Corrosion Behavior of Hydrogenated Iron in Oxygen-Containing Sulfuric Acid Solution

By measuring the amount of absorbed oxygen and analyzing the solution by means of photocolorimetry, the effect the cathodic hydrogenation exerts on iron corrosion in an aerated solution of 0.05 N H₂SO₄ + 1 N Na₂SO₄ at 20°C is studied. On control samples, the currents of iron dissolution (i _Fe) and oxygen reduction coincide with the limiting diffusion current of the latter . In the initial corrosion period of hydrogenated iron, the inequalities are valid, which can be explained by the interaction of active hydrogen forms with oxygen at the surface of corroding iron.     

Galvanic Corrosion of Al Alloys

In a systematic study of galvanic corrosion of Al alloys the effects of the dissimilar metal, the solution composition and area ratio have been studied using galvanic current and weight loss measurements, In 3.5% NaCl, galvanic corrosion rates of the Al alloys 1100, 20324,2219, 6061 and 7075 decrease with the nature of the dissimilar metal in the order AG>Cu> 4130 steel ?stainless steel ≈Ni>>Inconel 718?Ti-6A1-4V≈?Haynes 188>Sn>Cd. Coupling to zinc did not lead to cathodic protection of all A1 alloys. The potential difference of uncoupled dissimilar metals have been found to be a poor indication of galvanic corrosion rates. Dissolution rates of A1 alloys coupled to a given dissimilar material are higher in 3.5% NaCl than in tapwater and distilled water where they are found to be comparable. In assessing the galvanic corrosion behavior of a given A1 alloy as a function of environment, one has to consider the effect of the dissimilar metal. The dissolution rate of Al 6061 is, for example, higher in tapwater with Cu as cathode than in 3.5% NaCl with SS304L or Ti-6AI-4V as cathode. The effect of area ratio \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document} has been studied in 3.5% NaCl for area ratios of 0.1, 1.0 or 10. The galvanic current was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density \documentclass{article}\pagestyle{empty}\begin{document}$ i_{^g }^A $\end{document} with respect to the anode has been found to be directly proportional to the area ratio (\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document}), while the dissolution rate r_A of the anode was related to area ratio by \documentclass{article}\pagestyle{empty}\begin{document}$ r_A = k_{_2 } (1 + \frac{{A^C }}{{A^A }}) $\end{document}. The results obtained have been explained in terms of mixed potential theory.     

Thermodynamische Gesichtspunkte zum elektrochemischen Auf- und Abbau von Oxydschichten auf edleren Metallen

Thermodynamical considerations concerning the electrochemical build-up and removal of oxide layers on nobler metals On the strength of thermodynamical considerations, the electrochemical behaviour of gold, platinum and palladium has been investigated with the aid of the A/ΔU diagram. The P_H relationship of the Flade reference potential was found to be: \documentclass{article}\pagestyle{empty}\begin{document}$ U_{H,\ F,\ K} = U^\circ \ _{H,\ F,\ K} - 0,059\ p_{H.} $\end{document} This corresponds:

• for Pt = 0.98 V to the removal of PtO
• for Au = 1.37 V to the removal of AuO
• for Pd = 1.10 V to the removal of PdO₂.

     

熔剂中添加LaCl3对Mg合金显微组织与性能的影响

测试分析了含有不同量LaCl3的熔剂对Mg合金的力学性能、组织、断口形貌以及腐蚀行为的影响．结果表明，LaCl3以熔剂形式加入Mg合金中，合金内会形成粒状细小的Al10La2Mn7稀土相，该稀土相起到γ相形核核心的作用，使γ相得到细化．LaCl3可以提高合金的抗拉强度σb和延伸率δ当熔剂中含有5％的LaCl3时，σb和δ分别从161MPa和2．1％上升到最大值203MPa和4．2％．分别提高了26％和100％．之后，随着LaCl3加入量的进一步提高，在精炼过程中会造成熔剂结团，并增加Mg熔体内的夹杂，合金的力学性能反而下降．LaCl3不改变Mg合金的断裂机理，断口形貌仍为准解理断裂．研究还表明，含5％LaCl3的熔剂能明显改善Mg合金的耐蚀性，在5％Nacl溶液中腐蚀速率从1.10mg／(cm^2-d)下降到0．17mg／(cm^3-d)，降低了84％．     

