Korrosionsverhalten und Biokompatibilität von Titanlegierungen für Implantate

Corrosion behaviour and biocompatibility of titanium alloys for implants Generally titanium alloys have proved to be suitable for implants. But there exist scruples concerning to toxic alloying elements, which were the reason to start comparative examinations with various kinds of titanium alloys. Because of bad reproducibility and high expenditure the obvious way to qualify different alloys by biocompatibility was not practicable. Therefore those properties which can be regarded as prerequisites of good biocompatibility were tested in saline. These are high corrosion resistance and high resistance of the passive layers. Extensive tests demonstrated the suitability of all alloys but no significant differences between titanium and its alloys TiAl6V4, TiAl5Fe2,5, TiAl7Mo4 and TiAl5Nb7. High variances and outlayers indicate that surface treatment is more important than chemical compositions of titanium alloys.     

Kondensatorrohre aus Kupferwerkstoffen Richtlinien für Werkstoffauswahl und Betriebsbedingungen

Condenser tubes made of copper materials

• 1 Today, the copper alloys most generally used for condenser tubes are CuZn28Sn (Special brass 71 — Admiralty brass) CuZn20Al (Special brass 76 — Aluminium brass), as well as the copper-nickel alloys CuNi10Fe and CuNi30Fe. The high corrosion resistance of these materials is due to the electropositive normal potential of their base metal — copper — and to their ability to form a highly adhesive, protective sealing film. To counteract the dezinzification of copper-zinc condenser tube materials, alloying with arsenic or phosphorus is indispensable, and generally resorted to.
• 2 The properties of normal-type cooling waters and the phenomena of tube corrosion are discussed. In practice, the only difficulties are likely to arise if polluted waters are used. Especially at the time of commissioning, the tubes must be kept free of polluted water so as to ensure the formation of a dense and firm protective film.
• 3 The reaction of the tube material to the cooling water depends mainly on the p_H-value, on the carbonate, chloride and oxygen contents, and on the temperature and flow rate of the water.
• 4 The following practice rules are advised: For fresh water (containing less than 0.1 pC matter in dissolution) and flow rates exceeding 1.4 metres pr. second, tubes consisting of CuZn20Al or of a copper-nickel alloy should be used so as to avoid erosion-corrosion. If the sea water is greatly polluted, it is advisable — especially at flow rates around or above 3 metres pr. second — to use tubes consisting of CuNi10Fe or CuNi30Fe.

     

Die Korrosionsprobleme der Klein- und Mittelständischen Industrie - eine Herausforderung für die Gesellschaft für Korrosionsschutz

Corrosion problems in small and medium-sized companies - a challenge for Gesellschaft für Korrosionsschutz The Gesellschaft für Korrosionsschutz (GfKORR) attaches high priority to solving problems related to materials and corrosion encountered in small and medium-sized firms. In this connection historical trends are presented and existing activity in the fields of corrosion and corrosion protection in various institutions is analysed. It is demonstrated that, compared with large-scale industries, small and medium-sized industries have the greatest recourse to service organizations. Statistics, derived from the work of the Karl-Winnacker-Institut and the Bundesanstalt für Materialforschung und -prüfung, indicate the types and the distribution of corrosion projects. Implications for the future work of the society are given. In particular this entails the promotion of production and product-integrated corrosion protection which is applicable during the developmental stage of processes and products. It is intended that this approach to problems should replace additive corrosion protection which only takes effect when the damage has occurred.     

Zur Herstellung und Anwendung von Ionenaustauschermembranen für die Alkalisalzelektrolyse

Manufacture and application of ion exchange membranes for alkali salt electrolysis Up to 30% by weight of styrene-divi-nylbenzene have been grafted on non-crosslinked high-pressure polyethylene films. Addition of isooctane in different proportions, yields variable degrees of porosity. Sulfonation yields cation exchange membranes, while chlormethylation followed by amination yields anion exchange membranes. In order to characterize the membranes thus obtained, their ion exchange capacities, specific conductivities and permselectivities were determined. The cation exchange membranes were used as diaphragms in the KCl and sodium sulfate electrolysis. Current efficiency and chloride ion diffusion were determined as functions of voltage, current density and degree of porosity and were correlated with the properties cited above.     

