Untersuchungen über Inhibitoren der atmosphärischen Korrosion feinmechanischer Erzeugnisse

Investigations into atmospheric corrosion inhibitors for precision instruments Precision instruments can be protected against corrosion during shipment to tropical regions when inhibitor combinations are used formed by two components having different modes of action. Such a combination of dicyclohexylammoniumnitrite and dimethyldiethoxysilane have turned out to be efficient inhibitors. While the nitrite being a wellknown vapourphase inhibitor is deposited on metal surfaces as a film which is easily washed off the silane compound forms a hydrophobic layer protecting the inhibitor layer from being washed off by condensing moisture. According to the results obtained in condensing humidity conditions the combination tested is much more efficient than the components when used separately. The increased protection can be recognized after about 24 hours and after 96 hours 75% protection is afforded. Some metals suffer a slight decoloration (Al, Cd, Zn) while iron, copper and their alloys, nickel, chromium, anodized aluminium materials, chromated cadmium and zinc were uneffected; plastic materials and protective coatings are not altered by the inhibitors.     

Möglichkeiten der Bestimmung des Zustandes der Betauung und Befeuchtung der Oberfläche

Possibilities for the determination of the electrolyte formation on surfaces by condensation and moisture particle impact In order to control the presence of electrolyte films on surfaces measuring probes are attached to the piece to be studied and the change of the electrical resistance of the probes is measured. These probes are passive dipoles and form a system of metallic area electrodes separated from each other by a crevice of defined dimensions (geometrical shape and size are adjusted to the particular problem). The electrodes are applied to a support combining high insulation resistance, water resistance, low weight and good thermal conductivity. The probes are connected to an electronic system recording the signals from the individual probes, so that the duration and the frequency of moisture film formation can be determined; the recording strip further enables a differentiation to be made between condensation (dew formation) and direct impact of liquid particles.     

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 (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.     

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 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.     

Einsatz von Oberflächen- und Mikroanalysenverfahren bei der Untersuchung von Inhibitoren

Surface- and micro-analytical methods in the investigation of Inhibitors ESCA, AES, ISS, TOF-SIMS and LAMMA investigations concerning the composition and thickness of the protective layers formed when Cu, Ni and Co in water are inhibited with interface inhibitors (benzotriazole, tolyltriazole, mercaptobenzothiazole and 2-(5-aminopentyl)-benzimidazole), or unalloyed steels, likewise in water, are inhibited with interphase inhibitors, such as phosphonotricarboxylic acid, are reported. The layers formed by interface inhibitors are only a few monolayers thick. Information on the molecular structure of the layers is provided particularly by LAMMA and TOF-SIMS. Where Cu and Ni are concerned, quasi-polymeric molecules of the metal(I) benzotriazole type are formed, whereas in the case of Co, complexes of higher valency occur also. The same molecular structures are also observed on oxidized metal surface. The inhibitors layers cannot be removed from the surface of the metal with solvents, and they are also stable during prolonged exposure to air. The interphase inhibitors form substantially thicker layers. The mechanism of the protective layer formation is discussed with references to a variety of parameters.     

Inhibitoren der Korrosion 10 (1). Nachweis der Sekundärinhibition durch Allyl-triphenyl-phosphonium- bzw. arsoniumbromid und N-Allyl-chinaldiniumbromid

Corrosion inhibitors (10) Demonstration of the secondary inhibition by allyl triphenyl phosphonium and arsonium bromides and N-ally1 quinaldinium bromide Triphenyl allyl phosphonium (1) and arsonium (2) salts as well as allyl quinaldinium bromide (4) are corrosion inhibitors of moderate efficiency. In acid media they are reduced by carfinyl iron powder to yield triphenyl phosphine and triphenyl arsine respectively and quinaldine. The two products mentioned the first form a layer on carbonyl iron and, after extraction, may be identified by gas chromatography. The allyl group is eliminated by iron from 1, 2 and 4, yielding Pro-pene, propane and, probably, cyclopropane. The hydrocarbon quantities determined by gas chromatography are in good agreement with the values found in the gravimetric determination of allyl-onium salts after the reaction. Ally triphenyl phosphonium bromide ( I ) and allyl diphenyl sulfonium tetraborate (3) yield propene and propane in a 1:1 ratio. In the case of (2) and (4) this ratio is shifted to 14:l and 7:l respectively. The hydrocarbon proportion in the gas mix-ture is higher at the beginning of the reaction than toward its end; at the beginning, the Propane:propene ratio is also displaced, the formation of propane having priority.     

