• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.421-424
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• 2008

본 연구에서는 산 및 황산염 저항성에 미치는 시멘트 종류의 영향을 평가하기 위하여 물-결합재 비 32% 및 43%에 대해서 보통 포틀랜드 시멘트(OPC), 2성분계 시멘트(BBC), 및 3성분계 시멘트(TBC)와 같은 3종류의 시멘트를 사용한 콘크리트 공시체를 제작하였다. 제작된 콘크리트 공시체에 대해서 JSTM C 7401에 따라 5% 황산, 10% 황산나트륨 나트륨 및 10% 황산마그네슘 용액에 의한 침지실험을 통하여 재령에 따른 외관 변화 및 질량 감소율을 평가하였다. 재령 91동안의 침지실험 결과로부터, 콘크리트의 산 및 황산염에 대한 저항성은 물-결합재비가 감소할수록 증가하고, BBC와 TBC 콘크리트가 OPC 콘크리트보다 우수한 것으로 나타났다.

• 한국분말재료학회지
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• 제22권6호
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• pp.426-431
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• 2015

Microstructural examination of the Nb-Si-B alloys at Nb-rich compositions is performed. The Nb-rich corner of the Nb-Si-B system is favorable in that the constituent phases are Nb (ductile and tough phase with high melting temperature) and $T_2$ phase (very hard intermetallic compound with favorable oxidation resistance) which are good combination for high temperature structural materials. The samples containing compositions near Nb-rich corner of the Nb-Si-B ternary system are prepared by spark plasma sintering (SPS) process using $T_2$ and Nb powders. $T_2$ bulk phase is made in arc furnace by melting the Nb slug and the Si-B powder compact. The $T_2$ bulk phase was subsequently ball-milled to powders. SPS is performed at $1300^{\circ}C$ and $1400^{\circ}C$, depending on the composition, under 30 MPa for 600s, to produce disc-shaped specimen with 15 mm in diameter and 3 mm high. Hardness tests (Rockwell A-scale and micro Vickers) are carried out to estimate the mechanical property.

• 열처리공학회지
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• 제21권1호
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• pp.20-25
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• 2008

Structural studies have been performed on precipitation hardening and microstructural variations found in Ti-Al-Cr ternary $L1_0$- and $L1_2$-phase alloys using transmission electron microscopy. Both the $L1_0$ and $L1_2$ phase alloys harden by aging at 973 K after solution annealing at higher temperatures. The amount of age hardening of the $L1_2$ phase alloy is larger than that of the $L1_0$ phase alloy. The phase separation between $L1_0$ and $L1_2$ phase have not been observed by aging at 973 K. But $Al_2Ti$ was formed in each matrix alloy during aging. The crystal structure of the $Al_2Ti$ phase is a $Ga_2Zr$ type in the $L1_0$ and a $Ga_2Hf$ type in the $L1_2$ phase, respectively. At the beginning of aging the fine coherent cuboidal $Al_2Ti$-phase are formed in the $L1_0$ phase. By further aging, two variants of $Al_2Ti$ precipitates grow along the two {110} habit planes. On the other hand, in the $L1_2$ phase, the $Al_2Ti$ phase forms on the {100} planes of the $L1_2$ matrix lattice. After prolonged aging the precipitates are rearranged along a preferential direction of the matrix lattice and form a domain consisting of only one variant. It is suggested that the precipitation of $Al_2Ti$ in each matrix alloy occurs to form a morphology which efficiently relaxes the elastic strain between precipitate and matrix lattices.

• 한국세라믹학회지
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• 제20권3호
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• pp.211-216
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• 1983

