Microstructure and Magnetic Properties of Fe67.6-Pd32-In0.4 (at.%) Shape Memory Melt-Spun Ribbons.

Fe-~30 at.%Pd is a ferromagnetic shape memory alloy (SMA) with a reversible thermoelastic fcc-fct phase transformation. The advantage of adding a small amount of Indium to Fe-Pd SMAs is, among other things, the upward shift of the transformation temperatures, which allows us to maintain the material in the martensitic state (fct structure) at room temperature. In this work, we study the microstructure and the magnetic properties of nominally Fe67.6-Pd32-In0.4 (at.%) melt-spun ribbons. Energy-dispersive spectroscopy analysis showed a certain level of non-uniformity of Indium distribution in the as-spun ribbon. However, the attempt to homogenize the ribbon by annealing at 1273 K for 120 h resulted in an unfavoured structural change to bct martensite. Magneto strains induced by a 9 kOe magnetic field reached over 400 ppm for certain field orientations, which is around four times more than the magneto strains of near-binary Fe-Pd shape memory alloys.

Preparation and Characterization of Multilayer NiTi Coatings by a Thermal Plasma Process.

The deposition of multilayer coating of NiTi is carried out by a thermal plasma spraying process on a stainless steel substrate. The deposition of melted NiTi particles creates an adhesion layer on the substrate with the subsequent formation of multilayer coating with a certain thickness. Six layers of coating are created to achieve a certain thickness in terms of the sprayed sample. This paper aims to investigate multilayer NiTi coatings created through a thermal plasma process. The key variable feed rate was considered, as well as its effect on the microstructure characteristics. The shape memory effect associated with the coating properties was analyzed in detail. The variable feed rate was considered one of the most important parameters in the thermal plasma spraying process due to its ability to control the quality and compactness of the coating structure. The coatings were characterized by examining their microstructure, thermal, chemical, and microhardness. The indent marks were made/realized along the cross-section surface for the analysis of crack propagation resistance and wear properties. The coating's surface did not display segmentation crack lines. Nevertheless, the cross-sectional surfaces showed evidence of crack lines. There were eutectic zones of the interlamellar structure observed in the structure of the coating. The plasma-sprayed samples from thermo-mechanical analysis of the hysteresis curve provide strong confirmation of the shape memory effect.

Impact of Initial Cyclic Loading on Mechanical Properties and Performance of Nafion.

Nafion possesses many interesting properties such as a high ion-conductivity, hydrophilicity, and thermal and chemical stability that make this material highly suitable for many applications including fuel cells and various (bio-)chemical and physical sensors. However, the mechanical properties of a Nafion membrane that are known to be affected by the viscoplastic characteristics of the material itself have a strong impact on the performance of Nafion-based sensors. In this study, the mechanical properties of Nafion under the cyclic loading have been investigated in detail. After cyclic tensile loading (i.e., maximum elongation about 25% at a room temperature and relative humidity about 40%) a time-dependent recovery comes into play. This recovery process is also shown being strain-rate dependent. Our results reveal that the recovery behavior weakens after performing several stress-strain cycles. Present findings can be of a great importance in future design of various chemical and biological microsensors and nanosensors such as hydrogen or glucose ones.

Interfacial Adhesion of Thick NiTi Coating on Substrate Stainless Steel.

Interfacial adhesion of thick NiTi coating on substrate stainless steel is investigated here. NiTi coating was deposited on the substrate by using the thermal plasma spraying method. Deposition of NiTi coating was carried out by using various levels of input power under an Ar atmosphere. Multiple coating layers were deposited on the stainless steel surface for a specific thickness. The cross-section of the plasma-sprayed samples were prepared and characterized by using various techniques. The hardness of the coating layers on the surface and cross-section was examined. The thickness of the coating increased with the increase in power. No cracks were detected in the interface for the NiTi coating deposited at 12 kW power. However minor pores were observed at some regions along the interface at the sample prepared at 9 kW power. A good-quality coating layer was formed at the interface of the substrate. Primary phases of austenite and martensite were confirmed from the EBSD and XRD investigations. There was the presence of intermetallic and oxide phases in the coating layers. A less heat-affected zone of 10 µm of along the interface was confirmed without any diffusion of elements from the substrate to the coating layers. There was homogenous distribution elemental composition of Ni and Ti throughout the coating layers.

Shape Memory Behaviour of PMMA-Coated NiTi Alloy under Thermal Cycle.

Both poly(methyl methacrylate) (PMMA) and NiTi possess shape memory and biocompatibility behavior. The macroscale properties of PMMA-NiTi composites depend immensely on the quality of the interaction between two components. NiTi shape memory alloy (SMA) and superelastic (SE) sheets were spin coated on one side with PMMA. The composite was prepared by the spin coating method with an alloy-to-polymer-thickness ratio of 1:3. The bending stiffness and radius of curvature were calculated by using numerical and experimental methods during thermal cycles. The experimental radius curvatures in actuation have good agreement with the model. The change in shape results from the difference in coefficients of thermal expansion between PMMA and NiTi. Actuation temperatures were between 0 and 100 °C for the SMA-PMMA composite with a change in curvature from 10 to 120 mm with fixed Young's modulus of PMMA at 3 GPa, and a change in Young's modulus of NiTi from 30 to 70 GPa. PMMA-NiTi composites are useful as actuators and sensor elements.

An Overview of Thermal Plasma Arc Systems for Treatment of Various Wastes in Recovery of Metals.

