Doctor of Philosophy (Ph.D.), University of Dayton, 2018, Materials Engineering

Two-dimensional assemblies of colloidal gold nanoparticles were deposited via electrostatic self-assembly onto silicon substrates modified with aminopropyltriethoxysilane. Assemblies were tuned by systematically adjusting the pH and ionic strength of the nanoparticle solutions and the fraction of adsorbed aminosilane molecules on the silicon surfaces. The nanoparticles were characterized by their size distribution, solution stability and electrokinetic properties. The resulting two-dimensional assemblies varied in particle surface coverage, interparticle separation and lateral organization. Increasing solution pH intensified interparticle repulsions and reduced the charge density of the aminosilane substrate, thus decreasing the fractional monolayer coverage of particles. Additionally, increasing ionic strength reduced interparticle separations, which were described by radial distribution functions, and consequently produced denser particle assemblies. At long adsorption times, surface coverage approaches a maximum which was constrained by the extent of interparticle repulsion and particle-surface interactions. With strong surface attraction of the pure aminosilane surface, the particles were incapable of lateral rearrangement during the adsorption process and, at best, organized into liquid-like structures, in agreement with the random sequential adsorption model for colloidal monolayers. In an effort to circumvent this issue, non-binding alkylsilanes were incorporated into the modified surfaces, thereby reducing the aminosilane surface density and weakening the attractive potential of the surface. These mixed silane surfaces were characterized to reveal their chemical and interfacial energetic properties. At a particular threshold of reduced aminosilane density, nanoparticle coverage fell considerably and two-dimensional order degraded. The local geometries of particle assemblies were evaluated by Voronoi tessellation which provided indication of structural transf (open full item for complete abstract)

Committee: Erick Vasquez PhD (Committee Chair); Richard Vaia PhD (Advisor); Andrey Voevodin PhD (Committee Member); Paul Murray PhD (Committee Member); Donald Klosterman PhD (Committee Member) Subjects: Materials Science

MS, University of Cincinnati, 2006, Engineering : Materials Science

This thesis explores two independent topics-the effect of silane on adhesion between rubber and brass and the effect of pre-treatment of Al 2024 T3 on silane performance. In the investigation of the effect of a silane mixture on the adhesion between brass and natural rubber, TOFSIMS was used to characterize the brass panels that were subjected to vulcanization in squalene of different formulations. Based on the characterization data it was concluded that the sulfur based silane assisted in the formation of copper sulfides in squalene formulations with low levels of sulfur and cobalt. DCP and XPS techniques were employed to assess the effect of alkaline pretreatment of aluminum on silane performance. Based on the decrease in corrosion current of the silane coated aluminum substrate with decreasing molarity of the pretreatment solution it can concluded that there exists a correlation between aluminum pretreatment and silane performance.

Committee: Dr. Wim Van Ooij (Advisor) Subjects: Engineering, Materials Science

Doctor of Philosophy, Case Western Reserve University, 1991, Macromolecular Science

To study the effects of various silane coupling agent blends on composite properties, cylinders made of a benzyldimethylamine (BDMA)-catalyzed, nadic methyl anhydride (NMA)-cured diglycidyl ether of bisphenol-A (BDGE) were filled with 30 weight % of silica. The silica had been treated by silane blends of either γ-aminpropyltriethoxysilane (APS) and butyltriethoxysilane (BTS) or APS and ethyltriethoxysilane (ETS). A variety of techniques were utilized to compare the effects of BTS versus ETS and the concentration of amine in the silane blend. The results indicate the importance of structure and composition of the silane interphase on the properties of composite materials. The effect of varying composition of nonhydrolyzed silane coupling agent blends of APS and BTS on the cure of the epoxy matrix was studied by Fourier transform infrared spectroscopy (FTIR). The silane blends perturbed the kinetics of the alternating anhydride-epoxy copolymerization reaction, with the perturbation being a nonlinear function of the relative amine concentration in the system. The effect of hydrolyzed and nonhydrolyzed of various compositions of silane coupling agent blends of APS/BTS or APS/ETS on the cure of a BDMA-catalyzed, NMA-cured BDGE were investigated by FTIR. The presence of the amine group perturbs the alternating copolymerization of the anydride and epoxy groups by initiating and catalyzing the reaction. Hydrolysis also promoted the reaction rate. Samples containing ETS cured more rapidly than those containing BTS at the same composition. Imide formation was not significant in the presence of the alkyl-ended silanes. APS/BTS and APS/ETS silane coupling agent blends of varying composition were added to the epoxy matrix. 29Si nuclear magnetic resonance was utilized in order to determine the effect of composition of the silane coupling agent blend on the mobility of the various portions of the siloxane network. Hydrolysis caused an increase in the rigidity of the highly condens (open full item for complete abstract)

