Ice Growth Direction Research Articles

X-ray micro-tomographic imaging and modelling of saline ice properties in concrete frost salt scaling experiments

Frost salt scaling of concrete is related to cyclic freezing and melting of a few millimeter thick deicer solution on the surface of the concrete. It is almost absent when pure water is freezing and reaches a maximum at a so-called pessimum concentration that for NaCl is around 3%. Different mechanisms have been suggested to explain this pessimum and frost salt scaling in general, ranging from the transport of moisture and growth of ice within the pore space of concrete (“cryogenic suction”) to crack formation in the saline ice layer followed by spalling off the surface (“glue-spall”). Though in these theories the saline ice layer, that forms in concrete frost salt scaling experiments, plays a major role, so far little is known about its properties. We present a characterisation and an analysis of the microstructure of this saline ice layer by means of 3D X-ray microtomography. We found that the morphology of the saline ice is very similar to young, columnar sea ice, with lamellae of ice and brine oriented in the direction of freezing. On the basis of the microscopic 3D image data, we formulated percolation-based models of macroscopic properties (e.g., strength, thermal expansion coefficient, porosity metrics) relevant for different proposed frost salt scaling mechanisms. Model results and observations suggest that the ice growth velocity, direction and confinement, have a major impact on the pore structure of saline ice, thereby governing both mechanical and transport properties. These properties in turn are expected to affect proposed frost salt scaling mechanisms of concrete. The microstructure length scales in the ice-brine composite (lamellar spacing, pore width) are comparable to those for concrete (air void spacing and size), suggesting complex poro-mechanical interaction at the interface of concrete and saline ice. The results highlight the importance of studying saline ice properties to improve predictions of frost salt scaling processes.

A Stiff, Tough, and Thermally Insulating Air- and Ice-Templated Plant-Based Foam.

By forming and directionally freezing an aqueous foam containing cellulose nanofibrils, methylcellulose, and tannic acid, we produced a stiff and tough anisotropic solid foam with low radial thermal conductivity. Along the ice-templating direction, the foam was as stiff as nanocellulose–clay composites, despite being primarily methylcellulose by mass. The foam was also stiff perpendicular to the direction of ice growth, while maintaining λr < 25 mW m–1 K–1 for a relative humidity (RH) up to 65% and <30 mW m–1 K–1 at 80% RH. This work introduces the tandem use of two practical techniques, foam formation and directional freezing, to generate a low-density anisotropic material, and this strategy could be applied to other aqueous systems where foam formation is possible.

Bioinspired nacre-like 2024Al/B4C composites with high damage tolerance

The bio-inspired 2024Al/B4C composites with a laminate-reticular hierarchical architecture were constructed by squeeze casting of 2024Al into loose freeze-cast ceramic scaffolds. This pressurized infiltration process provided a clean and well-bonded interface without physical gaps. By regulating the initial suspension concentration (20, 25, 30 and 35 vol%), the effects of different ceramic content on the microstructure, damage-tolerance behavior and toughening mechanisms of the composites parallel and perpendicular to the ice-growth direction were investigated. The strength and toughness in the longitudinal direction were greater than that in the transverse direction. The 2024Al/20 vol% B4C composite in the longitudinal direction yielded the highest flexural strength of 658 MPa, crack-initiation toughness (KIc) of 18.4 MPa m1/2 and crack-growth toughness (KJc) of 27.5 MPa m1/2. The unique damage-tolerant properties were attributed to multiple toughening mechanisms, including crack deflection, branching and blunting, ductile-ligament bridging and multiple-crack propagation, as evidenced by the stable crack growth and rising R-curve behavior during fracture. The significantly decreased damage tolerance in the transverse direction was mainly due to inadequate toughening tools. On the other hand, both the flexural strength and fracture toughness reduced remarkably as the ceramic content increased. The 2024Al/35 vol% B4C composite fractured in a single-crack mode and the crack growth path was almost straight, showing a relatively low flexural strength (502 MPa) and crack-initiation toughness (9.1 MPa m1/2). The toughening mechanism was discussed in terms of the relationship between structural characteristics and cracking mode.

