• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.261-267
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• 1988

$\beta$-Sialon powder was prepared by the reduction-nitridation reaction from the mixture of Wando Pyrophyllite and carbon black at 135$0^{\circ}C$ in $N_2$ atmosphere. $\beta$-SiC powder was added to the prepared $\beta$-Sialon powder to make $\beta$-Sialon-SiC composite. The $\beta$-Sialon-SiC composites were sintered pressurelessly at 175$0^{\circ}C$ for 2h, using $Y_2O_3$ and $ZrO_2$(monoclinic) as sintering aids. Comparatively higher values of the fracture toughness (3.8 MN/㎥/2), M.O.R. (470 MN/$m^2$) and vickers microhardness (13.7 MN/$m^2$) were obtained when 10 wt% $Y_2O_3$ was added as a sintering aid. The improved fracture toughness and M.O.R. are assumed to be the results of crack deflection and crack branching by the second phase SiC particles.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.68-77
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• 2019

C/SiC composites were developed by a liquid silicon infiltration(LSI) method for use as heat-resistant parts of solid and liquid rocket propulsion engines. The heat resistance characteristics according to the composition ratio (carbon / silicon / silicon carbide) were evaluated by specimen test through arc plasma, supersonic torch test. An ablation equation for oxidation reactions was presented. Through the combustion test it was verified that various parts such as nozzle insert, exit cone and combustion chamber heat resistant parts for rocket propulsion can be manufactured and proved high ablation performance and thermal structure performance.

• Journal of the Korean Ceramic Society
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• v.50 no.4
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• pp.251-256
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• 2013

Multiwalled carbon nanotubes (MWCNTs) modified with Pd and $TiO_2$ composite catalysts were synthesized by the sol-gel method followed by solvothermal treatment at low temperature. The chemical composition and surface structure were characterized by X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Photocatalytic recycle degradation experiments were carried out under both UV and visible light irradiation in the presence of MWCNT/$TiO_2$ and Pd-MWCNT/$TiO_2$ composites. As expected, the nanosized Pd-MWCNT/$TiO_2$ photocatalysts had enhanced activity over the non Pd treated MWCNT/$TiO_2$ material in the degradation of a rhodamine B (Rh.B) solution. An increase in photocatalytic activity was observed and attributed to an increase in the photo-absorption effect by MWCNTs and the cooperative effect of Pd and $TiO_2$ nanoparticles. According to the recycled results, the as-prepared Pd-MWCNT/$TiO_2$ sample had a good effect on it.

• Composites Research
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• v.37 no.4
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• pp.343-349
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• 2024

The use of composite materials for structural fasteners is increasingly common, making it crucial to assess the deformation of these fasteners under fatigue behavior. In this study, clamp-type fasteners were manufactured using carbon fiber reinforced composites, and their structural stability and sectional damage rates were evaluated using electrical resistance measurement during fatigue behavior. While clamp-type composite fasteners exhibited minimal deformation in flat sections, significant deformation occurred in the bent sections due to fatigue. It was observed that insufficient angular stability led to concentrated damage in the bent sections. The dynamic fatigue behavior showed that the length change rate of the composite fasteners was within 0.6%, but the angular change rate reached up to 6%, indicating that the bent sections are the most critical areas. By utilizing the self-sensing capability of the composite fasteners, sectional damage behavior was assessed through electrical resistance measurement. Significant damage was noted in the bent sections due to fatigue, and 3D-CT results revealed substantial deformation and interfacial damage when the initial bend angle of the fasteners was less than 90 degrees. These findings highlight the importance of reinforcing the stiffness of the bent sections and establishing systematic angular standards in the development of composite fasteners.

• Applied Chemistry for Engineering
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• v.10 no.6
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• pp.843-847
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• 1999

In this research, C/SiC composites, i.e. activated carbon coated with SiC obtained from dichlorodimethylsilane(DDS) and hydrogen, have been made by chemical vapor infiltration(CVI) in a fluidized bed reactor. Activated carbons of sizes of 4~12, 12~20, and 20~40 mesh were used. After deposition the surface area, the amount and the shape of deposit of each sample were observed at different concentrations of reactant DDS, sizes of activated carbon, reaction pressures and reaction times. The experimental results showed that uniform deposition in the pores of sample was obtained at a lower concentration of DDS and a lower pressure. Additionally, from the observation that the pore diameter and the surface area have minimum values at a certain time of deposition, it was known that deposition occurred inside of the pore at first and then on the outside of particle. Small particles of SiC were deposited uniformly on the surface of activated carbon at lower DDS concentrations and lower reaction pressures. The results were confirmed by SEM, TGA, the pore size distribution analyzer and BET.

