Earticle

본 연구에서는 새도우마스크 제조공정 중 발생되는 Fe-Ni계 복합 폐산을 원료로 하여 공기압력 1 kg/cm2의 조건에서 분무열분해 공정에 의해 평균입도 100 nm 이하의 니켈 페라이트(NiFe2O4) 및 Fe2O3+NiO 나노 분말을 제조하였으며, 반응온도, 폐산 용액의 농도 및 nozzle tip 크기의 반응인자들의 변화에 따른 생성된 분말의 특성 변화를 파악하였다. 반응온도가 800oC로부터 1100oC로 변화함에 따라 분말의 평균입도는 40 nm로부터 100 nm 정도까지 증가하고 있었으며 조직은 더욱 치밀화되는 반면 입도분포는 점점 불균일하게 됨을 알 수 있었다. 반응온도의 증가에 따라 니켈 페라이트 상의 생성 비율이 현저히 증가하고 있었으며, 분말의 비표면적은 현저히 감소하고 있었다. 원료용액 내의 Fe 성분의 농도가 20 g/l로부터 200 g/l로 증가됨에 따라 분말의 평균 입도는 30 nm로부터 60 nm 정도까지 점점 증가하는 반면 입도분포는 더욱 불균일하게 나타나고 있었다. 또한 용액의 농도 증가에 따라 니켈 페라이트 상의 생성 비율이 증가하고 있었으며, 분말의 비표면적은 현저히 감소하였다. Nozzle tip 크기 증가에 따라 분말의 입도분포는 점점 불균일하게 나타나는 반면 평균 입도는 현저한 변화를 나타내지 않았다. Tip 크기가 2 mm까지는 tip 크기 증가에 따라 니켈 페라이트 상의 생성 비율에 현저한 변화는 나타나지 않는 반면 분말의 비표면적은 약간 감소하였다. Tip 크기가 3 mm 및 5 mm로 증가하는 경우에는 니켈 페라이트 상의 생성 비율이 점점 감소하고 있었으며, 분말의 비표면적은 약간씩 증가하고 있음을 알 수 있었다.

In this study, nano-sized Ni-ferrite and Fe2O3 condition of 1kg/cm2air pressure using the Fe-Ni complex waste acid solution generated during the manufacturing process of shadow mask. The averageparticle size of the produced powder was below 100 nm. The effects of the reaction temperature, the concentration of raw materialsolution and the nozle tip size on the properties of powder were studied. As the reaction temperature increased from 800oC to1100oC, the average particle size of the powder increased from 40 nm to 10 nm, the structure of the powder gradualy became solid,ction ofthe Ni-ferrite phase were also on the rise, and the surface area of the powder was greatly reduced. As the concentration of Fe in solu-tion increased from 20 g/l to 20 g/l, the average particle size of the powder gradualy increased from 30 nm to 60nm, while the dis-tribution of the particle size apeared more irregular. Along with the increase of the concentration of solution, the fraction of the Ni-ferrite phase was on the rise, and the surface area of the powder was greatly reduced. Along with the increase of the nozzle tip size,t change.As the nozzle tip size increased from 1 m to 2 m, the fraction of the Ni-ferrite phase showed no significant change, while thesurface area of the powder slightly reduced. As the nozzle tip size increased to 3 m and 5 mm, the fraction of the Ni-ferritephase gradually reduced, and the surface area of the powder slightly increased.

The use of combustible metals in products in various industries such as automobiles is increasing significantly as the rare metal industry has recently developed and the industrial structure has shifted to a high-tech industry. Several fires, presumed to be spontaneous combustion, occurred at an automobile parts processing company in our area. Although it is known that combustible solids do not spontaneously ignite, this study was conducted to technically analyze and suggest the possibility of spontaneous ignition of mixtures generated during metal processing.

