The Effect of Boron Oxide on the Crystallization Behavior of MgAl2O4 Spinel Phase during the Cooling of the CaO-SiO2-10 mass.% MgO-30 mass.%Al2O3 Systems

박주현 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.6

The microstructural characteristics of the CaO-SiO2-B2O3-10 mass.% MgO-30 mass.% Al2O3 systems solidified during slow cooling from 1600 °C were investigated using SEM-EDS and a thermochemical computation package. The effect of boron oxide on the crystallization behavior of the spinel in the aluminosilicate system was observed because boron oxide is believed to become a potential flux to reduce the melting point of the liquid oxides. The primary crystalline phase was spinel, mainly MgAl2O4, irrespective of the boron content. The liquidus temperature TL continuously decreased as the boron oxide content increased, indicating that the boron oxide decreased the activity of the MgAl2O4 spinel phase in liquid melts at high temperatures. The size of the spinel crystals increased as the temperature range for the solid + liquid coexisting region, viz. the mushy zone, increased. In the present systems, because the TL continuously decreased with the increase in the boron oxide content, the viscosity of the liquid oxide may have affected the crystallization behavior of the spinel during cooling. Based on these results, an injection of a small amount of B2O3 flux into molten steel containing liquid aluminosilicate inclusions is not recommended because large spinel crystals can originate from the changes in the thermophysical properties of the liquid inclusions due to the incorporation of boron oxide into the aluminosilicate networks.

Evaluation of Ag-doped (MnCo)₃O₄ spinel as a solid oxide fuel cell metallic interconnect coating material

Lee, Kunho,Yoon, Byoungyoung,Kang, Juhyun,Lee, Sanghun,Bae, Joongmyeon Elsevier 2017 International journal of hydrogen energy Vol.42 No.49

<P><B>Abstract</B></P> <P>To suppress vaporization of Cr oxides from the metallic interconnects of solid oxide fuel cells, studies on ceramic coating materials have been widely conducted. Among the studied materials, Mn-Co spinel has been a point of focus because of its benign reaction with metal substrates. This paper presents the evaluation results for a modified Mn-Co spinel. Ag was selected as a dopant for Mn-Co spinel, and various experiments were carried out to investigate the suitability of the doped spinel as an interconnect coating material. First, the lattice parameters were demonstrated to be stably maintained even though the Ag dopant is a precious metal. Second, the electrical conductivity was confirmed to be increased upon doping, and the thermal expansion coefficient of the doped material well matched that of AISI444. Third, through long-term oxidation and single-cell tests, the Ag-doped Mn-Co spinel was shown to be a useful coating material for compatible metallic interconnects in solid oxide fuel cell cathodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ag can be doped into Mn-Co spinel, and the resultant material shows high electrical conductivity. </LI> <LI> A long-term stability test shows that Ag-doped Mn-Co can effectively prevent metal oxidation. </LI> <LI> Ag-doped Mn-Co can successfully protect cathode triple phase boundaries against Cr deposition. </LI> </UL> </P>

Fabrication and electrical properties of sintered bodies composed of Mn(1.75-1.25X)Co2.5XNi1.25(1−X)O4 (0 ≤ X ≤ 0.6) with a cubic spinel structure

Takashi Yokoyama,Masaru Nakamura,Junichi Tatami,Toru Wakihara,Takeshi Meguro 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.5

Preparation of cubic spinel-type oxides, Mn(1.75−1.25X)Co2.5XNi1.25(1−X)O4 (0 ≤X≤ 0.6), and their electrical properties were investigated. The starting oxides, containing metals with a prescribed molar ratio, were heated to 1400℃ and held for 3 h in argon. The sintered bodies were cooled to 800 oC and then oxidized for 48 h in air to convert them into a cubic spinel structure. The electrical conductivities of the sintered bodies were confirmed to increase exponentially with an increase in the temperature, indicating that they have intrinsic NTC thermistor characteristics. In the region of 0 ≤ X≤ 0.4, the electrical conductivity increased with an increase in X and decreased with an increase in X in the region of 0.4 < X ≤ 0.6. The concentration of Mn4+ in the octahedral sites of the spinel structure was considered to be larger than that of Mn3+ because the sintered bodies were n-type semiconducting. The electrical conduction of the oxides prepared in this study was concluded to be controlled by a small polaron hopping mechanism. Preparation of cubic spinel-type oxides, Mn(1.75−1.25X)Co2.5XNi1.25(1−X)O4 (0 ≤X≤ 0.6), and their electrical properties were investigated. The starting oxides, containing metals with a prescribed molar ratio, were heated to 1400℃ and held for 3 h in argon. The sintered bodies were cooled to 800 oC and then oxidized for 48 h in air to convert them into a cubic spinel structure. The electrical conductivities of the sintered bodies were confirmed to increase exponentially with an increase in the temperature, indicating that they have intrinsic NTC thermistor characteristics. In the region of 0 ≤ X≤ 0.4, the electrical conductivity increased with an increase in X and decreased with an increase in X in the region of 0.4 < X ≤ 0.6. The concentration of Mn4+ in the octahedral sites of the spinel structure was considered to be larger than that of Mn3+ because the sintered bodies were n-type semiconducting. The electrical conduction of the oxides prepared in this study was concluded to be controlled by a small polaron hopping mechanism.