Anisotropic strength and fracture resistance of epoxy-ceramic composite materials produced by ultrasound freeze-casting

The anisotropic mechanical properties of ultrasound freeze cast epoxy-ceramic composite materials were studied by measuring flexural strength and fracture resistance curves (R-curves) using both unnotched and notched three-point beam bending experiments, respectively, cut in three different orientations relative to the directional freezing axis. Three ultrasound frequencies of 0.699, 1.39 and 2.097 MHz were used in order to introduce different length scales into the microstructure, with 0 MHz used as the control samples. For all cases, the composites showed higher strength and fracture resistance when the crack plane cut across the direction of ice growth (denoted as the YX orientation). The anisotropic properties were more evident for the material produced without ultrasound (0 MHz) where the flexural strength was approximately 160% higher for the YX orientation compared to two orthogonal orientations. Most of the fracture resistance increase was found to occur within a crack extension, Δ a , of ∼0.5 mm. Comparing the fracture resistance at Δ a = 0.5 mm for the highly anisotropic 0 MHz samples showed that the YX orientation was approximately 86% tougher than the two orthogonal orientations. When the ultrasound operation frequencies of 0.699, 1.39 and 2.097 MHz were applied, the amount of anisotropy in the strength and fracture resistance gradually decreased as the operating frequency increased. The high strength and fracture resistance for the YX orientation was attributed to the alignment of the ceramic particles along the freeze front direction creating a barrier for crack propagation. Ultrasound modifies the material microstructure, introducing relatively dense ceramic layers perpendicular to the freezing front direction that act as an additional, orthogonal barrier to crack propagation. The addition of the denser layers acts to improve the mechanical properties in the weaker orientations and reduce the overall anisotropy.

Controlling anisotropy of porous B4C structures through magnetic field-assisted freeze-casting

Anisotropic porous boron carbide (B4C) structures were successfully produced, for the first time, using the magnetic field-assisted freeze casting method. The effect of the magnetic field on the structure and mechanical strength of the formed porous B4C was compared for two different magnetic field directions that were either aligned with ice growth (vertical), or perpendicular to the ice growth direction (horizontal). It was shown that applying even a weak horizontal magnetic field of 0.1–0.3 T noticeably affected the alignment of mineral bridges between lamellar walls. Both the porosity and the channel widths decreased with increasing horizontal magnetic field strength. In the case of a vertical magnetic field, a larger strength of 0.4 T was required for highly aligned lamellar walls and larger channel widths. Compression strength tests indicated that the application of magnetic fields led to more homogeneously aligned channels, which resulted in increased compression strength in the longitudinal (parallel to the ice growth) direction. Applying a vertical magnetic field of 0.4 T with a cooling rate of 2 °C/min during the freezing step of the magnetic field-assisted freeze-casting method was found to result in the best conditions for producing highly anisotropic structures with large channel widths and fewer mineral bridges, which led to an increase in the mechanical strength.

Quantitative determination of tip undercooling of faceted sea ice with in situ experiments

Sea ice growth with lamellar microstructure containing brine channels has been extensively investigated. However, the quantitative growth information of sea ice remains lack due to the uncontrolled crystalline orientation in previous investigations. For the first time, we in situ observed the unidirectional growth of lamellar sea ice with well-manipulated ice crystal orientation and visualized tip undercooling of lamellar sea ice. With the real-time observation, interesting phenomena of doublon tip in cellular ice growth and growth direction shift of unidirectionally grown ice tip are discovered for the first time, which are attributed to the complex solutal diffusion and anisotropic interface kinetics in ice growth. The quantitative experiments provide a clear micro scenario of sea ice growth, and are suggested to promote relevant investigations of sea ice.