Committee: Jack Koenig (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2010, Polymer Engineering

The focus of this work was to study the effects of flexible silica backbones on elastic properties of silica aerogels. Two routes were examined. In the first, alkyl-chain bis-silanes were used in conjunction with tetraethoxysilane (TEOS) precursor to obtain silica aerogel backbones which were later reinforced by epoxy. The alkyl-chain bis-silanes at 15 mol % concentration were found to increase the elastic recovery from a state of 25% compressive strain significantly compared to traditional formulations without bis-silane. It was noted that a reduction in modulus was observed with aerogels containing bis-silane. The length of the alkyl-chain was observed to have no appreciable impact on the elastic response of the aerogels, or other material properties such as density or surface area. Finally, an amine functionalized bis-silane was demonstrated to exhibit elastic behavior while maintaining increased reinforcement. The second approach examined the effect of reducing the silica network connectivity on elastic response. For this purpose, a bifunctional silane, dimethyldiethoxysilane (DMDES), was substituted for a part of the tetrafunctional TEOS in the silane formulation. It was found that low concentrations, DMDES helped increase elastic response, but reduced the modulus. Higher concentrations of DMDES did not result in further enhancement of elastic response.

Committee: Sadhan Jana Dr. (Advisor) Subjects: Polymers

Master of Science, The Ohio State University, 1970, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy, University of Akron, 2023, Polymer Science

We have elucidated details of how the microscopic structure and dynamics of filler in reinforced rubbers influence mechanical properties. Studies were performed on highly loaded, silica-filled, crosslinked styrene-butadiene rubber (SBR). Properties of the compounds studied were varied by addition of silane coupling agents, silicas of different surface area, and by addition of well-characterized, anionically-polymerized, low molecular weight, dimethylamino end-functionalized SBR additives of linear or star molecular architecture. Samples were probed with a combination of Ultra-small Angle X-ray Scattering/Small Angle Scattering (USAXS/SAXS), X-ray Photon Correlation Spectroscopy (XPCS), and mechanical measurements. Investigation of samples with or without silane coupling agents confirms that coupling agents enhance filler dispersion. This enhanced dispersion leads to slower filler dynamics when the rubber is strained and a slower change in dynamics over time. These slower dynamics and slower evolution of dynamics correlate with slower macroscopic stress relaxation. Our work also examines the temporally heterogenous dynamics that underlie the stress relaxation process. During stress relaxation, filler dynamics intermittently speed up and slow down. These results indicate that while macroscopic stress relaxation appears to be a relatively simple process, the microscopic behavior is complex. Studies on rubbers containing high surface area, milled silica under dynamic strain reveal that while rubber containing milled silica and monosulfidic coupling agent shows a large Payne effect, the breakdown of filler is suppressed. We infer that debonding and/or yielding of bridging bound layers is responsible for the Payne effect in this sample. These bridging layers provide this rubber with a high modulus and low hysteresis. Addition of end-functionalized SBRs to rubber drastically affects mechanical properties. Rubber containing conventional silica and 20 kg/mol difunctio (open full item for complete abstract)

Committee: Mark Foster (Advisor); Roderic Quirk (Other); Jutta Luettmer-Strathmann (Committee Member); Mesfin Tsige (Committee Member); Junpeng Wang (Committee Member); Li Jia (Committee Chair) Subjects: Materials Science

