• 한국재료학회:학술대회논문집
• /
• 한국재료학회 2011년도 추계학술발표대회
• /
• pp.3.2-3.2
• /
• 2011

Nanofibers, one of various one-dimensional nanomaterials such as nanorods, nanowires and nanotubes have been successfully synthesized by many groups in recent years and their applications to chemical sensors, catalytic filters and biomedicine, etc. are extensively tested. In particular, there is a possibility that chemical sensors based on oxide nanofibers can overcome the shortcomings of chemical sensors based on single nanowires. In order to prepare oxide nanofibers, the electrospinning method is most widely used. In this work, we synthesized various oxide nanofibers including ZnO, SnO2 and CuO by employing an electrospinning method and various shapes of nanofibers including core-shell nanofibers and hollow nanofibers as well. The response properties of the various nanofibers to oxidizing and reducing gaseous species have been investigated systematically. The normal oxide nanofibers showed high sensitivity and quite fast response time to many gaseous species. Furthermore, derivatives of normal nanofibers including hollow nanofibers, core-shell nanofibers and heterostructured nanofibers display much superior sensing properties. These results hold promise for the practical application of oxide nanofibers to chemical sensors. In addition, the sensing mechanisms operated in the nanofibers will be discussed in detail.

• 대한화학회지
• /
• 제37권4호
• /
• pp.416-422
• /
• 1993

${\alpha},{\beta}$-구리 및 무금속의 프탈로시아닌을 비이온성 계면활성제를 사용하여 수용액 중에서 산화아연에 흡착시켰더니, 첨가시킨 색소가 모두 흡착되었다. 계면활성제를 사용하지 않고 술폰화된 프탈로시아닌의 나트륨염인 경우는 Langmuir 단분자 흡착성을 나타내었다. 흡착상태에 따른 증감특성을 알기 위하여 진동용량형 표면 전위계를 사용하여 광기전력을 측정하였더니, 산화아연의 고유파장과 프탈로시아닌 색소의 흡수파장에서 높은 광기전력을 나타내었다. 계면활성제를 이용하여 흡착시킨 프탈로시아닌은 산화아연에 대한 피복율(${\theta}_{BET}$)이 약 80%에서 광기전력이 크게 나타났고, 술폰화된 프탈로시아닌은 피복율(${\theta}_{BET}$)이 약 30% 부근에서 광기전력이 증가하는 경향을 나타내었다.

• Tribology and Lubricants
• /
• 제11권4호
• /
• pp.45-52
• /
• 1995

The wear behavior of alumina short fiber reinforced tin-bronze matrix composites was studied at the room temperature and an elevated temperature. The effect of the composition of specimens and the variation of wear conditions on the wear properties was examined by a pin-on-disc type wear testing machine. The wear mechanism according to the compositon of specimens at various wear conditions was discussed by the observation of the microstructure and the analysis of the composition on the worn surfaces. A thicker oxide layer on worn surfaces led to a lower wear loss because of the lubricating effect of oxide layers between pin and disc. As the testing temperature was raised to 350$^{\circ}$C, the fiber reinforced composites exibited markedly increased wear resistance even at a higher applied load since the reinforcement of composites with alumina fibers was not affected to a large extent by raising temperature. The results obtained by AES and EDS analysis indicated that the oxide layer of the worn surfaces formed at 350$^{\circ}$C was proved as Fe-oxide. This was explained by the faster formation of Fe-oxide than Cu-oxide at 350$^{\circ}$C.

• 한국전기전자재료학회논문지
• /
• 제23권8호
• /
• pp.617-621
• /
• 2010

($K_{0.5}Na_{0.5}$)($Nb_{0.96}Sb_{0.04}$)$O_3$+1.2 mol% $K_4CuNb_8O_{23}$ ceramics doped with iron oxide ($Fe_2O_3$) were prepared by a conventional mixed oxide method. And then, their piezoelectric and dielectric properties were investigated as a function of $Fe_2O_3$ addition. X-ray diffraction studies reveal that $Fe^{3+}$ diffuses into the NKN lattices to form a solid solution with a pure perovskite structure at room temperature. At the sintering temperature of $1,060^{\circ}C$, when 0.2 mol% $Fe_2O_3$ was doped, the piezoelectric constant ($d_{33}$), electromechanical coupling factor (Kp), and mechanical quality factor ($Q_m$) showed the excellent values of 131.67 pC/N, 0.436, and 696.36, respectively. Results show that $Fe_2O_3$ deped ($K_{0.5}Na_{0.5}$)($Nb_{0.96}Sb_{0.04}$)$O_3$+1.2 mol% $K_4CuNb_8O_{23}$ lead-free piezoelectric ceramics are a promising lead free material for piezoelectric transformer applications.

• Ocean and Polar Research
• /
• 제26권2호
• /
• pp.231-243
• /
• 2004

Sequential extraction was carried out on twenty two subsamples of three ferromanganese crusts from three seamounts (Lemkein, Lomilik, and Litakpooki) near the Marshall Islands in the western Pacific. The extraction was designed to fractionate Fe-Mn crust forming elements into low defined groups: (1) exchangeable and carbornate, (2) Mn-oxide, (3) Fe-oxyhyd.oxide, and (4) residual fraction. X-ray diffraction result shows that target material were well removed by each extraction step except for CFA in phosphatized crusts generation. According to chemical analysis of each leachate, most of elements in the Fe-Mn crusts are bound with two major phases. Mn, Ba, Co, Ni, Zn, (Fe, Sr, Cu, and V) are strongly bounded with Mn-oxide $({\delta}-MnO_2)$ phase, whereas Fe, Ti, Zr, Mo, Pb, Al, Cu,(V, P, and Zn) show chemical affinity with Fe-oxyhydroxide phase. This result indicates that significant amount of Al, Ti, and Zr can not be explained by detrital origin. Ca, Mg, K, and Sr mainly occur as exchangeable elements and/or carbonate phase. Outermost layer 1 and inner layer 2 which are both young crusts generations are similar in chemical speciations of elements. However, some of Fe-oxyhydroxide bounded elements (Pb, Y, Mo, Ba, Al, and V) in phosphatized innermost layer 3 are released during phosphatization and incorporated into phosphate (Pb, Y, Mo, and Ba) or Mn-oxide phase (Al and V). Our sequential extraction results reveal that chemical speciations of elements in the hydrogenetic crusts are more or less different from interelemental relationship calculated by statistical method based on bulk chemistry.

