Accepted Manuscript Raman spectroscopic analysis of iron chromium oxide microspheres generated by nanosecond pulsed laser irradiation on stainless steel M. Ortiz-Morales, J.J. Soto-Bernal, C. Frausto-Reyes, S.E. Acosta-Ortiz, R. Gonzalez-Mota, I. Rosales-Candelas PII: DOI: Reference:
S1386-1425(15)00311-X http://dx.doi.org/10.1016/j.saa.2015.03.015 SAA 13429
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
20 October 2014 24 February 2015 1 March 2015
Please cite this article as: M. Ortiz-Morales, J.J. Soto-Bernal, C. Frausto-Reyes, S.E. Acosta-Ortiz, R. GonzalezMota, I. Rosales-Candelas, Raman spectroscopic analysis of iron chromium oxide microspheres generated by nanosecond pulsed laser irradiation on stainless steel, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.03.015
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Raman spectroscopic analysis of iron chromium oxide microspheres generated by nanosecond pulsed laser irradiation on stainless steel M. Ortiz-Morales*1,2, J. J. Soto-Bernal1, C. Frausto-Reyes2, S. E. Acosta-Ortiz3, R. 1 1 Gonzalez-Mota , I. Rosales-Candelas 1
Instituto Tecnológico de Aguascalientes, Lab. de Optoelectronica, Av. A. Lopez Mateos 1801 Ote. Fracc. Bonagens Aguascalientes, 20256, México 2 Centro de Investigaciones en Óptica, A.C. Prol. Constitución 607, Fracc. Reserva Loma Bonita Aguascalientes, 20200, México 3 Lasertech, S.A. de C.V. Blvd. Olivares Santana 113, Fracc. El Dorado, Aguascalientes, 20235, México
*Corresponding Author. Tel. +52 (449) 4428124; fax. +52(449)4428127 e-mail addresses: [email protected] (M. Ortiz-Morales) [email protected] (J. J. Soto-Bernal)
Abstract 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 m-1.7 m, 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. Keywords: Iron chromium oxide microspheres, Laser irradiation, Raman Spectroscopy
1.
Introduction
The search for novel methods to synthesize iron oxide micro and nanoparticles is in continuous development, mainly due to their importance in various industrial fields and their scientific interest. Some of their uses are in the food industry, chemical coatings, catalysts, biochemical sensors and medical devices, among others [1-5]. These particles have new and novel properties that are being extensively studied in order to find new and better applications. Iron Chromium has been studied due to its improved catalytic effects in certain reactions when compared to Fe or Cr catalysts by themselves and the synthesis of iron and chromium oxides has been extensively reviewed [6-8]. The main methods used to synthesize iron and chromium oxides are physical, chemical and biological. Among the chemical methods, the thermal decomposition method offers improved control over the size and shape of iron oxide nanoparticles, which depends on the precursor and temperature [9-10]. One of the physical methods is laser thermal oxidation, a relatively new technique where most of the parameters involved are controlled in order to generate the appropriate oxide (with novel structures) on the surface of metallic materials [11-13]. Moreover, thermal effects can generate different microscopic morphologies and different phases on the surface of the samples, resulting in changes in the properties of the surface [14-15]. One of these changes involves the formation of spherical particles, mainly due to the heating effect generated on the surface by the focused laser and parameters such as scan speed, laser power, pulse width and frequency, among others. These particles are randomly generated by the heat induced by the laser spot and randomly distributed over the laser interaction zone; their composition depends on the original elemental composition of the sample, according to the elements with higher weight percentage (wt%) that are distributed over the surface. The size of these particles ranges from hundreds of nanometers to a few microns. In a previous work, Ortiz-Morales et al. conducted an experimental study on the generation of micro iron-oxide zones in order to identify the micro-oxide areas produced by laser irradiation on stainless steel plates [16]. There were some doubts regarding the Raman spectra of a particular area that presented two main Raman bands at 488 cm-1 and 675 cm-1; thus, it was carried out a study on the evolution of the oxide generated in this area and found its Raman spectrum as a function of laser power. This experiment allowed us to find that this oxide area was composed of a thin film of iron chromium oxide attached to the sample surface and microspheres (MS) of different sizes grouped in clusters.
The purpose of this work was to analyze the microspheres generated by a focused spot laser on the surface of stainless steel plates, to characterize the effect of laser power in the microspheres and to find the correlation between the main components of the sample and the laser power applied.
2.
Experimental setup
Two samples of commercial stainless steel plates with a thickness of 2 mm were used in this experiment, SE304 and SE430; they were cut into pieces with dimensions of 25 mm x 50 mm, cleaned with deionized water and dried in air. For irradiation, the samples were mounted on a fixed table at the focal length of the Ftheta lens of an Ytterbium pulsed fiber laser (IPG Photonics, model YLP-1-100-30-30HC) with a beam focused diameter of about 55 μm, an average output power of about 30 W and a wavelength of 1064 nm. The samples were irradiated using 10% to 99% of the maximum laser power (5 W and 29 W of average power, respectively) in 10% increments of laser power on ten 6 mm squares, a square for each percentage value. The width and repetition rate of the laser pulse used for irradiation were about 120 ns and 80 KHz, respectively. Each marked square had a hatch pattern, with spacing between lines of 0.2 mm. The laser scan was done using a scanning speed of 80 mm/s and three scanning cycles. Laser power was measured using a Gentec Power Meter model UNO and a power detector model UP19K-150W-H5. The Raman spectra of the microspheres were measured using a Micro-Raman (Renishaw system 1000B) with a 600 lines/mm grating, a CCD camera (Rem Cam 1024 × 256 pixels), focusing its 830 nm wavelength laser beam (with a spot-size of about 2 μm) in a back scattering geometry onto the sample [17], using the 50X objective of a Leica (DMLM) microscope. The instrument was calibrated using the 520 cm−1 Raman line of a silicon wafer. For data acquisition, Grams software was used. Measurements were made at several points in each area where the microspheres were present and along several lines for each marked square for every value of laser power applied. A representative spectrum is shown here. The Raman spectra were normalized to the most intense peak, without any previous base line correction or smoothing. The elemental composition of the microspheres was determined with EnergyDispersive X-ray Spectroscopy (EDS), by using a Scanning Electron Microscope system (SEM, JEOL JSM-5900LV). The SEM system was also used to measure the size of the microspheres. All measurements were made on the sample surface, in the zones with microspheres.
3.
