Inhibitoren der Korrosion 20(1)–Über die zeitliche Abhängigkeit der analytischen Zusammensetzung der Korrosionsprodukte des Eisens von der Menge an verbrauchtem Sauerstoff

Analytical composition of the corrosion products of iron as a function of time and of the oxygen consumed Using a modified standard method of analysis it is possible to analyze mixtures containing Fe⁰, Fe²⁺ and Fe³⁺. This method is used to study corrosion systems catalyzed by chlorides. According to the results obtained the amount of Fe²⁺ is approx constant at pH 7, irrespective of the oxygen quantityt consumed, Fe⁰ being oxidized to give Fe²⁺ and the latter being oxidized, at a comparable rate, to give Fe³⁺. At pH 3, however, Fe²⁺ is obtained almost exclusively, and beyond pH Fe³⁺ becomes predominating.     

Inhibitoren der Korrosion 17(1) Die Bedeutung des „Hart-Weich-Konzepts”︁ von Pearson für die Erkennung von Struktur-Wirkungsbeziehungen von Inhibitoren bei der Korrosion des Eisens in NaCl-Lösungen bei Gegenwart von Sauerstoff

Corrosion inhibitors 17 The importance of pearson's “hard-soft-concept” with respect to the recongnition of relationship between structure and activity of inhibitors of the corrosion of iron in sodium chloride solutions in the presence of oxygen On the base of a previously published postulate according to which Pearson's hard-soft-concept may form the base for finding inhibitors for specific applications it is shown with the aid of model inhibitors with “hard” functional groups that it is indeed feasible to derive defined relations between the structure and the activity of inhibitors. The hard groups used were the phosphoryl ?P(O)O and the carbonyl ?C?O groups. It has been shown that such compounds are able to form very stable and protective surface layers on iron and that the efficiency of the inhibitors clearly increases with increasing length of the aliphatic chain. As has been shown by eletrochemical measurements these acids have a bearing on the rest potential as well as on the current-potential behaviour; this fact points to rather variable compositions of the surface layer. In the case of polyfunctional acids sterical factors may have a bearing on inhibitor efficiency, too.     

Inhibitoren der Korrosion 23 (1) – Gibt es eine Struktur- Wirkungs-Beziehung bei organischen Inhibitoren der Korrosion von Aluminium?

Corrosion inhibitors 23 (1) – Does there exist a structure-efficiency relation in the organic inhibitors of aluminium corrosion? Over 400 organic compounds have been routinely tested as potential inhibitors for the corrosion and dissolution of aluminium in In HCl/2,5% NaCl solution, using 10^?2 m/l as the concentration of the organic compound being tested. It was attempted to derive a relationship between efficiency of the inhibitor with molecular structure. Particular attention was devoted to the following classes of compound: organoarsenic; phosphonic and phosphinic acids; aromatic aldehydes and ketones; aromatic and aliphatic carboxylic acids; dihydric phenols; tetrazolium salts and formazan compounds; sulphoxides and aromatic sulphonic acids; sulphonamides and sulphones. For a selected number if inhibitors, the dependence of concentration and the effect of an oxygen-containing atmosphere were studied. Compounds which show good inhibition in the corrosion of aluminium are consistently even better in the protection of zinc surfaces. The mechanism of the corrosion inhibition is not clear, but the results suggest that the total molecular structure of the inhibitor must be considered, with particular importance paid to the nature and the spatial relationship of the different functional groups.     

Inhibitoren der Korrosion 27 (1). Inhibitoren der Korrosion von Kupfer – Gibt es eine Struktur-Wirkungsbeziehung?

Inhibitors of corrosion 27 (1). Inhibitors of the corrosion of copper Does there exist a structure-effect-relation? Over 570 compounds of greatly varying structure have been tested under controlled conditions in agitation and pH-stat experiments designed to measure their effect as corrosion-protection agents for copper metal. The data were handled via a “SORT-F”-computer program, and the results so obtained show mostly a relationship with Pearson's “Hard-Soft” principle. Tailor-made synthesis of inhibitors following the principle is nevertheless of little value.     

