TY - JOUR A1 - Bender, S. A1 - Goellner, J. A1 - Heyn, Andreas A1 - Schmigalla, S. T1 - A new theory for the negative difference effect in magnesium corrosion JF - Materials and corrosion N2 - An unusual feature known as the negative difference effect (NDE) can be observed in magnesium when recording corrosion current density–potential curves. More hydrogen is evolved at a more positive potential which does not occur in conventional metals. Several models have been proposed in the literature in order to explain the phenomenon of NDE. They succeed in explaining some effects, and fail to deal with others. A new model, which explains the NDE by two electron consuming processes, is presented in this paper. By potentiostatic investigations of magnesium in a chloride electrolyte, measurements of hydrogen evolution and chemical analysis of the electrolyte the new model was experimentally verified. KW - Magnesium KW - Negativer Differenzeffekt KW - Korrosion KW - Korrosionsmechanismus KW - Current density-potential-curve KW - Magnesium alloys KW - Magnesium corrosion KW - Negative difference effect KW - Polarization measurements PY - 2012 DO - https://doi.org/10.1002/maco.201106225 SN - 0947-5117 SN - 1521-4176 VL - 63 IS - 8 SP - 707 EP - 712 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-25162 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Bender, S. A1 - Göllner, J. A1 - Heyn, Andreas A1 - Heilmaier, M. A1 - Schmidt, J. ED - Kainer, K.U. T1 - Basic examinations of pre-treatment and coating of magnesium alloys T2 - Magnesium T2 - 8th International conference on magnesium alloys and their applications CY - Weimar, Germany DA - 2009-10-26 KW - Magnesium KW - Korrosion KW - Beschichtung KW - Vorbehandlung KW - Elektrochemisches Rauschen PY - 2010 SN - 978-3-527-32732-4 SP - 1323 EP - 1330 PB - Wiley-VCH AN - OPUS4-20743 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bender, S. A1 - Heyn, Andreas T1 - Evaluation and Screening of the pre-treatment states of Mg-alloys using Electrochemical Noise T2 - EUROCORR 2009 - Corrosion from the nanoscale to the plant N2 - A successful application of magnesium alloys as light structural materials and for special applications, such as in the medical sector, depends significantly on their corrosion properties. Since the use of well-chosen surface coating systems can optimize these properties, many efforts are going in this direction. In general, any coating process must be seen in a close connection to the pre-treatment of the alloy surface, particularly for magnesium alloys. The pre-treatment is required to prepare the optimal surface for a coating system, in which adhesion and dissolution behaviour are the central properties. In the case of magnesium alloys this means a well-controlled removal of the casting or rolling skin, which would be prone to corrosion and poor adhesion. Additionally, in most cases the surface morphology should be smooth. An investigation of different pickling solutions and pickling parameters showed a wide range of effectiveness (i.e., the resulting mass loss and surface morphology). Another important and often underestimated fact is the comparatively strong tendency of magnesium to react with the atmosphere. For that reason, after a completed pickling and cleaning treatment the condition of the surrounding atmosphere and the time prior to coating of the surface should be taken into account because of the formation of different reaction layers. These layers have an effect on adhesion and the corrosion properties of the coating system as a whole. For a documentation of the influence of different atmospheres and the timedependence of the surface activity the measurement of the electrochemical noise is the preferred technique. This is because it shows instantaneously the actual activity, even in the absence of external excitation. The influence of different pre-treatments as well as exposure conditions and duration was investigated using electrochemical noise measurements as a screening method. As a result the pretreatment which is an important part of the coating process could be considerably improved. T2 - EUROCORR 2009 CY - Nice, France DA - 2009-09-06 KW - Magnesium KW - Pre-treatment KW - Pickling KW - Electrochemical noise PY - 2009 IS - Paper 8080 SP - 1 EP - 8 AN - OPUS4-20064 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rosemann, P. A1 - Bender, S. A1 - Heyn, Andreas A1 - Schmidt, J. T1 - Korrosion and Biokompatibilität beschichteter MgCa1,0 Magnesiumlegierungen T2 - 14. Sommerkurs Werkstoffe und Fügen am Institut für Werkstoff- und Fügetechnik N2 - Die Magnesiumlegierung Mg-Cal besitzt als potentielles bioabsorbierbares Implantatmaterial die Möglichkeit, vollständig vom menschlichen Körper absorbiert zu werden. Die mechanischen Kennwerte dieser Legierung liegen im Bereich des menschlichen Knochens und beide Legierungselemente (Mg, Ca) sind essentielle Spurenelemente im menschlichen Organismus. Der limitierende Faktor für den Einsatz ist die hohe Degradationsrate dieser Legierung. Um die Degradationsgeschwindigkeit zu verringern, wurden zwei Beschichtungssysteme auf Grundlage der Plasmachemischen Oxidation (PCO) und organischer Beschichtung