In this research, in order to increase the oxidation resistance of graphite, kaolin and alumina powder with different ratios (26A-74S, 49A-51S, 72A-28S) and slurry method were used to create an aluminosilicate coating on the graphite substrate. In order to reduce the difference in the coefficients of thermal expansion of graphite with aluminosilicate coating, aluminum metaphosphate coating as an interlayer was prepared on the surface of graphite by cathodic electrochemical treatment. The isothermal oxidation test of the samples was carried out in air at a temperature of 1250 °C for 1, 3 and 5 h. The microstructure, chemical composition, and phase components of the coating were, respectively, analyzed by scanning electron microscope equipped with an energy-dispersive spectrometer and X-ray diffraction. The results indicated that, by increasing the withdrawal speed of the samples in slurry method, the amount of changes in the weight of the samples has increased and therefore had a direct effect on oxidation. In addition, it was approved that, at high-temperature oxidation, AlPO4 glass phase forms on aluminum metaphosphate interlayer which retards graphite oxidation. Along with aluminum metaphosphate, aluminosilicate coating also produces a glass phase which fills and seals the voids on the surface which prevents the oxygen to reach the surface of graphite. The created double-layer coating including an interlayer of aluminum metaphosphate + slurry coating prepared with the ratio of 26A-74S as the optimal coating in this research was able to increase the oxidation resistance of graphite by 73% at a temperature of 1250 °C.

This study assessed the changes in the fiber properties of virgin and recovered fibers from lab-scale and pilot-scale depolymerization reactors based on the thermal air oxidation-resistance characteristics. Lab-scale and pilot-scale depolymerization reactors had different depolymerization volumes. Results showed that the lab-scale and pilot-scale peak solvent temperatures were 185 °C and 151 °C, respectively. The lab-scale had highest solvent temperature rate increase because of the small depolymerization volume and the dominant role of the cavitation volume. The structural properties of the recovered and virgin fibers were intact even after the depolymerization and after the pretreatment and oxidation-resistance test. We observed 1.213%, 1.027% and 0.842% weight loss for the recovered (lab-scale), the recovered (pilot-scale) and virgin fibers because of the removal of impurities from the surface and chemisorbed gases. Further, we observed 0.8% mass loss of the recovered fibers (lab-scale) after the oxidative-onset temperature because of the “cavitation erosion effect” from the dominant of the cavitation bubbles. The “cavitation erosion effect” was subdued because of the increased depolymerization volume in the pilot-scale reactor. Therefore, negligible impact of the pilot-scale mechanochemical recycling process on the structure and surface characteristics of the fibers and the possibility of reusing the recovered fibers recycling process were characteristic. Representative functional groups were affected by the thermal oxidation process. We conducted HPLC, HT-XRD, TGA– DSC, XPS, SEM, and AFM analysis and provided an extensive discussion of the test thereof. This study highlighted how misleading and insufficient small-lab-scale results could be in developing viable CFRP depolymerization process.

Accurate understanding of structural integrity and chemical reactivity of UO2 disposed in deep underground sites is of importance. Owing to the specific condition of the site location, UO2 may have substantially different properties from the conventional prediction. In this study, we demonstrate that the oxidation resistivity of UO2 is considerably modified by gadolinium (Gd), which is the element of neutron absorber and a byproduct of nuclear decay of radioactive U-235. Using density functional theory calculations, we investigate how the oxidation mechanism of UO2 changes with Gd incorporation in U lattice. Our study indicates that Gd remarkably enhances the thermodynamic stability of pristine UO2 against surface oxidation via three underlying mechanisms: (i) weakens the chemical bonding of adsorbed oxygen atom (O) with U, (ii) reduces active sites (U) for oxygen adsorption, and (iii) suppresses the subsurface diffusion of adsorbed O delaying the growth of the oxide layers on the UO2. Electronic and lattice structure analyses for Gd-doped UO2 indicate that amount of charge transfer from U to O is critically reduced and the lattice of the UO2 surface is contracted. Our results provide useful information for understanding long-term stability and improving the structural integrity of UO2 through the chemical doping process.

In the present work, a new hydrogen added argon heat treatment process that prevents the formation of hydrides and eliminates the dehydrogenation step, is developed. Dissolved hydrogen has a good effect on sintering properties such as oxidation resistance and density of greens. This process can also reduce costs and processing time. In the experiment, commercially available Ti-6Al-4V powders are used. The powders are annealed using tube furnace in an argon atmosphere at 700oC and 900oC for 120 min. Hydrogen was injected temporarily during argon annealing to dissolve hydrogen, and a dehydrogenation process was performed simultaneously under an argon-only atmosphere. Without hydride formation, hydrogen was dissolved in the Ti-6Al-4V powder by X-ray diffraction and gas analysis. Hydrogen is first solubilized on the beta phase and expanded the beta phases’ cell volume. TGA analysis was carried out to evaluate the oxidation resistance, and it is confirmed that hydrogen-dissolved Ti-6Al-4V powders improves oxidation resistance more than raw materials.

A metallic oxide layer of a heat-resistant element contributes to the high-temperature oxidation resistance by delaying the oxidation and has a positive effect on the increase in electrical resistivity. In this study, green compacts of Fecralloy powder mixed with amorphous and crystalline silica are oxidized at 950oC for up to 210 h in order to evaluate the effect of metal oxide on the oxidation and electrical resistivity. The weight change ratio increases as per a parabolic law, and the increase is larger than that observed for Fecralloy owing to the formation of Fe-Si, Fe-Cr composite oxide, and Al2O3 upon the addition of Si oxide. Si oxides promote the formation of Al2O3 and Cr oxide at the grain boundary, and obstruct neck formation and the growth of Fecralloy particles to ensure stable electrical resistivity.

