Effect of crystal orientation on freeze concentration of solutions

Freeze concentration is one of the methods to concentrate solution by making pure ice in the solution. In general, the ratio of condensation is focused on, and so the research on the concentration captured in ice is very limited. However, quality improvement of eliminating impurities from wastewater is a very important task. In this study, the difference of initial morphology of ice was focused on and the influence on the freeze concentration was studied. It was found that the concentration of solute captured in ice was in the following order, from bigger value, multi-crystal ice, a single crystal ice with growth direction in a-axis and a single crystal ice with growth direction in c-axis. It was clarified that the ratio of concentration between the solute captured in ice and the solute in the mother solution varied from 1/10 to 1/250, depending on the crystal orientation of the ice.     

Anisotropic thermal expansion of stoichiometric lithium niobate crystals grown along the normal direction of facets

In this paper, a stoichiometric lithium niobate (SLN) crystal with the size up to 20 × 20 × 18 mm³ was grown along the normal direction of the (0 1 2) facet from the 16 mol% K₂O fluxed melt by the top-seeded solution growth method. The anisotropic thermal expansion of the SLN crystal and congruent lithium niobate (CLN) crystal was measured along different directions by using a Shimadzu thermomechanical analyzer. As compared with CLN, the SLN crystal exhibited slightly larger thermal expansion along the Z-axis and slightly smaller expansion along the X-axis. Both the SLN and CLN crystals showed strong anisotropy in the thermal expansion. The thermal expansion coefficient of SLN along the X-axis (16.7 × 10⁻⁶ °C⁻¹ at 300 °C) is much larger than that along the Z-axis (2.5 × 10⁻⁶ °C⁻¹ at 300 °C). Based on the experimental data and polynomial fitting results, we calculated the thermal expansion coefficients for different directions. In the case of growing the SLN crystal along the normal direction of (0 1 2) facet, we studied the radial anisotropic thermal expansion and discussed the cracking problem of the crystal according to its actual growth morphology. It is found that the cracks of SLN can be suppressed by growing the crystal along the W-axis due to its reduced radial anisotropy in the thermal expansion.     

Three-dimensional measurement of ice crystals in frozen dilute solution

A Micro-Slicer Image Processing System (MSIPS) has been applied to observe the ice crystal structures formed in frozen dilute solutions. Several characteristic parameters were also proposed to investigate the three-dimensional (3-D) morphology and distribution of ice crystals, based on their reconstructed images obtained by multi-slicing a frozen sample with the thickness of 5 μm. The values of characteristic parameters were determined for the sample images with the dimension of 530×700×1000 μm. The 3-D morphology of ice crystals was found to be a bundle of continuous or dendrite columns at any freezing condition. The equivalent diameter of ice crystals were in the range of 73–169 μm, and decreased exponentially with increasing freezing rate at the copper cooling plate temperature of −20 to −80 °C. At the T_cp −40 °C, the volumes of ice crystals were in the range of 4.6×10⁴ μm³ to 3.3×10⁷ μm³, and 36 ice columns were counted in the 3-D image.     

The effect of perpendicular electric fields on the orientation of zinc oxide crystals during the oxidation of zinc thin films

The effect of direct current (d.c.) electric fields on the crystal orientation of zinc oxide thin films was investigated. Evaporated zinc thin films were oxidized in air under the application of perpendicular electric fields (detached electrodes) at different temperatures. The application of positive fields at 550 °C improved thec-axis orientations up to 1000 V cm^–1. Further increase in field strength caused thec-axis orientations to decline to their original values (no applied field). The application of negative normal fields at 550 °C deteriorated thec-axis orientations up to 800 V cm^–1. Thec-axis orientations improved to their original values by increasing the field strength to greater than 800 V cm^–1. The crystal size remained unchanged, but the surface morphology was affected by the application of the electric fields at temperatures above the melting point of zinc. No significant change in optical properties was detected for samples that were subjected to electric fields. Whenever thec-axis orientation improved, crystals on the film surface became rounded and a more ordered microstructure was observed. On the other hand, the deterioration ofc-axis orientation was manifested by the increase in the number of whisker-shaped crystal needles on the surface of the ZnO thin films.     

Microstructures ofa-axis oriented YBa2Cu3O7-δ thin films prepared by low temperature and template processes

Highly a-axis oriented epitaxial thin films of YBa₂Cu₃O_7– have been prepared by both a low temperature process and also a self-template technique. Films deposited at low temperature showed good crystallinity whereas films grown on a template exhibited a high transition temperature into the superconducting state. Detailed transmission electron microscopic investigations have been performed on these two kinds ofa-axis oriented films. Significant differences have been found in the microstructures of these films. The dominant defects formed in these films are misoriented grains which mainly show ac-axis orientation. The origin of the nucleation of misoriented grains is attributed to surface defects of the substrate. No boundary between the template layer and upper layer could be distinguished for films made by the self-template process. A thinc-axis intermediate layer with a thickness of 2–5 unit cells was observed at the interface between thea-axis film and the SrTiO₃ substrate for both kinds of films. The formation and influence of such an intermediate layer needs further study.     

