DSC analysis of Nd-Fe-B ribbons prepared by melt-spinning method with diverse compositions and cooling rates

Nd9.4Pr0.6Fe77.5-xB6Co6Ga0.5TixCx(x= 0, 1.5, 3, 4.5, 6) Melt-spun ribbons have been prepared at 15, 20 and 25 m/s quenching wheel speeds and were examined by using differential scanning calorimetry (DSC). It is remarkable that peak intensity increases with increasing solidification rate or the higher the Ti and C content of the structure. In both cases, the increased amounts of amorphous phase indicate their strongest peaks in the diagram. Another point related to the crystallization temperature of the ribbons in the presence of Ti and C, which will be discussed in detail in this manuscript

Effects of heat treatment on the magnetic properties of melt-spun Nd6Pr1Fe76B12Ti4C1Co3 nanocomposite ribbons

In this study, the effects of different annealing temperatures on the structure and magnetic properties of Nd-Fe-B nanocomposite permanent magnetic alloys with nominal composition of Nd6Pr1Fe76B12Ti4C1Co3 have been investigated. Melt Spinning (one of the most predominant ribbon synthesize methods) with constant wheel speed of V = 25 m/s was employed to produce ribbons. As-spun ribbons were examined by using xray diffractometer (XRD) with Cu-Kα radiation and differential scanning calorimetry (DSC). The ribbons were annealed at different temperatures in order to extract the best magnetic properties. The XRD and electron microscopy technique results confirm that grains are in the size of less than 50 nm. In addition, optimum magnetic properties were obtained at 720°C annealed temperature

Preparation and magnetic properties of Ni-Cr doped strontium hexaferrite

The Ni-Cr-substituted M-type Strontium Hexaferrite such as SrFe12-2xNixCrxO19, with x =0.2, 0.4, 0.6, 0.8 mol% has been successfully prepared by the sol-gel process. The ferrites were systematically investigated by using powder X-Ray diffractometer (XRD), High Resolution Scanning Electron Microscope (HR-SEM) and Vibrating Sample Magnetometer (VSM). The XRD analysis confirms the single phase and lattice constants (a and c), have been calculated from the XRD data using powderX software. The lattice parameter was found to increase with increasing nickel-chromium concentration. Values of coercivity are found to increase up to the substitution level of x = 0.0-0.2 and then decrease slightly while that of saturation decrease continuously with increase in Ni-Cr concentration

Dependence of microstructure and magnetic properties of (Nd,Pr)-(Fe,Ti,C)-B melt-spun ribbon on quenching wheel speed

Melt-spun ribbons with nominal composition of Nd6Pr1Fe76B12Ti4C1 have been prepared at different quenching wheel speeds (5, 7.5, 10 and 15 m/s) and investigated for microstructural and magnetic properties. The asspun ribbons were examined by using x-ray diffractometry (XRD) with Cu-kα radiation and differential scanning calorimetry (DSC) and vibrating sample magnetometry (VSM). Based on the results obtained, it was shown that the lower speeds increased the magnetic properties. Hence, a uniform Nd2Fe14B/Fe3B nanocomposite structure with fine soft grains can be developed at an optimum quenching wheel speed of about 5 m/s. Further, it is seen that the higher quenching wheel speed leads to a lower grain size and higher amorphous phase amount

Influence of Er on microstructural and dielectric properties of CaCu3Ti4O12

Erbium-doped CaCu3Ti(4−x)ErxO12 (x = 0, 0.02, 0.1, 0.2, 0.5, 1.0)—(CCTEO) samples were synthesized by using the sol–gel method. The crystal structure did not change on doping with erbium; and it remained cubic when all the six compositions were studied. It was found that lattice parameter increased slightly with Erbium doping. AFM studies showed that the particle size of the CCTEO powder ranged from 52 to 97 nm. The surface morphology of the samples sintered at 1,040 °C in air for 3 h was observed using a high resolution scanning electron microscope. It showed that the grain size was in the range of 0.7–5 µm for these samples. Er doping has been shown to reduce the dielectric loss remarkably while maintaining a high dielectric constant. This result indicates that 0.02 mol% of Er dopant can be used to improve the dielectric properties (dielectric constant- 164,000) of CaCu3Ti4O12

Magnetic-property enhancement of sized controlled cobalt-gold core-shell nanocrystals