This work aims at characterizing silicon grains and its compacts. In order to remove iron silicon grains were washed with 5N hydrochloride at 60-7$0^{\circ}C$ for 170 hrs, and then followed the chemical analysis by atomic absorption spectrophotometer X-ray diffraction analysis SEM observation and specific surface area determination by B. E. T. Mixtures of graded silicon particles with two or three different sizes were made into packings by mechanical vibration. The mixtures were used to make compacts with 10 mm in diameter and 70mm in length by isostatically pressing at 1, 208 kg/$cm^2$ (20 kpsi) and 4, 255kg/$cm^2$ (60 kpsi) respectively. Bulk densities of packings and compacts were measured. A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$ for the purpose of coating the uniform layer of magnesium oxide on the surface of particles. The results obtained are as follows: (1) About two thirds of iron content could be removed from silicon by washing silicon powders with hydrochloride. (2) Uniform layer of magnesium oxide on the surface of silicon could be prepared by spray-drying suspension and by decomposing it. (3) B. E. T. specific surface area of fine silicon particles was 2, 826.753$m^3$/kg. (4) In the binary system with two sizes of 40-53$\mu\textrm{m}$ particles and <10$\mu\textrm{m}$ particles the maximum bulk density of packing was 55% of theoretical value and that of compacts made at the pressure of 4, 255 kg./$cm^2$ (60 kpsi) was 73% of theoretical value. (5) In the ternary system with three sizes the maximum bulk density of packing was 1.43 g/$cm^3$and that of compacts was 1.80g/$cm^3$which is equivalent to 77.6% of theoretical value. The composition of the closest compact was consisted of 50% of 40-53$\mu\textrm{m}$ particles 20% of 10-30$\mu\textrm{m}$ particles and 30% of <10$\mu\textrm{m}$ parti-cles.

• 대한화학회지
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• 제38권9호
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• pp.653-659
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• 1994

pH 7인 수용액에서 2-thenoyltrifluoroacetone(TTA), n-octanol과 Triton X-100의 존재하에서 유로퓸과 사마륨의 형광세기가 크게 증가하였다. 또한 이 착물에 과량의 $La^{3+}$을 첨가할 때 형광세기가 100배 이상 증가하였다. 유로퓸과 사마륨의 최대 들뜨기 파장은 각각 345 nm과 380 nm이고, 최대 형광파장은 각각 617 nm, 567 nm 이었다. 유로퓸과 사마륨의 형광세기는 농도가 각각 $1{\times}10^{-7}∼1{\tiems}10^{-9}\;M,\;1{\tiems}10^{-5}∼1{\times}10^{-7}\;M$에서 직선적으로 증가하였고, 유로퓸은 $1{\times}10^{-11}\;M$ 그리고 사마륨은 $1{\times}10^{-8}\;M$까지 검출할 수 있었다.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2003년도 춘계학술연구발표회
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• pp.19-19
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• 2003

A cubic perovskite-type CaCu₃Ti₄O/sub 12/ compound has recently drawn a great attention because of an extraordinary high permittivity (～10⁴ at 1 kHz) at room temperature and its near temperature-independence over a wide temperature region, and thus numerous literature have been reported on CCTO polycrytalline ceramics and thin films. However, only a few literature have been reported on the CCTO single due to the lack of information about the CCTO primary phase field. On the basis of our recent experimental determination of the CCTO primary phase field, we could grow ACu₃Ti₄O/sub 12/(A=Ca, Sr) single crystals using both top-seeded solution growth and flux growth methods. This presentation will include three major parts. In part I, the thermal decomposition reaction of CCTO and its primary phase field in the CaO-CuO-TiO₂ ternary system will be presented. Detailed growth conditions of ACu₃Ti₄O/sub 12/(A=Ca, Sr) single crystals and characteristics of as-grown crystals will be followed in Part II. Part III will be comprised of dielectric properties of as-grown ACu₃Ti₄O/sub 12/(A=Ca, Sr) single crystals. Our experimental results will be compared with those of previous reports for discussion.

• Bulletin of the Korean Chemical Society
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• 제31권10호
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• pp.2813-2818
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• 2010

A novel method was developed for the speciation of chromium in natural water samples based on homogeneous liquid-liquid extraction and determination by flame atomic absorption spectrometry (FAAS). In this method, Cr(III) reacts with a new Schiff's base ligand to form the hydrophobic complex, which is subsequently entrapped in the sediment phase, whereas Cr(VI) remained in aqueous phase. The Cr(VI) assay is based on its reduction to Cr(III) by the addition of sodium sulfite to the sample solution. Thus, separation of Cr(III) and Cr(VI) could be realized. Homogeneous liquid-liquid extraction based on the pH-independent phase-separation process was investigated using a ternary solvent system (water-tetrabutylammonium ion ($TBA^+$)-chloroform) for the preconcentration of chromium. The phase separation phenomenon occurred by an ion-pair formation of TBA and perchlorate ion. Then sedimented phase was separated using a $100\;{\mu}L$ micro-syringe and diluted to 1.0 mL with ethanol. The sample was introduced into the flame by conventional aspiration. After the optimization of complexation and extraction conditions such as pH = 9.5, [ligand] = $1.0{\times}10^{-4}\;M$, [$TBA^+$] = $2.0{\times}10^{-2}\;M$, [$CHCl_3$] = $100.0\;{\mu}L$ and [$ClO_4$] = $2.0{\times}10{-2}\;M$, a preconcentration factor (Va/Vs) of 100 was obtained for only 10 mL of the sample. The relative standard deviation was 2.8% (n = 10). The limit of detection was sufficiently low and lie at ppb level. The proposed method was applied for the extraction and determination of chromium in natural water samples with satisfactory results.

