Chlorine Atmosphere Research Articles

ClSO and ClSO2 photochemistry: Implications for the Venusian atmosphere.

The electronic structure and spectroscopy of ClSOx (x = 1 and 2) isomers were investigated using coupled cluster theory and multireference interaction methods. In this study, the equilibrium geometry and harmonic vibrational frequencies of these isomers in their ground electronic state were shown. Our analysis of the vertical excitation energy and potential energy surface showed the photochemical instability of ClSO for wavelengths below 280nm. Furthermore, the photodissociation of ClSO was unlikely to cause the formation of diatomic ClS. At the same time, ClSO could form atomic chlorine and SO as a result of photodissociation through the repulsive states. In the case of ClSO2, a novel weakly bound Cl-SO2 isomer was identified, indicating the potential influences on the chlorine and SO2 reactions. The potential energy surface of the most stable ClSO2 isomer also indicated the potential production of SO2 in both its ground and excited states. In addition, the electronic spectrum of ClSO2 was predicted to be broad, with numerous significant peaks in the near-UV‒Vis range. Valuable new insights into the chemical role of chlorine and sulfur in Venus's atmosphere were provided, along with a discussion of a potential mechanism contributing to the H2O and SO2 depletion in Venus's atmosphere.

Global Mapping of HCl on Mars by IRTF/iSHELL

Hydrogen chloride (HCl)—a key marker of the chlorine cycle on Mars—has been recently discovered in the Martian atmosphere by the ExoMars/TGO mission. In-orbit data indicate that this molecule appears in the atmosphere only in a limited time period and specifically in the southern summer season. A snapshot global mapping of HCl is indispensable to examine its sources and sinks, but such observations are not currently possible from any orbiters. Here, we present the first spatially resolved map of HCl obtained with the ground-based NASA InfraRed Telescope Facility. We find clear features of HCl, demonstrating that HCl is present close to the surface. HCl is detected in the equatorial region for the first time, revealing that HCl is widely distributed on Mars. However, the spatial distribution of HCl is not uniform, and it is enhanced in the southern polar region. Interestingly, this nonuniform spatial distribution of HCl column abundance is strikingly similar to that of water vapor column abundance. This highlights the important role of water vapor in the evolution of HCl through the atmosphere, as previously noted, and suggests its potential involvement in the atmospheric chlorine source processes.

Investigations on the passive and pitting behaviors of the multiphase stainless steel in chlorine atmosphere

Multiphase stainless steel is a kind of stainless steel that obtains good mechanical properties. Nevertheless, the passive and pitting behaviors of multiphase stainless steel remain inadequately elucidated. This study aims to investigate the passive and pitting behaviors of multiphase stainless steel by employing Auger electron spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and electrochemical techniques. The conclusions drawn from this research are as follows: The main constituents of the passive film on multiphase stainless steel comprise FeO, Fe2O3, Cr2O3, and Cr(OH)2. The passive film on the martensitic phase displays largest thicknesses. The Cr content in the passive film of the ferritic phase is highest. Particularly, the passive film on the (111) orientation of martensitic phase is thicker than that on the (001) and (101) orientations. Pitting corrosion in multiphase stainless steel primarily initiates at phase interfaces and subsequently extends into the ferritic phase.

Microbiological analysis concerning the antibacterial effect of atomized Ionless® hypochlorous acid water in a nursery school environment

