Der Einfluß von Chlorid auf das Korrosionsverhalten von Nicrofer 3033 (1.4591) in mittelkonzentrierter heißer Schwefelsäure

The influence of chloride on the corrosion behaviour of Alloy 33 in medium concentrated hot sulfuric acid In the concentration-temperature field of 15 to 80 mass-% p. a. grade sulfuric acid and temperatures of 50 to 90 °C in which Alloy 33 is either corrosion resistant without and with small additions of Fe³⁺, the influence of chloride concentration on the degradation of its corrosion resistance has been determined. The evaluation of the critical chloride content has been carried out by gravimetrical means in tests of 7 days duration. For comparison materials used in sulfuric acid applications as Alloy 20 (2.4660) and Alloy 31 (1.4562) have been examined in form of random tests in the above mentioned concentration-temperature field. Based on polarization tests the influence of chloride ions in sulfuric acid solutions could be evaluated for the conditions of presence and absence of the oxidant Fe³⁺. The chloride concentration, which can be tolerated, diminishes with increasing acid concentration and temperature. If the oxidant Fe³⁺ is present in the sulfuric acid solution, higher chloride concentrations can be tolerated. Alloy 20 (2.4660) will in comparision to Alloy 33 (1.4591) be activated at significantly lower chloride concentrations. Compared to Alloy 33 (1.4591) the range of application of Alloy 31 (1.4562) is mainly restricted in Fe³⁺ containing sulfuric acid.     

Untersuchungen zur passivierenden Wirkung organischer Oxydationsmittel auf Eisen in neutralen und schwach sauren Lösungen. 2. Mitteilung: Aromatische Nitroverbindungen

Investigation into the passivation effect of organic oxidizing agents on the corrosion of iron in neutral weakly acid solutions. 2nd communication: Aromatic nitrocompounds The present communication is con cerned with the corrosion inhibiting properties of aromatic nitro compounds on iron in the neutral range. Nitrobenzenes (m-nitroaniline, p-chloronitrobenzene, M-nitrobenzoic acid, ethylester, p-nitrobenzaldehyde, p-nitrobenzonitrile) in concentrations between 0,25 · 10^?2 and 0.5 · 1^?2 Mole/litre act as stimulators in airsaturated 20% methanol of pH 6.8. Their combination with a 20% methanolic boric acid/borate solution of pH 6.8 – which, as such, only maintains passivity, yields passivating systems. From these examples as well as from others involving known inhibitors it appears highly probable that the prassivation of iron by corrosion inhibiting addition in the neutral range, too, requires a communication of oxidizing and non-oxidizing agents (combination principle )able to lower the critical passivation current density.     

Chemische und elektrochemische Reaktionen von Eisensulfid und Mangansulfid in sauren und neutralen Lösungen

Chemical and electrochemical reactions of iron sulfide and manganese sulfide in acid and neutral solutions The reactions which occur upon corrosion of massive iron sulfide and manganese specimens in perchloric acid and in neutral sodium chloride solution were elucidated by measurements of current-potential curves and by coulometric and analytical investigations on the processes. In acids the sulfides are dissolved by prevailing chemical reaction under evolution of H₂S. Upon applying anodic overpotentials electrochemical reactions occur simultaneously, however, with such low velocity that the contribution to corrosion of the sulfides is insignificant. Upon applying cathodic overpotentials some hydrogen discharge is observed on iron sulfide but not on manganese sulfide. In 3% sodium chloride solution both sulfides corrode very slowly upon anodic polarization, forming elementary sulfur according to MeS = Me²⁺ + S + 2e^? (Me = Fe or Mn). At high anodic potentials additional oxidation reactions occur in which three-valent iron and tetravalent manganese ions as well as sulfite and sulfate ions are formed. Iron sulfide and manganese sulfide inclusions can he isolated from steels only by electrochemical dissolution in neutral or weakly basic electrolytes, the potential during electrolysis must not be more positive than the corrosion potential of the sulfides.     

