Yearly Archives: 2008

Phosphate coatings against frictional corrosion at shafthub press-fit connections and as transmission element for forces and moments in press-fit connections


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Fig. 1: The active principle of the formation of conversion coatings

Phosphating baths are mostly developed for microcrystalline single-phase coatings which can be precipitated with high reproducibility. The titanium phosphate pretreatment of steel promotes the formation of hopeite. This reaction leads to a deceleration of the covering process of the free surface and consequently to an increase in the amount of iron containing phosphophyllite. The different alloys and structures of the steel types is the reason for different rates of the pickling attack. Multiphase phosphate coatings containing phosphophyllite show improved tribological properties compared to zinc calcium phosphate coatings. This can be seen especially on the significantly decreased stick-slip inclination. The use of manganese phosphate coatings is to be preferred for many press-fit connections because they can be reproducibly precipitated, guarantee a higher torque transmission und successfully prevent tribo-oxidation.

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Electrochemical Nucleation and Growth of Gold on Embedded Rhenium Nanowires


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Fig. 2: Gold deposits obtained on NiAl-Re by application of...

The formation of gold nanoelectrode arrays was investigated by electrodeposition of the metal along the pores left on directionally solidified NiAl-Re eutectics by selective dissolution of the rhenium fibre. After the necessary pre-treatment for the passivation of the NiAl matrix and dissolution of the rhenium fibres to create arrays of nanopores (diameter ~ 400 nm), the electrodeposition of gold into the pores was initially investigated by examining the growth of the deposits with the application of cathodic pulses. It was observed that the size of the gold deposits increased with the duration of the applied cathodic pulse once an initial charge of ~ 800 C/m2 was overcome. The necessity of applying charges larger than that to observe significant deposits is due to the occurrence of a series of processes alongside the electrodeposition: charging of the oxides present on the eutectic and reduction of any remaining rhenium oxide on the rhenium fibres. Electrodeposition under potentiostatic conditions yielded a better control over the obtained gold structures, and enabled the selective filling of the pores. However, the recorded current transients under those experimental conditions did not obey any of the proposed models for nucleation and growth accurately. This was explained by the simultaneous formation of rhenium oxides and the interference of this process on the recorded current. Nevertheless, the studies reported give initial information on the electrochemical processes that take place when complex metallic substrates are employed for electrodeposition.

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Toxicity Study of a Nanoparticle Containing Passivate Layer


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Fig. 1: Preparation of a sample for the TEM-cross section...

The authors report on the cell toxicity study of a nanoparticle containing chromium(III) passivation. The toxicity of abrasion from zinc plated and nano-passivated screws was tested with human A549 cells. As a reference system we used the abrasion from zinc plated and thick layer passivated screws. The tests showed no toxic potential of the nanoparticle-containing passivation layer, as can be seen by the normal growing behavior of the cells in presence of the abrasion.

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Microstructure and Wear-Resistance of APS Alumina on Steel


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Fig. 1: Schematic of the symmetric B-B (a) and GIABD (b) geometries

Phase composition and parameters of micro-structure and properties in plasma-sprayed alumina coatings on steel as a function of the substrate temperature (in the range 200 – 400 °C) and coating thickness have been analysed. It has been found that increasing the temperature of the substrate and the coating thickness from 90 to 500 μm leads to the change of the phase composition and residual macrostresses. In all the investigated coatings the predominating is γ-Al2O3 phase although some α-Al2O3 and amorphous alumina have been also formed. At higher substrate temperature and higher coating thickness a lower amount of the amorphous phase and a higher amount of the α-Al2O3 have been formed. In all the investigated coatings tensile residual macro-stresses parallel to the surface have been fixed. Their value is minimal in the thicker (500 μm) coating which together with the observed in this deposit minimal share of the amorphous phase and maximal contribution of the α-Al2O3 is in a good agreement with its maximal wear-resistance.

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