Master of Science, University of Akron, 2021, Polymer Science

As reinforced rubber is a widely used and essential material, numerous research studies have been conducted on it, but many questions remain because of the complexity of the filler networks. To achieve a better performance tire tread rubber, the technique of X-ray photon correlation spectroscopy (XPCS) has been used in the study of the microscopic dynamics of filler reinforced styrene-butadiene rubber (SBR) subjected to step strain. For the two-time plots, dynamic heterogeneity for two kinds of SBR samples, with and without S1 silane coupling agent, was observed. The susceptibility (휒 function) was employed to analyze the dynamical heterogeneity evidenced in the two-time correlation data quantitatively. The plots of maximum 휒 values at three different values of scattering vector, 푞, versus aging time show that dynamic heterogeneity decays in a few hundred seconds. A more detailed analysis shows that the dynamic heterogeneity of the sample with coupling agent decays in the first 75 s after stretching. Combined with the maxima 휒 versus scattering vector 푞 plots which have shown two different patterns, the deduction is that addition of a silane coupling agent effectively accelerates the decay of dynamic heterogeneity, but does not apparently influence the magnitude of 휒. According to previous research, the time at which 휒 reaches a maximum coincides with the relaxation time and the maximum value of 휒 indicates the magnitude of the dynamic heterogeneity. Plots of maximum 휒 value versus q and delay time make clear the trends in most of the measurements. For a given value of 푞, the delay time at which the maxima 휒 value occurs increases with aging time. In both samples, trends in 휒, such as how it varies with 푞 and at which delay time the maximum occurs, are similar for the stretching direction and perpendicular direction. However, further study indicates that the initial strong dynamic heterogeneity declines more slowly in the direction perpendi (open full item for complete abstract)

Committee: Foster Mark Dr. (Advisor); Tsige Mesfin Dr. (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Toledo, 2020, Chemistry

Transition-metal-catalyzed hydroelementation is one of the most important methods for the synthesis of functionalized molecules. Hydroboration and hydrosilylation are two important classes of hydroelementation reactions. In chapter 1, the applications of these transformations, recent catalyst development, and the operating mechanisms are briefly discussed. The challenges and scope in base-metal catalysis for hydroboration and hydrosilylation are also described. In chapter 2, the selective hydroboration of aldehydes and N-allylimines utilizing a well-defined cationic nickel complex is described. The catalyst displayed excellent selectivity toward aldehydes in the presence of ketones. A wide variety of functional groups were tolerated, including halogens, nitro, cyano, and alkenes for both aldehydes and imines. Electron-rich substrates were found to be significantly more reactive than their electron poor counterparts, a unique feature, reported for the first time in metal-catalyzed hydroboration. Stoichiometric reactions with the catalyst disclosed that the substates were activated through a Lewis acidic interaction and undergo hydroboration with pinacolborane (HBpin) under mild reaction conditions. In chapter 3, seven structurally similar cationic nickel(II)−alkyl complexes were synthesized by using a series of P, N ligands, following the previously developed protocol from our lab and their reactivity was explored in the hydrosilylation of alkenes. Newly synthesized catalysts were characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. The study showed that more electron-rich phosphines enhanced the overall reactivity of the hydrosilylation; in contrast, groups on the imine donor had little impact. Overall, these catalysts displayed reactivity and selectivity that was previously unknown or very rare in nickel-catalyzed hydrosilylation. In reactions with Ph2SiH2, 1,2-disubstituted vinylarenes showed complete benzylic selectivity for sil (open full item for complete abstract)

Committee: Joseph A. R. Schmidt (Committee Chair); Mark R. Mason (Committee Member); Wei Li (Committee Member); L.M. Viranga Tillekeratne (Committee Member) Subjects: Chemistry; Inorganic Chemistry; Organic Chemistry

Doctor of Philosophy, Case Western Reserve University, 2020, Macromolecular Science and Engineering