Inhibitoren der Korrosion 25(1) – Über die Rolle der Kationen in Neutralsalzen bei der Korrosion von Eisenwerkstoffen in Gegenwart von Sauerstoff

Corrosion inhibitors 25(1) – The role of the cation in a neutral salt in the corrosion of iron in the presence of oxygen The rate of uptake of oxygen, under standard conditions, in the corrosion of 500 mg DAB6 iron powder is dependent on the nature of the cation in a neutral salt (chloride). In the presence of alkali, quaternary ammonium, quaternary phosphonium and alkali-earth chlorides, the rate of oxygen uptake is comparable. With zinc, cadmium, nickel and cobalt chlorides a marked decrease in the oxygen uptake is observed between pH5 and pH7. This is probably due to a block in the cathodic area in the iron boundary layer through precipitation of the rather insoluble basic hydroxides of zinc, cadmium, nickel and cobalt.     

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 (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.     

Inhibitoren der Korrosion (11). Nachweis der auf Eisengrenzflächen gebildeten Sekundärinhibitoren durch UV-Absorptions- und Fluoreszenzspektroskopie

Identification, by UV absorption and fluorescence spectroscopy, of the secondary inhibitors formed on iron boundary faces In acid solution, triphenyl benzylphosphonium chloride forms a layer on an iron surface; this layer should, according to the results of UV reflexion spectroscopy, be identical with triphenyl phosphine. The mono- and bis-phosphonium salts, too, are degraded by reduction at the iron boundary surface; the anthracene derivatives formed by this reaction are identified by the same method; they turn out to be methyl anthracene. A further separation of the reaction products has been attempted by thin layer chromatography (investigation of the extracts in cyclohexanol and methanol) yields no clearly distinguishable fluorescence spectra.     

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 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.     

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.     

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.     

Anbindungsverhalten organischer Monomere auf Eisenoberflächen und Korrosion der durch die Anbindung chemisch modifizierten Oberflächen

Binding behaviour of organic monomers on iron surfaces and corrosion of the resultant chemically modified surfaces In this study a new concept is discussed, to anchor polymers onto metal surfaces by primary chemical bonds. Organic molecules with two functional groups are positioned between polymer and substrate, which should be bonded to reactive centers of the metal surface by one functional group and to the polymer by conventional C-C bonds. As a first in this direction, the reaction between simple aliphatic mercaptanes and iron surfaces has been studied in detail. Surface analytical investigations have proven, that mercaptane molecules can be bonded to metallic clean iron surfaces by Fe-S-R bonds. The reaction itself has to be performed under well controlled electro-chemical conditions. The stability of the bonds is quite large as well in air as in many different electrolytes. The stability is limited by a prolonged oxygen reduction at large cathodic overpotentials. Probably, the mercaptane molecules are chemically oxidised by the H₂O₂ formed during the reduction of oxygen and the resulting sulfonic acid desorbs from the electrode surface.     

Lokaler Korrosionsangriff unter Wasserstoffblasen,die an der Oberfläche von Zink haften

Pitting corrosion under hydrogen bubbles, adherent to the surface of zinc Investigation zinc alloys in acid solutions, it could be determined that under hydrogen bubbles which has adhered on the surface, annuker pitting corrosion took place. The types of corrosion attack were examined under a microscope during and after the corrosion test and in some cases under scanning electron microscope. The formation of the annular pittings can be interpreted as an impoverishment of hydrogen ions in the boundary layer between the hydrogen bubble and the surface of the specimen.     

Inhibitoren der Korrosion (14). pH-Wert-Änderungen in Suspensionen von Eisen in 0, 2 m NaCl-Lösungen unter den Bedingungen der Sauerstoffkorrosion

Corrosion inhibitors (14) pH variations in suspensions of iron in 0.2 m NaCl solutions under conditions of oxygen corrosion The pH of iron suspensions is deter-mined in a suitable apparatus under varying reaction conditions. The results are as follows:

• 1 In a suspension of 25 grs of carbonyl iron powder in 100 ml of pure water there is no pH variation, neither under nitrogen nor under oxygen.
• 2 When 25 g of carbonyl iron powder are introduced under 100ml 0.2 m NaCl solution, the pH value rises from 6.60 to 9.4-9.5 within three to eight minutes.
• 3 Determination of the dissolved Fe(OH)₂ quantity and conversion of the latter to pH units reveals, that the pH rise is due to (a) an exchange of OH^?-ions for CL^?-ions at the boun.