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Evaluation of Hot Tear Susceptibility of Al-Si-Mg-Cu Alloy System (Al-Si-Mg-Cu 합금계의 열간 균열 특성 평가방법에 관한 연구)

  • Son, Kwang-Suk;Park, Tae-Eun;Kim, Jin-Su;Kang, Sung-Min;Kim, Donggyu
    • Korean Journal of Metals and Materials
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    • v.48 no.5
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    • pp.436-444
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    • 2010
  • The hot tear susceptibility of Al alloys was investigated by using a constrained-rod mold designed to quantify 8 types of tear tendency. The severity of the crack was scored by 5 grades on a scale of 0 to 4, with 0 being "no crack formed" and 4 being "complete separation by crack". The Hot Tear Susceptibility index (HTS) which consists of crack type scores and position scores, was proposed to compare the hot tear tendency of Al alloys. A356.0 cast alloy and AA6061 wrought Al alloy showed an HTS value of 27.5 and 53 respectively. The effects of Si, Cu, and Mg content on hot tear tendency were also investigated with a constrained-rod mold. The variation of HTS values with alloying elements represents similar behavior in the variation of the solidification range in a pseudo binary phase diagram.

Efficient Adsorption of Methylene Blue from Aqueous Solution by Sulfuric Acid Activated Watermelone Rind (Citrullus lanatus)

  • Lee, Seo-Yun;Choi, Hee-Jeong
    • Applied Chemistry for Engineering
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    • v.32 no.3
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    • pp.348-356
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    • 2021
  • The lignocellulose-based dried watermelon rind (WR) was modified with sulfuric acid, namely SWR for enhancement of methylene blue (MB) adsorption from the aqueous solution. According to FT-IR analysis, after the modification of WR with sulfuric acid, the functional groups of R-SO3H, COOH and -OH groups was formated or enhanced on the surface of the WR. Moreover, the point of zero charge (pHpzc) was changed from 6.3 to 4.1 after modification, which widened the range for adsorbing of cationic dye MB. The adsorption process of MB onto the SWR was suitable for pseudo-2nd-order and Langmuir model and the maximum adsorption capacity of Langmuir was found to be 334.45 mg/g at pH 7. In adition, the adsorption process occurs through the electrostatic interaction, hydrogen bridge formation, electron donor-acceptor relationship, and 𝜋-𝜋 electron dispersing force between functional groups on the carbon surface with MB molecules. Depending on functional groups available on the SWR surface, the MB adsorption mechanism can occur in combination with various interactions.

Visible light assisted photocatalytic degradation of methylene blue dye using Ni doped Co-Zn nanoferrites

  • Thakur, Preeti;Chahar, Deepika;Thakur, Atul
    • Advances in nano research
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    • v.12 no.4
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    • pp.415-426
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    • 2022
  • Nickel substituted cobalt-zinc ferrite nanoparticles with composition Co0.5Zn0.5NixFe2-xO4 (x = 0.25, 0.5, 0.75, 1.0) were synthesized using a wet chemical method named citrate precursor method. Various characterizations of the prepared nanoferrites were done using X-ray powder diffractometry (XRD), Scanning electron microscopy (SEM), UV visible spectroscopy and Fourier transform spectroscopy technique (FT-IR). XRD confirmed the formation of cubic spinel structure of the samples with single phase having one characteristic peak at (311). The value of optical band gap (Eg) was found to decrease with Ni substitution and have values in the range 2.30eV to 1.69eV. A Fenton-type system was created by photocatalytic activity using source of visible light for removal of methylene blue dye. Observations revealed increase in the degradation of methylene blue dye with increasing nickel content in the samples. The degradation percentage was increased from 77.32% for x = 0.25 to 90.16% for x = 1.0 in one hour under the irradiation of visible light. Also, the degradation process was found to have pseudo first order kinetics model. Hence, it can be observed that synthesized nickel doped cobalt-zinc ferrites have good capability for water purification and its degradation efficiency enhanced with increase in nickel concentration.

