Gaseous Fluoride Research Articles

Nanoporous Structure Fabrication on Glass Surfaces for Enhanced Glass Adhesion Using Hydrogen Fluoride Gas.

The bonding between glass and other materials plays a crucial role when glass is used in industrial products. In this study, we propose a new approach to enhance the bonding strength of glass with other materials by fabricating nanoscale porous structures on glass surfaces via a chemical reaction with hydrogen fluoride gas. Herein, we present a methodology for controlling the thickness of the porous structure, clarify the relationship between the thickness and adhesion strength, investigate the shape of the formed porous structure, and propose a method to control its shape. Our findings reveal that the fabricated porous structure greatly improves the adhesion strength of the adhesive owing to the microscopic anchoring effect induced by the penetration of the adhesive into the porous structure. This approach is expected to be applied to architectural and automobile window glasses, solar panels, sensor cover glasses of autonomous vehicles, display devices (including smartphones), and wearable devices.

Adsorbtive removal of HF toxic gas via tinsulfide monolayer modification: A molecular perspective

Hydrofluoric Acid (HF) is considered one of the most hazardous chemicals used in industrial plants. Even small exposures to HF can have fatal consequences if not promptly and properly treated. Various research teams have presented numerous substances with the objective of capturing or detecting toxic HF gas. In this study, we explore the impact of HF gas on a single layer of SnS by employing density functional theory (DFT). The interaction nature between the gas molecule and the adsorbent is elucidated by analyzing the related adsorption energy, electronic structure properties and differential charge transfer. The findings indicate that HF is physically adsorbed on the pristine SnS with an adsorption energy value of −0.63 eV. By introducing a Sn mono vacancy defect, the modification of SnS enhances the adsorption energy to −1.26 eV, resulting in a chemisorption process. Molecular fluorine (F2) was discovered to undergo a barrierless reaction with SnS, resulting in the formation of fluorine-substituted SnS. It has been discovered that the substitution of fluorine atoms enhances the reactivity of SnS towards hydro-gen fluoride gas. The adsorption potential of the studied structures towards HF gas was determined to be in the following order: F2SnS > VSn–SnS > VS-SnS ∼ SnS. The current study is anticipated to offer new molecular insights that could lead to the creation of innovative devices for detecting or eliminating HF toxic gas from a specific atmosphere.

A case of recurrent convulsions caused by acute sulfuryl fluoride gas poisoning

Sulfuryl fluoride is a kind of pesticide with strong permeability, convenient use at low temperature, non-corrosive and other characteristics, which can kill food pests and has strong lethality to termites. In acute sulfuryl fluoride poisoning, patients can see recurrent convulsions, epileptic electroencephalogram abnormalities such as matrix spikes or high amplitude spikes. In this paper, a patient with sulfuryl fluoride poisoning with convulsion-based mental system symptoms was reported, and after clinical treatment with dexamethasone and phenobarbital sodium, the patient was cured and discharged.

Energetic properties of core–shell B@PVDF/AP composite micro-units prepared by electrostatic spraying technology

In this study, to improve the ignition and combustion performance of fuel boron (B) powder. The core–shell B@ polyvinylidene fluoride (PVDF)/ ammonium perchlorate (AP) composite micro-unit with the effect of erosion activation is successfully prepared by simple and controllable electrostatic spraying technology. The results of morphology and structural composition show that PVDF and AP are tightly wrapped on the surface of B, forming a uniform shell, which effectively prevents moisture absorption and oxidation of B during storage and transportation. The results of the thermal analysis show that the hydrofluoric acid (HF) gas generated by the decomposition of PVDF at about 100 °C in advance has a pre-ignition reaction (PIR) with the boron oxide (B2O3) film on the surface of B. The PIR generates boron fluoride (BF3) gas and breaks the B2O3 film. This reduces the initial oxidation temperature of B by 12.6 % and enhances the oxidation activity of B powder. In addition, the oxygen (O2) released by AP improves the combustion performance of B and strengthens the effect of erosion activation. It is also found that all samples can be successfully ignited and burned continuously, which improves the ignition and combustion performance of B powder. It is worth noting that the ignition delay time of the composite micro-unit sample with the stoichiometric ratio of B/PVDF/AP of 2: 1: 2 can be shortened to 0.454 s at most, which is 17 % lower than that of the physical mixed sample. Moreover, its combustion intensity and flame temperature also reach the best. These results show that the core–shell B@PVDF/AP composite micro-unit provides a great strategy for application in solid propellant and pyrotechnics.

