Some investigations into hydrogen sulphide adsorption by zinc

The adsorption of very low concentrations of H₂³⁵S from air by thin zinc foils was investigated using a continuous flow technique at room temperature. The H₂S uptake rate was markedly influenced by relative humidity, being very low below 65% r.h., having a higher constant value in the range 65–95% r.h. and reaching a maximum at 100% r.h. Autoradiography showed that adsorption was non-uniform and the lack of uniformity was suggested to be due to mechanical or chemical exposure of the underlying oxide surface.     

Sulfur effects on the internal carburization of Fe-Ni-Cr alloys

Several commercial and laboratory-cast model austenitic alloys have been exposed in both sulfur-free carburizing environments and also in carburizing atmospheres to which additions of H₂S have been made. These studies were concentrated over the temperature range 1223–1323 K at a fixed carbon activity (a_c=0.8) with sulfur activities ranging from 2.2×10^–12 bar to 1.4×10^–9 bar. Under conditions of sulfur adsorption, e.g., 5.5 × 10^–11 bar at 1273 K, the blocking of adsorption sites for methane resulted in a transition from the parabolic kinetics observed during sulfur-free carburization to surface controlled linear kinetics. Higher levels of H₂S promoted the formation of a surface layer of chromium sulfide which reduced internal carburization but became a problem itself. The role of minor alloying elements has been established and the use of thermodynamic phase stability diagrams in defining the optimum conditions for sulfur inhibition of carburization evaluated.     

The corrosion behavior of Fe-Al alloys in H2/H2S/H2O atmospheres at 700–900°C

The corrosion behavior of five Fe-Al binary alloys containing up to 40 at. % Al was studied over the temperature range of 700–900°C in a H₂/H₂S/H₂O mixture with varying sulfur partial pressures of 10^–7–10^–5 atm. and oxygen partial pressures of 10^–24–10^–2° atm. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants decreased with increasing Al content. The scales formed on Fe-5 and –10 at.% Al were duplex, consisting of an outer layer of iron sulfide (FeS or Fe_1–xS) and an inner complex scale of FeAl₂S₄ and FeS. Alloys having intermediate Al contents (Fe-18 and –28 at.% Al) formed scales that consisted of mostly iron sulfide and Al₂O₃ as well as minor a amount of FeAl₂S₄. The amount of Al₂O₃ increased with increasing Al content. The Fe 40 at.% Al formed only Al₂O₃ at 700°C, while most Al₂O₃ and some FeS were detected at T800°C. The formation of Al₂O₃ was responsible for the reduction of the corrosion rates.     

Sulfidation behavior of a ferritic commercial alloy in different sulfidizing environments at high temperature

The sulfidizing behavior of Fe–22Cr–4Al–0.15Zr (wt.%) was studied in two atmospheres: S₂ vapor over the range 4.4–25.4 Pa and H₂–H₂S mixtures corresponding to aP _{S 2} range 0.2–1.297 Pa in the temperature range 973–1373 K. It was found that the constitution of the gaseous phase is of great importance on the corrosion kinetics and the morphology of the corrosion products. Furthermore, a stratification phenomenon during scale growth was observed during the initial sulfidation stage in H₂–H₂S mixtures containing a sufficiently high H₂S partial pressure. This behavior was not observed during tests in puresulfur vapor.     

Effect of 1 wt.% yttrium addition on high-temperature sulfidation behavior of Fe-15Cr-4Al alloy

High-temperature sulfidation studies have been carried out on Fe-15Cr-4Al with and without 1% Y in the temperature range 700–1000°C in an H ₂-H₂ S environment over the sulfur pressure range of 10 ^–9–10^–3 atm. Two-layered and three-layered sulfide scales were observed in both alloys at low and high sulfur pressures, respectively. The pegging phenomenon, similar to that occurring in high-temperature oxidation, across the innermost layer and substrate was observed in the case of the yttrium-containing alloy. Yttrium was found to be associated with aluminum and chromium sulfides. The role of yttrium was more evident at low than at high sulfur pressures and was found to reduce the parabolic rate constants by a factor of about one-half to one-seventh, respectively.     

