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- ItemRoles of hydrogenation, annealing and field in the structure and magnetic entropy change of Tb-based bulk metallic glasses(New York : American Institute of Physics, 2013) Luo, Qiang; Schwarz, Björn; Mattern, Norbert; Shen, Jun; Eckert, JürgenThe reduction of open-volume regions in Tb-based metallic glass (MG) by annealing and hydrogen charging was found to rearrange the atomic structure and tune the magnetic behaviors. After crystallization, the magnetic structure and magnetic entropy change (MEC) alters due to the structural transformation, and a plateau-like-MEC behavior can be obtained. The hydrogen concentration after charging at 1mA/cm2 for 576 h reaches as high as 3290 w-ppm. The magnetization behavior and the MEC change due to the modification of the exchange interaction and the random magnetic anisotropy (RMA) upon hydrogenation. At low temperatures, irreversible positive MEC was obtained, which is related to the internal entropy production. The RMA-to-exchange ratio acts as a switch to control the irreversible entropy production channel and the reversible entropy transfer channel. The field dependence of the MEC is discussed in term of the competition among Zeeman energy, exchange interaction and RMA.
- ItemCrystal growth and thermodynamic investigation of Bi2M2+O4 (M = Pd, Cu)(London : RSC, 2021) Wolff, Nora; Klimm, Detlef; Habicht, Klaus; Fritsch, KatharinaPhase equilibria that are relevant for the growth of Bi2MO4 have been studied experimentally, and the ternary phase diagrams of Bi2O3–PdO2–Pd and Bi2O3–Cu2O–CuO and its isopleth section Bi2O3–CuO were redetermined. It is shown that every melting and crystallization process is always accompanied by a redox process at the phase boundary and that for both title compounds, the valence of the transition metal is lowered during melting. Vice versa, during crystal growth, O2 must be transported through the melt to the phase boundary. Based on these new insights provided by our thermodynamic studies, Bi2CuO4 single crystals with a length of up to 7 cm and a diameter of 6 mm were grown by the OFZ technique to be used for investigations of magnetic, electronic and thermal transport properties. The grown crystals were characterized by powder X-ray diffraction, Laue, magnetization and specific heat measurements.
- ItemSolvent-antisolvent interactions in metal halide perovskites(Cambridge : Soc., 2023) Bautista-Quijano, Jose Roberto; Telschow, Oscar; Paulus, Fabian; Vaynzof, YanaThe fabrication of metal halide perovskite films using the solvent-engineering method is increasingly common. In this method, the crystallisation of the perovskite layer is triggered by the application of an antisolvent during the spin-coating of a perovskite precursor solution. Herein, we introduce the current state of understanding of the processes involved in the crystallisation of perovskite layers formed by solvent engineering, focusing in particular on the role of antisolvent properties and solvent-antisolvent interactions. By considering the impact of the Hansen solubility parameters, we propose guidelines for selecting the appropriate antisolvent and outline open questions and future research directions for the fabrication of perovskite films by this method.
- ItemMorphology and crystallization of polypropylene/microfibrillated cellulose composites(Bangkok : King Mongkut’s University of Technology, 2014) Thanomchat, Sarit; Srikulkit, Kawee; Suksut, Buncha; Schlarb, Alois KarlMicrofibrillated cellulose (MFC) was prepared by controlling the re-precipitation of cellulose prepared in the mixture form of NaOH/Urea solubilized microcrystalline cellulose (MCC) and starch. The cellulose re-precipitation was carried-out in an HCl bath, resulting in a MFC form having relatively lower crystallinity than MCC. The XRD pattern of MFC indicated the partially crystalline structure arising from the imperfect orientation of a cellulose chain obstructed by a starch molecule in the precipitation step. Interestingly, the MFC morphology exhibited a web-like structure with a diameter in the range of 10-20 nm. The water retention value of MFC was extraordinarily high due to its extremely small diameter having high surface area. Further, surface silanization of MFC with organosilane was carried out. Then, the modified MFC was melt-mixed with polypropylene (PP) matrix via a simple melt mixing technique. The morphology and crystallization of the PP/MFC composites were measured. The morphology of organosilane treated MFC exhibited agglomeration of 10 microns in diameter with layered structures arising from the packing of microfibrils. The FTIR spectra showed hydrophobic characteristics of treated MFC observed by the disappearance of original cellulose hydroxyl group and bound water. The crystallinity of treated MFC increased when compared to the untreated MFC, indicating that cellulose chains of unmodified MFC underwent re-orientation occurring in the modification step due to its high crystallinity characteristic. For the PP/MFC-composite containing MFC loading, faster crystallization and higher spherulite growth rate, in case of higher MFC loading, were observed. In addition, the spherulite size decreased with an increase in the crystallization temperature. However, the degree of crystallinity was fairly independent on the MFC-loading. Therefore it can be concluded that the addition of MFC might enable shorter cycle times, resulting in cheaper processing cost in a view point of polymer processing.
