Wet Air Research Articles

Ba3Ti0.4W1.6O8.6: An Oxygen- and B-Site-Deficient 9R Hexagonal Perovskite Exhibiting Triple Conduction.

The hexagonal perovskite derivatives Ba3M'M″O8.5 featuring a hybrid structure composed of 9R hexagonal perovskite and palmierite structure motifs exhibit significant oxide ionic conductivity due to the highly disordered oxide-ion and M-cation sublattices. Herein, we report the structure and electrical properties of the perovskite Ba3Ti0.4W1.6O8.6. Three-dimensional (3D) electron diffraction (ED), neutron powder diffraction (NPD), and neutron pair distribution functions (nPDF) revealed a 9R hexagonal perovskite structure for Ba3Ti0.4W1.6O8.6 with fully occupied central M2 sites, partially occupied outer M1 sites, and oxygen-deficient cubic c-BaO2.6 sublayers. These cation and oxygen arrangements differ significantly from those in Ba3M'M″O8.5 and enable Ba3Ti0.4W1.6O8.6 to capture atmospheric water and O2, resulting in triple conduction (oxide ion, proton, and hole) under wet air conditions. Proton and oxide ion conductions predominate at temperatures <400 and >650 °C in wet Ar and dry air, respectively. Bond-valence site energy calculations, together with structure analysis, deciphered that the two-dimensional oxide-ion diffusion pathways along the c-BaO2.6 layers are disrupted by the M1 vacancies, thereby resulting in relatively low oxide ionic conductivity. Our findings open up a new strategy of utilizing the cation's propensity of coordination geometry to design new oxygen- and B-site-deficient perovskites and thus achieve desired conductivity.

The weather of 1740, the coldest year in central Europe in 600 years

Abstract. The winter of 1739/40 is known as one of the coldest winters in Europe since early instrumental measurements began. Many contemporary sources discuss the cold waves and compare the winter to that of 1708/09. It is less well known that the year 1740 remained cold until August and was again cold in October and that negative temperature anomalies were also found over Eurasia and North America. The 1739/40 cold season over northern mid-latitude land areas was perhaps the coldest in 300 years, and 1740 was the coldest year in central Europe in 600 years. New monthly global climate reconstructions allow us to address this momentous event in greater detail, while daily observations and weather reconstructions give insight into the synoptic situations. Over Europe, we find that the event was initiated by a strong Scandinavian blocking in early January, allowing the advection of continental cold air. From February until June, high pressure dominated over Ireland, arguably associated with frequent eastern Atlantic blocking. This led to cold-air advection from the cold northern North Atlantic. During the summer, cyclonic weather dominated over central Europe, associated with cold and wet air from the Atlantic. The possible role of oceanic influences (El Niño) and external forcings (eruption of Mount Tarumae in 1739) are discussed. While a possible El Niño event might have contributed to the winter cold spells, the eastern Atlantic blocking is arguably unrelated to either El Niño or the volcanic eruption. All in all, the cold year of 1740 marks one of the strongest, arguably unforced excursions in European temperature.

The catalytic wet air oxidation of pharmaceutical wastewater with alkali-activated Mn and Cu composites: preparation of precursors by calcination of kaolin with Mn and Cu

In recent decades, the concentration of pharmaceutical residues and narcotics has increased in municipal wastewater. Decomposing these toxic organic chemicals is challenging and requires new techniques and advanced catalytic materials. Precursors of metal composites were prepared by calcining an aqueous suspension of natural clay–based kaolin with Mn and Cu, binding chemically the active metals to the aluminosilicate frame structure of the precursor. The specific surface area of Mn and Cu composite was 67 m2/g and 81 m2/g, respectively. The mechanical durability was determined in terms of compressive strength, and 3.3 MPa and 3.6 MPa were obtained, respectively. In the CWAO of pharmaceutical wastewater, Mn composite gave the highest conversions of 54% and 46% of the chemical oxygen demand (COD) and total organic carbon (TOC), respectively. Metal composites were mechanically and chemically highly durable, inducing only 1.2 wt.% and 1.4 wt.% mass loss. In CWAO, Mn and Cu composite increased the biodegradation of organic species in the wastewater by 65% and 75%, respectively.