Epoxy adhesives constitute a large majority of the structural adhesive market. Most of these adhesives are 2-component systems consisting of a bisphenol A based resin and an amine based hardener. Bisphenol A is an endocrine disruptor and a known carcinogen, as well as derived from petroleum which in itself is a finite resource. Due to these disadvantages, BPA has been banned in multiple countries and replacements for BPA based resins are persistently sought. One of the most common amine curing agents used in epoxy adhesives is petroleum derived isophorone diamine (IPDA) which has been found to be toxic and a skin sensitizer. The need for adhesive systems that can replace bisphenol A based resins and petroleum based IPDA has never been more urgent. A family of biobased epoxies derived from diphenolic acid (DGEDP epoxies) were recently synthesized that have an estrogen binding capacity of an order of magnitude less than BPA but similar thermo mechanical properties to the diglycidyl ether of bisphenol A (DGEBA), the most commonly used epoxy resin derived from BPA. This family of resins, differing amongst each other only in ester chain length in terms of structure exhibited excellent potential as suitable replacements to DGEBA. Their curing kinetics with regards to IPDA were studied to determine which resin would be suitable for adhesive applications. Isoconversional analysis indicated that the resins cured via an autocatalytic mechanism and modeling of the curing behavior using the Kamal Sourour model showed that the methyl ester resin (DGEDP-methyl) exhibited unusually high curing rates. This resin was then chosen for further development as the resin component for a biobased adhesive. However, when lap shear samples on aluminum were prepared, DGEDP-methyl when cured with IPDA exhibited extremely brittle behavior failing at very low stresses. A commercially available highly aliphatic biobased epoxy resin (NC-514) derived from cashew nut shell liquid was hypot (open full item for complete abstract)

Committee: Ica Manas-Zloczower Prof. (Committee Chair); Donald Feke Prof. (Committee Member); Gary Wnek Prof. (Committee Member); Rigoberto Advincula Prof. (Committee Member) Subjects: Materials Science; Polymers; Sustainability

Doctor of Philosophy, The Ohio State University, 1986, Graduate School

Committee: Not Provided (Other) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 1981, Graduate School

Committee: Not Provided (Other) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 1975, Graduate School

Committee: Not Provided (Other) Subjects: Chemistry

Master of Sciences (Engineering), Case Western Reserve University, 2014, Materials Science and Engineering

Understanding transparent conductive oxide (TCO) degradation is critical to improving lifetimes of thin filmphotovoltaics, which utilize TCOs like aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), and fluorine-doped tin oxide (FTO). Commercial AZO, ITO, and FTO were exposed in accelerated and outdoor exposures in several configurations, utilizing environmental stressors such as irradiance, heat and humidity. Electrical and optical properties and surface energies were measured. Yellowness, haze, water contact angle and resistivity of different materials trended differently with exposure time and type, indicating different degradation mechanisms. Interfacial layers for photovoltaic applications were also studied for AZO and ITO. OPV's PEDOT:PSS degrades TCO optics only, suggesting decoupled optical and electrical degradation mechanisms. Hazing of AZO by PEDOT:PSS appears photo-sensitive; 5x outdoor exposures demonstrated higher haze than exposures with no light. 3-aminopropyltriethoxysilane was applied to improve TCO stability and exposed to damp heat. 3-aminopropyltriethoxysilane reduces AZO's resistivity increase and edge effects.

Committee: Roger French (Advisor); Ina Martin (Committee Member); Alp Sehirlioglu (Committee Member) Subjects: Alternative Energy; Energy; Engineering; Environmental Engineering; Environmental Science; Materials Science; Sustainability

PhD, University of Cincinnati, 2012, Engineering and Applied Science: Materials Science

