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The thermal stability of two distinct blended polymer systems was examined. A model for polyethylene was used to investigate the vulnerability of polyethylene to premature crosslinking in industrial crosslinking conditions. Careful experiments were conducted to gather evidence of the interaction between a peroxide crosslinking agent and a specific antioxidant additive. Multiple lines of evidence were combined to propose a complete mechanism of interaction between the two species. The mechanism was further tested and a hypothesis was proposed for the reduction in premature crosslinking exhibited when the two species are present in polyethylene blends. A specific aspect of the proposed mechanism warranted further investigation on its own. The acid-catalyzed degradation of the peroxide initiator was thoroughly investigated. The thermal degradation of polyvinyl chloride was also studied. Model compounds were reacted with carboxylates to determine the relative rates of stabilization at various polymer defect sites. These model studies were combined with weight loss and color change investigations of bulk polymer systems. The knowledge gained from the model and polymer studies allowed for the proposal and examination of two novel stabilizing salt systems. The efficacy of the new stabilizers is presented.

Acid treatment, especially at high temperatures, is very challenging since HCl is really corrosive to the metal equipment. The use of HCl is associated with face dissolution, corrosion, and iron precipitation. Organic acids are weak and less corrosive than HCl but they have a limitation, which means that they can't be used at high concentrations. The next option would be chelating agents. Chelating agents are used in well stimulation, iron control during acidizing, and removal of inorganic scales. Chelates such as ethylenediaminetetraacetic acid (EDTA), N-(hydroxyethyl)-ethylenediaminetetraacetic acid (HEDTA), L- glutamic acid-N, N diacetic acid (GLDA), and nitrilotriacetic acid (NTA) are used in high-pressure/high-temperature oil and gas wells. GLDA is environmentally friendly, which makes it favorable. One of the concerns with these chelates is their thermal stability at high temperatures because if they degrade at high temperatures, they may lose their functionality. This study describes the thermal stability of these chelates, thermal degradation products, and some methods to improve their stability. The thermal stability is determined by measuring the concentration before and after heating using a complexo-metric titration utilizing FeCl₃ as a titrant. The degradation products are identified using Mass Spectrometry (MS). A series of experiments were run in the lab at varying temperatures (300 to 400°F) up to 12 hours, and the results shows chelates are not stable at temperatures greater than 350°F. Furthermore, chelates with two nitrogen atoms are more stable than those with one nitrogen atom. Iminodiacetic acid (IDA), acetic acid, and [alpha]-hydroxy acids are the decomposition products. There is a layer of black deposition after the chelates are heated, which is analyzed using Scanning Electron Microscope (SEM). Some coreflood tests are conducted using these degraded chelates to investigate the effect of these solid precipitates on the permeability of carbonate and sandstone cores. Increasing ionic strength and raising pH results in a higher thermal stability. Some salts such as, NH₄Cl, KCl, Csformate, and NaBr are added to chelate solutions to enhance stability.

There is a raising need to design a safe and efficient cryogenic fuel tank for the new generation of reusable launch vehicles. The new tank design focuses on composite materials that can achieve the drastic reduction of empty/non-payload and structural weight. In addition to the materials to be compatible with cryogenic temperatures, interior components of the vehicle may be subjected to significantly elevated temperatures due to heat conduction from the vehicle surfaces during and after atmospheric re-entry. Therefore, there is the need to understand the performance of the composites after experiencing extreme thermal environments. Polymer-layered nanocomposites were studied to determine if they can reduce the permeation to the liquid nitrogen used as fuel in the next generation of space vehicles. Due to the non-permeable nature of the silicates and the exfoliated structure they adopt into the polymer matrix the addition of nanoclays into a polymer is expected to reduce the permeation to several gases without sacrificing the mechanical strength of the nanocomposite as well as providing additional improvements such as increase of thermal stability of the nanocomposite. Several types of matrixes modified with different types and content of nanoclays were tested and their permeability coefficient was calculated. The permeability values obtained for the different formulations assisted to understand the transport properties of nanoclay modified composites. In addition to this, thermal characterization was performed with the help of dynamic mechanical analysis, thermogravimetric analyses and differential scanning calorimetry studies. To determine if the nanoclay modified nanocomposites were affected by extreme temperatures the samples were subjected to thermal cycling. Comparison of the transport and thermal properties before and after cycling helped to analyze the effect of the addition of the nanoclays in the nanocomposites. Positron annihilation spectroscopy (PAS) was utilized to comprehend how the distribution of the free volume was affected by the presence of the nanoclays and by the thermal cycling applied. Different permeability models were utilized in an attempt to validate the experimental results of the different nanocomposite structures. This analysis was used to provide additional insight into many aspects of the experimental results obtained in this study.