Glass Dissolution Rates From MCC-1 and Flow-Through Tests

  • Jeong, Seung-Young
    • Proceedings of the Korean Radioactive Waste Society Conference
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    • 2004.06a
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    • pp.257-258
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    • 2004
  • The dose from radionuclides released from high-level radioactive waste (HLW) glasses as they corrode must be taken into account when assessing the performance of a disposal system. In the performance assessment (PA) calculations conducted for the proposed Yucca Mountain, Nevada, disposal system, the release of radionuclides is conservatively assumed to occur at the same rate the glass matrix dissolves. A simple model was developed to calculate the glass dissolution rate of HLW glasses in these PA calculations [1]. For the PA calculations that were conducted for Site Recommendation, it was necessary to identify ranges of parameter values that bounded the dissolution rates of the wide range of HLW glass compositions that will be disposed. The values and ranges of the model parameters for the pH and temperature dependencies were extracted from the results of SPFT, static leach tests, and Soxhlet tests available in the literature. Static leach tests were conducted with a range of glass compositions to measure values for the glass composition parameter. The glass dissolution rate depends on temperature, pH, and the compositions of the glass and solution, The dissolution rate is calculated using Eq. 1: $rate{\;}={\;}k_{o}10^{(ph){\eta})}{\cdot}e^{(-Ea/RT)}{\cdot}(1-Q/K){\;}+{\;}k_{long}$ where $k_{0},\;{\eta}$ and Eaare the parameters for glass composition, pH, $\eta$ and temperature dependence, respectively, and R is the gas constant. The term (1-Q/K) is the affinity term, where Q is the ion activity product of the solution and K is the pseudo-equilibrium constant for the glass. Values of the parameters $k_{0},\;{\eta}\;and\;E_{a}$ are the parameters for glass composition, pH, and temperature dependence, respectively, and R is the gas constant. The term (1-Q/C) is the affinity term, where Q is the ion activity product of the solution and K is the pseudo-equilibrium constant for the glass. Values of the parameters $k_0$, and Ea are determined under test conditions where the value of Q is maintained near zero, so that the value of the affinity term remains near 1. The dissolution rate under conditions in which the value of the affinity term is near 1 is referred to as the forward rate. This is the highest dissolution rate that can occur at a particular pH and temperature. The value of the parameter K is determined from experiments in which the value of the ion activity product approaches the value of K. This results in a decrease in the value of the affinity term and the dissolution rate. The highly dilute solutions required to measure the forward rate and extract values for $k_0$, $\eta$, and Ea can be maintained by conducting dynamic tests in which the test solution is removed from the reaction cell and replaced with fresh solution. In the single-pass flow-through (PFT) test method, this is done by continuously pumping the test solution through the reaction cell. Alternatively, static tests can be conducted with sufficient solution volume that the solution concentrations of dissolved glass components do not increase significantly during the test. Both the SPFT and static tests can ve conducted for a wide range of pH values and temperatures. Both static and SPFt tests have short-comings. the SPFT test requires analysis of several solutions (typically 6-10) at each of several flow rates to determine the glass dissolution rate at each pH and temperature. As will be shown, the rate measured in an SPFt test depends on the solution flow rate. The solutions in static tests will eventually become concentrated enough to affect the dissolution rate. In both the SPFt and static test methods. a compromise is required between the need to minimize the effects of dissolved components on the dissolution rate and the need to attain solution concentrations that are high enough to analyze. In the paper, we compare the results of static leach tests and SPFT tests conducted with simple 5-component glass to confirm the equivalence of SPFT tests and static tests conducted with pH buffer solutions. Tests were conducted over the range pH values that are most relevant for waste glass disssolution in a disposal system. The glass and temperature used in the tests were selected to allow direct comparison with SPFT tests conducted previously. The ability to measure parameter values with more than one test method and an understanding of how the rate measured in each test is affected by various test parameters provides added confidence to the measured values. The dissolution rate of a simple 5-component glass was measured at pH values of 6.2, 8.3, and 9.6 and $70^{\circ}C$ using static tests and single-pass flow-through (SPFT) tests. Similar rates were measured with the two methods. However, the measured rates are about 10X higher than the rates measured previously for a glass having the same composition using an SPFT test method. Differences are attributed to effects of the solution flow rate on the glass dissolution reate and how the specific surface area of crushed glass is estimated. This comparison indicates the need to standardize the SPFT test procedure.

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Pb(II) Removal from Aqueous Solutions Using Pinewood and Oakwood (소나무와 참나무를 이용한 Pb(II) 제거)