Magnesium (Mg) and its alloys are emerging as a possible biodegradable implant material. The corrosion behavior of pure Mg, AZ31, and AZ91D were evaluated in various In Vitro and In Vivo environments to investigate their potential application of being biomaterials. Mg implants may degrade too quickly in the body, before the natural healing process is complete. Anodization is known to be an effective approach for slowing down the initial corrosion rate of magnesium (Mg) and its alloys. Anodization was investigated to slow down the initial corrosion of Mg in a simulated body corrosive environment. Pure Mg and AZ91D alloy were anodized and their corrosion resistance was compared in terms of anodization behavior and parameters such as applied voltage and current with different anodization time. Electrochemical impedance spectroscopy, DC polarization, and immersion testing were used to evaluate the corrosion resistance of Mg samples and further optimize anodization parameters. The results showed that anodization increased the corrosion resistance of both pure Mg and AZ91D samples. Further characterization showed the anodized layers on both pure Mg and AZ91D consisted of Mg, O and Si, in the mixture of MgO and Mg2SiO4. The anodization of AZ91D was further investigated by studying the specific use of oxy-salts to improve the corrosion resistance of anodization coatings. Oxy-salts of silicate, phosphate, and carbonate were added separately to a sodium hydroxide alkaline electrolyte used for anodization. This modified process was investigated in terms of anodizing behavior, the surface properties of the film, and enhanced corrosion protection of the metal. Anodization of AZ91D using the silicate containing electrolyte generated sparks and increased the electrolyte temperature, and produced a thicker and more corrosion resistant layer than the other oxy-salts. In this process, MgO and SiO2 formed Mg2SiO4 at high temperature and silicon (Si) in the anodized coating was mainly (open full item for complete abstract)

Committee: Vesselin Shanov PhD (Committee Chair); YeoHeung Yun PhD (Committee Member); Stephen Clarson PhD (Committee Member); Mark Schulz PhD (Committee Member) Subjects: Metallurgy

PhD, University of Cincinnati, 2009, Engineering : Materials Science

Aerospace aluminum alloys such as Al alloy 2024-T3 and 7075-T6 are subject to localized corrosion due the existence of intermetallics containing Cu, Mg or Zn. Current protection measurement employs substantial use of chromate and high VOC organics, both of which are identified as environment and health hazards. The approach of this study is to utilize a combination of organofunctional silanes and a compatible inhibitor integrated into high-performance waterborne resins. First, an extensive pigment screening has been done to find replacements for chromates using the testing methodology for fast corrosion inhibition evaluation and pigment. Zinc phosphate and calcium zinc phosphomolybdate were found to have the best overall performance on Al alloys. Some new corrosion inhibitors were synthesized by chemical methods or modified by plasma polymerization for use in the coatings. Low-VOC, chromate-free primers (superprimer) were developed using these pigments with silane and acrylic-epoxy resins. The developed superprimer demonstrated good corrosion inhibition on aluminum substrates. The functions of inhibitor and silane in the coating were investigated. Both silane and inhibitor are critical for the performance of the superprimer. Silane was found to improve the adhesion of the coating to the substrate and also facilitate corrosion prevention. Addition of zinc phosphate to the coating improved the resistance of a scratched area against corrosion. The microstructure of the acrylic-epoxy superprimer coating was studied. SEM/EDAX revealed that the superprimer has a self-assembled stratified double-layer structure which accounts for the strong anti-corrosion performance of the zinc phosphate pigment. Zinc phosphate leaches out from the coating to actively protect the scratched area. The leaching of pigment was confirmed in the ICP-MS analysis and the leaching rate was measured. Coating-metal interface and the scribe of coated panels subjected to corrosion test was studied. To (open full item for complete abstract)

Committee: William Vanooij PhD (Committee Chair); Dale Schaefer PhD (Committee Member); Jude Iroh PhD (Committee Member); Stephen Clarson PhD (Committee Member) Subjects: Materials Science

