Accelerated and conventional development of magnetic high entropy alloys

High-entropy alloys (HEA) are of high current interest due to their unique and attractive combination of structural, physical, chemical or magnetic properties. HEA comprise multiple principal elements, unlike conventional alloys. The composition space of HEA is enormous and only a minuscule fraction has been studied. Magnetic HEA are a promising alternative to conventional soft magnetic metallic materials, which typically exhibit poor mechanical properties. We review the progress in the development of magnetic HEA. The influence of alloy composition, crystal structure, phase fraction and processing parameters on the magnetic properties are discussed. Magnetic HEA processed by advanced experimental high throughput techniques such as additive manufacturing, co-sputtering, diffusion multiples, rapid prototyping, and designed via combinatorial computational techniques, such as thermodynamic and phase diagram calculations, density functional theory, machine learning etc. are reviewed. Conventional processing techniques are also discussed. Future trends in magnetic HEA are outlined.     

Synthesis,characterization, and magnetic properties of carbon- and boron-oxide-encapsulated iron nanocapsules

Carbon- and boron-oxide-encapsulated iron nanocapsules have been synthesized by arc discharge in methane (CH4) and diborane (B2H6) atmospheres respectively. The characterization and magnetic properties of carbon- and boron-oxide-encapsulated iron nanocapsules [abbreviated as Fe(C) and Fe(B) respectively] were investigated and compared. The structure of the Fe(B) nanocapsules is different from that of the Fe(C) nanocapsules. The Fe(C) nanocapsules consist of a crystalline graphite shell and a core of alpha-Fe and/or Fe3C. The Fe(B) nanocapsules consist of an amorphous boron-oxide layer and a core of Fe(B) solid solution, alpha-Fe, gamma-Fe, FeB, and/or Fe3B phases. The saturation magnetizations of both the Fe(C) and the Fe(B) nanocapsules below 300 K decrease monotonically with increasing temperature. The coercivities of the Fe(C) and Fe(B) nanocapsules are almost 2 orders of magnitude higher than that of bulk Fe. The temperature dependence of magnetization at high temperatures indicates the existence of some phase transformations.     

相反转界面细乳液聚合法制备石蜡纳胶囊与表征

采用相反转乳化的界面细乳液聚合法制备了以交联聚甲基丙烯酯甲酯为壁材,以石蜡为芯材的纳胶囊。利用光学显微镜、激光粒度分析仪、透射电镜、红外光谱仪、差示扫描量热分析仪等研究了含氟助乳化剂FC-4430、丙烯酸十八酯(SA)及芯材投料量对聚合过程、产品表面形貌、粒径、化学结构、储热性能和包覆率的影响。结果表明,FC-4430对相反转有促进作用,可降低胶囊粒子尺寸且利于包封;SA能提高纳胶囊的包覆率和热稳定性;当FC-4430用量为0.4%,SA用量为2%,m(core)∶m(shell)为2∶1时,纳胶囊的相变潜热为91.7 J/g,包覆率为63.3%,包覆效率为95.0%,胶囊粒子为球形,表面光滑,粒径为0.6~1μm,呈明显的核壳结构,芯材直径为300~500 nm。     

Iron-included carbon nanocapsules coated with biocompatible poly(ethylene glycol) shells

Nanoparticles of iron carbides wrapped in multilayered graphitic sheets (carbon nanocapsules) were synthesized by electric plasma discharge in an ultrasonic cavitation field in liquid ethanol and purified by selective oxidation and magnetic separation. The particles had 100–200 nm in diameter after centrifuging for 10 min at 4000 rpm. Carbon nanocapsules were covered by wispy poly(ethylene glycol) PEG coating about 7–10 nm in thickness. The number of PEG chains coated on carbon nanocapsules could be estimated as 9.15%. The values of saturation magnetization Ms and coercivity Hc of purified carbon nanocapsules without PEG coating were 112 emu g⁻¹ and 75 Oe respectively. Magnetically soft carbon nanocapsules with a poly(ethylene glycol) coating on the surface may possibly be used as biocompatible magnetic nanoparticles in medical applications.     

