Ablation Gas Research Articles

A theoretical model considering the photochemical and photothermal behavior of arc radiation-induced gassing materials ablation

In this study, we introduce a theoretical model designed to explore both the photochemical and photothermal behavior of arc plasma radiation-induced ablation in gassing materials. We employ time-dependent density functional theory to analyze the photochemical behavior, while reactive force field molecular dynamics are used to explore the photothermal behavior. The phenomena, behavior and consequences of valence shell electronic excitation are analyzed in terms of ultraviolet (UV) absorption, electron-hole distribution, and Mayer bond order. Based on the photochemical findings, we apply a periodic electric field that corresponds to the vibration frequency of the permanent dipole moment to simulate infrared radiation, and convert UV photon energy into atomic kinetic energy to analyze UV radiation. This atomic-scale insight into photothermal behavior enables us to identify the final composition of ablation gases, including H2, CO, H2O, NH3, as well as specific cyanides, amines, and hydrocarbons. The results of the theoretical model and physical properties indicate that the concentration of hydrogen-containing gases in the ablation gas significantly affects the arc extinguishing capabilities of different polymers. Finally, we propose modification schemes suitable for polymers in power circuit breakers, considering UV absorption and smoke black production. Additionally, we present the potential application of theoretical models for calculating the ablation rate, necessitating further in-depth re-search.

Comparison of measurement and numerical calculation on spectral profile of ablation arc plasma around current zero in high-voltage gas circuit breakers

A product-scale interrupter with a rated voltage range of 245 kV to 362 kV and current condition of 20 kA root mean square has been examined to study the arc extinguishing process and the appearance of absorption spectrum by C2 molecules immediately before the current zero. The latter has elucidated the presence of C2 molecules outside the arc core, where the temperature is lower. The temporal behaviour of the C2 absorption spectrum and the emission spectrum of the S+ ion have been measured, which have indicated that polytetrafluoroethylene ablation gas is replaced by SF6 because of gas flow from the thermal puffer chamber to the stagnation point. The computed spectra agree well with the experimentally obtained spectra and show similarities to measured profiles. They show evidence of absorption by C2 molecules in the continuous spectrum and the reproduced band heads of the C2 Swan spectrum.

Relationship analyses on environmental factors-ablation performance based on ZrC-TaC system: Oxygen partial pressure and gas flow scouring

For better understanding on effects of ablation environmental factors (oxygen partial pressure P(O2) and gas flow scouring), multiple experiments and multiscale simulations based on thermally sprayed ZrC-TaC system were conducted. High P(O2) was found helpful to accelerate Ta2O5/ZrO2 mutual diffusion by variable P(O2) oxidation at 1500 ℃ (5-50 kPa). Effects of gas flow scouring was evaluated by flow filed simulation coupling laser and oxyacetylene ablations, from which its promotion effect on Ta2O5/ZrO2 diffusion efficiency was found. The increased Ta2O5/ZrO2 diffusion efficiency will accelerate the structure instability of Ta doped c-ZrO2 skeletons due to Zr-O bond length extension around Ta atoms.

Aerothermal effects of ablation on carbon-based space objects

The growing number of space objects is a potential risk not only for operational space systems but also for ground safety. To prevent possible collisions with the ground, it is necessary to accurately predict the trajectory and the survivability of space objects using re-entry analysis. Depending on the material of the space objects, ablation gas emissions should also be considered in re-entry analyses, because emissions can significantly affect the aerothermodynamics and gas-surface interaction. In this study, re-entry analyses of carbon-based space objects were performed, and ablation effects were analyzed. For the flow-field calculations, the trajectory of the space objects during re-entry was calculated based on three-degrees-of-freedom equations of motion. For the material response calculations, ablation modelling and quasi-one-dimensional in-depth temperature calculations for the ablating space objects were performed considering the surface energy balance. To independently consider the ablation effects of surface recession, ablation gas emission, and the chemical composition of the ablation gas, four space object models were considered. The re-entry of the space objects was analyzed under three trajectory scenarios, and then the effects of ablation on the trajectory and the survivability of the carbon-based space objects were assessed. Specifically, when considering the ablation gas emission, it was found that the maximum surface temperature and the final size of the space objects were different compared to that the predicted value only when melting was considered.