Dehnungsinduzierte Korrosionsprozesse

Strain-induced corrosion phenomena When investigating stress corrosion cracking phenomena in the past, application of a static load σ played a major role in the performance of experiments. A further influencing factor, to which until now was payed less attention, is the strain ? caused by a mechanical stress. Increasing attention is payed also to the variations with time of these influencing factors, \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \sigma $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot \varepsilon }$\end{document}. A strain, induced by a load may have the following effects: (i) break-up of a protective layer and/or (ii) mechanical stimulation of anodic metal dissolution. Both types of failures are discussed. The type of failure (i) is referred to as stress-induced, the type of failure (ii) as strain-induced corrosion. The authors discuss the question, whether type of failure (ii) is always involved in stress corrosion cracking. For some corroding systems, this question can clearly be answered in the negative, while in numerous systems the occurrence of stress corrosion cracking is markedly influenced by the strain rate. The relevant systems are described in detail. Essential for the authors' considerations is the existence of an upper and lower critical strain rate for the occurrence of stress corrosion cracking. Transition from strain-induced stress corrosion cracking to corrosion fatigue is given with relatively high upper critical strain rates. From the influence of strain rate upon stress corrosion cracking, conclusions are derived for the application of test methods for detecting susceptibility of metallic materials to stress corrosion cracking.     

Pressure dependencies of copper oxidation for low- and high-temperature parabolic laws

Studies of the oxidation kinetics of copper have been conducted in the thin-film range at temperatures of 383–398 K and in the oxygen pressure range of 0.278–21.27 kPa; whereas in the thick-film regime at 1123 K, studies have been conducted in the oxygen pressure range of 2.53–21.27 kPa. Furthermore, the effect of continuously impressed direct current with oxygen pressure variation in Wagner's parabolic range has been studied also in order to have a better understanding of the effective charge on the migrating species. In the low-temperature range, the rate constant, k_P ∝ \(P_{O_2 }^{1/4} \) , suggesting that the migration of neutral vacancies in the growing film predominates. At high temperature, 1123 K, in the Wagnerian regime, the observed approximate pressure dependencies of the parabolic rate constants are the following: $$\begin{gathered} {\text{k}}_{\text{p}} (normal oxidation) \propto \sim {\text{P}}_{{\text{O}}_{\text{2}} }^{{\text{1/7}}} \hfill \\ {\text{k}}_{\text{p}} (sample cathodic) \propto \sim {\text{P}}_{{\text{O}}_{\text{2}} }^{{\text{1/5}}} \hfill \\ \end{gathered} $$ and $${\text{k}}_{\text{p}} (sample anodic) \propto \sim {\text{P}}_{{\text{O}}_{\text{2}} }^{{\text{1/10}}} $$ .     

Partial Thermodynamic Properties of <Emphasis Type="Italic">γ</Emphasis>′-(Ni,Pt)<Subscript>3</Subscript>Al in the Ni-Al-Pt system