PhD, University of Cincinnati, 2009, Engineering : Materials Science

The film structure and surface morphology of a novel one-step epoxy-silane coating system were revealed by neutron reflectivity, Atomic Force Microscope (AFM) and Environmental Scanning Electron Microscope (ESEM). The bis-sulfur silane is enriched at the coating-substrate interface instead of uniformly distributed, which leads to a layered structure. The phase separation within bulk coating films was investigated by Ultra Small Angle X-ray Scattering (USAXS) and Small Angle Neutron Scattering (SANS). The epoxy-silane network forms branched morphologies without significant interface. No phase separation on scale range from 0.5 nm to 10.3 nm were observed. The protection mechanisms of the epoxy-silane coating system were studied in terms of coating structure, water response behavior, salt exclusion and hydrothermal stability. By comparing pure epoxy and epoxy-silane mixtures in various aqueous environments, the effects of the addition of silane were determined. The key mechanisms of silane-enhanced protection are: 1. Bis-sulfur silane is enriched at the substrate-coating interface and forms a SiO2-like interface region, which ensures excellent adhesion between coating and substrate. The addition of silane also increases the roughness of the epoxy-silane film. 2. The silane serves as a crosslinker, resulting in a denser and less hydrophilic bulk film compared to the neat epoxy. The hydrophobic nature of bis-sulfur silane also increases the overall hydrophobicity of the mixed film. 3. The salt exclusion effect is introduced to epoxy-silane film due to the addition of bis-sulfur silane fines the molecular-level free space. 4. The epoxy-silane film shows improved hydrothermal stability. The addition of bis-sulfur silane eliminates the hydroxyl groups formed during the cure process. The absence of hydroxyl group prevents the bond scission effect. The addition of silane also introduces the immunity of hydrothermal degradation to the film-substrate interface by the forma (open full item for complete abstract)

Committee: Dale Schaefer (Committee Chair); Jude Iroh (Committee Member); Vesselin Shanov (Committee Member); William Vanooij (Committee Member) Subjects: Engineering; Materials Science

PhD, University of Cincinnati, 2007, Engineering : Materials Science

This dissertation focuses on the relationship between substrate-surface chemistry (cleaning), reaction mechanism, film structure and water-barrier properties of water-based bis-amino silane and vinyl triacetoxysilane films. The work was undertaked to fulfill a SERDP (Strategic Environment Research and Development Program) requirement to understand the mechanism of corrosion protection in silane-based coatings. The majority of the work focuses on mixtures of the above two silanes. Such coatings are referred to as AV coatings. The chemistry of neat AV mixtures was studied by 13C NMR. The reaction mechanism was found to be the exchange of the hydrogen atom on the secondary amine group with the acetoxy group on the vinyl triacetoxysilane. The chemistry of the AV water solution was also investigated by 13C and 29Si NMR. The influence of the cleaning solution pH on the CRS surface chemistry and AV absorption was examined. The corrosion performance examination on CRS panels showed that the CRS surface is very sensitive to cleaning protocol. Optimum anti-corrosion performance was obtained after cleaning at pH ~ 9.5. The underlying mechanism for this observation is discussed. The morphologies and water barrier properties of AV films were studied at different A/V ratios. AV film was found susceptible to water penetration. About 30 vol% water is absorbed in the film with only slight thickness increase. Most water is physically absorbed in the void space with the least amount being absorbed near the stoichiometric A/V ratio of 3/1. Kinetic investigation of water uptake enables us to monitor water ingress providing more details on water absorption. Time-resolved D2O ingress in bis-amino silane and bis-sulfur silane film was studied by situ neutron reflectivity and Fourier transform infrared reflection-absorption spectroscopy. The absorbed water exists in two populations: one is dissolved in the polymer matrix (Henry's mode) and the other occupies unrelaxed free volume within (open full item for complete abstract)

