Advanced Photodegradation of Azo Dye Methyl Orange Using H2O2-Activated Fe3O4@SiO2@ZnO Composite under UV Treatment.

The Fe3O4@SiO2@ZnO composite was synthesized via the simultaneous deposition of SiO2 and ZnO onto pre-prepared Fe3O4 nanoparticles. Physicochemical methods (TEM, EDXS, XRD, SEM, FTIR, PL, zeta potential measurements, and low-temperature nitrogen adsorption/desorption) revealed that the simultaneous deposition onto magnetite surfaces, up to 18 nm in size, results in the formation of an amorphous shell composed of a mixture of zinc and silicon oxides. This composite underwent modification to form Fe3O4@SiO2@ZnO*, achieved by activation with H2O2. The modified composite retained its structural integrity, but its surface groups underwent significant changes, exhibiting pronounced catalytic activity in the photodegradation of methyl orange under UV irradiation. It was capable of degrading 96% of this azo dye in 240 min, compared to the initial Fe3O4@SiO2@ZnO composite, which could remove only 11% under identical conditions. Fe3O4@SiO2@ZnO* demonstrated robust stability after three cycles of use in dye photodegradation. Furthermore, Fe3O4@SiO2@ZnO* exhibited decreased PL intensity, indicating an enhanced efficiency in electron-hole pair separation and a reduced recombination rate in the modified composite. The activation process diminishes the electron-hole (e-)/(h+) recombination and generates the potent oxidizing species, hydroxyl radicals (OH˙), on the photocatalyst surface, thereby playing a crucial role in the enhanced photodegradation efficiency of methyl orange with Fe3O4@SiO2@ZnO*.

Sr(II) and Ba(II) Alkaline Earth Metal-Organic Frameworks (AE-MOFs) for Selective Gas Adsorption, Energy Storage, and Environmental Application.

Two new alkaline earth metal-organic frameworks (AE-MOFs) containing Sr(II) (UPJS-15) or Ba(II) (UPJS-16) cations and extended tetrahedral linker (MTA) were synthesized and characterized in detail (UPJS stands for University of Pavol Jozef Safarik). Single-crystal X-ray analysis (SC-XRD) revealed that the materials are isostructural and, in their frameworks, one-dimensional channels are present with the size of ~11 × 10 Å2. The activation process of the compounds was studied by the combination of in situ heating infrared spectroscopy (IR), thermal analysis (TA) and in situ high-energy powder X-ray diffraction (HE-PXRD), which confirmed the stability of compounds after desolvation. The prepared compounds were investigated as adsorbents of different gases (Ar, N2, CO2, and H2). Nitrogen and argon adsorption measurements showed that UPJS-15 has SBET area of 1321 m2 g-1 (Ar) / 1250 m2 g-1 (N2), and UPJS-16 does not adsorb mentioned gases. From the environmental application, the materials were studied as CO2 adsorbents, and both compounds adsorb CO2 with a maximum capacity of 22.4 wt.% @ 0 °C; 14.7 wt.% @ 20 °C and 101 kPa for UPJS-15 and 11.5 wt.% @ 0°C; 8.4 wt.% @ 20 °C and 101 kPa for UPJS-16. According to IAST calculations, UPJS-16 shows high selectivity (50 for CO2/N2 10:90 mixture and 455 for CO2/N2 50:50 mixture) and can be applied as CO2 adsorbent from the atmosphere even at low pressures. The increased affinity of materials for CO2 was also studied by DFT modelling, which revealed that the primary adsorption sites are coordinatively unsaturated sites on metal ions, azo bonds, and phenyl rings within the MTA linker. Regarding energy storage, the materials were studied as hydrogen adsorbents, but the materials showed low H2 adsorption properties: 0.19 wt.% for UPJS-15 and 0.04 wt.% for UPJS-16 @ -196 °C and 101 kPa. The enhanced CO2/H2 selectivity could be used to scavenge carbon dioxide from hydrogen in WGS and DSR reactions. The second method of applying samples in the area of energy storage was the use of UPJS-15 as an additive in a lithium-sulfur battery. Cyclic performance at a cycling rate of 0.2 C showed an initial discharge capacity of 337 mAh g-1, which decreased smoothly to 235 mAh g-1 after 100 charge/discharge cycles.