Results
3.1. Samples before irradiation
Using the EDS elemental analysis, the main components of the samples were determined, that is, those with the highest concentration in each sample, and it was found that both samples contained mostly Cr and Fe. Table 1 shows the weight % of the components of the samples, denoted as S1 for SE304 and S2 for SE430.
3.2. Irradiated samples
For 10% and 20% of laser power, there were no visible laser effects on the samples, neither with the SEM system (not shown). Figure 1 shows SEM images of a section of sample S1, where the marked pattern can be observed, as well as a detail of the main laser interaction zone, in this case for 50% of laser power. Figure 2 shows SEM images of the laser irradiated sample S1, from 30% to 99% of laser power. With 30%, a laser heat-affected zone began to appear, and with 40% there was a clear visible laser effect on the sample surface; however, there were no visible features, as it can be observed in Figure 2a and 2b, respectively. With 50%, some features began to appear throughout the main laser interaction zone in all the lines of the marked pattern. From the SEM images it can be observed that these features seem like microspheres (MS), as is shown in Figure 2c. The generated microspheres can be clearly seen starting from 50% to 99% of laser power. The EDS analysis showed that the laser-affected zones without microspheres (see figure 2a and 2b) vary mainly with respect to the percentage composition of O, Cr and Fe; this can be observed in the Table 2. For 30% and 40% of laser power, there was an increase of Oxygen and Chromium, but Iron content decreases. It is worth mentioning that the EDS measurements were done at the center of the laser heataffected zone. From 50% to 99% of laser power, the chromium content of the microspheres increases as laser power increases, while iron content decreases. Certainly, the presence and variation of oxygen content implies that there is an oxide. It is also remarkable the way in which the microspheres began to arrange themselves along the scanning direction of the laser at the edge of the main laser interaction zone (see Figure 2d). This is probably due to the tide effect produced by the laser beam as it passes along each line. Table 2 also shows that the maximum percentage of Oxygen
and Chromium is related to the minimum percentage of iron and the maximum laser power applied to the sample. Using the measuring tool of the SEM system, the average diameter of the microspheres was computed; for the biggest ones it was ~1.7 microns, while for the smallest ones it was ~0.2 microns, not taking into account some microspheres that appeared to be deeper into the oxide material and seem to be smaller; the average diameter of all microspheres was practically the same, without regard for the laser power applied. Figure 3 shows the SEM images for sample S2, in which the behavior of the material to laser irradiation is similar to that of sample S1, except for the composition percentage, as it can be seen in Table 2. The chromium and iron content is different from sample S1. For example, in sample S1 there is a maximum chromium and oxygen content of about 33 wt% and 20 wt%, respectively, and a minimum iron content about 32 wt%; but in S2 there is a maximum chromium content of about 22 wt%, a minimum iron content about 62 wt% and a markedly different oxygen content of only 9%. However, the increasing-decreasing tendency of the composition of the main elements, concerning laser power, was similar. Table 2 shows that the percentage composition of the main components shown in Table 1 changed for every value of laser power applied; the amount of oxygen indicates the presence of oxides on the sample surface. The ratio of Cr-Fe changed compared to the non irradiated samples, as shown in Table 3. For example, the Cr-Fe ratio for sample S1 increased from 0.4 to 1.0, suggesting that there was more ironchromium oxide in the microspheres when 99% of laser power was used than with 50% of laser power; the same occurred for sample S2, in which the Cr-Fe ratio increased from 0.222 to 0.350. This difference between the Cr-Fe ratios for S1 and S2 is possibly due to the iron-chromium content of each sample; sample S1 has more chromium and less iron than S2, as it can be seen in Table 1. It can also be noticed that the microspheres of sample S1 have a higher percentage of oxygen and chromium with 99% of laser power. However, the chromium content of sample S2 does not present the same behavior than any of the main components of S1. Table 3 also shows that O/Cr ratios are greater than O/Fe ratios, except for 90% and 99% of laser power in S1, where these ratios are almost the same.
3.3. Raman spectroscopy
Because Raman spectroscopy is a punctual technique, it was used to analyze the main zones affected by the laser heat and the microspheres produced in the areas where they appeared; this technique was also used to assess the association between the oxide areas and microspheres and the EDS results. Figure 4 shows the Raman spectra of the microspheres of sample S1; in these spectra it can be noticed that there are two main bands at ~675 cm-1 and ~488 cm-1 and a shoulder at about 630 cm-1. Raman spectroscopic studies established that the characteristic band around 670 cm-1 corresponds to Fe3O4 [18-28]; this Raman band appeared with all values of laser power, and only with 30% (not shown) and 40% of laser power this band appeared alone. Figure 5 shows the Raman spectra of microspheres for S2, the same bands can be seen in sample S1; however, the band at ~488 cm-1 for sample S2 has a lower Raman intensity compared with the spectra of the microspheres for sample S1, which can be associated with the Cr/Fe ratio, as is shown in Table 3. In addition, the shoulder at ~630 cm-1 is less noticeable in sample S2, which is also possibly related to the chromium oxide content [29], since it has the same behavior as the 488 cm-1 Raman band. According to J. E. Maslar et al. and O. Monnereau et al, the Raman band at 488 cm-1 is related to chromium oxide Cr8O21 [30-31]; however, to our knowledge, this is the first time that the iron chromium oxide content of microspheres could be related to the laser power applied when using laser thermal oxidation. A Raman band around 675 cm-1 can be noticed in the areas of both samples irradiated with 30% and 40% of laser power; the composition of those areas is similar in both samples, which could indicate the presence of iron oxide. However, there are no microspheres (see Figures 2a, 2b, 3a, 3b). In both samples, the Raman spectrum for a laser power of 40% does not show the band at ~488 cm-1, which may indicate that this area does not contain chromium oxide, given that this band is related to chromium oxide. The presence of oxygen in the EDS analysis for S1 and S2 for 30% and 40% of laser power may indicate the presence of chromium but not of chromium oxide, as metals does not give any Raman signal and the band around 488 cm-1 is related to chromium oxide, while there is only iron oxide according to the Raman band at 675 cm 1
. In order to find the peak ratio of the two main bands in each Raman spectrum,
fluorescence background reduction was performed numerically, following the methodology reported by Perez–Pueyo [32], who used mathematical morphology to remove the background from Raman spectra without modifying the Raman bands (not shown). Table 4 presents the peak ratios of Raman spectra for samples S1 and S2 (488 cm-1/675 cm-1).
