National Institute Of Materials Physics - Romania

Layered zinc hydroxynitrate (ZHN), with the chemical formula Zn-5 (OH)(8) (NO3)(2)center dot 2H(2)O, exhibits a range of special properties such as anion-exchange and intercalation capacity, as well as biocompatibility, making it attractive for a large variety of applications in fields from nanotechnology to healthcare and agriculture. In this study nanocrystalline ZHN doped with 1,000 ppm Mn2+ was prepared by two synthesis methods (coprecipitation and solid state reaction) using similar environment-friendly precursors. The complex morpho-structural [X-ray diffraction, scanning and transmission electron microscopy, textural analysis] and spectroscopic [Fourier transform infrared and electron paramagnetic resonance (EPR)] characterization of the two ZHN nanopowders showed similar crystalline structures with Mn2+ ions localized in the nanocrystals volume, but with differences in their morphological and textural characteristics, as well as in the doping efficiency. ZHN obtained by coprecipitation consists of larger nanoplatelets with more than two times larger specific surface area and pore volume, as well as a dopant concentration than in the ZHN sample obtained by solid state reaction. The thermal stability and the on-set of the structural phase transformation have been investigated at atomic scale with high accuracy by EPR, using Mn2+ as paramagnetic probes. The on-set of the ZHN structural phase transformation toward ZnO was observed by EPR to take place at 110 degrees C and 130 degrees C for the samples prepared by coprecipitation and solid state reaction, respectively, evidencing a manganese induced local decrease of the transformation temperature. Our results contribute to the selection of the most appropriate ZHN synthesis method for specific applications and in the development of new green, cost-effective synthesis routes for Mn2+ doped nano-ZnO.

The attraction towards Ti and its alloys reside in their superior mechanical and tribological features, as compared to CaPs, which are renowned for their compositional and structural features similar to those of natural bones. However, Ti-based materials suffer from limited biocompatibility and inertness when implanted for extended periods. As such, surface modification with ceramic coatings is required in order to achieve proper biomedical features and enhance their overall behavior in the human body. Hence, this study outlined for the first time the prospect of coating several Ti6Al4V substrates (disks) with bovine-bone derived hydroxyapatite (HA) by laser cladding technique with pre-placed slurry. During laser processing the input materials merge depending on the heating rate/temperature and clad materials. The proposed sample preparation set-up, followed for the first time in this study, involved the concomitant modulation of two parameters: the natural HA ratio (100 wt%, and 50 wt % HA + 50 wt% Ti blends) and laser beam power (500-1000 W range). The laser beam was applied after the ceramic slurries (prepared HA/HA-based blends mixed with polyvinyl alcohol) were placed inside the priorly machined channels on the metallic Ti disks. Partially overlapped cladding tracks (similar to 30% overlapping ratio) resulted and the investigations were further performed in cross-section view. The structural analyses confirmed the formation of calcium titanate as main phase for all samples and the arrest of HA only for those prepared with 100% HA ratio at low to medium laser powers. In addition, the morpho-compositional evaluation revealed the formation of a fully ceramic coating only for the latter sample sets. Further, the surface wettability (contact angle and surface free energy) and Vickers micro-hardness results led to the selection of the optimal technological parameters for the development of ceramic cladded layers with prospect compatibility with regenerative med-icine applications.

The scope of this study consists of setting up of an integrated cost-effective sampling & laboratory analyses procedure which delineates sampling, sub-sampling and analytical uncertainties in case of fine-grained extractive waste deposits. This procedure is designed to support the decision makers towards fine-grained waste deposits upcycling and land reclamation. This procedure consists of a balanced replicated sampling design (BRSD) coupled with a three split levels ANOVA data processing. The paper provides the readership with the mathematical backgrounds of the three split level ANOVA analysis (3L-ANOVA) and an Excel algorithm for its implementation. Also, the paper presents an example of implementation of the developed methods in the case of a Romanian iron ore tailings (IOT) old pond. The findings of the paper consist of: a) argues, based on OM, SEM-EDS, XRFS and XRD observations, that classical TOS is ineffective for fine-grained waste deposits; b) BRSD in conjunction with 3L-ANOVA analysis is the only approach fit for reliable characterization of the fine-grained stockpiles; c) sampling uncertainty is the critical factor of the uncertainty budget of the analyte concentration; d) Lilliefors approach is adequate for the hypothesis testing where or not the measurand is normal distributed; e) The outcomes of the BRDSD&3L-ANOVA investigations carried on Teliuc tailings, estimated at circa 5.5* 106 m3, consist mainly of mineral quantification at lot level i.e. quartz-54% (+/- 7%), hematite-15% (+/- 3%), calcite-11% (+/- 3%), MgO 3% (+/- 1%), Al2O3 9% (+/- 2%). The concentrations of some CRMs like Ti, V, Ba, Y, W were found at ACE limits and their associated relative expanded uncertainties overpass 50%. Thus, the expanded uncertainties clearly depict the reliability of acquired data for the decision makers regarding waste valorization. f) The IOT into Teliuc can be upcycled as minerals for cement and ceramic industries as well as for geopolymer manufacture. Also, IOT can be downcycles as filler in road construction and mine closure. Finally, the Teliuc yard can be rehabilitated with zero-waste left behind. The data exactness provided by this procedure can be increased to any desirable level through increasing the number of collected items, but the cost of sampling and analyses increases proportionally. In such circumstances, the posted approach can be tailored at the stakeholder request as to safely underpin the decision to turn fine-grained by-products into valuable secondary resources, facilitating a greater circularity of the mining industry.