  • Um, Byung-Hwan;Jo, Sung-Wook;Park, Seong-Jik
    • Journal of the Korean Wood Science and Technology
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    • v.42 no.4
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    • pp.450-459
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    • 2014
  • Crushed pinewood and oakwood were studied as an adsorbent for Pb(II) removal from aqueous solution. Batch adsorption experiments were carried out to describe the effects of contact time, initial Pb(II) concentration, pH, competing cations, and adsorbent dosage on the Pb(II) adsorption process. Kinetic studies revealed that the Pb(II) adsorption process for pinewood and oakwood followed both pseudo first and pseudo second order model. The Fruendlich model best described equilibrium adsorption data with correlation coefficients ($R^2$) of 0.956 and 0.950 for pinewood and oakwood. The maximum adsorption capacity of Pb(II) onto pinewood and oakwood was found to be 16.853 and 27.989 mg/g, respectively. The Pb(II) adsorption onto both pinewood and oakwood was increased as pH increased in the pH range 3-9. The presence of cations such as $Na^+$, $Ca^{2+}$, and $Al^{3+}$ decreased Pb(II) adsorption. The Pb(II) removal was greater in seawater than deionized water, resulting from the presence of $CO{_3}^{2-}$ and $OH^-$ ions in seawater. This study showed that pinewood and oakwood have a potential application in the remediation of Pb(II) contaminated water.

Seismic Response Analyses of the Structure-Soil System for the Evaluation of the Limits of the Site Coefficients (지반계수의 한계값 평가를 위한 구조물-지반체계에 대한 지진응답해석)

  • Kim, Yong-Seok
    • Journal of the Earthquake Engineering Society of Korea
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    • v.11 no.1 s.53
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    • pp.67-77
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    • 2007
  • Site coefficients in IBC and KBC codes have some limits to predict the rational seismic responses of a structure, because they take into account only the effect of the soil amplification without the effects of the structure-soil interaction. In this study, upper and lower limits of the site coefficients are estimated through the pseudo 3-D elastic seismic response analyses of structures built on the linear or nonlinear soil layers taking Into account the effects of the structure-soil interaction. Soil characteristics of site classes of A, B and C were assumed to be linear, and those of site classes of D and E were done to be nonlinear and the Ramberg-Osgood model was used to evaluate shear modulus and damping ratio of a soil layer depending on the shear wave velocity of the soil layer, Seismic analyses were performed with 12 weak or moderate earthquake records scaled the peak acceleration to 0.1g or 0.2g and deconvoluted as earthquake records at the bedrock located at 30m deep under the outcrop. With the study results of the elastic seismic response analyses of structures, new standard response spectrum and upper and lower limits of the site coefficients of $F_{a}\;and\;F_{v}$ at the short period range and the period of 1 second are suggested including the effects of the structure-soil interaction, and new site coefficients for the KBC code are also suggested.

A Study on Nonstoichiometry and Physical Properties of the Mixed Valency Sr$_{1+x}Er _{1-x} FeO _{4-y}$ Ferrite System (혼합원자가 Sr$_{1+x}Er _{1-x} FeO _{4-y}$ 훼라이트계의 비화학양론과 물성연구)

  • Chul Hyun Yo;Kwang Sun Ryu;Mu Sil Pyun;Sung Joo Lee;Joong Gill Choi
    • Journal of the Korean Chemical Society
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    • v.35 no.2
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    • pp.99-104
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    • 1991
  • Nonstoichiometric solid solutions of Sr$_{1+x}Er _{1-x} FeO _{4-y}$ system (x = 0.00, 0.25, 0.50, 0.75 and 1.00) with layered $K_2NiF_4$ type structure were prepared at 1350$^{\circ}$C under atmospheric pressure. By the analysis of X-ray diffraction, the crystallographic structures of the solid solution of all compositions were found to be pseudo-tetragonal system. Nonstoichiometric chemical formulas have been determined by Mohr salt analysis. It shows that the amount of Fe$^{4+}$ increases with increasing x up to 0.50 and then decreases, and the value of oxygen nonstoichiometry increases with increasing x value. Mixed valency states of Fe$^{3+}$ and Fe$^{4+}$ in the sample were identified again by Mossbauer spectroscopic analysis at 298 K. Electrical conductivity varied within the semiconductivity range of 10-2 ∼ 10-7(${\Omega}$-1cm-1), activation energy for electrical conduction decreased with the increment of the mole ratio of Fe$^{4+}$ or ${\tau}$ value. The conduction mechanism could be explained by the hopping model of the conduction electrons between the valency states of Fe$^{3+}$ and Fe$^{4+}$.

