• 한국세라믹학회지
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• 제39권8호
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• pp.715-720
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• 2002

Silicon nitride samples with aligned whisker seeds were prepared with different amounts of yttria and alumina as the sintering additives. Their sintering behaviors and the microstructural developments between 2123K and 2323K were examined. The sample with larger amount of the sintering additives showed faster densification and grain growth. Even though addition of the aligned whisker seeds slightly retarded densification of silicon nitride, it improved the flexural strength and the fracture toughness. Both the flexural strength and the fracture toughness of silicon nitride with the aligned whisker seeds were increased as the amount of the sintering additives was increased.

• 한국세라믹학회지
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• 제40권8호
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• pp.720-724
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• 2003

Aluminum nitride (AlN) powders were synthesized by using a mixture of an aluminum nitrate or sulfate salt and carbon (mole ratio of $Al^{3+}$ to carbon=L : 30). The AlN was obtained by calcining the mixture under a flow of nitrogen in the temperature range 1100-1$600^{\circ}C$ and then burning out the residual carbon. The process of conversion of the salt to AlN was monitored by XRD and $^{27}$ Al magic-angle spinning (MAS) NMR spectroscopy. The salt decomposed to ${\gamma}$-alumina and then converted to AlN without phase transition from ${\gamma}$-to-$\alpha$-alumina. $^{27}$ Al MAS NMR spectroscopy shows that the formation of AlN commenced at 110$0^{\circ}C$. AlN powders obtained from the sulfate salt were superior to those from the nitrate salt in terms of homogeneity and crystallinity. A very small amount of AlN whiskers was obtained by calcining a mixture of an aluminum sulfate salt and carbon at 115$0^{\circ}C$ for 40 h, and the growth of the whiskers is well explained by the particle-to-particle self-assembly mechanism.

• 한국세라믹학회지
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• 제31권1호
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• pp.79-87
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• 1994

AIN은 불안정하여 물과 접촉하면 12시간 이내에 172cal/g의 열을 내면서 가수분해되어 알루미나 삼수화물이 생성되었다. AIN의 가수분해 과정은 초기에 비정질 알루미나 수화물이 생성되었으며, 가수분해 조건에 따라 비정질알루미나 수화물의 용해-재석출과정으로 알루미나 삼수화물 특히 bayerite가 생성되었고, 응축과정으로 pseudo-boe-hmite가 AIN 입자표면에 생성되었다. 가수분해 온도 4$0^{\circ}C$ 이하에서는 비정질 알루미나 수화물이, 4$0^{\circ}C$와 6$0^{\circ}C$ 사이에서는 bayerite가 각각 생성되었고, 6$0^{\circ}C$ 이상의 경우는 초기에 pseudo-boehmite의 입자표면에 형성되었다. bayerite는 가수분해 시간이 길수록, 그리고 용액내 pH가 높을수록 잘 생성되었으나 pseudo-boehmite는 가수분해 반응이 급격히 일어날 때와 용액내 ethyl alcohol의 존재로 OH 기의 흡착을 방해하여 가수분해 반응이 억제될 때 잘 생성되었다. 그리고 pH=2.0인 용액에서는 AIN의 가수분해가 거의 일어나지 않았다.

• 한국세라믹학회지
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• 제38권11호
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• pp.987-992
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• 2001

내화물 등급의 저가 질화규소 분말을 분석 및 가공한 후, 소결조제을 첨가하여 가스압 소결하였다. 원료분말에는 다량의 free Si가 있었으며 Fe, Al, Ca등의 불순물도 각각 0.72wt%, 0.5wt%, 0.31wt%로 다량 존재하였다. 산소와 탄소의 함량도 각각 3.3wt%와 0.4wt%로 많았으며, 96%의 $\beta$-상과 4%의 $\alpha$-상으로 구성하였다. 원료 분말을 탈철처리 및 질화처리 하여 소결조제인 6wt% yttria와 2wt% alumina를 첨가하고, 1823K-2133 K의 온도 범위에서 1시간씩 소결하여 소결거동을 조사하였다. 또, 2123K에서 2시간동안 소결하여 충분히 치밀화된 소결체를 얻었다. 비교를 위하여 상용 질화규소 분말을 같이 소결하여 소결거동과 기계적 특성 등을 조사하였다. 저가의 분말을 상용 분말보다 치밀화 속도는 늦었다. 충분히 치밀화된 저가 분말의 소결체는 낮은 aspect rtio를 갖는 조대 결정립들이 다수 존재하였으며, 경도, 파괴인성, 꺽임강도, 내열 충격성 등이 상용 분말의 소결체 보다 떨어졌다.

• 한국분말재료학회지
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• 제13권6호
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• pp.432-438
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• 2006

Aluminum nitride (AlN) nanopowders with low degree of agglomeration and uniform particle size were synthesized by carbothermal reduction of alumina and subsequent direct nitridization. Boehmite powder was homogeneously admixed with carbon black nanopowders by ball milling. The powder mixture was treated under ammonia atmosphere to synthesize AlN powder at lour temperature. The effect of process variables such as boehmite/carbon black powder ratio, reaction temperature and reaction time on the synthesis of AlN nanopowder was investigated.