Fe0.79Si0.07B0.14 metallic glass gaskets for high-pressure research beyond 1†Mbar.

A gasket is an important constituent of a diamond anvil cell (DAC) assembly, responsible for the sample chamber stability at extreme conditions for X-ray diffraction studies. In this work, we studied the performance of gaskets made of metallic glass Fe0.79Si0.07B0.14 in a number of high-pressure X-ray diffraction (XRD) experiments in DACs equipped with conventional and toroidal-shape diamond anvils. The experiments were conducted in either axial or radial geometry with X-ray beams of micrometre to sub-micrometre size. We report that Fe0.79Si0.07B0.14 metallic glass gaskets offer a stable sample environment under compression exceeding 1 Mbar in all XRD experiments described here, even in those involving small-molecule gases (e.g. Ne, H2) used as pressure-transmitting media or in those with laser heating in a DAC. Our results emphasize the material's importance for a great number of delicate experiments conducted under extreme conditions. They indicate that the application of Fe0.79Si0.07B0.14 metallic glass gaskets in XRD experiments for both axial and radial geometries substantially improves various aspects of megabar experiments and, in particular, the signal-to-noise ratio in comparison to that with conventional gaskets made of Re, W, steel or other crystalline metals.

Gd(III) metal-organic framework as an effective humidity sensor and its hydrogen adsorption properties.

Metal-organic frameworks (MOFs) represent a class of nanoporous materials built up by metal ions and organic linkers with several interesting potential applications. The present study described the synthesis and characterization of Gd(III)-based MOF with the chemical composition [Gd(BTC)(H2O)]·DMF (BTC - trimesate, DMF = N,N'-dimethylformamide), known as MOF-76(Gd) for hydrogen adsorption/desorption capacity and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning and transmission electron microscopy. The crystal structure of MOF-76(Gd) consists of gadolinium (III) and benzene-1,3,5-tricarboxylate ions, one coordinated aqua ligand and one crystallization DMF molecule. The polymeric framework of MOF-76(Gd) contains 1D sinusoidally shaped channels with sizes of 6.7 × 6.7 Å propagating along c crystallographic axis. The thermogravimetric analysis, heating infrared spectroscopy and in-situ heating powder X-ray diffraction experiments of the prepared framework exhibited thermal stability up to 550 °C. Nitrogen adsorption/desorption measurement at -196 °C showed a BET surface area of 605 m2 g-1 and pore volume of 0.24 cm3 g-1. The maximal hydrogen storage capacity of MOF-76(Gd) was 1.66 wt % and 1.34 wt % -196 °C and -186 °C and pressure up to 1 bar, respectively. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Gd) is a suitable material for moisture sensing application with a fast response (11 s) and recovery time (2 s) in the relative humidity range of 11-98%.

High Temperature Oxidation Behavior of Creep Resistant Steels in Water Vapour Containing Environments.

This study describes the water vapour effect on the oxidation resistance of 9Cr creep resistant steels. Boiler P91 and MarBN steels were oxidized for 3000 h in a simulated humid atmosphere with ~10% water vapour. The oxidation kinetics had a stable course for 1000 h and was evaluated by the weight gain curves for both experimental steels and both oxidation temperatures. The oxidation rate was higher at 650 °C versus 600 °C, as reflected by the oxidation rate coefficient. A significant increase occurred after 1000 h of oxidation, which was related to the local breakdown oxide scale and oxide nodules were formed on steel. This oxidation behavior was influenced by the fact that a compact spinel structure of iron oxides and alloying elements were not formed on the steel. Analysis after 3000 h of exposure showed hematite Fe2O3 formed on the outer layer, magnetite Fe3O4 on the middle layer, and the bottom layer consisted of iron-chromium-spinel (Fe,Cr)2O3.

Structure-dynamics relationships in cryogenically deformed bulk metallic glass.