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Metallic glass is a class of materials which have a disordered structure of atoms, due to this, glasses lack grains and grain boundaries, which are present in their crystalline counterparts. Metallic glasses have many interesting properties worth investigating, such as high corrosion resistance or high mechanical strength. However, metallic glasses are metastable and will therefore crystallise if heated above the crystallisation temperature. MoSiZr alloys have been studied and to gain knowledge of how the composition affects the crystallisation temperature, which enables further improvement of thermal stability. Crystallisation temperatures of the MoSiZr alloys were investigated by heat treatments in vacuum and ex-situ X-ray diffraction and X-ray reflectivity analysis. The highest thermal stability of the alloys was exhibited by M48Si48Zr4, Mo43Si50Zr7, Mo50Si40Zr10 and Mo45Si43Zr12, they remained amorphous after heat treatment at 1073 K. The resulting crystalline phases are Mo3Si, Mo5Si3 and ZrO2. Oxidation of Zr in the alloys is present only when the Zr content is at least 10 at%, crystallisation is otherwise mainly driven by formation of Mo3Si. Further improvement of the thermal stability is possible by introducing new alloying elements at the cost of those that promote crystallisation. Keeping the content of Zr below 10 at% is of great importance to prevent oxidation.

3D VLSI with a CoolCube TM process allows vertically stacking several layers of devices with a unique connecting via density above a million/mm2. The thermal budget allowed to process the top transistor is currently limited by NiPt silicide stability of the bottom transistor. To extend the upper transistors thermal process window, Pre-Amorphization Implant (PAI) and Si-Capping were used to improve the stability of NiPt 15% on SiC:P and SiGe 30% :B accesses. While PAI enhances the silicide stability on SiC:P substrate from 600°C 2h to 700°C 2h, neither PAI nor Si-Capping improve silicide stability on SiGe 30% :B. To provide a solution for P accesses stability, NiCo 10% silicidation has been developed. Combined with PAI and Si-Capping, the germano-silicide offers a higher stability (up to 600°C 2h) than its NiPtSi 15% counterpart.

L-arginina fosfatada monohidratada (LAP) é um cristal semiorgânico altamente transparente com propriedades atrativas para conversão de freqüência. É facilmente crescido a partir de solução aquosa e apresenta casamento de fase para todos os processos não-lineares onde o KDP é casável em fase. Apresenta alto limiar de dano, excelente qualidade óptica, é menos higroscópico que o KDP e dispositivos não-lineares podem ser facilmente fabricados a partir deles. Neste trabalho apresentamos os resultados de diversos ensaios para avaliar a sua estabilidade térmica, mecânica e química. Concluiu-se que o cristal de LAP é estável para temperaturas inferiores à 100&#176C. Quando o material for submetido à processos que envolvem geração de grande quantidade de calor, tais como processamento do material por corte ou tomeamento (diamond tuming), ou em sistemas com lasers de alta intensidade, recomenda-se não exceder o limite de 100&#176C para assegurar que as propriedades do material não sejam alteradas / L-arginine phosphate monohydrate (LAP) is a highly transparent semiorganic crystal with atractive properties for frequency conversion. It is easily grown from aqueous solution, and it is phase matchable for alI nonlinear processes where KDP is phase matchable. lt has high damage threshold, exceHent optical quality, is less hygroscopic than KDP, and are easily fabricated into nonlinear devices. In this work we present the results of several tests to evaluate its thermal, mechanical, and chemical stabilities. It was found that LAP crystals are stable under temperatures up to 100&#176C. If this material is submited to processes involving the generation of considerable amount of heat, e.g. during cutting or diamond turning or due to high power lasers, it is recommended not to exceed the 100&#176C limit to ensure that crystal properties remain unchanged

