Browsing by Author "Wightman, James P."

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    Accelerated viscoelastic characterization of T300/5208 graphite- epoxy laminates
    Tuttle, M. E. (Virginia Polytechnic Institute and State University, 1984)
    The viscoelastic response of polymer-based composite laminates, which may take years to develop in service, must be anticipated and accommodated at the design stage. Accelerated testing is therefore required to allow long-term compliance predictions for composite laminates of arbitrary layup, based solely upon short-term tests. In this study, an accelerated viscoelastic characterization scheme is applied to T300/5208 graphiteepoxy laminates. The viscoelastic response of unidirectional specimens is modeled using the theory developed by Schapery. The transient component of the viscoelastic creep compliance is assumed to follow a power law approximation. A recursive relationship is developed, based upon the Schapery single-integral equation, which allows approximation of a continuous time-varying uniaxial load using discrete steps in stress. The viscoelastic response of T300/5208 graphite-epoxy at 149C to transverse normal and shear stresses is determined using 90-deg and 10-deg off-axis tensile specimens, respectively. parameters In each case the seven viscoelastic material required in the analysis are determined experimentally, using a short-term creep/creep recovery testing cycle. A sensitivity analysis is used to select the appropriate short-term test cycle. It is shown that an accurate measure of the power law exponent is crucial for accurate long-term predictions, and that the calculated value of the power law exponent is very sensitive to slight experimental error in recovery data. Based upon this analysis, a 480/120 minute creep/creep recovery test cycle is selected, and the power law exponent is calculated using creep data. A short-term test cycle selection procedure is proposed, which should provide useful guidelines when other viscoelastic materials are being evaluated. Results from the short-term tests on unidirectional specimens are combined using classical lamination theory to provide long-term predictions for symmetric composite laminates. Experimental measurement of the long-term creep compliance at 149C of two distinct T300/5208 laminates is obtained. A reasonable comparison between theory and experiment is observed at time up to 10 5 minutes. Discrepancies which do exist are believed to be due to an insufficient modeling of biaxial stress interactions, to the accumulation of damage in the form of matrix cracks or voids, and/or to interlaminar shear deformations which may occur due to viscoelastic effects or damage accumulation.
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    Adhesion of novel high performance polymers to carbon fibers: fiber surface treatment, characterization, and microbond single fiber pull-out test
    Heisey, Cheryl L. (Virginia Tech, 1993-11-05)
    The adhesion of carbon fibers to several high performance polymers, including a phosphorus-containing bismaleimide, a cyanate ester resin, and a pyridine-containing thermoplastic, was evaluated using the microbond single fiber pull-out test. The objective was to determine the chemical and mechanical properties of the fiber and the polymer which affect the fiber/polymer adhesion in a given composite system. Fiber/matrix adhesion is of interest since the degree of adhesion and the nature of the fiber/matrix interphase has a major influence on the mechanical properties of a composite. The surface chemical composition, topography, tensile strength, and surface energy of untreated AU-4 and commercially surface treated AS-4 carbon fibers were evaluated using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), single fiber tensile tests, and dynamic contact angle analysis. The commercial surface treatment which converted the AU-4 to the AS-4 fiber oxidized the carbon fiber surface. The surface of the AS-4 carbon fiber was further modified using air, oxygen, ammonia, and ethylene plasmas. The AS-4 fiber tow was also characterized following exposure to the aqueous poly(amic acid) solution used to disperse the matrix powder during aqueous suspension prepregging of thermoplastic matrix composites. The air and oxygen plasma treatments significantly oxidized and roughened the surface of the AS-4 carbon fibers. In addition, the air and oxygen plasma increased the the polar component of the AS-4 fiber surface energy. The ammonia plasma increased the concentration of nitrogen on the fiber surface, without significantly altering the fiber topography (at a nlagnification of 50,000X). The atomic oxygen present in the air and oxygen plasma treatments is capable of reacting with both the edge and basal planes in the carbon fiber structure. As a result, the oxygen-containing plasmas progressively ablated the organic material in the carbon fiber surface. Energetic species in the ammonia plasma cleaned the fiber surface and reacted with the carbon fiber surface, increasing the concentration of amine groups in the fiber surface. The ethylene plasma deposited a layer of plasma polymerized polymer on the carbon fiber surface. The AS-4 carbon fibers were coated with poly(amic acid) when the tow was wet with the aqueous suspension prepregging solution. The carbon fiber adhesion of bis(3-maleimido phenoxy) triphenylphosphine oxide was compared to that of Ciba-Geigy's Matrimid 5292 A/B bismaleimide system. With both bismaleimides, the carbon fiber adhesion increased significantly when the fiber received an oxidative commercial surface treatment or was exposed to an air or ammonia plasma prior to bonding. In contrast, the poly(pyridine-bis A) microbond pull-out test results showed that the carbon fiber adhesion of poly(pyridine-bis A) was not affected by the fiber surface chemical composition, fiber surface energy, or topography.