The atomistic mechanisms occurring during the processes of aging and rejuvenation in glassy materials involve very small structural rearrangements that are extremely difficult to capture experimentally. Here we use in-situ X-ray diffraction to investigate the structural rearrangements during annealing from 77 K up to the crystallization temperature in Cu44Zr44Al8Hf2Co2 bulk metallic glass rejuvenated by high pressure torsion performed at cryogenic temperatures and at room temperature. Using a measure of the configurational entropy calculated from the X-ray pair correlation function, the structural footprint of the deformation-induced rejuvenation in bulk metallic glass is revealed. With synchrotron radiation, temperature and time resolutions comparable to calorimetric experiments are possible. This opens hitherto unavailable experimental possibilities allowing to unambiguously correlate changes in atomic configuration and structure to calorimetrically observed signals and can attribute those to changes of the dynamic and vibrational relaxations (α-, ß- and γ-transition) in glassy materials. The results suggest that the structural footprint of the ß-transition is related to entropic relaxation with characteristics of a first-order transition. Dynamic mechanical analysis data shows that in the range of the ß-transition, non-reversible structural rearrangements are preferentially activated. The low-temperature γ-transition is mostly triggering reversible deformations and shows a change of slope in the entropic footprint suggesting second-order characteristics.

Thermosensitive Drug Delivery System SBA-15-PEI for Controlled Release of Nonsteroidal Anti-Inflammatory Drug Diclofenac Sodium Salt: A Comparative Study.

Mesoporous SBA-15 silica material was prepared by the sol-gel method and functionalized with thermosensitive polyethylenimine polymers with different molecular weight (g·mol-1): 800 (SBA-15(C)-800), 1300 (SBA-15(C)-1300) and 2000 (SBA-15(C)-2000). The nonsteroidal anti-inflammatory drug (NSAID) diclofenac sodium was selected as a model drug and encapsulated into the pores of prepared supports. Materials were characterized by the combination of infrared spectroscopy (IR), atomic force microscopy (AFM), transmission electron microscopy (TEM), photon cross-correlation spectroscopy (PCCS), nitrogen adsorption/desorption analysis, thermogravimetry (TG), differential scanning calorimetry (DSC) and small-angle X-ray diffraction (SA-XRD) experiments. The drug release from prepared matrixes was realized in two model media differing in pH, namely small intestine environment/simulated body fluid (pH = 7.4) and simulated gastric fluid (pH = 2), and at different temperatures, namely normal body temperature (T = 37 °C) and inflammatory temperature (T = 42 °C). The process of drug loading into the pores of prepared materials from the diclofenac sodium salt solutions with different concentrations and subsequent quantitative determination of released drugs was analyzed by UV-VIS spectroscopy. Analysis of prepared SBA-15 materials modified with polyethylenimines in solution showed a high ability to store large amounts of the drug, up to 230 wt.%. Experimental results showed their high drug release into the solution at pH = 7.4 for both temperatures, which is related to the high solubility of diclofenac sodium in a slightly alkaline environment. At pH = 2, a difference in drug release rate was observed between both temperatures. Indeed, at a higher temperature, the release rates and the amount of released drug were 2-3 times higher than those observed at a lower temperature. Different kinetic models were used to fit the obtained drug release data to determine the drug release rate and its release mechanism. Moreover, the drug release properties of prepared compounds were compared to a commercially available medicament under the same experimental conditions.

Mesoporous Silica as a Drug Delivery System for Naproxen: Influence of Surface Functionalization.

In this work we describe the relationship between surface modification of hexagonally ordered mesoporous silica SBA-15 and loading/release characteristics of nonsteroidal anti-inflammatory drug (NSAID) naproxen. Mesoporous silica (MPS) was modified with 3-aminopropyl, phenyl and cyclohexyl groups by grafting method. Naproxen was adsorbed into pores of the prepared MPS from ethanol solution using a solvent evaporation method. The release of the drug was performed in buffer medium at pH 2 and physiological solution at pH 7.4. Parent MPSs as well as naproxen loaded MPSs were characterized using physicochemical techniques such as nitrogen adsorption/desorption, thermogravimetric analysis (TG), Zeta potential analysis, Fourier transform infrared spectroscopy (FT-IR), and elemental analysis. The amount of naproxen released from the MPSs into the medium was determined by high-performance liquid chromatography (HPLC). It was shown that the adsorption and desorption characteristics of naproxen are dependent on the pH of the solution and the surface functionalization of the host.

