Synthesis and Characterization of Gadolinium Oxide-Hematite Magnetic Ceramic Nanostructures

Mixed-oxide nanostructures of the type xGd2O3-(1-x)α-Fe2O3 (x=0.1, 0.3, 0.5 and 0.7) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The systems were subsequently analyzed by Mӧssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The magnetic hyperfine field was studied as function of ball milling time for all sextets involved and found to be consistent with the formation of a limited solid solution in the systems investigated. The end-product was the gadolinium perovskite, represented by a doublet whose abundance was derived as function of the milling time. The XRPD patterns recorded for the equimolar composition were dominated by the diffraction peaks of GdFeO3 after 12 hours of milling. The hysteresis loops were recorded at 300 and 5 K in an applied magnetic field of 5 T and were interpreted as a superposition of paramagnetic behavior of gadolinium oxide and weak ferromagnetic behavior of hematite and gadolinium perovskite. The Morin transition of hematite was inferred from zero-field-cooling-field-cooling (ZFC-FC) curves measured with a magnetic field of 200 Oe in the 5-300 K temperature range and was found to depend on the ball milling time. Optical diffuse reflectance spectra showed that the compounds were semiconductors with an optical band gap of 2.1 eV.

Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO_(2) Thin Films

Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.

The impact of having an oxygen-rich microporous surface in carbon electrodes for high-power aqueous supercapacitors

The growth of electrical transportation is crucially important to mitigate rising climate change concerns regarding materials supply.Supercapacitors are high-power devices,particularly suitable for public transportation since they can easily store breaking energy due to their high-rate charging ability.Additionally,they can function with two carbon electrodes,which is an advantage due to the abundance of carbon in biomass and other waste materials(i.e.,plastic waste).Newly developed supercapacitive nanocarbons display extremely narrow micropores(<0.8 nm),as it increases drastically the capacitance in aqueous electrolytes.Here,we present a strategy to produce low-cost flexible microporous electrodes with extremely high power density(>100 kW kg^(-1)),using fourty times less activating agent than traditionnal chemically activated carbons.We also demonstrate that the affinity between the carbon and the electrolyte is of paramount importance to maintain rapid ionic diffusion in narrow micropores.Finally,this facile synthesis method shows that low-cost and bio-based free-standing electrode materials with reliable supercapacitive performances can be used in electrochemistry.

Oxidation of chalcopyrite in air-equilibrated acidic solution: Inhibition with phenacyl derivatives

The effects of 4-(2-hydroxyphenyl)-2-(morpholin-4-yl)-1,3-thiazole(Pr02), 1-(3,5-dibromo-2-hydroxyphenyl)-1-oxoethan-2-yl-N,N-diethyldithiocarbamate(Pr04) and 1-(5-bromo-2-hydroxy-3-methylphenyl)-1-oxoethan-2-yl-Oethyl xanthate(Pr06) on the aqueous oxidation of chalcopyrite(CuFeS2) in air-equilibrated solution at a temperature of 25 ℃ and a pH of 2.5 were studied. The effects were investigated by using potentiodynamic polarization, electrochemical impedance spectroscopy(EIS), scanning electron microscopy coupled with energy dispersive X-ray(SEM/EDX) analysis, aqueous batch experiments, Fourier transform infrared(FTIR) spectroscopy, Raman scattering and quantum chemical calculations. It is found that the anodic current densities decrease in the order of EtOH > Pr02 > Pr04 > Pr06. These results, along with those of the EIS measurements, show that Pr02, Pr04 and Pr06 are effective anodic inhibitors of chalcopyrite aqueous oxidation. Both Raman scattering and FTIR spectroscopy indicate that the elemental sulfur, polysulfide and ferric oxyhydroxides that form on the surface of the mineral are not responsible when it comes to the aqueous oxidation inhibition of chalcopyrite. Quantum chemical calculations show that the adsorption of the tested compounds on the chalcopyrite surface is energetically favorable and so, it can explain the inhibiting effects that were observed.