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    Adhesion study of thermoplastic polymides with Ti-6Al-4V alloy and PEEK-graphite composites
    Yoon, Tae-Ho (Virginia Tech, 1991)
    High glass transition (eg. 360 °C) melt processable thermoplastic polyimide homopolymers and poly(imide-siloxane) segmented copolymers were prepared from a number of diamines and dianhydrides via solution imidization, polydimethylsiloxane segment incorporation and molecular weight control with non-reactive phthalimide end-groups. The adhesive bond performance of these polyimides was investigated as a function of molecular weight, siloxane incorporation, residual solvent, test temperature, and polyimide structure via single lap shear samples prepared from treated Ti-6AI-4V alloy adherends and compression molded film adhesives or scrim cloth adhesives. The adhesive bond strengths increased greatly with siloxane segment incorporation at 10, 20 and 30 weight percent, and decreased slightly with total polymer molecular weight. As the test temperature was increased, adhesive bond strength increased, decreased or showed a maximum at some temperatures depending on the polyimide structure and siloxane content. The presence of residual solvent increased adhesive bond strength at ambient temperature but decreased the strength at the elevated temperatures. The variation of adhesive bond strength with residual solvent, siloxane and test temperature was attributed to the influence of these parameters on the brittle-ductile transition behavior of the polyimide system. This conclusion was supported by stress-strain measurements which indicated that tensile strength and modulus decreased with siloxane concentration and test temperature, demonstrating that there was an optimum combination of strength and strain for maximum adhesive bond strength. A model was developed to describe this behavior. The poly(imide-30%siloxane) segmented copolymer and a miscible poly(ether-imide) also demonstrated excellent adhesive bond strength with poly(arylene ether ketone) PEEK®-graphite composites. Oxygen or ammonia gas plasma treatment was very effective in further improving adhesive bond strength of melt laminated PEEK®-graphite composites.
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    Adsorption of organic compounds onto solids from aqueous solutions
    Wightman, James P.; Dole, Leslie R.; Jones, J.; King, Clarence A. (Water Resources Research Center, Virginia Polytechnic Institute and State University, 1971)
    The use of solids to remove pollutants is not novel in the sense that solids are used presently for this purpose. For example, the use of charcoal is well known, and the use of alumina in phosphate removal has been investigated. The removal of phenol from aqueous solutions on a variety of solids has been studied in this work. The rationale for this study is as follows. An aqueous solution containing a pollutant (phenol) is a three component system consisting of a solute (phenol) and solvent (water) in contact with a solid. The question arises, what about the removal of the pollutant by the solid? In many instances the kinds of solids that have been used are those which not only compete for the pollutant, but also compete for water. Thus, not only is the interaction between the pollutant and the solid important, but also the Interaction between the water and the sol id. In many systems, for example herbicides, insecticides, and phenol, there is a Iimited solute concentration, which means that there is a basic incompatability in the system to start with. Then as this solution is put in contact with a solid surface, the amount of pollutant and the amount of water removed become relevant. If the solid has an attraction for water in addition to the pollutant, water may be removed and block parts of the solid which could be effective in removing the pollutant. This study has been concerned with the adsorption of phenol from aqueous solutions on several solids chosen to alter the competition of water and phenol for the surface of the solid.
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    Advanced Chemical-Mechanical Dewatering of Fine Particles
    Asmatulu, Ramazan (Virginia Tech, 2001-03-12)
    In the present work, novel dewatering aids and a novel centrifuge configuration were developed and applied for the purpose of dewatering fine particles. Three different types dewatering reagents were tested in different filtration and centrifugation units. These chemicals included low-HLB surfactants, naturally occurring lipids, and modified lipids. Most of these reagents are insoluble in water; therefore, they were used in solutions of appropriate solvents, such as light hydrocarbon oils and short-chain alcohols. The role of these reagents was to increase the hydrophobicity of the coal and selected mineral particles (chalcopyrite, sphalerite, galena, talc, clay, phosphate, PCC and silica) for the dewatering. In the presence of these reagents, the water contact angles on the coal samples were increased up to 90o. According to the Laplace equation, an increase in contact angle with the surfactant addition should decrease the capillary pressure in a filter cake, which should in turn increase the rate of dewatering and help reduce the cake moisture. The use of the novel dewatering aids causes a decrease in the surface tension of water and an increase in the porosity of the cake, both of which also contribute to improved dewatering. A series of batch-scale dewatering tests were conducted on a variety of the coal and mineral samples using the novel dewatering aids. The results obtained with a Buchner funnel and air pressure filters showed that cake moistures could be reduced substantially, the extent of which depends on the particle size, cake thickness, drying time, reagent dosage, conditioning time, reagent type, sample aging, water chemistry, etc. It was determined that use of the novel dewatering aids could reduce the cake formation time by a significant degree due to the increased kinetics of dewatering. At the same time, the use of the dewatering aids reduced the cake moistures by allowing the water trapped in smaller capillaries of the filter cake. It was found that final cake moistures could be reduced by 50% of what can be normally achieved without using the reagents. However, the moisture reduction becomes difficult with increasing cake thickness. This problem can be minimized by applying a mechanical vibration to the cake, spraying a short-chain