Autoklavenanlage für Oxidation und Korrosion von Materialien mit Hochdruckwasser

Autoclave arrangement for oxidation and corrosion tests of materials in pressurized water The authors describe an arrangement with an autoclave for corrosion and oxidation tests in pressurized water and steam. The autoclave has been conceived for a pressure of 250 bar at 500 °C. It is equipped with four locks enabling the specimens to be exchanged during operation without any markable influence on the working conditions. The aggressive medium can be exchanged continuously at a rate of 2,5 l/h. In addition to pressure and temperature controls the arrangement is equipped with a water quality control system.     

Reaktionen zwischen Natriumpolysulfid und Stromabnehmermaterialien für Natrium/Schwefel-Batterien

Reactions between sodium polysulfide and materials for current feeds in sodium-sulfur batteries In order to measure corrosion rates of potential materials for current feeds in the sodium polysulfide melt of sodium-sulfur batteries changes with time of the thicknesses of thin films were measured using the 4-point resistance method. At the free corrosion potential the steady state corrosion rate of aluminium in Na₂S₄ at 350°C was ? 150 μm/a and the activation enthalpy around 300 kJ/mol. At sufficiently high cathodic currents the corrosion rates were observed to increase linearly with the square of the total current. Upon anodic polarisation the thickness of the passivating film was increased, but there was not much influence on the mean corrosion rate. However, there were indications of local differences of the corrosion rate. The steel X10CrA124 corroded by growth of a film according to the parabolic rate law until a steady state corrosion rate was attained being 90 μm/a at 350°C. The steel X10CrNiMoTi 18 10 not containing aluminium corroded at the rate of 1.5 mm/a. The corrosion rate of chromium was even higher. On the other hand, Stellite 6 and glassy carbon corroded at rates < 2 μm/a.     

Halbleitereigenschaften von Passivfilmen und ihre Bedeutung für die Lochkorrosion

Semiconductive properties of passive films and susceptibility to localized corrosion The semiconductor properties of the passive films on AISI 304 were studied by Mott-Schottky analysis and photoelectrochemical methods. The results were compared with the number of current transients during passivation at different potentials which describe the metastable pitting events. The results show that the onset potential for pit nucleation coincides with the potential at the point of zero charge in the passive film (flat-band potential). A simple electrostatic model is presented showing that the first step of the pit nucleation event - the adsorption of the pit inducing anions - is not possible until a region of positive space charge is present in the passive film. Furthermore the model is confirmed by the appearance of a maximum in the transient number occurring in the same potential range where drastic changes in the electronic properties of the passive film take place.     

Innen- und Außenkorrosion von Abgasanlagen für PKW — Prüfverfahren,Labor- und Feldergebnisse

Internal and external corrosion of exhaust systems for passenger vehicles — Test procedures, laboratory and field results Exhaust systems fulfill a variety of tasks and their durability, their mass and their costs are of particular importance. Within the framework of further quality improvements a minimum lifetime of 3 to 5 years is aimed for, depending on the vehicle type. The mass of the exhaust system should be reduced by 20 to 25% without any substantial increase in the cost to performance ratio. The technical concept for muffler systems which fulfill these conditions is examined in this paper. Special attention is given to corrosion, particularly as a result of the effects of exhaust condensate and to the constructional design possibilities for the prevention of corrosion. In spite of all the efforts made it has not been possible up to now to simulate the wet corrosion stability of a complete exhaust system in the laboratory. For this reason the practical testing of the corrosion stability of exhaust systems on test stretches and in traffic cannot be dispensed with.     