Sacrificial functional polystyrene template to prepare chitosan nanocapsules and in vitro drug release properties

In this study, biocompatible and biodegradable chitosan (CS) nanocapsules are successfully prepared in abundant and easily using carboxyl-functionalized polystyrene (PS) as sacrificial template and cross-linked CS with glutaraldehyde as the shell. First, the monodisperse functionalized PS templates be about 200 nm are made by emulsifier-free emulsion polymerization. Second, nanocapsules are accomplished by fabricating on the basis of chemical cross-linking on the surface of the PS template and removing the core via tetrahydrofuran. The templates and nanocapsules were characterized by FT–IR, ¹H NMR, FESEM, and TEM. All the results confirmed that the nanocapsules are accomplished via this method. By dissolution of ibuprofen in the chloroform droplets when prepare the carboxyl-functionalized PS, drug-loaded nanocapsules are also fabricated. It is found that the loaded drug can be released again in a sustained manner for up to 80 h. The nanocapsules walls have a prominent effect in slowing down the drug release rate.     

Silica-coated iron nanoparticles: Shape-controlled synthesis,magnetism and microwave absorption properties

Body-centered cubic (bcc) phase iron nanocrystals with granular, rod-like and flaky shapes were prepared through a simple surfactant-controlled chemical reduction route. In view of extra stability and enhanced manipulative ability, thus-prepared iron nanoparticles were morphology-retained modified with a thin silica shell through a Stöber process. A serial of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS), thermogravimetry (TG), vibrating sample magnetometer (VSM) and scalar network analyzer (SNA) were used to characterize the iron particles before and after silica coating. Results showed that the surface silica coating could effectively improve the oxidation resistance and microwave absorption performance of iron particles, while slightly influenced their magnetic properties. Furthermore, the flaky Fe@SiO₂ nanocapsules particles exhibited better microwave absorption performance than that of the granular and rod-like counterparts, which could be ascribed to the shape effect.     

Nanoparticles for drug delivery: review of the formulation and process difficulties illustrated by the emulsion-diffusion process

The elaboration of nanoparticles aqueous suspensions aimed at the drug delivery and related process development appear as difficult tasks, due to specificities related to the nanometric size. Such small sizes are required for specific applications in pharmacy. The switch of micrometric to nanometric field represents an actual challenge and cannot be considered as a simple scaling-down of chemical engineers. Ideas and concepts developed first in nanosciences have been adapted to the pharmaceutical application in drug delivery. In spite of drastic constraints due to pharmaceutical application, some parameters allow the control. A brief and not exhaustive review of the state-of-the-art on polymer particles used in the drug delivery field is presented. Attention was more particularly paid on preparation processes and their constraints by describing advantages and drawbacks of each process. The adaptation to the pharmaceutical field, the difficulties and pitfalls which are shared, with most research works in nanoscience, are illustrated thanks to our own results on nanocapsules obtained by "emulsion-diffusion" process presented as a case-study. Thanks to these results, we illustrate the peculiar features and difficulties encountered regarding nanocapsules preparation and characterization. Indeed, such a process allows to prepare nanocapsules of few hundreds nanometers diameter having an oil core surrounded by a polymeric membrane. The characterization of such soft particles colloidal suspensions is often difficult and involves heavy investigation techniques in order to highlight physical mechanisms leading to the nanocapsule properties. This is a key step regarding the final properties as a drug delivery system.     

Magnetic and Microwave-absorption Properties of Graphite-coated (Fe, Ni) Nanocapsules

The structure, magnetic and microwave-absorption properties of graphite-coated (Fe, Ni) alloy nanocapsules, synthesized by the arc-discharge method, have been studied. High-resolution transmission electron microscopy shows that the nanocapsules have a core/shell structure with (Fe, Ni) alloy as the core and graphite as the shell. All (Fe, Ni) alloy nanocapsules/paraffin composites show good microwave-absorption properties. The optimal reflection loss (RL) was found for (Fe70Ni30)/C nanocapsules/paraffin composites, being -47.84 dB at 14.6 GHz for an absorber thickness of 1.99 mm, while the RL values exceeding -10 dB were found in the 12.4- 17.4 GHz range, which almost covers the Ku band (12.4-18 GHz). For (Fe70Ni30)/C nanocapsules/paraffin composites, RL values can exceed -10 dB in the 11.4-18 GHz range with an absorber thickness of 1.91 mm, which cover the whole Ku band.     

