NaCl Vapor Research Articles

Adsorption of NaCl Vapor at Elevated Temperature on Mineral Adsorbents

Some mineral adsorbents were selected to remove NaCl vapor at elevated temperature. Results indicate that the activated alumina is the best adsorbent with the highest sodium compound content, under conditions of 1123 K, a gas velocity of 16 L/min, an adsorption time of 5 h, and a NaCl concentration of 0.13 mg/L. Results show that sodium compound content is dependent on the microporous structure and the chemical constitutes of the adsorbent, but the extent of the effects varies with each adsorbent. Results of XRD and SEM indicate that physical adsorption exists in the NaCl vapor-capture mechanism of the activated alumina. Its kinetics results indicate that both chemical adsorption and physical adsorption exist, and the adsorption process of the activated alumina is controlled by both the chemical adsorption control and the product-layer-diffusion control of physical adsorption.

Synergistic corrosion behavior of coated Ti60 alloys with NaCl deposit in moist air at elevated temperature

In the present paper, the corrosion behavior of Ti60 alloys with an aluminide, TiAlCr, and enamel coatings in moist air containing NaCl vapor at 700–800 °C were studied. The results showed that the TiAlCr and aluminide coatings failed to protect the substrate from corrosion due to the cyclic formation of volatile products during corrosion at 800 °C. However, an uneven continuous protective Al 2O 3 scale could form on the aluminide coating during corrosion at 700 °C. And the enamel coating could protect Ti60 from corrosion due to its high thermochemical stability and matched thermal expansion coefficient with substrates of Ti-base alloys during corrosion.

Corrosion behavior of thermal barrier coatings exposed to NaCl plus water vapor at 1050 °C

In the present investigation, NiCrAlY coating with the composition of Ni–24Cr–6Al–0.7Y is deposited on a nickel-based superalloy by low-pressure plasma spraying, and the top coating, ZrO 2, partially stabilized with Y 2O 3 (7 wt.%), is deposited on NiCrAlY coating by air plasma spraying. The cyclic corrosion behavior of NiCrAlY + YSZ coating exposed to NaCl plus water vapor has been investigated under atmospheric pressure at 1050 °C. The result shows that the cyclic oxidation life of NiCrAlY + YSZ coating in the presence of NaCl plus water vapor was shortened compared with that in NaCl vapor. The failure of the coating mainly happened near the interface between the bond coat and YSZ. The accelerated failure mechanism has been discussed based on the experimental results and thermodynamics.

Corrosion Inhibition of 304 Stainless Steel by Nano-Sized Ti/Silicone Coatings in an Environment Containing NaCl and Water Vapor at 400–600°C

The corrosion behavior of 304 stainless steel (SS) and its corrosion inhibition by brushing nano-sized Ti/silicone coatings on its surface in an environment containing a solid NaCl deposit and water vapor at 400–600°C was studied. Results indicated that water vapor or NaCl, especially water vapor plus NaCl accelerated the corrosion of the steel markedly. The corrosion scales of the uncoated steel had a duplex structure at 400–500°C and internal oxidation occurred for the uncoated steel at 600°C in an environment containing NaCl and water vapor. The corrosion of the 304SS was inhibited efficiently by the coatings at 400–500°C, and the coated steel suffered corrosion to some extent and most of the coatings were destroyed at 600°C. X-ray diffraction (XRD) indicated that the corrosion products of the uncoated steel were mainly Fe2O3, Cr2O3, NiO or Na2CrO4, and the coatings consisted mainly of TiO2 and SiO2 after exposure at 400–500°C. The good corrosion resistance of the nano-sized Ti/silicon coatings was attributed to the formation of SiO2, and TiO2 that resulted from the decomposition of the organic components in the coating and fast oxidation of nano-Ti powder respectively during the experiments, TiO2 mixed together with SiO2 and formed a new coating on the steel surface that played an important role in the protection of the steel.

Corrosion of HIPed β-Si6−zAlzOzN8−z (z =0, 1, 2, 3) ceramics by NaCl vapor

Abstract Tests for the corrosion of β-Si 6− z Al z O z N 8− z ( z =0, 1, 2, 3) (β-Si 3 N 4 and β-SiAlON) ceramics were carried out at 1300 °C for 3–24 h in NaCl vapor of various concentrations (1.67 × 10 −2 , 3.33 × 10 −2 , 5.0 × 10 −2 g l −1 ), which was carried by flowing Ar gas. The densified Si 3 N 4 and SiAlON ceramics were fabricated by HIPing under N 2 of 150 MPa at 1700 °C. The corroded surface was observed by optical and scanning electron microscopy (OM and SEM). The phases produced during corrosion were identified by X-ray diffraction. The thickness of the corroded scale was determined by cross sectional SEM observation. The Si 3 N 4 ceramics were hardly corroded by NaCl vapor, while the z =1 and 2 SiAlONs were slightly corroded with the formation of bubbles on the surface; the z =3 ceramics were severely corroded with the formation of Al 2 O 3 needle crystals and fine mullite crystals, depending on the NaCl vapor concentration. Quantitative X-ray microanalysis showed that 2 at.% Na is contained in all the scales of the SiAlONs. The severe corrosion of the z =3 SiAlON was explained on the basis of the kinetic results for the thickness of the scale.

