Eda Egüz

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Egüz

First Name

Eda

ORCID

0000-0001-6606-8102

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Publications 1 - 10 of 10

A proposal of new environmental friendly gases for the use in electrical insulation application, II
Egüz, Eda; Hösl, Andreas; Pachin, Juriy; et al. (2019)
Palladium Zinc Nanocrystals: Nanoscale Amalgamation Enables Multifunctional Intermetallic Colloids
Yarema, Olesya; Moser, Annina; Chang, Chun-Wei; et al. (2024)
Advanced Functional Materials
Intermetallic nanocrystals are emerging materials for energy, catalysis, and biomedical applications, but combining two or more metals at the nanoscale remains challenging. The amalgamation reaction represents a convenient method for hundreds of intermetallic compositions, as it relies on fast and efficient alloying of liquid metals into presynthesized metallic seeds. Here, Pd-Zn nanocrystals, prepared via Zn amide thermolysis on the surface of Pd nanocrystals and subsequent amalgamation alloying, are investigated. Size-uniform nanocrystals and control over a wide range of Pd-Zn compositions are achieved. This allows deriving a phase diagram at the nanoscale, in which miscibility gaps and three phases with broad solid solutions are detected. Furthermore, the formation of homogeneous ZnO shells for Pd-Zn compositions extending beyond phase solubility limits is observed. Full chemistry control for Pd-Zn nanocrystals enables a rational choice of materials for selected energy applications, achieveing an extended lifetime of Zn-ion batteries for Zn-rich PdZn2 stoichiometry, superior electrocatalytic properties for nearly stoichiometric PdZn halite phase, and the stability and efficiency of high-voltage cathodes benefiting from ZnO shell protection around Pd3Zn10 nanocrystals are reported. This paper exemplifies the multifunctionality of intermetallics Pd-Zn nanocrystals, while this methodology can be extended to many other bimetallic nanomaterials.
Measurements of Swarm Parameters in C4F7N:O2:CO2, C5F10O:O2:CO2 and C5F10O:O2:N2 Mixtures
Egüz, Eda; Chachereau, Alise; Hösl, Andreas; et al. (2019)
Proceedings of the 21st International Symposium on High Voltage Engineering
Positive Synergism in the Electric Strength of Binary Gas Mixtures
Egüz, Eda (2023)
SF6 is still today the standard in gas-insulated switchgear (GIS) and its replacement is a long term non-trivial process. Basic requirements that a potential environment-friendly gas insulation medium must meet are numerous and hardly satisfied by a single compound. Hence, the search for mixtures of gases still seem a realistic approach, and the currently dominant one emphasizes on the selection of large fluorinated compounds with insulation strengths a few times higher than in SF6, to be admixed in small quantities with gases of natural origin. The first SF6-alternative mixtures containing C4F7N or C5F10O molecules with air or with CO2 and O2 are today in use in medium and high voltage GIS. One of the downsides of these complex fluorinated molecules is the extensive and potentially harmful by-products to humans as well as equipment, from discharges in switching media in particular. This thesis is more inline with earlier research and investigates binary mixtures comprised of a thermally electron-attaching gas and an electron energy moderating compound with the aim of optimizing both compounds’ contribution to the electric strength by means of synergistic interaction. Hence, our research focuses on mixtures in which the electric strength exceeds that of the individual gases – referred to as positive synergism in the present work. In a first step, the physical mechanism leading to this effect is explained, taking as a basis SF6 mixtures with HFO1234ze(E). Measurements in these mixtures are performed with a Pulsed Townsend experiment and reaction rates as well as transport parameters are obtained. The deduced electric strengths are compared to breakdown measurement results. Focus is then placed on the characterization of electron energy moderation capabilities of gases. Compounds with similar molecular structure as HFO1234ze(E) are investigated – pure and in mixtures with SF6. Experimentally obtained characteristic energies in the pure compounds are related to the observed synergism in the mixtures and to simulated molecular quantities describing moderation. Furthermore, measurements in a different backbone molecule – trifluoropropyne – are performed, also, pure and in mixtures with SF6.
Discussion on the mechanism leading to positive synergism in SF6 mixtures with HFO1234ze(E)
Egüz, Eda; Pachin, Juriy; Franck, Christian (2022)
Journal of Physics D: Applied Physics
The electric strength in HFO1234ze(E)/SF6 mixtures is investigated with swarm and breakdown experiments. The density-reduced critical electric field as well as the breakdown voltage measured with both techniques, are found to be higher than that of the pure gases in mixtures with more than 10% SF6. The underlying mechanism for the observed positive synergy is investigated and the explanation proposed by Hunter and Christophorou (1985 J. Appl. Phys. 57 4377-85) is discussed for this mixture. The pressure-dependent attachment rate is found to increase with SF6 ratio thus satisfying the main requirement of the proposed mechanism in Hunter and Christophorou's study. It appears nevertheless that due to the fast saturation with pressure and low rates in the mixtures, the three-body attachment processes account only for a small increase in the electric strength. An alternative hypothesis is proposed which considers the strong reduction of electron energies via inelastic processes in HFO1234ze(E), and is qualitatively demonstrated based on measurements and simulations.
Electron transport parameters in CO2: A comparison of two experimental systems and measured data
Vass, Maté; Egüz, Eda; Chachereau, Alise; et al. (2020)
Journal of Physics D: Applied Physics