Mechanochemical Synthesis and Characterization of Molybdenum Dioxide-Hematite Nanostructures with Different Molarities

xMoO2-(1-x)α-Fe2O3 nanoparticle system with molarities x = 0.1, 0.3, 0.5 and 0.7 was successfully synthesized by mechanochemical activation of MoO2 and α-Fe2O3 mixtures for 0 - 12 hours of ball milling time. X-ray powder diffraction (XRD), M&ouml;ssbauer spectroscopy and magnetic measurements were used to study the phase evolution of the molybdenum dioxide-hematite nanoparticle system under the mechanochemical activation process. Rietveld refinement of the XRD patterns yielded the values of the crystallite size and lattice parameters as function of milling times and indicated the presence of Mo-substituted hematite and Fe-doped molybdenum dioxide at long milling times. The M&ouml;ssbauer studies yielded the magnetic hyperfine fields and the relative abundance of a quadrupole-split doublet as function of the milling time for all molar concentrations involved. Recoilless fraction was determined using our dual absorber method and was found to decrease with increasing ball milling time. Magnetic measurements recorded at 5 and 300 K in an applied magnetic field of 50,000 Oe showed the magnetic properties in the antiferromagnetic and canted ferromagnetic states. The Morin transformation was evidenced by zero-field cooling-field cooling (ZFC-FC) measurements in a magnetic field of 200 Oe.

Towards high degree of c-axis orientation in MgB_(2) bulks

The paper presents fabrication and characterization of spark plasma sintered textured(001) MgB_(2)with a record degree of orientation of about 40% and 16% by high-energy ultra-sonication and slip casting in high magnetic field(12 T) and 0 T magnetic field, respectively.Structural characterization was performed by X-ray diffraction, and electron microscopy. The analysis revealed unexpected preferred orientation also in the MgO secondary phase due to the epitaxial growth of(111) MgO on(001) MgB_(2). The influence of oriented microstructure on the superconducting characteristics expressed by critical current density(J_(c)), irreversibility field(H_(irr)), and on the pinning properties were assessed. High anisotropy versus sample orientation in applied magnetic field, H, was observed for J_(c), Hirr, pinning activation energy(U^(*))extracted from relaxation measurements. The zero-field critical current, J_(c0)and F_(p),maxare weakly or not dependent on the direction of H,while the other indicated parameters are significantly influenced. Results enable control of superconducting parameters by further optimization of microstructure through MgB_(2) texturing as a novel and viable strategy for development of bulk MgB2with enhanced properties when taking advantage of its anisotropy.

Effect of starting materials and sintering temperature on microstructure and optical properties of Y203:Yb^(3+)5 at%transparent ceramics

Y2O3:Yb^(3+)5 at%ceramics have been synthesized by the reactive sintering method using different commercial yttria powders(Alfa-Micro,Alfa-Nano,and ITO-V)as raw materials.It has been shown that all Y2O3 starting powders consist from agglomerates up to 5-7 μm in size which are fonned from 25-60 nm primary particles.High-energy ball milling allows to significantly decreasing the median particle size D50 below 500 nm regardless of the commercial powders used.Sintering experiments indicate that powder mixtures fabricated from Alfa-Nano yttria powders have the highest sintering activity,while(Y0.86La0.09Yb0.05)2O3 ceramics sintered at 1750℃for 10 h are characterized by the highest transmittance of about 45%.Y2O3:Yb^(3+)ceramics have been obtained by the reactive sintering at 1750-1825℃using Alfa-Nano Y2O3 powders and La2O3+Zr02 as a complex sintering aid.The effects of the sintering temperature on densification processes,microstructure,and optical properties of Y2O3:Yb^(3+)5 at%ceramics have been studied.It has been shown that Zr^(4+)ions decrease the grain growth of Y2O3:Yb^(3+)ceramics for sintering temperatures 1750-1775℃.Further increasing the sintering temperature was accompanied by a sharp increase of the average grain size of ceramics referred to changes of structure and chemical composition of grain boundaries,as well as their mobility.It has been determined that the optimal sintering temperature to produce high-dense yttria ceramics with transmittance of 79%-83%and average grain size of 8μm is 1800℃.Finally,laser emission at〜1030.7 nm with a slope efficiency of 10%was obtained with the most transparent Y203:Yb^(3+)5 at%ceramics sintered.

二氧化钛气凝胶基质中金纳米粒子的光催化活性和结构(英文)

TiO2 -Au aerogels containing different amounts of gold nanoparticles of different sizes (5 and 16 nm) were successfully synthesized using a sol-gel procedure, and were tested for salicylic acid photodegradation under UV irradiation. The structure and morphology of the obtained materials were investigated using X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption measurements. UV-Vis spectroscopy was used to study the optical properties. The effects of the gold nanoparticles on the TiO2 crystallization process were twofold, as follows: (i) the number of crystallized zones was strongly related to the concentration of the gold nanoparticles, and (ii) the smaller gold particles increased the time taken for the crystallization of the samples. It was found that the noble metal-doped samples exhibited higher degradation rates compared with bare titania. It was found that the most active photocatalyst in each studied system was the sample with the highest concentration of gold nanoparticles. Additionally, the highest degradation rate value was obtained with the smallest Au nanoparticles (46.4 10-3 μmol/(L·s).

