• Nuclear Engineering and Technology
• /
• v.53 no.12
• /
• pp.3952-3965
• /
• 2021

In this study, volcanic ash was used as raw material to prepare waste forms with different silicon/aluminum (Si/Al) molar ratios to immobilize sodium-salt waste (SSW) containing simulated ¹³⁷Cs. Effects of Si/Al molar ratios (3:1 and 2:1) and sodium salts on sintering behavior of waste forms and immobilization mechanism of Cs⁺ were investigated. Results indicated that the main mineral phase of sintered waste-form matrixes was albite, and the formation of major phases was found to depend on Si/Al molar ratios. Si/Al molar ratio of 2 was favorable for the formation of pollucite, and the formation and crystallization of mineral phases were also decided based on physicochemical characteristics of sodium salts. Furthermore, product consistency test results indicated that the immobilization of Cs⁺ was related to Si/Al molar ratio, types of sodium salts, and glassy phase. Waste forms with Si/Al molar ratio of 2 exhibited better ability to immobilize Cs⁺, whereas the influence of sodium salts and glassy phases on the immobilization of SSW showed more complicated relationship. In waste forms with Si/Al molar ratio of 2, Cs⁺ leaching concentrations of samples containing Na₂B₄O₇·10H₂O and NaOH were low. Na₂B₄O₇·10H₂O easily transformed into liquid phase during sintering to consequently achieve low temperature liquid-phase sintering, which is beneficial to avoid the volatilization of Cs⁺ at high temperature. Results clearly reveal that waste forms with Si/Al molar ratio of 2 and containing Na₂B₄O₇·10H₂O show excellent immobilization of Cs⁺.

• Nuclear Engineering and Technology
• /
• v.53 no.8
• /
• pp.2582-2590
• /
• 2021

The high-energy milling is one of the most extended techniques to produce Oxide dispersion strengthened (ODS) powder steels for nuclear applications. The consequences of the high energy mill process on the final powders can be measured by means of deformation level, size, morphology and alloying degree. In this work, an ODS ferritic steel, Fe-14Cr-5Al-3W-0.4Ti-0.25Y₂O₃-0.6Zr, was fabricated using two different mechanical alloying (MA) conditions (M_std and M_act) and subsequently consolidated by Spark Plasma Sintering (SPS). Milling conditions were set to evidence the effectivity of milling by changing the revolutions per minute (rpm) and dwell milling time. Differences on the particle size distribution as well as on the stored plastic deformation were observed, determining the consolidation ability of the material and the achieved microstructure. Since recrystallization depends on the plastic deformation degree, the composition of each particle and the promoted oxide dispersion, a dual grain size distribution was attained after SPS consolidation. M_act showed the highest areas of ultrafine regions when the material is consolidated at 1100 ℃. Microhardness and small punch tests were used to evaluate the material under room temperature and up to 500 ℃. The produced materials have attained remarkable mechanical properties under high temperature conditions.

• Korean Journal of Materials Research
• /
• v.21 no.7
• /
• pp.384-390
• /
• 2011

Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. $Ti_2O$, CaO, $CaTiO_3$, and $Ti_xP_y$ phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.

• Journal of Powder Materials
• /
• v.18 no.3
• /
• pp.250-255
• /
• 2011

The potential application of ultrafine cerium oxide (ceria, $CeO_2$) as an oxygen gas sensor has been investigated. Ceria was synthesized by a thermochemical process: first, a precursor powder was prepared by spray drying cerium-nitrate solution. Heat treatment in air was then performed to evaporate the volatile components in the precursor, thereby forming nanostructured $CeO_2$ having a size of approximately 20 nm and specific surface area of 100 $m^2/g$. After sintering with loosely compacted samples, hydrogen-reduction heat treatment was performed at 773K to increase the degree of non-stoichiometry, x, in $CeO_{2-x}$. In this manner, the electrical conductivity and oxygen-response ability could be enhanced by increasing the number of oxygen vacancies. After the hydrogen reduction at 773K, $CeO_{1.5}$ was obtained with nearly the same initial crystalline size and surface. The response time $t_{90}$ measured at room temperature was extremely short at 4 s as compared to 14 s for normally sintered $CeO_2$. We believe that this hydrogen-reduced ceria can perform capably as a high-performance oxygen sensor with good response abilities even at room temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.11a
• /
• pp.260-260
• /
• 2009

In high-efficiency crystalline silicon solar cell, If high-efficiency solar cells are to be commercialized, It is need to develop superior contact formation method and material that can be inexpensive and simple without degradation of the solar cells ability. For reason of plated metallic contact is not only high metallic purity but also inexpensive manufacture. It is available to apply mass production. Especially, Nickel, Copper are applied widely in various electronic manufactures as easily formation is available by plating. Ni is shown to be a suitable barrier to Cu diffusin as well as desirable contact metal to silicon. Nickel monosilicide has been suggested as a suitable silicide due to its lower resistivitym lower sintering temperature and lower layer stress than $TiSi_2$. In this paper, Nickel as a seed layer and diffusion barrier is plated by electroless plating to make nickel monosilicide.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.21 no.6
• /
• pp.926-931
• /
• 2012

Rotary bar was cutting tool being in use for deburring scale after welding metal and for eliminating sharp edges. It was necessary to develop exclusive 6-axis machine being possible to process machining continuously for making an cutting edge of rotary bar and to revise easily machining program. This study aimed at the structural analysis of strength according to the configuration of new made 6-axis machine and at the machining accuracy and durability of rotary bar. As a result of test, the runout of new rotary bar manufactured out of 6-axis machine was decreased from 0.385 mm to 0.027mm extensively than old one. And good cutting ability and durability was obtained equal quality compared with imported products.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1311-1312
• /
• 2006

Diamond tools were fabricated by cold pressing and sintering under pressure at the temperature up to $750^{\circ}C$. Investigation of the microhardness behaviour of the segments was showed that increasing the cobalt ratio causes the increase of the hardness of the matrix material. This caused to decrease of the wear rate of the matrix. Because the matrix wears more slowly than the diamonds, the space between the cutting edges and the matrix is constantly reduced. The swarf cannot be carried away properly, and the segment will continuously lose its ability to cut with higher cobalt contents.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.134-135
• /
• 2006

Ancorsteel 4300, a high performance Cr-Si-Ni-Mo steel, was unveiled two years ago as the first in a series of powder metallurgy alloys that will simulate wrought steel compositions. Advantages of this alloy include good compressibility, high hardenability, and excellent dimensional stability. More important, however, is that this alloy has the ability to be effectively sintered at $1120^{\circ}C$ and maintain oxygen contents below 500 ppm. This unique blend of performance and processing capabilities provides static and dynamic properties that exceed those of conventional powder metallurgy alloys and approach wrought gearing materials. A second Cr-Si-Ni-Mo alloy has now been developed that offers complimentary performance levels at a lower Mo content. This manuscript reviews properties of the two chromium steels with comparisons to traditional sinter-hardened and heat-treated powder metallurgy alloys.

• Electronic Materials Letters
• /
• v.14 no.6
• /
• pp.657-668
• /
• 2018

Organic-inorganic hybrid lead halide perovskites have been extensively investigated for various optoelectronic applications. Particularly, owing to their ability to form highly crystalline and homogeneous films utilizing low-temperature solution processes (< $150^{\circ}C$), perovskites have become promising photoactive materials for realizing high-performance flexible solar cells. However, the current use of mesoporous $TiO_2$ scaff olds, which require high-temperature sintering processes (> $400^{\circ}C$), has limited the fabrication of perovskite solar cells on flexible substrates. Therefore, the development of a low-temperature processable charge-transporting layer has emerged as an urgent task for achieving flexible perovskite solar cells. This review summarizes the recent progress in low-temperature processable electron- and hole-transporting layer materials, which contribute to improved device performance in flexible perovskite solar cells.

• Journal of Power System Engineering
• /
• v.15 no.6
• /
• pp.67-72
• /
• 2011

In the present study, crack healing effect and residual stress of $Al_2O_3$ ceramics were investigated by changing the sintering temperature and heat treatment conditions. And also it was investigated that the influence of different filler loadings of nano-sized SiC particles on the crack healing behavior of $Al_2O_3$ ceramics. The test samples were characterized by three point bend flexural tests to evaluate their mechanical properties. The morphological changes were studied by FE-SEM and EDS. The test results indicated that the $Al_2O_3$ with nano-sized SiC ceramics sintered at $1800^{\circ}C$ were showed highest density. Sintering temperature at $1800^{\circ}C$, the bending strength of heat treatment in air atmosphere specimens showed about 42 % increment in comparison to the un-heat treated specimens. The cracked specimens can be healed by heat treatment in vacuum atmosphere but the crack healing effect of $Al_2O_3$ ceramics, which is heat treated in air atmosphere was higher than that of heat treated in vacuum atmosphere. $Al_2O_3$ with 30 wt% of SiC ceramics indicated higher crack healing ability than that with 15 wt% of SiC ceramics. The FE-SEM images showed that the median cracks and pores were disappeared after heat treatment in air.