This study investigated the changes in microstructure and mechanical properties of C/SiC composites fabricated by a liquid silicon infiltration (LSI) process, utilizing carbon fibers surface pre-treated with Ar plasma. Analysis of the carbon fiber surface structure revealed that T300-grade and T700-grade carbon fibers possessed distinct initial surface structures, and applying surface pre-treatment under identical conditions resulted in differing surface structural deformations. Through cross-sectional images of each C/C carbonized preform, the crack spacing between fiber bundles and the matrix was analyzed. It was found that for T300-grade fibers subjected to surface pre-treatment, the crack spacing increased by up to 5.5 times compared to the untreated state, whereas for T700-grade fibers, it decreased to approximately 22

SiC/SiC composites were fabricated using the liquid silicon infiltration (LSI) process. The SiC fibers used were coated with h-BN/SiC/h-BN/SiC interfacial layer that has 4 layers of multi-coating structure. This study analyzed and evaluated the effects of interfacial coating thickness on the mechanical properties and microstructure of ceramic matrix composites (CMCs). The coating thicknesses applied were thin: 300 nm and thick: 2 μm, with a uniform layer coated using the low-pressure chemical vapor deposition (LPCVD) process. SEM and EDS analyses revealed that boron dissolved in the infiltrated Si from h-BN, damaging the coating layer at high temperature. Consequently, for specimens with thin coatings, the h-BN layer was entirely damaged, failing to protect the fibers and resulting in a decrease in mechanical properties. In contrast, thicker coatings sufficiently prevent the damage from the molten Si, protecting the fibers and inducing a pull-out morphology on the fracture surface, thereby exhibiting excellent flexural strength of 624 MPa. Additionally, the thickness of the coating layer affected the fiber volume fraction of the CMCs, with an increase in coating thickness resulting in a decrease in fiber volume fraction from 50 to 30

This study investigates the structural integrity of C/SiC composite structures with internal pressure channels for use in regeneratively cooled combustors of hypersonic scramjet engines. Pyrolysis segmented carbon preforms were bonded using the Liquid Silicon Infiltration (LSI) process to fabricate integrated C/SiC structures. Three bonding methods-phenolic resin, ceramic slurry, and prepreg-were compared. Shear tests were conducted to evaluate the interlaminar shear strength of the C/SiC matrix and the interface strength at bonded joints. The slurry-bonded specimens showed the best performance, due to their thin and uniform bond lines. Finite element analysis of the combustor geometry showed sufficient safety margins (>2) in the lower interlaminar regions. In the upper bonded regions, only the slurry-bonded case (case 3) was likely to meet structural safety requirements.

The present study examines the influence of fiber dispersion on the internal structure and mechanical strength of SiCf/SiC composites fabricated utilizing spread SiC fibers. The fiber volume ratio of specimens incorporating spread SiC fibers decreased by 9 percentage points compared to those without spreading, resulting in smoother impregnation of resin slurry between fibers and, consequently, minimizing matrix porosity. To assess and compare the fiber dispersion in each specimen, a method was proposed for quantifying and evaluating the separation distance between fibers in composite materials. The results revealed a 2.23 mu m increase in the distance between fibers in the spread specimen relative to the non-spread specimen, corresponding to a notable 42.6% increase in the distance between fiber surfaces. Moreover, a 3-point flexural test showcased a 49.3% higher strength in the spread specimen, coupled with a more uniformly distributed deviation in test data. These findings underscore the substantial impact of SiC fiber dispersion on achieving uniform densification of the SiCf/SiC matrix and enhancing mechanical strength.