Richtlinien für Werkstoffauswahl und Korrosionsschutz in der chemischen Industrie

Criteria for the selection of materials and corrosion protection in the chemical industry In chemical technology, the technical requirements to be met by materials as well as the protection measures against corrosion become more differentiated. On the other hand, owing to the technical progress in the sphere of materials number of alternative solutions to cope with these specifications is becoming available. The selection process, which has thus become more difficult, must lead to an overall solution representing the economic optimum; but must not become too expensive in the planning of new plant or in the corrosion protection of existing plant. A distinction is made between, and a brief outline given of, several stages in the material selection process, viz. formulation of requirements; selection methods prior to testing; laboratory tests; utilisation of technical testing plants; tests under operating conditions; determining the correct solution. The economic calculations designed to determine the most favourable technical solution call for numerous technical data (e.g., the corrosion rates under different corrosion conditions) as well as economic data (especially the capital and annual costs depending on the material). The calculation and estimating methods suitable for this purpose are described in detail. In order to reduce the costs incurred through corrosion, money must be spent on certain protective measures. This relationship is illustrated by the phenomenon of cost substitution. Finally, a synopsis is given of all the practicable methods suitable for determining the optimum conditions.     

Korrosionsschutz – Eine Basis für die Elektronik und Mikrosystemtechnik

Corrosion protection – A basis for electronics and microtechnic systems The number of microtechnic systems grows rapidly and so their influence to the general fail‐safe of technology. Their reliable function in increasing rough environmental conditions is mainly determined by the corrosion protection measures. The corrosion investigation founding shows nevertheless unfortunately deficiencies.     

Korrosions- und Verschleißeigenschaften von Werkstoffen für die chemische Verfahrenstechnik

Corrosion and wear behaviour of materials for chemical engineering It has been estimated that 7.4 percent of all corrosion related failures are mechanically assisted (i.e. involve wear), and that such failure consume, or render useless, 37 million pounds of highly alloyed materials per year. Despite this, relatively little is known of the basic wear behaviour of alloys commonly used in the chemical processing industries, and little attention has been paid to the design of alloys for conditions involving simultaneous corrosion and wear. The objectives of this paper are three-fold. First, the various types of wear are described, and the alloy characteristics required to combat each of these types are discussed. Second, new wear data are presented for several alloys commonly used in the chemical processing industries. Third, a comparison is drawn between these well established materials and a newly introduced cobalt-based alloy designed specifically for corrosion/wear service. The conclusions of the paper are that hardness is a poor indicator of performance for most of wear, that the nickel-chromium-molybdenum alloys are considerably more resistant to cavitation erosion and galling than the austenitic and duplex stainless steels, and that the cobald-based alloy possesses exceptional resistance to slurry erosion, cavitation erosion, and galling.     

Verbesserter Schutz gegen Korrosion und Reibkorrosion für Luftfahrtwerkstoffe durch PVD-Beschichtungen

Improved protection against corrosion and fretting corrosion for aircraft materials by PVD-coatings To substitute the ecologically critical cadmium as corrosion and fretting-corrosion protecting coating for aircraft materials aluminium-based PVD-coatings were tested. Apart from pure Al-coatings, Mg- or Li-alloyed Al-platings, in some cases additionally covered with a tribologically active top-coat (AlN; CrN), were deposited by IBAD- and Arc-techniques on the mild steel 1.7734, the martensitic chromium-steel 1.4548 and the titanium-based alloy 3.7164. In the condensed water- and salt-spray-test the corrosion protection for 1.7734 by Al-, Al/AlMg3- or AlLi-IBAD-coatings was not satisfactory because of the relatively high porosity of these coatings and an inhomogeneous Mg- and Li-distribution in the Al/AlMg3-IBAD- and AlLi-IBAD-platings. By depositing the more homogeneous Arc-coatings AlMg3 and above all AlLi a long-time corrosion protection could be achieved. In comparison to a Cd-plated 1.7734 the fretting-corrosion resistance was slightly improved by an AlLi/AlN-Arc-coating. The corrosion resistance of the electrochemically noble materials 1.4548 and 3.7164 in the condensed water- and the salt-spray-test was not affected by the deposited platings. In comparison to a Cd-coating, the fretting-corrosion resistance was improved by a TiC/i-C-IBAD-plating.     

