Effects of Flux Composition on the Element Transfer and Mechanical Properties of Weld Metal in Submerged Arc Welding

방국수,박찬,정홍철,이종봉 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.3

Submerged arc welding was performed using metal-cored wires and fluxes with different compositions. The effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the weld metal, i.e., △ quantity. Both carbon and manganese show negative △ quantity in most combinations, indicating the transfer of the elements from the weld metal to the slag during welding. The amount of transfer, however, is different depending on the flux composition. More basic fluxes yield less negative △C and △Mn through the reduction of oxygen content in the weld metal and presumably higher Mn activity in the slag, respectively. The transfer of silicon, however, is influenced by Al2O3, TiO2 and ZrO2 contents in the flux. △Si becomes less negative and reaches a positive value of 0.044 as the oxides contents increase. This is because Al, Ti, and Zr could replace Si in the SiO2 network, leaving more Si free to transfer from the slag to the weld metal. Accordingly, the Pcm index of weld metals calculated from chemical compositions varies from 0.153 to 0.196 depending on the wire/flux combination, and it almost has a linear relationship with the tensile strength of the weld metal. Submerged arc welding was performed using metal-cored wires and fluxes with different compositions. The effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the weld metal, i.e., △ quantity. Both carbon and manganese show negative △ quantity in most combinations, indicating the transfer of the elements from the weld metal to the slag during welding. The amount of transfer, however, is different depending on the flux composition. More basic fluxes yield less negative △C and △Mn through the reduction of oxygen content in the weld metal and presumably higher Mn activity in the slag, respectively. The transfer of silicon, however, is influenced by Al2O3, TiO2 and ZrO2 contents in the flux. △Si becomes less negative and reaches a positive value of 0.044 as the oxides contents increase. This is because Al, Ti, and Zr could replace Si in the SiO2 network, leaving more Si free to transfer from the slag to the weld metal. Accordingly, the Pcm index of weld metals calculated from chemical compositions varies from 0.153 to 0.196 depending on the wire/flux combination, and it almost has a linear relationship with the tensile strength of the weld metal.

Electron-transfer properties of high-valent metal-oxo complexes

Elsevier Publishing Company 2013 Coordination chemistry reviews Vol.257 No.9

Electron-transfer properties of heme and non-heme high-valent metal-oxo complexes are overviewed in relation to their reactivity toward oxidation of substrates. The rate constants of electron transfer from a series of electron donors to various heme and non-heme high-valent metal-oxo complexes such as compound I and compound II of horseradish peroxidase (HRP), (TMP)Mn<SUP>IV</SUP>(O) ((TMP=tetramesityl-porphyrinate dianion), (TBP<SUB>8</SUB>Cz)Mn<SUP>V</SUP>(O) (TBP<SUB>8</SUB>Cz=octa-tert-butylphenylcorrolazinate trianion) and [(L)Fe<SUP>IV</SUP>(O)]<SUP>2+</SUP>, where L=TMC, 1,4,8,11-tetra-methyl-1,4,8,11-tetraazacyclotetradecane; Bn-TPEN, N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine; N4Py, N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine; bisp, 3,7-diazabicyclo[3.3.1]nonane) were evaluated in light of the Marcus theory of electron transfer in order to determine the reorganization energy (λ) for electron transfer. The λ value increases in the order: 1.3eV (compound I of HRP), 1.53eV [(TBP<SUB>8</SUB>Cz)Mn<SUP>V</SUP>(O)], 1.6eV (compound II of HRP), 1.7eV [(TMP)Mn<SUP>IV</SUP>(O)], 2.05eV [(bisp)Fe<SUP>IV</SUP>(O)]<SUP>2+</SUP>, 2.37eV [(TMC)Fe<SUP>IV</SUP>(O)]<SUP>2+</SUP>), 2.55eV ([(Bn-TPEN)Fe<SUP>IV</SUP>(O)]<SUP>2+</SUP>), 2.74eV ([(N4Py)Fe<SUP>IV</SUP>(O)]<SUP>2+</SUP>). The λ value of compound I of HRP is the smallest among those of high-valent metal-oxo complexes, because the site of the reduction is on the porphyrin ligand, whereas the site of the reduction is on the metal for the other high-valent metal-oxo complexes. The λ values of high-valent metal-oxo porphyrins are generally smaller than those of non-heme iron(IV)-oxo complexes. The effects of Lewis acidic metal ions and Bronsted acids on the one-electron reduction of high-valent metal-oxo complexes are also overviewed in relation to their enhancement of the oxidizing ability towards reductants.