erzeugt und untersucht. Das Korrosionsverhalten dieser Schichtsysteme wurde dabei mit dem Elektrochemischen Rauschen analysiert. Zusätzlich wurde der Einfluss von Wasserstoffentwicklung und eines ansteigenden pHWert auf die Zelltoxizität untersucht. Die Ergebnisse zeigen, dass eine Kombination von beiden Schichtsystemen zu einem viel versprechenden Degradationsverhalten führt. T2 - 14. Sommerkurs Werkstoffe und Fügen am Institut für Werkstoff- und Fügetechnik CY - Magdeburg, Germany DA - 23.09.2011 KW - Magnesium KW - Magnesium-Calcium KW - Implantat KW - Beschichtung KW - Plasmachemische Oxidation KW - Korrosion KW - Elektrochemisches Rauschen PY - 2011 SN - 978-3-940961-56-3 SP - 135 EP - 138 AN - OPUS4-24491 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rosemann, P. A1 - Bender, S. A1 - Heyn, Andreas A1 - Schmidt, J. T1 - In vitro corrosion and biocompatibility of coated MgCa1.0 magnesium alloys JF - Materials science forum N2 - As bio-absorbable implant material the magnesium alloy Mg-1Ca is able to degrade in-vivo. The mechanical properties of this alloy are similar to those of human bone; both Mg and Ca are essential elements in human body. The main problem is the high corrosion rate of this alloy. Two coating systems based on plasma-chemical oxidation and an organic dip coating are applied onto MgCa1.0 magnesium alloy in order to slow down the corrosion rate. The corrosion behaviour of the coated alloys was investigated with electrochemical noise measurements. The influence of hydrogen evolution and increasing pH-value on the cytotoxicity was examined. The results of these investigations suggest that a combination of both coating systems leads to promising degradation properties. KW - Biocompatibility KW - Biodegradation KW - Magnesium KW - Plasma-Chemical Oxidation PY - 2011 DO - https://doi.org/10.4028/www.scientific.net/MSF.690.409 SN - 0255-5476 VL - 690 SP - 409 EP - 412 PB - Trans Tech Publications CY - Aedermannsdorf, Switzerland AN - OPUS4-23875 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rosemann, P. A1 - Schmidt, J. A1 - Heyn, Andreas T1 - Short and long term degradation behaviour of Mg-1Ca magnesium alloys and protective coatings based on plasma-chemical oxidation and biodegradable polymer coating in synthetic body fluid JF - Materials and corrosion N2 - The main problem limiting the application of magnesium alloys as biodegradable implant material is its high degradation rate. In order to slow down the corrosion rate an extrusion process and specific coating systems based on plasma-chemical oxidation (PCO) and organic dip coating with poly(ʟ-lactid-co-caprolacton) (PLLC) were applied on Mg–1Ca magnesium alloy. The additional PLLC coating is used to delay the start of substrate corrosion, while the purpose of the PCO coating is to decrease the substrate corrosion rate. The corrosion behaviour was investigated in synthetic body fluid (SBF) through measurement of the hydrogen evolution rate in long term tests and polarisation and electrochemical noise measurements in short term tests. The results showed significant differences between the cast and extruded alloys and a decrease of the corrosion rate due to corrosion product formation. The combination of both coating systems resulted in a significant delay of metal substrate corrosion and all coating systems showed good correlation between short and long term tests. The combination of the three investigation methods provides the possibility to gain more information about the degradation behaviour and break down of protective coatings. KW - Coatings KW - Corrosion KW - Electrochemical noise KW - Magnesium KW - Plasma-chemical oxidation PY - 2013 DO - https://doi.org/10.1002/maco.201206590 SN - 0947-5117 SN - 1521-4176 VL - 64 IS - 8 SP - 714 EP - 722 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-29074 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmigalla, S. A1 - Bender, S. A1 - Heyn, Andreas A1 - Schmidt, J. A1 - Hort, N. T1 - Investigation of biodegradation behaviour of an Mg-1Ca alloy influenced by heat treatment and applying plasma-chemical oxidation layers JF - Materials and corrosion N2 - The degradation behaviour of an Mg-1Ca alloy is investigated in vitro to figure out the possibilities of influencing the degradation behaviour of such an alloy by applying heat treatment as well as the use of a coating system based on plasma-chemical oxidation. It is shown that an optimised solution annealing (T4-heat treatment) can reduce the degradation rate while an additional ageing between 240 and 300 °C (T6-heat treatment) increases it. A coating generated by plasma-chemical oxidation reduces the degradation rate in the immersion test. Its effect is depending on the former heat treatment of the Mg-1Ca alloy as well as on the parameter during plasma-chemical oxidation. KW - Biodegradation KW - Magnesium alloys KW - Plasma-chemical oxidation KW - Magnesium KW - Thermal treatment KW - Corrosion KW - Electrochemistry PY - 2013 DO - https://doi.org/10.1002/maco.201106433 SN - 0947-5117 SN - 1521-4176 VL - 64 IS - 7 SP - 578 EP - 584 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-28933 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -