Crystallization of Cobalt Amorphous Alloys Under Field Annealing

Abstract

Crystallization of Co-rich amorphous ribbons annealed under a 10 Oe external magnetic field at the early 30 minutes from their glassy status to supercooled liquid status is investigated by high-resolution transmission microscope (HR-TEM), Selected Area Fourier Transform (SA-FT), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Results indicate that the short-rang ordering feature can be refined very well in specimen annealed under temperatures about 87.4 degrees C below their glass transition (Tg), showing refined salt-pepper morphologies with a mean length changing from 1.2 +/- 0.8 nm to 0.8 +/- 0.2 nm and a mean width shifting from 0.5 +/- 0.2 nm to 0.3 +/- 0.1 nm. When the amorphous ribbons are field-annealed at temperature near to Tg (i.e., 450 degrees C), ultra-fine nanocrystalline structures can be formed on the top surface of ribbons with size of 3.5 +/- 0.5 nm and inter-grain spacing of about 0.4 +/- 0.2 nm even though the inner parts of the ribbons are still in amorphous phases. The nanocrystalline areas are featured by the formation of doped hcp cobalt phase orientated along the c-axis, with the inter-plane spacing ranging from 4 A to 6 A. When the annealing temperature is above Tg, the grain sizes are increased dramatically with multi-phased nanocrystals precipitating from the amorphous substrate, and finally reaching almost complete crystallization at 600 degrees C, causing greatly coarsening of the nanocrystal structures.

Magnetic field driving gradient effects on the microstructure in amorphous–nanocrystalline cobalt alloy ribbons

“…3b-d). Different from the typical salt-pepper contrast nanostructure for the amorphous phase as observed in TEM images of the as-spun ribbons, 33 the annealed samples exhibit nanocrystalline features with distinct and unique characteristics that cannot be completely seen in their XRD patterns (Fig. 2) or SEM images (Fig.…”

“…In our previous article, the HR-TEM confirmed that the as-spun ribbons are indeed in amorphous phases, showing typical salt-pepper morphologies. 33 All the annealed ribbons exhibit cross-section morphologies distinguished from the as-spun ribbons due to the spots of corrosion of crystalline grains across the ribbons. The ribbons annealed without field show many precipitated particles dispersed across the ribbon (dark areas in Fig.…”

“…There are also other cubic (Co, Fe)(Si, B) phases precipitating from the matrix, as indicated by the feature at 48.9 (star). 33 Comparing the ribbons annealed under the longitudinal field and the ribbons annealed in zero field, it is obvious that the longitudinal field not only enhances the crystallization of some phases precipitating under the conventional annealing condition, but also favors multiple phased crystallization via the formation of the (Co, Fe, Si) 4 B and CoB phases, the peaks for the [200] plane of the fcc Co phase, and other cubic (Co, Fe)(Si, B) phases.…”

“…The Co-rich amorphous ribbons were prepared by a rapid solidification process or by spraying the molten alloy onto a rotating copper roller. 33 An ingot with composition of Co 68.15 Fe 4.35 Si 12.5 B 15 (atom%) was first prepared using a high-frequency induction melting (HFIM) process (NEW-ADR-05) in which bulk cobalt (99.98%, Jinchuan Inc. Gansu, China), iron (99.8%, Taiyuan Steel Plant, China), silicon (99%, Guizhou 906 Plant, China) and boron (99.999%, Japan) were melted to produce an alloy. To ensure chemical and structural homogeneity, the ingot was re-melted 3 to 5 times, under an Ar atmosphere, in an arc melting furnace.…”

Highly Efficient Electrochemical CO2 Reduction Reaction to CO with One‐Pot Synthesized Co‐Pyridine‐Derived Catalyst Incorporated in a Nafion‐Based Membrane Electrode Assembly

“…There is a clear overlap of the Co and O distributions, and subsequent image analysis indicates that the position of the N signal is highly correlated to that of the Co (Figure S5, Supporting Information). X-ray diffraction (XRD) (Figure 3e) showed several wide peaks, assigned to CoO (JCPDS 43-1004) and poorly crystallized Co metal, [52,53] superimposed on a broad background due to the ketjenblack. Figure 3f shows the results of X-ray photoelectron spectroscopy (XPS) measurements of Co 2p binding energy.…”