Polymers and polymer nanocomposites have been studied under conditions of extremely high heating rates. Traditionally, these materials have been examined by the flammability research community using methods which have heating rates on the order of 10 degrees C/min. In this study, we have examined how polypropylene-nanoclay (montmorillonite) and polypropylene-carbon nanotube nanocomposites behave subjected to heating rates on the order of one million degrees C/min when irradiated with a 1064 nm Nd-YAG variable pulse millisecond laser. Time-resolved temperature data and mass loss data was collected for each sample as well as post-mortem surface characterization using spectroscopy and electron microscopy. The analysis shows that the nanospecies are effective in providing a protective barrier that decreases the amount of degradation and mass loss to the underlying polymer material. The effect is clearly seen after irradiating with a single pulse and multiple pulses. A comparison between the performance of the nanoclay and carbon nanotube composites is given.

The electrical and electromechanical properties of lithium niobate single crystals are investigated at high-temperatures. The total electrical conductivity is determined as a function of temperature by impedance spectroscopy for Z-cut crystals with different lithium content. For stoichiometric lithium niobate (sLN) the activation energy is found to be (1.49 ± 0.03) eV in the temperature range from 500 to 900 °C.

Further, the piezoelectric properties (resonance frequency, Q-factor) of X-cut lithium niobate crystals are determined at high temperatures for samples with compositions ranging from congruent to stoichiometric and, subsequently, compared to the conductivity data in order to identify loss contributions.

In this context, the high-temperature stability is examined for X- and Z-cut samples with compositions ranging from congruent to stoichiometric. Series of samples with and without additional alumina protection layers are annealed in air at 900 °C for approximately 50 h. Subsequently, depth profiles are measured by SNMS. In all cases, no lithium loss is observed and, therefore, a high-temperature stability of sLN for at least 50 h at 900 °C can be assumed in ambient air.

Further, the influence of protective layers with different thicknesses and compositions is investigated for X- and Z-cut samples. A lithium loss in the first 300 nm is observed for the Z-cut samples, while the X-cut samples show a behavior dependent on the type of protecting layer.

Effects of adding Erbium(Er) to Aluminum Nitride thin films on their structural and piezoelectric are reported along with stability of the films after annealing them at temperatures up to 600° C. The thin films samples were deposited on the (001) p-type silicon substrates by reactive magnetron sputtering, using the Er alloyed Aluminum targets with Er atomic concentrations of 0, 1, 3 and 4% and the magnetron sputtering power of 200 W. The samples were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XPS analysis was used to confirm the stoichiometry of AlN phase, Er atomic content and its possible chemical state in the films. Results show that alloying with Er results in higher piezoelectric coefficient d33 as compared to that in Er-free AlN thin films. Structural analysis of the films by XRD shows the shift of (0002) AlN peak to lower 2θ values upon Er doping, indicating the presence of uniform internal compressive stress.

The oxidation and diffusion of Molybdenum layer sputter-deposited on 2μm CVD diamond grown on silicon substrate has been studied. The Mo layer was protected by refractory metal silicide barrier layer. The samples were annealed in air ambient at 500°C over 30 hours. The oxidation of the samples was monitored with Rutherford Backscattering Spectroscopy (RBS). The effect of reactive sputtering of refractory silicide target in argon-nitrogen gas mixture (5% nitrogen by flow rate) on the barrier characteristics was investigated. The sheet resistivity of the barrier layer on SiC substrates as a function of annealing time in air at 500°C is reported. The surface structure and morphology of the refractory silicide films was determined with X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).

The availability of high-temperature stable surface acoustic wave (SAW) devices would enable realization of wireless sensors for monitoring high-temperature processes. One of the most promising substrate materials for SAW based high-temperature sensors is langasite (LGS, La3Ga5SiO14). It can be excited piezoelectrically up to its melting point at 1470 °C. However, gallium evaporation and degradation of the electrodes limit the application of LGS in SAW sensors for harsh environments to some extent.

The objectives of this work include the investigation of the gallium loss in the vicinity of the langasite surface in oxidizing, reducing and vacuum conditions at temperatures up to 900 °C. The gallium content in the vicinity of the LGS surface is not decreased after annealing the samples in air, while a significant gallium loss occurs in vacuum and reducing atmospheres (0.5 % H2/Ar). The latter results in a gallium oxide deficient region of 1.5 μm below the surface after annealing for 12 hours at 900 °C. The gallium loss is virtually completely suppressed after protecting the surface with a thin alumina film.

Further, thin-film electrodes based on platinum and platinum/rhodium are tested. While conventional platinum based electrodes are completely destroyed at 900 °C within hours due to agglomeration, alumina protected electrodes can be operated at least for several days at this temperature. After 400 hours at 700 °C, the alumina protected platinum electrodes show insignificant degradation. The influence of alumina passivation layers on the stability of the SAW devices is examined. Different electrode configurations are tested with respect to their long-term frequency stability at 650 °C.

Grain boundary chemistry in an X750 Ni alloy was analyzed by atom probe tomography in an effort to clarify the possible roles of elemental segregation and carbide presence on the stress corrosion cracking behavior of Ni alloys. Two types of cracks are observed: straight cracks along twin boundaries and wavy cracks at general boundaries. It was found that carbides (M23C6 and TiC) are present at both twin and general boundaries, with comparable B and P segregation for all types of grain boundaries. Twin boundaries intercept γ’ precipitates while the general boundaries wave around the γ’ and carbide precipitates. Near a crack tip, oxidation takes place on the periphery of carbide precipitate.

