Showing papers in "Journal of The Korean Ceramic Society in 2011"

Synthesis and Characterization of Metal (Pt, Pd and Fe)-graphene Composites

Abstract: In this study, we prepared graphene by using the modified Hummers-Offeman method and then introduced the metals (Pt, Pd and Fe) for dispersion on the surface of the graphene for synthesis of metal-graphene composites. The characterization of the prepared graphene and metal-graphene composites was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and transmission electron microscopy (TEM). According to the results, it can be observed that the prepared graphene consists of thin stacked flakes of shapes having a well-defined multilayered structure at the edge. And the metal particles are dispersed uniformly on the surface of the graphene with an average particle size of 20 ㎚.

Influence of sintering atmosphere on abnormal grain growth behaviour in potassium sodium niobate ceramics sintered at low temperature

Abstract: The present study aims to identify the effect of sintering atmosphere [O 2 , 75N 2 -25 H 2 (mol%) and H 2 ] on microstructural evolution at the relatively low sintering temperature of 1040℃. Samples sintered in O 2 showed a bimodal microstructure consisting of fine matrix grains and large abnormal grains. Sintering in 75 N 2 - 25 H 2 (mol %) and H 2 caused the extent of abnormal grain growth to increase. These changes in grain growth behaviour are explained by the effect of the change in step free energy with sintering atmosphere on the critical driving force necessary for rapid grain growth. The results show the possibility of fabricating (K 0.5 Na 0.5 )NbO 3 at low temperature with various microstructures via proper control of sintering atmosphere.

Multiferroic Property and Crystal Structural Transition of BiFeO₃-SrTiO₃ Ceramics

Abstract: Solid solutions of the (1?x)BiFeO 3-x SrTiO₃ ceramic system (x = 0~0.4) are explored here in attempts to obtain multiferroic properties in these systems. The polarization-electric field hysteresis, magnetization-magnetic field curves, and dielectric properties are also characterized. This solid-solution system shows a crystal structural transition from a noncentrosymmetric (R3c) structure to a centrosymmetric (Pm-3m) structure at 0.3 ＜ x ＜ 0.4. The solid solution ceramic shows unsaturated M-H behavior and low remanent magnetization over the composition region of 0.1 ≤ x ≤ 0.3. The 0.7BiFeO₃-0.3SrTiO₃ system shows the largest value of M s at 0.17 emu/g and the smallest value of H c at 1.06 kOe. The P-E hysteresis curves were not saturated under an electric field as high as E = 70 ㎸/㎝. This system is considered to have multiferroic characteristics in the composition range of 0.1 ≤ x ≤ 0.3.

Application of Generalized Transmission Line Models to Mixed Ionic-Electronic Transport Phenomena

Abstract: Application of a generalized equivalent circuit including the electrode condition for the Hebb-Wagner polarization in the frequency domain proposed by Jamnik and Maier can provide a consistent set of material parameters, such as the geometric capacitance, partial conductivities, chemical capacitance or diffusivity, as well as electrode characteristics. Generalization of the shunt capacitors for the chemical capacitance by the constant phase elements (CPEs) was applied to a model mixed conducting system, Ag 2 S, with electron-blocking AgI electrodes and ion-blocking Pt electrodes. While little difference resulted for the electron-blocking cell with almost ideal Warburg behavior, severely non-ideal behavior in the case of Pt electrodes not only necessitates a generalized transmission line model with shunt CPEs but also requires modelling of the leakage in the cell approximately proportional to the cell conductance, which then leads to partial conductivity values consistent with the electron-blocking case. Chemical capacitance was found to be closer to the true material property in the electron-blocking cell while excessively high chemical capacitance without expected silver activity dependence resulted in the electron-blocking cell. A chemical storage effect at internal boundaries is suggested to explain the anomalies in the respective blocking configurations.

Improved Luminescence Properties of Polycrystalline ZnO Annealed in Reduction Atmosphere

Abstract: The luminescence properties of polycrystalline ZnO annealed in reducing ambience (H₂/N₂) have been studied. An effective quenching of green luminescence with enhanced UV emission from polycrystalline ZnO is observed for the reduced ZnO. The variations of the UV and green luminescence band upon reduction treatment are investigated as a function of temperature in the range between 20 and 300 K. Upon annealing treatment in reducing ambience, the optical quality of polycrystalline ZnO is improved. The UV to green intensity ratio of sintered ZnO approaches close to zero (~0.05). However, this ratio reaches more than 13 at room temperature for polycrystalline ZnO annealed at 800℃ in reducing ambience. Furthermore, the full width at half maximum (FWHM) of the UV band of polycrystalline ZnO is reduced compared to unannealed polycrystalline ZnO. Electron paramagnetic resonance (EPR) measurements clearly show that there is no direct correlation between the green luminescence and oxygen vacancy concentration for reduced polycrystalline ZnO.