Magnetic Properties of Ni Nanoparticles and Ni（C） Nanocapsules

Structure and magnetic properties of Ni nanoparticles and Ni(C) nanocapsules were studied.The carbon atoms hardly affect the lattice of Ni to form Ni-C solid solution or nickel carbides.The large thermal irreversibility in zero-field-cooled and zero-field magnetization curves indicates magnetic blocking with a wide energy barrier.Saturation magnetization,remanent magnetization and coercivity of Ni(C) nanocapsules decrease with increasing temperature.magnetization,remanent magnetization and coercivity of Ni(C) nanocapsules decrease with increasing temperature.     

Reversible pore-structure evolution in hollow silica nanocapsules: large pores for siRNA delivery and nanoparticle collecting

The effective modulation of pore sizes for nanoporous silica nanoparticles still remains a great challenge not satisfactorily solved. In this paper, the pore sizes in the shell of hollow silica nanocapsules are well-tuned by a reversible Si-O bond breakage and reformation process under mildly alkaline conditions (e.g., Na(2) CO(3) solution). The pores in nanosized hollow silica capsules can be modulated from 3.2 nm to larger than 10 nm by a novel, surfactant-directing alkaline-etching (SDAE) strategy. Interestingly, the pores can be fully filled through the regrowth of the dissoluted silicates by bonding to silanols (Si-OH) on the wall surface to generate the nonporous hollow silica nanocapsules. The large-sized pore hollow silica nanocapsules exhibit excellent siRNA-loading capabilities and intracellular transfection efficiencies in vitro. In addition, the large pores in the shell of hollow silica nanocapsules are explored as channels for collecting superparamagnetic, small-sized Fe(3) O(4) nanoparticles as contrast agents for magnetic resonance imaging, initiating a special approach towards pore-size modulation and multifunctionalization of silica-based nanostructural materials for nanobiomedical applications.     

FePt nanocluster films for high-density magnetic recording

High anisotropy L1(0) ordered FePt thin films are considered to have high potential for use as high areal density recording media, beyond 1 Tera bit/in2. In this paper, we review recent results on the synthesis and magnetic properties of L1(0) FePt nanocomposite films. Several fabrication methods have been developed to produce high-anisotropy FePt films: epitaxial and non-epitaxial growth of (001)-oriented FePt:X (X = Au, Ag, Cu, C, etc.) composite films that might be used for perpendicular media; monodispersed FePt nanocluster-assembled films grown with a gas-aggregation technique and having uniform cluster size and narrow size distribution; self-assembled FePt particles prepared with chemical synthesis by reduction/decomposition techniques, etc. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. FePt and related films show promise for development as heat-assisted magnetic recording media at extremely high areal densities. The self-assembled FePt arrays show potential for approaching the ultimate goal of single-grain-per-bit patterned media.     

Wrap-bake-peel process for nanostructural transformation from beta-FeOOH nanorods to biocompatible iron oxide nanocapsules

The thermal treatment of nanostructured materials to improve their properties generally results in undesirable aggregation and sintering. Here, we report on a novel wrap-bake-peel process, which involves silica coating, heat treatment and finally the removal of the silica layer, to transform the phases and structures of nanostructured materials while preserving their nanostructural characteristics. We demonstrate, as a proof-of-concept, the fabrication of water-dispersible and biocompatible hollow iron oxide nanocapsules by applying this wrap-bake-peel process to spindle-shaped akagenite (beta-FeOOH) nanoparticles. Depending on the heat treatment conditions, hollow nanocapsules of either haematite or magnetite were produced. The synthesized water-dispersible magnetite nanocapsules were successfully used not only as a drug-delivery vehicle, but also as a T2 magnetic resonance imaging contrast agent. The current process is generally applicable, and was used to transform heterostructured FePt nanoparticles to high-temperature face-centred-tetragonal-phase FePt alloy nanocrystals.     

