Corrosion Properties of Thermally Annealed and Co-sputtered Nickel Silicide Thin Films

The corrosion properties of nickel silicide thin films are addressed by means of polarisation experiments in combination with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) characterisation before and after the polarisation runs. The thin films studied included two pairs of nickel silicide of different compositions fabricated on Si wafer by means of ion-beam sputter deposition technique. For one pair, thin films were prepared by co-sputtering Si and Ni targets. To achieve higher crystallinity, the other pair was prepared by Ni sputter deposition followed by subsequent thermal annealing at 280 °C and 480 °C to develop single silicide phase of Ni2Si and NiSi in individual film, respectively. The variation of the binding energy (BE) of Ni 2p3/2 core-level peak in the XPS measurement in accordance with the Si content for this binary system follows a Boltzmann's relationship. The electrochemical polarisation tests conducted in 1.00 M HCl solution showed almost the same behaviour for the tested specimens irrespective of structure or film composition, still, the SEM and XPS studies together with optical microscopy showed that the Ni2Si, leaner in Si, experienced thin film corrosion, whilst the NiSi appeared to be more resistant. Clearly, composition is found to be a more important design factor to tailor the corrosion properties than the structure for this binary silicide system

Galling related surface properties of powder metallurgical tool steels alloyed with and without nitrogen

Two types of powder metallurgical tool steels (i.e. with and without nitrogen) are investigated with respect to their galling related surface properties. Despite similar macrohardness values, Vancron 40 (nitrogen alloyed) exhibits superior wear behaviour as compared to Vanadis 10 (without nitrogen); demonstrating approximately 20 times longer life span when used as die material in powder compaction. The main failure mechanism is mild abrasive wear for Vancron 40 and early severe galling for Vanadis 10. One important difference causing the tribological discrepancy is supposed to be associated with the preferred formation of solid lubricant oxides of the Magnéli type on the Vancron 40 surface as compared to Vanadis 10. The VN precipitates in Vancron 40 have half the thermal conductivity compared to that of the VC precipitates existing in Vanadis 10. Hence, as a result of the local accumulation of frictional heat generated during powder compaction (or any other type of forming process), Magnéli phases of V2O5 and/or VO2 are more easily formed and maintained on the Vancron 40 surface. With regard to surface oxides, the tool steels were studied by means of X-ray photoelectron spectroscopy (XPS). The tool steel surfaces were examined by means in situ SEM/AFM and electron backscatter diffraction (EBSD) for local adhesion force measurements and understanding the orientation of the phases, respectively. In addition, pin-on-disc wear tests were performed on the tool steels and the worn surfaces were analysed using scanning election microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS)

Corrosion behaviour of amorphous Ni-Si thin films on AISI 304L stainless steel

Nanoscale Ni-Si thin films are widely used in commercial microelectronic devices because of their promising electrical properties as well as their chemical stability. However, their application In corrosive environment has not been frequently addressed in the literature. In this study, amorphous Ni0.66Si0.33, Ni0.40Si0.60, and Ni0.20Si0.80 thin films are prepared on AISI 304L stainless steel by means of ion-beam sputter (IBS) deposition and their corrosion behaviour is studied using potentiodynamic polarisation measurements. The electrochemical measurements were conducted in 0.05 M HCl solution at room temperature. By means of optical interferometer, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), the surface morphology and chemical composition of the thin films were examined before and after the electrochemical measurement. The evaluated results showed that the Ni-Si thin films may exhibit improved corrosion resistance over the 304L substrate provided that Si content is high enough to facilitate the formation of a Si-rich passive film

Effect of Temperature Gradient and Sulphur Dioxide Addition on Erosion-corrosion of Iron- and Nickel-based Alloys

In this study, high temperature erosion-corrosion with trace amounts of added SO(2) and the role of isothermal or thermal gradient conditions are studied. The studies are focused on 304L as the model material, but results for other alloys (Alloy 625 and 9Cr1Mo-steel) are also included to support the results and trends observed. The experiments include 550 degrees C exposures in the erosion-corrosion rig under isothermal and thermal gradient conditions. The internal cooling used to create the thermal gradient meant that the 550 degrees C material temperature could be maintained, despite of the higher bed temperature of 750 degrees C. Laboratory oxidation experiments in a similar environment are also included as reference tests. The evaluation of material degradation was done by using a combination of different techniques such as scanning electron microscopy (SEM) including X-ray microanalyses, Auger and Xray electron spectroscopy. The results demonstrate three important aspects related to erosion-corrosion attack in fluidized bed combustion. First, provided oxide growth is rapid enough leading to thickness in the micrometer range, low material wastage is obtained as demonstrated for the 9Cr1Mo - steel and also for the 304L and Alloy 625 materials when exposed to air plus 50ppm added SO(2) in isothermal conditions. Because of the large catalytic surface in the test rig for the thermodynamically favored oxidation of SO(2) in air, significant presence of SO(3) is expected. The material wastage is then also associated with a shift in erosion pattern with maximum material wastage at the impact of erodent (called type B). Detailed microstructure investigation of oxide in question on the 304L showed that the inner part of the oxide then is dense and possibly isolated from the environment and also Cr-rich. Adding a temperature gradient then returns the wastage pattern to type A for both 304L and Alloy 625 and leads to increased wastage for the former material. The resulting oxide thickness is also smaller and always less than 0.2 mu m. The laboratory reference tests showed a similar range of average oxide thickness for air and air plus SO(2). However, in air plus 50ppm SO(2) the tendency for break away corrosion on 304L was less than for air exposed samples

X-ray photoelectron spectroscopy studies of indium tin oxide nanocrystalline powder

Indium tin oxide films and coatings are widely used and can be produced by different techniques including dip and spin-coating of suspensions of nano-particles. To achieve high quality films the nano-powder has to be fully characterized. Hence, three co-precipitated nanocrystalline indium tin oxide powders of different particle size were investigated by use of X-ray photoelectron spectroscopy. The analysis indicated that indium and tin are in oxide state, i.e. no metallic component could be observed. In addition, measurements by use of X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy and transmission electron microscopy were performed. They showed that indium tin oxide primary particles are slightly elliptical and facetted in shape, respectively. The powders have a body center cubic lattice type and the lattice parameter is 1.01 nm. Measured by both X-ray photoelectron spectroscopy and energy dispersive X-ray, the tin content was determined to be 5-6 at.%

Modern approaches to marine antifouling coatings

Marine structures such as platforms, jetties and ship hulls are subject to diverse and severe biofouling. Methods for inhibiting both organic and inorganic growth on wetted substrates are varied but most antifouling systems take the form of protective coatings. Biofouling can negatively affect the hydrodynamics of a hull by increasing the required propulsive power and the fuel consumption. This paper reviews the development of antifouling coatings for the prevention of marine biological fouling. As a result of the 2001 International Maritime Organization (IMO) ban on tributyltin (TBT), replacement antifouling coatings have to be environmentally acceptable as well as maintain a long life. Tin-free self-polishing copolymer (SPC) and foul release technologies are current applications but many alternatives have been suggested. Modern approaches to environmentally effective antifouling systems and their performance are highlighted