An experimental study on ice formation around horizontal long tubes

The results of an experimental study are presented where the growth rate of ice on the outside of cooled copper tubes was studied. The tubes, which were immersed in water in an insulated vessel, were internally cooled by circulating glycol through them.It was found that axial growth rate of ice is distinct at low values of the coolant Reynolds number and short freezing times. The slope of the ice thickness with axial distance showed moderate dependency on time but varied with coolant flow rate, and with Stanton and Biot numbers.A key result from the experiments is the abrupt ice thickness enlargements on the surface of tube bends. This anomaly may be attributed to internal flow disturbances of the coolant, and creation of local eddies inside the bends that enhance growth of ice. The effect was evident for a low Reynolds number (Re = 251.9 and Bi < 1), and fades out for large Reynolds number flows.     

Film thickness dependence of critical current density for YBa2Cu3O7 films post-annealed at a low oxygen partial pressure

The variation of critical current density at 77 K as a function of film thickness was studied for YBa₂Cu₃O₇ films on (100) LaAlO₃ substrates. Film thicknesses were in the range 0.2–1.6m. The films were deposited by co-evaporation and post-annealed under conditions which have previously resulted in high-quality films (750°C and an oxygen partial pressure of 29 Pa). The critical current density at 77 K exceeds 1 MA cm^–2 for the thinner films, and decreases with increasing film thickness in excess of about 0.4m. The decrease is in rough agreement with a switch fromc-axis toa-axis growth at about this critical thickness. A good anticorrelation was found between room temperature resistivity and critical current density at 77 K. The results are compared to those obtained before by post-annealing at 850°C in 1 atm of oxygen.     

Synthesis and characterization of Nb2AlC thin films

We report on the synthesis and characterization of epitaxial c-axis oriented Nb₂AlC thin films deposited on c-axis sapphire (Al₂O₃) substrates by magnetron sputtering. Selected area electron diffraction reveal that independent of substrate temperature or film stoichiometry, there is the growth of a secondary phase not found in bulk, Nb₅Al₃C_x with a- and c-axis lattice constants of 7.746 Å and 5.246 Å, respectively. Scanning electron micrographs reveal large surface features, many with hexagonal shape and faceted texture. Atomic force microscopy topographical measurements indicate a surface roughness of approximately 15% of the total film thickness. Electrical transport measurements show typical metal-like conduction with a room temperature resistivity of ≈ 0.9 μΩ-m and a residual resistivity ratio of 2.5. A superconducting transition was found at ≈ 440 mK.     

Growth, thermal and spectroscopic characteristics of LiNd(WO4)2 crystal

Crystal growth, thermal and optical characteristics of LiNd(WO₄)₂ crystal have been investigated. The LiNd(WO₄)₂ crystal up to Ø15 × 32 mm³ has been grown by Czochralski technique. The hardness is about 5.0 Mohs’ scale. The specific heat at 50 °C is 0.42 J g⁻¹ K⁻¹. The thermal expansion coefficient for c- and a- axes is 1.107 × 10⁻⁵ and 2.104 × 10⁻⁵ K⁻¹, respectively. The absorption and fluorescence spectra and the fluorescence decay curve of LiNd(WO₄)₂ crystal were measured at room temperature. Some spectroscopic parameters such as the intensity parameters, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and emission cross sections were estimated.     

Freezing phenomena of supercooled water under impacts of ultrasonic waves

In order to clarify effects of ultrasonic waves on supercoold water, ultrasonic waves were applied to supercooled water. Frequency of the ultrasonic waves applied was 45 kHz, and the intensities of the waves were 0.13 and 0.28 W cm⁻², respectively. Four cases of experimental conditions were selected; a case of a free surface, a case of an oil-water surface, a case of a free surface with a dipped metal bar and a case of an oil–water surface with a dipped metal bar. For each experimental condition, water was cooled at a constant cooling rate and the ultrasonic wave was applied from underneath until the water in a test tube solidified. It was found that in the case of 0.28 W cm⁻², the ultrasonic wave had distinct effects on freezing of supercooled water for all experimental conditions. On the other hand, in the case of 0.13 W cm⁻², the ultrasonic wave had an effect on freezing of supercooled water only under existence of a free surface and a metal bar.     

Effect of Sputtering Parameters on Superconducting Properties of GdBaCuO Epitaxial Thin Film Deposited by ICP Method

Thin films of GdBaCuO (GBCO) have been deposited in situ onto LaAlO₃ single crystal substrates by inverted cylindrical sputtering pattern (ICP). The superconductive properties of the thin films' dependence on the substrate temperature and sputtering pressure have been systematically investigated. By optimization of the deposition parameter, high-quality c-axis epitaxial GBCO thin films of T _c0>92 K were reproducibly grown. The T _c of the best sample is as high as 93.2 K. Upon changing the target composition to GdBa₂Cu₄O _y (Gd₁₂₄), it was observed that the samples always show some a-axis oriented films, implying that excess copper would favor a-axis growth in thin films. The superconductivity of the thin films under higher substrate temperature (T _s>800°C) was clearly improved by the procedure of special post-oxygenization at 400°C with an ozone atmosphere. This is very useful for preparing large-area thin films of GBCO.     

The elimination of defects in Czochralski grown lithium niobate

A method is described for growing large LiNbO₃ single crystals from the melt, completely free of low-angle grain boundaries. This crystalline perfection was achieved by eliminating localized cellular structures, which were introduced by thermal supercooling due to faceted growth. These defects were distributed only near the developed (012)_h and (0 –1 –2)_h planes when the growth of these planes as facets could be reduced rapidly in the conical part of the boule. Low-angle grain boundaries along the z-axis and polygonization of dislocations were induced by the stresses around the cellular structure. Voids and a corrugated interface have also been observed as a cell-boundary groove trail. The observation of cellular structures indicated that their formation was strongly dependent on growth in the radial direction and the pulled rate. Furthermore, to eliminate these structures, it was found most effective to keep the crystal growth rate, G, at less than 10 mm h^–1.     

Dimensionless correlations of frost properties on a cold plate

This study proposes dimensionless correlations for predicting the properties of frost formed on a cold plate. Frosting experiments are carried out to obtain the correlations with various environmental parameters including the air temperature, air velocity, absolute humidity, and cooling plate temperature. The thickness, density, surface temperature, effective thermal conductivity, average heat and mass transfer coefficients of the frost layer are correlated as functions of the Reynolds number, Fourier number, absolute humidity, and dimensionless temperature by using a dimensional analysis. The correlations proposed in this study agree well with the experimental data within a maximum error of 10%, and can be used to predict the average frost properties in the following ranges: the air temperature of 5–15 °C, air velocity of 1.0–2.5 m s⁻¹, absolute humidity of 0.00322–0.00847 kg kg_a⁻¹, and cooling plate temperature of −35–−15 °C.     

Motion of etch defects on (0 0 1) Li2B4O7 single crystal wafer

Three types of etch defects were observed on a (0 0 1) lithium tetraborate (Li₂B₄O₇:LB4) single crystal wafer. Type I appeared all over the +c plane taking a four-sided pyramidal shape. The etch defects on the −c plane were differentiated into two types; Type II corresponded to dislocation arrays and presented a four-sided pyramidal shape while Type III was distributed all over the −c plane, forming a eight-sided hillock. After annealing the wafer at 850 °C in several different atmospheres, the density of Types I and II did not change while that of Type III was reduced by two order of magnitude in the oxygen atmosphere. This might suggest that the formation mechanism of each of these defects was different and they showed the various motions for the thermal treatment.     

Microstructure and electrical properties of YBCO thin films

Microstructures of c-axis oriented YBCO thin films made by high-pressure d.c. sputtering on LaAlO₃ and MgO substrates were examined by TEM. The a-axis oriented grains, second phases and micro-twins were frequently observed in the film. The a-axis oriented grains expanded along their c-axis directions during film growth. The a- and b-axis misorientations were observed in the film on MgO due to serious lattice mis-match between YBCO and MgO. The second phases were often accompanied with a-axis oriented grains suggesting they act as nuclei. These observed results were correlated with the measured T _c and J _c of the films.     