Influence of Cr content on the corrosion of Fe-Cr alloys: The synergistic effect of NaCl and water vapor

The corrosion behavior of pure Fe and Fe-Cr alloys with different Cr content in the presence of a solid NaCl deposit and water vapor at 600degreesC was studied. Results indicated that the corrosion of pure Fe was severe even in air at 600degreesC and the scale formed on the surface was compact and uniform. However, with a solid NaCl deposit on its surface, the corrosion of pure iron in air was suppressed to some extent, but the presence of water vapor in the atmosphere causes accelerated corrosion. Under the synergistic effect of NaCl and water vapor, the corrosion of pure iron is accelerated more significantly. In contrast with the known effect of Cr content on the oxidation of Fe-Cr alloys, an increasing Cr content in Fe-Cr alloys increases the corrosion rate of the alloys under the synergistic effect of solid NaCl and water vapor. A mechanism to explain the effect of water vapor and NaCl on the corrosion of pure iron and Fe-Cr alloy is proposed.

Microstructure and properties of various fluorine-containing SiAlON ceramics synthesized by HIPing

Abstract An attempt was made to prepare various F-doped β-, O-, X-, and α-SiAlONs from a mixture of Si 3 N 4 , SiO 2 , Al 2 O 3 , AlN, or Y 2 O 3 using AlF 3 or topaz as the fluorine source by HIPing at 1500–1800°C and 150 MPa. The phases were identified and the z , x , and m/n values determined for β-, O-, and α-SiAlONs by X-ray diffraction. When AlF 3 was used, a single phase ceramic (O-SiAlON) was produced from a mixture of α-Si 3 N 4 and SiO 2 at 1500°C, with a mixture of O- and β-SiAlONs formed at 1700°C. A mixture of α-Si 3 N 4 , AlN, and Y 2 O 3 with AlF 3 produced β-/Y-α-SiAlON ceramics at 1730°C. The use of topaz produced the β-SiAlON ceramic with a trace of mullite from a mixture of α-Si 3 N 4 and AlN at 1770°C and mixed phase β-/O-SiAlON ceramics from α-Si 3 N 4 and SiO 2 at 1700°C. Single phase X-SiAlON could not be obtained under the present conditions. The microstructures of the single phase O- and β-SiAlON ceramics and the β-/Y-α-SiAlON mixture showed the growth of O- and β-SiAlON and Y-α-SiAlON crystals with hexagonal and/or long rod-like or platy shapes in a matrix of F-containing glassy phase. The compositions of the SiAlON crystals and the glass phase were semi-quantitatively determined by EDX; the total glass phase was estimated by a quantitative Rietveld XRD powder method. The F-doped β-SiAlON ceramics showed better corrosion resistance towards NaCl vapor and lower Vickers hardnesses.

Epitaxial (001) Fe films with unidirectional anisotropy

It has been shown that single-crystal (001) Fe films grown on the cleaved LiF substrates in the presence of NaCl vapor are characterized by an asymmetric and displaced hysteresis loop of a transitional antiferromagnetic layer of a metamagnetic nature in a certain range of remagnetizing fields. Such shape of the hysteresis loop is explained by possible existence between the film and the substrate.

Mechanisms of simultaneous oxidation-chloridation of austenitic stainless steels by NaCl in air

Simultaneous oxidation-chloridation behavior of austenitic stainless steels by NaCl in air was investigated at 650°C. Surface oxide scales of the test alloys had double-layered structures that consisted of inner spinel layer and outer Fe2O3 layer. Condensed and gaseous chlorides were formed below the scale surface by NaCl vapor diffusing inward via pores or cracks of the scales. The rate of internal and uniform attack mainly depended on the porosity of the inner spinel layer. In order to predict the complex mixed oxidation behavior of alloys, new types of thermodynamic stability diagrams were utilized, which was constructed by computer-assisted calculations of phase equilibria of the multi-component reacting systems using the Thermo-CaIc program. The overall mixed oxidation process including the initial stage of reaction, the rapid formation and growth of the scale and the transport of gaseous species through the oxide scale was elucidated.