IntroductionIn daycare centers, infants come in close contact with each other, and contact, droplet, and mouth-to-mouth infections may occur owing to sharing of toys. Additional effective disinfection methods should be considered aside from wiping with disinfectants—including alcohol or sodium hypochlorite solution—for environmental disinfection of daycare centers. We aimed to examine the usefulness of hypochlorous acid water atomization in the effective disinfection of the classroom environment and toys at a nursery school. MethodsEnvironmental cultures of the nursery and toys were prepared to evaluate the species and bacterial load and to assess the contaminated areas. Staphylococcus aureus petri dishes were placed at high-frequency contact sites, and hypochlorous acid water was atomized to achieve a 0.03-ppm atmospheric chlorine concentration. After the atomization, the amount of S. aureus bacteria on the Petri dish and the changes in bacterial count isolated from the environment and toys were evaluated. ResultsHypochlorous acid water atomization was performed for 5 h to avoid condensation. After a 3-h atomization, ≥99.99% of S. aureus was eliminated on petri dishes; furthermore, a significant disinfection effect was observed on environmental bacteria at least 1 h after atomization. For rubber and textile toys, the significant disinfection effect was observed 1 h after atomization, and for plastic toys, the effect was observed 3 h after atomization. ConclusionsHypochlorous acid water atomization is a useful strategy to disinfect nursery school classrooms.

First quantitative constraints on chlorine 36 dry deposition velocities on grassland: Comparing measurements and modelling results

Once released into the atmosphere, radionuclide dry deposition represents a major transfer process. It can be accurately characterized by its deposition velocity. However, this parameter is poorly constrained for most radionuclides, including chlorine 36. Chlorine 36 is a radionuclide of cosmogenic and anthropogenic origin. It may be discharged into the environment as gases and/or particles during the decommissioning of nuclear plants and the recycling of nuclear fuels. In this study, chlorine 36 deposition velocities are, for the first time, experimentally determined on grass downwind from the Orano La-Hague plant. The atmospheric chlorine 36 measurements were on average 50 nBq.m−3 for the gaseous fraction and 19 nBq.m3 for the particulate fraction. To measure the chlorine 36 transferred from the atmosphere to the grass, a method was devised for extracting the chlorides contained in solid matrices. With this method, chlorides were extracted with a mean efficiency of 83%. Chlorine 36 concentrations in the grass were on average 4 μBq.g−1, suggesting fast uptake of atmospheric chlorine 36. The yielded 36Cl dry deposition velocities varied with the season and were between 1 × 10−3 and 6 × 10−3 m s−1. The chlorine 36 depositions were modelled by adapting the existing deposition models and based on meteorological and micro-meteorological data. The dry deposition velocities calculated by the model showed less than one order of magnitude of difference with those determined experimentally. The deposition fluxes calculated by the model showed that the atmospheric depositions were predominantly gaseous chlorine 36 (>97%). However, on remote sites, the particulate fraction could be larger and have a greater influence on dry deposition. As chlorine 36 is a highly soluble and bioavailable element, these results will enable a better study of its behaviour in the environment and a more accurate evaluation of its dosimetric impact.

Formulation of the cosmic ray–driven electron-induced reaction mechanism for quantitative understanding of global ozone depletion

This paper formulates the cosmic ray-driven electron-induced reaction as a universal mechanism to provide a quantitative understanding of global ozone depletion. Based on a proposed electrostatic bonding mechanism for charge-induced adsorption of molecules on surfaces and on the measured dissociative electron transfer (DET) cross sections of ozone-depleting substances (ODSs) adsorbed on ice, an analytical equation is derived to give atmospheric chlorine atom concentration: [Formula: see text] where Φe is the prehydrated electron (epre-) flux produced by cosmic ray ionization on atmospheric particle surfaces, [Formula: see text] is the surface coverage of an ODS, and ki is the ODS's effective DET coefficient that is the product of the DET cross section, the lifetimes of surface-trapped epre- and Cl-, and the particle surface area density. With concentrations of ODSs as the sole variable, our calculated results of time-series ozone depletion rates in global regions in the 1960s, 1980s, and 2000s show generally good agreement with observations, particularly with ground-based ozonesonde data and satellite-measured data over Antarctica and with satellite data in a narrow altitude band at 13 to 20 km of the tropics. Good agreements with satellite data in the Arctic and midlatitudes are also found. A previously unreported effect of denitrification on ozone loss is found and expressed quantitatively. But this equation overestimates tropospheric ozone loss at northern midlatitudes and the Arctic, likely due to increased ozone production by the halogen chemistry in polluted regions. The results render confidence in applying the equation to achieve a quantitative understanding of global ozone depletion.