• 한국재료학회지
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• 제3권3호
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• pp.207-214
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• 1993

$Li_2O-Al_2O_3-SiO_3$계 결정화유리의 저온합성을 위하여 출방원료로서 각 해당 금속 알콕시드를 사용하였다. 알코올을 용매로 충분히 첨가하고, drying control chemical additive로 dimethy1 formamide를 적당량 첨가한 혼합용용액을 과잉의 물로 충분히 가수분해시킨 습윤겔을 저온으로 건고하여 균열이 없는 건조된 monolith겔을 합성하였다. 건조겔로부터 750-$950^{\circ}C$로 10시간 이상 소결하여 저열팽창성을 나타내는 ${\beta}$-eucrypytite(${\beta}$-quartz 고용체), $Li_2O\cdot Al_2O_3\cdot 3SiO_2$및 ${\beta}$-spodumene등의결정상을 석출시켰다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2012년도 춘계학술발표회 논문집
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• pp.308-308
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• 2012

Electrodeposition of thermoelectric materials, including binary and ternary compounds, have been attracting attentions, because its many advantages including cost-effectiveness, rapid deposition rate, and ease of control their microstructure and crystallinity by adjusting electrodeposition parameters. In this work, $Bi_xTe_y$ films were potentiostatically electrodeposited using Au/Ni(80/20 nm)/Si substrate as the working electrode in solutions consisting of 10mM $TeO_2$ and 1M $HNO_3$ where $Bi(NO_3)_3$ was varied from 2.5 to 10 mM. Prior to electrodeposition potentiostatically, linear sweep voltammograms (LSV) were acquired with a standard three-electrode cell. The $Bi_xTe_y$ films deposited using the electrolyte containing low Bi ions shows p-type conductivity, which might be attributed by the large incorporation of Te phases. Near stoichiometric $Bi_2Te_3$ thin films were obtained from electrolytes containing 5mM $Bi(NO_3)_3$. This film shows the maximum Seebeck coefficient of $-100.3{\pm}12.7{\mu}V/K$. As the increase of Bi ions in electrolytes decreases the Seebeck coefficient and resistivity. The maximum power factor of $336.2{\mu}W/m{\cdot}K^2$ was obtained from the film deposited using the solution of 7.5mM $Bi(NO_3)_3$.

• Advances in concrete construction
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• 제13권1호
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• pp.71-81
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• 2022

Aluminosilicate materials as precursors are heterogenous in nature, consisting of inert and partially reactive portion, and have varying proportions depending upon source materials. It is essential to assess the reactivity of precursor prior to synthesize geopolymers. Moreover, reactivity may act as decisive factor for setting molar concentration of NaOH, curing temperature and setting proportion of different precursors. In this experimental work, the reactivities of two precursors, low calcium (fly ash (FA)) and high calcium (ground granulated blast furnace slag (GGBS)), were assessed through the dissolution of aluminosilicate at (i) three molar concentrations (8, 12, and 16 M) of NaOH solution, (ii) 6 to 24 h dissolution time, and (iii) 20-100℃. Based on paratermeters influencing the reactivity, different proportions of ternary binders (two precursors and ordinary cement) were activated by the combined NaOH and Na2SiO3 solutions with two alkaline activators to precursor ratios, to synthesize the geopolymer. Reactivity results revealed that GGBS was 20-30% more reactive than FA at 20℃, at all three molar concentrations, but its reactivity decreased by 32-46% with increasing temperature due to the high calcium content. Setting time of geopolymer paste was reduced by adding GGBS due to its fast reactivity. Both GGBS and cement promoted the formation of all types of gels (i.e., C-S-H, C-A-S-H, and N-A-S-H). As a result, it was found that a specified mixing proportion could be used to improve the compressive strength over 30 MPa at both the ambient and hot curing conditions.