원자력 극한환경용 세라믹 열교환기 소재로서 반응소결 SiC 세라믹스 제작성

Abstract: Silicon carbide (SiC) is a candidate material for heat exchangers for VHTR (Very High Temperature Gas Cooled Reactor) due to its refractory nature and high thermal conductivity. This research has focused on demonstration of physical properties and mock-up fabrication for the future heat exchange applications. It was found that the SiC-based components can be applied for process heat exchanger (PHE) and intermediate heat exchanger (IHX), which are operated at 400~1000℃, based on our examination for the following aspects: optimum fabrication technologies (design, machining and bonding) for compact design, thermal conductivity, corrosion resistance in sulfuric acid environment at high temperature, and simulation results on heat transferring and thermal stress distribution of heat exchanger mock-up.

Decomposition Mechanism of Waste Hard Metals using by ZDP (Zinc Decomposition Process)

Abstract: Decomposition promoting factors and decomposition mechanism in the zinc decomposition process of waste hard metals which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility amount was suppressed and zinc valatilization pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP. Reaction was done for 2 h at 650℃, which 100 % decomposed the waste hard metals that were over 30 ㎜ thick. As for the separation-decomposition of waste hard metals, zinc melted alloy formed a liquid composed of a mixture of γ-β₁ phase from the cobalt binder layer (reaction interface). The volume of reacted zone was expanded and the waste hard metal layer was decomposed-separated horizontally from the hard metal. Zinc used in the ZDP process was almost completely removed-collected by decantation and volatilization-collection process at 1000℃.

Densification and Mechanical Properties of Silicon Nitride Containing Lu 2 O 3 -SiO 2 Additives

Abstract: Gas pressure sintering (GPS) of reaction bonded silicon nitride (RBSN) was performed using Lu 2 O 3 -SiO 2 additive and the properties were compared with those of specimens prepared using high purity Si 3 N 4 powder. The relative density of RBSN and compacted Si 3 N 4 powder were 68.9 and 47.1%, and total linear shrinkage after sintering at 1900℃ were 14.8 and 42.9%, respectively. High nitrogen partial pressure (5MPa) was required during sintering at 1900℃ in order to prevent the decomposition of the nitride and to promote the formation of SiC. The relative density and 4-point bending strength of RBSN and Si3N4 powder compact were 97.7%, 954MPa and 98.2%, 792MPa, respectively, after sintering at 1900℃. The sintered RBSN also showed high fracture toughness of 9.2MPam 1/2 .

Material Properties Evaluation of 1-3 type Piezo-composite Fabricated with Ceramic Injection Molding Technology

Abstract: Generally the piezo-composites have superior hydrostatic response characteristics than PZT ceramics due to both the stress amplification effect in axial direction and stress reduction effects in radial direction. This paper described material properties of a 1-3 type piezo-composite that fabricated with ceramic injection molding (CIM) technology. The electro-mechanical performances of the composite have been analyzed using FEM and the physical properties of the composite have been measured with the vol% of the PZT ceramics. Based on the results, the k t increased rapidly as the vol% of the PZT ceramics increased up to 30 vol% and saturated the constant value in the above region. Also the experimental results have good agreement with the simulation values of the composite. Finally we developed the composites having high piezoelectric properties than the PZT ceramics with the CIM technology.

Effects of Ceramics on Dielectric Properties of Polystyrene / Ceramics Composites at Microwave Frequencies

Abstract: Dependencies of dielectric properties on MgTa₂O?, MgNb₂O?, and MgWO₄ (Mg-based ceramics) fillers of the polystyrene (PS) matrix composites were investigated as a function of frequency. With increasing frequency from 1 ㎓ to 7.3 ㎓, the dielectric constant (K) of the composites was not changed significantly, while the dielectric loss (tanδ) of the composites was slightly decreased. The K, tanδ, and temperature coefficient of resonant frequency (TCF) of the composites were dependent on the type and amount of ceramics at 11 ㎓. Also, several theoretical models have been employed to predict the effective dielectric constant of the composites and the results were compared with experimental data. Typically, a K value of 6.67, tanδ of 0.56×10?³, and TCF of ?4.99 ppm/℃ were obtained for the PS composites with 0.4 volume fraction of MgNb₂O? at 11 ㎓.