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The Components of the Sap from Gorosoe(Acer mono Max.) and Sugar Maple(Pseudo-sieboldianum Kom.) (고로쇠나무 및 당단풍나무 수액의 성분조성)

  • 성낙주;정미자;김윤숙;이일숙;조종수
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.24 no.6
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    • pp.911-916
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    • 1995
  • Even though the saps have been consumed as beverage in Korea for a very long period of time, a little research has been conducted on the chemical composition. We determined mineral, free sugar, composition amino acids and nucleotides in the sap of Gorosoe(Acer mono Max.) and Sugar Maple(Pseudo-sieboldianum Kom.) collected from Sancheong, Kurye and Hamyang. The contents of solid, crude protein and ash were 1.1~3.3%, 0.03~0.12% and 0.02~0.05% in the sap of Gorosoe and Sugar Maple, respectively. The detectable nucleotides were CMP, UMP, IMP, GMP, AMP and hypoxanthine. Free sugar that we determined in the sap of Gorosoe and Sugar Maple were sucrose, fructose and glucose, but maltose was not detected. The chief component of saccharides in the sap was sugar and ranged from 7.1 to 36.6g/L. Especially, the sucrose contents in the sap of Gorosoe and Sugar Maple from Hamyang were higher 3.7 and 2.2 times than those from the other samples. The prominent minerals in the sap were calcium and potassium. The calcium concentration was ranged from 99.0~153.3mg/L in the sap of Gorosoe and was ranged from 21.2~32.4mg/L in that of sugar maple. The sap of Gorosoe and Sugar Maple were composed of 18 and 15 kinds of amino acid respectively, and the total contents of amino acid were in the range of 0.7~29.3mg%. The major amino acids in the sap of Gorosoe were taurine, serine, glutamic acid and aspartic acid in decreasing order. Taurine contents in the sap of Gorosoe and Sugar Maple was found to be the dominant amino acid.

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Characteristics of $Ta_{2}O_{5}$ Films by RF Reactive Sputtering (RF 반응성 스펏터링으로 제조한 $Ta_{2}O_{5}$ 막의 특성)

  • Park, Wug-Dong;Keum, Dong-Yeal;Kim, Ki-Wan;Choi, Kyu-Man
    • Journal of Sensor Science and Technology
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    • v.1 no.2
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    • pp.173-181
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    • 1992
  • Tantalum pentoxide($Ta_{2}O_{5}$) thin films on p-type (100) silicon wafer were fabricated by RF reactive sputtering. Physical properties and structure of the specimens were examined by XRD and AES. From the C-V analysis, the dielectric constant of $Ta_{2}O_{5}$ films was in the range of 10-12 in the reactive gas atmosphere in which 10% of oxygen gas is mixed. The ratio of Ta : 0 was 1 : 2 and 1 : 2.49 by AES and RBS examination, respectively. The heat-treatment at $700^{\circ}C$ in $O_{2}$ ambient led to induce crystallization. When the heat-treatment temperature was $1000^{\circ}C$, the dielectric constant was 20.5 in $O_{2}$ ambient and 23 in $N_{2}$ ambient, respectively. The crystal structure of $Ta_{2}O_{5}$ film was pseudo hexagonal of ${\delta}-Ta_{2}O_{5}$. The flat band voltage shift(${\Delta}V_{FB}$) of the specimens and the leakage current density were decreased for higher oxygen mixing ratio. The maximum breakdown field was 2.4MV/cm at the oxygen mixing ratio of 10%. The $Ta_{2}O_{5}$ films will be applicable to hydrogen ion sensitive film and gate oxide material for memory device.

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Synthesis of High Purity Al2O3 from Low Grade Bauxite Ore(II) (저품위 Bauxite로부터 고순도 Al2O3의 합성(II))

  • Kwon, Kung-Taek;Song, Yon-Ho;Lee, Chul-Tae
    • Applied Chemistry for Engineering
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    • v.5 no.4
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    • pp.597-608
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    • 1994
  • A new process for the production of high purity ${\alpha}-Al_2O_3$ from ammonium aluminium sulfate solution abtained through the sulfation of low grade bauxite ore with $(NH_4)_2SO_4$, and leaching of the sulfated product was investigated. This process is consisted of solvent extraction for Fe component removal from ammonium aluminum sulfate solution and homogeneous precipitation of Al containing precipitate from the refined ammonium aluminium sulfate solution by using urea as precipitator. The optimum conditions of solvent extraction with Alamine 336 as extractant were shaking time of 4min, organic phase ratio to aqueous phase of 0.25. The types of precipitation products from this precipitation were amorphous alumina gel, pseudo-boehmite and crystalline boehmite in the lower temperature of $100^{\circ}C$, in the range from $125^{\circ}C$ to $150^{\circ}C$, and above $150^{\circ}C$, respectively. And also amorphous alumina gel hydrate in $1000^{\circ}C$ and crystalline boehmite in $1250^{\circ}C$ were tranfered to ${\alpha}-Al_2O_3$, respectively. This alumina was identified as ${\alpha}-Al_2O_3$ of purity 99.7%.

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