Committee: Dr. Dale Schaefer (Advisor) Subjects: Engineering, Materials Science

MS, University of Cincinnati, 2007, Engineering : Chemical Engineering

Protein fouling is a critical factor governing membrane performance in various filtration processes. In this study, we report two new surface modification techniques to modify 0.22greek small letter mu mixed cellulose esters membranes (MCE) and 0.20greek small letter mu, positively charged durapore membranes to reduce protein fouling. The first step in the modification of MCE membranes involves coating of the membrane with a monolayer of allyldimethylchlorosilane (ADCS). The silanized membrane is then covalently linked to Pluronic F127, a triblock copolymer of polyethylene oxide and polypropylene oxide (PEO–PPO–PEO) by UV irradiation at wavelengths >215 nm. The presence of PEO groups on the membrane surface increased the wettability of the membrane. Contact angle measurements confirmed that the degree of Pluronic grafting on the silanized membrane was a function of the UV exposure time. The hydraulic permeability and flux decline of the modified membrane during bovine serum albumin (BSA) filtration were nearly identical to the unmodified membrane. The modified membranes exhibited better cleaning characteristics compared to unmodified membranes upon back flushing with saline solution. The positively charged durapore membranes have been dip coated with random copolymers poly (oligoethylene glycol methacrylate co methacrylic acid), (OEGMA/MA), under four different conditions. The electrostatic adsorption of OEGMA/MA onto the membrane surface has been verified by streaming potential measurements. The ability of the modified membranes to resist protein adsorption has been verified by FTIR spectra. The hydraulic permeability and the flux decline data of the modified membranes were similar to the unmodified membranes and the cleaning characteristic of modified membranes showed improved performance.

Committee: Dr. Chia-Chi Ho (Advisor) Subjects: Engineering, Chemical

MS, University of Cincinnati, 2007, Engineering : Materials Science

Chromates used as pretreatments for metals and as anti-corrosive pigments in primers have been found to be a strong carcinogen and hence there is considerable pressure from environmentalists and government agencies for its replacement. Dr. Van Ooij and his research group have developed an array of environmentally friendly hydrophobic silane based pretreatments for corrosion protection of metals. However these coatings are extremely thin, of the order of a few hundred nanometers and hence unable to provide long term corrosion protection like a paint film which has thickness in microns. To eliminate this problem, the idea of Superprimer was conceptualized. “Superprimers” are self-priming coatings containing a mixture of polymer resin and silane as the binder and chromate-free, environmentally friendly corrosion inhibitor make a complete primer formulation. Thus, by adding the right silane to a coating resin, the chromate pretreatment step would be eliminated and the chromate pigment would be replaced by an environmentally friendly anti-corrosive pigment. This research deals with the evaluation of polyurethane-silane superprimer coatings as potential replacement of chromate pretreatment and chromat-containing high VOC primers for corrosion protection of AA 2024-T3 aluminum alloy. The silane chosen was BTSE because of its dipodal structure, hydrophobicity and ability to hydrolyze in water. EIS revealed that the hydrophobicity of the coatings increased considerably due to addition of 4 % BTSE silane improving its impedance and water barrier properties. RAIR and NMR spectroscopy showed hydrolysis and self condensation to siloxanes of the silane molecules. The formation of the siloxane network enhances the tensile strength, Tg and thermal degradation behavior of the coating, as detected by tensile testing, DSC and TGA, respectively. ToF_SIMS and EDXS studies of the interface indicated the presence of siloxane layer at the interface between the metal and coating. It indi (open full item for complete abstract)

Committee: Dr. William Van Ooij (Advisor) Subjects: Engineering, Materials Science

MS, University of Cincinnati, 2006, Engineering : Materials Science

The Environmental Protection Agency (EPA) in the US has imposed legislations on the use of hexavalent chromium and solvents contributing to emission of volatile organic compounds in primer coatings. This has led researchers to pursue development of alternative environmentally-friendly coatings which would eliminate chromate conversion coatings (CCC). This thesis discusses the work done towards the development of a novel, chromate-free, low-VOC, water-based, organic coating system for corrosion protection of AA 2024-T3 aerospace alloy. These special coatings which can be applied directly to the metal are termed as ‘superprimers' and consist of novolac epoxy binder, silanes, polyurethane and non-chromate inhibitors. Coating evaluation tests were employed to compare the performance of the superprimer coatings with controls. SEM, FTIR and NMR were carried out to understand the chemistry of the coatings. The requirement for a conversion coating was obviated and the coating system developed was on par with the chromate-based control coating in terms of performance.

Committee: Dr. William Van Ooij (Advisor) Subjects: Engineering, Materials Science