CO2 number density measurement in a shock tube with preheated carbon surface

The interaction between a heated carbon-based material and high-temperature air may produce ablation gas species such as CO2, affecting heat transfer onto the surface of a thermal protection system. The prediction of ablation gas production is critical for heat flux prediction and the design of a thermal protection system. In this study, we present a system that measures the number density of CO2 formed by the gas–surface interaction between a hot carbon surface and high-temperature gas. The heated carbon wall is exposed to high-temperature air by using a shock tube and surface heating model. The surface temperature of the carbon wall is measured using two-color ratio pyrometry. The number density of CO2 is predicted by performing numerical calculations for the shock tube flow with gas–surface interaction modeling. The number density of CO2 molecules is measured using infrared emission spectroscopy. The measured CO2 number density is 9.60 × 1023 m−3 at an area-weighted average surface temperature of 1212 K. The measured number density matches the predicted value within an error of 6%. The proposed system is applicable for CO2 number density measurement under various gas–surface interaction conditions, and it can be used for the investigation of ablative gas production and numerical research on gas–surface interactions.

Laser damage resistance of plasma-sprayed alumina and honeycomb skeleton/alumina composite ceramic coatings

Al2O3 and honeycomb skeleton-Al2O3 composite coatings on Titanium alloy (Ti–6Al–4V) were prepared by atmospheric plasma spraying. A laser ablation experiment on as-sprayed coatings was performed. In this paper, the laser damage resistance, microstructure, phase composition of Al2O3 coatings were examined. 3D Dimensional Confocal Microscopy, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Energy Dispersive Spectrometry (EDS) characterized the laser damage morphology, microstructure, phase composition, and element analysis, respectively. The influence of the honeycomb skeleton on the laser ablation damage on as-sprayed coatings was investigated by a comparative analysis of the laser damage morphology with different laser ablation times and gas flow. The results show that the honeycomb skeleton raises thermal conductivity and thermal diffusivity. Moreover, a “tower”-like dendrite was generated during the laser irradiation of the composite coating. The honeycomb skeleton refined the structure, suppressed crack propagation, and reduced the influence of gas flow on cracks. Under the same experimental laser ablation parameters, the laser damage area of the honeycomb skeleton-Al2O3 composite coating was smaller than that of the Al2O3 coating. It was demonstrated that the laser damage resistance of the honeycomb skeleton-Al2O3 composite coating was superior to that of the Al2O3 coating.

Stagnation-point heating and ablation analysis of orbital re-entry experiment

In this study, stagnation-point heating and ablation analysis of the orbital re-entry experiment (OREX) are performed including the air and ablation gas mixture. In gas–gas interactions, the ablation gas is ejected into the shock layer, and the interaction between the air and ablation gases is fully considered. The two-temperature model is employed to describe the thermochemical nonequilibrium flows of the OREX flight conditions. The state-of-art chemical-kinetic parameters of 19-species, including the air and carbon-related ablation gas species, are assessed and utilized to calculate the re-entry flows. In gas–surface interactions, three types of ablation models, the fully equilibrium model, Park model, and surface thermochemistry model of the Zhluktov–Abe and Prata models, are employed to describe the ablation on the surface of carbon–carbon composite CC material of the thermal protection system. For the selected trajectory points of the OREX flight conditions, quasi-one-dimensional thermochemical nonequilibrium flow calculations are carried out, and the results are analyzed in detail. From the calculated results of the re-entry flows, it was found that the production of CO, CO2, and CN is the dominant mechanism of the surface heating on the ablating surface. Heat loss by surface recession is relatively small in OREX flight conditions. The total amount of surface recession due to ablation is approximately 0.22–0.32 mm in the selected range of the OREX flight. Heat loss from surface radiation increases with the surface temperature, and the amount of heat loss is comparable to the amount of surface heating at the trajectory point of 7481.5 s in the OREX flight.