High-valent metal-oxo complexes generated in catalytic oxidation reactions using water as an oxygen source

Fukuzumi, Shunichi,Kojima, Takahiko,Lee, Yong-Min,Nam, Wonwoo Elsevier Publishing Company 2017 Coordination chemistry reviews Vol.333 No.-

<P><B>Abstract</B></P> <P>High-valent metal-oxo complexes are produced by successive electron-transfer oxidation of metal complexes with one-electron oxidants in the presence of water, which is an oxygen source in the generation of the metal-oxo complexes. Then, metal-oxo complexes oxidize substrates to yield oxygenated substrates, accompanied by the regeneration of reduced metal complexes. Thus, the oxidation of substrates using one-electron oxidants can be catalyzed by metal complexes via formation of high-valent metal-oxo complexes by the electron-transfer oxidation of metal complexes in the presence of water as an oxygen source. When water is used as a substrate, water is oxidized by one-electron oxidants to evolve dioxygen via an OO bond formation process. The one-electron oxidants used for the formation of high-valent metal-oxo complexes can be replaced by much weaker oxidants, when a photosensitizing metal complex, such as [Ru(bpy)<SUB>3</SUB>]<SUP>2+</SUP> (bpy=2,2′-bipyridine), is employed as a photocatalyst, an oxidized form of the photocatalyst, which is generated via photoinduced electron transfer from the excited state to a weaker oxidant, can oxidize metal complexes in the presence of water to afford the high-valent metal-oxo complexes. Thus, the oxidation of substrates, including water oxidation, by weak oxidants can be catalyzed by metal complexes under photoirradiation of the photocatalyst using water as an oxygen source.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Generation of metal-oxo complexes by proton-coupled electron transfer. </LI> <LI> Catalytic oxygenation of substrates by metal complexes using water as an oxygen source. </LI> <LI> Catalytic water oxidation by one-electron oxidants with metal complexes. </LI> <LI> Photocatalytic oxidation of water and substrates with metal complexes. </LI> </UL> </P>

Numerical study on conjugate heat transfer in a liquid-metal-cooled pipe based on a four-equation turbulent heat transfer model

Li Xian-Wen,Su Xing-Kang,Gu Long,Wang Xiang-Yang,Fan Da-Jun 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.5

Conjugate heat transfer between liquid metal and solid is a common phenomenon in a liquid-metalcooled fast reactor's fuel assembly and heat exchanger, dramatically affecting the reactor’s safety and economy. Therefore, comprehensively studying the sophisticated conjugate heat transfer in a liquidmetal-cooled fast reactor is profound. However, it has been evidenced that the traditional Simple Gradient Diffusion Hypothesis (SGDH), assuming a constant turbulent Prandtl number (Prt, usually 0.85 - 1.0), is inappropriate in the Computational Fluid Dynamics (CFD) simulations of liquid metal. In recent decades, numerous studies have been performed on the four-equation model, which is expected to improve the precision of liquid metal’s CFD simulations but has not been introduced into the conjugate heat transfer calculation between liquid metal and solid. Consequently, a four-equation model, consisting of the Abe k ε turbulence model and the Manservisi kq εq heat transfer model, is applied to study the conjugate heat transfer concerning liquid metal in the present work. To verify the numerical validity of the four-equation model used in the conjugate heat transfer simulations, we reproduce Johnson’s experiments of the liquid lead-bismuth-cooled turbulent pipe flow using the four-equation model and the traditional SGDH model. The simulation results obtained with different models are compared with the available experimental data, revealing that the relative errors of the local Nusselt number and mean heat transfer coefficient obtained with the four-equation model are considerably reduced compared with the SGDH model. Then, the thermal-hydraulic characteristics of liquid metal turbulent pipe flow obtained with the four-equation model are analyzed. Moreover, the impact of the turbulence model used in the four-equation model on overall simulation performance is investigated. At last, the effectiveness of the four-equation model in the CFD simulations of liquid sodium conjugate heat transfer is assessed. This paper mainly proves that it is feasible to use the four-equation model in the study of liquid metal conjugate heat transfer and provides a reference for the research of conjugate heat transfer in a liquidmetal-cooled fast reactor