Effect of annealing treatment on electrochemical properties of Mm-based hydrogen storage alloys for Ni/MH batteries

Several multi-component Mm-based hydrogen storage alloys with cobalt content from 0.8–1.0 have been prepared. The hydrogen absorption–desorption characteristics in gas–solid reactions and the electrochemical properties as MH electrodes have been investigated. The addition of small amounts of Al effectively lowers the hydrogen equilibrium pressure and improves the cycling stability of the alloys. Electrochemical measurements show that the MmNi_3.4Co_1.0Mn_0.5Al_0.1 alloy exhibits a maximum electrochemical capacity of 322 mA h g⁻¹ with a capacity decay of about 19.5% after 100 cycles. Annealing treatments flatten the plateau region and lower the hydrogen equilibrium pressure, which results in an increase of hydrogen uptake below 1 atm. The increasing trend of hydrogen storage capacity from the as-cast sample to the annealed sample in the gas–solid reactions is in good agreement with the electrochemical results. The electrochemical discharge capacity of the MmNi_3.4Co_1.0Mn_0.5Al_0.1 alloy increases to 334 mA h g⁻¹ and 340 mA h g⁻¹ after annealing for 3 h and 28 h, respectively, from 322 mA h g⁻¹ in the as-cast condition. The electrochemical cycling stability of the annealed samples was also greatly improved. The capacity decay for both annealed samples is about 8.3% and 6.8%, respectively, after 100 charge–discharge cycles. It was suggested that annealing treatments enhance the compositional homogeneity and cause the secondary phase (separated phase) to dissolve in main phase, which result in the improvement of electrochemical cycling stability of the alloy electrodes.     

Phase Diagram of the Ni–Cr–S System at 873 K between 10−4 and 10−8 Pa

The phase diagram of the Ni–Cr–S system was determined at 873 Kby sulfidation of thin Ni-Cr alloy sheets (22, 50, 66.6, and 80 at.% Cr) at10^–4.0, 10^–5.5, 10^–7.0,and 10^–8.0 Pa in H₂S–H₂ gasmixtures. X-ray diffraction analysis identified two sulfides,NixCr_3–xS₄ (03S₂,while concentration profiles were measured by electron-probe microanalysis(EPMA). The compositions of the terminal sulfides and alloys in equilibriumwere determined at sulfur pressures below 10^–5.5 Pa, whereasat 10^–4.0 Pa they were obtained from the Cr₃S₄and Ni₃S₂ phases at their interface. The proposedphase diagram shows that the solubility limit of Cr into Ni₃S₂is only a few atomic percent Cr, while the Ni content in Cr₃S₄decreases rapidly with decreasing sulfur pressures from 14 at.% Ni, a metalratio N_Ni/(N_Ni+N_Cr) of 0.32, at 10^–4.0Pa to a negligible value at sulfur pressures below 10^–8.0 Pa.     

Quantum chemistry study on the effect of Cl ion on anodic dissolution of iron in H2S-containing sulfuric acid solutions

The effect of Cl⁻ ion on the anodic dissolution of iron in H₂SO₄ solutions containing low H₂S level has been studied by electrochemical polarization curve measurements. The total energy and binding energy of the competitive adsorption for Cl⁻ and HS⁻ ions have been calculated with CNDO/2 method, as well as the net charge distribution of iron atoms at an anodic potential. The results showed that certain concentration of Cl⁻ ion inhibit the anodic reaction of iron accelerated by HS⁻. However, when Cl⁻ ion reached saturated adsorption, it began to promote the anodic reaction of iron due to the increased negative charge of iron atoms.     

