Arc Plasma Research Articles

Holistic analysis of a gliding arc discharge using 3D tomography and single-shot fluorescence lifetime imaging

Gliding arc plasmas, a versatile form of non-thermal plasma discharges, hold great promise for sustainable chemical conversion in electrified industrial applications. Their relatively high temperatures compared to other non-thermal plasmas, reactive species generation, and efficient energy transfer make them ideal for an energy-efficient society. However, plasma discharges are transient and complex 3D entities influenced by gas pressure, mixture, and power, posing challenges for in-situ measurements of chemical species and spatial dynamics. Here we demonstrate a combination of innovative approaches, providing a comprehensive view of discharges and their chemical surroundings by combining fluorescence lifetime imaging of hydroxyl (OH) radicals with optical emission 3D tomography. This reveals variations in OH radical distributions under different conditions and local variations in fluorescence quantum yield with high spatial resolution from a single laser shot. Our results and methodology offer a multidimensional platform for interdisciplinary research in plasma physics and chemistry.

Free arc heating effect in double-layers hybrid arc source

Keyhole welding process is easily achieved with plasma arc heat source, but the welding speed for a stable keyhole is hard to increase because of the low-level heat input. Higher welding current will increase the heat input, but the induced heavy arc pressure acts to damage the keyhole stability. The narrow window of welding current creates limited usable range of heat input. Double-layers hybrid arc heat source is developed by compositing an outer layer of free arc into the center plasma arc jet. Set the plasma arc current level to create enough arc pressure to open a keyhole, the outer layer arc is used to control additional heat power into the weld pool but has little effect to influence the arc pressure. The free arc heating effect in the hybrid arc is figured out: (1) much faster welding speed can be achieved, it increases from 3 mm/s to 4.75 mm/s after additional 80 A/80 A free arcs are used, and (2) the increase of welding speed is highly related to the total heat input in the hybrid arc and is unrelated to the free arc number; (3) the calculated efficiency factor is selected as 0.75 for the added free arc. The developed hybrid arc is proved to be a robust method to increase the manufacturing efficiency.

Physical and chemical characteristics of plasma-activated water generated by hybrid dielectric barrier discharge and gliding arc discharge

This research explores the synergistic application of Dielectric Barrier Discharge (DBD) and Gliding Arc Plasma Jet (GAPJ) in a Hybrid Plasma Discharge (HPD) setup for enhanced water activation. The HPD system demonstrated balanced and sustained generation of reactive oxygen and nitrogen species (RONS), maintaining efficiency at higher specific input energy (SIE) values. Comparative analyses with DBD and GAPJ systems highlighted the superior performance of the HPD system in generating RONS and modifying water’s molecular structure. Key observations included a decrease in water’s pH and an increase in oxidation-reduction potential, total dissolved solids, and conductivity, stabilizing beyond 5 l min−1 airflow and 10 min of treatment. UV−Vis spectroscopy identified nitrites, nitrates, hydrogen peroxide, and nitrous acid, while Raman spectroscopy captured shifts in vibrational modes, particularly in librational and O–H stretching bands. These changes correlated with alterations in reactive species concentrations and pH levels. Overall, the HPD system emerged as a versatile and efficient approach for generating plasma-activated water, suitable for applications in microbial deactivation, surface sterilization, and electrocatalytic process optimization, offering stable and continuous production of reactive species across a range of SIE values.

Design of a long-lived Mo2C-MoO2@GC-N electrocatalyst by the ambient DC arc plasma for the hydrogen evolution reaction

A crucial challenge in hydrogen production through electrolysis is developing inexpensive, earth-abundant, and highly efficient Pt-free electrocatalysts for the hydrogen evolution reaction (HER). Molybdenum carbide is ideal for this application because of its special electrical structure, low cost, and advantageous characteristics. Herein, the long-lived electrocatalysts for HER have been synthesized via the direct current (DC) arc discharge plasma method under ambient air conditions, and the relationship between the properties of materials and catalytic characteristics has been established. The samples differed in the ratio of molybdenum, graphite, and melamine. The sample with the highest proportion of melamine in the initial mixture has Mo2C-MoO2 heterointerfaces, which demonstrates the highest and most stable electrocatalytic activity with the overpotential of 148mV at 10 mA·cm-2 and Tafel slope of 63mV·dec-1 in alkaline electrolyte. Meanwhile, the electrodes demonstrated long-lived electrochemical durability for two weeks and investigated the features of forming a stable system for HER.

