Many modern automotive and aerospace components are heat-formed at temperatures up to 900 degrees C. Due to the high tool temperature, insulations are employed to reduce the heat loss and the energy consumption of the process. However, current insulation materials for the force flow of these processes still require active countercooling. In this study, the performance of a novel hybrid structure with improved insulation capability for such applications was investigated. It consisted of an outer frame made of an oxide fiber composite (OFC) and a paperbased ceramic (PBC) as a filler. The mechanical and thermal properties for both materials were determined and implemented in a finite element model (FEM) to numerically design the layout of a hybrid structure. Experimental load tests in process-oriented conditions validated the simulation results. The hybrid insulation appears promising, as mechanical stability and good insulation capabilities were confirmed.

High temperature-resistant fabrics can be used as a reinforcement structure in ceramic matrix composites. They often need a coating for oxidation protection and mechanical decoupling from the matrix. Atomic layer deposition (ALD) provides very thin conformal coatings even deep down into complex or porous structures and thus might be a suitable technique for this purpose. Carbon fiber fabrics (size 300 mm × 80 mm) and SiC fiber fabrics (size 400 mm × 80 mm) were coated using ALD with a multilayer system: a first layer made of 320 cycles of alumina (Al2O3) deposition, a second layer made of 142 cycles of titania-furfuryl alcohol hybrid (TiO2-FFA), and a third layer made of 360 cycles of titanium phosphate (TixPOy). Scanning electron microscopy reveals that the coatings are uniform and that the thickness of each layer is almost independent of the place in the reactor while coating. Appearance and thickness do not show any dependence on the type of fiber used as a substrate. Energy dispersive x-ray spectroscopy confirmed the expected elemental composition of each layer. Thermogravimetric analysis under oxidizing environment revealed that the first layer increases the onset temperature of fiber oxidation significantly, while the following two layers improve the oxidative protection only to a much smaller degree. Varying the geometry and size of the sample holder and especially the stacking of several fabric specimens on top of each other allowed increasing the total area of coated fabric up to 560 cm2 per batch. It was demonstrated that four-layered fiber coatings could be obtained with high uniformity even on these much more complicated geometries.

Alumina (Nextel™ 610) fibre reinforced YAG-ZrO2 matrix composites were successfully joined by using different brazing alloys, metallic interlayers and a glass-ceramic. All joints were mechanically stable and free of cracks. Three commercial brazing alloys and a new alloy based on Ti/Cu/Al interlayers were selected to join these composites for applications in a non-oxidizing environment. A glass-ceramic based on SiO2-Al2O3-CaO-MgO was developed in case the joined component needs to be oxidation resistant. To evaluate the thermal stability, all joined composites were aged up to 100h in air at 550°C for brazing joints or 850°C and 930°C for glass-ceramic joints. The mechanical strength was measured using single lap and four point bending tests before and after ageing. Four point bending tests on glass-ceramic joined samples showed an average joint strength of about 70MPa which is 35% of as-received composites.

Exposing bundles of carbon and quartz fibers as well as silicon wafers to sequential pulses of gaseous TiCl4/furfuryl alcohol (FFA) and H2O/TiCl4/furfuryl alcohol, respectively gave rise to conformal organic/inorganic coatings on all of these substrates. The deposition during the FFA pulse is self-limiting and the process shows a linear growth per cycle of (0.65 ± 0.05) nm/cycle in the absence of water pulses and (1.68 ± 0.04) nm/cycle in the presence of water pulses. A possible reaction mechanism comprises classic atomic layer deposition steps as well as a polymerization route of furfuryl alcohol, which leads to the release of water during the furfuryl alcohol pulse and further comprises hydrolytic ring opening of furan rings and/or hydrolytic cleavage of Ti–Cl bonds. Since an additional subsequent water pulse significantly enhances the growth, it seems that without additional water pulse these reactions are limited by the amount of water that is formed or desorbed. Oxidizing the coated carbon fibers at 700 °C gave rise to thin-walled titania microtubes with wrinkled tube walls. Titania/carbon-hybrid microtubes were obtained by coating quartz fibers with TiO2/FFA, pyrolysis at 600 °C under nitrogen atmosphere, and subsequent etching with hydrogen fluoride. Energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy (of coated silicon wafers) confirm that the coating consists predominantly of titanium, oxygen, carbon, and comprises residual chlorine. The stoichiometry is TiO2C3.5Cl0.1 before and TiO1.8C1.4 after the pyrolysis. According to XPS and thermogravimetric analysis, the molar ratio of titania to furfuryl alcohol is approximately 1.