从废NiPt靶材中回收铂、镍的研究

针对废NiPt靶材,提出采用选择性溶解-中和沉淀工艺回收镍,铂富集物王水溶解-氧化水解除杂-氯化铵沉淀-煅烧工艺回收铂。结果表明,在硫酸浓度40%、溶解温度85℃、溶解时间4 h、液固比4的条件下,镍溶解率大于99.4%,镍回收率大于99%。铂富集物通过王水溶解、氧化水解除杂、氯化铵沉淀、煅烧后,获得纯度大于99.99%的海绵铂,铂回收率大于99.5%。     

Korrosionsuntersuchungen an einigen Werkstoffen in Propionitril/Dichlorpropionitril,Dichlorpropionitril/Schwefelsäure/Dichlorpropionsäure und in Dichlorpropionatlösung

Investigation into the corrosion of some materials of construction in propionitrile/dichloropropionitrile, dichloropropionitrile/sulfuric acid/dichloropropionic acid and dichloropropionate solutions The present paper deals with investigations into the corrosion behaviour of and practical experience gained with a number of materials used in the process involving the chlorination of propionitrile, in the presence of HCl and Cl₂, to yield dichloropropiodinitrile, and in its saponification to dichloropropionic acid in 65% sulfuric acid. The reactions mentioned are process stages involved in the production from acrylonitrile of sodium α,α'-dichloropropionate which is used as a herbicide. The investigation included various noble metals, alloys resistant to hydrogen chloride, impregnated electrographites and enamel on steel. The behaviour of the different materials under the conditions encountered in practice is described. Tables and photographs are used to illustrate the behaviour and the corrosion losses as well as the condition of various materials and structural parts. As far as possible the authors indicate the cause found of the failure of various materials. In addition, data are presented concerning the feasibility of applying various protective coatings and paints to steel plate for the containers used for storing sodium dichloropropionate solution prior to recovering the salt as such.     

Inhibition of Iron Corrosion in Different Acid Media by N-Decyl- Pyridinium Derivatives

Abstract

Some derivatives of the N-Decyl-Pyridinium ion (DP) have been tested as iron corrosion inhibitors in sulphuric and hydrochloric acid solutions at 25°c and 70°c. Theseinhibitors were tested both as bromides (in hydrochloric and in sulphuric acid solutions) and as hydroxides or sulphates (in sulphuric acid solutions). The efficiency of theDP ion can be improved by the introduction of suitable subsituents in the 3-position of the aromatic ring. In all the acid solutions tested, the most efficient ion at 25°c proved to be the N-Decyl-3-hydroxy-Pyridinium (D30P) ion, while at 70°C,. the N-Decyl-3-carboxy-Pyridinium (D3CP) ion was the most efficient.

These derivativesact mainly by physical adsorption between the organic cations and the anions (Cr^? or Br^?) pre-adsorbed at the metal surfaceof the electrode. But in order to explain all the experimental data other types of interactions have to be considered, such as: Van der Waals attractive forces between the aliphatic chains, interaction of Πelectrons with the metal surface, and adsorption on to the metal surface via –COOH and –OH groups. The organic cations studied inhibit mainly the H⁺ ion discharge, but when present in higher concentrations they also inhibit the iron dissolution reaction.     

Inhibitoren der Korrosion 21 (1) – Autoxidationsstudien an Fe2+-Salzen der Tetramethylen-1,4-bis-phosphonsäure,der Hexamethylen-1,6-bis-phosphonsäure,der Benzol-1,4-bis-phosphonsäure,der Phosphorsäure und Pyrophosphorsäure als Modell einer die Korrosion des Eisens hemmenden Deckschicht

Corrosion Inhibitors 21 (1) – Investigations into the autoxidation of Fe²⁺ salts of tetramethylene-1,4-bis-, hexamethylene-1,6-bis-, benzene-1,4-bis-phosphonic acids, phosphoric acid and pyrophosphoric acid as a model of a surface layer inhibiting the corrosion of iron The efficiency of organic bisphosphonic acids as inhibitors of the corrosion of iron is due to the fact that Fe²⁺ ions leaving the iron surface react with the acid immediately and give rise to the formation of threedimensional surface layers. The more dense the structure of these layers, the more resistant these network is against oxygen and the more resistant to hydrolysis are the Fe? OP bonds, the better the protective effect. Oxygen as well as chloride ions are then prevented excess to the metal surface. The distribution of phosphorus in the precipitates obtained during the model experiments yields information concerning the degree of crosslinking.     