Raman analysis of microspheres showed the same tendency of Chromium oxide content as EDS analysis of the microspheres, that is, a direct relationship to the laser power applied. Laser thermal oxidation is a relatively new technique that could be used to synthesize iron oxide and iron chromium oxide microspheres.
4.
Conclusions
Iron Chromium oxide microspheres with different Cr/Fe ratios were generated on the surface of stainless steel samples by pulsed laser irradiation. These microspheres were analyzed by Raman spectroscopy and EDS, and it was found that the Cr/Fe ratios were dependent on the laser power applied. These results have shown that it is possible to establish a correlation between the two main bands at 675 cm-1 and 488 cm-1, the ratio of which would be proportional to the Iron-chromium oxide content in the samples. The microspheres were generated with a certain chromium and iron content percentage, which could be related to the iron and chromium content of the samples and the laser power applied to them. Both analysis techniques revealed that the iron chromium oxide content in the microspheres is directly related to the laser power density applied. Finally, to our knowledge, there are no other reports that relate the Raman spectral bands at 488 cm-1 and 675 cm-1 with iron chromium oxide and the 488 cm-1 band with chromium oxide, nor the generated iron chromium-oxide micro-spheres with the laser power applied.
Acknowledgements
Authors would like to acknowledge to Centro de Investigaciones en Optica and LaserTech S.A. de C.V. for the opportunity to make this work and the opportunity to continue working on this field.
References 1. P. Xu, G. M. Zeng, D. L. Huang et al., “Use of iron oxide nanomaterials in wastewater treatment: a review,” Science of the Total Environment, 424 (2012) 1– 10. 2. Pragnesh N. Dave and Lakhan V. Chopda, “Application of Iron Oxide Nanomaterials for the Removal of Heavy Metals,” Journal of Nanotechnology, (2014) 14, http://dx.doi.org/10.1155/2014/398569. 3. D.P. Nguyen et al, “Crystallization and magnetic properties of amorphous iron– chromium oxide nanoparticles synthesized by sonochemistry”, Adv. Nat. Sci.: Nanosci. Nanotechnol., 2012, 3, doi:10.1088/2043-6262/3/1/015017 4. C. Nithya Shanthi, Rakesh Gupta, Arun Kumar Mahato, “Traditional and emerging applications of microspheres: A Review”, International Journal of Pharm. Tech. Research 2 (2010) 675-681. 5. D. P. Nguyen, X. S. Trinh, T. C. Hoang, N. D. Nguyen, V. T. Le, M. H. Nguyen, H. N. Nguyen and H. H. Nguyen, Amorphous iron-chromium oxide nanoparticles prepared by sonochemistry, J. Non-Cryst. Solids, 358 (2012) 537-543. 6. A. Khaleel, I. Shehadi and M. Al-Shamisi, Nanostructured chromium-iron mixed oxides: Physicochemical properties and catalytic activity, Colloids and Surfaces A: Physicochem. Eng. Aspects, 355 (2010) 75-82. 7. M. Sorescu, L. Diamandescu, D. Tarabasanu-Mihaila, S. Krupa and M. Feder, Iron and chromium mixed-oxide nanocomposites, Hyperfine Interact., 196 (2010) 359. 8. X. Liu, K. Shen, Y. Wang, Y. Wang, Y. Guo, Y. Guo, Z. Yong and G. Lu, Preparation and catalytic properties of Pt supported Fe–Cr mixed oxide catalysts in the aqueous-phase reforming of ethylene glycol, Catal. Commun. 9 (2008) 2316. 9. T. Hyeon, S. S. Lee, J. Park, Y. Chung, and B. N. Hyon, “Synthesis of highly crystalline and monodisperse maghemite nanocrystallites without a size-selection process,” Journal of the American Chemical Society, 123 (2001) 12798–12801. 10. S. Belaid, S. Laurent, M. Vermeersch, L. V. Elst, D. P. Morga, and R. N. Muller, “A new approach to follow the formation of iron oxide nanoparticles synthesized by thermal decomposition”, Nanotechnology, vol. 24, no. 5. 11. J. Yang, J.S. Lian, Q.Z. Dong, Z.X. Guo, “Nano-structured films formed on the AISI 329 stainless steel by Nd-YAG pulsed laser irradiation”, Appl. Surf. Sci. 229 (2004) 2-8. 12. Chengyun Cui, Jiandong Hu, Yuhua Liu, Zuoxing Guo, “Microstructure evolution on the surface of stainless steel by Nd:YAG pulsed laser irradiation”, Appl. Surf. Sci. 254 (2008) 3442–3448. 13. B. Raillard, L. Gouton, E. Ramos-Moore, S. Grandthyll, F. Müller, F. Mücklich, Ablation effects of femtosecond laser functionalization on steel surfaces, Surface & Coatings Technology 207 (2012) 102–109. 14. N. Watanabe, N. Takahashi, K. Tsushima, Non-equilibrium garnet films grown by pulsed laser deposition, Mater. Chem. Phys. 54 (1998) 173–176. 15. Chengyun Cui, Jiandong Hu, Yuhua Liu, Kun Gao, Zuoxing Guo, Formation of nano-crystalline and amorphous phases on the surface of stainless steel by NdYAG pulsed laser irradiation, Applied Surface Science 254 (2008) 6779–6782. 16. M. Ortiz-Morales, C. Frausto-Reyes, J.J. Soto-Bernal, S.E. Acosta-Ortiz, R. Gonzalez-Mota, I. Rosales-Candelas, “Infrared nanosecond pulsed laser irradiation of stainless steel: Micro iron-oxide zones generation”, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 681–685. 17. J. Medina-Valtierra, C. Frausto-Reyes, M. Ortiz-Morales, Phase transformation in semi-transparent TiO2 films irradiated with CO2 laser, Mater. Lett. 66 (2012) 172– 175.