Cobalt nanoparticles and cobalt-gold core-shell nanoparticles were synthesized via reverse-micelle microemulsion method with emphasis on size control. Cobalt nanoparticles become easily oxidized therefore coating a gold shell on cobalt nanoparticles was necessary and can effectively reduce the oxidation of Co while maintaining most of its magnetic properties. Controlling the size of nanoparticles was performed by adjusting the water to surfactant ratio of reverse micelle solution during synthesis. X-ray diffraction data was used to calculate the crystallinity percentage and percentage of phases presented in Co-Au core-shell nanoparticles. The results from transmission electron microscopy, and field emission electron microscopy combined to energy dispersive x-ray spectroscopy provide direct evidence for shell growth. The average coating layer (shell thickness) in all cases observed to be 4-5 nm. Magnetic properties of samples were investigated using a vibrating sample magnetometer before and after annealing. Magnetic properties enhanced after annealing in all cases. An increase in saturation magnetization after annealing was due to increase in cystallinity percentage. A simple method was applied to measure a totally intrinsic blocking temperature in zero field cooled-warmed (ZFC-W) curves without employing an external magnetic field. The B-field dependence temperature data of Co-Au nanoparticles before and after annealing showed an intrinsic blocking temperature of 45 and 40 K respectively

Phase transformation, structure and magnetic properties of Nd9.4Pr0.6FebalTixCxCo6Ga0.5B6 ribbons prepared by melt-spinning method

The effect of Carbon and Titanium additions on the phase constitution, microstructures and the magnetic properties of Nd-Fe-B isotropic nanocomposite processed from Nd9.4Pr0.6FebalCo6B6Ga0.5TixCx (x=0, 3, 6) ribbons has been investigated. As-spun ribbons were examined by using X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). Optimally quenched and annealed Nd9.4Pr0.6FebalCo6B6Ga0.5TixCx (x=0, 3, 6) ribbons at 750 °C for 10 minutes, which was composed of Nd2Fe14B grains separated by α-Fe grain boundary phase, shows addition of Ti suppresses formation of primary Fe and promotes formation of ferromagnetic iron-borides. Carbon addition is effective for grain refinement and suppression of unfavourable formation of TiB2; resulting in improvement of magnetic properties. The results show that Titanuim and Carbon additions enhance the glass forming ability and increase the crystallization temperature. XRD results of annealed ribbons indicate that Ti and C react to form TiC. The grain size was substantially refined by the addition of Ti due to the formation of Ti-enriched amorphous grain boundaries. The XRD and Atomic force microscope (AFM) technique results confirm that grains are in the size of less than 70 nm. Furthermore, addition of C enhanced the enrichment of Ti in the grain boundary phase, which led to the increase of the coercivity and the maximum energy product

Recording-media-related morphology and magnetic properties of crystalline CoPt3 and CoPt3-Au core-shell nanoparticles synthesized via reverse microemulsion

A comparative experimental study of the magnetic properties of CoPt3 and CoPt3/Au nanoparticles as well as a detailed study of the structural properties of the samples by X-ray diffraction, Transmission electron microscopy, and vibrating sample magnetometer is presented in this work. In addition, the effect of particle size on the structure and magnetic properties of nanoparticles prepared by microemulsion is studied. The correlation between particle size, crystallinity, and magnetization was studied as well. CoPt nanoparticles have been studied intensively over the last decade because of their increased magnetic anisotropy in the ordered phase that can be interesting for high density magnetic recording. A significant high coercivity for as-prepared CoPt3 and CoPt3-Au nanoparticles was obtained at room temperature and enhanced after annealing. The focused aim of our study is to obtain high coercivity at room temperature that follows the Curie-Weiss law. This indicates an interacting system in which the nanoparticles behave like single domain ferromagnetic materials in the particle size range of 8 to 35 nm. In addition, the interaction increases by cooling the samples to low temperature around 15 K. Temperature dependence 1/M graph was obtained to investigate the behavior of nanoparticles at low temperature and shows the best fit with Curie-Weis mode

Estudi dels exosomes com a mecanisme de comunicació intercel·lular en patologies pancreàtiques