Thermal plasma systems are being used for the recovery of metals from complex waste and minerals. The latter contain multiphase metals in various forms that are extremely tedious to separate. Thermal plasma arc melts the waste and minerals for qualitative plasma products for powder industries. In this overview, we briefly report a description of the various thermal plasma systems and their uses in recovering metal from metal-containing materials in the form of waste or minerals. Various plasma arc systems, such as transferred, nontransferred, and extended arc, have enabled the development of an efficient and environmentally friendly way to recover valuable metals from industrial wastes such as red mud and minerals such as ilmenite.

Utilization of Red Mud as a Source for Metal Ions-A Review.

An overview is presented on the prospective use of red mud as a resource in this review. Various scopes are suggested for the utilization of red mud to maintain a sustainable environment. The potential use of red mud covers the valuable metal recovery that could emphasize the use of red mud as a resource. Red mud could act as reduced slag in the metallurgical field for the extraction of minerals and metals for upscale application. Although many studies have revealed the potential utilization of red mud, most of them are only limited to a lab-scale basis. Therefore, a large-scale investigation on recycling of red mud for the extraction in the area of the metal recovery section will draw attention to the extensive use of red mud. Metal ions of major elements Fe (44 wt.%), Al (18.2 wt.%), Si (14.3 wt.%), Ti (9.3 wt.%), Na (6.2 wt.%), Ca (4.4 wt.%) as major elements and of Mg, V, Mn, Cr, K as minor elements and rare earth elements such as Ce (102 mg/kg), La (56 mg/kg), Sc (47 mg/kg), Nd (45 mg/kg), Sm (9 mg/kg). Moreover, an appropriate in-house metal recovery facility with the alumina industry will come out as a cost-benefit analysis.

Effects of Filler Distribution on Magnetorheological Silicon-Based Composites.

The smart materials subclass of magnetorheological elastomer (MRE) composites is presented in this work, which aimed to investigate the influence of filler distribution on surface morphology. Iron particles with sizes ranging from 20 to 150 µm were incorporated into the elastomer matrix and a 30% volume fraction (V%) was chosen as the optimal quantity for the filler amount in the elastomer composite. The surface morphology of MRE composites was examined by 3D micro-computed tomography (µCT) and scanning electron microscopy (SEM) techniques. Isotropic and anisotropic distributions of the iron particles were estimated in the magnetorheological elastomer composites. The filler particle distribution at various heights of the MRE composites was examined. The isotropic distribution of filler particles was observed without any influence from the magnetic field during sample preparation. The anisotropic arrangement of iron fillers within the MRE composites was observed in the presence of a magnetic field during fabrication. It was shown that the linear arrangement of the iron particle chain induced magnetization within the composite. Simulation analysis was also performed to predict the particle distribution of magnetization in the MREs and make a comparison with the experimental observations.

Effect of high temperature on the microstructural evolution of fiber reinforced geopolymer composite.

Physical evolution of geopolymeric minerals derived from metakaolin and synthesized with sodium, mixed-alkali and potassium activating solutions (Na- K) during thermal exposure. The geopolymer composites were prepared with 40 V% of fiber reinforcement such as carbon, E-glass, and basalt at the direction of in plain. Fiber reinforced geopolymer composites were exposed to the room and elevated temperatures inside the oven at air medium for a period of 30 min. The durability of the composites and internal structures with surface microstructures were examined after high temperature exposures. According to the results, geopolymer implied a prominent influence on the thermal shrinkage with the increasing of Si/Al ratios. This was attributed to the densification caused by reduction in porosity during dehydroxylation and sintering. In the case of carbon fiber reinforced composite shows transition in strength after 600 °C due to the oxide protective layer that increases the flexural strength and toughness of the composite. The flexural strength of the carbon reinforced composite increases from 17.8 to 55.8 MPa at 1000 °C. Whereas, E-glass reinforced composite shows expansion in a matrix with cage like structure helps in the sliding mechanism of fiber within the matrix, thus strength reduces towards high temperature. In case of basalt reinforces composite complete conversions into a ceramic like structure after exposure to high temperature. As a result, the crystalline nature of ceramic assists in toughened the composite structure with a brittle nature.

Molecular design of melt-spinnable co-polymers as Si-B-C-N fiber precursors.

Two series of co-polymers with the general formula [B(C2H4SiCH3(NH)x(NCH3)y)3]n, i.e., composed of C2H4SiCH3(NH)x and C2H4SiCH3(NCH3)y (C2H4 = CHCH3, CH2CH2) building blocks in a well defined x : y ratio, have been synthesized by hydroboration of dichloromethylvinylsilane with borane dimethyl sulfide followed by successive reactions with lithium amide and methylamine according to controlled ratios. The role of the chemistry behind their syntheses has been studied in detail by solid-state NMR, FT-IR and elemental analyses. Then, the intimate relationship between the chemistry and the melt-spinnability of these polymers was discussed. By keeping x = 0.50 and increasing y above 0.50, i.e., obtaining methylamine excess, the co-polymers contained more ending groups and especially more tetracoordinated boron, thus allowing tuning very precisely the chemical structure of the preceramic polymer in order to meet the requirements for melt-spinning. The curing treatment under ammonia at 200 °C efficiently rendered the green fibers infusible before their subsequent pyrolysis under nitrogen at 1000 °C to generate Si-B-C-N ceramic fibers. Interestingly, it could be possible to produce also low diameter hollow fibers with relatively high mechanical properties for a further exploration as membrane materials.