alcohol on the cake and by adding a small amount of an appropriate coagulant, such as alum and CaCl2 to the coal and mineral slurries. The novel dewatering aids were also tested using several different continuous filters, including a drum filter, disc filter and horizontal belt filter (HBF). The results obtained with these continuous filtration devices were consistent with those obtained from the batch filters. Depending on the coal and mineral samples and the type of the reagent, 40 to 60% reductions in moisture were readily achieved. When using vacuum disc filters, the cake thickness increased substantially in the presence of the novel dewatering aids, which could be attributed to the increased kinetics of dewatering. A dual vacuum system was developed in the present work in order to be able to control the cake thickness, which was necessary to achieve lower cake moistures. It was based on using a lower vacuum pressure during the cake formation time, while a full vacuum pressure was used during the drying cycle time. Thus, use of the dual vacuum system allowed the disc filter to be used in conjunction with the novel dewatering aids. Its performance was similar to that of HBF, which is designed to control cake thickness and cake formation time independently. The effectiveness of using the novel dewatering aids were also tested in a full-continuous pilot plant, in which coal samples were cleaned by a flotation column before the flotation product was subjected to the disc filter. The tests were conducted with and without using novel dewatering aids. These results were consistent with those obtained from the laboratory and batch-scale tests. The novel centrifuge developed in the present work was a unit, which combined a gravity force and air pressure. The new centrifuge was based on increasing the pressure drop across the filter cake formed on the surface of the medium (centrifuge wall). This provision made it possible to take advantage of Darcy s law and improve the removal of capillary water, which should help lower the cake moisture. A series of tests were conducted on several fine coal and mineral particles and obtained more than 50% moisture reduction even at very fine particle size (2 mm x 0). Based on the test results obtained in the present work, two proof-of-concept (POC) plants have been designed. The first was for the recovery of cyclone overflows that are currently being discarded in Virginia, and the other was for the recovery of fines from a pond in southern West Virginia. The former was designed based on the results of the plant tests conducted in the present work. Cost vs. benefit analyses were conducted on the two POC plants. The results showed very favorable internal rates of return when using the novel dewatering aids. Surface chemistry studies were conducted on the coal samples based on the results obtained in the present investigation. These consisted mainly of the surface characterization of the coal samples (surface mineral composition, surface area, zeta potential, x-ray photoelectron microscopy (XPS)), acid-base interactions of the solids and liquids, dewatering kinetic tests, contact angle measurements of the coal samples and surface force measurements using AFM. In addition, carbon coating on a silica plate using palsed laser deposition (PLD) and Langmuir-Blodgett (LB) film deposition tests were conducted on the sample to better understand the surfactant adsorption and dewatering processes. The test results showed that the moisture reductions on the fine particles agree well with the surface chemistry results.
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    Application of localized hybrid methods of stress analysis to some problems in the mechanics of composites
    Tsai, Ming-Yi (Virginia Tech, 1990)
    A new method of stress analysis which combines an experimental technique — moire interferometry, and a numerical method — finite element analysis, is presented. In this localized hybrid method, the displacement fields which the moire experiments provide in some local regions of interest are used as input data for finite element stress analyses. Two important and controversial problems in the mechanics of composites are investigated using the localized hybrid method. One is a thermally loaded bimetal plate, and the other involves the Iosipescu shear specimen popularly used to determine the shear modulus and strength of a fiber reinforced composite. Before applying the localized hybrid analysis, the mechanics of the problems are discussed individually, through a numerical study and strength of materials analysis. Based on these fundamental studies, the localized hybrid method is applied to stress or strain analyses of moire experimental results, and special techniques of this method are developed to handle these data. For the thermally loaded plate, several finite element models, simulating 2-D and 3-D mechanics, are used to assess the stress state at the interface near the free surface, and identify a boundary layer. It is shown that high gradients and stress turnaround are documented in stress component normal to the interface, along the surface line crossing the interface, and a boundary layer is identified in the small region near the interface around the free surfaces. These observations are also confirmed by the hybrid analysis of moire experimental results. However, additional variations of the localized hybrid method were needed to capture the three-dimensional nature of the problem. A comparison of numerical results with experimental data resolved an apparent anomaly between experiments and mechanics principles. For the Iosipescu shear specimen, the 3-D mechanics associated with twisting is proposed for accounting for the inconsistent and variable results in the literatures. The results form the localized hybrid analysis indicate that uniformity and purity of shear stress state in the test section cannot be accomplished for each fiber orientation specimens; the 0° specimens suffer from a load proximity effect, the 90° specimens are affected by apparent in- and out-plane bending, and the 0°/90° specimens are midway between those. Several variations of the localized hybrid method of stress analysis have been presented for three-dimensional problems in the mechanics of solids. It is showed that the approach developed not only provides a powerful and efficient technique for the reduction of experimental data, but also gives a good insight into the mechanics of the experimental observations.