Measurements were made to determine how Pt influences the partial thermodynamic properties of Al and Ni in γ′-(Ni,Pt)₃Al and liquid in the Ni-Al-Pt system. The activities of Al and Ni were measured with a multiple effusion-cell mass spectrometer (multi-cell KEMS). For a constant X _Al = 0.24, adding Pt, from X _Pt = 0.02-0.25, reduces a(Al) almost an order of magnitude, from 2 × 10⁻⁴ to 2 × 10⁻⁵, at 1560 K. This occurred for of −203 ± 10 kJ mol⁻¹ and the a(Al) decrease was due to increasing from −60 to −40 J mol⁻¹ K⁻¹ with Pt addition. The large negative and indicate Al-atoms are highly ordered in γ′-(Ni,Pt)₃Al. Nickel activity, a(Ni), remained essentially constant, ∼0.7, indicating an increasing ternary interaction between Ni-atoms and (Al + Pt)-atoms with Pt addition, where γ_Ni increased from about 0.7 to 1.2. This is supported by in the range 6.1-7.1 ± 1.5 kJ mol⁻¹ at 1520 K, and a positive , which suggest disorder on the Ni-lattice. For a consistent X _Al = 0.27, adding Pt, from X _Pt = 0.10–0.25, also reduces a(Al) but only by a factor of about 3, while a(Ni) remained essentially constant, with γ_Ni increasing from about 0.7 to 0.95. A dramatic change in the mixing behavior was observed between the and 0.27 series of alloys, where and are seen to increase about 50 kJ mol⁻¹ and 20 J mol⁻¹ K⁻¹ at T = 1566 K, respectively. In contrast, decreased about 16 kJ mol⁻¹ at T = 1520 K and changed from a positive to a negative value. This article was presented at the Multi-Component Alloy Thermodynamics Symposium sponsored by the Alloy Phase Committee of the joint EMPMD/SMD of The Minerals, Metals, and Materials Society (TMS), held in San Antonio, Texas, March 12–16, 2006, to honor the 2006 William Hume-Rothery Award recipient, Professor W. Alan Oates of the University of Salford, UK. The symposium was organized by Y. Austin Chang of the University of Wisconsin, Madison, WI, Patrice Turchi of the Lawrence Livermore National Laboratory, Livermore, CA, and Rainer Schmid-Fetzer of the Technische Universitat Clausthal, Clauthal-Zellerfeld, Germany.     

Kinetics and mechanism of high-temperature sulfidation of an Fe-23.4Cr-18.6Al Alloy in H2S-H2 atmospheres

Sulfidation of an Fe-23.4Cr-18.6Al (at.%) alloy was investigated in H₂S-H₂ atmospheres, Pa, at 973 K. It was found over this pressure range that sulfidation after an early transient period followed the parabolic rate law, being diffusion controlled. An investigation was carried out of the scales formed during early transient sulfidation over the sulfur pressure range Pa. Fully developed scales were multilayered consisting of an inner compact layer of equiaxed grains, an intermediate layer of equiaxed and columnar grains exhibiting a small degree of porosity, and an outer porous layer of distinct plates and needles. The grains of the inner and intermediate layers contained quarternary sulfide phases. The following phases were identified: spinels (CrFe)Al₂S₄ and (FeAl)Cr₂S₄, hexagonal (FeCr)Al₂S₄, (CrAlFe)₂S₃, and (CrAlFe)₅S₆. The plates and needles were composed of hexagonal (FeCr)Al₂S₄ and (CrAlFe)₂S₃ at and 10^–5 Pa from which pyrrhotite, FeS, grew at .     

Effects of water vapour and oxygen partial pressures on low carbon steel oxidation in N2–H2–H2O mixtures

A low carbon, low silicon steel was oxidised at temperatures of 900–1000 °C in flowing N₂–H₂–H₂O gas mixtures in which oxygen and water vapour partial pressures were varied independently. Scales of dense, single‐phase, coarse grained wüstite grew rapidly, according to parabolic kinetics. Both the scaling rate and the oxide grain growth increased with $p_{{\rm O}_{2} } $ at constant $p_{{\rm H}_{2} {\rm O}} $ , and also with $p_{{\rm H}_{2} {\rm O}} $ at constant $p_{{\rm O}_{2} } $ . An inert marker experiment showed that significant oxygen transport but majority metal transport supported scale growth. Gas composition effects are interpreted using point defect models involving formation of hydroxyl species on anion sites as well as cation vacancies.     

Structure/property relationships in sintered and thermally sprayed WC-Co

Thermally sprayed WC-Co is widely used as a wear-resistant coating for a variety of applications. Although it is well established that thermal spray processes significantly affect chemistry, microstructure, and the phase distribution of WC-Co coatings, little is known about how these changes influence wear resistance. In this study, the microstructure and wear behavior of sintered and thermally sprayed WC-Co materials are examined. Powders of WC-12 wt% Co and WC-17 wt% Co were pressed and sintered, as well as thermally sprayed by high-velocity oxy-fuel (HVOF), air plasma spray (APS), and vacuum plasma spray (VPS) techniques. Results indicated considerable differences in the resulting microstructures, mechanical properties, and wear resistance. The thermally sprayed coatings showed anisotropic fracture toughness, whereas the sintered materials did not. It was also shown that a combined mechanical property/microstructure parameter, based on considerations of indentation fracture mechanisms, can be used in most cases to describe abrasive and erosive wear resistance of thermally sprayed WC-Co materials as follows: Wear resistance a whereK _ic is the indentation fracture toughness,H is hardness, andV ^Co _f is the volume fraction of cobalt. This relationship provides a means for assessing wear resistance of WC-Co coatings intended for industrial applications requiring abrasion and/or erosion resistance.     