Diode-Type Hydrogen Sensor Employing Pd-coated Pt Electrodes and Anodized Titania under Gaseous Atmosphere and Its Application to Oil-Deterioration Monitoring

The H2-sensing properties of the diode-type sensor using Pd-coated Pt electrodes and an anodized titania film (Pd/Pt/TiO2 sensor) were investigated in air and N2 at 250°C. The current (I)–voltage (V) characteristics of the Pd/Pt/TiO2 sensor were largely dependent on the composition of the gaseous atmospheres, and the sensor showed a large H2 response in wet air, which was comparable to that in wet N2. This indicates that the H2 response are hardly dependent on the oxygen concentration under a wet gaseous atmosphere. In addition, the oil-deterioration monitoring properties of the Pd/Pt/TiO2 sensor were also examined at 30°C. The sensor also exhibited nonlinear I–V characteristics in fresh and deteriorated oils, and the magnitudes of the current and resistance responses were largely dependent on the deterioration of the oils. These results clearly indicate that the Pd/Pt/TiO2 sensor can monitor the deterioration of oils.

Unsteady-state entropy generation analysis of the counter-flow dew-point evaporative coolers

The surging demand for air conditioning, especially in hot climates, underscores the urgency of strategies aimed at curbing fossil fuel reliance and fostering energy saving strategy. Despite the longstanding utility and advantages of the conventional mechanical vapor compression refrigeration system, sustainability hurdles persist owing to its pronounced electricity demand. While evaporative cooling, harnessing water evaporation, emerges as a more efficient alternative, its efficacy is contingent upon environmental conditions. Addressing this, dew-point evaporative cooling (DPEC) presents an innovative direction, showcasing superior efficiency by directing supply air into a wet channel. This study delves into the thermodynamic losses within a counter-flow configured DPEC system, employing a transient entropy generation model rooted in the second law of thermodynamics to provide a comprehensive analysis of DPEC’s performance. Key findings that emerged from this study reveal that (1) the transient entropy generation is intricately distributed across different layers of the dew point evaporative cooling (DPEC) system, including dry air, wet air, the channel plate, and the water film; (2) Parametric analyses highlight the significant impact of factors on entropy generation, inlet air temperature has a minimal effect on system efficiency, but higher temperatures increase thermal losses. Excessive humidity limits evaporative potential, while low humidity significantly increases entropy generation. The system performs optimally at a working ratio of 0.3 and lower air velocities (within the inlet air velocity range of 0.6 to 2.2 m/s). Channel length has little impact, while the system is more sensitive to channel height, with a height of 2.5–3.5 mm being conducive to better performance. Experimental validation demonstrates the model’s accuracy in predicting system performance. The research contributes to a deeper understanding of DPEC systems, offering insights for achieving optimal operating conditions and enhancing overall efficiency in the pursuit of sustainable development.

Effect of Ca doping at A or B sites on electrochemical performance of La1.9In0.1Ce2O7 proton conductors