The alkali metal thermal-to-electric converter (AMTEC) is a technology that converts thermal energy into electrical energy. It can operate with various heat sources, does not require fuel injection, and produces no harmful emissions, making it an environmentally friendly technology. Currently, Mo-based metallic materials are mainly used as electrode materials for AMTEC. However, when operated at temperatures above 800°C, the coarsening of electrode particles and the formation of Na-Mo-based secondary phases have a negative impact on the durability of the cell. In this study, Na-based oxides, widely known as electrode materials for secondary batteries, were applied as electrode materials for AMTEC. The electrode materials were synthesized via a solid-state reaction method that involved grinding and heat treatment at 950°C. The crystal structure and microstructure of the materials were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. To facilitate effective coating of the electrode material onto the surface of the beta-alumina solid electrolyte (BASE), physical treatments (e.g., sandpapering) and chemical treatments (e.g., chemical etching) were employed to optimize the BASE surface. Through this process, it was confirmed that the interface contact between the electrode and the BASE was successfully formed after chemical treatment. For electrochemical performance evaluation, cells with small-area and large-area electrodes were prepared by coating the cylindrical BASE surface. At an operating temperature of 600°C, the small-area cell (electrode area: 3 cm²) exhibited a maximum power output of approximately 1.02W (0.34W/cm2). The large-area cell (electrode area: 4.2 cm²) achieved an excellent power output of 10.13W (0.23W/cm2). This study confirmed for the first time that Na-based oxide electrode materials show great potential as electrodes for AMTEC. The detailed findings of this research will be discussed further in the presentation.

Purpose The aim of this study was to conduct a nationwide population-based study to estimate the incidence of primary sclerosing cholangitis in patients with ulcerative colitis (UC-PSC) and investigate healthcare use, medication use, surgery, cancer, and death as adverse clinical events of UC-PSC. Methods We identified incident cases of UC with (UC-PSC) or without PSC (UC-alone) between 2008 and 2018 using health insurance claims data in Korea. Univariate (crude hazard ratio (HR)) and multivariate analyses were performed to compare the risk of adverse clinical events between groups. Results A total of 14,406 patients with UC using population-based claims data were detected in the cohort. Overall, 3.38% (487/14,406) of patients developed UC-PSC. During a mean follow-up duration of approximately 5.92 years, the incidence of PSC in patients with UC was 185 per 100,000 person-years. The UC-PSC group showed statistically more frequent healthcare use (hospitalization and emergency department visits: HRs, 5.986 and 9.302, respectively; P < .001), higher immunomodulator and biologic use (azathioprine, infliximab, and adalimumab: HRs, 2.061, 3.457, and 3.170, respectively; P < .001), and higher surgery rate (operation for intestinal obstruction, and colectomy: HRs, 9.728 and 2.940, respectively; P < .001) than did the UC-alone group. The UC-PSC group also showed significantly higher colorectal cancer and biliary tract cancer (HRs, 2.799 and 36.343, respectively; P < .001) and mortality (HR, 4.257) rates than did the UC-alone group. Conclusion Patients with UC-PSC have higher risks of colorectal cancer, biliary tract cancer, and death than do patients with UC-alone. Although considered a rare disease, managing this complex and costly disease requires recognition of the impact of increased burden on healthcare services.

This paper investigates the impact of fiber dispersion on the internal structure and mechanical strength of SiCf/SiC composites manufactured using spread SiC fibers. The fiber volume ratio of the specimen to which spread SiC fiber was applied decreased by 9%p compared to the non-spread specimen, and the resin slurry impregnated between the fibers more smoothly, resulting in minimal matrix porosity. In order to compare the fiber dispersion of each specimen, a method was proposed to quantify and evaluate the separation distance between fibers in composite materials. The results showed that the distance between fibers in the spread specimen increased by 2.23 & mu;m compared to the non-spread specimen, with a significant 42.6% increase in the distance between fiber surfaces. Furthermore, the 3pt bending test demonstrated a 49.3% higher flexural strength in the spread specimen, accompanied by a more uniform deviation in test data. These findings highlight the significant influence of SiC fiber dispersion on achieving uniform densification of the SiCf/SiC matrix and increasing mechanical strength.

