPS, and Raman spectroscopy. Sample extraction during the reaction allows for probing of the rate of the reaction in order to determine the end point of the reaction, which for C12-SWCNTs (at −78 °C) is 30 min.Item Assessing Photocatalytic Oxidation Using Modified TiO2 Nanomaterials for Virus Inactivation in Drinking Water: Mechanisms and Application(2013-06-05) Liga, Michael; Li, Qilin; Alvarez, Pedro J.; Barron, Andrew R.; Tao, Yizhi JanePhotocatalytic oxidation is an alternative water treatment method under consideration for disinfecting water. Chlorine disinfection can form harmful byproducts, and some viruses (e.g. adenoviruses) are resistant to other alternative disinfection methods. Photocatalytic oxidation using nano-sized photocatalytic particles (e.g. TiO2, fullerene) holds promise; however, it is limited by its low efficiency and long required treatment times. This research focuses on improving virus inactivation by photocatalytic oxidation by modifying catalysts for improved activity, by analyzing virus inactivation kinetics, and by elucidating the inactivation mechanisms of adenovirus serotype 2 (AdV2) and bacteriophage MS2. Modifying TiO2 with silver (nAg/TiO2) or silica (SiO2-TiO2) improves the inactivation kinetics of bacteriophage MS2 by a factor of 3-10. nAg/ TiO2 increases hydroxyl radical (HO•) production while SiO2 increases the adsorption of MS2 to TiO2. These results suggest that modifying the photocatalyst surface to increase contaminant adsorption is an important improvement strategy along with increasing HO• production. The inactivation kinetics of AdV2 by P25 TiO2 is much slower than the MS2 inactivation kinetics and displays a strong shoulder, which is not present in the MS2 kinetics. nAg/TiO2 initially improves the inactivation rate of AdV2. SiO2-TiO2 reduces the AdV2 inactivation kinetics since adsorption is not significantly enhanced, as it is with MS2. Amino-C60 is highly effective for AdV2 inactivation under visible light irradiation, making it a good material for use in solar disinfection systems. The efficacy of amino-fullerene also demonstrates that singlet oxygen is effective for AdV2 inactivation. When exposed to irradiated TiO2, AdV2 hexon proteins are heavily damaged resulting in the release of DNA. DNA damage is also present but may occur after capsids break. With MS2, the host interaction protein is rapidly damaged, but not the coat protein. The kinetics of MS2 inactivation are rapid since it may quickly lose its ability to attach to host cells, while AdV2 kinetics are slower since the entire capsid must undergo heavy oxidation before inactivation occurs. Adenovirus inactivation likely occurs through breaching the capsid followed by radical attack of DNA and core proteins.Item Bi-Phasic photocatalytic particles prepared by sequential layer depositions for water cleaning and purification(One Central Press, 2016) Gomez, Virginia; Rome, Bertrand; Barron, Andrew R.; Dunnill, Charles W.Bi-phasic photocatalyic particles have been prepared in the form of Janus-like structures (bi-phasic materials with two distinct properties on opposing sides of the particle) using a new synthetic procedure consisting of the sequential layer depositions of semiconductor oxide materials onto soluble substrates. A number of different systems have to date been investigated with an aim of photocatalytic applications. A general synthetic regime consists of utilising simple sol-gel chemistry to deposit sequential layers of photocatalytic material on top of a soluble substrate. The substrate can subsequently be removed yielding extremely fragile disks that fracture into bi-phasic powders of Janus like particles. These particles have two unique sets of properties contained in different faces of the same particle, aimed at the simultaneous reduction and oxidation of toxic species in water. This new synthetic technique is investigated for photocatalyic applications with an eye to efficient water purification, utilising the synergistic effect of the two materials to create highly effective photocatalysts. The photocatalytic activity of anatase/rutile (TiO2) bi-phasic nanoparticle composites enhanced with platinum and deposited on the surface of polycarbonate filters has been successfully demonstrated. Deposition of the photocatalyst on filters overcomes expensive and time consuming recycling processes, adds porosity to the set up and reduces the scattering of nanoparticle dispersions.Item C60 Amino Acids and Peptides(2011) Strom, T. Amanda; Barron, Andrew R.Since the discovery of the buckyball in 1985, researchers have imagined its