Fluorite proton conductors La1.8In0.1Ca0.1Ce2O7-δ and La1.9In0.1Ce1.9Ca0.1O7-δ (LICaC and LICCa) were synthesized by solid state reaction. The effect of Ca doping at A site or B site on La1.9In0.1Ce2O7 was studied by X-ray diffraction (XRD), Inductively Coupled Plasma Mass Spectrometry (ICP), scanning electron microscopy (SEM) and electrical conductivity measurement. XRD shows that the LICaC and LICCa were successfully synthesized, and Ca was doped to the expected sites. The measured mass ratios of each element by ICP were in good agreement with their theoretical values. In addition, SEM also found that the surface of the sample was dense without holes. The conductivities of LICaC and LICCa were studied at 400–800 ℃, and their highest conductivities were 7.28×10−4 and 5.56×10−3 S·cm−1, respectively. The conductivity of LICCa doped at the B site is better than that of LICaC doped at the A site. In the wet air at 800 ℃, the proton transference numbers of LICaC and LICCa are 0.5 and 0.52, respectively. LICaC and LICCa were used as electrolytes to prepare fuel cells and their performance was tested. The electrolyte thickness of LICAC and LICCA was about 0.9 mm. At 700 ℃, the maximum power density of LICaC and LICCa electrolyte-based single cells are 124.51 and 162.26 mW cm−2, respectively. The results show that LICCa has good proton conductivity and has potential as an electrolyte for high-performance fuel cells.

Investigation of samarium and neodymium co-doped BaCeO3 electrolyte for proton-conducting solid oxide fuel cells

BaCe0.8Sm0.2-xNdxO3-δ (x = 0, 0.05, 0.1, 0.15) powder was prepared using the glycine-nitrate combustion method, its crystal structure, microscopic morphology and electrochemical properties were investigated. X-ray diffraction analysis showed that the BaCe0.8Sm0.2-xNdxO3-δ powder with orthorhombic perovskite structure could be obtained after calcined at 1150 °C. Scanning electron microscopy showed that BaCe0.8Sm0.2-xNdxO3-δ sintered samples exhibited a dense structure. Electrochemical impedance tests showed that the substitution of Nd3+ improved the electrical conductivity of the BaCeO3-based electrolyte materials. The proton conductivity of BaCe0.8Sm0.15Nd0.05O3-δ samples reaches a maximum value of 0.035 S cm−1 in a wet air environment at 700 °C.

Impact of H2 Reduction on the Performance and Stability of Phenol Catalytic Wet Air Oxidation (CWAO) Over Cu−Ce/AC Catalysts

AbstractIn this study, we utilized the carbon precursor derived from walnut shells to synthesize a series of Ce‐modified Cu‐based carbon catalysts (Cu−Ce/AC) via the impregnation method. We investigated the performance and stability of Cu−Ce/AC catalysts for CWAO phenol after H2 reduction at various temperatures. The Cu−Ce/AC‐250 catalyst exhibited its highest performance at 250 °C, achieving complete phenol conversion. Characterization results from techniques including XRD, BET, FTIR, ICP‐OES, SEM‐EDS, XPS, and H2‐TPR indicated that the active components of the H2‐reduced catalysts were more evenly distributed across the catalyst surface, thereby enhancing the availability of reactive sites for phenol oxidation. Simultaneously, under the appropriate temperature, the H2 atmosphere can reduce a portion of the Cu2+ on the catalyst surface to Cu+, thereby mitigating the loss of Cu components.

A Na-Free Surface Enables "Three-In-One" Enhancement of Structural, Interfacial and Air Stability for Sodium-Ion Battery Cathodes.

O3-type layered oxides are regarded as one of the most promising cathode materials for sodium-ion batteries. However, the multistep phase transitions, severe electrode/electrolyte parasitic reactions, and moisture sensitivity are challenging for their practical application because of the highly active Na+. Here, a Na-free layer is built on the surface of NaNi1/3Mn1/3Fe1/3O2 (NMF111) via a leaching treatment and the subsequent surface reconstruction. Accordingly, both the structural degradation from bulk to surface and the overgrowth of the solid electrolyte interface (SEI) are greatly ameliorated, which results in the improved capacity retention of modified NMF111 from 58.3% to 89.6% after 400 cycles at 1 C. Besides, the Na-free surface with rock-salt structure prevents the H+/Na+ exchange and then enables good reversibility and low polarization of the optimal NMF111 when exposed to wet air (50% RH) for 4 days. This work opens a new avenue for the comprehensive cyclability improvement of layered oxides via surface reconstruction.