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    Applications of high resolution solid state carbon-13 NMR to the study of multicomponent polymer systems
    Lin, Tso-Shen (Virginia Polytechnic Institute and State University, 1983)
    The technique of high resolution solid state carbon-13 NMR, achieved with magic angle spinning (MAS) and high power 13c-1H dipolar decoupling and cross polarization, was applied to a number of multicomponent polymer systems. Specific problems which were addressed are: (1) the nature of domain structure and molecular motion of two thermoplastic elastomer systems, including a series of styrene isoprene-styrene linear triblock copolymers (SIS’s) of various compositions, molecular weights and sample histories, and a poly(ester)- urethane based on poly(1,4-butylene adipate) and 4,4¹ -diphenylmethane diisocyanate, (2) the compatibility at the molecular level of polymer blends containing poly{vinylidene fluoride) (PVF2), including solution and mechanical blends with poly{methyl methacrylate) {PMMA}, poly(vinyl acetate} (PVAc) and poly(vinyl methyl ether) (PVME). For the thermoplastic copolymers, higher degree of phase separation between the hard and soft domains was indicated by two facts: First, ¹³C resonances of either domain could be selectively observed with different experimental conditions. Second, there was a one-component, first-order, spin-lattice relaxation behavior of the ¹³C nuclei in the soft domains. For the SIS copolymers, results of T₁ and T₂* determinations (beth with MAS) suggest that molecular motion, in terms of frequency, was independent of composition, molecular weight and selective casting solvents. However, from static spectra, molecular motion of the isoprene blocks was found to be more anisotropic for the samples cast from a poor solvent for polyisoprene {MEK) in contrast to samples cast from a good solvent of polyisoprene (hexane). For the polymer blends of poly(vinylidene fluoride), the level of molecular intermixing was reflected through the degree of ¹³C NMR signal attenuations of the non-PVF₂ polymers. These attenuations are mainly due to undecoupled intermolecular ¹³C-¹⁹F dipolar interactions. With a MAS rate of 2KHz, resolution of the intimacy of mixing between the two constituent polymers in the blends was estimated to be in the range of 3 to 4 angstroms. Varying degrees of NMR signal attenuations among the individual chemically different carbons of a polymer support a postulation of weak intermolecular 'acid-base' association between the acidic protons of PVF₂ and basic carbonyl groups in the case of both the PMMA and PVAc.
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    Aspects of amidization of chitosan
    Toffey, Ackah (Virginia Tech, 1996)
    The intent of this research was to develop an understanding of an amidized chitosan-from-chitosan regeneration process discovered in our laboratory. In this study several characterization methods including DMTA, TMA, TGA, X-ray diffraction, FTIR, solid state CP-MAS ¹³C NMR, and HPLC were used to study the transformation of various ionic complexes of chitosan (N-acylate) to their respective N-acyl homologs of chitosan; and several properties of these materials were examined. DMTA and TMA provided information on changes in Tg as well as modulus-changes and glass formation underlying the transformation of the N-acylate to the N-acyl derivative. X-ray diffraction and FTIR shed some insights on the morphology of the N-acetyl homolog of chitosan in relation to native chitin. Solid state CP-MAS ¹³C NMR provided evidence of the conversion of N-acylate to N-acetyl. Enzymatic hydrolysis of native chitin and amidized chitosan homologs and subsequent identification of fractions by HPLC allowed a comparison of various amidized chitosan homologs in terms of their recognition and degradation by chitinolytic enzymes. Solid state CP-MAS ¹³C showed that the heat treatment of the ionic complex of chitosan results in thermal dehydration leading to the formation of the N-acetyl group at the C-2 of chitin. The DS of amidized chitosan varied between 0.1 and 0.6. Tg-changes with time and heating temperature were used as a variable to monitor amidization. Kinetics analysis indicated that the amidization of various ionic complexes of chitosan is a first order, two-phase process with activation energies of 14±1 kcal/mol and 21±2 kcal/mol for the first and second phase, respectively. These values did not vary with the type of acid used in the formation of the chitosan complex. This two-phase behavior is explained with the influence of vitrification on chain mobility. In situ DMTA was found to be a suitable technique for monitoring the phase transformation of chitosonium acetate and chitosonium propionate from a rubbery to a glassy phase (vitrification). Consequently, the concept of TTT-cure diagram analysis was used to describe such phase changes and map out vitrification and full cure curves. As in thermosets, the vitrification curve describing glass formation in these materials is S-shaped. The time to full cure decreased with increasing heating temperature. The activation energy for vitrification is the same irrespective of the type of acid used in the preparation of chitosan complex. Thermal analysis revealed that the Tg of N-acyl homologs of chitin displays a stepwise relationship with length of N-acyl substituent. These materials are characterized by two transitions designated as β- and α-relaxation. Additionally, enzymatic hydrolysis of N-acyl homologs of chitosan using an enzyme mixture of chitinase, chitosanase, and β-N-acetylglucosaminidase and subsequent identification of fractions revealed that these enzymes recognize and degrade chitin irrespective of the N-acyl substituent at the C-2 position of chitin at any DS.