Microstructural characterization of gadolinium-rich phases in titanium alloys

This study explores the microstructural characteristics of gadolinium (Gd)-rich phases in titanium (Ti) alloys through comprehensive electron microscopy analysis. The Ti alloys were produced using plasma arc melting and subsequently hot-forged. Elaborate material characterization, including scanning electron microscopy, electron backscatter diffraction, and energy dispersive spectroscopy, revealed the formation of round or angular Gd oxides and elongated Gd-rich grains within the alloy. High-magnification transmission electron microscopy and X-ray diffraction confirmed the presence of the FCC-type γ-Gd phase, influenced by the oxygen intake during casting, coexisting with Gd2O3 due to their similar crystal structures. The study also observed internal twins in the Gd grains, potentially delaying the transformation to the stable α-Gd phase. The significant mechanical property differences between the Gd-rich phases and the Ti matrix caused defects at phase interfaces during hot processing, weakening the Gd phase. This work enhances the understanding of Gd phase formation and its implications on the mechanical properties of Ti–Gd alloys.

Optimizing methane plasma pyrolysis for instant hydrogen and high-quality carbon production

The European Green Deal has set a target for Europe to achieve net-zero greenhouse gas emissions by 2050, necessitating a transition to more sustainable energy sources. Hydrogen gas (H2) has emerged as a promising solution, with methane pyrolysis presenting a viable method for its production. This study explores the optimization of methane plasma pyrolysis for hydrogen and high-quality carbon production. Employing a statistical approach by a design of experiment software, critical process parameters are systematically analyzed to predict their impact within a defined range. Additionally, the paper conducts comprehensive characterization of the solid carbon produced during pyrolysis using imaging, spectroscopic and elemental analysis, and gas sorption analysis methods. The experimental investigation was conducted using a thermal plasma reactor with several settings of influential parameters including methane gas (CH4) content in the plasma gas, electric current, and arc length. The DC-transferred plasma arc is formed using a variable gas mixture of argon gas (Ar) and CH4, with a constant flow rate of 5 Nl/min. Thirteen tests were designed, evaluating responses such as power input, process stability, and H2 yield. The H2 yield indicates the hydrogen produced from CH4, with 100% representing total conversion. While the process exhibited inconstancy, attributed to reactor design constraints, a high H2 yield of 67%–100% was achieved. The results indicate that a higher CH4 content in the plasma gas and extended arc lengths disturb the plasma arc, hence reducing the H2 yield. Increased power input, achieved through higher amperage levels, and a wider reaction zone eased by extending the arc length both led to an improved H2 yield. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) revealed microstructural differences, with carbon samples from the filter exhibiting finer textures and carbon samples from the reactor larger sizes and dendritic particles. Raman spectroscopy confirmed crystalline graphitic-like structures with low defect concentrations, a finding supported by X-ray diffraction (XRD) analysis. Inductively coupled plasma mass spectroscopy (ICP-MS) analysis confirmed high-purity carbon with slight impurities from initial filter contamination. Brunauer-Emmett-Teller (BET) specific surface area calculations based on gas sorption analysis showed significant variations, with filter-collected samples exhibiting 40–170 m2/g and reactor-collected ones showing 7–30 m2/g.

Synthesis of chromium carbide powder by vacuum-free electric arc plasma method

Chromium carbide powders were synthesized by vacuum-free electric arc method using pure chromium and carbon powder as starting components. The powders obtained in the experimental series were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), laser diffraction and differential thermal analysis. In the experiments, electrical parameters were recorded, and the thermal field generated in the reaction zone was measured using an infrared camera and tungsten‑rhenium thermocouples. The study results show the feasibility of plasma arc discharge synthesis of chromium carbide compounds Cr3C2 and Cr7C3 within 60 s at current intensity of 200 A. SEM analysis of the resulting powder shows that it consists of acute-angled particles of ∼9 to ∼50 μm in size. An updated design of the discharge circuit employed in the study significantly increases the purity of the final product. Vacuum-free electric arc synthesis of chromium carbide has been studied for the first time.

Closed-Loop Control of Dynamic Oblique Shock with Arc Plasma

The fluctuations caused by the dynamic shock wave and its interaction with the boundary layer bring formidable challenges for aerodynamic design and stable control of supersonic aircraft. The mechanism of closed-loop control for dynamic oblique shock stabilizing with arc plasma is numerically studied. Two types of dynamic oblique shocks are formed in supersonic airflow by a compression ramp rotation and incoming Mach number variation, respectively. A closed-loop controller is established to connect the arc plasma deposited power with the pressure ratio across the dynamic shock by using the proportional-integral method. It realizes the shock pressure ratio stabilized in the desired target value with a local overshoot appearing at the initial excitation and a more stable flow downstream of the oblique shock during excitation state for both types of dynamic shock control. The effects of arc plasma length and ramp rotating speed on the closed-loop control for the dynamic shocks induced by ramp rotation are further discussed. Results show that the arc plasma with longer length is more favorable to the dynamic oblique shock control with lower energy consumption and total pressure loss. The pressure ratio fluctuation is increased at higher ramp rotation speed, but its standard deviation is still limited to 0.3% of the desired target value during excitation state.

Preparation, Deformation Behavior and Irradiation Damage of Refractory Metal Single Crystals for Nuclear Applications: A Review.

Refractory metal single crystals have been applied in key high-temperature structural components of advanced nuclear reactor power systems, due to their excellent high-temperature properties and outstanding compatibility with nuclear fuels. Although electron beam floating zone melting and plasma arc melting techniques can prepare large-size oriented refractory metals and their alloy single crystals, both have difficulty producing perfect defect-free single crystals because of the high-temperature gradient. The mechanical properties of refractory metal single crystals under different loads all exhibit strong temperature and crystal orientation dependence. Slip and twinning are the two basic deformation mechanisms of refractory metal single crystals, in which low temperatures or high strain rates are more likely to induce twinning. Recrystallization is always induced by the combined action of deformation and annealing, exhibiting a strong crystal orientation dependence. The irradiation hardening and neutron embrittlement appear after exposure to irradiation damage and degrade the material properties, attributed to vacancies, dislocation loops, precipitates, and other irradiation defects, hindering dislocation motion. This paper reviews the research progress of refractory metal single crystals from three aspects, preparation technology, deformation behavior, and irradiation damage, and highlights key directions for future research. Finally, future research directions are prospected to provide a reference for the design and development of refractory metal single crystals for nuclear applications.

Surface melt nitriding and strengthening mechanism of plasma torched M50 bearing steel

This paper presents a new plasma torch nitriding technology for the first time to realize the surface nitriding of bearing steel for strengthening. By adjusting the plasma torch current parameters in the range of 120–160 A, M50 bearing steel was carried out at a nitriding speed of 2 s/cm2. After nitriding, the nitrogen content was increased from 0.00732 wt% in the original M50 steel up to 0.416 wt%, and the thickness of the nitrided layer was up to 2.51 mm. FeN0.076, Fe2N and Fe3N phases were formed in the steel, which was beneficial to increase the hardness and strength of bearing steel. The Vickers hardness of the original M50 bearing steel was 241 HV0.2. However, the highest surface hardness of specimen after nitriding was increased up to 778 HV0.2, which was attributed to the effect of sub-surface hardness strengthening within 2 mm from the depth of nitride surface. The average wear coefficient and the volumetric wear rate of the specimen after nitriding were decreased by about 32 % and 70 %, respectively. TEM observation showed that after nitriding, the structure of nitrided layer was martensite. The precipitates in the steel changed from large-sized, irregular and aggregated carbides (M23C6, M4C3 and M2C) to small-sized, spherical and uniformly distributed carbon‑nitrogen composite precipitates (M23(C, N)6, M7(C, N)3) in the steel sub-surface, but no obvious precipitates were formed on the surface of nitrided specimens. At depths of 1 mm and 2 mm, the size of the precipitates was reduced by about 68 % and 41 %, respectively, and the area of the precipitates was reduced from 18.4 % to 2.3 % and 3.7 %, respectively, compared to the original M50 bearing steel. It was concluded that the nitrided layer were strengthened synergistically with nitrogen solid solution, nitrogen-containing precipitates and martensite.