In order to improve the degree of matrix densification of SiCf/SiC composites based on liquid silicon infiltration (LSI) process, the microstructure and mechanical properties of composites according to various pyrolysis temperatures and melt infiltration temperatures were investigated. Comparing the microstructures of SiCf/C carbon preform by a one-step pyrolysis process at 600 degrees C and twostep pyrolysis process at 600 and 1600 degrees C, the width of the crack and microcrack formation between the fibers and matrix in the fiber bundle increased during the two-step pyrolysis process. For each pyrolysis process, the density, porosity, and flexural strength of the SiCf/SiC composites manufactured by the LSI process at 1450-1550 degrees C were measured to evaluate the degree of matrix densification and mechanical properties. As a result, the SiCf/SiC composite that was fabricated by the two-step pyrolysis process and LSI process showed an 18% increase in density, 16%p decrease in porosity, and 150% increase in flexural strength on average compared to the composite fabricated by the one-step pyrolysis process. In addition, among the SiCf/SiC specimens fabricated by the LSI process after the same two-step pyrolysis process, the specimen that underwent the LSI process at 1500 degrees C showed 30% higher flexural strength on average than those at 1450 or 1550 degrees C. Furthermore, under the same pyrolysis temperature, the mechanical strength of SiCf/SiC specimens in which the LSI process was performed at 1500 degrees C was higher than that of the 1550 degrees C although both porosity and density were almost similar. This is because the mechanical properties of the Tyranno-S grade SiC fibers degraded rapidly with increasing LSI process temperature.

This study has a different direction from the existing technology of applying recycled carbon fiber obtained by recycling waste CFRP to CFRP again. A study was conducted to utilize recycled carbon fiber as a raw material for manufacturing a carbon/carbon (C/C) composite material comprising carbon as a matrix. First, it was attempted to recycle a commonly used epoxy resin composite material through a thermal decomposition process. By applying the newly proposed oxidation-inert atmosphere conversion technology to the pyrolysis process, the residual carbon rate of 1 similar to 2% was improved to 19%. Through this, the possibility of manufacturing C/C composite materials utilizing epoxy resin was confirmed. However, in the case of carbon obtained by the oxidation-inert atmosphere controlled pyrolysis process, the degree of oxygen bonding is high, so further improvement studies are needed. In addition, short-fiber C/C composite material specimens were prepared through the crushing and disintegrating processes after thermal decomposition of waste CFRP, and the optimum process conditions were derived through the evaluation of mechanical properties.

The present work involved the application of a two-step sintering (TSS) technique for typical Ce0.9Gd0.1O2-delta-La0.6Sr0.4Co0.2Fe0.8O3-delta (GDC-LSCF) composites and its effect on the microstructure and resultantly mechanical and O-2-permeating properties. The samples obtained by conventional sintering (CS) performed at 1100, 1250, and 1400 degrees C for 3 h exhibited maximum flexural strength and hardness values of 142 MPa and 8.71 GPa, respectively. However, the application of a TSS procedure produced fine-grained microstructures with improved mechanical properties. In particular, with the use of a typical 1250/1200 TSS protocol, increases of approximately 31 % and 7% in the flexural strength and hardness values, respectively, were observed compared to those obtained using the CS method. Moreover, thick-film (similar to 60 mu m) GDC-LSCF membrane prepared by tape casting and the TSS technique showed remarkably 1.5-2 times higher oxygen permeation flux than membrane sintered by CS method. The results are discussed and explained in detail.

The present work demonstrates the effectiveness of a novel hybrid process comprising chemical vapor infiltration (CVI), electrophoretic deposition (EPD), and liquid silicon infiltration (LSI) techniques for the successful fabrication of low-porosity SiCf/SiC composites. For this purpose, fiber/matrix interphase dual coating layers of BN and SiC were coated onto SiC fabrics using CVI. A ceramic matrix consisting of SiC and carbon black nanoparticles was then infiltrated into the fine voids of the fabrics using EPD. Finally, LSI was performed to obtain dense microstructures with low porosities by filling the remaining small gaps and reacting Si with C to form SiC. Microstructural results observed by scanning electron microscopy revealed a dense structure with no damage to the fibers. The experimental density was found to be 2.62 g/cc, with an open porosity of 0.55. The room-temperature flexural strength was evaluated to be 111 MPa, and the composites displayed little fiber pull-out.