Variations in the Thermal Low-Pressure Location Index over the Qinghai–Tibet Plateau and Its Relationship with Summer Precipitation in China

The thermal and dynamic effects of the special topography of the Qinghai–Tibet Plateau have a significant impact on rainfall in China. Utilizing NCEP/NCAR monthly reanalysis data alongside precipitation observations from 1936 monitoring stations across China spanning from 1966 to 2022, this study establishes a location index for the thermal low-pressure center situated over the Qinghai–Tibet Plateau. Temporal variations in the location index and summer (July) precipitation patterns in China were studied. Over the past six decades, thermal low-pressure centers have been predominantly positioned near 90° E and 32.5° N within a geopotential height of 4360 gpm, with their distribution extending from east to west rather than from south to north. The longitudinal and latitudinal position indices showed the same linear trend, with a negative trend before the 21st century, and then began to turn positive. Mutation analysis highlights pronounced weakening mutations occurring in 1981 and 1973, with the longitudinal index transitioning from an interannual cycle of approximately 6–8 years, while the latitudinal index displays quasi-cyclic oscillations of 5 and 8 and 12–14 years. Strong negative correlations are evident between the location indices and precipitation along the southeastern edge of the Qinghai–Tibet Plateau and in southern China, contrasting with the positive correlations observed in the central-eastern plateau, northwest, north, and the Huang-Huai region of China. The center of the thermal low is located to the east and north, corresponding to the deeper surface thermal low in most areas east of China, and the stronger transport of warm and wet air from the southwest wind, leading to greater convergence of southwest wind and northwest wind in China’s northern region. The south of the Yangtze River is controlled by the strengthening West Pacific subtropical high and South Asia high, resulting in a significant decrease in precipitation, and the warm and humid air from the southwest on the west side of the West Pacific subtropical high is also transported to the north, increasing the precipitation in most parts of the north.

Enhanced prednisone removal by catalytic wet air oxidation using sewage sludge derived catalyst

Sewage sludge-based catalysts have been used for the first time for the catalytic wet air oxidation (CWAO) of prednisone, a glucocorticoid pharmaceutical pollutant present in various aquatic environmental matrices. This research focuses on transforming dry sludge into carbonaceous catalysts through pyrolysis and post-treatment. Various parameters have been considered for the synthesis, finding that pyrolysis temperature and acid washing are determinant for specific surface area development. The sewage sludge derived catalysts exhibit high catalytic activity in the CWAO of prednisone (Dcat= 0.3 g·L−1, T= 100 °C, P= 15 bar). The development of porosity enhances their catalytic properties, the C-750-N catalysts demonstrated the highest activity for prednisone with 66 % TOC reduction, initial reaction rate 0.0092 mg·s−1 and 66 % CO2 selectivity. The study provides valuable insights into the synthesis, characterization, and application of sewage sludge-derived catalysts, offering a sustainable solution for wastewater treatment and pharmaceutical pollutant removal. Our present study indicates that catalysts with unique reforming properties may be potentially applicable for prednisone treatment and industrial applications.

Low Temperature Fast Mixed OH−/H+ Ionic Conductor in Doped Strontium Cerates

AbstractThe drawbacks of high temperature solid oxide fuel cells (HT‐SOFCs) prompt efforts to lower operating temperatures to near ambient temperatures (NAT). Here the high mixed OH−/H+ ionic conductivity in doped SrCeO3 below 100 °C is reported. The SrCe0.8Y0.2O3−δ (SCYO20) electrolyte demonstrates a high ionic conductivity of 12 mS cm−1 in water and 9 mS cm−1 in wet air at 60 °C and an excellent long‐term stability over 100 h. Solid state nuclear magnetic resonance confirms the presence of protons and hydroxide ions in the hydrated oxides and their correlation with Y dopant. Demonstration of direct ammonia fuel cells using the SCYO20 electrolyte indicates the practical application value of this material. The OH− conduction of SrCe0.7Sn0.2Y0.1O3−δ (SCSY721) is demonstrated by electrolysis of D2O. The introduction of KOH significantly increases the availability of OH− feed ions, leading to a remarkable improvement of ionic conductivity of SCSY721 electrolyte which is increased by 27 times, 56.34 mS cm−1 in 6 m KOH at 90 °C. The increased ionic conductivity due to the presence of high concentration of extrinsic conducting ions, here are OH− ions, is called as ‘feeding effect’. This study offers new electrolyte materials for cost‐effective, and durable electrochemical devices such as NAT‐SOFCs.