Impulse bit and ablation characteristics of double cylindrical pulsed plasma thruster

Previous studies have shown that the performance of coaxial pulsed plasma thrusters depends on the ratio of propellant surface area-to-cavity volume. In this work, a double cylindrical propellant was introduced to increase the operation ratio compared to coaxial propellants; the results demonstrated that the geometric parameter obtained by dividing the ratio by the hollow diameter greatly influences the impulse bit. Also, direct observations and mass shot measurements revealed a higher density of the ablation gas from the cylindrical part than from the hollow part.

Development and application of MOQUICO code to study molten corium-concrete interaction

After the Fukushima nuclear accident, great attention is being paid to the late-phase behavior of the severe accident in the reactor, especially the molten corium-concrete interaction (MCCI). The MCCI process is very complex, involving physical and chemical reactions, heat and mass transfer processes. Many factors will affect the final result, with a high degree of uncertainty and there are still many unknowns based on current knowledge. In this paper, aimed at the MCCI phenomena in the containment cavity during a hypothetical accident in the nuclear power plant, an MCCI analysis code MOQUICO was developed by coupling the models of molten corium-concrete heat transfer, the concrete pyrolysis, and the corium cooling characteristics. The code MOQUICO was validated using the CCI-2, CCI-3 and SURC-2 tests with limestone-common sand concrete (LCS), siliceous concrete (SIL), and basaltic concrete (BAS), respectively. The simulant axial and radial ablation depths, upward heat flux and melt temperature agreed well with the experimental measurements. Afterwards, the code was used to simulate the typical PWR and BWR nuclear power plants. The ablation depth and gas production were analyzed for both simulations. Furthermore, the corium cooling was studied with eight different water injection moments for PWR and sensitivity analysis for decay heat and concrete type was conducted for BWR. The analysis proved that the developed code is capable of simulating MCCI and related phenomena of Light Water Reactor (LWR).

Nanomedicine-Enabled Photonic Thermogaseous Cancer Therapy.

Local photothermal hyperthermia for tumor ablation and specific stimuliresponsive gas therapy feature the merits of remote operation, noninvasive intervention, and in situ tumor‐specific activation in cancer‐therapeutic biomedicine. Inspired by synergistic/sequential therapeutic modality, herein a novel therapeutic modality is reported based on the construction of two‐dimensional (2D) core/shell‐structured Nb2C–MSNs–SNO composite nanosheets for photonic thermogaseous therapy. A phototriggered thermogas‐generating nanoreactor is designed via mesoporous silica layer coating on the surface of Nb2C MXene nanosheets, where the mesopores provide the reservoirs for NO donor (S‐nitrosothiol (RSNO)), and the core of Nb2C produces heat shock upon second near‐infrared biowindow (NIR‐II) laser irradiation. The Nb2C–MSNs–SNO‐enabled photonic thermogaseous therapy undergoes a sequential process of phototriggered heat production from the core of Nb2C and thermotriggered NO generation, together with photoacoustic‐imaging (PAI) guidance and monitoring. The constructed Nb2C–MSNs–SNO nanoreactors exhibit high‐NIR‐induced photothermal effect, intense NIR‐controlled NO release, and desirable PAI performance. Based on these unique theranostic properties of Nb2C–MSNs–SNO nanocomposites, sequential photonic thermogaseous therapy with limited systematic toxicity on efficiently suppressing tumor growth is achieved by PAI‐guided NIR‐controlled NO release as well as heat generation. Such a thermogaseous approach representes a stimuli‐selective strategy for synergistic/sequential cancer treatment.