Stable and Anisotropic Freezing Framework With Interaction Between IISPH Fluids and Ice Particles

In this paper, we present a novel method that can stably express the directional ice form caused by freezing of flowing water. The key to the proposed framework is to reflect the flow of fluids with viscosity in the direction of ice growth. Water is simulated by applying a new viscous technique to the implicit incompressible fluid simulation, and the proposed anisotropic freezing solution is used to express directional ice and glaze effects. The conditions under which water particles turn into ice particles are calculated according to a new energy function based on humidity and water flow. The humidity is approximated based on the virtual water film on the surface of the object, and the flow of fluid is incorporated into our anisotropic freezing solution to guide the growth direction of the ice. As a result, the proposed technique reliably produces glaze and directional freezing effects according to the flow direction of viscous water.

안정적이고 이방성한 빙결 모델링을위한 암시적 비압축성 유체와 얼음 입자간의 상호작용 기법

In this paper, we propose a new method to stable simulation the directional ice shape by coupling of freezing solver and viscous water flow. The proposed ice modeling framework considers viscous fluid flow in the direction of ice growth, which is important in freezing simulation. The water simulation solution uses the method of applying a new viscous technique to the IISPH(Implicit incompressible SPH) simulation, and the ice direction and the glaze effect use the proposed anisotropic freezing solution. The condition in which water particles change state to ice particles is calculated as a function of humidity and new energy with water flow. Humidity approximates a virtual water film on the surface of the object, and fluid flow is incorporated into our anisotropic freezing solution to guide the growth direction of ice. As a result, the results of the glaze and directional freezing simulations are shown stably according to the flow direction of viscous water.

Development of an icing simulation code for rotating wind turbines

This study aims to develop a three-dimensional icing simulation code named WISE (Wind turbine Icing Simulation code with performance Evaluation) integrated into OpenFOAM®. The freely available source code can contribute to icing simulations that require parallel computations. The rotational motion is explained by a Moving Reference Frame (MRF) in both aerodynamic and droplet fields. The thin water film theory is applied in the thermodynamic module. To verify WISE, ice accretion shapes on NREL Phase VI under rime and glaze icing conditions were considered. The ice accretion shapes obtained by WISE were compared against FENSAP-ICE and another numerical simulation without the MRF method for the droplet field. For the rime condition, the icing limits, maximum thickness, and its location are well predicted by WISE compared with FENSAP-ICE while the simulation without the MRF method overestimates the icing limits and maximum thickness. For the glaze condition, only WISE and FENSAP-ICE results are compared where the icing limits are slightly different. On the suction side, WISE accurately predicts the maximum thickness, ice growth direction, and icing limits. However, the thickness of ice on the pressure side is underestimated. It might be necessary to have a turbulence model that can predict the flow transition.

Banana Leaflike C-Doped MoS2 Aerogels toward Excellent Microwave Absorption Performance.

We describe the design and manufacturing method of a lightweight C-doped MoS2 aerogel with a special regular banana leaflike microstructure used for high-performance microwave absorbers. The aerogel precursor was first fabricated by a self-assembly process between alginate (Alg) and ammonium thiomolybdate (ATM), where Alg as a template was assembled with ATM into regular banana leaflike architectures along the ice growth direction during oriented freezing. After pyrolysis at 900 °C, the C-doped MoS2 aerogels maintained low densities and porous hierarchal banana leaflike structures, where the banana leaves ranged in diameter from about 2 to 5 μm with the growth of small branches. Benefitting from these features, the C-doped MoS2 aerogel possessed excellent microwave absorption performance in the frequency range of 2-18 GHz. The minimum reflection loss (RL) reached -43 dB at 5.4 GHz with a matching thickness of 4 mm, and the effective microwave absorption band (RL < -10 dB) reached 4 GHz (14-18 GHz) at a thickness of 1.5 mm. Our findings also provide strategies for designing MoS2 aerogel nanostructures for electronic devices, catalysis, and other potential applications.