potential in fields ranging from materials science to medicinal chemistry. The unique size, shape and hydrophobicity of C 60 fullerene endow it with the ability to interact with biological superstructures such as enzymes and membranes making it attractive as a potential pharmacophore. In this regard, we have developed a new, simple route to water soluble fullerene amino acids, both alkyl and aryl, through the dipolar addition of azido starting materials. The synthesis of our phenylalanine derivative, including the chromatographic purification, requires only one day for its completion. We have subsequently used our C 60 phenylalanine derivative in the synthesis of a series of C 60 peptides for the purposes of enzyme inhibition, specifically human immunodeficiency virus Type 1 protease, a critical viral enzyme responsible for the maturation of the virus and a popular target of medicinal chemists. We have demonstrated the ability of our C 60 amino acids and peptides to inhibit HIV-1 PR in a cell-free fluorescence based assay at low nanomolar concentrations. Graphite, or specifically graphene, has recently come to the forefront of nanomaterials research due to it similar scale, properties, and reaction pathways as other more costly carbon nanostructures such as carbon nanotubes. We have demonstrated the high yield functionalization of graphitic starting materials through the thermal decomposition of azido amino acids to their corresponding nitrene. The result is an inexpensive, highly functionalized, carbon based scaffold.Item Carbon Nanomaterials for Detection, Assessment and Purification of Oil and Natural Gas(2014-04-21) Hwang, Chih-Chau; Tour, James M.; Barron, Andrew R.; Tomson, Mason B.This thesis studies several carbon nanomaterials. Their synthesis and characterization are studied as well as their potential applications to the oil industry. The carbon nanomaterials studied here include mesoporous carbon (CMK-3), sulfur- or nitrogen-doped porous carbon (SPC or NPC), and commercial carbon black (CB). Through appropriate functionalization, these carbon nanomaterials exhibit unique properties and their performances in detection, assessment as well as purification of oil and natural gas are studied and demonstrated. First, it was shown that amine-modified CMK-3 composites, polyethylenimine-CMK-3 (PEI-CMK-3) and polyvinylamine-CMK-3 (PVA-CMK-3) can be synthesized through in situ polymerization of amine species within the channels of the CMK-3. The synthesis process results in the entrapped amine polymers interpenetrating the composite frameworks of the CMK-3, improving the CO2 capture performance and recycle stability. CO2 uptake by the synthesized composites was determined using a gravimetric method at 30 °C and 1 atm; the 39% PEI-CMK-3 composite had ~12 wt% (3.1 mmol/g) CO2 uptake capacity and the 37% PVA-CMK-3 composite had ~13 wt% (3.5 mmol/g) CO2 uptake capacity. A desorption temperature of 75 °C was sufficient for regeneration. The CO2 uptake was the same when using 10% CO2 in a 90% CH4, C2H6 and C3H8 mixture, underscoring this composite’s efficacy for CO2 sequestration from natural gas. Secondly, nucleophilic porous carbons (SPC and NPC) were synthesized from simple and inexpensive carbon-sulfur and carbon-nitrogen precursors. A strong sorbate-sorbent interaction between CO2 and nucleophilic centers in the porous carbon was established using spectroscopic and heat of sorption data. Raman spectroscopy supports the assertion that the nucleophilic centers react with the CO2 to produce carbonate anions that further cause polymerization in the porous carbon channels to form poly(CO2) under much lower pressure than previously reported for such polymer formation. Once returned to ambient conditions, the poly(CO2) depolymerizes during the pressure swing, leading to a sorbent that can be easily regenerated without the thermal energy input that is required for traditional liquid phase sorbents. The synergy between the nucleophilic centers and the high surface area porous carbon produces a sorbent with high CO2 capacity, selectivity, and volumetric efficiency, so that the materials have potential to be used for CO2 removal from natural gas streams. As energy demand continues to increase, it is desirable to produce as much oil as possible from existing oil wells. Tracers have long been used to map entry/exit well correlations in the oil-field, but they do not provide any information about the environment between the entry and exit locations. Hence, the third part of this thesis will show that nanoparticles possessing functionalized carbon black (fCB) cores and sulfated polyvinyl alcohol (sPVA) addends can be designed to transport hydrocarbon detection molecules through subsurface rock formations. The sPVA-fCBs are stable under high-temperature and salinity conditions and are transported through a variety of oilfield rock types. A non-radioactive probe molecule that is easily detectable by mass spectrometry, triheptylamine (THA), was adsorbed onto the sPVA-fCBs. The THA was selectively released when the nanoparticles were passed through a column of isooctane-containing crushed rock, providing a path to both entry and exit correlations and a measure of oil content. This study simulates detection and quantitative analysis of the hydrocarbon content in downhole rock formations, which is a critically needed assessment in older oilfields. Crude oil is classified as “sour” when it contains a total sulfur content greater than 0.5%. Among these sulfur species, H2S is the one of main impurities in sour crude. The sour crude is toxic and corrosive to the materials of construction in pipelines and other holding and transportation vessels. Since the sulfur amount in a sample of crude depends on where it was found, if the concentration of the sulfur species in the subsurface could be accurately monitored, then geologists might be able to evaluate the quality of the crude before large scale extraction ensues. The last part of the thesis covers polyvinyl alcohol functionalized carbon black (PVA-CB). The particles have high stability under high temperature and salinity conditions, and they acts as a carrier to transport molecular cargo efficiently through simulated oilfield formations. After being functionalized with H2S-sensitive moieties, the functionalized PVA-CB can be pumped through H2S-containing oil and water in porous rock and the H2S content can be determined based on the fluorescent enhancement of the H2S-sensitive addends.Item Carbon Nanotubes(Rice University, 2013-09-30) Flood, Dennis J.; Barron, Andrew R.Item Carboxylation and Decarboxylation of Aluminum Oxide Nanoparticles Using Bifunctional Carboxylic Acids and Octylamine(Hindawi, 2016) Alexander, Shirin; Gomez, Virginia; Barron, Andrew R.The carboxylation of alumina nanoparticles (NPs), with bifunctional carboxylic acids, provides molecular anchors that are used for building more complexed structures via either physisorption or chemisorption. Colloidal suspensions of the NPs may be prepared by covalently bonding a series of carboxylic acids with secondary functional groups (HO2C-R-X) to the surface of the NPs: lysine (X = NH2), p-hydroxybenzoic acid (X = OH), fumaric acid (X = CO2H), and 4-formylbenzoic acid (X = C(O)H). Subsequent reaction with octylamine at either 25°C or 70°C was investigated. Fourier transform IR-attenuated reflectance spectroscopy (FTIR-ATR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) along with energy dispersive X-ray (EDX) analysis were used to characterize the bifunctionalized monolayers and/or multilayer corona surrounding the alumina NPs and investigate the reaction mechanism of octylamine with the functional groups (X) of the NPs. Except for the fumaric functionalized NPs, addition of octylamine to the functionalized NPs leads to removal of excess carboxylic acid corona from the surface via an amide formation. The extent of the multilayer is dependent on the strength of the acid⋯acid interaction.Item Catalyst Residue and Oxygen Species Inhibition of the Formation of Hexahapto-Metal Complexes of Group 6 Metals on Single-Walled Carbon Nanotubes(MDPI, 2017) Wright, Kourtney D.; Barron, Andrew R.The reaction of Group 6 metals with SWCNT has the potential to bridge the resistive SWCNT…SWCNT junctions by the formation of “Cr(SWCNT)2” complexes analogous to Cr(C6H6)2. This study reports that the formation of such species is very sensitive to oxidation by a residual iron oxide catalyst used for the growth of the SWCNTs and adsorbed/bound oxygen functionality. The reaction of raw HiPco SWCNTs with M(CO)6 and (C7H8)M(CO)3 (M = Cr, W) or (C6H6)Cr(CO)3 results in the formation of the Group 6 metal oxides. Annealing and acid treating the HiPco SWCNTs to reduce the catalyst content allows for the observation of zero valent metals by XPS, while the use of very high purity SWCNTs and graphene allows for the addition of primarily zero valent Group 6 metals, including the bis-hexahapto metal complex.Item Catalytic Growth of Carbon Nanotubes by Direct Liquid Injection CVD Using the Nanocluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y](MDPI, 2018) Esquenazi, Gibran L.; Brinson, Bruce; Barron, Andrew R.The