Experimental study on single-phase heat transfer and pressure drop of refrigerants in a plate heat exchanger with metal-foam-filled channels

Bamorovat Abadi, Gholamreza,Moon, Chanhee,Kim, Kyung Chun Elsevier 2016 Applied thermal engineering Vol.102 No.-

<P><B>Abstract</B></P> <P>Metal-foam-filled channels are proposed to increase the heat transfer area between hot and cold flows in plate heat exchangers. This experimental study focuses on the single-phase heat transfer mechanism of R245fa refrigerant in a metal-foam-filled plate heat exchanger instead of more commonly used air or water in single-phase experiments. The refrigerant-side heat-transfer coefficient and pressure-drop data are reported. Different metal foams with various pore densities of values of 20, 30, and 60pore per inch (PPI) were examined. Cases were studied with uniform PPI and with two different PPI along the flow direction. A complete heat exchanger test section with an overall volume of 0.001m<SUP>3</SUP> that is able to generate 1–2kW heat duty in this range of experimental conditions is manufactured. The result shows that inserting 60-PPI metal foam increases the refrigerant-side heat transfer coefficient by up to 5.1 times compared to the plate heat exchanger without the metal foam insert. As expected, the pressure drop penalty is huge. The 60-PPI metal foam had the greatest pressure drop, which was 5.7 times that of an empty-channel heat exchanger.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heat exchanger with metal-foam-filled channels is manufactured. </LI> <LI> Single-phase experiments are performed. </LI> <LI> The effect of metal foam configuration and pore density is analyzed. </LI> <LI> With 60PPI metal foam the overall HTC increased by 5.1 times. </LI> <LI> With 60PPI metal foam the pressure drop increased by 5.7 times. </LI> </UL> </P>

Molecular Wire World Having Metal Complexes

Choi, Chang-Shik Korean Society of Photoscience 2014 Rapid communication in photoscience Vol.3 No.3

Development of molecular and supramolecular systems showing efficient photoinduced energy or electron transfer are of current research interest due to their applications in various chemical and biological processes. Various polypyridine metal complexes including Ru(II), Ru(III), Os(II), Pt(II), Fe(II), Re(I), Ir(III) and so on as a metal center introduce for expanding some more understanding of molecular-scale photoelectronics. Their complexes are concisely classified by the types of relay ligands as follows; (a) metal-direct ligand-metal system; dinuclear or trinuclear systems, (b) metal-nonconjugated ligand-metal system and metal-nonconjugated ligand system having flexible/rigid ligand, (c) metal-conjugated ligand-metal system, and (d) conjugated ligand-metal-conjugated ligand system and metal-self assembly ligand-metal system. It is pointed out that the role played by the relay ligands is important in constructing the metal complexes.

A Study on the Change of Wire Feeding Speed in GTA Welding (Ⅰ) - Changes in the Modes of Metal Transfer -

Daekyu Park,Jehyoung Cho,박영환 대한용접접합학회 2023 대한용접·접합학회지 Vol.41 No.3

GTA welding (GTAW) is a representative welding technique employed for pipe root gap welding. Although this technique allows the control of the current and wire feeding speed as independent variables, it is difficult to determine these variables to ensure appropriate quality. In the pipe root gap welding task, the parameters of automated welding applications are difficult to determine due to gap and misalignment. Accordingly, this study was conducted to examine changes in the modes of metal transfer according to the welding current and wire feeding speed. In the various processes of GTAW, changes in volume transfer form yield certain advantages and disadvantages, necessitating appropriate tuning procedures to maintain a desired quality. Changes in heat input ratio (HIR), which relates to the welding heat input (HI) and wire feeding speed, were observed to predict modes of metal transfer. According to changes in welding current and wire feeding speed, metal transfer was expressed as an index, and a regression equation was formulated to predict the modes of metal transfer through said index.

Is metal nanofluid reliable as heat carrier?