- ItemProperties of the Ti40Zr10Cu36Pd14 BMG modified by Sn and Nb aqdditions(Heidelberg : Springer, 2016) Sypien, Anna; Stoica, Mihail; Czeppe, TomaszThe results of investigation of the influence of additions of 2 and 3 at.% of Sn and simultaneously of Sn and 3 at.% Nb on microstructure and properties of the bulk metallic glasses of composition (Ti40Cu36−x Zr10Pd14Sn x )100−y Nb y are reported. It was found that the additions of Sn increased the temperatures of glass transition (T g), primary crystallization (T x ), melting, and liquidus as well as supercooled liquid range (ΔT) and glass forming ability (GFA). The nanohardness and elastic modulus decreased in alloys with 2 and 3 at.% Sn additions, revealing similar values. The 3 at.% Nb addition to the Sn-containing amorphous phase decreased as well all the T g, T x , T L, and T m temperatures as ΔT and GFA; however, relatively larger values of this parameters in alloys containing larger Sn content were preserved. In difference to the previously published results, in the case of the amorphous alloys containing small Nb and Sn additions, a noticeable amount of the quenched-in crystalline phases was not confirmed, at least of the micrometric sizes. In the case of the alloys containing Sn or both Sn and Nb, two slightly different amorphous phase compositions were detected, suggesting separation in the liquid phase. Phase composition of the alloys determined after amorphous phase crystallization was similar for all compositions. The phases Cu8Zr3, CuTiZr, and Pd3Zr were mainly identified in the proportions dependent on the alloy compositions.
- ItemStructure formation of ultrathin PEO films at solid interfaces-complex pattern formation by dewetting and crystallization(Basel : MDPI AG, 2013) Braun, H.-G.; Meyer, E.The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupture caused by dewetting. With crystallisable polymers such as polyethyleneoxide (PEO), molecular self-assembly into partial ordered lamella structures is studied as an additional source of pattern formation. Morphological features in ultrathin PEO films (thickness < 10 nm) result from an interplay between dewetting patterns and diffusion limited growth pattern of ordered lamella growing within the dewetting areas. Besides structure formation of hydrophilic PEO molecules, n-alkylterminated (hydrophobic) PEO oligomers are investigated with respect to self-organization in ultrathin films. Morphological features characteristic for pure PEO are not changed by the presence of the n-alkylgroups.
- ItemEffect of Molar Mass on Critical Specific Work of Flow for Shear-Induced Crystal Nucleation in Poly (l-Lactic Acid)(Basel : MDPI, 2021) Du, Mengxue; Jariyavidyanont, Katalee; Kühnert, Ines; Boldt, Regine; Androsch, RenéThe concept of specific work of flow has been applied for the analysis of critical shearing conditions for the formation of crystal nuclei in poly (l-lactic acid) (PLLA). Systematic variation in both time and rate of shearing the melt in a parallel-plate rheometer revealed that these parameters are interconvertible regarding the shear-induced formation of crystal nuclei; that is, low shear rate can be compensated for by increasing the shear time and vice versa. This result supports the view that critical shearing conditions can be expressed by a single quantity, providing additional options for tailoring polymer processing routes when enhanced nuclei formation is desired/unwanted. Analysis of PLLA of different mass-average molar masses of 70, 90, 120, and 576 kDa confirmed improved shear-induced crystal nucleation for materials of higher molar mass, with critical specific works of flow, above which shear-induced nuclei formation occurs, of 550, 60, 25, and 5 kPa, respectively.