Inhibition der Korrosion 15 (1) Über die Wirkungsweise von Korrosionsinhibitoren des Eisens in Säuren sowie in NaCl-Lösungen bei Gegenwart von Sauerstoffen

Corrosion inhibitors(15) Mode of action of inhibitors of the corrosion of iron in acids and in NaCl solutions in the presence of oxygen A review is given of electrochemical and other methods which may be used for studying the mechanism of corrosion inhibition. Non-electrochemical methods include UV and IR reflexion spectroscopy, extinction of fluorescence by amines, ellipsometry, electron microscopy and X-ray methods. Chemical methods involve direct analysis of the protective surface layers, electron microprobe analysis and the Warburg method. As to inhibition mechanism as such examples are given to show the effect of structural parameters, the importance of bonding and electron bonding, the effect of reaction resulting in the formation of product able to act as secondary inhibitors (in the context, emphasis is placed on onium compounds, sulfoxides). Finally, data are presented concerning the inhibitor effect of some technical surface active compounds, glycin and sarcosin derivatives, aromatic carboxylic acids and organic phosphonic acids.     

Über das Beizen von Warmband mit Salzsäure und die totale Regeneration der salzsauren Beizbäder sowie die Rolle der Inhibitoren bei diesen Verfahren

Pickling of hot rolled steel with hydrochloric acid and the total regeneration of pickling baths with hydrochloric acid as well as the part played by inhibitors in this process After a discussion of the differences between the pickling method with sulphuric acid and hydrochloric acid, the advantages of pickling with hydrochloric acid are discussed. These consist mainly in a shorter pickling time and a more attractive, brighter and not excessively pickled surface. The latest development in pickling technique, especially for hot rolled steel, consists in carrying out the pickling process in a high vertical enclosed pickling tower where the pickling acid is sprayed or flooded on the continually moving steel. The pickling temperature is about 85°C, the pickling time 35 to 40 seconds. For pickling with sulphuric or hydrochloric acid by the tank method as well as by the feed method and the tower pickling method, the inhibitors must comply with very exacting conditions as it is absolutely necessary to avoid disturbances such as foam formation, segregation of decomposition products, or any effect on the regeneration method. The best regeneration method for pickling baths with hydrochloric acid is spray roasting. After segregation of the iron oxide, the hydrochloric acid vapours are condensed as approx. 20 per cent. HCl in an azeatropic mixture of hydrochloric acid and water in an adiabatically working column and are returned to the pickling circuit. The rinsing liquids are returned to the circuit. Since, in practice, hydrochloric acid and iron oxide are the only substance, this total regeneration method does not give rise to drain water problems. Cost comparisons show that the method of total regeneration of pickling baths with hydrochloric acid is cheaper not only in regard to capital investment but also cheaper than pickling with sulphuric acid have therefore already been converted to pickling with hydrochloric acid.     

Inhibitoren der Korrosion (8) Über die Abhängigkeit der Korrosionsinhibierung des Eisens in Salzsäure von der Struktur quartärer Phosphoniumsalze

Inhibition of the corrosion of iron in hydrochlorid acid as a function of the structure of quaternary phosphonium salts In the case of quaternary phospho-nium salts there is no direct relation between their inhibiting power in deaer-ated acid media and the polarographi-cally determined reduction potentials. The inhibiting effect can in a first line be attributed to sterical factors con-nected with the fragments formed after incorporation of two electrons and be-coming fixed to the iron surface. Biphosphonium salts having saturated or unsaturated bridges are excellent in-hibitors under the conditions mentioned. Most efficient are biphosphonium salts having chaines of 4 to 10 methylene groups between the phosphonium cen-tres. The rigid p-phenylene radikal is less suitable as a linking principle. Phe-nyl phosphine and diphenyl phosphine in low concentrations accelerate corro-sion and exhibit a protective effect only in higher concentrations. Polymers having incorporated phos-phonium centres are only moderate inhibitors when compared to biphospho-nium salts. The synthesis is outlined and some physical and chemical properties are given.     