Effect of Mullite Generation on the Strength Improvement of Porcelain

Abstract: Alumina powder was added in a general porcelain (Backja) with clay, feldspar and quartz contents to promote the mullite (3Al₂O₃ㆍ2SiO₂) generation in the porcelain. Low melting materials (B₂O₃(450℃), MnO₃(940℃), CuO(1080℃)) were doped at ~3 wt% to modify the sinterability of porcelain with a high alumina contents and promote the mullite generation. Green body was made by slip casting method with blended slurry and then, they were fired at 1280°C for 1hr by a 2℃/min. Densifications of samples with high alumina contents (20~30 wt%) were impeded. As the doping contents of low melting materilas increased, the sinterability of samples was improved. The shrinkage rate and bulk density of samples were improved by doping with low melting materials. Mullite phase increased with increasing the low melting contents in the phase analyses. This means lots of alumina and quartz were transformed into mullite phase by low melting contents doping. In the results, high bending strength of samples with high alumina contents was accomplished by improving the densification and mullite generation in the porcelain.

Stabilization of Wet Foams for Porous Ceramics Using Amphiphilic Particles

Abstract: Wet foams formed through direct foaming were stabilized using various concentrations of amiphiphilic particles that could control pore size and porosity. These porous materials showed moderate strength upon compression with high porosity. Bubble size and wet foam stability were tailored by amphiphile concentration, particle concentration, contact angle, and pH of the suspension to obtain crack-free porous solid after sintering. Closed and open pores were obtained with sizes of 30~300 μm and porosities of over 80%.

Growing Behavior of Nanocrystalline TiN Films by Asymmetric Pulsed DC Reactive Magnetron Sputtering

Abstract: Nanocrystalline TiN films were deposited on Si(100) substrate using asymmetric pulsed DC reactive magnetron sputtering. We investigated the growing behavior and the structural properties of TiN films with change of duty cycle and pulsed frequency. Grain size of TiN films were decreased from 87.2 nm to 9.8 nm with decrease of duty cycle. The 2θ values for (111) and (200) crystallographic planes of the TiN films were also decreased with decrease of duty cycle. This shift in 2θ could be attributed to compressive stress in the TiN coatings. Thus, the change of plasma parameter has a strong influence not only on the microstructure but also on the residual stresses of TiN films.

Fabrication of Hydroxyapatite Ceramics to Mimic the Natural Bone Structure

Abstract: The objective of our study was to produce an imitation bone material consisting of hydroxyapatite with a compact and spongy structure. This study shows the ideal content of SiO 2 and the sintering temperature to produce imitation bone that has the mechanical properties of natural bone. On the basis of our determination of the ideal conditions, a compact part was produced and its mechanical properties were tested. A compact part made of 0.5 wt% SiO 2 and sintered at 1350℃ showed excellent mechanical properties. The bioactivity of the compact part under this condition was tested, and it was found to be bioactive. The porous part was produced by controlling the powder size, and the dual structure was manufactured by combining the compact and porous parts. A water permeability test confirmed that the dual structure had an interconnected pore structure. Therefore, this dual-body structure is feasible for use in the creation of implants.

Effect of Batch Melting Temperature and Raw Material on Iron Redox State in Sodium Silicate Glasses

Abstract: In this study, the redox state of iron in sodium silicate glasses was varied by changing the melting conditions, such as the melting temperature and particle size of iron oxide. The oxidation states of the iron ion were determined by wet chemical analysis and UV-Vis spectroscopy methods. Iron commonly exists as an equilibrium mixture of ferrous ions, Fe²?, and ferric ions Fe³?. In this study, sodium silicate glasses containing nanoparticles of iron oxide (0.5% ㏖) were prepared at various temperatures. Increase of temperature led to the transformation of ferric ions to ferrous ions, and the intensity of the ferrous peak in 1050 ㎚ increased. Nanoparticle iron oxide caused fewer ferrous ions to be formed and the Fe²?/Fe³? equilibrium ratio compared to that with micro-oxide iron powder was lower.