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    Aspects of Wood Adhesion: Applications of 13C CP/MAS NMR and Fracture Testing
    Schmidt, Robert G. (Virginia Tech, 1998-01-28)
    Phenol Formaldehyde (PF) and polymeric isocyanate (pMDI) are the two main types of adhesives used in the production of structural wood-based composites. Much is unknown about various aspects of adhesion between these two types of resins and wood. The present research describes the development of techniques which will permit an enhanced understanding of 1.) the extent of cure of PF within a wood based composite, 2.) the scale of molecular level interactions between PF and pMDI and wood, 3.) mechanical performance and durability of wood-adhesive bonds. Correlations were established between conventional methods of characterization of neat PF (thermomechanical analysis, swelling studies) and measurements made using 13C CP/MAS NMR. These correlations were then utilized to characterize PF cured in the presence of wood. The use of 13C labeled PF allowed estimates of relative degrees of resin conversion to be made. The use of 13C and deuterium labeled PF allowed qualitative estimates of resin molecular rigidity to be made. The scale of molecular level interactions between PF and pMDI and wood was probed using NMR relaxation experiments. Evidence was shown to suggest the formation of an interpenetrating polymer network (IPN) morphology existing at both types of wood-resin interphases. The formation of the IPN morphology was strongly influenced by resin molecular weight, cure temperature and the presence of solvent. A new test geometry for the evaluation of the fracture toughness of wood-adhesive bonds was developed. Consistent and reliable results were obtained. It was found that low molecular weight PF possessed enhanced durability over high molecular weight.
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    Assessment of coal liquefaction behavior through product characterization with hyphenated chromatographic/spectroscopic methods
    Hellgeth, John William (Virginia Polytechnic Institute and State University, 1986)
    The understanding of liquefaction behaviors, related to a coal's properties and a recycle solvent's composition, is essential for the development of an efficient direct liquefaction process. In this dissertation, a study of the liquefaction behaviors of an Eastern us bituminous and four Western US subbituminous coals is presented. The experimental approach has been to examine their behaviors under various reaction conditions with in-house microautoclave reactor and Kerr McGee pilot plant liquefaction runs. In-house runs involved surveys of coal types and process solvent compositions with variations in reaction times, temperatures and atmospheres. Runs performed at Kerr McGee examined the use of tetrahydroquinoline (TBQ) as a process solvent with a Wyoming coal. Liquefaction activities were assessed through determinations of coal conversion to both solvent-soluble products and distillate yields. Per the in-house liquefaction studies, a novel microautoclave reactor design and product recovery methods were developed, evaluated and employed. The reaction chemistries of !n !!S!! metal species and basic nitrogen heterocycles were investigated specifically. Changes in trace element concentrations were ascertained by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and Size Exclusion Chromatography/ICP-AES (SEC/ICP-AES). Pates of basic nitrogen components in distillate and solvent-soluble residuum products were examined by nitrogen mass balance determinations, Gas Chromatography/Pourier Transform Infrared Spectrometry (GC/PTIR) and Gas Chromatography/Mass Spectrometry (GC/MS). Conversions to soluble products demonstrated the expected dependencies of liquefaction on coal rank, elemental composition and petrography. The western subbituminous coals showed extreme sensitivity to drying and solvent-soaking pretreatments. Metal content analyses revealed that metals exist as complexed species in the liquefaction process. Higher conversions to toluene-soluble materials were obtained with THQ in contrast to other H-donor solvents. Adduction of THQ was significant in the non-distillate product stream, however. The direct coupling of Reversed Phase HPLC separations with PTIR (RP-HPLC/PTIR) detection through on-line, post-column extraction was developed. Though intended for application to coal-liquefied product (CLP) analysis, this system was evaluated rigorously for both chromatographic and spectral performance. Throughout this investigation, the overall utility of these hyphenated methods for CLP analysis was explored. These methods demonstrated exceptional performance in providing a wealth of qualitative and quantitative information in a rapid manner.
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    Availability and distribution of heavy metals from sewage sludge in the plant-soil continuum
    Rappaport, Bruce D. (Virginia Polytechnic Institute and State University, 1986)
    An investigation was conducted using in situ lysimeters (1.5 m x 2.3 m) to determine Cd, Cu, Ni, and Zn availabilities for barley (Hordeum vulgare L.) and corn (Zea mays L.) grown on four sludge-amended soils. These lysimeters were constructed in Acredale silt loam (Typic Ochraqualf), Bojac loamy sand (Typic Hapludult), Davidson clay loam (Rhodie Paleudult), and Groseclose silt loam (Typic Hapludult) soils. An aerobically digested sewage sludge from a sewage system with major industrial inputs was applied at rates of 0, 42, and 84 dry Mg ha-t to the lysimeters in the poorly-drained Acredale soil. Rates of 0, 42, 84, 126, 168, and 210 dry Mg ha-1 were applied to the lysimeters in the well-drained Bojac, Davidson, and Groseclose soils. Tissue metal concentrations were determined in 1984 and 1985 for a three crop rotation, which consisted of corn, barley, and corn on the Acredale soil. Increases in sludge-borne Ni and Zn led to increases in Ni and Zn concentrations in corn earleaf, corn grain, and barley silage. Copper concentration was increased in barley silage but not in corn grain and stover. On this poorly-drained soil, metal movement did not occur below the Ap horizon even when Cu was applied in excess of USEPA guidelines. Although there were increases in metal levels, all four metals were within the range considered normal for corn and barley growth. Soil, corn, and barley plants were sampled in 1984 and 1985 to determine Cd, Cr, Cu, Ni, and Zn availabilities for crops grown on the sludge-amended Bojac, Davidson, and Groseclose soils. Levels of DTPA-extractable Cd, Cu, Ni, and Zn in the Ap horizon of these soils increased linearly with sludge rate. Corn grain and stover yields were not decreased on the Bojac, Davidson, and Groseclose soils when 4.5, 5105, 760, 43.0, 135, and 620 kg ha-1 of Cd, Cr, Cu, Ni, Pb, and Zn were added as a sludge-amendment. Copper and Zn applied in excess of 480 and 60 kg ha- 1 of USEPA guidelines, respectively on the Bojac, Davidson, and Groseclose soils were not phytotoxic to corn plants in 1984. Corn and barley tissue sampled for three consecutive seasons had Cr concentrations <2.8 mg kg-1.
