J.J. Suñol

Martensitic phase transformation in rapidly solidified Mn50Ni40In10 alloy ribbons

Heusler alloy Mn50Ni40In10 was produced as preferentially textured ribbon flakes by melt spinning, finding the existence of martensitic-austenic transformation with both phases exhibiting ferromagnetic ordering. A microcrystalline three-layered microstructure of ordered columnar grains grown perpendicularly to ribbon plane was formed between two thin layers of smaller grains. The characteristic temperatures of the martensitic transformation were MS=213K, Mf=173K, AS=222K, and Af=243K. Austenite phase shows a cubic L21 structure (a=0.6013(3)nm at 298K and a Curie point of 311K), transforming into a modulated fourteen-layer modulation monoclinic martensite.

Thermal and magnetic field-induced martensite-austenite transition in Ni50.3Mn35.3Sn14.4 ribbons

Thermal and field-induced martensite-austenite transition was studied in melt spun Ni50.3Mn35.3Sn14.4 ribbons. Its distinct highly ordered columnarlike microstructure normal to ribbon plane allows the direct observation of critical fields at which field-induced and highly hysteretic reverse transformation starts (H=17kOe at 240K), and easy magnetization direction for austenite and martensite phases with respect to the rolling direction. Single phase L21 bcc austenite with TC of 313K transforms into a 7M orthorhombic martensite with thermal hysteresis of 21K and transformation temperatures of MS=226K, Mf=218K, AS=237K, and Af=244K.

XPS surface study of nanocrystalline Ti–Ru–Fe materials

Abstract The surface properties of Ti:Ru:Fe (2− x :1+ x /2:1+ x /2) (with x =0, 0.25, 0.5, 0.75, and 1) and Ti:Ru:Fe:O (2:1:1: w ) (with w =0.0, 0.5, 1.0, 1.5, and 2.0) have been determined by X-ray photoelectron spectroscopy (XPS) in both their as-milled state and after being in contact with a chlorate oxidizing solution. The O surface concentrations of both sets of samples are almost identical, indicating that the O-free samples readily react with air. All samples in their as-milled state have an elemental Ti, Ru and Fe surface contents that closely follow that expected from their bulk composition, indicating that there is no surface enrichment in any of the elements. In the as-milled state, more than 90% of Ti and Fe atoms are in the highest possible oxidation state, while Ru is in the metallic state. Following immersion of the samples in an oxidizing chlorate electrolyte, the Ru surface concentration decreases by a factor of two. This is also accompanied by an increase in the oxidation state of the Ru atoms left at the surface from 0 to +4. From a comparison between the Ru 3 d 5/2,3/2 core level spectra of the electrodes with those of crystalline and hydrated RuO 2 , it is postulated that dissolution and re-deposition of Ru in the form of hydrated RuO 2 occurs at open circuit potential in the chlorate electrolyte. The consequences of these findings for the electrocatalytic activity of the electrodes in chlorate electrolyte are finally discussed.

Characterization of mechanically alloyed nanocrystalline fe(Al): crystallite size and dislocation density

A nanostructured disordered Fe(Al) solid solution was obtained from elemental powders of Fe and Al using a high-energy ball mill. The transformations occurring in the material during milling were studied with the use of X-ray diffraction. In addition lattice microstrain, average crystallite size, dislocation density, and the lattice parameter were determined. Scanning electron microscopy (SEM) was employed to examine the morphology of the samples as a function of milling times. Thermal behaviour of the milled powders was examined by differential scanning calorimetry (DSC). The results, as well as dissimilarity between calorimetric curves of the powders after 2 and 20 h of milling, indicated the formation of a nanostructured Fe(Al) solid solution.

Martensitic transformation in Ni50.4Mn34.9In14.7 melt spun ribbons

Single phase microcrystalline ribbon flakes with the average elemental composition Ni50.4Mn34.9In14.7 were produced by rapid quenching using melt spinning technique. Fracture cross section micrographs of ribbons show the formation of a columnar-like microstructure, with the longer axis of grains aligned perpendicular to ribbon plane. X-ray diffraction and thermomagnetic analysis show that samples are single phase with L21-type austenite as high-temperature parent phase (Curie point of 284 K). At low temperatures austenite transforms into a ten-layered structurally modulated monoclinic martensite. The characteristic phase transition temperatures and thermal hysteresis of the reversible martensite–austenite transformation were MS = 262 K, Mf = 245 K, AS = 262 K, Af = 270 K and ΔT = 10 K. The crystalline directions [2 2 0] of austenite and [1 2 5] of martensite were found preferentially oriented normal to the ribbon plane. The measurement of magnetization isotherms up to 80 kOe confirmed the occurrence of the field-induced reverse martensitic transformation.

