γ-Iron Phase Stabilized at Room Temperature by Thermally Processed Graphene Oxide

Abstract

Stabilizing nanoparticles on surfaces, such as graphene, is a growing field of research. Thereby, iron particle stabilization on carbon materials is attractive and finds applications in charge-storage devices, catalysis, and others. In this work, we describe the discovery of iron nanoparticles with the face-centered cubic structure that was postulated not to exist at ambient conditions. In bulk, the γ-iron phase is formed only above 917 °C, and transforms back to the thermodynamically favored α-phase upon cooling. Here, with X-ray diffraction and Mössbauer spectroscopy we unambiguously demonstrate the unexpected room-temperature stability of the γ-phase of iron in the form of the austenitic nanoparticles with low carbon content from 0.60% through 0.93%. The nanoparticles have controllable diameter range from 30 nm through 200 nm. They are stabilized by a layer of Fe/C solid solution on the surface, serving as the buffer controlling carbon content in the core, and by a few-layer graphene as an outermost shell.

Green Synthesis of Iron Nanoparticles for Investigation of Biofilm Inhibition Property

“…The figure 3C projects the X‐RD analysis diffractogram of the particles with four prominent peaks at 2θ values of 38.14°, 44.4°, 64.75°, and 77.9°. The peaks at 44.4°, 64.75°, and 77.9° indicate that the particles are predominantly in α‐Fe 0 bcc crystalline state with planes (110), (200), and (211), respectively [44] . In addition, there is one more prominent peak at 38.14° which can be corroborated to FeOOH (ironoxyhydroxide) [45] .…”

“…The peaks at 44.4°, 64.75°, and 77.9°i ndicate that the particles are predominantly in α-Fe 0 bcc crystalline state with planes (110), (200), and (211), respectively. [44] In addition, there is one more prominent peak at 38.14°which can be corroborated to FeOOH (ironoxyhydroxide). [45] The DLS hydrodynamic size ( Figure 3D) is about 31 nm, which is quite greater than that of TEM size, a size of the core particle.…”

Thermal Evolution of C–Fe–Bi Nanocomposite System: From Nanoparticle Formation to Heterogeneous Graphitization Stage

“…Signs of C–Fe interactions can be discussed by considering the XRD data recorded so far, and the different C–Fe and Fe–O phase diagrams as shown in Supplementary Figure S8. According to the literature, the presence stabilized γ -Fe is mitigated by temperature and the Fe–C interactions taking place at high temperatures (Khannanov et al, 2018). Above the peritectic temperatures (740°C), nucleation sites for γ -Fe can form by increasing the diffusive carbon content as described in other studies (Wirth et al, 2012).…”

Fe3O4 Templated Pyrolyzed Fe−N−C Catalysts. Understanding the role of N‐Functions and Fe3C on the ORR Activity and Mechanism

“…[15,23,29,62] In the spectrum appears a new singlet associated with antiferromagnetic iron γ-Fe fcc particles typically formed above 917 °C and later quenching. [63] The development and stabilization of these allotropic iron species are due to the graphitization of the carbon matrix that kinetically hinders its thermodynamically favored conversion to α-Fe. [63] The above is corroborated by the decrease of the α-Fe species content (Δ [%α-Fe(NP-PANI-NH3)-%α-Fe(NP-PANI-N2)] = À 26 % relative % area).…”