• Nuclear Engineering and Technology
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• 제56권1호
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• pp.106-113
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• 2024

Understanding the tritium release and retention behavior of candidate tritium breeder materials is crucial for breeder blanket design. Recently, a melt spraying process was developed to prepare Li₄SiO₄ pebbles, which were subsequently subjected to the in-pile tritium production and extraction platform in China Mianyang Research Reactor (CMRR) to investigate their in-situ tritium release behavior and irradiation performance. The results demonstrate that HT is the main tritium release form, and adding hydrogen to the purge gas reduces tritium retention while increasing the HT percent in the purge gas. Post-irradiation experiments reveal that the irradiated pebbles darken in color and their grains swell, but the mechanical properties remain largely unchanged. It is concluded that the tritium residence time of Li₄SiO₄ made by melt spraying method at 467 ℃ is approximately 23.34 h. High-density Li₄SiO₄ pebbles exhibit tritium release at relatively low temperatures (<600 ℃) that is mainly controlled by bulk diffusion. The diffusion coefficient at 525 ℃ and 550 ℃ is 1.19 × 10^-11 cm²/s and 5.34 × 10^-11 cm²/s, respectively, with corresponding tritium residence times of 21.3 hours and 4.7 hours.

• 한국재료학회지
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• 제24권2호
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• pp.116-122
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• 2014

$Bi_2Sr_2CaCu_2O_x$(Bi-2212) and $Bi_2Sr_2Ca_2Cu_3O_y$(Bi-2223) high-Tc superconductors(HTS) have been manufactured by plasma spraying, partial melt process(PMP) and annealing treatment(AT). A Bi-2212/2223 HTS coating layer was synthesized through the peritectic reaction between a 0212 oxide coating layer and 2001 oxide coating layer by the PMP-AT process. The 2212 HTS layer consists of whiskers grown in the diffusion direction. The Bi-2223 phase and secondary phase in the Bi-2212 layer were observed. The secondary phase was distributed uniformly over the whole layer. As annealing time goes on, the Bi-2212 phase decreases with mis-orientation and irregular shape, but the Bi-2223 phase increases because a new Bi-2223 phase is formed inside the pre-existing Bi-2212 crystals, and because of the nucleation of a Bi-2223 phase at the edge of Bi-2212 crystals by diffusion of Ca and Cu-O bilayers. In this study the spray coated layer showed superconducting transitions with an onset Tc of about both 115 K, and 50 K. There were two steps. Step 1 at 115 K is due to the diamagnetism of the Bi-2223 phase and step 2 at 50 K is due to the diamagnetism of the Bi-2212 phase.

• 동력기계공학회지
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• 제9권4호
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• pp.90-95
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• 2005

The wire-arc process is a low-cost thermal spray method simply utilizes electrical energy to melt the feedstock wire. It is more userful for field applications, especially to coat large surface area. In this paper, a special Fe-based alloy coatings by using the wire-arc process were developed. Nanoscale composite coatings were achieved either during spraying or through a post heat treatment. As-sprayed Fe-based alloy coatings had been an amorphous matrix structure, after heating to $700^{\circ}C$ for 10 minutes a solid state transformation occurred in the some fraction of amorphous matrix which resulted in the formation of nanostructured recrystallized phase. Scanning electron microscopy (SEM) and field emotional scanning electron microscope(FE-SEM) were applied to analyze the microstructure of the coatings. Additionally hardness and bend resistance of the Fe-based alloy coatings were examined, and these results were compared with those of partially stabilized zirconia(PSZ) coatings by using the plasma spray process.

• 접착 및 계면
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• 제14권2호
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• pp.95-100
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• 2013

본 연구에서는 메탈로센 폴리올레핀(metallocene polyolefin, me-PO)과 점착부여제(tackifier)를 이용해 열용융형 감압접착제(hot-melt pressure sensitive adhesives, HMPSAs)를 제조하여 물리적 특성을 확인하였고, me-PO가 HMPSAs의 용도에서 스타이렌계 블록 코폴리머(styrenic block copolymers, SBCs)를 대체하여 사용 가능한지에 대해 고찰하였다. 또한, me-PO를 베이스 폴리머로 사용한 HMPSAs의 성능을 최적화하기 위하여 점착부여제가 가져야 할 특성을 알아보고자 하였다. me-PO를 이용하여 Dahlquist Criterion을 만족하는 HMPSAs를 얻기 위해서는 점착부여제와 함께 10% 이상의 프로세스 오일을 혼합 사용하여야 했고, Spray Type의 Applicator에 적합한 수준의 점도를 가지는 HMPSAs를 얻기 위해서는 상대적으로 결정화도가 낮은 제2의 me-PO를 사용해야 했다. 그리고, 분자량이 큰 점착부여제를 사용하면 SBCs계 HMPSAs에 비해 부족한 유지력을 개선시키는데 기여하는 것으로 밝혀졌다.

• 한국자동차공학회논문집
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• 제22권5호
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• pp.20-28
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• 2014

The high velocity oxygen fuel spraying (HVOF) is a kind of surface modification process technology to form the sprayed coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. It is desirable to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesion, however, because a semi-molten powder in a spray process has the low efficiency and become a factor that degrades the mechanical property by the inducement of pore-forming within the coating layer. To improve the wear resistance, corrosion resistance and heat resistance, in this study, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps for oil and water used in ironwork are produced with $420J_2$ and the coating layers of plungers are formed by the powders of WC-Co-Cr and WC-Cr-Ni including the high hardness WC. The surface of these plungers is modified by the super-mirror face grinding machine using variable air pressure developed in this laboratory, and then the characteristics of cross-sectional microstructure, and surface roughness and hardness values between no operation and 100 days-operation are examined and made a comparison. The fine tops and bottoms on surface roughness curve of oil-hydraulic pump plunger sprayed by WC-Cr-Ni are molded more and higher than those of water-hydraulic pump sprayed by WC-Co-Cr because the plunger diameter of oil-hydraulic pump is 0.4 times smaller than that of water-hydraulic pump and the pressure of oil-hydraulic pump exerted on the plunger is operated with the 70 bars higher than that of water-hydraulic pump. As a result, it is found that the values of centerline average surface roughness and maximum height for oil-hydraulic pump plunger are bigger than those of water-hydraulic pump plunger.

• 한국분무공학회지
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• 제11권2호
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• pp.59-68
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• 2006

Experimental results of the metal powder production with internal mixing, internal impinging and the atomizer coupled with substrate design are presented in this paper. In a test with internal mixing atomizer, mean powder size was decreased from $37{\mu}m\;to\;23{\mu}m$ for Pb65Sn35 alloy as the gas-to-melt mass ratio was increased from 0.04 to 0.17. The particle size further reduces to $16.01{\mu}m$ as the orifice area is increased to $24mm^2$. The micrograph of the metal powder indicates that very fine and spherical metal powder has been produced by this process. In a test program using the internal impinging atomizers, the mean particle size of the metal powder was decreased from $22{\mu}m\;to\;12{\mu}m$ as the gas-to-melt-mass ratio increased from 0.05 to 0.22. The test results of an atomizer coupled with a substrate indicates that the deposition rate of the molten spray on the substrate is controlled by the diameter of the substrate, the height of the substrate ring and the distance of the substrate from the outlet of the atomizer. This in rum determines the powder production rate of the spraying processes. Experimental results indicate that the deposition rate of the spray forming material decreases as the distance between the substrate and the atomizer increases. For example, the deposition rate decreases from 48% to 19% as the substrate is placed at a distance from 20cm to 40cm. On the other hand, the metal powder production rate and its particle size increases as the subsrate is placed far away from the atomizer. The production of metal powder with mean particle size as low as $3.13{\mu}m$ has been achieved, a level which is not achievable by the conventional gas atomization processes.

• 한국표면공학회지
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• 제46권5호
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• pp.181-186
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• 2013

We performed plasma spraying for 2001 (Bi:Cu = 2:1), 0212 (Sr:Ca:Cu = 2:1:2) oxide powders. $Bi_2Sr_2CaCu_2Ox$ (2212) superconductor has been prepared by PMP-AT (partial melting process-annealing treatment). The 2212 phase is synthesized between Sr-Ca-Cu oxide coating layer (0212) and Bi-Cu oxide coating layer (2001) by movement of partial melted Bi on 2001 layer and the diffusion reaction (Cu, Sr, Ca) after PMP-AT. There are two different coating layers on joining process. The one is ABAB coating layers and the other is BAAB coating layers by arrangement of 2001 (A), 0212 (B) layers. We performed heat treatment these two different coating layers processes under same PMP-AT conditions. We obtained Bi-2212 superconducting layers at each experimental condition, and the result of MPMS, the critical temperature was showed about 78 K. But the microstructure images and result of EDS as each experimental variable were showed about the qualitatively different Bi-2212 superconducting phases. We also deduced the generation mechanism of Bi-2212 superconducting layer as a result of these experimental data, microstruc ture images, EDS data and phase diagram.

• 한국자동차공학회논문집
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• 제24권3호
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• pp.285-293
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• 2016

The high velocity oxygen fuel(HVOF) thermal spray is a kind of surface modification techniques to produce the sprayed coating layer. This process is to form the coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. The efficiency of thermal spraying is dropped, however, because the semi-molten powder in a spray process become a factor that degrades the mechanical property by the formed pore within the coating layer. Therefore, it is necessary to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesive force. In this study, to improve the wear resistance, corrosion resistance and heat resistance, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps used in ironworks are manufactured with STS $420J_2$ and are coated by the powders of WC-Co-Cr and WC-Cr-Ni including the WC of high hardness using a HVOF thermal sprayer developed in this laboratory. These are called by the surface-modified plungers. The surface roughness, hardness, and surface and cross-sectional microstructure of these two surface-modified and conventional ceramic plungers are measured and compared before operation with after operation for 100 days. It is found that the values of centerline average surface roughness and maximum height for conventional ceramic plunger are 9.5 to 10.8 and 5.2 to 5.7 times higher than those of surface-modified ones coated by WC-Co-Cr and WC-Cr-Ni because the fine tops and bottoms on surface roughness curve of conventional ceramic plunger are approximately 100 times higher than those of surface-modified ones. In addition, the pores and scratches in the surface microstructure are considerably formed in the order of conventional ceramic, WC-Cr-Ni and WC-Co-Cr surface-modified plungers. The greater the WC content of high hardness powder is less the change in the plunger surface.