National Institute Of Materials Physics - Romania

Tungsten is the primary candidate armour material for the divertor target of the European demonstration fusion power plant. During operation at high temperature, pure tungsten is subject to fracture and recrystallization which results in a loss of strength and worsening of the thermal properties. Additionally, loss-of-coolant accidents with simultaneous air ingress can generate volatile and radioactive tungsten oxides. Advanced W-alloys were developed as alternative and upgrading armour materials of pure tungsten, such as potassium-doped tungsten laminates and self-passivating tungsten alloys. Three mock-ups were manufactured using potassium-doped tungsten laminates, W-10Cr-0.5Y and W-10Cr-0.5Y-0.5Zr as armour materials, each of them consisting of n degrees 4 blocks. The fabrication required optimization and upscaling of the ITER-like process which foresees oxygen-free high conductivity copper as interlayer joined to W-alloy armour block and CuCrZr ITER grade pipe welded to the Cu/W-alloy blocks by hot radial pressing. For quality control of the fabrication steps, non-destructive examination by ultrasonic testing was done on the monoblocks as received, after casting, after hot radial pressing and after high heat flux testing. The results demonstrated that these W-alloys can be used as armour materials of the European demonstration fusion power plant divertor target.

Antidepressant drugs play a crucial role in the treatment of mental health disorders, but their efficacy and safety can be compromised by drug degradation. Recent reports point to several drugs found in concentrations ranging from the limit of detection (LOD) to hundreds of ng/L in wastewater plants around the globe; hence, antidepressants can be considered emerging pollutants with potential consequences for human health and wellbeing. Understanding and implementing effective degradation strategies are essential not only to ensure the stability and potency of these medications but also for their safe disposal in line with current environment remediation goals. This review provides an overview of degradation pathways for amitriptyline, a typical tricyclic antidepressant drug, by exploring chemical routes such as oxidation, hydrolysis, and photodegradation. Connex issues such as stability-enhancing approaches through formulation and packaging considerations, regulatory guidelines, and quality control measures are also briefly noted. Specific case studies of amitriptyline degradation pathways forecast the future perspectives and challenges in this field, helping researchers and pharmaceutical manufacturers to provide guidelines for the most effective degradation pathways employed for minimal environmental impact.

When a severe plastic deformation (SPD) process is performed at high temperatures, it becomes more versatile. Designed originally for the bulk nanoconstruction of hard-to-deform alloys, high-speed high-pressure torsion (HSHPT) is an SPD method used in this research for assembling multiple layers of shape memory nanocomposites. Three hard-to-deform magnetic alloys in the cast state were used. Soft magnetic shape memory alloys, NiFeGa and FePdMn, and a potentially hard magnetic alloy, CoZr, were assembled in various composites. Both grain refinement and strong layer bonding were achieved in ZrCo/FePdMn and ZrCo/NiFeGa composites in seconds. The very short SPD time is specific to HSHPT because of the intense friction that occurs under high pressures, which generates huge amounts of heat. After SPD, the temperature rises in bulk material like a pulse, being dissipated mostly through heat conduction. The SPD parameters were carefully controlled with an advanced automation system using a programmable logic controller. Nevertheless, the major drawbacks of high-pressure torsion were overcome, and large SPD discs were obtained. Various investigation techniques (optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and atomic force microscopy) show well-defined interfaces as well as a fine and ultrafine structure.

The CuFeTaTiW multicomponent alloy has been devised as an interlayer thermal barrier in nuclear fusion re-actors. In order to predict the phase constitution of this alloy, two different lines of work were performed: (a) simulation using Molecular dynamics and Monte Carlo and (b) study of the influence of mechanical alloying parameters on the structures formed. The simulation results show that the most stable structure is achieved starting from a bcc type-structure and using Monte Carlo simulation. In fact, in these conditions the separation into two bcc phases Fe-Ta-W and Cu-Ti is predicted at room temperature. However, the experimental preparation of the materials with mechanical alloying revealed that from 2 h of milling a single bcc phase is formed. The structure of the milled powder was not much influenced by the amount of the process control agent and the by the size of the W starting particles, but generally there was formation of Ta2H from the reaction between the powders and the process control agent.