Die Bedeutung der Schadensanalyse für die Werkstoffentwicklung,Konstruktion und Fertigung im Chemieapparatebau

The importance of case histories with respect to materials, development, design and construction of chemical plant The analysis of case histories can be considered to be an important special steel of materials testing, since the mechanical and chemical stresses and actions characteristic of the chemical industry may give rise to materials behaviour scarcely to be forecasted. The results obtained by such an analysis are the basis for decisions concerning the development of materials with increased resistance to chemical, mechanical and thermal actions; these improvements are achieved by addition of specific alloying elements variations of the materials productions processes as well as mechanical and thermal treatment. The analysis may as well yield important results concerning equipment design, the aim being a design combining a minimum of mechanical stresses and a maximum of chemical resistance; important aspects in this respect are plant excessibility and materials behaviour under welding conditions.     

Untersuchungen und Betrachtungen zur Anwendung von Kunststoffen für Lebensmittel XVI. Mitteilung: Diffusionsvorgänge an PVC-Schläuchen für Lebensmittel

Investigations into and considerations concerning the use of plastics in contact with foodstuffs. XVIth Communication: Diffusion processes in PVC hoses for food products Milk hoses of PVC react with the constituents of milk and – during the subsequent cleaning operations – also with water and cleaning solutions. The diffusion processes taking place in this connection are studied with the aid of specially designed simulating methods (rotating, milk- filled annular hose, testing apparatus reproducing the operation and cleaning of milking machines). After the tests one has determined in particular the transition of plasticiser into the liquid and the transition of fat into the plastic material, while in the case of cleaning solutions the water absorption by the plastic has been determined. The loss of plasticiser and the absorption of fatty materials depend primarily from the swelling condition of the PVC: the higher the swelling of the plastic, the easier the loss of plasticiser. During the contact with milk the then existing fatty film on the plastic inhibits water absorption, but this effect is eliminated by the cleaning operations. With increasing time embrittlement connected with cracking is observed.     

Probenhalterungen für elektrochemische Korrosionsversuche

Specimen holders for electrochemical corrosion tests In order to yield reproducible and reliable results in electrochemical testing the apparatus and in particular the specimen holders must make sure, that the following requirements are fulfilled: defined area; identical distance between specimen and reference electrode; good electrical contact between specimen and cable; no admission of electrolyte to metal surfaces outside the specimen. The autors have designed holders which enable experimental setups to be assembled which meet theses requirements. The types of holders include holders for determining current density/potential curves and holders for galvanic corrosion studies.     

Elektrolytisches Korrosionsverhalten metallischer Gläser auf Eisen-, Nickel- und Kobaltbasis

Electrolytical corrosion behaviour of iron-, nickel- and cobalt-base metallic glasses The corrosion behaviour of the three amorphous metals Fe₄₀Ni₄₀B₂₀, Ni₇₈Si₈B₁₄ and Co₅₈Ni₁₀Fe₅Si₁₁B₁₆ was investigated in 0,5 M sulfuric acid and in a boric acid/borax buffer solution. Cyclic voltammograms of the three alloys were measured between hydrogen and oxygen evolution. In case a passive region occurred the corrosion rate in this region was increased by two or three orders of magnitude. Otherwise a potential region with small net current density was observed between hydrogen evolution and active dissolution. This is explained by inhibition of the cathodic partial current density of the hydrogen evolution reaction. All three materials showed increased susceptibility to local corrosion.     

Nichteisenmetalle für die Meerestechnik

Non-ferrous metals for ocean engineering Following a comparative survey of the corrosion behaviour of various non-ferrous metals in sea water the author deals with the individual variables (flow rate, water depth, aeration) and the mechanical requirements such metals have to meet. Possible applications of Cu and Ni alloys are listed in this context, reference is made to recently developed alloys: weldable CuNi casting alloys, high strength CuNi alloys for use in sea water at high flow rates, high strength NiCrMo alloy for ropes which even during extended exposure to sea water must not loose their strength nor be susceptible to crevice corrosion.