Nano-Strand Formation via Gas Phase Reactions from Al-Co-Fe Reacted with CaF2-SiO2-Al2O3-MgO Flux at 1350 °C: SEM Study and Thermochemistry Calculations

The submerged arc welding (SAW) process is operated at high temperatures, up to 2500 °C, in the arc cavity formed by molten oxy-fluoride flux (slag). These high arc cavity temperatures and the complex interaction of gas–slag–metal reactions in a small space below the arc render the study of specific chemical interactions difficult. The importance of gas phase reactions in the arc cavity of the SAW process is well established. A low-temperature (1350 °C) experimental method was applied to simulate and study the vaporisation and re-condensation behaviour of the gas species emanating from oxy-fluoride flux. Energy dispersive X-ray spectroscopy (EDX) analyses and reaction thermochemistry calculations were combined to explain the role of Al as a de-oxidiser element in gas phase chemistry and, consequently, in nano-strand formation reactions. EDX element maps showed that the nano-strands contain elemental Ti only, and the nano-strand end-caps contain Co-Mn-Fe fluoride. This indicates a sequence of condensation reactions, as Ti in the gas phase is re-condensed first to form the nano-strands and the end-caps formed from subsequent re-condensation of Co-Mn-Fe fluorides. The nano-strand diameters are approximately 120 nm to 360 nm. The end-cap diameter typically matches the nano-strand diameter. Thermochemical calculations in terms of simple reactions confirm the likely formation of the nanofeatures from the gas phase species due to the Al displacement of metals from their metal fluoride gas species according to the reaction: yAl + xMFy ↔ xM + yAlFx. The gas–slag–metal equilibrium model shows that TiO2 in the flux is transformed into TiF3 gas. Formation of Ti nano-strands is possible via displacement of Ti from TiF3 by Al to form Al-fluoride gas.

Resource Recovery of Spent Lithium-Ion Battery Cathode Materials by a Supercritical Carbon Dioxide System.

The increasing global market size of high-energy storage devices due to the boom in electric vehicles and portable electronics has caused the battery industry to produce a lot of waste lithium-ion batteries. The liberation and de-agglomeration of cathode material are the necessary procedures to improve the recycling derived from spent lithium-ion batteries, as well as enabling the direct recycling pathway. In this study, the supercritical (SC) CO2 was innovatively adapted to enable the recycling of spent lithium-ion batteries (LIBs) based on facilitating the interaction with a binder and dimethyl sulfoxide (DMSO) co-solvent. The results show that the optimum experimental conditions to liberate the cathode particles are processing at a temperature of 70 °C and 80 bar pressure for a duration of 20 min. During the treatment, polyvinylidene fluoride (PVDF) was dissolved in the SC fluid system and collected in the dimethyl sulfoxide (DMSO), as detected by the Fourier Transform Infrared Spectrometer (FTIR). The liberation yield of the cathode from the current collector reaches 96.7% under optimal conditions and thus, the cathode particles are dispersed into smaller fragments. Afterwards, PVDF can be precipitated and reused. In addition, there is no hydrogen fluoride (HF) gas emission due to binder decomposition in the suggested process. The proposed SC-CO2 and co-solvent system effectively separate the PVDF from Li-ion battery electrodes. Thus, this approach is promising as an alternative pre-treatment method due to its efficiency, relatively low energy consumption, and environmental benign features.

Single-shot wavelength meter on a chip based on exponentially increasing delays and in-phase quadrature detection

A solid-state wavelength measuring instrument based on a SiO2 photonics platform is presented. The chip-scale wavemeter device has no moving parts and allows instantaneous wavelength measurement with high precision and accuracy over a nominal bandwidth of 40 nm in the O-band. The wavemeter design is based on multimode interferometer (MMI) couplers and a multi-band Mach–Zehnder interferometer (MZI) structure with exponentially increasing optical path differences. Design of the MMI couplers is supported by simulations using the Finite-Difference Time-Domain (FDTD) method. A hydrogen fluoride gas cell is used in conjunction with the chip-scale wavemeter to determine the wavelength relative to traceable absorption lines. This approach does not rely on knowledge of the effective or group refractive indices to estimate wavelength. The fabrication, experimental evaluation and calibration of the device are discussed. Observed performance indicates a spectral support of 37.378 nm (i.e., frequency bandwidth 6.608 THz), with a resolution of 6.1 pm (1.1 GHz) at 1σ, corresponding to 1 part in 6,127.