Observation of nitrogen oxide-influenced chlorine chemistry and source analysis of Cl2 in the Yangtze River Delta, China

Atmospheric chlorine (Cl)- and nitrogen (N)-containing species such as Cl2, ClNO2, and N2O5 participate actively in atmospheric chemistry by triggering radical reactions that lead to the formation of secondary pollutants. Despite of their importance in atmospheric chemistry, the measurements of these species are scarce, due to analytical challenges. Herein, we report observation results of Cl2, ClNO2, and N2O5 from measurements using high-resolution time-of-flight chemical ionization mass spectrometry (HR-ToF-CIMS) in Shanghai and Changzhou in the highly industrialized and populated Yangtze River Delta (YRD) of East China. In Changzhou, the maximum concentrations of N2O5, ClNO2, and Cl2, were 0.4, 1.3, and 0.5 ppbv (1-min averages), respectively, while they were 0.5, 5.7, and 1.1 ppbv, respectively, in Shanghai. Much higher ClNO2 levels were found in Shanghai compared to Changzhou, although the concentrations of the precursor (N2O5) are similar, indicating different heterogenous N2O5 uptake and Cl activation efficiency at these two sites. The diurnal variation of Cl2 in Shanghai shows a strong daytime peak, which is contradictory to its fast lost by photolysis during daytime; the diurnal pattern of Cl2 in Changzhou shows a prominent night peak and a much smaller daytime peak than that in Shanghai. The heterogeneous uptake of ClNO2 and the photolysis of O3 on chloride-containing aerosols are believed to contribute to efficient Cl2 formation at night and day, respectively. The estimated heterogeneous uptake coefficient of O3 is 0.004 ± 0.007, with a maximum of 0.034. Further analysis on these heterogeneous reactions with the help of aerosol composition data (chloride, liquid water content, pH etc.) was also performed to ascertain the role of the secondary formation of Cl2 in daytime Shanghai. Through simple estimation methods, the maximum daytime production rate of Cl2 was estimated to be 0.95 ppbv h−1, while daytime photolysis of Cl2 contributed to 98% of Cl formation. Our results indicate that there is a large secondary source of Cl2 in the YRD region during the day, which can contribute substantially to Cl formation and requires more investigations.

Widespread detection of chlorine oxyacids in the Arctic atmosphere

Chlorine radicals are strong atmospheric oxidants known to play an important role in the depletion of surface ozone and the degradation of methane in the Arctic troposphere. Initial oxidation processes of chlorine produce chlorine oxides, and it has been speculated that the final oxidation steps lead to the formation of chloric (HClO3) and perchloric (HClO4) acids, although these two species have not been detected in the atmosphere. Here, we present atmospheric observations of gas-phase HClO3 and HClO4. Significant levels of HClO3 were observed during springtime at Greenland (Villum Research Station), Ny-Ålesund research station and over the central Arctic Ocean, on-board research vessel Polarstern during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) campaign, with estimated concentrations up to 7 × 106 molecule cm−3. The increase in HClO3, concomitantly with that in HClO4, was linked to the increase in bromine levels. These observations indicated that bromine chemistry enhances the formation of OClO, which is subsequently oxidized into HClO3 and HClO4 by hydroxyl radicals. HClO3 and HClO4 are not photoactive and therefore their loss through heterogeneous uptake on aerosol and snow surfaces can function as a previously missing atmospheric sink for reactive chlorine, thereby reducing the chlorine-driven oxidation capacity in the Arctic boundary layer. Our study reveals additional chlorine species in the atmosphere, providing further insights into atmospheric chlorine cycling in the polar environment.

