Discharge Optical Emission Spectroscopy Research Articles

Corrosion Protection of AISI 316L Stainless Steel with the Sol-Gel Yttria Stabilized ZrO2 Films: Effects of Sintering Temperature and Doping

Nanostructured sol–gel zirconia (ZrO2) films containing 3, 5 and 7 mol % Y2O3 of one and three layers were prepared on stainless steel X2CrNiMo17-12-2 (AISI 316L) surface by the dip coating method. Yttria stabilized zirconia (YSZ) deposited films were sintered at 400 and 600 °C. For the preparation of sol zirconium(IV) butoxide was used as precursor, i-propyl alcohol as a solvent with addition of nitric acid as a catalyst, acetylacetone as chelating agent and water for hydrolysis. Thickness of sol-gel YSZ films deposited on stainless steel was determined by glow- discharge optical emission spectrometry (GD- OES). It was found that thickness of deposited films is barely affected by yttria content while increases by increasing the number of layers and temperature of sintering. The crystal structure of films was determined by X- ray diffraction. The corrosion resistances of uncoated and coated specimens were studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated marine environment (3.5 wt. % NaCl aqueous solution) at room temperature. The influence of yttria stabilized zirconia (YSZ) layers number and temperature of sintering on the corrosion protection was examined as well. Sol-gel derived YSZ films are capable of appreciable improvement in corrosion resistance of stainless steel in the investigated corrosive medium.

Influence of the surface chemistry-structure relationship on the nanoscale friction of nitrided and post-oxidized iron

The relationship between the friction behavior and surface properties such as surface chemistry, morphology and phase distribution is not fully understood. In the case of surface treatments involving steels, the alloying elements introduce non-controllable variables in tribological experiments. We further advance this discussion by designing experiments where the friction behavior of a conical diamond tip sliding on different plasma nitrided and post-oxidized pure iron substrates was determined. Also, a detailed chemical and microstructural surface characterization using discharge optical emission spectroscopy, X-ray diffraction, and atom probe tomography was performed. Implementing composition profiling and localized elemental distribution analysis throughout the outermost layer, the formation of iron oxide with non-homogenous morphology was detected. Although the coefficient of friction decreases as a function of the post-oxidation time, the friction force is under a relative great dispersion at intermediate post-oxidation times. The dispersion of the friction force obtained from the sliding analyses can be understood as a combination of surface chemistry and different phases (structure) at the surface.

Thermochemical heat treatment of steel substrates using borane–amine adducts as precursors

A novel approach to gas boronising has been carried out to systematically test organoboranes as precursors for low pressure gas boronising. The precursors of the group of borane–amine adducts were synthesised and subsequently applied to gas boronising of steel 42CrMo4 (AISI 4140). Characterisation of the boride layers was performed using glow discharge opticalemission spectroscopy, X-ray photoelectron spectroscopy, SEM, and metallography. Ultramicrohardness was also determined and the wear behaviour was simulated. With the precursors borane–triethylamine adduct and borane–diethylamine adduct gas boronising was possible. Single phased iron boride layers of type Fe2 B with a thickness of several micrometres were generated. The carbon, nitrogen, and oxygen contamination of the boride layers was low. The boride layers are not completely compact which results in a lower hardness compared with commercial powder pack boronised samples. The wear behaviour is similar to powder pack boronised steels and is significantly better than the untreated samples.

In-depth profile analysis by radiofrequency glow discharge optical emission spectrometry using pressure as variable parameter

The analytical potential of radiofrequency glow discharge optical emission spectroscopy (rf-GD-OES), keeping constant the delivered power and the dc-bias while leaving the pressure as a free parameter, is investigated for in-depth profile analysis of conducting zinc-based coatings on steel. Results are compared with those achieved with a direct current (dc)-GD-OES in its common in-depth profiling mode of operation (constant current intensity, maintaining fixed the voltage at the expense of modifying the pressure). Under the selected operation conditions (40 W of delivered power and −400 V of dc-bias for rf-GD; −690 V and 11 mA for dc-GD), sputtering rates for different matrices (e.g., brass, stainless-steel, aluminium/silicon, nickel alloy) were of the same order when comparing both discharges. Precisions achieved in the measurement of sputtering rates for five replicates (burns) were between ±2.3 and ±10.8% for rf-GD and ±1.9 and ±7.2% for dc-GD. Reliable values for the emission yields of each analyte emission line under study (Zn, Fe, Ni, Si, Cu, Al and Pb) in the different matrix reference samples selected were achieved. Better correlation coefficients of the plots of emission intensity versus the product of sputtering rate times and analyte concentration in the case of dc-GD-OES were observed. The conversion from qualitative profiles (emission intensities versus time of acquisition) into quantitative profiles (concentration of the elements versus sputtered depth) was attempted by rf-GD-OES as well. Good results were obtained using the selected operation conditions for materials such as electroplated ZnNi, galvanneal and hot-dipped Zn. Such results were in agreement with those average values obtained in a dc-GD-OES laboratory intercomparison project for the same materials.