Wafer Sawing 공정의 폐슬러리로부터 금속 실리콘 회수에 관한 연구

Abstract: Metallurgical grade silicon was recovered from slurry waste for ingot sawing process by acid leaching and thermal treatment. SiC abrasive was removed by gravity concentration and centrifugation. Metal impurities were removed by the acid leaching using HF/HCl. The remaining SiC was separated by the thermal treatment at 1600℃ in an inert atmosphere by the difference in melting points. The purity of the obtained silicon was found to be around 99.7%.

Electrochemical Performances of LiMn 2 O 4 :Al Synthesized by Solid State Method

Abstract: Al doped LiMn 2 O 4 (LiMn 2 O 4 :Al) synthesized by several Al doping process and Solid State method. The Al contents in Mn 1-x Al x O 2 for LiMn 2 O 4 :Al were analyzed 1.7 wt% by EDS. The LiMn 2 O 4 :Al confirmed cubic spinel structure and approximately 5 μm particles regardless of three kinds of doping process by solid state method. In the result of electrochemical performances, initial discharge capacity had 115 mAh/g in case of LiMn 2 O 4 and 111 mAh/g of LiMn 2 O 4 :Al after 100th cycle at room temperature. But the capacity retention results showed that LiMn 2 O 4 and LiMn 2 O 4 :Al were 44% and 69% respectively in the 100th cycle at 60℃. Therefore we are confirmed that LiMn 2 O 4 :Al increased the capacity retention about 25% than LiMn 2 O 4 , thus the effect of Al dopping on LiMn 2 O 4 capacity retention.

Synthesis and Characterization of CoFe 2 O 4 /SiO 2 using Cobalt Precursors from Recycling Waste Cemented Carbide

Abstract: We report the preparation of nanocrystalline cobalt ferrite, CoFe 2 O 4 , particles using recycled Co 3 O 4 and their surface coating with silica using micro emulsion method. Firstly, the Co 3 O 4 powders were separated from waste cemented carbide with acid-base chemical treatment. The cobalt ferrite nanoparticles with the size 10 nm are prepared by thermal decomposition method using recycled Co 3 O 4 . SiO 2 was coated onto the CoFe 2 O 4 particles by the micro-emulsion method. The SiO 2 -coated CoFe 2 O 4 particles were studied their physical properties and characterized by X-ray diffraction (XRD), high resolution-transmission electron microscopy (TEM) analysis and CIE Lab value.

A Study on the Characteristics of ALC Material with Melamine Resin

Abstract: ALC(Autoclaved Lightweight Concrete) is produced using quartz sand, lime and cement and water. And aluminum powder is used for blowing agent. ALC is manufactured by autoclave chamber under high-temperature and high-pressure. Generally, ALC is 1/4 levels lighter than concrete and mortar, because it has a lot of pores. So density of ALC is about 0.45~0.65 g/㎤. But, ALC has a weakness, typically low strength, with its porous structure. So, it is necessary to excellent strength properties for extensive apply of ALC materials in high porosity. In this study, melamine resin was used to improve the strength characteristics of ALC materials. We performed compressive and bending strength measurements. Compressive strength of ALC with 2% melamine resin increased 26.88% than ‘melamine-free’ ALC. Also we performed functionality evaluation such as thermal conductivity, sound absorption, and flame-resistance.

Mechanical Behavior of Layered YSZ Thermal Barrier Coatings using Indentation Test

Abstract: In this study, we investigated the mechanical behaviors of layered thermal barrier coatings by indentations. Various single and double-layered thermal barrier coatings were deposited by air plasma spray process using different type of commercialized YSZ (Yttria stabilized zirconia) starting powders. Indentation stress-strain curve, load-displacement curve and hardness of the single and the double-layered thermal barrier coatings were obtained experimentally and analyzed. The indentation damages at the same loads were compared, and thus, the results depend on the structure of each coating. The result indicates improvement in damage resistances from tailoring of layered structures in the component of gas turbine system is expected.

Flexural Strength of Macroporous Silicon Carbide Ceramics

Abstract: Macroporous silicon carbide (SiC) ceramics were fabricated by powder processing and polymer processing using carbon-filled polysiloxane as a precursor. The effects of the starting SiC polytype, template type, and template content on porosity and flexural strength of macroporous SiC ceramics were investigated. The β-SiC powder as a starting material or a filler led to higher porosity than α-SiC powder, owing to the impingement of growing α-SiC grains, which were transformed from β-SiC during sintering. Typical flexural strength of powder-processed macroporous SiC ceramics fabricated from α-SiC starting powder and polymer microbeads was 127 MPa at 29% porosity. In contrast, that of polymer-processed macroporous SiC ceramics fabricated from carbon-filled polysiloxane, β-SiC fillers, and hollow microspheres was 116 MPa at 29% porosity. The combination of α-SiC starting powder and a fairly large amount (10 wt%) of Al2O3-Y2O3 additives led to macroporous SiC ceramics with excellent flexural strength.