Nine, Md.J.,Chung, H.,Tanshen, Md.R.,Osman, N.A.B.A.,Jeong, H. Elsevier Scientific Pub. Co 2014 Journal of hazardous materials Vol.273 No.-

A pre- and post experimental analysis of copper-water and silver-water nanofluids are conducted to investigate minimal changes in quality of nanofluids before and after an effective heat transfer. A single loop oscillating heat pipe (OHP) having inner diameter of 2.4mm is charged with aforementioned nanofluids at 60% filling ratio for end to end heat transfer. Post experimental analysis of both nanofluids raises questions to the physical, chemical and thermal stability of such suspension for hazardless uses in the field of heat transfer. The color, deposition, dispersibility, propensity to be oxidized, disintegration, agglomeration and thermal conductivity of metal nanofluids are found to be strictly affected by heat transfer process and vice versa. Such degradation in quality of basic properties of metal nanofluids implies its challenges in practical application even for short-term heat transfer operations at oxidative environment as nano-sized metal particles are chemically more unstable than its bulk material. The use of the solid/liquid suspension containing metal nanoparticles in any heat exchanger as heat carrier might be detrimental to the whole system.

An experimental study on the thermal and hydraulic characteristics of open-cell nickel and copper foams for compact heat exchangers

Kim, Dae Yeon,Kim, Kyung Chun Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.130 No.-

<P><B>Abstract</B></P> <P>High-porosity open-cell metal foams made of copper and nickel were inserted into a rectangular channel containing R245fa refrigerant with mass flux ranging from 76 to 391 kg/m<SUP>2</SUP> s. The single-phase heat transfer from the surrounding channels is driven by hot water in a closed cycle and ranges from 0.53 to 1.37 kW. The heat transfer and pressure drop across the embedded metal-foam samples were measured while maintaining constant conditions of the refrigerant inlet pressure and hot water supply. The heat transfer coefficient was calculated based on a modified Wilson-plot method. The results were compared with published correlations, and new correlations are proposed to take into account the characteristics of the foam geometry and material. In addition, three parameters are introduced to compare different types of metal foam samples. The results of the experiment show that the metal-foam-filled channel increases the Colburn <I>j</I>-factor by up to 6.3 times compared to an empty channel. As a result, the metal foams with higher pore density and higher thermal conductivity perform better than other samples in single-phase flow.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Single phase flow heat transfer measurement in a vertical channel filled with metal-foams. </LI> <LI> Characteristics of fluid flow and heat transfer of R245fa in a hot-water-driven test facility. </LI> <LI> Foams made of copper and nickel were compared. </LI> <LI> Correlations developed for average heat transfer coefficient and pressure drop. </LI> </UL> </P>

중금속 오염 농경지의 식물유효태 예측 모델식 개발: 우리나라 폐광산 인근 농경지 토양 사례 연구

임가희 ( Ga Hee Lim ),김계훈 ( Kye Hoon Kim ),서병환 ( Byoung Hwan Seo ),김권래 ( Kwon Rae Kim ) 한국환경농학회 2014 한국환경농학회지 Vol.33 No.4

BACKGROUND: Application of the transfer functions derived from local soil data is necessary in order to develop proper management protocols for agricultural soils contaminated with heavy metals through phytoavailability control of the heavy metals. The aim of this study was to derive the transfer functions of Korean agricultural soils affected by the abandoned mining sites and evaluate suitability of the derived transfer functions. METHODS AND RESULTS: 142 agricultural soils affected by the abandoned mining sites were collected and analyzed. Two extraction methods, including 1 M NH4NO3 extraction and 0.01 M Ca(NO3)2 extraction were applied to determine phytoavailable metal pools in soils. Multiple stepwise regression of phytoavailable metal pools against the corresponding total metal concentration and soil properties was conducted to derive suitable transfer functions for estimating phytoavailable heavy metal pools. Applicability of the derived transfer functions was examinedby calculating NME and NRMSE. CONCLUSION: Soil pH and organic matter were valid variables for derivation of the transfer functions which were applicable for estimating phytoavailable metal concentrations in the soils being contaminated by heavy metals. In addition, it was confirmed that transfer functions need to be developed based on local soil conditions to accurately estimate heavy metal-phytoavailability.