Matrix volatilization in a flow reactor for multi-element analysis of high purity germanium by ICP-MS

The preconcentration procedure of the trace elements for germanium analysis by mass-spectrometry with inductively coupled plasma (ICP-MS) has been developed. Trace elements were concentrated by matrix volatilization in a chlorine atmosphere. Chlorine gas is produced on site by the electrolysis of hydrochloric acid. Chlorine gas interacts with the germanium in samples during heating in the quartz cups and forms volatile germanium tetrachloride. Solid residues of trace elements concentrate were remained in the quartz cups after matrix volatilization and dissolved by mixture of nitric and hydrochloric acids for ICP-MS analysis. The behavior of analytes in the process of volatilization at different heating temperatures was studied. It is shown that the 43 elements (Ag, Al, Ba, Be, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Gd, Hf, Ho, La, Li, Lu, Mg, Mn, Na, Nb, Nd, Ni, Pb, Pd, Pr, Pt, Rb, Rh, Ru, Sc, Sm, Sr, Tb, Th, Ti, Tm, U, Yb, Zn and Zr) are quantitatively remains in the impurities concentrates. The efficiency of using of the different internal standards: 82Se, 115In, 185Re, 187Re and 209Bi for multi-element analysis by ICP-MS were studied. It is shown that preliminary matrix volatilization allows to decrease the limits of detection (LODs) of the analytes from 2.5 to 1700 times compare to conventional ICP-MS analysis. The LODs of 43 elements is in the range from 0.001 to 4 ng g−1. Accuracy of the proposed ICP-MS methods was confirmed by spike experiment and comparing with the results of independent method. This proposed matrix volatilization procedure provides to examine the high purity germanium with a total content of 43 trace elements from 0.0000014 wt%.

Application of copper(II)-based chemicals induces CH3Br and CH3Cl emissions from soil and seawater

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) are major carriers of atmospheric bromine and chlorine, respectively, which can catalyze stratospheric ozone depletion. However, in our current understanding, there are missing sources associated with these two species. Here we investigate the effect of copper(II) on CH3Br and CH3Cl production from soil, seawater and model organic compounds: catechol (benzene-1,2-diol) and guaiacol (2-methoxyphenol). We show that copper sulfate (CuSO4) enhances CH3Br and CH3Cl production from soil and seawater, and it may be further amplified in conjunction with hydrogen peroxide (H2O2) or solar radiation. This represents an abiotic production pathway of CH3Br and CH3Cl perturbed by anthropogenic application of copper(II)-based chemicals. Hence, we suggest that the widespread application of copper(II) pesticides in agriculture and the discharge of anthropogenic copper(II) to the oceans may account for part of the missing sources of CH3Br and CH3Cl, and thereby contribute to stratospheric halogen load.

