• S SUASMORO

Articles written in Bulletin of Materials Science

• Ti–Zr coating on graphite through powder immersion reaction-assisted coating (PIRAC) and its oxidation kinetics at $T = 1000^{\circ}$C

Coating of graphite with a metal alloy Ti–Zr was carried out on a block of graphite sample; the sample was initially dipped in ZrO$_2$ containing a natural starch solution and then proceeded to powder immersion reaction-assisted coating (PIRAC) after drying. Ti powder containing 4 wt% iodine was used as depositing material, and the process was carried out at 850−950$^{\circ}$C for 10 h. The characterizations include X-ray diffraction, scanning electron microscopy and the hardness test. The coating thickness is proportional to the temperature of the PIRAC process, while the percentage of Zr is inversely proportional to the temperature of PIRAC treatment. All the characterizations revealed that the coated layer was a Ti–Zr alloy with hexagonal crystalline symmetry similar to $\alpha$-Ti. An oxidation kinetic assessment at 1000$^{\circ}$C of uncoated graphite shows a burns-off mechanism, while for a coated sample reveals a reaction of Ti with oxygen produces TiO$_2$; the reaction kinetics obey a diffusional mechanism.

• Local structure analysis of $B$O$_6$ ($B = {\rm Fe, Cu}$) octahedron correlated with the magnetic properties of Cu-doped Ba$_{0.5}$Sr$_{0.5}$FeO$_{3–\delta}$

Perovskite-based Ba$_{0.5}$Sr$_{0.5}$Fe$_{1–x}$Cu$_x$O$_{3–\delta}$ (BSFCO-$x$, $x = 0–0.2$) was synthesized by sol–gel self-combustionmethod. The crystallinity was evaluated through X-ray diffraction, besides further local structure analysis, using X-ray absorption spectroscopy (XAS) showed a cubic symmetry for $x = 0.05$; 0.10, which was tetragonal at higher values, $x =0.15; 0.20$. XAS analysis predicted the oxidation state (OS) of Cu to be a mixture of 3$+$ and 2$+$, while Fe includes 3$+$ and 4$+$. Conversely, the OS of Fe and Cu in the octahedron site influence the number of an unpair electron that determine the magnetic properties of perovskite. In addition, the magnetization for Ba$_{0.5}$Sr$_{0.5}$FeO$_{3–\delta}$ is 0.172 emu g$^{-1}$, originating from the ferromagnetic ordering Fe$^{3+}$($t_{2g}^3 e_g^2$)–O(2p)–Fe$^{4+}$($t_{2g}^3 e_g^1$) interaction. This effect increase, due to the presence of oxygen vacancy in BSFCO-0.05, which weakens the $d–p$ interaction of Fe-O, while the generation of higher Cu doping to increase the amount of Fe$^{4+}$ leads to a decline in Cu$^{3+}$. Therefore, Cu doping is confirmed to play a role in the paramagnetic–ferromagnetic transition.

• # Bulletin of Materials Science

Volume 44, 2021
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Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020