Magnetic behavior of Sm-Co-based permanent magnets during order/disorder phase transformations

The structural transformation from the metastable disordered TbCu7-type SmCo7 structure to the equilibrium ordered Th2Zn17-type Sm2Co17 structure was revealed by x-ray diffraction analysis using Reitveld refinement. The magnetic properties depended strongly on the stage of the transformation, as the coercivity strongly depended on the annealing temperature. The as-solidified alloy in the TbCu7-type structure had a coercivity of 4 kOe, which increased to greater than 9 kOe. The coercivity decreased to around 5 kOe as the transformation neared completion upon annealing at higher temperatures. The magnetization processes were also strongly influenced by the structural state. Initially it was totally controlled by nucleation followed by the domain wall pinning-controlled magnetization process

Magnetic behavior of Sm-Co-based permanent magnets during order/disorder phase transformations

The structural transformation from the metastable disordered TbCu7-type SmCo7 structure to the equilibrium ordered Th2Zn17-type Sm2Co17 structure was revealed by x-ray diffraction analysis using Reitveld refinement. The magnetic properties depended strongly on the stage of the transformation, as the coercivity strongly depended on the annealing temperature. The as-solidified alloy in the TbCu7-type structure had a coercivity of 4 kOe, which increased to greater than 9 kOe. The coercivity decreased to around 5 kOe as the transformation neared completion upon annealing at higher temperatures. The magnetization processes were also strongly influenced by the structural state. Initially it was totally controlled by nucleation followed by the domain wall pinning-controlled magnetization process

Rapidly Solidified Rare-Earth Permanent Magnets: Processing, Properties, and Applications

Rapidly solidified rare-earth-based permanent magnets are considered to have better potential as permanent magnets compared to the conventional bulk materials, which can be attributed to their improved microstructure and better magnetic properties compared to rare-earth magnets synthesized by the conventional (powder metallurgy) routes. The performance (quality) of these magnets depends on the thermodynamics and kinetics of the different processing routes, such as atomization, melt spinning, and melt extraction. Here, we review the various processing routes of rapidly solidified rare-earth permanent magnets and the related properties and applications. In the review, some specific alloy systems, such as Sm–Co-based alloys, Nd–Fe–B, and interstitially modified Fe-rich rare-earth magnets are discussed in detail mentioning their processing routes and subsequently achieved crystal structure, microstructure and magnetic properties, and the related scopes for various applications. Some newly developed nanocomposites and thin-film magnets are also included in the discussion

Crystal structure, microstructure and magnetic properties of rapidly solidified samarium-cobalt based alloys

The SmCo-based permanent magnets are drawing much more attention since the early 1970\u27s for their highly attractive features such as, high energy product (15 MGOe–30 MGOe), reliable coercive force, best temperature characteristics and excellent corrosion and oxidation resistance. These interesting and highly demanding features have made Sm-Co the ideal material in dynamic applications such as generators and motors. The melt-spun ribbons of Sm-Co-based magnetic materials produced by rapid solidification exhibited higher anisotropy, improved microstructures and better magnetic properties (Mr ∼ 8.5 kG, Hc ∼ 4.1 kOe and (BH)max ∼ 18.2 MGOe and a high remanence ratio of 0.9). This research reports the structure and magnetic properties of rapidly solidified SmCo permanent magnets of simple binary alloy systems modified with Nb and C additions. Melt spinning at 40 m/s resulted in the formation of the metastable TbCu7-type structure in all instances regardless of alloying additions. While the unalloyed Sm12Co88 alloy displayed a coercivity of 0.5 kOe, alloying additions resulted in a systematic and profound increase in coercivity, with maximum values exceeding 37 kOe. TEM revealed the presence of fcc Co, formed as a result of the non-equilibrium processing. The alloying additions had a profound influence on the scale of the microstructure, reducing the SmCo7 grains from the micron-scale to the 100 nm range and the scale of the Co from 80 nm to 10 nm. The nanoscale Co soft magnetic phase enables exchange coupling to the hard magnetic phase, resulting in high remanence ratios (∼0.7). For a range of compositions, from SmCo5.67 to SmCo8, the coercivity was highest in Sm-rich compositions (17.5 kOe) and decreased to ∼3 kOe as Sm content decreased. At higher wheel speed during melt-spinning, the higher chances of formation of Co precipitate and the reduced size of Co precipitates helped to improve the remanence. At higher wheel speed and at higher concentration of alloying additions the magnetization process was dominated by pinning mechanism. During the order-disorder phase transformations, the as-solidified alloys in the TbCu7-type structure exhibited coercivsty as high as 7.85 kOe, which increased to greater than 9 kOe by heat-treatment. The magnetization processes were also strongly influenced by the structural state during order-disorder phase transformations, initially it was totally controlled by nucleation followed by the domain wall pinning