Microstructure and high-temperature tribological behaviours of nano-HfC reinforced Inconel 625 composite coating by plasma-transferred arc welding

The study involved plasma arc transfer welding (PTAW) for preparing coatings of Inconel 625 alloys that contained different amounts of nano-sized hafnium carbide (nano-HfC) particles. The impact of nano-HfC on the microstructure evolution and mechanical properties of PTAWed Inconel 625 were investigated. The research reveals that nano-HfC decomposes during the high-temperature plasma arc process and then react with O element to generate nano-HfO2. These HfO2 can serve as nucleation sites for MC carbides, which restricts the growth of secondary dendrite arms, leading to a more disordered grain growth direction. Simultaneously, the decomposition of HfC can increase the C/Nb ratio of the matrix, effectively suppressing Laves phase formation while encouraging the development of MC carbides. Compared with IN625, the wear rate of composites at room temperature and 600 °C were decreased. Notably, at 600 °C, the wear rate of the coating with 0.5 wt% HfC is the lowest among all the samples, as reflected by a noteworthy reduction in wear rate of 50 %. This is mainly attributed to the refinement of γ matrix, reduction of Laves phase as well as precipitation of the fine-sized MC carbides. This work illustrates that adding nano-HfC is an effective way to improve the wear resistance of the PTAWed Inconel 625.

Prebiotic Formation of Peptides Through Bubbling and Arc Plasma.

The abiotic synthesis of peptides, widely regarded as one of the key chemical reactions on the prebiotic Earth, is thermodynamically constrained in solution. Herein, a simulation of the lightning phenomenon on the sea surface using bubble bursting and arc plasma under ambient conditions enables dipeptide formation of six amino acids with conversion ratios ranging from 2.6 % to 25.5 %. Additionally, we observed the formation of biologically active tripeptides and investigated the stereoselectivity of the dipeptide formation reaction. By utilizing a mixture of 20 amino acids in the reaction, 102 possible dipeptides were generated. These results establish experimental constructions to mimic achievable prebiotic conditions and provide a credible pathway for endogenous biopolymer synthesis on prebiotic Earth.

Effect of laser-assisted irradiation on plasma electrolytic oxidation of titanium alloys: Arc spot evolution characteristics and photoelectric synergistic mechanisms

Laser irradiation can be employed as an auxiliary energy field to optimize functional plasma electrolytic oxidation (PEO) coatings. Herein, the mechanism of the effect of laser-assisted irradiation on the morphology and composition of ceramic coatings prepared by PEO of titanium alloys in electrolytes with sodium tetraborate-based is discussed from the perspective of plasma arc spot evolution and photoelectric synergistic effect. X-ray diffraction (XRD), transmission electron microscopy (TEM), Mott-Schottky (M-S), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to analyze the coating characteristics. The results showed that laser-assisted irradiation promoted the oxidation of the coatings, accelerated the conversion of the anatase phase to the rutile phase, reduced the oxygen vacancy defects and formed the "ant nest" porous microstructure. Monitoring of the voltage, electric field, and plasma discharge arc spot indicated that laser-assisted irradiation restricted the electric field diffusion on the anode surface, reduced the termination voltage, and significantly increased the intensity (maximum discharge percentage increased from 14.238 % to 20.358 %) and uniformity of distribution of the plasma discharge. Instantaneous photoresponse curves and electrochemical impedance spectroscopy confirmed that the PEO coatings exhibited fast and sustained photoelectric response under simultaneous laser irradiation, progressively enhanced with increasing laser irradiation energy. The photogenerated electrons excited by the semiconductor TiO2 coating under the simultaneous irradiation of laser can be used as the initial carriers of the electron avalanche, which induces the generation of a plasma on the surface of the anode and thus enhances the plasma discharge behavior, which is the fundamental reason for the optimization of the coating characteristics.