• 센서학회지
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• 제14권5호
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• pp.343-349
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• 2005

Carbon nitride films were deposited on various substrates for humidity sensors with meshed electrode by reactive RF magnetron sputtering system. As the ratio of injected nitrogen was decreased, the sensitivity of sensor was increased. When the ratio of injected nitrogen was $50{\sim}70%$, the sample showed the best linearity. The sensor impedance changed from $95.4{\;}k{\Omega}$ to $2.1{\;}k{\Omega}$ in a relative humidity range of 5 % to 95 %. The humidity sensors based on silicon wafer revealed higher lineality and faster response than those of alumina or quartz substrates. The adsorption saturation time of the sample was about 80 sec, and its desorption time was about 90 sec.

• 한국분무공학회지
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• 제8권1호
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• pp.16-22
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• 2003

Zeta potential measurements of colloid particles suspended in a liquid are performed by a Zeta Meter developed. There are many applications of colloid stability in spray technology, paints, wastewater treatment, and pharmaceuticalse. Zeta potentials of charged particles are obtained by measuring the electrophoretic velocities of the particles using video enhanced microscopy and image analysis program. The values of zeta potential of polystyrene latex(PSL), $silica(SiO_2)$M, polyvinylidence difluoride(PVDF), silicon nitride, and alumina particles in deionized (DI) water were measured to be -40.5, -31.9, -25.2, -15.1 and -10.1mV, respectively. The particles having high zeta potential less than -20 mV are stable in DI water, because the double layers of them have strong repulsive forces mutually, and the particles having low zeta potential over -20mV are unstable due to Van Der Waals forces. Silica(>20nm), PSL, aluminum and PVDF particles were found to be stable that would remain separate and well disperse, while silicon nitride and alumina particles were found to be unstable that would gradually agglomerate in DI water.

• 한국세라믹학회지
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• 제36권9호
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• pp.954-964
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• 1999

The effect of fabrication variables and microstructures on the compressive strength of open cell alumina zirconia and silicon nitride ceramics fabricated by polymeric sponge method was investigated. Bulk density and compressive strength of open cell ceramics were mainly affected by coating characteristics of ceramic slurry on polymeric sponge that controlled a shape thickness and defect of the struts. Sintering temperature was optimized for enhancement of strut strength and compressive strength of open cell ceramics. Relative density and compressive strength behaviors were relatively well matched with the predicted values. Open cell ceramics of lower relative density below 0.1 prepared by first relatively well matched with the predicted values. Open cell ceramics of lower relative density below 0.1 prepared by first coating of ceramic slurry had thin triangular prismatic struts that were often broken or longitudinally cracked. With an application of second coating of slurry shape of struts was transformed into thickner cylindrical one and defects in struts were healed but the relative density increased over 0.2 Open cell zirconia had both the highest bulk density and compressive strength and alumina had the lowest compressive strength while silicon nitrides showed relatively high compressive strength and the lowest density. Based upon the analysis open cell silicon nitride was expected to be one of potential structural ceramics with light weight.

• Transactions on Electrical and Electronic Materials
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• 제4권2호
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• pp.1-4
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• 2003

The purpose of this study was to investigate the characteristics of slurry including phosphoric acid for chemical-mechanical planarization of copper and tantalum nitride. In general, the slurry for copper CMP consists of alumina or colloidal silica as an abrasive, organic acid as a complexing agent, an oxidizing agent, a film forming agent, a pH control agent and additives. Hydrogen peroxide (H$_2$O$_2$) is the material that is used as an oxidizing agent in copper CMP. But, the hydrogen peroxide needs some stabilizers to prevent decomposition. We evaluated phosphoric acid (H$_3$PO$_4$) as a stabilizer of the hydrogen peroxide as well as an accelerator of the tantalum nitride CMP process. We also estimated dispersion stability and zeta potential of the abrasive with the contents of phosphoric acid. An acceleration of the tantalum nitride CMP was verified through the electrochemical test. This approach may be useful for the development of the 2$\^$nd/ step copper CMP slurry and hydrogen peroxide stability.

• 한국해양공학회지
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• 제23권5호
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• pp.32-38
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• 2009

Silicon nitride samples with aligned whisker seeds were prepared with different amounts of yttria and alumina as the sintering additives. Their sintering behaviors and the microstructural developments between $1850^{\circ}C$ and $2050^{\circ}C$ were examined. The sample with larger amount of the sintering additives showed faster densification and grain growth. Even though addition of the aligned whisker seeds slightly retarded densification of silicon nitride, it improved the flexural strength and the fracture toughness. Both the flexural strength and the fracture toughness of silicon nitride with the aligned whisker seeds were increased as the amount of the sintering additives was increased.