• Journal of the Korean Ceramic Society
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• v.55 no.4
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• pp.376-380
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• 2018

Microstructural characterization of Ni-yttria-stabilized zirconia (YSZ) anodes using secondary electron images has been limited by a lack of contrast between Ni and YSZ phases. This paper reports a sample preparation method for obtaining secondary electron images that allow the detection of Ni, YSZ, and pore phases together. Ni-YSZ anode samples were obtained by reducing NiO-YSZ samples prepared by using the mixed oxide method. Colloidal silica polishing and electrolytic etching were performed on the Ni-YSZ samples. The morphological change of the sample surface after each polishing process is examined.

• Journal of the Korean Ceramic Society
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• v.15 no.4
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• pp.205-212
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• 1978

The hydration reaction of the slag-gypsum system was studied by X-ray diffraction, differential thermal analysis, optical icroscopic observation, and measurement of heat liberation of hydration. 1. Domestic granulated slag was almost noncrystalized state, and its mineral compositions calculated were 46.53% of gehlenite, 28.14% of akermanite, and 19.04% of wollastonite. 2. The slag quenched with water at relatively high temperature had better reactivity. 3. The production of ettringite, CSH gel and AH3 gel were stimulated by effect of $Ca(OH)_2$, $Mg(OH)_2$ and calcined dolomite as activators, and the strength of hardened body would be developed by forming compacted microstructure.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.289-295
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• 1989

The properteis of the composition of second reports with Al2O3 and CaO have been investigated. The amount of Al2O3 addition was 5-20w/o, the composition ranges of maximum strength and the microstructure have been studied. In the same method, the effects of CaO on the theoretical composition of tricalcium phosphate have been studied.

• Journal of the Korean Ceramic Society
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• v.27 no.8
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• pp.1034-1042
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• 1990

Investigation for the preparation of high strength hardened cement paste using ordinary portland cement, hydroxypropyl methyl cellulose(HPMC) with various admixtures was carried out. The cement paste was mixed with 0.1 of water cement ratio by twin roll mill and cured 60 days in humidity chamber. When the quartz powder or white cement was added to the paste, the flexural strength was 900∼1000kg/㎠ and the Young's modulus was 8∼9×105kg/㎠. When the silicafume was added, the flexural strength was 800kg/㎠ and the Young's modulus was 6×105kg/㎠.

• Journal of the Korean Ceramic Society
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• v.24 no.1
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• pp.56-62
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• 1987

Tetragonal phase PZT ceramics with a tetragonality of c/a=1.027 to 1.041 were sintered at 1275$^{\circ}C$ for one hour. And the directionality of domain arrangement, microstructure, dielectric and aging properties were investigated. With increasing tetragonality, the directionality of domain arrangement of 180$^{\circ}$-domain on the surface is smaller than that in the internal part of specimens. Dielectric constants after poling are increased due to the increased internal energy or decreased due to the microcracks created by poling.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.97-105
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• 1999

In the binary system of SiC and carbon, porosity and pore size distribution of green body was controlled by varying pH, by the addition of polyelectrolyte dispersants, and by using different particle size of starting powders. The preforms having different green microstructure were fabricated by slip casting from suspensions having different dispersion condition. The reaction bonding process was carried out for these preforms. The condition of reaction bonding was 1600$^{\circ}C$ and 20 min. under vacuum atmosphere. The analyses of optical and SEM were studied to investigate the effect of green microstructure on that of reaction bonded silicon carbide and subsequently the mechanical properties of sintered body was investigated. Different green microstructures were obtained from suspensions having different dispersion condition. It was found that the pore size could be remarkably reduced for a fine SiC(0.5$\mu\textrm{m}$). The bimodal microstructure was not found in the present study, which is frequently observed in the typical reaction bonded silicon carbide. It is considered that the ratio between SiC and C was responsible for the formation of bimodal microstructure. For the preform fabricated from the well dispersed suspension, the 3-point bending strength of reaction-bonded silicon carbide was 310${\pm}$40 MPa compared to the specimen fabricated from relatively agglomerated particles having lower value 260${\pm}$MPa.