- ItemStructure Mediation and Properties of Poly(l-lactide)/Poly(d-lactide) Blend Fibers(Basel : MDPI, 2018) Yang, Bo; Wang, Rui; Ma, Hui-Ling; Li, Xiaolu; Brünig, Harald; Dong, Zhenfeng; Qi, Yue; Zhang, XiuqinPoly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) blend as-spun fibers (50/50, wt.%) were prepared by melt spinning. Structure mediation under temperature and stress and properties of poly(l-lactic acid)/poly(d-lactic acid)(PLLA/PDLA) as-spun fibers were investigated by wide-angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC). The results show that highly oriented stereocomplex (SC) crystals can be formed in PLLA/PDLA blend fibers drawn at 60 °C and annealed at 200 °C. However, at drawn temperature of 80 °C, only lower oriented SC crystals can be formed. For PLLA/PDLA blend fibers drawn twice at 60 °C (PLLA/PDLA-60-2), the crystallinity of SC crystals increases with annealing temperature in the range of 200 to 215 °C, while the degree of orientation decreases slightly. When the annealing temperature is 210 °C, the crystallinity and orientation of SC crystals in PLLA/PDLA-60-2 fibers reach 51% and −0.39, respectively. Moreover, PLLA/PDLA-60-2-210 fibers exhibit excellent heat-resistant property even at 200 °C. The results indicate that the oriented PLLA/PDLA blend fibers with high SC crystals content can be regulated in a short time.
- ItemA new strategy to improve viscoelasticity, crystallization and mechanical properties of polylactide(Amsterdam [u.a.] : Elsevier Science, 2021) Huang, Ying; Müller, Michael Thomas; Boldt, Regine; Zschech, Carsten; Gohs, Uwe; Wießner, SvenBiodegradable polylactide/masticated natural rubber (PLA/mNR) blends were prepared by electron induced reactive processing (EIReP) without using any chemical additives. The PLA/mNR blends showed droplet-matrix morphology with decreased mNR particle size after EIReP treatment. The absolute value of complex viscosity and storage modulus increased significantly for the EIReP modified blends, suggesting the improved melt strength and elasticity. The crystallization investigation showed that the cold crystallization peak of PLA phase gradually disappeared after EIReP modification. Instead, the crystallization peak arose during melt cooling process. Consequently, the crystallinity of PLA phase increased from 6.2% to 39.0% as the mNR content increased from 0 to 20 wt%. It was found that the softening temperature of PLA examined by dynamic mechanical analysis increased effectively with the characters of higher modulus compared to the non-modified blends. The EIReP modified blends exhibited excellent mechanical properties with 7-fold increase of impact toughness compared with neat PLA, implying a superior interfacial adhesion and chain interactions between the two polymer phases. Furthermore, the thermogravimetric analysis demonstrated that the thermal stability was slightly enhanced for the EIReP modified blends.
- ItemStructural evolution in Ti-Cu-Ni metallic glasses during heating(New York : American Institute of Physics, 2015) Gargarella, P.; Pauly, S.; Stoica, M.; Vaughan, G.; Afonso, C.R.M.; Kühn, U.; Eckert, J.The structural evolution of Ti50Cu43Ni7 and Ti55Cu35Ni10 metallic glasses during heating was investigated by in-situ synchrotron X-ray diffraction. The width of the most intense diffraction maximum of the glassy phase decreases slightly during relaxation below the glass transition temperature. Significant structural changes only occur above the glass transition manifesting in a change in the respective peak positions. At even higher temperatures, nanocrystals of the shape memory B2-Ti(Cu,Ni) phase precipitate, and their small size hampers the occurrence of a martensitic transformation.