The Effects of Ambient Temperature and Atmospheric Humidity on the Diffusion Dynamics of Hydrogen Fluoride Gas Leakage Based on the Computational Fluid Dynamics Method.

In order to investigate the impact of environmental temperature and atmospheric humidity on the leakage and diffusion of hydrogen fluoride (HF) gas, this study focused on the real scenario of an HF chemical industrial park. Based on the actual dispersion scenario of HF gas, a proportionally scaled-down experimental platform for HF gas leakage was established to validate the accuracy and feasibility of numerical simulations under complex conditions. Using the validated model, the study calculated the complex scenarios of HF leakage and diffusion within the temperature range of 293 K to 313 K and the humidity range of 0% to 100%. The simulation results indicated that different environmental temperatures had a relatively small impact on the hazardous areas (the lethal area, severe injury area, light injury area, and maximum allowable concentration (MAC) area) formed by HF gas leakage. At 600 s of dispersion, the fluctuation range of hazardous area sizes under different temperature conditions was between 3.11% and 13.07%. In contrast to environmental temperature, atmospheric relative humidity had a more significant impact on the dispersion trend of HF leakage. Different relative humidity levels mainly affected the areas of the lethal zone, light injury zone, and MAC zone. When HF continued to leak and disperse for 600 s, compared to 0% relative humidity, 100% relative humidity reduced the lethal area by 35.7%, while increasing the light injury area and MAC area by 27.26% and 111.6%, respectively. The impact on the severe injury area was relatively small, decreasing by 1.68%. The results of this study are crucial for understanding the dispersion patterns of HF gas under different temperature and humidity conditions.

Fabrication of Superhydrophobic Nanostructures on Glass Surfaces Using Hydrogen Fluoride Gas.

Water-repellent glass surfaces have become increasingly important to ensure clear visibility in outdoor cameras, sensors, and automotive windows. In this study, we investigated a process for the formation of nanoscale structures on a glass surface using chemical reactions with hydrogen fluoride gas. Using this approach, nanostructures with superhydrophobicity, superhydrophilicity, and antireflective properties were formed on glass surfaces with minimal processing time. This mask-free method, working at atmospheric pressure, can be efficiently integrated within the float process, a mainstream manufacturing technique for flat glass, to introduce nanostructures onto the glass surface. Notably, after treatment with (1-H, 1-H, 2-H, 2-H-tridecafluorooctyl)trimethoxysilane (FAS-13), a typical hydrophobic agent, the resulting surface exhibited a maximum water contact angle of 162°. Owing to its low reflectivity and superhydrophobicity, this surface is anticipated to find applications in not only the design of architectural window glass and vehicle windows but also the development of solar panels and sensor cover glass for autonomous vehicles.

Etching mechanism of amorphous hydrogenated silicon nitride by hydrogen fluoride

We report the etching mechanism of amorphous hydrogenated silicon nitride by hydrogen fluoride (HF) gas using density functional theory (DFT) calculations. Since silicon nitride films are deposited as amorphous with a significant amount of hydrogen, we constructed an amorphous substrate model with a hydrogen concentration of 25 at.% using molecular dynamics simulation and DFT calculations. We then created slab models with different degrees of fluorination and simulated all possible fluorination pathways. The pathways involving cleavage of Si–N or Si–Si bonds showed low activation energies of 0.90 eV or lower, while the pathways involving cleavage of a Si–H bond showed high activation energies of 1.54 eV or higher. NH3, SiF4, SiH2F2, and SiHF3 were released with low activation energies, indicating that etching would be favorable. Next, we modeled the formation and desorption of the (NH4)2SiF6 salt on the fluorinated surface. The salt formation was exothermic with low activation energies, consistent with self-limited etching at low temperatures. At temperatures of 152 °C or higher, (NH4)2SiF6 would desorb, leaving no solid residue, consistent with the high etch rate at elevated temperatures. Our DFT calculations using the amorphous hydrogenated slab model successfully explained the silicon nitride etching process, which could not be explained by a crystalline Si3N4 slab model.

Enhanced azeotropic C2ClF5/C3F8 separation by TMA+ exchanged MFI zeolites for ultrapure fluorine electronic gas

AbstractThe demand for the azeotropic C2ClF5/C3F8 separation continues to rise owing to the significance of ultrapure fluoride gases for the electronic industry. With a boiling point differential of 1.1 K, separating an azeotropic mixture of C2ClF5/C3F8 through sorption‐based processes under ambient conditions is a preferable alternative to the current energy‐intensive cryogenic separation method. Here, we report the highly efficient C2ClF5/C3F8 adsorption separation in quaternary alkylammonium ions modified MFI type zeolites with interlaced channels which provide a cooperative effect conferred by specific interaction sites and optimal pore size. A path‐regulatory mechanism was proposed, whereby TMA+ cations located at intersections resembling “train turnouts” force gas molecules to switch traffic channels to confined sinusoidal channels affecting the C2ClF5/C3F8 recognition sites and diffusion behavior. Molecular simulations were conducted to reveal the separation mechanism, and the breakthrough experiment validated the effectiveness of this adsorbent at 298 K outperforming conventional adsorbents for the challenging azeotropic separation.

Exploring the sensing potential of Fe-decorated h-BN toward harmful gases: a DFT study.

Gas sensing technology has a broad impact on society, ranging from environmental and industrial safety to healthcare and everyday applications, contributing to a safer, healthier, and more sustainable world. We studied pure and Fe-decorated hexagonal boron nitride (h-BN) gas sensor for monitoring of carbon-based gases using density functional theory (DFT). The calculations utilized the Generalized Gradient Approximation with the Perdew-Burke-Ernzerhof (GGA-PBE) exchange-correlation functional. The novelty of our study lies in the investigation of the adsorption of harmful gases such as carbonyl sulfide, carbinol, carbimide, and carbonyl fluoride on both pure and Fe-decorated h-BN. The deviation in structural, electronic, and adsorption properties of h-BN due to Fe decoration has been studied along with the sensing ability to design said material towards carbon monoxide (CO), carbon dioxide (CO2), carbonyl sulfide (COS), carbinol, (CH4O), carbimide (CH2N2), and carbonyl fluoride (CF2O) gases. Gases such as CO, COS, CH2N2, and CF2O exhibited chemisorption, while CO2, and CH4O exhibited physisorption behavior. The introduction of Fe altered the semiconductor properties of h-BN and rendered it metallic. Enhanced electronic properties were observed due to a robust hybridization occurring between the d-orbitals of Fe-decorated BN and the gas molecules. The extended recovery periods observed for gases, aside from CO2, indicate their adhesive interactions with Fe-decorated h-BN. The reduction in desorption duration as temperature rises allows Fe-decorated h-BN to function as a reversible gas sensor. This research opens up a novel pathway for the synthesis and advancement of cost-effective, environmentally friendly double-atom catalysts with high sensitivity for capturing and detecting molecules such as CO, COS, CH2N2, CO2, CH4O, and CF2O.

Open-source flow setup for rapid and efficient [18 F]fluoride drying for automation of PET tracer syntheses.

One of the key strategies for radiochemical research facilities is the automation of synthesis processes. Unnecessary manual operations increase the radiation exposure of personnel, while simultaneously threatening the reliability of syntheses. We have previously reported an affordable open-source system comprising 3D-printed continuous flow reactors, a custom syringe pump, and a pressure regulator that can be used to perform radiofluorinations. In this paper, we address additional essential processes that are needed for radiotracer development and synthesis, with the aim of making laboratory work safer and research more efficient. We have designed and evaluated a fully automated system for rapidly and effectively processing and drying aqueous [18 F]fluoride that can be directly connected to the cyclotron. This process relies on triflyl fluoride gas generation and allows nucleophilic [18 F]fluoride to be prepared safely in a hotcell within 10min and an activity recovery of 91.7±1.6% (n = 5). Owing to the need for convenient radiofluorinated prosthetic ligands, we have adapted our continuous flow system to produce [18 F]fluoroethyl tosylate (FEOTs) and [18 F]fluoroethyl triflate (FEOTf), prosthetic groups that are widely used for late-stage fluoroethylation of PET tracers. The processes as well as the radiolabeling of different groups are compared and comprehensively discussed. Having a method providing [18 F]fluoroethyl tosylate (FEOTs) as well as [18 F]fluoroethyl triflate (FEOTf) quickly and highly efficiently is beneficial for radiochemical research.