Magnetic properties of glass-ceramics obtained by crystallization of iron-rich borosilicate glasses

The specific dynamic magnetic response and magnetic relaxation phenomena in magnetite-based glass-ceramics by controlled crystallization of Fe-rich borosilicate glasses with 25 wt% Fe2O3, in the presence of two types of nucleating agents, Cr2O3 and P2O5, were investigated. The magnetic response is complex and shows contributions arising from two subsystems: a system with collective characteristics, superspin-glass like, and another one with single particle characteristics (superparamagnetic) with dipolar interaction. The nucleating agents have strong influence on the characteristic temperatures and anisotropy energy.

Versatile techniques based on the Thermionic Vacuum Arc(TVA)and laser-induced TVA methods for Mg/Mg:X thin films deposition-A review

Magnesium and magnesium thin alloy films were deposited using a thermionic vacuum arc(TVA),which has multiple applications in the field of metallic electrodes for diodes and batteries or active corrosion protection.An improved laser-induced TVA(LTVA)method favors the crystallization processes of the deposited magnesium-based films because the interaction between laser and plasma discharge changes the thermal energy during photonic processes due to the local temperature variation.Plasma diagnosis based on current discharge measurements suggests an inelastic collision between the laser beam and the atoms from the plasma discharge.The morphology and surface properties of the obtained thin films differ between these two methods.While the amorphous character is dominant for TVA thin films,enabling a smooth surface,the LTVA method produces rough surfaces with prominent crystallinity,less hydrophobic character and lower surface energy.The smooth surfaces obtained by the TVA methods produce metallic electrodes with good electrical contact,ensuring better diodes and battery charge transport.Both methods allow uniform magnesium alloys to be obtained,but the laser used in the LTVA on the discharge plasma controls the added metal or element ratio.

Ferritin surplus in mouse spleen 14 months after intravenous injection of iron oxide nanoparticles at clinical dose

In this study, we followed the biodegradation of ultra-small superparamagnetic iron oxide nanoparticles injected intravenously at clinical doses in mice. An advanced fitting procedure for magnetic susceptibility curves and low- temperature hysteresis loops was used to fully characterize the magnetic size distribution as well as the magnetic anisotropy energy of the injected P904 nano- particles （Guerbet Laboratory）. Additional magnetometry measurements and transmission electronic microscopy observations were systematically performed to examine dehydrated samples from the spleen and liver of healthy C57B16 mice after nanoparticle injection, with sacrifice of the mice for up to 14 months. At 3 months after injection, the magnetic properties of the spleen and liver were dramatically different. While the liver showed no magnetic signals other than those also present in the reference species, the spleen showed an increased magnetic signal attributed to ferritin. This surplus of ferritin remained constant up to 14 months after injection.

Vapor transport growth of MoS2 nucleated on SiO2 patterns and graphene flakes

Vapor transport growth of atomically thin MoS2 layers on patterned substrates is investigated, as it is a step towards the self-aligned growth and formation of heterojunctions, which could be useful in future applications. Enhanced formation of MoS2 flakes at the pattern edges is observed on both the substrates examined, namely, patterned thermal SiO2 on Si（100） and graphene flakes on SiO2. The diffusion driven growth leads to the formation of MoS2 monolayers （MLs） with sizes of tens of micrometers around the edges of SiO2 patterns. The growth mode and the optical quality of the MoS2 flakes can be controlled by varying the substrate temperature. Besides the lateral growth, 3R-type pyramids are obtained on prolonging the growth. Lateral MoS2-graphene heterostructures are obtained by using graphene flakes on SiO2 as a substrate.

Independent and complementary bio-functional effects of CuO andGa_(2)O_(3) incorporated as therapeutic agents in silica-and phosphate-based bioactive glasses