18. S. C. Tjong, Laser raman spectroscopic studies of the surface oxides formed On iron chromium alloys at elevated temperatures, Mat. Res. Bull. 18 (1983) 157-165. 19. Ming Chen, Jinfu Shu, Xiande Xie and Ho-kwang Mao. Natural CaTi2O4structured FeCr2O4 polymorph in the Suizhou meteorite and its significance in mantle mineralogy. Geochimica et Cosmochimica Acta 67 (2003) 3937–3942. 20. C. A. Melendres, M. Pankuch, Y.S. Li, R.L. Knight, Surface enhanced Raman spectroelectrochemical studies of the corrosion films on iron and chromium in aqueous solution environments, Electrochimica Acta 37 (1992) 2747. 21. G. Xi, C. Wang, X. Wang, The Oriented Self-Assembly of Magnetic Fe3O4 Nanoparticles into Monodisperse Microspheres and Their Use as Substrates in the Formation of Fe3O4 Nanorods, European Journal of Inorganic Chemistry, 3 (2008) 425-431. 22. O. N. Shebanova, P. Lazor, Raman spectroscopic study of magnetite (FeFe2O4): a new assignment for the vibrational spectrum, Journal of Solid State Chemistry 174 (2003) 424-430. 23. N. Pinna, S. Grancharov, P. Beato, P. Bonville, Magnetite Nanocrystals: Nonaqueous Synthesis, Characterization, and Solubility, Chemistry of Materials 17 (2005) 3044-3049. 24. J.E. Maslar, W.S. Hurst, W.J. Bowers, J.H. Hendricks, M.I. Aquino, In Situ Raman Spectroscopic Investigation of Aqueous Iron Corrosion at Elevated Temperatures and Pressures, Journal of the Electrochemical Society 147 (2000) 2532. 25. D.L.A. de. Faria, S.V. Silva, M.T. de Oliveria, Raman microspectroscopy of some iron oxides and oxyhydroxides, Journal of Raman Spectroscopy 28 (1997) 873. 26. R.K.S. Raman, B. Gleeson, D.J. Young, Laser Raman spectroscopy: a technique for rapid characterization of oxide scale layers Materials Science and Technology 14 (1998) 373. 27. Ying-Sing Li, JeffreyS.Church, AndreaL.Woodhead, Infrared and Raman spectroscopic studies on iron oxide magnetic nano-particles and their surface modifications, Journal of Magnetism and Magnetic Materials 324 (2012) 1543–1550 28. K.F. McCarty and D.R. Boehme. A Raman study of the systems Fe3−xCrxO4 and Fe2−xCrxO3, Journal of Solid State Chemistry 79 (1989) 19–27. 29. Ming Chen, Jinfu Shu, Xiande Xie and Ho-kwang Mao. Natural CaTi2O4-structured FeCr2O4 polymorph in the Suizhou meteorite and its significance in mantle mineralogy. Geochimica et Cosmochimica Acta 67 (2003) 3937–3942. 30. O. Monnereau, et al., Chromium oxides mixtures in PLD films investigated by Raman spectroscopy, Journal Of Optoelectronics and Advanced Materials 12 (2010) 1752-1758 31. J. E. Maslar, W. S. Hurst, T. A. Vanderah and I. Levin, The Raman spectra of Cr3O8 and Cr2O5, J. Raman Spectrosc. 32 (2001) 201–206. 32. R. Perez-Pueyo, M. J. Soneira, and S. Ruiz-Moreno, “Morphology-based automated baseline removal for Raman spectra of artistic pigments,” Appl. Spectrosc. 64 (2010) 595–600.
Fig. 1. SEM image of sample S1; (a) irradiated pattern for 50% of laser power; (b) amplified detail. Fig. 2. SEM Images of sample S1 irradiated with (a) 30%, (b) 40%, (c) 50%, (d) 70%, (e) 80% and (f) 99% of laser power. Fig. 3. SEM Images of sample S2 irradiated with (a) 30%, (b) 40%, (c) 50%, (d) 70%, (e) 80% and (f) 99% of laser power. Fig. 4. Normalized Raman spectra of microspheres, showing the two main bands for Chromium oxide and Iron oxide centered around 488 cm-1 and 675 cm-1, respectively, for S1. Fig. 5. Normalized Raman spectra of microspheres for S2, showing the two bands for Chromium oxide and Iron oxide centered around 488 cm-1 and ~675 cm-1, respectively. Table 1 EDS analysis of the elemental composition of stainless steel samples S1and S2 before laser irradiation (elements with higher wt%). Sample Elements Cr Fe Ni WT % S1 17.33 68.71 7.63 S2 15.85 80.28 ----
Table 2 Composition of microspheres for each value of laser power for S1 and S2; the main zones affected by laser heat (30% and 40%) appear in bold (elements with higher wt%). Laser Power 30 40 50 60 70 80 90 99 % Avg. Laser Power Watts Element
O Cr Fe O Cr Fe
5.0
8.0
11.5
15.5
Sample S1 Composition Percentage 5.05 19.48 12.43 14.24 15.60 19.88 22.09 29.02 62.76 51.54 54.07 44.97 Sample S2 Composition Percentage 3.90 17.84 11.22 10.27 15.35 14.91 14.45 14.67 75.35 64.96 64.99 70.37
18.5
22
25.5
29.0
12.42 27.82 45.64
12.63 29.00 45.90
15.80 32.86 38.71
19.92 33.10 31.95
14.87 11.65 68.16
11.74 18.98 62.38
11.97 21.63 61.72
9.79 21.46 64.91
Table 3 Ratios of the main components of the microspheres, with the main areas affected by laser heat in bold. Laser Non 30 40 50 60 70 80 90 99 power % Irradiated Avg. Laser Power Watts Non
5.0
8.0
11.5
15.5
18.5
22.0
25.5
29.0
0.249 0.324 0.080
0.386 0.980 0.378
0.409 0.563 0.230
0.645 0.491 0.317
0.610 0.446 0.272
0.643 0.436 0.280
0.849 0.481 0.408
1.036 0.602 0.623
0.204 0.254 0.052
0.230 1.197 0.275
0.222 0.776 0.173
0.208 0.700 0.146
0.171 1.276 0.218
0.304 0.619 0.188
0.350 0.553 0.194
0.331 0.456 0.151
Irradiated S1 Ratios Cr/Fe 0.252 O/Cr ---O/Fe ---S2 Ratios Cr/Fe 0.197 O/Cr ---O/Fe ----
Table 4 Peak ratios (488 cm-1/675 cm-1) of Raman spectra of samples S1 and S2 for different laser powers. Laser Power Peak ratio Peak ratio % SE304 SE430 40 0.025 0.007 50 0.166 0.027 60 0.250 0.211 70 0.384 0.174 80 0.608 0.345 90 0.723 0.333 99 0.914 0.364
Graphical abstract
Highlights Generation of Iron chromium oxide microspheres. Commercial stainless steel plates irradiated with an Ytterbium pulsed fiber laser. Raman spectroscopy analysis of iron chromium oxide microspheres. Energy-Dispersive X-ray spectroscopy analysis of Iron chromium oxide microspheres. Iron chromium oxide ratio is related to the applied laser power.
