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Elastooptic Materials
Published in Marvin J. Weber, and TECHNOLOGY, 2020
The purification of the lead halides is complicated by its insolubility in water, alcohol, and other organic solvents, oxidation in the presence of moisture at high temperature, and the formation of oxyhalides and mixed halides due to residual halide impurities. Purification is carried out by repeated directional freezing at high temperature gradients. A well cleaned quartz tube was used for the container. Crystals are grown from purified material in one-zone and two-zone furnaces. The purified source material was sealed into tapered cylindrical quartz ampoules 28 mm in diameter. Growth was initiated in a thin capillary tube that formed the cold end of the ampoule. Growth was carried out at rates between 1 and 2 cm/day. Laue patterns show that the crystals grow dominantly in the <001> direction whenever growth is initiated without seeds.
Problems with Explicit Solutions
Published in Vasilios Alexiades, Alan D. Solomon, Mathematical Modeling of Melting and Freezing Processes, 2018
Vasilios Alexiades, Alan D. Solomon
or non-equilibrium lever rule [PORTER-EASTERLING], [KURZ-FISHER]. It expresses the composition of solid in terms of the initial composition C0 and the phase diagram for a dilute alloy solidifying directionally with no diffusion in the solid and perfect mixing in the liquid. Note that it is based on mass balance alone, PROBLEM 10, hence independent of the heat transfer process, and it constitutes the fundamental equation for directional freezing and zone-refining [PFANN], [HERINGTON]. The (uniform) composition of the remaining liquid, which changes with time, (57), may also be simply expressed in terms of the liquid fraction fL = 1 − fS = 1 − X(t)/l as () Cliqiud=C0fLk−1.
Extracellular Matrix–Derived Biomaterials: Molecularly Defined Ingredients and Processing Techniques
Published in Gilson Khang, Handbook of Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine, 2017
H.R. Hoogenkamp, L.R.M. Versteegden, T.H. van Kuppevelt, W.F. Daamen
The freezing temperature influences the formation of ice crystals (which become pores after lyophilization), including their size and orientation (see Fig. 28.6).279 In several tissues, the ECM is oriented either unidirectionally (e.g., cartilage) or radially (e.g., muscle fibers in the diaphragm). A scaffold with unidirectional pores can be created by applying a vertical temperature gradient to a collagen suspension (see Fig. 28.6), which mimics the ECM of healthy cartilage.278 A similar principle can be applied to guide the generation of muscle cells in the correct orientation using a scaffold with a radial pore structure. This can be achieved by applying directional freezing from inside-out using a centrally positioned cooled tube.280
Design of multi-auxetic microstructures for sound absorbing applications
Published in Advanced Composite Materials, 2023
Generally, to improve the sound-absorbing performance in the low-frequency range by using the existing sound-absorbing material such as polyurethane foam, it is necessary to increase the thicknesses of the sound-absorbing material [5]. Therefore, it is required to develop sound-absorbing materials with thin thicknesses that exhibit excellent sound absorption performance [6]. In the study of sound absorbing materials using the existing porous structure, an open cell structure was created in which the polymer polyol was opened when polyurethane foam was foamed using a polyurethane foam composition [7]. Also, studies on improving sound absorption performance using nanomaterials have also been reported recently. One of them is a graphene-based sound-absorbing material in which graphene oxide is stacked layer-by-layer by a directional freezing method. The other is an energy absorber that implements a spider web or wavy microstructure by using the van der Waals force between graphene sheets while manufacturing reduced graphene oxide. In addition, Oh et al. reported a three-dimensional porous foam coated with two-dimensional graphene oxide for acoustic wave and impact energy dissipation [8]. However, the prior method of manufacturing a nanoscale structure using a carbon-based nanomaterial has problems in that it requires a long manufacturing time because the manufacturing process is very complicated. Moreover, there is no technology for tuning the microstructure to have improved sound absorption performance in a specific frequency range [9].
Experimental and computational evaluation of the degree of micro-collapse formations in freeze-dried cakes
Published in Drying Technology, 2023
Kyuya Nakagawa, Daiki Morishita, Tetsuo Suzuki, Noriaki Sano
Figure 4 shows the distribution of in freeze-dried cakes. Directional freezing and drying are known to be responsible for variations in the heterogeneity of freeze-dried cakes.[21–25] It is known that the velocity of the freezing front during the freezing step contributes to the formation of ice crystal microstructures,[26] which considerably affect the kinetics of the subsequent drying process.[24,27,28] The temperature of the sublimation front during drying is related to the drying kinetics, which can result in heterogeneity of the degree of collapse in freeze-dried cakes. In the freezing-and-drying system employed herein, freezing tends to progress from the bottom to the top, whereas sublimation occurs in an opposite manner. As shown in Figure 4, the values of vary relatively significantly along the vertical direction, and not so much along the horizontal direction. In particular, the zones near the bottom and top appear to show higher values of than those at the center zones. These results are consistent with the visual appearances of the freeze-dried cakes.
Preparation of sponge-like macroporous PVA hydrogels via n-HA enhanced phase separation and their potential as wound dressing
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Ruirui Feng, Rongzhan Fu, Zhiguang Duan, Chenhui Zhu, Xiaoxuan Ma, Daidi Fan, Xian Li
Chae et al. [34] reported a simple method to make porous PVA matrix via solvent evaporation in PVA solution, but the system requires chemical crosslinking to stabilize the structure. Chen, et al. [20] reported a macroporous PVA-HA/PAA composite hydrogel through a combination of freezing-thawing, PEG dehydration, and annealing method. The annealing treatment up to 120 °C improved crystalline and crosslinking of hydrogel. Sinha et al. [35] reported an in situ synthetic method to produce PVA/HA macroporous composite hydrogel through freezing-thawing method, where calcium ions were bonded to PVA molecules before HA nanoparticles were in situ synthesized. The microporous structure from this method could be as big as 100 μm, but most of them were incomplete pores. Su et al. [36] produced macroporous PVA/HA composite hydrogels with aligned channels through directional freezing-thawing method. Although channels length could be more than 100 μm, channels size were limited to 2–5 μm even after eight freezing-thawing cycles.