Fast-current-heating devices to study in situ phase formation in metallic glasses by using high-energy synchrotron radiation.

Details of fast-resistive-heating setups, controlled heating ranging from ∼101 K s-1 to ∼103 K s-1, to study in situ phase transformations (on heating and on cooling) in metallic glasses by high-energy synchrotron x-ray diffraction are discussed. Both setups were designed and custom built at the Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden) and have been implemented at the P02.1 Powder Diffraction and Total Scattering Beamline and the P21.1 Swedish Materials Science Beamline at PETRA III storage ring, DESY, Hamburg. The devices are interchangeable at both beamlines. Joule heating is triggered automatically and is timed with the incident beam and detector. The crystallization process can be controlled via a feedback circuit by monitoring the change in the time-dependent resistivity and temperature of glasses. Different ambient atmospheres, such as vacuum and inert gases (He and Ar), can be used to control oxidation and cooling. The main focus of these devices is on understanding the crystallization mechanism and kinetics in metallic glasses, which are brittle and for which fast heating gives defined glass-crystal composites with enhanced plasticity. As an example, phase-transformation sequence(s) in a prototyped Cu-Zr-based metallic glass is described on heating, and a crystalline phase beneficial to the plasticity is identified.

Cytotoxicity study and influence of SBA-15 surface polarity and pH on adsorption and release properties of anticancer agent pemetrexed.

Mesoporous material SBA-15 was functionalized with different polar and nonpolar groups: 3-aminopropyl, (SBA-15-NH2), 3-isocyanatopropyl (SBA-15-NCO), 3-mercaptopropyl (SBA-15-SH), methyl (SBA-15-CH3) and phenyl (SBA-15-Ph). The resulting surface grafted materials were investigated as matrices for controlled drug delivery. Anticancer agent, pemetrexed (disodium pemetrexed heptahydrate) was selected as a model drug and loaded in the unmodified and functionalized SBA-15 materials. Materials were characterized by elemental analysis, infrared spectroscopy, transmission electron microscopy, nitrogen adsorption/desorption analysis, small angle X-ray scattering, powder X-ray diffraction, solid state NMR spectroscopy and thermogravimetry. It was shown that surface modification has an impact on both encapsulated drug amount and release properties. Release experiments were performed into two media with different pH: simulated body fluid (pH = 7.4) and simulated gastric fluid (pH = 2). In general, the effect of pH was reflected by the lower release of pemetrexed under acidic conditions (pH = 2) compared to slightly alkaline saline environment (pH = 7.4). The release rate of pemetrexed from propylamine-, propylisocyanate- and phenyl-modified SBA-15 was found to be effectively controlled by intermolecular interactions as compared to that from pure SBA-15, SBA-15-SH, and SBA-15-CH3, that evidenced a steady and similar release. The highest release was observed for methyl-functionalized material whose hydrophobic surface accelerates the pemetrexed release. The data obtained from release studies were fitted using various kinetic models to determine the pemetrexed release mechanism and its release rate. The best correlations were found for Korsmeyer-Peppas and Higuchi models. Moreover, the theoretical three-parameter model for drug release kinetic was applied to calculate the strength of drug-support interactions. The in vitro cell study was performed on SKBR3 cancer cells and obtained results demonstrated that the modification of the mesoporous silica material by grafted polar/nonpolar groups may significantly affect the compatibility of this material with cells, drug release from this material and subsequent biological activity of PEM.

Doxorobicin as cargo in a redox-responsive drug delivery system capped with water dispersible ZnS nanoparticles.