X-ray Diffraction Analysis of Residual Stress in Laminated Ceramic

Abstract: The strength of ceramic was improved by lamination by suppressing the propagation of cracks with compressive residual stress in the face layer of the laminate. Hot pressed SiAlON+SiC/SiC/SiAlON+SiC laminate discs were fabricated for tailored residual stress. The residual stress in this laminate was studied by X-ray diffraction (XRD). There was considerable compressive residual stress in the face layer. A Finite Element Analysis (FEA) was performed to support the measured XRD results and to determine the stress field in the laminate. The residual stress measured by XRD had satisfactory agreement with the analytically calculated and FEA values. The measured value by XRD was ?385±20 MPa over most of the face layer. The calculated and FEA values were ?386MPa and ?371MPa, respectively. FEA also showed significantly modified stresses and the maximum tensile stress near the edge region which are possible crack generators in the presence of flaws or contact damage.

Heat Treatment Effect on the Microstructure of 8YSZ Thick Film

Abstract: In order to fabricate 8YSZ thick film by silk screen printing, YSZ(yttria-stabilized zirconia) commercial powder was used as starting materials. Paste for screen printing was made by mixing 8YSZ powder and organic vehicles. 8YSZ thick film was formed on Al₂O₃ substrate. The crystal structure, and microstructure were investigated. Grain size of 8YSZ was increased with increasing calcination temperature and rapid grain growth was shown after calcination at 1300℃. Microstructure showed the mixture of large and small grain size after 1400℃ sintering. Shrinkage rate of 8YSZ thick film sintered at 1400℃ was more than 40%.

Synthesis of One-dimensional Spinel LiMn 2 O 4 Nanostructures as a Positive Electrode in Lithium Ion Battery

Abstract: This paper presents the synthesis of one-dimensional spinel LiMn 2 O 4 nanostructures using a facile and scalable two-step process. LiMn 2 O 4 nanorods with average diameter of 100 nm and length of 1.5 μm have been prepared by solid-state lithiation of hydro-thermally synthesized β-MnO 2 nanorods. LiMn 2 O 4 nanowires with diameter of 10 nm and length of several micrometers have been fabricated via solid-state lithiation of β-MnO 2 nanowires. The precursors have been lithiated with LiOH and reaction temperature and pressure have been controlled. The complete structural transformation to cubic phase and the maintenance of 1-D nanostructure morphology have been evaluated by XRD, SEM, and TEM analysis. The size distribution of the spinel LiMn 2 O 4 nanorods/wires has been similar to the MnO 2 precursors. By control of reaction pressure, cubic 1-D spinel LiMn 2 O 4 nanostructures have been fabricated from tetragonal MnO 2 precursors even below 500℃.

CMP 공정에서 슬러리와 웨이퍼 형상이 SiC 웨이퍼 표면품질에 미치는 영향

Abstract: The effect of slurry composition and wafer flatness on a material removal rate (MRR) and resulting surface roughness which are evaluation parameters to determine the CMP characteristics of the on-axis 6H-SiC substrate were systematically investigated. 2-inch SiC wafers were fabricated from the ingot grown by a conventional physical vapor transport (PVT) method were used for this study. The SiC substrate after the CMP process using slurry added oxidizers into slurry consisted of KOH-based colloidal silica and nano-size diamond particle exhibited the significant MRR value and a fine surface without any surface damages. SiC wafers with high bow value after the CMP process exhibited large variation in surface roughness value compared to wafer with low bow value. The CMPprocessed SiC wafer having a low bow value of 1im was observed to result in the Root-mean-square height (RMS) value of 2.747 A and the mean height (Ra) value of 2.147 A.