Mass-Spectrometric Study of the Temperature Variation in the Dimer-to-Monomer Ratio in the Free-Surface Vaporization Fluxes from Alkali Halide Single Crystals

A mass-spectrometric method is used to investigate the kinetics of the vaporization of LiF (970–1070 K), NaCl (722–889 K), KCl (780–900 K), KBr (724–918 K), and CsI (656–838 K) single crystals. A dimer-to-monomer ratio, JD/JM, in the fluxes vaporizing from free surfaces of these crystals are calculated, using the currents of M+, MX+, and M2X+ ions formed via electron impact ionization of the molecules MX and M2X2 (M is the alkali atom; X is the halogen). It is found that the dimer-to-monomer ratio increases with temperature at a continually increasing rate in the LiF and NaCl cases. In the KCl, KBr, and CsI cases, this rate passes through a maximum. Such a specific temperature variation in JD/JM is discussed through the analysis of proposed mechanisms of dimer formation in light of the terrace–ledge–kink and surface charge models.

TiAlの耐酸化性に及ぼす微量NaCl蒸気を含む酸素中での予備酸化の効果

TiAlの耐酸化性に及ぼす微量NaCl蒸気を含む酸素中での予備酸化の効果

Synergistic effect of NaCl and water vapor on the corrosion of 1Cr-11Ni-2W-2Mo-V steel at 500-700°C

The corrosion behavior of 1Cr-11Ni-2W-2Mo-Vsteel was studied in the presence of a NaCl deposit andwater vapor at 500-700°C. Results indicated thatcorrosion was not obvious without an NaCl deposit, while corrosion was accelerated remarkably by thesimultaneous presence of NaCl and water vapor at anytemperature. Optical microscopy (OM), X-ray diffraction(XRD), scanning electron microscopy (SEM), andelectron-probe microanalysis (EPMA) were used to analyze thecorrosion products. A mechanism of the synergisticeffect of water vapor and NaCl on corrosion of the steelis proposed.

Effect of trace amounts of NaCl vapor on high-temperature oxidation of TiAl

The effect of trace amounts of NaCl vapor on thehigh-temperature oxidation of TiAl was examined bythermogravimetry and analysis of the scale formed onTiAl. The mass gain due to oxidation at 1273 K in O2 with trace amounts of NaCl vaporwas far lower than that in pure O2 withoutNaCl vapor. This low mass gain in the atmosphere withtrace amounts of NaCl vapor resulted from the saturationbehavior of mass gain during the initial period ofoxidation. It was found from X-ray photoemissionspectroscopy (XPS) analyses of the specimen surface thatthe oxide film formed during the initial period in theatmosphere with trace amounts of NaCl vapor consisted ofdense Al2O3, thus, the lowoxidation rate of TiAl was attributed to a protectiveoxide film of denseAl2O3.

Ti-6Al-4V合金の高温酸化に及ぼす微量NaCl蒸気の影響

The effect of trace of NaCl vapor on oxidation of Ti-6 mass%Al-4 mass%V alloy at 923 to 1073 K was investigated by measurement of mass change of specimens, observation and analysis of scales formed on the specimens. In O2 atmospheres containing NaCl vapor, the alloy was oxidized acceleratedly. An increase in concentration of NaCl vapor increased the oxidation rate of the alloy. Such an accelerated oxidation occurred at the temperatures above 973 K. Scales formed on the alloy after the accelerated oxidation consisted of rutile-TiO2. For a scale formed in O2 with 123.0 vol ppm NaCl vapor, V2O5 was observed in the vicinity of the scale/metal interface. These scales were porous, and contained voids. On the basis of the experimental results and a thermodynamical equilibrium discussion, a mechanism that NaCl vapor induced the formation of molten V2O5 to cause accelerated oxidation of the alloy was presented.

ＴｉＡｌの高温酸化に及ぼす微量ＮａＣｌ蒸気を含む酸素中での予備酸化の効果

ＴｉＡｌの高温酸化に及ぼす微量ＮａＣｌ蒸気を含む酸素中での予備酸化の効果

純TiならびにTi-6 mass%Al合金の高温酸化に及ぼす微量NaCl蒸気の影響

The effect of trace amounts of NaCl vapor on the oxidation behavior of pure Ti and Ti-6 mass%Al alloy was investigated by thermogravimetry in a temperature range from 923 to 1073 K. Observation and identification of scales were performed. In addition, hardness measurement of the metal substrate beneath the scale was performed. The formation of scales consisting of periodically stacked layers was observed for pure Ti after oxidation in O2 without NaCl vapor. On the other hand, the addition of NaCl vapor resulted in the formation of scales consisting of a single layer without a continuous crack. The oxidation kinetics for pure Ti in O2 containing NaCl vapor followed a parabolic rate law, and the oxidation rate increased with increasing concentration of NaCl vapor. The marker experiment showed that the rate-determining step in this parabolic oxidation was outward diffusion of titanium ions through a rutile TiO2 layer. Therefore, NaCl vapor in O2 appears to promote the outward diffusion of titanium ions through the scale. The oxidation rate for a Ti-6 mass%Al alloy, whose kinetics followed a parabolic rate law, also increased with increasing concentration of NaCl vapor. However, in the O2 containing NaCl vapor the oxidation rate for the Ti-6 mass%Al alloy was lower than that for pure Ti. The decrease in the oxidation rate by aluminum addition to titanium seemed to be attributable to the fact that an inner layer consisting of α-Al2O3 formed at the oxide/metal interface inhibited the outward diffusion of titanium ions.