Crystal phase-driven performance of MnO2 in aqueous phase low-temperature thermal catalysis: Synergistic interactions between Mn3+ and surface lattice oxygen

Catalytic oxidation at mild conditions is crucial for mitigating the high pressure and high temperature challenges associated with current catalytic wet air oxidation (CWAO) technologies in wastewater treatment. Among potential materials for catalytic oxidation reactions, polycrystalline MnO2 existed in natural minerals holds considerable promise. However, the relationships between different crystal phases of MnO2 and their catalytic activity sources in aqueous phase remain uncertain and subject to debate. In this research, we synthesized various MnO2 crystal phases, comprising α-, β-, δ-, γ-, ε-, and λ-MnO2, and assessed their catalytic oxidation efficiency during low-temperature heating for treatment of organic pollutants. Our findings demonstrate that λ-MnO2 exhibits the highest catalytic activity, followed by δ-MnO2, γ-MnO2, α-MnO2, ε-MnO2, and β-MnO2. The variations in catalytic activity among different MnO2 are attributed to variances in their oxygen vacancy abundance and redox activity. Furthermore, we identified the primary active species, which include Mn3+ and superoxide radicals (•O2–) generated by surface lattice oxygen of MnO2. This research highlights the critical role of crystal phases in influencing oxygen vacancy content, redox activity, and overall catalytic performance, providing valuable insights for the rational design of MnO2 catalysts tailored for effective organic pollutant degradation in CWAO applications.

The Influence of Au Loading and TiO2 Support on the Catalytic Wet Air Oxidation of Glyphosate over TiO2+Au Catalysts

This study aimed to explore the impact of varying amounts of added Au (0.5 to 2 wt.%) and the structural characteristics of anatase TiO2 supports (nanoparticles (TP, SBET = 88 m2/g) and nanorods (TR, SBET = 105 m2/g)) on the catalytic efficiency of TiO2+Au catalysts in eliminating the herbicide glyphosate from aqueous solutions via the catalytic wet air oxidation (CWAO) process. The investigation was conducted using a continuous-flow trickle-bed reactor. Regardless of the TiO2 support and the amount of Au added, the addition of Au has a positive effect on the glyphosate degradation rate. Regarding the amount of Au added, the highest catalytic activity was observed with the TP + 1% Au catalyst, which had a higher Schottky barrier (SB) than the TP + 2% Au catalyst, which helped the charge carriers in the TiO2 conduction band to increase their reduction potential by preventing them from returning to the Au. The role of glyphosate degradation product adsorption on the catalyst surface is crucial for sustaining the long-term catalytic activity of the investigated TiO2+Au materials. This was particularly evident in the case of the TR + 1% Au catalyst, which had the highest glyphosate degradation rate at the beginning of the CWAO experiment, but its catalytic activity then decreased over time due to the adsorption of glyphosate degradation products, which was favoured by the presence of strong acidic sites. In addition, the TR + 1% Au solid had the smallest average Au particle size of all analyzed materials, which were more easily deactivated by the adsorption of glyphosate degradation products. The analysis of the degradation products of glyphosate shows that the oxidation of glyphosate in the liquid phase involves the rupture of C–P and C–N bonds, as amino-methyl-phosphonic acid (AMPA), glyoxylic acid and sarcosine were detected.