The diffusion of iodide defects has been considered the most important degradation mechanism of methylammonium lead iodide (MAPI) in solar cells. The present study demonstrates the importance of the pressure inside this material on the dynamics of iodide defects, using molecular dynamics simulations. It is known that the diffusion coefficient of an iodide vacancy is an order of magnitude higher than that of interstitial iodide. We show that this difference systematically increases with increased tensile strain and that both diffusion coefficients tend to zero when a compressive strain is applied. This result suggests that compression of the MAPI can be a good solution to reduce its degradation rate. Besides, the statistical aspect of deriving the diffusion coefficient from the mean squared displacement (MSD) is discussed in terms of the initial conditions (positions and velocities) of the atoms and the simulation time, considering different seeds of the pseudorandom number generator used in the simulations performed with the LAMMPS software.

Active and stable materials that utilize solar radiation for promoting different reactions are critical for emerging technologies. Two of the most common polymeric carbon nitrides were prepared by the thermal polycondensation of melamine. The scope of this work is to investigate possible structural degradation before and after photoelectrochemical testing. The materials were characterized using synchrotron radiation and lab-based techniques, and subsequently degraded photoelectrochemically, followed by post-mortem analysis. Post-mortem investigations reveal: (1) carbon atoms bonded to three nitrogen atoms change into carbon atoms bonded to two nitrogen atoms and (2) the presence of methylene terminals in post-mortem materials. The study concludes that polymeric carbon nitrides are susceptible to photoelectrochemical degradation via ring opening.

In the view of the advantages of using P, N, Si and graphene oxide (GO) for the development of flame retardants materials, a multi-structure synergistic composite was synthesized by grafting a novel nitrogen-containing polyhedral oligomeric silsesquioxane (HAK) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) on the surface of GO nanosheet. In the first step, 2-hydroxyethyl acrylate was selectively reacted, and then, HAK was synthetized by the condensation of the aza-Michael addition product with 3-(methacryloyloxy)propyltrimethoxysilane. Finally, the GO obtained by an innovative variant of Marcano-Tour improved exfoliation method was functionalized, first with DOPO, and then with HAK. The structural, morphological and surface properties of GO and GO-DOPO-HAK were investigated by means of XRD, TEM-EDX, FT-IR, Raman, zeta potential and XPS techniques, and it was evidenced the functionalization of GO with DOPO, and then with HAK. The performed microscale combustion calorimetry (MCC) and TG measurements indicated a great potential of the GO-DOPO-HAK as flame retardant material as the obtained residual weight for this sample was found to be the highest one compared to the other investigated samples. MCC analyses further revealed a major decrease in heat release capacity (HRC) and a significant increase in char yield, results that confirm the great potential of GO-DOPO-HAK as flame retardancy material. [GRAPHICS] .

Novel biomaterials with promising bone regeneration potential, derived from rich, renewable, and cheap sources, are reported. Thus, thin films were synthesized from marine-derived (i.e., from fish bones and seashells) hydroxyapatite (MdHA) by pulsed laser deposition (PLD) technique. Besides the physical-chemical and mechanical investigations, the deposited thin films were also evaluated in vitro using dedicated cytocompatibility and antimicrobial assays. The morphological examination of MdHA films revealed the fabrication of rough surfaces, which were shown to favor good cell adhesion, and furthermore could foster the in-situ anchorage of implants. The strong hydrophilic behavior of the thin films was evidenced by contact angle (CA) measurements, with values in the range of 15-18 degrees. The inferred bonding strength adherence values were superior (i.e., similar to 49 MPa) to the threshold established by ISO regulation for high-load implant coatings. After immersion in biological fluids, the growth of an apatite-based layer was noted, which indicated the good mineralization capacity of the MdHA films. All PLD films exhibited low cytotoxicity on osteoblast, fibroblast, and epithelial cells. Moreover, a persistent protective effect against bacterial and fungal colonization (i.e., 1- to 3-log reduction of E. coli, E. faecalis, and C. albicans growth) was demonstrated after 48 h of incubation, with respect to the Ti control. The good cytocompatibility and effective antimicrobial activity, along with the reduced fabrication costs from sustainable sources (available in large quantities), should, therefore, recommend the MdHA materials proposed herein as innovative and viable solutions for the development of novel coatings for metallic dental implants.

Despite the high coercive field (E-c = 7.3 kV/mm) and the high conductivity (2.1 x 10(-7) (omega m)(-1)) of (Bi0.5Na0.5)TiO3 (BNT) ceramics, their microstructure and electric properties can be tailored by appropriate substitutions at the A and/or B-sites. In this paper, we offer a comprehensive review of the up-to-date advances on doped lead-free BNT ceramics, highlighting the role of the nature and concentration of dopants on the stoichiometry, microstructure, density, dielectric properties, and piezoelectric properties of the solid solutions obtained after doping. For each composition presented in this review, the synthesis method and the sintering technique of the ceramics are also given because of the well-known connection between powder processing (its morphology), ceramics densification (its density), and the macroscopic properties of the final product. A substitution mechanism for each dopant that explains the role of the dopant on the structure and electrical properties of the BNT matrix is also described in detail. Our review provides knowledge for the development of new solid solutions of BNT.

We studied here the influence of Li+ ions on the benzene rings of nematic mixture E7, which is electrochemically adsorbed onto gold electrode surface, to highlight the ability of this mixture for the applications in the field of the rechargeable Li+-ion batteries. Raman spectra support the changes observed in electrochemical analyses while contact angle measurements show that wetting properties of E7 layer were modified after deposition of this mixture onto gold support and the doping with Li+ ions.

Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI(2.6)Cl(0.4) hybrid perovskite (MA-methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1(-x)Zn(x)I(2.6)Cl(0.4) based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion efficiency) range, compared to pristine MAPbI(2.6)Cl(0.4) based devices.