High temperature polyarylene networks produced through the step-growth thermal cyclopolymerization of mono-ortho-diynylarene (MODA) and bis-ortho-diynylarene (BODA) monomers have been shown to produce high yielding glassy carbon once pyrolyzed at 1000 °C. In this study the homo- and co-polymerization of both monomers will be studied, and the effects of copolymer composition on the processability when applied to carbonization and carbon-carbon composites. The carbon products from these high temperature polymer matrices will also be characterized. MODA and BODA are prepared through a Sonogashira coupling reaction and are polymerized through a heat-initiated Bergman Cyclization reaction mechanism. This work seeks to show how BODA-MODA copolymers can attenuate current composite processing limitations, and improve mechanical properties while retaining high temperature properties including high carbon yields.

Thesis (M.S.)--Pennsylvania State University, 1995. / Includes bibliographical references (leaves 72-84).

Carbon/Carbon (C/C) composite is defined as a carbon fiber reinforced carbon matrix. Since 1958 research has been carried out on the C/C composites. The main reason for the development of new C/C composites is the number of advantages it has to offer when compared with the regular materials. The areas where C/C composites are being used extensively are aerospace, military, etc. These C/C composites have better physical, mechanical, thermal properties when compared to steel. That is the reason C/C brakes made a huge impact in the aerospace industry. The main drawback associated with the C/C brakes which are used in aerospace applications is the oxidation of the composite at higher temperatures. Also other problem linked with the C/C brake is the migration of the inhibitors on to the friction surface of the brake which can eventually decrease the friction coefficient of the brake material. So, characterizing the commercially available Anti-Oxidant(A/O) system, developing a new A/O system which can not only provide better oxidation protection, but also an improved anti-oxidant migration resistance will be our main goal of this project.

Carbon-carbon composite brakes are one third the weight of typical steel brakes, and they attain strength and frictional properties at temperatures up to 1600°C. C/C composite brakes can endure high temperatures, but in the presence of oxygen they will begin to oxidize at 400°C. Anti-oxidant systems must be applied to the non-rubbing surfaces of the C/C composite stators and rotors to prevent oxidation. Currently, commercial phosphorus based coating materials are made of crystalline metal phosphates that are derived from heat treated phosphoric acid-based liquid precursors painted on the non-rubbing surface of C/C composites. These crystalline metal phosphate coatings are very porous and tend to move to the friction surface when exposed to increased levels of relative humidity. This anti-oxidant migration towards the rubbing surface causes a drop in frictional properties. Migration reduction and oxidation inhibition was improved upon with advanced anti-oxidant systems. The advanced antioxidants analyzed protected the C/C composite from thermal and catalytic oxidation six to ten times better at 650°C than commercial materials. At 871°C, the antioxidants protected the C/C composite from thermal oxidation ten times better than commercial materials. Migration of the antioxidant to the rubbing surfaces was eliminated through the use of advanced antioxidant compositions. The predicted life of the antioxidants was modeled using Avrami's equation. Characterization of the antioxidants was further analyzed through the use of SEM, EDS, and XRD systems.

