간행물
한국재료학회지 KCI 등재 SCOPUS Korean Journal of Materials Research
- 발행기관 한국재료학회
- 자료유형 학술지
- 간기 월간
- ISSN 2799-8525 (Print)2799-8681 (Online)
- 수록기간 1991 ~ 2024
- 주제분류 공학 > 재료공학 공학 분류의 다른 간행물
- 십진분류KDC 530DDC 620
권호리스트/논문검색
제22권 제9호 (2012년 9월) 10건
1.
2012.09
구독 인증기관 무료, 개인회원 유료
We investigate the effects of redox reaction on preparation of high purity α-alumina from selectively ground aluminum dross. Preparation procedure of the α-alumina from the aluminum dross has four steps: i) selective crushing and grinding, ii) leaching process, iii) redox reaction, and iv) precipitation reaction under controlled pH. Aluminum dross supplied from a smelter was ground to separate metallic aluminum. After the separation, the recovered particles were treated with hydrochloric acid(HCl) to leach aluminum as aluminum chloride solution. Then, the aluminum chloride solution was applied to a redox reaction with hydrogen peroxide(H2O2). The pH value of the solution was controlled by addition of ammonia to obtain aluminum hydroxide and to remove other impurities. Then, the obtained aluminum hydroxide was dried at 60˚C and heat-treated at 1300˚C to form α-alumina. Aluminum dross was found to contain a complex mixture of aluminum metal, aluminum oxide, aluminum nitride, and spinel compounds. Regardless of introduction of the redox reaction, both of the sintered products are composed mainly of α-alumina. There were fewer impurities in the solution subject to the redox reaction than there were in the solution that was not subject to the redox reaction. The impurities were precipitated by pH control with ammonia solution, and then removed. We can obtain aluminum hydroxide with high purity through control of pH after the redox reaction. Thus, pH control brings a synthesis of α-alumina with fewer impurities after the redox reaction. Consequently, high purity α-alumina from aluminum dross can be fabricated through the process by redox reaction.
4,000원
2.
2012.09
구독 인증기관 무료, 개인회원 유료
In crystalline solar cells, the substrate itself constitutes a large portion of the fabrication cost as it is derived fromsemiconductor ingots grown in costly high temperature processes. Thinner wafer substrates allow some cost saving as morewafers can be sliced from a given ingot, although technological limitations in slicing or sawing of wafers off an ingot, as wellas the physical strength of the sliced wafers, put a lower limit on the substrate thickness. Complementary to these economicaland techno-physical points of view, a device operation point of view of the substrate thickness would be useful. With this inmind, BC-BJ Si and GaAs solar cells are compared one to one by means of the Medici device simulation, with a particularemphasis on the substrate thickness. Under ideal conditions of 0.6µm photons entering the 10µm-wide BC-BJ solar cells atthe normal incident angle (θ=90o), GaAs is about 2.3 times more efficient than Si in terms of peak cell power output:42.3mW·cm−2 vs. 18.2mW·cm−2. This strong performance of GaAs, though only under ideal conditions, gives a strongindication that this material could stand competitively against Si, despite its known high material and process costs. Within thelimitation of the minority carrier recombination lifetime value of 5×10−5 sec used in the device simulation, the solar cell poweris known to be only weakly dependent on the substrate thickness, particularly under about 100µm, for both Si and GaAs.Though the optimum substrate thickness is about 100µm or less, the reduction in the power output is less than 10% from thepeak values even when the substrate thickness is increased to 190µm. Thus, for crystalline Si and GaAs with a relatively longrecombination lifetime, extra efforts to be spent on thinning the substrate should be weighed against the expected actual gainin the solar cell output power.
3,000원
3.
2012.09
구독 인증기관 무료, 개인회원 유료
Various adhesive materials are used in flip chip packaging for electrical interconnection and structural reinforcement. In cases of COF(chip on film) packages, low temperature bonding adhesive is currently needed for the utilization of low thermal resistance substrate films, such as PEN(polyethylene naphthalate) and PET(polyethylene terephthalate). In this study, the effects of anhydride and dihydrazide hardeners on the low-temperature snap cure behavior of epoxy based non-conductive pastes(NCPs) were investigated to reduce flip chip bonding temperature. Dynamic DSC(differential scanning calorimetry) and isothermal DEA(dielectric analysis) results showed that the curing rate of MHHPA(hexahydro-4-methylphthalic anhydride) at 160˚C was faster than that of ADH(adipic dihydrazide) when considering the onset and peak curing temperatures. In a die shear test performed after flip chip bonding, however, ADH-containing formulations indicated faster trends in reaching saturated bond strength values due to the post curing effect. More enhanced HAST(highly accelerated stress test) reliability could be achieved in an assembly having a higher initial bond strength and, thus, MHHPA is considered to be a more effective hardener than ADH for low temperature snap cure NCPs.
4,000원
4.
2012.09
구독 인증기관 무료, 개인회원 유료
We investigated cleaning effects using NH4OH solution on the surface of Cu film. A 20 nm Cu film was deposited on Ti / p-Si (100) by sputter deposition and was exposed to air for growth of the native Cu oxide. In order to remove the Cu native oxide, an NH4OH cleaning process with and without TS-40A pre-treatment was carried out. After the NH4OH cleaning without TS-40A pretreatment, the sheet resistance Rs of the Cu film and the surface morphology changed slightly(δRs:~10mΩ/sq.). On the other hand, after NH4OH cleaning with TS-40A pretreatment, the Rs of the Cu film changed abruptly (δRs:till~700mΩ/sq.); in addition, cracks showed on the surface of the Cu film. According to XPS results, Si ingredient was detected on the surface of all Cu films pretreated with TS-40A. This Si ingredient(a kind of silicate) may result from the TS-40A solution, because sodium metasilicate is included in TS-40A as an alkaline degreasing agent. Finally, we found that the NH4OH cleaning process without pretreatment using an alkaline cleanser containing a silicate ingredient is more useful at removing Cu oxides on Cu film. In addition, we found that in the NH4OH cleaning process, an alkaline cleanser like Metex TS-40A, containing sodium metasilicate, can cause cracks on the surface of Cu film.
4,000원
5.
2012.09
구독 인증기관 무료, 개인회원 유료
This paper focuses on the after synthesis of CdTe quantum dots(QDs) in aqueous solution. CdTe nanoparticles were prepared in aqueous solution using mercaptocarboxylic acid or thioglycolic acid(TGA) as stabilizing agents. QDs emit light smaller than the nano size. The contents of the mercaptocarboxylic acid, and a kind of raw material, were revealed for a period of time. We succeeded in synthesizing a very high quality QDs solution; we discussed how to make QDs better and to keep them stabilized. TGA is known as one of the best stabilizing agents. Many papers have mentioned that TGA is a good stabilizing agent. We dramatically confirmed the state of QDs after the experiments. The QDs solution can be influenced by several factors. Different content of TGA can influence the stability of the CdTe solution. Most papers deal with the synthesis of CdTe, so we decided to discuss the after synthesis process for the stability of the CdTe solution.
4,000원
6.
2012.09
구독 인증기관 무료, 개인회원 유료
La1-xSrxMnO3(LSM,0≤x≤0.5) powders as the air electrode for solid oxide fuel cell were synthesized by a glycine-nitrate combustion process. The powders were then examined by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The as-formed powders were composed of very fine ash particles linked together in chains. X-ray maps of the LSM powders milled for 1.5 h showed that the metallic elements are homogeneously distributed inside each grain and in the different grains. The powder XRD patterns of the LSM with x< 0.3 showed a rhombohedral phase; the phase changes to the cubic phase at higher compositions(x≥0.3) calcined in air at 1200˚C for 4 h. Also, the SEM micrographs showed that the average grain size decreases as Sr content increases. Composite air electrodes made of 50/50 vol% of the resulting LSM powders and yttria stabilized zirconia(YSZ) powders were prepared by colloidal deposition technique. The electrodes were studied by ac impedance spectroscopy in order to improve the performance of a solid oxide fuel cell(SOFC). Reproducible impedance spectra were confirmed using the improved cell, which consisted of LSM-YSZ/YSZ. The composite electrode of LSM and YSZ was found to yield a lower cathodic resistivity than that of the non-composite one. Also, the addition of YSZ to the La1-xSrxMnO3 (0.1≤x≤0.2) electrode led to a pronounced, large decrease in the cathodic resistivity of the LSM-YSZ composite electrodes.
4,000원
7.
