National Institute Of Materials Physics - Romania

The particle reinforcement of fusion-relevant tungsten through the incorporation of tungsten sub-carbide W2C particles at the grain boundaries is demonstrated as an effective way of eliminating the harmful W oxide, enhancing densification and stabilising the composite's microstructure and flexural strength at room and high temperatures. The W2C particles are formed in situ during the sintering by carbon diffusion from WC nano-particles added as a precursor to the W matrix. Even in an extremely fast sintering process using Field-Assisted Sintering Technology (FAST, 1900 degrees C, 5 min), the added WC completely transforms to W2C, resulting in a W-W2C composite. While at least 5 vol % of WC nanoparticles are needed to eliminate the oxide, approximately 10 vol % result in a W-W2C composite with favourable characteristics: high density, high flexural strength at RT (>1200 MPa) as well as at elevated temperatures, and high thermal conductivity, which remains above 100 W/mK up to 1000 degrees C.

Three-dimensional (3D) fibrous networks based on metal oxides were obtained by a bio-inspired approach: the replication of an ecological daily-waste, the eggshell membrane (ESM). The biomorphic process consists in the immersion of the ESM into aqueous solutions containing the metal salt precursors followed by the calcination of the metal ions impregnated ESM. Biomorphic ZnO, CuO and ZnO-CuO composite networks were obtained, their morphological, structural, compositional, optical, photocatalytical and electrical properties being evaluated. The scanning electron microscopy investigations proved that the hierarchical structure of the original organic template is perfectly replicated into inorganic architectures consisting of interconnected fibers containing metal oxide nanoparticles as building blocks. The photocatalytical properties of the metal oxide networks under solar simulator irradiation were tested through the degradation of methylene blue. Using Si/SiO2 patterned with interdigitated metallic electrodes as substrates during the calcination step, the electrical properties of the selfcontacted metal oxide networks were investigated. Thus, by replicating the unique architecture of the ESM, 3D metal oxide interwoven meshwork can be easily developed for various applications in fields such as photocatalysis, sensing, optoelectronic devices, etc.

We developed a new type of chalcohalide glasses with physicochemical and nonlinear optical properties that are tunable by composition. It is found that more than 60 mol.% CdCl2 heavy metal halide can be dissolved into the ternary Ge Sb S system and forming stable glasses. The visible-light transparency range is extended to shorter wavelengths with the addition of CdCl2, which is beneficial for the optical quality control and infra-red (IR) system alignment. The third-order optical nonlinearity (TONL) is studied using the femtosecond Z-scan method. The results show that both the nonlinear refractive index and two photon absorption co-efficient decrease with CdCl2. Benefiting from the favorable property-tailoring effects of CdCl2, the TONL figure of merit (FOM) can be improved to meet the requirement (FOM < 1) for all-optical switching and IR photonic applications.

Magnetic Fe@Y composites (carbon-coated magnetic iron nanoparticles incorporated in zeolite Y) with 5-8 wt % Fe were synthesized and characterized. Overall acidity of the samples ranged between 2.0 and 2.47 mmol/g and is mostly attributed to Lewis acid sites. The obtained materials were proven to catalyze the hydrolysis of the marine sulfated polysaccharide ulvan with high conversion rates. The distribution of the reaction products depended on the reaction conditions and the concentration of ulvan. The catalytic property catalytic performance correlations clearly showed that the acid zeolite Y is the active phase for the hydrolysis of ulvan, while the iron nanoparticles enable the catalyst separation in a magnetic field. Under oxygen pressure, the selectivity was completely changed to favor succinic acid production. All Fe@Y composites were recycled 10 times with no change in their catalytic performance after recovery via a simple magnetic separation and washing with water.

Carbon layers are deposited on 100 nm thick atomically clean (001) lead zirconate titanate (PZT) in ultrahigh vacuum, ruling out the presence of any contaminants. X-ray photoelectron spectroscopy is used to assess the substrate surface or interface composition, substrate polarization and the thickness of carbon layers, which ranges from less than one monolayer (1 ML) of graphene to several monolayers. Atomically clean PZT(001) exhibit inwards polarization, and this polarization reverses the sign upon carbon deposition. Cationic vacancies are detected near the PZT surface, consistent with heavy p doping of these films near the surface. The carbon layers exhibited a consistent proportion of atoms forming in-plane sp(2) bonds, as detected by near-edge absorption fine structure (NEXAFS) analysis and confirmed partially by scanning tunneling microscopy (STM). In situ poling with simultaneous in-plane transport measurements revealed the presence of resistance anti-hysteresis versus the polarization orientation for films with less than 1 ML carbon amount, evolving towards 'normal' hysteresis for thicker carbon films. The anti-hysteresis is explained in terms of a mixed screening mechanism, involving charge carriers from the sp(2) carbon layers together with holes or ionized acceptors in PZT(001) near the interface. For thicker films, the compensation mechanism becomes extrinsic, involving mostly electrons and holes from carbon, yielding the expected hysteresis.