[ ] was coated with , MgO and respectively by sol-gel method and cured at 900 and . The coated oxides did not react with at but reacted with it to form at . The specimen coated with at formed a dense protecting layer and showed the best oxidation resistance at in air. However, the dense protecting layers did not form in and MgO coated specimens cured even at . MgO coated specimen showed the worst improvement in the oxidation resistance because the reactivity of MgO with was highest. On the other hand, the electrical conductivities were measured in MgO and coated specimens to have TiCx but could not be measured in the coated ones because of the nonconductive dense protected layers.

In order to clarify the wear resistance as cutting tools, the effect of oxygen addition on oxidation behavior of the β-Si3N4 ceramics with 5 mass% Y2O3 and 2 or 4 mass% Al2O3 was investigated by performing oxidation tests in air at 1300° to 1400°C and cutting performance tests. From test results, we could conclude that the mechanical properties of β-Si3N4 ceramics depending on oxygen introduction are much effective on cutting performance improvements of β-Si3N4 ceramics.

In order to prevent the oxide formation on the surface of nano-size iron particles and thereby to improve the oxidation resistance, iron nanoparticles synthesized by a chemical vapor condensation method were directly soaked in hexadecanethiol solution to coat them with a polymer layer. Oxygen content in the polymer-coated iron nanoparticles was significantly lower than that in air-passivated particles possessing iron-core/oxide-shell structure. Accordingly, oxidation resistance of the polymer-coated particles at an elevated temperature below in air was times higher than that of the air- passivated particles.

Chop molding composites and 2D carbon/carbon composites were manufactured by hot press molding method. Phenol resin of novolac type was used for matrix precursor and PAN-based carbon, PAN-based graphite and pitch-based carbon fiber were used for reinforcement and boron oxide was used for oxidation retardant. All of the composites were treated by 2000℃ and 2400℃ graphitization process, respectively. After graphitization process, amount of a boron residue in carbon/carbon composites is much according to irregularity of used raw materials. Under the presence of boron in carbon/carbon composites, catalytic effect of boron was a little at 2000℃ graphitization temperature. However, it was quite at 2400℃ graphitization.

폴리아크릴로나트릴(PAN)계 탄소섬유 및 안정화 PAN섬유를 사용하여 제조한 페놀수지 복합재료의 열주기 산화저항성에 섬유표면의 인산코팅 유.무가 미치는 영향을 조사하였다. 각 복합재료의 열주기 산화저항성은 열중량분석기의 원리를 응용하여, 공기중에서 hot zone과 cold zone을 주기적으로 반복이동하는 열충격조건에 노출되면서 초래되는 복합재료의 중량변화를 측정하여 비교하였다. 시험변수로는 hot zone에 노출된 온도, 시간 및 싸이클횟수를 선정하였다. 이 시험방법은 비교적 단순하며, 작은 크기의 시편으로도 가능하고, 중량변화가 온-라인 모니터에서 직접 감지되므로 데이타의 신뢰성이 ?다. 각 시험조건에서 인산코팅한 섬유를 사용한 복합재료가 그렇지 않은 재료보다 고온에서의 높은 산화저항성 때문에 우수한 열주기저항성을 보여 주었다. 또한 인산코팅의 존재 여부가 열주기시험 후의 탄소섬유-페놀수지 및 안정화 PAN섬유-페놀수지 복합재료의 미세구조에 미치는 영향을 조사하였다.

합금원소(Cr, V, Si. Mo, Nb)가 첨가된 TiAi 금속간화합물의 고온 산화거동을 대기중의 900~1100˚C에서 관찰하였다. 산화반응물은 XRD, SEM, WDX을 이용하여 분석하였다. 등온 산화에 있어서 Cr과 V이 각각 첨가된 시편은 무게증가가 많았으나, Si, Mo, Vb가 각각 첨가된 시편은 상대적으로 무게증가각 적었아. 그리고, Cr과 V이 각각 첨가된 시편의 산화속도는 TiAi의 그것보다 항상 크게 나타났으며, Si, Mo, Vb가 각각 첨가된 시편의 산화속도는 TiAi의 그것보다 향상되지 않고, Si, Mo또는 Nb 첨가는 내산화성을 향상시킨다. Si, Mo, Nb이 각각 첨가된 TiAI합금표면에 형성된 산화물은 보호막 역할을 함으로 산소와 합금원소의 확산을 감소시키는 역할을 하였다. 특히, Nb는 산화의 초기단계에서는 AI2O3를 형성하려는 경향이 강하기 때문에 연속적인 AI2O3층과 조밀한 Tio2+AI2O3 혼합층이 형성되었다. Nb가 첨가된 합금의 백금 marker 실험결과에 따르면, 산소가 주로 합금내부로 확산하여 합금표면에서 산화물을 형성하였다. 900˚C에서의 열반복주기(thermal cyclic)산화실험 결과, 다른 합금원소와 비교해 볼 때 Cr또는 Nb첨가가 금속기지와 산화층간의 접착력을 향상시키는 것으로 나타났다.