고체산화물 연료전지 연결재용 세라믹 소재

박범경,송락현,이승복,임탁형,박석주,박종욱,이종원,Park, Beom-Kyeong,Song, Rak-Hyun,Lee, Seung-Bok,Lim, Tak-Hyoung,Park, Seok-Joo,Park, Chong-Ook,Lee, Jong-Won 한국세라믹학회 2014 한국세라믹학회지 Vol.51 No.4

An interconnect in solid oxide fuel cells (SOFCs) electrically connects unit cells and separates fuel from oxidant in the adjoining cells. The interconnects can be divided broadly into two categories - ceramic and metallic interconnects. A thin and gastight ceramic layer is deposited onto a porous support, and metallic interconnects are coated with conductive ceramics to improve their surface stability. This paper provides a short review on ceramic materials for SOFC interconnects. After a brief discussion of the key requirements for interconnects, the article describes basic aspects of chromites and titanates with a perovskite structure for ceramic interconnects, followed by the introduction of dual-layer interconnects. Then, the paper presents protective coatings based on spinel-or perovskite-type oxides on metallic interconnects, which are capable of mitigating oxide scale growth and inhibiting Cr evaporation.

반응성 때려내기 방법에 의한 스피넬 형 ZnCo₂O₄ 박막의 성장과 전기적 물성

송인창,김현중,심재호,김효진,김도진,임영언,주웅길,Song, In-Chang,Kim, Hyun-Jung,Sim, Jae-Ho,Kim, Hyo-jin,Kim, Do-jin,Ihm, Young-Eon,Choo, Woong-Kil 한국재료학회 2003 한국재료학회지 Vol.13 No.8

We report the synthesis of cubic spinel $ZnCo_2$$O_4$thin films and the tunability of the conduction type by control of the oxygen partial pressure ratio. Zinc cobalt oxide films were grown on$ SiO_2$(200 nm)/Si substrates by reactive magnetron sputtering method using Zn and Co metal targets in a mixed Ar/$O_2$atmosphere. We found from X-ray diffraction measurements that the crystal structure of the zinc cobalt oxide films grown under an oxygen-rich condition (the $O_2$/Ar partial pressure ratio of 9/1) changes from wurtzite-type $Zn_{1-x}$ $Co_{X}$O to spinel-type $ZnCo_2$$O_4$with the increase of the Co/Zn sputtering ratio,$ D_{co}$ $D_{zn}$ . We noted that the above structural change accompanied by the variation of the majority electrical conduction type from n-type (electrons) to p-type (holes). For a fixed $D_{co}$ $D_{zn}$ / of 2.0 yielding homogeneous spinel-type $_2$O$ZnCo_4$films, the type of the majority carriers also varied, depending on the$ O_2$/Ar partial pressure ratio: p-type for an $O_2$-rich and n-type for an Ar-rich atmosphere. The maximum electron and hole concentrations for the Zn $Co_2$ $O_4$films were found to be 1.37${\times}$10$^{20}$ c $m^{-3}$ and 2.41${\times}$10$^{20}$ c $m^{-3}$ , respectively, with a mobility of about 0.2 $\textrm{cm}^2$/Vs and a high conductivity of about 1.8 Ω/$cm^{-1}$ /.

A highly porous MgAl2O4 spinel-supported Mn3O4 as a reusable catalyst for glycolysis of postconsumer PET waste

Haoxiang Zhang,Jong In Choi,Jung-Weon Choi,Se-Min Jeong,이평수,홍도영 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.115 No.-

A porous MgAl2O4 spinel-supported Mn3O4 catalyst, which is an efficient and robust catalyst for polyethyleneterephthalate (PET) glycolysis, was synthesized from MgAl-layered double hydroxide (LDH)as a template via thermal and chemical treatment, followed by Mn oxide loading. A mesoporous structurein the MgAl2O4 spinel provided a high surface area (278 m2/g) and defects in which Mn3O4 was highlydispersed and strongly stabilized by the substitution of Al3+ and incorporation of Mn cation into thedefects. The strong interaction of Mn oxide and the porous MgAl2O4 spinel support led to a dramaticincrease of moderate acidic and basic properties, and to high resistance for Mn leaching during glycolysis. Using the Mn3O4/p-spMgAl800 catalyst, a yield of bis(2-hydroxyethyl) terephthalate > 95 % was achievedwithin 3 h at 190 C. Despite eleven recycling times with regeneration, the catalytic activity remainedwithout significant deactivation and was completely recovered after thermal regeneration at 500 C.