2012.09
구독 인증기관 무료, 개인회원 유료
Among the various roll-to-roll printing technologies such as gravure, gravure-offset, and reverse offset printing,reverse offset printing has the advantage of fine patterning, with less than 5µm line width. However, it involves complexprocesses, consisting of 1) the coating process, 2) the off process, 3) the patterning process, and 4) the set process of the ink.Each process demands various ink properties, including viscosity, surface tension, stickiness, and adhesion with substrate orcliché; these properties are critical factors for the printing quality of fine patterning. In this study, Ag nano ink was developedfor reverse offset printing and the effect of polyvinylpyrrolidone(PVP), used as a capping agent of Ag nano particles, on theprinting quality was investigated. Ag nano particles with a diameter of ~60nm were synthesized using the conventional polyolsynthesis process. Ethanol and ethylene glycol monopropyl ether(EGPE) were used together as the main solvent in order tocontrol the drying and absorption of the solvents during the printing process. The rheological behavior, especially ink adhesionand stickiness, was controlled with washing processes that have an effect on the offset process and that played a critical rolein the fine patterning. The electrical and thermal behaviors were analyzed according to the content of PVP in the Ag ink. Finally,an Ag mesh pattern with a line width of 10µm was printed using reverse offset printing; this printing showed an electricalresistivity of 36µΩ·cm after sintering at 200oC.
4,000원
8.
2012.09
구독 인증기관 무료, 개인회원 유료
To fabricate a precise micro metal mold, the electrochemical etching process has been researched. We investigated the electrochemical etching process numerically and experimentally to determine the etching tendency of the process, focusing on the current density, which is a major parameter of the process. The finite element method, a kind of numerical analysis, was used to determine the current density distribution on the workpiece. Stainless steel(SS304) substrate with various sized square and circular array patterns as an anode and copper(Cu) plate as a cathode were used for the electrochemical experiments. A mixture of H2SO4, H3PO4, and DIW was used as an electrolyte. In this paper, comparison of the results from the experiment and the numerical simulation is presented, including the current density distribution and line profile from the simulation, and the etching profile and surface morphology from the experiment. Etching profile and surface morphology were characterized using a 3D-profiler and FE-SEM measurement. From a comparison of the data, it was confirmed that the current density distribution and the line profile of the simulation were similar to the surface morphology and the etching profile of the experiment, respectively. The current density is more concentrated at the vertex of the square pattern and circumference of the circular pattern. And, the depth of the etched area is proportional to the current density.
4,000원
9.
2012.09
구독 인증기관 무료, 개인회원 유료
Green phosphors K2BaW2O8:Tb3+(1.0mol%) were synthesized by solid state reaction method. Differential thermalanalysis was applied to trace the reaction processes. Three endothermic values of 95, 706, and 1055oC correspond to the lossof absorbed water, the release of carbon dioxide, and the beginning of the melting point, respectively. The phase purity of thepowders was examined using powder X-ray diffraction(XRD). Two strong excitation bands in the wavelength region of 200-310nm were found to be due to the WO42− exciton transition and the 4f-5d transition of Tb3+ in K2BaW2O8. The excitationspectrum presents several lines in the range of 310-380nm; these are assigned to the 4f-4f transitions of the Tb3+ ion. The strongemission line at around 550nm, due to the 5D4→7F5 transition, is observed together with weak lines of the 5D4→7FJ(J=3,4, and 6) transitions. A broad emission band peaking at 530nm is observed at 10K, while it disappears at room temperature.The decay times of Tb3+ 5D4→7F5 emission are estimated to be 4.8 and 1.4ms, respectively, at 10 and 295 K; those of theWO42− exciton emissions are 22 and 0.92µs at 10 and 200K, respectively.
4,000원
10.
2012.09
구독 인증기관 무료, 개인회원 유료
Geopolymer cements and geopolymer resins are newly advanced mineral binders that are used in order to reducethe carbon dioxide generation that accompanies cement production. The effect of additives on the compressive strength ofgeopolymerized class-F fly ash was investigated. Blast furnace slag, calcium hydroxide(Ca(OH)2), and silica fume powders wereadded to fly ash. A geopolymeric reaction was initiated by adding a solution of water glass and sodium hydroxide(NaOH) tothe powder mixtures. The compressive strength of pure fly ash cured at room temperature for 28 days was found to be as lowas 291kgf/cm−2, which was not a suitable value for use in engineering materials. On the contrary, addition of 20wt% and40wt% of blast furnace slag powders to fly ash increased the compressive strength to 458kgf/cm−2 and 750kgf/cm−2,respectively. 5wt% addition of Ca(OH)2 increased the compressive strength up to 640kgf/cm−2; further addition of Ca(OH)2further increased the compressive strength. When 2wt% of silica fume was added, the compressive strength increased to 577kgf/cm−2; the maximum strength was obtained at 6wt% addition of silica fume. It was confirmed that the addition of CaO andSiO2 to the fly ash powders was effective at increasing the compressive strength of geopolymerized fly ash.
4,000원