Sulfidation of iron at high temperatures and diffusion kinetics in ferrous sulfide

The kinetics and mechanism of iron sulfidation have been studied as a function of temperature (950–1200 K) and sulfur pressure (10^–3-0.065 atm). It has been stated that a compact Fe_1–yS scale on iron grows according to the parabolic rate law as a result of outward lattice diffusion of metal ions through cation vacancies. The activation energy of sulfidation increases with sulfur pressure and the 1/n exponent increases with temperature. This nontypical dependence of iron sulfidation kinetics on temperature and pressure results from the analogous effect of both these parameters on defect concentration in ferrous sulfide. The chemical diffusion coefficients,D_FeS, and diffusion coefficients of defects, D_d, in ferrous sulfide have been calculated on the basis of parabolic rate contacts of iron sulfidation and deviations from stoichiometry in ferrous sulfide. It has been shown thatD_FeS is practically independent of cation vacancy concentration whereas the diffusion coefficient of defects depends strongly on that parameter. A comparison of self-diffusion coefficients of iron in Fe_1–yS calculated from the kinetics of iron sulfidation to those obtained from radioisotopic studies indicates that within the range studied of temperatures and sulfur vapor pressures the outward diffusion of iron across the scale occurs preferentially along the c axis of columnar ferrous sulfide crystals.     

Studies of the kinetics of nickel sulfidation in H2S-H2 mixtures in the temperature range 450–600°C

The reaction between pure nickel and H₂S-H₂ mixtures containing 1–65% H₂S has been studied over the temperature range 450–600°C. The sulfidation of nickel in the temperature range 560–600°C has been found to follow a linear rate law at low concentrations of H₂S and a parabolic rate law at higher concentrations (10% and 65% H₂S); X-ray examination of the scale formed on the metal showed it to be almost entirely -Ni₃S₂. On the basis of the kinetics and marker studies it can be concluded that the sulfide scale on nickel is formed by the outward transport of the metal and the inward transport of sulfur. In the temperature range 450–500°C the sulfidation of nickel follows a parabolic rate law. In mixtures containing 10% H₂S the scale formed contains voids, the occurrence of which is connected with formation of Ni₇S₆. It has also been shown that the rate of transport through the Ni₃S₂ layer has an essential influence on the formation of a continuous layer of Ni₇S₆. Marker studies have shown that both nickel and sulfur appear to be mobile in -Ni₃S₂.     

Stress corrosion cracking of B13, a new high strength aluminium lithium alloy

The present paper focuses on the study of SCC behaviour of a new Al–Cu–Li alloy. For this purpose, two conventional media – NaCl and NaCl + H₂O₂ – were used for comparison with commercial alloys 7075 and 8090. This new alloy shows lower susceptibility to SCC than conventional alloys as it does not undergo environmentally-induced embrittlement in NaCl solutions and in 1 M NaCl + 0.3% H₂O₂ in which the 7075 and 8090 alloys, respectively, undergo environmentally-induced fracture.Solution composition was modified in order to determine the environmental conditions and strain rates under which this new alloy will crack due to a stress corrosion cracking phenomenon. The addition of 0.6 M sulphates to 1 M NaCl + 0.3% H₂O₂ solution allows the definition of a range of strain rate (between 10⁻⁷ and 10⁻⁶ s⁻¹) in which this new alloy undergoes stress corrosion cracking.     

Sulfidation properties of an Fe-26.6 at.% Cr alloy at temperatures of 973–1173 K in H2S-H2 atmospheres at sulfur Pressures 104–10−6 Pa

An investigation is reported on the sulfidation properties of an Fe-26.6 at. % Cr alloy at 973, 1073, and 1173 K in H₂S-H₂ atmospheres at sulfur pressures 10⁴ 10^–6 Pa. The sulfidation kinetics when plotted according to a parabolic relationship usually exhibited an early slow transient period before onset of parabolic kinetics. Scales contained up to three layers. A triplex (CrFe)S_x/(CrFe)₃S₄/-(FeCr)S_x scale was formed at high sulfur pressures (range I), a single-phase (FeCr)S_x or a duplex (CrFe)S_x/(FeCr)S scale at intermediate sulfur pressures (range II), and a single-phase (CrFe)S_x scale at low sulfur pressures (range III). These pressure ranges at 973 K were: range I = 10^–2Pa, 10^–2 > (range II) 10^–5 Pa, and range III .     

