A new measurement protocol was used for microscopic chemical analysis of surface oxide films with lateral resolution of 1 μm. The native air-formed oxide and an anodic passive film on austenite and ferrite phases of a 25Cr-7Ni super duplex stainless steel were investigated using synchrotron hard X-ray photoemission electron microscopy (HAXPEEM). Pre-deposited Pt-markers, in combination with electron backscattering diffraction mapping (EBSD), allowed analysis of the native oxide on individual grains of the two phases and the passive film formed on the same area after electrochemical polarization of the sample. The results showed a certain difference in the composition of the surface films between the two phases. For the grains with (001) crystallographic face // sample surface, the native oxide film on the ferrite contained more Cr oxide than the austenite. Anodic polarization up to 1000 mV/ Ag/AgCl in 1M NaCl solution at room temperature resulted in a growth of the Cr-and Fe-oxides, diminish of Cr-hydroxide, and an increased proportion of Fe 3+ species.
Uniform endless fibers are ubiquitous and their applications range from functional textiles over biomedical engineering to high-performance filtering and drug delivery systems. Here, we report a new method for the direct, reproducible fabrication of uniform polymer and composite micro-/nanofibers using a microfluidic gas flow focusing nozzle (Gas Dynamic Virtual Nozzle (GDVN)) relinquishing the need for external fiber pulling mechanisms. Compared to other methods, this technique is inexpensive, user-friendly and permits precise fiber diameter control (~250 nm to ~15 µm), high production rate (m/s-range) and direct fiber deposition without clogging due to stable, gas-focused jetting. Control over shape (flat or round) and surface patterning are achieved by simply tuning the air pressure and polymer concentration. The main thinning process happens after the polymer exits the device and is, therefore, mostly independent of the nozzle’s internal geometry. Nevertheless, the lithography-based device design is versatile, allowing for precise flow-field control for operation stability as well as particle alignment control. As an example, we demonstrate the successful production of endless hematite nanocomposite fibers which highlights this technology’s exciting possibilities that can lead to the fabrication of multifunctional/stimuli-responsive fibers with thermal and electrical conductivity, magnetic properties and enhanced mechanical stability.
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