Highly coercive rapidly solidified Sm–Co alloys

Highly coercive (Hc up to 37 kOe at 300 K), high remanent permanent magnets have been achieved by rapid solidification of binary Sm–Co alloys and Sm–Co alloys modified with Nb and C. Rapidly solidified SmCox alloys with x ranging from 5 to 11.5 formed predominantly a solid solution TbCu7-type SmCo7 phase, although hcp Co was observed for x\u3e7.3. A coercivity value of 10 kOe was observed for xx, as primary dendrites. Additions of 3 at. % Nb or 3 and 5 at. % C profoundly affected the coercivity values. Transmission electron microscopy (TEM) investigations revealed the origin of the improved coercivity. The addition of Nb resulted in a significant reduction in microstructural scale. The SmCo7 grain size decreased systematically with Nb content, reaching 150–200 nm at 3 at. % Nb. The addition of C also significantly enhanced the coercivity, which systematically increased with C content and reached 37 kOe at 5 at. % C. The effect of C, however, resulted in morphological changes as TEM revealed the formation of an intergranular phase that effectively isolated the hard magnetic SmCo7 grains from one another, reducing magnetic interactions. Excellent isotropic energy products of 6–8 MGOe were also achieved

Rapidly Solidified Rare-Earth Permanent Magnets: Processing, Properties, and Applications

Rapidly solidified rare-earth-based permanent magnets are considered to have better potential as permanent magnets compared to the conventional bulk materials, which can be attributed to their improved microstructure and better magnetic properties compared to rare-earth magnets synthesized by the conventional (powder metallurgy) routes. The performance (quality) of these magnets depends on the thermodynamics and kinetics of the different processing routes, such as atomization, melt spinning, and melt extraction. Here, we review the various processing routes of rapidly solidified rare-earth permanent magnets and the related properties and applications. In the review, some specific alloy systems, such as Sm–Co-based alloys, Nd–Fe–B, and interstitially modified Fe-rich rare-earth magnets are discussed in detail mentioning their processing routes and subsequently achieved crystal structure, microstructure and magnetic properties, and the related scopes for various applications. Some newly developed nanocomposites and thin-film magnets are also included in the discussion

Resputtering Effect on Nanocrystalline Ni-Ti Alloy Films

We report on the effect of resputtering on the properties of nanocrystalline Ni-Ti alloy thin films deposited using co-sputtering of Ni and Ti targets. In order to facilitate the formation of nanocrystalline phases, films were deposited at room temperature and 573 K (300 A degrees C) with substrate bias voltage of -100 V. The influence of substrate material on the composition, surface topography microstructure, and phase formations of nanocrystalline Ni-Ti thin films was also systematically investigated. The preferential resputtering of Ti adatoms was lesser for Ni-Ti films deposited on quartz substrate owing to high surface roughness of 4.87 nm compared to roughness value of 1.27 nm for Si(100) substrate

A Family of 2D-MXenes: Synthesis, Properties, and Gas Sensing Applications

Gas sensors, capable of detecting and monitoring trace amounts of gas molecules or volatile organic compounds (VOCs), are in great demand for numerous applications including diagnosing diseases through breath analysis, environmental and personal safety, food and agriculture, and other fields. The continuous emergence of new materials is one of the driving forces for the development of gas sensors. Recently, 2D materials have been gaining huge attention for gas sensing applications, owing to their superior electrical, optical, and mechanical characteristics. Especially for 2D MXenes, high specific area and their rich surface functionalities with tunable electronic structure make them compelling for sensing applications. This Review discusses the latest advancements in the 2D MXenes for gas sensing applications. It starts by briefly explaining the family of MXenes, their synthesis methods, and delamination procedures. Subsequently, it outlines the properties of MXenes. Then it describes the theoretical and experimental aspects of the MXenes-based gas sensors. Discussion is also extended to the relation between sensing performance and the structure, electronic properties, and surface chemistry. Moreover, it highlights the promising potential of these materials in the current gas sensing applications and finally it concludes with the limitations, challenges, and future prospects of 2D MXenes in gas sensing applications

Sensors in advancing the capabilities of corrosion detection: A review

Corrosion can cause serious damage, which leads to large economic loss, sometimes combined with environmental pollution, or risk of personnel injuries. Today, corrosion has a far-reaching impact on society and the associated degradation of materials, owing to the increased complexity and diversity of materials systems, which comprise not only metallic materials but also ceramics, polymers, and composites, all of which are vulnerable to environmental extremes. Early detection, proper diagnosis, and efficient prevention measures are the most essential parts in preventing or limiting the scope of such damages. Corrosion detection (inspection and monitoring) provides assistance and knowledge to identify the problem, examine the performance of the material, alternate materials evaluation, and development of strategies for materials protection towards a specific environment. Significantly, these sensor detection techniques are useful to determine the average rate of corrosion or type of attack, or both, that arise during the exposure. The data obtained from these sensors can allow providing an early warning, resulting in corrosion-induced failure and producing controlling statistics concerning maintenance necessities and ongoing conditions of the system that gets detected. In this review, sensors implementing both physical and electrochemical techniques with respect to the recent developments in the field and laboratory are discussed towards sensitivity and selectivity along with their advantages and disadvantages. In addition, various standard methods developed for inspecting and monitoring the corrosion directly or indirectly are also described in detail.This work was supported by the UREP grant # UREP24-133-2-036 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu