M.C. Merino

Metal release from ceramic coatings for dental implants.

OBJECTIVES Two types of ceramic coatings on commercially pure titanium for dental implant applications with different Ca/P ratios in the range from 1.5 to 4.0, and two different thicknesses (∼5 and ∼15μm) were examined with the aim of underpinning the effect of coating composition, thickness and microstructure on the corrosion behavior and hydroxyapatite forming ability in SBF. METHODS Bioactive coatings were formed on Ti by plasma electrolytic oxidation (PEO). The composition, structure, and morphology of the materials were characterized before and after the immersion in simulated body fluid solution (SBF) at 37°C for up to 4 weeks. All the materials were screened with respect to metal ion release into SBF. RESULTS Only thick PEO coating with overstoichiometric Ca/P ratio of 4.0 exhibited capacity to induce the precipitation of hydroxyapatite over the short period of 1 week. Long term Ti(4+) ion release from all PEO-coated materials was 2-3 times lower than from the uncoated Ti. Metal ion release is attributed mostly to chemical dissolution of the coating at initial stages of immersion. SIGNIFICANCE The long term stability was greater for thin PEO coating with overstoichiometric Ca/P ratio of 2.0, which exhibited ∼95ngcm(-2) of Ti(4+) ions release over 4 weeks. Thin PEO coatings present economically more viable option.

The influence of Cr addition on the corrosion resistance of Fe73.5Si13.5B9Nb3Cu1 metallic glass in SO2 contaminated environments

Abstract The influence of Cr concentration on the corrosion resistance of Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 metallic glass in simulated environments contaminated with SO 2 has been studied (0.1 M Na 2 SO 4 ). The corrosion kinetics has been analysed using direct current electrochemical techniques. Moreover, gravimetric tests were conducted in order to establish the reliability of the data obtained electrochemically. Cyclic polarisation measurements were made to study the possibility of localised corrosion. Every test was determined with the same material in different states: amorphous, nanocrystalline and crystalline. Furthermore, the study has also focused on the modification of the magnetic properties in the material as a result of Cr addition and the exposition to an aggressive medium. These properties mainly depend on the Cr concentration, as well as on the material state (amorphous, crystalline or nanocrystalline).

Improvement of Corrosion Behavior of A3xx.x/SiCp Composites in 3.5 wt % NaCl Solution by Ce Surface Coatings

The effects of the silicon carbide particles (SiCp) proportion and the matrix composition of aluminum matrix composites (A3xx.x/ SiCp) modified by cerium-based conversion or electrolysis coating were evaluated in 3.5 wt %NaCI aerated solution. The intermetallic compounds were preferentially covered by cerium-based conversion coating obtained by immersion in 50°C solution of Ce(III) salt, and the intermetallic compounds, SiCp, and aluminum matrix were covered by electrolysis treatment performed in ethylene glycol monobutyl ether solution. The kinetic of the corrosion process was studied on the basis of gravimetric tests, and the corrosion process was evaluated by electrochemical impedance spectroscopy. The nature of both Ce coating and corrosion products was analyzed before and after accelerated testing by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and low-angle X-ray diffraction to determine the influence of microstructural changes on corrosion behavior during exposure to the corrosive environment. The corrosion process is influenced more by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement. Both cerium-treated surfaces present better behavior to chloride solution corrosion than original composite surfaces without treatment; however, electrolysis affords a higher degree of protection than the conversion treatment because the coating is more extensive.

Influence of Cr addition on the corrosion resistance and magnetic properties of amorphous Fe73.5Si13.5B9Nb3Cu1 in simulated industrial environments

Abstract The influence of Cr concentration on the corrosion resistance of Fe73.5Si13.5B9Nb3Cu1 amorphous alloy in simulated industrial environments contaminated with SO2 has been studied. The corrosion kinetics have been analysed using DC electrochemical techniques. Moreover, gravimetric tests were conducted to establish the reliability of the data obtained electrochemically. Every test was determined with the same material in different states: amorphous, nanocrystalline and crystalline. Furthermore, the study has also focused on the modification of the magnetic properties (coercive field and saturation magnetisation) in the material as a result of Cr addition and the exposure to an aggressive medium. These properties mainly depend on the Cr concentration, as well as on the material state (amorphous, crystalline, or nanocrystalline).

Electrochemical Estimation of the Corrosion Rate of Magnesium/Aluminium Alloys

The corrosion rate of AZ31, AZ80, and AZ91D magnesium/aluminium alloys immersed in 3.5 wt.% NaCl was determined comparing gravimetric and electrochemical measurements. The findings revealed that, for all investigated materials, a fraction of the metallic surface exposed to the corrosive medium did not reveal a normal electrochemical response to the applied signal. This may be associated with phenomena such as partial disintegration of specimens into fine metallic particles, electrochemical formation of Mg

Native Air-Formed Oxide Film and its Effect on Magnesium Alloys Corrosion

The present work uses X-ray photoelectron spectroscopy (XPS) analysis to compare the chemical composition of native oxide films formed spontaneously on commercial pure magnesium and AZ31, AZ80 and AZ91D magnesium alloys. The study considers both the outer surface and inner regions of the films with the assistance of argon ion bombardment. Possible relationships are established between the alloy Al content and the native oxide film characteristics. The Al content is very similar in the oxide films on all three studied alloys. XPS identifies a much greater film thickness on AZ80 and AZ91D specimens than on AZ31 and pure Mg specimens, which seems to be related with the presence ofphase (Mg17Al12) on the AZ91D alloy surface and of the eutectic � -Mg/� on the AZ80 alloy surface. Considerable Ca segregation is observed (directly related with the calcium impurities content in the bulk material) towards the outer surface of the metal, where it appears in the form of calcium oxide. Direct correspondence is found between the thickness of the native oxide film formed spontaneously on the surface of magnesium and its alloys and their subsequent corrosion resistance in exposure to a 3.5 wt% NaCl solution.

The Application of X-Ray Photoelectron Spectroscopy in Understanding Corrosion Mechanisms of Magnesium and Mg-Al Alloys

The authors present a review of their research work on the application of X-ray photoelectron spectroscopy (XPS) to characterise thin (~ 3 nm) natural oxide films that spontaneously form on the surface of magnesium and its alloys in contact with the oxygen in air, and thick (> 1 μm) corrosion films rich in carbonates and other species that form during exposure to a humid atmosphere. The results obtained can provide much useful information about the protection mechanisms of these materials. Emphasis is placed on the relationship between the alloys Al content and the characteristics of the natural oxide film and the relationship between segregation of calcium impurities from the bulk to the outer surface of the metal and repercussions on electrochemical behaviour. The natural oxide film may alone be sufficiently protective in less aggressive environments, making it of interest to know its characteristics. A detailed study will also be made of the changes in chemical composition that may occur in this passivating film with increasing exposure time to a humid atmosphere, deteriorating or reinforcing its anticorrosive properties. In particular, an attempt will be made to research the effect on corrosion behaviour of: (a) the time the different specimens are exposed to the aggressive agent (humid atmosphere); (b) the possible formation during corrosive attack of layers that are rich in carbonates and other species; and (c) the presence of aluminium (alloying element) on the protective properties of the corrosion layers.

Influence of Gd on the Corrosion Behavior of AM50 and AZ91D Magnesium Alloys

The corrosion behavior of AM50 and AZ91D Mg alloys containing 0.2 wt% to 1.0 wt% Gd was evaluated in 3.5 wt% sodium chloride (NaCl) solution using electrochemical, gravimetric, and hydrogen evoluti...

Salt spray corrosion behaviour of new Mg–Al alloys containing Nd or Gd

Abstract The influence of chloride concentration on the salt spray corrosion behaviour of new AZ91D and AM50 alloys containing rare earth (RE) elements was evaluated. The corrosion rate of both materials increased with increasing chloride concentration, particularly for NaCl concentrations above 2 wt-%. The addition of Nd or Gd reduced the amount of β-Mg17Al12 phase and resulted in the formation of RE containing intermetallics that were less noble than the Al–Mn inclusions but more noble than the β-Mg17Al12 phase. The latter modifications decreased the corrosion rate of the AM50 alloy by up to 90% but did not give a clear benefit to the corrosion resistance of the AZ91D alloy.

Effect of Reinforcement Coating on Corrosion Behavior of AA6061/SiC/20p Composite in High Relative Humidity Environments

Abstract A study of the influence of silicon dioxide (SiO2) active coatings on silicon carbide (SiC) reinforcement particles of an aluminum metal composite, AA6061 (UNS A96061)/SiC/20p (Al-Mg-Si alloy reinforced with 20 vol% of SiC particles), exposed to a high relative humidity environment (98% RH and 50°C), was carried out under simulation in a climatic chamber. To improve processibility, SiC particles were coated prior to composite manufacture by a casting procedure, using the sol-gel technique. The corrosion resistance of the composites was analyzed to determine the influence of the manufacturing variables. The nature of corrosion products before and after accelerated testing was analyzed by scanning electron microscopy (SEM) and low-angle x-ray diffraction (XRD), determining the influence of microstructural changes on corrosion behavior during exposure to the aggressive environment. The kinetics of the corrosion process was characterized on the basis of gravimetric tests. The corrosion damage to comp...