AN ABSTRACT OF THE THESIS OFChristoph Michael Goettler, for the Master of Science degree in Mechanical Engineering, presented on Nov 6, 2020, at Southern Illinois University Carbondale. TITLE: EFFECT OF DENSITY ON FRICTION AND WEAR PERFORMANCE OF CARBON-CARBON COMPOSITE MATERIALSMAJOR PROFESSOR: Dr. Peter FilipCarbon-carbon (C/C) composite materials exhibit high thermal conductivity, high thermal stability, low density, and high mechanical strength. Due to these properties, C/C composites are ideal for use in high performance braking systems. However, C/C composites are incredibly expensive to manufacture, and thus improving the longevity of these materials is vital. C/C composite materials inherently have a density gradient due to manufacturing limitations. By determining the effect of density on friction and wear performance of C/C composite materials, manufacturers could use that data to alter manufacturing methods to improve the lifespan of C/C composites. In this study, the effect of density on friction and wear performance of C/C composite materials was studied. Friction tests were conducted through use of a universal mechanical tester (UMT) manufactured by Bruker and subsequent analysis was done through use of scanning electron microscopy, energy dispersive x-ray spectroscopy, and polarized light microscopy. Numerous samples from depths of 0 mm and 5 mm were taken from two C/C composite materials with varying matrices and friction tested at varying conditions to determine friction properties, friction surface characteristics, microstructure just below the friction surface characteristics, friction layer characteristics, and wear characteristics. Density, apparent density, and apparent porosity gradients were also measured to be able to correlate observations to density differences. It was observed that while density does not seem to be the main cause in differences in friction and wear performance of C/C materials at depths of 0 mm and 5 mm, there still existed significant differences in friction performance, wear performance, and post friction test material characteristics when comparing 0 mm samples to 5 mm samples. In conclusion, density was not found to be a significant cause in variations in friction performance. However, friction surface depth was found to have a significant effect on friction performance, wear performance, and the friction surface. Further research is needed to be able to determine the exact cause of the variations in performance at depths of 0 mm and 5 mm. Keywords: carbon-carbon, composite, C/C, density, friction, wear, brake

Carbon-carbon and carbon-nitrogen bond forming events are essential in chemistry. Although numerous stoichiometric/catalytic methods provided elegant and powerful solutions enabling those processes, the use of scarce/toxic reagents and harsh conditions is still ubiquitous in this field. As a result, extensive research has been conducted in the development of environmentally benign and inexpensive reagents for such transformations, however, general solutions remain a challenge. In this context, one of the focuses of our lab is to enable those processes in a more practical and sustainable fashion by using hypervalent iodine reagents. In this dissertation we demonstrate the synthetic applications of λ3-iodane reagents towards the formation of challenging carbon-carbon and carbon-nitrogen bonds in a complementary way to the methods already reported. Chapter 1 of this dissertation outlines the general electronic structure, geometry, synthesis and reactivity of λ3-iodanes as serves and background regarding these reagents. Chapter 2 highlights the applications of λ3-iodanes to access high-oxidation state transition metals until the year of 2017. This literature review provides detailed information about how λ3-iodanes can be applied to access 1st, 2nd and 3rd row high-oxidation complexes, as well as mechanistic details and synthetic utility of high-valent transition metals. Chapter 3 demonstrates our efforts to generate selective carbon-nitrogen and carbon-carbon products from a high-valent nickel complex. This led to important information of this mechanism adopted by the reaction and how the choice of oxidant can impact 1e- versus 2e- oxidative pathways on “hard” nickel pincer scaffolds. Chapter 4 describes our efforts towards the selective formation of α-C(sp2)-C(sp2) bonds at the α-position of enones via a reductive Iodonium-Claisen rearrangement. We demonstrate the utility of β-pyridinium silyl enol ethers as a platform for direct α-arylation, and how the 2-iodo-aryl-α-arylated enones can be used to access diverse heterocyclic structures. Chapter 5 demonstrates our initial efforts towards the selective C2 or C3 carbon-nitrogen bond formation on indoles. By exposing different indoles to (bis)cationic nitrogen-ligated HVI (N-HVI) reagents we found that selective C2 or C3 C-H indole-pyridinium salts can be formed in good to excellent yield. Although, this project is not finished yet, we anticipate the indole-pyridinium salts generated could serve as platform for accessing diverse piperidines, pyridones and primary amines through straightforward procedures. The combined chapters of this dissertation highlight the applications of λ3-iodanes towards transition metals and emphasize the applications of these reagents to enable challenging C–C and C–N bond formation events. More importantly, this dissertation serves as a guide for future development of the hypervalent iodine field. / Chemistry

ABSTRACT The effects of restoration on dissolved organic carbon (DOC) dynamics were examined at the Boi~-des-Bel peatland. This study included both laboratory measurements of DOC production by different peatland vegetative components and field measurements of DOC dynamics within a recently restored, a cutover and a natural peatland. Shrub and herbaceous plant material were found to be the most significant producers of DOC in the short term. Moss, peat and straw samples had a high potential to release DOC ;;ontinuously under warm, moist and aerobic conditions. On a short timescale, all components have the potential to release the three dissolved organic matter (DOM) fractions examined with humic acid (HA) most prominently being produced by shrubs and herbaceous plants and hydrophilic (HPI) and hydrophobic (HPO) fractions by mosses, peat and straw. Comparison of growing season results over three study years at the restored and cutover site indicated that DOC concentrations increased after restoration while DOC export decreased due to lowered runoff caused by the blockage of drainage ditches. Compared to the natural peatland, both the restored and the cutover site had a more humic DOM character. No difference could be found between the character of DOM released from the restored and cutover sites. The most active layer of DOM production was the top 75 em where the water iii table fluctuated during the season. Water storage units such as pools and ditches also play an important role in DOM export from the site. Spring snowmelt was found to be the most significant DOC export event of the study season in 2001, when export values were significantly larger than those measured during the growing season. Solubility of the different DOM fractions was the main controlling factor on the DOM character seen at the outflows. Storm events contributed significantly to the summer DOC output. DOC dynamics were affected by antecedent moisture conditions and differences emerged between the restored and cutover site during this period. The results of this study emphasize the importance of managing water table fluctuations and the restoration (reestablishment) of Sphagnum species in order to improve the retention of DOM within cutover peatlands. / Thesis / Master of Science (MS)

For hypersonic flight to enable rapid global transport and allow routine space access thermal protection systems must be developed that can survive the extreme aerothermal heating and oxidation for extended periods of time. Ultra high temperature ceramics (UHTCs) are the only potential materials capable of surviving the extreme hypersonic environment however extensive research in processing science and their oxidation properties are required before engineering systems can be developed for flight vehicles. Investigating the role of oxides during processing of ultra high temperature ceramics shows they play a critical role in both synthesis of ceramic powders and during densification. During spark plasma sintering of UHTCs the oxides can result in the formation of vapor filled pores that limit densification. A low temperature heat treatment can remove the oxides responsible for forming the vapor pores and also results in a significant improvement of the densification through a particle surface physical modification. The surface modification breaks up the native continuous surface oxide increasing the surface energy of the powder and removing the oxide as a barrier to diffusion that must be overcome before densification can begin. During synthesis of UHTCs from sol-gel the B₂O₃ phase acts as the main structure of the gel limiting the transition metal oxide network. While heat treating to form diborides the transition metal oxide undergoes preferential reduction forming carbides that reduce B₂O₃ while at high temperature encourage particle growth and localized extreme coarsening. To form phase pure borides B₂O₃ is required in excessive quantities to limit residual carbides, however carbide reduction and grain growth are connected. When the UHTC systems of ZrB₂-SiC are exposed to oxidation, either as dense ceramics or coatings on Carbon-Carbon composites, at high temperatures they undergo a complex oxidation mechanism with simultaneous material transport, precipitation and evaporation of oxide species that forms a glass ceramic protective oxygen barrier on the surface. The composite effect observed between the oxides of ZrB₂-SiC enables them to survive extreme oxidizing environments where traditional SiC oxidation barrier coatings fail.

Metal nanoparticles have received much interest for their application in catalysis due to high surface-to-volume ratios resulting in more available active sites. Ideally these catalysts are heterogeneous and allow for facile separation from the catalytic reaction mixture making them ideal for industrial application. Dispersed metal nanoparticles are explored due to their high reactivity in solution and are stabilized by surfactants and polymers. However, it is difficult to determine whether or not a catalyst is truly heterogeneous as a certain degree of leaching from the metal nanoparticle is inevitable. Determining the mechanisms involved in nanocatalysis is also a challenge. In this study, a series of dispersed palladium nanocatalysts in the Suzuki reaction with phenylboronic acid and bromobenzene were characterized before and after catalysis to determine what changes occur. Samples where characterized before and after the catalytic reaction by XPS, SEM, and EDS to monitor changes in particle size and composition. Reaction mixtures after catalysis were analyzed by ICP-MS for leached palladium species to determine if concentrations were high enough for homogeneous catalysis to take place. The dispersed palladium nanoparticles studied experienced growth during the catalytic process and a significant amount of leaching. XPS analysis indicates the presence of aromatic species on the particle surface after the catalytic reaction. The aromatic species is likely biphenyl, the product of the catalytic reaction, as the presence of boron and bromine was not found in XPS and EDS analysis.