1. 원료 형태별 청국장의 발효시간에 따른 건물중은 콩, 환, 분말의 모든 원료형태에서 발효시간이 경과할수록 건물의 중량이 감소하는 경향을 보였다. 2. 원료 형태별 청국장의 발효시간에 따른 진의 길이 변화를 측정한 결과, 모든 원료 형태에서 발효시간이 경과할수록 진의 길이가 증가하는 경향을 보였으며, 48시간 이후에는 그 증가치가 완만함을 보였다. 태광콩을 콩의 형태로 발효하였을 때 진의 생성이 가장 많았고, 분말을 1cm의 두께로 발효하였을때 진이 거의 생성되지 않았다. 3. 원료 형태별 청국장의 발효시간에 따른 생균수의 변화를 측정한 결과, 콩 형태로 발효시켰을 경우 모든 품종에서 비슷한 수준의 생균수가 측정되었다. 환 형태로 발효시켰을 경우 12시간 이후에 생균수가 급격히 증가하다가 24시간 이후 증가치가 완만해졌다. 분말형태로 발효시켰을 경우 시간에 따라 경시적으로 증가하였다. 4. 원료 형태별 청국장의 발효시간에 따른 색도의 변화를 측정한 결과, 모든 원료 형태에서 발효시간이 경과할수록 명도는 흑색에 가까워졌고, 색상과 채도의 경우는 각각 적색과 황색을 띠는 쪽으로 변화하였다. 5. 원료 형태별 청국장의 발효시간에 따른 pH의 변화를 측정한 결과, 모든 원료 형태에서 발효시간이 경과할수록 알칼리성으로 변화하였다. 6. 원료 형태별 청국장의 발효시간에 따른 isoflavone 함량의 변화를 측정한 결과, 발효 후 48시간까지 isoflavone의 함량이 증가하다 감소하는 경향을 보였다. 7. 청국장을 건조온도를 달리하여 균의 재생능력을 실험해본 결과 동결건조를 하였을 때 가장 많은 수의 균이 존재하였다. 8. 분말 또는 분말 (환)의 형태로 청국장을 만들 경우 종자 이용 시 보다 청국장의 품질이 떨어졌으며 분말 (환)을 이용하여 경제적인 청국장 제조를 위해서는 더 많은 연구가 필요한 것으로 고려되어 진다.

The possibility of making Cheongukjang by the use of soy-powder and pill type re-made from soy-powder was investigated. Some of experimental results obtained are summarized as follows; 1. Regardless of three different types for the source material of Cheonggukjang, soybean seed, soy-power, and pill, the dry weight of fermented Cheonggukjang showed continuously decreasing trends along with the time of fermentation applied. 2. In all type of source materials, the length of viscous substance during fermentation was increased along with the time of fermentation, and the rate of elongation was much reduced after 48hr of fermentation. Out of four soybean varieties tested, Taekwangkong produced longest viscous substance fermented in the type of soybean seed. No viscous substance was formed when the depth of soy-powder in the fermentation box was shallow, one centimeter. 3. Not much difference was observed in the number of microbes, Bacillus licheniformis B1, in all soybean varieties. The number was proportionally increased in the type of powder but it increased rapidly from 12 hour to 24 hour with low rate of increase thereafter in the pill type. 4. Along with the time of fermentation in all types, the color of Cheonggukjang changed from yellow to dull. At the same time, the tone of color and chroma changed into reddish and yellow, respectively. 5. Along with the time of fermentation in all types, pH of Cheonggukjang changed in alkali. 6. Along with the time of fermentation, the content of isoflavone in Cheonggukjang increased by 48hr but decreased thereafter. 7. In general, the quality of Cheonggukjang fermented in types of soy-powder and pill re-made from soy-powder was lower than that of soybean seed. More study is seemed to be needed to produce high quality Cheonggukjang by the use of soy-power.

Widespread commercialization of solid oxide fuel cells (SOFCs) is expected to be realized in various application fields with the advent of cost-effective fabrication of cells and stacks in high volumes. Cost-reduction efforts have focused on production yield, power density, operation temperature, and continuous manufacturing. In this article, we examine several issues associated with processing for SOFCs from the standpoint of the bimodal packing model, considering the external constraints imposed by rigid substrates. Optimum compositions of composite cathode materials with high volume fractions of the second phase (particles dispersed in matrix) have been analyzed using the bimodal packing model. Constrained sintering of thin electrolyte layers is also discussed in terms of bimodal packing, with emphasis on the clustering of dispersed particles during anisotropic shrinkage. Finally, the structural transition of dispersed particle clusters during constrained sintering has been correlated with the structural stability of thin-film electrolyte layers deposited on porous solid substrates.

In this paper, two kinds of advanced powder processing techniques Metal Injection Molding (MIM) and Direct Laser Forming (DLF) are introduced to fabricate complex shaped Ti alloy parts which are widely used for medical and aerospace applications. The MIM process is used to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe or Cr powders. Enhanced tensile strength of 1030 MPa with 15.1% elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification and also the solution strengthening in beta phase. However, their fatigue strength was lower compared to wrought materials, but was improved by HIP. Subsequently, the effect of feeding layer height (FLH) on the characteristics of the DLF compacts was investigated. In the case of 100 ${\mu}m$ FLH, surface roughness was improved and nearly full density (99.8%) was obtained. Also, tensile strength of 1080 MPa was obtained, which is higher than the ASTM value.

In this paper, two kinds of advanced powder processing techniques Metal Injection Molding (MIM) and Direct Laser Forming (DLF) are introduced to fabricate complex shaped Ti alloy parts which are widely used for medical and aerospace applications. The MIM process is used to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe or Cr powders. Enhanced tensile strength of 1030 MPa with 15.1% elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification and also the solution strengthening in beta phase. However, their fatigue strength was lower compared to wrought materials, but was improved by HIP. Subsequently, the effect of feeding layer height (FLH) on the characteristics of the DLF compacts was investigated. In the case of 100 μm FLH, surface roughness was improved and nearly full density (99.8%) was obtained. Also, tensile strength of 1080 MPa was obtained, which is higher than the ASTM value.

To apply a thermal barrier coating, the coating materials must satisfy the basic requirements. This paper explains composite powder processing and the characterization of sintered materials. The composite powders were prepared by two types of method: conventional ball-milling and chemical precipitation. The morphology of the powder differed with the processing method. In chemically precipitated powder, the surface of zirconia was coated with LaPO4. The samples were fabricated from these powders, using the PECSed method. The flexural strength of the nanocomposites was decreased with an increase in the amount of LaPO4 due to its poor mechanical properties. However, the thermal properties, such as thermal conductivity and high temperature stability, were lower and more stable than that of the monolith.

Prevalence of Bacillus cereus was determined in red pepper powder samples obtained from various processing steps (n=60), swabs of machinery surfaces (n=35), and air samples of the processing room (n=17) during red pepper powder production. The detection rate of B. cereus was high (over 85%) in samples of raw materials and washing steps and decreased to 40% in samples obtained from later stages of processing, i.e. milling, metal detection, and final products. B. cereus was detected in 2.9 and 11.8% of swabs and air samples, respectively. The genetic similarity of B. cereus isolates obtained from various processing steps was compared to identify the sources of contamination for red pepper powder using the repetitive-sequence-based polymerase chain reaction method. For 20 isolates of B. cereus from two independent samplings, 50% of the isolates, which were clustered, consisted of two or more isolates with a similarity greater than 95%. For the isolates obtained from raw materials, crude milling, and milling step of the independent sampling, high genetic similarity (>99.4%) was observed, suggesting that these isolates may have originated from the same clone. The prevalence of B. cereus and molecular typing result suggest possible routes of contamination, such as the transfer of clone contaminated in raw materials to the red pepper powder and cross contamination during processing. Based on this result, more intervention studies to prevent pathogen contamination during red pepper powder processing are needed to insure good hygienic level of products.

A recycling process of Mg alloy chips to obtain superconducting MgB2 is proposed. In the present process, mechanical milling was used to mix and grind AZ31 chips and boron powder. Fine AZ31/boron powder mixture can be fabricated via a mechanical milling process. Mechanical milling can reduce the process time to synthesize MgB2 powder. An AZ31/boron mixture via mechanical milling can be reacted completely to MgB2 by heating at 700℃ for 3 h. Sintered MgB2 bodies produced by a pulsed electric current sintering technique showed approximately 30 K as the superconducting critical temperature.

The microstructure and electrical conductivity of CNTs dispersed $Al_2O_3$ nanocomposites depending on the powder processing and CNTs content were demonstrated. The composite powders with homogeneous dispersion of CNTs could be synthesized by a catalytic route for direct formation of CNTs on nano-sized Fe dispersed $Al_2O_3$ powders. The sintered nanocomposite using the composite powder with directly synthesized CNTs showed homogeneous microstructure and enhanced elelctrical conductivity. The influence of powder processing on the properties of sintered nanocomposites was discussed by the observed microstructural features.

The suspension plasma spray (SPS) technique has been used to obtain dense $Y_2O_3$ coatings and to overcome the drawbacks of the conventional air plasma spray (APS). SPS uses suspensions containing micrometer or sub-micrometer sized powders dispersed in liquid media. In this study, microstructure developments and mechanical properties have been investigated as functions of particle size of source material and plasma processing parameters such as plasma power and stand-off distance. The microstructure of the coating was found to be highly related to the particle size and the plasma processing parameters, and it was directly reflected in the hardness and the adhesion strength. When fine powder (BET $16.4m^2/g$) was used as a raw material in the suspension, there was, with increasing stand-off distance, a change from a dense structure with a slightly bumpy surface to a porous structure with a cauliflower-like surface. On the other hand, when a coarse powder (BET $2.8m^2/g$) was used, the coating density was lower, with microscopic splats on the surface. Using fine $Y_2O_3$ powders, the coating layer with an optimum short stand-off distance showed a high hardness of approximately 90% of that of sintered $Y_2O_3$ and an adhesion strength several times higher than that of the coating by conventional APS.

In this paper, CuInSe2 nanostructures have been synthesized via a solvothermal method using diethyamine as a solvent. Various morphologies of CuInSe2 were obtained from the reaction of cupric chloride, indium chloride and selenium powder by changing the solvothermal conditions. The effect of the experimental parameters such as reaction time, temperature and concentration of the selenium powder were studied. The crystalline structures and morphologies of the products were characterized by means of X- ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) techniques,respectively. The results show that the morphology and dimensions of the CIS nanostructures obtained can be controlled through selective processing conditions. The optical properties and band gaps were estimated with a UV-Vis spectrophotometer. The electrical resistances of the samples were recorded by using four point probes.

The effect of compositional and processing variables on a nitriding reaction of silicon powder compact and subsequent post sintering of RBSN (Reaction-Bonded Silicon Nitride) was investigated. The addition of a nitriding agent enhanced nitridation rate substantially at low temperatures, while the formation of a liquid phase between the nitriding agent and the sintering additives at a high temperature caused a negative catalyst effect resulting in a decreased nitridation rate. A liquid phase formed by solely an additive, however, was found to have no effect on nitridation for the additive amount used in this research. The original site of a decomposing pore former was loosely filled by a reaction product ($Si_3N_4$), which provided a specimen with nitriding gas passage. For SRBSN (Sintered RBSN) specimens of high porosity, only a marginal dimensional change was measured after post sintering. Its engineering implication for near-net shaping ability is discussed.

This study examined process?structure relationships in laser powder bed fusion of Al?.₁CoCrFeNi + Cu composites, focusing on densification, elemental distribution, and solidification cracking. Mechanically mixed Al?.₁CoCrFeNi and Cu powders were processed across a range of laser powers (100?250?W) and scan speeds (200?800?mm/s). Increased volumetric energy density (VED) improved densification, with a plateau near 200?J/mm³ yielding ~96% relative density; however, this value was still below application-grade thresholds. At low VED, insufficient thermal input and short melt pool residence times promoted Cu segregation, while higher VED facilitated improved elemental mixing. Elemental mapping showed partial co-segregation of Ni with Cu at low energies. Solidification cracks were observed across all processing conditions. In high VED regimes, cracking exhibited a minimal correlation with segregation behavior and was primarily attributed to steep thermal gradients, solidification shrinkage, and residual stress accumulation. In contrast, at low VED, pronounced Cu segregation appeared to exacerbate cracking through localized thermal and mechanical mismatch.

Mechanochemical processing (MCP) involves several high-energy collisions of powder particles with the milling media and results in the increased reactivity/sinterability of powder. The present paper shows results of mechanochemical processing (MCP) of silicon nitride powder mixture with the relevant sintering additives. The effects of MCP were studied by structural changes of powder particles themselves as well as by the resulting sintering/densification ability. It has been found that MCP significantly enhances reactivity and sinterability of the resultant material: silicon nitride ceramics could be pressureless sintered at $1500^{\circ}C$. Nevertheless, a degree of a silicon nitride crystal lattice and powder particle destruction (amorphization) as detected by XRD studies, is limited by the specific threshold. If that value is crossed then particle's surface damage effects are prevailing thus severe evaporation overdominates mass transport at elevated temperature. It is discussed that the cross-solid interaction between particles of various chemical composition, triggered by many different factors during mechanochemical processing, including a short-range diffusion in silicon nitride particles after collisions with other types of particles plays more important role in enhanced reactivity of tested compositions than amorphization of the crystal lattice itself. Controlled deagglomeration of $Si_3N_4$ particles during the course of high-energy milling was also considered.