Preparation of Mg(OH) 2 Dispersion and its Application to PET Non-woven Textile as Flame Retardant Coating

Abstract: Magnesium hydroxide as a non-halogen flame retardant has increasing attention due to its non-toxicity, high decomposition temperature and smoke suppressant ability during combustion. For the application of magnesium hydroxide retardant to the textile by soaking and coating method, the prerequisite for the coating is a small particle size, stable dispersion, and adhesion to the textile. The dispersion of Mg(OH) 2 particles and stability of the coating was checked by monitoring the change of transmittance and backscattering by varying the types of dispersion agents, binder, solvent, and Mg(OH) 2 source, and their compositions in the coating. The Mg(OH) 2 dispersion coating was applied to PET(poly(ethylene terephthalate)) non-woven textile. The physical properties are characterized by surface morphology, amount of coating, particle dispersion, and adhesion test. The flame retardant Mg(OH) 2 coated textile has been compared by limited oxygen index(LOI) and thermal gravimetry and differential scanning calorimetry(TG-DSC). It was found that phosphorous additive may give synergistic effect on Mg(OH) 2 flame retardant coating to make the flame retardant PET non-woven textile.

Preparation and Characterization of Low k Thin Film using a Preceramic Polymer

Abstract: Recently, variety of organic and inorganic hybrid materials have recently investigated as alternative routes to SiOC, SiO 2 thin film formation at low temperatures for applications in electronic ceramics. Specially, silicon based polymers, such as polycarbosilane, polysilane and polysilazane derivatives have been studied for use in electronic ceramics and have been applied as dielectric or insulating materials. In this study, Polycarbosilane(PCS), which Si-CH 2 -Si bonds build up the backbone of the polymer, has been investigated as low-k materials using a solution process. After heat treatment at 350℃ under N 2 atmosphere, chemical composition and dielectric constant of the thin film were SiO 0.27 C 1.94 and 1.2, respectively. Mechanical property measured using nanoindentor shows 1.37 GPa.

Effect of Crystal Structural Environment of Pr 3+ on Photoluminescence Characteristics of Double Tungstates

Abstract: In this article, the effect of the crystal structural environment of Pr³? ions on the photoluminescence (PL) characteristics of double tungstates, such as A(M 1-x Pr x )W₂O? (A=Li, Cs, M = In, Y, Sc, La; 0.007≤x≤0.1) and La 1.96 Pr 0.04 W₃O₁₂ are characterized. By varying the ion radius in A and M sites, the structural environment of Pr³? ions were modified. The structural criteria, that is, the point charge electrostatic potentials V around the Pr³? activator, were calculated using the crystal structural parameters. The point charge potential V can be a valid criterion for ³P? quenching in various double tungstates. When the calculated V values are large (＞ 6.0), the luminescence from the ³P? level becomes dominant. When the calculated V values are about 3.8, the ¹D₂ line appears weakly but ³P?-level luminescence is absent. When the calculated V values are small (＜ 2.0), the luminescence from the ¹D₂ level becomes dominant and ³P?-level luminescence is absent. At 2.0＜V＜4.0, the ³P? quenching to ¹D₂ level occurs substantially in accordance with the structural criterion of the point charge potential model.

고체산화물연료전지 연결재용 La 0.7 Ca 0.3 Cr 0.9 Co 0.1 O 3-δ 조성계에 Ca Source 변화에 따른 소결 및 전기적 특성에 관한 연구

Abstract: Effects on sintering and electrical properties of La 0.7 Ca 0.3 Cr 0.9 Co 0.1 O 3-δ system, a interconnect material for cylindrical and flat tubular solid oxide fuel cells (SOFC), have been investigated by Ca-source when using CaCO₃ and CaF₂.. When using CaCO₃ and CaF₂ was mixing as Ca-source, single phased perovskite solid solution was observed for each sample. The sintering temperature was decreased by CaF₂ contents was increased. When using 0.1 mole CaF₂ was densely sintered at 1400℃ and relative density was 93.8%. Also, electrical conductivity in oxidation and reducing atmosphere was 47, 4.3 S/㎝, respectively, due to F?ion enhance the electrical conductivity in reducing atmosphere.

Fe-2.3%Cr-1.6%W 합금의 고온산화 부식속도와 스케일 분석

Abstract: The T23 steel, whose composition was Fe-2.3%Cr-1.6%W, was arc-melted, and oxidized between 600℃ and 900℃ in air for up to 7 months. The amount of precipitates in the arc-melted microstructure was as large as 11.4 vol.%. The precipitates increased the oxidation rate of the arc-melted T23 steel. Owing to the low amount of Cr in the T23 steel, breakaway oxidation occurred after a few hours during oxidation above 700oC in both arc-melted and as-received T23 steels. The scales that formed on arc-melted and asreceived T23 steels were similar to each other. They consisted primarily of the outer Fe₂O₃ layer and the inner (Fe₂O₃, FeCr₂O₄)-mixed layer. The precipitates increased the microhardness and the oxidation rates.