There is significant research showing that essential oils extracted from the plants have antibacterial effects. The purpose of this study was to develop a biocomposite based on hydroxyapatite coated with Artemisia absinthium essential oil and to highlight its antibacterial activity. Therefore, present studies are aimed at developing new materials combining hydroxyapatite with Artemisia absinthium essential oil, in order to avoid postoperative infections. The purpose of this work is to highlight the antimicrobial properties of the Artemisia absinthium essential oil-hydroxyapatite composites obtained by a simple method and at low costs. The structural properties and antimicrobial efficiency of the Artemisia absinthium essential oil-hydroxyapatite composite have been studied. The samples based on Artemisia absinthium essential oil analyzed in this study showed that wormwood essential oil presented the highest efficacy against the fungal strain of C. parapsilosis. It has been shown that wormwood essential oil has a strong antimicrobial effect against the microbial strains tested in this study. Furthermore, the antimicrobial properties of the biocomposites based on hydroxyapatite and essential oil are due to the presence of the essential oil in the samples.

In this work, ZnO-CdS composite powders synthesized by a simple chemical precipitation method were thoroughly characterized. The morphological, structural, compositional, photocatalytical, and biological properties of the prepared composites were investigated in comparison with those of the pristine components and correlated with the CdS concentration. ZnO-CdS composites contain flower-like structures, their size being tuned by the CdS amount added during the chemical synthesis. The photocatalytic activity of the composites was analyzed under UV irradiation using powders impregnated with methylene blue; the tests confirming that the presence of CdS along the ZnO in composites can improve the dye discoloration. The biological properties such as antioxidant capacity, antibacterial activity, and cytotoxicity of the ZnO, CdS, and ZnO-CdS composites were evaluated. Thus, the obtained composites presented medium antioxidant effect, biocidal activity against Escherichia coli, and no toxicity (at concentrations less than 0.05 mg/mL for composites with a low CdS amount) for human fibroblast cells. Based on these results, such composites can be used as photocatalytic and/or biocidal additives for photoactive coatings, paints, or epoxy floors, which in their turn can provide a cleaner and healthier environment.

The present paper reports the dependence of structural and functional properties on the porosity level with values down to 50% in BaTiO3 ceramics. Micro-porosity (pore size below 15 pm) with (0-3) connectivity has been produced by using dried pollen particles as sacrificial template. The properties of such porous ceramics are mostly affected by porosity, but also by possible small doping with foreign ions resulted from the template and by small variations of Ba/Ti stoichiometry at the ceramic-pore interfaces, as observed by a shift of the Curie temperature towards lower values when porosity level increases. The dielectric relaxation evidenced a few processes characterised by different activation energies which seem to be not affected by porosity, i.e. they might be assigned to the ceramic part and not to the ceramic-pore interfaces. When increasing porosity, a regular tilting of P(E) loops and increasing of coercivity and reducing polarization were observed, as result of reduction of active ferroelectric component and to the field inhomogeneity in such ceramics.

Magnetic iron oxides have been used in biomedical applications, such as contrast agents for magnetic resonance imaging, carriers for controlled drug delivery and immunoassays, or magnetic hyperthermia for the past 40 years. Our aim is to investigate the effect of pressure and temperature on the structural, thermal, and magnetic properties of iron oxides prepared by hydrothermal synthesis at temperatures of 100-200 degrees C and pressures of 20-1000 bar. It has been found that pressure influences the type of iron oxide crystalline phase. Thus, the results obtained by Mossbauer characterization are in excellent agreement with X-ray diffraction and optical microscopy characterization, showing that, for lower pressure values (<100 bar), hematite is formed, while, at pressures >100 bar, the major crystalline phase is goethite. In addition, thermal analysis results are consistent with particle size analysis by X-ray diffraction, confirming the crystallization of the synthesized iron oxides. One order of magnitude higher magnetization has been obtained for sample synthesized at 1000 bar. The same sample provides after annealing treatment, the highest amount of good quality magnetite leading to a magnetization at saturation of 30 emu/g and a coercive field of 1000 Oe at 10 K and 450 Oe at 300 K, convenient for various applications.

A study on clay mineral polymer nanocomposites (CPN), namely polyaniline/montmorillonite-cetyltrimethylammonium bromide (PANI/Mt-CTAB), poly o-anisidine/montmorillonite-cetyltrimethylammonium bromide (poly(o-ANIS)/Mt-CTAB) and poly o-anisidine-co-aniline/montmorillonite-cetyltrimethylammonium bromide (poly(o-ANIS-co-ANI)/Mt-CTAB), synthesized by oxidative chemical polymerization method is presented. The nanocomposites have been characterized by Fourier transform infrared spectroscopy, UV-vis spectroscopy, and cyclic voltammetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and thermogravimetry and differential scanning calorimetry analysis. By UV-vis measurements different electronic transitions for the CPNs were pointed out. The voltammograms indicate that the synthetized materials are electroactive. The FTIR analysis reveals the characteristic bands of the polymers and of the Mt-CTAB. The shift of the bands to higher/lower wavenumbers demonstrate the interaction between the pristine polymers macromolecular chains and the montmorillonite (Mt). The intercalation of the polymers inside the mineral clay was confirmed by the increased interlayer distance connected with the position of the 011 diffraction plane of the Mt., and the intercalation and exfoliation states were highlighted in the scanning and transmission electron microscopy images. The obtained results are encouraging in respect with the purpose to use them in the field of photovoltaic applications.