Über die Korrosion feuerfester keramischer Werkstoffe im Plasma von Verbrennungsgasen

The corrosion of refractory ceramic materials in the plasma of combustion gases The paper describes the testing of the corrosion resistance of refractory ceramics based on Al₂O₂, MgO and ZrO₂, as well as of phosphate cements, in flowing ionized gases as are present in the cornbustion products of conventional combustibles. A qualitative interpretation of the corrosion phenomena has been obtained experimentally using known test conditions and available thermodynamic and chechemical data.     

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.     

Über die Inhibitorwirkung der Fettsäuren bei der Korrosion des Eisens in saurer Lösung

Inhibiting effect of fatty acids on the corrosion of iron in acid media Fatty acids (C₁–C₁₂) in acid media (0.01 M HClO₄ + 0.2 M NaClO₄) have partially inhibiting and partially stimulating effects on the corrosion of iron. Short chain acids (C₁ to C₇) in concentrations below 5·10^?5 M act as stimulators, in higher concentrations as inhibitors. Beyond C₈ the stimulating effect gradually disappears. As to the inhibition mechanism the fatty acids are of the mixed type (though the anodic control predominates); they are not chemisorbed but only physically adsorbed by van der Waals forces and become desorbed when the temperature is increased.     

Die Rolle der Begleitstoffe von Abgaskondensaten aus der Erdgasverbrennung bei der Korrosion von Wärmetauschern

Impurity constituents of flue gas condensates and their significance for the corrosion of heat exchangers This paper presents investigations concerning the acidic constituents of flue gas condensates which may be generated by the combustion of natural gas. Nature, origin and concentration of relevant constituents will be presented. Their corrosive impact on components of domestic heating facilities will be discussed taking into consideration usual materials based on aluminium, stainless steel and copper. It will be shown that condensates are considered as diluted and aerated acids with a moderately reduced pH. With respect to aluminium based alloys and stainless steels the corrosive potential of condensates is deduced from their content of strong acids. When condensing is forced due to techniques which are used in condensing boilers there is an effect of dilution active which results in a reduction of the corrosiveness. The primary corrosion mechanism of copper is related to the presence of oxygen in the condensate. Therefore the dilution of condensates is of restricted significance. Unprotected copper is known to be unsuitable for condensing conditions.     

Inhibitoren der Korrosion 24 (1) – Zur Vergleichbarkeit der Abhängigkeit der Korrosion und Korrosionsinhibierung von der Chloridionen- und Inhibitorkonzentration am Beispiel von DAB6-Eisen und 1405-Stahl (auch phosphatiert)

Comparability of the dependence of corrosion and corrosion inhibition on chloride ion and inhibition on chloride ion and inhibitor concentration on the example of pure iron and steel 1405 (also phosphated) The rates of uptake of O₂ under standard conditions were measured for iron powder shaken with and without added inhibitor in dependence on the amount of iron and the chloride ion concentration. The results show that the standard procedure used allows a trustworthy measure of the inhibitor efficiency to be drawn from the observed effect. The relationship between the results for DAB 6 iron powder with 1405 steel plates was confirmed by experiments performed on filings from the plates. The rate of corrosion of phosphatized 1405 steel plate is efficiently suppressed by inhibitors with phosphonic acid groups. A treatment of the unphosphatized steel plates with phosphonic acid containing inhibitors in an analogous manner to phosphatizing leads to unsatisfactory results. The conclusion was drawn that the pH value of the inhibitor at the surface layer is important for the attainment of optimal effect.     

Inhibitoren der Korrosion 31 (1). Beitrag zur Inhibierung der Korrosion von Zink und Messing

Inhibitors of corrosion 31 (1). Contribution to the inhibition of the corrosion of zinc and brass The following compounds approved as inhibitors of the corrosion of copper are investigated as inhibitors of the corrosion of zinc and brass: 2-aminopyrimidine (A), 5-aminotetrazole monohydrate (B), benzotriazole (C), Kupferron (D), 2-mercaptopyrimidine (E), 2-mercaptothiazoline (F), 2-methyl-4-amino-5-cyanopyrimidine (G), tetrazine-B (H) and 2-amino-3,4,1-dithiazoline-1,5, thione (I). In the presence of the compounds A, B, C, E and G zinc plates are totally corroded in 15 days using standard conditions. With the compounds D, F and H the protective values are 29%, 14% and 39%. A more differentiated information is obtained with acid consumption-time-curves at constant pH using zinc powder. Only the compound C slows down the corrosion. The other compounds enhance the corrosion. In corrosion studies with mixtures of copper and zinc powders the compounds B–I inhibit the corrosion of copper. The acceleration of the corrosion in the presence of compound A was investigated. The corrosion of brass (plate, grain, powder) proceeds with primary removal of zinc. The compounds A, E, F and H are good inhibitors. The inhibition values for brass 64/36 are better than for brass 90/10. The composition of the protecting layers produced on the surface of brass in the presence of the organic inhibitors is determined by X-ray fluorescence measurements. With the inhibitors A, B, E, F and G the content of copper is over 90%, but 80% in the presence of the inhibitors C and H, which delay also the corrosion of zinc. The conception of primary loss of zinc and the subsequent production of a copper-rich copper-inhibitor-protection-layer is confirmed by determining the composition of the precipitations and of the solutions produced during the corrosion of brass.     

Inhibitoren der Korrosion 28 (1). 2-Aminopyrimidin (2-AP) als an Inhibitor der the Korrosion des Kupfers in Salzlösungen unter Sauerstoff

Inhibiors of corrosion 28 (1). 2-Aminopyrimidine (2-AP) as an inhibior of the corrosion of copper in salt solutions under oxygen 2-Aminopyrimidine is at present the best inhibitor known for the corrosion of copper, as measured under controlled conditions. A protective coating is created on the copper in conjunction with Cu¹⁺ ion as these form leave the surface. The coating at the surface was studied on variation of: (a) the concentration of 2-AP and Cu²⁺ ions, (b) the rate of agitation of the liquid medium and (c) the type of anion present in the corrosive medium. Some insight into the nature of the coating process was obtained via a rest-potential/time measurements, current voltage curves, polarisation/resistance curves and experiments interrupted in the course of the corrosion, all carried out with/without 2-AP and with/without added Cu²⁺ ions.     

Über einige Aspekte der atmosphärischen Korrosion von Stahl

To some aspects of the atmospheric corrosion of steel The corrosion of unalloyed steel (St 38 u 2) in pure moist air and by existence of low molecular saturated monocarbonic acids have been studied with microphotometric method. Moreover the electrochemical behaviour of this steel in adequate aqueous solutions has been characterized. It was found that steel - in distinction to pure iron - corroded already in moist air without pollutants in case the relative humidity is (RH) ≥70%. The action of the volatile monocarbonic acids on the corrosion were dependent on the pH value of water film which had been absorbed on the oxide layer of iron material. Oxygen acted as passivator above of pH_crit and the anions of these carbonic acids stabilized the surface hydroxyl groups on the strength of formation of bridging complexes. Final general conclusions about the mechanism of the atmospheric corrosion of iron materials are deduced.     

Inhibitoren der Korrosion 7 (1) Nachweis gemeinsamer Wirkungsprinzipien bei der Inhibierung der Säurekorrosion von Eisen,Zink, Aluminium (und Raney-Nickel)

Identification of mechanisms common to the inhibition of the acid corrosion of iron, zinc, aluminium (and Raney nickel) The dissolution of powder and chips of the above metals in diluted and deaerated hydrochloric acid is well inhibited by dibenzyl sulfoxide, benzyl quinolinium bromide and diphenylphosphonium chloride; triphenyl arsine chloride and tribenzylsulfonium hydrogen sulfate are less effective, while diphenyldithiophosphinic acid, thiourea, O-tolyl thiourea and mercaptobenzthiazol in low concentrations act as accelerators.     