S1386-1425(15)00311-X http://dx.doi.org/10.1016/j.saa.2015.03.015 SAA 13429
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
20 October 2014 24 February 2015 1 March 2015
Please cite this article as: M. Ortiz-Morales, J.J. Soto-Bernal, C. Frausto-Reyes, S.E. Acosta-Ortiz, R. GonzalezMota, I. Rosales-Candelas, Raman spectroscopic analysis of iron chromium oxide microspheres generated by nanosecond pulsed laser irradiation on stainless steel, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.03.015
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Raman spectroscopic analysis of iron chromium oxide microspheres generated by nanosecond pulsed laser irradiation on stainless steel M. Ortiz-Morales*1,2, J. J. Soto-Bernal1, C. Frausto-Reyes2, S. E. Acosta-Ortiz3, R. 1 1 Gonzalez-Mota , I. Rosales-Candelas 1
Instituto Tecnológico de Aguascalientes, Lab. de Optoelectronica, Av. A. Lopez Mateos 1801 Ote. Fracc. Bonagens Aguascalientes, 20256, México 2 Centro de Investigaciones en Óptica, A.C. Prol. Constitución 607, Fracc. Reserva Loma Bonita Aguascalientes, 20200, México 3 Lasertech, S.A. de C.V. Blvd. Olivares Santana 113, Fracc. El Dorado, Aguascalientes, 20235, México
*Corresponding Author. Tel. +52 (449) 4428124; fax. +52(449)4428127 e-mail addresses: [email protected] (M. Ortiz-Morales) [email protected] (J. J. Soto-Bernal)
Abstract 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 m-1.7 m, 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. Keywords: Iron chromium oxide microspheres, Laser irradiation, Raman Spectroscopy
1.
Introduction
The search for novel methods to synthesize iron oxide micro and nanoparticles is in continuous development, mainly due to their importance in various industrial fields and their scientific interest. Some of their uses are in the food industry, chemical coatings, catalysts, biochemical sensors and medical devices, among others [1-5]. These particles have new and novel properties that are being extensively studied in order to find new and better applications. Iron Chromium has been studied due to its improved catalytic effects in certain reactions when compared to Fe or Cr catalysts by themselves and the synthesis of iron and chromium oxides has been extensively reviewed [6-8]. The main methods used to synthesize iron and chromium oxides are physical, chemical and biological. Among the chemical methods, the thermal decomposition method offers improved control over the size and shape of iron oxide nanoparticles, which depends on the precursor and temperature [9-10]. One of the physical methods is laser thermal oxidation, a relatively new technique where most of the parameters involved are controlled in order to generate the appropriate oxide (with novel structures) on the surface of metallic materials [11-13]. Moreover, thermal effects can generate different microscopic morphologies and different phases on the surface of the samples, resulting in changes in the properties of the surface [14-15]. One of these changes involves the formation of spherical particles, mainly due to the heating effect generated on the surface by the focused laser and parameters such as scan speed, laser power, pulse width and frequency, among others. These particles are randomly generated by the heat induced by the laser spot and randomly distributed over the laser interaction zone; their composition depends on the original elemental composition of the sample, according to the elements with higher weight percentage (wt%) that are distributed over the surface. The size of these particles ranges from hundreds of nanometers to a few microns. In a previous work, Ortiz-Morales et al. conducted an experimental study on the generation of micro iron-oxide zones in order to identify the micro-oxide areas produced by laser irradiation on stainless steel plates [16]. There were some doubts regarding the Raman spectra of a particular area that presented two main Raman bands at 488 cm-1 and 675 cm-1; thus, it was carried out a study on the evolution of the oxide generated in this area and found its Raman spectrum as a function of laser power. This experiment allowed us to find that this oxide area was composed of a thin film of iron chromium oxide attached to the sample surface and microspheres (MS) of different sizes grouped in clusters.
The purpose of this work was to analyze the microspheres generated by a focused spot laser on the surface of stainless steel plates, to characterize the effect of laser power in the microspheres and to find the correlation between the main components of the sample and the laser power applied.
2.
Experimental setup
Two samples of commercial stainless steel plates with a thickness of 2 mm were used in this experiment, SE304 and SE430; they were cut into pieces with dimensions of 25 mm x 50 mm, cleaned with deionized water and dried in air. For irradiation, the samples were mounted on a fixed table at the focal length of the Ftheta lens of an Ytterbium pulsed fiber laser (IPG Photonics, model YLP-1-100-30-30HC) with a beam focused diameter of about 55 μm, an average output power of about 30 W and a wavelength of 1064 nm. The samples were irradiated using 10% to 99% of the maximum laser power (5 W and 29 W of average power, respectively) in 10% increments of laser power on ten 6 mm squares, a square for each percentage value. The width and repetition rate of the laser pulse used for irradiation were about 120 ns and 80 KHz, respectively. Each marked square had a hatch pattern, with spacing between lines of 0.2 mm. The laser scan was done using a scanning speed of 80 mm/s and three scanning cycles. Laser power was measured using a Gentec Power Meter model UNO and a power detector model UP19K-150W-H5. The Raman spectra of the microspheres were measured using a Micro-Raman (Renishaw system 1000B) with a 600 lines/mm grating, a CCD camera (Rem Cam 1024 × 256 pixels), focusing its 830 nm wavelength laser beam (with a spot-size of about 2 μm) in a back scattering geometry onto the sample [17], using the 50X objective of a Leica (DMLM) microscope. The instrument was calibrated using the 520 cm−1 Raman line of a silicon wafer. For data acquisition, Grams software was used. Measurements were made at several points in each area where the microspheres were present and along several lines for each marked square for every value of laser power applied. A representative spectrum is shown here. The Raman spectra were normalized to the most intense peak, without any previous base line correction or smoothing. The elemental composition of the microspheres was determined with EnergyDispersive X-ray Spectroscopy (EDS), by using a Scanning Electron Microscope system (SEM, JEOL JSM-5900LV). The SEM system was also used to measure the size of the microspheres. All measurements were made on the sample surface, in the zones with microspheres.
3.
Results
3.1. Samples before irradiation
Using the EDS elemental analysis, the main components of the samples were determined, that is, those with the highest concentration in each sample, and it was found that both samples contained mostly Cr and Fe. Table 1 shows the weight % of the components of the samples, denoted as S1 for SE304 and S2 for SE430.