The fabrication of continuous carbon fiber-reinforced carbon-silicon carbide matrix (C-f/C-SiC) cross-ply composites is highly attractive from a practical viewpoint due to their homogeneous microstructures and isotropic mechanical properties. However, the properties of C-f/C-SiC composites depend significantly on their processing conditions and temperatures, especially the pyrolysis conditions and temperatures. In this study, cross-ply C-f/C-SiC composites were fabricated using different pyrolysis protocols with phenolic resin via a liquid silicon infiltration. The effects of the pyrolysis conditions on the microstructures of the composites and their mechanical properties as well as on crack formations were evaluated at room temperature. Pyrolysis was performed at 600 degrees C for 1 h in a nitrogen atmosphere at different heating rates. The flexural strength varied from a minimum of 47 +/- 3 MPa to a maximum of 62 +/- 6 MPa (similar to 35% increase) depending on the pyrolysis conditions.

As interest in environmental pollution has increased, research in the field of filtration has been concentrated. While various types of filters have been developed, research on nanomaterial filtration has been limited. Since then, the development of new materials such as carbon nanotubes (CNTs) has accelerated the study of new filters. Especially, CNTs have been among the most attractive materials ever synthesized for the development of nano-technologies. However, there are fundamental technical problems to be solved the development of new CNT composites. One of these problems is the development of a CNTs filter with excellent adsorption behavior and a filter that is capable of filtering a specific substance. In addition, it is necessary to develop a technology to increase the uniform distribution of CNTs, and to reduce the high processing cost of CNT composite production. In general, the chemical pathways for the production of CNTs include hydrocarbon gases, such as methane (CH4) and acetylene (C2H2), through metal nanoparticle catalysts. However, nano-metal particles have a strong coagulation phenomenon at high temperature by catalytic chemical vapor deposition (CCVD) method. In this review, attempts were made by applying three different reaction techniques to form CNTs on biomorphic carbon materials (BCM) coated with catalyst materials to control the shape and size of CNTs. Hierarchical carbon substrates with pore size of 100 similar to 300 mu m were developed using carbonization reaction. Linde type A (LTA) zeolite, silicalite-1, and mesoporous SiO2 template crystals were simultaneously synthesized and coated on the BCM by an in-situ hydrothermal process to synthesize high-yield CNTs composites.

Porous carbon materials are promising candidates for anode materials in rechargeable potassium-ion batteries. However, their high surface area and low crystallinity usually cause side reactions with electrolytes and slanted charge/discharge profiles. Herein, we report the synthesis of porous carbon microspheres with highly graphitized structure and enhanced potassium-ion storage properties. The prepared carbon microspheres exhibit a low working potential of ~0.2 V, high Coulombic efficiency, and a stable reversible capacity of 292.0 mAh/g after 100 cycles, which is significantly higher than that of commercial graphite (137.5 mAh/g after 100 cycles). These desirable performances are attributed to the high crystallinity of carbon and its porous structure, which provide active sites for potassium-ion storage and alleviate the stress caused by the large volume change during the insertion and extraction of potassium ions.

Carbon fiber reinforced SiC composites (C/SiC) have high-temperature stability and excellent thermal shock resistance, and are currently being applied in extreme environments, for example, as aerospace propulsion parts or in high-performance brake systems. However, their low thermal conductivity, compared to metallic materials, are an obstacle to energy efficiency improvements via utilization of regenerative cooling systems. In order to solve this problem, the present study investigated the bonding strength between carbon fiber and matrix material within ceramic matrix composite (CMC) materials, demonstrating the relation between the microstructure and bonding, and showing that the mechanical properties and thermal conductivity may be improved by treatment of the carbon fibers. When fiber surface was treated with a nitric acid solution, the observed segment crack areas within the subsequently generated CMC increased from 6 to 10%; moreover, it was possible to enhance the thermal conductivity from 10.5 to 14 W/m.K, via the same approach. However, fiber surface treatment tends to cause mechanical damage of the final composite material by fiber etching.

The structural modification of copper oxide thin films was investigated by controlling the thermal annealing atmosphere and temperature, which in turn affected their optical and electrical properties. Copper oxide thin films were deposited by spray pyrolysis deposition at 300 degrees C to give a uniform surface consisting of submicron-size grains with cubic Cu2O crystalline structure. As the Cu2O thin films were thermally annealed at less than 700 degrees C, they were transformed into the CuO phase. However, a mixed phase of CuO and Cu2O was observed at temperatures above 800 degrees C. As the thermal annealing temperature was increased from 400 to 700 degrees C, the optical bandgap energy of the copper oxide thin films was decreased from 2.54 to 1.91 eV and the electrical charge carrier concentration was decreased gradually due to the improved crystalline quality. In this way, the crystalline structure of the copper oxide and its corresponding optical and electrical properties could be controlled by thermal annealing.