Exploring nanoscale magnetism in advanced materials with polarized X-rays

Nanoscale magnetism is of paramount scientific interest and high technological relevance. To control magnetization on a nanoscale, both external magnetic fields and spin polarized currents, which generate a spin torque onto the local spin configuration, are being used. Novel ideas of manipulating the spins by electric fields or photons are emerging and benefit from advances in nano-preparation techniques of complex magnetic materials, such as multiferroics, ferromagnetic semiconductors, nanostructures, etc.Advanced analytical tools are needed for their characterization. Polarized soft X-rays using X-ray dichroism effects are used in a variety of spectroscopic and microscopic techniques capable of quantifying in an element, valence and site-sensitive way basic properties of ferro(i)- and antiferromagnetic systems, such as spin and orbital moments, nanoscale spin configurations and spin dynamics with sub-ns time resolution. Future X-ray sources, such as free electron lasers will provide an enormous increase in peak brilliance and open the fs time window to studies of magnetic materials. Thus fundamental magnetic time scales with nanometer spatial resolution can be addressed.This review provides an overview and future opportunities of analytical tools using polarized X-rays by selected examples of current research with advanced magnetic materials.     

Microstructure,mechanical and tribological properties of high velocity oxy fuel thermal spray coating: A review

Iron alloy based amorphous coating materials have enormous potential in wide range of applications such as petrochemical, aerospace, ocean, and electronic communications due to their better mechanical properties, chemical properties, magnetic properties and tribological properties. The industrial applications of coating are increasing rapidly due to many advancements in the material development and coating deposition techniques. The present paper reviewed the recent progresses in deposition technologies, development of new high order alloys and composite based coating materials. In this regard, change in microstructure, elemental composition, mechanical and tribological properties on performance of iron alloy based coating properties were presented. It can be concluded that the tribological properties of coating is dependent on pre-coating and post-coating factors. Pre-coating factors include coating deposition techniques, coating layer thickness and coating parameters such as spray distance, oxygen flow rate etc. Post-coating factors include microstructure, hardness, fracture toughness and adhesion strength. Therefore, multi-criteria decision making techniques can be the best approach to find the optimum formulation of coating materials to achieve desired set of objectives under the conflicting criteria.     

碳纳米洋葱制备方法的研究进展

碳纳米洋葱是继富勒烯与碳纳米管之后的又一新型碳纳米材料,在润滑剂、磁性材料等领域具有广阔的应用前景.综述了碳纳米洋葱的主要合成方法(电弧放电法、等离子体法、电子束照射法、热处理法、热解法和化学气相沉积法)及其特点,讨论了碳洋葱的形成机理,并简单介绍了碳纳米洋葱的性能及其应用.     

Preparation of stimuli-responsive nano-sized capsules based on cyclodextrin polymers with redox or light switching properties

We report the preparation and encapsulation properties of stimuli-responsive nanocapsules, self-assembled by the noncovalent interactions of cyclodextrinappended polymers (host) and complementary ferrocene or azobenzene carriers (guest). The encapsulation process was significantly accelerated by applying (electro) chemical or light stimulus, enabling the easier and faster diffusion of guest molecules through the polymer layers. The nanocapsules were characterized by dynamic light scattering, confocal microscopy, ESEM, AFM, UV–visible and fluorescence spectroscopy, and electrochemical techniques. The encapsulation and release properties of the nanocapsules were reversible and could be repeated several times, indicating that the prepared nanoassemblies are very stable.