In this work, we have prepared and investigated a redox-responsive drug delivery system (DDS) based on a porous carrier. Doxorubicin (DOX), a chemotherapy medication for treatment of different kinds of cancer, was used as a model drug in the study. DOX was loaded in ordered hexagonal mesoporous silica SBA-15, a nanoporous material with good biocompatibility, stability, large pore size and specific surface area (S BET = 908 m2 g-1, V P = 0.79 cm3 g-1, d = 5.9 nm) and easy surface modification. To prepare the redox-responsive system, cystamine derivative ligands, with redox active disulphide linkers were grafted onto the surface of SBA-15. To ensure no significant premature release of DOX from the porous system, thioglycolic acid modified ZnS nanoparticles (ZnS-COOH NPs) were used as pore capping agents. The grafted redox-responsive cystamine derivative ligand containing disulphide linkers was bonded by a peptide bond to the thioglycolic acid groups of ZnS-COOH NPs, capping the pores. Once the disulphide bond was cleaved, the ZnS-COOH NPs caps were released and pores were opened to deliver the DOX cargo. The dithiol bond was cleavable by redox active molecules such as dithiothreitol (DTT) or glutathione, the concentration of which in cancer cells is 4 times higher than in healthy cells. The redox release of DOX was studied in two different media, physiological saline solution with DTT and saline without DTT. The prepared DDS proved the concept of redox responsive release. All samples were characterised by powder X-ray diffraction (XRD), transition electron microscopy (TEM), nitrogen adsorption/desorption at 77 K, Fourier-transform infrared spectroscopy (FTIR), thermal analysis and zeta potential measurements. The presence of semiconducting ZnS nanoparticle caps on the pore openings was detected by magnetic measurements using SQUID magnetometry showing that such cargo systems could be monitored using magnetic measurements which opens up the possibilities of using such drug delivery systems as theranostic agents.

A mechanochemical route for the synthesis of VNbO5 and its structural re-investigation using structure solution from powder diffraction data.

A new and solvent-free synthesis route has been adopted and optimized to prepare crystalline VNbO5 from the mechanochemical reaction between Nb2O5 and V2O5 as starting reagents. The substantially amorphous mixture of equimolar pentoxide V and Nb metals observed after extended mechanical treatment transforms into a crystalline powder following calcination under mild conditions at 710 K. The structure solution of the X-ray diffraction pattern using a global optimization approach, combined with Rietveld refinement, points to a space group P212121 (no. 19) different from Pnma (no. 62) previously proposed in the literature assuming it to be isostructural to VTaO5. The new space group helps to describe weak peaks that remained previously unaccounted for and allows more reliable determination of atomic fractional coordinates and interatomic distance distribution. The as-prepared VNbO5 has been tested as a dopant (5 wt%) for the purpose of solid state hydrogen storage, decreasing significantly the release of hydrogen of MgH2/Mg (620 K) and further enhancing the hydrogen sorption kinetic properties.

Structure and Hydrogenation Properties of a HfNbTiVZr High-Entropy Alloy.

A high-entropy alloy (HEA) of HfNbTiVZr was synthesized using an arc furnace followed by ball milling. The hydrogen absorption mechanism was studied by in situ X-ray diffraction at different temperatures and by in situ and ex situ neutron diffraction experiments. The body centered cubic (BCC) metal phase undergoes a phase transformation to a body centered tetragonal (BCT) hydride phase with hydrogen occupying both tetrahedral and octahedral interstitial sites in the structure. Hydrogen cycling of the alloy at 500 °C is stable. The large lattice strain in the HEA seems favorable for absorption in both octahedral and tetrahedral sites. HEAs therefore have potential as hydrogen storage materials because of favorable absorption in all interstitial sites within the structure.

Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl.

The low cost, rare earth free τ-phase of MnAl has high potential to partially replace bonded Nd2Fe14B rare earth permanent magnets. However, the τ-phase is metastable and it is experimentally difficult to obtain powders suitable for the permanent magnet alignment process, which requires the fine powders to have an appropriate microstructure and high τ-phase purity. In this work, a new method to make high purity τ-phase fine powders is presented. A high purity τ-phase Mn0.55Al0.45C0.02 alloy was synthesized by the drop synthesis method. The drop synthesized material was subjected to cryo milling and  followed by a flash heating process. The crystal structure and microstructure of the drop synthesized, cryo milled and flash heated samples were studied by X-ray in situ powder diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy and electron backscatter diffraction. Magnetic properties and magnetic structure of the drop synthesized, cryo milled, flash heated  samples were characterized by magnetometry and neutron powder diffraction, respectively. The results reveal that the 2 and 4 hours cryo milled and flash heated samples both exhibit high τ-phase purity and micron-sized round particle shapes. Moreover, the flash heated samples display high saturation magnetization as well as increased coercivity.