Near-Zero Thermal Expansion in Freeze-Cast Composite Materials

Most materials expand when heated, which can lead to thermal stress and even failure. Whereas thermomiotic materials exhibit negative thermal expansion, the creation of materials with near-zero thermal expansion presents an ongoing challenge due to the need to optimize thermal and mechanical properties simultaneously. The present work describes the preparation and properties of polymer–ceramic composites with low thermal expansion. Ceramic scaffolds, prepared by freeze-casting of low-thermal-expansion Al2W3O12, were impregnated with poly(methylmethacrylate) (PMMA). The resulting composites can have a coefficient of thermal expansion as low as 2 × 10−6 K−1, and hardness values of 4.0 ± 0.3 HV/5 (39 ± 3 MPa) and 16 ± 3 HV/5 (160 ± 30 MPa) parallel and perpendicular to the ice growth, respectively. The higher hardness perpendicular to the ice growth direction indicates that the PMMA is acting to improve the mechanical properties of the composite.

Freeze‐Casting of Surface‐Magnetized Iron(II,III) Oxide Particles in a Uniform Static Magnetic Field Generated by a Helmholtz Coil

Research is conducted into freeze‐casting of surface‐magnetized Fe3O4 particles under uniform, low‐strength magnetic fields (5.2 mT) to mimic the mechanical characteristics of natural human bone. Freeze‐casting is a technique that fabricates porous materials by directionally freezing and sublimating an aqueous slurry. A novel, Helmholtz coil‐based freeze‐caster is developed and it is shown that, during freeze‐casting, the use of this Helmholtz coil generates a more uniform magnetic field than permanent magnets. This uniform magnetic field, applied in the direction of ice growth, keeps particles from agglomerating and results in an increase of 55% in both the ultimate compressive strength and the elastic modulus of porous surface‐magnetized Fe3O4 scaffolds. These increases can be linked to a reduction in the porosity that occurs due to magnetic interactions between particles in the presence of the field. These results offer a novel method for the fabrication of bone‐inspired biomaterials and structural materials.

Unified icing theory based on phase transition of supercooled water on a substrate

Lack of knowledge on substrate icing hinders us from predicting the effects of typical substrate properties in icing and anti-icing research. The pattern formation and tip shape of icing on a substrate must be explored to understanding the physics of icing on a substrate. In this paper, the pattern, velocity and tip shape of ice on substrates with different thermal conductivities and surface energies are evaluated in a series of experiments. Experimental results show that as supercooling and thermal conductivity increase, the ice on substrate evolves from a single-needle dendrite to a smooth ice film. In contrast, for free icing the same evolution process can be completed at a higher supercooling than substrate icing. Experimental results on hydrophilic and Plexiglas surfaces demonstrate an abruptly decrease of velocity and Peclet number of ice occurs at approximately 271.6 K, whereas the tip shape of ice does not change obviously; while for free icing this phenomenon is not found. Furthermore, a theoretical analysis on phase transition of substrate icing is performed. It shows that the surface energy of substrates can increase the size of metastable cubic ice and reduce the temperature on the ice tip by 1.5 K compared to free ice, thereby causing the decrease in the velocity and Peclet number of ice. Also the heat conduction of substrates decrease the heat flux in ice growth direction and lead to absolute stability of substrate icing in lower supercooling compared to free icing. In terms of the comparison between free icing and substrate icing, a unified icing theory is proposed to describe the equilibrium icing mode, the non-equilibrium growth state, and the corresponding growth equations. Using this theory, the velocity and pattern of substrate icing with different supercooling, thermal conductivity, and surface energy can be predicted well, as well as these results of free icing.

Stiff, porous scaffolds from magnetized alumina particles aligned by magnetic freeze casting

Bone consists of a hard mineral phase and a compliant biopolymer phase resulting in a composite material that is both lightweight and strong. Osteoporosis that degrades spongy bone preferentially over time leads to bone brittleness in the elderly. A porous ceramic material that can mimic spongy bone for a one-time implant provides a potential solution for the future needs of an aging population. Scaffolds made by magnetic freeze casting resemble the aligned porosity of spongy bone. A magnetic field applied throughout freezing induces particle chaining and alignment of lamellae structures between growing ice crystals. After freeze drying to extract the ice and sintering to strengthen the scaffold, cubes from the scaffold center are mechanically compressed along longitudinal (z-axis, ice growth direction) and transverse (y-axis, magnetic field direction) axes. The best alignment of lamellar walls in the scaffold center occurs when applying magnetic freeze casting with the largest particles (350nm) at an intermediate magnetic field strength (75mT), which also agrees with stiffness enhancement results in both z and y-axes. Magnetic moments of different sized magnetized alumina particles help determine the ideal magnetic field strength needed to induce alignment in the scaffold center rather than just at the poles.