Preparation under non-identical conditions involving the reduction of sol-gel-derived precursors of various Zn:Fe atomic ratios (0.97:0.03, 0.8:0.2 and 0.4:0.6) in a hydrogen-containing atmosphere was used to obtain composites of nanosized ferromagnetic (FM) alpha-Fe and antiferromagnetic (AFM) FeO in different concentrations and of the desired magnetic responses. ZnO nanoparticles, developed in all preparation stages, served primarily as a matrix for the separation of Fe (and FeO) nanoparticles, preventing their agglomeration and coarsening. The average crystallite/particle size is about 5-32 nm, 10-75 nm and 21-31 nm for FeO, Fe and ZnO, respectively. Magnetisation investigations of FeO-Fe-ZnO nanocomposites revealed a coexistence of ferromagnetic and superparamagnetic behaviours ascribed to the Fe nanoparticles in different magnetic states. All samples exhibit the exchange bias effect, EB. Values up to 375 Oe for coercivity at 300 K, 600 Oe for coercivity, 223 for coercivity enhancement and 243 Oe for EB field at 5 K were measured. The magnitude of EB depends on the processing conditions - the EB field and coercivity enhancement are larger for samples processed under conditions of a higher degree of non-equilibrium. The presence of FeO appears crucial for the occurrence of EB, irrespective of its quantity. The EB is ascribed primarily to the exchange coupling between the AFM and FM spins at the FeO/Fe interfaces of nanostructures after field-cooling from above the TN of FeO and below the Curie temperature of Fe. An approach based on magnetically disordered AFM/FM interfaces featuring like spin-glass systems was adopted to explain the EB effects. An aspect of practical relevance is the suppression of room temperature coercivity in apparent correlation with the training of the EB; an attempt has been made to understand the origin of this suppression.

In the present work, single phase CoSb3 skutterudite nanomaterials were prepared via a ball milling method, and their thermoelectric characteristics were compared with the samples synthesized by the solvo-hydrothermal method. Thermoelectric transport properties were recorded in the temperature regime of 300-830 K. Both samples exhibit p-type conduction behavior with a positive sign of Seebeck coefficient. CoSb3 ball mill sample exhibit higher resistivity of 127 x 10(-5)Omega.m at 300 K as compared to CoSb3 solvo-hydrothermal sample with 4.85 x 10(-5)Omega.m. However, CoSb3 ball mill sample show enhanced Seebeck coefficient of 183 mu V/K at 473 K where CoSb3 solvo-hydrothermal sample depict 98 mu V/K at 650 K. Furthermore, the total thermal conductivity of sintered CoSb3 ball mill and CoSb3 solvo-hydrothermal samples was found to be 3.02 Wm(-1)K(-1) and 3.23 W m(-1)K(-1) at room temperature and reaches a significantly lower value of 2.47 W m(-1)K(-1) and 2.46 W m(-1)K(-1) at 580 and 670 K, respectively. The dimensionless figure of merit ZT values of CoSb3 ball mill and CoSb3 solvo-hydrothermal obtained are 0.053 and 0.060 at 650 and 700 K, respectively. A systematic tuning of processing parameters by ball milling method can lead to better thermoelectric efficiency.

The thermodynamic and kinetic simulations based on the re-assessment of the thermodynamic and kinetic database of the Ni-Ti-Cu system were employed to predict the phenomena of mechanical alloying, spark plasma sintering and thermal properties of the intriguing Ni-Ti-Cu system. Thermodynamic calculations are presented for the stable and unstable phases of NiTiCu materials and support a correlation with the evolving microstructure during the technological process. Also, the thermal conductivity, the thermal diffusivity and the specific heat of spark plasma sintered and aged Cu-alloyed NiTi-based shape memory alloys (NiTiCu) with two compositions, Ni45Ti50Cu5 and Ni40Ti50Cu10, are evaluated and the influence of mechanical alloying and precipitates on thermal properties is discussed. Measurements of these thermal properties were carried out from 25 degrees C up to 175 degrees C using the laser flash method, as well as differential scanning calorimetry. The thermal hysteresis of the 20 mm diameter samples was between 8.8 and 24.5 degrees C. The observed T0 temperatures from DSC experimental transformation features are in reasonable accordance with the thermodynamic predictions. The determined k values are between 20.04 and 26.87 W/m K and in agreement with the literature results. Moreover, this paper can provide some suggestions for the preparation of NiTiCu shape memory alloys and their applications.

