• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.2
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• pp.183-189
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• 2020

The purpose of this study is to investigate the compressive and tensile properties of high volume slag cement-based fiber-reinforced composite incorporating phase change material. Four mixtures were determined according to calcium hydroxide and expansive admixture, and the compressive strength and tension tests were performed. Test results showed that four mixtures showed a compressive strength over 51MPa and a tensile ductility over 3.2%. It was observed that calcium hydroxide and expansive admixture influenced the compressive and tensile performance, and the strength, ductility, and cracking patterns of composite could be improved by including proper amount of calcium hydroxide and expansive admixture.

• Journal of Advanced Marine Engineering and Technology
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• v.10 no.4
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• pp.57-66
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• 1986

The microstructure and mechanical properties of unidirectionally solidified Al-Fe-Ni and Al-Fe-B alloys have been studied in varying the some conditions. To investigate the change of microstructure and mechanical properties was carried out by the varying the composition and solidification rate from 1.2 to 80 mm/min at temperature gradient 60 .deg. C/cm. The results obtained are as follow; 1. In proportion to the increase of the solidification rate, the type of crystallized phase of these composite alloys was changed by added element. a) The crystallized phase of composite alloy in added nikel was changed from the rod-type fiber to platetype fiber. b) The crystallized phase of composite alloy in added boron was changed from the plate-type fiber to rod-type fiber. 2. The strength was rapidly increased with the changing process of crystallized fiber from the plate-type fiber to the rod-type.

• Korean Journal of Materials Research
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• v.16 no.1
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• pp.50-57
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• 2006

Phase mixtures of Titanium boride, nitride, and carbide powder were produced by the reduction of a mixture of titanium and boron oxides with carbon via a gas-solid phase reaction. Boron oxides produce a vapour phase or decompose to a metal sub-oxide gaseous species when reduced at elevated temperature. The mechanism of BO sub-oxide gas formation from $B_2O_3$ and its subsequent reduction to titanium diboride for the production of uniform size hexagonal platelets is explained. These gaseous phases are critical for the formation of boride, nitride and carbide ceramics. For the production of ceramic phase composite microstructures, the nitrogen partial pressure was the most critical factor. Some calculated equilibrium phase fields has been verified experimentally. The theoretical approach therefore identifies conditions for the formation of phase mixtures. The thermodynamic and kinetic factors that govern the phase constituents are also discussed.

• Korean Journal of Materials Research
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• v.27 no.6
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• pp.325-330
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• 2017

Photoelectron-hole separation efficiency plays an important role in the enhancement of the photocatalytic activity of photocatalysts towards the degradation of organic molecules. In this study, $TiO_2/TiOF_2$ heterostructured composite powders with suitable band structures, which structures are able to separate photoelectron-hole pairs, have been synthesized using a simple and versatile ultrasonic spray pyrolysis process. In addition, their phase volume fractions have been controlled by varying the pyrolysis temperature from $400^{\circ}C$ to $800^{\circ}C$. The structural and optical properties of the synthesized powders have been characterized by X-ray diffraction, scanning electronic microscopy and UV-vis spectroscopy. The powder with a phase volume ratio close to 1, compared with single $TiOF_2$ and other composite powders with different phase volume fractions, was found to have superior photocatalytic activity for the degradation of rhodamine B. This result shows that the $TiO_2/TiOF_2$ heterostructure promotes the separation of the photoinduced electrons and holes and that this powder can be applicable to environmental cleaning applications.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.4
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• pp.632-639
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• 1997

Relative density and microstructure of the pressureless sintered TiC-$TiB_2$ composite has been studied. The maximum sintered density was 95% and the critical amounts of sintering aids were 1 wt% Fe and 3 wt% Ni. It was found that TiC matrix phase inhibited effectively grain growth of the dispersed $TiB_2$ phase. The TEM investigation reveals that the Ni-rich precipitates were solidified from the liquid phase, confirmed by the presence of the waved and/or step phase boundaries. The precipitates also acts as the origin of the dislocation formation in the matrix phases.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.2
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• pp.175-183
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• 2016

A poroelastic composite material, containing different material phases and filled with fluids, serves as a model to formulate the overall ablative behaviors of such materials. This article deals with the assessment of variation in nondeterministic poroelastic properties of two-phase composite materials using micromechanical representative volume element (RVE) models. Considering the configuration and arrangement of pores in a matrix phase, various RVEs are modeled and analyzed according to their porosity. In order to quantitatively investigate the effects of microstructure, changes in effective elastic moduli and poroelastic parameters are measured via finite element (FE) analysis. The poroelastic parameters are calculated from the effective elastic moduli and the pore-pressure-induced strains. The reliability of the numerical results is verified through image-based FE models with the actual shape of pores in carbon-phenolic ablative materials. Additionally, the variation of strain energy density is measured, which can possibly be used to evaluate microstress concentrations.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.634-639
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• 1998

$Y_2O_3$ and $Nb_2O_5$ co-doped zirconia composites containing 10~30 vol% $Al_2O_3$ with two different particle sizes were sintered for 5 h at $1550^{\circ}C$ to evaluate low-temperature phase stability of the composite using X-ray diffractometry after heat-treatments for 1000 h at $250^{\circ}C$ in air or for 5 h at $180^{\circ}C$ in 0.3 MPa $H_2O$ vapor pressure. No tetragonal to monoclinic phase transformation during degradation, so called enhanced low-temperature phase stability, was observed for all composites. It is concluded that Nb addition to the composite for the phase stability is more effective than $Al_2O_3$ addition. The optimum combination of strength (670 MPa) and fracture toughness ($7.1{\textrm} {MPam}^{1/2}$) were obtained for the composite containing 20 vol% of $Al_2O_3$ with 2.8 $\mu$m to 0.2 $\mu$m, the flexural strength increases but the fracture toughness decreases.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.53-59
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• 1991

The reaction product between Si3N4 and ZrO2 has been studied by heat treatment of Si3N4-Zr(Y)O2 composite in high vacuum(<10-5 torr) and in air at $700^{\circ}C$. ZrN was formed after heat treatment in vacuum and easily oxidized after heat treatment in air. The amount of ZrN is related to the Y2O3 content dissolved in ZrO2. After the heat treatment in air the toughness increased and the spalling due to the oxidation of ZrN in specimen surface was observed. As a result, it is suggested that the formation of ZrN phase in Si3N4-ZrO2 composite enhance the toughness of the composite in an oxidation conditon.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.7
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• pp.2931-2938
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• 2011

Effective thermal conductivity of three-phase composites, consisting of matrix and two kinds of spherical inclusions, has been derived as an explicit form by extending modified Eshelby model (MEM) for two-phase composites. The present results are compared with those by differential effective medium model (DEMM), which are also compared with the experimental results of two- and three-phase composites in the literatures to be validated. For two-phase composites, the results by MEM are better than those by DEMM for the inclusion volume fraction smaller than 0.5. Comparisons between the results by two models and experimental results have been made for three-phase composite, resulting in that MEM predicts better than DEMM for smaller volume fraction of the inclusion having larger inclusion-to-matrix thermal conductivity ratio, but DEMM predicts better as its volume fraction increases. It has been observed through parametric study that its volume fraction is the critical factor affecting the deviation of predictions by the two models. The results by them show a good agreement with the three-phase composite proposed by Molina et al..

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.04a
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• pp.5.2-8
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• 1999