3.2. Irradiated samples
For 10% and 20% of laser power, there were no visible laser effects on the samples, neither with the SEM system (not shown). Figure 1 shows SEM images of a section of sample S1, where the marked pattern can be observed, as well as a detail of the main laser interaction zone, in this case for 50% of laser power. Figure 2 shows SEM images of the laser irradiated sample S1, from 30% to 99% of laser power. With 30%, a laser heat-affected zone began to appear, and with 40% there was a clear visible laser effect on the sample surface; however, there were no visible features, as it can be observed in Figure 2a and 2b, respectively. With 50%, some features began to appear throughout the main laser interaction zone in all the lines of the marked pattern. From the SEM images it can be observed that these features seem like microspheres (MS), as is shown in Figure 2c. The generated microspheres can be clearly seen starting from 50% to 99% of laser power. The EDS analysis showed that the laser-affected zones without microspheres (see figure 2a and 2b) vary mainly with respect to the percentage composition of O, Cr and Fe; this can be observed in the Table 2. For 30% and 40% of laser power, there was an increase of Oxygen and Chromium, but Iron content decreases. It is worth mentioning that the EDS measurements were done at the center of the laser heataffected zone. From 50% to 99% of laser power, the chromium content of the microspheres increases as laser power increases, while iron content decreases. Certainly, the presence and variation of oxygen content implies that there is an oxide. It is also remarkable the way in which the microspheres began to arrange themselves along the scanning direction of the laser at the edge of the main laser interaction zone (see Figure 2d). This is probably due to the tide effect produced by the laser beam as it passes along each line. Table 2 also shows that the maximum percentage of Oxygen
and Chromium is related to the minimum percentage of iron and the maximum laser power applied to the sample. Using the measuring tool of the SEM system, the average diameter of the microspheres was computed; for the biggest ones it was ~1.7 microns, while for the smallest ones it was ~0.2 microns, not taking into account some microspheres that appeared to be deeper into the oxide material and seem to be smaller; the average diameter of all microspheres was practically the same, without regard for the laser power applied. Figure 3 shows the SEM images for sample S2, in which the behavior of the material to laser irradiation is similar to that of sample S1, except for the composition percentage, as it can be seen in Table 2. The chromium and iron content is different from sample S1. For example, in sample S1 there is a maximum chromium and oxygen content of about 33 wt% and 20 wt%, respectively, and a minimum iron content about 32 wt%; but in S2 there is a maximum chromium content of about 22 wt%, a minimum iron content about 62 wt% and a markedly different oxygen content of only 9%. However, the increasing-decreasing tendency of the composition of the main elements, concerning laser power, was similar. Table 2 shows that the percentage composition of the main components shown in Table 1 changed for every value of laser power applied; the amount of oxygen indicates the presence of oxides on the sample surface. The ratio of Cr-Fe changed compared to the non irradiated samples, as shown in Table 3. For example, the Cr-Fe ratio for sample S1 increased from 0.4 to 1.0, suggesting that there was more ironchromium oxide in the microspheres when 99% of laser power was used than with 50% of laser power; the same occurred for sample S2, in which the Cr-Fe ratio increased from 0.222 to 0.350. This difference between the Cr-Fe ratios for S1 and S2 is possibly due to the iron-chromium content of each sample; sample S1 has more chromium and less iron than S2, as it can be seen in Table 1. It can also be noticed that the microspheres of sample S1 have a higher percentage of oxygen and chromium with 99% of laser power. However, the chromium content of sample S2 does not present the same behavior than any of the main components of S1. Table 3 also shows that O/Cr ratios are greater than O/Fe ratios, except for 90% and 99% of laser power in S1, where these ratios are almost the same.
3.3. Raman spectroscopy
Because Raman spectroscopy is a punctual technique, it was used to analyze the main zones affected by the laser heat and the microspheres produced in the areas where they appeared; this technique was also used to assess the association between the oxide areas and microspheres and the EDS results. Figure 4 shows the Raman spectra of the microspheres of sample S1; in these spectra it can be noticed that there are two main bands at ~675 cm-1 and ~488 cm-1 and a shoulder at about 630 cm-1. Raman spectroscopic studies established that the characteristic band around 670 cm-1 corresponds to Fe3O4 [18-28]; this Raman band appeared with all values of laser power, and only with 30% (not shown) and 40% of laser power this band appeared alone. Figure 5 shows the Raman spectra of microspheres for S2, the same bands can be seen in sample S1; however, the band at ~488 cm-1 for sample S2 has a lower Raman intensity compared with the spectra of the microspheres for sample S1, which can be associated with the Cr/Fe ratio, as is shown in Table 3. In addition, the shoulder at ~630 cm-1 is less noticeable in sample S2, which is also possibly related to the chromium oxide content [29], since it has the same behavior as the 488 cm-1 Raman band. According to J. E. Maslar et al. and O. Monnereau et al, the Raman band at 488 cm-1 is related to chromium oxide Cr8O21 [30-31]; however, to our knowledge, this is the first time that the iron chromium oxide content of microspheres could be related to the laser power applied when using laser thermal oxidation. A Raman band around 675 cm-1 can be noticed in the areas of both samples irradiated with 30% and 40% of laser power; the composition of those areas is similar in both samples, which could indicate the presence of iron oxide. However, there are no microspheres (see Figures 2a, 2b, 3a, 3b). In both samples, the Raman spectrum for a laser power of 40% does not show the band at ~488 cm-1, which may indicate that this area does not contain chromium oxide, given that this band is related to chromium oxide. The presence of oxygen in the EDS analysis for S1 and S2 for 30% and 40% of laser power may indicate the presence of chromium but not of chromium oxide, as metals does not give any Raman signal and the band around 488 cm-1 is related to chromium oxide, while there is only iron oxide according to the Raman band at 675 cm 1
. In order to find the peak ratio of the two main bands in each Raman spectrum,
fluorescence background reduction was performed numerically, following the methodology reported by Perez–Pueyo [32], who used mathematical morphology to remove the background from Raman spectra without modifying the Raman bands (not shown). Table 4 presents the peak ratios of Raman spectra for samples S1 and S2 (488 cm-1/675 cm-1).
Raman analysis of microspheres showed the same tendency of Chromium oxide content as EDS analysis of the microspheres, that is, a direct relationship to the laser power applied. Laser thermal oxidation is a relatively new technique that could be used to synthesize iron oxide and iron chromium oxide microspheres.