The latest generation of fighter aircraft utilizes a 270Vdc power system [1]. Such high voltage DC power systems are difficult to protect with conventional circuit breakers because the current does not automatically go to zero twice per cycle during a fault like it does in an AC power system and thus arcing of the contacts is a problem. Solid state power controllers (SSPCs) are the solid state equivalent of a circuit breaker that do not arc and which can respond more rapidly to a fault than a mechanical breaker [2]. Present SSPCs are limited to lower voltages and currents by the available power semiconductors [8,9]. This dissertation presents design and experimental results for a SSPC that utilizes SiC power JFETs for the SSPC power switch to extend SSPC capability to higher voltages and currents in a space that is smaller than what is practically achievable with a Si power switch. The research started with the thermal analysis of the SSPCs power switch, which will guide the development of a SiC JFET multi-chip power module to be fabricated by Solid State Devices Inc. (SSDI) using JFETs from SiCED and/or Semisouth LLC. Multiple multi-chip power modules will be paralleled to make the SSPC switch. Fabricated devices were evaluated thermally both statically and dynamically and electrically both statically and dynamically. In addition to the SiC module research a detailed design of the high voltage SSPC control circuit capable of operating at 200andamp;ordm;C was completed including detailed analysis, modeling and simulations, detailed schematic diagrams and detailed drawings. Finally breadboards of selected control circuits were fabricated and tested to verify simulation results. Methods for testing SiC JFET devices under transient thermal conditions unique to the SSPC application was also developed.

In order to obtain diamond-like carbon (DLC) thin films with improved mechanical, tribological, thermal and corrosion properties for practical applications, the structure and properties of various DLC thin films including hydrogen-free DLC, hydrogenated DLC, and DLC-MoS2 composites synthesized under different conditions were investigated in this thesis. The research methodologies and the main results are summarized in following paragraphs. Hydrogen-free DLC thin films were synthesized by biased target ion beam deposition (BTIBD) method, while hydrogenated DLC thin films were deposited by ion beam deposition technique using a Kaufman-type ion source and an end-Hall ion source. DLC-MoS2 composite thin films were also synthesized using BTIBD technique in which MoS2 was produced by sputtering a MoS2 target while DLC was simultaneously deposited by ion beam deposition. The influence of processing parameters on the bonding structure, morphology and properties of the deposited films was investigated using atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, synchrotron based near edge X-ray absorption fine structure spectroscopy, X-ray diffraction, scanning electron microscopy, nanoindentation, ball-on-disk and corrosion testing. Finally, the influence of annealing temperature on the structure and properties of pure DLC and DLC-MoS2 composite films in ambient air and low pressure environments was studied. In the case of BTIBD method, hydrogen-free DLC thin films with exceptionally high smoothness and low friction coefficient were prepared by biased target sputtering of graphite target without additional ion bombardment either by negative bias of substrate or assisting ion source. For ion beam deposition technique with Kaufman ion source, the DLC thin films synthesized at ion energies of 300 eV showed the highest sp3 content and optimum properties. Regarding end-Hall ion source, the best properties achieved in DLC films synthesized at ion energies of 100 eV. Comparing with pure DLC and pure MoS2 films, the DLC-MoS2 films deposited at low biasing voltages showed better tribological properties including lower coefficient of friction and wear coefficient in ambient air environment. Also, comparing with pure DLC films, the DLC-MoS2 thin films showed a slower rate of graphitization and higher structure stability throughout the range of annealing temperatures, indicating a relatively higher thermal stability.