• 마이크로전자및패키징학회지
• /
• 제28권2호
• /
• pp.29-37
• /
• 2021

3 차원 패키징을 위한 저온 Cu-Cu직접 접합부의 계면접착에너지를 향상시키기 위해 Cu박막 표면에 대한 Ar/N₂ 2단계 플라즈마 처리 전, 후 Cu표면 및 접합계면에 대한 화학결합을 X-선 광전자 분광법(X-ray photoelectron spectroscopy)을 통해 정량화한 결과, 2단계 플라즈마 처리로 인해 Cu표면에 Cu₄N이 형성되어 Cu산화를 효과적으로 억제하는 것을 확인하였다. 2단계 플라즈마 처리하지 않은 Cu-Cu시편은 표면 산화막의 영향으로 접합이 제대로 되지 않았으나 2단계 플라즈마 처리한 시편은 효과적인 표면 산화방지효과로 인해 양호한 Cu-Cu접합을 형성하였다. Cu-Cu직접접합 계면의 정량적 계면접착에너지를 double cantilever beam 시험방법 및 4점 굽힘(4-point bending, 4-PB) 시험방법을 통해 비교한 결과, 각각 1.63±0.24, 2.33±0.67 J/m²으로 4-PB 시험의 계면접착에너지가 더 크게 측정되었다. 이는 계면파괴역학의 위상각(phase angle)에 따른 계면접착에너지 증가 거동으로 설명할 수 있는데 즉, 4-PB의 계면균열선단 전단응력성분 증가로 인한 계면거칠기의 효과에 기인한 것으로 판단된다.

• Transactions on Electrical and Electronic Materials
• /
• 제10권4호
• /
• pp.135-139
• /
• 2009

$H_2S$ micro-gas sensors have been developed employing $SnO_2$:CuO composite thin films. The films were prepared by e-beam evaporation of Sn and Cu metals on silicon substrates, followed by oxidation at high temperatures. Results of various studies, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal that $SnO_2$ and CuO are mutually non-reactive. The CuO grains, which in turn reside in the inter-granular regions of $SnO_2$, inhibit grain growth of $SnO_2$ as well as forming a network of p-n junctions. The film showed more than a 90% relative resistance change when exposed to $H_2S$ gas at 1 ppm in air at an operating temperature of $350^{\circ}C$ and had a short response time of 8 sec.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2009년도 하계학술대회 논문집
• /
• pp.160-161
• /
• 2009

In this study, in order to develop the lead free piezoelectric ceramics with excellent piezoelectric properties, (Na,K)$NbO_3$ ceramics according to the amount CuO addition were fabricated using a conventional mixed oxide process and their piezoelectric and dielectric characteristics were investigated. At the 0.8mol% CuO added composition, density, electromechanical coupling factor(kp), echanical quality factor(Qm), dielectric constant$(\varepsilon_r$) and piezoelectric constant($d_{33}$) showed the optimum value of $4.459g/cm^3$, 0.469, 540, 410, 69.57pC/N, respectively.

• 한국재료학회지
• /
• 제28권10호
• /
• pp.578-582
• /
• 2018

ZnO crystals with different morphologies are synthesized through thermal evaporation of the mixture of Zn and Cu powder in air at atmospheric pressure. ZnO crystals with wire shape are synthesized when the process is performed at $1,000^{\circ}C$, while tetrapod-shaped ZnO crystals begin to form at $1,100^{\circ}C$. The wire-shaped ZnO crystals form even at $1,000^{\circ}C$, indicating that Cu acts as a reducing agent. As the temperature increases to $1,200^{\circ}C$, a large quantity of tetrapod-shaped ZnO crystals form and their size also increases. In addition to the tetrapods, rod-shaped ZnO crystals are observed. The atomic ratio of Zn and O in the ZnO crystals is approximately 1:1 with an increasing process temperature from $1,000^{\circ}C$ to $1,200^{\circ}C$. For the ZnO crystals synthesized at $1,000^{\circ}C$, no luminescence spectrum is observed. A weak visible luminescence is detected for the ZnO crystals prepared at $1,100^{\circ}C$. Ultraviolet and visible luminescence peaks with strong intensities are observed in the luminescence spectrum of the ZnO crystals formed at $1,200^{\circ}C$.

• 한국전기전자재료학회논문지
• /
• 제23권5호
• /
• pp.379-382
• /
• 2010

In this study, in order to develop the lead-free piezoelectric ceramics with high piezoelectric and dielectric properties, $(K_{0.5}Na_{0.5})(Nb_{0.97}Sb_{0.03})O_3$ ceramics were fabricated using a conventional mixed oxide process and their piezoelectric and dielectric characteristics were investigated according to the $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition. $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition enhanced density, electromechanical coupling factor($k_p$) piezoelectric constant $d_{33}$ and mechanical quality factor($Q_m$). At the 0.9 mol% $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition, density, electromechanical coupling factor($k_p$), dielectric constant(${\varepsilon}_r$) and piezoelectric constant($d_{33}$) of specimen showed the optimum values of 0.46, 471, and 148 pC/N, respectively.