4.
Conclusions
Iron Chromium oxide microspheres with different Cr/Fe ratios were generated on the surface of stainless steel samples by pulsed laser irradiation. These microspheres were analyzed by Raman spectroscopy and EDS, and it was found that the Cr/Fe ratios were dependent on the laser power applied. These results have shown that it is possible to establish a correlation between the two main bands at 675 cm-1 and 488 cm-1, the ratio of which would be proportional to the Iron-chromium oxide content in the samples. The microspheres were generated with a certain chromium and iron content percentage, which could be related to the iron and chromium content of the samples and the laser power applied to them. Both analysis techniques revealed that the iron chromium oxide content in the microspheres is directly related to the laser power density applied. Finally, to our knowledge, there are no other reports that relate the Raman spectral bands at 488 cm-1 and 675 cm-1 with iron chromium oxide and the 488 cm-1 band with chromium oxide, nor the generated iron chromium-oxide micro-spheres with the laser power applied.
Acknowledgements
Authors would like to acknowledge to Centro de Investigaciones en Optica and LaserTech S.A. de C.V. for the opportunity to make this work and the opportunity to continue working on this field.
References 1. P. Xu, G. M. Zeng, D. L. Huang et al., “Use of iron oxide nanomaterials in wastewater treatment: a review,” Science of the Total Environment, 424 (2012) 1– 10. 2. Pragnesh N. Dave and Lakhan V. Chopda, “Application of Iron Oxide Nanomaterials for the Removal of Heavy Metals,” Journal of Nanotechnology, (2014) 14, http://dx.doi.org/10.1155/2014/398569. 3. D.P. Nguyen et al, “Crystallization and magnetic properties of amorphous iron– chromium oxide nanoparticles synthesized by sonochemistry”, Adv. Nat. Sci.: Nanosci. Nanotechnol., 2012, 3, doi:10.1088/2043-6262/3/1/015017 4. C. Nithya Shanthi, Rakesh Gupta, Arun Kumar Mahato, “Traditional and emerging applications of microspheres: A Review”, International Journal of Pharm. Tech. Research 2 (2010) 675-681. 5. D. P. Nguyen, X. S. Trinh, T. C. Hoang, N. D. Nguyen, V. T. Le, M. H. Nguyen, H. N. Nguyen and H. H. Nguyen, Amorphous iron-chromium oxide nanoparticles prepared by sonochemistry, J. Non-Cryst. Solids, 358 (2012) 537-543. 6. A. Khaleel, I. Shehadi and M. Al-Shamisi, Nanostructured chromium-iron mixed oxides: Physicochemical properties and catalytic activity, Colloids and Surfaces A: Physicochem. Eng. Aspects, 355 (2010) 75-82. 7. M. Sorescu, L. Diamandescu, D. Tarabasanu-Mihaila, S. Krupa and M. Feder, Iron and chromium mixed-oxide nanocomposites, Hyperfine Interact., 196 (2010) 359. 8. X. Liu, K. Shen, Y. Wang, Y. Wang, Y. Guo, Y. Guo, Z. Yong and G. Lu, Preparation and catalytic properties of Pt supported Fe–Cr mixed oxide catalysts in the aqueous-phase reforming of ethylene glycol, Catal. Commun. 9 (2008) 2316. 9. T. Hyeon, S. S. Lee, J. Park, Y. Chung, and B. N. Hyon, “Synthesis of highly crystalline and monodisperse maghemite nanocrystallites without a size-selection process,” Journal of the American Chemical Society, 123 (2001) 12798–12801. 10. S. Belaid, S. Laurent, M. Vermeersch, L. V. Elst, D. P. Morga, and R. N. Muller, “A new approach to follow the formation of iron oxide nanoparticles synthesized by thermal decomposition”, Nanotechnology, vol. 24, no. 5. 11. J. Yang, J.S. Lian, Q.Z. Dong, Z.X. Guo, “Nano-structured films formed on the AISI 329 stainless steel by Nd-YAG pulsed laser irradiation”, Appl. Surf. Sci. 229 (2004) 2-8. 12. Chengyun Cui, Jiandong Hu, Yuhua Liu, Zuoxing Guo, “Microstructure evolution on the surface of stainless steel by Nd:YAG pulsed laser irradiation”, Appl. Surf. Sci. 254 (2008) 3442–3448. 13. B. Raillard, L. Gouton, E. Ramos-Moore, S. Grandthyll, F. Müller, F. Mücklich, Ablation effects of femtosecond laser functionalization on steel surfaces, Surface & Coatings Technology 207 (2012) 102–109. 14. N. Watanabe, N. Takahashi, K. Tsushima, Non-equilibrium garnet films grown by pulsed laser deposition, Mater. Chem. Phys. 54 (1998) 173–176. 15. Chengyun Cui, Jiandong Hu, Yuhua Liu, Kun Gao, Zuoxing Guo, Formation of nano-crystalline and amorphous phases on the surface of stainless steel by NdYAG pulsed laser irradiation, Applied Surface Science 254 (2008) 6779–6782. 16. M. Ortiz-Morales, C. Frausto-Reyes, J.J. Soto-Bernal, S.E. Acosta-Ortiz, R. Gonzalez-Mota, I. Rosales-Candelas, “Infrared nanosecond pulsed laser irradiation of stainless steel: Micro iron-oxide zones generation”, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 681–685. 17. J. Medina-Valtierra, C. Frausto-Reyes, M. Ortiz-Morales, Phase transformation in semi-transparent TiO2 films irradiated with CO2 laser, Mater. Lett. 66 (2012) 172– 175.