Photochemistry of HCl in the martian atmosphere

The recent discovery of HCl in the martian atmosphere using the ExoMars Trace Gas Orbiter (Korablev et al., 2021, Sci. Adv. 7, eabe4386) during a global dust storm indicates a correlation between the HCl appearance and dust. Here this idea is studied using one-dimensional photochemical modeling on two summer midlatitude sites in the aphelion and perihelion seasons (LS = 70° at 40°N and LS = 250° at 40°S). Dissociation energies of chlorides lead to the conclusion that FeCl3 is the most active chloride that can form gaseous chlorine species in reactions with H and O, while NaCl is probably the most abundant chloride and may contribute to the production of HCl as well. Heterogeneous loss of the atmospheric chlorine is expected by Cl on FeCl2 and by HCl and HOCl on water ice. We have included five heterogeneous reactions that control HCl abundances, and probabilities of four of those are unknown and chosen to fit the observed HCl. The models involve 35 reactions of the standard CO2-H2O-NO chemistry and 38 reactions of chlorine chemistry that determine vertical profiles of nine chlorine species. Along with the five heterogeneous chlorine reactions, three reactions of heterogeneous loss of OH, HO2, and H2O2 on water ice are included in the models. Alternative mechanisms of the production of HCl in the martian atmosphere are related to electric discharges and not considered here because of the lack of observational evidences for those discharges. The background atmospheres at the chosen sites, including vertical profiles of temperature, density, H2O, and dust and water ice aerosol, are calculated using the Thermal Emission Spectrometer database. The calculated abundances of O3, H2O2, and the O2 dayglow at 1.27 μm agree with observations and other models. The predicted HCl at perihelion varies from 2 ppb at the surface to 10 ppb above 55 km, in agreement with the observed 0.5–5 ppb at 5–35 km. The model cannot reproduce the observed cutoff in HCl above 35 km. The lifetime of HCl is 70 days at perihelion, close to some estimates based on the observations. The abundance of HCl in aphelion is ≈1.5 ppt at equilibrium and 60 ppt if the HCl lifetime is constant. The effects of HCl chemistry on major photochemical products are low on Mars. Photolysis of the high-altitude water vapor near perihelion facilitates production of H and hence HCl, and this explains the observed correlation between H2O and HCl.

Pyrolysis of Porous Organic Polymers under a Chlorine Atmosphere to Produce Heteroatom-Doped Microporous Carbons.

Three types of cross-linked porous organic polymers (either oxygen-, nitrogen-, or sulfur-doped) were carbonized under a chlorine atmosphere to obtain chars in the form of microporous heteroatom-doped carbons. The studied organic polymers constitute thermosetting resins obtained via sol-gel polycondensation of resorcinol and five-membered heterocyclic aldehydes (either furan, pyrrole, or thiophene). Carbonization under highly oxidative chlorine (concentrated and diluted Cl2 atmosphere) was compared with pyrolysis under an inert helium atmosphere. All pyrolyzed samples were additionally annealed under NH3. The influence of pyrolysis and additional annealing conditions on the carbon materials’ porosity and chemical composition was elucidated.

Chemical vapor transport for intercalation reactions: Synthesis of a 1st stage DyCl3 graphite intercalation compound

In this work, we present a chemical vapor transport process involving the gaseous species DyAl3Cl12(g) in order to perform the intercalation of dysprosium trichloride into graphite. Even if it is known that such a reaction must be performed under chlorine atmosphere, this work reveals that an increase of the Cl2 pressure in the synthesis reactor improves the intercalation yield. By combination of gravimetric measurement, EDX analysis and 00l X-ray diffraction experiments, we evidence the synthesis of a novel 1st stage DyCl3-Graphite Intercalation Compound (GIC). The sample obtained in this study is a mixture of 1st stage DyCl3-GIC and 2nd stage AlCl3-GIC. However, considering the 1st stage DyCl3-GIC, the data collected in this work are in agreement with a IC repeat distance of 982 pm and a C8.1DyCl3.9 formula. Along the c-axis, the intercalated sheet is three-layered and exhibits a Cl-Dy-Cl stacking sequence existing in pristine chloride.

Kinetics of the formation and destruction of PCDD/Fs in a laboratory tubular furnace

A kinetic model has been developed for the formation of selected congeners of PCDD/Fs during the thermal decomposition of different wastes in a horizontal reactor. Previously published data on the decomposition of wastes have been correlated using a kinetic model that only considers process parameters, such as the presence of different amounts of oxygen in the atmosphere of reaction, chlorine and metals in the waste. The effect of both chlorine and metals is modelled through an equation assuming a “saturation effect”, i.e., that a certain amount of each substance produces the maximum rate, and that higher amounts do not increase the rate. The presence of oxygen is modelled by a destruction reaction over part of the PCDD/Fs produced. The model, which uses data from more than 64 experiments, correlated the emissions of three selected congeners: 1,2,3,6,7,8-HxCDD, OCDF and 2,3,7,8-TCDF, which are enough to estimate the total amount and toxicity of an emission.