The novel processing route for the synthesis of carbon nanotubes (CNTs) on silicalite-1 template coated biomorphic carbon is reported in this paper. First of all, biomorphic carbon with 20-35 mu m pore dimension was prepared by carbonizing Cypress under Ar atmosphere, thereafter, a silicalite-1 crystals were synthesized and homogeneously coated on biomorphic carbon by an in situ hydrothermal process. Finally, multi-walled carbon nanotubes synthesized on the Co-metal nanoparticles loaded silicalite-1 template loaded on biomorphic carbon with acetylene (C2H2) as a carbon source by the catalytic chemical vapor deposition (CCVD) method. In this study, we focused on varying the reaction time for obtaining better CNTs yield and the characterization morphology, crystallinity, surface area of CNTs were investigated. Multi-walled CNTs with inner diameter of 7.31nm and outer diameter 38.53 nm and the maximum yield of 23.71% nm were synthesized at 650 degrees C for 180 min and the I-D/I-G of 0.97-1.00 of CNTs was obtained.

BACKGROUND:Gastrointestinal (GI) diseases are common in patients with human immunodeficiency virus (HIV) infection. There are few reports on the epidemiology and endoscopic findings of gastric cancer in patients with HIV infection in the era of combination antiretroviral therapy (cART). We retrospectively analyzed upper GI endoscopic findings in patients with HIV infection and investigated their role as gastric cancer screening.MATERIALS AND METHODS:We retrospectively investigated endoscopies conducted in Korean patients with HIV infection referred for endoscopy at a tertiary hospital between January 2004 and December 2018. Endoscopic and pathologic findings were analyzed according to the reason for endoscopy, patient age, and cART duration. All endoscopic findings were reevaluated by gastroenterologists.RESULTS:Three hundred ten endoscopies in 201 patients with HIV infection were investigated. Of these, 118 (38.1%) endoscopies in 81 (40.1%) patients were performed for cancer screening purposes. Gastric cancer was found in 4 patients (2.0%); one of them presented with gastric cancer at the time of HIV diagnosis, and the other 3 patients were diagnosed with early gastric cancer on screening endoscopy, which was cured with endoscopic submucosal dissection or surgery. The prevalence of gastric cancer in screening endoscopies was 3.7%. Atrophic gastritis was a more common finding in screening endoscopies than in diagnostic endoscopies (P <0.001), and was significantly associated with longer durations of cART (P <0.001). The overall prevalence of gastric cancer, atrophic gastritis, and intestinal metaplasia was 2.0, 57.8, and 25.4%, respectively. The prevalence of atrophic gastritis and intestinal metaplasia increased with age.CONCLUSION:Regular gastric cancer screening might be useful for early diagnosis and treatment of gastric cancer in patients with HIV infection.

In this paper, we report on the selection of an optimal sintering temperature for Ce0.9Gd0.1O2-delta-La0.6Sr0.4Co0.2Fe0.8O3-delta composites through characterization of their microstructural, mechanical, and elastic properties. For this selection, sintering was performed mainly at three different temperatures-1100, 1250, and 1400 degrees C for 3 h. The samples were systematically investigated in terms of their relative density, microstructure, flexural strength, hardness, elastic modulus, and Poisson's ratio. An increase in density with an increase in sintering temperature was observed to cause a significant improvement in the flexural strength, hardness, and elastic modulus. However, an excessively high temperature (> 1250 degrees C) was detrimental to the flexural strength and hardness because of the occurrence of grain growth. The optimal sintering temperature was identified to be 1250 degrees C from an analysis of samples with superior mechanical properties and adequate elastic properties. The optimal flexural strength and hardness were found to be 211 +/- 21 MPa and 9.34 +/- 0.5 GPa, respectively, at room temperature.