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2. Structural and electronic properties of rare earth chromites: A computational and experimental study

Author

Shi, Jianhang, Fernando, Gayanath W., Dang, Yanliu, Suib, Steven L., and Jain, Menka

Subjects
Condensed Matter - Materials Science
Abstract

In this work, the structural, optical, and electronic properties of rare-earth perovskites of the general formula RCrO3, where R represents the rare-earth Gd, Tb, Dy, Ho, Er, and Tm, have been studied in detail. These compounds were synthesized through a facile citrate route. X-ray diffraction, Raman spectroscopy, and UV-Vis spectroscopy were used to reveal the structural evolutions in RCrO3. The lattice parameter, Cr3+-O2--Cr3+ bond angle, and CrO6 octahedral distortions were found to strongly depend on the ionic radii of the rare-earth element. First-principles calculations based on density-functional theory within the generalized gradient approximation (GGA) of Perdew- Burke- Ernzerhof (PBE) and strongly constrained-and-appropriately normed (SCAN) meta-GGA were also employed to calculate the structural and electronic properties of RCrO3. The ground-state energy, lattice constants, electronic structure, and density of states (DOS) of RCrO3 were calculated. These provide some insights into the electronic characteristics of the series of RCrO3 compounds. The calculated values of lattice parameters and band gaps with Hubbard U correction (SCAN+U) agree well with values measured experimentally and show more accuracy in predicting the ground-state crystal structure and band structure compared to PBE+U approximation. The band gap of RCrO3 is found to be independent of the ionic radii of the element R from both experiments and calculations, Comment: 17 pages, 10 figures, 8 tables

Published
2022

12. Decomposition characteristics of C4F7N-based SF6-alternative gas mixtures.

Author

Gao, Wenqiang, Posada, Luisa, Shiravand, Vahid, Shubhashish, Shubhashish, Price, Capri, Zhang, Boya, Potyrailo, Radislav, Younsi, Karim, Shan, Shiyao, Ndiaye, Ibrahima, Cabrera, Charlotte, Zhou, Jierui, Perret, Maxime, Berteloot, Thomas, Kieffel, Yannick, Laso, Andres, Uzelac, Nenad, Suib, Steven L., and Cao, Yang

Subjects
MOLECULAR sieves, REAL gases, ELECTRIC power distribution grids, CATALYSIS, ACCELERATED life testing, GAS mixtures
Abstract

C4F7N [2,3,3,3-tetrafluoro-2-(trifluoromethyl)propanenitrile]/CO2 gas mixtures are being developed as an eco-friendly electrical insulator to replace SF6, the most potent greenhouse industrial gaseous dielectric. However, recent studies have reported complicated and often conflicting decomposition pathways for C4F7N/CO2 gas mixtures, which has raised concerns. In this work, the decomposition characteristics of C4F7N/CO2 gas mixtures were studied comprehensively by both designed computations and experiments. Computations were performed starting from fundamental propositions of C4F7N/CO2 decompositions, which were further experimentally verified by pyrolysis, long-term thermal aging with/without catalytic materials (industrial-grade molecular sieves 4A), and electrical decomposition by spark discharge. The results of both computations and experiments suggest that in an ideal thermal decomposition, C4F7N is likely to decompose into C2F6 and small fluoronitriles first at high temperatures. The generation of C3F6 and C2N2 from C4F7N thermal decomposition at lower temperatures appears because of the catalytic effect of incompatible materials, for example, the industrial-grade molecular sieves 4A that we tested. The electron impact dissociation of C4F7N plays an important role in C4F7N electrical decomposition, leading to additional formation of distinctive small molecules of CF4 and C2N2 of low concentrations. It was pointed out based on a real arcing test in a load disconnector that the decomposition of C4F7N gas mixtures in real applications will be at a much moderate and manageable rate than what was obtained from the highly accelerated laboratory tests presented in this work. The signatures of decomposition products extracted in this study provide invaluable guidance for developing decomposition-based diagnosis and fixation of decomposition byproducts toward SF6-free power grids. [ABSTRACT FROM AUTHOR]

Published
2024
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22. (Ga1−xAlx)4B2O9: controlled surface acid–base properties and catalytic behavior towards the Strecker reaction.

Author

Wang, Weilu, Fan, Zhong, Tang, Shiji, Wu, Yun, Xu, Ke, Luo, Binbin, and Suib, Steven L.

Subjects
LEWIS acids, LEWIS bases, LEWIS basicity, METAL catalysts, BASICITY
Abstract

Solid bases are valuable catalysts for industrial syntheses. However, controlling the basicity of these catalysts remains a challenge. Ga4B2O9, due to μ3-O within its structure, could behave as a special solid base catalyst exhibiting intrinsic Lewis basicity. In this work, a sol–gel method was proposed to obtain continuously adjustable acidity and basicity of the metal borate catalyst (AlxGa1−x)4B2O9. According to the results of NH3-TPD, CO2-TPD, and the systematic experimental design, Lewis basic sites originating from GaO5 groups in (AlxGa1−x)4B2O9 boost the Strecker reaction rather than the Lewis acid sites related to unsaturated Al. This work illustrates the possible application of bulk-type solid solutions with simultaneous Lewis acid and base sites for the first time. A reaction mechanism has also been proposed based on the catalytic reaction results. [ABSTRACT FROM AUTHOR]

Published
2024
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30. Investigation of Titanium Nitride as an Effective Interphase for Carbon-Fiber-Reinforced Silicon Carbide Ceramic Matrix Composites

Author

Wickramathilaka, Kaveendra Yasas, Valus, Joseph, Shuster, Seth, Purgay, Ryan, Suleiman, Yara, and Suib, Steven L.