Diffusion of molecular vapors through heated graphite

The reasons for the elimination of interferences in a filter furnace used as an atomizer in electrothermal atomic absorption spectroscopy (ETAAS), are examined theoretically and experimentally. The results of observations of stepped or multipeak background absorption signals for NaCl, NaI, KCl, KBr, KI, CaCl 2 and MgSO 4, which are characteristic for each matrix and different types of graphite used, leads to hypotheses about the formation of molecule-graphite intercalation composites. These are treated as stable compounds of different stoichiometry having substantial specific enthalpy of formation. The validity of the idea is confirmed with the measurements of the rate of NaCl vapor release through a graphite filter as a function of temperature, and comparison with the literature data for similar compounds of alkali metals. The effect of implantation of molecular particles into a crystalline lattice leads to reduction of their diffusion rate through graphite, which in turn provides time-resolved background and atomic absorption signals. Further investigations and development of the idea to understand the analytical effect are proposed.

Homoepitaxial growth investigated by high-resolution He atom scattering: NaCl onto NaCl(001)

The homoepitaxial growth of NaCl vapor deposited onto the cleaved (001) surface of NaCl was studied with a nearly monoenergetic (ΔE/E≂2%) He atom beam. In comparison with reflection high-energy electron diffraction, the He atom is unique for epitaxial studies in that it is uncharged, nondestructive, and sensitive only to the outer surface layer. The oscillations in the scattered intensities of the specular and Bragg peaks due to the layer-by-layer growth were examined by measuring the angular distributions as a function of coverage, surface temperature (150–400 K) and incident He atom wave vector (6–8 Å−1). The periodic variation in the relative heights of the specular and Bragg peaks with Δkz=‖kfz−kiz‖ showed that under these conditions the growth is two-dimensional with a terrace height of 2.8 Å or half the bulk face-centered-cubic lattice spacing. In addition, scattering cross sections for adsorbed NaCl at low coverages were determined with respect to these same parameters. The cross sections for substrate temperatures above 250 K decline rapidly, which suggests that surface diffusion becomes much more rapid above this point. Previous studies had reported high mobilities down to temperatures considerably lower.

Investigation of chloride salt decomposition and pre-atomization interferences in electrothermal atomic absorption spectrometry

The decomposition and vaporization of NaCl, MgCl2 and NiCl2 in an electrothermal atomizer have been studied using ion chromatography, radioactive tracers and flame atomic absorption spectrometry (FAAS). Solutions of the individual chloride salts were injected to deposit 50–200 µg on to a pyrolytic graphite platform in a pyrolytic graphite coated graphite tube. The solutions were dried and then pyrolysed at a temperature in the range 200–1200 °C. The residue on each platform was then analysed to determine the amount in micromoles of metal and chloride remaining at each temperature. This allowed formation of pyrolysis curves for the salts, similar to those produced in conventional electrothermal AAS (ETAAS) for analyte elements. Magnesium chloride and NiCl2 exhibited partial hydrolysis with the heating programme used, but significant vaporization of MgCl2 and NiCl2 also occurred. The decomposition and vaporization of 100 or 200 µg masses of the chloride salts caused pre-atomization step losses of Cd, Ga and Pb, in the range 300–1000 °C, as indicated by radioactive tracer analysis and inductively coupled plasma mass spectrometry. The interference was in the order Ni-Cl2>MgCl2>NaCl. Partial hydrolysis of MgCl2 to MgO minimized the pre-atomization losses of the analytes at higher temperatures due to a chemical modification effect similar to that caused by MgNO3. The study illustrates that, in the presence of high masses (50–200 µg) of chloride salts, pre-atomization loss of analyte elements can be a major cause of chemical interference in ETAAS if too high a char temperature is selected and the use of chemical modification is ignored.

Accelerated Oxidation of Chromium by Trace of Sodium Chloride Vapor

The effect of NaCl vapor on high temperature oxidation of Cr in O 2 were examined by using a two-zone furnace. Concentrations of NaCl in flowing O 2 were varied from 1.4 to 123 vol ppm at temperatures from 973 to 1223 K. When Cr was heated in O 2 with NaCl vapor, it was oxidized acceleratedly with formine nonprotective Cr 2 O 3 . The oxidation rate increased with NaCl concentration. Both mass-gain by oxide formation and mass-loss after descaling showed maximum values at about 1023 K