The incorporation of therapeutic-capable ions into bioactive glasses(BGs),either based on silica(SBGs)or phosphate(PBGs),is currently envisaged as a proficient path for facilitating bone regeneration.Inconjunction with this view,the single and complementary structural and bio-functional roles of CuO andGa_(2)O_(3)(in the 2e5 mol%range)were assessed,by deriving a series of SBG and PBG formulations startingfrom the parent glass systems,FastOs®BG e 38.5SiO2d36.1CaOd5.6P2O5d19.2MgOd0.6CaF2,and50.0P2O5d35.0CaOd10.0Na_(2)Od5.0 Fe2O_(3)(mol%),respectively,using the process of melt-quenching.The inter-linked physico-chemistry e biological response of BGs was assessed in search of bio-functional triggers.Further light was shed on the structural role e as network former or modifier e ofCu and Ga,immersed in SBG and PBG matrices.The preliminary biological performance was surveyedin vitro by quantification of Cu and Ga ion release under homeostatic conditions,cytocompatibility assays(in fibroblast cell cultures)and antibacterial tests(against Staphylococcus aureus).The similar(Cu)anddissimilar(Ga)structural roles in the SBG and PBG vitreous networks governed their release.Namely,Cuions were leached in similar concentrations(ranging from 10e35 ppm and 50e110 ppm at BG doses of 5and 50 mg/mL,respectively)for both type of BGs,while the release of Ga ions was 1e2 orders ofmagnitude lower in the case of SBGs(i.e.,0.2e6 ppm)compared to PBGs(i.e.,9e135 ppm).This wasattributed to the network modifier role of Cu in both types of BGs,and conversely,to the network former(SBGs)and network modifier(PBGs)roles of Ga.All glasses were cytocompatible at a dose of 5 mg/mL,while at the same concentration the antimicrobial efficiency was found to be accentuated by the coupledrelease of Cu and Ga ions from SBG.By collective assessment,the most prominent candidate material forthe further development of implant coatings and bone graft substitutes was delineated as the38.5SiO2d34.1CaOd5.6P2O5d16.2MgOd0.6CaF2d2.0CuOd3.0Ga_(2)O_(3)(mol%)SBG system,which yiel-ded moderate Cu and Ga ion release,excellent cytocompatibility and marked antibacterial efficacy.

New solutions for combatting implant bacterial infection based on silver nano-dispersed and gallium incorporated phosphate bioactive glass sputtered films:A preliminary study

Ag/Ga were incorporated into resorbable orthopaedic phosphate bioactive glasses(PBG,containing P,Ca,Mg,Na,and Fe)thin films to demonstrate their potential to limit growth of Staphylococcus aureus and Escherichia coli in post-operative prosthetic implantation.Dual target consecutive co-sputtering was uniquely employed to produce a 46 nm Ag:PBG composite observed by high resolution TEM to consist of uniformly dispersed~5 nm metallic Ag nano-particles in a glass matrix.Ga^(3+)was integrated into a phosphate glass preform target which was magnetron sputtered to film thicknesses of~400 or 1400 nm.All coatings exhibited high surface energy of 75.4-77.3 mN/m,attributed to the presence of hydrolytic P-O-P structural surface bonds.Degradation profiles obtained in deionized water,nutrient broth and cell culture medium showed varying ion release profiles,whereby Ga release was measured in 1400 nm coating by ICP-MS to be~6,27,and 4 ppm respectively,fully dissolving by 24 h.Solubility of Ag nanoparticles was only observed in nutrient broth(~9 ppm by 24 h).Quantification of colony forming units after 24 h showed encouraging antibacterial efficacy towards both S.aureus(4-log reduction for Ag:PBG and 6-log reduction for Ga-PBG≈1400 nm)and E.coli(5-log reduction for all physical vapour deposited layers)strains.Human Hs27 fibroblast and mesenchymal stem cell line in vitro tests indicated good cytocompatibility for all sputtered layers,with a marginal cell proliferation inertia in the case of the Ag:PBG composite thin film.The study therefore highlights the(i)significant manufacturing development via the controlled inclusion of metallic nanoparticles into a PBG glass matrix by dual consecutive target co-sputtering and(ii)potential of PBG resorbable thin-film structures to incorporate and release cytocompatible/antibacterial oxides.Both architectures showed prospective bio-functional performance for a future generation of endo-osseous implant-type coatings.

Magnetic glass-ceramics

We present the magnetic properties of magnetic glass ceramics obtained by crystallization of Fe containing borosilicate glass.Two types of nucleators have been used:Cr2O3 and P2O5.The role of the nucleators proved to be crucial in the size and morphology of the crystallites developed within glassy matrix as well in the magnetic response.The former stimulates the growth of regular single crystals uniformly dispersed within the matrix whereas the latter leads to the formation of grains made of tiny(30 nm),nanocrystals.The magnetic response depends on the amount of Fe ions left dispersed within glassy matrix as paramagnetic ions.Although P2O5 leads to the best structural magnetite,almost 42%of Fe ions are left dispersed in the matrix without magnetic interaction.In the case of Cr2O3,the paramagnetic Fe is decreased to 12%but structural deficiency in the occupancy of the Fe sites of magnetite is revealed by Mössbauer spectroscopy.