Effect of the finishing oil of acrylic fibers in the optical rotation of the Raman scattered light.

Polarized Raman spectra have been obtained from polyacrylonitrile copolymers fibers with vinyl acetate Poly(AN-co-VA), and methyl acrylate Poly(AN-co-MA) with finishing and without finishing, in order to show the effect of the finishing in the optical rotation of the Raman scattered light. The polarized Raman spectra were used to calculate the depolarization ratios for both fibers. These values reveal that there is antisymmetric Raman scattering in the form of anomalous depolarization for some bands due to a dipolar interaction between the polar headgroup of the finishing with the polar nitrile group of the fiber causing changes in the orientation of fiber polymer chains, or pseudo antisymmetric Raman scattering due to planar hydrocarbons of the oil finishing which are optically active and are aligned when they are applied to the acrylic fibers during the spinning process. Although the finishing should not affect the physical or chemical properties of the fibers, in this work is shown that the finishing could introduce optical activity in the different wavenumbers of the Raman signal and this effect is proportional to the finishing content. According to the results obtained in this work, Raman polarized spectroscopy can provide an express method to identify acrylic fibers with finishing and without finishing agents.

Raman spectroscopic analysis of iron chromium oxide microspheres generated by nanosecond pulsed laser irradiation on stainless steel.

Iron chromium oxide microspheres were generated by pulsed laser irradiation on the surface of two commercial samples of stainless steel at room temperature. An Ytterbium pulsed fiber laser was used for this purpose. Raman spectroscopy was used for the characterization of the microspheres, whose size was found to be about 0.2-1.7 µm, as revealed by SEM analysis. The laser irradiation on the surface of the stainless steel modified the composition of the microspheres generated, affecting the concentration of the main elemental components when laser power was increased. Furthermore, the peak ratio of the main bands in the Raman spectra has been associated to the concentration percentage of the main components of the samples, as revealed by Energy-Dispersive X-ray Spectroscopy (EDS) analysis. These experiments showed that it is possible to generate iron chromium oxide microspheres on stainless steel by laser irradiation and that the concentration percentage of their main components is associated with the laser power applied.

Infrared nanosecond pulsed laser irradiation of stainless steel: micro iron-oxide zones generation.

Nanosecond-pulsed, infrared (1064 nm) laser irradiation was used to create periodic metal oxide coatings on the surface of two samples of commercial stainless steel at ambient conditions. A pattern of four different metal oxide zones was created using a galvanometer scanning head and a focused laser beam over each sample. This pattern is related to traverse direction of the laser beam scanning. Energy-dispersive X-ray spectroscopy (EDS) was used to find the elemental composition and Raman spectroscopy to characterize each oxide zone. Pulsed laser irradiation modified the composition of the stainless steel samples, affecting the concentration of the main components within each heat affected zone. The Raman spectra of the generated oxides have different intensity profiles, which suggest different oxide phases such as magnetite and maghemite. In addition, these oxides are not sensible to the laser power of the Raman system, as are the iron oxide powders reported in the literature. These experiments show that it is possible to generate periodic patterns of various iron oxide zones by laser irradiation, of stainless steel at ambient conditions, and that Raman spectroscopy is a useful punctual technique for the analysis and inspection of small oxide areas.