18. S. C. Tjong, Laser raman spectroscopic studies of the surface oxides formed On iron chromium alloys at elevated temperatures, Mat. Res. Bull. 18 (1983) 157-165. 19. Ming Chen, Jinfu Shu, Xiande Xie and Ho-kwang Mao. Natural CaTi2O4structured FeCr2O4 polymorph in the Suizhou meteorite and its significance in mantle mineralogy. Geochimica et Cosmochimica Acta 67 (2003) 3937–3942. 20. C. A. Melendres, M. Pankuch, Y.S. Li, R.L. Knight, Surface enhanced Raman spectroelectrochemical studies of the corrosion films on iron and chromium in aqueous solution environments, Electrochimica Acta 37 (1992) 2747. 21. G. Xi, C. Wang, X. Wang, The Oriented Self-Assembly of Magnetic Fe3O4 Nanoparticles into Monodisperse Microspheres and Their Use as Substrates in the Formation of Fe3O4 Nanorods, European Journal of Inorganic Chemistry, 3 (2008) 425-431. 22. O. N. Shebanova, P. Lazor, Raman spectroscopic study of magnetite (FeFe2O4): a new assignment for the vibrational spectrum, Journal of Solid State Chemistry 174 (2003) 424-430. 23. N. Pinna, S. Grancharov, P. Beato, P. Bonville, Magnetite Nanocrystals: Nonaqueous Synthesis, Characterization, and Solubility, Chemistry of Materials 17 (2005) 3044-3049. 24. J.E. Maslar, W.S. Hurst, W.J. Bowers, J.H. Hendricks, M.I. Aquino, In Situ Raman Spectroscopic Investigation of Aqueous Iron Corrosion at Elevated Temperatures and Pressures, Journal of the Electrochemical Society 147 (2000) 2532. 25. D.L.A. de. Faria, S.V. Silva, M.T. de Oliveria, Raman microspectroscopy of some iron oxides and oxyhydroxides, Journal of Raman Spectroscopy 28 (1997) 873. 26. R.K.S. Raman, B. Gleeson, D.J. Young, Laser Raman spectroscopy: a technique for rapid characterization of oxide scale layers Materials Science and Technology 14 (1998) 373. 27. Ying-Sing Li, JeffreyS.Church, AndreaL.Woodhead, Infrared and Raman spectroscopic studies on iron oxide magnetic nano-particles and their surface modifications, Journal of Magnetism and Magnetic Materials 324 (2012) 1543–1550 28. K.F. McCarty and D.R. Boehme. A Raman study of the systems Fe3−xCrxO4 and Fe2−xCrxO3, Journal of Solid State Chemistry 79 (1989) 19–27. 29. Ming Chen, Jinfu Shu, Xiande Xie and Ho-kwang Mao. Natural CaTi2O4-structured FeCr2O4 polymorph in the Suizhou meteorite and its significance in mantle mineralogy. Geochimica et Cosmochimica Acta 67 (2003) 3937–3942. 30. O. Monnereau, et al., Chromium oxides mixtures in PLD films investigated by Raman spectroscopy, Journal Of Optoelectronics and Advanced Materials 12 (2010) 1752-1758 31. J. E. Maslar, W. S. Hurst, T. A. Vanderah and I. Levin, The Raman spectra of Cr3O8 and Cr2O5, J. Raman Spectrosc. 32 (2001) 201–206. 32. R. Perez-Pueyo, M. J. Soneira, and S. Ruiz-Moreno, “Morphology-based automated baseline removal for Raman spectra of artistic pigments,” Appl. Spectrosc. 64 (2010) 595–600.
Fig. 1. SEM image of sample S1; (a) irradiated pattern for 50% of laser power; (b) amplified detail. Fig. 2. SEM Images of sample S1 irradiated with (a) 30%, (b) 40%, (c) 50%, (d) 70%, (e) 80% and (f) 99% of laser power. Fig. 3. SEM Images of sample S2 irradiated with (a) 30%, (b) 40%, (c) 50%, (d) 70%, (e) 80% and (f) 99% of laser power. Fig. 4. Normalized Raman spectra of microspheres, showing the two main bands for Chromium oxide and Iron oxide centered around 488 cm-1 and 675 cm-1, respectively, for S1. Fig. 5. Normalized Raman spectra of microspheres for S2, showing the two bands for Chromium oxide and Iron oxide centered around 488 cm-1 and ~675 cm-1, respectively. Table 1 EDS analysis of the elemental composition of stainless steel samples S1and S2 before laser irradiation (elements with higher wt%). Sample Elements Cr Fe Ni WT % S1 17.33 68.71 7.63 S2 15.85 80.28 ----
Table 2 Composition of microspheres for each value of laser power for S1 and S2; the main zones affected by laser heat (30% and 40%) appear in bold (elements with higher wt%). Laser Power 30 40 50 60 70 80 90 99 % Avg. Laser Power Watts Element
O Cr Fe O Cr Fe
5.0
8.0
11.5
15.5
Sample S1 Composition Percentage 5.05 19.48 12.43 14.24 15.60 19.88 22.09 29.02 62.76 51.54 54.07 44.97 Sample S2 Composition Percentage 3.90 17.84 11.22 10.27 15.35 14.91 14.45 14.67 75.35 64.96 64.99 70.37
18.5
22
25.5
29.0
12.42 27.82 45.64
12.63 29.00 45.90
15.80 32.86 38.71
19.92 33.10 31.95
14.87 11.65 68.16
11.74 18.98 62.38
11.97 21.63 61.72
9.79 21.46 64.91
Table 3 Ratios of the main components of the microspheres, with the main areas affected by laser heat in bold. Laser Non 30 40 50 60 70 80 90 99 power % Irradiated Avg. Laser Power Watts Non
5.0
8.0
11.5
15.5
18.5
22.0
25.5
29.0
0.249 0.324 0.080
0.386 0.980 0.378
0.409 0.563 0.230
0.645 0.491 0.317
0.610 0.446 0.272
0.643 0.436 0.280
0.849 0.481 0.408
1.036 0.602 0.623
0.204 0.254 0.052
0.230 1.197 0.275
0.222 0.776 0.173
0.208 0.700 0.146
0.171 1.276 0.218
0.304 0.619 0.188
0.350 0.553 0.194
0.331 0.456 0.151
Irradiated S1 Ratios Cr/Fe 0.252 O/Cr ---O/Fe ---S2 Ratios Cr/Fe 0.197 O/Cr ---O/Fe ----
Table 4 Peak ratios (488 cm-1/675 cm-1) of Raman spectra of samples S1 and S2 for different laser powers. Laser Power Peak ratio Peak ratio % SE304 SE430 40 0.025 0.007 50 0.166 0.027 60 0.250 0.211 70 0.384 0.174 80 0.608 0.345 90 0.723 0.333 99 0.914 0.364
Graphical abstract
Highlights Generation of Iron chromium oxide microspheres. Commercial stainless steel plates irradiated with an Ytterbium pulsed fiber laser. Raman spectroscopy analysis of iron chromium oxide microspheres. Energy-Dispersive X-ray spectroscopy analysis of Iron chromium oxide microspheres. Iron chromium oxide ratio is related to the applied laser power.