Influence of anisotropic grains (platelets) on the microstructure and uniaxial compressive response of ice-templated sintered alumina scaffolds

Ice-templated ceramics have unique lamellar pore morphology that offers better compressive mechanical properties in comparison to the typical ceramic foams with isotropic pore morphology. However, for very high-level porosity (>65 vol%) strength difference diminishes. This investigation reveals that by inducing anisotropic grains within the matrix of a fine-grained ceramic, uniaxial compressive response of the ice-templated sintered scaffolds can be markedly enhanced without causing any considerable modification of the total porosity. To address this innovative materials design strategy, we synthesized a series of microstructures by systematically varying the anisotropic grains content in an aqueous suspension and the freezing kinetics to investigate the process-microstructure correlations and understand the structure-property relationships. Microstructural investigations revealed the unique arrangements of the platelets within and out of the lamella walls, where the upward moving ice fronts aligned the platelets' in-plane direction to the ice-growth direction. In the low freezing front velocity regime, platelets were observed to be mainly within the lamella walls, whereas platelets started to develop lamellar bridges with the increasing velocity. As a result, a transition of the pore morphology occurred with the increasing platelets content and the freezing front velocity. A novel method based on the rigorous microstructural analysis is developed to estimate the distribution of the platelets within and out of the walls and the variation of the platelets distribution with the composition and freezing front velocity. A drastic improvement of the compressive mechanical properties (stiffness, strength, energy absorption capacity) was measured due to the platelets' addition, which has been related to the platelets' distribution within and out of the walls and the pore morphology modifications. Results are rationalized based on the role of the platelets during the compressive deformation.

Porous SiCnw/SiC ceramics with unidirectionally aligned channels produced by freeze-drying and chemical vapor infiltration

The current study introduces a methodology for the fabrication of porous silicon carbide nanowire/silicon carbide (SiCnw/SiC) ceramics with macroscopic unidirectionally aligned channels and reports on their microstructural and mechanical properties. The material was produced by freezing of a water-based slurry of β-SiC nanowires (SiCnw) with control of the ice growth direction. Pores were subsequently generated by sublimation of the columnar ice during freeze-drying. Chemical vapor infiltration (CVI) of SiC into the open pore network of the SiCnw aerogel with unidirectionally aligned channels, resulted in the formation of highly porous SiCnw/SiC ceramics which exhibited a unique microstructure as identified by scanning electron microscopy. The pore size distribution and the mechanical properties of the as-fabricated porous ceramics were examined by mercury intrusion porosimetry and three-point bending and compression tests, respectively, while phase composition was investigated through X-ray diffraction.

Supercooling enhancement by adding antifreeze protein and ions to water in a narrow space

The control of ice crystal growth has been an important issue in various fields, such as the quality maintenance and improvement of food texture in frozen food, and the storages of tissues and organs in hospitals. The adding of antifreeze protein to food or organs has been focused on recently because it is appropriate for controlling ice growth. However, the effects of ions, which are originally contained in the substances being preserved, on the activities of antifreeze protein have not yet been clarified in a thermal non-equilibrium state. We therefore conducted experiments on the unidirectional freezing of dilute aqueous solutions of winter flounder antifreeze protein, sodium chloride or sodium permanganate in a narrow space between two cover glasses. The temperatures at ice/solution interfaces were measured with a small thermocouple. The concentration of antifreeze protein was estimated by fluorescence microscopy, and the concentration of permanganate ion was measured from the intensity of transmitted light. It was found that the depression of interface temperature (defined as the difference between the interface temperature of the solution and that of pure water) of the mixed solution was much lower than the sum of the depression of the interface temperatures of two solutions of single solute. In addition, we found that the protein concentration increases with time, while the ion concentration decreases slightly in the front regions of the most advanced points of serrated interfaces in the mixed solution. The diffusion of ions to the ice growth direction enhances the protein diffusion to the front-edge regions. This is possibly the reason for the low value of the interface temperature of the mixed solution. Simultaneously, high concentration regions of the protein in the bottom-edge region deteriorate the diffusion of ions. This is reason for the deterioration of the depression of interface temperature due to an increase in the interface velocity in the cases of mixed solutions.