Aluminum phosphate was deposited onto bundles of carbon fibers and flat glassy carbon substrates using atomic layer deposition by exposing them to alternating pulses of trimethylaluminum and triethylphosphate vapors. Energy dispersive X-ray spectroscopy (EDXS) and solid state nuclear magnetic resonance (SS-NMR) spectra confirmed that the coating comprises aluminum phosphate (orthophosphate as well as other stoichiometries). Scanning electron microscopic (SEM) images revealed that the coatings are uniform and conformal. After coating, the fibers are still separated from each other like the uncoated fibers. Thermogravimetric analysis (TGA) indicates an improvement of oxidation resistance of the coated fibers compared to uncoated fibers.

Layers of alumina, titania and double layers of alumina/titania (and reverse) were deposited onto bundles of carbon fibers in an atomic layer deposition process. Scanning electron microscopy (SEM) images of the coated carbon fibers revealed that each fiber of a bundle was coated homogenously and separately and that no bridges were formed between the fibers. Transmission electron microscopy and SEM images showed that the coating was conformal, uniform, had a good adhesion to the fiber surface and that the morphology of the coating surface was similar to that of fiber surface. In case of double layers, the average deposition rate of coatings did not depend on the sequence of layer deposition. After coating, the carbon fibers were selectively removed by thermal oxidation in air at temperatures of 550 °C and 900 °C, leading to metal oxide microtubes.

A series of cationic diblock copolymers, poly(N-isopropylacrylamide)48-block-poly((3-acrylamidopropyl)trimethylammonium chloride)X, abbreviated as PNIPAAM48-b-PAMPTMA+X (X = 0, 6, 10, 14, and 20), has been synthesized, and their adsorption onto silicon oxynitride from aqueous solution has been investigated using dual polarization interferometry. The polymer adsorption was modeled by using a lattice mean-field theory, and a satisfactory consistency between theory and experiments was found in terms of surface excess and layer thickness. Both theory and experiments show that the adsorption is limited by steric repulsion for X < Xmax and by electrostatic interactions for X > Xmax. Modeling demonstrates that significant surface charge regulation occurs due to adsorption. Both the nonionic and cationic block exhibit nonelectrostatic affinity to silicon oxynitride and thus contribute to the driving force for adsorption, and modeling is used for clarifying how changes in the nonelectrostatic affinity affects the surface excess. The segments of the nonionic and cationic blocks seem less segregated when both have a nonelectrostatic affinity for the surface compared to the case where the segments had no surface affinity. Adsorption kinetics was investigated experimentally. Two kinetic regimes were observed: the adsorption rate is initially controlled by the mass transfer rate to the surface and at higher coverage is limited by the attachment rate.

Bundles of alumina microtubes were prepared by depositing alumina onto bundles of “endless” carbon fibers via pulsed chemical vapor deposition and subsequent removal of the fibers. Thin alumina films were deposited onto “endless” carbon fibers at 77 °C by gas phase exposures to sequential pulses of trimethylaluminum and water vapor, respectively. The carbon fibers were selectively removed using thermal oxidation in air at temperatures exceeding 550 °C. The length of the tubes was primarily limited by the dimension of the used furnace. The longest tubes thus had a length of 30 cm. Scanning electron microscopic (SEM) images of the microtubes revealed that each individual tube was separated from its neighbors and that the tubes had an almost uniform wall thickness. SEM and transmission electron microscopic (TEM) images indicate that the inner side of the wall has the same morphology as the fiber template. As deposited, the alumina films have a predominantly amorphous structure; this is transformed into a polycrystalline structure during thermal oxidation. At low thermal oxidation temperatures, such as 550 °C, the alumina microtubes still comprise a substantial fraction of amorphous structure, at higher oxidation temperatures, 900 °C or above, a dominating polycrystalline structure (with bigger grains) is formed. This transformation gives rise to grain boundaries. These grain boundaries might facilitate oxygen diffusion and thus oxidative removal of the fiber templates.

Cationic PNIPAAM Block Copolymer Adsorption on Silicon Oxynitride : Effects of the Length of the Charged Block