Two experimental apparatuses used to obtain electron transport coefficients in gases are compared based on measurements in CO2 over a wide range of E/N-values. The operation principles of the two experimental systems as well as their data acquisition methods are different. One operates under the Time Of Flight (TOF) principle, where the transport coefficients are obtained by fitting the theoretical form of the electron density of a swarm in an unbounded region, n(x,t), to the measured current at different values of thedrift length, I(L,t). The other experimental apparatus operates in the Pulsed Townsend (PT) mode, where the electron transport coefficients are obtained by fitting the spatial integral of n(x,t) over the drift region to the measured, time-dependent current signal, I(L,t). In both apparatuses, the measured E/N range was extended as much as possible to allow a large overlap for the comparison of the results. The bulk drift velocity, W, obtained by the two systems agrees well (within a few %) over a wide range of E/N-values (100 Td≤E/N≤1000 Td). The agreement between the data sets for the longitudinal component of the bulk diffusion tensor, DL, is less satisfactory, the TOF data show systematically higher values (by 10–50 % depending on E/N) than the PT measurements. Significant differences are also found below 100 Td in case of the effective ionisation fre-quency, νeff, and the (Steady State) Townsend ionisation coefficient, αeff, where the TOF apparatus is unable to give accurate results. Our comparison justifies the correctness of the measured data over the range of agreement and also indicates the interval in E/N where the data obtained by each of the experimental systems can be taken to be reliable.The limits of the operating regimes of the two setups, stemming from the hardware and from the physical limits, are discussed.
Improved Estimation of Uniform AC Electric Breakdown Field Strength of HFO1234ze(E)
Basu, Devayan; Pachin, Juriy; Egüz, Eda; et al. (2023)
IEEE Transactions on Dielectrics and Electrical Insulation
The gas number-density reduced ac electric breakdown field strength (E/N)bd in pure HFO1234ze(E) is investigated from 0.45 to 4 bar with a variable electrode gap distance of 4.88, 10 and 13.32 mm. The aim of the present contribution is to clarify two aspects that are contradictorily reported in the literature. First, the pressure dependence of (E/N)bd and secondly the fact that the first breakdown value in HFO1234ze(E) can be significantly different from subsequent breakdowns in the same arrangement. To clarify these two aspects, particular attention is paid to improving the experimental procedure and considering the role of electrode surface roughness and solid dissociation products caused by the breakdowns. The methodology of experimentation has been improved, compared to standard breakdown experiments: a freshly polished set of electrodes is used for every breakdown measurement and the electrode surface is preconditioned with low-energy breakdowns in CO2 to reduce the possibility of micro-protrusions. Quantitative analysis confirms the improved and reproducible surface characteristics due to the preconditioning. The (E/N)bd values measured this way, show an increase with pressure up to 3 bar in 4.88 mm gap distance. In addition, it is confirmed that HFO1234ze(E) is a non-self-restoring gas. Subsequent breakdowns can be significantly lower than the first one across the measured pressure range and this decrease in breakdown strength increases, as energy input to the breakdown becomes higher.
Positive synergy of SF6 and HFO1234ze(E)
Hösl, Andreas; Pachin, Juriy; Egüz, Eda; et al. (2020)
IEEE Transactions on Dielectrics and Electrical Insulation
We measure mixtures of SF6 and HFO1234ze(E) (C3H2F4) and determine the critical electric field strength (E/N)crit in a Pulsed Townsend experiment. HFO1234ze(E) is an environmentally friendly alternative to SF6 for electrical insulation, since contrary to SF6 its global warming potential is negligible. While SF6 is unsurpassed in its electron attachment efficiency of thermal electrons, HFO1234ze(E) appears to moderate electron energies very efficiently. The electron attachment, on the other hand, is much weaker. We find a positive synergism in SF6/HFO1234ze(E) mixtures in the sense that the mixture of both compounds has a higher electric field strength than each gas separately. A maximum (E/N)crit of 425 Td is reached for a mixture of 40% SF6 and 60% HFO1234ze(E). A mixture of 90% HFO1234ze(E) and 10% SF6 has a critical electric field of 360 Td, similar to pure SF6. We attribute this effect to the high efficiency of HFO1234ze(E) in moderating down the electron energies, which enhances electron attachment to SF6 and reduces electron impact ionization.
Synergism in SF6 mixtures with C=C−C backbone compounds
Egüz, Eda; Pachin, Juriy; Vemulapalli, Hanut; et al. (2023)
Journal of Physics D: Applied Physics
A positive synergy in the electric strength was observed in a previous study in SF6/HFO1234ze(E) mixtures which was shown to result from a strong electron energy moderation capability of HFO1234ze(E) combined with thermal electron attachment of SF6 (Egüz et al 2022 J. Phys. D: Appl. Phys.55 315203). In the present work, the electron energy moderation properties of compounds with a similar C=C−C backbone are investigated. Swarm and breakdown measurements are performed in pure gases and in mixtures with SF6. Compounds with a trifluoromethyl group (−CF3) showed lower characteristic energy and as a consequence a positive synergism with SF6. Descriptors related to electron energy moderation are identified and computed; a clear trend is found from the analysis of descriptors related to inelastic processes which suggest(s) that vibrational excitations may be the main source of electron energy loss in the compounds showing positive synergy.
Measurement and modeling of electron and anion kinetics in N2O discharges
Hösl, Andreas; Pachin, Juriy; Egüz, Eda; et al. (2020)
Journal of Physics D: Applied Physics
From Pulsed Townsend measurements in nitrous oxide (N2O) we obtain swarm parameters for various electron and in particular anion processes. We discuss various assumptions on the discharge model in literature, and motivate a suitable model. Our findings agree with modern sources on the electron swarm parameters. Contrary to many sources however we find evidence for electron detachment from O- with a coefficient of approximately 3.2 * 10^{-20} m^2, and we suggest further changes to the commonly accepted discharge model. Based on the obtained swarm parameters, an electric strength dependent on pressure is estimated and compared to breakdown measurements.

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Eda Egüz

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