Thermodynamic Stability of LixNiO2 and Polyvinylidene Difluoride Materials for Lithium+ Ion Batteries

LixNiO2 (LNO), a layered Li-ion battery cathode has been investigated for decades. LNO has been shown to proceed through multiple phase transitions at different states of lithiation as well as at different temperatures. However, in these experiments it has always been paired with additional materials typically found in the creation of cathodes, such as carbon black, aluminum foil and polyvinylidene difluoride binder. This paper investigates the thermal stability of LNO as a stand-alone material as well as a component of a traditional cathode through performing thermal gravimetric analysis (TGA), variable temperature powdered X-ray diffraction (VT-PXRD) and solid-state nuclear magnetic resonance (ss-NMR) at different states of lithiation and high temperatures. The reduction to nickel metal was found at temperatures exceeding 500 °C for the traditional cathodes at all states of charge due to the creation of lithium fluoride from hydrogen fluoride gas being released as polyvinylidene difluoride degrades. Nickel metal was also identified for the stand-alone LNO at lithium concentrations greater than x = 0.32 at temperatures of 600 °C as the system becomes depleted of oxygen and lithium due to the creation of lithium oxide. These finding indicate that the thermal stability of LNO at temperatures over 200 °C is sensitive to the presence of fluorine as well as the state of charge of the battery. Typical batteries do not reach these temperatures during cycling, but in the case of thermal runaway and recycling it is important to know the chemical reactions occurring at these temperatures and concentrations as toxic and corrosive hydrogen fluoride gas is released. An investigation into less fluorinated binder options is desirable to reduce the addressed issues.

Study on thermal conversion and detoxification mechanism of fluorine during co-combustion of meager coal and spent cathode carbon block

Fluoride is a toxic and harmful ingredient in the spent cathode carbon blocks (SCCB). Gaseous fluoride pollution is a significant potential pollution source in the process of boiler collaborative disposal of SCCB. In this paper, meager coal and SCCB were used as fuel, the mixing ratio and temperature were variables, the law of thermal conversion of fluorine during the co-combustion process was studied, and the properties of ash residue were discussed. At the same time, CaO was added to the furnace to reveal the influence of temperature on the effect of fluorine fixation in the furnace. The results showed that combustion was the most suitable method for removing soluble fluorine from SCCB, and the thermal conversion rate of soluble fluorine was up to 99.68–99.98%. The higher the combustion temperature, the higher the conversion of gaseous fluoride, and the worse the effect of fluorine fixation in the furnace. It is not suitable for fluorine fixation in the furnace when the furnace temperature exceeded 1100 ℃. The higher the mixing ratio of SCCB, the higher the production of gaseous fluoride, and a proper mixing ratio is vital for co-combustion. Ash residue after mixing 10% SCCB combustion belongs to general industrial solid waste. This study has important theoretical significance for determining the applicable furnace type, the appropriate mixing ratio and effective fluoride treatment measures in the co-combustion process of coal and SCCB.

Assessment of Particulate and Gaseous Fluoride in Phosphate Fertilizer Industry

Fluorides are emitted in both gaseous and particle forms in the industrial sector. However, studies usually only report total fluoride content. Therefore, the study aimed to assess the particulate, gaseous fluoride and correlate it with the respirable dust particles in Single Super Phosphate (SSP), Granular Single Super Phosphate (GSSP), and administration divisions of the industry. Respirable dust particles, particulate fluoride, and hydrogen fluoride in the work environment were collected on a filter cassette containing an MCE filter paper (0.8 micron 37-mm) and Na2CO3 impregnated backup pad, respectively, using a personal sampler. The fluoride samples were analyzed using Ion Selective Electrode (ISE) and expressed as milligrams per meter cube (mg.m-3). The respirable dust, particulate, and gaseous fluoride content were found to have statistically significant differences (p<0.001) between the divisions (SSP, GSSP, and administration) in the static monitoring, whereas, in the case of personal monitoring, no significant differences were observed. Average airborne respirable, particulate, and gaseous fluoride levels in static monitoring were 1.37, 1.03, 0.20 mg.m-3, 0.018, 0.008, 0.001 mg.m-3, and 0.808, 0.403, 0.026 ppm in SSP, GSSP and administration respectively, whereas in personal monitoring the average respirable, particulate and gaseous fluoride concentrations were 1.18, 0.85, 0.30 mg.m-3, 0.0013, 0.007, 0.002 mg.m-3 and 0.356, 0.258, 0.011 ppm in SSP, GSSP and administration respectively. The present study observed that the levels of fluoride decreased with an increase in distance from SSP, followed by GSSP and administration. It indicates that the fluoride exposure was inversely proportional to the distance of the source. This study outcome will help to design a policy and intervention to mitigate fluoride exposure among workers.