In vitro biodegradable and mechanical performance of biphasic calcium phosphate porous scaffolds with unidirectional macro-pore structure

In this study, porous biphasic calcium phosphate (BCP) scaffolds were fabricated by a freeze–gel casting technique using a tertiary-butyl alcohol (TBA) based slurry. After sintering, unidirectional macropore channels of scaffolds aligned regularly along the TBA ice growth direction were tailored simultaneously with micropores formed in the outer wall of the pore channels. The synthesized porous BCP scaffolds (two different sintering temperatures) exhibit compressive strength of 46.8MPa for 43.0% porosity and 33.1MPa for 45.9% porosity, respectively. After immersion in Hank's balanced salt solution (HBSS) for 1, 2, 4, 8 weeks, a precipitation started to be formed with individual small granules on the scaffolds surface. In the case of BCP scaffolds sintered at 1200°C, β-TCP were slowly degraded with increasing the immersing time; on the other hand, α-TCP (from BCP scaffolds sintered at 1300°C) was extremely degraded within 1 week of immersing. This behavior could be due to a fast hydrolysis (dissolution–reprecipitation) as a phase transformation from α-TCP to brushite or apatite compared to the β-TCP. After immersion in HBSS, overall the compressive strength of the scaffolds reduced by the gradual degradation in biological environment solution. This behavior is consistent with the degradation behavior of scaffolds after immersion in HBSS.

Synthesis, characterization and biocompatibility evaluation of sol–gel derived bioactive glass scaffolds prepared by freeze casting method

In this study, a new class of bioactive glass scaffolds was prepared through freeze casting method for bone tissue engineering applications. After analyzing the structural characteristics of the scaffolds, in vitro biological evaluations were assessed through monitoring alkaline phosphatase (AP) activity of osteoblast cells and soaking in simulated body fluid (SBF) for different time intervals. It was shown that the scaffolds consisted of bioactive glass plates with interconnected pores between them, aligned along the ice growth direction. The ability of the scaffolds for supporting the growth of human fetal osteoblastic cells (hFOB 1.19) was approved. Moreover, inductively coupled plasma-atomic emission spectrometry (ICP-AES) showed meaningful compositional changes of calcium, phosphorus and silicon in SBF solution, indicating the apatite forming ability of the scaffolds. The present investigation revealed that freeze casting could be an effective method for the preparation of highly bioactive scaffolds. In addition, the scaffolds proved to be highly compatible for the proposed works in vivo.

동결-젤 주조 공정 기반 삼차부틸알코올을 이용한 단일방향 기공구조를 가지는 이상인산칼슘 세라믹 지지체의 제조 및 특성평가

Porous biphasic calcium phosphate scaffolds were fabricated by a freeze-gel casting technique using a tertiary-butyl alcohol (TBA)-based slurry. After sintering, unidirectional macropore channels of scaffolds aligned regularly along the TBA ice growth direction were tailored simultaneously with micropores formed in the outer wall of the pore channels. The crystallinity, micro structure, pore configuration, bulk density, and compressive strength for the scaffolds were investigated with X-ray diffractometery, scanning electron microscopy analysis, a water immersion method, and a universal test machine. The results revealed that the sintered porosity and pore size generally resulted in a high solid loading which resulted in low porosity and small pore size, which relatively increased the higher compressive strength. After being sintered at 1100-1300℃, the scaffolds showed an average porosity and compressive strength in the range 35.1-74.9% and 65.1-3.0 MPa, respectively, according to the processing conditions.