Microstructure and magnetic properties of Ni50Mn37Sn13 Heusler alloy ribbons

The Heusler alloy Ni50Mn37Sn13 was successfully produced as ribbon flakes of thickness around 7–10μm melt spinning. Fracture cross section micrographs in the ribbon show the formation of a microcrystalline columnarlike microstructure, with their longer axes perpendicular to the ribbon plane. Phase transition temperatures of the martensite-austenite transformation were found to be MS=218K, Mf=207K, AS=224K, and Af=232K; the thermal hysteresis of the transformation is 15K. Ferromagnetic L21 bcc austenite phase shows a Curie point of 313K, with cell parameter a=0.5971(5)nm at 298K, transforming into a modulated 7M orthorhombic martensite with a=0.6121(7)nm, b=0.6058(8)nm, and c=0.5660(2)nm, at 150K.

Properties of PMMA artificially aged

Abstract We report the effects of artificial aging poly(methyl methacrylate) (PMMA). The aging of samples was performed using a xenon-arc lamp to simulate solar radiation. The maximum time of artificial aging was 1570 h, equivalent to 750 days of solar exposure. The purpose of this work is to study the properties of PMMA and their change with aging time. Analysis of chemical modification and structural change were performed by means of Fourier transformed infrared spectrophotometry (FTIR). The spectra confirmed that the aging process is initially promoted by hydrogen abstraction producing chain breaking and formation of the carbon–carbon non-saturated bonds and shorter macromolecular chains, such as vinyl, vinylidene and methyl. Calorimetric measurements of samples by differential scanning calorimetry (DSC) detected changes of glass transition temperatures. Finally, the fracture toughness was measured by tensile test measurements. The toughness decreased ∼40% after 1570 h.

Ni59.0Mn23.5In17.5 Heusler alloy as the core of glass-coated microwires: Magnetic properties and magnetocaloric effect

Heusler Ni59.0Mn23.5In17.5 alloy was prepared as the metallic core of a glass-coated microwire with a total diameter of 41.8 μm. X-ray diffractograms performed at room temperature and 100 K show a highly ordered L21 cubic structure characteristic of the austenitic phase in Heusler alloys. Thermomagnetic curves measured in the temperature range from 50 K up to 400 K show ferromagnetic coupling in the austenite with the Curie temperature around 246 K. Hysteresis loops measured at different temperatures indicate a soft ferromagnetic behaviour, confirming the microwire axis as the magnetization easy direction. The magnetic entropy variation reaches a maximum value of 1.75 J/kgK at the ferro-to-paramagnetic phase transition for a magnetic field change of 30 kOe. After short annealing, the Curie temperature is almost unchanged while the maximum entropy change increases up to 2.01 J/kgK. Refrigerant capacity and its dependence on both working temperature range and applied field value are evaluated for all microw...

Comparison of the thermal behavior of three cellulose fibers mercerized or submitted to solar degradation

Comparison of Lyocell, modal and viscose fibers was performed by means of differential scanning calorimetry, thermogravimetry and scanning electron microscopy. Thermal analysis was performed in air atmosphere. Samples were mercerized (21.3 g 100 mL-1) or submitted to solar radiation (seven months). Solar degraded samples presents a higher thermal stability and are initially less degraded. Furthermore, Lyocell fiber is the most stable under thermal degradation conditions. Heating produces a reduction of the fiber diameter (about 50%).

Comparison of Fe-Ni-P-Si alloys prepared by ball milling

Abstract Fe–Ni–P–Si alloys were synthesized from powders in a planetary ball-mill. The microstructure and thermal properties of the milled powders were measured by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The diffraction peaks of the individual powders are not detected after the first 32 h of milling time. During milling amorphous and amorphous-like phases are formed. Differential scanning calorimetry results show exothermic reactions for all of the compositions indicating a recovery process as well as crystallization of the amorphous phase. The crystallization products are compared to starting powders. The use of Fe and Ni in the alloy reduces both the energy of formation of the amorphous phase and the time necessary to produce this phase.The incorporation of Si into the Fe–Ni-based alloy favors the formation of a more stable amorphous phase. Moreover, the use of Fe 3 P as starting powder increases the time to form the amorphous phase. The larger the Si content, the greater the thermal stability of the amorphous phase produced during mechanical alloying.