Solvent-particles interactions during composite particles formation by pulsed laser melting of α-Fe2O3

Abstract

This work thoroughly investigates chemical solvent-particles interactions during the formation of composite particles by pulsed laser melting of α-Fe2O3. Two solvents, with different dielectric constants, such as ethyl acetate (εr = 6) and ethanol (εr = 24.6), were examined in terms of their effect on the morphology, size, and phase composition of iron oxide composites. We calculated the laser fluence curves using the heating-melting-evaporation approach to identify the critical particle size that undergoes the phase changes first. We assessed the temperature of the particles irradiated with 390 mJ/pulse.cm2 in both solvents, including the heat dissipation between the particles and the liquid. The phase diagram of the Fe–O–C–H system was calculated to determine the temperature–pressure relationship of the system in equilibrium. We also employed an in situ GC–MS analysis to identify the volatile products during irradiation. Based on our experimental results, we concluded that the final diameter of the composites increases from 400 to 600 nm, along with the decreasing dielectric constant of the solvent, which is related to the different polarization of the organic liquid and the degree of particle agglomeration. The reduction of hematite in ethanol proceeded much faster, ending up with Fe/FeCx, while in ethyl acetate, it ended up with Fe3O4. Among all the particles, those with a diameter of 200 nm have the highest temperature and undergo the phase transition first. The temperature of a 200 nm composite particle in ethanol is slightly lower than in ethyl acetate, i.e. 1870 K as compared to 1902 K. Phase equilibrium diagrams proved the existence of Fe, FeO, and Fe3O4 as the preferred phases at about 1900 K. Our research provides a new insight into the process of submicron particle formation during pulsed laser irradiation and allows proposing a mechanism for the growth of particles of different size and phase composition depending on the solvent.

Controlling the Magnetic Properties of Fe-Based Composite Nanoparticles

“…Phase diagrams calculated as the dependence of particle size on the required laser fluence J for Fe 2 O 3 systems explain the differences in the results obtained at two different wavelengths. In the case of the 2nd harmonic, as shown in previous work [21], the laser fluence has a minimum value of 200 mJ/pulse cm 2 for particles with a diameter of about 200 nm. The calculations shown in Fig.…”

“…The size, morphology, and composition of obtained particles can be tuned in a controllable manner by experimental parameters, such as wavelength, laser fluence, irradiation time, solvent, and molar ratio of irradiated materials [20]. This paper complements earlier reports on the irradiation of α-Fe 2 O 3 nanoparticles dispersed in ethyl acetate [21] by investigating the effects of irradiation using a laser beam in the ultraviolet range with a wavelength of 355 nm (3rd harmonics). By changing the laser fluence and irradiation time, α-Fe 2 O 3 is reduced to Fe 3 O 4 , FeO, and Fe.…”

“…To gain insight into the changes in the composition of nanoparticles during irradiation, we irradiated them with a laser fluence of 166 mJ/pulse cm 2 as a function of irradiation time. Compared to the irradiation of hematite with a wavelength of 532 nm (2nd harmonics) [21], higher energy was needed to obtain particles of similar sizes and composition, i.e., 180 mJ gave magnetite particles with a size of 600 nm, while in the case of the 3rd harmonic, 100 mJ was sufficient for the complete reduction of hematite to magnetite and obtaining particles with dimensions of 650 nm. Figure 3 shows changes in both particle size and composition for irradiation times ranging from 15 to 180 min.…”

“…The irradiated material melts and subsequently merges to form submicrometer-sized spherical particles. The latter technique, referred to as pulsed laser irradiation in liquids (PLIL), proved to be a comprehensive and promising method for the synthesis of colloidal submicrometer spheres with outstanding properties [20][21][22][23][24][25][26][27][28][29][30][31]. So far, it has been shown to be an effective approach for the synthesis and control of a variety of composite particles with various morphology (core-shell, alloy) and compositions, which are not only metals or oxides, but also non-equilibrium bimetallic alloys (AuFe, AuCo, and AuNi).…”

Alternative Local Melting‐Solidification of Suspended Nanoparticles for Heterostructure Formation Enabled by Pulsed Laser Irradiation

“…This process is alternatively repeated during pulsed laser irradiation of suspensions (PLIS), initially known as pulsed laser melting in liquid (PLML). [14][15][16][17][18][19][20] In 2007, Ishikawa et al [21] reported for the To display phase diagrams with the functionality of laser/suspension parameters, the reaction first time that unlike the laser ablation process used to produce smaller nanoparticles, PLML uses lower laser fluences and forms larger particles than the original constituents by melting. Later, an absorption model was introduced to calculate the temperature of suspended particles irradiated by a pulsed laser [22] followed by the addition of a cooling term to the model to calculate the temperature even more accurately.…”