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    Birefringent single-arm fiber optic enthalpimeter for catalytic reaction monitoring
    Richmond, Eric William (Virginia Tech, 1990)
    Changes in heat content are almost universally associated with chemical reactions. Thermometry as an analytical tool has been extensively researched and developed. Finding solutions to problems involving thermal isolation, specificity, sensitivity, and cross-sensitivity remain as active areas of interest. Fiberoptic interferometers, which use phase phenomena associated with propagating light, are extremely sensitive to heat. This research has focused on a special "birefringent" optical fiber. Two channels of information are generated in this single-fiber interferometer which correspond to the heat evolved from a catalytic reaction isolated on the fiber surface. Because of the unique transduction mechanism associated with the "birefringent" optical fiber, this device is sensitive to heat and remarkably insensitive to pressure. Details of the characterization and development of the birefringent optical fiber into a useful analytical probe are presented.
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    Boron chemistry in selected Virginia soils and hydroxy aluminum and iron systems
    Jin, Ji-yun (Virginia Polytechnic Institute and State University, 1985)
    Greenhouse and laboratory experiments were conducted to investigate the distribution of native B, the availability of native and applied B in 14 Virginia soils and the specific reactions of B in soil and hydroxy Al and Fe systems. Total B in the 14 soils ranged from 21.5 to 96.3 mg kg⁻¹. Only a small portion of the total B was in soil solution, non-specifically and specifically adsorbed forms and Mn minerals. These fractions of B are readily available to plants. A large part of the total B was associated with non-crystalline and crystalline Al and Fe minerals and soil silicates. These forms of B contribute little to B absorption by plants. Hot water soluble B, NH₄-acetate extractable B, mannitol exchangeable B and Mehlich III extractable B from the soils closely correlated with the concentrations in corn plants from native B in the greenhouse experiment. A yield response of corn plants to B application did not occur on the soils. Both tissue B concentration from applied B and maximum B adsorption by the soils closely correlated with soil clay, hydroxylamine hydrochloride extractable Mn and NH₄—oxalate (pH 3.25) extractable Al and Fe (under UV light). These data indicated that soil clay and Al-, Fe- and Mn-oxides and hydroxides have high affinities to adsorb B in plant unavailable forms. Boron adsorption on both gibbsite and goethite was pH and temperature dependent. At pH 6.5, boric acid was major species in the system and B was absorbed by the negatively charged surface of gibbsite and the positively charged surface of goethite. At pH 10, borate was primarily species in the system and B was adsorbed on negatively charged surfaces of both minerals. Boron adsorption was greater at pH 10 than at pH 6.5. An increase in temperature increased B adsorption on both minerals at both pH levels. This indicated that the B adsorption was an exothermic process. Boron adsorption on gibbsite and goethite shifted the ZPC of the minerals downward. This verified that specific B adsorption occurred on the surfaces. Aluminum substitution in goethite increased the affinity of the surface for B adsorption.
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    A calorimetric study of the immersion of bituminous coal in liquids
    Hollenhead, James B. (Virginia Tech, 1988-02-05)
    The surface properties of coal greatly affect its use in industrial processes such as gasification, liquefaction and the use of coal slurries. In addition, such processes also involve reagent penetration into coal pores and the oxidative state of the coal surface. Reagent penetration into coal was examined by determining the heat and kinetics of immersion of Pocahontas No. 3 coal in water, methanol, a series of n-alkanes, and several cyclic and heterocyclic hydrocarbons. Results indicate that the heat of immersion is sensitive to the carbon chain length of the wetting liquid and its ability to hydrogen bond to coal. The time of immersion is insensitive to carbon chain length but is increased by the presence of nitrogen in a cyclic hydrocarbon. The oxidation of both unextracted and extracted coal at 3200C was followed by immersional measurements in water. The heat of immersion increased rapidly with oxidation time, leveling off after 3 hours of oxidation. Extraction with methanol or pyridine prior to oxidation and immersion lowered the time of immersion in water compared to the unextracted case. The oxidation of coal was also followed by x-ray photoelectron spectroscopy (XPS). The XPS oxygen/carbon ratios correlated linearly with the heats of immersion for the extracted, oxidized coals. Thus, XPS was shown to be a useful ancillary technique to heat of immersion for the study of coal surfaces.