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Facile approach for temperature-responsive polymeric nanocapsules with movable magnetic cores

A novel facile approach was developed to prepare the well-defined temperature-responsive polymeric nanocapsules with movable magnetic cores (TPNMCs) based on the organic/inorganic sandwich-structured composite nanoparticles with temperature-responsive crosslinked shells via the one-pot approach surface-initiated atom transfer radical copolymerization (SI-ATRP) of N-isopropyl acrylamide (NIPAM) and N,N′-methylenebisacrylamide (MBA) from the surfaces of the Fe₃O₄@SiO₂ core-shell nanoparticles, followed by the selective removal of the silica layer. Based on the temperature-induced volume phase transition and impressive magnetic response, the TPNMCs are expected to be used for the targeted controlled release of sensitive molecules, such as enzymes, proteins or DNA, by responding to the changing the environmental temperature.     

Chitosan nanocapsules as carriers for oral peptide delivery: effect of chitosan molecular weight and type of salt on the in vitro behaviour and in vivo effectiveness

We have recently reported preliminary data showing the efficacy of chitosan nanocapsules as carriers for oral peptide delivery. In the present work, our aim was to investigate the influence of some chitosan properties, such as the molecular weight and type of salt, on the interaction of these nanocapsules with the Caco-2 cells and also on their in vivo effectiveness. Chitosan nanocapsules were prepared by the solvent displacement technique using high (450 kDa) and medium (160 kDa) molecular weight chitosan glutamate as well as high molecular weight chitosan hydrochloride (270 kDa). The results indicated that the size of the nanocapsules was dependent on the chitosan molecular weight, whereas the zeta potential and the association efficiency of salmon calcitonin were not affected by the chitosan properties. Upon incubation with the Caco-2 cells, chitosan nanocapsules exhibited a dose-dependent cellular viability, which was hardly affected by, either the chitosan molecular weight or, the type of salt. In addition, it was observed that the transepithelial electrical resistance of the Caco-2 monolayer was not significantly modified upon their exposure to chitosan nanocapsules. The results of the in vivo studies, following oral administration to rats, indicated that chitosan nanocapsules were able to reduce significantly the serum calcium levels, and to prolong this reduction for at least 24 hours, irrespective of the type of chitosan salt and molecular weight of chitosan. Consequently, the performance of chitosan nanocapsules as oral carriers for salmon calcitonin was not affected by the characteristics of chitosan.     

壳聚糖基纳米胶囊的制备及应用研究新进展

壳聚糖是自然界产量最大的氨基多糖,具有较好的生物降解性、生物相容性、成膜性及良好的抗菌性.主要阐述了近年来制备壳聚糖基纳米胶囊的一些方法,如离子交联法、界面聚合法及层层自组装法等,并着重综述了近年来壳聚糖基纳米胶囊在医药、食品及纺织领域的应用研究进展.最后,根据现阶段的研究状况对壳聚糖基纳米胶囊的研究前景做了展望.     

Characterization of coatings

The variety of physical and chemical properties of coatings is determined by their thickness, structure and chemical composition. A fundamental understanding of coating properties, as well as of their reproducibility, therefore requires a good knowledge of these parameters.During the last few years great progress has been made in the field of chemical analysis (including depth distribution) of thin films and coatings. This progress is mainly the result of the combination of recently developed surface analytical techniques such as Auger electron spectroscopy (AES), photoelectron spectroscopy (UPS, XPS), ion scattering spectroscopy (ISS) and secondary ion mass spectroscopy (SIMS), on one hand, and controlled simultaneous surface etching by sputtering on the other.With these surface analytical techniques the chemical composition of the uppermost monolayers is detected by energy or mass analysis of ion- (ISS, SIMS), electron- (AES) or photon- (UPS, XPS) induced emission of ions (ISS, SIMS) or electron (AES, UPS, XPS), respectively. By combining these techniques with sputtering, the depth distribution of elements and compounds can also be determined with a lateral resolution of some microns.In order to recognize the capabilities and limitations of these techniques for coating analysis, the fundamental emission processes as they appear in the various analytical techniques, as well as the details of the sputtering process, have to be taken into account. The main features such as detection limits, isotope sensitivity, detection of compounds etc. of these techniques will be compared for some typical examples.Other methods, such as high energy ion backscattering and the detection of sputtered particles in the gas phase, will also be considered.