Combination of pulsed laser ablation and inert gas condensation for the synthesis of nanostructured nanocrystalline, amorphous and composite materials.

A new instrument combining pulsed laser ablation and inert gas condensation for the production of nanopowders is presented. It is shown that various nanostructured materials, such as regular metallic, semiconducting, insulating materials, complex high entropy alloys, amorphous alloys, composites and oxides can be synthesized. The unique variability of the experimental set-up is possible due to the reproducible control of laser power (pulse energy and repetition rate), laser ablation pattern on the target, and experimental conditions during the inert gas condensation, all of which can be controlled and optimized independently. Microstructure analysis of the as-prepared composite and amorphous Ni60Nb40 nanopowders establishes the instrument's ability for the synthesis of materials with unique compositions and atomic structure. It is further shown that small variations of the synthesis parameters can influence materials properties of the final product, in terms of particle size, composition and properties. As an example, the laser power has been used to control the magnetic properties of amorphous Ni60Nb40 nanopowders. A few selected examples of the manifold possibilities of the new synthesis apparatus are presented in this report together with detailed structural characterization of the produced nanopowders.

Secondary shock wave: Implication for laser ablation inductively coupled plasma mass spectrometry

Shadowgraphs of the dynamic evolution of nanosecond laser-induced ablation plumes outside of BCR-2G and BIR-1G geological standard samples at atmospheric pressure are captured. The model of the secondary shock wave is proposed and experimentally verified. Experimental results indicate that the secondary waves appear at 74 ns for the BCR-2G sample and at 98 ns for the BIR-1G sample, which result from the reflection of the backward moving gas on the sample surface. Under the same condition, the ablation threshold of the BCR-2G sample is lower than that of the BIR-1G sample. Furthermore, the ablation rate (crater depth per laser pulse) of the BCR-2G sample is higher than that of the BIR-1G sample. The secondary shock wave induces larger-diameter particles or clusters which have been regarded as a fractionation source. Debris redeposition plays a role in the laser ablation and inductively coupled plasma mass spectrometry. The suppression of the secondary shock wave effect is possible using low viscosity ablation gas which can expand the shock wave front, leading to less collision and aggregation of the ablated particles. As a result, the debris redeposition will be attenuated and the larger particle or cluster induced elemental fractionation can be expected to be suppressed in practice.

IQuant2: Software for Rapid and Quantitative Imaging Using Laser Ablation-ICP Mass Spectrometry.

We report on the development of a software program named iQuant2 which creates visual images from two-dimensional signal intensity data obtained by a laser ablation-ICP-mass spectrometry (LA-ICPMS) technique. Time-resolved signal intensity profiles can be converted to position resolved signal intensity data based on the rastering rate (μm s−1) of the laser ablation. Background signal intensities obtained without laser ablation (gas blank) are used as the background, and all of the blank-subtracted intensity data can be used for the imaging analysis. With this software, deformation of the created image can be corrected visually on a PC screen. The line profile analysis between the user-selected points can be observed using the iQuant2 software. To accomplish this, data points on the profile line were automatically calculated based on the interpolation between the analysis points. The resulting imaging data can be exported and stored as JPEG, BMP or PNG formats for further processing. Moreover, a semi-quantitative analysis can be made based on the coupling of the external correction of the RSF (relative sensitivity factor) using NIST SRM610 with normalization of the corrected signal intensity data being 100%. The calculated abundance data for major elements are in reasonable agreement with the values obtained by electron probe micro analyzer (EPMA). With the software developed in this study, both the rapid imaging and semi-quantitative determinations can be made.