Abstract

Ceramic matrix composites (CMCs) have played a significant role in increasing the efficiency of gas turbine engines. CMCs combine the high temperature resistance of ceramics with the high mechanical strength of ceramic fibers into a single unit. Interphase layers are a crucial component in CMCs, as they prevent ceramic fibers from oxidation and introduce strengthening mechanisms into the composite. Hexagonal boron nitride and pyrolytic carbon are the most commonly used interphase layers in the aerospace industry. Other than that, very few materials have been evaluated as interphase layers. In this study, we explore the possibilities of using titanium nitride as an interphase layer in single-tow CMCs (mini composite) representative of a unidirectional composite at a smaller scale. T-300 carbon fibers were coated with TiN by atmospheric pressure chemical vapor infiltration using TiCl4, N2, and H2. The deposition temperature, precursor flow rate ratio, total precursor flow rate, and deposition time were optimized to obtain high-quality coatings. The best coating was produced at 800 °C, 4:1 H2[TiCl4]/N2ratio, 125 standard cubic centimeters per minute (N2+ H2[TiCl4]) total flow precursor flow rate, and 2 h of deposition time. At these conditions, the coatings displayed good fiber coverage, good fiber adhesion, minimum fiber linkage, and minimum surface roughness. There was minimum fiber degradation after TiN coating, with a retention of 95% of the initial Young’s modulus and 26% of the ultimate tensile strength of the carbon fiber. Adding the TiN interphase coating to the Cf/SiC CMC increased the ultimate tensile strength of the composite by 1122% and Young’s modulus by 150%.

Published
2024
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35. Covalent Organic Framework Functionalized with Fluorescein Isothiocyanate for the Selective and Sensitive Detection of Toxic Mycotoxin.

Author

Sui, Wubin, Jin, Qianqian, Shi, Tiesheng, Yu, Yanxin, and Suib, Steven L.

Abstract

Staining of foods by toxic mycotoxins is a general severe problem in the world. To explore simple methods for effective monitoring of mycotoxin-stained foods has extraordinary significance. Herein, we designed and prepared a covalent organic framework (COF)-derived fluorescent composite (DhBd-PT-COF-FITC) by anchoring a continually utilized fluorescent tag, fluorescein isothiocyanate (FITC), in the nanopore channel of a two-dimensional imine COF (DhBd-PT-COF) to detect a major existent mycotoxin of moldy sugar cane3-nitropropionic acid (3-NPA), which is closely related to toxicosis events of humans. Tying FITC molecules into the pore channels of DhBd-PT-COF can not only enhance the fluorescence intensity of FITC by relying on the confinement effect of DhBd-PT-COF but also retain inherent pH-responsive characteristics. As a result, DhBd-PT-COF-FITC showed the selective and sensitive response to 3-NPA. The detection limit of DhBd-PT-COF-FITC toward 3-NPA is achieved to be ultralow as 12.5 nM. More attractively, facile recovery of DhBd-PT-COF-FITC can be obtained via simple alkaline treatment. The prepared sensor has also been used to detect 3-NPA in actual sugar cane samples with satisfying recovery. Our work not only exhibits fascinating performance of COF-derived fluorescent composites toward 3-NPA monitoring but also offers a prospective approach to develop various specific materials for other targets. [ABSTRACT FROM AUTHOR]

Published
2024
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36. Structure and defect analysis of different polysilazane‐derived silicon carbide systems.

Author

Shuster, Seth, Bamonte, Scott, Valus, Joseph, Purgay, Ryan, Arif, Fayaz, March, Seth, and Suib, Steven L.

Subjects
SILICON carbide, ELECTRON energy loss spectroscopy, POLYMERS, SCANNING transmission electron microscopy, SILICON nitride, X-ray photoelectron spectroscopy, ELECTRONIC ceramics
Abstract

Polysilazane (PSZ) polymers offer the ability to form silicon carbide (SiC) or silicon nitride (Si3N4) via thermal pyrolysis. The majority of studies surrounding this polymer have focused on the decomposition of PSZ to amorphous glass. Investigations into the structural defects and bonding environments of the final ceramic systems are not as frequently discussed. Examining structural defects/abnormalities can help better use PSZ‐derived ceramics in electronic and high‐temperature applications, where phase identity and microstructure are important. In this work, three PSZ‐derived polymers were synthesized with different C/N ratios (1.33, 1.0, and 1.2) via the ammonolysis condensation reaction with chlorinated silanes. The samples were named PSZ‐SiCF1‐3. Samples were then pyrolyzed under Ar in a tube furnace at 1600°C for 5 h. Characterization included X‐ray diffraction (XRD), Raman spectroscopy, X‐ray photoelectron spectroscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy. XRD measurements uncovered arbitrary stacking fault (SF) measurements of 3C‐SiC to be 4.12, 1.08, and 2.12 (unitless) for samples PSZ‐SiCF1‐3. Results were supported through Raman spectroscopy and TEM. High carbon content, not higher residual nitrogen content, was more impactful for SF formation. This highlights the importance of SFs in the microstructural evolution of non‐oxide ceramics. [ABSTRACT FROM AUTHOR]

Published
2024
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49. Arsenate Anion–π Interactions on Amine-Modified Polydivinylbenzene in Aqueous Systems: Experimental and Theoretical Investigation

Author

Macharia, John, primary, Jafari, Tahereh, additional, Song, Kevin, additional, Sahoo, Sanjubala, additional, Moharreri, Ehsan, additional, Meguerdichian, Andrew, additional, Amin, Alireza S., additional, Manthina, Venkata, additional, Khakpash, Nasser, additional, Miao, Ran, additional, and Suib, Steven L., additional

Published
2024
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