Investigation of the Interaction of Hydrogen Fluoride with Quartz by Measuring Surface Conductivity

The change in surface conductivity under the influence of hydrogen fluoride (HF) gas on quartz isexperimentally studied. It is shown that the surface conductivity of quartz changes by a factor of more than108 during the reaction. Possible heterogeneous chemical processes determining the observed experimentalresults are considered.

Fullerenol-based toxic fluoride gas sensing: A promising way to monitoring Li-ion battery status

In order to demonstrate the feasibility of fullerenol-based toxic fluoride gas sensing, the density functional theory is utilized for adsorption mechanism study. The dominant adsorption conformations of HF/PF5/POF3 is analyzed according to Boltzmann distribution based on Gibbs free energy. The intermolecular interaction of these dominant conformation is revealed by the independent gradient model based on Hirshfeld partition (IGMH) method, which shows that the main driving force of adsorption is the hydrogen bond. After considering the thermodynamic correction, the adsorption free energy of fullerenols with HF turns from negative to positive at 95 °C, showing a transition between adsorption and desorption. The superior recovery characteristic is thus indicated. The Hirshfeld atomic charge shows that HF exhibit as an electron acceptor during the adsorption process. The charge transfer and density of states analysis illustrate the significant bonding effect that existed between fullerenol and gas. And the energy gap shows a decrease after adsorption, which results in an increase in conductivity. It can be deduced that fullerenol can transform the presence of the toxic fluoride gas into an electrical signal, and therefore exhibit a promising way as gas sensor for Li-ion battery status monitoring.

Gas-phase etching mechanism of silicon oxide by a mixture of hydrogen fluoride and ammonium fluoride: A density functional theory study

We report the selective etching mechanism of silicon oxide using a mixture of hydrogen fluoride (HF) and NH4F gases. A damage-free selective removal of native oxide has been used in semiconductor manufacturing by forming and removing the ammonium fluorosilicate [(NH4)2SiF6] salt layer. A downstream plasma of NF3/NH3 or a gas-phase mixture of HF and NH4F was used to form (NH4)2SiF6. We modeled and simulated the fluorination of silicon oxide and the salt formation by density functional theory calculation. First, we simulated the successive fluorination of silicon oxide using SiO2 slab models. The fluorination reactions of SiO2 surfaces by the mixture produced a volatile SiF4 molecule or a surface anion of –OSiF4−* with an NH4+ cation with low activation energies. Unlike HF, NH4F produced surface salt species consisting of a surface anion and an ammonium cation. Next, we simulated the (NH4)2SiF6 formation from the two reaction products on fluorinated SiO2 surfaces. (NH4)2SiF6 can be formed exothermally with low activation energies (0.27 or 0.30 eV). Finally, we compared silicon with SiO2 to demonstrate the inherently selective etching of silicon oxide. The fluorination reactions of silicon by the mixture showed the activation energies significantly higher than the SiO2 cases, 1.22–1.56 eV by HF and 1.94–2.46 eV by NH4F due to the less stable transition state geometries. Therefore, the selective salt formation on silicon oxide, not on silicon, is expected in near-room temperature processing, which enables selective etching of silicon oxide.

The role of silanol groups on the reaction of SiO2 and anhydrous hydrogen fluoride gas

AbstractIt is essential to etch SiO2 for producing silica glass components, semiconductor devices, and so on. Although wet‐etching with hydrogen fluoride (HF) solutions is usually employed for this purpose, it faces a drawback that microstructures stick during the drying of the solution. To overcome this problem, we have developed a dry‐etching technique with gaseous HF at high temperatures. In the present study, an interesting phenomenon was found that silicon thermal oxides were much less etched than vitreous silica by gaseous HF. Such difference had not been found in wet‐ or humid HF gas etching. Because their bulk chemical formulae are the same (SiO2), it was suggested that the surface species affected the reaction rate. In fact, preprocessing with water vapor plasma remarkably increased the etching rate on the thermal oxides layer, and vacuum heating almost completely suppressed the reaction on the vitreous silica and the plasma‐treated thermal oxides. These results indicate that the surface silanol groups enhance the reaction between SiO2 and gaseous HF. Based on the results, a model of chain reaction for SiO2 and gaseous HF was proposed, where the surface silanol groups act as the reaction center.