• Composites Research
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• v.14 no.3
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• pp.18-31
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• 2001

Interfacial and microfailure properties of the modified steel, carbon and glass fibers/cement composites were investigated using electro-pullout test under tensile and compressive tests with acoustic emission (AE). The hand-sanded steel composite exhibited higher interfacial shear strength (IFSS) than the untreated and even neoalkoxy zirconate (Zr) treated steel fiber composites. This might be due to the enhanced mechanical interlocking, compared to possible hydrogen or covalent bonds. During curing process, the contact resistivity decreased rapidly at the initial stage and then showed a level-off. Comparing to the untreated case, the contact resistivity of either Zr-treated or hand-sanded steel fiber composites increased to the infinity at latter stage. The number of AE signals of hand-sanded steel fiber composite was much more than those of the untreated and Zr-treated cases due to many interlayer failure signals. AE waveforms for pullout and frictional signals of the hand-sanded composite are larger than those of the untreated case. For dual matrix composite (DMC), AE energy and waveform under compressive loading were much higher and larger than those under tensile loading, due to brittle but well-enduring ceramic nature against compressive stress. Vertical multicrack exhibits fur glass fiber composite under tensile test, whereas buckling failure appeared under compressive loading. Electro-micromechanical technique with AE can be used as an efficient nondestructive (NDT) method to evaluate the interfacial and microfailure mechanisms for conductive fibers/brittle and nontransparent cement composites.

• Composites Research
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• v.34 no.6
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• pp.357-372
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• 2021

The energy harvesting device is known to be promising as an alternative to solve the resource shortage caused by the depletion of petroleum resources. In order to overcome the limitations (environmental pollution and low mechanical properties) of piezoelectric elements capable of converting mechanical motion into electrical energy, many studies have been conducted on a polymer matrix-based composite piezoelectric energy harvesting device. In this paper, the output performance and related applications of the reported piezoelectric composites are reviewed based on the applied materials and processes. As for the piezoelectric fillers, zinc oxide, which is advantageous in terms of eco-friendliness, biocompatibility, and flexibility, as well as ceramic fillers based on lead zirconate titanate and barium titanate, were reviewed. The polymer matrix was classified into piezoelectric polymers composed of polyvinylidene fluoride and copolymers, and flexible polymers based on epoxy and polydimethylsiloxane, to discuss piezoelectric synergy of composite materials and improvement of piezoelectric output by high external force application, respectively. In addition, the effect of improving the conductivity or the mechanical properties of composite material by the application of a metal or carbon-based secondary filler on the output performance of the piezoelectric harvesting device was explained in terms of the structure of the composite material. Composite material-based piezoelectric harvesting devices, which can be applied to small electronic devices, smart sensors, and medicine with improved performance, can provide potential insights as a power source for wireless electronic devices expected to be encountered in future daily life.

• Korean Journal of Materials Research
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• v.8 no.4
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• pp.312-316
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• 1998

ZnO- TiO$_2$, and Sn0$_2$ - Ti0$_2$ ceramic composites doped with TiO$_2$ were prepared and their electrical and 1000ppm CO gas sensing properties were investigated. The phases of samples were analyzed by XRD, and the microsturctures of the fractured surface of samples were observed by SEM. A carbon monoxide gas sensitivity was de¬fined as the ratio of the resistance in dry air atmosphere(R$drt air$) to the resistance in 1000ppm CO gas atmosphere(R$_co$) The CO gas sensitivity of Smol% Ti0$_2$-added ZnO decreased about 1.7 times compared to that of pure ZnO. On the other hand, the maximum CO gas sensitivity of Ti0$_2$-added SnO$_2$ increased about 2.5 times compared to that of pure SnO$_2$. Therefore, the CO gas sensitivies of SnO$_2$-TiO$_2$ composite were better than those of ZnO- Ti0$_2$ and the temper¬ature range showing the maximum sensitivity for Sn0$_2$-TiO$_2$ composite was lower than that for ZnO- Ti0$_2$.