Der Einfluss von Oxidationsmitteln auf die Korrosionsbeständigkeit von Nicrofer 3127 hMo in niedrig‐ und mittelkonzentrierter Schwefelsäure

The influence of oxidants on the corrosion resistance of Alloy 31 in low and medium concentrated sulfuric acid The isocorrosion lines < 0.1 mm/y were determined for Nicrofer 3127 hMo (1.4562, Alloy 31) by weight loss measurements after 24 h immersion in areated sulfuric acid of technical and p.a. grades in the concentration range up to 90% – both without and with 1 g/l chloride. The free corrosion potential indicates that the superior corrosion resistance of Nicrofer 3127 hMo in the technical acid grade can be attributed to the content of oxidants in the acid. The presence of oxidants leads to metastable passivity in technical sulfuric acid with concentrations ≥ 20% at temperatures that can be 10–50 K higher than in p.a. acid depending on the acid concentration. For sulfuric acid concentrations up to 10% the content of oxidants in the technical acid is too small to improve the corrosion resistance of Nicrofer 3127 hMo as compared with that in p.a. acid. Similar behaviour was observed for Nicrofer 3127 hMo in sulfuric acid containing chlorides. However the activating effect of the chlorides limits the region of corrosion resistance to lower temperatures in comparison with the chloride free‐acid.     

High Temperature Corrosion of the Alloy Ni4Mo in a hydrogen chloride atmosphere

Specimens of the alloy Ni₄Mo were tested in a hydrogen chloride atmosphere at temperatures between 400° – 850° C. The corrosion of the alloy was followed by gravimetric analyses and microstructural examinations. It was found that the layer formed on the specimens due to corrosion is adherent but porous, thus allowing the volatilization of some of the corrosion products. The formation of various kinds of oxides and chlorides was observed. The exact composition of the scale depended on the temperature of exposure to hydrogen chloride and on the amount of oxygen present as an impurity in the test apparatus. The formation of a domain structure in the uncorroded alloy affects the morphology of the scale/alloy interface.     

Einfluß von Natriumchlorid auf die Oxidation von hochlegierten Chrom- und Chrom-Nickel-Stählen

Effects of sodium chloride on the oxidation of high alloy Cr- and Cr-Ni-steels The effects on the oxidation were investigated of solid NaCl deposits on the oxide scales of the technical steels X10 CrMoV 12 1, X15 CrNiSi 20 12 and X10 CrNiSi 25 20 at 700°C. Independent of the alloy composition the presence of NaCl(s) initiated a markedly accelerated Fe₂O₃ growth on the surface of preoxidized samples, under formation of voluminous, nonprotective layers. Below these scales on the metallic matrix in all cases chloride was detected. The oxides grow according to the mechanism of active oxidation in which chlorine plays a catalytic role. The presence of the chloride at the oxide/metal interface reduces the adhesion of the oxide scale and leads to spalling upon cooling to room temperature. The effects observed are independent of the alloy composition, however, the thickness of the oxide scale is decisive which means the diffusion distance for the gaseous iron chloride.     

The Effects of KCl,NaCl and K<Subscript>2</Subscript>CO<Subscript>3</Subscript> on the High-Temperature Oxidation Onset of Sanicro 28 Steel

The present study investigates the early stages in the oxidation process of Sanicro 28 (Fe31Cr27Ni) stainless steel when exposed to an alkali salt (KCl, NaCl or K₂CO₃) for 2 h at 450 and 535 °C. After the exposure, the oxidized samples were analyzed with a combinatory method (CA, XPS and SEM–EDX). It was found that all three salts were corrosive, and the overall oxidation reaction rate was much higher at 535 °C than at 450 °C. There were clear differences in terms of the impact of cations (Na⁺, K⁺) and anions (Cl^?, CO₃ ^2?) on the initial corrosion process at both temperatures. When focusing on the cations, the presence of potassium ions resulted in a higher rate of chromate formation than in the presence of sodium ions. When studying the effect of anions, the oxidation of iron and chromium occurred at higher rates in the presence of both chloride salts than in the presence of the carbonate salt, and chloride salts seemed to possess higher diffusion rate in the gas phase and along the surface than carbonate salts. Moreover, at the higher temperature of 535 °C, the formed chromate reacted further to chromium oxide, and an ongoing oxidation process of iron and chromium was identified with a significantly higher reaction rate than at 450 °C.     