[cat] La pancreatitis aguda és un procés inflamatori del pàncrees desencadenat per una activació inapropiada dels enzims pancreàtics. En la seva variant més severa, la malaltia progressa acompanyada d’afectacions no només a nivell local sino també sistèmic, essent la síndrome de resposta inflamatòria sistèmica (SIRS) i el dany pulmonar que se’n deriva una de les afectacions més primerenques i la principal causa de mortalitat dels pacients. Diferents estudis han identificat l’increment en l’expressió i secreció de múltiples mediadors inflamatoris, generats tant a nivell local com sistèmic. No obstant, el mecanisme patogènic de la malaltia encara es desconeix, de manera que en les fases inicials de la malaltia no és possible predir si un pacient desenvoluparà una variant lleu o severa de pancreatitis. A llarg dels últims anys, però, el descobriment dels exosomes ha revolucionat el camp de la comunicació intercel·lular. Aquestes vesícules extracel·lulars són capaces de transferir proteïnes, miRNAs i mRNAs de manera encapsulada, tot protegint-los del medi extracel·lular i transportant-los fins a òrgans i indrets del cos allunyats del seu focus de síntesi. En aquesta tesi, utilitzant un model experimental de pancreatitis aguda induïda per taurocolat sòdic en rata, hem avaluat el paper dels exosomes en la propagació de la resposta inflamatòria sistèmica. Els resultats obtinguts indiquen que posteriorment a la inducció de la malaltia hi ha un increment de la concentració d’exosomes circulants, els quals presenten un perfil proteic diferent dels exosomes circulants que hi ha en condicions control. Mitjançant experiments de marcatge i seguiment d’aquestes vesícules hem determinat que els exosomes circulants són capaços de creuar la barrera alveolocapil·lar i d’arribar fins l’espai aveolar, on són captats pels macròfags pulmonars residents. A més, en experiments in vitro es demostra com els exosomes secretats en condicions inflamatòries activen i polaritzen els macròfags cap a un fenotip de tipus proinflamatori. L’anàlisi proteòmic dels exosomes circulants mostra com, durant la pancreatitis aguda severa, aquestes vesícules presenten una gran quantitat de proteïnes sintetitzades majoritàriament pel teixit hepàtic, suggerint que el fetge podria estar secretant nous exosomes i alliberant-los al torrent sanguini en el transcurs de la malaltia. Aquesta hipòtesi va ser reforçada amb nous experiments de marcatge i seguiment dels exosomes, gràcies als quals es va observar com els exosomes generats a la cavitat peritoneal durant la pancreatitis aguda severa són filtrats i retinguts pel teixit hepàtic. En conjunt, els resultats obtinguts reforcen la idea que el fetge tindria un paper central durant la pancreatits aguda i que cal tenir-lo en compte per comprendre quin mecanisme regula l’extensió de la resposta inflamatòria en el transcurs de la malaltia. En tot aquest procés, a més, la lectina REG3-beta podria tenir un paper destacat. Aquesta proteïna d’estrès és una de les més sintetitzades pel pàncrees durant la pancreatitis aguda, la concentració de la qual pot arribar a augmentar fins a 100 vegades durant la fase aguda de la malaltia. La seva funció específica, però, a dia d’avui encara no s’ha descrit ben bé, tot i que se li han atribuït certes propietats antiinflamatòries, mitogèniques i d’opsonització de bacteris. En aquesta tesi es demostra com REG3-beta és capaç d’unir-se a la membrana dels exosomes circulants. A més, hem caracteritzat com aquesta unió depèn del seu domini lectina, i que comporta un bloqueig de la captació de les vesícules per part de les seves cèl·lules diana, impedint que aquestes alliberin els seus mediadors i duguin a terme la seva funció.[eng] Severe acute pancreatitis is an inflammatory disease of the pancreas which progresses accompanied by local and systemic alterations, being lung damage and SIRS the leading causes of death. Despite multiple inflammatory mediators have been detected and described, the pathogenic mechanism of the disease is still unknown. However, over the last few years the discovery of exosomes has revolutionized the field of intercellular communication, since they are able to transfer mediators such as proteins, miRNAs and mRNAs to distant organs. In this work, using an experimental model of taurocholate-induced acute pancreatitis in rats, we evaluated the role of exosomes in the extent of the systemic inflammatory response. Our results indicate that during acute pancreatitis, there is an increase in the concentration of circulating exosomes. By fluorescent exosome tracking in vivo experiments we demonstrate that circulating exosomes are able to cross the alveolocapillary barrier, be phagocyted by alveolar macrophages and polarize them to a proinflammatory phenotype in vitro. The proteomic analysis of circulating exosomes showed that, during acute pancreatitis, exosomes present a large number of proteins synthesized mainly by the hepatic tissue, suggesting that the liver is secreting new exosomes and releasing them into the bloodstream during the course of the disease. This hypothesis was reinforced with new tracking experiments, where we observed that that exosomes generated in the peritoneal cavity during severe acute pancreatitis are filtered and retained by the liver tissue. Overall, these results reveal that the liver would play a central role during severe acute pancreatitis and that it should be taken into account to understand which mechanism regulates the extent of the inflammatory response. The lectine REG3-beta could also play a prominent role in all this process. REG3-beta is the main protein synthesised by the pancreas during acute pancreatitis, the concentration of which can increase up to 100 times. Its specific function has not yet been described, although certain anti-inflammatory, mitogenic and opsonising properties have been attributed to it. In this thesis we demonstrate that REG3-beta binds to the membrane of circulating exosomes and that this interaction depends on its lectin domain. Consequently, this interaction blocks the exosome capture by target cells, preventing them from releasing their mediators and blocking their function

Influence of process-induced microstructure and additives (CO, AL, TI, C) on magnetic properties of ND-FE-B based isotropic hard magnetic materials

Nanocrystalline permanent magnets offer original magnetic features as a result of surface or interface consequences which are different from properties of bulk or microcrystalline materials. The main reason for this is the grain size and the presence or absence of intergranular stages. Most of the NdFeB research literature has only very superficially dealt with the question of how to improve the magnetic properties of the NdFeB materials. The literature has covered in great detail the answers for the case of Rare Earth-Iron-Boron-based materials obtained from high amounts of rare earth material. Thus, this work was a fresh attempt to critically track the influence of process-induced microstructure, additives and annealing temperature on magnetic properties of (Nd, Pr)-(Fe, Ti, C, Co, Al)-B isotropic nanocomposite alloys with unique compositions, containing medium amounts of boron and lesser amounts of rare earth material. Various routes were used to organize them, such as direct quenching with different roll rates, devitrification of amorphous over-quenched ribbons by annealing at different temperature ranges and mechanical alloying technique. The results of a methodical analysis of the relationship between microstructure and magnetic properties in isotropic nanocrystalline (Nd,Pr)-(Fe,Ti,C,Co,Al)-B permanent magnets were provided in the present study. The first section explains how microstructure and magnetic properties of (Nd,Pr)-(Fe,Ti,C)-B Melt-spun ribbons are dependent on the solidification rate (quenching wheel speed). Based on these results, the lower speeds were shown to increase the magnetic properties. Thus, we can develop a uniform Nd2Fe14B/Fe3B nanocomposite structure with fine soft grains at an optimum 5m/s quenching wheel speed. Moreover, it was shown that increasing quenching wheel speed results in reduced grain size and higher amount of amorphous phase. The second section, presents the impact of Titanium, Carbon, Cobalt and Aluminum additions on the crystallization behavior, microstructure and magnetic properties of (Nd,Pr)-Fe-B alloys with different compositions. It was shown that additions of Ti and C improved the glass forming ability and raised the temperature of crystallization. Ti addition led to considerable refinement of grain size as a result of the formation of amorphous grain boundaries enriched with Ti. Further C addition led to the enhancement of Ti enrichment in the grain boundary stage that increased coercivity and maximum energy product. The best magnetic properties were obtained from the samples which contain 3 atomic percentages of Titanium and Cobalt. In addition, it was shown that additions of Co increase the temperature of crystallization. Additionally, substitution of Co enhances the generation of 2:14:1 phase that leads to a considerable increase in coercivity of the ribbons. The appropriate substitution of Co makes intergranular exchange coupling of the grains stronger and results in the improvement of the remanence and energy product for the (Nd,Pr)2(Fe,Ti,C)14B/Fe3B type ribbons. The best magnetic properties were achieved for ribbons with Co3. Nevertheless, small aluminum addition improves coercivity. The Al and Co combination leads to Nd3Co and Nd(Fe,Al)2 formation at the grain triple points after heating and results in better magnetic isolation of grains. Also, the uniform grain boundary distribution and increasing anisotropy field of the alloys improve alloy coercivity. The third section investigates the effects of different annealing temperatures on the magnetic properties and structure of Nd-Fe-B nanocomposite permanent magnetic alloys with different compositions. Generally, it has been shown that the amorphous alloys’ crystallization behavior is strongly dependent on the temperature of heat treatment and the size and volume fraction of α-Fe and Nd2Fe14B can be manipulated by subsequent thermal processing. Furthermore, magnetic properties are highly dependent on the grain size of the hard and soft magnetic phase. Hence, the increase and decrease of annealing temperature will increase and decrease the magnetic properties. Finally, the best magnetic properties in type (E) and type (F) were achieved at 720 oC and 700 oC annealing temperatures respectively, with the (BH)max=60.48 KJ/m3 in type (F) ribbons