Quasi-Ternary System Ag2Se-CdSe-Ga2Se3

Phase equilibria in the quasi-ternary system Ag₂Se-CdSe-Ga₂Se₃ were investigated by differential thermal and x-ray phase analysis methods. Phase diagrams of nine vertical sections were constructed. The boundaries of seven single-phase fields were determined which are solid solution ranges of system components and intermediate phases. We constructed the isothermal section at 820 K and the liquidus surface projection, and have determined the position in the system of six invariant processes with the participation of liquid: $ {\text{L}}_{{{\text{U}}_{1} }} + {\upzeta} {\leftrightarrows} {\upbeta} + {\upeta} $ L U 1 + ζ ? β + η (1145 K), $ {\text{L}}_{{{\text{U}}_{ 2} }} + \upzeta \leftrightarrows \upgamma + \upeta $ L U 2 + ζ ? γ + η (1138 K), $ \text{L}_{{U_{3} }} + \upeta \leftrightarrows \updelta + \upgamma $ L U 3 + η ? δ + γ (1113 K), $ {\text{L}}_{{{\text{E}}_{ 1} }} \leftrightarrows \upbeta + \updelta + \upeta $ L E 1 ? β + δ + η (1083 K), $ {\text{L}}_{{{\text{E}}_{ 2} }} \leftrightarrows \upalpha + \upbeta + \upvarepsilon $ L E 2 ? α + β + ε (969 K), $ {\text{L}}_{{{\text{E}}_{ 3} }} \leftrightarrows \upbeta + {\updelta} + \upvarepsilon $ L E 3 ? β + δ + ε (963 K). Two invariant processes in the sub-solidus part, $ \upbeta + \updelta \leftrightarrows \upeta + \uplambda $ β + δ ? η + λ and $ \upbeta + \updelta \leftrightarrows \upvarepsilon + \uplambda $ β + δ ? ε + λ at 968 and 938 K, respectively, were investigated as well.     

Elektronenoptische und röntgenographische Untersuchung einer Eisenphosphat-Schutzschicht auf Eisen

Electron-optical and radiographical examination of a protective iron phosphate layer on iron The protective effect of a novel anticorrosive containing phosphoric acid has been examined for its dependence on mineralogical conditions. The base material contains, intro alia, phosphoric acid, potash mica, organic wetting agents and dyeing agents. Vivianite formation has been precluded by radiographic comparison with natural vivianite and with data quited in technical literature. The scraped protective layer was found to contain, apart from muscovite and α iron, dendritic formations which were observed under the electron microscope and identified, from their diffraction interferences, as cubic form of the potassium iron (III) phosphate leucophosphite \documentclass{article}\pagestyle{empty}\begin{document}$ KFe_2 [OH(PO_4)_2] \cdot 2\ H_2 O. $\end{document} KFe₂[OH(PO₄)₂] · 2 H₂O. Precision zone diffraction diagrams of individual dendrites showed a_o = 7.75 ± 0.05 Å and the transmission directions [100]^X [010]^X [202]^X, identical to those observed with natural pharmacosiderite, an iron arsenate corresponding to leucophosphite. Natural and synthetic leucophosphite are monoclinic; if Fe³⁺ is replaced by Al³⁺, and (PO₄)^3? by (AsO₄)^3?, a cubic alumopharmacosiderite is formed. The formation is thereofore interpreted as a cubic modification of leucophosphite, corresponding to pharmacosideriote. A structure comparison shows the epitactic growth of the leucophosphite with [110] and [333] on α iron [100] and [111]. The presence of leucophosphite directly on the iron surface is proved by electron diffraction with grazing incidence of the electron ray.     