Untersuchungen über den Einfluß des Gefügezustandes auf das Korrosionsverhalten hochlegierter,rost- und säurebeständiger Stähle in reiner sowie in chloridhaltiger Schwefelsäure

Corrosion Properties of High Alloyed Stainless Steels in Pure as well as in Chloride Containing Sulfuric Acid The corrosion behaviour of the high alloyed stainless steels material no. 1.4439 (X3CrNiMoN17135), 1.4539 (X2NiCrMoCu25205), 1.4503(X3NiCrMoCuTi2723) as well as the reference materials AlSI 316 L and alloy 825 was tested in diluted sulfuric acid (5, 10, 20 and 50%) at 50, 100 and 150°C. The test solutions additionally contained impurities as chlorides and cupric ions. On the material side the effect of various microstructures was checked as well: material as received (commercial production), solution annealed under laboratory conditions, cold deformed and for two selected steels electroslag remelted. Corrosion testing methods are: the immersion test will sheet coupons and the measurement of the weightloss; electrochemical testing, i.e. Current potential-and free corrosion potential-time-curves. No pitting corrosion is observed in the presence of chloride ions. In some cases the general corrosion rate is lowered if chloride ions are present. This beneficial effect of chloride ions, however, is observed only at low chloride concentrations (500 ppm). Annealing under laboratory conditions as well as electroslag remelting does not generally improve the corrosion resistance. A negative effect by cold deformation is only observed for standard stainless steel AlSI 316. Cupric ions added to the 20% sulfuric acid solution improve the corrosion resistance of all steels investigated to that extent, that they can be used in practice up to 100°C provided that the concentration of cupric ions in the solution is sufficiently high (2000 ppm). Electrochemical test results indicate that the positive effect of cupric ions is due to the shift of the free corrosion potential into the potential range of stable passivity. Copper alloyed stainless steels show the highest corrosion resistance.     

Korrosion des Hastelloy C 4 und anderer metallischer Werkstoffe in heißen,konzentrierten Salzlaugen

Corrosion of Hastelloy C4 and different metallic materials in hot concentrated salt brines In a quaternary salt brine saturated at 55°C with magnesium chloride, potassium chloride and sodium chloride, polarization curves were measured in the temperature range from 100°C to 200°C at different materials in order to study their corrosion behaviour. Steels and nickel corrode in the active state. The corrosion current density of an unalloyed steel at 100°C was about 20 μA/cm² corresponding to a removal rate of 0.2 mm/a. Iron-silicon and nickel corrode significantly slower at a rate of a few μA/cm². Steady state corrosion rates of Hastelloy C 4 and of titanium at 100°C are 10 nA/cm² and less than 4.5 nA/cm², respectively. For both materials, the susceptibility to pitting grows with the temperature and with the chloride concentration. The steady state corrosion rates of passive Hastelloy C 4 depend on temperature according to an activation enthalpy of 85 kJ/mol and become about 5 μA/cm² at 200°C. Even at high temperatures steady states are attained rather slowly within about one day. The critical pitting potentials approach the corrosion potentials in deaerated solution at a rate of about 0.8 mV/K. At 200°C the critical pitting potential is only 90 mV positive to the corrosion potential. Thus, Hastelloy C 4 may be used at high temperatures, only if it is cathodically protected.     