growth of carbon nanotubes (CNTs) by direct liquid injection chemical vapor deposition (DLICVD) has been studied using the polyoxometalate cluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y] (FeMoC) as the catalyst with either ethanol or toluene as the carbon source. In order to screen different growth conditions a single large batch of FeMoC is required in order to eliminate variation in the catalyst precursor. The preparation of 6 g of FeMoC is possible by scaling (10×) literature reagent ratios. DLICVD studies of the FeMoC derived carbon product were evaluated by Raman spectroscopy and scanning electron microscopy (SEM) to determine the quality (G:D ratio) and purity of CNT content. With the use of ethanol as the carbon source, increasing the temperature in the injection zone (aspiration temperature) above 250 °C increases the yield, and results in a slight increase in the G:D ratio. The maximum yield is obtained with a growth temperature of 900 °C, while the G:D ratio is the highest at higher temperatures. Faster solution injection rates increase yield, but with a significant decrease in G:D, in fact no CNTs are observed in the product for the highest injection rate (10 mL/h). An optimum catalyst concentration of 1.25 wt.% is found, which influences both the catalyst:C and catalyst:H ratios within the system. Growth at 800 °C is far more efficient for toluene as a carbon source than ethanol. The resulting “process map” allows for large quantities of CNTs to be prepared by DLICVD.Item Cement hydration inhibition and crosslinking in the guar-borate system(2001) Bishop, Maximilienne; Barron, Andrew R.The hydration of cement and its individual mineral phases in the presence of different inhibitors has been investigated. The behavior of an exemplary oligo-phosphate, nitriltris(methylene)phosphonic acid (H6ntmp), is compared to the behavior of more traditional retarders. The reaction between H6ntmp and calcium hydroxide, tricalcium silicate, tricalcium aluminate, and cement have revealed that the calcium phosphonate complex, [Ca(H 4ntmp)]infinity, plays a role in inhibition with phosphonates. NMR and XPS data suggest that the presence of uncoordinated P-O bonds in calcium phosphonates lends phosphonates the unique ability to simultaneously complex calcium ions while adhering to hydrating aluminate surfaces, promoting heterogeneous nucleation of calcium phosphonates at the surface of aluminate minerals and blocking normal hydration reactions. Reactions with tartaric acid also forms a calcium complex on top of the aluminate phases. In contrast, sucrose, appears to act directly on the silicate phases actually accelerates the reactions of the aluminate phases. The reactions of borate ions with diols and monosaccharides have been used to model cross-linking in the guar-borate system. Specifically, the reactions of borate with alcohols were characterized by 11B NMR to determine which reactions are most favorable. It was found that the acidity of the hydroxyl groups plays an important role in the efficiency of cross-linking, and has a greater effect on the energy of the resulting borate-diol complexes than the conformation (i.e., cis versus trans) in reactions of borate with cyclohexanediols and monosaccharides. The role of Group 1 metal salts in the borate-diol reactions was also investigated by 11B NMR and by the synthesis of model compounds. It was found that the metal cations play an important role in stabilizing the borate-diol complexes in the solid state. In solution, it was found that cross-linking is enhanced by the presence of strongly coordinating cations, as opposed to more purely ionic cations, and cross-linking is decreased in the presence of non-coordinating ammonium cations.Item CFD Analysis of the Location of a Rear Wing on an Aston Martin DB7 in Order to Optimize Aerodynamics for Motorsports(MDPI, 2022) O’Driscoll, Thomas P.; Barron, Andrew R.The purpose of this study is to identify the initial lateral and vertical location and angle of attack of a GT4-style rear wing on the rear downforce for an Aston Martin DB7 Vantage, prior to installation. The tests were completed with a two-dimensional model, using the Computational Fluid Dynamics (CFD) software, Fluent Ansys. The tests were completed using a range of velocities: 60–80 mph. Optimization of the position of the rear wing aerodynamic device was permitted under the Motorsport UK rules for multiple race series. The results show that while the drag decreases the farther back the wing is located, the desired configuration for the rear wing with regard to downforce is when it is