The oxidation behavior and corrosion mechanism of SiC matrix ceramics in a high temperature wet air environment

The oxidation behavior and corrosion mechanism of SiC ceramics were investigated at high temperatures ranging from 1000 ℃ to 1200 ℃ in wet environments (75 % water/25 % air). The results demonstrate the formation of protective SiO2 layers, which effectively inhibit further oxidation at 1000 ℃ and 1100 ℃. However, simultaneous oxidation and water vapor corrosion occur at 1200 ℃, leading to substantial weight loss and the development of numerous porous layers that can reach up to 30 μm after 10 h oxidation. The YAG phases in the SiC ceramics react with SiO2 to generate Y2Si2O7, Y2SiO5, and/or Al2Si2O7 phases during oxidation process, which exhibit enhanced corrosion resistance under wet environments.

Electrochemical behaviour of redox-robust electrode in contact with protonic electrolyte: Case of double-layered Sr2Fe1.5Mo0.5O6-δ - Ce0.8Sm0.2O2-δ composite

Electrochemical devices based on proton-conducting oxides offer a significant potential for implementation in a variety of high-temperature electrochemical applications. It is a well-known fact that electrochemical devices require active electrodes to function optimally. Over the last few years, Sr2Fe1.5Mo0.5O6-δ has received much attention as an effective redox-robust electrode for oxygen conducting electrolytes. This study presents, for the first time, the results of investigations on a double-layered composite electrode based on Sr2Fe1.5Mo0.5O6-δ in contact with a barium-free proton-conducting electrolyte La0.9Sr0.1ScO3-δ. It was found that the investigated electrode exhibits low polarization resistance about 0.15 and 0.22 Ohm cm2 in wet air and wet hydrogen at 600 °C, respectively. In addition, the electrode exhibits acceptable redox stability and CO2 tolerance. Also, the results of electrochemical impedance spectra analysis and a discussion on the parallel pathways of hydrogen oxidation and oxygen reduction reactions and the nature of rate-determining steps are presented in the manuscript. The obtained results show the high prospects for a Sr2Fe1.5Mo0.5O6-δ - based composite electrode for protonic ceramic electrochemical cells.

Removal and complete combustion of 1,4-dioxane in water by a two-step reaction combining adsorption and catalytic combustion

Catalytic wet air oxidation is not so effective to decompose 1,4-dioxane in water, while there have been several studies on this reaction. As an alternative, we propose a two-step purification system for removal and complete combustion of 1,4-dioxane, where the first step is removing 1,4-dioxane from water by adsorption, and in the second step, the adsorbent is heated to release 1,4-dioxane, and the released 1,4-dioxane is completely combusted by gas-phase catalytic reaction. We had searched for adsorbents and combustion catalysts suitable for the system and found a high-silica MFI zeolite and Pt/SiO2, respectively. The high-silica MFI zeolite adsorbed up to 121 mg g−1 of 1,4-dioxane, and 1.1 mmol L−1 of 1,4-dioxane in water was almost completely removed by 10 g L−1 dose. The zeolite was reusable for adsorption-desorption cycles at least five times without any loss of the performance. Pt/SiO2 was highly active for the complete combustion of 1,4-dioxane even at 200 °C. By using the high-silica MFI zeolite and Pt/SiO2, we conducted the release of 1,4-dioxane from the zeolite by heating and the gas-phase catalytic combustion of 1,4-dioxane using two reactors connected in series, which were filled with the zeolite and Pt/SiO2, respectively, and demonstrated that all 1,4-dioxane was released by 300 °C and was completely combusted in the upstream and downstream reactors, respectively.