Present work reports a systematic study on the evaluation of magnetic inhomogeneities in non-stoichiometric Mg0 & sdot;5Ca0 & sdot;5Fe2O4 nanoferrite (MCNF) by conducting exhaustive dc -magnetization, ac -susceptibility and Fe-57 Mossbauer spectroscopic measurements and exchange bias investigations using training protocol down to 6 K. Rietveld fitting to PXRD established the formation of anticipated spinel fcc phase of MCNF (non-stoichiometric) along with a minute impurity phase of calcite. Scherrer method and HRTEM micrographs illustrated broad size distribution of MCNF nanoparticles with an average nanocrystallite size of -15 nm. Combined 57Fe Mo center dot ssbauer spectroscopic and dc -magnetization analysis establishes coexistence of ferrimagnetic (67 %) & superparamagnetic (33 %) states at 300 K with notable M-s = 22 emu/g, M-r = 4 emu/g & H-c = 130 Oe and blocking of most of the nanoparticles of MCNF below 300 K. The coercivity followed the size -modified Kneller law for ferrimagnetic nanoparticles and the saturation magnetization abides the Bloch law. Moreover the frequencydependent ac -susceptibility investigations revealed two magnetic transitions: (i) A transition at - 330 K in the low frequency data attributed to the relaxation of blocked particles of bigger sizes under the superparamagnetic (SPM) regime and (ii) an irregularity at low temperatures is assigned to surface spin glass freezing. Surface spin glass freezing was further affirmed by the ageing experiments and dynamic scaling law. Furthermore, even the best fit to the dynamic scaling couldn't assert the existence of conventional spin glass phase due to slower spin -flip time of surface spins. A soft ferrimagnetic core of MCNF is enveloped with disordered surface spins, which manifest spin glass state. Concurrently, the findings of exchange bias at 30 K and training effect at 6 K affirmed that MCNF nanoparticles are presenting themselves as FM core- SG shell system. Our experimental findings suggested magnetic inhomogeneities comprised of superparamagnetism, ferrimagnetism and disordered surface spin glass state in the non-stoichiometric MCNF.

Dense samples of MgB2, with a relative density of 98.3-99.1 %, were prepared by ex-situ spark plasma sintering using a raw powder supplied by Alfa Aesar. Samples were added with Ge-based organometallics (repagermanium/RGe, propagermaniu/PGe, linear Ge-based organometallic/GeSP, and Na-doped octamer/8THGP-Na) for the starting composition (MgB2)(Ge-based organometallics)0.0014. Except for the 8THGP-Na, they have a similar chemical composition in respect to Ge and C, while the crystal structure differs. Below 20 K, all studied additions increased the critical current density, Jc, and the irreversibility field, Hirr. Samples added with GeSP and 8THGPNa have marginal differences regarding superconducting characteristics. The best Jc and Hirr are obtained for the sample added with RGe. This sample has the highest amount of carbon in the crystal lattice of MgB2. Results point out that there is a complex influence of the additive on carbon behaviour. Although in general it is accepted that a higher amount of carbon produces higher Jc and Hirr, a comparison with the literature indicates that C-rich raw MgB2 powders (e.g. the C-enhanced MgB2 nanopowder produced by Pavezyum) are not suitable to promote strong superconductivity enhancement in the samples added with indicated organometallics, and the origin, states, and evolution of carbon should to be carefully assessed.

The paper describes the chemical modification of the graphene oxide (GO) surface with glucosamine, which was conjugated to GO via a carbodiimide-mediated amidation-type reaction. The efficiency of the reaction was confirmed by FT-IR and Raman spectroscopy and elemental analysis. The elaborated functionalization significantly reduces the agglomeration of graphene oxide platelets. The interactions at the interface of GO and two types of ceramic nanoparticles (ZrO2 and Al2O3 with particle sizes of 58 nm and 158 nm, respectively) were examined by zeta potential measurements at different pH values. The viscosity of ZrO2 suspensions (35 vol% of solid loading) at 1.5 s- 1 increases from 24.8 Pas to 170.7 Pas and 142.7 Pas with the addition of GO and f-GO, respectively. The interfaces at ceramic-graphene heterostructures obtained by slip casting method have been analyzed by SEM. The investigations revealed the presence of multilayer graphene oxide and flexible single-layer f-GO within the ceramic matrix.