• Korean Journal of Materials Research
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• v.32 no.5
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• pp.258-263
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• 2022

Porous ceramics have the advantages of low density, low thermal conductivity, and excellent mechanical properties. Among porous ceramic manufacturing methods, the replica template method allows the easy manufacturing of porous filters with the highest porosity and pores of the desired size, but it also has the disadvantage that the resulting filters have low mechanical strength. To overcome this shortcoming, mullite (3Al₂O₃·2SiO₂) whiskers, which have excellent thermal stability and high mechanical strength, were introduced in porous ceramic structure. The mullite whiskers were synthesized using a composition of Al₂O₃, flyash and MoO₃. The morphologies and crystal structures of the mullite whiskers with MoO₃ contents were investigated in detail. When the porous ceramic with mullite whiskers was fabricated using 20 wt% MoO₃ catalyst the most uniform microstructure was obtained, and the mullite whiskers showed the highest aspect ratio of 47.03. The porosity and compressive strength of the fabricated porous ceramic were 82.12 % and 0.83 MPa, respectively.

• Journal of the Korean Ceramic Society
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• v.53 no.3
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• pp.349-353
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• 2016

We prepared a number of reaction-bonded silicon carbides (RBSCs) made from various mixing ratios of raw SiC particles, and investigated their microstructure and etch characteristics by Reactive Ion Etch (RIE). Increasing the amount of $9.5{\mu}m$-SiC particles results in a microstructure with relatively coarser Si regions. On the other hand, increasing that of $2.6{\mu}m$-SiC particles produces much finer Si regions. The addition of more than 50 wt% of $2.6{\mu}m$-SiC particles, however, causes the microstructure to become partially coarse. We also evaluated their etching behaviors in terms of surface roughness (Ra), density and weight changes, and microstructure development by employing Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscope (SEM) techniques. During the etching process of the prepared samples, we confirmed that the residual Si region was rapidly removed and formed pits isolating SiC particles as islands. This leads to more intensified ion field on the SiC islands, and causes physical corrosion on them. Increased addition of $2.6{\mu}m$-SiC particles produces finer residual Si region, and thus decreases the surface roughness (Ra.) as well as causing weight loss after etching process by following the above etching mechanism.

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.567-574
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• 2005

Densification of SiC powder with additives of total amount of2, 4, 8 $wt\%$ Al-B-C was carried out by Spark Plasma Sintering (SPS). The unique features of the process are the possibilities of a very fast heating rate and a short holding time to obtain fully dense materials. The heating rate and applied pressure were kept at $100^{\circ}C/min$ and 40 MPa, while the sintering temperature and holding time varied from 1700 - $1800^{\circ}C$ for 10 - 40 min, respectively. The SPS-sintered specimens with different amount of Al-B-C at $1800^{\circ}C$ reached near-theoretical density. The $3C{\rightarrow}6H,\;15R{\rightarrow}4H$ phase transformation of SiC was enhanced by increasing the additive amount. The microstructure of SiC sintered up to $1750^{\circ}C$ consisted of fine equiaxed grains. In contrast, the growth of large elongated grains in small matrix grains was shown in sintered bodies at $1800^{\circ}C$, and the plate-like grains interlocking microstructure had been developed by increasing the holding time at $1800^{\circ}C$. The grain growth rate decreases with increasing amount of Al-B-C in SiC starting powder, however, the both of volume fraction and aspect ratio of large grains in sintered body increased.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.45-55
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• 1997

Various kinds of amorphous silicates were used as raw materials to synthesize building materials based on calcium silicate hydrates. Relationships between the reactivities of silicates and castabilities of the building materials were investigated. In addition, effects of the reactivities of silicates on the mechanical properties of casted specimens were studied by analyzing microstructures and hydrates produced. As the reactivity of silicate increase, the press castability increases and the crystal size of hydrate and pore size also increase. For the mechanical properties, the flexural strength increases with decreasing crystal size and densifing microstructure. The compressive strength is greatly dependent on the den-sification of microstructure rather than crystal size of hydrate. Based on the results, diatomous ma-terials are desirable due to high reactivity and formation of densified microstructure. Slag and fly ash may be partially used as raw materials with amorphous silicates to manufacture building materials based on calcium silicate hydrates.