Influence of sulfur on the nature and morphology of carbides formed on the surfaces of Fe-Ni-Cr alloys at high temperatures

The influence of sulfur upon surface carbide formation on a range of Fe-Ni-Cr alloys has been investigated at a temperature of 1273 K. The addition of small amounts of H₂S, up to 100 ppm (range of = 2.2×10^–12 to 5.5×10 su–11 bar), to a H₂-CH₄ carburizing atmosphere (a_c=0.8) was found to significantly modify the behavior from that normally observed in the sulfur-free environment. The carburization of these alloys in the H₂-CH₄ atmosphere led to the formation of globular particles of M₇C₃ on the surface of the alloy, but the addition of H₂S affected the type, morphology, and distribution of the surface carbides. Initially, the lower carbon containing M₂₃C₆ was formed, which transformed to M₇C₃ at a rate determined by the concentration of sulfur in the environment. The morphology of the M₇C₃ was modified by the presence of sulfur, and the carbide exhibited a preferred crystallographic orientation in the [001] direction. Particles of manganese sulfide were formed on the commercial alloys at > 2.3 × 10^–11 bar at 1273 K, and these served as nucleation sites for carbides sothat, in contrast to the behavior in sulfur-free conditions, complete surfacecarbide layers were formed.     

Oxidation-sulfidation behavior of iron-chromium-nickel alloys

Oxidation-sulfidation studies of Fe-Cr-8Ni alloys with 4, 12, and 22 wt. % Cr were conducted at 750 and 875°C in multicomponent gas mixtures that contained CO, CO₂, CH₄, H₂, and H₂S. The reaction processes resulted in parabolic kinetics. A chromium concentration in the range 0–12 wt. % in the alloy had a negligible effect on the parabolic rate constant; however, the rate constant for the alloy with 22 wt. % Cr was significantly lower. For a given sulfur partial pressure, the oxygen partial pressures required for the formation of a continuous oxide layer in an Fe-22Cr-8Ni alloy were 10² to 10³ times those calculated for Cr-Cr₂O₃ equilibrium at temperatures of 875 and 750° C, respectively.Work supported by the U.S. Energy Research and Development Administration.On visiting appointment from the Academy of Mining and Metallurgy, Cracow, Poland through a fellowship of the International Atomic Energy Agency.     

Hydrogen penetration rates of iron. Effect of halide ions,hydrogen sulfide and hexynol

The effect of the halides (Cl^?, Br^? and I^?) on the rates of the hydrogen evolution reaction (h. E. R.) and hydrogen penetration (h. P.) of iron in H₂SO₄ is determined. The H. E. R. and H. P. of Fe in these same electrolytes with the addition of H₂S are also studied. The inhibition of corrosion and h. p. in the H₂S environment by hexynol are compared. With halide addition her., i_corr and h. p. decreased in the following order, Cl^?> Br^?> I^?. H₂S catalyzed both the h. e. r. and h. p. The catalytic activity does not appear dependent on the H₂S concentration for the H. E. R. but does for H. P. The fraction of hydrogen generated which is absorbed by Fe is greater during corrosion when a new surface is formed continuously than during cathodic polarization. The addition of the acetylenic alcohol, hexynol, in H₂SO₄ containing H₂S and halides inhibited the h. e. r. corrosion and h. p.     

The corrosion of Fe-Mo alloys in H2/H2O/H2S atmospheres

The corrosion of Fe-Mo alloys containing up to 40 wt.% Mo was studied over the temperature range 600–980C in a H₂/H₂O/H₂S mixture having a sulfur pressure of 10^–5 atm. and an oxygen pressure of 10^–20 atm. at 850C. All alloys were two-phase, consisting of an Fe-rich solid solution and an intermetallic compound, Fe₃Mo₂. The scales formed on Fe-Mo alloys were bilayered, consisting of an outer layer of iron sulfide (FeS) and of a complex inner layer whose composition and microstructure were a function of the reaction temperature and of the Mo content of the alloys. No oxides formed under any conditions. The corrosion kinetics followed the parabolic rate law at all temperatures. The addition of Mo caused only a slight decrease of the corrosion rate. Platinum markers were always located at the interface between the inner and outer scales, indicating that outer scale growth was primarily due to outward diffusion of iron, while the inner scale growth had a contribution from inward diffusion of sulfur.     