Characteristics of radioactive aerosols during the pre-decommission phase of the experimental shielding reactor

The decommissioning of nuclear reactors is a global concern, in part because of the generation of radioactive aerosols that can lead to internal radiation exposure. At present, radioactive aerosols generated during nuclear decommissioning have not been actively studied, and data collected from the actual decommissioning are limited. This paper presents a study of radioactive aerosols generated during the pre-decommission phase of an experimental shielding reactor. Among all the on-site operations, cutting resulted in the highest levels of radioactivity. Plasma arc cutting, in particular, had a maximum gross α and β radioactivity over 0.10 and 0.14 Bq/m3, respectively. Assumed AMAD (activity median aerodynamic diameter) values are employed to assess the impact of particle size on the internal exposure dose resulting from the inhalation of 137Cs aerosols. This assessment is based on the Human Respiratory Tract Model of International Commission on Radiological Protection. When cutting stainless steel by plasma arc, the internal exposure dose caused by 137Cs aerosols with an AMAD of 0.1 µm is estimated to be nearly four times as that of aerosols with an AMAD of 10 µm. Results show that the internal exposure dose is highly dependent on the AMAD, implying the importance of measuring size-related parameters of radioactive aerosols in the future nuclear decommissioning. This study has revealed some characteristics of radioactive aerosols released in decommissioning operations, which can serve as a valuable reference for controlling and removing aerosols during the decommissioning of nuclear facilities.

Cold Atmospheric Plasma (CAP) Treatment of In Vitro Cultivated Plum Plantlets—A Possible Way to Improve Growth and Inactivate Plum Pox Virus (PPV)

Plasma technology, relatively new in the fields of biomedicine, agriculture, and ecology, is the subject of intensive research as a prospective means of decontamination of various microorganisms (bacteria, viruses, and fungi). The objectives of the present study were to follow the effect of cold atmospheric plasma (CAP) treatment on in vitro grown plum plants (Prunus domestica L. ‘Kyustendilska sinya’ cv.) and the possibility of eradicating or inactivating plum pox virus (PPV) causing Sharka disease by CAP. The source tree is naturally co-infected by PPV (both M and D strains). In the experiments, two different plasma sources were used. First, a surface-wave-sustained Argon plasma torch and second, an underwater diaphragm discharge. For the treatments, nodal segments (10 mm in length) from in vitro cultured plum plants with or without one leaf were prepared. Apical shoots from treated plants (PPV-positive and negative clones as well non-treated controls) were cultivated in vitro for four passages. Then they were rooted and acclimatized to ex vitro conditions, and their virus status was observed periodically for more than 3 years after treatment for the appearance of Sharka symptoms. All plants, acclimatized to ex vitro conditions, were tested for PPV by immune capture–reverse transcription–polymerase chain reaction (IC-RT-PCR). As a first step in understanding the plasma treatment of living plants, a plasma treatment variant causing no damage must be established; this has been done in our previous works. Treatment of plants by plasma with parameters that have been carefully selected leads to better development than the non-treated plants. In the treated in vitro plants, no significant differences were found in the number and length of shoots compared to the control plantlets. In ex vitro acclimated plants, greater stem length was reported, but no differences in leaf number were observed. No significant differences in growth were recorded between the control and plants that were treated twice or three times. At this stage, 3 years after ex vitro cultivation in a greenhouse, Sharka symptoms were not registered on treated in vitro negative PPV plants, and the virus was not detected by IC-RT-PCR. Very mild symptoms were showing in CAP-treated PPV-positive plants. Development of typical Sharka symptoms on non-treated controls were observed.

Reversal of the electric field and the anode fall in DC arcs in air during contact opening

A unified one-dimensional model of an arc plasma in air, between copper electrodes, that includes the change of the gap distance is presented. The occurrence of multiple reversals of the electric field and the anode voltage drop is observed. The evolution of the spatial distribution of the electron and heavy particle temperatures with the gap distance and the opening speed is also studied. The model quantitatively predicts a number of plasma properties under conditions that are relevant to the contact separation in low-voltage switching devices.

Insight in NO synthesis in a gliding arc plasma via gas temperature and density mapping by laser-induced fluorescence

A gliding arc (GA) plasma, operating at atmospheric pressure in a gas mixture of 50% N2 and 50% O2, is studied using laser-induced fluorescence spectroscopy. The main goal is to determine the two-dimensional distribution of both the gas temperature and the NO ground state density in the afterglow. As GA plasma discharges at atmospheric pressure normally produce rather high NO x densities, the high concentration of relevant absorbers, such as NO, may impose essential restrictions for the use of ‘classical’ laser-induced fluorescence methods (dealing with excitation in the bandhead vicinity), as the laser beam would be strongly absorbed along its propagation in the afterglow. Since this was indeed the case for the studied discharge, an approach dealing with laser-based excitation of separate rotational lines is proposed. In this case, due to a non-saturated absorption regime, simultaneous and reliable measurements of both the NO density and the gas temperature (using a reference fitting spectrum) are possible. The proposed method is applied to provide a two-dimensional map for both the NO density and the gas temperature at different plasma conditions. The results show that the input gas flow rate strongly alters the plasma shape, which appears as an elongated column at low input gas flow rate and spreads laterally as the flow rate increases. Finally, based on temperature map analysis, a clear correlation between the gas temperature and NO concentration is found. The proposed method may be interesting for the plasma-chemical analysis of discharges with high molecular production yields, where knowledge of both molecular concentration and gas temperature is required.

