Generation Of Amorphous Phase Research Articles

Rapid amorphization of CrMnFeCoNi high-entropy alloy under ultrasonic vibrations

Due to the distinct design concept, high-entropy alloys (HEAs) exhibit unusual properties and lead an emerging new field. In this work, we show that a typical face-centered cubic crystalline phase CoCrFeNiMn HEA can be readily transformed into the amorphous phase under the ultrasonic vibration treatment (UVT) at a frequency of 20000 Hz. The nanoscale hierarchical features include twins, stacking faults bands, hexagonal-close packed phase bands and even amorphous bands can be obviously identified in samples treated by different UVT energies. The dominant mechanism of ultrasonic vibration-induced amorphization is that the grain refinement promotes the formation of amorphous phases when the defect density at the grain boundaries reaches a critical level. In addition, the mechanical instability is easily induced by ultrasonic vibration at high strain rate to generate amorphous phase inside the grains. As a consequence of UVT, the HEA samples revealed significant mechanical performance improvement owing to the microstructure evolution especially the generation of amorphous phase, such as yielding strength and hardness. This rapid amorphization process provides not only a candidate strengthening mechanism for HEA, but also a novel approach to unveil the pending crystal-amorphous transition problem.

Microstructural investigation of thermo-mechanically processed lithium slag for geopolymer precursor using various characterization techniques

Lithium slag is an emerging industrial waste due to the increasing demand for lithium rechargeable batteries attributed to the recent boom in the automobile industry and space exploration. It is extracted as a powder residue in sedimentary tanks after the refining process of lithium extraction. In this study, the effect of thermo-mechanical processing on the chemical reactivity of lithium slag is assessed by TESCAN Integrated Mineral Analyzer (TIMA), X-ray Fluorescence (XRF), Rietveld quantitative refinement techniques. The chemical, mineral, and crystallographic phase composition of processed lithium slag specimens were assessed and compared by XRF, TIMA, and Rietveld quantitative refinement techniques, respectively. The results of thermo-mechanical processing indicated that the mineral and crystallographic transformation of Spodumene to feldspars (Anorthite, Muscovite, Albite) occurred by crystallite agglomeration. The chemical reactivity of lithium slag is gauged in terms of amorphous alumino-silicates present in feldspars and unidentified phases. Characterization of unidentified phase is evident that it majorly contains micro-nano sized alumino-silicate rich particles with similar spectral signatures to that of feldspar, some fraction of it is aggregated into other phases due to its reactivity. The concentration of the amorphous phase is proportionate with the thermo-mechanical processing energy. However, the thermo-mechanical processing energy is also optimized based on the generation of amorphous phase and reduction in particle size. Therefore, the G1C700 processed regime resulted in one of the maximum amounts of amorphous phase (52.60%). The mineral phase transformation of Spodumene to Anorthite (+10.46%) and unidentified phase (+8.24%) along with D50 value of 13.26 µm, consequently releasing 0.45 kg of carbon emissions upon thermo-mechanical processing. Hence, G1C700 lithium slag is recommended for its use as a geopolymer precursor.

Wet milling induced physical and chemical instabilities of naproxen nano-crystalline suspensions

Wet-milling is the most common approach to formulate nano-crystalline suspensions. The effect of high intensity wet-milling on the physical and chemical stability of a poorly soluble drug was investigated. Naproxen (1%, w/v) was suspended in two different stabilizers (i.e. HPMC E15 and Tween 80) and stabilizer concentrations (0.2% or 0.6%, w/v) in distilled water. Wet-milling was performed at two different speeds (i.e. 3,400 rpm and 2,000 rpm) for four continuous hours. The milled samples were analyzed for physical and chemical instabilities. Wet-milling of naproxen-HPMC E15 at high milling intensity caused both physical and chemical instabilities as observed by particle size measurement and chemical analysis, respectively. The naproxen-Tween 80 formulations were stable regardless of milling intensity. Naproxen-HPMC E15 wet-milled samples, showed an IR peak shift suggesting strong bond formation or molecular interaction (i.e. amorphous phase). In addition, naproxen has a strong interaction with HPMC E15 as determined by MTDSC (i.e. melting point depression). The generation of amorphous phase at the naproxen-HPMC E15 crystal surface may be responsible for both aggregation and degradation during wet milling. Decarboxylated naproxen was identified as a degradation product. Milling intensity and/or selection of stabilizer/s are crucial for the stability of nano-crystalline suspensions.