Kinetic alteration of the 6Mg(NH2)2-9LiH-LiBH4 system by co-adding YCl3 and Li3N.

The 6Mg(NH2)2-9LiH-LiBH4 composite system has a maximum reversible hydrogen content of 4.2 wt% and a predicted dehydrogenation temperature of about 64 °C at 1 bar of H2. However, the existence of severe kinetic barriers precludes the occurrence of de/re-hydrogenation processes at such a low temperature (H. Cao, G. Wu, Y. Zhang, Z. Xiong, J. Qiu and P. Chen, J. Mater. Chem. A, 2014, 2, 15816-15822). In this work, Li3N and YCl3 have been chosen as co-additives for this system. These additives increase the hydrogen storage capacity and hasten the de/re-hydrogenation kinetics: a hydrogen uptake of 4.2 wt% of H2 was achieved in only 8 min under isothermal conditions at 180 °C and 85 bar of H2 pressure. The re-hydrogenation temperature, necessary for a complete absorption process, can be lowered below 90 °C by increasing the H2 pressure above 185 bar. Moreover, the results indicate that the hydrogenation capacity and absorption kinetics can be maintained roughly constant over several cycles. Low operating temperatures, together with fast absorption kinetics and good reversibility, make this system a promising on-board hydrogen storage material. The reasons for the improved de/re-hydrogenation properties are thoroughly investigated and discussed.

Thermal expansion of Pd-based metallic glasses by ab initio methods and high energy X-ray diffraction.

Metallic glasses are promising structural materials due to their unique properties. For structural applications and processing the coefficient of thermal expansion is an important design parameter. Here we demonstrate that predictions of the coefficient of thermal expansion for metallic glasses by density functional theory based ab initio calculations are efficient both with respect to time and resources. The coefficient of thermal expansion is predicted by an ab initio based method utilising the Debye-Grüneisen model for a Pd-based metallic glass, which exhibits a pronounced medium range order. The predictions are critically appraised by in situ synchrotron X-ray diffraction and excellent agreement is observed. Through this combined theoretical and experimental research strategy, we show the feasibility to predict the coefficient of thermal expansion from the ground state structure of a metallic glass until the onset of structural changes. Thereby, we provide a method to efficiently probe a potentially vast number of metallic glass alloying combinations regarding thermal expansion.

Synthesis, structures and thermal decomposition of ammine MxB12H12 complexes (M = Li, Na, Ca).

A series of ammine metal-dodecahydro-closo-dodecaboranes, MxB12H12·nNH3 (M = Li, Na, Ca) were synthesized and their structural and thermal properties studied with in situ time-resolved synchrotron radiation powder X-ray diffraction, thermal analysis, Fourier transformed infrared spectroscopy, and temperature-programmed photographic analysis. The synthesized compounds, Li2B12H12·7NH3, Na2B12H12·4NH3 and CaB12H12·6NH3, contain high amounts of NH3, 43.3, 26.6 and 35.9 wt% NH3, respectively, which can be released and absorbed reversibly at moderate conditions without decomposition, thereby making the closo-boranes favorable 'host' materials for ammonia or indirect hydrogen storage in the solid state. In this work, fifteen new ammine metal dodecahydro-closo-dodecaborane compounds are observed by powder X-ray diffraction, of which six are structurally characterized, Li2B12H12·4NH3, Li2B12H12·2NH3, Na2B12H12·4NH3, Na2B12H12·2NH3, CaB12H12·4NH3 and CaB12H12·3NH3. Li2B12H12·4NH3 and Na2B12H12·4NH3 are isostructural and monoclinic (P21/n) whereas Na2B12H12·2NH3 and CaB12H12·3NH3 are both trigonal with space groups P3[combining macron]m1 and R3[combining macron]c, respectively. Generally, coordination between the metal and the icosahedral closo-borane anion is diverse and includes point sharing, edge sharing, or face sharing, while coordination of ammonia always occurs via the lone pair on nitrogen to the metal. Furthermore, a liquid intermediate is observed during heating of Li2B12H12·7NH3. This work provides deeper insight into the structural, physical, and chemical properties related to thermal decomposition and possible ammonia and hydrogen storage.

