A metal-organic framework with ultrahigh glass-forming ability

Glass-forming ability (GFA) is the ability of a liquid to avoid crystallization during cooling. Metal-organic frameworks (MOFs) are a new class of glass formers (1?3), with hitherto unknown dynamic and thermodynamic properties. We report the discovery of a new series of tetrahedral glass systems, zeolitic imidazolate framework?62 (ZIF-62) [Zn(Im2?xbImx)], which have ultrahigh GFA, superior to any other known glass formers. This ultrahigh GFA is evidenced by a high viscosity ? (105 Pa?s) at the melting temperature Tm, a large crystal-glass network density deficit (??/?g)network, no crystallization in supercooled region on laboratory time scales, a low fragility (m = 23), an extremely high Poisson?s ratio (? = 0.45), and the highest Tg/Tm ratio (0.84) ever reported. Tm and Tg both increase with benzimidazolate (bIm) content but retain the same ultrahigh Tg/Tm ratio, owing to high steric hindrance and frustrated network dynamics and also to the unusually low enthalpy and entropy typical of the soft and flexible nature of MOFs. On the basis of these versatile properties, we explain the exceptional GFA of the ZIF-62 systempublishersversionPeer reviewe

Metal-organic framework crystal-glass composites.

The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. Recent research has revealed solid-liquid transitions within the family, which we use here to create a class of functional, stable and porous composite materials. Described herein is the design, synthesis, and characterisation of MOF crystal-glass composites, formed by dispersing crystalline MOFs within a MOF-glass matrix. The coordinative bonding and chemical structure of a MIL-53 crystalline phase are preserved within the ZIF-62 glass matrix. Whilst separated phases, the interfacial interactions between the closely contacted microdomains improve the mechanical properties of the composite glass. More significantly, the high temperature open pore phase of MIL-53, which spontaneously transforms to a narrow pore upon cooling in the presence of water, is stabilised at room temperature in the crystal-glass composite. This leads to a significant improvement of CO2 adsorption capacity

Structural renovation and economic feasibility of conveyor belt idlers

V podjetju Premogovnik Velenje, d. o. o., za transport lignita iz rudnika uporabljajo tračni transporter, ki je podprt s podpornimi valjčki, vgrajenimi v nosilce. Valjčki, ki jih trenutno uporabljajo, so nerazstavljivi. Če se pokvari samo ležaj, se menja celoten valjček. Najbolj pogosto so naročeni valjčki premera (133 x 670 mm), ki so vgrajeni pri tako imenovanem glavnem odvozu premoga v nosilce, pod kotom 10°. Podjetje DBSS, d. o. o., je včasih izdelovalo te valjčke v manjši količini, vendar so bili ti drugačni. S pomočjo stiskalnice oziroma z uporabo zunanje sile so bili ti valjčki razstavljivi, kar je omogočalo ob okvari ležaja oziroma drugega dela valjčka zamenjavo poškodovanega elementa. Težavo predstavljajo stroški, saj so pri razstavljivih podpornih valjčkih precej veliki. V diplomskem delu je predstavljena rekonstrukcija razstavljivih valjčkov, izdelava tehniške dokumentacije ter stroškovni preračun izdelave izbrane serije podpornih valjčkov.In company Premogovnik Velenje d. o. o., for the transport of lignite from the mine, they use a belt conveyor, which is supported by support rollers built into the beams. The rollers they are currently using are non - detachable, which means that if only the bearing fails, the entire roller is replaced. The largest number of rollers ordered are rollers with diameter 133 mm and length 670 mm, which are installed at the so - called main coal outlet in the beams at an angle of 10 °. DBSS d. o. o. sometimes made these rollers in smaller numbers, but they were different, because with the help of a press or using external force, these rollers were disassembled, which allowed in case of failure of the bearing or other part of the roller, to replace this damaged element. However, the detachable support rollers were quite expensive. The diploma thesis presents the reconstruction of detachable rollers, the preparation of technical documentation and the cost calculation of the production of a series of support rollers

Nanocomposites of LLDPE and Surface-Modified Cellulose Nanocrystals Prepared by Melt Processing

Cellulose nanocrystals (CNCs) were surface modified by esterification in tetrahydrofuran (THF) at 25 °C using different catalysts and anhydrides bearing different alkyl side chain lengths. Unmodified and acetic anhydride (AcAnh)-modified CNCs were studied as potential nanofillers for linear low-density poly(ethylene) (LLDPE). Nanocomposites were prepared by melt processing. Determination of the size and size distribution of CNCs in the nanocomposites by SEM revealed an enhanced compatibility of the AcAnh-modified CNCs with the LLDPE matrix, since the average size of the aggregates of the modified CNCs (0.5–5 μm) was smaller compared to that of the unmodified CNCs (2–20 μm). Tensile test experiments revealed an increase in the nanocomposites’ stiffness and strain at break—by 20% and up to 90%, respectively—at the CNC concentration of 5 wt %, which is close to the critical percolation concentration. Since the CNC nanofiller simultaneously reduced LLDPE crystallinity, the reinforcement effect of CNCs was hampered. Therefore, the molding temperature was increased to 120 °C, and, in this way, the greatest increase of the Young’s modulus was achieved (by ~45%). Despite the enhanced compatibility of the AcAnh-modified CNCs with the LLDPE matrix, no additional effect on the mechanical properties of the nanocomposites was observed in comparison to the unmodified CNC

Synthesis of organic cathode materials with pyrazine and catechol motifs for rechargeable lithium and zinc batteries

Although there are many reports on novel small organic cathode materials for rechargeable lithium and zinc batteries, there is still a lack of materials obtained with a facile synthesis from commercially available precursors, which also exhibit satisfactory cycling stability. Herein, we report a simple synthetic procedure for the simultaneous introduction of carbonyl and pyrazine units into small organic cathode materials. Materials were prepared through a condensation reaction between aromatic diamines and the sodium salt of rhodizonic acid. Building on an already known oxidized diquinoxalinecatechol (ODQC) material with cycling stability issues stemming from the dissolution in the electrolyte, we designed an expanded conjugated structure tetraquinoxalinecatechol (TQC). The ODQC shows fast capacity fading in Li-organic batteries having capacity retention of 16.8 % after 300 cycles at a current density of 50 mAg-1. The synthesis of the bigger TQC analog with lower solubility improves cycling stability with a high capacity retention of 82 % after 300 cycles at a current density of 50 mAg-1 and a maximum specific capacity of 223 mAhg-1 at an average voltage of 2.42 V vs. Li/Li+. In Zn-organic battery employing an aqueous electrolyte, TQC delivers a high maximum specific capacity of 301 mAhg-1 at 50 mAg-1 with an average voltage of 0.76 V, and 71 % capacity retention after 100 cycles

Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary

The alkali fullerides, A3C60 (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs3C60 polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/kBTc = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/kBTc decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached