• Journal of Advanced Marine Engineering and Technology
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• v.19 no.3
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• pp.50-61
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• 1995

In recent years, many ceramic researchers have discoved various methods of joining ceramic to metal. However, most of these joining methods are perfomed under vacuum and pressured circumstances. So, when we join ceramic to metal,the proceedings are very complicated and require a very high cost. The purpose of this study is to develop a new joining method of an alumina ceramic to an aluminum metal in air atmosphere. The joining condition, such as copper metallizing, nickel plating, brazing, etc. was investigated through the shear strength test of the trial joint. The results obtained from the above experimenta are summarized as follows : 1) In the case of the $Al_2O_3$/$Al_2O_3$joint, the shear strength of the joint was affected by the various foctor such as kaolin content, copper metallizing thickness, firing temperature, firing time. 2) The better shear strength of the $Al_2O_3$/Al joint was obtained when Ni plating was conducted under higher current density than existing plating condition. 3) The shear strength of the $Al_2O_3$/Al joint increases with the Ni plating thickness is confined to the range of this paper. 4) The shear strength of the thermal-shocked specimen($Al_2O_3$/Al joint) was far more deteriorated than that of the as-bonded specimen.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.3
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• pp.463-470
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• 1996

Ceramic membrane consisting of an ${\alpha}-Al_{2}O_{3}$ support and Fe doped $TiO_{2}$ top layer was prepared by the sol-gel method. The supported Fe doped $TiO_{2}$ top layer was made by dip coating the support in a mixed sol. The microstructure of the composite membranes was studied by SEM after calcination at $550~850^{\circ}C$. After sintering at $650^{\circ}C$ for 1 hr., the average particle diameter of the Fe doped $TiO_{2}$ top layer was ~40 nm. The supported Fe doped $TiO_{2}$ composite membranes exhibited much higher heat resistance than the $TiO_{2}$ membrane. The Fe doped $TiO_{2}$ composite membrane retained a crack-free microstructure and narrow particle size distribution even after calcination up to $650^{\circ}C$.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.1
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• pp.14-20
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• 2003

Piezoelectric ultrasonic transducers for high temperature contact measurement were developed. These high temperature ultrasonic transducers (HTUT) consisted of bismuth titanate piezoceramic element whose Curie temperature is higher than $600^{\circ}C$, a backing material of the mixture of tungsten powder and inorganic binder, an inner alumina tube, a wear Plate and a housing. The operational frequencies or the HTUT were 1.04 and 2.08 MHz, respectively. Various commercially available couplants for high temperature were evaluated and compared. As a couplant for high temperature ultrasonic testing between HTUT and test specimen, gold epoxy was selected. The peak amplitude of pulse-echo signals from steel test specimen decreased with increasing temperature. The operational temperature of the HTUT reached up to $500^{\circ}C$ at which the continuous contact measurement was possible.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.3 s.40
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• pp.33-38
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• 2006

Aerosol slurry composed of dielectric materials, distilled water, and deflocculants was sprayed on the substrates, through a high-pressure spray gun as an aerosol. The coated layers were cofired together with $Al_{2}O_{3}$ substrates and green sheets on which the inner connectors were printed. Although the coating rate of coated layers strongly depended on slurry viscosity, spray shape, and the pressure of the spray gun, the coated density was not changed. Buried conductors were maintained as printed by high pressure spray coating method, because the pressing process was not used. At the optimum condition of air controller step 3-4 and slurry viscosity c.p 2000-4000, dense and uniform layers could be achieved. Comparing with conventional lamination process using green sheets, spray coating method enabled thin dielectric layers of $20{\sim}50{\mu}m$.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.129-129
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• 2017

열전재료는 열에너지를 전기에너지로 또는 전기에너지를 열에너지로 직접 변환하는데 가장 널리 사용되는 재료이다. $Bi_2Te_3$계 열전 재료는 400K 이하의 비교적 저온 영역에서 높은 성능지수(Dimensionless Figure of merit, ZT($={\alpha}2{\sigma}T/{\kappa}$, ${\alpha}$: 제백계수, ${\sigma}$: 전기전도도, T: 절대온도, ${\kappa}$: 열전도도))를 나타내는 열전재료이며 자동차 시트나 정수기 등에 응용되고 있다. 열전모듈은 제조시 수십 개에서 수백 개 이상의 n형 및 p형 열전소자를 알루미나($Al_2O_3$)와 같은 세라믹 기판(substrate) 상에 접합된 동 전극 위에 전기적으로 서로 직렬로 접합시켜 제조한다. 기존의 열전모듈의 제조방법에는 동 전극 위에 위에 Sn합금 분말과 플럭스(flux)의 혼합물인 솔더페이스트를 스크린 인쇄법을 사용하여 동 전극에 도포한 다음, 그 위에 열전소자를 얹고 약 520K의 열풍을 가하여 솔더를 용융시켜 열전소자와 동 전극을 접합시킨다. 스크린 인쇄법에서는 인쇄 압력이 일정하지 않으면, 솔더페이스트 층의 두께가 균일하지 않게 되어 열전소자 접합부의 불량을 유발시킨다. 그러나 열모듈은 단 하나의 접합 불량이 모듈 전체의 열전변환성능에 심각한 영향을 줄 수 있기 때문에 본 연구에서는 이러한 문제점을 해결하기 위해, 솔더페이스트를 도포하지 않고 열전소자를 직접 동 전극과 접합할 수 있는 방법을 고안하였다. 무전해도금을 이용한 니켈층을 형성시킨 $Bi_2Te_3$계 열전소자 표면에 약 $50{\mu}m$의 주석도금층을 전기도금법을 구사하여 형성시켰다. 그 후, wire cutting을 통하여 $3mm{\times}3mm{\times}3mm$의 크기로 절단한 주석도금된 열전소자를 동 전극에 얹고 1.1KPa의 압력을 가하면서 523K의 핫플레이트 위에서 3분간 방치하여 직접(direct) 열압착 접합을 실시하였다. 접합부의 단면을 SEM을 이용하여 관찰한 결과, 동 전극과 열전소자 사이의 계면에 용융 후 응고된 주석층이 결함없이 균일하게 형성된 양호한 접합부를 관찰할 수 있었다. 따라서, 솔더페이스트를 이용하지 않고, 열전소자 표면에 주석도금을 실시한 후, 동 전극과 직접 열압착 본딩을 실시하는 방법은 균일한 접합계면을 얻을 수 있는 새로운 공정으로 기대된다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.81-81
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• 2018

Bi-Te계 열전소자는 상온에서의 열전 효율이 우수하기 때문에 항공, 컴퓨터 등의 열전발전 또는 열전냉각 모듈에 널리 사용된다. 이 열전소자를 활용한 열전모듈은 다수의 n형 및 p형 열전소자가 세라믹 위에 형성된 Cu 전극에 전기적으로 직렬이 되도록 서로 솔더링 접합이 되어 있는 구조를 가지고 있다. 이처럼 직렬 연결된 방식에서는 높은 접합강도를 필요로 한다. 열전모듈 제작 시 Bi-Te 계 소자를 바로 Cu 기판에 접합시키면 솔더에 들어있는 Sn과 기판의 Cu가 접합하는 과정에서 소재 내로 확산하여 접합강도를 저하시킨다. 이러한 열전모듈의 접합강도 저하를 막기 위해 무전해 Ni-W-P 도금층을 확산 방지층으로 적용하였다. 본 연구에서는 Ni-W-P 도금이 Bi-Te 계 열전 모듈의 접합강도에 미치는 영향을 조사하였다. 본 연구에서는 Bi-Te계 열전소자에 양호한 밀착성을 가지는 Ni-W-P 도금층을 형성시키기 위해서 알루미나 분말을 이용한 sand-blasting 방법을 사용하여 Bi-Te 소재 표면에 분사하는 방법으로 표면을 거칠게 하였다. 그 후 무전해 Ni-W-P 도금을 $85^{\circ}C$에서 20분간 실시하여 약 4um의 Ni-W-P 도금층을 형성시켰다. 열전 모듈은 Sn-Ag-Cu 솔더를 사용하여 제작하였으며 접합강도는 Bonding tester를 사용하여 측정하였다. 제작한 열전 모듈의 단면 및 파단면 관찰을 통하여 접합강도가 변하는 요인을 조사하였다. 제작한 열전 모듈의 단면을 FE-EPMA로 관찰한 결과 Ni-W-P 도금층이 Bi-Te 소자와 Sn과 Cu사이의 확산을 방지하는 확산방지층 역할을 하는 것을 관찰할 수 있었다. 또한 열처리 전 열전모듈과 200도, 150시간 열처리 후 접합강도를 각각 측정해 본 결과, 열처리 후의 접합강도가 상승하는 것을 확인 할 수 있었다. 따라서 Bi-Te계 열전모듈 제작에 무전해 Ni-W-P 도금층을 형성시키므로 인해 확산방지층의 생성과 접합강도의 상승에 도움을 주었다.

• Korean Journal of Materials Research
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• v.8 no.10
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• pp.879-883
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• 1998

In the vacuum casting process for superalloys, molten metal are poured into the heated ceramic mold up to $1000^{\circ}C~1700^{\circ}C$. The mold has to have the high temperature strength during casting and made by hlgh purity alumina. In this sturdy, the mold was made by low purity alumina and changed silica contents intended to have high strength The 7.7wt.% SiOz specimens have 10- 55% higher strength than others in room and high temp. Therefore, the cast mold has been developed in this study for single crystal vacuum cast by controlling the ratio of fused alumina and colloidal silica which are used commercially for conventional casting in industries.

• Journal of the Korean Institute of Gas
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• v.23 no.5
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• pp.24-34
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• 2019

In this study, the experimental studies were conducted to analyzing characteristics of combustion and flame stabilizing according to with and without water tube in boiler. The burner has consisted of SiC foam where has the location of submerged flame between a ceramic board acting as flash-back arrestor. Porous burner is also insulated to minimize heat loss in the radial direction. In the condition of fixed equivalence ratio, the flame mode was divided into three stability zones by the flow rate. The main factor for blow-off and flash-back depends on mixture flow rate. Consequently, the case of burner with water-tube has higher NOx emissions than without case. This result explains that the presence of water-tube makes the heat loss resistant to ambient temperature with increasing of NOx. This tendency was proved by predicting the relationship between O₂ emission and NO production rate, and by analysing temperature profiles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.397-397
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• 2007

Diamondlike carbon (DLC) coatings were deposited on alumina ceramic seals using a plasma immersion ion deposition technique (PIID). Then they were subjected to tribological tests using a pin-on-disc tribometer under a high load (1.3 GPa) and under elevated temperatures up to 400C. Coefficients of friction (COFs) were recorded and compared with that of the untreated alumina while the wear tracks were analyzed using SEM with EDS to characterize the DLC films. To enhance the DLC adhesion to the substrate, various interlayers including Si and Cr were deposited using the PIID process or an ion beam assisted deposition (IBAD) method. It was observed that the DLC coating, if adhering well to the substrate, reduced the COFs significantly, from 0.4-0.8 for the uncoated alumina to about 0.05-0.1, within the tested temperature range. The adhesion was determined by the interlayer type and possibly by the application method. Cr interlayer did not perform as well as the Si interlayer. This could also be due to the fact that the Cr interlayer and the subsequent DLC coating had to be done in two different processing systems, while both the Si interlayer and the subsequent DLC film were deposited in one system without breaking the chamber. The coating failure mode was found to be delamination between the Cr and the alumina substrate. In contrast, the Si interlayer with proper DLC deposition procedures resulted in very good adhesion and hence excellent tribological performance. Further study may lead to future DLC applications of ceramic seals.

• Journal of Technologic Dentistry
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• v.46 no.3
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• pp.107-113
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• 2024

Purpose: This study aimed to develop dental alumina ceramic dressers, evaluate their abrasive wear characteristics based on particle size, and identify dental dressers with optimal particle size and performance. Methods: Commercial ceramic dressers (n=5) were selected as the control group, whereas alumina ceramic dressers with 80-grit and 120-grit particles were fabricated as the experimental groups (n=5 each). Prepared specimens were assessed for surface roughness, wear resistance, and abrasiveness against a wear-inducing element (SUS304 stainless steel ball). Means and standard deviations were calculated for each test. Statistical analysis was performed using the Kruskal-Wallis H test with Bonferroni correction (α=0.05) via SPSS Statistics ver. 23.0 (IBM). Results: Surface roughness was highest in the 80-grit group (22.734±1.308 ㎛), followed by 120-grit group (21.804±0.785 ㎛), and lowest in control group (15.782±0.223 ㎛). Wear resistance was greatest in 120-grit group (0.007±0.002 g), followed by the 80-grit group (0.007±0.004 g), and lowest in the control group (0.370±0.010 g). Furthermore, abrasiveness against the wear-inducing element (SUS304 stainless steel ball) was highest in 120-grit group (0.017±0.003 g), followed by the 80-grit group (0.015±0.003 g), and lowest in control group (0.010±0.001 g). Conclusion: Based on the combined results of surface roughness, wear resistance, and abrasiveness against a wear-inducing element, the newly developed alumina ceramic dressers show promise for clinical application.