Ultra-stiff metallic glasses through bond energy density design.

The elastic properties of crystalline metals scale with their valence electron density. Similar observations have been made for metallic glasses. However, for metallic glasses where covalent bonding predominates, such as metalloid metallic glasses, this relationship appears to break down. At present, the reasons for this are not understood. Using high energy x-ray diffraction analysis of melt spun and thin film metallic glasses combined with density functional theory based molecular dynamics simulations, we show that the physical origin of the ultrahigh stiffness in both metalloid and non-metalloid metallic glasses is best understood in terms of the bond energy density. Using the bond energy density as novel materials design criterion for ultra-stiff metallic glasses, we are able to predict a Co33.0Ta3.5B63.5 short range ordered material by density functional theory based molecular dynamics simulations with a high bond energy density of 0.94 eV Å-3 and a bulk modulus of 263 GPa, which is 17% greater than the stiffest Co-B based metallic glasses reported in literature.

The effect of Sr(OH)2 on the hydrogen storage properties of the Mg(NH2)2-2LiH system.

The doping effect of Sr(OH)2 on the Mg(NH2)2-2LiH system is investigated considering different amounts of added Sr(OH)2 in the range of 0.05 to 0.2 mol. Experimental results show that both the thermodynamic and the kinetic properties of Mg(NH2)2-2LiH are influenced by the presence of Sr(OH)2. The addition of 0.1 mol Sr(OH)2 leads to a decrease in both the dehydrogenation onset and peak temperatures of ca. 70 and 13 °C, respectively, and an acceleration in the de/re-hydrogenation rates of one time at 150 °C compared to Mg(NH2)2-2LiH alone. Based on differential scanning calorimetry (DSC) analysis, the overall reaction enthalpy of the 0.1 Sr(OH)2-doped sample is calculated to be 44 kJ per mol-H2 and there are two absorption events occurring in the doped sample instead of one in the pristine sample. For the applied experimental conditions, according to the in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and Fourier Transform Infrared spectroscopy (FT-IR) analysis, the reaction mechanism has been finally defined: Sr(OH)2, Mg(NH2)2 and LiH react with each other to form SrO, MgO and LiNH2 during ball milling. After heating, SrO interacts with Mg(NH2)2 producing MgO and Sr(NH2)2. Then Mg(NH2)2, LiNH2 and Sr(NH2)2 react with LiH to produce Li2NH, SrNH, Li2Mg(NH)2 and Li2Mg2(NH)3 in traces. After re-hydrogenation, LiSrH3, LiH and LiNH2 are formed along with amorphous Mg(NH2)2. The reasons for the improved kinetics are: (a) during dehydrogenation, the in situ formation of SrNH appears to increase the interfacial contacts between Mg(NH2)2 and LiH and also weakens the N-H bond of Mg(NH2)2; (b) during absorption, the formation of LiSrH3 at around 150 °C could be the key factor for improving the hydrogenation properties.

Transparent polycrystalline cubic silicon nitride.

Glasses and single crystals have traditionally been used as optical windows. Recently, there has been a high demand for harder and tougher optical windows that are able to endure severe conditions. Transparent polycrystalline ceramics can fulfill this demand because of their superior mechanical properties. It is known that polycrystalline ceramics with a spinel structure in compositions of MgAl2O4 and aluminum oxynitride (γ-AlON) show high optical transparency. Here we report the synthesis of the hardest transparent spinel ceramic, i.e. polycrystalline cubic silicon nitride (c-Si3N4). This material shows an intrinsic optical transparency over a wide range of wavelengths below its band-gap energy (258 nm) and is categorized as one of the third hardest materials next to diamond and cubic boron nitride (cBN). Since the high temperature metastability of c-Si3N4 in air is superior to those of diamond and cBN, the transparent c-Si3N4 ceramic can potentially be used as a window under extremely severe conditions.