Correlation between Microstructure and Chemical Composition of Zinc Oxide Gas Sensor Layers and Their Gas-Sensitive Properties in Chlorine Atmosphere.

In this article, we present results concerning the impact of structural and chemical properties of zinc oxide in various morphological forms and its gas-sensitive properties, tested in an atmosphere containing a very aggressive gas such as chlorine. The aim of this research was to understand the mechanism of chlorine detection using a resistive gas sensor with an active layer made of zinc oxide with a different structure and morphology. Two types of ZnO sensor layers obtained by two different technological methods were used in sensor construction. Their morphology, crystal structure, specific surface area, porosity, surface chemistry and structural defects were characterized, and then compared with gas-sensitive properties in a chlorine-containing atmosphere. To achieve this goal, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL) methods were used. The sensing properties of obtained active layers were tested by the temperature stimulated conductance method (TSC). We have noticed that their response in a chlorine atmosphere is not determined by the size of the specific surface or porosity. The obtained results showed that the structural defects of ZnO crystals play the most important role in chlorine detection. We demonstrated that Cl2 adsorption is a concurrent process to oxygen adsorption. Both of them occur on the same active species (oxygen vacancies). Their concentration is higher on the side planes of the zinc oxide crystal than the others. Additionally, ZnO sublimation process plays an important role in the chlorine detection mechanism.

Boron Nitride Nanotubes for Optical Fiber Chemical Sensing Applications

Boron nitride nanotubes (BNNTs) are 1-D hollow fibrous nanomaterials. They are thermally stable up to 800 °C in open air and up to 1000 °C in a pure chlorine atmosphere, are electrically insulating, and possess superlative mechanical properties. Since the BNNT assembly is highly porous and easily penetrated by liquids and gases, BNNT thin film coated on optical fiber can be used as a novel sensing medium with enhanced sensitivity and selectivity. In this letter, uniform BNNT films have been successfully coated on optical fibers and tapered optical fibers (TOFs). A BNNT-coated TOF sensor has been developed for various liquids and gases sensing applications. We demonstrated experimentally that the BNNT-coated TOF can be used as a level sensor for liquids, even for those with refractive indices smaller than that of silica such as the organic solvents like acetone, hexane, tetrahydrofuran, ethyl ether, and dimethylformamide. As to gas sensing, HCl was selectively detected with enhanced sensitivity due to its high polarity and good affinity to the OH/NH2 functionalized BNNTs. The BNNT-coated optical fiber sensors can be potentially used at high temperatures and in some harsh environments.

Emissions and Marine Boundary Layer Concentrations of Unregulated Chlorocarbons Measured at Cape Point, South Africa.

Unregulated chlorocarbons, here defined as dichloromethane (CH2Cl2), perchloroethene (C2Cl4), chloroform (CHCl3), and methyl chloride (CH3Cl), are gases not regulated by the Montreal Protocol. While CH3Cl is the largest contributor of atmospheric chlorine, recent studies have shown that growth in emissions of the less abundant chlorocarbons could pose a significant threat to the recovery of the ozone layer. Despite this, there remain many regions for which no atmospheric monitoring exists, leaving gaps in our understanding of global emissions. Here, we report on a new time series of chlorocarbon measurements from Cape Point, South Africa for 2017, which represent the first published high-frequency measurements of these gases from Africa. For CH2Cl2 and C2Cl4, the majority of mole fraction enhancements were observed from the north, consistent with anthropogenically modified air from Cape Town, while for CHCl3 and CH3Cl, we found evidence for both oceanic and terrestrial sources. Using an inverse method, we estimated emissions for south-western South Africa (SWSA). For each chlorocarbon, SWSA accounted for less than 1% of global emissions. For CH2Cl2 and C2Cl4, we extrapolated using population statistics and found South African emissions of 8.9 (7.4-10.4) Gg yr-1 and 0.80 (0.64-1.04) Gg yr-1, respectively.