Untersuchungen zum Korrosionsverhalten nichtrostender Stähle in Phosphorsäure in Abhängigkeit von dem Chlorid- und Fluoridgehalt und einer Wärmebehandlung beim Schweißen

Investigations into the corrosion behaviour of stainless steels in phosphoric acid in dependence on the chloride and fluoride contents and a heat-treatment during welding In the present investigation the corrosion behaviour of recently developed high-alloyed austenitic (X 2 NiCrMoCU 25 20) and austenitic-ferritic (X 2 CrNiMoCuN 25 5) steel has been tested towards phosphoric acid, the composition and concentration of which was adjusted to correspond to crude phosphoric acid with varying contents of Cl^?, F^?, Fe³⁺, and SO₃. Current density-voltage curves were recorded on steel test-specimens at room temperature, 45°C, and 80°C. In addition, test-pieces of both steels, after annealing treatment between 800°C and 500°C, as well as welded specimens of similar type were examined for the effect of heat input and consequent structural alterations on the corrosion behaviour. Both steels exhibit good corrosion resistance towards pure phosphoric acid. Cl^? and F^? ion impurities render the acid more aggressive. Austenitie-ferritic steel reacts more sensitively than austenitic steel towards heat input, resulting in deterioration in corrosion resistance. This may be attributed to the precipitation of inter-metallic phases in the ferritic structure.     

Electrochemical and surface analytical studies of synergistic effect of phosphonate,Zn2+ and ascorbate in corrosion control of carbon steel

Synergistic inhibition of corrosion of carbon steel in low chloride environment using ascorbate as a synergist along with 2‐phosphonobutane‐1,2,4‐tricarboxylic acid (PBTC) and Zn²⁺ is presented. The synergistic effect of ascorbate has been established from the present studies. In the presence of ascorbate, lower concentrations of PBTC and Zn²⁺ are sufficient in order to obtain good inhibition, thus making this formulation more environmentally friendly. Potentiodynamic polarisation studies inferred that this mixture functions as a mixed inhibitor, predominantly cathodic. Impedance studies revealed that an immersion period of 24 h is necessary for the formation of the protective film, with a very high charge transfer resistance. The film is stable even at 60 °C in the presence of the inhibitor in the corrosive environment. The surface analysis by X‐ray photoelectron spectroscopy (XPS) showed the presence of iron, oxygen, phosphorus, carbon and zinc in the protective film. The XPS spectra inferred the presence of oxides/hydroxides of iron(III), Zn(OH)₂ and [Zn(II)–PBTC–ascorbate] complex in the surface film. This inference was further supported by the reflection absorption Fourier transform infrared spectrum of the surface film. A plausible mechanism of corrosion inhibition has been proposed.     

Modellvorstellungen über den Reaktionsverlauf und Diskussion der Funktionen passivierender Zusätze bei der chemischen Passivierung von Eisen im pH-Bereich schwach sauer,neutral, basisch

Possible models of the reaction mechanism and discussion of the functions of passivating additions during the chemical passivation of iron in weakly acid, neutral and basic pH ranges A model has been developed describing the reactions occurring during chemical passivation of an oxide free iron surface in the pH-range weakly acid, neutral, basic. It covers the region approximately up to the Flade potential, i. e. the socalled region of incomplete passivity where Fe²⁺-species still pass into the solution. The model is based on facts known about the composition of the passive layer, about the conditions of synthesis, the composition and oxidizability of magnetite and about structural conceptions of its formation. Finally the model and experimental results are used to discuss the rǒle the constituent parts of chemically passivating systems of the type – oxidant/nonoxidizing agent – play in realizing passivation.     

Zur Korrosion des Hafnium – Oxide und Hydride

Corrosion of hafnium – oxides and hydrides Investigations concerning the growth and behaviour of hafnium as well as electrode kinetics have been performed on hafnium (Goodfellow and Material Research Company) in various electrolytes (acidic, alkaline and Cl^?-containing solutions). Conventional electrochemical methods and impedance spectroscopy were applied. Corrosion rates derived from electrochemical measurements were found to be significantly higher than the published data obtained from the loss weight observed usually over long of time. – The DK was evaluated to be 11.5. – SIMS profiles indicate that the oxide layer in not uniform, due to the nonstoichiometry of the Hf oxide at 22°C. The layer shows a very low n-conductivity – quasi insulator behaviour; the Mott-Schottky-plot leads to the flat band potential U = ? 10 mV. The initial oxide layer was determined by capacity measurements to 2.7 nm. Cl₂-evolution begins at U = 0.5 V in 0.5 M NaCl solution. In the cathodic potential region hydrogen is generated at Hf oxide at U = ? 1.69 ? 0.058 V. With respect to the hydrogen induced cracking of Hf the behaviour of hydrogen in Hf was investigated using the nuclear physics ¹⁵N-method. After cathodic polarisation hydrogen is absorbed by hafnium and the hydride HfH_1.6 is formed. The hydrogen diffusion coefficient is determined to D_20° = 3.8 × 10^?11 cm²s^?1. At 385°C hydrogen is released from HfH_1.6. The results are discussed and compared to those found for titanium and zirconium.     