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    Capillary supercritical fluid chromatography
    Hensley, Jack Lee (Virginia Polytechnic Institute and State University, 1986)
    The modification of a gas chromatograph for capillary supercritical fluid was demonstrated. The resulting instrument was used to characterize the performance of capillary columns manufactured specifically for SFC applications. The columns were tested for inertness, efficiency, and immobilization before and after extraction with the supercritical CO₂ solvent. Stable deactivation layers were obtained with polyethylene glycol pyrolysis of Carbowax 20M and Superox 20M. Crosslinking was evaluated with dicumyl peroxide (DCP) and azo-t-butane (ATB) as free radical initiators with OV-1701 as a stationary phase. ATB was found to yield more efficient crosslinking and had less effect on column polarity. Quantitative reproducibility of SFC was evaluated for alkanes, alcohols and acids on columns which were deactivated by polyethylene glycol pyrolysis or by mixed cyclic siloxanes. Both gave better reproducibility than an untreated column but the overall reproducibility of the polyglycol deactivation was better than the cyclic deactivation. Liquid CO₂ extraction was performed on a variety of spices and food products. This sample preparation proved useful in isolating CO₂ soluble materials from complex matrices which were insoluble in CO₂.
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    Carbon fiber surface treatments for improved adhesion to thermoplastic polymers
    DeVilbiss, Thomas Alexander (Virginia Polytechnic Institute and State University, 1987)
    The effect of anodization in NaOH, H₂SO₄, and amine salts on the surface chemistry of carbon fibers was examined by x-ray photoelectron spectroscopy (XPS). The surfaces of carbon fibers after anodization in NaOH and H₂SO₄ were examined by scanning transmission electron microscopy (STEM). angular dependent XPS, ultraviolet (UV) absorption spectroscopy of the anodization bath, secondary ion mass spectrometry, and polar/dispersive surface energy analysis. Hercules AS-4, Dexter Hysol XAS, and Union Carbide T-300 fibers were examined by STEM, angular dependent XPS, and breaking strength measurement before and after commercial surface treatment. The fibers from the three companies were anodized to create similar surface chemistry on each fiber. XPS was used to compare the surface chemistry after anodization. Adhesion of carbon fibers to polysulfone, polycarbonate, and polyetherimide was studied using the fiber critical length test. Oxygen and nitrogen were added to the fiber surfaces by anodization in amine salts. Analysis of the plasmon peak in the carbon 1s signal indicated that H₂SO₄ anodization affected the morphological structure of the carbon fiber surface. UV absorption spectra of the anodization bath, SIMS, and angular dependent XPS indicate that NaOH anodization removes amorphous carbon from the fiber. The oxygen and nitrogen content on the fiber surfaces were affected by commercial surface treatment. The Union Carbide fiber had much lower oxygen content after laboratory anodization than the Hercules or Dexter Hysol fibers. The breaking strength of all three fibers was increased by anodization. Laboratory anodization resulted in better fiber/matrix adhesion than the commercial surface treatment for the Hercules and Dexter Hysol fibers. Fiber/matrix adhesion was better for the commercially treated Union Carbide fiber than for the laboratory treated fiber. The work of adhesion of carbon fibers to thermoplastic resins was calculated using the geometric mean relationship. A correlation was observed between the dispersive component of the work of adhesion and the interfacial adhesion.
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    The catalytic activity of anodic oxides on aluminum
    Madeleine, Teresa Catherine (Virginia Polytechnic Institute and State University, 1988)
    The dehydration of isopropanol over anodic oxides was studied. The catalytic activity of the anodic oxides prepared in phosphoric, sulfuric, and oxalic acid was compared to the activity of ν-Al₂O₃. The effect of various thermal treatments on the catalytic activity was examined. IR spectroscopy proved useful for the study of the effect of thermal treatment on the acidity of the oxides. X-ray photoelectron spectroscopy (XPS) was employed to examine the oxide surfaces both before and after use as a catalyst. The acidity of the oxides was studied by various methods and related to the activity of the oxides. The acidity of the oxide surfaces was studied by the adsorption of pH indicators on the oxide surfaces. The adsorption of gaseous bases, ammonia and pyridine, was studied by IR spectroscopy and temperature programmed desorption mass spectrometry. It was thus possible to differentiate between Lewis and Brønsted acid sites and to determine the quantity of the acid sites on the various oxides.
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    Catalytic reaction in the process of carbon monoxide disintegration
    Xu, Ming-Wei Paul (Virginia Polytechnic Institute and State University, 1984)
    The catalytic effects of selected iron phases (metal, oxides, sulfides, and carbides) on the Boudouard reaction (2 CO = CO₂ + C) were studied, in an effort to more fully understand the disintegration of refractories when exposed to CO for long periods of time. Based on computer generated equilibrium phase maps (SOLGASMIX program), experimental kinetic data including activation energies and x-ray diffraction data of iron phases, the following conclusions were reached: (1) Ferric oxide (Fe₂O₃ ) is most catalytic; (2) Active iron atom generated by the reduction of Fe₂O₃ is a catalyst for carbon monoxide disintegration; (3) The catalytic process consists of the adsorption of CO, the formation of intermediates FeC, Fe₂C , and Fe₃C , and the decomposition of these intermediates.