Anodic Dissolution of Nickel from the Inherent and NiZn Intermetallic Phases in Acidic Sulfate Solutions. I. Nickel

For comparative investigation of the anodic dissolution kinetics of nickel from its own phase and NiZn intermetallic compound, the literature data are generalized and supplemented with new results concerning the anodic behavior of individual nickel in acidic sulfate environments. During the anodic dissolution of nickel at all the stages either in its passive or active state, the main role is shown to be played by the adsorption of water. HSO^– ₄, Cl^–, and I^– anions decelerate the active dissolution of nickel in a potential range from 0.0 to 0.2 V and accelerate it in a range from 0.2 to 0.3 V.     

High-temperature sulfur corrosion of iron-chromium alloys

The kinetics and the mechanism of sulfurization of Fe-Cr alloys containing from 0.35 to 74 at. % Cr were studied in the temperature range 700–1000°C. The sulfurization was conducted in sulfur vapor at atmospheric pressure. The reaction rate was determined by the continuous gravimetric method. The scale composition was studied by X-ray and electron microprobe methods. The contribution of the reactants to the process of material transport through the scale was examined with both the marker method and the autoradiographic method using the radioactive isotope³⁵S. It has been found that, irrespective of alloy composition and temperature, the sulfurization follows a parabolic rate law. On the dilute alloys (up to about 2 at. % Cr) the scales formed are monophase consisting of Fe_1–xS only. In the range 2–40 at. % Cr the scale is a heterophase mixture of Fe_1–xS and the mixed spinel FeFe_2–xCr_xS₄. On the chromium-rich alloys the scale is monophase and is built of a solid solution of FeS in Cr₂S₃. The scale growth on the alloys under examination proceeds without the participation of the inward diffusion of sulfur. The mechanism of the scale formation has been proposed.     

Sulfidation kinetics and scale structures of chromium at temperatures of 973–1173 K and 104–10−6 Pa sulfur pressures

The sulfidation behavior of chromium was investigated over a temperature range of 973–1173 K in H₂S-H₂ gas mixtures of 10⁴–10^–6 Pa sulfur partial pressures using thermogravimetry, X-ray diffractometry, optical and scanning electron microscopy, and electron-probe microanalysis. Sulfidation kinetics are rapid for short periods and obey a linear rate law at low sulfur pressures, whereas at high sulfur pressures sulfidation tends to be parabolic. The surface morphologies can be divided into four types: at high sulfur pressures a petal-like crystal of Cr₂S₃(rho. and tri.) (type 1), at intermediate sulfur pressures a twinlike structure of Cr₃S₄ (type 2), at low sulfur pressures a flat surface with numerous hexagonal pits of Cr_1–xS (type 3), and a fine twinlike structure of ordered Cr_1–xS (type 4). At 973 K, the sulfur pressure ranges are type 1 at > 10^–4, type 2 at , and type 3 at . The critical sulfur pressure where type 2 was formed, 10^–5 Pa at 973 K, shifts toward higherressures at higher temperatures and becomes 10^–3 Pa at 1073 K and 10^–1 Pa at 1173K. Type 4 is observed at 1173K and 10^–6 Pa sulfur pressure. Thesulfide scale is composed of two distinct layers: an external layer, which is dense with a fine columnar structure, and an inner layer, which is porous with a layered structure of sulfides and voids. The external scale is composed offour layers at high sulfur pressures: at the scale-gas interface Cr₂S₃(rho.), next Cr₂S₃(tri.), third Cr₃S₄, and innermost Cr_1–xS. With decreasing sulfur pressures,the number of layers in the external scale was reduced. Pt markers were positioned between the external and inner scales.Emeritus Professor.     

High-temperature thermoplastic strengthening of steels St3sp and 09G2S

Conclusions We worked out a regime of high-temperature thermoplastic treatment of steels St3sp and 09G2S consisting in austenization at 1020°C, strain (=200%, =5.7%) at 940°C with subsequent cooling at a rate >100°C/sec.As a result of such treatment the tensile strength of steel St3sp is increased to 1230 N/mm², of steel 09G2S to 960 N/mm², and the conventional yield strength to 1100 and 840 N/mm², respectively.N. É. Bauman Moscow State Technical University. All-Union Research Institute of Metallurgical Machinery Construction. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 18–19, July, 1991.