“Template-assisted synthesis” strategy to improve the bifunctional catalytic activity of oxygen electrode for reversible protonic ceramic electrochemical cell

Reversible protonic ceramic electrochemical cell (R-PCEC) is a new energy conversion device that can achieve efficient conversion between chemical energy and electrical energy. However, the oxygen electrode has poor activity towards oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which hinders the large-scale application of R-PCEC. Therefore, in order to improve the catalytic activity of oxygen electrodes, La0.5Sr0.5Co0.2Fe0.8O3 (LSCF) is prepared using mesoporous silica SiO2 (SBA-15) and polymethyl methacrylate (PMMA) as templates, and it was combined with BaZr0.1Ce0.7Y0.2O3-δ (BZCY) to form a composite oxygen electrode for R-PCEC. Compared to the LSCF with solid-state reaction method, LSCF with hard-template method shows higher specific surface area and more oxygen vacancy, resulting in excellent ORR catalytic activity. In addition, LSCF prepared using PMMA as a template exhibits the best ORR catalytic activity, and the single cell with this composite oxygen electrode shows the highest maximum power density of 406 mW cm−2 in fuel cell (FC) mode with wet H2 (3%H2O) and air as the fuel and oxidant, respectively. Additionally, it demonstrates a current density of −973 mA cm−2 at 1.3 V in electrolysis cell (EC) mode with wet air (10%H2O) as the oxidant. The single cell also shows good reversibility in FC mode and EC mode. This work provides a new strategy to improve the bifunctional activity of oxygen electrode in R-PCEC.

Effective decolorization of sulfur black dye and assessment of anti-microbial activity using core/shell nanoparticles based on chitosan

Sulfur dyes, a type of dye produced in large quantities is known for its depth of color. But huge quantities of sulfides, electrolytes, and inorganic salts present in effluents containing sulfur dyes cause serious problems to environment, human, and aquatic life. Hence, in this research, chitosan – sodium tripolyphosphate@TiO2 [chitosan – TPP@TiO2] polymeric core/shell nanoparticles were synthesized by Ionic Gelation Method and their decolorization of sulfur black dye was examined. Structural confirmation was established through XRD and HR-TEM measurements. Surface morphological studies with elemental analysis were investigated using HR-SEM and EDS. Core/shell formation was confirmed through XPS measurements and their optical and thermal properties were explored. Sulfur black dye decolorization studies showed 88.3% decolorization within 6 min under dark conditions at ambient conditions due to the combined effects of adsorption and catalytic wet air oxidation (CWAO). The anti-bacterial and anti-fungal activities of chitosan – TPP@TiO2 core/shell nanoparticles were analyzed.

Improving lightning protection with corona minimising air terminals

A comprehensive approach to lightning protection is comprised of four key steps, namely protection against direct lightning strikes, dealing with surges and transients, dissipation of lightning currents via earthing and bonding, and protecting people. This paper deals with new research findings associated with direct-strike protection with lightning rods or “air terminals”, namely the effect of accumulated corona space charge around the tips of these components. There is now a great deal of consensus amongst lightning researchers and practitioners that space charge accumulation reduces the efficiency of an air terminal by inhibiting the initiation and development of an upward leader, a critical stage in the lightning attachment process. The paper describes measurements carried out in a high-voltage laboratory to quantify the amount of corona discharge that would be emitted under thunderstorm conditions from a variety of air terminals of different geometries. A unique, previously unreported aspect of these experiments was the corona testing of air terminals under dry and wet conditions. The results of these experiments showed that corona discharge (and hence space charge accumulation) from a standard Franklin rod is substantially higher than from the range of significantly blunter “corona minimising” air terminals that were tested. The previously reported polarity difference in corona characteristics was also observed, i.e., the magnitude of negative corona was larger than positive corona for the same ambient electric field. Differences in corona discharge were also observed under wet and dry conditions, where wet air terminals were found to produce modestly more corona. The paper then addresses the optimisation of air terminals, i.e., minimising corona discharge, for practical lightning protection applications, where the air terminal radius of curvature is tailored to its height and position of installation. Various researchers have made these calculations, the outcomes of which are summarised in this paper. In general, radii of curvature in the range 1–100 mm are required, depending on the installation height and location of the air terminal.