positioned ca. 1850 mm back from the center point of the car, with an attack angle of 5°. Unusually, this is to the front of the boot/rear deck, but it is remarkably similar to where Aston Martin set the rear wing on their Le Mans car in 1995, above where the rear windscreen met the boot hinge, which was based upon wind tunnel studies using a scale model. Our results suggest that while 2D simulations of these types cannot give absolute values for downforce due to aerodynamic device location, they can provide low costs, fast simulation time, and a route for a wide range of cars, making the approach accessible to club motorsports, unlike complex 3D simulation and wind tunnel experimentation.Item Characterization via nuclear magnetic resonance of Portland cement and related materials(2007) Edwards, Christopher Lane; Barron, Andrew R.The physicochemical and engineering performance properties of several API class G and H ordinary Portland cements (OPCs) from various foreign and domestic sources have been investigated. The engineering performance properties are found to vary from sample to sample, and sources for this variation were sought out and identified. Magic angle spinning (MAS) 29Si nuclear magnetic resonance (NMR) experiments were marked by unusual relaxation behavior due to paramagnetism inherent in OPCs. A model system was created to mimic the paramagnetism of the cements and the system's relaxation behavior was analyzed. The iron in the calcium aluminoferrite (C4AF) provides the paramagnetism sufficient to substantially increase the relaxation rates of the 29Si in the tricalcium silicate (C3S) and dicalcium silicate (C2S) of cement. Several relaxation techniques were evaluated for analyzing cement relaxation, and saturation recovery was identified as the preferred technique. Correlations of data from the saturation recovery experiments with engineering performance properties, especially the strength development of cement pastes, were obtained facilely. An error analysis of the NMR and engineering performance testing techniques was conducted, which indicated that NMR measurements produced less error than the engineering performance tests. A best practice, modified from the saturation recovery experiment, is proposed for use in property correlations. Additionally, 13C MAS NMR was used to characterize various fluorinated single-walled carbon nanotubes (F-SWNTs), which proved surprisingly effective in attenuating 13C-19F dipolar interactions and quantifying the extent of functionalization present at high degrees of reaction. The mixed-metal nanocluster known as FeMoC was also characterized by MAS NMR. The impact of the paramagnetic Fe3+ in the Keplerate cage on the 31P nuclei in the caged Keggin ion of FeMoC was evident in the greatly reduced relaxation times measured.Item Chemical control over ceramic porosity using carboxylate-alumoxanes(2005-08-30) Barron, Andrew R.; Bailey, Diane Amy; Wiesner, Mark Robert; Jones, Christopher Daniel; Callender, Rhonda Lynn; Rice University; United States Patent and Trademark OfficeThis invention relates generally to a method for controlling the pore size, pore size distribution and porosity of aluminum-oxide based ceramics through the choice of substituents on carboxylate-alumoxanes and aluminum-oxide nanoparticles. The method allows for the formation of intra-granular pores in the nanometer range to be created in alumina and aluminum oxide ceramic bodies. The control over pore size and pore size distribution is accomplished through the use of different chemical substituents on the carboxylate-alumoxanes and aluminum-oxide nanoparticles. The size and distribution of pores within the alumina-oxide ceramic are dependent on the identity of the carboxylate substituents. In particular the formation of intra-versus inter-granular porosity is dependent on the identity of the carboxylate substituents. The invention also provides methods for the manufacture of ceramic coatings on ceramic and carbon fibers for composite applications and ceramic membranes with nanometer sized pores. The pore size, pore size distribution and porosity, and hence the strength, permeability and surface adhesion, of the ceramic coating is controlled by the choice of substituent on the carboxylate-alumoxane. Thermolysis of self supporting spun layers of the carboxylate-alumoxanes results in disks of alumina with controlled pore size, pore size distribution and porosity. In an alternative method a porous substrate is dipped or coated with a solution of the carboxylate-alumoxane, followed by thermolysis to produce a composite membrane.