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    Characterization and patterned polymer films from a novel self-assembly process
    Liu, Yanjing (Virginia Tech, 1996-05-03)
    The layer-by-layer molecular-level manipulation of ionic polymer have been utilized to fabricate ultrathin multilayer films (SAMp). In this process, monolayers of polycations and polyanions are sequentially adsorbed onto a substrate surface by alternately dipping the substrate into aqueous solutions of poly(vinylamine) backbone azo (PDYE), poly(sodium 4-styrenesulfonate) (PSS), and poly(al1ylamine hydrochloride) (PAH). The ionic attractions developed between the oppositely charged polymers promote strong interlayer adhesion and a uniform and linear multilayer deposition process. UV/Vis absorbance, contact angle, and ellipsometry measurements revealed that in all cases the bilayer deposition process was linear and highly producible from layer to layer and film thickness of up to 1 µm can be easily obtained by repeating the deposition process. The typical thickness of bilayer film depend on the solution concentration. Contact angle and UV/Vis spectroscopy measurements demonstrated that the deposition time for a full monolayer coverage of azo dye and PAH was about 20 seconds. Our results showed that the mechanical stability of these SAMp films was remarkable, and SAMp films can only be removed from the substrate by scraping. SAMp films are stable in the common organic solvents and even in the high acidic media (6M HCl aqueous solution). The conformation of these films are thermally stable at high temperature. In an attempt to develop patterned surfaces of sulfonate and thiol functionality, close-packed, well-ordered (3-mercaptopropyl)trimethoxysilane (MPS) monolayer were formed on the surfaces of single crystal silicon, quartz, and glass by allowing hydrolyzed silane to self-assemble from a dilute hydrocarbon solution. The films of MPS were irradiated with an ozone-producing UV light source results in efficient conversion of the surface-localized thiol groups to sulfonated groups, a complete photo-oxidation of the thiol surface was obtained and characterized by x-ray photoelectron spectroscopy (XPS) and contact angle measurements. Sulfonated self-assembled films can be used as good organic templates for the deposition of SAMp films and for micropatterning of organic surfaces based on our results. Such results significantly extend the application of SAMp films since the sulfonate-functionalized surface can be introduced into the surfaces of aromatic polymers, metals, ceramics, semiconductors, and plastics. So that the process of SAMp deposition can be carried out onto many different substrate surfaces. The novel self-assembly technique combined with photolithography was used to develop three different methods of micropatterning fabrication in an attempt to achieve the goal of full-color flat-panel display. The characteristic of distinguishing our methods from the existed ones is that the patterning is done first and then the vertical multilayers were built-up on the patterned areas. Moreover, in this process, SAMp films were used as active species. Scanning Electron Microscopy (SEM) was employed to confirm the patterning technique. In order to block the further growth of the second film type on the sites of first film type, several molecules with inert function groups were tried. UV/Vis absorbance and contact angle measurements revealed that dodecyltrimethylammonium bromide (DTAB) atop the PAH/PSS SAMp film could prevent further adsorption of the ionic polymers.
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    Characterization of block copolymers and polymer blends by inverse gas chromatography
    Sheehy, Daniel P. (Virginia Polytechnic Institute and State University, 1984)
    The accuracy and utility of using Inverse Gas Chromatography (IGC) to characterize the microphase structure of block copolymers, and the strength of the thermodynamic interactions between the components of polymer blends and the unlike segments of block copolymers was examined. There were three parts to the study. First, the Scott ternary solution model, which is used for the study of thermodynamic interactions in polymer blends, was extended to low molecular weight mixtures. From vapor-liquid equilibrium data in the literature, the Gibbs free energy of mixing of binary mixtures (GM ) calculated with the model were compared to experimental values. Mixtures containing ketones, aromatics hydrocarbons, chlorinated hydrocarbons, alcohols and water were studied. With the exception of mixtures containing water and low molecular weight alcohols, a fair to good correlation between theoretical and experimental values was observed. Second, the Gibbs free energy of mixing of nitrocellulose, polyvinyl chloride and poly(vinylidene fluoride) containing blends were measured with the Scott model from IGC data. For the nitrocellulose containing blend, the calculated Gibbs free energy of mixing values were large in magnitude (-2.0 to -5.0 calories/gram) and in fair agreement with the experimental heats of mixing determined from microcalorimetry measurements. For the remaining blends, the IGC data could not be distinguished from the results normally obtained for immiscible blends. The calculated GM values were small in magnitude relative to the experimental error of the quantities. Concerning the block copolymers, the relative incompatibility of the constituent blocks of perfectly alternating block copolymers of polydimethylsiloxane and bis-A-polycarbonate and styrene-isoprene-styrene triblock copolymers was reflected in the measured GM values. Overall, it was concluded that IGC is a good method for characterizing thermodynamic interaction between blend and copolymer constituents, but a severe limitation of the method is that the interactions are often too weak to measure accurately. Finally, the microphase structure of the above copolymers were studied by IGC from the retention behavior of hydrocarbon probes below the upper glass transition temperature of the copolymers. The degree of microphase separation, the size of the hard phases and the continuity of the soft phases in the copolymers characterized, and the results obtained were consistent with small angle x-ray, electron microscopy and differential scanning calorimetry data on the same materials.