Sea ice growth rates near ice shelves

Sea ice growth rates near ice shelves are influenced by ocean-ice shelf interactions. Sea ice growth rates and ocean observations from McMurdo Sound, Antarctica in 1999 and 2000 are presented in this paper. Growth rate measurements were made for an individual platelet crystal through video camera observations. It was found that the crystal grew in discontinuous, episodic bursts at rates of the order of 10^− 6 m s^− 1. Sea water 0.15 m beneath the lower ice surface was measured to be supercooled by 0.01 K. Indications are that supercooling was continuous over the period of episodic platelet ice crystal growth and the growth bursts are attributed to the influence of variable currents. Growth rates for bulk sea ice (i.e., columnar and incorporated platelet ice) and heat fluxes were derived from ice temperature measurements. The growth rates for bulk sea ice were found to be of the order of 10^− 7 m s^− 1, an order of magnitude less than the rates for the individual platelet ice crystal. The residual of the energy balance suggested that a negative oceanic heat flux (i.e., heat transport down into the ocean) occurred, in addition to conduction of heat up into the atmosphere. Both salinity-based growth rate models and an oxygen isotope-based growth rate model (Eicken, 1998) were found to under-predict growth rates compared to those derived from ice temperature measurements. In addition, inverting the growth rates predicted by the models and integrating over the depth of the core failed to accurately predict the date of initial sea ice formation. Modifications are proposed to the models for sea ice formation occurring near ice shelves, where platelet ice formation is likely. Differences between bulk and individual platelet ice crystal growth rates are discussed with reference to heat fluxes, oceanic flows and the Eicken (1998) model.     

Modelling the freezing of butter

Butter is a water-in-oil emulsion so its behaviour during freezing is very different from that of most food products, for which water forms a continuous phase. The release of latent heat during freezing is controlled as much by the rate of crystallization of water in each of the water droplets as by the rate of heat transfer. Measurements of the freezing of butter show that the release of latent heat from the freezing water depends on the degree of supercooling, which, in turn, depends on the cooling medium temperature, the size of the butter item, the packaging and the type of butter. Four modelling approaches were tested against the experimental data collected for a 25 kg block of butter. A “sensible heat only model” accurately predicted the butter temperature until temperatures at which water freezing becomes significant were reached. An “equilibrium thermal properties model” predicted a temperature plateau near the initial freezing point of the butter in a manner that was inconsistent with the measured data. A third model used a stochastic approach to ice nucleation based on supercooling using classical homogeneous nucleation theory. The predicted temperatures showed that supercooling-driven nucleation alone is not sufficient to predict the freezing behaviour of butter. A fourth approach took account of time-dependent nucleation and ice crystal growth kinetics using classical Avrami crystallization theory. The relationship between the ice crystal growth rate and the supersaturation was assumed to be linear. The model predicted the experimental data accurately, particularly by predicting the slow rebound in the temperature following supercooling that is found when freezing butter under some conditions.     

Structural and Thermal Properties of Cu1 – xAgxInS2Chalcopyrite Solid Solutions

The anisotropic thermal expansion of Cu_{1 – x} Ag _x InS₂chalcopyrite solid solutions was studied by x-ray diffraction from 80 to 650 K. Over the entire temperature range studied, the thermal expansion of the solid solutions was found to be anisotropic: thec-axis thermal expansion is considerably smaller than thea-axis thermal expansion. The solid solutions with 0.55 <x< 1.0 exhibit negative c-axis thermal expansion. The composition dependences of the thermal expansion coefficients and anisotropy parameters are nonlinear. The anisotropy parameters rise monotonically with increasing x. The correlation between the thermal expansion anisotropy and tetragonal distortion = 2 – c/ais considered. Directions of zero thermal expansion are identified.     

Continuous Deposition of YBCO Films for Coated Conductor Using PLD Method

A reel-to-reel PLD system was set up for studying YBCO coated conductor. YBCO films could be continuously grown on the CeO₂/YSZ/Y₂O₃ buffered Ni-5W tape. Some deposition parameters were investigated. XRD θ–2θ scans were employed to characterize the c-axis orientation and in-plane texture of YBCO films deposited with different laser repetition rates and tape moving speeds. We investigated the dependence of critical current I _c on laser repetition rates and tape moving speeds for YBCO films. It had been found that a-axis oriented grains appeared as YBCO layer thickness increased, which prevented the values of I _c improved.     

The effect of supercooling on ice structure in tuna meat observed by using X-ray computed tomography

Several studies have reported that freezing a homogeneous food such as soy bean curd with deep supercooling (supercooled freezing) results in the formation of many particle ice and homogenous ice structure. However, ice crystal morphology may be affected by the cellular structure of the food. In this study, the ice crystal structure in tuna meat, a cellular food, frozen by the supercooled freezing method was investigated by X-ray computed tomography and compared with ice structures in tuna meat frozen by conventional freezing methods. The results showed that rod-like ice crystals grew parallel with the myofibers, and inhomogeneous ice structures formed in tuna meat frozen by the supercooled freezing method regardless of the degree of supercooling, in contrast to the ice structure in frozen soy bean curds. These ice crystals linked with each other to form rod-like ice structures due to mobility limitations imposed by the cellular structure.