Plasma plume enhancement of a dual-anode vacuum arc thruster with magnetic nozzle

Vacuum arc thruster (VAT) is a type of pulsed electric propulsion device that generates thrust based on vacuum arc discharges, it has great candidate for micro-newton force applications in orbit. To improve both the thrust and longevity of the VAT, a novel dual-anode structure, comprising a central anode and a ring anode, was developed. We conducted an investigation into the plasma discharge and acceleration process within the influence of a magnetic nozzle. The dual-anode architecture resulted in a reduction in the initial plasma impedance, thereby enhancing ion current and velocity. Analysis of surface parameters during discharge revealed a synergistic mechanism between the two insulator-conducting films, enabling a co-cyclic distribution of energy and resistance fluctuations within the discharge. Consequently, the dual-anode setup demonstrated a lifespan extension of at least twofold. Comparative analyses of arc energy, plasma velocity, ion current, and thrust variations with magnetic field strength were conducted between the dual-anode and single-anode configurations under magnetic nozzle influence. Results showed that the dual-anode structure increased ion current and velocity when subjected to magnetic nozzle influence, resulting in a thrust increase of up to 303%. Additionally, we developed a theoretical model for the diffusion coefficient to elucidate the adaptive splitting phenomenon of the arc within the dual-anode structure under magnetic field influence. This model suggests that the dual-anode structure can achieve a more significant enhancement in beam current from the magnetic nozzle compared to the single-anode configuration.

Long-term ablation behavior of Al4SiC4-YB4 modified Cf/ZrB2-SiC composites at 2600 °C

Long-term ablation behavior of Al4SiC4-YB4 modified Cf/ZrB2-SiC composites was characterized by air plasma torch at 2600 °C for 300 s. The phase composition and the microstructure evolution of the composites were investigated. The addition of YB4 promotes the formation of nano t-Zr0.92Y0.08O1.96 crystals, decreasing the phase transition stress in the oxide layer and reducing the volatilization of the glassy phase. However, the addition of Al4SiC4 reduces the melting point of Zr-based oxides and the viscosity of the oxide layer. Therefore, the air plasma torch blows the oxide layer away, leading to the increase of linear recession rate.

Histological Depth of Burn with Bipolar Plasma Arc – Is That the Cause for Urethral Sphincter Damage in Bipolar Transurethral Resection of the Prostate?

Introduction: The bipolar plasma button is gaining acceptance as a modality to perform endoscopic enucleation of the prostate. The plasma arc during activation of the button electrode extends for a distance beyond the edge of the evaporated area as seen on endoscopy. The extent of tissue affected by the intense heat of the arc is not certain. The histologically measurable depth of burn may have relevance during apical dissection, where thermal spread has been implicated in sphincter injury. Objectives: Our objective was to assess the histological depth of burn in animal tissue using a bipolar button electrode. Materials and Methods: Using a KENTAMED hARTT 400 electrosurgical unit machine, the following cuts were made over three freshly acquired goat liver specimens in a normal saline bath: (a) 280 W single superficial cuts using cutting current, (b) 280 W multiple deep cuts in the same groove using cutting current, and (c) 140 W, 2 s contact with coagulation current. Samples were fixed in neutral buffered formalin and processed paraffin embedded, and sections were stained with hematoxylin and eosin. The extent of thermal effect beyond the evaporated tissue edge was assessed on histopathology by a senior pathologist. Results: The histological depth of injury (involving about 5–6 rows of hepatocytes) did not extend more than 0.5 mm beyond the grossly visible edge of evaporated tissue. Conclusions: We found that the histological depth of burn in animal tissue extended only 0.5 mm beyond the grossly visible edge of the evaporation defect unlikely contributing to sphincter injury.