Coastal Sea Salt Chlorine Deposition Linked to Intertropical Convergence Zone (ITCZ) Oscillation in French Guiana

AbstractSea salt chloride is a major component of atmospheric aerosol and its behavior is an essential element in determining the climate. Two atmospheric chlorine deposition measurement procedures were performed between 2004 and 2008 by the French Guiana Regional Air Observatory (ORA), in the coastal plain of Sinnamary. The main goal was to determine the background spatial distribution of marine chlorine in order to evaluate the impact of Ariane rocket hydrogen chloride emission. To determine the chlorine concentration level, weekly samples from 10 sites were analyzed. A seasonal pattern was identified. For every site, a high sea salt chlorine deposition level was observed from December to April and a low level from July to October. The ratio of high to low mean chloride concentration RHC/LC shows that just under half of the variation in chlorine deposition can be linked to the variation of sea salt production with low-level wind speed. Equations relating mean sea salt chlorine concentration and the distance to shore were studied, taking into account parameters found in other tropical regions, with a focus on neighboring Brazil. The wind rotation between the two seasons, and the sea salt chlorine loss per kilometer equation found for dry deposition, were used to calculate RHC/LC. It appears that the observed rotation (60°) explains 88% of RHC/LC. Finally, inland sea salt chlorine deposition behavior in this region was linked to intertropical convergence zone oscillation through variations in wind speed and direction.

Effect of Mo on corrosion behavior of Ni20Cr–xMo alloys in air with NaCl–KCl–CaCl2 vapor at 570°C

AbstractThe effect of Mo on the corrosion behavior of Ni20Cr–xMo alloys in an oxidizing chlorine‐containing atmosphere using air mixed with the salt‐vapor mixture of NaCl–KCl–CaCl2 at 570°C was investigated. The results revealed that the corrosion performance of the Ni20Cr alloys in the oxidizing chlorine atmosphere was improved by Mo addition of up to 3 wt%. The Mo‐free alloy formed a potassium chromate during corrosion as a result of the reaction between the Cr2O3 scale and KCl vapor. The chromate formation increased the chlorine potential at the scale surface and induced the breakdown of the protective Cr2O3 scale, resulting in internal chromium chloride precipitates and a Cr‐depleted zone. In contrast, the presence of Mo resulted in the formation of a NiO scale, which did not react with the salt vapors and, therefore, prevented the formation of chromates. The beneficial effect of Mo on the high‐temperature chlorination of Ni–Cr alloys in salt‐vapor‐containing atmospheres was ascribed to the suppression of chlorine generation due to NiO scale formation.

Different Approaches to Oxygen Functionalization of Multi-Walled Carbon Nanotubes and Their Effect on Mechanical and Thermal Properties of Polyamide 12 Based Composites

In this work the preparation of polyamide 12 (PA12) based composites reinforced with pristine and surface-modified carbon nanotubes is reported. A qualitative and quantitative evaluation of multi-walled carbon nanotube functionalization with oxygen containing reactive groups achieved by different procedures of chemical treatment is presented. Simple strong oxidative acid treatment as well as chlorination with subsequent chloroacetic acid treatment were applied. Carbon nanotubes (CNTs) were also subjected to chlorine and ammonia in gaseous atmosphere with small differences in after-ammonia treatment. Commercial COOH-functionalized carbon nanotubes were compared with nanotubes that were laboratory modified. The effect of CNT functionalization was evaluated basing on the improvement of mechanical and thermal properties of polyamide 12 composites prepared by in situ polymerization. It was found that high concentration of oxygen-containing functional groups on nanotube surface is not sufficient to improve the composite performance if the structure of carbon nanotubes is defective. Indeed, the best effects were achieved for composites containing nanotubes modified under mild conditions, seemingly due to a compromise between morphology and surface chemical structure.