금속수산화물 나노시트를 이용한 스피넬 코발트 산화물 나노큐브 합성

이종현 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

We developed a novel synthetic process for crystalline spinel Co₃O₄ nanocubes by topochemical reaction of exfoliated Co(OH)₂ nanosheet which shows unique nanoscopic nature; a larger surface area of active hydroxide layers and a much narrower oxidation-reduction for divalent Co ions in hydroxide layer compared to bulk Co(OH)₂. Our approach doesn't require additional high-temperature calcination for increasing crystallinity and organic stabilizer for anti-aggregation. We measured electrocatalytic oxygen reduction reaction (ORR) performance of the nanocubes supported on porous carbon by using cyclic voltammetry and linear sweep voltammetry under oxygen saturated 0.1M KOH solutions. The incorporation of manganese cations in Co₃O₄ nanocube has dramatically reduced the onset potential and increased the current density. When the value of the manganese ratio reaches down to 0.005, the spinel oxide nanocube catalyst exhibited the best performance in ORR.

Protective coating based on manganese–copper oxide for solid oxide fuel cell interconnects: Plasma spray coating and performance evaluation

Waluyo, Nurhadi S.,Park, Seong-Sik,Song, Rak-Hyun,Lee, Seung-Bok,Lim, Tak-Hyoung,Hong, Jong-Eun,Ryu, Kwang Hyun,Bin Im, Won,Lee, Jong-Won Elsevier 2018 Ceramics international Vol.44 No.10

<P><B>Abstract</B></P> <P>A solid oxide fuel cell (SOFC) stack requires metallic interconnects to electrically connect unit cells, while preventing fuel from mixing with oxidant. During SOFC operations, chromia scales continue to grow on the interconnect surfaces, resulting in a considerable increase of interfacial resistance, and at the same time, gaseous Cr species released from the chromia scales degrades the cathode performance. To address these problems, in this study, protective Mn<SUB>2</SUB>CuO<SUB>4</SUB> coatings are fabricated on metallic interconnects (Crofer 22 APU) <I>via</I> a plasma spray (PS) process. The PS technique involves direct spray deposition of molten Mn<SUB>2</SUB>CuO<SUB>4</SUB> onto the interconnect substrate and leads to the formation of high-density Mn<SUB>2</SUB>CuO<SUB>4</SUB> coatings without the need for post-heat-treatment. The thickness, morphology, and porosity of the PS-Mn<SUB>2</SUB>CuO<SUB>4</SUB> coating are found to depend on the processing parameters, including plasma arc power, gas flow rate, and substrate temperature. The PS-Mn<SUB>2</SUB>CuO<SUB>4</SUB> coating fabricated with optimized parameters is completely impermeable to gases and has high adhesion strength on the interconnect substrate. Furthermore, no resistive chromia scales are formed at the coating/substrate interface during the PS process. As a result, the PS-Mn<SUB>2</SUB>CuO<SUB>4</SUB>-coated interconnects show a very low area-specific resistance below 10 mΩ cm<SUP>2</SUP> at 800 °C in air and excellent stability during both continuous operation and repeated thermal cycling. This work suggests that an appropriate combination of the material and coating process provides a highly effective protective layer for SOFC interconnects.</P>

Theoretical and Experimental Studies on the Kinetics of Cation Redistribution Processes in Complex Oxides

Jianmin Shi,Klaus-Dieter Becker 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.1

The kinetics of cation reequilibration have been studied theoretically and experimentally in complex oxides after an external perturbation of equilibrium by temperature jumps. A general kinetic model for cation redistribution amongst non-equivalent sites in complex oxides is derived based on a local homogeneous point defect mechanism involving cation vacancies. Temperature-jump optical relaxation spectroscopy has been established to investigate cation kinetic processes in spinels and olivines. The kinetic model satisfactorily describes the experimental absorbance relaxation kinetics in cobalt containing olivines and in nickel containing spinels. It is found that the kinetics of cation redistribution in complex oxides shows a strong temperature- and compositiondependence. Activation energies for cation redistribution in Co-Mg olivines are found to range between 200 and 220 kJ/mol whereas an energy barrier of about 230 kJ/mol is observed in the case of nickel gallate spinel.

Theoretical and Experimental Studies on the Kinetics of Cation Redistribution Processes in Complex Oxides

Shi, Jianmin,Becker, Klaus-Dieter The Korean Ceramic Society 2010 한국세라믹학회지 Vol.47 No.1

The kinetics of cation reequilibration have been studied theoretically and experimentally in complex oxides after an external perturbation of equilibrium by temperature jumps. A general kinetic model for cation redistribution amongst non-equivalent sites in complex oxides is derived based on a local homogeneous point defect mechanism involving cation vacancies. Temperature-jump optical relaxation spectroscopy has been established to investigate cation kinetic processes in spinels and olivines. The kinetic model satisfactorily describes the experimental absorbance relaxation kinetics in cobalt containing olivines and in nickel containing spinels. It is found that the kinetics of cation redistribution in complex oxides shows a strong temperature- and composition-dependence. Activation energies for cation redistribution in Co-Mg olivines are found to range between 200 and 220 kJ/mol whereas an energy barrier of about 230 kJ/mol is observed in the case of nickel gallate spinel.