Influence of Hydrogen and Water Vapour on the Kinetics of Chromium Oxide Growth at High Temperature

In support of the selection of structural materials for heat exchangers in helium-cooled high temperature reactors, the oxidation behaviour of the Ni-base chromia-former alloy 230 was investigated at 850 °C in diluted helium atmosphere with a low water vapour content. In such a media, the equivalent partial pressure of oxygen (imposed by the $ P_{{{\text{H}}_{2} {\text{O}}}} $ / $ P_{{{\text{H}}_{2}}} $ ratio) is very low ( $ P_{{{\text{O}}_{ 2} }}^{\text{eq}} $ around 10^?16 Pa). The equivalent partial pressure of oxygen has no straight influence on the parabolic rate constant (k _p); on the other hand, $ P_{{{\text{H}}_{2} }} $ and $ P_{{{\text{H}}_{2} {\text{O}}}} $ demonstrate a complex influence on k _p. Photoelectrochemistry analyses revealed that this oxide could simultaneously contain two types of cationic defects. Specific oxidation tests with D₂O showed that the oxide scale also contains hydrogen. A mechanist model is proposed in order to describe the scale growth using both cationic defects. Those theoretical results show, at least qualitatively, how $ P_{{{\text{H}}_{2} }} $ and $ P_{{{\text{H}}_{2} {\text{O}}}} $ may concurrently influence the oxidation rate.     

Sulfidation properties of an Fe-26.4Cr-8Al-6Mn alloy at 973 and 1073 K in H2S-H2 atmospheres,10^{ - 4} \leqslant {\text{P}}_{{\text{S}}_{\text{2}} } \leqslant 10^2 {\text{Pa}}

The sulfidation behavior of an Fe-26.4Cr-8Al-6Mn (at.%) alloy in H₂S-H₂ atmospheres, \(10^{ - 4} \leqslant {\text{P}}_{{\text{S}}_{\text{2}} } \leqslant 10^2 {\text{Pa}}\) .     

Internal oxidation of Fe–3%Si alloys annealed under H2O–H2 atmosphere

Internal oxidation phenomena during decarburization annealing are very important in the manufacturing process of grain oriented electrical steel. In the present study, the internal oxidation of nearly pure Fe–3%Si alloy was investigated, as a basic study for decarburization annealing. Annealing was performed at various $P_{{\rm H}_{{\rm 2}} {\rm O}} /P_{{\rm H}_{{\rm 2}} } $ ratios and at 1123 K for 300 s. The transition of external to internal oxidation took place at $P_{{\rm H}_{{\rm 2}} {\rm O}} /P_{{\rm H}_{{\rm 2}} } $ around 0.01. The morphologies of oxide in the internal oxidation zone (IOZ) were filamentary or needle‐like shapes and different from the reported oxide shapes in industrial electrical steel. These peculiar morphologies affected the kinetic aspects such as the depth and the enrichment of oxide in the IOZ.     

Kinetics of iron removal from metallurgical grade silicon with pressure leaching

In this paper, the kinetics of pressure leaching for purification of metallurgical grade silicon with hydrochloric acid was investigated. The effects of particle size, temperature, total pressure, and concentration of hydrochloric acid on the kinetics and mechanism of iron removal were studied. It was found that the reaction kinetic model followed the shrinking core model, and the apparent activation energy of the leaching reaction was 46.908 kJ/mol. And the apparent reaction order of iron removal with pressure leaching was 0.899. The kinetic equation was ob-tained and the mathematical model of iron removal from metallurgical grade silicon (MG-Si) was given as follows: 1-2/3x-(1-x)2/3=exp(5.1654-4811.4591/T+1.287lnp+1.046ln[C])·t/r02· The values calculated from the equation were consistent with the experimental results.     

Sulfidation properties of Fe-Al alloys at 1173 K in H2S-H2 atmospheres

The sulfidation kinetics and morphological development of reaction products are reported for Fe-9 and 18 at.% Al alloys exposed at 1173 K to H₂S-H₂ atmospheres at sulfur pressures in the range 10^–1–10³ Pa. The Fe-9 Al alloy sulfidized parabolically at Pa giving rise to a duplex scale composed of an outer Al-doped FeS layer and an inner FeS + FeAl₂S₄ lamellar layer and to an internal sulfidation zone containing Al₂S₃ precipitates. The Fe-18 Al alloy which was sulfidized at .