Inhibitoren der Korrosion 30 (1,2) – Vergleichende Studien über das Verhalten bekannter und bisher unbekannter Inhibitoren der Korrosion des Kupfers unter Standardbedingungen (Sauerstoff,NaCl, pH 4,1, 22°C)

Corrosion Inhibitors 30 (1.2)-Comparative Studies on the Behaviour of Known and Unknown Corrosion Inhibitors of Copper Using Standard Conditions (Oxygen, NaCl, pH 4.1, 22°C) The following compounds were tested as inhibitors for the corrosion of copper samples under controlled (standard) conditions: benzotriazole (BTA); 5-aminotetrazole monohydrate (5-AT); 2,5-diphenyl-3-(4-chlorophenyl)-tetrazolium nitrate (Tetrazin-B); α- and β-naphthylamine; phenylthiourea; xanthanehydride; 2-mercaptothiazoline (2-MT) and cupferron (N-phenyl-N-nitrosohydroxylamine as its ammonium salt). The following measurements were applied: determination of the rate of O₂-uptake in agitation experiments and monitoring of the course of corrosion by the pH-stat method with variable: (a) inhibitor concentration; (b) structure of the copper sample (granules, dust, plate); (c) presence of added Cu²⁺-ions and (d) pH. Further information on the composition and structure of the surface coatings responsible for the inhibition was gathered from mass spectra, rest-potential/time and current/voltage curves and measurements of the polarisation resistance.     

Inhibitoren der Korrosion (9) Nachweis der Sekundärinhibitoren bei einigen Sulfoxiden,Triphenylarsinoxid und einigen Sulfoniumsalzen

Demonstration of secondary inhibitors of some sulfoxides, triphenyl arsene oxide and some sulfonium salts The inhibition values of some dibenzyl sulfoxide and structurally related com-pounds, and of triphenyl ursine oxide are determined. Sulfoxides and ursine oxides are (a) displaced, after protona-tion, into the cathodic regions and (b) converted, after electron acception, into secondary inhibitors which are liable to coordination (thioethers and tertarsines). The secondary inhibitors are either ad-sorbed by the metal and then suppress the dissolution of iron, or they are not fixed on the metal (e. g. diphenyl sul-fide) and have no protective action in that case. In the case Of dibenzyl sulf- oxide about 90% of the compound can be obtained by dissolution from the iron surface as dibenzyl sulfide, while the solution still contains 16% of non-converted dibenzyl sulfoxide. In the be found on the iron surface as tri-phenyl arsine, the rest is in solution as protonated triphenyl ursine oxide. From case of triphenyl ursine oxide 70% can the four sulfonium salts studied, only tribenzyl sulfonium hydrogen sulfate is subject to reduction to any greater ex-tent, the three other sulfonium salts can be isolated from the testmedium up to 90% without having undergone a transformation. Diphenyl allyl salfo-nium tetrafluoborate yields in the test medium, as the result of a reductive de-composition, 1 to 2% of a propenepro-pane mixture.     

Über den beschleunigenden Einfluß von Schwefeldioxid und Wasser auf die atmosphärische Korrosion von verrosteten Eisen

The accelerating effect of sulphur dioxide and water on the atmospheric corrosion of rusty iron The atmospheric corrosion process of rusty steel was observed in the laboratory in an atmosphere with 1, 10 and 100 p.p.m. SO₂, respectively, at a temperature of 30°C. It was found that the correlation of the corrosion rate with humidity can, in the range between critical humidity and nearly 100 per cent. Relative humidity, be represented by a rising quadratic parabolic equation. The differences in the three SO₂ concentrations had no influence on the corrosion kinetics, which is explained by the fact that, under the testing conditions, the rust was fully saturated with SO₄^2?. On the strength of these and earlier results, the authors submit a new working theory concerning the atmospheric corrosion of already rusty steel, introducing the theories of Heusler and Florianovitsch-Kolotyrkin into the sphere of atmospheric corrosion.     

Über den Einfluß von Schwefelwasserstoff auf die Korrosion des Eisens in sauren Lösungen

The influence of hydrogen sulphide on the corrosion of iron in acid solutions A considerable change of the polarisation behaviour of iron electrodes in acidic perchlorate and sulphate solutions was observed if they where saturated with hydrogen sulfide gas. H₂S markedly increased the anodic current densities and increases the corrosion rates by a factor of ten. The anodic Tafel slopes d log i_A/dE are only about half as steep as those in the absence of hydrogen sulphide. It is probable that the SH^?-ions behave as catalysts of the iron dissolution reaction in a similar manner as the OH^?-ions, but are adsorbed almost to saturation.