Korrosion von ölgefeuerten Zentralheizungskesseln

Corrosion of oil-fired domestic boilers Depending on the surface temperature of the flue gas side the corrosion of oil fired domestic boilers proceeds either mainly by acid corrosion or by oxygen corrosion:

• – At surface temperatures of 60°C and higher the corrosion mechanism of acid corrosion prevails and the corrosion rates amount to 0.1–0.3 mm/year (values referred to continuous burner operation). The corrosion products consist of soluble iron(II)- and iron(III)sulfates. Higher corrosion rates can be attributed to an appreciable catalytic formation of sulfur trioxide on the corrosion products formed on the convective heating surfaces.
• – At surface temperatures of 40°C the mechanism of oxygen corrosion already dominates and the corrosion rates are about ten times higher (1.5–3 mm/year, referred to continous burner operation). The high portion of ioron oxide hydrates, especially goethit (α-FeOOH), makes the corrosion products difficult to remove.
• – Distinctly reduced service lives are also expected for the so called reduced temperature boilers (“Niedertemperaturkessel”) and low temperature boiers (“Tieftemperaturkessel”): According to the manufacturers these boilers may be operated at boiler water temperatures well below 60°C, as they are equipped with constructive measures to enhance the surface temperature on the flue gas side. However, these measures are only fully effective under stationary conditions.

Some of the results were obtained from weight loss measurements on test specimen made from St 35.8 and gray cast iron, that were exposed to the flue gases of an oil fired experimental boiler. Other important results come from field measurements of the sulfuric acid content of about 30 boilers that are in practical use.     

Inhibitoren der Korrosion 22 (1) — Einfluß von pH,Sauerstoff, Fremdionen,Art und Konzentration von Säuren auf den Korrosionsverlauf von Aluminium

Corrosion inhibitors 22 (1) – Influence of pH, oxygen, added ions, type and concentration of acids on the corrosion of aluminium Corrosion of aluminium in the presence of oxygen is practically independent from the pH and proceeds with oxygen consumption and hydrogen evolution. This behaviour is found in a solution of acetate buffer with sodium chloride as well as in inorganic (nitric, sulfuric, phosphoric, hydrochloric) acids as in organic acids. In the case of the latter the results are not as clear; in acetic acid the corrosion rate is not influenced by sodium chloride and the same applies to formic acid. While oxalic acid gives rise to hydrogen evolution in the presence of sodium chloride only and citric acid does not give rise to any hydrogen evolution. The solution which appears to be optimum for testing organic inhibitors of aluminium corrosion is unaqueous 1 N hydrochloric acid solution with 2.5% sodium chloride under nitrogen.     

CO还原Fe2O3-NiO复合物形成Fe-Ni合金的非等温还原动力学（英文）

研究采用CO还原不同比例Fe2O3-NiO复合物的非等温还原动力学及机理。结果表明:随着NiO含量的增加,样品的还原程度不断提高,NiO的存在提高氧化铁还原率。在还原开始阶段,NiO优先被还原,Ni作为催化剂可以提高氧化铁的还原率。NiO含量的增加促进镍铁相(FeNi3)的增加,但导致铁纹石相(Fe,Ni)和镍纹石相(Fe,Ni)的减少。金属镍、金属铁及镍铁合金的形成导致微观颗粒具有均匀性。在还原初始阶段,气体产物中CO浓度大于CO2浓度,然后逐渐减小,当温度在400~500°C内,Fe2O3-NiO复合物的还原速率达到最大值,成核长大模型可以揭示还原机理。在温度低于1000°C的条件下,成核长大过程是还原反应速率的限制环节。