Ablation performance of a 4D-braided C/C composite in a parameter-variable channel of a Laval nozzle in a solid rocket motor

Ablation of a 4D-braided C/C composite fabricated with axial rods in the parameter-variable channel of a Laval nozzle (or a convergent-divergent nozzle, a tube that is pinched in the middle) was performed in the experimental conditions of a solid rocket motor. Gas-solid flow and erosion were also simulated with the discrete phase model. The ablation of the composite was caused by thermochemical and mechanical erosion and was analyzed based on the morphology of different sections of the channel in the nozzle with different angles between the gas flow direction and the surface of the composite (ablation angle). Results showed that the ablation behavior was related to the velocity, concentration, collision angle to the surface and the wall shear force of particles in the ablation gas. The ablation gradually increased with the rate of gas flow and was a maximum at the maximum ablation angle of 45° in the compression section. In the expansion section, beyond the throat, ablation decreased significantly. The maximum linear and mass ablation rates were 0.056 mm/s and 0.157 kg/m2·s, respectively. The carbon fibers formed a tapered tip, whose sharpness depended on the ablation angle and the braiding direction.

Development and verification of molten corium–concrete interaction code

During a severe accident of Pressurized Water Reactor(PWR), the core materials was heated, melt located on the lower head of Reactor Pressure Vessel(RPV). With the temperature rise, the corium will melt through the lower head and discharge into the reactor cavity. Those corium will interact with the concrete and damage the integrity of the containment, so some coolability method should used to quench the corium. In order to investigate the progress of MCCI, a MCCI analysis code, that is MOCO, was developed. The MOCO includes the heat transfer behavior in axial and radial directions from the molten corium to the basemat and sidewall concrete, crust generation and growth, and coolability mechanisms reveal the concrete erosion and gas release, which are important for the interaction process. Cavity ablation depth, melt temperature, and gas release are the key parameters in the interaction research. The physical-chemistry reaction is also involved in MOCO code. In the present paper, the related MCCI experiment data were used to verify the models of the MOCO and the calculation results of MOCO were also compared with other MCCI analysis codes.

Modeling of Heat Transfer Attenuation by Ablative Gases During the Stardust Reentry

Modern space vehicles designed for planetary exploration use ablative materials to protect the payload against the high heating environment experienced during reentry. To properly model and predict the aerothermal environment of the vehicle, it is imperative to account for the gases produced by ablation processes. The present study aims to examine the effects of the blowing of ablation gas in the outer flow field. Using six points on the Stardust entry trajectory at the beginning of the continuum regime, from 81 to 69 km, the various components of the heat flux are compared to air-only solutions. Although an additional component of the heat flux is introduced by mass diffusion, this additional term is mainly balanced by the fact that the translational–rotational component of the heat flux, the main contributor, is greatly reduced. Although a displacement of the shock is observed, it is believed that the most prominent effects are caused by a modification of the chemical composition of the boundary layer, which reduces the gas-phase thermal conductivity.

Dense Plasma Focus - From Alternative Fusion Source to Versatile High Energy Density Plasma Source for Plasma Nanotechnology

The dense plasma focus (DPF), a coaxial plasma gun, utilizes pulsed high current electrical discharge to heat and compress the plasma to very high density and temperature with energy densities in the range of 1-10×1010 J/m3. The DPF device has always been in the company of several alternative magnetic fusion devices as it produces intense fusion neutrons. Several experiments conducted on many different DPF devices ranging over several order of storage energy have demonstrated that at higher storage energy the neutron production does not follow I4 scaling laws and deteriorate significantly raising concern about the device's capability and relevance for fusion energy. On the other hand, the high energy density pinch plasma in DPF device makes it a multiple radiation source of ions, electron, soft and hard x-rays, and neutrons, making it useful for several applications in many different fields such as lithography, radiography, imaging, activation analysis, radioisotopes production etc. Being a source of hot dense plasma, strong shockwave, intense energetic beams and radiation, etc, the DPF device, additionally, shows tremendous potential for applications in plasma nanoscience and plasma nanotechnology. In the present paper, the key features of plasma focus device are critically discussed to understand the novelties and opportunities that this device offers in processing and synthesis of nanophase materials using, both, the top-down and bottom-up approach. The results of recent key experimental investigations performed on (i) the processing and modification of bulk target substrates for phase change, surface reconstruction and nanostructurization, (ii) the nanostructurization of PLD grown magnetic thin films, and (iii) direct synthesis of nanostructured (nanowire, nanosheets and nanoflowers) materials using anode target material ablation, ablated plasma and background reactive gas based synthesis and purely gas phase synthesis of various different types of nanostructured materials using DPF device will discussed to establish this device as versatile tool for plasma nanotechnology.