In this study, we describe a detailed investigation of cobalt complexes containing redox-active ligands. We have prepared an electronic series of the complex in three oxidation states: [CoIII(ap)2]-, CoIII(isq)(ap), and [CoIII(CH3CN)(isq)2]+. Characterization shows that the metal center remains cobalt(III) through the redox changes and indicates that the oxidation state changes occur with gain or loss of electrons from the ligand set. While CoIII(isq)(ap) reacts with halide radicals to form a new cobalt-halide bond in a single electron reaction, [CoIII(ap)2]- appears to be prone to multi-electron reactivity in reactions with sources of "Cl+". Both reactions occur with electrons derived from the ligand set. Mechanistic studies suggest a single, two electron step is responsible for the bond-formation. Similarly, [CoIII(ap)2]- reacts with alkyl halides to pseudo-oxidatively add the alkyl at the cobalt center. The product of the reaction can be isolated and fully characterized and was found to be best assigned as CoIII(alkyl)(isq)2. This assignment indicates that the reaction occurs, again, with the new bond formed with two electrons formally derived from the ligand set and with no change in oxidation state at the metal center. Mechanistic investigations of the pseudo-oxidative addition suggest the reaction is SN2-like. The reaction occurs with a wide scope of alkyl halides, including those containing beta-hydrogens. The cross-coupling reaction of CoIII(alkyl)(isq)2 with RZnX forms a new carbon-carbon bond. Similarly, the two electron oxidized complex [CoIII(CH3CN)(isq)2]+ reacts with organozinc reagents to couple two carbon nucleophiles and form a new carbon-carbon bond. Both reactions are successful with both sp2 and sp3 carbons. When followed substoichiometrically, the homocoupling reaction can be observed to form CoIII(alkyl)(isq)2. This indicates that the homocoupling and cross-coupling reactions proceed by the same mechanism. However, both reactions have low yields. The yield of the reactions are decreased by steric bulk of the alkyl or aryl fragments or around the metal center created by substituents on the ligand. Also, while the steric congestion disfavors the addition of the first alkyl fragment, the addition of the second alkyl fragment and subsequent rapid elimination of the coupling product is almost completely inhibited. This result also implies that the coupling of the two alkyl fragments is entirely inner-sphere requiring installation of both for coupling. In a complementary study, use of bidentate or tridentate stabilizing ligands in combination with one redox-active catechol-derived or amidophenol-derived ligand was investigated. With the synthesis of (triphos)CoII(cat) and the one electron oxidized [(triphos)CoII(sq)]+, it is evident that the oxidation occurs at the ligand and not the metal. Reaction of (triphos)CoII(cat) with a Cl+ reagent generated a new material which we tentatively describe as (triphos)CoIII(Cl)(sq). This implies that the two electrons used to create the new cobalt-halide bond are derived from both the ligand and the metal, one from each. We believe the complex is unreactive with organic halides due to the steric bulk surrounding the metal center. Similar cobalt complexes containing tridentate or bidentate phosphine ligands or a tridentate pyrazol ligand in combination with a catechol-derived or amidophenol-derived ligand resulted in unsuccessful synthesis or unstable complexes. Throughout the course of both of these studies, steric crowding at the metal center is a problem disfavoring the facilitated reactivity. We have however shown that the amidophenol ligands have favorable molecular orbital overlap with the cobalt to act as an electron reservoir and facilitate reactivity at the metal center. We have also shown that this combination can create a proclivity to facilitate multi-electron reactions at the metal that is naturally prone to radical reactions.