Nanophase Eu-doped Y2(CO3)3 and Eu-doped Zr(OH)4 are seeded into explosive fireballs to record the temperatures inside the fireball. The heat from the explosion decomposes the materials and converts them into Eu-doped Y2O3 and Eu-doped ZrO2, respectively. The optical signatures of these materials are compared with those of samples heated in a pyroprobe. By comparing the full-width half-max (FWHM) of the excitation peak of Eu-doped Y2(CO3)3 or comparing the ratio of two fluorescence peaks and the peak position of Eu-doped Zr(OH)4, we are able to deduce the temperatures inside the explosive fireball.

Currently, ceramics are being used under increasingly demanding environments. These materials have to exhibit phase stability and resist chemical attack during service. This research involves the study of the high-temperature stability of ceramic materials in gas turbines. SiC/SiC ceramic matrix composites (CMCs) are being increasingly used in the hot-sections of gas turbines, especially for aerospace applications. These CMCs are prone to recession of their surface if exposed to a flow of high-velocity water vapor, and to hot-corrosion when exposed to molten alkali salts. The objective of this investigation was the development of a hybrid system containing an environmental barrier coating (EBC) for protection of the CMC from chemical attack and a thermal barrier coating (TBC) that allows a steep temperature gradient across it to lower the temperature of the CMC for increased lifetimes. The EBC used was a functionally graded mullite (3Al2O3∙2SiO2) coating deposited by chemical vapor deposition (CVD), while the TBC layer was yttria-stabilized zirconia (YSZ) deposited by air plasma spray (APS). The stability of this system was investigated, via adhesion between the two coating layers and the substrate, the physical and chemical stability of each layer at high temperature, and the performance under severe thermal shock and exposure to hot corrosion.

The fracture behaviour of individual grain boundaries has been studied in order to understand the mechanisms controlling stress corrosion cracking in nuclear reactors. In particular, the role of oxidation in facilitating crack initiation and propagation has been reviewed. Nickel alloys from pressurized water reactors (PWRs) have been tested in simulated primary water conditions to induce grain boundary oxidation. Microcantilevers containing an oxidized grain boundary plane have been prepared and tested for fracture. The brittle nature of the oxide was demonstrated and the required stress to fracture measured.

This paper investigates the underlying physics governing the explosion driven expansion and fragmentation of spherical beds packed of partially saturated sand with varying mass fractions of interstitial oil. The breakup onset of the sand shells is characterized by the formation of fragments/agglomerates consisting of a large number of constituent grains, which in later time present themselves as prolific and regular jetting streams. Test data show a postponed jetting formation when sand shells are subject to the explosion with a higher detonation velocity, meanwhile a reduced jet mass scale is observed. A kinetic energy driven breakup model is proposed based on the instability criterion involving the opposing forces of stabilizing inertial pressures and destabilizing viscous resistance. This analytical model is capable of predicting the onset of granular material fragmentation as well as the characteristic fragment size, which is consistent with the experimental results.

The boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) oriented Type Ib diamond substrates using a Microwave Plasma Chemical Vapor Deposition (MPCVD) technique. Raman spectrum showed a few additional bands at the lower wavenumber regions along with the zone center optical phonon mode for diamond. The change in the peak profile of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. A modification in surface morphology of the film with increasing boron content had been observed by atomic force microscopy. Four point probe electrical measurement indicated that different conduction mechanisms are operating in various temperature regions for these semiconducting films.

A method is presented to map reaction diagrams for metastable phases by treating a rod-shaped sample under high pressure in a known temperature gradient, such that each point on the sample is treated at a unique, known temperature. After quenching to ambient conditions the structural properties of the sample can be studied by spectroscopic or other techniques. The accuracy and resolution in temperature is mainly limited by the uncertainties in the measured temperature distribution during treatment and the uncertainty in position during analysis. The method is tested by re-mapping the polymerization reaction of C60 under high pressure in the range 0.8 – 2 GPa. Preliminary data show surprisingly sharp "reaction boundaries" at certain temperatures, signalling the onset of dimerization and polymerization of the material.

The sulfur-iodine thermo-chemical cycle (S-I cycle) is one of the promising nuclear hydrogen production methods combined with a high temperature gas-cooled reactor. However, extremely corrosive environments limit the selection of structural materials. Therefore, in this study, corrosion behaviors of several metallic materials were investigated to screen the candidate metallic materials. Coupon type specimens were exposed for 100 h in simulated SO3 and HI decomposer conditions at 850 °C. After 100 h exposure, the surface treated Alloy 617 showed the superior weight change in both environments. However, scanning electron microscope observation showed oxide spallation for EB-treated and NiAl coated Alloy 617. On the other hand, the Ni3Al coated Alloy 617 showed better corrosion resistance in SO3 decomposer condition, such that only formed external Al-rich oxide layer. Especially, in a HI decomposer condition, the damage on the Ni3Al coated Alloy 617 was considerably less significant probably due to the protection by very thin aluminum-rich oxide on the surface.

Surface acoustic wave (SAW) devices are ideal candidates for gas sensors due to their small size, low cost of production and high sensitivity. Increasing restrictions on pollution and emissions create the necessity for sensors that can operate in the harsh environments found in vehicle exhaust systems and industrial production. Gallium nitride (GaN) is a robust, chemically inert, piezoelectric semiconductor, making it an attractive material for SAW devices designed to detect and monitor gases in harsh environments. In this work, SAW devices designed to operate at the 5th and 7th harmonics are fabricated on GaN thin films and their performance is measured through insertion loss, signal to noise ratio, operating frequency and quality factor. Devices are directly exposed to the exhaust gas of a common diesel engine. Device performance is then re-measured and compared. SAW devices fabricated in this work have measured operating frequencies above 1 GHz, and quality factors up to and higher than 2000, depending on the harmonic mode. SAW devices on GaN showed good chemical stability and measured changes in device performance after exhaust exposure was negligible.