Determination of U–Pb Ages for Young Zircons using Laser Ablation‐ICP‐Mass Spectrometry Coupled with an Ion Detection Attenuator Device

We have developed new analytical procedures to measure precise and accurate 238U–206Pb and 235U–207Pb ages for young (~ 1 Ma) zircons using laser ablation‐ICP‐mass spectrometry. For young zircons, both careful correction for the background counts and analysis of very small Pb/U ratios (i.e., 206Pb/238U < 0.00016 and 207Pb/235U < 0.0001 for 1 Ma zircons) are highly desired. For the correction of the background, the contribution of the background signal intensities for the analytes, especially for the residual signal intensities for 206Pb and 207Pb, was defined through laser ablation of synthesised zircons (ablation blank) containing negligible Pb. The measured signal intensities for 202Hg, 206Pb and 207Pb signals obtained by the ablation blank were slightly higher than those obtained by data acquisition without laser ablation (gas blank). For the wider dynamic range measurements on Pb/U ratios, an attenuator device for the ion detection system was employed to extend the capability to monitor high‐intensity signals (i.e., > 3 Mcps). Through the attenuator device, the ion currents were reduced to 1/450 of the signal intensity without the attenuator. Because the switching time for the attenuator was shorter than 1 ms, signal intensities for only specific isotopes could be reduced. With attenuation of the 238U signal, counting statistics on 206Pb and 207Pb isotopes could be improved and counting loss on the 238U signal could be minimised. To demonstrate the reliability of this new analytical technique, 238U–206Pb and 235U–207Pb ages for three young zircon samples (collected from Osaka Group Pink Volcanic Ash, Kirigamine and Bishop Tuff) were measured. The data presented here demonstrate clearly that the present technique could become a major analytical tool for in situ U–Pb age determination of young zircons (~ 1 Ma).

Optimizing gated detection in high-jitter kilohertz powerchip laser-induced breakdown spectroscopy

Powerchip lasers provide short, reproducible ablation pulses at rates in excess of a kilohertz, but the pulse to pulse jitter resulting from their passive Q-switches has prevented previous intra-pulse gated measurements. We have performed time-resolved measurements of the analytical figures of merit for the powerchip LIBS determination of copper in aluminum under air, argon and helium atmospheres. Minimum limits of detection were measured 25–125 ns after ablation and were as much as 15× better than the ungated values. These optimal delays would not require an optical delay line in most cases as a result of the short insertion delay of modern ICCDs. Argon cover gas was found to improve LODs slightly. Using gated detection, 1064 nm laser ablation and argon cover gas, we calculate a LOD as low as 0.65 ppm of copper.

Effect of Cu particles on the ablation properties of C/C composites

To improve the ablation property, Cu particles were introduced into carbon/carbon (C/C) composites through liquid precursor infiltration combined with in-situ reaction. Compared to pure C/C composites, the modified composites displayed better mechanical property and ablation resistance under oxyacetylene torch when the Cu content was below 8 wt. %. For C/C–Cu composites with 8 wt. % Cu, a 14% decline of linear ablation rate was obtained while defective fibers and laminar matrix survived after ablation. Analyses of ablation behavior depending on ablation time indicated that overflowing of Cu gas weakened the scouring of ablation gas and the Cu gas reduced the partial pressure of oxidizing species, which led to the improved ablation property.